Grid-connected and off-grid switching circuit topology suitable for energy storage system

Abstract

The invention belongs to the technical field of safe and stable operation of a power grid, and particularly relates to a grid-connected and off-grid switching circuit topology suitable for an energy storage system, which comprises the energy storage system and a grid-connected and off-grid switching system, the grid-connected and off-grid switching system comprises a bidirectional thyristor assembly connected between a power grid side and an energy storage system. A driving loop of the bidirectional thyristor assembly supplies power through a power grid side. An existing energy storage system is connected with a power grid through a conventional circuit breaker or a contactor to achieve the grid-connected and off-grid switching function, according to the technical scheme, the switching time can be shortened to 0-10 ms from 40-70 ms, rapid disconnection between the energy storage system and the power grid side is achieved, and overload faults, caused by slow disconnection, of the energy storage system or an external power grid are avoided.

Description

Technical Field

[0001] The invention relates to an on-grid and off-grid switching circuit topology suitable for an energy storage system, and belongs to the technical field of safe and stable operation of power grids. Background Art

[0003] To achieve this goal, the installed capacity of wind power and photovoltaic power generation will be greatly increased, and will eventually replace traditional thermal power generation. The future new power system that carries a high proportion of new energy will face many challenges. For example, the high proportion of new energy access will lead to a decrease in the system's anti-disturbance ability, and the power supply will shift from mainly controllable and continuous coal-fired power generation to strongly uncertain and weakly controllable new energy power generation. The operational safety risks are prominent, the difficulty of operational safety management and control is increasing, and the safety and stability of power supply face great challenges.

[0004] At present, the safety and stability of power supply are guaranteed by parallel power supply of energy storage system and external power grid, which is specifically achieved through the on-grid and off-grid switching function of the energy storage system: when the energy storage system and the external power grid are operating normally, the two are connected in parallel to supply power to the load; when the energy storage system fails, the external power grid supplies power to the load alone; when the external power grid loses power, the energy storage system operates in an island mode and supplies power to the load alone.

[0005] In the prior art, the energy storage system is connected to the grid through a circuit breaker or contactor to achieve the on-grid and off-grid switching function. However, the circuit breaker or contactor is a mechanical switch, and it takes a long time for the disconnection from the grid, about 40ms to 70ms. The energy storage system cannot be quickly disconnected from the grid, which will cause the energy storage system to not only supply power to the power-maintaining load when operating off-grid, but also to supply power to the grid. The grid load is infinite, which will cause an overload failure of the energy storage system. Summary of the invention

[0006] The purpose of the present invention is to provide an on-grid and off-grid switching circuit topology suitable for an energy storage system, so as to solve the overload problem of the energy storage system or the external power grid caused by the slow disconnection of the existing on-grid and off-grid switching circuit topology.

[0007] To achieve the above-mentioned purpose, the scheme of the present invention includes an energy storage system and an on-grid and off-grid switching system. The energy storage system is connected to the load side after being connected in parallel with the external power grid on the grid side. The on-grid and off-grid switching system includes a bidirectional thyristor assembly connected between the grid side and the energy storage system; the driving circuit of the bidirectional thyristor assembly is powered by the grid side.

[0008] When the external grid on the grid side 3 loses power, the bidirectional thyristor drive circuit has no power supply and therefore no longer provides a drive signal. The bidirectional thyristor will automatically turn off when the current passes through zero. At a grid frequency of 50 Hz, the maximum thyristor turn-off time is 10 ms. The technical solution of the present invention can quickly disconnect the energy storage system from the grid, thereby avoiding the situation where the energy storage system needs to supply power not only to the power-maintaining load but also to the grid when operating off-grid, thereby causing an overload failure of the energy storage system. When the energy storage system fails, the grid may also be overloaded due to the untimely disconnection of the energy storage system, thereby ensuring the safe operation of the energy storage system.

[0009] Furthermore, the bidirectional thyristor assembly includes bidirectional thyristors respectively connected in series on the live wires of each phase before the grid side is connected in parallel with the energy storage system, and each phase on the grid side of the bidirectional thyristor assembly is connected to the neutral wire through a resistor.

[0010] When the bidirectional thyristor is turned off and the energy storage system is off-grid, the bidirectional thyristor will generate leakage current. Therefore, each phase on the grid side of the bidirectional thyristor is connected to the neutral line through a resistor, so that the leakage current flows to the neutral line through the resistor, thereby discharging safely and ensuring the safety of people and equipment.

[0011] Furthermore, the bidirectional thyristor assembly also includes a heat sink and a heat dissipation fan for dissipating heat from the bidirectional thyristor.

[0012] A radiator and a cooling fan are provided to dissipate heat for the bidirectional thyristor, thereby extending the service life of the bidirectional thyristor and ensuring the safety of the equipment.

[0013] Furthermore, the on-grid and off-grid switching system also includes a dual-power static switching switch, a first input end of the dual-power static switching switch is connected to the parallel connection between the grid side and the energy storage system, a second input end is connected to the grid side, and an output end of the dual-power static switching switch is connected to the load side; a control electromagnet at the first input end is connected to the parallel connection between the grid side and the energy storage system, a control electromagnet at the second input end is connected to the grid side, and a first circuit breaker is connected between the contact point where the grid side is connected to the second input end and the bidirectional thyristor assembly.

[0014] When the external power grid and the energy storage system are operating normally, the first input terminal of the dual power static switching switch 7 is connected, and at this time, the energy storage system and the external power grid operate in parallel; when the energy storage system fails, the first circuit breaker is cut off, the first input internal electromagnet power supply terminal of the dual power static switching switch 7 has no current and is disconnected, and the second input terminal is connected, so that the failed energy storage system is automatically bypassed. At this time, the external power grid supplies power to the continuous load to ensure the reliability of the power supply to the equipment;

[0015] Furthermore, a second circuit breaker is provided on the line connecting the second input end to the grid side, so as to mechanically cut off the circuit when a fault occurs in the second input end of the dual power static switch and the circuit breaker cannot be automatically disconnected.

[0016] Further, the first circuit breaker and / or the second circuit breaker is replaced by a contactor.

[0017] Furthermore, the energy storage system includes an energy storage battery and an energy storage converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the circuit topology of the present invention.

[0019] Reference numerals:

[0020] 1: Energy storage converter; 2: Energy storage battery; 3: Grid side; 4: First circuit breaker; 5: Second circuit breaker; 6: Bidirectional thyristor assembly; 7: Dual power static switching switch; 8: Load side. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] Example 1

[0023] The following is combined with Figure 1 , a scheme of the present invention is applicable to the grid-connected and off-grid switching circuit topology of the energy storage system. The technical scheme of the present invention includes an energy storage battery 2, an energy storage converter 1, a circuit breaker 4 and a circuit breaker 5, a bidirectional thyristor assembly 6, and a dual-power static switching switch 7. The energy storage battery 2 is connected to one end of the energy storage converter 1. The energy storage converter 1 can convert the current of the energy storage battery 2 during the charging and discharging process into AC and DC. A branch at the other end of the energy storage converter 1 is sequentially connected to the bidirectional thyristor assembly 6 and one end of the circuit breaker 4. A branch at the other end of the circuit breaker 4 is connected to the grid side 3. Another branch at the other end of the circuit breaker 4 is connected to one end of the circuit breaker 5. The other end of the circuit breaker 5 is connected to the control electromagnet of the second input end of the dual-power static switching switch 7. The energy storage converter 1 is connected in parallel with the bidirectional thyristor assembly 6 to the control electromagnet of the first input end of the dual-power static switching switch 7. The output end of the dual-power static switching switch 7 is connected to the load side 8.

[0024] The thyristor assembly 6 in the present invention includes three bidirectional thyristors, three resistors, a radiator and a cooling fan for dissipating heat for the thyristors, and a thyristor drive circuit that can supply power to the thyristors through the grid side. The three bidirectional thyristors are respectively connected in series to the live wires of each phase before the grid side 3 is connected in parallel with the energy storage system, and each phase of the bidirectional thyristor grid side is connected to the neutral line through a resistor.

[0025] When the circuit topology in the present invention is used to switch the energy storage converter on and off the grid, the first circuit breaker 4 and the second circuit breaker 5 are both closed. When the external power grid and the energy storage system are operating normally, the first input terminal of the dual-power static switching switch 7 is connected. At this time, the energy storage system and the external power grid operate in parallel; when the energy storage system fails, the first circuit breaker is cut off, the first input internal electromagnet power supply terminal of the dual-power static switching switch 7 has no current and is disconnected, and the second input terminal is connected, so that the failed energy storage system is automatically bypassed. At this time, the external power grid supplies power to the continuous load to ensure the reliability of the power supply of the equipment;

[0026] When the energy storage system fails, the first input internal electromagnet power supply end of the dual power static switching switch 7 has no current and is disconnected, so that the failed energy storage system is automatically bypassed. At this time, the external power grid is used to supply power to the continuous load to ensure the reliability of the power supply to the equipment; when the external power grid on the grid side 3 loses power, the bidirectional thyristor drive circuit has no power supply and therefore no longer provides a drive signal. The bidirectional thyristor will automatically turn off when the current passes through zero. At a grid frequency of 50Hz, the thyristor off time is a maximum of 10ms, so that the energy storage system can quickly and automatically switch to an off-grid operation state and supply power to the load alone.

[0027] In addition, when the bidirectional thyristor is turned off and the energy storage system is off-grid, the bidirectional thyristor will generate leakage current. Therefore, each phase on the grid side of the bidirectional thyristor is connected to the neutral line through a resistor, so that the leakage current flows to the neutral line through the resistor, thereby discharging safely and ensuring the safety of people and equipment.

[0028] Example 2

[0029] A method according to another embodiment of the present invention is applicable to a grid-connected and off-grid switching circuit topology of an energy storage system. Based on the first embodiment, the following adjustments are made:

[0030] The energy storage battery 2 in Example 1 is replaced with other energy storage devices;

[0031] The specific number of bidirectional thyristors and resistors is adjusted according to the number of phases of the specific application circuit;

[0032] In some application circuits, the circuit breaker 4 and the circuit breaker 5 may be replaced by a contactor, or the circuit breaker 5 may not be provided; the bidirectional dual-power static switching switch 7 in Example 1 may also not be provided.

Claims

1. A grid-connected and off-grid switching circuit topology suitable for an energy storage system, characterized in that: It includes an energy storage system and an on-grid and off-grid switching system. The energy storage system is connected to the load side after being connected in parallel with an external power grid on the power grid side. The on-grid and off-grid switching system includes a bidirectional thyristor assembly connected between the power grid side and the energy storage system. The driving circuit of the bidirectional thyristor assembly is powered by the power grid side.

2. The on-grid and off-grid switching circuit topology applicable to the energy storage system according to claim 1, characterized in that: The bidirectional thyristor assembly comprises bidirectional thyristors respectively connected in series on the live wires of each phase before the grid side is connected in parallel with the energy storage system, and each phase on the grid side of the bidirectional thyristor assembly is connected to the neutral wire through a resistor.

3. The on-grid and off-grid switching circuit topology applicable to the energy storage system according to claim 1, characterized in that: The bidirectional thyristor assembly also includes a radiator and a heat dissipation fan for dissipating heat from the bidirectional thyristor.

4. The on-grid and off-grid switching circuit topology applicable to the energy storage system according to claim 1, characterized in that: The on-grid and off-grid switching system also includes a dual-power static switching switch, a first input end of the dual-power static switching switch is connected to the parallel connection between the power grid side and the energy storage system, a second input end is connected to the power grid side, and an output end of the dual-power static switching switch is connected to the load side; a control electromagnet at the first input end is connected to the parallel connection between the power grid side and the energy storage system, a control electromagnet at the second input end is connected to the power grid side, and a first circuit breaker is connected between the contact point where the power grid side is connected to the second input end and the bidirectional thyristor assembly.

5. The grid-connected and off-grid switching circuit topology applicable to the energy storage system according to claim 4, characterized in that: The line connecting the second input end to the grid side is provided with a second circuit breaker.

6. The on-grid and off-grid switching circuit topology applicable to the energy storage system according to claim 5, characterized in that: The first circuit breaker and / or the second circuit breaker are replaced by contactors.

7. The grid-connected and off-grid switching circuit topology applicable to the energy storage system according to claim 1, characterized in that: The energy storage system includes an energy storage battery and an energy storage converter.

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