EPS (also known as backup power) increase versatility of hybrid inverter. EPS enables the inverter to work in both grid-connected mode and off-grid mode (island mode). In grid-connected mode, solar energy firstly goes to backup loads and normal loads. The excess energy is stored in the battery or goes to the grid. Meanwhile, the battery, or the grid, or both can supply power for the backup loads under the condition that power from the PV and battery is less than the backup load power. The maximum output power (for example, the max output current) capability for backup loads, can be larger than inverter’s rated AC output power. Take the popular 25KW 3-phase hybrid inverter in the market as an example, the inverter allows 37.9A maximum AC output current, while In grid-connected mode supports 43KW maximum output power (63A maximum output current) for backup loads. In off-grid mode, hybrid inverter makes sure of a seamless energy supply by obtaining energy from the solar or battery during grid outages or emergencies.

Different from inverter 3-phase current sampling, theoretically speaking, EPS 3-phase current sampling is not used for power stage control, and does not need to consider DC component suppression because for the backup loads and does not do harm to the grid, grid load and grid equipment even out of range. However, this is used for backup loads power statistics, using hall-effect current sensor with high accuracy and low drift benefits the metering accuracy and reliability.