Control strategy of bi-directional converter for PV-VRB energy storage system

Abstract

Importance and interest for Photovoltaic installations have been increased in the

recent times. But this brings new and many challenges to the electricity grid. The

output power of the PV system is naturally intermittent and fluctuating due to the

fluctuating sun irradiation and temperature, in contrast to the conventional power

plants based on fossil fuels. Thus the reliability of the supply is challenged.

One of the potential solutions to overcome this challenge is to integrate an energy

storage system with the PV system. One of the good solutions is to use Battery

Energy Storage System along with the PV Installations as the reliability of the supply

system is increased.

The project aims in integrating Vanadium Redox Flow Battery (VRB) with the PV

system. Vanadium Redox Flow Battery has many advantages compared to

conventional batteries. It has relatively high number of cycles, rare self-discharging

rate and independent power and energy rating. Thus VRB has excellent

characteristics and thus suitable for large scale energy storage applications.

The PV-VRB integrated system can provide a reliable supply. When the PV system

supply is more than the required demand the excess power is used for charging the

VRB. When the output from the PV system is lower than the demand, the VRB

discharges and compensates for the power mismatch between PV system and the

grid.

The VRB is connected to the DC bus by a bidirectional converter which determines

and controls the mode of operation of the VRB (charging and discharging) in order

to maintain the PV output power. A control strategy for the bi-directional converter

is developed and the results have been simulated and analysed.