①. Peak shaving and valley filling, provide reserve capacity, and ensure the safe and stable operation of the power grid
One of the characteristics of grid operation is that power generation, power supply and electricity consumption are completed at the same time, and cannot be stored on a large scale and for a long time. The electricity load is always high and low, and it is impossible to be balanced. The large peak-valley difference has become one of the most prominent problems in the operation of the power grid. The battery energy storage station can adjust the peak and fill the valley, improve the operating conditions of some thermal power units, and the variable voltage load operation is a stable output operation, thereby reducing the operating cost of the thermal power plant And power generation costs, reducing operating accidents.
The vast majority of peak shaving in China’s power grid can only be borne by conventional power plants, most of which are borne by coal-fired power plants, which increases coal consumption and brings hidden dangers to the safety and stable operation of the power grid. The peak shaving of battery energy storage stations fills valleys It can greatly reduce the peak-valley difference of the system, increase the guarantee rate of system power supply, reduce the number and time of power-off limit, and improve the operating conditions of the thermal power and nuclear power units of the system, so that these units can basically maintain stable operation in the high-efficiency area , It is not necessary to frequently increase or decrease output or start shutdown groups during operation, thereby reducing unit coal consumption, saving fuel consumption, and ensuring safe and stable operation of the power grid.
The battery energy storage station starts and stops quickly, is easy to change working conditions, and is convenient to adjust. Its response speed is in seconds. However, it takes 5 to 8 hours for a large coal power unit to go from cold to full load, so the battery energy storage station is a good accident backup power. Using the battery energy storage station as a hot reserve capacity to cope with unforeseen power generation or load needs can save the startup cost of thermal power reserve units and reduce the operating costs of thermal power units when their output is low.
②. Frequency modulation and voltage regulation to improve power quality
Frequency is one of the important quality indicators of the power system. According to the grid frequency requirements stipulated by China, the power grid cycle should be controlled at 50±0.2Hz. Some power systems in Western Europe stipulate that the frequency error is not more than ±0.1Hz in normal time. With the development of power systems, the requirements for frequency will inevitably become more stringent.
The problem of power system frequency modulation is essentially a problem of the balance of active power during normal operation. Frequency modulation is very important to the power grid. Regardless of whether it is the highest or the lowest load operation, it is required to maintain the cycle stability. Because the system load changes all the time, sometimes it changes drastically, which makes the system frequency change greatly. For this reason, the frequency modulation unit selected by the power grid must have the characteristics of responsiveness, adjust output in time, and adapt to instantaneous changes in load. The battery energy storage station has no mechanical parts, and only adjusts the input/output power through the control of power electronic devices. It has very good load tracking control performance, while the load increase rate of ordinary large thermal power units is only 1% of the rated output per minute~ 2%, which is far from meeting the requirements of climbing when the system load changes drastically. The battery energy storage station has the characteristics of rapid start and stop, flexible and reliable operation, and can adjust its work output in a wide range, which can respond to the instantaneous and short-term load of the power system It responds quickly to changes, can adapt to changes in the rapid increase and decrease of load, satisfies the trend of rapid changes in system load, improves the frequency qualification rate of the power grid, and keeps the frequency of the power grid stable.
Insufficient or surplus reactive power in the power system will cause fluctuations in the grid voltage, which will not only affect the quality of power supply and damage electrical equipment, but also directly affect the safe and reliable operation of the power system. Therefore, when the reactive power is insufficient in the system, it is often necessary to set up a camera or change the synchronous engine to phase-modulated operation to increase the reactive power output and supplement the system’s reactive power deficiency. With the expansion of grid capacity, the requirements for reactive power capacity are also increasing day by day. Insufficient reactive power of the grid will cause the system voltage to drop, and excess reactive power will cause the system voltage to rise, which directly threatens the power supply quality and safe operation of the grid. The battery energy storage power station uses power electronic devices for rectification/inversion to make energy storage The station has four-quadrant operation characteristics, which can absorb or emit reactive power at any time during charging/discharging, thereby regulating system reactive power, improving system voltage stability, improving power quality of the distribution network, and reducing the reactive power of the distribution network. Power investment and reduce network loss.