CN102694471A - Auxiliary power supply system for photovoltaic inverter - Google Patents

Abstract

The invention provides a photovoltaic inverter auxiliary power supply system, which is characterized in that it includes a starting circuit unit, the input end of the starting circuit unit is connected to the DC bus voltage of the inverter, and the DC bus voltage of the inverter is also connected to the power supply In the conversion circuit, the output end of the starting circuit unit is connected to the current-limiting delay trigger circuit unit, the enable end of the power control unit is connected to the control unit, and the control unit enables the power control unit according to the second voltage control signal generated by the back-end detection and protection circuit unit , the power control unit is connected with the bootstrap circuit unit, and when the power control unit can generate a stable DC voltage, the bootstrap circuit unit works under the control of the first voltage control signal generated by the back-end detection and protection circuit unit. The invention has the advantages of: adopting a double closed-loop feedback control system to ensure the stability of the output voltage of the auxiliary power supply; adopting the logic combination of the control signal and the reset circuit of the controller to ensure the stable operation of the control.

Description

Photovoltaic inverter auxiliary power system

technical field

The invention relates to a photovoltaic inverter auxiliary power supply system, which belongs to the technical field of solar photovoltaic power generation.

Background technique

The auxiliary power supply of the photovoltaic inverter is quite different from the common switching power supply. Usually, the power of ordinary switching power supply is that the AC power of the grid is transformed and rectified, and then connected to its input terminal, so the voltage of switching power supply is relatively stable. However, in the photovoltaic grid-connected system, the direct current output from the solar panel is directly connected to the input terminal of the auxiliary power supply without going through the rectification link; in addition, with the change of the sunlight intensity and the ambient temperature, the voltage at the output terminal of the photovoltaic array will appear larger. fluctuations. Therefore, the input terminal voltage of the auxiliary power supply of the photovoltaic grid-connected inverter is unstable, which requires a wider operating voltage range of the auxiliary power supply system of the solar inverter. However, in practical applications, it is often encountered that due to the fluctuation of the output power of the photovoltaic array, the power demand of the system cannot be met all the time, causing the auxiliary power supply to start and stop repeatedly; or although the auxiliary power supply can be started, it cannot reach the required wide input voltage range. Problem with the auxiliary power supply working properly.

Contents of the invention

The purpose of the present invention is to provide an auxiliary power supply system for solar photovoltaic inverters with settable start voltage, avoiding repeated start and stop, low power consumption and high efficiency.

In order to achieve the above object, the technical solution of the present invention is to provide a photovoltaic inverter auxiliary power supply system, which is characterized in that it includes a starting circuit unit, the input end of the starting circuit unit is connected to the DC bus voltage of the inverter, and the inverter The DC bus voltage of the inverter is also connected to the power conversion circuit. The power conversion circuit includes a flyback transformer and a power control unit. The output terminal of the start-up circuit unit is connected to the current-limiting delay trigger circuit unit. The circuit unit provides the turn-on threshold voltage for the power control unit to enable the flyback transformer to work, the enabling terminal of the power control unit is connected to the control unit, and the control unit enables the power control unit according to the second voltage control signal generated by the back-end detection and protection circuit unit, The power supply control unit is connected with the bootstrap circuit unit. When the power supply control unit can generate a stable DC voltage, the bootstrap circuit unit works under the control of the first voltage control signal generated by the back-end detection and protection circuit unit, and the bootstrap circuit unit The current-limiting delay trigger circuit unit is controlled to provide the working voltage V _cc for the power supply control unit, and at the same time, the bootstrap circuit unit shuts down the start-up circuit unit, thereby completing the start-up process.

Preferably, the starting circuit unit includes a first zener diode, the cathode of the first zener diode is connected to the DC bus voltage of the inverter, and the anode of the first zener diode is respectively connected to the drain of the first resistor and the MOSFET tube. The poles are connected, the first resistor is connected in series with the second resistor and the third resistor in turn, the third resistor is connected to the cathode of the third Zener diode, the anode of the third Zener diode is connected to the anode of the second diode, and the second diode The cathode of the first MOSFET is connected to the bootstrap circuit unit, the source of the first MOSFET is connected to the fourth resistor, the fourth resistor is connected to the bootstrap circuit unit, and the gate of the first MOSFET is connected to the collector of the first triode , the base of the first transistor is connected to the fifth resistor, the fifth resistor is connected to the bootstrap circuit unit, the emitter of the first transistor is connected to the cathode of the fourth Zener diode, and the anode of the fourth Zener diode Grounded, the starting voltage _U0 is given by the base of the first triode through the fifth resistor, the sum of the voltage stabilization value of the first Zener diode and the third Zener diode and the starting voltage _U0 is the starting circuit unit The minimum value of the DC bus voltage, that is, when the DC bus voltage of the inverter is higher than the minimum value, the starting circuit unit will start to work.

Preferably, the power conversion circuit includes a flyback transformer, one end of the primary coil of the flyback transformer is connected to the DC bus voltage, and the other end is connected to the drain of the second MOSFET, and the voltage output from the secondary coil of the flyback transformer is output voltage V _out , the voltage output terminal of the secondary coil of the flyback transformer is also connected back to the stabilized voltage input terminal of the power control unit, the output terminal of the power control unit is connected to the gate of the second MOSFET tube, and the second MOSFET tube The sources of each are grounded and connected to the control unit through an eighteenth resistor.

Preferably, the control unit includes a fifth triode, the base of the fifth triode is connected to the second voltage control signal through a tenth resistor, and the fifth triode is connected between the emitter and the base of the fifth triode. connected to the eleventh resistor, the emitter of the fifth transistor is connected to the reference voltage V _ref , the collector of the fifth transistor is respectively connected to the enable terminal of the power control unit and the source of the second MOSFET.

Preferably, the current-limiting delay trigger circuit unit includes a current-limiting circuit and a first capacitor, and the startup circuit unit charges the first capacitor through the current-limiting circuit. The power supply control unit provides the turn-on threshold voltage. After the bootstrap circuit unit is started, the bootstrap circuit unit provides the power control unit with an operating voltage V through the voltage dividing resistor included in the current-limiting delay trigger circuit unit _cc .

Preferably, the bootstrap circuit unit includes a fourth transistor, the collector of the fourth transistor is respectively connected to the anodes of the sixth diode and the fifth diode, and the sixth diode and the fifth diode The cathode of the tube is respectively connected to the starting circuit unit and the current-limiting delay trigger circuit unit, the emitter of the fourth triode is connected to the power conversion circuit, and the base of the fourth triode is connected to the The first voltage control signal.

The advantages of the present invention are: the use of a double closed-loop feedback control system ensures the stability of the output voltage of the auxiliary power supply; the logic combination of the control signal and the controller reset circuit ensures the stable operation of the control and prevents the control system from being unstable due to unstable power supply Create disorder. The further advantages of the present invention are: 1. The start-up circuit composed of reverse diodes can set the start-up voltage value and start-up power of the auxiliary power supply system, thereby preventing the auxiliary power supply from being turned on when the light is too weak to protect the inverter; The circuit only works during the start-up process. After the power supply is stable, the start-up circuit will automatically shut down; 2. The auxiliary power system has a wide working range, no loss in the system, and extremely low power consumption, which is especially suitable for photovoltaic inverter systems.

Description of drawings

Fig. 1 is a schematic diagram of the location of the auxiliary power supply system provided by the present invention in the entire photovoltaic inverter system;

Fig. 2 is the control flow diagram of the photovoltaic inverter auxiliary power supply system provided by the present invention;

Figure 3 is a bootstrap circuit diagram for starting the photovoltaic inverter;

Fig. 4 is the auxiliary power conversion and control circuit diagram of the photovoltaic inverter.

Detailed ways

In order to make the present invention more comprehensible, a preferred embodiment is described in detail below with accompanying drawings.

Aiming at the requirements of the photovoltaic inverter auxiliary power supply, the present invention designs a solar photovoltaic inverter auxiliary power supply system that can realize bootstrapping after startup, avoid repeated start and stop, low power consumption and high efficiency. The position of the system in the photovoltaic inverter system is shown in Figure 1. One end is connected to the DC bus voltage of the inverter, and the other end is connected to the detection and protection circuit unit to output the required power supply voltage for each part of the inverter. Referring to FIG. 3 and FIG. 3 , the present invention specifically includes five circuit units, which are starting circuit unit 1 , current-limiting delay trigger circuit unit 2 , bootstrap circuit unit 3 , power conversion circuit unit 4 and control circuit unit 5 . The input end of the starting circuit unit 1 is connected to the DC bus voltage of the inverter, and the DC bus voltage of the inverter is also connected to the power conversion circuit 4. The power conversion circuit 4 includes a flyback transformer T1 and a power control unit, and the starting circuit unit 1 The output end is connected to the current-limiting delay trigger circuit unit 2. During the start-up process, the current-limiting delay trigger circuit unit 2 provides the power supply control unit with the turn-on threshold voltage to make the flyback transformer T1 work. The enabling terminal CS of the power supply control unit Connect the control unit 5, the control unit 5 enables the power control unit according to the second voltage control signal K2 generated by the back-end detection protection circuit unit, the power control unit is connected with the bootstrap circuit unit 3, when the power control unit can generate a stable DC voltage Finally, the bootstrap circuit unit 3 works under the control of the first voltage control signal K1 generated by the back-end detection and protection circuit unit, and the bootstrap circuit unit 3 controls the current-limiting delay trigger circuit unit 2 to provide the power supply control unit with an operating voltage V _cc , at the same time, the bootstrap circuit unit 3 turns off the startup circuit unit 1, thereby completing the startup process.

The circuit of the specific embodiment of the auxiliary power supply system is as shown in Fig. 3 and Fig. 4 . In addition to detecting the bus voltage in real time, this circuit can also turn on the starting circuit unit 1, the current-limiting delay trigger circuit unit 2, the bootstrap circuit unit 3, and the power conversion circuit unit 4 of the auxiliary power system sequentially according to the set voltage threshold. , and can prevent the auxiliary power supply from starting and stopping repeatedly when the bus voltage drops. The specific instructions are as follows:

The starting circuit unit 1 includes a first voltage stabilizing diode D1, the cathode of the first voltage stabilizing diode D1 is connected to the DC bus voltage of the inverter, and the anode of the first voltage stabilizing diode D1 is connected to the first resistor R1 and the MOSFET tube M1 respectively. The drains are connected, the first resistor R1 is connected in series with the second resistor R2 and the third resistor R3 in sequence, the third resistor R3 is connected to the cathode of the third Zener diode D3, and the anode of the third Zener diode D3 is connected to the second diode D2 The anode of the second diode D2 is connected to the cathode of the sixth diode D6 of the bootstrap circuit unit 3, the source of the first MOSFET tube M1 is connected to the fourth resistor R4, and the fourth resistor R4 is connected to the bootstrap circuit unit 3, the cathode of the sixth diode D6 is connected, the gate of the first MOSFET M1 is connected to the collector of the first transistor Q1, the base of the first transistor Q1 is connected to the fifth resistor R5, and the fifth resistor R5 is connected to the bootstrap circuit unit 3, the emitter of the first triode Q1 is connected to the cathode of the fourth Zener diode D4, the anode of the fourth Zener diode D4 is grounded, and the base of the first transistor Q1 passes through The fifth resistor R5 provides the start-up voltage U ₀ , which is determined by the fourth zener diode D4, and the sum of the regulated value of the first zener diode D1 and _the third zener diode D3 and the start-up voltage U ₀ is the turn-on The minimum value of the DC bus voltage of the starting circuit unit, that is, when the DC bus voltage value of the inverter is higher than the minimum value, the starting circuit unit starts to work.

The current limiting trigger circuit unit 2 includes a current limiting circuit composed of a second transistor Q2, a third transistor Q3, a sixth resistor R6 and a seventh resistor R7. In the process that the starting circuit unit 1 generates the starting voltage _U0 which is about the voltage reference value, the current limiting circuit composed of the sixth resistor R6 and the second triode Q2 and the third triode Q3 as the main components is used for the first A capacitor C1 is charged, and when the voltage of the first capacitor C1 reaches the turn-on threshold voltage of the power control chip in the power control unit, the power control chip triggers the flyback transformer T1 to work. The function of the current limiting circuit is to prevent the charging current of the first capacitor C1 from being too large, so that the starting circuit is overloaded.

As shown in FIG. 4 , the power conversion circuit 4 includes a flyback transformer T1, and a nineteenth resistor R19, a sixth capacitor C6, a tenth zener diode D10, and a ninth zener diode are connected to the primary coil of the flyback transformer T1. D9, one end of the primary coil is connected to the DC bus voltage, and the other end is connected to the drain of the second MOSFET tube M2. The output voltage V _out is produced by the voltage output terminal of the secondary coil of the flyback transformer T1, and the seventh diode D7, the eighth diode D8, the first fuse F1, the second The fuse F2, the fourth capacitor C4, the fifth capacitor C5, the twentieth resistor R20 and the twenty-first resistor R21. The voltage output terminal of the secondary coil of the flyback transformer T1 is also connected back to the voltage stabilizing input terminal FB of the power supply control unit. Among them, the power control unit adopts the power control chip UCC2801D. The voltage output terminal of the secondary coil is divided by the voltage divider circuit composed of the twelfth resistor R12 and the thirteenth resistor R13, and then passes through the fourteenth resistor R14, the fifteenth resistor R15, the second capacitor C2 and the third capacitor. The capacitor C3 is connected to the constant voltage input terminal FB of the power control chip UCC2801D. The output terminal OUT of the power control chip UCC2801D is connected to a voltage divider circuit composed of the sixteenth resistor R16 and the seventeenth resistor R17, and the gate of the second MOSFET M2 is connected to the seventeenth resistor R17. The source of the second MOSFET M2 is grounded and connected to the control unit 5 through the eighteenth resistor R18 respectively.

The control unit 5 includes a fifth transistor Q5, the base of the fifth transistor Q5 is connected to the second voltage control signal K2 through a tenth resistor R10, and the emitter and the base of the fifth transistor Q5 are connected across The eleventh resistor R11, the emitter of the fifth transistor Q5 is connected to the reference voltage V _ref , the collector of the fifth transistor Q5 is respectively connected to the enabling terminal CS of the power control chip UCC2801D and the source of the second MOSFET M2 .

The bootstrap circuit unit 3 includes a fourth transistor Q4, the collector of the fourth transistor Q4 is respectively connected to the anodes of the sixth diode D6 and the fifth diode D5, and the sixth diode D6 and the fifth and second diodes are respectively connected to each other. The cathode of the pole tube D5 is respectively connected to the start-up circuit unit 1 and the current-limiting delay trigger circuit unit 2, the emitter of the fourth triode Q4 is connected to the power conversion circuit 4, and the base of the fourth triode Q4 The pole is connected to the first voltage control signal K1 through the ninth resistor R9.

In the auxiliary power supply system provided by the present invention, the first voltage control signal K1 generated by the back-end detection and protection circuit unit is connected to the bootstrap circuit unit 3 to form a closed-loop feedback. At the same time, the second voltage control signal K2 signal generated by the detection and protection circuit unit Connecting to the power conversion circuit unit 4 constitutes a closed-loop feedback.

The control flow of the auxiliary power supply system of the present invention is shown in Figure 2, where it needs to be explained: 1. The second voltage control signal K2 is unstable, making the first voltage control signal K1 unstable, and the auxiliary power supply cannot work normally; 2. The second After the voltage control signal K2 is stable, the auxiliary power supply can be turned on, and the power supply is bootstrapped within the voltage setting range, so that the auxiliary power supply chip can work normally.

When the DC bus voltage of the inverter is greater than the minimum value of the DC bus voltage for starting the starting circuit unit, the starting circuit unit 1 starts and outputs the starting voltage U ₀ , and at the same time, the second voltage control signal K2 will be placed at a high level to enable The power control chip UCC2801D, otherwise, the second voltage control signal K2 is always kept at a low level. The first capacitor C1 is charged by the start-up voltage _U0 . When the first capacitor C1 is fully charged, the opening threshold voltage is provided through the working power port Vcc of the power control chip UCC2801D, and the power control chip UCC2801D starts to work. The flyback transformer T1 is controlled by the power control chip UCC2801D to generate a DC voltage, and the DC voltage is fed back to the stabilized input terminal FB of the power control chip UCC2801D. After being regulated by the power control chip UCC2801D, a stable DC voltage is output. It is judged whether the stable direct current voltage is stable, and if it is stable, the first voltage control signal K1 is set at a high level to turn on the bootstrap circuit unit 3 , and the first voltage control signal K1 has been in a low level state before this. The bootstrap circuit unit 3 applies the stable DC voltage to the anodes of the fifth diode D5 and the sixth diode D6, and the fifth diode D5 provides the working voltage V _cc for the power control chip UCC2801D through the eighth resistor R8 , so that the power control chip UCC2801D can output a PWM signal through the output terminal OUT, so that the flyback transformer T1 forms voltages of different potentials to supply power to various parts of the solar inverter. At the same time, the sixth diode D6 forcibly pulls up the collector potential of the first transistor Q1, making the first transistor Q1 saturated and conducting, and then pulls down the gate potential of the first MOSFET M1 to about the voltage reference value, the first MOSFET M1 is turned off, so that the startup circuit unit 1 is turned off, and the startup process of the auxiliary power supply ends.

Claims (6)

1. A photovoltaic inverter auxiliary power supply system, characterized in that: comprising a starting circuit unit (1), the input end of the starting circuit unit (1) is connected with the inverter DC bus voltage, and the inverter DC bus voltage The voltage is also connected to the power conversion circuit (4), the power conversion circuit (4) includes a flyback transformer (T1) and a power control unit, and the output end of the starting circuit unit (1) is connected to the current-limiting delay trigger circuit unit (2). During the start-up process, the current-limiting delay trigger circuit unit (2) provides the power supply control unit with the turn-on threshold voltage to make the flyback transformer (T1) work, and the enabling terminal (CS) of the power supply control unit is connected to the control unit (5), The control unit (5) enables the power control unit according to the second voltage control signal (K2) generated by the back-end detection and protection circuit unit, and the power control unit is connected to the bootstrap circuit unit (3). When the power control unit can generate a stable DC After the voltage is applied, the bootstrap circuit unit (3) works under the control of the first voltage control signal (K1) generated by the back-end detection and protection circuit unit, and the current-limiting delay trigger circuit unit (2) is controlled by the bootstrap circuit unit (3). ) provides the working voltage V _cc for the power control unit, and at the same time, the bootstrap circuit unit (3) shuts down the startup circuit unit (1), thereby completing the startup process. 2. A photovoltaic inverter auxiliary power supply system as claimed in claim 1, characterized in that: the starting circuit unit (1) includes a first Zener diode (D1), the first Zener diode (D1) The cathode is connected to the DC bus voltage of the inverter, the anode of the first zener diode (D1) is respectively connected to the first resistor (R1) and the drain of the MOSFET tube (M1), and the first resistor (R1) is connected in series with the first Two resistors (R2) and a third resistor (R3), the third resistor (R3) is connected to the cathode of the third Zener diode (D3), and the anode of the third Zener diode (D3) is connected to the second diode (D2 ), the cathode of the second diode (D2) is connected to the bootstrap circuit unit (3), the source of the first MOSFET (M1) is connected to the fourth resistor (R4), and the fourth resistor (R4) is connected to The bootstrap circuit unit (3) is connected, the gate of the first MOSFET (M1) is connected to the collector of the first transistor (Q1), and the base of the first transistor (Q1) is connected to the fifth resistor ( R5) is connected, the fifth resistor (R5) is connected to the bootstrap circuit unit (3), the emitter of the first transistor (Q1) is connected to the cathode of the fourth Zener diode (D4), and the fourth Zener diode ( The anode of D4) is grounded, and the base of the first triode (Q1) provides the start-up voltage U ₀ through the fifth resistor (R5), and the first voltage regulator diode (D1) and the third voltage regulator diode (D3) The sum of the stabilized voltage value and the start-up voltage U ₀ is the minimum value of the DC bus voltage for starting the start-up circuit unit, that is, the start-up circuit unit starts to work only when the DC bus voltage value of the inverter is higher than the minimum value. 3. A photovoltaic inverter auxiliary power system as claimed in claim 1, characterized in that: said power conversion circuit (4) comprises a flyback transformer (T1), and one end of the primary coil of the flyback transformer (T1) Connect the DC bus voltage, the other end is connected to the drain of the second MOSFET tube (M2), the output voltage V _out is produced by the voltage output terminal of the secondary coil of the flyback transformer (T1), and the output voltage V out of the flyback transformer (T1) The voltage output terminal of the secondary coil is also connected back to the stabilized voltage input terminal (FB) of the power control unit, the output terminal (OUT) of the power control unit is connected to the gate of the first MOSFET (M2), and the gate of the second MOSFET (M2) The sources are respectively grounded and connected to the control unit (5) through the eighteenth resistor (R18). 4. A photovoltaic inverter auxiliary power system as claimed in claim 3, characterized in that: said control unit (5) includes a fifth triode (Q5), the base of the fifth triode (Q5) The pole is connected to the second voltage control signal (K2) through the tenth resistor (R10), and the eleventh resistor (R11) is connected between the emitter and the base of the fifth triode (Q5). The emitter of the transistor (Q5) is connected to the reference voltage V _ref , and the collector of the fifth triode (Q5) is respectively connected to the enabling terminal (CS) of the power control unit and the source of the MOSFET (M2). pole. 5. A photovoltaic inverter auxiliary power system as claimed in claim 1, characterized in that: the current-limiting delay trigger circuit unit (2) includes a current-limiting circuit and a first capacitor (C1), and the starting The circuit unit (1) charges the first capacitor (C1) through the current limiting circuit. In the start-up phase, the charged first capacitor (C1) provides the turn-on threshold voltage for the power control unit. During the bootstrap After the circuit unit (3) is started, the bootstrap circuit unit (3) provides the power supply control unit with an operating voltage V _cc through the voltage dividing resistor included in the current-limiting delay trigger circuit unit (2). 6. A photovoltaic inverter auxiliary power supply system as claimed in claim 1, characterized in that: said bootstrap circuit unit (3) includes a fourth triode (Q4), a fourth triode (Q4) The collectors of the collectors are respectively connected to the anodes of the sixth diode (D6) and the fifth diode (D5), and the cathodes of the sixth diode (D6) and the fifth diode (D5) are respectively connected to the starting circuit unit (1) and the current-limiting delay trigger circuit unit (2), the emitter of the fourth triode (Q4) is connected to the power conversion circuit (4), and the base of the fourth triode (Q4) The first voltage control signal (K1) is connected through a ninth resistor (R9).

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