What is PCS? -Bidirectional energy storage converter PCS

Energy storage converter, also known as bidirectional energy storage inverter, English name PCS (Power Conversion System), is used in grid-connected energy storage and micro-grid energy storage and other AC-coupled energy storage systems to connect battery packs and power grids (or Load) is a device that realizes two-way conversion of electric energy. It can not only invert the DC power of the storage battery into AC power, and transmit it to the grid or use it for AC loads; it can also rectify the AC power of the grid into DC power to charge the battery.

The power storage converter (PCS) is composed of software and hardware circuits such as power, control, protection, and monitoring. Divided into single-camera and three-camera, single-phase PCS usually consists of a bidirectional DC-DC step-down device and a DC/AC converter. The DC terminal is usually 48Vdc and the AC terminal is 220Vac. The three-phase PCS is divided into two types. The low-power three-phase PCS is composed of a bidirectional DC-DC buck-boost device and a DC/AC AC-DC conversion two-stage device. The high-power three-phase PCS is composed of a DC/AC AC-DC conversion first-stage device. Energy storage converters are divided into three types: high-frequency isolation, power frequency isolation and non-isolation. Single-phase and low-power three-phase PCS below 20kW generally adopt high-frequency isolation, and 50kW to 250kW generally adopt power frequency isolation. , 500kW and above generally adopt the method of non-isolation.

Important technical parameters of energy storage converters: Due to different application occasions, the functions and technical parameters of energy storage converters are quite different. When selecting, attention should be paid to system voltage, power factor, peak power, conversion efficiency, switching time, etc. , the selection of these parameters has a great influence on the function of the energy storage system.

It is the voltage of the battery pack and the input voltage of the energy storage converter. The energy storage inverters of different technologies have a large difference in system voltage. The energy storage converter with a single-phase two-stage structure is about 50V, and the energy storage converter with a three-phase two-stage structure is between 150V-550V. The three-phase energy storage converter with power frequency isolation transformer is between 500V-800V, and the three-phase energy storage converter without power frequency isolation transformer is between 600V-900V.

When the energy storage inverter is running normally, the power factor should be greater than 0.99. When the system participates in power factor regulation, the power factor range should be as wide as possible.

There are two switching times for energy storage inverters. One is charging and discharging switching. Large-scale energy storage reverse flow should be able to quickly switch operating states. Usually, it is required to be between 90% rated power grid-connected charging state and 90% rated power grid-connected discharging state. , the switching time is not greater than 200ms, and the second is applied to the switching between grid-connected mode and off-grid mode, and the switching time is not greater than 100ms.

Energy storage converters mainly have two working modes: grid-connected and off-grid. The grid-connected mode realizes bidirectional energy conversion between the battery pack and the grid. With the characteristics of grid-connected inverters, such as anti-islanding, automatic tracking of grid voltage phase and frequency, low voltage ride-through, etc., according to the requirements of grid dispatching or local control, PCS converts the AC power of the grid into DC power, charging the battery pack, has the function of battery charge and discharge management; during the peak load period of the grid, it inverts the DC power of the battery pack into AC power and feeds it back to the public grid; when the power quality is not good, it feeds the power grid Or absorb active power, provide reactive power compensation, etc. Off-grid mode, also known as isolated grid operation, means that the power conversion system (PCS) can be disconnected from the main grid according to actual needs and meet the set requirements, and provide local partial loads with AC that meets the power quality requirements of the grid. electrical energy.

In a micro-grid system composed of multiple energy sources, energy storage converters are the core equipment, because renewable energy sources such as photovoltaics and wind power are volatile, and loads are also volatile, and fuel-fired generators can only generate electricity and cannot absorb electricity. If there are only photovoltaic, wind and fuel generators in the system, the operation of the system may be unbalanced. When the power of renewable energy is greater than the power of the load, the system may fail, and the energy storage converter can absorb energy and send out energy. Energy, and the reaction speed is fast, and it plays a balancing role in the system.