Relay protection circuit

Abstract

The utility model provides a relay protection circuit. The relay protection circuit comprises a first normally open relay, a second normally open relay, a first triode, a second triode and a starting resistor. The first normally-open relay is connected with the second normally-open relay, the first normally-open relay is connected into a power grid, and the second normally-open relay is connected with the alternating current output end of the inverter; the circuit controls connection and disconnection of a loop through the first normally-open relay, the second normally-open relay, the first triode and the second triode. According to the scheme, by adopting the structure, the circuit provided by the utility model has the characteristics of simple structure and more perfect protection effect, solves the fault risk existing in a single relay circuit, and can more reliably and safely cope with the condition that the inverter breaks down.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic circuits, in particular to a relay protection circuit. BACKGROUND

[0002] In the current photovoltaic inverter, the grid-connected circuit generally uses a single relay as a protection switch to connect the grid, so that the inverter can work normally; at the same time, the connection between the inverter and the grid is isolated when the inverter is not working or fails, so as to ensure the safety of personnel and equipment; however, when the relay is damaged before being powered on or during operation, the isolation protection function will fail, which will cause the inverter to fail to work normally, and even damage the inverter, solar panels and other equipment; at the same time, the damage of the relay will cause abnormal output of the inverter AC side, which will pollute the grid, cause the quality of the grid to decrease, damage the power supply equipment, and even cause electric shock and other dangerous situations.

[0003] Therefore, it is of great practical significance and application value to design a new type of protection circuit to improve the safety and reliability of the inverter. CONTENT OF THE INVENTION

[0004] In view of the above problems in the prior art, the present application provides a photovoltaic system under-voltage control circuit and a photovoltaic system circuit.

[0005] According to one aspect of the present application, a relay protection circuit is provided, comprising: a first normally open relay, a second normally open relay, a first triode, a second triode and a starting resistor;

[0006] The first normally open relay is connected to the second normally open relay, the first normally open relay is connected to the grid, and the second normally open relay is connected to the inverter AC output end;

[0007] The circuit connects and disconnects the loop through the first normally open relay, the second normally open relay, the first triode and the second triode; in the loop connection state, after the MCU sends an input starting voltage signal to the first normally open relay and the second normally open relay, the starting resistor is used for voltage division, so that the base voltage of the first triode and the second triode is greater than the conduction voltage, the first triode and the second triode are turned on, the +12V input at one end of the first normally open relay and the second normally open relay forms a loop, a voltage difference is formed across the coil of the relay, the coil is powered on, a magnetic field is generated in the coil, the respective contacts are closed, the inverter output is connected to the grid, and the inverter starts to work and is connected to the grid.

[0008] In the circuit disconnect state, after the MCU stops sending the starting level signal, the base voltage of the first transistor and the second transistor is less than the conduction voltage, the first transistor and the second transistor are cut off, the relay coil is powered off, the contact is disconnected, the inverter stage output is disconnected from the power grid, and the inverter stops working.

[0009] In a preferred embodiment of the present application, first switch diodes and second switch diodes are connected in parallel across the built-in coils of the first normally open relay and the second normally open relay, respectively, to prevent reverse current or voltage from damaging the relays or their circuit elements and to improve the switching speed of the relays and the accuracy of signal inversion.

[0010] In a preferred embodiment of the present application, a resistor is connected in series across the two ends of the coil of the first relay and the coil of the second relay, respectively, to limit current and quickly dissipate the induced electromotive force generated when the relays are turned off.

[0011] In a preferred embodiment of the present application, two parallel-to-ground capacitors are connected to the ground terminals of the first normally open relay and the second normally open relay, respectively, to filter the loop signal and reduce the total equivalent series resistance (ESR).

[0012] The relay protection circuit provided in the embodiments of the present application includes a first normally open relay, a second normally open relay, a first transistor, a second transistor, and a starting resistor. The first normally open relay is connected to the second normally open relay, the first normally open relay is connected to the power grid, and the second normally open relay is connected to the AC output end of the inverter. The circuit connects and disconnects the loop through the first normally open relay, the second normally open relay, the first transistor, and the second transistor. In the loop connection state, after the MCU sends an input starting level signal to the first normally open relay and the second normally open relay, respectively, the starting resistor is used for voltage division, the base voltage of the first transistor and the second transistor is greater than the conduction voltage, the first transistor and the second transistor are turned on, a loop is formed between the +12V input at one end of the first normally open relay and the second normally open relay and the ground, a voltage difference is formed across the two ends of the coil of the relay, the coil is powered on, a magnetic field is generated in the coil, the respective contacts are closed, the inverter stage output is connected to the power grid, the inverter starts working, and the inverter is connected to the power grid. In the loop disconnect state, after the MCU stops sending the starting level signal, the base voltage of the first transistor and the second transistor is less than the conduction voltage, the first transistor and the second transistor are cut off, the relay coil is powered off, the contact is disconnected, the inverter stage output is disconnected from the power grid, and the inverter stops working. In the present scheme, the above structure is adopted, the circuit of the present application has the characteristics of simple structure and more perfect protection, the fault risk of a single relay circuit is solved, and the inverter can more reliably and more safely cope with the situation of inverter failure. BRIEF DESCRIPTION OF DRAWINGS

[0013] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments thereof as taken in conjunction with the accompanying drawings:

[0014] Figure 1 It is a structure schematic view of a relay protection circuit according to an embodiment of the present application. DETAILED DESCRIPTION

[0015] In a photovoltaic power generation system, a grid-connected circuit of a photovoltaic inverter generally adopts a single relay as a protection switch to connect a power grid, so that the inverter can work normally; meanwhile, the connection between the inverter and the power grid is isolated when the inverter does not work or fails, so as to ensure the safety of personnel and equipment; however, when the relay fails before being powered on or during working, the isolation protection function will be invalid, which will cause the inverter to fail to work normally, and even the inverter, solar panels and other equipment can be damaged; meanwhile, the damage of the single relay will cause the abnormal output of the AC side of the inverter, which will pollute the power grid, cause the quality of the power grid to decrease, damage the power supply equipment, and even cause electric shock and other dangerous situations. Based on this, the present application provides a relay protection circuit to cope with the potential danger caused by the failure of the single relay. The present application will be described in detail below through specific embodiments.

[0016] Referring to Figure 1 As shown in the embodiment, the relay protection circuit provided in the embodiment includes a first normally open relay RY1, a second normally open relay RY2, a first triode Q1, a second triode Q2, a first switching diode D1, a second switching diode D2 and a starting resistor, wherein the starting resistor includes a first starting resistor R1, a second starting resistor R2, a third starting resistor R4 and a fourth starting resistor R5; a pin 2 of the first normally open relay RY1 and a pin 5 of the second normally open relay RY2 are respectively connected to a pin 3 and a pin 4 of the second normally open relay RY2 in correspondence, a pin 3 and a pin 4 of the RY1 are respectively connected to AC-L and AC-N lines of the power grid side, and a pin 2 and a pin 5 of the RY2 are respectively connected to AC-L1 and AC-L2 lines of the AC output side of the inverter.

[0017] The circuit is connected and turned off by the first relay RY1, the second relay RY2, the first transistor Q1 and the second transistor Q2; in the loop connection state, the MCU sends an input starting level signal to the first normally open relay RY1-ON and the second normally open relay RY2-ON, respectively, and the first starting resistor R1, the second starting resistor R2, the third starting resistor R4 and the fourth starting resistor R5 are used for voltage division, so that the base voltage Vbe of the first transistor Q1 and the second transistor Q2 is greater than the conduction voltage, the first transistor Q1 and the second transistor Q2 are turned on, the +12V input at one end of the first normally open relay RY1 and the second normally open relay RY2 forms a loop, a voltage difference is formed across the coil of the relay, the coil is energized, a magnetic field is generated in the coil, the respective contacts are closed, the inverter output is connected to the power grid, and the inverter starts to work and is connected to the power grid.

[0018] In the loop disconnection state, after the MCU stops sending the starting level signal, the base voltage of the first transistor Q1 and the second transistor Q2 is less than the conduction voltage, the first transistor Q1 and the second transistor Q2 are cut off, the relay coil is de-energized, the contacts are disconnected, the inverter output is disconnected from the power grid, and the inverter stops working.

[0019] In the above embodiment of the application, the first normally open relay RY1 and the second normally open relay RY2 have a built-in coil, and one switch diode is connected in parallel across each end of the coil, which is the first switch diode D1 and the second switch diode D2, to prevent reverse current or voltage from damaging the relay or its circuit elements, thereby improving the switching speed of the relay and the accuracy of signal inversion.

[0020] In another preferred embodiment of the application, a first current limiting resistor R3 and a second current limiting resistor R6 are connected in series across the coil of the first normally open relay RY1 and the second normally open relay, respectively, to limit the current and quickly dissipate the induced electromotive force generated when the relay is turned off; and two parallel ground capacitors, a first filter capacitor C1 and a second filter capacitor C2, are connected to the loop to filter the loop signal and reduce the total ESR (equivalent series resistance) to improve the reliability and stability of the circuit.

[0021] The utility model discloses a protection circuit for single relay fault, including normally open relay RY1, RY2, triode Q1, Q2, switch diode D1, D2, starting resistance R1, R2, R4, R5, current -limiting resistance R3, R6, filter capacitance C1, C2, the pin 2 of relay RY1, pin 5 are connected with the pin 3 of relay RY2, pin 4 correspond respectively, the pin 3 of RY1, pin 4 are connected with the AC-L of electric network, AC-N line respectively, the pin 2 of RY2, pin 5 are connected with the AC-L1 of inverter alternating -current output side, AC-L2 line respectively, when the single relay appears damage, MCU detection circuit to appear the fault, will stop sending starting level signal to RY1-ON, RY2-ON, and the contact of another relay will be disconnected, and the connection of inverter and electric network will be cut off, realizes isolation protection function.

[0022] When one relay (RY1 or RY2) in the inverter is damaged before power-up or in the working process, the MCU can judge whether the inverter is faulty by sampling the voltage of the power grid side or the inverter side, if the inverter is faulty, the MCU will stop sending the starting level signal, so that the contact of another relay is disconnected, the circuit is cut off, the power grid, the inverter and other devices are isolated and protected, and the maintenance personnel can be safer to repair or check the inverter.

[0023] The specific embodiments of the utility model are described above. It should be understood that the utility model is not limited to the above specific embodiments, and various modifications or changes can be made by those skilled in the art within the scope of claims, which does not affect the essential content of the utility model.

Claims

1. A relay protection circuit, characterized by comprising: The utility model relates to a circuit for controlling the start and stop of the inverter, comprising: a first normally open relay, a second normally open relay, a first transistor, a second transistor and a starting resistor; the first normally open relay is connected to the second normally open relay, the first normally open relay is connected to the power grid, and the second normally open relay is connected to the AC output end of the inverter; the circuit is connected and disconnected by the first normally open relay, the second normally open relay, the first transistor and the second transistor; in the connected state, after the MCU sends an input starting level signal to the first normally open relay and the second normally open relay, the starting resistor divides the voltage to make the base voltage of the first transistor and the second transistor greater than the conduction voltage, the first transistor and the second transistor are turned on, the +12V input at one end of the first normally open relay and the second normally open relay forms a loop with the ground, a voltage difference is formed between the two ends of the coil of the relay, the coil is powered on, a magnetic field is generated in the coil, the respective contacts are closed, the inverter output is connected to the power grid, and the inverter starts to work and is connected to the grid; in the disconnected state, after the MCU stops sending the starting level signal, the base voltage of the first transistor and the second transistor is less than the conduction voltage, the first transistor and the second transistor are cut off, the relay coil is powered off, the contacts are disconnected, the inverter output is disconnected from the power grid, and the inverter stops working.

2. The protection circuit of claim 1, wherein first and second switching diodes are connected in parallel across the coil of the first normally open relay and the second normally open relay, respectively, to prevent reverse current or voltage from damaging the relay or its circuit elements and to improve the switching speed of the relay and the accuracy of signal inversion.

3. Protection circuit according to claim 1 or 2, characterized in that a resistor is connected in series across the coil of the first normally open relay and the second normally open relay, respectively, to limit the current and quickly dissipate the induced electromotive force generated when the relay is turned off.

4. The circuit of claim 1 or 2, wherein two parallel-to-ground capacitors are connected to the ground end of the first normally open relay and the second normally open relay to filter the loop signal and reduce the total equivalent series resistance (ESR).

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