[Dry goods] analysis of high-voltage direct-storage energy storage technology

High voltage direct storage energy storage circuit diagram

The DC voltage of a single energy storage battery cell is not more than 4V. The DC voltage of the battery system normally used for energy storage is 600-800V. How does PCS directly connect to the 3kV and above voltage level grid without the transformer, and the voltage matching problem is solved first.

The high-voltage direct-storage energy storage system introduced by Zhiguang Storage can be composed of a battery unit and a single-phase PCS module (H-Cell, as shown in Figure A1 above). The voltage superposition principle is used to achieve high-voltage direct output. The H-Cell battery pack DC power is converted into several hundred volts AC by single-phase PCS; the single-phase PCS AC side with multiple identical hardware structures is connected in series to form a single-phase high-voltage energy storage device, which generates single-phase high-voltage alternating current matched with the grid voltage; Three sets of single-phase high-voltage energy storage devices Y with identical hardware structure are connected to form a three-phase high-voltage energy storage device, that is, directly output three-phase symmetric high-voltage alternating current that matches the grid voltage.

The power supply equipment connected to the grid must meet the strict harmonic index requirements to avoid harmonic pollution of the power grid and threaten the normal operation of the power grid. In general, the higher the switching frequency of the power electronic device, the better the output harmonic performance, but as the switching frequency increases, the device generates heat, and the operating efficiency and stability deteriorate. The high-voltage direct-storage energy storage system adopts the carrier phase shift control algorithm, which can achieve the purpose of improving system efficiency and reducing output harmonics. A single H-Cell operates at a lower switching frequency f. After the output voltages of the N H-Cells are phase-shifted, the equivalent output switching frequency of the system output line voltage is 2Nf, and the equivalent switching frequency is increased by 2N times. The energy system can make the power device (IGBT) operate at a lower switching frequency and output a low-harmonic AC with an approximate sine wave. It can meet the harmonic index requirements of accessing the public power grid without special filter processing.

Zhiguang high-voltage energy storage device harmonic test value

Energy storage batteries are costly, and their cycle life is usually only a few thousand times, improving the overall efficiency of the energy storage system and significantly improving the economics of the system. The high-voltage direct-storage energy storage system introduced by Guangzhou Zhiguang Energy Storage Technology Co., Ltd. eliminates the energy storage grid-connected transformer and filtering device, which improves the overall efficiency of the system by about 2%. Taking a system with a cycle life of 6,000 times and 2MW/2MWh as an example, the overall efficiency of the system is increased by 2%, that is, 40.8 kWh of electric energy is consumed in one charging process, and 40 kWh of electric energy is consumed in one discharge process, so the operating cost of the battery during the whole life cycle (charging) The reduction in consumption can be reduced by 244.8 MWh, the operating income (reduced discharge consumption) can be increased by 240 MWh, and the overall benefit is increased by 484.8 MWh.

Zhiguang high voltage direct energy storage device efficiency

Affected by factors such as manufacturing process error and usage environment, even if two single cells produced in the same batch cannot be identical in performance, battery balancing control is required for MW-class battery energy storage systems with large battery capacity. Especially important. The traditional MW-class energy storage system basically adopts the battery passive equalization technology. Due to the large number of batteries and large single-cell capacity, it is difficult to effectively use the battery active equalization technology, and the battery “barrel effect” is obvious.

Each H-Cell output power of Zhiguang high-voltage direct-storage energy storage system can be effectively controlled, and it is easy to realize intra-phase and phase-to-phase H-Cell active equalization control. In-phase equalization control - Since the H-Cell in the phase is a series structure, the output current of each H-Cell is the same, and the output voltage can be different. By redistributing the total output voltage between the H-Cells in the phase, Realize the redistribution of output power to achieve the purpose of active balancing of the battery between the H-Cells in the phase. Phase-to-phase equalization control - Since the system uses the Y-connection method, there is no zero-sequence current path, so the zero-sequence voltage component in the safe range can be injected when needed, and additional power is added between the phases to achieve phase-to-phase equalization control without affecting Total system output power.

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