Ground fault active full compensation device using energy storage unit

Abstract

The utility model discloses a ground fault active full-compensation device using an energy storage unit, which comprises a controller, an active power compensator, a boosting transformer, a full-compensation switching high-voltage switch and an energy storage unit for providing electric energy for the active power compensator and absorbing excess energy when the active power compensator is switched on and off a grid, the AC input end of the energy storage unit is connected with an AC power supply, and the positive and negative ends of the energy storage unit are respectively connected with the DC side bus positive and negative electrodes of the active power compensator. According to the utility model, the energy storage unit is arranged in the system to provide a working power supply for the active power compensator, so that the battery of the energy storage unit can be charged with lower power, and the active current, the reactive current and the harmonic current of a system fault point can be compensated with higher current, thereby reducing the power supply capacity required by the rated power work of the active power compensator; the addition of other equipment is avoided, the equipment investment is reduced, and the occupied area is saved.

Description

Technical Field

[0001] The utility model relates to the technical field of single-phase grounding protection of distribution networks, in particular to an active full compensation device for grounding faults. Background Art

[0002] The active full compensation device for ground faults (referred to as the full compensation device) consists of a step-up transformer, a vacuum contactor, an active power compensator, a controller, etc. It can compensate the current at the single-phase ground fault point to close to 0, completely eliminate the arc when a single-phase ground fault occurs, and can also use the disturbance method to accurately select the line. It is the optimal solution to solve single-phase ground faults.

[0003] Active power compensators (APCs) typically require AC power, and the power of an APC is generally 100kVA. Therefore, if the secondary side of a grounding transformer is used to power the APC, this requires a 100kVA margin on the secondary side of the grounding transformer. However, since most grounding transformers do not have sufficient margin, an additional power transformer (10kV or 35kV) is required to power the APC. This, in turn, requires additional switchgear and bays. This not only increases the equipment but also the floor space required, leading to higher costs.

[0004] In addition, during the transition process of the active power compensator (APC) being connected to the grid after a ground fault occurs and the active power compensator (APC) being disconnected from the grid after the ground fault disappears, electric energy will be injected into the DC side, causing the DC voltage to increase or even cause the overvoltage protection to trip. Therefore, it is necessary to add an energy discharge device to avoid this situation. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide an active full compensation device for ground faults with low cost and high safety.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0007] An active full compensation device for ground faults using an energy storage unit includes a controller, an active power compensator, a step-up transformer, and a fully compensated switching high-voltage switch. The device also includes an energy storage unit that provides electrical energy to the active power compensator and absorbs excess energy when the active power compensator is switched on and off the grid. The AC input terminal of the energy storage unit is connected to a single-phase 220V AC power supply or a three-phase 380V AC power supply, and the positive and negative terminals of the energy storage unit are respectively connected to the positive and negative terminals of the DC-side busbar of the active power compensator.

[0008] The above-mentioned active full compensation device for ground faults using an energy storage unit, the energy storage unit includes a DC converter, a battery pack and an inverter connected in sequence, the controlled end of the battery pack is connected to a battery management module, the DC converter is connected to the active power compensator, and the AC input end of the inverter is connected to a single-phase AC 220V power supply or a three-phase AC 380V power supply.

[0009] In the above-mentioned ground fault active full compensation device using an energy storage unit, the converter is a single-phase H-bridge topology structure or a three-phase bridge topology structure.

[0010] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is as follows.

[0011] The utility model provides working power for the active power compensator by arranging an energy storage unit in the system. When the system is operating normally, the battery of the energy storage unit is charged with relatively low power. After the battery is fully charged, the battery power is kept constant in a constant voltage manner. When the system is grounded, the characteristic of the battery that can output relatively high current is utilized to compensate for the active current, reactive current and harmonic current of the system fault point, thereby reducing the power capacity required for the rated power operation of the active power compensator, avoiding the need to add power transformers, switch cabinets and other equipment when the secondary capacity of the grounding transformer is insufficient, reducing equipment investment and saving floor space.

[0012] In addition, by providing an energy storage unit, the present invention can store excess energy in the battery pack during the transition process of the active power compensator being connected to the grid after a ground fault occurs and the active power compensator being off the grid after the ground fault disappears, thereby effectively preventing the occurrence of DC overvoltage during the transition process and improving the safety and stability of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the system wiring diagram of the utility model;

[0014] Among them: JDB. Z-type grounding transformer, XH. arc suppression coil; KM. fully compensated switching high-voltage switch, B. step-up transformer, KZQ. controller, APC. active power compensator, DC / DC. direct current converter, BAT. battery pack, BMS. battery management module, PCS. converter. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0016] An active full compensation device for ground faults using an energy storage unit, the system wiring diagram is as follows Figure 1As shown, it includes a controller KZQ, an active power compensator APC, a step-up transformer B, a fully compensated switching high-voltage switch KM, an arc suppression coil XH, a grounding transformer JDB and an energy storage unit. The energy storage unit provides power for the active power compensator APC and absorbs excess energy when the active power compensator APC is put into or taken off the grid.

[0017] The energy storage unit includes a DC converter DC / DC, a battery pack BAT and a converter PCS connected in sequence. The controlled end of the battery pack BAT is connected to the battery management module BMS. The positive and negative ends of the DC converter DC / DC are respectively connected to the positive and negative poles of the DC side bus of the active power compensator APC. The AC input end of the converter PCS is connected to a single-phase AC 220V power supply or a three-phase AC 380V power supply; accordingly, the converter PCS uses a single-phase H-bridge topology or a three-phase bridge topology.

[0018] One end of the step-up transformer B is grounded, and the other end is connected to the busbar through a grounding transformer. The neutral point of the grounding transformer is grounded through an arc suppression coil. The secondary side of the step-up transformer B is connected to the output end of the active power compensator APC, and the controlled end of the active power compensator APC is connected to the output end of the controller.

[0019] During normal system operation, the power converter (PCS) rectifies single-phase or three-phase AC power into DC power to charge the battery pack (BAT). To minimize grounding transformer capacity, the energy storage unit's charging power can be controlled to a very low value, such as 10 kW. This virtually eliminates the need to increase the capacity of the grounding transformer or power transformer. The battery management module (BMS) monitors the battery pack's (BAT) status and maintains balanced voltage across the battery cells within the BAT.

[0020] When a single-phase grounding fault occurs in the system, the full compensation device's controller, KZQ, controls the active power compensator (APC) to invert the DC power from the battery pack (BAT) into AC power with adjustable amplitude and phase. This power is then injected into the neutral point of the grounding transformer (JDB) via the step-up transformer (B), compensating for the active, reactive, and harmonic currents at the fault point. Because multiple battery packs are connected in parallel, the output current can be very high, reaching a maximum of 420A, for example. The active power compensator (APC) can provide compensation at rated power, ensuring effective compensation.

[0021] During the process of active power compensator APC being connected to the grid when system grounding occurs and active power compensator APC being disconnected from the grid when grounding disappears, the active power compensator APC stores excess energy in the battery pack BAT, which can effectively prevent the occurrence of DC overvoltage during the transition process and improve the safety and stability of equipment operation.

[0022] When the present invention is applied to a 10.5kV distribution network, considering that the compensation time after a ground fault occurs in the system is two hours, the following three battery pack configuration schemes are possible:

[0023] Battery pack configuration plan 1:

[0024] An active full ground fault compensation device using energy storage units, to meet a compensation capacity of 10kV / 15A, assuming a step-up transformer with a transformation ratio of 25, requires a low-voltage side current of 375A and an output voltage of 300V. The capacity is 375A x 300V x 2h = 225kWh. If 280Ah / 0.5C batteries are used, three clusters need to be connected in parallel, with a maximum discharge current of 280 x 0.5 x 3 = 420A. The voltage of a single cell is 3.2V, so the required number of batteries is 225kWh / 280A / 3.2V = 251.

[0025] Therefore, three battery clusters can be selected in parallel, with six battery string PACKs in each cluster. Each battery string PACK consists of 16 battery cells connected in series, resulting in a total of 288 batteries and a battery capacity of 3×6×16×3.2×280=258.048kWh.

[0026] Battery pack configuration option 2:

[0027] An active full ground fault compensation device using energy storage units requires a 10kV / 15A compensation capacity. Assuming a 25-ratio step-up transformer, the low-voltage side current is 375A and the output voltage is 300V. Without a DC / DC converter, the battery must still be able to output the rated voltage at its lowest voltage. Assuming an output voltage of 300V and a minimum lithium-ion battery voltage of 2.5V, the number of batteries connected in series is 300V x 1.414 / 2.5V = 170. Therefore, 11 packs containing 16 cells each can be used, for a total of 176 cells. The low-voltage side current required is 375A. If 280Ah / 0.5C batteries are used, three packs in parallel are required, resulting in a maximum discharge current of 280 x 0.5 x 3 = 420A.

[0028] Therefore, three parallel battery clusters can be used, with 11 packs per cluster and 16 cells per pack connected in series. The battery capacity is 11 × 16 × 3.2 × 280 × 3 = 473.088 kWh.

[0029] Battery pack configuration plan three:

[0030] An active full ground fault compensation device using energy storage units, to meet a compensation capacity of 10kV / 15A, assuming a step-up transformer with a transformation ratio of 25, requires a low-voltage side current of 375A and an output voltage of 300V. If the system primarily contains reactive and harmonic currents, with a very low active current (calculated as 3A), the battery pack capacity can be significantly reduced by considering only converter losses, capacitor losses, and the very low active current. To meet the compensation capacity of 3A active current (compensating reactive current only requires considering the active losses of the APC and DC / DC converter, which are very small), assuming a step-up transformer with a transformation ratio of 25, the required low-voltage side current is 75A and an output voltage of 300V, resulting in a capacity of 75A × 300V × 2h = 45kWh. If 280Ah / 0.5C batteries are used, three clusters need to be connected in parallel. The maximum discharge current is 280×0.5×3=420A, and the number of batteries required is 45kWh / 420A / 2 / 3.2=17.

[0031] Therefore, three battery clusters can be connected in parallel, with one pack per cluster and 24 cells per pack connected in series. The battery capacity is 1 × 24 × 3.2 × 280 × 3 = 64.512 kWh.

[0032] The above are only three possible battery pack configurations. Other configurations can be set according to the actual operating status of the system.

Claims

1. An active full compensation device for ground faults using an energy storage unit, comprising a controller (KZQ), an active power compensator (APC), a step-up transformer (B), and a fully compensated high-voltage switch (KM), characterized in that: It also includes an energy storage unit that provides power to the active power compensator (APC) and absorbs excess energy when the active power compensator (APC) is put into or taken off the grid. The AC input end of the energy storage unit is connected to a single-phase AC 220V power supply or a three-phase AC 380V power supply, and the positive and negative terminals of the energy storage unit are respectively connected to the positive and negative terminals of the DC side bus of the active power compensator (APC).

2. An active full ground fault compensation device using an energy storage unit according to claim 1, wherein the energy storage unit comprises a direct current converter (DC / DC), a battery pack (BAT), and a current transformer (PCS) connected in sequence, the controlled end of the battery pack (BAT) being connected to a battery management module (BMS), the direct current converter (DC / DC) being connected to an active power compensator (APC), and the AC input end of the current transformer (PCS) being connected to a single-phase 220V AC power supply or a three-phase 380V AC power supply.

3. The active full compensation device for ground faults using an energy storage unit according to claim 2, wherein the current transformer (PCS) is a single-phase H-bridge topology structure or a three-phase bridge topology structure.

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