Photovoltaic + Energy Storage + DG

Work with AC or DC coupled PV farm, BESS can automatically act as backup power for loads when grid fails. DG will be acting as secondary back-up when both battery and solar energy runs out.

System Operation Logic:

Photovoltaic power supplies the load first, and the surplus power is used to charge the battery. If photovoltaic power is not enough, the battery will supply power. If photovoltaic power and battery energy storage are not enough, the mains power will supplement. If the mains power is also cut off, diesel generators will be used to supply power.

Application Control Logic:

On-grid Operation Mode

The energy storage is connected to the grid in PQ mode, and only the residual photovoltaic power is charged, not the mains power.

PV power supply the loads firstly, with excess electricity used to charge the batteries. When the state of charge (SOC) of the storage exceeds a certain value, EMS will forbid all power to charge the battery, and limit the pv power and prevent the pv power feed to grid.

When pv power is insufficient, both the pv and the batteries supply the load together.

When pv power is not generating electricity, the mains power and batteries supply the load together.

When the SOC of the storage is below a certain value, EMS will forbid the battery discharge, and then the grid will supply the loads.

Off-grid Operation Mode

When the utility power fails, the STS quickly shuts down and simultaneously triggers a switch in the PCS to islanding VF mode, achieving a seamless transfer between grid-connected and islanding modes.

When pv is enough, pv supply the loads firstly, the extra power charge the battery, If the SOC of the energy storage exceeds the threshold, EMS will limit the pv power, protect from the over charge.

When pv is insufficient, both the pv and the batteries supply the load together.

When there is no photovoltaic power generation, battery supply the loads.

When the SOC of the energy storage falls below a certain level and the utility power is lost, the EMS initiates the diesel generator via dry contacts to serve as the system voltage source, with the ATS automatically switching to the diesel generator.

After the startup of the diesel generator, when the voltage on the grid side of the STS recovers, the energy storage system automatically synchronizes with the grid side voltage and closes the STS static transfer switch to achieve grid-connected operation.

When the utility power is restored, the ATS automatically switches back to the utility power, and the EMS controls the shutdown of the diesel generator through dry contacts.