CN106208735A - The matrix converter of a kind of third-harmonic zero-sequence voltage and control method - Google Patents

Abstract

The invention relates to a matrix converter and a control method for third harmonic injection. The matrix converter includes: a front-stage circuit, an intermediate stage circuit, a rear-stage circuit and a control module; the front-stage circuit is connected to a three-phase input power supply, and is used to rectify the input alternating current to obtain six-pulse direct current; the intermediate stage circuit and The front-stage circuit is connected to generate the third harmonic and inject it into the front-stage circuit according to the six-pulse direct current; the rear-stage circuit is connected to the front-stage circuit and the intermediate stage circuit, and is used to invert the six-pulse direct current to obtain preset conditions The alternating current; the control module is connected with the front-stage circuit, the intermediate-stage circuit, and the rear-stage circuit, and is used to obtain the working parameters of the three and generate corresponding control instructions to control the output voltage and output current of the three. The invention does not need to use the energy storage capacitor of the direct current bus, can reduce the volume of the matrix converter, and can also reduce the power consumption of the circuit, that is, the conversion efficiency is high.

Description

A Matrix Converter and Control Method for Third Harmonic Injection

technical field

The invention relates to the technical field of power conversion, in particular to a matrix converter for third harmonic injection and a control method.

Background technique

With the rapid development of power electronics technology, it has been widely used in energy saving and new energy development. Among them, power converters, as the core of power electronics technology, are widely used in various AC-AC power conversion occasions, such as AC variable frequency drive, new energy power generation heart uninterruptible power supply and other fields.

The structure of the post-inversion stage of the AC-AC converter is the same, and the difference is only in the front-end converter. Existing front-end converters include passive front-end converters, active front-end converters and hybrid active front-end converters.

Passive front-end converters have the advantages of high conversion efficiency, low EMI interference, low cost, simple structure and high reliability, and are widely used in the fields of variable frequency speed regulation and renewable energy power generation. However, passive front-end converters also have the characteristics of unidirectional energy flow and poor input current quality.

Active front-end converters, such as voltage-mode and current-mode back-to-back PWM converters, have most of the characteristics of ideal AC-AC power converters, but their bulky energy storage components lead to low power density and reliability. Another active front-end converter, the indirect matrix converter, does not require intermediate energy storage equipment. Relevant research has achieved remarkable results, but there are still nonlinear problems such as narrow pulses caused by the synchronization of the rectifier stage and inverter stage modulation, Restricted input side reactive power control range, high switching loss and EMI noise, etc.

The hybrid front-end converter has the advantages of low switching loss and low cost. At the same time, due to the control of active switches, the input current quality and power factor have been significantly improved, so it is a compromise solution. The hybrid front-end converter has: grid commutation (diode) and forced commutation (active switch); the input characteristics are improved through the switching of active switches; passive devices such as diodes bear the main current stress and power transfer tasks, active The volt-ampere capacity of the switch is small; incomplete controllability leads to limited performance, such as input current sine degree, input power factor and power flow direction, etc.

Contents of the invention

Aiming at the defects in the prior art, the present invention provides a third harmonic injection matrix converter and a control method to solve the problems of large volume and high cost of the matrix converter in the prior art, so as to improve the conversion efficiency of the matrix converter And realize the two-way flow of energy.

In a first aspect, the present invention provides a matrix converter for third harmonic injection, wherein the matrix converter includes: a front-stage circuit, an intermediate-stage circuit, a rear-stage circuit, and a control module;

The front-stage circuit is connected to a three-phase input power supply, and is used to rectify the input alternating current to obtain six-pulse direct current;

The intermediate stage circuit is connected to the preceding stage circuit, and is used to generate third harmonics and inject them into the preceding stage circuit according to the six-pulse direct current;

The rear-stage circuit is connected to the front-stage circuit and the intermediate-stage circuit, and is used to invert the six-pulse direct current to obtain an alternating current with preset conditions;

The control module is connected with the front-stage circuit, the intermediate-stage circuit, and the post-stage circuit, and is used to obtain the operating parameters of the three and generate corresponding control instructions to control the output voltage and output current of the three.

Optionally, the pre-stage circuit includes a filter circuit and a three-phase rectification circuit; wherein,

The filter circuit includes filter capacitor C _Fa , filter capacitor C _Fb , filter capacitor C _Fc and filter inductor L _Fa , filter inductor L _Fb , filter inductor L _Fc ; the filter inductor L _Fa , filter inductor L _Fb , filter inductor L _Fc are respectively connected in series on the three-phase input power supply; the first ends of the filter capacitor C _Fa , the filter capacitor C _Fb and the filter capacitor C _Fc are sequentially connected to the output terminals of the filter capacitors C _Fa , _CFb , and C _Fc to Nodes P _a , P _b , P _c , the second terminals are connected;

The three-phase rectifier circuit includes an upper bridge arm composed of 3 switching tubes S _a+ , S _b+ , and S _c+ and a lower bridge arm consisting of 3 switching tubes S _a- , S _b- , and S _c- ; wherein, the The first poles of the switching tubes S _a+ , S _b+ , and S _c+ are connected to the positive pole of the DC bus, and the second poles are sequentially connected to the first poles of the switching tubes S _a- , S _b- , and S _c- on the Nodes P _a , P _b , P _c ; the second poles of the switch tubes S _a- , S _b- , S _c- are connected to the negative pole of the DC bus.

Optionally, the intermediate stage circuit includes a double Buck half-bridge circuit and bidirectional switches S _a , S _b , S _c ;

The double Buck half-bridge circuit includes switching tubes _Sy+ , _Sy- and inductor _Ly ; the first pole of the switching tube _Sy+ is connected to the positive pole of the DC bus, and the second pole is connected to the first pole of the switching tube _Sy- node P ₁ ; the first end of the inductor Ly is connected to node P ₁ , and the second end is connected to node P ₂ ;

The bidirectional switch S _a includes switching tubes _Say and S _ya , the bidirectional switch S _b includes switching tubes S _by and _Syb , and the bidirectional switch S _c includes switching tubes S _cy and _Syc ; the switching tubes S _ya , _Syb and S The first pole of _yc is connected to node P ₂ , and the second pole is sequentially connected to the first poles of the switching transistors _Say , S _by and S _cy ; the second poles of the switching transistors _Say , S _by and S _cy are sequentially connected to the node P _a , P _b , P _c .

Optionally, the latter stage circuit includes a three-phase voltage-type inverter; the three-phase voltage-type inverter includes an upper bridge arm composed of switch tubes S _r+ , S _s+ , and S _t+ and switch tubes S _r- , The lower bridge arm composed of S _s- and S _t- ;

The first poles of the switching tubes S _r+ , S _s+ , and S _t+ are connected to the positive pole of the DC bus, and the second poles are sequentially connected to the first poles of the switching tubes S _r- , S _s- , and S _t- ; the switching tubes The second poles of S _r- , S _s- , S _t- are connected to the negative pole of the DC bus.

Optionally, the subsequent circuit further includes a clamping circuit; the clamping circuit includes a fast recovery diode D _c and a capacitor C _c , the positive pole of the fast recovery diode D _c is connected to the positive pole of the DC bus, and the negative pole is connected to the positive pole of the DC bus. The first pole of the capacitor C _c is connected; the second pole of the capacitor C _c is connected to the negative pole of the DC bus.

In the second aspect, the present invention also provides a control method for a matrix converter with third harmonic injection, the control method includes a control method for a front-stage circuit and a control method for a subsequent-stage circuit.

Optionally, the control method of the pre-stage circuit includes:

Obtaining the voltages u _aF , u _bF , u _cF of the filter capacitors in the preceding stage circuit, the DC bus voltage U _pn and the third harmonic injection current i _{y of the inductor L y ;}

Calculate the phase lock angles of the voltages u _aF , _ubF , and u _cF , and determine the sector according to the phase lock angles, thereby controlling the three-phase rectifier circuit and each of the three bidirectional switches S _a , S _b , and S _c Tube on and off;

Obtain the reference value i _y * of the third harmonic injection current;

A switching command is generated according to the difference Δi _y between the current reference value i _y * and the third harmonic injection current i _y to adjust the duty cycle of the switching tube S _y+ .

Optionally, the control method of the pre-stage circuit includes:

Obtain the actual output current ir, is, it of each phase in the three-phase voltage inverter;

Acquiring the voltage reference value and current reference value of each phase in the three-phase voltage-type inverter;

Carry out dq transformation on the current reference value and the actual output current ir, is, it respectively to obtain the reference value i _d *, i _q * and the actual value i _d , i _q output, and calculate the difference Δi _d , Δi _q ;

Adjust the difference Δi _d and Δi _q PI and then perform dq inverse transformation to obtain the variation of each phase circuit current, so as to generate and adjust the switching tube in the three-phase voltage type inverter according to the variation of each phase circuit current Switch command of S _r+ , S _s+ , S _t+ duty cycle.

Optionally, calculating the phase-locking angles of the voltages u _aF , _ubF , and u _cF , and determining the sector according to the phase-locking angles, so as to control the three-phase rectifier circuit and the three bidirectional switches S _a , S _b 1. In the step of turning on and turning off each switch tube in S _c , the following method is used to determine the sector including:

The interval of u _a >u _b >u _c is set as sector Ⅰ;

The interval of u _b >u _a >u _c is set as sector II;

The interval of u _b >u _c >u _a is set as sector III;

The interval of u _c >u _b >u _a is set as sector IV;

The interval of u _c >u _a > _ub is set as sector Ⅴ;

The interval of u _a >u _c >u _b is set as sector VI;

And the control method of each switching tube includes:

At any time in each sector, among the switches S _a+ , S _b+ , and S _c+ of the upper bridge arm, the switch corresponding to the largest instantaneous value of the input voltage, and the switches S _a- , S _b- , and S _c- of the lower bridge arm The switch corresponding to the smallest instantaneous value of the input voltage is always on, and the remaining switch tubes are always off;

Among the three bidirectional switches of the third harmonic injection circuit, the corresponding bidirectional switch with the smallest absolute value of the instantaneous voltage value is turned on, the other bidirectional switches are turned off, and third harmonic current is injected into the phase power supply.

Optionally, when the subsequent stage circuit includes a clamping circuit, the control method further includes:

When the matrix converter stops working, the clamping circuit absorbs the energy stored in the load leakage inductance; when the matrix converter works normally, the clamping circuit does not work.

It can be seen from the above technical solution that the present invention rectifies the AC input from the three-phase input power supply by setting the pre-stage circuit to obtain six-pulse direct current, and then injects the third harmonic into the pre-stage circuit through the intermediate stage circuit, and the pre-stage circuit is controlled by power frequency The switching tube operates, and then high-frequency adjustment is used for the switching tube in the intermediate stage circuit, so that the front stage circuit inputs sinusoidal three-phase current, and at the same time, there is no need to use the energy storage capacitor of the DC bus, which can reduce the volume of the matrix converter. In addition, only the intermediate stage circuit controls the high-frequency turn-on and turn-off of the switch tube when the third harmonic is injected, which can reduce circuit power consumption and improve conversion efficiency.

Description of drawings

The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the accompanying drawings:

Fig. 1 is the structural representation of the matrix converter of third harmonic injection of the present invention;

Fig. 2 is the waveform diagram of the three-phase rectification circuit in Fig. 1;

Fig. 3 is a schematic diagram of a switching tube switch of the three-phase rectifier circuit in Fig. 1;

FIG. 4 is a schematic diagram of the energy flow of the three-phase rectifier circuit shown in FIGS. 1 to 3;

Fig. 5 is a schematic diagram of modulation of the three-phase voltage-type inverter in Fig. 1;

6 is a schematic diagram of a control module of a matrix converter for third harmonic injection provided by the present invention;

Fig. 7 is the schematic diagram of experimental data in the matrix converter of third harmonic injection of the present invention;

Figure 8 (a) and (b) are schematic diagrams of waveforms of the intermediate stage circuit, that is, the third harmonic injection circuit;

Figure 9 (a) and (b) are schematic diagrams of matrix transformation waveforms under different modulation coefficients and different frequencies;

Figure 10 (a) and (b) are schematic diagrams of the waveforms of the matrix converter under different power factors;

Fig. 11(a) and (b) are schematic diagrams of dynamic performance waveforms of a step change of a reference value in a matrix converter.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

An embodiment of the present invention provides a third harmonic injection matrix converter, as shown in FIG. 1 , including: a front-stage circuit 101 , an intermediate-stage circuit 102 , a post-stage circuit 103 and a control module (not shown in the figure).

The pre-stage circuit 101 is connected to the three-phase input power supply, and is used to rectify the input AC power to obtain six-pulse DC power. The intermediate stage circuit 102 is connected to the front stage circuit 101, and is used to generate the third harmonic and inject it into the front stage circuit 101 according to the above-mentioned six-pulse direct current. The injection of the third harmonic ensures the sinusoidal symmetry of the input current. The rear-stage circuit 103 is connected to the front-stage circuit 101 and the intermediate-stage circuit 102, and is used for inverting the above-mentioned six-pulse direct current to obtain alternating current with preset conditions. The control module is connected with the pre-stage circuit 101, the intermediate-stage circuit 102, and the post-stage circuit 103, and is used to obtain the operating parameters of the three and generate corresponding control instructions to control the output voltage and output current of the three.

In practical applications, as shown in FIG. 1 , the pre-stage circuit 101 includes a filter circuit 1011 and a bidirectional three-phase rectifier circuit 1012 . The filter circuit 1011 includes filter capacitor C _Fa , filter capacitor C _Fb , filter capacitor C _Fc and filter inductance L _Fa , filter inductance L _Fb , filter inductance L _Fc ; the filter inductance L _Fa , filter inductance L _Fb , filter inductance L _Fc are respectively connected in series on the three-phase input power supply; the first ends of the filter capacitor C _Fa , the filter capacitor C _Fb and the filter capacitor C _Fc are sequentially connected to the output ends of the filter capacitors C _Fa , _CFb , and C _Fc At nodes P _a , P _b , and P _c , the second ends are connected. The three-phase rectifier circuit 1012 includes an upper bridge arm composed of three switching tubes S _a+ , S _b+ , and S _c+ and a lower bridge arm consisting of three switching tubes S _a- , S _b- , and S _c- ; wherein the switch The first poles of the transistors S _a+ , S _b+ , and S _c+ are connected to the positive pole of the DC bus, and the second poles are sequentially connected to the node with the first poles of the switching transistors S _a- , S _b- , and S _c- P _a , P _b , P _c ; the second poles of the switch tubes S _a- , S _b- , S _c- are connected to the negative pole of the DC bus.

It should be noted that, in the embodiment of the present invention, the three-phase rectification circuit uses a power frequency cycle to perform the switching action, which can reduce the power consumption of the circuit.

In addition, the three-phase input power supply 100 in the embodiment of the present invention is a three-phase power supply with constant amplitude, frequency, and power factor angle, such as the three-phase power supply provided by the national grid.

As shown in FIG. 1 , the above intermediate stage circuit 102 is a third harmonic injection circuit including a double Buck half-bridge circuit and bidirectional switches S _a , S _b , S _c . Wherein, the double Buck half-bridge circuit includes switch tubes S _y+ , S _y- and inductor L _y . The first pole of the switch tube _Sy+ is connected to the positive pole of the DC bus, and the second pole is connected to the first pole of the switch tube _Sy- to the node P ₁ ; the first end of the inductor _Ly is connected to the node P ₁ , and the second end is connected to the node P ₂ . The bidirectional switch S _a includes switching tubes _Say and S _ya , the bidirectional switch S _b includes switching tubes S _by and _Syb , the bidirectional switch S _c includes switching tubes S _cy and _Syc ; the switching tubes S _ya , _Syb and _Syc The first pole is connected to node P ₂ , the second pole is sequentially connected to the first poles of the switching transistors _Say , S _by and S _cy ; the second poles of the switching transistors _Say , S _by and S _cy are sequentially connected to the node P _a , P _b , P _c .

As shown in FIG. 1 , the latter stage circuit 103 includes a three-phase voltage source inverter 1032 . The three-phase voltage inverter includes an upper bridge arm composed of switch tubes S _r+ , S _s+ , S _t+ and a lower bridge arm formed by switch tubes S _r- , S _s- , S _t- . The first poles of the switching tubes S _r+ , S _s+ , and S _t+ are connected to the positive pole of the DC bus, and the second poles are sequentially connected to the first poles of the switching tubes S _r- , S _s- , and S _t- ; the switching tubes S _r- , S _{s -} , the second pole of S _t- is connected to the negative pole of the DC bus.

In practical applications, when the matrix converter stops working, part of the energy will be stored in the leakage inductance in the load, and this part of energy will flow back to the matrix converter and damage the switching tubes in the matrix converter. In order to solve the above problems, the present invention implements In the example, the subsequent stage circuit 103 further includes a clamping circuit 1031 . As shown in FIG. 1 , the clamping circuit 1031 includes a fast recovery diode D _c and a capacitor C _c . The positive pole of the fast recovery diode Dc is connected to the positive pole of the DC bus, and the negative pole is connected to the first pole of the capacitor _Cc ; the second pole of the capacitor _Cc is connected to the negative pole of the DC bus _. In this way, the energy stored in the leakage inductance can flow back into the capacitor _Cc , preventing damage to the matrix converter. It should be noted that the capacitor C _c is different from the large-capacity energy storage capacitor in the prior art, the capacity of the capacitor C _c is much smaller than the capacity of the energy storage capacitor, and the capacitor C _c is.

There is a charging process when the matrix converter starts to work. When the voltage of the capacitor C _c is greater than the DC bus voltage, the diode is cut off. The matrix converter stops working. The energy stored in the leakage inductance of the load will increase the positive voltage of the DC bus, and the diode will be turned on, so that the capacitor C _c can absorb the current in the leakage inductance, and prevent the energy from flowing back to the matrix converter to damage the matrix converter. in the switch tube. In addition, the volume of the above-mentioned capacitors is small, which can greatly reduce the volume of the matrix converter

Figure 2 shows the waveform diagram of the front-stage three-phase rectifier of the matrix converter, including: (a) three-phase input power supply voltage u _a , u _b , u _c and six-pulse DC voltage after bidirectional three-phase rectifier u _pn . ( _b ) Three-phase input power supply current _ia , ib, _ic . (c) Input current i _ra of phase a of the rectifier after the three-phase filter. (d) The third harmonic injection current reference value i _y *. It can be seen from Figure 2 that under the condition of input unit power factor, the peak value of the current passing through the third harmonic injection circuit is only half of the current amplitude at the input side of the converter, so the components of the third harmonic injection circuit can be selected with a smaller current rating devices, which can reduce the cost of the matrix converter.

As shown in Figure 3, a power cycle is divided into six sectors in the time domain according to the magnitude relationship of the instantaneous value of the three-phase input power supply voltage. The specific division method is: u _a > u _b > u _c interval setting sector Ⅰ; the interval of u _b >u _a >u _c is set as sector II; the interval of u _b >u _c >u _a is set as sector III; the interval of u _c >u _b >u _a is set The interval of u _c > u _a > u _b is set as sector V; the interval of u _a > u _c > u _b is set as sector VI. At any time in each sector, among the three switches S _a+ , S _b+ , and S _c+ of the upper bridge arm, the switch corresponding to the largest instantaneous value of the input voltage, and the three switches S _a- , S _b- , and S _c- of the lower bridge arm Among them, the switch corresponding to the minimum instantaneous value of the input voltage is always turned on, and the remaining 4 switches are always turned off. When the energy flows in the forward direction, the current flows through the diode; when the energy flows in the reverse direction, the IGBT switch tube connected in antiparallel with the diode carries the current.

The three bidirectional switches of the third harmonic injection circuit are determined by the phase with the smallest absolute value of the instantaneous voltage value in the three-phase input power supply, that is, the corresponding bidirectional switch with the smallest absolute value of the instantaneous voltage value is turned on, and the other bidirectional switches are turned off. This phase power injects third harmonic current.

When the voltage of the three-phase input power supply has the following relationship: u _a >u _b >u _c , u _b <0, if the energy flows forward, as shown in Figure 4(a), the current in the bidirectional three-phase rectifier circuit Flowing through the anti-parallel diodes of the switching tubes S _a+ and S _c- , the third harmonic injection current of phase b flows through the anti-parallel diodes of the switching tubes S _yb and S _by . When the energy flows in the opposite direction, as shown in Figure 4(b), in the bidirectional three-phase rectification circuit, the circuit flows through the switches S _a+ and S _c- , and the b-phase third harmonic injection current flows through the switch S _yb Anti-parallel diode and switch S _by .

In the embodiment of the present invention, the three-phase voltage-type inverter adopts the carrier modulation strategy, as shown in Figure 5, assuming that the three-phase expected output voltage is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ;</span>$

Where U _om is the magnitude of the desired output voltage, ω _o is the angular frequency of the desired output voltage, and φ is the power factor angle of the desired output voltage.

First obtain the modulation signal u _io * as The zero-sequence voltage u _no is defined as u _no =-[max(u _r ,u _s ,u _t )+min(u _r ,u _s ,u _t )]/2, so far the normalized modulation signal can be obtained and the duty cycle d _i of each bridge arm is which is d _i corresponds to the duty cycle of S _r+ , S _s+ , and S _t+ .

Fig. 6 shows a schematic diagram of the control module of the matrix converter. The control module controls the front-stage circuit, the intermediate-stage circuit and the rear-stage circuit.

A method for controlling a three-phase rectifier in a pre-stage circuit comprises the following steps:

Step 1: Collect the data during the working process of the pre-stage three-phase rectifier circuit; the data includes the voltages u _aF , u _bF , u _cF at both ends of the filter capacitors of each phase of the pre-stage three-phase filter circuit, and the harmonics flowing through the third harmonic injection circuit The third harmonic injection current i _y of the wave injection inductor L _y and the intermediate DC bus voltage u _pn .

Step 2: Phase-lock the collected three-phase voltages u _aF , u _bF , and u _cF through a phase-locked loop (PLL) to obtain a phase-lock angle θ. Determine the sector according to the phase-lock angle θ (the sector is determined according to the above-mentioned sector division method), so as to control the turn-on and turn-off of each switch tube in the three-phase rectifier circuit and the three bidirectional switches;

Step 3: Obtain the reference value of the third harmonic injection current.

First, pass the collected A-phase filter capacitor voltage u _aF through a band-pass filter to obtain the 5th harmonic voltage u _h5 ; secondly, multiply u _h5 by sin(5θ) and pass it through a low-pass filter to obtain U ₅ sin (φ _u5 ), and U ₅ sin (φ _u5 ) as the input of the PI regulator. The output of the PI regulator is the reference input power value P* of the three-phase power supply; finally, it is calculated according to the following formula:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}^{<span\; class="notranslate">\; *</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; m</span>}}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

Among them, I _qm is the reactive current component of the three-phase input power supply side, is the power factor angle of the three-phase input power supply, which is determined by the demand, U _im is the amplitude of the three-phase input power supply voltage, and ω _i is the angular frequency of the three-phase input power supply.

Step 4: According to the difference Δi _y between the third harmonic injection current reference value i _y * obtained in step 3 and the sampled i _y , the duty ratio of the IGBT switch S _y+ is PI adjusted to obtain the IGBT in the double Buck circuit The dynamic duty ratio of the switching tube _Sy+ .

The control method of the three-phase voltage-type inverter in the subsequent stage includes the following steps:

Step 1: Collect the data during the working process of the subsequent three-phase voltage inverter circuit, including the output currents i _r , i _s , and it of each phase of the subsequent three-phase voltage inverter circuit _.

Step 2: Obtain the reference value of the three-phase voltage type inverter circuit. The reference value of the output current of the three-phase voltage type inverter circuit is calculated according to the three-phase expected output voltage and the load. The three-phase expected output voltage is;

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ;</span>$

Where U _om is the magnitude of the desired output voltage, ω _o is the angular frequency of the desired output voltage, φ is the power factor angle of the desired output voltage, and the load impedance is Z.

Then the three-phase current reference value is

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Z</span>}\\ {\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Z</span>}\\ {\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Z</span>}\end{array}\right.<span\; class="notranslate">\; .</span>$

Step 3: According to the dq-transformed reference value i _d *, i _q * of the output current of the three-phase voltage-type inverter circuit obtained in step 1, and the difference Δi _d between the dq-transformed i _d and i _q obtained by sampling, and then After Δi _q is inversely transformed by dq, the duty cycle of the switch tubes S _r+ , S _s+ , and S _t+ in the three-phase voltage inverter circuit is PI adjusted, and the switch tube S _r+ in the three-phase voltage inverter circuit is adjusted , S _s+ , S _t+ dynamic duty cycle.

A control method for a front-end three-phase rectifier, including:

A feed-forward term k is superimposed in the reference value of the third harmonic injection current controller; where,

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; ,</span>$

u _max = max(u _aF , u _bF , u _cF ), u _mid = mid(u _aF , u _bF , u _cF ), u _min = min(u _aF , u _bF , u _cF ).

In order to verify the effectiveness of the third harmonic injection matrix converter and the control method provided by the embodiment of the present invention, the experimental data of the above-mentioned matrix converter in an embodiment of the present invention are shown in Figure 7, including rated power, three-phase input The amplitude and frequency of the power supply voltage, the amplitude of the output reference voltage of the three-phase inverter circuit, the switching frequency of the IGBT switch tube, the inductance and capacitance value of the three-phase input filter, the inductance value of the third harmonic injection, and the three-phase voltage inverter The variable circuit outputs the filter inductance value and the load resistance value.

Figure 8(a) and (b) show the waveform diagrams of the third harmonic injection circuit. As shown in Figure 8, it includes: three-phase input power supply a-phase voltage u _a , current _{ia , third harmonic injection current i y ,} and three-phase voltage-type inverter r-phase output current. Figure 8(a) is the waveform diagram when the third harmonic injection circuit is not working, and Figure 8(b) is the waveform diagram when the third harmonic injection circuit is working. From the comparison of the two sets of diagrams, it can be seen that when the third harmonic injection circuit is working, The harmonic distortion of the input current and output current of the matrix converter injected by the third harmonic is smaller, and the waveform quality is high.

Fig. 9 shows a schematic diagram of waveforms under different modulation coefficients and different frequencies in the matrix converter. As shown in Figure 9, the input side power factor angle in the experimental matrix converter Set to 0. In Fig. 9(a) and Fig. 9(b), the output parameters of the converter are set as mi =0.7, f _o =40Hz and _mi =1, _{f o =} 100Hz respectively. It can be seen from the figure that under different output frequencies and modulation coefficients, the input and output currents of the matrix converter are perfect sinusoidal waveforms, and the input current and input voltage are in phase.

Fig. 10 shows schematic diagrams of waveforms under different power factors. As shown in FIG. 10 , the output parameters of the matrix converter are set as mi =1, _{f o =} 40Hz. In Figure 10(a), the input power factor angle is set to π/6, that is, the input current lags the input voltage by π/6. In Figure 10(b), the input power factor angle is set to -π/6, that is, the input current leads the input voltage by π/6. The magnitude of the output current is about 5.6A, which shows that the maximum voltage transfer ratio of the matrix converter can reach 0.866 under different input power factor angles.

FIG. 11 shows a schematic diagram of a dynamic performance waveform of a step change of a reference value in a matrix converter. In Fig. 11(a), the initial value of the output active current reference value _{id_ref} is +6A, and it changes step by step from +6A to -6A at the moment of 0.15s. In Fig. 11(b), the initial value of the output active current reference value _{id_ref} is -6A, and changes stepwise from -6A to +6A at the moment of 0.15s. It can be seen from Figure 11 that the matrix converter with third harmonic injection can switch quickly and smoothly in the two operating modes of motoring and power generation, and has good dynamic performance.

In the present invention, the terms "first", "second", and "third" are used for descriptive purposes only, and should not be understood as indicating or implying relative importance. The term "plurality" means two or more, unless otherwise clearly defined.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention. within the bounds of the requirements.

Claims (10)

1. A third harmonic injected matrix converter, characterized in that the matrix converter comprises: the circuit comprises a front-stage circuit, a middle-stage circuit, a rear-stage circuit and a control module;

the pre-stage circuit is connected with a three-phase input power supply and is used for rectifying input alternating current to obtain six-pulse direct current;

the middle-stage circuit is connected with the preceding-stage circuit and is used for generating third harmonic according to the six-pulse-wave direct current and injecting the third harmonic into the preceding-stage circuit;

the post-stage circuit is connected with the pre-stage circuit and the intermediate-stage circuit and is used for inverting the six-pulse-wave direct current to obtain alternating current under preset conditions;

the control module is connected with the preceding stage circuit, the intermediate stage circuit and the subsequent stage circuit and used for acquiring working parameters of the preceding stage circuit, the intermediate stage circuit and the subsequent stage circuit and generating corresponding control instructions to control output voltage and output current of the preceding stage circuit, the intermediate stage circuit and the subsequent stage circuit.

2. The matrix converter according to claim 1, wherein the pre-stage circuit includes a filter circuit and a three-phase rectification circuit; wherein,

the filter circuit comprises a filter capacitor C_FaFilter capacitor C_FbFilter capacitor C_FcAnd a filter inductance L_FaFilter inductor L_FbFilter inductor L_Fc(ii) a The filter inductor L_FaFilter inductor L_FbFilter inductor L_FcAre respectively connected in series with a three-phase input power supply; the filter capacitor C_FaThe filter capacitor C_FbAnd said filter capacitor C_FcThe first end of the filter is connected with a filter capacitor C in sequence_Fa、C_Fb、C_FcAt node P_a、P_b、P_cThe second end is connected;

the three-phase rectification circuit comprises 3 switching tubes S_a+、S_b+、S_c+Upper bridge arm and 3 switch tubes S_a-、S_b-、S_c-A lower bridge arm; wherein, the switch tube S_a+、S_b+、S_c+The first pole of the switch is connected with the positive pole of the direct current bus, and the second pole of the switch is connected with the switch tube S in sequence_a-、S_b-、S_c-Is connected to the node P_a、P_b、P_c(ii) a The switch tube S_a-、S_b-、S_c-The second pole of the second diode is connected with the negative pole of the direct current bus.

3. The matrix converter of claim 1, wherein the intermediate stage circuit comprises a doublet Buck half-bridge circuit and bidirectional switch S_a、S_b、S_c；

The double Buck half-bridge circuit comprises switching tubes Sy +, Sy-and an inductor Ly; the first pole of the switch tube Sy + is connected with the positive pole of the direct current bus, and the second pole is connected with the first pole of the switch tube Sy-at the node P₁(ii) a The first end of the inductor Ly is connected with a node P₁The second end is connected with the node P₂；

Two-way switch S_aComprising a switching tube S_ayAnd S_yaTwo-way switch S_bComprising a switching tube S_byAnd S_ybTwo-way switch S_cComprising a switching tube S_cyAnd S_yc(ii) a The switch tube S_ya、S_ybAnd S_ycFirst pole of (2) connecting node P₂The second pole is connected with the switch tube S in turn_ay、S_byAnd S_cyA first pole of (a); the switch tube S_ay、S_byAnd S_cyIs in turn connected to node P_a、P_b、P_c。

4. The matrix converter according to claim 1, wherein the post-stage circuit includes a three-phase voltage-type inverter; the three-phase voltage type inverter comprises a switch tube S_r+、S_s+、S_t+Upper bridge arm and switch tube S_r-、S_s-、S_t-A lower bridge arm;

the switch tube S_r+、S_s+、S_t+The first pole of the switch tube is connected with the positive pole of the direct current bus, and the second pole of the switch tube is sequentially connected with the switch tube S_r-、S_s-、S_t-A first pole of (a); the switch tube S_r-、S_s-、S_t-Is connected with the negative pole of the direct current bus.

5. The matrix converter according to claim 4, wherein the post-stage circuit further comprises a clamping circuit; the clamping circuit comprises a fast recovery diode D_cAnd a capacitor C_cSaid fast recovery diode D_cThe anode of the capacitor is connected with the anode of the direct current bus, and the cathode of the capacitor is connected with the capacitor C_cTo the first pole of the first electrode; the capacitor C_cThe second pole of the second diode is connected with the negative pole of the direct current bus.

6. A control method of a third harmonic injection matrix converter is characterized by comprising a control method of a front-stage circuit and a control method of a rear-stage circuit.

7. The control method according to claim 6, wherein the control method of the preceding stage circuit includes:

obtaining the voltage u of the filter capacitor in the preceding stage circuit_aF、u_bF、u_cFDC bus voltage U_pnAnd an inductance L_yThird harmonic injection current i_y；

Calculating said voltage u_aF、u_bF、u_cFAccording to the phase-locked angle, the sector is determined, so as to control the three-phase rectification circuit and three two-way switches S_a、S_b、S_cThe on and off of each switching tube;

acquiring a third harmonic injection current reference value iy;

according to the current reference value iy and the third harmonic injection current i_yDifference value Δ i therebetween_yGenerating a switching command to regulate the switching tube S_y+The duty cycle of (c).

8. The control method according to claim 6 or 7, wherein the control method of the preceding stage circuit includes:

acquiring actual output currents ir, is and it of each phase in the three-phase voltage type inverter;

acquiring reference values of voltages and currents of all phases in the three-phase voltage type inverter;

d q conversion is respectively carried out on the current reference value and the actual output currents ir, is and it to obtain reference values id and iq and actual values id and iq output, and a difference value delta i is calculated_d、Δi_q；

For the difference value Δ i_d、Δi_qCarrying out dq inverse transformation after PI regulation to obtain the variable quantity of each phase of circuit current, and generating and regulating a switching tube S in the three-phase voltage type inverter according to the variable quantity of each phase of circuit current_r+、S_s+、S_t+And switching instructions of duty ratio.

9. Control method according to claim 7, characterized in that said calculation of said voltage u_aF、u_bF、u_cFAccording to the phase-locked angle, the sector is determined, so as to control the three-phase rectification circuit and three two-way switches S_a、S_b、S_cIn the step of turning on and off each switching tube, determining the sector in which the switching tube is located by the following method includes:

u_a>u_b>u_cthe interval of (a) is set as a sector I;

u_b>u_a>u_cthe interval of (a) is set as sector II;

u_b>u_c>u_athe interval of (c) is set to sector iii;

u_c>u_b>u_ais set as sector IV;

u_c>u_a>u_bis set to sector v;

u_a>u_c>u_bthe interval of (c) is set as a sector VI;

and the control method of each switching tube comprises the following steps:

switching tube S of upper bridge arm at any time in each sector_a+、S_b+、S_c+The switch with the largest instantaneous value of the corresponding input voltage, and the switch tube S of the lower bridge arm_a-、S_b-、S_c-The switch with the minimum corresponding input voltage instantaneous value is always conducted, and the rest switch tubes are always turned off;

and the three bidirectional switches of the third harmonic injection circuit turn on the corresponding bidirectional switch with the minimum absolute value of the instantaneous voltage value, turn off other bidirectional switches, and inject third harmonic current into the phase power supply.

10. The control method according to claim 9, wherein when the post-stage circuit includes a clamp circuit, the control method further comprises:

when the matrix converter stops working, the clamping circuit absorbs energy stored in load leakage inductance; when the matrix converter normally works, the clamping circuit does not work.