In the transmission lines of the power system, reactive power is generated even without additional inductive loads due to the presence of line inductance. These reactive powers will affect the voltage drop of the line. In order to maintain voltage stability at various nodes of the power grid, reactive power compensation equipment such as synchronous cameras and static reactive power compensators in generators and substations need to generate or absorb reactive power in a timely manner.
The energy storage system can not only store and release energy, but also improve the stability and power quality of the power system through reactive power compensation function.
1 Power factor
Power factor (PF) is an important parameter in AC circuits, which reflects the ratio of useful power (also known as active power) to apparent power in the circuit. In an AC circuit, the power provided by the power source to the load includes active power and reactive power. Active power refers to the actual power used for doing work, such as converting electrical energy into mechanical energy, thermal energy, etc. Reactive power is the power used to establish magnetic and electric fields, but does not perform external work. The apparent power is the vector sum of active power and reactive power, whose value is equal to the product of voltage and current. The power factor can be calculated by dividing the active power by the apparent power.
The mathematical expression is: power factor=active power/apparent power
When the power factor is low, a larger current is required in the circuit to transmit the same active power, which means an increase in energy loss in the line. By increasing the power factor, the current in the line can be reduced, thereby reducing line resistance losses and improving energy transmission and utilization efficiency.
2 Principle of reactive power compensation for energy storage system
1. The concept of reactive power
Reactive power refers to the energy absorbed by an electric or magnetic field from a power source during a portion of a cycle in an AC circuit with inductance and capacitance, while releasing energy during another portion of the cycle. The average power during the entire cycle is zero, but energy is constantly exchanged between the power source and reactive elements (inductance, capacitance). The unit of reactive power is var or kvar.
2. Principle of reactive power compensation for energy storage systems
The energy storage system can achieve reactive power compensation for the power system by controlling its output of active and reactive power.
When the reactive power in the power system is insufficient, the energy storage system can output reactive power to improve the voltage stability of the power system; When there is excess reactive power in the power system, the energy storage system can absorb the reactive power to prevent the power system voltage from being too high. Specifically, when there is a significant demand for reactive power in the power system, energy storage systems can provide reactive power through discharge operations, improving the overall operational efficiency of the power system and reducing line losses.
When the voltage deviates from the rated value, the energy storage system can accurately adjust the output or absorption of reactive power, maintain the stability of the grid voltage, and prevent damage to the power system caused by high or low voltage. Compared to traditional reactive power compensation devices such as static reactive power compensators, reactive power generators, etc., energy storage systems have more flexible, efficient, and reliable characteristics.
3. Energy storage inverter function
The energy storage inverter has a four quadrant operation function, which can simultaneously output or absorb reactive and active power, and has frequency and voltage regulation functions. The reactive power compensation technology based on energy storage has the advantages of fast response speed, continuous adjustability, and controllable scale, and is suitable for new power systems with high proportion of new energy and high power electronics. The new power system dominated by new energy plays a more important role in providing reactive power compensation technology for energy storage.
3 Reactive power compensation operation steps for energy storage system
(1) Monitoring the status of the power system: Firstly, by monitoring key parameters such as voltage, current, and power factor in real-time, a comprehensive understanding of the current operating status of the power system can be obtained;
(2) Calculate reactive power demand: Based on the actual situation of the power system, comprehensively evaluate the reactive power demand of various equipment (such as transformers, motors, etc.), and calculate the total required reactive power;
(3) Develop and implement energy storage system control strategies: Based on the calculated reactive power demand, develop specific control strategies for the energy storage system, including determining charging and discharging modes, rates, and times, and perform real-time control of the energy storage system according to the developed control strategies;
(4) Monitoring and adjustment: During the operation of the energy storage system, continuously monitor the status changes of the power system, and dynamically adjust and optimize the control strategy of reactive power according to the actual situation to ensure the stable operation of the power system.
4 Application scenarios
As a new type of power system regulation method, energy storage system has the advantages of fast response, flexible control, and high efficiency and energy saving. By utilizing the reactive power compensation function of the energy storage system reasonably, the stability of the power system can be improved, the quality of electrical energy can be enhanced, and the operation of the power system can be optimized.
The application of reactive power compensation technology in energy storage systems is very extensive in the power system. By introducing energy storage systems and implementing reactive power compensation control, the power factor of the system can be effectively improved, transmission losses can be reduced, and the quality of the power grid can be enhanced. In industrial enterprises, photovoltaic systems, and charging stations, reactive power compensation control can also be achieved through energy storage systems to improve system stability and efficiency.