A grid-connected and off-grid switching device and photovoltaic power generation system

Abstract

The embodiment of the application discloses a kind of on-grid and off-grid switching device and photovoltaic power generation system, it is related to energy technical field, it solves how to reduce the open-loop output end output open-loop voltage fluctuation of DC-DC power conversion circuit Problem.The emitter or source of the first switch tube is connected with the positive output end of DC-DC power conversion circuit, the base or gate of the first switch tube is connected with the collector or drain of the second switch tube, the emitter or source of the second switch tube and the emitter or source of the third switch tube are connected with one end of the first resistance, the other end of the first resistance is connected with the negative output end of DC-DC power conversion circuit, the collector or drain of the third switch tube is connected with the collector or drain of the first switch tube, the second resistance and the third resistance connected in series are connected between the collector or drain of the third switch tube and the negative output end of DC-DC power conversion circuit, and the connection point of the second resistance and the third resistance is connected with the base or gate of the third switch tube.

Description

Technical Field

[0001] This application relates to the field of energy technology, and in particular to a grid-connected / off-grid switching device and a photovoltaic power generation system. Background Technology

[0002] A photovoltaic (PV) power generation system includes a PV inverter and a grid-connected / off-grid switching device, which can also be called a whole-house backup power box. The input terminal of the PV inverter is used to connect to the output terminal of the PV array, the output terminal of the PV inverter is connected to the inverter port of the grid-connected / off-grid switching device, the load port of the grid-connected / off-grid switching device is used to connect to the load, and the grid port of the grid-connected / off-grid switching device is used to connect to the power grid.

[0003] Specifically, the grid-connected / off-grid switching device includes two switches connected in series between the inverter port and the grid port, with the connection point of the two switches connected to the load port. The device also includes a rectifier circuit and a direct current to direct current (DC-DC) power conversion circuit. The input of the rectifier circuit is connected to the inverter port, and its output is connected to the input of the DC-DC power conversion circuit. The open-loop output of the DC-DC power conversion circuit is connected to the load in the grid-connected / off-grid switching device to provide power to the load.

[0004] However, on the one hand, power fluctuations in the load connected to the open-loop output terminal of the grid-connected switching device will lead to significant fluctuations in the open-loop voltage output of the DC-DC power conversion circuit. On the other hand, if the DC-DC power conversion circuit also includes a closed-loop output terminal, the cross-regulation rate will cause significant fluctuations in the open-loop voltage output during the adjustment of the closed-loop voltage. Significant fluctuations in the open-loop voltage output of the DC-DC power conversion circuit will fail to meet the power supply requirements of the load connected to the open-loop output terminal in the grid-connected switching device, and may even damage the load. Therefore, reducing the fluctuations in the open-loop voltage output of the DC-DC power conversion circuit has become an urgent problem to be solved. Summary of the Invention

[0005] This application provides a grid-connected / off-grid switching device and a photovoltaic power generation system, which solves the problem of how to reduce the fluctuation of the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit.

[0006] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0007] A first aspect of this application provides a grid-connected switching device, comprising: a first switch and a second switch connected in series, the first switch and the second switch being connected between the inverter port and the grid port of the grid-connected switching device, and the connection point of the first switch and the second switch being connected to the load port of the grid-connected switching device; a rectifier circuit, a capacitor, and a DC-DC power conversion circuit, wherein the input terminal of the rectifier circuit is connected to the inverter port, the output terminal of the rectifier circuit is connected to the input terminal of the DC-DC power conversion circuit, the output terminal of the rectifier circuit includes a positive output terminal and a negative output terminal, and the capacitor is connected between the positive output terminal and the negative output terminal of the rectifier circuit. The DC-DC power converter circuit comprises a first switch, a second switch, a third switch, and a first resistor. Its open-loop output includes a positive output and a negative output. The emitter or source of the first switch is connected to the positive output of the DC-DC power converter circuit. The base or gate of the first switch is connected to the collector or drain of the second switch. The base or gate of the second switch receives a reference voltage. The emitters or sources of the second and third switches are connected to one end of the first resistor. The other end of the first resistor is connected to the negative output of the DC-DC power converter circuit. The collector or drain of the third switch is connected to the collector or drain of the first switch. A second and third resistor are connected in series between the collector or drain of the third switch and the negative output of the DC-DC power converter circuit. The junction of the second and third resistors is connected to the base or gate of the third switch. The collector or drain of the third switch and the negative output of the DC-DC power converter circuit are connected to the load in the grid-connected / off-grid switching device. The first switching transistor is a PNP transistor, PMOS, or PIGBT, while the second and third switching transistors are NPN transistors, NMOS, or NIGBTs.

[0008] Based on this scheme, a step-down circuit is implemented using the first to third switching transistors and the first to third resistors. When the power fluctuation of the load in the grid-connected switching device causes the open-loop voltage output of the DC-DC power conversion circuit to fluctuate above the voltage threshold, the third switching transistor will turn on due to the voltage division effect of the first to third resistors. After the third switching transistor turns on, the second switching transistor will turn off due to the turn-off condition. After the second switching transistor turns off, the first switching transistor will turn off due to the turn-off condition. The DC-DC power conversion circuit will stop supplying power to the load, thereby reducing the open-loop voltage supplied to the load by the open-loop output of the DC-DC power conversion circuit. Therefore, the fluctuation of the open-loop voltage can be reduced. Furthermore, no controller is required to control the first to third switching transistors, resulting in a simpler topology and lower cost. When the first to third switching transistors are transistors, they do not need to operate in the linear amplification region, resulting in lower power consumption and higher reliability.

[0009] In conjunction with the first aspect, in one embodiment, the grid-connected / off-grid switching device further includes a controller, and the DC-DC power conversion circuit further includes a closed-loop output terminal. The controller is used to acquire the voltage or current of the closed-loop output terminal and output a pulse width modulation signal. The voltage or current of the closed-loop output terminal is used to determine the duty cycle of the pulse width modulation signal, and the pulse width modulation signal is used to control the switching transistors in the DC-DC power conversion circuit.

[0010] Based on this scheme, a step-down circuit is implemented using the first to the third switching transistors and the first to the third resistors. During the adjustment of the closed-loop voltage at the closed-loop output terminal, if the open-loop voltage at the open-loop output terminal fluctuates significantly due to cross-adjustment, the first switching transistor is turned off, and the DC-DC power conversion circuit stops supplying power to the load. This reduces the open-loop voltage supplied to the load by the open-loop output terminal of the DC-DC power conversion circuit, thereby reducing the fluctuation of the open-loop voltage. Furthermore, the topology is simpler, the cost is lower, the power consumption is lower, and the reliability is higher.

[0011] In conjunction with the first aspect, in one embodiment, the grid-connected switching device further includes a reference voltage source, the positive terminal of which is connected to the positive output terminal of the DC-DC power conversion circuit, the negative terminal of which is connected to the negative output terminal of the DC-DC power conversion circuit, and the output terminal of which is connected to the base or gate of the second switching transistor.

[0012] Based on this scheme, a reference voltage is provided by a reference voltage source, which can provide a stable reference voltage and improve the stability and reliability of the grid-connected and off-grid switching device.

[0013] In conjunction with the first aspect, in one embodiment, the reference voltage source includes a Zener diode and a fourth resistor and a fifth resistor connected in series. The fourth resistor and the fifth resistor are connected between the positive terminal and the negative terminal of the reference voltage source. The connection point of the fourth resistor and the fifth resistor is connected to the cathode of the Zener diode. The anode of the Zener diode is connected to the negative terminal of the reference voltage source. The cathode of the Zener diode is also connected to the output terminal of the reference voltage source.

[0014] Based on this scheme, compared with other methods of implementing the reference voltage source, using a Zener diode to implement the reference voltage source results in a simpler circuit topology, lower cost, and better stability. This reduces the circuit topology complexity and cost of the grid-connected switching device and improves reliability.

[0015] In conjunction with the first aspect, in one embodiment, the DC-DC power conversion circuit is a flyback DC-DC power conversion circuit.

[0016] Based on this scheme, the reliability and safety of the grid-connected switching device can be improved because the flyback DC-DC power conversion circuit has the advantages of current isolation and high safety.

[0017] In conjunction with the first aspect, in one embodiment, when the voltage across the second and third resistors is greater than a voltage threshold, the voltage at the connection point of the second and third resistors is greater than a reference voltage, the third switch is turned on, the second switch is turned off, and the first switch is turned off.

[0018] Based on this scheme, when the open-loop voltage output from the open-loop output terminal of the DC-DC power conversion circuit fluctuates, the first switch is turned off, and the DC-DC power conversion circuit will stop supplying power to the load. This reduces the open-loop voltage supplied to the load from the open-loop output terminal of the DC-DC power conversion circuit, thereby reducing the fluctuation of the open-loop voltage, avoiding damage to the load in the grid-connected switching device, and improving the reliability of the grid-connected switching device.

[0019] In conjunction with the first aspect, in one embodiment, when the voltage across the second and third resistors is less than or equal to a voltage threshold, the voltage at the connection point of the second and third resistors is less than or equal to a reference voltage, the third switch is turned off, the second switch is turned on, and the first switch is turned on.

[0020] Based on this scheme, if the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit does not fluctuate, the first switching transistor will be turned on, thereby providing power to the load in the grid-connected / off-grid switching device.

[0021] A second aspect of this application provides a photovoltaic power generation system, comprising a photovoltaic inverter and a grid-connected switching device. The input terminal of the photovoltaic inverter is connected to the output terminal of a photovoltaic array. The output terminal of the photovoltaic inverter is connected to the inverter port of the grid-connected switching device. The grid port of the grid-connected switching device is connected to the power grid, and the load port of the grid-connected switching device is connected to a load. The grid-connected switching device includes: a first switch and a second switch connected in series, the first switch and the second switch being connected between the inverter port and the grid port, and the connection point of the first switch and the second switch being connected to the load port. A rectifier circuit, a capacitor, and a DC-DC power conversion circuit are also included. The input terminal of the rectifier circuit is connected to the inverter port, and the output terminal of the rectifier circuit is connected to the input terminal of the DC-DC power conversion circuit. The output terminal of the rectifier circuit includes a positive output terminal and a negative output terminal, and the capacitor is connected between the positive and negative output terminals of the rectifier circuit. The DC-DC power converter circuit comprises a first switch, a second switch, a third switch, and a first resistor. Its open-loop output includes a positive output and a negative output. The emitter or source of the first switch is connected to the positive output of the DC-DC power converter circuit. The base or gate of the first switch is connected to the collector or drain of the second switch. The base or gate of the second switch receives a reference voltage. The emitters or sources of the second and third switches are connected to one end of the first resistor. The other end of the first resistor is connected to the negative output of the DC-DC power converter circuit. The collector or drain of the third switch is connected to the collector or drain of the first switch. A second and third resistor are connected in series between the collector or drain of the third switch and the negative output of the DC-DC power converter circuit. The junction of the second and third resistors is connected to the base or gate of the third switch. The collector or drain of the third switch and the negative output of the DC-DC power converter circuit are connected to the load in the grid-connected / off-grid switching device. The first switching transistor is a PNP transistor, PMOS, or PIGBT, while the second and third switching transistors are NPN transistors, NMOS, or NIGBTs.

[0022] In conjunction with the second aspect, in one embodiment, the grid-connected / off-grid switching device further includes a controller, and the DC-DC power conversion circuit further includes a closed-loop output terminal. The controller is used to acquire the voltage or current of the closed-loop output terminal and output a pulse width modulation signal. The voltage or current of the closed-loop output terminal is used to determine the duty cycle of the pulse width modulation signal, and the pulse width modulation signal is used to control the switching transistors in the DC-DC power conversion circuit.

[0023] In conjunction with the second aspect, in one embodiment, the grid-connected switching device further includes a reference voltage source, the positive terminal of which is connected to the positive output terminal of the DC-DC power conversion circuit, the negative terminal of which is connected to the negative output terminal of the DC-DC power conversion circuit, and the output terminal of which is connected to the base or gate of the second switching transistor.

[0024] In conjunction with the second aspect, in one embodiment, the reference voltage source includes a Zener diode and a fourth resistor and a fifth resistor connected in series. The fourth resistor and the fifth resistor are connected between the positive terminal and the negative terminal of the reference voltage source. The connection point of the fourth resistor and the fifth resistor is connected to the cathode of the Zener diode. The anode of the Zener diode is connected to the negative terminal of the reference voltage source. The cathode of the Zener diode is also connected to the output terminal of the reference voltage source.

[0025] In conjunction with the second aspect, in one embodiment, the DC-DC power conversion circuit is a flyback DC-DC power conversion circuit.

[0026] In conjunction with the second aspect, in one embodiment, when the voltage across the second and third resistors is greater than a voltage threshold, the voltage at the connection point of the second and third resistors is greater than a reference voltage, the third switch is turned on, the second switch is turned off, and the first switch is turned off.

[0027] In conjunction with the second aspect, in one embodiment, when the voltage across the second resistor and the third resistor is less than or equal to a voltage threshold, the voltage at the connection point of the second resistor and the third resistor is less than or equal to a reference voltage, the third switch is turned off, the second switch is turned on, and the first switch is turned on.

[0028] The description of the second aspect in this application can be referred to the detailed description of the first aspect; and the beneficial effects of the second aspect can be referred to the analysis of the beneficial effects of the first aspect, which will not be repeated here. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the circuit topology of a photovoltaic power generation system;

[0030] Figure 2 A schematic diagram illustrating an application scenario of a grid-connected / off-grid switching device provided in an embodiment of this application;

[0031] Figure 3 This is a circuit topology diagram of a grid-connected / off-grid switching device provided in an embodiment of this application;

[0032] Figure 4 A schematic diagram of another on-grid / off-grid switching device provided in an embodiment of this application;

[0033] Figure 5A circuit topology diagram of another on-grid / off-grid switching device provided in the embodiments of this application;

[0034] Figure 6 This is a schematic diagram of the circuit topology of another on-grid / off-grid switching device provided in an embodiment of this application. Detailed Implementation

[0035] The following sections will discuss the fabrication and use of various embodiments in detail. However, it should be understood that many applicable inventive concepts provided in this application can be implemented in a variety of specific environments. The specific embodiments discussed are merely illustrative of specific ways of implementing and using this description and technology, and do not limit the scope of this application.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly known to one of ordinary skill in the art.

[0037] Each circuit or other component may be described or referred to as "for" performing one or more tasks. In this context, "for" is used to imply a structure by indicating that the circuit / component includes a structure (e.g., a circuit system) that performs one or more tasks during operation. Therefore, even when the specified circuit / component is currently inoperable (e.g., not turned on), it can still be referred to as "for performing that task." Circuits / components used with the term "for" include hardware, such as circuits that perform operations.

[0038] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings. In this application, the character " / " generally indicates that the preceding and following objects are in an "or" relationship. In the embodiments of this application, the words "first," "second," etc., do not limit the quantity or order.

[0039] In this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or illustration. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0040] Before introducing the embodiments of this application, the background technology involved in this application will be introduced first.

[0041] like Figure 1The diagram shows a circuit topology of a photovoltaic power generation system 100. The photovoltaic power generation system 100 includes a photovoltaic inverter 110 and a grid-connected / off-grid switching device 120. The input terminal of the photovoltaic inverter 110 is connected to the output terminal of the photovoltaic array 200, and the output terminal of the photovoltaic inverter 110 is connected to the inverter port of the grid-connected / off-grid switching device 120. The load port of the grid-connected / off-grid switching device 120 is connected to a load 300, and the grid port of the grid-connected / off-grid switching device 120 is connected to the power grid 400.

[0042] Specifically, refer to Figure 1 The grid-connected / off-grid switching device 120 includes two switches (a first switch K1 and a second switch K2) connected in series between the inverter port and the grid port. The connection point of the two switches is connected to the load port. The grid-connected / off-grid switching device 120 also includes a rectifier circuit 121, a DC-DC power conversion circuit 122, and a first capacitor C1 and a second capacitor C2 connected in series. The input terminal of the rectifier circuit 121 is connected to the inverter port, and the output terminal of the rectifier circuit 121 is connected to the input terminal of the DC-DC power conversion circuit 122. The open-loop output terminal of the DC-DC power conversion circuit 122 is connected to the load 123 in the grid-connected / off-grid switching device 120 to provide power to the load 123. For example, the load 123 can be a fan of the energy management assistant (EMMA) in the grid-connected / off-grid switching device 120. The output terminal of the rectifier circuit 121 includes a positive output terminal and a negative output terminal, and the first capacitor C1 and the second capacitor C2 are connected between the positive and negative output terminals of the rectifier circuit 121.

[0043] Continue to refer to Figure 1 When the power of the load 123 in the grid-connected switching device 120 fluctuates, the open-loop voltage output of the DC-DC power conversion circuit 122 will fluctuate significantly. If the DC-DC power conversion circuit 122 also includes a closed-loop output, the open-loop voltage output of the closed-loop output will fluctuate significantly due to the cross-regulation rate during the adjustment of the closed-loop voltage. The cross-regulation rate is a concept in multi-output switching power supplies, describing the impact of changes in the load of other output circuits on the output voltage of a particular output circuit. Specifically, the cross-regulation rate is defined as S = ΔV / V × 100%, where "S" represents the cross-regulation rate, "ΔV" represents the change in output voltage of a particular output circuit, and "V" represents the rated output voltage of a particular output circuit.

[0044] If the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit 122 fluctuates significantly, it will be unable to meet the power supply requirements of the load 123 in the grid-connected switching device 120, and may even cause damage to the load 123. Therefore, how to reduce the fluctuation of the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit 122 has become an urgent problem to be solved.

[0045] In one implementation, continue to refer to Figure 1 The grid-connected switching device 120 may also include a step-down circuit 124, which is connected between the open-loop output terminal of the DC-DC power conversion circuit 122 and the input terminal of the load 123. The step-down circuit 124 is used to reduce the open-loop voltage when the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit 122 is greater than the voltage threshold, thereby reducing the fluctuation of the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit 122 and improving the safety and reliability of the grid-connected switching device 120.

[0046] In one embodiment, the buck converter 124 can be a standard buck converter circuit (also known as a Buck circuit). However, a standard buck converter circuit requires a controller to control the switching transistor, resulting in a complex topology and high cost. Alternatively, the buck converter 124 can be a linear regulator circuit. However, the transistor in a linear regulator circuit operates in the linear amplification region for extended periods, increasing the risk of transistor damage. This leads to high power consumption and low reliability in the buck converter 124. Furthermore, due to the limitation of the voltage Vce between the collector and emitter of the transistor, the open-loop voltage fluctuation remains significant, failing to meet the power supply requirements of the load 123. In summary, using a standard buck converter circuit or a linear regulator circuit to reduce open-loop voltage fluctuations in the buck converter 124 results in problems such as complex topology, high cost, high power consumption, and low reliability.

[0047] Based on this, this application provides a grid-connected switching device. The grid-connected switching device uses a switching transistor and a resistor to implement a step-down circuit, which can reduce the fluctuation of the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit. Furthermore, it does not require a controller to control the switching transistor, resulting in a simpler topology and lower cost. When the switching transistor is a transistor, it does not need to operate in the linear amplification region, resulting in lower power consumption and higher reliability.

[0048] In one implementation, such as Figure 2 As shown, the on-grid / off-grid switching device 500 provided in this application embodiment can be used as an independent device.

[0049] In one implementation, such as Figure 2The diagram shown illustrates an application scenario of a grid-connected / off-grid switching device 500 provided in this embodiment. This grid-connected / off-grid switching device 500 can replace the aforementioned grid-connected / off-grid switching device 120 and is applied to the aforementioned photovoltaic power generation system 100, which also includes a photovoltaic inverter 110. The input terminal of the photovoltaic inverter 110 is connected to the output terminal of the photovoltaic array 200, and the output terminal of the photovoltaic inverter 110 is connected to the inverter port of the grid-connected / off-grid switching device 500. The load port of the grid-connected / off-grid switching device 500 is connected to the load 300, and the grid port of the grid-connected / off-grid switching device 500 is connected to the power grid 400. The photovoltaic array 200 converts solar energy into direct current (DC), the photovoltaic inverter 110 converts the DC power into alternating current (AC), and the grid-connected / off-grid switching device 500 is used for grid-connected / off-grid switching.

[0050] like Figure 3 The diagram shown is a circuit topology diagram of a grid-connected switching device 500 provided in an embodiment of this application. The grid-connected switching device 500 includes: a first switch K1 and a second switch K2 connected in series, the first switch K1 and the second switch K2 being connected between the inverter port and the grid port of the grid-connected switching device 500, and the connection point of the first switch K1 and the second switch K2 being connected to the load port of the grid-connected switching device 500. It also includes a rectifier circuit 510, a capacitor C, and a DC-DC power conversion circuit 520. The input terminal of the rectifier circuit 510 is connected to the inverter port, and the output terminal of the rectifier circuit 510 is connected to the input terminal of the DC-DC power conversion circuit 520. The output terminal of the rectifier circuit 510 includes a positive output terminal and a negative output terminal, and the capacitor C is connected between the positive output terminal and the negative output terminal of the rectifier circuit 510.

[0051] Reference Figure 3 The off-grid switching device 500 also includes a first switch Q1, a second switch Q2, a third switch Q3, and a first resistor R1. The open-loop output of the DC-DC power conversion circuit 520 includes a positive output and a negative output. The emitter (E) or source (S) of the first switch Q1 is connected to the positive output of the DC-DC power conversion circuit 520. The base (B) or gate (G) of the first switch Q1 is connected to the collector (C) or drain (D) of the second switch Q2. The base or gate of the second switch Q2 is used to receive the reference voltage Vref. The emitter or source of the second switch Q2 and the emitter or source of the third switch Q3 are connected to one end of the first resistor R1. The other end of the first resistor R1 is connected to the negative output of the DC-DC power conversion circuit 520. The collector or drain of the third switch Q3 is connected to the collector or drain of the first switch Q1. The first resistor R1 is used to protect the third switch Q3 when it is turned on.

[0052] Continue to refer to Figure 3 The grid-connected switching device 500 also includes a second resistor R2 and a third resistor R3 connected in series. The second resistor R2 and the third resistor R3 are connected between the collector or drain of the third switching transistor Q3 and the negative output terminal of the DC-DC power conversion circuit 520. The connection point of the second resistor R2 and the third resistor R3 is connected to the base or gate of the third switching transistor Q3. The collector or drain of the third switching transistor Q3 and the negative output terminal of the DC-DC power conversion circuit 520 are connected to the load 530 in the grid-connected switching device 500 to provide power to the load 530. For example, the load 530 can be the fan of the energy management assistant EMMA in the grid-connected switching device 500. The circuit consisting of the rectifier circuit 510, capacitor C, DC-DC power conversion circuit 520, first switching transistors Q1 to third switching transistors Q3, and first resistors R1 to third resistors R3 can be referred to as an auxiliary power supply.

[0053] In this embodiment, the first switch Q1 is a PNP transistor, a p-channel metal-oxide-semiconductor field-effect transistor (PMOS), or a p-channel gate insulated gate bipolar transistor (PIGBT), while the second switch Q2 and the third switch Q3 are NPN transistors, NMOS, or NIGBTs. This application does not limit the specific types of the first switch Q1, second switch Q2, and third switch Q3; reference continues to the previous section. Figure 3 In this embodiment, the first switch Q1 is a PNP transistor, and the second switch Q2 and the third switch Q3 are NPN transistors, as an example for illustrative purposes.

[0054] In one implementation, reference Figure 3When the voltage across the second resistor R2 and the third resistor R3 is greater than the voltage threshold, the voltage at the connection point of the second resistor R2 and the third resistor R3 is greater than the reference voltage Vref. The voltage at the base of the third switch Q3 is greater than the voltage at its emitter, and the voltage at its collector is greater than the voltage at its emitter. Since there is current at the base, the third switch Q3 will conduct. This embodiment does not limit the specific values ​​of the voltage threshold and the reference voltage Vref. The voltage at the base of the second switch Q2 is the reference voltage Vref. After the third switch Q3 is turned on, the voltage at the emitter of the second switch Q2 is the voltage at the positive output terminal of the DC-DC power conversion circuit 520. Since the voltage at the emitter of the second switch Q2 is greater than the voltage at its base, the second switch Q2 will turn off. After the second switch Q2 is turned off, there is no current at the base of the first switch Q1, and the first switch Q1 will turn off. After the first switch Q1 is turned off, the voltage output to the load 530 from the collector of the third switch Q3 and the negative output terminal of the DC-DC power conversion circuit 520 will decrease. Therefore, when the open-loop voltage output at the open-loop output terminal of the DC-DC power conversion circuit 520 fluctuates beyond the voltage threshold, the fluctuation of the open-loop voltage can be reduced. It can be understood that the circuit composed of the first switch Q1 to the third switch Q3 and the first resistor R1 to the third resistor R3 can be called a buck circuit.

[0055] In one embodiment, the voltage threshold can be adjusted by selecting a second resistor R2 and a third resistor R3 with different resistance values. In this embodiment, the specific values ​​of the second resistor R2 and the third resistor R3 are not limited.

[0056] In one implementation, continue to refer to Figure 3 When the voltage across the second resistor R2 and the third resistor R3 is less than or equal to the voltage threshold, the voltage at the connection point of the second resistor R2 and the third resistor R3 is less than or equal to the reference voltage Vref. The voltage at the base of the third switch Q3 is less than or equal to the voltage at its emitter, and the third switch Q3 will turn off. The voltage at the base of the second switch Q2 is the reference voltage Vref. After the third switch Q3 turns off, the voltage at the emitter of the second switch Q2 is the voltage at the negative output terminal of the DC-DC power converter circuit 520. The voltage at the base of the second switch Q2 is greater than the voltage at its emitter, the voltage at its collector is greater than the voltage at its emitter, and there is current at its base, so the second switch Q2 will turn on. Similarly, the voltage at the base of the first switch Q1 is greater than the voltage at its emitter, the voltage at its collector is greater than the voltage at its emitter, and there is current at its base, so the first switch Q1 will turn on. Therefore, the collector of the third switch Q3 and the negative output terminal of the DC-DC power converter circuit 520 can continuously supply power to the load 530.

[0057] In one embodiment, the first switch K1 and the second switch K2 include a relay or a contactor. The specific types of the two switches are not limited in this application embodiment.

[0058] In one embodiment, when the output terminal of the photovoltaic inverter 110 outputs single-phase AC power, the above-mentioned rectifier circuit 510 can be a single-phase rectifier circuit; when the output terminal of the photovoltaic inverter 110 outputs three-phase AC power, the above-mentioned rectifier circuit 510 can be a three-phase rectifier circuit. This application embodiment does not limit this.

[0059] In one embodiment, the DC-DC power conversion circuit 520 described above includes isolated, non-isolated, buck, or boost types. The isolated DC-DC power conversion circuit includes a flyback DC-DC power conversion circuit. The embodiments of this application do not limit the specific type of the DC-DC power conversion circuit 520.

[0060] In one embodiment, the DC-DC power conversion circuit 520 is a flyback DC-DC power conversion circuit. Since the flyback DC-DC power conversion circuit has the advantages of current isolation and high safety, the reliability and safety of the grid-connected switching device 500 can be improved.

[0061] In one implementation, such as Figure 4 The diagram shown is a circuit topology schematic of another on-grid / off-grid switching device 500 provided in an embodiment of this application, which is consistent with the above. Figure 3 Compared to the circuit topology of the grid-connected switching device 500 shown, the difference lies in that the capacitor C includes a first capacitor C1 and a second capacitor C2 connected in series, which can increase the withstand voltage of the capacitor C and improve the reliability of the grid-connected switching device 500.

[0062] In one embodiment, the step-down circuit composed of the first switch Q1 to the third switch Q3 and the first resistor R1 to the third resistor R3 provided in this application can also be applied to the auxiliary power supply of equipment such as optimizers, photovoltaic inverters or uninterruptible power supplies (UPS) to reduce the fluctuation of the open-loop voltage output of the DC-DC power conversion circuit in the auxiliary power supply. This application does not limit this aspect.

[0063] The grid-connected switching device 500 provided in this application embodiment uses first switching transistors Q1 to third switching transistors Q3 and first resistors R1 to third resistors R3 to implement a step-down circuit. When the power fluctuation of the load 530 causes the open-loop output voltage of the DC-DC power conversion circuit 520 to fluctuate above the voltage threshold, the third switching transistor Q3 will turn on due to the voltage division effect of the first resistors R1 to third resistors R3. After the third switching transistor Q3 turns on, the second switching transistor Q2 will turn off due to the turn-off condition. After being turned off, the first switch Q1 will turn off if the turn-off condition is met, and the DC-DC power conversion circuit 520 will stop supplying power to the load 530. This reduces the open-loop voltage supplied to the load 530 by the open-loop output of the DC-DC power conversion circuit 520, thus reducing the fluctuation of the open-loop voltage. Furthermore, the controller is not required to control the first switch Q1 to the third switch Q3, resulting in a simpler topology and lower cost. When the first switch Q1 to the third switch Q3 are transistors, the transistors do not need to operate in the linear amplification region, resulting in lower power consumption and higher reliability.

[0064] In one implementation, such as Figure 4 As shown, the grid-connected / off-grid switching device 500 also includes a controller 540, and the DC-DC power conversion circuit 520 also includes a closed-loop output terminal. The controller 540 is used to acquire the voltage or current of the closed-loop output terminal and output a pulse width modulation (PWM) signal. The voltage or current of the closed-loop output terminal is used to determine the duty cycle of the PWM signal, and the PWM signal is used to control the switching transistors in the DC-DC power conversion circuit 520.

[0065] In one embodiment, the grid-connected / off-grid switching device 500 may further include a voltage detection circuit or a current detection circuit, so that the controller 540 can obtain the voltage or current at the closed-loop output terminal through the voltage detection circuit or the current detection circuit. For details, please refer to the prior art, and the embodiments of this application will not be described in detail here.

[0066] In one implementation, since the open-loop output terminal and the closed-loop output terminal of the DC-DC power conversion circuit 520 are reinforcedly insulated, power is supplied to the load 530 through the open-loop output terminal, thereby meeting the safety design specifications. Reinforced insulation refers to a series of measures and designs taken in electrical equipment or systems to improve insulation performance and ensure the safe operation of equipment and the safety of personnel.

[0067] In one embodiment, the DC-DC power conversion circuit 520 may include multiple open-loop output terminals, and the grid-connected switching device 500 may also include multiple buck circuits provided in the embodiments of this application. The multiple open-loop output terminals are respectively connected to the multiple buck circuits one by one. The embodiments of this application do not limit the specific number of open-loop output terminals in the DC-DC power conversion circuit 520 or the specific number of buck circuits in the grid-connected switching device 500.

[0068] In one embodiment, the controller 540 includes a digital signal processing (DSP) chip or a microcontroller unit (MCU), which may also be referred to as a single-chip microcomputer. This application embodiment does not limit this.

[0069] The grid-connected switching device 500 provided in this application embodiment uses a first switch Q1 to a third switch Q3 and a first resistor R1 to a third resistor R3 to implement a step-down circuit. During the adjustment of the closed-loop voltage output at the closed-loop output terminal, if the open-loop voltage output at the open-loop output terminal fluctuates significantly due to cross-adjustment, the first switch Q1 is turned off, and the DC-DC power conversion circuit 520 stops supplying power to the load 530. This reduces the open-loop voltage supplied by the open-loop output terminal of the DC-DC power conversion circuit 520 to the load 530, thereby reducing the fluctuation of the open-loop voltage. Furthermore, the topology is simpler, the cost is lower, the power consumption is lower, and the reliability is higher.

[0070] In one implementation, such as Figure 5 The diagram shown is a circuit topology diagram of another grid-connected switching device 500 provided in an embodiment of this application. The grid-connected switching device 500 also includes a reference voltage source 550. The positive terminal of the reference voltage source 550 is connected to the positive output terminal of the DC-DC power conversion circuit 520, the negative terminal of the reference voltage source 550 is connected to the negative output terminal of the DC-DC power conversion circuit 520, and the output terminal of the reference voltage source 550 is connected to the base or gate of the second switching transistor Q2 to provide the aforementioned reference voltage Vref.

[0071] In one implementation, such as Figure 6The diagram shown is a circuit topology diagram of another grid-connected / off-grid switching device 500 provided in this application embodiment. The aforementioned reference voltage source 550 includes a Zener diode (ZD) ZD and a fourth resistor R4 and a fifth resistor R5 connected in series. The fourth resistor R4 and the fifth resistor R5 are connected between the positive and negative terminals of the reference voltage source 550. The connection point of the fourth resistor R4 and the fifth resistor R5 is connected to the cathode of the Zener diode ZD. The anode of the Zener diode ZD is connected to the negative terminal of the reference voltage source 550, and the cathode of the Zener diode ZD is also connected to the output terminal of the reference voltage source 550. This Zener diode ZD can also be called a Zener diode. Alternatively, the reference voltage source 550 can be implemented using a reference voltage chip, a resistor divider, etc., and this application embodiment does not limit this implementation.

[0072] Compared with other methods of implementing the reference voltage source 550, the grid-connected switching device 500 provided in this application embodiment uses a Zener diode ZD to implement the reference voltage source 550. This results in a simpler circuit topology, lower cost, and better stability of the Zener diode ZD. This reduces the complexity and cost of the circuit topology of the grid-connected switching device 500 and improves its reliability.

[0073] Based on this, such as Figure 2 As shown in the figure, this application embodiment also provides a photovoltaic power generation system 100, which includes a photovoltaic inverter 110 and a grid-connected / off-grid switching device 500. The input terminal of the photovoltaic inverter 110 is connected to the output terminal of the photovoltaic array 200, and the output terminal of the photovoltaic inverter 110 is connected to the inverter port of the grid-connected / off-grid switching device 500. The grid port of the grid-connected / off-grid switching device 500 is connected to the power grid 400, and the load port of the grid-connected / off-grid switching device 500 is connected to the load 300. The circuit topology of the grid-connected / off-grid switching device 500 is as described above. Figures 2 to 6 The circuit topology of the on-grid / off-grid switching device 500 shown in any of the attached figures.

[0074] The above detailed description of the grid-connected / off-grid switching device 500 and the analysis of its beneficial effects can be applied to the photovoltaic power generation system 100, and will not be repeated here in the embodiments of this application.

[0075] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A grid-connected / off-grid switching device, characterized in that, The on-grid / off-grid switching device includes: A first switch and a second switch are connected in series, the first switch and the second switch are connected between the inverter port and the grid port of the grid-connected switching device, and the connection point of the first switch and the second switch is connected to the load port of the grid-connected switching device. The system includes a rectifier circuit, a capacitor, and a DC-DC power conversion circuit. The input terminal of the rectifier circuit is connected to the inverter port, and the output terminal of the rectifier circuit is connected to the input terminal of the DC-DC power conversion circuit. The output terminal of the rectifier circuit includes a positive output terminal and a negative output terminal, and the capacitor is connected between the positive output terminal and the negative output terminal of the rectifier circuit. The DC-DC power conversion circuit comprises a first switch, a second switch, a third switch, and a first resistor. The open-loop output of the DC-DC power conversion circuit includes a positive output terminal and a negative output terminal. The emitter or source of the first switch is connected to the positive output terminal of the DC-DC power conversion circuit. The base or gate of the first switch is connected to the collector or drain of the second switch. The base or gate of the second switch is used to receive a reference voltage. The emitter or source of the second switch and the emitter or source of the third switch are connected to one end of the first resistor. The other end of the first resistor is connected to the negative output terminal of the DC-DC power conversion circuit. The collector or drain of the third switch is connected to the collector or drain of the first switch. A second resistor and a third resistor are connected in series. The second resistor and the third resistor are connected between the collector or drain of the third switching transistor and the negative output terminal of the DC-DC power conversion circuit. The connection point of the second resistor and the third resistor is connected to the base or gate of the third switching transistor. The collector or drain of the third switching transistor and the negative output terminal of the DC-DC power conversion circuit are connected to the load in the grid-connected switching device. The first switching transistor is a PNP transistor, PMOS, or PIGBT; The second and third switching transistors are NPN transistors, NMOS transistors, or NIGBT transistors.

2. The grid-connected / off-grid switching device according to claim 1, characterized in that, The grid-connected / off-grid switching device also includes a controller, and the DC-DC power conversion circuit also includes a closed-loop output terminal; The controller is used to acquire the voltage or current at the closed-loop output terminal and output a pulse width modulation signal. The voltage or current at the closed-loop output terminal is used to determine the duty cycle of the pulse width modulation signal. The pulse width modulation signal is used to control the switching transistor in the DC-DC power conversion circuit.

3. The grid-connected / off-grid switching device according to claim 1 or 2, characterized in that, The grid-connected / off-grid switching device further includes a reference voltage source. The positive terminal of the reference voltage source is connected to the positive output terminal of the DC-DC power conversion circuit, the negative terminal of the reference voltage source is connected to the negative output terminal of the DC-DC power conversion circuit, and the output terminal of the reference voltage source is connected to the base or gate of the second switching transistor.

4. The grid-connected / off-grid switching device according to claim 3, characterized in that, The reference voltage source includes a Zener diode and a fourth resistor and a fifth resistor connected in series. The fourth resistor and the fifth resistor are connected between the positive terminal and the negative terminal of the reference voltage source. The connection point of the fourth resistor and the fifth resistor is connected to the cathode of the Zener diode. The anode of the Zener diode is connected to the negative terminal of the reference voltage source. The cathode of the Zener diode is also connected to the output terminal of the reference voltage source.

5. The grid-connected / off-grid switching device according to claim 1, characterized in that, The DC-DC power conversion circuit is a flyback DC-DC power conversion circuit.

6. The grid-connected / off-grid switching device according to claim 1, characterized in that, When the voltage across the second resistor and the third resistor is greater than the voltage threshold, the voltage at the connection point of the second resistor and the third resistor is greater than the reference voltage, the third switch is turned on, the second switch is turned off, and the first switch is turned off.

7. The grid-connected / off-grid switching device according to claim 6, characterized in that, When the voltage across the second resistor and the third resistor is less than or equal to the voltage threshold, the voltage at the connection point of the second resistor and the third resistor is less than or equal to the reference voltage, the third switch is turned off, the second switch is turned on, and the first switch is turned on.

8. A photovoltaic power generation system, characterized in that, The photovoltaic power generation system includes a photovoltaic inverter and a grid-connected / off-grid switching device. The input terminal of the photovoltaic inverter is used to connect to the output terminal of the photovoltaic array. The output terminal of the photovoltaic inverter is connected to the inverter port of the grid-connected / off-grid switching device. The grid port of the grid-connected / off-grid switching device is used to connect to the grid. The load port of the grid-connected / off-grid switching device is used to connect to the load. The on-grid / off-grid switching device includes: A first switch and a second switch are connected in series, the first switch and the second switch are connected between the inverter port and the grid port, and the connection point of the first switch and the second switch is connected to the load port; The system includes a rectifier circuit, a capacitor, and a DC-DC power conversion circuit. The input terminal of the rectifier circuit is connected to the inverter port, and the output terminal of the rectifier circuit is connected to the input terminal of the DC-DC power conversion circuit. The output terminal of the rectifier circuit includes a positive output terminal and a negative output terminal, and the capacitor is connected between the positive output terminal and the negative output terminal of the rectifier circuit. The DC-DC power conversion circuit comprises a first switch, a second switch, a third switch, and a first resistor. The open-loop output of the DC-DC power conversion circuit includes a positive output terminal and a negative output terminal. The emitter or source of the first switch is connected to the positive output terminal of the DC-DC power conversion circuit. The base or gate of the first switch is connected to the collector or drain of the second switch. The base or gate of the second switch is used to receive a reference voltage. The emitter or source of the second switch and the emitter or source of the third switch are connected to one end of the first resistor. The other end of the first resistor is connected to the negative output terminal of the DC-DC power conversion circuit. The collector or drain of the third switch is connected to the collector or drain of the first switch. A second resistor and a third resistor are connected in series. The second resistor and the third resistor are connected between the collector or drain of the third switching transistor and the negative output terminal of the DC-DC power conversion circuit. The connection point of the second resistor and the third resistor is connected to the base or gate of the third switching transistor. The collector or drain of the third switching transistor and the negative output terminal of the DC-DC power conversion circuit are connected to the load in the grid-connected switching device. The first switching transistor is a PNP transistor, PMOS, or PIGBT; The second and third switching transistors are NPN transistors, NMOS transistors, or NIGBT transistors.

9. The photovoltaic power generation system according to claim 8, characterized in that, The grid-connected / off-grid switching device also includes a controller, and the DC-DC power conversion circuit also includes a closed-loop output terminal; The controller is used to acquire the voltage or current at the closed-loop output terminal and output a pulse width modulation signal. The voltage or current at the closed-loop output terminal is used to determine the duty cycle of the pulse width modulation signal. The pulse width modulation signal is used to control the switching transistor in the DC-DC power conversion circuit.

10. The photovoltaic power generation system according to claim 9, characterized in that, The grid-connected / off-grid switching device further includes a reference voltage source. The positive terminal of the reference voltage source is connected to the positive output terminal of the DC-DC power conversion circuit, the negative terminal of the reference voltage source is connected to the negative output terminal of the DC-DC power conversion circuit, and the output terminal of the reference voltage source is connected to the base or gate of the second switching transistor.

11. The photovoltaic power generation system according to any one of claims 8-10, characterized in that, When the voltage across the second resistor and the third resistor is greater than the voltage threshold, the voltage at the connection point of the second resistor and the third resistor is greater than the reference voltage, the third switch is turned on, the second switch is turned off, and the first switch is turned off.

12. The photovoltaic power generation system according to claim 11, characterized in that, When the voltage across the second resistor and the third resistor is less than or equal to the voltage threshold, the voltage at the connection point of the second resistor and the third resistor is less than or equal to the reference voltage, the third switch is turned off, the second switch is turned on, and the first switch is turned on.

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