Photovoltaic power supply is different from traditional power supply. Its output power changes drastically with changes in light intensity, temperature and other environmental factors, and it is uncontrollable. Therefore, if photovoltaic power generation is to replace traditional energy sources to achieve large-scale grid-connected power generation, it will The impact of power grid impact cannot be ignored.

Photovoltaic power generation has the characteristics of high output level in a short time at noon, low output level in other periods, and output during the day and no output at night. Energy storage technology has the characteristics of being able to realize the time-space translation of electric energy. The output is transferred to other time periods to reduce the peak output of the power station and reduce the abandonment of light.

During the working process of the battery energy storage system, the principle of minimizing the charge and discharge times of the energy storage system is to prolong the service life of the energy storage system. During the peak period of photovoltaic power generation, the charging of the battery energy storage system is controlled, and the output of the photovoltaic power station is peak-shaving. After the peak period of photovoltaic power generation, the discharge of the battery energy storage system is controlled. The discharge control of the energy storage system can assist in smoothing the fluctuation of photovoltaic output and assisting system peak regulation, so as to maximize the role of energy storage. According to the different functions of energy storage and discharge, three working modes of the energy storage system can be divided, which are peak clipping, peak clipping + stabilization, and peak clipping + transfer.

Working mode one: peak clipping

During the peak output period of the photovoltaic power station, the charging of the battery energy storage system is controlled with peak shaving as the application goal. After the peak period of photovoltaic output and during the photovoltaic daytime output period, the power of the battery energy storage system is controlled to amplify and discharge to the battery energy storage system. The lower limit of the SOE working range, and then the energy storage system stops working to ensure that the working time of the energy storage system is within the power generation time of the photovoltaic power station, without additionally increasing the working time of the photovoltaic power station, reducing the impact on the work arrangement of the photovoltaic power station due to the configuration of the energy storage system Impact.

Working mode two: peak clipping + smoothing

During the peak hours of photovoltaic power station output, the charging of the battery energy storage system is controlled with peak load reduction as the application goal. The output fluctuations of large-scale photovoltaic power plants can be divided into two categories, one is slow changes in the output of photovoltaic power plants, such as periodic changes in the output of photovoltaic power plants caused by the alternation of day and night; the other is sudden changes in the output of photovoltaic power plants, such as caused by floating clouds A sudden drop in the output of photovoltaic power plants. The first round of changes is large, but the changes are slow; the second type of changes is unpredictable and sudden, and in serious cases, the output will be reduced from full power to below 30% of the rated value within 1~2s. After the peak period of photovoltaic output, control the discharge of the energy storage system with the goal of smoothing the fluctuation of the output of the photovoltaic power station during the alternation of day and night, and discharge it to the lower limit of the SOE operating range of the battery energy storage system. If it has entered the night, the output of the photovoltaic power station will decrease. When it reaches 0, the SOE of the energy storage system is still greater than 0.2, and the energy storage system is controlled to discharge at a constant power at the rated power until the SOE is close to 0.2, and then the energy storage system is controlled to stop working.

Working mode three: peak cutting + transfer

During the peak hours of photovoltaic power station output, the charging of the battery energy storage system is controlled with peak load reduction as the application goal. The output period of the photovoltaic power station is from 8:30 to 18:30, and the evening peak of the load occurs between 18:00 and 22:00. During this period, the photovoltaic power station has basically no output, and it can be assisted by controlling the discharge of the battery energy storage system. System peak regulation, in order to reduce the number of actions of the energy storage system and simplify the operation of the battery energy storage system, the battery energy storage system is controlled to discharge at a constant power, and the discharge is at the lower limit of the SOE working range of the battery energy storage system, and then the energy storage system stops Work.

As the proportion of photovoltaic power generation system in the power grid continues to increase, its impact on the power grid must be effectively managed to ensure the safety and reliability of power supply. The application of energy storage system in photovoltaic power generation system can solve the problem of unbalanced power supply in photovoltaic power generation system to meet the requirements of normal operation. Energy storage systems are crucial to the stable operation of photovoltaic power plants. The energy storage system not only ensures the stability and reliability of the system, but also is an effective way to solve dynamic power quality problems such as voltage pulses, inrush currents, voltage dips, and instantaneous power interruptions.