High-voltage start-up protection circuit for photovoltaic inverter and control method of high-voltage start-up protection circuit

Abstract

The invention discloses a high-voltage starting protection circuit for a photovoltaic inverter and a control method of the high-voltage starting protection circuit, the circuit compares sampling current of the photovoltaic inverter through a wave-by-wave current limiting circuit, a wave sealing signal is output when the sampling current is greater than preset current, and a control circuit is used for outputting a PWM (Pulse-Width Modulation) signal. The control circuit receives the wave sealing signal and adjusts the duty ratio of the PWM signal according to the bus voltage of the photovoltaic inverter, the control circuit controls an inversion power tube of the photovoltaic inverter to seal waves when receiving the wave sealing signal, and the current adjusting circuit adjusts the preset current according to the duty ratio of the PWM signal. The preset current for wave-by-wave current-limiting and wave-sealing protection can dynamically change along with the bus voltage of the photovoltaic inverter, so that the photovoltaic inverter can be started to generate power at a normal time point in extremely low temperature weather, more generating capacity is ensured, and the electricity demand of a user is met.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of photovoltaic inverters, and in particular to a high-voltage startup protection circuit for a photovoltaic inverter and a control method thereof. Background Art

[0002] Currently, photovoltaic inverters are all integrated with a high-voltage startup protection circuit to ensure system safety and stability. Existing high-voltage startup protection circuits for photovoltaic inverters all achieve system protection through fixed wave-by-wave current limiting. During high-voltage startup, the stress superimposed on the inverter power transistors inside the inverter is fixed. As a result, in extremely low-temperature weather conditions, the voltage at the inverter input will be very high just after the sun rises, directly triggering the wave-by-wave current limiting protection during startup, preventing the machine from starting and generating electricity at the normal time. To successfully start generating electricity, users need to reduce the number of photovoltaic panels in series to lower the voltage at the inverter input or wait for the ambient temperature to rise to reduce the voltage at the inverter input. Doing so will reduce the overall power generation, making it difficult for users to accept. Summary of the Invention

[0003] The present invention provides a high-voltage startup protection circuit for a photovoltaic inverter and a control method thereof, aiming to solve the problem that the photovoltaic inverter cannot be started and generate electricity at normal time under extremely low temperature weather conditions.

[0004] In the first aspect, an embodiment of the present invention provides a high-voltage starting protection circuit for a photovoltaic inverter, which includes: a wave-by-wave current limiting circuit, which is used to compare the sampled current of the photovoltaic inverter and output a blocking signal when the sampled current is greater than a preset current; a control circuit, which is connected to the wave-by-wave current limiting circuit and connected to the photovoltaic inverter bus and the inverter power tube, is used to output a PWM signal, and adjust the duty cycle of the PWM signal according to the bus voltage of the photovoltaic inverter, and control the inverter power tube of the photovoltaic inverter to block the wave when receiving the blocking signal; a current regulation circuit, which is connected to the wave-by-wave current limiting circuit and the control circuit, is used to adjust the preset current according to the duty cycle of the PWM signal.

[0005] Furthermore, the wave-by-wave current limiting circuit includes a current comparison unit and a wave-enclosing drive unit, the input end of the current comparison unit is connected to the current regulation circuit, the output end of the current comparison unit is connected to the input end of the wave-enclosing drive unit, and the output end of the wave-enclosing drive unit is connected to the control circuit, wherein the current comparison unit is used to compare the sampled current with the preset current, and the wave-enclosing drive unit is used to output the wave-enclosing signal according to the comparison result.

[0006] Furthermore, the current comparison unit includes a first comparison unit and a second comparison unit, the input end of the first comparison unit is connected to the current regulation circuit, the input end of the second comparison unit is connected to the output end of the first comparison unit and the photovoltaic inverter bus, and the output end of the second comparison unit is connected to the input end of the wave-enclosing drive unit, wherein the first comparison unit and the second comparison unit cooperate to compare the sampled current with the preset current.

[0007] Furthermore, the first comparison unit includes a first operational amplifier, a first resistor and a first capacitor, and the second comparison unit includes a second operational amplifier, a second resistor, a third resistor and a second capacitor. The non-inverting input terminal of the first operational amplifier is connected to the current regulation circuit through the first resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal, the first capacitor is connected between the non-inverting input terminal of the first operational amplifier and ground, the non-inverting input terminal of the second operational amplifier is connected to the output terminal of the first operational amplifier through the second resistor, the inverting input terminal of the second operational amplifier receives the collection current through the third resistor, the output terminal of the second operational amplifier is connected to the input terminal of the wave encapsulation driving unit, and the second capacitor is connected between the non-inverting input terminal of the second operational amplifier and ground.

[0008] Furthermore, the wave sealing drive unit includes a first transistor, a second transistor, a fourth resistor and a fifth resistor, the base of the first transistor is connected to the output end of the second operational amplifier, the collector is connected to the power supply, the emitter is grounded through the fourth resistor and connected to the base of the second transistor through the fifth resistor, the collector of the second transistor is connected to the control circuit, and the emitter is grounded.

[0009] Furthermore, the current regulation circuit includes a first MOS transistor, a first inductor, a third capacitor, and a sixth resistor. The gate of the first MOS transistor is connected to the control circuit, the drain is connected to the power supply through the first inductor, and the source is grounded. One end of the sixth resistor is connected to the drain of the first MOS transistor, and the other end is connected to the non-inverting input of the first op amp. One end of the third capacitor is connected between the sixth resistor and the non-inverting input of the first op amp, and the other end is grounded.

[0010] Furthermore, the high-voltage startup protection circuit for the photovoltaic inverter also includes a hardware overvoltage protection circuit, which is connected to the control circuit and connected to the input side bus of the photovoltaic inverter, and is used to compare the bus voltage of the photovoltaic inverter and output a blocking signal and an alarm signal to the control circuit when the bus voltage is greater than a preset protection voltage.

[0011] Furthermore, the hardware overvoltage protection circuit includes a third comparison unit and a fourth comparison unit, the input end of the third comparison unit is connected to the power supply, the input end of the fourth comparison unit is connected to the output end of the third comparison unit and the input side bus of the photovoltaic inverter, and the output end of the fourth comparison unit is connected to the control circuit, wherein the third comparison unit and the fourth comparison unit cooperate to compare the bus voltage on the input side of the photovoltaic inverter with the preset protection voltage.

[0012] Furthermore, the third comparison unit includes a third operational amplifier, a seventh resistor, and an eighth resistor; the fourth comparison unit includes a fourth operational amplifier, a ninth resistor, and a tenth resistor; the non-inverting input terminal of the third operational amplifier is connected to the power supply through the seventh resistor and the eighth resistor in sequence; the inverting input terminal of the third operational amplifier is connected to the output terminal; the non-inverting input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier through the ninth resistor; the inverting input terminal of the fourth operational amplifier is connected to the input side bus of the photovoltaic inverter through the tenth resistor; and the output terminal of the fourth operational amplifier is connected to the control circuit.

[0013] In a second aspect, the present invention also provides a control method for a high-voltage starting protection circuit, which is applied to the high-voltage starting circuit of the photovoltaic inverter described in the first aspect above, the method comprising: obtaining the bus voltage of the photovoltaic inverter; comparing the bus voltage with a first preset voltage and a second preset voltage, wherein the first preset voltage is greater than the second preset voltage; if the bus voltage is greater than the first preset voltage, controlling the inverter power tube of the photovoltaic inverter to block the wave; if the bus voltage is greater than the second preset voltage and less than the first preset voltage, calculating the real-time duty cycle according to the bus voltage, and outputting a first PWM signal with the real-time duty cycle to drive the current regulation circuit to operate; if the bus voltage is less than the second preset voltage, outputting a second PWM signal with a preset duty cycle to drive the current regulation circuit to operate.

[0014] The present invention provides a high-voltage startup protection circuit for a photovoltaic inverter and a control method thereof. The high-voltage startup protection circuit for the photovoltaic inverter compares the sampled current of the photovoltaic inverter through a wave-by-wave current limiting circuit, and outputs a blocking signal when the sampled current is greater than a preset current. The control circuit is used to output a PWM signal and adjust the duty cycle of the PWM signal according to the bus voltage of the photovoltaic inverter. When the control circuit receives the blocking signal, it controls the inverter power tube of the photovoltaic inverter to block the wave. The current regulating circuit adjusts the preset current according to the duty cycle of the PWM signal, thereby dynamically adjusting the wave-by-wave current limiting and blocking protection threshold of the wave-by-wave current limiting circuit according to the bus voltage of the photovoltaic inverter. This enables the photovoltaic inverter to start and generate electricity at a normal time even in extremely low temperature weather, thereby ensuring more power generation and meeting user electricity demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 A partial circuit diagram of a high-voltage startup protection circuit for a photovoltaic inverter provided by an embodiment of the present invention;

[0017] Figure 2 Another partial circuit diagram of a high-voltage startup protection circuit for a photovoltaic inverter provided by an embodiment of the present invention;

[0018] Figure 3 A schematic flow chart of the steps of the method provided in an embodiment of the present invention.

[0019] Reference numerals:

[0020] 1. Wave-by-wave current limiting circuit; 11. Current comparison unit; 111. First comparison unit; 112. Second comparison unit; 12. Wave-sealing driving unit; 2. Current regulation circuit; 3. Control circuit; 4. Hardware overvoltage protection circuit; 41. Third comparison unit; 42. Fourth comparison unit. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] Directional terms used herein, such as "upper," "lower," "front," "back," "left," "right," "inner," "outer," and "side," refer only to directions in the accompanying drawings. Therefore, these directional terms are intended to illustrate and facilitate understanding of the present invention and are not intended to limit the present invention. Furthermore, in the accompanying drawings, similar or identical structures are denoted by the same reference numerals.

[0023] In order to facilitate understanding of the present invention, the high voltage startup protection circuit for photovoltaic inverter provided by the embodiment of the present invention is first described. Figure 1An embodiment of the present invention provides a high-voltage startup protection circuit for a photovoltaic inverter, which includes: a wave-by-wave current limiting circuit 1, used to compare the sampled current of the photovoltaic inverter and output a blocking signal when the sampled current is greater than a preset current; a control circuit 3, connected to the wave-by-wave current limiting circuit 1 and connected to the photovoltaic inverter bus and the inverter power tube, used to output a PWM signal, and adjust the duty cycle of the PWM signal according to the bus voltage of the photovoltaic inverter, and control the inverter power tube of the photovoltaic inverter to block the wave when receiving the blocking signal; a current regulation circuit 2, connected to the wave-by-wave current limiting circuit 1 and the control circuit 3, used to adjust the preset current according to the duty cycle of the PWM signal.

[0024] Traditional high-voltage startup protection circuits for photovoltaic inverters implement system protection through fixed, wave-by-wave current limiting. During high-voltage startup, the stress applied to the inverter's internal power transistors is fixed. Consequently, in extremely cold weather, just as the sun rises, the voltage at the inverter input will be very high, triggering the wave-by-wave current limiting protection during startup. This causes the inverter's power transistors to block the power supply, preventing the inverter from starting and generating power at normal times. To successfully start and generate power at normal times, users must reduce the number of photovoltaic panels in series, lowering the voltage at the inverter input, or wait for the ambient temperature to rise, causing the voltage at the inverter input to drop, before starting. Both of these practices reduce overall power generation and are detrimental to users.

[0025] In order to solve the problem that the photovoltaic inverter cannot start to generate electricity at normal time under extremely low temperature weather conditions, this embodiment provides a high-voltage starting circuit, which is mainly used in photovoltaic inverters, such as Figure 1 As shown, the high-voltage startup protection circuit for a photovoltaic inverter in this embodiment includes a wave-by-wave current limiting circuit 1, a control circuit 3, and a current regulation circuit 2. The wave-by-wave current limiting circuit 1 is connected to the photovoltaic inverter bus, specifically to the input-side DC bus or the output-side AC bus of the photovoltaic inverter. The control circuit 3 is connected to the wave-by-wave current limiting circuit 1 and is connected to the photovoltaic inverter bus and the inverter power transistor. Specifically, the control circuit 3 is connected to the input-side DC bus and the output-side AC bus of the photovoltaic inverter, and is connected to the inverter power transistor of the photovoltaic inverter. The inverter power transistor of the photovoltaic inverter is an IGBT, which is a key component in the inverter circuit portion of the photovoltaic inverter. The control circuit 3 controls the inverter output current by driving the inverter power transistor of the photovoltaic inverter. The current regulation circuit 2 is connected to both the wave-by-wave current limiting circuit 1 and the control circuit 3.

[0026] In practical applications, the wave-by-wave current limiting circuit 1 is used to compare the sampled current of the photovoltaic inverter and output a blocking signal when the sampled current of the photovoltaic inverter exceeds a preset current. Specifically, the wave-by-wave current limiting circuit 1 compares the sampled value of the photovoltaic inverter's sampled current, which is collected by a sampling circuit or sampling device on the photovoltaic inverter bus. The wave-by-wave current limiting circuit 1 compares the sampled current of the photovoltaic inverter with the preset current. Specifically, if the bus voltage of the photovoltaic inverter exceeds the preset current, the wave-by-wave current limiting circuit 1 outputs a blocking signal to the control circuit 3. The blocking signal is an enable signal for the control circuit 3 to block the inverter power transistors of the photovoltaic inverter. Upon receiving the blocking signal output by the wave-by-wave current limiting circuit 1, the control circuit 3 controls the inverter power transistors of the photovoltaic inverter to block the current. At this time, the photovoltaic inverter cannot start generating electricity, protecting system safety. In addition to controlling the blocking of the inverter power transistors of the photovoltaic inverter, the control circuit 3 also outputs a PWM signal to drive the operation of the current regulation circuit 2. The current regulation circuit 2 can adjust the preset current according to the duty cycle of the PWM signal output by the control circuit 3.

[0027] In a specific application, control circuit 3 detects and obtains the bus voltage of the photovoltaic inverter in real time, and adjusts the duty cycle of the output PWM signal based on the bus voltage of the photovoltaic inverter. The process of adjusting the duty cycle by control circuit 3 will be described in detail in the method provided below and will not be further explained here. The duty cycle of the PWM signal output by control circuit 3 varies with the bus voltage of the photovoltaic inverter. The preset current used by the wave-by-wave current limiting circuit 1 is regulated by current regulation circuit 2, and the preset current serves as a comparison signal. Therefore, under normal circumstances, the preset current changes dynamically with the inverter's bus voltage, that is, the preset current is a dynamically changing comparison signal. Only when the duty cycle of the PWM signal given by control circuit 3 is fixed, the preset current becomes a fixed comparison signal. Therefore, in actual applications, when the bus voltage of the photovoltaic inverter increases, since the preset current is dynamically adjusted based on the bus voltage of the photovoltaic inverter, and the bus voltage is within a safe range, as long as the sampled current of the photovoltaic inverter is less than the preset current, the wave-by-wave current limiting circuit 1 will not output a blocking signal, and control circuit 3 will not block the wave, allowing the photovoltaic inverter to start generating electricity. Therefore, in extremely low temperature weather, even if the input voltage of the photovoltaic inverter is high, as long as it is still within the overvoltage protection range, the current regulation circuit 2 will increase the preset current used for comparison with the photovoltaic inverter sampling current, that is, to achieve a dynamic and gradual current limiting protection threshold. The photovoltaic inverter can start generating electricity at the normal time when the sun rises, meeting the user's power generation needs.

[0028] In a further embodiment, referring to Figure 1The wave-by-wave current limiting circuit 1 includes a current comparison unit 11 and a wave-enclosing drive unit 12. The input end of the current comparison unit 11 is connected to the current regulation circuit 2 and connected to the busbar of the photovoltaic inverter. The output end of the current comparison unit 11 is connected to the input end of the wave-enclosing drive unit 12. The output end of the wave-enclosing drive unit 12 is connected to the control circuit 3. The current comparison unit 11 is used to compare the sampled current with the preset current, and the wave-enclosing drive unit 12 is used to output the wave-enclosing signal according to the comparison result. In a specific implementation, the wave-by-wave current limiting circuit 1 includes a current comparison unit 11 and a wave-enclosing drive unit 12. The input end of the current comparison unit 11 is connected to the current regulation circuit 2 and connected to the busbar of the photovoltaic inverter. The output end of the current comparison unit 11 is connected to the input end of the wave-enclosing drive unit 12. The output end of the wave-enclosing drive unit 12 is connected to the control circuit 3. In actual applications, the current comparison unit 11 compares the sampled current of the photovoltaic inverter with the preset current, and the wave-sealing signal is generated by the wave-sealing driving unit 12. The wave-sealing driving unit 12 decides whether to output the wave-sealing signal to the control circuit 3 based on the comparison result of the current comparison unit 11. Specifically, when the comparison result of the current comparison unit 11 is that the sampled current is greater than the preset current, the wave-sealing driving unit 12 outputs the wave-sealing signal to the control circuit 3, so that the control circuit 3 can control the power tube of the photovoltaic inverter to perform wave-sealing.

[0029] In a further embodiment, referring to Figure 1The current comparison unit 11 includes a first comparison unit 111 and a second comparison unit 112. The input end of the first comparison unit 111 is connected to the current regulation circuit 2, the input end of the second comparison unit 112 is connected to the output end of the first comparison unit 111 and the photovoltaic inverter bus, and the output end of the second comparison unit 112 is connected to the input end of the wave-enclosing drive unit 12. The first comparison unit 111 and the second comparison unit 112 cooperate to compare the bus voltage of the photovoltaic inverter with the preset current. In a specific implementation, the current comparison unit 11 includes a first comparison unit 111 and a second comparison unit 112. The input end of the first comparison unit 111 is connected to the current regulation circuit 2, the output end of the first comparison unit 111 is connected to the input end of the second comparison unit 112, the input end of the second comparison unit 112 is also connected to the photovoltaic inverter bus, and the output end of the second comparison unit 112 is connected to the input end of the wave-enclosing drive unit 12. In actual application, the first comparison unit 111 and the second comparison unit 112 cooperate to compare the bus voltage of the photovoltaic inverter with the preset current. Specifically, the first comparison unit 111 provides a reference signal to the second comparison unit 112 based on the comparison of the preset current. The second comparison unit 112 then compares the sampling current of the photovoltaic inverter based on the reference signal provided by the first comparison unit 111. The enclosing wave driving unit 12 decides whether to output the enclosing wave signal based on the comparison result of the second comparison unit 112.

[0030] In a further embodiment, referring to Figure 1The first comparison unit 111 includes a first operational amplifier U3, a first resistor R9, and a first capacitor C3. The second comparison unit 112 includes a second operational amplifier U4, a second resistor R13, a third resistor R12, and a second capacitor C4. The non-inverting input of the first operational amplifier U3 is connected to the current regulation circuit 2 through the first resistor R9. The inverting input of the first operational amplifier U3 is connected to the output. The first capacitor C3 is connected between the non-inverting input of the first operational amplifier U3 and ground. The non-inverting input of the second operational amplifier U4 is connected to the output of the first operational amplifier U3 through the second resistor R13. The inverting input of the second operational amplifier U4 receives the collected current through the third resistor R12. The output of the second operational amplifier U4 is connected to the input of the wave-enclosing driving unit 12. The second capacitor C4 is connected between the non-inverting input of the second operational amplifier U4 and ground. In a specific implementation, the inverting input of the first operational amplifier U3 is connected to the output through the resistor R10 to implement a voltage following function, and the output voltage follows the input voltage. The non-inverting input of the second operational amplifier U4 is connected to the output of the first operational amplifier U3 through the second resistor R13. The voltage output by the current regulating circuit 2 is followed by the first operational amplifier U3 and serves as the reference signal for the non-inverting input of the second operational amplifier U4. It is a voltage signal. Therefore, the reference signal at the non-inverting input of the second operational amplifier U4 changes dynamically with the voltage signal output by the current regulating circuit 2. The inverting input of the second operational amplifier U4 is connected to the photovoltaic inverter bus through the third resistor R12. The output of the second operational amplifier U4 is connected to the input of the wave-sealing drive unit 12 through the resistor R15, and is connected to the power supply V1 through the resistor R14. The second operational amplifier U4 compares the sampled current with the reference signal that changes with the output signal of the current regulating circuit, as shown in FIG. Figure 1 As shown, I represents the sampling current of the photovoltaic inverter. The sampling current can be the machine-side sampling current or the grid-side sampling current. The sampling current I forms a voltage signal that can be used for operational amplifier comparison after passing through the third resistor R12. When the voltage signal formed by the sampling current I through the third resistor R12 is greater than the reference signal of the second operational amplifier U4, the output terminal of the second operational amplifier U4 outputs a low-level signal to the wave-enclosing driving unit 12; when the voltage signal formed by the sampling current I through the third resistor R12 is less than the reference signal of the second operational amplifier U4, the output terminal of the second operational amplifier U4 outputs a high-level signal to the wave-enclosing driving unit 12. The wave-enclosing driving unit 12 generates a wave-enclosing signal according to the level signal at the output terminal of the second operational amplifier U4 and outputs it to the control circuit 3.

[0031] In a further embodiment, referring to Figure 1The wave encapsulation drive unit 12 includes a first transistor Q1, a second transistor Q3, a fourth resistor R16, and a fifth resistor R17. The base of the first transistor Q1 is connected to the output terminal of the second operational amplifier U4, the collector is connected to the power supply, the emitter is grounded through the fourth resistor R16, and is connected to the base of the second transistor Q3 through the fifth resistor R17. The collector of the second transistor Q3 is connected to the control circuit 3, and the emitter is grounded. In a specific implementation, the wave encapsulation drive unit 12 includes a first transistor Q1, a second transistor Q3, a fourth resistor R16, and a fifth resistor R17. The base of the first transistor Q1 is connected to the output terminal of the second operational amplifier U4, the collector of the first transistor Q1 is connected to the power supply V1, the emitter of the first transistor Q1 is grounded through the fourth resistor R16, and is also connected to the base of the second transistor Q3 through the fifth resistor R17. The collector of the second transistor Q3 is connected to the control circuit 3 as the output terminal of the wave encapsulation signal, and the emitter of the second transistor Q3 is connected to ground. In actual applications, the first transistor Q1 is a PNP transistor, and the second transistor Q3 is an NPN transistor. The second op amp U4 outputs high and low level signals to the base of the first transistor Q1 by comparing the sampled current of the photovoltaic inverter. When the output of the second op amp U4 outputs a low level, the first transistor Q1 is turned on, and V1 is applied to the base of the second transistor Q3, causing the base of the second transistor Q3 to be high, thereby turning on the transistor. The collector of the second transistor Q3 is then connected to ground, and the collector of the second transistor Q3 is low, which is output as the blocking signal QD to the control circuit 3, causing the control circuit 3 to block the inverter power transistors of the photovoltaic inverter.

[0032] In one embodiment, referring to Figure 1The current regulation circuit 2 includes a first MOS transistor Q2, a first inductor L1, a third capacitor C2, and a sixth resistor R8. The gate of the first MOS transistor Q2 is connected to the control circuit 3, the drain is connected to the power supply through the first inductor L1, and the source is grounded. One end of the sixth resistor R8 is connected to the drain of the first MOS transistor Q2, and the other end is connected to the non-inverting input terminal of the first operational amplifier U3. One end of the third capacitor C2 is connected between the sixth resistor R8 and the non-inverting input terminal of the first operational amplifier U3, and the other end is grounded. In a specific implementation, the current regulation circuit 2 includes a first MOS transistor Q2, a first inductor L1, a third capacitor C2, and a sixth resistor R8. The gate of the first MOS transistor Q2 is connected to the control circuit 3 to receive the PWM signal from the control circuit 3. The drain of the first MOS transistor Q2 is connected to the power supply V1 through the first inductor L1. The source of the first MOS transistor Q2 is connected to ground. One end of the sixth resistor R8 is connected to the drain of the first MOS transistor Q2, and the other end of the sixth resistor R8 is connected to the non-inverting input terminal of the first operational amplifier U3. One end of the third capacitor C2 is connected between the sixth resistor R8 and the non-inverting input terminal of the first operational amplifier U3, and the other end of the third capacitor C2 is grounded. Thus, the first MOS transistor Q2, the first inductor L1, the third capacitor C2, and the sixth resistor R8 constitute a circuit capable of implementing a step-down function. The output voltage of this circuit serves as a reference signal for the non-inverting input terminal of the first operational amplifier U3. The circuit is regulated by the duty cycle of the PWM signal output by the control circuit 3, and the maximum output voltage does not exceed the voltage of the power supply V1. In practical applications, control circuit 3 modulates the duty cycle of the PWM signal based on the bus voltage of the photovoltaic inverter, thereby controlling the switching frequency of first MOS transistor Q2 and dynamically adjusting the reference signal at the non-inverting input of first op amp U3. The output of first op amp U3 follows the input, which in turn dynamically adjusts the reference signal at the non-inverting input of second op amp U4. This allows second op amp U4 to dynamically adjust the reference signal as it compares the sampled current of the photovoltaic inverter with the bus voltage of the photovoltaic inverter. In practical applications, when the sampled value of the photovoltaic inverter's bus voltage is greater than the output voltage of power supply V1 after step-down, the output of second op amp U4 outputs a low level to drive the blocking drive unit 12 to generate a blocking signal, which is output to control circuit 3, thereby controlling the blocking of the inverter power transistors of the photovoltaic inverter.

[0033] In one embodiment, referring to Figure 2The high-voltage startup protection circuit for the photovoltaic inverter also includes a hardware overvoltage protection circuit 4, which is connected to the control circuit 3 and connected to the input-side bus of the photovoltaic inverter. It is used to compare the bus voltage of the photovoltaic inverter and output an alarm signal to the control circuit 3 when the bus voltage is greater than the preset protection voltage. In a specific implementation, the high-voltage startup protection circuit also includes a hardware overvoltage protection circuit 4, which is connected to the control circuit 3 and connected to the input-side bus of the photovoltaic inverter. In actual application, the hardware overvoltage protection circuit 4 compares the bus voltage on the input side of the photovoltaic inverter with the preset protection voltage by comparing the bus voltage on the input side of the photovoltaic inverter. Specifically, the preset protection voltage is the maximum protection value of the system overvoltage alarm. When the bus voltage on the input side of the photovoltaic inverter is greater than the preset protection voltage, the hardware overvoltage protection circuit 4 will output a blocking signal and an alarm signal to the control circuit 3. The control circuit 3 will execute blocking after receiving the blocking signal output by the hardware overvoltage protection circuit 4, so that the photovoltaic inverter cannot be started. At the same time, the control circuit 3 will report hardware overvoltage upon receiving the alarm signal to prompt the user. The hardware overvoltage report can be a buzzer alarm or a light indication.

[0034] In a further embodiment, referring to Figure 2 The hardware overvoltage protection circuit 4 includes a third comparison unit 41 and a fourth comparison unit 42. The input end of the third comparison unit 41 is connected to the power supply, the input end of the fourth comparison unit 42 is connected to the output end of the third comparison unit 41 and the input side bus of the photovoltaic inverter, and the output end of the fourth comparison unit 42 is connected to the control circuit 3. The third comparison unit 41 and the fourth comparison unit 42 cooperate to compare the bus voltage on the input side of the photovoltaic inverter with the preset protection voltage. In a specific implementation, the hardware overvoltage protection circuit 4 includes a third comparison unit 41 and a fourth comparison unit 42. The input end of the third comparison unit 41 is connected to the power supply V1, the input end of the fourth comparison unit 42 is connected to the output end of the third comparison unit 41 and the input side bus of the photovoltaic inverter, and the output end of the fourth comparison unit 42 is connected to the control circuit 3. The third comparison unit 41 and the fourth comparison unit 42 cooperate to compare the bus voltage on the input side of the photovoltaic inverter with the preset protection voltage. Specifically, the third comparison unit 41 provides a reference voltage for the fourth comparison unit 42 based on the voltage provided by the comparison power supply V1, and the fourth comparison unit 42 compares the bus voltage on the input side of the photovoltaic inverter based on the reference voltage provided by the third comparison unit 41. The control circuit 3 decides whether to report a hardware overvoltage based on the comparison result of the fourth comparison unit 42.

[0035] In a further embodiment, referring to Figure 2The third comparison unit 41 includes a third operational amplifier U1, a seventh resistor R1, and an eighth resistor R2. The fourth comparison unit 42 includes a fourth operational amplifier, a ninth resistor R3, and a tenth resistor R4. The non-inverting input terminal of the third operational amplifier U1 is connected to the power supply through the seventh resistor R1 and the eighth resistor R2 in sequence. The inverting input terminal of the third operational amplifier U1 is connected to the output terminal. The non-inverting input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier U1 through the ninth resistor R3. The inverting input terminal of the fourth operational amplifier is connected to the input side bus of the photovoltaic inverter through the tenth resistor R4. The output terminal of the fourth operational amplifier is connected to the control circuit 3. In a specific implementation, the third comparison unit 41 includes a third operational amplifier U1, a seventh resistor R1, and an eighth resistor R2; the fourth comparison unit 42 includes a fourth operational amplifier, a ninth resistor R3, and a tenth resistor R4; the positive phase input terminal of the third operational amplifier U1 is connected to the power supply V1 through the seventh resistor R1 and the eighth resistor R2 in sequence; the negative phase input terminal of the third operational amplifier U1 is connected to the output terminal; the positive phase input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier U1 through the ninth resistor R3; the negative phase input terminal of the fourth operational amplifier is connected to the input side bus of the photovoltaic inverter through the tenth resistor R4; and the output terminal of the fourth operational amplifier is connected to the control circuit 3. In actual applications, the voltage of the power supply V1 is divided by the seventh resistor R1 and the eighth resistor R2 to obtain a preset protection voltage, which is then input to the positive phase input terminal of the third operational amplifier U1; the negative phase input terminal of the third operational amplifier U1 is connected to the output terminal to realize a voltage following function; the output voltage of the third operational amplifier U1 follows the input voltage, and provides a reference voltage for the positive phase input terminal of the fourth operational amplifier. Figure 2 As shown, the sampling value Vbus of the bus voltage on the input side of the photovoltaic inverter is input into the inverting input terminal of the fourth operational amplifier. The fourth operational amplifier compares the bus voltage on the input side of the photovoltaic inverter with a fixed reference voltage. When the sampling value of the bus voltage on the input side of the photovoltaic inverter is greater than the reference voltage, the output of the fourth operational amplifier is low, and a low-level alarm signal OVP is output to the control circuit 3, so that the control circuit 3 reports hardware overvoltage to the user.

[0036] In summary, in the circuit of the present application, the preset current used for wave-by-wave current limiting and wave blocking protection changes dynamically with the bus voltage of the photovoltaic inverter. As long as the bus voltage of the photovoltaic inverter is within the safe overvoltage protection range, the photovoltaic inverter can also start to generate electricity at normal times in extremely low temperature weather, ensuring more power generation and meeting the user's electricity needs.

[0037] See also Figure 3 , Figure 3 Flowchart of the control method of the high-voltage startup protection circuit provided by the embodiment of the present invention. The high-voltage startup circuit of the photovoltaic inverter applied to the above embodiment has been described in detail in the above embodiment. For the sake of brevity, it will not be repeated here. The method is described in detail below. Figure 3 As shown, the method includes steps: S110-S150.

[0038] S110: Obtain the bus voltage of the photovoltaic inverter.

[0039] In a specific implementation, the control circuit of the photovoltaic inverter high-voltage starting circuit is connected to the photovoltaic inverter bus through a voltage sampling circuit or device. The control circuit system can obtain the bus voltage of the photovoltaic inverter in real time, where the input side bus voltage is the DC bus voltage and the output side voltage is the AC bus voltage.

[0040] S120. Compare the bus voltage with a first preset voltage and a second preset voltage, wherein the first preset voltage is greater than the second preset voltage.

[0041] In a specific implementation, after the control circuit system obtains the bus voltage of the photovoltaic inverter, it compares the bus voltage with a first preset voltage and a second preset voltage. The first preset voltage is greater than the second preset voltage. Specifically, the first preset voltage is the maximum overvoltage protection threshold set by the system, and the second preset voltage is the threshold set by the system for executing dynamic wave-by-wave current limiting control. By comparing the bus voltage with the first preset voltage and the second preset voltage, the system can determine the bus voltage condition of the photovoltaic inverter.

[0042] S130: If the bus voltage is greater than the first preset voltage, control the inverter power tube of the photovoltaic inverter to block the wave.

[0043] In a specific implementation, when the control circuit system determines that the bus voltage is greater than the first preset voltage, it indicates that the bus voltage of the photovoltaic inverter has exceeded the maximum overvoltage protection threshold. At this time, the system controls the inverter power tube of the photovoltaic inverter to shut down the wave, and the photovoltaic inverter cannot be started to protect the stability of the system. In particular, the control circuit can also issue an alarm to prompt the user at the same time as the wave is shut down.

[0044] S140: If the bus voltage is greater than the second preset voltage and less than the first preset voltage, calculate the real-time duty cycle according to the bus voltage, and output a first PWM signal with the real-time duty cycle to drive the current regulation circuit to operate.

[0045] In a specific implementation, when the control circuit system determines that the bus voltage is greater than the second preset voltage and less than the first preset voltage, it indicates that the bus voltage of the photovoltaic inverter has not exceeded the maximum overvoltage protection threshold, and the system will not have an overvoltage risk. At the same time, the threshold for executing dynamic wave-by-wave current limiting control is reached. At this time, the control circuit system calculates the real-time duty cycle according to the bus voltage, and outputs a first PWM signal with a real-time duty cycle to drive the current regulation circuit in the high-voltage starting circuit to operate, so that the current regulation circuit dynamically adjusts the preset current of the wave-by-wave current limiting circuit for wave-by-wave current limiting protection, thereby realizing dynamic wave-by-wave current limiting control. The photovoltaic inverter is started only when the bus voltage is less than the dynamically changing preset current, and is shut down when it is greater than the dynamically changing preset current.

[0046] S150: If the bus voltage is less than the second preset voltage, output a second PWM signal with a preset duty cycle to drive the current regulation circuit to operate.

[0047] In a specific implementation, when the control circuit system determines that the bus voltage is less than a second preset voltage, indicating that the bus voltage of the photovoltaic inverter has not reached the threshold for executing dynamic wave-by-wave current limiting control, the system does not perform wave-by-wave current limiting control. At this time, the control circuit system outputs a second PWM signal with a preset duty cycle to drive the current regulation circuit in the high-voltage starting circuit to operate. The preset duty cycle is a duty cycle value set by the system. The control circuit system outputs the second PWM signal with a preset duty cycle to drive the current regulation circuit to operate. The current regulation circuit adjusts the preset current used by the wave-by-wave current limiting circuit for wave-by-wave current limiting protection to a fixed value. The wave-by-wave current limiting threshold is fixed to maintain full-load operation of the photovoltaic inverter. The photovoltaic inverter starts when the sampled current is less than the fixed preset current and shuts down when it is greater than the fixed preset current.

[0048] The method of the present application obtains the bus voltage of the photovoltaic inverter, compares the bus voltage with a first preset voltage and a second preset voltage, and when the first preset voltage is greater than the second preset voltage, controls the inverter power tube of the photovoltaic inverter to block the wave, and when the bus voltage is greater than the second preset voltage and less than the first preset voltage, calculates the real-time duty cycle according to the bus voltage and outputs a first PWM signal with the real-time duty cycle to drive the current regulation circuit to operate; when the bus voltage is less than the second preset voltage, outputs a second PWM signal with a preset duty cycle to drive the current regulation circuit to operate, thereby achieving different wave-by-wave current limiting protection strategies according to the bus voltage of the photovoltaic inverter, thereby improving the reliability of power generation of the photovoltaic inverter.

[0049] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A high voltage startup protection circuit for a photovoltaic inverter, characterized in that: include: A wave-by-wave current limiting circuit is used to compare the sampled current of the photovoltaic inverter and output a wave-closing signal when the sampled current is greater than a preset current; A control circuit is connected to the wave-by-wave current limiting circuit and is connected to the busbar and inverter power tube of the photovoltaic inverter, and is used to output a PWM signal, adjust the duty cycle of the PWM signal according to the busbar voltage of the photovoltaic inverter, and control the inverter power tube of the photovoltaic inverter to close the wave when receiving the closing wave signal; A current regulating circuit is connected to the wave-by-wave current limiting circuit and the control circuit, and is used to adjust the size of the preset current according to the duty cycle of the PWM signal.

2. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 1, characterized in that: The wave-by-wave current limiting circuit includes a current comparison unit and a wave-enclosing drive unit, wherein the input end of the current comparison unit is connected to the current regulation circuit, the output end of the current comparison unit is connected to the input end of the wave-enclosing drive unit, and the output end of the wave-enclosing drive unit is connected to the control circuit, wherein the current comparison unit is used to compare the sampled current with the preset current, and the wave-enclosing drive unit is used to output the wave-enclosing signal according to the comparison result.

3. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 2, characterized in that: The current comparison unit includes a first comparison unit and a second comparison unit, wherein the input end of the first comparison unit is connected to the current regulation circuit, the input end of the second comparison unit is connected to the output end of the first comparison unit and the photovoltaic inverter bus, and the output end of the second comparison unit is connected to the input end of the wave-enclosing drive unit, wherein the first comparison unit and the second comparison unit cooperate to compare the sampled current with the preset current.

4. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 3, characterized in that: The first comparison unit includes a first operational amplifier, a first resistor and a first capacitor; the second comparison unit includes a second operational amplifier, a second resistor, a third resistor and a second capacitor; the non-inverting input terminal of the first operational amplifier is connected to the current regulating circuit through the first resistor; the inverting input terminal of the first operational amplifier is connected to the output terminal; the first capacitor is connected between the non-inverting input terminal of the first operational amplifier and ground; the non-inverting input terminal of the second operational amplifier is connected to the output terminal of the first operational amplifier through the second resistor; the inverting input terminal of the second operational amplifier is connected to the photovoltaic inverter bus through the third resistor; the output terminal of the second operational amplifier is connected to the input terminal of the wave-enclosing driving unit; and the second capacitor is connected between the non-inverting input terminal of the second operational amplifier and ground.

5. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 4, characterized in that: The wave sealing driving unit includes a first transistor, a second transistor, a fourth resistor and a fifth resistor. The base of the first transistor is connected to the output end of the second operational amplifier, the collector is connected to the power supply, the emitter is grounded through the fourth resistor and connected to the base of the second transistor through the fifth resistor. The collector of the second transistor is connected to the control circuit, and the emitter is grounded.

6. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 4, characterized in that: The current regulation circuit includes a first MOS transistor, a first inductor, a third capacitor, and a sixth resistor. The gate of the first MOS transistor is connected to the control circuit, the drain is connected to the power supply through the first inductor, and the source is grounded. One end of the sixth resistor is connected to the drain of the first MOS transistor, and the other end is connected to the non-inverting input of the first operational amplifier. One end of the third capacitor is connected between the sixth resistor and the non-inverting input of the first operational amplifier, and the other end is grounded.

7. The high-voltage startup protection circuit for a photovoltaic inverter according to any one of claims 1 to 6, characterized in that: The high-voltage startup protection circuit for the photovoltaic inverter also includes a hardware overvoltage protection circuit, which is connected to the control circuit and connected to the input side bus of the photovoltaic inverter, and is used to compare the bus voltage of the photovoltaic inverter and output a blocking signal and an alarm signal to the control circuit when the bus voltage is greater than a preset protection voltage.

8. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 7, characterized in that: The hardware overvoltage protection circuit includes a third comparison unit and a fourth comparison unit, wherein the input end of the third comparison unit is connected to a power supply, the input end of the fourth comparison unit is connected to the output end of the third comparison unit and the input side bus of the photovoltaic inverter, and the output end of the fourth comparison unit is connected to the control circuit, wherein the third comparison unit and the fourth comparison unit cooperate to compare the bus voltage on the input side of the photovoltaic inverter with the preset protection voltage.

9. The high-voltage startup protection circuit for a photovoltaic inverter according to claim 8, characterized in that: The third comparison unit includes a third operational amplifier, a seventh resistor, and an eighth resistor. The fourth comparison unit includes a fourth operational amplifier, a ninth resistor, and a tenth resistor. The non-inverting input terminal of the third operational amplifier is connected to the power supply through the seventh resistor and the eighth resistor in sequence. The inverting input terminal of the third operational amplifier is connected to the output terminal. The non-inverting input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier through the ninth resistor. The inverting input terminal of the fourth operational amplifier is connected to the input side bus of the photovoltaic inverter through the tenth resistor. The output terminal of the fourth operational amplifier is connected to the control circuit.

10. A control method for a high voltage startup protection circuit, characterized in that: The high-voltage startup protection circuit for a photovoltaic inverter according to any one of claims 1 to 9, the method comprising: Get the bus voltage of the photovoltaic inverter; According to the comparison between the bus voltage and a first preset voltage and a second preset voltage, wherein the first preset voltage is greater than the second preset voltage; If the bus voltage is greater than the first preset voltage, controlling the inverter power tube of the photovoltaic inverter to turn off the wave; If the bus voltage is greater than the second preset voltage and less than the first preset voltage, a real-time duty cycle is calculated according to the bus voltage, and a first PWM signal having the real-time duty cycle is output to drive the current regulation circuit to operate; If the bus voltage is less than the second preset voltage, a second PWM signal with a preset duty cycle is output to drive the current regulation circuit to operate.

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