A photovoltaic shutdown PLC drive circuit and control method thereof

Abstract

The present invention discloses a photovoltaic shutdown PLC drive circuit and a control method thereof, comprising a photovoltaic module, an input capacitor C1, a switch tube Q1, a freewheeling diode D1, a first output resistor R1, an output capacitor C2, a second output resistor R2, a PLC signal acquisition circuit, a first output terminal, and a second output terminal; the PLC signal acquisition circuit comprises a signal acquisition inductor L1, a signal acquisition resistor R2, and a signal acquisition capacitor C3; the voltage signal of the PLC signal acquisition circuit is connected to the gate of the switch tube Q1 after passing through a PLC signal amplification and processing circuit module and a signal drive switch circuit; the freewheeling diode D1 has its cathode connected to the first output terminal and its anode connected to the source of the switch tube Q1; the output capacitor C2 is connected in series with the first output resistor R1 and then connected in parallel with the freewheeling diode D1. The present invention not only meets the safety requirements of rapid shutdown, but also has high reliability, fast response speed, low cost, and high efficiency.

Description

Technical Field

[0001] The present invention relates to a photovoltaic drive circuit and a control method thereof, and in particular to a photovoltaic circuit breaker PLC drive circuit and a control method thereof. Background Art

[0002] Rapid shutdown is a photovoltaic power plant safety protection concept introduced from the United States. It was developed to protect firefighters and photovoltaic power plant installers and maintenance personnel. Because a photovoltaic power plant has a high DC voltage on its DC side, which remains constant as long as the sun is shining, firefighters are unable to extinguish the fire until the entire plant is completely destroyed.

[0003] Therefore, the US National Electrical Code (NEC) 2014 and NEC 2017 both set clear requirements for rapid DC shutdown on PV power plants. These requirements will officially take effect on January 1, 2019. The NEC 2017 stipulates: "Outside of a string, if the controller is installed within 0.3 meters of the array and more than 1 meter from the access point, after rapid shutdown is activated, the system voltage must drop to 30V within 30 seconds; within a string, it must drop to 80V within 30 seconds to facilitate safety and rescue measures." Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a photovoltaic shutdown PLC drive circuit and a control method thereof, which can meet the rapid shutdown safety requirements and ensure the safety and reliability of the system.

[0005] The technical solution adopted by the present invention to solve the above technical problems is to provide a photovoltaic shutdown PLC driving circuit, including a photovoltaic component, an input capacitor C1, a switch tube Q1, a freewheeling diode D1, a first output resistor R1, an output capacitor C2, a second output resistor R2, a PLC signal acquisition circuit, a first output terminal and a second output terminal; the PLC signal acquisition circuit includes a signal acquisition inductor L1, a signal acquisition resistor R2 and a signal acquisition capacitor C3, the signal acquisition resistor R2 and the signal acquisition capacitor C3 are connected in series and then connected in parallel with the signal acquisition inductor L1; the voltage signal of the PLC signal acquisition circuit is passed through The PLC signal amplification and processing circuit module and the signal drive switching circuit are connected to the gate of the switch tube Q1; the input capacitor C1 is connected in parallel with the photovoltaic component, the positive electrode of the photovoltaic component is connected to the first output terminal, the negative electrode of the photovoltaic component is connected to the drain of the switch tube Q1, the source of the switch tube Q1 is connected to one end of the signal acquisition inductor L1, and the other end of the signal acquisition inductor L1 is connected to the second output terminal; the cathode of the freewheeling diode D1 is connected to the first output terminal, the anode of the freewheeling diode D1 is connected to the source of the switch tube Q1, and the output capacitor C2 is connected in series with the first output resistor R1 and then connected in parallel with the freewheeling diode D1.

[0006] Furthermore, the input end of the PLC signal amplification and processing circuit module is the voltage signals PLC1 and PLC2 of the PLC signal acquisition circuit, and the output end of the PLC signal amplification and processing circuit module is connected to the signal amplification resistor R3; the signal amplification resistor R3 is connected in series with the capacitor C4, the inductor L2, the inductor L3 and the capacitor C6, and the other end of the capacitor C6 is grounded. The two ends of the inductor L3 are connected in parallel with the amplification processing capacitor C5, and the voltage signal at the connection point between the inductor L2 and the inductor L3 is the output signal PLC_AD.

[0007] Furthermore, the capacitor C4, the inductor L2, the inductor L3, the capacitor C4, the capacitor C6 and the capacitor C5 form a bandpass filter, and the center frequency of the bandpass filter is 100KHZ to 160KZ.

[0008] Furthermore, the signal-driven switching circuit includes a voltage comparator, a switch tube Q2, a switch tube Q3, and a switch tube Q4. One input signal of the voltage comparator is the output signal PLC_AD, and the other input signal is the reference voltage Vref. The output end of the voltage comparator is connected to one end of the capacitor C7, and the capacitor C7 is connected in series with the diode D2, the resistor R5, and the resistor R6. The base of the switch tube Q2 is connected to the other end of the resistor R6, and the emitter of the switch tube Q2 is connected to the ground; the intersection of the capacitor C7 and the diode D2 is grounded through the resistor R4, and the intersection of the resistor R5 and the resistor R6 is connected to the ground. The capacitor C8 is grounded; the collector of the switching tube Q2 is connected to one end of the resistor R8, and the other end of the resistor R8 is connected to the base of the switching tube Q4; the collector of the switching tube Q4 is connected to the power supply VCC, and a resistor R7 is connected between the base and collector of the switching tube Q4; the emitter of the switching tube Q4 is connected in series with the resistor R11 and the resistor R9 to drive the switching tube Q1; the collector of the switching tube Q3 is connected to the intersection of the resistor R11 and the resistor R9, the emitter of the switching tube Q3 is connected to ground, the base of the switching tube Q3 is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the control signal EN.

[0009] Furthermore, when there is no forward current in the freewheeling diode D1 , the impedance between the first output terminal and the second output terminal is in a range of 0.75-1.5 ohms.

[0010] In order to solve the above technical problems, the present invention also provides a control method for the above-mentioned photovoltaic shut-off PLC drive circuit, which includes the following steps: S1) the voltage signals PLC1 and PLC2 of the PLC signal acquisition circuit generate an output signal PLC_AD after passing through the PLC signal amplification processing circuit module, and the output signal PLC_AD generates an output signal CPU_CAP after passing through the voltage comparator of the signal drive switch circuit; S2) first turn off the control signal EN of the signal drive switch circuit, and then detect the output signal PLC_AD and the output signal CPU_CAP. If the output signal PLC_AD is detected and the output signal CPU_CAP is not detected at the same time, the control signal EN is turned on; S3) the output signal CPU_CAP is captured cyclically. When the output signal CPU_CAP is detected, the control signal EN of the signal drive switch circuit is turned off.

[0011] Compared with the prior art, the present invention has the following beneficial effects: the photovoltaic shutdown PLC drive circuit and control method provided by the present invention can not only meet the rapid shutdown safety requirements, but also have high reliability, fast response speed, low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the power output circuit of the photovoltaic shutdown PLC drive circuit in the embodiment of the present invention;

[0013] Figure 2 A PLC signal amplifying and processing circuit of a photovoltaic shutdown PLC driving circuit in an embodiment of the present invention;

[0014] Figure 3 A PLC signal driving switch circuit of a photovoltaic shutdown PLC driving circuit in an embodiment of the present invention;

[0015] Figure 4 It is the power supply and control module of the photovoltaic shutdown PLC drive circuit in the embodiment of the present invention;

[0016] Figure 5 4 is a control flow chart of the photovoltaic shutdown PLC drive circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the accompanying drawings and examples.

[0018] Please refer to Figure 1The photovoltaic shutdown PLC driving circuit provided by the embodiment of the present invention includes a photovoltaic module, an input capacitor C1, a switch tube Q1, a freewheeling diode D1, a first output resistor R1, an output capacitor C2, a second output resistor R2, a PLC signal acquisition circuit, a first output terminal and a second output terminal; the PLC signal acquisition circuit includes a signal acquisition inductor L1, a signal acquisition resistor R2 and a signal acquisition capacitor C3, the signal acquisition resistor R2 and the signal acquisition capacitor C3 are connected in series and then connected in parallel with the signal acquisition inductor L1; the input capacitor C1 is connected in parallel with the photovoltaic module, and the photovoltaic module is connected in parallel. The positive electrode of the voltaic component is connected to the first output terminal 1-1, the negative electrode of the photovoltaic component is connected to the drain of the switch tube Q1, the source of the switch tube Q1 is connected to one end of the signal acquisition inductor L1, the other end of the signal acquisition inductor L1 is connected to the second output terminal 1-2, the second output resistor R2 and the signal acquisition capacitor C3 are connected in series and then connected in parallel with the signal acquisition inductor L1; the cathode of the freewheeling diode D1 is connected to the first output terminal 1-1, the anode of the freewheeling diode D1 is connected to the source of the switch tube Q1, and the output capacitor C2 is connected in series with the first output resistor R1 and then connected in parallel with the freewheeling diode D1.

[0019] In the embodiment of the present invention, the signal acquisition resistor R2 and capacitor C3 are connected in series and then connected in parallel with the signal acquisition inductor L1. This method can control the impedance of the parallel connection within the required range of 0.75-1.5 ohms based on the small inductor L1. The advantages are that the inductor L1 is small, the loss is small, the heat is low, and the system reliability is good. The output capacitor C2 is connected in series with the first output resistor R1 and then connected in parallel with the freewheeling diode D1. When there is no forward current in the diode, the impedance between the first output terminal 1-1 and the second output terminal 1-2 can be within the required range of 0.75-1.5 ohms. The advantage of the capacitor and resistor being connected in series is that it can improve the reliability of the system and will not cause serious heat generation due to capacitor failure; and the impedance range between the first output terminal 1-1 and the second output terminal 1-2 can be adjusted by the resistor. An optional set of values is: the inductor L1 value is 0.75uH, the resistor R2 is 0.4 ohms, the capacitor C3 is 1uf, the resistor R1 is 0.6 ohms, and the capacitor C2 is 1uf.

[0020] Please continue to refer to Figure 2The PLC signal amplification and processing circuit module of the present embodiment takes as input the voltage signals PLC1 and PLC2 from the PLC signal acquisition circuit, and its output is connected to a signal amplification resistor R3. The signal amplification resistor R3, capacitor C4, inductor L2, inductor L3, and capacitor C6 are connected in series, with the other end of capacitor C6 grounded. A signal amplification capacitor C5 is connected in parallel with inductor L3, and the output signal PLC_AD is the voltage signal at the connection point between inductors L2 and L3. In other words, inductor L2, inductor L3, capacitors C4, capacitor C6, and capacitor C5 form a bandpass filter. For signals with a center frequency of 130 kHz, greater than 160 kHz, and less than 100 kHz, after passing through the circuit, the maximum value of the output signal PLC_AD is less than the reference voltage Vref.

[0021] Now refer to Figure 3 The signal driving switch circuit of the embodiment of the present invention includes a voltage comparator U1, a switch tube Q2, a switch tube Q3 and a switch tube Q4. The input signal of the voltage comparator U1 is the signal PLC_AD and the input reference voltage Vref. The output signal of the voltage comparator U1 is CPU_CAP. The output of the voltage comparator U1 is connected to one end of the capacitor C7. The capacitor C7, the diode D2, the resistor R5 and the resistor R6 are connected in series. The other end of the resistor R6 is connected to the base of the switch tube Q2, and the emitter of the switch tube Q2 is connected to the ground; one end of the resistor R4 is connected to the intersection of the capacitor C7 and the diode D2, and the other end is connected to the ground. The capacitor C8 is connected to the resistor R 5 is connected to the intersection of resistor R6, and the other end is connected to ground; one end of the resistor R8 is connected to the collector of the switching tube Q2, and the other end is connected to the base of the switching tube Q4; the collector of the switching tube Q4 is connected to the power supply VCC, and the resistor R7 is connected in parallel with the base and collector of the switching tube Q4; the emitter of the switching tube Q4 is connected in series with the resistor R11 and the resistor R9 to drive the switching tube Q1; the collector of the switching tube Q3 is connected to the intersection of the resistor R11 and the resistor R9, the emitter of the switching tube Q3 is connected to ground, the base of the switching tube Q3 is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the control signal EN.

[0022] In the embodiment of the present invention, the circuit composed of capacitor C7, capacitor C8, diode D2, resistor R4, resistor R5 and resistor R6 can drive the switch tube Q2 (not limited to the transistor) only when the AC signal is output, thereby avoiding the safety hazard caused by the voltage comparator U1 outputting a high level to turn on the transistor due to a previous stage failure; the high and low levels output by the voltage comparator U1 charge the capacitor C8, and the combination of R5, C8, and R6 can charge the capacitor C8 when there is a PLC signal and discharge the capacitor C8 when there is no PLC signal, which can ensure that there is no PLC signal for two cycles. The voltage of capacitor C8 can drive the switch tube Q2, thereby realizing that the switch tube Q1 is turned on when there is a PLC signal and the switch tube Q1 is turned off for a certain period of time when there is no PLC signal.

[0023] Please continue to refer to Figure 4 The power supply + control unit of the embodiment of the present invention has the photovoltaic module VPV, the signal PLC_AD and the signal CPU_CAP as inputs; and has the power supply VCC and the control signal EN as outputs.

[0024] Now refer to Figure 5 The control flow chart shows that the program first turns off the control signal EN, that is, outputs a high level, then detects and analyzes the PLC signal, and turns on the control signal EN, that is, outputs a low level, and the program then loops to capture the signal CPU_CAP; when the signal CPU_CAP that does not meet the required frequency is detected, the control signal EN is turned off, that is, outputs a high level. At this time, the system may fail or an arc may occur, thereby being able to protect the system well.

[0025] The photovoltaic shutdown PLC drive circuit and control method provided by the present invention only enables the switch tube Q1, but does not directly turn on the switch tube Q1. The PLC hardware circuit turns the switch tube Q1 on and off. The PLC hardware circuit can only turn on the switch tube Q1 after the switch tube Q1 is enabled. The advantages are as follows:

[0026] (1) Perfectly realize the integration of software and hardware, with good security, high reliability and fast response speed;

[0027] (2) Low cost and high efficiency.

[0028] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the definition of the claims.

Claims

1. A control method for a photovoltaic shutdown PLC drive circuit, characterized in that: The photovoltaic shutdown PLC driving circuit includes a photovoltaic component, an input capacitor C1, a switch tube Q1, a freewheeling diode D1, a first output resistor R1, an output capacitor C2, a second output resistor R2, a PLC signal acquisition circuit, a first output terminal and a second output terminal; The PLC signal acquisition circuit includes a signal acquisition inductor L1, a signal acquisition resistor R2, and a signal acquisition capacitor C3. The signal acquisition resistor R2 and the signal acquisition capacitor C3 are connected in series and then in parallel with the signal acquisition inductor L1. The voltage signal of the PLC signal acquisition circuit passes through the PLC signal amplification and processing circuit module and the signal drive switch circuit and is connected to the gate of the switch tube Q1. The input capacitor C1 is connected in parallel with the photovoltaic module, the positive electrode of the photovoltaic module is connected to the first output terminal, the negative electrode of the photovoltaic module is connected to the drain of the switch tube Q1, the source of the switch tube Q1 is connected to one end of the signal acquisition inductor L1, and the other end of the signal acquisition inductor L1 is connected to the second output terminal; the cathode of the freewheeling diode D1 is connected to the first output terminal, the anode of the freewheeling diode D1 is connected to the source of the switch tube Q1, and the output capacitor C2 is connected in series with the first output resistor R1 and then connected in parallel with the freewheeling diode D1; When the freewheeling diode D1 has no forward current, the impedance between the first output terminal and the second output terminal is in the range of 0.75-1.5 ohms; The control method comprises the following steps: S1) The voltage signals PLC1 and PLC2 of the PLC signal acquisition circuit are passed through the PLC signal amplification processing circuit module to generate an output signal PLC_AD, and the output signal PLC_AD is passed through the voltage comparator of the signal drive switch circuit to generate an output signal CPU_CAP; S2) First, turn off the control signal EN of the signal driving switch circuit, then detect the output signal PLC_AD and the output signal CPU_CAP. If the output signal PLC_AD is detected and the output signal CPU_CAP is not detected, turn on the control signal EN; S3) cyclically capture the output signal CPU_CAP, and when the output signal CPU_CAP is detected, turn off the control signal EN of the signal driving switch circuit.

2. The control method of the photovoltaic shutdown PLC drive circuit according to claim 1, characterized in that: The input end of the PLC signal amplification and processing circuit module is the voltage signals PLC1 and PLC2 of the PLC signal acquisition circuit, and the output end of the PLC signal amplification and processing circuit module is connected to the signal amplification resistor R3; the signal amplification resistor R3 is connected in series with the capacitor C4, the inductor L2, the inductor L3 and the capacitor C6, and the other end of the capacitor C6 is grounded. The two ends of the inductor L3 are connected in parallel with the amplification processing capacitor C5, and the voltage signal at the connection point between the inductor L2 and the inductor L3 is the output signal PLC_AD.

3. The control method of the photovoltaic shutdown PLC drive circuit according to claim 2, characterized in that: The capacitor C4, the inductor L2, the inductor L3, the capacitor C4, the capacitor C6 and the capacitor C5 form a bandpass filter, and the center frequency of the bandpass filter is 100KHZ to 160KZ.

4. The control method of the photovoltaic shutdown PLC drive circuit according to claim 2, characterized in that: The signal-driven switching circuit includes a voltage comparator, a switch tube Q2, a switch tube Q3, and a switch tube Q4. One input signal of the voltage comparator is the output signal PLC_AD, and the other input signal is the reference voltage Vref. The output end of the voltage comparator is connected to one end of a capacitor C7. The capacitor C7 is connected in series with a diode D2, a resistor R5, and a resistor R6. The base of the switch tube Q2 is connected to the other end of the resistor R6, and the emitter of the switch tube Q2 is connected to the ground. The intersection of the capacitor C7 and the diode D2 is grounded through the resistor R4, and the intersection of the resistor R5 and the resistor R6 is connected through the capacitor C7. C8 is grounded; the collector of the switching tube Q2 is connected to one end of the resistor R8, and the other end of the resistor R8 is connected to the base of the switching tube Q4; the collector of the switching tube Q4 is connected to the power supply VCC, and a resistor R7 is connected between the base and collector of the switching tube Q4; the emitter of the switching tube Q4 is connected in series with the resistors R11 and R9 to drive the switching tube Q1; the collector of the switching tube Q3 is connected to the intersection of the resistors R11 and R9, the emitter of the switching tube Q3 is connected to ground, the base of the switching tube Q3 is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the control signal EN.

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