Voltage flexible control circuit applied to photovoltaic power station

Abstract

A voltage flexible control circuit applied to a photovoltaic power station comprises a three-phase AC / DC rectifying circuit with fault-tolerant capability and a high-efficiency current-sharing three-phase multi-stage DC / AC inverter circuit, and the output side of the three-phase AC / DC rectifying circuit with fault-tolerant capability is connected with the input side of the high-efficiency current-sharing three-phase multi-stage DC / AC inverter circuit; in the three-phase AC / DC rectifying circuit with the fault-tolerant capability, the primary side of the isolation transformer is a single-pole rectifying circuit with six switching tubes. The method has a certain fault-tolerant capability, can automatically switch to a fault working mode when a switch or a bridge arm fails, and ensures the stable operation of the system. Meanwhile, the inverter circuit adopts a three-phase coupling inductor design and a multi-level output structure, so that the harmonic content and the current stress and loss of a switching device can be remarkably reduced, the demand on an output filter is reduced, and the electric energy quality of output alternating current and the stability and adaptability of the system are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic conversion and relates to a voltage flexible control circuit applied to a photovoltaic power station. Background Art

[0002] With the booming photovoltaic industry, the proportion of PV power stations in the energy mix continues to increase, placing increasingly stringent demands on power conversion and control technologies. As a core technology in photovoltaic systems, flexible voltage control circuits precisely adjust voltage and current under varying operating conditions, improving power conversion efficiency and system stability. They offer functions such as DC-AC conversion, dynamic voltage regulation, rapid power response, and harmonic suppression. This makes them crucial in grid-connected inverters, distributed energy resources, and microgrid systems. Traditional voltage control circuits primarily utilize two-level or three-level topologies, which suffer from low power density, high harmonic distortion, complex filters, and slow dynamic response. Furthermore, high current stress and losses in switching devices shorten their service life and lead to uneven load current distribution, which can easily create local hotspots and concentrated power losses, compromising system stability. Traditional rectifiers often utilize uncontrolled or semi-controlled bridge rectifiers. Switch failure can render the system inoperable. Summary of the Invention

[0003] In order to address the deficiencies in the prior art, the present invention provides a voltage-flexible control circuit for use in photovoltaic power stations, comprising a three-phase AC / DC rectifier circuit with fault tolerance and a three-phase multi-stage DC / AC inverter circuit with high efficiency and current sharing. This circuit provides strong technical support for the efficient, stable, and flexible operation of photovoltaic systems, simplifies the circuit structure, reduces costs, and has strong fault tolerance, high reliability, high power quality, and high conversion efficiency.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] A voltage-flexible control circuit for a photovoltaic power station includes a three-phase AC / DC rectifier circuit with fault tolerance and a three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing, wherein the output side of the three-phase AC / DC rectifier circuit with fault tolerance is connected to the input side of the three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing;

[0006] In the three-phase AC / DC rectifier circuit with fault tolerance, the primary side of the isolation transformer is a unipolar rectifier circuit with six switches. On the primary side of the isolation transformer, the A-phase input terminal is directly connected to the same-name terminal of the isolation transformer via the first input inductor L1, and the first bidirectional switch ZA, DC blocking capacitor C3, and leakage inductor L4 are connected in series in sequence in the circuit. On the secondary side of the isolation transformer, the positive polarity terminal of the first secondary-side rectifier D1 is connected to the same-name terminal of the secondary winding of the isolation transformer, and the positive polarity terminal of the second secondary-side rectifier D2 is connected to the opposite-name terminal of the secondary winding of the isolation transformer. The first secondary-side rectifier D1 and the second secondary-side rectifier D2 are connected in parallel and then connected to the inductor L5. The positive electrode of the capacitor C4 is connected to the inductor L5, and the negative electrode of the capacitor C4 is connected to the midpoint of the secondary winding of the isolation transformer. The load R0 is connected in parallel to the inductor C4, and both sides of the load R0 are the output sides of the three-phase AC / DC rectifier circuit with fault tolerance.

[0007] Furthermore, the three-phase AC / DC rectifier circuit with fault tolerance includes a first input inductor L1, a second input inductor L2, a third input inductor L3, a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first fuse FA, a second fuse FB, a third fuse FC, a first bidirectional switch ZA, a second bidirectional switch ZAB, a third bidirectional switch ZBC, a fourth bidirectional switch ZC, a first bus capacitor C1, a second bus capacitor C2, a DC blocking capacitor C3, a first thyristor HA, a second thyristor HB, a third thyristor HC, a leakage inductor L4, an isolation transformer K1, a first secondary-side rectifier tube D1, a second secondary-side rectifier tube D2, an inductor L5, a capacitor C4, and a load R0;

[0008] Phase A is connected to the first input inductor L1, and then to the source of the first switching transistor S1 and the drain of the fourth switching transistor S4. Phase B is connected to the second input inductor L2, and then to the source of the third switching transistor S3 and the drain of the sixth switching transistor S6. Phase C is connected to the third input inductor L3, and then to the source of the fifth switching transistor S5 and the drain of the second switching transistor S2. The drains of the first switching transistor S1, the third switching transistor S3, and the fifth switching transistor S5 are connected to the positive terminal of the first bus capacitor C1. The sources of the fourth switching transistor S4, the sixth switching transistor S6, and the second switching transistor S2 are connected to the negative terminal of the second bus capacitor C2.

[0009] In a unipolar rectifier circuit with six switches on the primary side of the isolation transformer, a first fuse FA, a second fuse FB, and a third fuse FC are connected in series to the three phases A, B, and C respectively after the input inductor on the three-phase power input side; a first thyristor HA, a second thyristor HB, and a third thyristor HC are connected across the input inductor on the three-phase power input side and the first DC bus capacitor C1 and the second DC bus capacitor C2.

[0010] Furthermore, the efficient current-sharing three-phase multi-level DC / AC inverter circuit includes the seventh switch tube S7 to the twelfth switch tube S12 forming an A-phase switch tube combination, the thirteenth switch tube S13 to the eighteenth switch tube S18 forming a B-phase switch tube combination, and the nineteenth switch tube S19 to the twenty-fourth switch tube S24 forming a C-phase switch tube combination; the first coupled inductor J1 to the third coupled inductor J3 forming a coupled inductor of phase A, the fourth coupled inductor J4 to the sixth coupled inductor J6 forming a coupled inductor of phase B, and the seventh coupled inductor J7 to the ninth coupled inductor J9 forming a coupled inductor of phase C;

[0011] The source of the seventh switch transistor S7 is connected to the drain of the tenth switch transistor S10, the source of the eighth switch transistor S8 is connected to the drain of the eleventh switch transistor S11, the source of the ninth switch transistor S9 is connected to the drain of the twelfth switch transistor S12, the source of the thirteenth switch transistor S13 is connected to the drain of the sixteenth switch transistor S16, the source of the fourteenth switch transistor S14 is connected to the drain of the seventeenth switch transistor S17, the source of the fifteenth switch transistor S15 is connected to the drain of the eighteenth switch transistor S18, the source of the nineteenth switch transistor S19 is connected to the drain of the twenty-second switch transistor S22, the source of the twentieth switch transistor S20 is connected to the drain of the twenty-third switch transistor S23, and the source of the twenty-second switch transistor S22 is connected to the drain of the twenty-fourth switch transistor S24;

[0012] The drains of the seventh switch tube S7, the eighth switch tube S8, the ninth switch tube S9, the thirteenth switch tube S13, the fourteenth switch tube S14, the fifteenth switch tube S15, the nineteenth switch tube S19, the twentieth switch tube S20, and the twenty-first switch tube S21 are connected to the positive polarity end of the DC bus;

[0013] The sources of the tenth switch tube S10, the eleventh switch tube S11, the twelfth switch tube S12, the sixteenth switch tube S16, the seventeenth switch tube S17, the eighteenth switch tube S18, the twenty-second switch tube S22, the twenty-third switch tube S23, and the twenty-fourth switch tube S24 are connected to the negative polarity end of the DC bus;

[0014] The source of the seventh switch S7 is connected to the positive end of the coupling inductor J1, the source of the eighth switch S8 is connected to the positive end of the coupling inductor J2, and the source of the ninth switch S9 is connected to the positive end of the coupling inductor J3. The negative ends of the coupling inductors J1, J2, and J3 are connected to the same point and then connected in series to the output load of phase A.

[0015] The source of the thirteenth switch S13 is connected to the positive end of the coupling inductor J4, the source of the fourteenth switch S14 is connected to the positive end of the coupling inductor J5, and the source of the fifteenth switch S15 is connected to the positive end of the coupling inductor J6. The negative ends of the coupling inductors J4, J5, and J6 are connected to the same point and then connected in series to the output load of phase B.

[0016] The source of the nineteenth switch tube S19 is connected to the positive polarity end of the coupling inductor J7, the source of the twentieth switch tube S20 is connected to the positive polarity end of the coupling inductor J8, and the source of the twenty-first switch tube S21 is connected to the positive polarity end of the coupling inductor J9. The negative polarity ends of the coupling inductors J7, J8, and J9 are connected to the same point and then connected in series to the output load of phase C.

[0017] The technical concept of the present invention is as follows: In a fault-tolerant three-phase AC / DC rectifier circuit, the AC / DC conversion portion utilizes a fault-tolerant three-phase isolated single-stage AC / DC converter. This converter requires only six main switches and auxiliary components, such as fuses and bidirectional switches, to achieve AC / DC conversion. In normal operating mode, the bidirectional switches and thyristors are disconnected, and the converter operates as a six-switch single-stage rectifier, rectifying three-phase AC power into DC power, which is then isolated and filtered by a transformer and output filter. If a switch or an entire bridge arm fails, the system automatically switches to fault operating mode. By controlling the on / off state of the bidirectional switches and thyristors, the midpoint of the bridge arm is connected to the midpoint of the capacitor, reconfiguring the AC / DC converter into a four-switch voltage source inverter and continuing stable operation.

[0018] In the fault-tolerant three-phase AC / DC rectifier circuit, in normal operating mode, the second bidirectional switch ZAB, the third bidirectional switch KBC, and the first thyristor HA, the second thyristor HB, and the third thyristor HC in the AC / DC conversion section are disconnected. The conversion circuit operates as a six-switch single-stage rectifier, rectifying three-phase AC power into DC power. The specific operating process is as follows: Three-phase AC power enters the converter through the input inductor L, with the inductor L for each phase performing filtering and current limiting. The six main switches S1-S6 are turned on and off according to a specific control strategy, achieving AC / DC and DC-DC conversion functions. This control strategy utilizes decoupled power control and sinusoidal pulse-width modulation technology within a synchronous reference frame to ensure the quality and stability of the output power.

[0019] The rectified DC power is isolated and filtered by a transformer and output filter, providing a stable DC power source for the DC / AC conversion section. The transformer has a turns ratio of n:1, and the output filter, consisting of inductor L5 and capacitor C4, further improves the stability of the DC power.

[0020] In this highly efficient, current-sharing, three-phase, multi-level DC / AC inverter circuit, the on / off switching of any of the three phases is controlled by the coordinated operation of six switching transistors. Through the coordinated operation of multiple switching devices, the DC / AC circuit can generate a multi-level PWM voltage waveform, significantly reducing harmonic content, improving the power quality of the output AC power, and reducing the need for output filters. Furthermore, the use of insulated gate bipolar transistor power semiconductor devices offers high frequency, high power density, and low loss.

[0021] Furthermore, the highly efficient, current-sharing three-phase, multi-level DC / AC inverter circuit utilizes three-phase coupled inductors, which evenly distribute the load phase current across the three windings. Each winding draws only one-third of the load phase current, reducing current stress and losses in the switching devices. The coupled inductors also offer high impedance to harmonic currents, effectively suppressing their flow and further improving the quality of the output power.

[0022] The circuit of the present invention comprises a fault-tolerant three-phase AC / DC rectifier circuit and a highly efficient, current-sharing three-phase, multi-level DC / AC inverter circuit, forming an AC / DC / AC circuit. This circuit exhibits a certain degree of fault tolerance and automatically switches to a fault-operating mode in the event of a switch or bridge arm failure, ensuring stable system operation. Furthermore, the inverter circuit utilizes a three-phase coupled inductor design and a multi-level output structure, significantly reducing harmonic content, current stress, and losses in switching devices, reducing the need for output filters and improving the power quality of the output AC power as well as the stability and adaptability of the system.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The AC / DC / AC converter circuit designed in this invention is compact and low-cost. The AC / DC conversion circuit adopts a single-stage design, requiring only six main switches and some auxiliary components, simplifying the circuit structure and reducing costs.

[0025] 2. The DC / AC inverter circuit in the present invention utilizes a three-phase coupled inductor to evenly distribute the load phase current among the three windings. The current of each winding is only one-third of the load phase current, which reduces the current stress and loss of the switching devices and further reduces the system cost and volume.

[0026] 3. Strong fault tolerance and high reliability: The AC / DC circuit has fault tolerance. When a switch or the entire bridge arm fails, it can automatically switch to the fault working mode. By controlling the on and off of the bidirectional switch and the thyristor, the circuit can continue to operate stably after reconfiguration, avoiding the entire system shutdown caused by the fault and ensuring uninterrupted power supply to the photovoltaic power station.

[0027] 4. High power quality and conversion efficiency: The DC / AC circuit utilizes a multi-level design, resulting in low output voltage harmonics and high power quality. This multi-level output voltage reduces harmonics and the need for output filters, further reducing system cost and size. Furthermore, energy losses during AC / DC and DC / AC conversion are reduced, significantly improving overall conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the topological structure of the voltage flexible control circuit of the present invention.

[0029] Figure 2 This is a control flow chart of the fault working mode of the three-phase AC / DC rectifier circuit with fault tolerance in the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] Reference Figure 1 and Figure 2 A voltage-flexible control circuit for a photovoltaic power station includes a three-phase AC / DC rectifier circuit with fault tolerance and a three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing, wherein the output side of the three-phase AC / DC rectifier circuit with fault tolerance is connected to the input side of the three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing;

[0032] In the three-phase AC / DC rectifier circuit with fault tolerance, the primary side of the isolation transformer is a unipolar rectifier circuit with six switches. On the primary side of the isolation transformer, the A-phase input terminal is directly connected to the same-name terminal of the isolation transformer via the first input inductor L1, and the first bidirectional switch ZA, DC blocking capacitor C3, and leakage inductor L4 are connected in series in sequence in the circuit. On the secondary side of the isolation transformer, the positive polarity terminal of the first secondary-side rectifier D1 is connected to the same-name terminal of the secondary winding of the isolation transformer, and the positive polarity terminal of the second secondary-side rectifier D2 is connected to the opposite-name terminal of the secondary winding of the isolation transformer. The first secondary-side rectifier D1 and the second secondary-side rectifier D2 are connected in parallel and then connected to the inductor L5. The positive electrode of the capacitor C4 is connected to the inductor L5, and the negative electrode of the capacitor C4 is connected to the midpoint of the secondary winding of the isolation transformer. The load R0 is connected in parallel to the inductor C4, and both sides of the load R0 are the output sides of the three-phase AC / DC rectifier circuit with fault tolerance.

[0033] Furthermore, the three-phase AC / DC rectifier circuit with fault tolerance includes a first input inductor L1, a second input inductor L2, a third input inductor L3, a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first fuse FA, a second fuse FB, a third fuse FC, a first bidirectional switch ZA, a second bidirectional switch ZAB, a third bidirectional switch ZBC, a fourth bidirectional switch ZC, a first bus capacitor C1, a second bus capacitor C2, a DC blocking capacitor C3, a first thyristor HA, a second thyristor HB, a third thyristor HC, a leakage inductor L4, an isolation transformer K1, a first secondary-side rectifier tube D1, a second secondary-side rectifier tube D2, an inductor L5, a capacitor C4, and a load R0;

[0034] Phase A is connected to the first input inductor L1, and then to the source of the first switching transistor S1 and the drain of the fourth switching transistor S4. Phase B is connected to the second input inductor L2, and then to the source of the third switching transistor S3 and the drain of the sixth switching transistor S6. Phase C is connected to the third input inductor L3, and then to the source of the fifth switching transistor S5 and the drain of the second switching transistor S2. The drains of the first switching transistor S1, the third switching transistor S3, and the fifth switching transistor S5 are connected to the positive terminal of the first bus capacitor C1. The sources of the fourth switching transistor S4, the sixth switching transistor S6, and the second switching transistor S2 are connected to the negative terminal of the second bus capacitor C2.

[0035] In a unipolar rectifier circuit with six switches on the primary side of the isolation transformer, a first fuse FA, a second fuse FB, and a third fuse FC are connected in series to the three phases A, B, and C respectively after the input inductor on the three-phase power input side; a first thyristor HA, a second thyristor HB, and a third thyristor HC are connected across the input inductor on the three-phase power input side and the first DC bus capacitor C1 and the second DC bus capacitor C2.

[0036] Furthermore, the efficient current-sharing three-phase multi-level DC / AC inverter circuit includes the seventh switch tube S7 to the twelfth switch tube S12 forming an A-phase switch tube combination, the thirteenth switch tube S13 to the eighteenth switch tube S18 forming a B-phase switch tube combination, and the nineteenth switch tube S19 to the twenty-fourth switch tube S24 forming a C-phase switch tube combination; the first coupled inductor J1 to the third coupled inductor J3 forming a coupled inductor of phase A, the fourth coupled inductor J4 to the sixth coupled inductor J6 forming a coupled inductor of phase B, and the seventh coupled inductor J7 to the ninth coupled inductor J9 forming a coupled inductor of phase C;

[0037] The source of the seventh switch transistor S7 is connected to the drain of the tenth switch transistor S10, the source of the eighth switch transistor S8 is connected to the drain of the eleventh switch transistor S11, the source of the ninth switch transistor S9 is connected to the drain of the twelfth switch transistor S12, the source of the thirteenth switch transistor S13 is connected to the drain of the sixteenth switch transistor S16, the source of the fourteenth switch transistor S14 is connected to the drain of the seventeenth switch transistor S17, the source of the fifteenth switch transistor S15 is connected to the drain of the eighteenth switch transistor S18, the source of the nineteenth switch transistor S19 is connected to the drain of the twenty-second switch transistor S22, the source of the twentieth switch transistor S20 is connected to the drain of the twenty-third switch transistor S23, and the source of the twenty-second switch transistor S22 is connected to the drain of the twenty-fourth switch transistor S24;

[0038] The drains of the seventh switch tube S7, the eighth switch tube S8, the ninth switch tube S9, the thirteenth switch tube S13, the fourteenth switch tube S14, the fifteenth switch tube S15, the nineteenth switch tube S19, the twentieth switch tube S20, and the twenty-first switch tube S21 are connected to the positive polarity end of the DC bus;

[0039] The sources of the tenth switch tube S10, the eleventh switch tube S11, the twelfth switch tube S12, the sixteenth switch tube S16, the seventeenth switch tube S17, the eighteenth switch tube S18, the twenty-second switch tube S22, the twenty-third switch tube S23, and the twenty-fourth switch tube S24 are connected to the negative polarity end of the DC bus;

[0040] The source of the seventh switch S7 is connected to the positive end of the coupling inductor J1, the source of the eighth switch S8 is connected to the positive end of the coupling inductor J2, and the source of the ninth switch S9 is connected to the positive end of the coupling inductor J3. The negative ends of the coupling inductors J1, J2, and J3 are connected to the same point and then connected in series to the output load of phase A.

[0041] The source of the thirteenth switch S13 is connected to the positive end of the coupling inductor J4, the source of the fourteenth switch S14 is connected to the positive end of the coupling inductor J5, and the source of the fifteenth switch S15 is connected to the positive end of the coupling inductor J6. The negative ends of the coupling inductors J4, J5, and J6 are connected to the same point and then connected in series to the output load of phase B.

[0042] The source of the nineteenth switch tube S19 is connected to the positive polarity end of the coupling inductor J7, the source of the twentieth switch tube S20 is connected to the positive polarity end of the coupling inductor J8, and the source of the twenty-first switch tube S21 is connected to the positive polarity end of the coupling inductor J9. The negative polarity ends of the coupling inductors J7, J8, and J9 are connected to the same point and then connected in series to the output load of phase C.

[0043] Reference Figure 2In the three-phase AC / DC rectifier circuit with fault tolerance, when a switch or the entire bridge arm fails, the control system will quickly detect the fault signal and automatically switch to the fault working mode. The working process is as follows:

[0044] S1, perform fault detection: By monitoring the current, voltage and other parameters in the circuit, determine whether there is a switch or bridge arm failure.

[0045] S2 switches between normal and fault operating modes: Upon detecting a fault, the control system issues commands to turn the bidirectional switch and thyristor on and off. Specifically, the midpoint of the bridge arm is connected to the midpoint of the capacitor, reconfiguring the AC / DC converter into a four-switch voltage source inverter.

[0046] S3, completes AC / DC rectification operation during fault conditions: In fault-operated mode, the AC / DC converter continues to operate stably, rectifying three-phase AC power to DC power, providing power for the DC / AC conversion section. The DC / AC conversion section continues to operate normally, converting DC power to AC output, ensuring uninterrupted power supply to the PV power station.

[0047] The voltage-flexible control circuit of the present invention primarily comprises an AC / DC converter and a DC / AC converter, with both normal and fault operating modes. The AC / DC converter's input is connected to a three-phase AC grid, while its output is connected to the DC / AC converter's input. The DC / AC converter's output is connected to a photovoltaic power plant's load or grid-connected circuit.

[0048] If a switch or an entire bridge arm in the AC / DC converter fails, the control system quickly detects the fault signal and automatically switches to fault-tolerant operation. By controlling the on / off of the bidirectional switch and thyristor, the midpoint of the bridge arm is connected to the midpoint of the capacitor, reconfiguring the AC / DC converter into a four-switch voltage source inverter and continuing stable operation. At this point, the DC / AC converter continues to function normally, converting DC power into AC output, ensuring uninterrupted power supply to the photovoltaic power station.

[0049] In normal operating mode, the AC / DC / AC converter circuit operates in two phases. In the AC / DC rectification phase, the three-phase AC power Vabc is rectified by the fault-tolerant three-phase AC / DC rectifier circuit. The three-phase AC power flows through input inductors L1, L2, and L3 into the rectifier circuit, which suppresses input current ripple and reduces high-order harmonics and noise interference. Rectification is achieved by controlling the on / off sequence of the first through sixth switching transistors S1 through S6. Finally, the DC voltage is stabilized by the DC bus capacitors C1 and C2.

[0050] During the DC / AC inverter stage, the DC power after forward AC / DC rectification enters a three-phase, multi-stage DC / AC inverter circuit with coupled inductors. The multi-stage bridge arm structure design coordinates the control of a total of 18 switching tubes in three phases. Through SPWM sinusoidal pulse width modulation, the switching tube of each phase is controlled on and off to output three-phase sinusoidal AC power. Finally, the output is output through the three-phase coupled inductors to achieve current balancing, making the conduction and switching losses of the devices more evenly distributed, while effectively suppressing high-frequency common-mode noise.

[0051] If a switch or an entire branch of a three-phase AC / DC converter fails, the circuit automatically switches to fault-tolerant operation. After the AC / DC / AC converter circuit enters fault-tolerant operation, during the AC / DC rectification phase, the monitoring system detects abnormal input current in a phase or abnormal bus voltage fluctuations, issuing a fault signal. The fault-tolerant three-phase AC / DC rectifier circuit activates backup bidirectional switches ZA, ZAB, ZBC, and ZC, changing the topology and reconfiguring the three-phase rectifier to four-switch rectification mode. The bidirectional switches are switched on and off according to the control strategy until the fault is corrected, at which point the circuit returns to six-switch rectification mode.

[0052] The embodiments of this specification are merely examples of implementations of the invention and are provided for illustrative purposes only. The scope of protection of the present invention should not be considered limited to the specific embodiments described in these embodiments. The scope of protection of the present invention also extends to equivalent technical means that can be conceived by a person of ordinary skill in the art based on the invention.

Claims

1. A voltage flexible control circuit applied to a photovoltaic power station, characterized in that: It includes a three-phase AC / DC rectifier circuit with fault tolerance and a three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing, wherein the output side of the three-phase AC / DC rectifier circuit with fault tolerance is connected to the input side of the three-phase multi-level DC / AC inverter circuit with high efficiency and current sharing; In the three-phase AC / DC rectifier circuit with fault tolerance, the primary side of the isolation transformer is a unipolar rectifier circuit with six switches. On the primary side of the isolation transformer, the A-phase input terminal is directly connected to the same-name terminal of the isolation transformer via the first input inductor L1, and the first bidirectional switch ZA, DC blocking capacitor C3, and leakage inductor L4 are connected in series in sequence in the circuit. On the secondary side of the isolation transformer, the positive polarity terminal of the first secondary-side rectifier D1 is connected to the same-name terminal of the secondary winding of the isolation transformer, and the positive polarity terminal of the second secondary-side rectifier D2 is connected to the opposite-name terminal of the secondary winding of the isolation transformer. The first secondary-side rectifier D1 and the second secondary-side rectifier D2 are connected in parallel and then connected to the inductor L5. The positive electrode of the capacitor C4 is connected to the inductor L5, and the negative electrode of the capacitor C4 is connected to the midpoint of the secondary winding of the isolation transformer. The load R0 is connected in parallel to the inductor C4, and both sides of the load R0 are the output sides of the three-phase AC / DC rectifier circuit with fault tolerance.

2. A voltage flexible control circuit for a photovoltaic power station according to claim 1, characterized in that: The three-phase AC / DC rectifier circuit with fault tolerance includes a first input inductor L1, a second input inductor L2, a third input inductor L3, a first switching tube S1, a second switching tube S2, a third switching tube S3, a fourth switching tube S4, a fifth switching tube S5, a sixth switching tube S6, a first fuse FA, a second fuse FB, a third fuse FC, a first bidirectional switch ZA, a second bidirectional switch ZAB, a third bidirectional switch ZBC, a fourth bidirectional switch ZC, a first bus capacitor C1, a second bus capacitor C2, a DC blocking capacitor C3, a first thyristor HA, a second thyristor HB, a third thyristor HC, a leakage inductor L4, an isolation transformer K1, a first secondary-side rectifier D1, a second secondary-side rectifier D2, an inductor L5, a capacitor C4, and a load R0; Phase A is connected to the first input inductor L1, and then to the source of the first switching transistor S1 and the drain of the fourth switching transistor S4. Phase B is connected to the second input inductor L2, and then to the source of the third switching transistor S3 and the drain of the sixth switching transistor S6. Phase C is connected to the third input inductor L3, and then to the source of the fifth switching transistor S5 and the drain of the second switching transistor S2. The drains of the first switching transistor S1, the third switching transistor S3, and the fifth switching transistor S5 are connected to the positive terminal of the first bus capacitor C1. The sources of the fourth switching transistor S4, the sixth switching transistor S6, and the second switching transistor S2 are connected to the negative terminal of the second bus capacitor C2. In a unipolar rectifier circuit with six switches on the primary side of the isolation transformer, a first fuse FA, a second fuse FB, and a third fuse FC are connected in series to the three phases A, B, and C respectively after the input inductor on the three-phase power input side; a first thyristor HA, a second thyristor HB, and a third thyristor HC are connected across the input inductor on the three-phase power input side and the first DC bus capacitor C1 and the second DC bus capacitor C2.

3. A voltage flexible control circuit for a photovoltaic power station according to claim 1 or 2, characterized in that: The high-efficiency current-sharing three-phase multi-level DC / AC inverter circuit includes the seventh to twelfth switching tubes S7 to S12 forming an A-phase switching tube combination, the thirteenth to eighteenth switching tubes S13 to S18 forming a B-phase switching tube combination, and the nineteenth to twenty-fourth switching tubes S19 to S24 forming a C-phase switching tube combination; the first to third coupled inductors J1 to J3 forming a coupled inductor for phase A, the fourth to sixth coupled inductors J4 to J6 forming a coupled inductor for phase B, and the seventh to ninth coupled inductors J7 to J9 forming a coupled inductor for phase C; The source of the seventh switch transistor S7 is connected to the drain of the tenth switch transistor S10, the source of the eighth switch transistor S8 is connected to the drain of the eleventh switch transistor S11, the source of the ninth switch transistor S9 is connected to the drain of the twelfth switch transistor S12, the source of the thirteenth switch transistor S13 is connected to the drain of the sixteenth switch transistor S16, the source of the fourteenth switch transistor S14 is connected to the drain of the seventeenth switch transistor S17, the source of the fifteenth switch transistor S15 is connected to the drain of the eighteenth switch transistor S18, the source of the nineteenth switch transistor S19 is connected to the drain of the twenty-second switch transistor S22, the source of the twentieth switch transistor S20 is connected to the drain of the twenty-third switch transistor S23, and the source of the twenty-second switch transistor S22 is connected to the drain of the twenty-fourth switch transistor S24; The drains of the seventh switch tube S7, the eighth switch tube S8, the ninth switch tube S9, the thirteenth switch tube S13, the fourteenth switch tube S14, the fifteenth switch tube S15, the nineteenth switch tube S19, the twentieth switch tube S20, and the twenty-first switch tube S21 are connected to the positive polarity end of the DC bus; The sources of the tenth switch tube S10, the eleventh switch tube S11, the twelfth switch tube S12, the sixteenth switch tube S16, the seventeenth switch tube S17, the eighteenth switch tube S18, the twenty-second switch tube S22, the twenty-third switch tube S23, and the twenty-fourth switch tube S24 are connected to the negative polarity end of the DC bus; The source of the seventh switch S7 is connected to the positive end of the coupling inductor J1, the source of the eighth switch S8 is connected to the positive end of the coupling inductor J2, and the source of the ninth switch S9 is connected to the positive end of the coupling inductor J3. The negative ends of the coupling inductors J1, J2, and J3 are connected to the same point and then connected in series to the output load of phase A. The source of the thirteenth switch S13 is connected to the positive end of the coupling inductor J4, the source of the fourteenth switch S14 is connected to the positive end of the coupling inductor J5, and the source of the fifteenth switch S15 is connected to the positive end of the coupling inductor J6. The negative ends of the coupling inductors J4, J5, and J6 are connected to the same point and then connected in series to the output load of phase B. The source of the nineteenth switch tube S19 is connected to the positive polarity end of the coupling inductor J7, the source of the twentieth switch tube S20 is connected to the positive polarity end of the coupling inductor J8, and the source of the twenty-first switch tube S21 is connected to the positive polarity end of the coupling inductor J9. The negative polarity ends of the coupling inductors J7, J8, and J9 are connected to the same point and then connected in series to the output load of phase C.

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