The Power Conversion System(PCS)is a key device in energy storage systems.It is used to achieve energy conversion and bi-directional energy flow between energy storage batteries and the power grid.It can convert DC to AC or vice versa,to meet the charging and discharging requirements of the power grid for energy storage systems.

Working Principle of the PCS :

Bi-directional Conversion Based on Power Electronics Technology

The PCS energy storage converter mainly relies on power electronics technology.It achieves bidirectional AC/DC power conversion by controlling the switching states of power semi-conductor devices(such as IGBT -Insulated Gate Bipolar Transistors).

Grid-Connected Mode

In grid-connected mode,the PCS works in coordination with the power grid to enable bidirectional energy exchange between the energy storage device and the grid.When the grid requires the energy storage system to discharge,the PCS responds quickly,converting the DC power from the energy storage device into AC power and feeding it into the grid.When there is surplus power in the grid or when electricity prices are low,the PCS switches to charging mode,converting the AC power from the grid into DC power for storage.In addition,the PCS has functions such as anti-islanding protection,grid synchronization,and low-voltage ride-through to ensure stable grid operation and reliable power supply.

Off-Grid Mode

In off-grid mode,the PCS can operate independently of the power grid,providing stable AC power to local loads.In this mode,the PCS becomes the core power supply device,offering reliable power support for remote areas and emergency backup power scenarios.

Four-Quadrant Operation

The energy storage converter is a four-quadrant converter with controllable AC and DC sides.It can perform constant power or constant current control according to microgrid monitoring instructions,charging or discharging the battery while smoothing the output of fluctuating power sources such as wind and solar energy.

Topology and Control Strategy

Common topologies include single-stage,two-stage,and three-level energy storage PCS topologies.The single-stage energy storage PCS consists of a PWM converter.Its working principle is to invert the power output from the high-voltage battery bank through the PWM converter,and then regulate and control it through LCL filtering and a step-up transformer to match the output voltage with the grid and feed it back to the grid,and vice versa.The two-stage energy storage PCS adds a bidirectional DC/DC converter stage to the single-stage structure,which is used to control and regulate the voltage level.