A direct current conversion circuit, a photovoltaic power generation system and a control method

Abstract

This application proposes a DC-DC converter circuit, a photovoltaic power generation system, and a control method, belonging to the field of photovoltaic power generation. The DC-DC converter circuit includes: a first sub-circuit, a second sub-circuit, and an energy storage inductor; the first sub-circuit includes: a first switching device, a first diode, a first capacitor, and a third capacitor; the second sub-circuit includes: a second switching device, a second diode, a second capacitor, and a fourth capacitor; the control method includes: within one switching cycle, controlling the first and second switching devices to turn on or off by adjusting the duty cycle, output voltage, and input voltage to increase or decrease the current of the energy storage inductor, thereby controlling the output voltage to rise or fall. This application achieves three-level functionality while improving the operating state of the power switching devices and increasing system operating efficiency.

Description

Technical Field

[0001] This application belongs to the field of photovoltaic power generation, specifically relating to a DC-DC converter circuit, a photovoltaic power generation system, and a control method. Background Technology

[0002] In the field of photovoltaic power generation, soft-switching circuits are generally used to realize the DC-DC converter function. There are two main implementation methods: one is to add active and passive components to the DC-DC converter to achieve soft switching of the power devices. This method involves a large number of components and requires additional detection, resulting in complex control, high cost, and poor reliability. The other method involves adding a passive buffer circuit containing resistors. This method has high energy loss, with energy consumed in the resistors during operation, leading to a decrease in circuit efficiency. With the trend towards higher frequencies, the switching losses and electromagnetic interference of power devices are becoming increasingly prominent issues. Summary of the Invention

[0003] Based on the above technical problems, this application proposes a DC-DC converter circuit, a photovoltaic power generation system, and a control method.

[0004] In a first aspect, this application proposes a DC-DC converter circuit, comprising: a first sub-circuit, a second sub-circuit, and an energy storage inductor;

[0005] The first sub-circuit includes: a first switching device, a first diode, a first capacitor, and a third capacitor; the second sub-circuit includes: a second switching device, a second diode, a second capacitor, and a fourth capacitor;

[0006] The emitter of the first switching device is connected to the negative terminal of the first diode, the positive terminal of the first diode is connected to the first terminal of the third capacitor, the collector of the first switching device is connected to the first terminal of the first capacitor, and the second terminal of the first capacitor is connected to the second terminal of the third capacitor.

[0007] The collector of the second switching device is connected to the positive terminal of the second diode, the negative terminal of the second diode is connected to the first terminal of the fourth capacitor, the emitter of the second switching device is connected to the first terminal of the second capacitor, the second terminal of the second capacitor is connected to the second terminal of the first capacitor, and the second terminal of the fourth capacitor is connected to the second terminal of the third capacitor.

[0008] The first end of the energy storage inductor is connected to the emitter of the first switching device, and the second end of the energy storage inductor is connected to the collector of the second switching device.

[0009] The first sub-circuit further includes a first freewheeling diode connected in parallel between the collector and emitter of the first switching device.

[0010] The second sub-circuit further includes a second freewheeling diode connected in parallel between the collector and emitter of the second switching device.

[0011] The DC-DC converter circuit further includes: a first passive lossless absorption unit and a second passive lossless absorption unit;

[0012] The first passive lossless absorption unit includes: a first resonant inductor, a first resonant capacitor, a first energy storage capacitor, a sixth diode, a seventh diode, and an eighth diode;

[0013] The second passive lossless absorption unit includes: a second resonant inductor, a second resonant capacitor, a second energy storage capacitor, a third diode, a fourth diode, and a fifth diode;

[0014] The negative terminal of the sixth diode is connected to the negative terminal of the first diode, the positive terminal of the sixth diode is connected to the negative terminal of the seventh diode, the positive terminal of the seventh diode is connected to the negative terminal of the eighth diode, and the positive terminal of the eighth diode is connected to the first terminal of the third capacitor; the first terminal of the first resonant capacitor is connected to the negative terminal of the sixth diode, and the second terminal of the first resonant capacitor is connected to the positive terminal of the seventh diode; the first terminal of the first energy storage capacitor is connected to the positive terminal of the sixth diode, the second terminal of the first energy storage capacitor is connected to the first terminal of the first resonant inductor, and the second terminal of the first resonant inductor is connected to the positive terminal of the eighth diode;

[0015] The anode of the third diode is connected to the anode of the second diode, the cathode of the third diode is connected to the anode of the fourth diode, the cathode of the fourth diode is connected to the anode of the fifth diode, and the cathode of the fifth diode is connected to the first terminal of the fourth capacitor. The first terminal of the second resonant capacitor is connected to the anode of the third diode, the second terminal of the second resonant capacitor is connected to the cathode of the fourth diode, the first terminal of the second energy storage capacitor is connected to the anode of the fourth diode, the second terminal of the second energy storage capacitor is connected to the cathode of the second diode and the first terminal of the second resonant inductor, and the second terminal of the second resonant inductor is connected to the first terminal of the fourth capacitor.

[0016] Secondly, this application proposes a photovoltaic power generation system, including the DC-DC converter circuit described in the first aspect.

[0017] Thirdly, a control method for a DC-DC converter circuit, implemented using the DC-DC converter circuit described in the first aspect, includes:

[0018] Within one switching cycle, when the duty cycle is greater than or equal to the preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in boost mode;

[0019] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first and second switching devices are simultaneously turned on to increase the current of the energy storage inductor, thereby increasing the output voltage V0. Here, V1 is the terminal voltage of the first capacitor, V2 is the terminal voltage of the second capacitor, V3 is the terminal voltage of the third capacitor, and V4 is the terminal voltage of the fourth capacitor. th1 V is the first voltage threshold. th2 This is the second voltage threshold;

[0020] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first switching device is turned off while the second switching device is turned on, or the first switching device is turned on while the second switching device is turned off, so as to reduce the current of the energy storage inductor and control the output voltage V0 to decrease.

[0021] When the first switching device is turned off and the second switching device is turned on, the second capacitor charges, the third capacitor discharges, and the midpoint voltage rises. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the sum of the midpoint voltage and the input voltage V. i The voltage between the negative terminals.

[0022] When the first switching device is turned on and the second switching device is turned off, the fourth capacitor charges, the first capacitor discharges, and the midpoint voltage drops. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the difference between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0023] The method further includes: within one switching cycle, when the duty cycle is less than a preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in buck converter mode;

[0024] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first and second switching devices are simultaneously turned off to reduce the current in the energy storage inductor and control the output voltage V0 to decrease, wherein V V V1 is the terminal voltage of the first capacitor, V2 is the terminal voltage of the second capacitor, V3 is the terminal voltage of the third capacitor, and V4 is the terminal voltage of the fourth capacitor. th1 V is the first voltage threshold. th2 This is the second voltage threshold;

[0025] In |V1-V2| <V th1 And |V3-V4| <V t42 In this case, the first switching device is turned off while the second switching device is turned on, or the first switching device is turned on while the second switching device is turned off, to increase the current of the energy storage inductor and control the output voltage V0 to rise.

[0026] When the first switching device is turned off and the second switching device is turned on, the second capacitor charges, the third capacitor discharges, and the midpoint voltage rises. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the sum of the midpoint voltage and the input voltage V. i The voltage between the negative terminals.

[0027] When the first switching device is turned on and the second switching device is turned off, the fourth capacitor charges, the first capacitor discharges, and the midpoint voltage drops. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the difference between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0028] Beneficial effects:

[0029] This application proposes a DC-DC converter circuit, a photovoltaic power generation system, and a control method. While achieving the three-level function of the circuit, it improves the operating state of the power switching devices, thereby improving the efficiency and electromagnetic interference of the three-level Buck-Boost circuit under high-frequency operating conditions, and increasing the system efficiency. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a DC-DC converter circuit according to an embodiment of this application;

[0031] Figure 2 This is the passive soft-switching three-level Buck-Boost circuit topology of an embodiment of this application;

[0032] Figure 3 This is a block diagram of a three-level circuit control according to an embodiment of this application. Detailed Implementation

[0033] The present disclosure will be further described below with reference to the embodiments shown in the accompanying drawings.

[0034] With the trend towards higher frequencies, the switching losses and electromagnetic interference of power devices have become increasingly prominent issues. To improve the efficiency and reduce electromagnetic interference of three-level Buck-Boost circuits under high-frequency operating conditions, it is necessary to design a Buck-Boost circuit that can improve the operating state of power switching devices and increase system efficiency while achieving three-level functionality. Buck circuit represents a buck converter circuit, and Boost circuit represents a boost converter circuit.

[0035] To address the aforementioned problems, this application proposes a DC-DC converter circuit, a photovoltaic power generation system, and a control method. Targeting the issue of new energy utilization, by analyzing the characteristics of the DC-DC converter circuit in the photovoltaic power generation system and combining it with soft-switching technology, a novel Buck-Boost circuit is proposed to improve system operating efficiency. The proposed DC-DC converter circuit is then applied to the DC-DC stage of photovoltaic power generation.

[0036] Because this application employs a unique circuit structure, combined with soft-switching control technology, it improves the system's output efficiency while achieving three-level functionality.

[0037] Example 1:

[0038] This embodiment proposes a DC-DC converter circuit, including: a first sub-circuit, a second sub-circuit, and an energy storage inductor L1;

[0039] The first sub-circuit and the second sub-circuit have a symmetrical structure;

[0040] The first sub-circuit includes: a first switching device S1, a first diode D1, a first capacitor C1, and a third capacitor C3;

[0041] The second sub-circuit includes: a second switching device S2, a second diode D2, a second capacitor C2, and a fourth capacitor C4;

[0042] The emitter of the first switching device S1 is connected to the negative terminal of the first diode D1, the positive terminal of the first diode D1 is connected to the first terminal of the third capacitor C3, the collector of the first switching device S1 is connected to the first terminal of the first capacitor C1, and the second terminal of the first capacitor C1 is connected to the second terminal of the third capacitor C3.

[0043] The collector of the second switching device S2 is connected to the positive terminal of the second diode D2, the negative terminal of the second diode D2 is connected to the first terminal of the fourth capacitor C4, the emitter of the second switching device S2 is connected to the first terminal of the second capacitor C2, the second terminal of the second capacitor C2 is connected to the second terminal of the first capacitor C1, and the second terminal of the fourth capacitor C4 is connected to the second terminal of the third capacitor C3.

[0044] The first end of the energy storage inductor L1 is connected to the emitter of the first switching device S1, and the second end of the energy storage inductor L1 is connected to the collector of the second switching device S2. The energy storage inductor L1 is first charged by the input voltage and then discharged to the output terminal.

[0045] The first sub-circuit further includes: a first freewheeling diode Ds1 connected in parallel between the collector and emitter of the first switching device S1, wherein the anode of the first freewheeling diode Ds1 is connected to the emitter of the first switching device S1, and the cathode of the first freewheeling diode Ds1 is connected to the collector of the first switching device S1.

[0046] The second sub-circuit further includes: a second freewheeling diode Ds2 connected in parallel between the collector and emitter of the second switching device S2. The positive terminal of the second freewheeling diode Ds2 is connected to the emitter of the second switching device S2, and the negative terminal of the second freewheeling diode Ds2 is connected to the collector of the second switching device S2.

[0047] The DC-DC converter circuit further includes: a first passive lossless absorption unit and a second passive lossless absorption unit;

[0048] The first passive lossless absorption unit includes: a first resonant inductor L2, a first resonant capacitor Cr1, a first energy storage capacitor Cs1, a sixth diode D6, a seventh diode D7, and an eighth diode D8.

[0049] The second passive lossless absorption unit includes: a second resonant inductor L3, a second resonant capacitor Cr2, a second energy storage capacitor Cs2, a third diode D3, a fourth diode D4, and a fifth diode D5;

[0050] The negative terminal of the sixth diode D6 is connected to the negative terminal of the first diode D1, the positive terminal of the sixth diode D6 is connected to the negative terminal of the seventh diode D7, the positive terminal of the seventh diode D7 is connected to the negative terminal of the eighth diode D8, and the positive terminal of the eighth diode D8 is connected to the first terminal C3 of the third capacitor; the first terminal of the first resonant capacitor Cr1 is connected to the negative terminal of the sixth diode D6, and the second terminal of the first resonant capacitor Cr1 is connected to the positive terminal of the seventh diode D7; the first terminal of the first energy storage capacitor Cs1 is connected to the positive terminal of the sixth diode D6, the second terminal of the first energy storage capacitor Cs1 is connected to the first terminal of the first resonant inductor L2, and the second terminal of the first resonant inductor L2 is connected to the positive terminal of the eighth diode D8;

[0051] The anode of the third diode D3 is connected to the anode of the second diode D1, the cathode of the third diode D3 is connected to the anode of the fourth diode D4, the cathode of the fourth diode D4 is connected to the anode of the fifth diode D5, and the cathode of the fifth diode D5 is connected to the first terminal C4 of the fourth capacitor. The first terminal of the second resonant capacitor Cr2 is connected to the anode of the third diode D3, the second terminal of the second resonant capacitor Cr2 is connected to the cathode of the fourth diode D4, the first terminal of the second energy storage capacitor Cs2 is connected to the anode of the fourth diode D4, the second terminal of the second energy storage capacitor Cs2 is connected to the cathode of the second diode D2 and the first terminal of the second resonant inductor L3, and the second terminal of the second resonant inductor L3 is connected to the first terminal C4 of the fourth capacitor.

[0052] This embodiment proposes a DC-DC converter circuit, including two symmetrical sub-circuits, each connected to a source lossless absorption unit. The resonance between the first resonant inductor L2, the first resonant capacitor Cr1, and the first energy storage capacitor Cs1, and between the second resonant inductor L3, the second resonant capacitor Cr2, and the second energy storage capacitor Cs2, achieves zero-current turn-on of the switching transistor and zero-current turn-off of the freewheeling diode, as well as zero-voltage turn-off of the switching transistor and zero-voltage turn-on of the freewheeling diode. Simultaneously, in each cycle, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 collect resonant energy and ultimately transfer it to the load, achieving lossless operation of the absorption circuit. This embodiment achieves three-level functionality while improving the operating state of the power switching devices and increasing system efficiency.

[0053] Example 2:

[0054] This embodiment proposes a photovoltaic power generation system, including the aforementioned DC-DC conversion circuit.

[0055] The DC-DC converter circuit includes: a first sub-circuit, a second sub-circuit, and an energy storage inductor L1;

[0056] The first sub-circuit and the second sub-circuit have a symmetrical structure;

[0057] The first sub-circuit includes: a first switching device S1, a first diode D1, a first capacitor C1, and a third capacitor C3;

[0058] The second sub-circuit includes: a second switching device S2, a second diode D2, a second capacitor C2, and a fourth capacitor C4;

[0059] The emitter of the first switching device S1 is connected to the negative terminal of the first diode D1, the positive terminal of the first diode D1 is connected to the first terminal of the third capacitor C3, the collector of the first switching device S1 is connected to the first terminal of the first capacitor C1, and the second terminal of the first capacitor C1 is connected to the second terminal of the third capacitor C3.

[0060] The collector of the second switching device S2 is connected to the positive terminal of the second diode D2, the negative terminal of the second diode D2 is connected to the first terminal of the fourth capacitor C4, the emitter of the second switching device S2 is connected to the first terminal of the second capacitor C2, the second terminal of the second capacitor C2 is connected to the second terminal of the first capacitor C1, and the second terminal of the fourth capacitor C4 is connected to the second terminal of the third capacitor C3.

[0061] The first end of the energy storage inductor L1 is connected to the emitter of the first switching device S1, and the second end of the energy storage inductor L1 is connected to the collector of the second switching device S2.

[0062] The first sub-circuit further includes: a first freewheeling diode Ds1 connected in parallel between the collector and emitter of the first switching device S1, wherein the anode of the first freewheeling diode Ds1 is connected to the emitter of the first switching device S1, and the cathode of the first freewheeling diode Ds1 is connected to the collector of the first switching device S1.

[0063] The second sub-circuit further includes: a second freewheeling diode Ds2 connected in parallel between the collector and emitter of the second switching device S2. The positive terminal of the second freewheeling diode Ds2 is connected to the emitter of the second switching device S2, and the negative terminal of the second freewheeling diode Ds2 is connected to the collector of the second switching device S2.

[0064] The DC-DC converter circuit, such as Figure 2 As shown, it also includes: a first passive lossless absorption unit and a second passive lossless absorption unit;

[0065] The first passive lossless absorption unit includes: a first resonant inductor L2, a first resonant capacitor Cr1, a first energy storage capacitor Cs1, a sixth diode D6, a seventh diode D7, and an eighth diode D8.

[0066] The second passive lossless absorption unit includes: a second resonant inductor L3, a second resonant capacitor Cr2, a second energy storage capacitor Cs2, a third diode D3, a fourth diode D4, and a fifth diode D5;

[0067] The negative terminal of the sixth diode D6 is connected to the negative terminal of the first diode D1, the positive terminal of the sixth diode D6 is connected to the negative terminal of the seventh diode D7, the positive terminal of the seventh diode D7 is connected to the negative terminal of the eighth diode D8, and the positive terminal of the eighth diode D8 is connected to the first terminal C3 of the third capacitor; the first terminal of the first resonant capacitor Cr1 is connected to the negative terminal of the sixth diode D6, and the second terminal of the first resonant capacitor Cr1 is connected to the positive terminal of the seventh diode D7; the first terminal of the first energy storage capacitor Cs1 is connected to the positive terminal of the sixth diode D6, the second terminal of the first energy storage capacitor Cs1 is connected to the first terminal of the first resonant inductor L2, and the second terminal of the first resonant inductor L2 is connected to the positive terminal of the eighth diode D8;

[0068] The anode of the third diode D3 is connected to the anode of the second diode D1, the cathode of the third diode D3 is connected to the anode of the fourth diode D4, the cathode of the fourth diode D4 is connected to the anode of the fifth diode D5, and the cathode of the fifth diode D5 is connected to the first terminal C4 of the fourth capacitor. The first terminal of the second resonant capacitor Cr2 is connected to the anode of the third diode D3, the second terminal of the second resonant capacitor Cr2 is connected to the cathode of the fourth diode D4, the first terminal of the second energy storage capacitor Cs2 is connected to the anode of the fourth diode D4, the second terminal of the second energy storage capacitor Cs2 is connected to the cathode of the second diode D2 and the first terminal of the second resonant inductor L3, and the second terminal of the second resonant inductor L3 is connected to the first terminal C4 of the fourth capacitor.

[0069] This embodiment proposes a photovoltaic power generation system. A DC-DC converter circuit is used as the DC-DC conversion stage of the photovoltaic power generation system. During the conversion process, soft-switching technology is incorporated. A first resonant inductor L2, a first resonant capacitor Cr1, a first energy storage capacitor Cs1, and a second resonant inductor L3, a second resonant capacitor Cr2, and a second energy storage capacitor Cs2 are employed. The resonance between these components achieves zero-current turn-on of the switching transistor and zero-current turn-off of the freewheeling diode, as well as zero-voltage turn-off of the switching transistor and zero-voltage turn-on of the freewheeling diode. Simultaneously, in each cycle, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 collect resonant energy and ultimately transfer it to the load, achieving lossless operation of the absorption circuit. This solves the problems of switching losses and electromagnetic interference in power devices, improving the system's operating efficiency.

[0070] Example 3:

[0071] In this embodiment, a three-level input is used. The working principle of the three-level circuit is as follows: The main circuit of the three-level circuit is as follows: Figure 1As shown, "0" and "1" represent the off and on states of the first switching device S1 and the second switching device S2, respectively. Based on the different switching state combinations of the first switching device S1 and the second switching device S2, namely "00", "01", "10", and "11", the circuit has four operating modes. At the same time, the voltage level is generated by the voltage division of the first input capacitor C1 and the second input capacitor C2, and the third output capacitor C3 and the fourth output capacitor C4. Therefore, there is a problem of midpoint voltage balance. Thus, in the control of the three-level circuit, the three additional conditions of input and output voltage magnitude and midpoint voltage balance must be considered. Based on the magnitude of the input and output voltages, the operating region of the three-level circuit is divided into two parts.

[0072] This embodiment proposes a control method for a DC-DC converter circuit, implemented using the aforementioned DC-DC converter circuit, including:

[0073] Within one switching cycle, when the duty cycle is greater than or equal to the preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in boost circuit mode. In this embodiment, the preset duty cycle is 0.5, but it can be set to other values ​​in practical applications.

[0074] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first switching device S1 and the second switching device S2 are simultaneously turned on to increase the current of the energy storage inductor L1, thereby increasing the output voltage V0. Here, V1 is the terminal voltage of the first capacitor C1, V2 is the terminal voltage of the second capacitor C2, V3 is the terminal voltage of the third capacitor C3, and V4 is the terminal voltage of the fourth capacitor C4. th1 V is the first voltage threshold. th2 This is the second voltage threshold;

[0075] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first switching device S1 is turned off while the second switching device S2 is turned on, or the first switching device S1 is turned on while the second switching device S2 is turned off, so as to reduce the current of the energy storage inductor L1 and control the output voltage V0 to decrease.

[0076] When the first switching device S1 is turned off and the second switching device S2 is turned on, the second capacitor C2 charges, the third capacitor C3 discharges, and the midpoint voltage rises. The midpoint is between the second terminal of the first capacitor C1 and the second terminal of the second capacitor C2. The midpoint voltage is the voltage between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0077] When the first switching device S1 is turned on and the second switching device S2 is turned off, the fourth capacitor C4 charges, the first capacitor C1 discharges, and the midpoint voltage drops. The midpoint is between the second terminal of the first capacitor C1 and the second terminal of the second capacitor C2. The midpoint voltage is the voltage between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0078] In this embodiment, when the duty cycle D ≥ 0.5 and the output voltage V0 is greater than the input voltage V... i In the case where the DC-DC converter operates in boost mode and the midpoint voltage is balanced (i.e., the terminal voltages V1, V2, V3, and V4 of the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 vary around a certain voltage value), only the first switching device S1 and the second switching device S2 in the operating state "11" can be used to increase the inductor current. Decreasing the inductor current can be achieved in two ways: "01" and "10". However, these two modes have different effects on the midpoint voltage. In the "01" mode, the second capacitor C2 is charged and the third capacitor C3 is discharged, causing the midpoint voltage to rise. In the "10" state, the first capacitor C1 is discharged and the fourth capacitor C4 is charged, causing the midpoint voltage to fall. As for the operating state "00", although it can be used to decrease the inductor current, it does not conform to the principle of three-level converter operating mode switching, i.e., two switches cannot operate simultaneously, i.e., there cannot be a situation where "11" switches to "00". Therefore, when D>0.5, the "00" operating mode is not used.

[0079] The control method for the DC-DC converter circuit further includes: within one switching cycle, when the duty cycle is less than a preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in buck converter mode;

[0080] In |V1-V2| <V th1 And |V3-V4| <V th2 In this case, the first switching device S1 and the second switching device S2 are simultaneously turned off to reduce the current of the energy storage inductor L1, thereby reducing the output voltage V0. Here, V1 is the terminal voltage of the first capacitor C1, V2 is the terminal voltage of the second capacitor C2, V3 is the terminal voltage of the third capacitor C3, and V4 is the terminal voltage of the fourth capacitor C4. th1 V is the first voltage threshold. th2 This is the second voltage threshold;

[0081] In |V1-V2| <V th1 And |V3-V4| <V th2In the event that the first switching device S1 is turned off while the second switching device S2 is turned on, or the first switching device S1 is turned on while the second switching device S2 is turned off, the current of the energy storage inductor L1 is increased, thereby controlling the output voltage V0 to rise.

[0082] When the first switching device S1 is turned off and the second switching device S2 is turned on, the second capacitor C2 charges, the third capacitor C3 discharges, and the midpoint voltage increases. The midpoint is between the second terminal of the first capacitor C1 and the second terminal of the second capacitor C2. The midpoint voltage is the voltage between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0083] When the first switching device S1 is turned on and the second switching device S2 is turned off, the fourth capacitor C4 charges, the first capacitor C1 discharges, and the midpoint voltage drops. The midpoint is between the second terminal of the first capacitor C1 and the second terminal of the second capacitor C2. The midpoint voltage is the voltage between the midpoint and the input voltage V. i The voltage between the negative terminals.

[0084] Taking a preset duty cycle of 0.5 as an example, the duty cycle D < 0.5, and the output voltage V0 is greater than the input voltage V. i In this case, the DC-DC converter circuit operates in buck converter mode. Only when the first switching device S1 and the second switching device S2 are in the "00" operating mode can they be used to reduce the inductor current. There are two options for increasing the inductor current: "01" and "10". Their effects on the midpoint voltage are different. In the "01" state, the second capacitor C2 is charged and the third capacitor C3 is discharged, and the midpoint voltage rises. In the "10" state, the first capacitor C1 is discharged and the fourth capacitor C4 is charged, and the midpoint voltage drops. For the same reason, when the DC-DC converter circuit operates in buck converter mode, the operating state "11" is not used.

[0085] Three-level control mode: M0 is 0 when the duty cycle is greater than 0.5, such as... Figure 3 The closed-loop control shown has M0 set to 1 when the value is less than 0.5; the input voltage V... i When the voltage is greater than the output voltage V0, M1 = 1; when it is less than V0, M1 = 0. When the voltage at the first capacitor C1 is greater than the voltage at the second capacitor C2, M2 = 1; when it is less than V0, M2 = 0. When the voltage at the third capacitor C3 is greater than the voltage at the fourth capacitor C4, M3 = 1; when it is less than V0, M3 = 0. The control block diagram is as follows: Figure 3As shown, the three-level circuit still uses closed-loop control, but its output signal does not directly drive the switching transistors, that is, it does not directly drive the first switching device S1 and the second switching device S2. Instead, it acts as a logic signal M0. The working logic M1 and the midpoint balancing logics M2 and M3 work together to control the gate signals of the first switching device S1 and the second switching device S2 to achieve the three-level function.

[0086] This embodiment controls the on and off states of the first switching device S1 and the second switching device S2. The following is a detailed analysis of the operating logic when the duty cycle D > 0.5. Due to the symmetry of the circuit structure, only the commutation process of the first sub-circuit (including the first passive lossless absorption unit, which comprises the first resonant inductor L2, the first resonant capacitor Cr1, the first energy storage capacitor Cs1, the sixth diode D6, the seventh diode D7, and the eighth diode D8) is analyzed. Each cycle's workflow is divided into 8 stages:

[0087] 1. t0-t1: Assume that before time t0, the first switching device S1 and the second switching device S2 are turned on, and the current in the energy storage inductor L1 increases linearly. At time t0, the first switching device S1 is turned off with zero voltage, and at the same time, the eighth diode D8 is turned on naturally, and the first resonant capacitor Cr1 begins to charge. The charging ends at time t1.

[0088] 2. t1-t2: At time t1, the first switching device S1 is turned off, and the input current discharges through the eighth diode D8 to the first resonant capacitor Cr1. The tube voltage of the first switching device S1 rises from zero, realizing the zero-voltage turn-off of the first switching device S1.

[0089] 3. t2-t3: At time t2, the first resonant capacitor Cr1 discharges to 0, the sixth diode D6 and the seventh diode D7 are turned on, and the terminal voltage of the first resonant inductor L2 is equal to V6; the first energy storage capacitor Cs1 resonates and discharges to the output terminal through the first resonant inductor L2.

[0090] 4. t3-t4: At time t3, when the current in inductor L1 rises to a certain level, the seventh diode D7 and the eighth diode D8 are turned off, and the sixth diode D6 discharges the first energy storage capacitor Cs1. The slow change of V6 provides the conditions for the zero-voltage turn-on of the first diode D1.

[0091] 5. t4-t5: At time t4, the first energy storage capacitor Cs1 discharges to 0, the sixth diode D6 turns off, and the first diode D1 turns on naturally. The stored energy in the first energy storage capacitor Cs1 is completely transferred to the load R. L The load current is output through the first diode D1.

[0092] 6. t5-t6: At time t5, the reverse recovery of the first diode D1 ends, and the first diode D1 turns off. Since V6 and V5 are both equal to 0, the seventh diode D7 naturally turns on. The first resonant inductor L2, the first energy storage capacitor Cs1, and the first resonant capacitor Cr1 begin to resonate. The voltage across the first diode D1 rises from zero resonance, achieving zero-current turn-off of the first diode D1. The peak current of the first switching device S1 is equal to the sum of the input current and the peak current of the resonant inductor. At time t6, the seventh diode D7 turns on, and the resonance process ends.

[0093] 7. t6-t7: At time t6, the first resonant capacitor Cr1 discharges, and the eighth diode D8 conducts. The first resonant inductor L2, the first energy storage capacitor Cs1, the sixth diode D6, and the eighth diode D8 begin the second resonant process. At time t7, the second resonant process ends.

[0094] 8. t7-t8: At time t7, the sixth diode D6 and the eighth diode D8 are turned off. Afterwards, the voltages of the first resonant capacitor Cr1 and the first energy storage capacitor Cs1 remain unchanged, and the circuit enters a stable operating state where the first switching device S1 and the second switching device S2 are turned on. The circuit then returns to the same operating state as at the beginning of stage 1, until the next switching cycle.

[0095] This embodiment proposes a control method for a DC-DC converter circuit. The closed-loop circuit logic signal M0, the working logic M1, and the midpoint balancing logics M2 and M3 work together to control the gate signals of the first switching device S1 and the second switching device S2, achieving a three-level function. This controls the first switching device S1 and the second switching device S2 to turn on or off, thereby increasing or decreasing the current in the energy storage inductor L1, and thus controlling the output voltage V0 to rise or fall. This embodiment solves the problems of switching losses and electromagnetic interference in power devices, improving system operating efficiency.

[0096] The various embodiments in this disclosure are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0097] The scope of protection of this disclosure is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from its scope and spirit. If such modifications and variations fall within the scope of the claims of this disclosure and their equivalents, then the intent of this disclosure also includes such modifications and variations.

Claims

1. A direct current conversion circuit, characterized by include: First sub-circuit, second sub-circuit, energy storage inductor; The first sub-circuit includes: a first switching device, a first diode, a first capacitor, and a third capacitor; the second sub-circuit includes: a second switching device, a second diode, a second capacitor, and a fourth capacitor; The emitter of the first switching device is connected to the negative terminal of the first diode, the positive terminal of the first diode is connected to the first terminal of the third capacitor, the collector of the first switching device is connected to the first terminal of the first capacitor, and the second terminal of the first capacitor is connected to the second terminal of the third capacitor. The collector of the second switching device is connected to the positive terminal of the second diode, the negative terminal of the second diode is connected to the first terminal of the fourth capacitor, the emitter of the second switching device is connected to the first terminal of the second capacitor, the second terminal of the second capacitor is connected to the second terminal of the first capacitor, and the second terminal of the fourth capacitor is connected to the second terminal of the third capacitor. The first end of the energy storage inductor is connected to the emitter of the first switching device, and the second end of the energy storage inductor is connected to the collector of the second switching device. Within one switching cycle, when the duty cycle is greater than or equal to the preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in boost mode; exist ,and In this case, the first and second switching devices are simultaneously turned on to increase the current of the energy storage inductor and control the output voltage V0 to rise. The terminal voltage of the first capacitor is . This is the terminal voltage of the second capacitor. This is the terminal voltage of the third capacitor. This is the terminal voltage of the fourth capacitor. The first voltage threshold, This is the second voltage threshold; exist ,and In this case, the first switching device is turned off while the second switching device is turned on, or the first switching device is turned on while the second switching device is turned off, so as to reduce the current of the energy storage inductor and control the output voltage V0 to decrease.

2. The dc-to-dc conversion circuit of claim 1, wherein The first sub-circuit further includes a first freewheeling diode connected in parallel between the collector and emitter of the first switching device.

3. The dc-to-dc conversion circuit of claim 1, wherein The second sub-circuit further includes a second freewheeling diode connected in parallel between the collector and emitter of the second switching device.

4. The dc-to-dc conversion circuit of claim 1, wherein The DC-DC converter circuit further includes: a first passive lossless absorption unit and a second passive lossless absorption unit; The first passive lossless absorption unit includes: a first resonant inductor, a first resonant capacitor, a first energy storage capacitor, a sixth diode, a seventh diode, and an eighth diode; The second passive lossless absorption unit includes: a second resonant inductor, a second resonant capacitor, a second energy storage capacitor, a third diode, a fourth diode, and a fifth diode; The negative terminal of the sixth diode is connected to the negative terminal of the first diode, the positive terminal of the sixth diode is connected to the negative terminal of the seventh diode, the positive terminal of the seventh diode is connected to the negative terminal of the eighth diode, and the positive terminal of the eighth diode is connected to the first terminal of the third capacitor; the first terminal of the first resonant capacitor is connected to the negative terminal of the sixth diode, and the second terminal of the first resonant capacitor is connected to the positive terminal of the seventh diode; the first terminal of the first energy storage capacitor is connected to the positive terminal of the sixth diode, the second terminal of the first energy storage capacitor is connected to the first terminal of the first resonant inductor, and the second terminal of the first resonant inductor is connected to the positive terminal of the eighth diode; The anode of the third diode is connected to the anode of the second diode, the cathode of the third diode is connected to the anode of the fourth diode, the cathode of the fourth diode is connected to the anode of the fifth diode, and the cathode of the fifth diode is connected to the first terminal of the fourth capacitor. The first terminal of the second resonant capacitor is connected to the anode of the third diode, the second terminal of the second resonant capacitor is connected to the cathode of the fourth diode, the first terminal of the second energy storage capacitor is connected to the anode of the fourth diode, the second terminal of the second energy storage capacitor is connected to the cathode of the second diode and the first terminal of the second resonant inductor, and the second terminal of the second resonant inductor is connected to the first terminal of the fourth capacitor.

5. A photovoltaic power system, characterized by, The DC-DC converter circuit includes any one of claims 1 to 4.

6. A control method for a DC-DC converter circuit, implemented using the DC-DC converter circuit described in any one of claims 1 to 4, characterized in that, include: In one switch cycle, when the duty cycle is greater than or equal to a preset duty cycle, and the output voltage V0 is greater than the input voltage V i , the direct current conversion circuit works in a boost circuit mode. exist ,and In this case, the first and second switching devices are simultaneously turned on to increase the current of the energy storage inductor and control the output voltage V0 to rise. The terminal voltage of the first capacitor is . This is the terminal voltage of the second capacitor. This is the terminal voltage of the third capacitor. This is the terminal voltage of the fourth capacitor. The first voltage threshold, This is the second voltage threshold; exist ,and In this case, the first switching device is turned off while the second switching device is turned on, or the first switching device is turned on while the second switching device is turned off, so as to reduce the current of the energy storage inductor and control the output voltage V0 to decrease.

7. The control method of a DC conversion circuit according to claim 6, characterized by, When the first switching device is turned off and the second switching device is turned on, the second capacitor charges, the third capacitor discharges, and the midpoint voltage rises. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the sum of the midpoint voltage and the input voltage V. i The voltage between the negative terminals.

8. The control method of a DC conversion circuit according to claim 6, characterized by, When the first switching device is turned on and the second switching device is turned off, the fourth capacitor charges, the first capacitor discharges, and the midpoint voltage drops. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the difference between the midpoint and the input voltage V. i The voltage between the negative terminals.

9. The control method of a DC conversion circuit according to claim 6, characterized by, The method further includes: within one switching cycle, when the duty cycle is less than a preset duty cycle and the output voltage V0 is greater than the input voltage V... i In this case, the DC-DC converter circuit operates in buck converter mode; exist ,and In this situation, the first and second switching devices are simultaneously turned off to reduce the current in the energy storage inductor and lower the output voltage V0. The terminal voltage of the first capacitor is . This is the terminal voltage of the second capacitor. This is the terminal voltage of the third capacitor. This is the terminal voltage of the fourth capacitor. The first voltage threshold, This is the second voltage threshold; exist ,and In this case, the first switching device is turned off while the second switching device is turned on, or the first switching device is turned on while the second switching device is turned off, to increase the current of the energy storage inductor and control the output voltage V0 to rise.

10. The control method of a DC conversion circuit according to claim 9, characterized by, When the first switching device is turned off and the second switching device is turned on, the second capacitor charges, the third capacitor discharges, and the midpoint voltage rises. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the sum of the midpoint voltage and the input voltage V. i The voltage between the negative terminals.

11. The control method of the DC conversion circuit according to claim 9, characterized by, When the first switching device is turned on and the second switching device is turned off, the fourth capacitor charges, the first capacitor discharges, and the midpoint voltage drops. The midpoint is between the second terminals of the first and second capacitors, and the midpoint voltage is the difference between the midpoint and the input voltage V. i The voltage between the negative terminals.

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