CN108258889A - Photovoltaic inverter auxiliary power system - Google Patents

Abstract

The invention relates to an auxiliary power supply system of a photovoltaic inverter, which comprises a control module, a rectifying module connected with the control module and an auxiliary power supply module connected with the rectifying module, wherein the control module comprises a relay RE L AY, a starting voltage comparison unit and a timing unit which are respectively connected with the relay RE L AY, the rectifying module comprises a rectifying bridge, the alternating current input end of the rectifying bridge is respectively connected with a switch K1 of the relay RE L AY and then connected with a power grid, and the direct current output end of the rectifying bridge is connected with the auxiliary power supply module.

Description

Photovoltaic inverter auxiliary power system

technical field

The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic inverter auxiliary power supply system.

Background technique

The commonly used methods of taking power for the auxiliary power supply of photovoltaic inverters are divided into three types: taking power from the grid, taking power from the power grid and the DC bus of the photovoltaic inverter, and taking power from the DC bus of the photovoltaic inverter. Among them, when taking power through the first two ways of taking power, the photovoltaic inverter will have standby loss at night, and a rectifier bridge and a large input capacitor are required.

However, when taking power from the DC bus of the photovoltaic inverter, the output power of photovoltaic power generation components fluctuates greatly under low light conditions such as rising sun, sunset, and rainy weather, which cannot always meet the power demand of the system, causing the auxiliary power supply to start and stop repeatedly, which will cause It will cause greater damage to the auxiliary power supply and photovoltaic inverter.

Contents of the invention

Based on this, the present invention provides an auxiliary power supply system for a photovoltaic inverter, which consumes less power and can avoid repeated startup and shutdown of the auxiliary power supply.

In order to realize the purpose of the present invention, the present invention adopts following technical scheme:

A photovoltaic inverter auxiliary power system, characterized in that it includes a control module, a rectifier module connected to the control module, and an auxiliary power module connected to the rectifier module; the control module includes a relay RELAY, and connected to the The starting voltage comparison unit and the timing unit of the relay RELAY; the rectification module includes a rectifier bridge; the AC input terminals of the rectifier bridge are respectively connected to the switch K1 of the relay RELAY and then connected to the grid; the DC output of the rectifier bridge The terminal is connected to the auxiliary power module; the control module is used to control the auxiliary power module to obtain power from the grid when the output power of the photovoltaic inverter is reduced and unstable.

The auxiliary power supply system of the above-mentioned photovoltaic inverter, through the cooperation of the start-up voltage comparison unit and the timing unit in the control module, controls the relay RELAY to be turned on or off, and then controls the connection or cut-off of the power grid and the auxiliary power module, which can avoid the auxiliary power module Start and stop repeatedly to reduce the standby power consumption of the auxiliary power module at night.

In one of the embodiments, the photovoltaic inverter auxiliary power system further includes a starting voltage module, and the starting voltage module is provided with an input terminal V_pv for connecting to photovoltaic power generation components; the starting voltage module is connected to the rectifying module , the starting voltage module is also connected to the auxiliary power module.

In one of the embodiments, the starting voltage module includes resistors R1, R2 and R3, a regulator tube ZD1 and a capacitor C1; one end of the resistor R1 is connected to the input terminal V_pv, and the resistors R1, R2 and R3 are sequentially connected in series and grounded; the voltage regulator tube ZD1 is connected in parallel with the resistor R3; the positive pole of the capacitor C1 is connected to the cathode of the voltage regulator tube ZD1, and the negative pole of the capacitor C1 is grounded.

In one of the embodiments, the control module further includes a transistor Q1, and resistors R4, R5 and R6; the input end of the coil of the relay RELAY is connected to the positive pole of the capacitor C1, and the output end of the coil of the relay RELAY connected to the collector of the triode Q1, the base of the triode Q1 is connected to the output end of the starting voltage comparison unit after being connected to the resistor R4; the base of the triode Q1 is also connected to the resistor R5 and then connected to the The output terminal of the timing unit; the emitter of the triode Q1 is grounded; the output terminal of the starting voltage comparison unit is connected to the resistor R6 and then connected to the timing unit.

In one of the embodiments, the startup voltage comparison unit includes resistors R8, R9, and R10, and an operational amplifier; one end of the resistor R8 is connected to the input terminal V_pv, and the resistors R8, R9, and R10 are connected in series and grounded. The non-inverting input of the operational amplifier is connected between the resistor R9 and the resistor R10; the inverting input of the operational amplifier is connected to a regulator tube ZD2 and then grounded, and the inverting input of the operational amplifier is also connected to the ground. A resistor R11 is connected, and the other end of the resistor R11 is connected with a +12V supply voltage; a resistor R12 is also connected between the output terminal of the operational amplifier and the non-inverting input terminal of the operational amplifier, so that the operational amplifier becomes a hysteretic comparator.

In one embodiment, the timing unit includes resistors _RA , _RB and R13, field effect transistor Q2, capacitors CT and C3, and a timer U1; the resistors _RA , _RB and R13 are connected in series; The opposite ends of the resistance _RA are respectively connected to pin 4 and pin 7 of the timer U1; the opposite ends of the resistance R _B are respectively connected to pin 7 and pin 6 of the timer U1; One end of R13 is connected to the resistor _RB , and the other end is connected to the drain of the field effect transistor Q2; the gate of the field effect transistor Q2 is connected to the resistor R6, and the source of the field effect transistor Q2 is grounded.

In one of the embodiments, pin 4 and pin 8 of the timer U1 are both connected to the reference voltage VCC, pin 2 and pin 6 of the timer U1 are connected to the positive pole of the capacitor CT, and the capacitor CT is The negative pole is grounded; pin 5 of the timer U1 is connected to the positive pole of the capacitor C3, and the negative pole of the capacitor C3 is grounded; pin 1 of the timer U1 is grounded, and pin 3 of the timer U1 is connected to the resistor R5 , to output a timing signal.

In one of the embodiments, the auxiliary power module includes a transformer TX1, a field effect transistor Q3, a power chip U2, a capacitor C4 and a load _RL ; one end of the primary coil of the transformer TX1 is connected to the rectifier bridge BD, and the The one end of the primary coil of the transformer TX1 is also connected to the input terminal V_pv; the other end of the primary coil of the transformer TX1 is connected to the drain of the field effect transistor Q3, the source of the field effect transistor Q3 is grounded, and the field effect transistor Q3 The gate of the power supply chip U2 is connected; the opposite ends of the secondary coil of the transformer TX1 are respectively connected to the opposite ends of the load _RL ; the capacitor C4 is connected in parallel with the load _RL , and the capacitor C4 The positive pole is also connected to the reference voltage VCC, the negative pole of the capacitor C4 is grounded; the power chip U2 is connected to the secondary coil of the transformer TX1.

In one embodiment, a diode D3 is further connected between the primary coil of the transformer TX1 and the input terminal V_pv; a diode D4 is further connected between the secondary coil of the transformer TX1 and the load _RL .

In one of the embodiments, the input end of the coil of the relay RELAY is also connected to a diode D1; the cathode of the diode D1 is connected to the input end of the coil of the relay RELAY, and the anode of the diode D1 is connected to the reference voltage VCC.

Description of drawings

Fig. 1 is a module block diagram of a photovoltaic inverter auxiliary power supply system in a preferred embodiment of the present invention;

Fig. 2 is a circuit diagram of the photovoltaic inverter auxiliary power system shown in Fig. 1;

Fig. 3 is the circuit schematic diagram of the starting voltage comparison unit shown in Fig. 2;

Fig. 4 is the circuit principle diagram of the timing unit shown in Fig. 2;

FIG. 5 is a simplified block diagram of the internal principle of the timer U1 in the timing unit shown in FIG. 4 .

Notes on drawings:

10-starting voltage module, 20-control module, 21-starting voltage comparison unit, 22-timing unit, 23-operational amplifier, 30-rectification module, 40-auxiliary power supply module.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the associated drawings. Preferred embodiments of the invention are shown in the accompanying drawings. However, the present invention can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

It should be noted that when an element is referred to as being “fixed” to another element, it can be directly on the other element or there can also be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or intervening elements may also be present.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention.

Please refer to FIG. 1 to FIG. 5 , which is a photovoltaic inverter auxiliary power system in a preferred embodiment of the present invention, including a starting voltage module 10 , a control module 20 connected to the starting voltage module 10 , a rectifying module 30 connected to the control module 20 , And the auxiliary power supply module 40 connected to the starting voltage module 10 and the rectification module 30 respectively.

The starting voltage module 10 includes resistors R1 , R2 and R3 , a regulator diode ZD1 and a capacitor C1 . The starting voltage module 10 is provided with an input terminal V_pv, which is used to connect to the photovoltaic power generation component and receive the voltage provided by the photovoltaic power generation component. One end of the resistor R1 is connected to the input terminal V_pv, and the resistors R1, R2 and R3 are connected in series in sequence and then grounded. The regulator ZD1 is connected in parallel with the resistor R3, specifically, the cathode of the regulator ZD1 is connected between the resistors R2 and R3, and the anode of the regulator ZD1 is grounded. The capacitor C1 is connected in parallel with the voltage regulator tube ZD1, specifically, the positive electrode of the capacitor C1 is connected to the cathode of the voltage regulator tube ZD1, and the negative electrode of the capacitor C1 is grounded. Further, in this embodiment, the anode of the capacitor C1 is also connected to a +12V power supply voltage.

The control module 20 includes a relay RELAY, a transistor Q1 , resistors R4 , R5 and R6 , a starting voltage comparison unit 21 , and a timing unit 22 . The input terminal of the coil of the relay RELAY is connected to the positive pole of the capacitor C1, the output terminal of the coil of the relay RELAY is connected to the collector of the transistor Q1, the base of the transistor Q1 is connected to the resistor R4 and then connected to the output terminal of the starting voltage comparison unit 21, the base of the transistor Q1 The pole is also connected to the output terminal of the timing unit 22 after connecting the resistor R5; the emitter of the triode Q1 is grounded. In this embodiment, the startup voltage comparison unit 21 is also connected to the timing unit 22 , specifically, the output terminal of the startup voltage comparison unit 21 is connected to the timing unit 22 after being connected to a resistor R6 .

Further, in order to ensure the control stability of the relay RELAY, the input end of the coil of the relay RELAY is also connected to a diode D1, the cathode of the diode D1 is connected to the input end of the coil of the relay RELAY, and the anode of the diode D1 is connected to the reference voltage VCC.

Further, in order to enhance the filtering effect and voltage stability, a capacitor C2 and a resistor R7 are respectively connected in parallel between the base and the emitter of the transistor Q1.

As shown in FIG. 3 , the startup voltage comparison unit 21 includes resistors R8 , R9 and R10 , and an operational amplifier 23 . One end of the resistor R8 is connected to the input terminal V_pv, and the resistors R8, R9 and R10 are connected in series in sequence and then grounded. The non-inverting input terminal of the operational amplifier 23 is connected between the resistor R9 and the resistor R10. The inverting input terminal of the operational amplifier 23 is connected to a regulator transistor ZD2 and then grounded. In this embodiment, the inverting input end of the operational amplifier 23 is also connected to a resistor R11, and the other end of the resistor R11 is connected to a +12V power supply voltage. The output terminal of the operational amplifier 23 is connected to the resistor R4, and the output terminal of the operational amplifier 23 is also connected to the resistor R6. The output level of the operational amplifier 23 enters the timing unit 22 after passing through the resistor R6 to make the timing unit 22 work.

Furthermore, a resistor R12 is also connected between the output terminal of the operational amplifier 23 and the non-inverting input terminal, so that the operational amplifier 23 becomes a hysteresis comparator, which can effectively reduce the repeated restart of the system when the output voltage of the photovoltaic power generation module is at a critical point. The phenomenon.

Further, in this embodiment, the positive power supply end of the operational amplifier 23 is connected to the diode D2 and then connected to the reference voltage VCC, and the negative power supply end of the operational amplifier 23 is grounded. In order to ensure the operation of the operational amplifier 23 is stable, the positive power supply terminal of the operational amplifier 23 is also connected to the +12V power supply voltage.

As shown in FIG. 4 , the working principle diagram of the timing unit 22 . The timing unit 22 includes resistors _RA , _RB and R13, a field effect transistor Q2, capacitors CT and C3, and a timer U1. In this embodiment, the timer U1 is a 555 timer. Resistors R _A , R _B and R13 are connected in series in sequence. The opposite ends of the resistor R _A are respectively connected to pin 4 and pin 7 of the timer U1; the opposite ends of the resistor R _B are respectively connected to the pin 7 and pin 6 of the timer U1; one end of the resistor R13 is connected to the resistor R _B , and the other is One end is connected to the drain of the field effect transistor Q2. The gate of the field effect transistor Q2 is connected to the resistor R6, and receives the output level of the operational amplifier 23, and the source of the field effect transistor Q2 is grounded.

In this embodiment, pin 4 and pin 8 of the timer U1 are both connected to the reference voltage VCC, pin 2 and pin 6 are connected to the positive pole of the capacitor CT, and the negative pole of the capacitor CT is grounded. Pin 5 of the timer U1 is connected to the positive pole of the capacitor C3, and the negative pole of the capacitor C3 is grounded. Pin 1 of timer U1 is grounded, and pin 3 of timer U1 is connected to resistor R5 to output a timing signal.

Further, in this embodiment, a resistor R14 is connected between the gate and the drain of the field effect transistor Q2, which can protect the field effect transistor Q2 from electrostatic breakdown.

The rectification module 30 includes a rectification bridge BD. The two AC input ends of the rectifier bridge BD are respectively connected to the switch K1 of the relay RELAY, and then connected to the grid. The rectifier bridge BD is provided with a DC positive pole and a DC negative pole, the DC positive pole of the rectifier bridge BD is connected to the auxiliary power module 40 , and the DC negative pole of the rectifier bridge BD is grounded.

The auxiliary power module 40 includes a transformer TX1, a field effect transistor Q3, a power chip U2, a capacitor C4 and a load _RL . One end of the primary coil of the transformer TX1 is connected to the DC positive pole of the rectifier bridge BD to obtain power from the grid. The one end of the primary coil of the transformer TX1 is also connected to the input terminal V_pv, specifically, a diode D3 is connected between the one end of the primary coil of the transformer TX1 and the input terminal V_pv. The other end of the primary coil of the transformer TX1 is connected to the drain of the field effect transistor Q3, the source of the field effect transistor Q3 is grounded, and the gate of the field effect transistor Q3 is connected to the power chip U2. The opposite ends of the secondary coil of the transformer TX1 are respectively connected to the opposite ends of the load _RL , and a diode D4 is further connected between the secondary coil of the transformer TX1 and the load RL. The load _RL is also connected in parallel with a capacitor C4, the positive pole of the capacitor C4 is also connected to the reference voltage VCC, and the negative pole of the capacitor C4 is grounded. The power chip U2 is also connected to the secondary coil of the transformer TX1, and the other end of the power chip U2 is grounded. In this embodiment, the voltage for the first start-up of the power chip U2 comes from the voltage provided by the photovoltaic power generation module.

In order to ensure a stable power input to the primary coil of the transformer TX1, the auxiliary power module 40 further includes resistors R15, R16, R17 and capacitors C5, C6. One end of the resistor R15 is connected to one end of the primary coil of the transformer TX1, the resistor R15 is connected in series with the resistor R16 and the resistor R17 in sequence, and the resistor R17 is also grounded. The positive pole of the capacitor C5 is connected to the primary coil of the transformer TX1, and the negative pole of the capacitor C5 is grounded. The positive pole of the capacitor C6 is connected between the resistor R16 and the resistor R17, and the negative pole of the capacitor C6 is grounded. The anode of the capacitor C6 is also connected to the reference voltage VCC.

working principle:

When the power chip U2 starts for the first time, the power chip U2 receives the voltage provided by the photovoltaic power generation module. When the obtained voltage reaches the starting voltage of the power chip U2, the power chip U2 sends out a PWM signal to drive the auxiliary power module 40 to work. The reference voltage VCC provides The voltage is supplied to the power chip U2, and the voltage of the reference voltage VCC ensures stable operation of the auxiliary power module 40 on the one hand, and is supplied to the power chip U2 as a feedback voltage to adjust the duty ratio of the PWM signal.

When the voltage value of the reference voltage VCC supplied to the power chip U2 is lower than the preset value of the reference voltage VCC, the PWM signal of the power chip U2 outputs a high level, driving the field effect transistor Q3 to conduct, at this time, the primary coil of the transformer TX1 The voltage is positive at the top and negative at the bottom, and the transformer TX1 stores energy. Since the primary coil of the transformer TX1 is opposite to the terminal with the same name of the secondary coil, the induced voltage on the secondary coil is negative at the top and positive at the bottom. At this time, the diode D4 is reverse biased, and the energy of the load _RL is provided by the capacitor C4.

When the voltage value of the reference voltage VCC supplied to the power chip U2 is equal to or greater than the preset value of the reference voltage VCC, the PWM signal of the power chip U2 outputs a low level, driving the field effect transistor Q3 to turn off, at this time, the primary coil of the transformer TX1 The excitation current above maintains the original direction, and the excitation current causes the primary coil of the transformer TX1 to induce an upper-negative and lower-positive voltage. At this time, the induced voltage generated by the secondary coil of the transformer TX1 is upper positive and lower negative, so that the diode D4 becomes forward-conducting, and the transformer TX1 sends the stored energy to the load _RL and the capacitor C4.

Thus, the auxiliary power module 40 constitutes a flyback switching power supply.

After the photovoltaic inverter auxiliary power system is officially started, if the voltage provided by the photovoltaic power generation component is lower than the voltage provided by the rectifier module 30, the control module 20 switches the grid connection rectifier module 30 through the relay RELAY, and connects the rectified current to Auxiliary power supply module 40 , grid power is used as the input of auxiliary power supply module 40 . On the contrary, the output voltage of the photovoltaic power generation module is used as the input of the auxiliary power supply module 40 .

The starting voltage comparison unit 21 and the timing unit 22 jointly control the relay RELAY, which has the following logical relationship:

The output of the startup voltage comparison unit 21 The output of timing unit 22 Relay status 1 x turn on x 1 turn on 0 0 turn off

1: Indicates output high level;

0: Indicates output low level;

X: represents 1 or 0.

In this embodiment, a minimum PV input voltage is set, denoted as V_pv1. When the voltage obtained by the photovoltaic inverter reaches V_pv1, the inverter can light up the screen and enter the standby state. In addition, a minimum PV shutdown voltage is also set, which is recorded as V_pv2. When the voltage obtained by the photovoltaic inverter is lower than V_pv2, the inverter will completely power off and shut down.

In this embodiment, the auxiliary power module 40 cannot be started at a voltage lower than V_pv1 or V_pv2 .

There is a situation in the operation of the starting voltage comparison unit 21: when the voltage provided by the photovoltaic power generation module rises from zero to greater than the set minimum PV input voltage V_pv1, the starting voltage comparison unit 21 outputs a high level for turning on the relay RELAY , the switch K1 of the relay RELAY is turned on, and the power grid is switched to the auxiliary power module 40 for power supply. As long as the relay RELAY is turned on, the working state of the auxiliary power module 40 will not be affected by the photovoltaic power generation component, that is, it will not cause repeated restarts due to insufficient voltage provided by the photovoltaic power generation component. In the practical application of photovoltaic inverters, this process corresponds to the process of rising the sun in the morning.

There is also another situation in the operation of the starting voltage comparison unit 21: when the voltage provided by the photovoltaic power generation module drops to the minimum PV shutdown voltage V_pv2, the starting voltage comparison unit 21 outputs a low level, and the timing unit 22 starts timing at this time, setting After a certain time, the timing unit 22 outputs a low level, and the relay RELAY is turned off, that is, the switch K1 of the relay RELAY is turned off, effectively cutting off the power supply of the ground grid to the auxiliary power module 40 . In the practical application of photovoltaic inverters, this process corresponds to the process of sunset in the evening.

Specifically, as shown in Figure 4, when the starting voltage comparison unit 21 outputs a high level, the timing loop in the timing unit 22 does not work, that is, the resistors RA, RB and capacitor CT do not work, and the timing unit 21 outputs a continuous high level. The level signal keeps the relay RELAY turned on, the switch K1 of the relay RELAY is kept in the pull-in state, and the auxiliary power module 40 is connected to the power grid. When the starting voltage comparison unit 21 outputs a low level, the timing loop in the timing unit 22 works, that is, the resistors _RA , _RB and capacitor CT start timing. After the set time, the timing unit 22 outputs a low level signal, so that the relay The RELAY is turned off, the switch K1 of the relay RELAY is turned off, and the connection between the auxiliary power supply module 40 and the grid is cut off.

As shown in Figure 5, it is a simplified block diagram of the internal principle of the timer U1.

When the voltage provided by the photovoltaic power generation module is greater than or equal to the minimum PV input voltage V_pv1, the starting voltage comparison unit 21 outputs a high level, and the relay RELAY is turned on. Since the timer U1 has just been powered on, the voltage on pin 2 of the timer U1 is zero, and the lower comparator C2 outputs a high level, which makes the flip-flop RS set, Output low level, then timer U1 outputs high level. At this time, because the starting voltage comparison unit 21 outputs a high level, the field effect transistor Q2 is turned on. Resistor R13 only acts as a current limiter when capacitor CT is discharged, and its resistance value is very small. The voltage on capacitor CT will always be clamped to 0V by FET Q2, and resistors _RA , _RB and capacitor CT will not work.

When the voltage provided by the photovoltaic power generation module is lower than the minimum PV shutdown voltage V_pv2, the starting voltage comparison unit ₂₁ outputs _a low level. to charge. When the voltage value of capacitor CT exceeds , the lower comparator C2 outputs a low level, and the flip-flop RS still maintains the original state. When the voltage value of capacitor CT exceeds , the upper comparator C1 outputs a high level, and the flip-flop RS is reset, making Output high level, then timer U1 outputs low level. The discharge tube T1 inside the timer U1 is turned on, and the capacitor CT is discharged through the resistor _RB . At this time, the voltage comparison unit 21 and the timing unit 22 both output low level, therefore, the relay RELAY is turned off, that is, the switch K1 of the relay RELAY is turned off, and the power supply of the grid to the auxiliary power module 40 is cut off to ensure that there is no photovoltaic power generation. During the night when the components are powered, the standby power consumption of the auxiliary power supply is close to zero.

In the work of the timing unit 22, counting from the cut-off of the field effect transistor Q2, until the timing time when the timing unit 22 outputs a low level, according to the charging formula of the capacitor: in

V ₀ is the initial voltage value on the capacitor CT, here is 0V;

V _u is the limit charging voltage value on the capacitor CT, which is equal to the voltage value of the reference voltage VCC;

V _t is the voltage value on the capacitor CT at time t, where

R = R _A + R _B .

Therefore, according to the formula, t=( _RA + _RB )C·ln3 can be obtained, and the timing time Td=t. Further, in practical applications, the required timing time Td can be set by setting the resistance values of the resistor _RA and the resistor _RB respectively.

The above photovoltaic inverter auxiliary power system, through the cooperation of the starting voltage comparison unit 21 and the timing unit 22 in the control module 20, controls the relay RELAY to be turned on or off, and then controls the connection or cutoff of the power grid and the auxiliary power module 40. Avoid repeated startup and shutdown of the auxiliary power module 40, and reduce the standby power consumption of the auxiliary power module 40 at night.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A photovoltaic inverter auxiliary power supply system, characterized in that it comprises a control module, a rectifier module connected to the control module, and an auxiliary power module connected to the rectifier module; the control module includes a relay RELAY, and respectively Connect the starting voltage comparison unit and the timing unit of the relay RELAY; the rectifier module includes a rectifier bridge; the AC input terminals of the rectifier bridge are respectively connected to the switch K1 of the relay RELAY and then connected to the grid; the rectifier bridge The DC output terminal is connected to the auxiliary power module; the control module is used to control the auxiliary power module to obtain power from the grid when the output power of the photovoltaic inverter is reduced and unstable. 2. The photovoltaic inverter auxiliary power supply system according to claim 1, characterized in that, it also includes a starting voltage module, the starting voltage module is provided with an input terminal V_pv for connecting photovoltaic power generation components; the starting voltage module The rectifier module is connected, and the starting voltage module is also connected with the auxiliary power module. 3. The photovoltaic inverter auxiliary power system according to claim 2, wherein the starting voltage module includes resistors R1, R2 and R3, voltage regulator tube ZD1 and capacitor C1; one end of the resistor R1 is connected to the The input terminal V_pv, the resistors R1, R2 and R3 are sequentially connected in series and then grounded; the voltage regulator tube ZD1 is connected in parallel with the resistor R3; the positive pole of the capacitor C1 is connected to the cathode of the voltage regulator tube ZD1, and the capacitor The negative terminal of C1 is grounded. 4. The photovoltaic inverter auxiliary power system according to claim 3, wherein the control module further comprises a triode Q1, and resistors R4, R5 and R6; the input end of the coil of the relay RELAY is connected to the The positive pole of the capacitor C1, the output end of the coil of the relay RELAY is connected to the collector of the triode Q1, the base of the triode Q1 is connected to the output end of the starting voltage comparison unit after the resistor R4 is connected; the triode The base of Q1 is also connected to the resistor R5 and then connected to the output terminal of the timing unit; the emitter of the triode Q1 is grounded; the output terminal of the starting voltage comparison unit is connected to the resistor R6 and then connected to the timing unit. 5. The photovoltaic inverter auxiliary power system according to claim 4, wherein the starting voltage comparison unit includes resistors R8, R9 and R10, and an operational amplifier; one end of the resistor R8 is connected to the input terminal V_pv, the resistors R8, R9 and R10 are connected in series in sequence and grounded; the non-inverting input terminal of the operational amplifier is connected between the resistor R9 and the resistor R10; the inverting input terminal of the operational amplifier is connected to a regulator tube After ZD2 is grounded, the inverting input terminal of the operational amplifier is also connected to a resistor R11, and the other end of the resistor R11 is connected to a +12V supply voltage; the output terminal of the operational amplifier is connected to the positive phase input of the operational amplifier. A resistor R12 is also connected between the terminals, so that the operational amplifier becomes a hysteresis comparator. 6. The photovoltaic inverter auxiliary power system according to claim 5, wherein the timing unit includes resistors _RA , _RB and R13, field effect transistor Q2, capacitors CT and C3, and a timer U1; The resistors R _A , R _B and R13 are connected in series in sequence; the opposite ends of the resistor R _A are respectively connected to pin 4 and pin 7 of the timer U1; the opposite ends of the resistor R _B are respectively connected to the Pin 7 and pin 6 of the timer U1; one end of the resistor R13 is connected to the resistor _RB , and the other end is connected to the drain of the field effect transistor Q2; the gate of the field effect transistor Q2 is connected to the resistor R6, the source of the field effect transistor Q2 is grounded. 7. The photovoltaic inverter auxiliary power system according to claim 6, wherein pins 4 and 8 of the timer U1 are connected to the reference voltage VCC, and pins 2 and 6 of the timer U1 are connected to the reference voltage VCC. The pin is connected to the positive pole of the capacitor CT, and the negative pole of the capacitor CT is grounded; the 5 pin of the timer U1 is connected to the positive pole of the capacitor C3, and the negative pole of the capacitor C3 is grounded; the 1 pin of the timer U1 is grounded , pin 3 of the timer U1 is connected to the resistor R5 to output a timing signal. 8. The photovoltaic inverter auxiliary power system according to claim 1, wherein the auxiliary power module includes a transformer TX1, a field effect transistor Q3, a power chip U2, a capacitor C4 and a load _RL ; the transformer TX1 One end of the primary coil of the transformer TX1 is connected to the rectifier bridge BD, and this end of the primary coil of the transformer TX1 is also connected to the input terminal V_pv; the other end of the primary coil of the transformer TX1 is connected to the drain of the field effect transistor Q3 , the source of the field effect transistor Q3 is grounded, and the gate of the field effect transistor Q3 is connected to the power chip U2; the opposite ends of the secondary coil of the transformer TX1 are respectively connected to the opposite ends of the load _RL ; the capacitor C4 is connected in parallel with the load _RL , the anode of the capacitor C4 is also connected to the reference voltage VCC, and the cathode of the capacitor C4 is grounded; the power chip U2 is connected to the secondary coil of the transformer TX1. 9. The photovoltaic inverter auxiliary power system according to claim 8, wherein a diode D3 is also connected between the primary coil of the transformer TX1 and the input terminal V_pv; the secondary coil of the transformer TX1 A diode D4 is also connected between the load _RL . 10. The photovoltaic inverter auxiliary power system according to claim 1, characterized in that, the input end of the coil of the relay RELAY is also connected to a diode D1; the negative pole of the diode D1 is connected to the coil of the relay RELAY At the input end, the anode of the diode D1 is connected to the reference voltage VCC.