Energy storage converter, also known as bidirectional energy storage inverter, English name PCS (Power Conversion System), is used in AC-coupled energy storage systems such as grid-connected energy storage and micro-grid energy storage, connecting battery packs and power grids (or load), it is a device that realizes bidirectional conversion of electric energy. It can not only invert the DC power of the battery into AC power, and transmit it to the power grid or use it for the AC load; it can also rectify the AC power of the power grid into DC power to charge the battery.
The energy storage converter (PCS) is composed of power, control, protection, monitoring and other software and hardware. Divided into single-camera and three-camera, single-phase PCS is usually composed of bidirectional DC-DC buck-boost device and DC/AC AC-DC conversion device. The DC end is usually 48Vdc, and the AC end 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 use high-frequency isolation. For 50kW to 250kW, power frequency isolation is generally used. , 500kW or more generally adopts the way of non-isolation.
Important technical parameters of energy storage converters: Due to different applications, the functions and technical parameters of energy storage converters are quite different. When choosing, you should pay attention to system voltage, power factor, peak power, conversion efficiency, switching time, etc. , the choice of these parameters has a great influence on the function of the energy storage system.
system voltage
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 of the single-phase two-stage structure is about 50V, and the energy storage converter of the 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.
power factor
When the energy storage inverter is in normal operation, the power factor should be greater than 0.99. When the system participates in power factor adjustment, the power factor range should be as wide as possible.
switching time
The energy storage inverter has two switching times. One is charging and discharging switching. The large-scale energy storage countercurrent should be able to quickly switch the operating state. 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 more than 200ms, and the second is for switching between grid-connected mode and off-grid mode, and the switching time is not more than 100ms.
The energy storage converter mainly has two working modes: grid-connected and off-grid. The grid-connected mode realizes bidirectional energy conversion between the battery pack and the grid. It has 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 scheduling or local control, PCS converts the AC power of the grid into DC power can charge the battery pack and has the function of battery charge and discharge management; during the peak load period of the power grid, it inverts the DC power of the battery pack into AC power and feeds it back to the public power 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, that is, 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.
Summarize
In a micro-grid system composed of multiple energy sources, the energy storage converter is the core equipment, because renewable energy sources such as photovoltaics and wind power are fluctuating, and the load is also fluctuating. Absorb electrical energy. If there are only photovoltaic, wind and fuel generators in the system, the system operation may be unbalanced. When the power of the renewable energy is greater than the load power, the system may fail. Therefore, it is difficult for the photovoltaic grid-connected inverter to be compatible with the fuel generator. The energy storage converter can absorb energy and emit energy, and the response speed is fast, which plays a balancing role in the system.