Research On Rapid Charge Method For VRB And Modeling In VRB-PV Energy Storage System

Vanadium Redox Flow Battery (VRB), as a new type of chemical batteries, hasreceived much attention because it has the power and capacity of independent design,macro current charge and discharge, super-deep discharge and long life. Some VRBstudies are focused on the key materials, system model and demonstration project.This paper takes VRB as research subject and makes a thorough study on its chargemethod and model of stand-alone photovoltaic (PV) storage system with VRB.Based on the existing charge technique, according to the operation principle andelectrochemical mechanism of VRB, an intermittent charge method with variablecurrent and constant-voltage was introduced under the guidance of the J. A.MAS’slaw. The characteristics of this charge method are that charging current decreases stepby step and break time is be taken to eliminate polarization of VRB in charge progress.For a single VRB, better charging parameters were achieved under a series ofcharging and discharging tests. Compared with the constant-current andconstant-voltage charge method，the proposed method not only got the same dischargecapacity，but also reduced half of charging time. Moreover，its discharge capacity didnot decrease after many recharge cycles. Meanwhile, the effects of state of charge(SOC) and electrolyte flow on the VRB performance are investigated under this newmethod. All experimental results demonstrate that a fast, high efficiency anddamage-less charge method has been realized.VRB is considered particularly suited for the large and medium-sized energystorage system. As a result, a5.3kW PV hybrid power system with a40kWh VRB asan energy storage device was developed. The hybrid system includes a PV powergeneration module with its maximum power point tracking (MPPT) controller, abidirectional charger and a VRB energy storage module, etc. The effects of solarirradiation and load variation on the VRB response characteristics and the powerbalance performance of the hybrid system are investigated based on Matlab software. The simulation results show that the VRB has good charge-discharge characteristicsand can be capable of rapid response to balance the output power and to smooth solarfarm output power fluctuations. Moreover it also verifies the PV-VRB hybrid systemmodel has excellent stability. It is a good designing reference for engineering scale up.