A photovoltaic shutdown monitoring system

Abstract

The present invention discloses a photovoltaic shutdown monitoring system, which includes a plurality of photovoltaic modules and a wireless data collector, and each photovoltaic module is provided with a shutdown module; the photovoltaic modules and the shutdown modules are first connected in series to form a plurality of photovoltaic module strings, and the plurality of photovoltaic module strings are connected in parallel to a photovoltaic busbar box or a PLC signal generator, the photovoltaic busbar box or the PLC signal generator is connected to an inverter, the wireless data collector collects data of the photovoltaic modules and the shutdown modules through wireless communication, and uploads the collected data to a summarizer through RS485 communication, and the summarizer is connected to a monitoring platform; the shutdown module includes a PLC signal processing module and a wireless communication module, and the PLC signal processing module is connected to a control unit. The present invention can not only meet 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 device, and more particularly to a photovoltaic shutdown monitoring system. Background Art

[0002] Rapid shutdown is a photovoltaic power station safety protection concept introduced from the United States. The concept of rapid shutdown is proposed for the protection of firefighters, photovoltaic power station installation and maintenance personnel. Because there is DC high voltage on the DC side of the photovoltaic power station, as long as there is sunlight, the DC high voltage on the battery panel side always exists. Once a fire occurs in the photovoltaic power station, firefighters cannot carry out fire fighting and rescue work until the entire power station is burned out.

[0003] Therefore, the National Electrical Code NEC 2014 and NEC 2017 in the United States have put forward clear requirements for the rapid shutdown of the DC side of photovoltaic power stations, which will be officially implemented on January 1, 2019. NEC 2017 stipulates that: "Outside the string, when the controller is installed within 0.3 meters of the array and within a range more than 1 meter from the access point, after using rapid shutdown, the system needs to drop to 30V within 30 seconds; within the string, it needs to drop to 80V within 30 seconds to facilitate taking safety rescue measures." Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a photovoltaic shutdown monitoring system that can meet the safety requirements of rapid shutdown 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 monitoring system, which includes a plurality of photovoltaic modules and a wireless data collector, and each photovoltaic module is equipped with a shutdown module; the photovoltaic modules and the shutdown modules are first connected in series to form a plurality of photovoltaic module strings, and the plurality of photovoltaic module strings are connected in parallel to a photovoltaic busbar box or a PLC signal generator, the photovoltaic busbar box or the PLC signal generator is connected to an inverter, the wireless data collector collects data of the photovoltaic modules and the shutdown modules through wireless communication, and uploads the collected data to a summarizer through RS485 communication, and the summarizer is connected to a monitoring platform; the shutdown module includes an input capacitor C21, a switching transistor Q21, a freewheeling diode D21, a first output resistor R21, an output capacitor C22, a second output resistor R22, a sampling inductor L21, a signal sampling resistor R22, a signal sampling capacitor C23, a PLC signal processing module, a wireless communication module, a first output terminal and a second output terminal; the signal sampling resistor R22 and the signal sampling capacitor C23 are connected in series and then connected in parallel with the signal sampling inductor L21, and the PLC signal processing module is connected to a control unit; the PLC signal processing module receives the voltage signal across the signal sampling inductor L21, amplifies and processes it, and then sends it to the control unit, and the control unit outputs a driving signal and connects it to the gate of the switching transistor Q21; the input capacitor C21 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 switching transistor Q21, the source of the switching transistor Q21 is connected to one end of the signal sampling inductor L21, and the other end of the signal sampling inductor L21 is connected to the second output terminal; the cathode of the freewheeling diode D21 is connected to the first output terminal, the anode of the freewheeling diode D21 is connected to the source of the switching transistor Q21, and the output capacitor C22 is connected in series with the first output resistor R21 and then connected in parallel with the freewheeling diode D21.

[0006] Further, the PLC signal generator is a voltage-type PLC and is at the front end of the photovoltaic busbar box. The plurality of photovoltaic module strings are respectively connected in series with capacitors and then connected in parallel to one end of the primary side of a mutual inductor T1, and the other end of the primary side of the mutual inductor T1 is connected to the negative electrode of the inverter; one end of the secondary side of the mutual inductor T1 is connected to a capacitor C12 and a resistor R1 in series and then connected to one end of the PLC signal generator, and the other end of the secondary side of the mutual inductor T1 is connected to an inductor L1 in series and then connected to the other end of the PLC signal generator.

[0007] Further, the PLC signal generator is a voltage-type PLC and is located at the rear end of the photovoltaic busbar box. One end of the primary side of the transformer T2 is connected to the positive pole of the inverter after being connected in series with the capacitor C11, and the other end of the primary side of the transformer T2 is connected to the negative pole of the inverter; one end of the secondary side of the transformer T2 is connected to one end of the PLC signal generator after being connected in series with the capacitor C13 and the resistor R2, and the other end of the secondary side of the transformer T2 is connected to the other end of the PLC signal generator after being connected in series with the inductor L2.

[0008] Further, the PLC signal generator is a current-type PLC and is located at the front end of the photovoltaic busbar box. The cables of the multiple photovoltaic module strings pass through the transformer T3 and form the primary side of the transformer T3. One end of the secondary side of the transformer T3 is connected to one end of the PLC signal generator after being connected in series with the capacitor C15 and the resistor R3, and the other end of the secondary side of the transformer T3 is connected to the other end of the PLC signal generator after being connected in series with the inductor L3. Capacitor C14 is connected in parallel at both ends of the secondary side of the transformer T3.

[0009] Further, the PLC signal generator is a current-type PLC and is located at the rear end of the photovoltaic busbar box. The negative or positive cable of the inverter passes through the transformer T4 and forms the primary side of the transformer T4. One end of the secondary side of the transformer T4 is connected to one end of the PLC signal generator after being connected in series with the capacitor C16 and the resistor R4, and the other end of the secondary side of the transformer T4 is connected to the other end of the PLC signal generator after being connected in series with the inductor L4. Capacitor C17 is connected in parallel at both ends of the secondary side of the transformer T4.

[0010] Further, a weak load unit is provided between the negative and positive poles of the inverter to form a DC current loop. The weak load unit includes a capacitor C18, a zener diode DZ1, and a Darlington transistor; the capacitor C18 is connected in parallel with the negative and positive poles of the inverter. The collector of the Darlington transistor is connected to the positive pole of the inverter. The emitter of the Darlington transistor is connected to the negative pole of the inverter after being connected in series with the resistor R6. The positive pole of the inverter is connected to the base of the Darlington transistor after being connected in series with the resistor R5. One end of the zener diode DZ1 is connected to the base of the Darlington transistor, and the other end is connected to the negative pole of the inverter. Capacitor C19 is connected in parallel at both ends of the zener diode DZ1.

[0011] Further, when there is no forward current in the freewheeling diode D21, the impedance range between the first output terminal and the second output terminal is 0.75 - 1.5 ohms.

[0012] The present invention has the following beneficial effects compared with the prior art: The photovoltaic shutdown monitoring system provided by the present invention can not only meet the safety requirements of rapid shutdown, but also has high reliability, fast response speed, low cost, and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1It is the photovoltaic module and disconnector module circuit in the embodiment of the present invention;

[0014] Figure 2 It is a system architecture diagram of wireless communication and PLC communication in the embodiment of the present invention;

[0015] Figure 3 It is another system architecture diagram of wireless communication and PLC communication in the embodiment of the present invention;

[0016] Figure 4 It is the circuit diagram of the voltage - type PLC signal generator at the front end of the photovoltaic bus - bar box in the embodiment of the present invention;

[0017] Figure 5 It is the circuit diagram of the voltage - type PLC signal generator at the rear end of the photovoltaic bus - bar box in the embodiment of the present invention;

[0018] Figure 6 It is the circuit diagram of the current - type PLC signal generator at the front end of the photovoltaic bus - bar box in the embodiment of the present invention;

[0019] Figure 7 It is the circuit diagram of the current - type PLC signal generator at the rear end of the photovoltaic bus - bar box in the embodiment of the present invention;

[0020] Figure 8 It is the internal weak - load circuit diagram of the PLC signal generator in the embodiment of the present invention. Detailed implementation manners

[0021] The present invention will be further described below in conjunction with the drawings and embodiments.

[0022] Please refer to Figure 1 , the photovoltaic shutdown monitoring system provided by the embodiment of the present invention includes: a plurality of photovoltaic modules and wireless data collectors, and each photovoltaic module is equipped with a disconnector module; the photovoltaic modules and disconnector modules are first connected in series to form a plurality of photovoltaic module strings, and the plurality of photovoltaic module strings are connected in parallel to a photovoltaic bus - bar box or a PLC signal generator, the photovoltaic bus - bar box or the PLC signal generator is connected to an inverter, the wireless data collector collects data of the photovoltaic modules and disconnector modules through wireless communication, and uploads the collected data to a summarizer through RS485 communication, and the summarizer is connected to a monitoring platform;

[0023] The disconnector module includes an input capacitor C21, a switching transistor Q21, a free - wheeling diode D21, a first output resistor R21, an output capacitor C22, a second output resistor R22, a signal - collecting inductor L21, a signal - collecting resistor R22, a signal - collecting capacitor C23, a PLC signal - processing module, a wireless communication module, a first output terminal 1 - 1 and a second output terminal 1 - 2;

[0024] The signal acquisition resistor R22 and the signal acquisition capacitor C23 are connected in series and then connected in parallel with the signal acquisition inductor L21. The PLC signal processing module is connected to the control unit. The PLC signal processing module receives the voltage signal at both ends of the signal acquisition inductor L21 and sends it to the control unit after amplification. The control unit outputs a driving signal and connects it to the gate of the switch tube Q21.

[0025] The input capacitor C21 is connected in parallel with the photovoltaic component, the positive electrode of the photovoltaic 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 Q21, the source of the switch tube Q21 is connected to one end of the signal acquisition inductor L21, and the other end of the signal acquisition inductor L21 is connected to the second output terminal 1-2; the cathode of the freewheeling diode D21 is connected to the first output terminal 1-1, the anode of the freewheeling diode D21 is connected to the source of the switch tube Q21, and the output capacitor C22 is connected in series with the first output resistor R21 and then connected in parallel with the freewheeling diode D21.

[0026] The signal acquisition resistor R22 and capacitor C23 of the embodiment of the present invention are connected in series and then connected in parallel with the signal acquisition inductor L21. This method can control the impedance after parallel connection within the required range of 0.75-1.5 ohms on the basis of the small inductance L21. The advantages are that the inductance L21 is small, the loss is small, the heat is low, and the system reliability is good. After the output capacitor C22 is connected in series with the first output resistor R21 and then connected in parallel with the freewheeling diode D21, 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 when there is no forward current in the diode. The advantage of the capacitor and the resistor in series is that the reliability of the system can be improved, and serious heat will not be caused by 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 inductance L21 value is 0.75uH, the resistor R22 is 0.4 ohms, the capacitor C23 is 1uf, the resistor R21 is 0.6 ohms, and the capacitor C22 is 1uf.

[0027] The control unit (plus power supply) of the present invention is connected to the wireless communication module and the PLC signal processing module at the same time, and realizes PLC communication and wireless communication at the same time; wireless communication is used to collect data, and PLC communication is used to open and close the output of the photovoltaic module, relying on cable communication. In this way, the quality of PLC communication is only related to the distance between the photovoltaic module and the junction box, and the reliability is very good; the PLC carrier frequency is low, the data collection is slow, and it may affect the opening and closing of the circuit breaker, which is not suitable for large power station systems or multiple series-parallel systems. Wireless communication has the advantage of collecting data and is not limited by the size of the power station. In this way, data collection and safe opening and closing are separated, and the reliability, safety and real-time performance of the system are perfectly realized.

[0028] Reference now Figure 2, in the embodiments of the present invention, the photovoltaic module + disconnector modules 11 to 1n are connected in series, the photovoltaic module + disconnector modules 21 to 2n are connected in series, and the photovoltaic module + disconnector modules m1 to mn are connected in series. Then, these strings String1, String2, …, Stringm are connected in parallel to a photovoltaic busbar box or a PLC signal generator, and then connected to an inverter. The order of the photovoltaic busbar box and the PLC signal generator can be swapped. The wireless data collector collects the data of the photovoltaic module + disconnector module through wireless communication, and the collected data is uploaded to the aggregator through 485 communication, and then the data is uploaded to the monitoring platform.

[0029] The PLC signal generator in the embodiments of the present invention can be voltage type or current type, and can be placed in the front stage of the photovoltaic busbar box or in the rear stage of the photovoltaic busbar box. Figure 3 and Figure 2 is basically the same, except that the PLC signal generator is at the rear end of the photovoltaic busbar box.

[0030] Now refer to Figure 4 , the PLC signal generator is a voltage-type PLC and is at the front end of the photovoltaic busbar box. The photovoltaic string 1 (String1) is connected in series with the capacitor C1, the photovoltaic string 2 (String2) is connected in series with the capacitor C2, and the photovoltaic string m (Stringm) is connected in series with the capacitor Cm and then connected in parallel to one end of the primary side of the transformer T1. The other end of the primary side of the transformer T1 is connected to the negative pole INV- of the inverter. All photovoltaic strings are connected in parallel to one end of the primary side of the transformer T1, unaffected by the subsequent photovoltaic busbar box and the subsequent circuit. In addition, all photovoltaic strings are controlled by one unit, which will not cause PLC signal crosstalk and can effectively avoid PLC communication failure. One end of the secondary side of the transformer T1 is connected in series with the capacitor C12 and the resistor R1 and then connected to one end of the PLC signal generator, and the other end of the secondary side of the transformer T1 is connected in series with the inductor L1 and then connected to the other end of the PLC signal generator. Different strings are isolated by the capacitors C1, C2, …, Cm.

[0031] Now refer to Figure 5 , the PLC signal generator is a voltage-type PLC and is at the rear end of the photovoltaic busbar box. The positive pole INV+ of the inverter is connected in series with the capacitor C11 and then connected to one end of the primary side of the transformer T2. The other end of the primary side of the transformer T2 is connected to the negative pole INV- of the inverter; one end of the secondary side of the transformer T2 is connected in series with the capacitor C13 and the resistor R2 and then connected to one end of the PLC signal generator, and the other end of the secondary side of the transformer T2 is connected in series with the inductor L2 and then connected to the other end of the PLC signal generator. Only one high-voltage capacitor C11 is needed to achieve PLC communication, with good reliability, low cost and small volume. Since the PLC signal generator is behind the photovoltaic busbar box, the output of the busbar box has only INV+ and INV-, and different strings are isolated by the diodes of the photovoltaic busbar box.

[0032] Now refer to Figure 6 , the PLC signal generator is a current-type PLC and is at the front end of the photovoltaic busbar box. The m cables of photovoltaic string 1 (String1), photovoltaic string 2 (String2), …, photovoltaic string m (Stringm) pass through the current transformer T3. The string cables are the primary side of the current transformer T3. One end of the secondary side of the current transformer T3 is connected in series with the capacitor C15 and the resistor R3 and then connected to one end of the PLC signal generator. The other end of the secondary side of the current transformer T3 is connected in series with the inductor L3 and then connected to the other end of the PLC signal generator. The capacitor C14 is connected in parallel with both ends of the secondary side of the current transformer T3. It is equivalent to that the primary side is a single-turn coil composed of m wires, and the PLC currents among the cables are basically the same. All cables directly pass through the magnetic ring without the need for an external circuit, and the safety is good.

[0033] Now refer to Figure 7 , the PLC signal generator is a current-type PLC and is at the rear end of the photovoltaic busbar box. The negative cable INV- of the inverter (it can also be the positive cable INV+) passes through the current transformer T4. The negative cable (it can also be the positive cable) is the primary side of the current transformer T4. One end of the secondary side of the current transformer T4 is connected in series with the capacitor C16 and the resistor R4 and then connected to one end of the PLC signal generator. The other end of the secondary side of the current transformer T4 is connected in series with the inductor L4 and then connected to the other end of the PLC signal generator. The capacitor C17 is connected in parallel with both ends of the secondary side of the current transformer T3. Only one cable is needed and there is no need to pass through the PCB board. The structure is simple and the safety is good.

[0034] When the PLC signal generator is a current-type PLC or a voltage-type PLC at the rear end of the photovoltaic busbar box, a weak load unit needs to be added. Please continue to refer to Figure 8 , the capacitor C18 of the weak load unit is connected in parallel with the negative INV- and positive INV+ of the inverter. The triodes Q1 and Q2 form a Darlington triode, the collector is connected to the positive INV+, the emitter is connected in series with the resistor R6 and then connected to the negative INV- of the inverter. The positive INV+ of the inverter is connected in series with the resistor R5 and then connected to the base of the triode. One end of the zener diode DZ1 is connected to the base of the triode, and the other end is connected to the negative INV- of the inverter. The capacitor C19 is connected in parallel with the zener diode DZ1. In this way, a weak DC current loop is formed between the negative INV- and positive INV+ of the inverter to ensure that the diode of the busbar box is forward-conducted. The AC resistance of the diode is low to ensure the smooth passage of the PLC signal. At the same time, a capacitor C18 needs to be added, which can provide a low-impedance loop for the PLC to avoid the instability or failure of the PLC signal caused by too long cables at the rear stage.

[0035] Although the present invention has been disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the claims.

Claims

1. A photovoltaic shutdown monitoring system, characterized in that, it includes multiple photovoltaic modules and a wireless data collector, and each photovoltaic module is equipped with a shutdown module; the photovoltaic modules and the shutdown modules are first connected in series to form multiple photovoltaic module strings, and the multiple photovoltaic module strings are connected in parallel to a photovoltaic busbar box or a PLC signal generator, the photovoltaic busbar box or the PLC signal generator is connected to an inverter, the wireless data collector collects data of the photovoltaic modules and the shutdown modules through wireless communication, and uploads the collected data to a summarizer through RS485 communication, and the summarizer is connected to a monitoring platform; the shutdown module includes an input capacitor C21, a switching transistor Q21, a freewheeling diode D21, a first output resistor R21, an output capacitor C22, a second output resistor R22, a sampling inductor L21, a signal sampling resistor R22, a signal sampling capacitor C23, a PLC signal processing module, a wireless communication module, a first output terminal and a second output terminal; the signal sampling resistor R22 and the signal sampling capacitor C23 are connected in series and then connected in parallel with the signal sampling inductor L21, and the PLC signal processing module is connected to a control unit; the PLC signal processing module receives the voltage signal at both ends of the signal sampling inductor L21, amplifies and processes it, and then sends it to the control unit, and the control unit outputs a driving signal and is connected to the gate of the switching transistor Q21; the input capacitor C21 is connected in parallel with the photovoltaic module, the positive pole of the photovoltaic module is connected to the first output terminal, the negative pole of the photovoltaic module is connected to the drain of the switching transistor Q21, the source of the switching transistor Q21 is connected to one end of the signal sampling inductor L21, and the other end of the signal sampling inductor L21 is connected to the second output terminal; the cathode of the freewheeling diode D21 is connected to the first output terminal, the anode of the freewheeling diode D21 is connected to the source of the switching transistor Q21, and the output capacitor C22 and the first output resistor R21 are connected in series and then connected in parallel with the freewheeling diode D21.

2. The photovoltaic shutdown monitoring system according to claim 1, characterized in that, the PLC signal generator is a voltage-type PLC and is at the front end of the photovoltaic busbar box, and the multiple photovoltaic module strings are respectively connected in series with capacitors and then connected in parallel to one end of the primary side of a mutual inductor T1, and the other end of the primary side of the mutual inductor T1 is connected to the negative pole of the inverter; one end of the secondary side of the mutual inductor T1 is connected to the capacitor C12 and the resistor R1 in series and then connected to one end of the PLC signal generator, and the other end of the secondary side of the mutual inductor T1 is connected to the inductor L1 in series and then connected to the other end of the PLC signal generator.

3. The photovoltaic shutdown monitoring system according to claim 1, characterized in that, the PLC signal generator is a voltage-type PLC and is at the rear end of the photovoltaic busbar box, the positive pole of the inverter is connected in series with the capacitor C11 and then connected to one end of the primary side of a mutual inductor T2, and the other end of the primary side of the mutual inductor T2 is connected to the negative pole of the inverter; one end of the secondary side of the mutual inductor T2 is connected to the capacitor C13 and the resistor R2 in series and then connected to one end of the PLC signal generator, and the other end of the secondary side of the mutual inductor T2 is connected to the inductor L2 in series and then connected to the other end of the PLC signal generator.

4. The photovoltaic shutdown monitoring system according to claim 1, characterized in that, the PLC signal generator is a current-type PLC and is at the front end of the photovoltaic busbar box. The cables of the multiple photovoltaic module strings pass through the current transformer T3 and form the primary side of the current transformer T3. One end of the secondary side of the current transformer T3 is connected in series with the capacitor C15 and the resistor R3 and then connected to one end of the PLC signal generator. The other end of the secondary side of the current transformer T3 is connected in series with the inductor L3 and then connected to the other end of the PLC signal generator. Both ends of the secondary side of the current transformer T3 are shunted with the capacitor C14.

5. The photovoltaic shutdown monitoring system according to claim 1, characterized in that, the PLC signal generator is a current-type PLC and is at the rear end of the photovoltaic busbar box. The negative or positive cable of the inverter passes through the current transformer T4 and forms the primary side of the current transformer T4. One end of the secondary side of the current transformer T4 is connected in series with the capacitor C16 and the resistor R4 and then connected to one end of the PLC signal generator. The other end of the secondary side of the current transformer T4 is connected in series with the inductor L4 and then connected to the other end of the PLC signal generator. Both ends of the secondary side of the current transformer T4 are shunted with the capacitor C17.

6. The photovoltaic shutdown monitoring system according to claim 4 or 5, characterized in that, a weak load unit is arranged between the negative and positive poles of the inverter to form a DC current loop. The weak load unit includes a capacitor C18, a zener diode DZ1 and a Darlington transistor. The capacitor C18 is connected in parallel with the negative and positive poles of the inverter. The collector of the Darlington transistor is connected to the positive pole of the inverter. The emitter of the Darlington transistor is connected in series with the resistor R6 and then connected to the negative pole of the inverter. The positive pole of the inverter is connected in series with the resistor R5 and then connected to the base of the Darlington transistor. One end of the zener diode DZ1 is connected to the base of the Darlington transistor, and the other end is connected to the negative pole of the inverter. Both ends of the zener diode DZ1 are shunted with the capacitor C19.

7. The photovoltaic shutdown monitoring system according to claim 1, characterized in that, when there is no forward current in the freewheeling diode D21, the impedance range between the first output terminal and the second output terminal is 0.75 - 1.5 ohms.

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