CN118157443A - An isolated inverter circuit - Google Patents

Abstract

The present invention discloses an isolated inverter circuit, belonging to the technical field of switch power supply, comprising an input capacitor C _in , a first inductor L ₁ , a second inductor L ₂ , a first switch bridge arm composed of switch tubes Q ₁ and Q ₂ , a second switch bridge arm composed of switch tubes Q ₃ and Q ₄ , a bus capacitor C _bus , a transformer T , a resonant inductor L _r , a resonant capacitor _Cr and a rectifier flip circuit. The inverter circuit of the present invention can increase the bus voltage to twice the input voltage, thereby reducing the effective value of the primary current. The inductor connected in series with the leading arm can introduce a positive DC bias to the primary excitation current of the transformer, thereby improving the soft switching condition of the primary switch tube. Therefore, the inverter circuit of the present invention can obtain high efficiency in low-voltage input applications.

Description

An isolated inverter circuit

Technical Field

The invention belongs to the technical field of switching power supplies, and in particular relates to an isolated inverter circuit.

Background technique

Inverters play an important role in the power system. They can convert direct current into alternating current and play an important role in various fields such as new energy and automotive applications.

Low-voltage input application products, such as photovoltaic micro inverters or vehicle inverters, usually use isolated topology. Lower input voltage requires a larger voltage gain, which causes the primary current of traditional inverters to be too large, making it difficult for the inverter to achieve higher efficiency. For this application field, research and development of new inverter devices has become a hot research direction.

Summary of the invention

In view of the deficiencies of the prior art, the present invention proposes an isolated inverter circuit which can better optimize efficiency and cost.

In order to solve the above technical problems, the isolated inverter circuit of the present invention comprises:

Input capacitor C _in , first inductor L ₁ , second inductor L ₂ , first switch bridge arm composed of switch tubes Q ₁ and Q ₂ , second switch bridge arm composed of switch tubes Q ₃ and Q ₄ , bus capacitor C _bus , transformer T , resonant inductor L _r , resonant capacitor _Cr and rectifier flip circuit.

A DC input voltage source _Vin is connected in parallel with the input capacitor _Cin , a positive electrode of the input capacitor _Cin is connected to one end of the first inductor _L1 and the second inductor _L2 , the other end of the first inductor _L1 is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , the other end of the second inductor _L2 is connected to the source of the switch tube _Q3 and the drain of the switch tube _Q4 , the drain of the switch tube _Q1 and the drain of the switch tube _Q3 are connected to the positive electrode of the bus capacitor _Cbus , the source of the switch tube _Q2 , the source of the switch tube _Q4 , the negative electrode of the _input capacitor Cin and the negative electrode of the bus capacitor _Cbus are connected to the negative end of the DC input voltage source and the primary ground, the same-name end of the primary winding of the transformer T is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , and the opposite-name end is connected to the source of the switch tube _Q3 and the drain of the switch tube _Q4 , the same-name end of the secondary winding of the transformer T is connected to one end of the resonant inductor _Lr , and the resonant inductor L The other end of _r is connected to the first input end of the rectifier flip circuit, the opposite end of the secondary winding of the transformer T is connected to one end of the resonant capacitor _Cr , the other end of the resonant capacitor _Cr is connected to the second input end of the rectifier flip circuit, and the output end of the rectifier flip circuit is connected to the load or the power grid.

The midpoints of the first switch bridge arm and the second switch bridge arm respectively output high-frequency square wave signals, and the first switch bridge arm and the second switch bridge arm adopt a phase shift control or a mixed control mode of frequency control and phase shift control, so that the inverter circuit outputs an AC sinusoidal voltage or current. Among them, the bridge arm with a leading phase is called a leading arm, and the bridge arm with a lagging phase is called a lagging arm.

Preferably, the rectifier-flipping circuit comprises an output rectifier circuit and a cycloconverter.

Preferably, the output rectifier circuit includes a full-bridge rectifier circuit composed of four diodes _Do1 to _Do4 and an output capacitor _Co. The cathodes of diodes _Do1 and _Do3 are connected to one end of the output capacitor _Co1 , the anode of _Do1 is connected to the cathode of _Do2 and serves as the first input end of the rectifier flip circuit, the anode of _Do3 is connected to the cathode of _Do4 and serves as the second input end of the rectifier flip circuit, and the anode of _Do2 and the anode of _Do4 are connected to the other end of the output capacitor _Co1 .

Preferably, the output rectifier circuit includes a voltage doubler rectifier circuit composed of diodes _Do1 and _Do2 and capacitors _Co1 and _Co2 ; the cathode of diode _Do1 is connected to one end of capacitor _Co1 , the anode of diode _Do1 is connected to the cathode of _Do2 and serves as the first input end of the rectifier flip circuit, the other end of capacitor _Co1 is connected to one end of capacitor _Co2 and serves as the second input end of the rectifier flip circuit, and the anode of _Do2 is connected to the other end of the output capacitor _Co2 .

Preferably, the cycloconverter comprises a full-bridge circuit composed of switch tubes Q ₅ to Q ₈ , and the cycloconverter inverts the half-wave sinusoidal voltage signal output by the output rectifier circuit into a sinusoidal voltage signal.

Preferably, the rectifier flip circuit is composed of switch tubes _S1 to _S4 and capacitors _Co1 and _Co2 . The source of switch tube _S1 is connected to one end of capacitor _Co1 , the drain of switch tube _S1 is connected to the drain of switch tube _S2 , the source of switch tube _S2 is connected to the source of switch tube _S3 and serves as the first input end of the rectifier flip circuit, the other end of capacitor _Co1 is connected to one end of capacitor _Co2 as the second input end of the flip circuit, the drain of switch tube _S3 is connected to the drain of switch tube _S4 , and the source of switch tube _S4 is connected to the other end of capacitor _Co2 .

Preferably, the rectifier flip circuit includes switch tubes _S1 to _S4 and capacitors _Co1 and _Co2 . The source of the switch tube _S1 is connected to the source of the switch tube _S3 and serves as the first input terminal of the rectifier flip circuit, the drain of the switch tube _S1 is connected to the drain of the switch tube _S2 , the source of the switch tube _S2 is connected to one end of the capacitor _Co1 and serves as the first output terminal of the rectifier flip circuit, the drain of the switch tube _S3 is connected to the drain of the switch tube _S4 , the source of the switch tube _S4 is connected to one end of the capacitor _Co2 and serves as the second output terminal of the rectifier flip circuit, and the other end of the capacitor _Co1 is connected to the other end of the capacitor _Co2 and serves as the second input terminal of the rectifier flip circuit.

As an advantage, the inductor connected to the midpoint of the lagging arm can be omitted.

The present invention has the following characteristics and beneficial effects:

The inverter circuit of the present invention can increase the bus voltage to twice the input voltage, thereby reducing the effective value of the primary current. Furthermore, the inductor connected in series with the super-lead arm can introduce a positive DC bias to the primary excitation current of the transformer, thereby improving the soft switching condition of the primary switch tube. Therefore, the inverter circuit of the present invention can achieve high efficiency in low-voltage input applications.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

FIG1 shows a first embodiment of an isolated inverter of the present invention;

FIG2 shows the main working waveforms of the first embodiment of the isolated inverter of the present invention in the positive half cycle of the output AC;

FIG3 shows a first modal diagram of the first embodiment of the isolated inverter of the present invention;

FIG4 shows a second mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG5 shows a third mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG6 shows a fourth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG7 shows a fifth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG8 shows a sixth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG9 shows a seventh mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG10 shows an eighth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG11 shows a ninth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG12 shows a tenth mode diagram of the first embodiment of the isolated inverter of the present invention;

FIG13 shows the waveform of the voltage signal v _ws on the secondary side of the isolated inverter transformer of the present invention within a switching cycle;

FIG14 shows the amplitude waveform of v _ws when the phase difference α changes continuously within half a power frequency cycle;

FIG15 shows a comparison of the efficiency of the isolated inverter of the present invention and the isolated inverter without DC bias;

FIG16 shows a second embodiment of the isolated inverter of the present invention;

FIG17 shows a third embodiment of an isolated inverter of the present invention;

FIG18 shows a fourth embodiment of an isolated inverter of the present invention;

FIG. 19 shows a fifth embodiment of the isolated inverter of the present invention.

Detailed ways

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

The present invention provides an isolated inverter circuit, a first embodiment of which is shown in FIG1 .

The isolated inverter circuit includes: an input capacitor C _in , a first inductor L ₁ , a second inductor L ₂ , a first switch bridge arm composed of switch tubes Q ₁ and Q ₂ , a second switch bridge arm composed of switch tubes Q ₃ and Q ₄ , a bus capacitor C _bus , a transformer T, a resonant inductor L _r , a resonant capacitor _Cr , and a rectifier flip circuit 101 .

A DC input voltage source _Vin is connected in parallel with the input capacitor _Cin , a positive electrode of the input capacitor _Cin is connected to one end of the first inductor _L1 and one end of the second inductor _L2 , the other end of the first inductor _L1 is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , the other end of the second inductor _L2 is connected to the source of the switch tube _Q3 and the drain of the switch tube _Q4 , the drain of the switch tube _Q1 and the drain of the switch tube _Q3 are connected to the positive electrode of the bus capacitor _Cbus , the source of the switch tube _Q2 , the source of the switch tube _Q4 , the negative electrode of the _input capacitor Cin and the negative electrode of the bus capacitor _Cbus are connected to the negative end of the DC input voltage source and the primary ground, the gates of the switch tubes _Q1 to _Q4 receive the driving signals _VGQ1 to _VGQ4 generated by the control circuit, the same-name end of the primary winding of the transformer T is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , and the opposite-name end is connected to the source of the switch tube _Q3 and the drain of the switch tube Q4. ₄ , the same-name terminal of the secondary winding of the transformer T is connected to one end of the resonant inductor _Lr , and the other end of the resonant inductor _Lr is connected to the first input end of the rectifier flip circuit 101, the opposite-name terminal of the secondary winding of the transformer T is connected to one end of the resonant capacitor _Cr , and the other end of the resonant capacitor _Cr is connected to the second input end of the rectifier flip circuit 101, and the output end of the rectifier flip circuit 101 is connected to the load or the power grid.

The midpoints of the first switch bridge arm and the second switch bridge arm respectively output square wave signals, and the first switch bridge arm and the second switch bridge arm adopt a phase shift control or a mixed control mode of frequency control and phase shift control, so that the inverter circuit outputs an AC sinusoidal voltage or current. Among them, the bridge arm with a leading phase is called a leading arm, and the bridge arm with a lagging phase is called a lagging arm.

The rectifier flip circuit 101 is composed of switch tubes _S1 to _S4 and capacitors _Co1 and _Co2 . The source of the switch tube _S1 is connected to one end of the capacitor _Co1 , the drain of the switch tube _S1 is connected to the drain of the switch tube _S2 , the source of the switch tube _S2 is connected to the source of the switch tube _S3 and serves as the first input end of the rectifier flip circuit 101, the other end of the capacitor _Co1 is connected to one end of the capacitor _Co2 and serves as the second input end of the flip circuit 101, the drain of the switch tube _S3 is connected to the drain of the switch tube _S4 , and the source of the switch tube _S4 is connected to the other end of the capacitor _Co2 .

The midpoints of the first switch bridge arm and the second switch bridge arm respectively output high-frequency square wave signals, and the first switch bridge arm and the second switch bridge arm adopt a phase shift control or a mixed control mode of frequency control and phase shift control, so that the inverter circuit outputs an AC sinusoidal voltage or current. Among them, the bridge arm with a leading phase is called a leading arm, and the bridge arm with a lagging phase is called a lagging arm.

The rectifier flip circuit 101 has two functions: rectification and waveform flip. The control waveform of the switch tubes _Qs1 to _Qs4 is a high-low frequency mixed waveform. In the positive half cycle of the output AC, the control signals of the switch tubes _Qs1 and _Qs3 are high level so that the switch tubes _Qs1 and _Qs3 remain constantly turned on, and the control signals of the switch tubes _Qs2 and _Qs4 are high frequency signals. When current flows through the switch tubes _Qs2 and _Qs4 , the switch tubes _Qs2 and _Qs4 are turned on, and when the current flowing through the switch tubes _Qs2 and _Qs4 drops to zero, the switch tubes _Qs2 and _Qs4 are turned off. In the negative half cycle of the output AC, the control signals of the switch tubes Q _S2 and Q _S4 are high level so that the switch tubes Q _S2 and Q _S4 remain constantly turned on. The control signals of the switch tubes Q _S1 and Q _S3 are high frequency signals. When current flows through the switch tubes Q _S1 and Q _S3 , the switch tubes Q _S1 and Q _S3 are turned on, and when the current flowing through the switch tubes Q _S1 and Q _S3 drops to zero, the switch tubes Q _S1 and Q _S3 are turned off.

FIG2 shows the main working waveforms of the first embodiment of the isolated inverter of the present invention in the positive half cycle of the output AC, including the control signals _vGQ1 ~ _vGQ4 of the switch tubes _Q1 ~ _Q4 , the control signals _vGS1 ~ _vGS4 of the switch tubes _Qs1 ~ _Qs4 , the input current i _dc , the inductor currents i _L1 and i _L2 , the primary current i _r of the transformer and the secondary current i _s . In one switching cycle, the circuit has ten working modes:

Mode 1: (t ₀ -t ₁ ): At time t ₀ , switch tube Q ₂ is turned off, Q ₁ is not turned on yet, Q ₃ remains turned off, and Q ₄ remains turned on. At this time, the secondary switch tubes S ₁ and S ₃ are turned on, S ₂ and S ₄ remain turned off, no current flows through the secondary loop, and the output capacitor maintains the load energy. On the primary side, due to the conduction of Q ₄ , the current i _L2 flowing through the inductor L ₂ increases under the _{excitation of} the input voltage Vin; at the same time, the difference i _L1 -i _Lm between the current i _L1 flowing through the inductor L ₁ and the transformer excitation current i _Lm charges the output capacitor C _{oss_Q2} of Q ₂ and discharges the output capacitor C _{oss_Q1} of Q _1. FIG3 shows the first mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 2: (t ₁ -t ₂ ): At time t ₁ , the voltage across _{Coss_Q1} discharges to zero, Q ₁ is turned on at zero voltage, Q ₂ and Q ₃ remain off, and Q ₄ remains on, and the bus capacitor voltage V _bus is applied to the primary winding W _p of the transformer T through Q ₁ and Q ₄ ; on the secondary side, the secondary sides S ₁ and S ₃ remain on, and at the same time, the switch tube S ₂ is turned on at zero voltage, and the secondary winding W _s of the transformer, the resonant inductor L _r , and the resonant capacitor C _r form a loop through the switch tubes S ₁ and S ₂ and the output capacitor _Co1 , and the resonant inductor L _r and the resonant capacitor C _r begin to resonate. The secondary resonant current _is is mapped to the primary winding _Wp of the transformer to form _iwp , and the current _iL2 flowing through the inductor _L2 continues to rise under the excitation of the input voltage _Vin , while the difference between the input voltage _Vin and the DC bus capacitor voltage across the inductor _L1 is a negative value, so the inductor current _iL1 decreases. At the same time, the difference _iL1 - _iP between the inductor current _iL1 and the primary current _ip flows into the capacitor _Cbus . Wherein, _ip = _iLm + _iwp . When _iL1 - _ip <0, the current actually injected into the capacitor _Cbus is a negative value, which means that the capacitor _Cbus flows out energy. FIG4 shows the second modal diagram of the first embodiment of the isolated inverter of the present invention.

Mode 3: (t ₂ -t ₃ ): At time t ₂ , the switch tube Q ₄ is turned off, Q ₃ is not turned on yet, Q ₂ remains turned off, and Q ₁ remains turned on. At this time, the secondary switch tubes S ₁ , S ₂ and S ₃ remain turned on, and the secondary winding W _s of the transformer, the resonant inductor L _r , and the resonant capacitor C _r form a loop through the switch tubes S ₁ and S ₂ and the output capacitor _Co1 , and the resonant inductor L _r and the resonant capacitor C _r continue to resonate. The secondary resonant current i _s drops rapidly and is mapped to the primary winding W _p of the transformer to form i _wp . The two ends of the inductor L ₁ continue to bear negative pressure, and the inductor current i _L1 continues to drop. The primary current i _p and the inductor current i _L2 discharge the output capacitor _{Coss_Q3} of Q ₃ and charge the output capacitor _{Coss_Q4} of Q _4. FIG. 5 shows the third mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 4: (t ₃ -t ₄ ): At t ₃ , the voltage across _{Coss_Q3} is discharged to zero, Q ₃ is turned on at zero voltage, Q ₂ and Q ₄ remain off, and Q ₁ remains on. The voltage across the primary winding W _p of the transformer T is short-circuited to 0V by Q ₁ and Q ₃ , and the excitation inductor current circulates through Q ₁ and Q ₃ , showing a positive amplitude and remaining unchanged. At this time, the secondary side switches S ₁ , S ₂ and S ₃ remain on, and the secondary winding W _s of the transformer, the resonant inductor L _r , and the resonant capacitor C _r form a loop through the switches S ₁ and S ₂ and the output capacitor _Co1 . The resonant inductor L _r and the resonant capacitor C _r continue to resonate, and the secondary side resonant current i _s continues to decrease and is mapped to the primary winding W _p of the transformer. Since _Q1 and _Q3 are turned on, the difference between the input voltage _Vin and the DC bus capacitor voltage across inductors _L1 and _L2 is negative, so the inductor currents _iL1 and _iL2 decrease. Fig. 6 shows the fourth mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 5: (t ₄ -t ₅ ): At time t ₄ , the secondary resonant current i _s drops to zero, S ₂ is turned off, no current flows through the secondary loop, and the output capacitor maintains the load energy. On the primary side, Q ₁ and Q ₃ remain on, Q ₂ and Q ₄ remain off, and the transformer excitation current i _Lm circulates through transformers Q ₁ and Q _3. Since Q ₁ and Q ₃ are turned on, the difference between the input voltage _Vin and the DC bus capacitor voltage borne by inductors L ₁ and L ₂ is a negative value, so the inductor currents i _L1 and i _L2 continue to drop. FIG. 7 shows the fifth mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 6: At time _t5 , the switch tube _Q1 is turned off, _Q2 is not turned on yet, _Q4 remains turned off, and _Q3 remains turned on. At this time, the secondary side switches _S1 and _S3 are turned on, but since _S2 and _S4 remain turned off, no current flows through the secondary side loop, and the output capacitor maintains the load energy. Since _Q3 is turned on, the difference between the input voltage _Vin and the DC bus capacitor voltage borne by the inductor _L2 is a negative value, so the inductor current _iL2 decreases. Since this interval time is very short, the inductor current _iL1 can be approximately regarded as unchanged. The difference current _ip - _iL1 ( _ip ＝ _iLm > _iL1 ) between _ip and _iL1 discharges the output capacitor _{Coss_Q2} of _Q2 and charges the output capacitor _{Coss_Q1} of _Q1 . FIG8 shows the sixth mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 7: At _t6 , the voltage across _{Coss_Q2} is discharged to zero, _Q2 is turned on at zero voltage, _Q1 and _Q4 remain off, and _Q3 remains on, and the bus capacitor voltage _Vbus is applied to the primary winding _Wp of the transformer T through _Q2 and _Q3 ; at this time, the secondary switch tubes _S1 and _S3 remain on, and _S4 is turned on at zero voltage, and the secondary winding _Ws of the transformer, the resonant inductor _Lr , and the resonant capacitor _Cr form a loop through the switch tubes _S3 and _S4 and the output capacitor _Co2 , and the resonant inductor _Lr and the resonant capacitor _Cr begin to resonate. The secondary resonant current i _s is mapped to the primary winding _Wp of the transformer, and the current i _L1 flowing through the inductor _L1 increases under the excitation of the input voltage V _in , while the difference between the input voltage V _in and the DC bus capacitor voltage flowing through the inductor _L2 is a negative value, so the inductor current i _L2 keeps decreasing, and the current provided to the outside by the capacitor C _bus is i _p -i _L2 inflow. A short period of time before this interval, i _p -i _L2 <0, and the current flowing out of the actual capacitor C _bus is negative, which means that the capacitor C _bus absorbs energy. FIG9 shows the seventh mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 8: At _t7 , the switch tube _Q3 is turned off, _Q4 is not turned on yet, _Q1 remains turned off, and _Q2 remains turned on. At the same time, the secondary switch tubes _S1 , _S3 and _S4 remain turned on, and the secondary winding _Ws of the transformer, the resonant inductor _Lr , and the resonant capacitor _Cr form a loop through the switch tubes _S3 and _S4 and the output capacitor C _o2 , and the resonant inductor _Lr and the resonant capacitor _Cr continue to resonate. The secondary resonant current i _s is mapped to the primary winding _Wp of the transformer, and the current i _L1 flowing through the inductor _L1 increases under the excitation of the input voltage V _in . The difference i _p -i _L2 between the primary current i _p and the current i _L2 flowing through the inductor _L2 charges the output capacitor C _{oss_Q3} of _Q3 and discharges the output capacitor C _{oss_Q4} of _Q4 . At the same time, the inductor current i _L2 flows into the primary winding of the transformer, generating a negative DC bias in the excitation current. FIG. 10 shows an eighth mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 9: At time _t8 , the voltage across _{Coss_Q4} is discharged to zero, _Q4 is turned on, _Q1 and _Q3 remain off, and _Q2 remains on. There is no current flow path for capacitor _Cbus , and the voltage across it remains unchanged. The voltage across the primary winding _Wp of transformer T is clamped to 0V through _Q2 and _Q4 . At this time, the secondary switch tubes _S1 , _S3 and _S4 remain turned on, and the secondary winding _Ws of the transformer, the resonant inductor _Lr , and the resonant capacitor _Cr form a loop through the switch tubes _S3 and _S4 and the output capacitor _Co2 , and the resonant inductor Lr and the resonant capacitor Cr continue to resonate. The secondary resonant current i _s is mapped to the primary winding _Wp of the transformer, and the currents i _L1 and i _L2 flowing through the inductors _L1 and _L1 rise under the _{excitation of} the input voltage Vin. FIG11 shows the ninth mode diagram of the first embodiment of the isolated inverter of the present invention.

Mode 10: At time _t9 , the secondary current _is drops to zero, and the secondary switch tube _S4 is turned off. However, since _S2 remains turned off, no current flows through the secondary loop, and the output capacitor maintains the load energy; on the primary side, _Q2 and _Q4 remain on, and _Q1 and _Q3 remain off. On the primary side, the transformer excitation current _iLm circulates through _Q2 and _Q4 , and the currents _iL1 and _iL2 flowing through the inductors _L1 and _L2 rise under the _excitation of the input voltage Vin. FIG12 shows the tenth mode diagram of the first embodiment of the isolated inverter of the present invention.

When the first embodiment of the isolated inverter of the present invention operates in the negative half cycle of the output AC, there are similar ten operating modes, which will not be described in detail here.

According to the main working waveforms of the first embodiment of the isolated inverter of the present invention in the positive half cycle of the output AC as shown in FIG2 and the above description of the working mode, the soft switching conditions for the primary switch tube of the isolated inverter of the present invention to achieve zero voltage switching are:

When Q ₂ is turned off, the difference i _L1 -i _Lm between the current i _L1 flowing through the inductor L ₁ and the transformer excitation current i _Lm charges the output capacitor C _{oss_Q2} of Q ₂ and discharges the output capacitor C _{oss_Q1} of Q _1. That is, Q ₁ achieves zero voltage turn-on through (i _L1 -i _Lm )/2.

When Q ₁ is turned off, the difference current i _p -i _L1 (i _p =i _Lm >i _L1 ) between i _p and i _L1 discharges the output capacitor C _{oss_Q2} of Q ₂ and charges the output capacitor C _{oss_Q1} of Q _1. That is, Q ₂ achieves zero voltage turn-on through (i _p -i _L1 )/2.

When the switch tube _Q4 is turned off, the primary current i _p and the inductor current i _L2 discharge the output capacitor C _{oss_Q3} of _Q3 and charge the output capacitor C _{oss_Q4} of _Q4 . That is, _Q3 achieves zero voltage turn-on through (i _p +i _L2 )/2.

When the switch _Q3 is turned off, the difference i _p -i _L2 between the primary current _{i p} and the current i _L2 flowing through the inductor L2 charges the output capacitor _{Coss_Q3} of _Q3 and discharges the output capacitor _{Coss_Q4} of _Q4 . That is, _Q4 achieves zero voltage turn-on through (i _p -i _L2 )/2.

Therefore, by reasonably designing the parameters, the isolated inverter of the present invention can realize zero voltage turn-on of the primary switch tube in the entire power frequency cycle. The essential mechanism is that the inductor current i _L1 is introduced into the primary side circuit of the isolated inverter transformer of the present invention as a positive DC bias, which improves the soft switching condition of the primary switch tube. If the primary side circuit of the isolated inverter transformer has no DC bias, its lagging bridge arm switch tube can only rely on the transformer excitation current to achieve soft switching, and it is difficult to achieve soft switching of the switch tube in the entire power frequency cycle through the design of the converter parameter design.

To further describe the principle of the present invention, FIG. 13 shows the waveform of the voltage signal v _ws on the secondary side of the isolated inverter transformer of the present invention in a switching cycle, where α is the phase shift angle between the primary switch bridge arms, which is determined by the control signals v _GQ1 to v _GQ4 generated by the control circuit. When α changes dynamically in a power frequency cycle, the v _ws waveform is expanded by Fourier series, and the following can be obtained:

Among them, ω＝ _2πfs , _fs is the operating frequency of the primary switch tube, and N is the turns ratio of the secondary winding of the transformer relative to the primary winding. When _fs and the resonant frequency of the resonant unit composed of _Lr and _Cr are When the equivalent impedance of the resonant unit is low impedance relative to the fundamental frequency (resonant frequency f _r ), and high impedance for higher frequencies. Therefore, at the resonant frequency point, the higher-order components of v _ws can be ignored, thus obtaining equation (2).

At this time, v _ws is simplified to a high-frequency sine wave whose amplitude f(α) is affected by the phase shift angle α. Therefore, if the phase difference α between the first square wave generating circuit and the second square wave generating circuit is controlled to change continuously, the amplitude NV _bus f(α) of v _ws can be changed continuously accordingly, as shown in FIG14. Therefore, by controlling the phase difference α to change continuously as shown in FIG14 within half of the power frequency cycle through the control circuit, that is, the first 1/4 sinusoidal cycle controls the phase difference α to increase continuously from 0 to π, and the second 1/4 sinusoidal cycle controls the phase difference α to decrease continuously from π to 0, then f(α) can be made into a sinusoidal half wave. Furthermore, since the output rectifier flipping circuit has peak detection and flipping functions, a sinusoidal AC output voltage waveform of the power frequency can be obtained on the output side.

Figure 15 shows the efficiency comparison between the isolated inverter of the present invention and the isolated inverter without DC bias. It can be seen that the isolated inverter of the present invention has been significantly improved in efficiency due to the introduction of DC bias, which enables the primary switch to achieve zero voltage turn-on in the entire power frequency cycle.

FIG. 16 shows a second embodiment of the isolated inverter of the present invention, wherein the inductor _L2 connected to the hysteresis switch bridge arm can be omitted without affecting the normal operation of the inverter.

FIG17 shows a third embodiment of the isolated inverter of the present invention. The rectifier-flipping circuit 101 includes an output rectifier circuit and a cycloconverter. The output rectifier circuit includes a full-bridge rectifier circuit composed of four diodes _Do1 to _Do4 and an output capacitor _Co ; the cycloconverter includes a full-bridge circuit composed of switch tubes _Q5 to _Q8 . The two midpoints of the full-bridge rectifier circuit serve as the two input ends of the rectifier-flipping circuit 101, the two output ends of the full-bridge rectifier circuit serve as the two input ends of the cycloconverter, and the two midpoints of the full-bridge circuit composed of switch tubes _Q5 to _Q8 serve as the two output ends of the rectifier-flipping circuit 101 to output an AC output voltage.

FIG18 shows a fourth embodiment of the isolated inverter of the present invention. The rectifier-flipping circuit 101 includes an output rectifier circuit and a cycloconverter. The output rectifier circuit includes a voltage-doubling rectifier composed of diodes _Do1 - _Do2 and capacitors _Co1 - _Co2 ; the cycloconverter includes a full-bridge circuit composed of switch tubes _Q5 - _Q8 . The two midpoints of the voltage-doubling rectifier circuit serve as the two input ends of the rectifier-flipping circuit 101, the two output ends of the full-bridge rectifier circuit serve as the two input ends of the cycloconverter, and the two midpoints of the full-bridge circuit composed of switch tubes _Q5 - _Q8 serve as the two output ends of the rectifier-flipping circuit 101 to output an AC output voltage.

FIG19 shows a fifth embodiment of the isolated inverter of the present invention. The rectifier flip circuit 101 includes switch tubes _S1 to _S4 and capacitors _Co1 and _Co2 . The source of the switch tube _S1 is connected to the source of the switch tube _S3 and serves as the first input terminal of the rectifier flip circuit 101, the drain of the switch tube _S1 is connected to the drain of the switch tube _S2 , the source of the switch tube _S2 is connected to one end of the capacitor _Co1 and serves as the first output terminal of the rectifier flip circuit 101, the drain of the switch tube _S3 is connected to the drain of the switch tube _S4 , the source of the switch tube _S4 is connected to one end of the capacitor _Co2 and serves as the second output terminal of the rectifier flip circuit 101, and the other end of the capacitor _Co1 is connected to the other end of the capacitor _Co2 and serves as the second input terminal of the rectifier flip circuit 101.

Well-known implementation methods and operating means are not described in detail herein to avoid confusing the various technical implementation schemes of the present invention. However, for those skilled in the art, the lack of one or more specific details or components does not affect the understanding and implementation of the present invention.

The specific implementation methods and methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only the specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, combinations, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims (9)

1. An isolated inverter circuit, characterized in that it comprises: an input capacitor C _in , a first inductor L ₁ , a second inductor L ₂ , a first switch bridge arm composed of switch tubes Q ₁ and Q ₂ , a second switch bridge arm composed of switch tubes Q ₃ and Q ₄ , a bus capacitor C _bus , a transformer T , a resonant inductor L _r , a resonant capacitor _Cr and a rectifier flip circuit; A DC input voltage source _Vin is connected in parallel with the input capacitor _Cin , a positive electrode of the input capacitor _Cin is connected to one end of the first inductor _L1 and the second inductor _L2 , the other end of the first inductor _L1 is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , the other end of the second inductor _L2 is connected to the source of the switch tube _Q3 and the drain of the switch tube _Q4 , the drain of the switch tube _Q1 and the drain of the switch tube _Q3 are connected to the positive electrode of the bus capacitor _Cbus , the source of the switch tube _Q2 , the source of the switch tube _Q4 , the negative electrode of the _input capacitor Cin and the negative electrode of the bus capacitor _Cbus are connected to the negative end of the DC input voltage source and the primary ground, the same-name end of the primary winding of the transformer T is connected to the source of the switch tube _Q1 and the drain of the switch tube _Q2 , and the opposite-name end is connected to the source of the switch tube _Q3 and the drain of the switch tube _Q4 , the same-name end of the secondary winding of the transformer T is connected to one end of the resonant inductor _Lr , and the resonant inductor L The other end of _r is connected to the first input end of the rectifier flip circuit, the opposite end of the secondary winding of the transformer T is connected to one end of the resonant capacitor _Cr , the other end of the resonant capacitor _Cr is connected to the second input end of the rectifier flip circuit, and the output end of the rectifier flip circuit is connected to the load or the power grid. 2. The isolated inverter circuit according to claim 1 is characterized in that the midpoints of the first switch bridge arm and the second switch bridge arm respectively output high-frequency square wave signals, and phase shift control or a mixed control method of frequency control and phase shift control is adopted between the first switch bridge arm and the second switch bridge arm, so that the inverter circuit outputs an AC sinusoidal voltage or current, wherein the bridge arm with leading phase is called the leading arm, and the bridge arm with lagging phase is called the lagging arm. 3. The isolated inverter circuit according to claim 2 is characterized in that the rectifier flip circuit is composed of switch tubes _S1 ~ _S4 and capacitors _Co1 and _Co2 ; the source of the switch tube _S1 is connected to one end of the capacitor _Co1 , the drain of the switch tube _S1 is connected to the drain of the switch tube _S2 , the source of the switch tube _S2 is connected to the source of the switch tube _S3 and serves as the first input end of the rectifier flip circuit, the other end of the capacitor _Co1 is connected to one end of the capacitor _Co2 as the second input end of the flip circuit, the drain of the switch tube _S3 is connected to the drain of the switch tube _S4 , and the source of the switch tube _S4 is connected to the other end of the capacitor _Co2 . 4. The isolated inverter circuit according to claim 2 is characterized in that the rectifier flip circuit includes switch tubes S1~S4 and capacitors Co1 and Co2; the source of the switch tube S1 is connected to the source of the switch tube S3 and serves as the first input end of the rectifier flip circuit, the drain of the switch tube S1 is connected to the drain of the switch tube S2, the source of the switch tube S2 is connected to one end of the capacitor Co1 and serves as the first output end of the rectifier flip circuit, the drain of the switch tube S3 is connected to the drain of the switch tube S4, the source of the switch tube S4 is connected to one end of the capacitor Co2 and serves as the second output end of the rectifier flip circuit, and the other end of the capacitor Co1 is connected to the other end of the capacitor Co2 and serves as the second input end of the rectifier flip circuit. 5 . The isolated inverter circuit according to claim 2 , wherein the rectifier-flip circuit comprises an output rectifier circuit and a cycloconverter. 6. The isolated inverter circuit according to claim 5 is characterized in that the output rectifier circuit comprises a full-bridge rectifier circuit composed of four diodes _Do1 to _Do4 and an output capacitor _Co ; the cathodes of diodes _Do1 and _Do3 are connected to one end of the output capacitor _Co1 , the anode of _Do1 is connected to the cathode of _Do2 and serves as the first input end of the rectifier flip circuit, the anode of _Do3 is connected to the cathode of _Do4 and serves as the second input end of the rectifier flip circuit, and the anode of _Do2 and the anode of _Do4 are connected to the other end of the output capacitor _Co1 . 7. The isolated inverter circuit according to claim 5 is characterized in that the output rectifier circuit includes a voltage doubling rectifier circuit composed of diodes _Do1 and _Do2 and capacitors _Co1 and _Co2 ; the cathode of diode _Do1 is connected to one end of capacitor _Co1 , the anode of diode _Do1 is connected to the cathode of _Do2 and serves as the first input end of the rectifier flip circuit, the other end of capacitor _Co1 is connected to one end of capacitor _Co2 and serves as the second input end of the rectifier flip circuit, and the anode of _Do2 is connected to the other end of output capacitor _Co2 . 8. The isolated inverter circuit according to any one of claims 5 to 7, characterized in that the cycloconverter comprises a full-bridge circuit composed of switch tubes _Q5 to _Q8 ; the cycloconverter flips the sinusoidal half-wave voltage signal output by the output rectifier circuit into a sinusoidal voltage signal. 9 . The isolated inverter circuit according to claim 8 , wherein the inductor connected to the midpoint of the lagging arm is omitted.