CN113541520A

CN113541520A - SVPWM-based resonant DC link three-phase inverter modulation method

Info

Publication number: CN113541520A
Application number: CN202110817703.3A
Authority: CN
Inventors: 褚恩辉; 亢云旌; 张天宇; 王志勇; 任绍宁; 廖伟良
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2021-07-20
Filing date: 2021-07-20
Publication date: 2021-10-22
Anticipated expiration: 2041-07-20
Also published as: CN113541520B

Abstract

The present invention provides a modulation method of a resonant DC link three-phase inverter based on SVPWM, which adopts a four-stage wave generation mode, adjusts the switching sequence through the polarity of the load phase current, and keeps the DC bus voltage under zero vector at 0 at the same time. , so that the commutation circuit of the resonant DC link three-phase inverter maintains the operating frequency of one switching cycle as one time, and the quasi-ZVS turn-off times of the main power switch tube in each switching cycle is automatically controlled by the load. The 3 times adapting to the commutation control is reduced to 1 time; in addition, by increasing the shunt dead time, the superposition of the resonant current of the commutation circuit and the load current is avoided, thereby maximally suppressing the current stress of the commutation switch tube. The invention reduces the turn-off loss of the main power switch tube on the basis of ensuring that all switch tubes realize soft switching action and maintains the low operating frequency of the commutator circuit, and avoids the superposition of the resonant current and the load current of the commutator circuit. Thus, the efficiency of the inverter is effectively improved.

Description

SVPWM-based resonant DC link three-phase inverter modulation method

Technical Field

The invention relates to the technical field of inverters, in particular to a modulation method of a resonant direct-current link three-phase inverter based on SVPWM.

Background

In recent years, soft switching inverters have been widely used in various applications such as motor driving, induction heating, and new energy grid connection. By introducing a converter circuit into a hard-switching inverter, the soft-switching technology can reduce switching loss to realize high frequency of the inverter, and can reduce dv/dt and di/dt of a switching tube to suppress electromagnetic interference (EMI) of the inverter. Therefore, soft switching technology is an important approach to improve inverter performance.

Resonant dc link inverters are an important class of soft switching inverters. The converter circuit of the power supply system periodically returns the voltage of the direct-current bus to zero, so that the zero-voltage condition of the main power switch tube is realized. In 1989, the resonant dc link inverter was proposed by doctor d.m. divan (diwan) at the university of wisconsin, usa. The topological structure of the circuit breaker is very simple, but the voltage stress of a switching tube is high, and pulse width modulation (PWM for short) cannot be realized. To solve these problems, d.m.divan (diwan) further proposed an active clamp resonant dc link inverter; the voltage stress of the switching tube is limited to the sum of the voltage of the direct current power supply and the voltage of the clamping capacitor, and PWM is realized.

After this, a parallel resonant dc link inverter is proposed, the voltage stress of the switching tubes being further limited to the dc supply voltage. However, various problems still exist in the topology structure of the existing parallel resonance direct current link inverter. The converter circuit of the inverter with the parallel resonance direct current link needs to resonate by using a split capacitor at an input end, so that the potential of a neutral point is changed; some converter circuits use coupling inductors or transformers, so that the design difficulty is increased; some converter circuits need to detect the current value of the resonant inductor in real time, so that the difficulty of detection and control is increased.

The Chinese invention patent CN106533224A was published in 2017, 3 and 22 months "A novel resonance direct current link soft switching inverter and a modulation method thereof provide a novel parallel resonance direct current link inverter. The topological structure of the inverter is shown in figure 1, and the converter circuit comprises a bus switch tube S_LFirst commutation switch tube S_a1Second commutation switch tube S_a2Main converter capacitor C_LFirst auxiliary commutation capacitor C_a1Second auxiliary commutation capacitor C_a2First commutation inductance L_a1Second commutation inductance L_a2First auxiliary diode D_a1A second auxiliary diode D_a2Third auxiliary diode D_a3And a fourth auxiliary diode D_a4. The parallel resonance direct current link inverter does not utilize an input split capacitor for resonance, does not use a coupling inductor or a transformer, and does not need to detect the current of a resonance inductor, so that the parallel resonance direct current link inverter has high research value.

However, as shown in fig. 3, for a conventional Sinusoidal Pulse Width Modulation (SPWM) resonant dc link inverter, six main power switching transistors of the inverter bridge need to operate once in one switching period, so that the converter circuit needs to operate six times to manufacture six zero-voltage notches, so as to realize soft switching of all the main power switching transistors. This limits the improvement of the inverter switching frequency and the operation efficiency, reduces the quality of the output waveform, and increases the high-frequency common mode voltage.

As shown in fig. 4, although the chinese invention patent CN106533224A proposes a novel modulation method for a resonant dc link soft switching inverter, which reduces the number of operations of a converter circuit in each switching cycle from six to four, the operation frequency is still high. Therefore, it is important to make the inverter circuit operate once in each switching period, so that the inverter circuit and the inverter bridge have the same operating frequency.

Subsequently, chinese invention patent CN107493025A discloses "a load adaptive commutation control method of a resonant dc link three-phase inverter" in 2017, 12 and 19, and proposes a load adaptive commutation control method of a novel parallel resonant dc link inverter. As shown in fig. 5, the modulation strategy uses a sawtooth wave with positive and negative alternate slopes as a carrier instead of a conventional triangular wave to reduce the operating frequency of the commutation circuit from four times per switching cycle to once per switching cycle. The sawtooth carrier with the positive and negative alternating slopes is characterized in that: the slope of the sawtooth carrier is constant, but the slope of the sawtooth carrier changes with the direction of the output phase current, the direction of the output phase current is positive, the slope of the sawtooth carrier is positive, the direction of the output phase current is negative, and the slope of the sawtooth carrier is negative. The modulation strategy reduces the operating frequency of the inverter circuit, thereby improving the efficiency of the inverter.

However, the load adaptive commutation control of the inverter still has the following defects: the turn-off times of the quasi-ZVS (zero voltage) of the main power switching tube are excessive, and the main power switching tube needs to be turned off for three times of quasi-ZVS (zero voltage) in one switching period, so that the turn-off loss of the main power switching tube is increased, and the efficiency of an inverter is reduced; ② the first commutation switch tube S_a1And a second commutation switch tube S_a2The current stress of the inverter circuit is too large, and is the superposition of the resonant current of the inverter circuit and the load current, which increases the loss of the inverter circuit and further reduces the efficiency of the inverter.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a modulation method of a resonant direct-current link three-phase inverter based on a space vector pulse width modulation technology (SVPWM for short). The method of the invention combines SVPWM to solve the above problems through the mutual cooperation between the inverter bridge and the converter circuit. Firstly, the method changes the modulation strategy of the inverter bridge from the traditional seven-segment wave-sending mode to the four-segment wave-sending mode, thereby reducing the phase change times of the inverter bridge in each switching period from six times to three times; secondly, the direct-current bus voltage under the zero vector is kept to be zero, so that when the inverter bridge is switched from the zero vector to the non-zero vector and the non-zero vector is switched to the zero vector, the total action times of the converter circuit are reduced from twice to once; meanwhile, by the distribution method of the polarity change vector of the load phase current, when the inverter bridge is switched between non-zero vectors, the converter circuit does not need to act; thereby ensuring that all switch tubes are realOn the basis of the existing soft switching action and the maintenance of one action per switching period of the commutation circuit, the turn-off times of the main power switch tube in each switching period of the quasi-ZVS (zero voltage) is reduced to one time; on the other hand, the method avoids the superposition of the resonant current of the converter circuit and the load current by increasing the shunt dead time, and maximally inhibits the first converter switch tube S_a1And a second commutation switch tube S_a2Current stress of (2).

The invention provides a modulation method of a resonant direct-current link three-phase inverter based on SVPWM (space vector pulse width modulation), which comprises two parts, namely vector synthesis and vector distribution;

setting 1 in the inverter bridge state to indicate that a main power switch tube on the phase bridge arm is switched on, setting 0 to indicate that a main power switch tube under the phase bridge arm is switched on, selecting a corresponding vector and calculating a duty ratio in a vector synthesis mode, synthesizing two non-zero vectors adjacent to the reference vector when the reference vector falls into sectors I to VI under a two-phase static coordinate system, supplementing the rest duty ratio through a zero vector, and only adopting one zero vector in each switching period;

setting load phase current to flow out of an output point of an inverter bridge arm as positive, arranging corresponding vectors in a vector distribution mode and generating a switching sequence, wherein the switching sequence is a zero vector, a non-zero vector X1, a non-zero vector X2 and a zero vector in a four-section wave generation mode, and the wave generation sequence of the non-zero vector is related to the phase current polarity of the bridge arm with phase commutation when switching between the non-zero vector and the non-zero vector; when two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is positive, and the bridge arm with the phase is switched from an upper main power switch tube to an anti-parallel diode of a lower main power switch tube by adjusting the wave sending sequence; when the two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is negative, and the lower main power switch tube of the bridge arm with the phase change is switched to the anti-parallel diode of the upper main power switch tube by adjusting the wave-sending sequence.

Further, when the reference vector falls in sector I, a non-zero vector 100 and a non-zero vector 110 are used for synthesis, and the rest is addedThe lower duty cycle is supplemented by zero

vector

000 or 111; when the reference vector is in sector I and the phase current I is loaded in phase B_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 110 and a zero vector 111; when the reference vector is in sector I and the phase current I is loaded in phase B_b>At 0, the switching sequence is zero vector 000, non-zero vector 110, non-zero vector 100, zero vector 000.

Further, when the reference vector falls in sector II, a non-zero vector 110 and a non-zero vector 010 are used for synthesis, and the rest duty cycle is supplemented by a zero

vector

000 or 111; when the reference vector is in sector II and the A phase loads phase current i_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 110 and a zero vector 111; when the reference vector is in sector II and the A phase loads phase current i_a>At 0, the switching sequence is zero vector 000, non-zero vector 110, non-zero vector 010, zero vector 000.

Further, when the reference vector falls in sector III, non-zero vector 010 and non-zero vector 011 are used for synthesis, and the rest duty cycle is supplemented by zero

vector

000 or 111; when the reference vector is in sector III and C phase load phase current i_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 011 and a zero vector 111; when the reference vector is in sector III and C phase load phase current i_c>At 0, the switching sequence is zero vector 000, non-zero vector 011, non-zero vector 010, zero vector 000.

Further, when the reference vector falls in the sector IV, a non-zero vector 011 and a non-zero vector 001 are used for synthesis, and the rest duty cycle is supplemented by a zero

vector

000 or 111; when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 011 and a zero vector 111; when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b>At 0, the switching sequence is zero vector 000, non-zero vector 011, non-zero vector 001, and zero vector 000.

Further, when the reference vector falls in sector V, a non-zero vector 001 and a non-zero vector 101 are used for synthesis, and the rest of the duty cycle is supplemented by a zero

vector

000 or 111; when reference is made toPhase current i of A phase load measured in sector V_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 101 and a zero vector 111; when the reference vector is in the sector V and the phase of A load phase current i_a>At 0, the switching sequence is zero vector 000, non-zero vector 101, non-zero vector 001, zero vector 000.

Further, when the reference vector falls in sector VI, a non-zero vector 101 and a non-zero vector 100 are used for synthesis, and the remaining duty cycle is supplemented by a zero

vector

000 or 111; when the reference vector is in the sector VI and the phase I of the C-phase load phase_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 101 and a zero vector 111; when the reference vector is in the sector VI and the phase I of the C-phase load phase_c>At 0, the switching sequence is zero vector 000, non-zero vector 101, non-zero vector 100, zero vector 000.

Further, the modulation strategy of the commutation circuit in the resonant dc link three-phase inverter is as follows: when the inverter bridge is in a zero vector, the converter circuit does not act, and the voltage of the direct-current bus is maintained at zero; when the bus switch tube is turned off, the second commutation switch tube is not immediately turned on, but the shunt dead time delta is delayed₃Then opening the circuit; when each switching period starts, the bus switch tube, the first commutation switch tube and the second commutation switch tube are all turned off; when the inverter bridge is switched from a zero vector to a non-zero vector X1, a delay time delta is elapsed₀Then, the first current conversion switch tube is switched on; after a delay time delta₁Then, the bus switch tube is switched on; after a delay time delta₂Then, the first commutation switch tube is turned off; shunting dead time delta before switching inverter bridge from non-zero vector X2 to zero vector₃Adding delay time delta₄When the bus bar is in a closed state, the bus bar switching tube is disconnected; passing shunt dead time delta₃Then, the second current conversion switch tube is switched on; after a delay time delta₄And then the second commutation switch tube is turned off.

The invention has the beneficial effects that:

the invention provides a modulation method of a three-phase inverter of a resonant direct-current link based on SVPWM (space vector pulse width modulation), which is used for ensuring all switching tubes to be real compared with load self-adaptive commutation controlThe existing soft switching action and the keeping commutation circuit only act once in each switching period, the turn-off times of the main power switch tube in each switching period, namely the zero-voltage (ZVS), is reduced from three times to one time, and the first commutation switch tube S is maximally restrained_a1And a second commutation switch tube S_a2The current stress of the three-phase inverter reduces the loss of the three-phase inverter in the resonant direct-current link and improves the efficiency of the inverter.

Drawings

Fig. 1 is a schematic circuit diagram of a resonant dc link three-phase inverter according to an embodiment of the present invention, in which: 1. a current conversion circuit; 2. an inverter bridge; 3. a load circuit; 4. a control circuit;

FIG. 2 is an equivalent circuit diagram of FIG. 1;

fig. 3 is a schematic diagram of switching signals of a three-phase inverter bridge of a resonant direct-current link three-phase inverter under the traditional SPWM in the embodiment of the present invention;

fig. 4 is a schematic diagram of switching signals of a three-phase inverter bridge of a resonant direct-current link three-phase inverter under a modulation method of the resonant direct-current link three-phase inverter based on SVPWM in the embodiment of the present invention;

fig. 5 is a schematic diagram of switching signals of a three-phase inverter bridge of a resonant direct-current link under a sawtooth carrier modulation strategy of positive and negative alternation of slope in the embodiment of the invention;

fig. 6 is a characteristic working waveform diagram of a resonant direct-current link three-phase inverter under a load adaptive commutation control strategy in the embodiment of the invention;

FIG. 7 shows the reference vector in the method of the present invention in the embodiment of the present invention in sector I (phase current I of phase-B load phase)_b<0) Vector synthesis graph of (2);

FIG. 8 shows the reference vector in the method of the present invention in the embodiment of the present invention in sector I (phase current I of phase-B load phase)_b>0) Vector synthesis graph of (2);

fig. 9 is a schematic diagram of switching signals of a three-phase inverter bridge of a resonant direct-current link three-phase inverter under the method of the invention in the embodiment of the invention;

FIG. 10 is a waveform diagram of characteristic operation of main components of a resonant DC link three-phase inverter in the embodiment of the present invention under the method of the present invention;

fig. 11 is a commutation working mode equivalent circuit diagram of a resonant dc link three-phase inverter in the embodiment of the present invention under the method of the present invention; in the figure, (a) is an equivalent circuit diagram of mode 0; (b) an equivalent circuit diagram of mode 1; (c) an equivalent circuit diagram of mode 2; (d) an equivalent circuit diagram of mode 3; (e) an equivalent circuit diagram of mode 4; (f) an equivalent circuit diagram of mode 5; (g) an equivalent circuit diagram of mode 6; (h) an equivalent circuit diagram of mode 7; (i) an equivalent circuit diagram of mode 8; (j) an equivalent circuit diagram of mode 9; (k) an equivalent circuit diagram of mode 10;

FIG. 12 shows a main power switch S of a resonant DC-link three-phase inverter according to an embodiment of the present invention from mode 0 to mode 10 under the method of the present invention₁Drive signal v_gS1Main power switch tube S₃Drive signal v_gS3And a main power switch tube S₅Drive signal v_gS5A simulated waveform diagram of (1);

FIG. 13 is a bus bar switch tube S of a resonant DC link three-phase inverter from mode 0 to mode 10 under the method of the present invention in an embodiment of the present invention_LDrive signal v_gSLFirst commutation switch tube S_a1Drive signal v_gSa1And a second commutation switch tube S_a2Drive signal v_gSa2A simulated waveform diagram of (1);

FIG. 14 shows a first commutation inductance L from mode 0 to mode 10 of a resonant DC-link three-phase inverter according to an embodiment of the present invention_a1Current i of_La1A second commutation inductor L_a2Current i of_La2And the DC bus voltage v_DClinkA simulated waveform diagram of (1);

FIG. 15 shows a first auxiliary commutation capacitor C of a resonant DC-link three-phase inverter according to an embodiment of the present invention from mode 0 to mode 10 under the method of the present invention_a1Voltage v of_Ca1A second auxiliary commutation capacitor C_a2Voltage v of_Ca2And a main converter capacitor C_LVoltage v of_CLA simulated waveform diagram of (1);

FIG. 16 shows a resonant DC link three-phase inverter according to an embodiment of the present inventionBus bar switch tube S under the method of the invention_LOn-time voltage v of_SLAnd current i_SL/DLA simulated waveform diagram of (1);

FIG. 17 is a bus switch tube S of a resonant DC link three-phase inverter in the embodiment of the present invention under the method of the present invention_LVoltage v at turn-off_SLAnd current i_SLA simulated waveform diagram of (1);

FIG. 18 shows a first commutation switch tube S of a resonant DC link three-phase inverter in the method of the present invention_a1On-time voltage v of_Sa1And current i_Sa1A simulated waveform diagram of (1);

FIG. 19 is a first commutation switch tube S of a resonant DC link three-phase inverter in the method of the invention_a1Voltage v at turn-off_Sa1And current i_Sa1A simulated waveform diagram of (1);

FIG. 20 shows a second commutation switch tube S of the resonant DC link three-phase inverter in the method of the present invention_a2On-time voltage v of_Sa2And current i_Sa2A simulated waveform diagram of (1);

FIG. 21 shows a second commutation switch tube S of the resonant DC link three-phase inverter in the method of the invention_a2Voltage v at turn-off_Sa2And current i_Sa2A simulated waveform diagram of (1);

FIG. 22 shows a main power switch tube S of a resonant DC link three-phase inverter in an embodiment of the present invention under the method of the present invention₁Voltage v at turn-on_S1And current i_S1A simulated waveform diagram of (1);

FIG. 23 shows a main power switch tube S of a resonant DC link three-phase inverter in an embodiment of the present invention under the method of the present invention₁Voltage v for realizing ZVS (zero voltage) turn-off_S1And current i_S1A simulated waveform diagram of (1);

FIG. 24 shows a main power switch tube S of a resonant DC link three-phase inverter in an embodiment of the present invention under the method of the present invention₁Voltage v for realizing quasi-ZVS (zero voltage) turn-off_S1And current i_S1A simulated waveform diagram of (1);

FIG. 25 shows the main power switch S of the resonant DC link three-phase inverter in one switching cycle according to the method of the present invention₁Buffer capacitor C₁Voltage v of_C1Main power switch tube S₃Buffer capacitor C₃Voltage v of_C3Main power switch tube S₅Buffer capacitor C₅Voltage v of_C5And the DC bus voltage v_DClinkA simulated oscillogram;

FIG. 26 is a diagram of a main power switch tube S of a resonant DC link three-phase inverter in a switching period under load adaptive commutation control according to an embodiment of the present invention₁Buffer capacitor C₁Voltage v of_C1Main power switch tube S₃Buffer capacitor C₃Voltage v of_C3Main power switch tube S₅Buffer capacitor C₅Voltage v of_C5And the DC bus voltage v_DClinkA simulated oscillogram;

FIG. 27 shows the first commutation inductance L of the resonant DC-link three-phase inverter in one inverter output period under the M method of the present invention in the embodiment of the present invention_a1Current i of_La1And a second commutation inductor L_a2Current i of_La2A simulated waveform diagram of (1);

FIG. 28 shows the first commutation inductance L of the resonant DC link three-phase inverter in one inverter output period under the load adaptive commutation control according to the embodiment of the present invention_a1Current i of_La1And a second commutation inductor L_a2Current i of_La2A simulated waveform diagram of (1);

FIG. 29 is a three-phase output phase current i of the resonant DC link three-phase inverter according to the embodiment of the present invention under the method of the present invention_a、i_b、i_cThe simulated waveform of (2).

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.

The specific structure of the resonant direct-current link three-phase inverter disclosed by the invention is referred to a novel resonant direct-current link soft switching inverter and a modulation method thereof disclosed in patent CN106533224A of China in 2017, 3, month and 22, and as shown in FIG. 1, the resonant direct-current link three-phase inverter comprises a converter circuit 1, an inverter bridge 2, a load circuit 3, a control circuit 4 and a direct-current power supply E;

the converter circuit 1 comprises a bus switch tube S_LFirst commutation switch tube S_a1The second commutation switch tube S_a2First commutation inductance L_a1A second commutation inductor L_a2Main converting capacitor C_LA first auxiliary commutation capacitor C_a1A second auxiliary commutation capacitor C_a2Anti-parallel diode D of bus switch tube_LA first auxiliary diode D_a1A second auxiliary diode D_a2A third auxiliary diode D_a3And a fourth auxiliary diode D_a4。

The inverter bridge is a three-phase inverter bridge and comprises an A-phase inverter bridge, a B-phase inverter bridge and a C-phase inverter bridge.

The A-phase inverter bridge comprises a first main power switch tube S₁An anti-parallel fly-wheel diode D of the first main power switch tube₁The parallel buffer capacitor C of the first main power switch tube₁The second main power switch tube S₂And an anti-parallel fly-wheel diode D of the second main power switch tube₂Parallel buffer capacitor C with second main power switch tube₂First main power switch tube S₁Is connected with a second main power switch tube S₂Collector of the first main power switch tube S₁And a second main power switch tube S₂The outgoing line at the connecting point of (a) is an a-phase alternating current output end.

The B-phase inverter bridge comprises a first main power switch tube S₃An anti-parallel fly-wheel diode D of the first main power switch tube₃The parallel buffer capacitor C of the first main power switch tube₃The second main power switch tube S₄And an anti-parallel fly-wheel diode D of the second main power switch tube₄Parallel buffer capacitor C with second main power switch tube₄First main power switch tube S₃Is connected with a second main power switch tube S₄Collector of the first main power switch tube S₃And a second main power switch tube S₄At the connecting point ofThe outgoing line is a B alternating current output end.

The C-phase inverter bridge comprises a first main power switch tube S₅An anti-parallel fly-wheel diode D of the first main power switch tube₅The parallel buffer capacitor C of the first main power switch tube₅The second main power switch tube S₆And an anti-parallel fly-wheel diode D of the second main power switch tube₆Parallel buffer capacitor C with second main power switch tube₆First main power switch tube S₅Is connected with a second main power switch tube S₆Collector of the first main power switch tube S₅And a second main power switch tube S₆The outgoing line at the connecting point of the transformer is a C-shaped alternating current output end.

First main power switch tube S of each phase inverter bridge₁、S₃And S₅The collectors of the inverter bridge are connected with each other to serve as the positive end of the inverter bridge, and the second main power switch tube S of each phase of the inverter bridge₂、S₄And S₆Are connected to each other as the negative terminal of the inverter bridge.

The load circuit is a three-phase resistive-inductive load and comprises three resistors R_a、R_b、R_cAnd three inductors L_a、L_b、L_cResistance R_a、R_bAnd R_cOne end of the resistor R is respectively connected with the A-phase alternating current output end, the B-phase alternating current output end and the C-phase alternating current output end, and the resistor R_a、R_bAnd R_cAre respectively connected with an inductor L at the other end_a、L_bAnd L_cOne terminal of (1), inductance L_a、L_bAnd L_cWhile the output phase currents i of the A-phase AC output terminal, the B-phase AC output terminal and the C-phase AC output terminal are connected together_a、i_bAnd i_cSampled by the sensor and used as an input signal d_ia、d_ibAnd d_icRespectively, to the control circuit 4.

The negative pole of the DC power supply E is connected with the negative end of the inverter bridge, and the positive pole of the DC power supply E is connected with the bus switch tube S_LCollector electrode of (2), bus bar switch tube S_LThe emitting electrode of the bus is connected with the positive end of the inverter bridge and the inverse of the bus switch tubeParallel diode D_LAnode of the switch tube S_LEmitter of (2), anti-parallel diode D of bus switch tube_LCathode of the switch tube S_LThe collector electrode of (1).

Main current conversion capacitor C_LPositive pole of S is connected with bus switch tube_LCollector and first commutation switch tube S_a1Collector electrode of (1), main converter capacitor C_LNegative pole of (2) connecting bus switch tube S_LOf the first commutation switch tube S_a1Is connected with the first commutation inductor L_a1One terminal of (1), the first commutation inductor L_a1The other end of the connecting rod is connected with a bus switch tube S_LOf the second commutation switch tube S_a2Is connected with the negative electrode of the direct current power supply E, and a second commutation switch tube S_a2Is connected with the second commutation inductor L_a2One terminal of (1), a second commutation inductor L_a2The other end of the connecting rod is connected with a bus switch tube S_LAn emitter of (1).

First auxiliary diode D_a1Is connected with the first commutation switch tube S_a1The first auxiliary diode D_a1Anode of (2) is connected with a first auxiliary commutation capacitor C_a1Negative electrode of (1), first auxiliary commutation capacitor C_a1Is connected with a second auxiliary commutation capacitor C_a2Negative electrode and bus bar switch tube S_LEmitter of (2), second auxiliary commutation capacitor C_a2Is connected with a second auxiliary diode D_a2A second auxiliary diode D_a2Anode of the first commutation switch tube S is connected with the second commutation switch tube S_a2The collector electrode of (1).

Third auxiliary diode D_a3Is connected with the anode of a direct current power supply E, and a third auxiliary diode D_a3Anode of (2) is connected with a second auxiliary commutation capacitor C_a2And a fourth auxiliary diode D_a4Is connected with the negative pole of the DC power supply E, and a fourth auxiliary diode D_a4Is connected with a first auxiliary commutation capacitor C_a1The negative electrode of (1).

Bus switch tube S_LFirst commutation switch tube S_a1The second commutation switch tube S_a2And each main power in the inverter bridgeSwitch tube S_x(x is 1,2,3,4,5,6) is connected to an existing control circuit 4, and a signal d is sent from the control circuit 4_SL、d_Sa1、d_Sa2、d_Sx(x is 1,2,3,4,5,6) respectively controls the bus switch tube S_LFirst commutation switch tube S_a1The second commutation switch tube S_a2Main power switch tubes S in the inverter bridge_x(x ═ 1,2,3,4,5,6) on and off, with output phase currents i for a, B, and C phases_a、i_bAnd i_cSampled by the sensor and used as an input signal d_ia、d_ibAnd d_icRespectively, to the control circuit 4.

Bus switch tube S_LFirst commutation switch tube S_a1The second commutation switch tube S_a2Main power switch tubes S in the inverter bridge_xAll-controlled switching devices are adopted (x ═ 1,2,3,4,5,6), and in a specific embodiment, a power transistor, an insulated gate bipolar transistor, a power field effect transistor, an injection enhancement insulated gate transistor, an integrated gate commutated thyristor or an intelligent power module can be adopted.

Anti-parallel diode D of bus switch tube_LA first auxiliary diode D_a1A second auxiliary diode D_a2A third auxiliary diode D_a3The fourth auxiliary diode D_a4And anti-parallel fly-wheel diode D of each main power switch tube in inverter bridge_x(x ═ 1,2,3,4,5,6) fast recovery diodes or high frequency diodes may be used in specific implementations.

The three-phase inverter in the resonant direct-current link is suitable for various inversion occasions and can play an important role in the fields of industrial production, transportation, communication systems, power systems, new energy systems, various power systems, aerospace and the like. The working process of the resonant dc link three-phase inverter in the present embodiment is analyzed below by taking its application in a variable frequency speed control system as an example.

In order to further explain the working principle of the resonant direct-current link three-phase inverter, an equivalent circuit diagram 2 is used instead of the diagram 1. To simplify the analysis, assume: all devices are in ideal working states; ② for resistive loadsThe inductance is far larger than the first commutation inductance L_a1And a second commutation inductor L_a2The load current at the moment of switching state transition of each main power switching tube in the inverter bridge is regarded as a constant current source I_oThe value of the current value depends on the instantaneous value of the output phase current of each phase and the switching state of 6 main power switching tubes of the inverter bridge; thirdly, at the moment of the switching state transition of each main power switching tube in the inverter bridge, each anti-parallel freewheeling diode in the inverter bridge is equivalent to D_inv(ii) a Parallel buffer capacitors in the inverter bridge are equivalent to C_invTaking out C_inv＝3C_xWhen any one of the first main power switch tube and the second main power switch tube of each phase of bridge arm of the inverter bridge is switched on, the buffer capacitors connected in parallel with the first main power switch tube and the second main power switch tube are short-circuited, and the capacitors on 3 bridge arms are equivalent to 3 buffer capacitors connected in parallel during normal operation.

As shown in fig. 3, for the resonant dc link inverter using the conventional SPWM, in one switching period, six main power switching transistors of the inverter bridge need to operate once, so that the converter circuit needs to operate six times to manufacture six zero voltage notches, so as to implement soft switching operations of all the main power switching transistors. This limits the improvement of the inverter switching frequency and the operation efficiency, reduces the quality of the output waveform, and increases the high-frequency common mode voltage. As shown in fig. 4, when the inverter bridge is in a circulating current state, that is, the upper main power switching tubes of the three-phase bridge arm are all turned on or the lower main power switching tubes are all turned on, the three-phase load is short-circuited by the inverter bridge, and no energy is exchanged between the dc power supply E and the three-phase load, so that it is feasible to maintain the dc bus voltage at zero all times through the converter circuit. Since the conventional SPWM has two circulating current states in one switching period, the number of operations of the inverter circuit in each switching period can be reduced from six to four, but the operation frequency is still high.

Fig. 5 shows a specific electric energy conversion process of the load adaptive commutation control, which is a modulation strategy using a sawtooth wave with a positive and negative alternating slope as a carrier. The three-phase inverter bridge switching signals of the resonant dc link three-phase inverter in the present embodiment under the sawtooth carrier modulation strategy with alternating positive and negative slopes are as shown in fig. 5. In fig. 5, a solid line in the switching signals of the three-phase inverter bridge represents the switching signals of the first main power switching tubes of the bridge arms of each phase, that is, the switching signals of the main power switching tubes of the upper bridge arm; the dotted line represents the switching signal of the second main power switching tube of each phase bridge arm, namely the switching signal of the main power switching tube of the lower bridge arm. Since it is necessary to determine the direction of the slope of the sawtooth carrier from the direction of the output phase current, fig. 5 exemplifies that the a-phase output phase current is negative, the B, C-phase output phase current is positive, that is, the slope of the a-phase sawtooth carrier is negative, and the slopes of the B-phase and C-phase sawtooth carriers are positive.

The specific content of the sawtooth carrier modulation strategy with the positive and negative alternating slopes is as follows: the sawtooth wave with alternating positive and negative slopes is used for replacing the traditional triangular wave as the carrier, the slope of the sawtooth carrier is unchanged, but the slope of the sawtooth carrier changes along with the direction of the output phase current, the direction of the output phase current is positive, the slope of the sawtooth carrier is positive, the direction of the output phase current is negative, and the slope of the sawtooth carrier is negative. The application of the sawtooth carrier waves with the positive and negative alternate slopes can enable the moment when the anti-parallel freewheeling diode on the inverter bridge conducts current conversion to the main power switch tube opposite to the same bridge arm to be concentrated on the vertical edge of the sawtooth carrier waves, and the current conversion circuit acts before and after the vertical edge of the sawtooth carrier waves, so that the soft switching of the corresponding main power switch tube is realized. Therefore, the soft switching of all main power switching tubes can be realized by only once action of the commutation circuit in one switching period, and the action frequency of the commutation circuit is reduced to 1/6 of the traditional triangular carrier modulation strategy.

As can be seen from fig. 5, under the load adaptive commutation control, the turn-off times of the main power switch tube of the resonant dc link three-phase inverter in one switching period is three times. Quasi ZVS (zero voltage) turn-off does not completely eliminate turn-off losses of the main power switching tube, thus reducing the efficiency of the inverter. As can be seen from fig. 6, under the load adaptive commutation control, when the bus bar switch tube S is in the on-off state_LAfter the second commutation switch tube S is turned off_a2Immediately turning on to enable the capacitor C stored in the first auxiliary commutation capacitor_a1The energy of the first commutation switch tube S is converted into resonance current in the resonance process to cause the first commutation switch tube S_a1And a second commutation switch tube S_a2The current stress of the converter circuit is too large, and the resonance current and the load current are superposed, so that the loss of the converter circuit is increased.

The invention provides a modulation method of a three-phase inverter of a resonant direct-current link based on SVPWM, which solves the problems through the mutual cooperation between the three-phase inverter and a converter circuit. Firstly, the method changes the modulation strategy of the inverter bridge from the traditional seven-segment wave-sending mode to the four-segment wave-sending mode, thereby reducing the phase change times of the inverter bridge in each switching period from six times to three times; secondly, the direct-current bus voltage under the zero vector is kept to be zero, so that when the inverter bridge is switched from the zero vector to the non-zero vector and the non-zero vector is switched to the zero vector, the total action times of the converter circuit are reduced from twice to once; meanwhile, by the distribution method of the polarity change vector of the load current, when the inverter bridge is switched between non-zero vectors, the converter circuit does not need to act; therefore, on the basis of ensuring that all the switching tubes realize soft switching action and keeping the commutation circuit to act once in each switching period, the turn-off frequency of the main power switching tube in each switching period is reduced to one; on the other hand, the novel SVPWM method avoids superposition of resonant current and load current of the converter circuit by increasing shunt dead time, and maximally inhibits the first converter switching tube S_a1And a second commutation switch tube S_a2Current stress of (2).

A modulation method of a resonance direct current link three-phase inverter based on SVPWM (space vector pulse width modulation), aiming at the resonance direct current link three-phase inverter, comprises two parts, namely vector synthesis and vector distribution;

when the reference vector falls in sector I, it is synthesized using non-zero vector 100 and non-zero vector 110, the remaining duty cycle being supplemented by zero

vector

000 or 111;

when the reference vector falls in sector II, a non-zero vector 110 and a non-zero vector 010 are used for synthesis, and the rest duty cycle is supplemented by a zero

vector

000 or 111;

when the reference vector falls in the sector III, synthesizing by adopting a non-zero vector 010 and a non-zero vector 011, and supplementing the rest duty ratio by a zero

vector

000 or 111;

when the reference vector falls in the sector IV, synthesizing by adopting a non-zero vector 011 and a non-zero vector 001, and supplementing the rest duty ratio by a zero

vector

000 or 111;

when the reference vector falls in sector V, a non-zero vector 001 and a non-zero vector 101 are used for synthesis, and the rest of the duty cycle is supplemented by a zero

vector

000 or 111;

when the reference vector falls in sector VI, a combination is made using non-zero vector 101 and non-zero vector 100, with the remaining duty cycle being supplemented by zero

vector

000 or 111.

And setting the load phase current to flow out of an output point of an inverter bridge arm as positive, wherein the vector distribution mode is characterized in that: a four-section wave-sending mode is adopted, the switching sequence is a zero vector, a non-zero vector X1, a non-zero vector X2 and a zero vector, and the wave-sending sequence of the non-zero vector is related to the phase current polarity of a bridge arm with phase change when the non-zero vector is switched;

when two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is positive, and the bridge arm with the phase is switched from an upper main power switch tube to an anti-parallel diode of a lower main power switch tube by adjusting the wave sending sequence; when the two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is negative, and the lower main power switch tube of the bridge arm with the phase change is switched to the anti-parallel diode of the upper main power switch tube by adjusting the wave-sending sequence;

for example, when the reference vector is in sector I, the two non-zero vectors will cause phase change in the B-phase bridge arm during switching, as shown in fig. 7, if the B-phase load phase current I_b<0, make the inverter bridge switch from non-zero vector 100 to non-zeroVector 110, then the phase of the bridge arm of the B phase is changed from 0 to 1; if the phase B load phase current i is as shown in FIG. 8_b>0, switching the inverter bridge from a non-zero vector 110 to a non-zero vector 100, and then switching the phase of the B-phase bridge arm from 1 to 0, so that the main power switching tube of the phase-switching bridge arm can realize quasi-ZVS (zero voltage) turn-off under the action of the load phase current;

when the reference vector is in sector I and the phase current I is loaded in phase B_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 110 and a zero vector 111;

when the reference vector is in sector I and the phase current I is loaded in phase B_b>When 0, the switching sequence is a zero vector 000, a non-zero vector 110, a non-zero vector 100 and a zero vector 000;

when the reference vector is in sector II and the A phase loads phase current i_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 110 and a zero vector 111;

when the reference vector is in sector II and the A phase loads phase current i_a>When 0, the switching sequence is a zero vector 000, a non-zero vector 110, a non-zero vector 010 and a zero vector 000;

when the reference vector is in sector III and C phase load phase current i_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 011 and a zero vector 111;

when the reference vector is in sector III and C phase load phase current i_c>When 0, the switching sequence is zero vector 000, non-zero vector 011, non-zero vector 010 and zero vector 000;

when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 011 and a zero vector 111;

when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b>When 0, the switching sequence is a zero vector 000, a non-zero vector 011, a non-zero vector 001 and a zero vector 000;

when the reference vector is in the sector V and the phase of A load phase current i_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 101 and a zero vector 111;

when the reference vector is inSector V and A phase load phase current i_a>When 0, the switching sequence is a zero vector 000, a non-zero vector 101, a non-zero vector 001 and a zero vector 000;

when the reference vector is in the sector VI and the phase I of the C-phase load phase_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 101 and a zero vector 111;

when the reference vector is in the sector VI and the phase I of the C-phase load phase_c>At 0, the switching sequence is zero vector 000, non-zero vector 101, non-zero vector 100, zero vector 000.

Secondly, aiming at the resonant direct-current link three-phase inverter, the modulation strategy applied by the converter circuit is as follows: when the inverter bridge is in a zero vector, the converter circuit does not act, and the voltage of the direct-current bus is maintained at zero; when bus switch tube S_LAfter the second commutation switch tube S is turned off_a2Not switched on immediately, but rather delayed shunt dead time delta₃Then opening the circuit; at the beginning of each switching cycle, the bus bar switch tube S_LFirst commutation switch tube S_a1And a second commutation switch tube S_a2All are turned off; when the inverter bridge is switched from a zero vector to a non-zero vector X1, a delay time delta is elapsed₀Then, the first commutation switch tube S_a1Opening; after a delay time delta₁Rear, bus switch tube S_LOpening; after a delay time delta₂Then, the first commutation switch tube S_a1Turning off; shunting dead time delta before switching inverter bridge from non-zero vector X2 to zero vector₃Adding delay time delta₄Time, bus switch tube S_LTurning off; passing shunt dead time delta₃Then, the second commutation switch tube S_a2Opening; after a delay time delta₄Then, the second commutation switch tube S_a2And (6) turning off.

In the load self-adaptive commutation control of the resonant direct-current link three-phase inverter provided in the Chinese patent CN107493025A, each switching period inverter bridge commutates for four times, a zero-voltage groove is manufactured on a commutation circuit, the ZVS (zero voltage) condition of the inverter bridge in the primary commutation process is realized, and the other three main power switching tubes all realize quasi-ZVS (zero voltage) turn-off; in the novel SVPWM method, each switching period of the inverter bridge carries out three phase changes, a zero voltage groove is manufactured on a converter circuit, the ZVS (zero voltage) condition of the inverter bridge in the two-time phase change process is realized, and the other primary main power switching tubes realize quasi-ZVS (zero voltage) turn-off. Therefore, the novel SVPWM method reduces the turn-off times of the quasi-ZVS (zero voltage) of the main power switch tube, thereby reducing the loss of the inverter bridge.

Under the load self-adaptive commutation control, when a bus switch tube S_LAfter the second commutation switch tube S is turned off_a2Immediately turning on and storing in the first auxiliary commutation capacitor C_a1The energy of the first commutation switch tube S is converted into resonance current in the resonance process, so that the first commutation switch tube S_a1And a second commutation switch tube S_a2The current stress is overlarge, which is the superposition of the resonant current and the load current of the converter circuit, and the loss of the converter circuit is increased; under the load self-adaptive commutation control, the first commutation switch tube S_a1Current stress i_Sa1maxAnd a second commutation switch tube S_a2Current stress i_Sa2maxRespectively as follows:

wherein E is the voltage value of the direct current power supply, C_aIs the capacitance value of the main commutation capacitor, C_bIs the capacitance of the first or second converter capacitor, L is the inductance of the first or second converter inductor, I_omaxIs the maximum load current.

Under the method of the invention, when the bus bar switches the tube S_LAfter the second commutation switch tube S is turned off_a2In delay shunt dead time delta₃Then it is turned on and stored in the first auxiliary commutation capacitor C_a1The energy in (1) passes through the load current I_oReleasing; under the novel SVPWM method, a first commutation switch tube S_a1Current stress i_Sa1maxAnd a second commutation switch tube S_a2Current stress i_Sa2maxRespectively as follows:

i_Sa2max＝0 (4)

at this time, C is added_aThe value of (A) is taken as small as possible, so that the first commutation switch tube S can be enabled_a1Is approximately the maximum load phase current, and the second commutation switch tube S_a2The current stress of the converter circuit is zero, thereby reducing the loss of the converter circuit.

The characteristic working waveform of the modulation method of the resonant dc link three-phase inverter based on SVPWM proposed in this embodiment is shown in fig. 10, and the phase current I of the load is loaded in the sector I and the sector B_b<0 is an example, wherein I_oRepresenting the load current, I_aRepresents the A-phase load phase current in the switching period, I_cRepresents the C-phase load phase current, S, for that switching period_LIndicating bus switch tube S_LDriving waveform of (1), S_a1Indicating the first commutation switch tube S_a1Driving waveform of (1), S_a2Indicating a second commutation switch tube S_a2V is a drive waveform of_CLRepresenting the main converter capacitance C_LVoltage v of_CinvRepresents the equivalent capacitance C_invVoltage of i_CLRepresenting the main converter capacitance C_LCurrent of (i)_CinvRepresents the equivalent capacitance C_invCurrent of v_Ca1Representing the first auxiliary commutation capacitance C_a1Voltage of i_Ca1Representing the first auxiliary commutation capacitance C_a1Current of (i)_La1Representing the first commutation inductance L_a1The current of (2). The inverter primary commutation process includes 11 operation modes, an equivalent circuit diagram of the 11 operation modes is shown in fig. 11, wherein a solid line represents an element operating in the corresponding mode, a dashed line represents an element not operating in the corresponding mode, and the operation mode of the circuit is specifically analyzed below.

Mode 0[ -t₀]: an equivalent circuit diagram shown in FIG. 11(a), t₀Before the moment of time, the user can use the mobile phone,bus switch tube S_LFirst commutation switch tube S_a1And a second commutation switch tube S_a2Are all turned off. The inverter bridge is under zero vector 111, and the load current I_oIs zero. t is t₀At this time, the initial state of the equivalent circuit is: main current conversion capacitor C_LVoltage v of_CLIs a DC power supply voltage E and an equivalent capacitor C_invVoltage v of_CinvA first auxiliary commutation capacitor C_a1Voltage v of_Ca1And a second auxiliary commutation capacitor C_a2Voltage v of_Ca2Are all zero. t is t₀At that time, the inverter bridge switches from zero vector 111 to non-zero vector 100, and mode 0 ends.

Mode 1[ t ]₀～t₁]: as shown in the equivalent circuit diagram of FIG. 11(b), at t₀At the moment, the inverter bridge is switched from a zero vector 111 to a non-zero vector 100, and the load current I_oChanging from zero to A-phase load phase current I in the switching period_a. Equivalent diode D at this time_invOn, the load current I_oThrough an equivalent diode D_invFollow current is performed. At this time, the direct-current bus voltage is zero, so that the main power switching tube of the inverter bridge realizes ZVS (zero voltage) switching. At t₁At the moment, the first commutation switch tube S_a1On, mode 1 ends.

Mode 2[ t ]₁～t₂]: as shown in the equivalent circuit diagram of FIG. 11(c), at t₁At the moment, the first commutation switch tube S_a1On, since the DC power supply voltage E is completely applied to the first commutation inductor L_a1Upper, first commutation inductance L_a1Current i in_La1Linearly rising from zero, load current I_oBy an equivalent diode D_invTo the first commutation inductance L_a1And (6) converting current. First commutation switch tube S_a1After being switched on, the first commutation inductor L_a1Current i in_La1Rises linearly from zero due to the first commutation inductance L_a1And the first commutation switch tube S_a1In series, so the first commutation switch tube S_a1Quasi ZCS (zero current) switching-on is realized. When the first commutation inductor L_a1Current i in_La1Up to the load current I_oTime, equivalent diodeD_invOff, mode 2 ends.

Mode 3[ t ]₂～t₃]: as shown in the equivalent circuit diagram of FIG. 11(d), at t₂Time of day, equivalent diode D_invOff, load current I_oCompletely commutates to the first commutation inductance L_a1First commutation inductance L_a1And a main current conversion capacitor C_LAnd an equivalent capacitance C_invResonance begins. Equivalent capacitance C_invCharging, main commutation capacitor C_LDischarging, first commutation inductance L_a1Current i in_La1The resonance rises. When the equivalent capacitance C_invVoltage v of_CinvRising to DC supply voltage E, main commutation capacitor C_LVoltage v of_CLWhen the voltage drops to zero, the bus switch tube S_LIs connected in parallel with the diode D_LOn, first commutation inductance L_a1Current i in_La1To a maximum value i_La1maxAnd mode 3 ends.

Mode 4[ t ]₃～t₄]: as shown in the equivalent circuit diagram of FIG. 11(e), at t₃Time of day, bus switch tube S_LIs connected in parallel with the diode D_LAnd (4) opening. First commutation inductance L_a1Current i of_La1One part passes through a bus switch tube S_LIs connected in parallel with the diode D_LAnd a first commutation switch tube S_a1Circulating current, another part is load current I_o. During which the bus-bar switch tube S is switched on_LDue to bus switch tube S_LIs connected in parallel with the diode D_LConducting and bus switch tube S_LRealizing ZVZCS (zero voltage current) switching-on. When the first commutation switch tube S_a1When off, mode 4 ends.

Mode 5[ t ]₄～t₅]: as shown in the equivalent circuit diagram of FIG. 11(f), at t₄At the moment, the first commutation switch tube S_a1Shut-off, bus switch tube S_LOpening, first auxiliary diode D_a1And (4) opening. At the moment, the direct current power supply passes through the bus switch tube S_LPower is supplied to the load. First commutation inductance L_a1And a first auxiliary commutation capacitor C_a1Starting resonance, the first commutation inductance L_a1To the energy ofAn auxiliary current conversion capacitor C_a1Transfer, first auxiliary commutation capacitor C_a1The voltage at the two ends rises from zero, which can be known from kirchhoff's voltage law, and at the moment, the first auxiliary commutation capacitor C_a1Voltage at two ends and first commutation switch tube S_a1The voltages at the two ends are equal, so the first commutation switch tube S_a1A quasi ZVS (zero voltage) turn-off is achieved. At t₅At that time, the first auxiliary commutation capacitor C_a1The voltage across both ends rises to E and mode 5 ends.

Mode 6[ t ]₅～t₆]: as shown in FIG. 11(g), at t₅At that time, the first auxiliary commutation capacitor C_a1The voltage at both ends rises to E, and a bus switch tube S_LShut-off, bus switch tube S_LIs connected in parallel with the diode D_LAnd a fourth auxiliary diode D_a4And (4) opening. First commutation inductance L_a1The residual energy passes through the first auxiliary diode D_a1The fourth auxiliary diode D_a4And bus switch tube S_LIs connected in parallel with the diode D_LFed back to the DC power supply, the first commutation inductor L_a1Current i in_La1The linearity decreases. When the first commutation inductor L_a1Current i in_La1Down to a load current I_oTime, bus switch tube S_LIs connected in parallel with the diode D_LOff, mode 6 ends.

Mode 7[ t ]₆～t₇]: as shown in FIG. 11(h), at t₆Time of day, bus switch tube S_LIs connected in parallel with the diode D_LShut-off, bus switch tube S_LAnd (4) opening. First commutation inductance L_a1The residual energy passes through the first auxiliary diode D_a1The fourth auxiliary diode D_a4And bus switch tube S_LFed back to the DC power supply, the first commutation inductor L_a1Current i in_La1The linear reduction continues. When the first commutation inductor L_a1Current i in_La1Down to zero, the first auxiliary diode D_a1And a fourth auxiliary diode D_a4Off, mode 7 ends.

Mode 8[ t ]₇～t₈]: as shown in FIG. 11(i), at t₇At the moment, the first auxiliary diode D_a1And a fourth auxiliary diode D_a4When the circuit is turned off, the circuit is in a stable state, and the direct current power supply passes through the bus switch tube S_LPower is supplied to the load. During the period, the inverter bridge is switched from the non-zero vector 100 to the non-zero vector 110, and because the B-phase current is less than zero, the main power switch tube of the inverter bridge realizes quasi-ZVS (zero voltage) turn-off and the load current I_oPhase current I carried by phase A_aPhase current I of load changed into C phase_c。t₉Time of day, bus switch tube S_LOff, mode 8 ends.

Mode 9[ t ]₈,t₉]: as shown in FIG. 11(j), at t₈Time of day, bus switch tube S_LOff, fourth auxiliary diode D_a4And (4) opening. Main current conversion capacitor C_LA first auxiliary commutation capacitor C_a1And an equivalent capacitance C_invThe energy exchange is started. Main current conversion capacitor C_LLinearly charged, first auxiliary commutating capacitor C_a1And an equivalent capacitance C_invAnd (4) linear discharging. Due to the fact that the bus bar is connected with a switch tube S_LParallel main commutation capacitor C_LThe voltage of the bus switch tube S rises from zero_LA quasi ZVS (zero voltage) turn-off is achieved. t is t₉At all times, the main commutation capacitor C_LIs raised to the DC supply voltage E, and a first auxiliary commutation capacitor C_a1And an equivalent capacitance C_invIs reduced to zero, the equivalent diode D_invOn and mode 9 ends.

Mode 10[ t ]₉,t₁₀]: as shown in FIG. 11(k), at t₉Time of day, equivalent diode D_invOn, the load current I_oThrough an equivalent diode D_invAnd then follow current. t is t₁₀At the moment, the inverter bridge is switched from a non-zero vector 110 to a zero vector 111, and because the direct current bus voltage is zero at the moment, the main power switch tube of the inverter bridge realizes ZVS (zero voltage) switching and the load current I_oPhase current I carried by phase C_cBecomes zero. At which point the circuit returns to mode 0 and begins the next commutation.

In order to verify the correctness of the theory, a simulation platform shown in fig. 1 is built for verification, and the corresponding simulation result is described below.

Under the method of the invention, the main power switch tube S from mode 0 to mode 10 of the resonant DC link three-phase inverter₁Drive signal v_gS1Main power switch tube S₃Drive signal v_gS3And a main power switch tube S₅Drive signal v_gS5The simulated waveform diagram of (2) is shown in fig. 12, and the waveform is consistent with the characteristic working waveform of fig. 9 as can be seen from the simulated waveform diagram of fig. 12, thereby proving the correctness of the commutation working mode of the main power switch tube.

Under the method of the invention, the bus switch tube S from mode 0 to mode 10 of the resonant DC link three-phase inverter_LDrive signal v_gSLFirst commutation switch tube S_a1Drive signal v_gSa1And a second commutation switch tube S_a2Drive signal v_gSa2The simulated waveform diagram of (2) is shown in fig. 13, and the simulated waveform diagram of fig. 13 shows that the waveform is consistent with the characteristic working waveform diagram of fig. 10, which proves that the bus switch tube S_LFirst commutation switch tube S_a1And a second commutation switch tube S_a2Correctness of the commutation operational mode.

Under the method of the invention, the first commutation inductor L from mode 0 to mode 10 of the resonant DC link three-phase inverter_a1Current i of_La1A second commutation inductor L_a2Current i of_La2And the DC bus voltage v_DClinkAs shown in fig. 14, the first auxiliary commutation capacitor C from mode 0 to mode 10 of the resonant dc link three-phase inverter in this embodiment_a1Voltage v of_Ca1A second auxiliary commutation capacitor C_a2Voltage v of_Ca2And a main converter capacitor C_LVoltage v of_CLAs shown in fig. 15; as can be seen from the simulation waveforms of fig. 14 and 15, the waveforms are consistent with the characteristic operating waveforms of fig. 10, and the correctness of the commutation operating mode of the commutation circuit is proved.

Under the method of the invention, the resonant DC loopBus switch tube S of three-phase inverter_LVoltage v at turn-on_SLAnd current i_SL/DLThe simulation waveform of (2) is shown in FIG. 16, and the bus bar switch tube S can be seen from the simulation waveform of FIG. 16_LAfter being turned on, the anti-parallel diode D_LIs conducted, so that the bus switch tube S_LRealizing ZVZCS (zero voltage current) switching-on.

Under the method, the bus switch tube S of the resonant direct-current link three-phase inverter_LVoltage v at turn-off_SLAnd current i_SLThe simulation waveform of (2) is shown in FIG. 17, and the bus switch tube S can be seen from the simulation waveform of FIG. 17_LVoltage v after turn-off_SLLinearly rising, so that the bus bar switch tube S_LA quasi ZVS (zero voltage) turn-off is achieved.

Under the method, the first commutation switch tube S of the resonant direct-current link three-phase inverter_a1Voltage v at turn-on_Sa1And current i_Sa1The simulation waveform of (2) is shown in fig. 18, and the first commutation switch tube S can be seen from the simulation waveform of fig. 18_a1Current i after turn-on_Sa1Linearly rising, so that the first commutation switch tube S_a1Quasi ZCS (zero current) switching-on is realized.

Under the method, the first commutation switch tube S of the resonant direct-current link three-phase inverter_a1Voltage v at turn-off_Sa1And current i_Sa1The simulation waveform of (2) is shown in fig. 19, and the first commutation switch tube S can be seen from the simulation waveform of fig. 19_a1Voltage v after turn-on_Sa1Resonance rises, so that the first commutation switch S_a1A quasi ZVS (zero voltage) turn-off is achieved.

Under the method, the second commutation switch tube S of the resonant direct-current link three-phase inverter_a2Voltage v at turn-on_Sa2And current i_Sa2The simulated waveform diagram of (2) is shown in fig. 20, and the second commutation switch tube S can be seen from the simulated waveform diagram of fig. 20_a2Voltage v before and after turn-on_Sa2And current i_Sa2Are all 0, therefore the second commutation switch tube S_a2Realizing ZVZCS (zero voltage current) switching-on.

Under the method, the second commutation switch tube S of the resonant direct-current link three-phase inverter_a2Voltage v at turn-off_Sa2And current i_Sa2The simulated waveform diagram of (2) is shown in fig. 21, and the second commutation switch tube S can be seen from the simulated waveform diagram of fig. 21_a2Before and after turn-off its voltage v_Sa2And current i_Sa2Are all 0, therefore the second commutation switch tube S_a2A ZVZCS (zero voltage current) turn-off is achieved.

Under the method, the main power switch tube S of the resonant direct-current link three-phase inverter₁Voltage v at turn-on_S1And current i_S1The simulation waveform of (2) is shown in FIG. 22. from the simulation waveform of FIG. 22, it can be seen that the main power switch tube S₁Voltage v at turn-on_S1Zero, so the main power switch tube S₁ZVS (zero voltage) turn-on is achieved.

Under the method, the main power switch tube S of the resonant direct-current link three-phase inverter₁Voltage v at turn-off_S1And current i_S1The simulated waveform of (2) is shown in FIG. 23, and the main power switch tube S can be seen from the simulated waveform of FIG. 23₁Voltage v at turn-off of_S1Zero, so the main power switch tube S₁ZVS (zero voltage) turn-off is achieved.

Under the method, the main power switch tube S of the resonant direct-current link three-phase inverter₁Voltage v at turn-off_S1And current i_S1The simulation waveform of (2) is shown in FIG. 24. from the simulation waveform of FIG. 24, it can be seen that the main power switch tube S₁After turn-off voltage v_S1Rises linearly, so that the main power switch S₁A quasi ZVS (zero voltage) turn-off is achieved.

The operation waveform of the switching tube is described as follows: under the method, all the switch tubes of the resonant direct-current link three-phase inverter realize soft switching.

Under the method, the main power switch tube S of the resonant direct-current link three-phase inverter₁Buffer capacitor C₁Voltage v of_C1Main power switch tube S₃Buffer capacitor C₃Voltage v of_C3Main power switch tube S₅Buffer capacitor C₅Voltage v of_C5And the DC bus voltage v_DClinkThe simulation waveform diagram is shown in fig. 25, and it can be seen from the simulation waveform diagram of fig. 25 that the main power switch tube realizes one quasi ZVS (zero voltage) turn-off every switching period.

Under the load self-adaptive commutation control strategy, a main power switch tube S of a resonant direct-current link three-phase inverter₁Buffer capacitor C₁Voltage v of_C1Main power switch tube S₃Buffer capacitor C₃Voltage v of_C3Main power switch tube S₅Buffer capacitor C₅Voltage v of_C5And the DC bus voltage v_DClinkSimulation waveform diagram as shown in fig. 26, it can be seen from the simulation waveform of fig. 26 that the main power switch tube realizes three times of quasi ZVS (zero voltage) turn-off every switching period. As can be seen from comparing fig. 25 and fig. 26, the novel SVPWM method provided in this embodiment reduces the turn-off times of the main power switch tube per switching period of the quasi ZVS (zero voltage), thereby reducing the switching loss of the main power switch tube and improving the efficiency of the inverter.

Under the method, the first conversion inductor L of the resonant direct-current link three-phase inverter in one inverter output period_a1Current i of_La1And a second commutation inductor L_a2Current i of_La2Fig. 27 shows a simulated waveform diagram of (a), and it can be seen from the simulated waveform diagram of fig. 27 that the first commutation inductance L is_a1Has a current peak value of 60A, and a second commutation inductance L_a2Has a current peak value of 0A.

Under the load self-adaptive commutation control strategy, a first commutation inductor L of a resonant direct-current link three-phase inverter in one inverter output period_a1Current i of_La1And a second commutation inductor L_a2Current i of_La2The simulation waveform of (2) is shown in fig. 28, and the first commutation inductance L can be seen from the simulation waveform of fig. 28_a1Current peak value and second commutation inductance L_a2The current peak values of (a) and (b) are all 87A. As can be seen from comparing fig. 27 and 28, the first commutation inductance L is reduced by the method of the present invention_a1And a second commutation inductor L_a2Current stress of, therebyThe first commutation switch tube S is reduced_a1And a second commutation switch tube S_a2The current stress reduces the loss of the converter circuit and improves the efficiency of the inverter.

Under the method, the three-phase output phase current i of the resonant direct-current link three-phase inverter_a、i_b、i_cThe simulated waveform of (2) is shown in FIG. 29, from which it can be seen that the three-phase output phase current i of the inverter_a、i_b、i_cThe waveform of (a) is still smooth and has little distortion.

In summary, compared with the prior art, the invention has the following advantages: compared with the load self-adaptive commutation control in the prior art, the modulation method of the SVPWM-based resonant DC link three-phase inverter reduces the turn-off times of the main power switch tube in each switching period from three times to one time on the basis of ensuring that all switch tubes realize soft switching action and keeping the low action frequency of a commutation circuit, and maximally inhibits the first commutation switch tube S_a1And a second commutation switch tube S_a2The current stress of the three-phase inverter in the resonant direct-current link is reduced, and the efficiency of the three-phase inverter in the resonant direct-current link is improved.

Claims

1. A modulation method of a resonant direct-current link three-phase inverter based on SVPWM is characterized in that: the modulation method of the resonant direct-current link three-phase inverter comprises two parts, namely vector synthesis and vector distribution;

selecting corresponding vectors and calculating duty ratios in a vector synthesis mode, synthesizing two non-zero vectors adjacent to the reference vectors when the reference vectors fall into sectors I to VI under a two-phase static coordinate system, supplementing the rest duty ratios by the zero vectors, and only adopting one zero vector in each switching period;

arranging corresponding vectors in a vector distribution mode and generating a switching sequence, wherein the switching sequence is a zero vector, a non-zero vector X1, a non-zero vector X2 and a zero vector by adopting a four-section wave-transmitting mode, and the wave-transmitting sequence of the non-zero vector is related to the phase current polarity of a bridge arm with phase commutation when switching between the non-zero vectors; when two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is positive, and the bridge arm with the phase is switched from an upper main power switch tube to an anti-parallel diode of a lower main power switch tube by adjusting the wave sending sequence; when the two non-zero vectors are switched, the phase current polarity of the bridge arm with the phase change is negative, and the lower main power switch tube of the bridge arm with the phase change is switched to the anti-parallel diode of the upper main power switch tube by adjusting the wave-sending sequence.

2. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in sector I, it is synthesized using non-zero vector 100 and non-zero vector 110, the remaining duty cycle being supplemented by zero vector 000 or 111; when the reference vector is in sector I and the phase current I is loaded in phase B_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 110 and a zero vector 111; when the reference vector is in sector I and the phase current I is loaded in phase B_b>At 0, the switching sequence is zero vector 000, non-zero vector 110, non-zero vector 100, zero vector 000.

3. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in sector II, a non-zero vector 110 and a non-zero vector 010 are used for synthesis, and the rest duty cycle is supplemented by a zero vector 000 or 111; when the reference vector is in sector II and the A phase loads phase current i_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 110 and a zero vector 111; when the reference vector is in sector II and the A phase loads phase current i_a>At 0, the switching sequence is zero vector 000, non-zero vector 110, non-zero vector 010, zero vector 000.

4. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in sector III, non-zero vector 010 and non-zero vector are usedThe zero vector 011 is synthesized, and the rest duty ratio is supplemented by the zero vector 000 or 111; when the reference vector is in sector III and C phase load phase current i_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 010, a non-zero vector 011 and a zero vector 111; when the reference vector is in sector III and C phase load phase current i_c>At 0, the switching sequence is zero vector 000, non-zero vector 011, non-zero vector 010, zero vector 000.

5. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in the sector IV, synthesizing by adopting a non-zero vector 011 and a non-zero vector 001, and supplementing the rest duty ratio by a zero vector 000 or 111; when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 011 and a zero vector 111; when the reference vector is in the sector IV and the phase current i is loaded in the B phase_b>At 0, the switching sequence is zero vector 000, non-zero vector 011, non-zero vector 001, and zero vector 000.

6. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in sector V, a non-zero vector 001 and a non-zero vector 101 are used for synthesis, and the rest of the duty cycle is supplemented by a zero vector 000 or 111; when the reference vector is in the sector V and the phase of A load phase current i_a<When 0, the switching sequence is a zero vector 111, a non-zero vector 001, a non-zero vector 101 and a zero vector 111; when the reference vector is in the sector V and the phase of A load phase current i_a>At 0, the switching sequence is zero vector 000, non-zero vector 101, non-zero vector 001, zero vector 000.

7. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: when the reference vector falls in sector VI, it is synthesized using non-zero vector 101 and non-zero vector 100, and the remaining duty cycle is supplemented by zero vector 000 or 111; when the reference vector is in sector VI andc-phase load phase current i_c<When 0, the switching sequence is a zero vector 111, a non-zero vector 100, a non-zero vector 101 and a zero vector 111; when the reference vector is in the sector VI and the phase I of the C-phase load phase_c>At 0, the switching sequence is zero vector 000, non-zero vector 101, non-zero vector 100, zero vector 000.

8. The modulation method of the SVPWM-based resonant DC link three-phase inverter according to claim 1, characterized in that: the modulation strategy of the commutation circuit in the resonant direct-current link three-phase inverter is as follows: when the inverter bridge is in a zero vector, the converter circuit does not act, and the voltage of the direct-current bus is maintained at zero; when the bus switch tube is turned off, the second commutation switch tube is not immediately turned on, but the shunt dead time delta is delayed₃Then opening the circuit; when each switching period starts, the bus switch tube, the first commutation switch tube and the second commutation switch tube are all turned off; when the inverter bridge is switched from a zero vector to a non-zero vector X1, a delay time delta is elapsed₀Then, the first current conversion switch tube is switched on; after a delay time delta₁Then, the bus switch tube is switched on; after a delay time delta₂Then, the first commutation switch tube is turned off; shunting dead time delta before switching inverter bridge from non-zero vector X2 to zero vector₃Adding delay time delta₄When the bus bar is in a closed state, the bus bar switching tube is disconnected; passing shunt dead time delta₃Then, the second current conversion switch tube is switched on; after a delay time delta₄And then the second commutation switch tube is turned off.