Development Of10kW Bidirectional Converter For Vanadium Redox Flow Battery Energy Storage System

The rapid development of energy storage technology has made large-scaleoperation of grid-connected new energy distributed generation systems possible. As anew environmental protection energy storage battery, vanadium redox flow batteryhas wide prospect in the future market in the energy storage systems. As electricalinterface between the power grid and energy storage carrier, energy storage converterhas been related to the safe and stable operation of the whole energy storage system.Therefore, the research of the bidirectional converter for vanadium redox flow batteryenergy storage system has fatal significance.First the general design scheme of10kW bidirectional converter for vanadiumredox flow battery energy storage system is presented in this paper, bidirectionalhalf-bridge DC/DC topology and bidirectional three-phase bridge DC/AC topologywith LCL filter are selected as the structure of multilevel energy storage converter,and a brief analysis is given about the working principle of the circuit. This papermainly studies the control strategy of DC/AC circuit with LCL filter on thegrid-connected mode, and a system mathematical model is set up in the synchronousdq reference frame. A current dual-loop control strategy is educed from the passivedamping method for LCL filter by using method of equivalent transformation to thesystem structure diagram, and a decoupling control is adopted. This paper focuses onthe design method of currents dual-loop controller adopting expected frequencycharacteristics, as well as emphatically analyzes the impact on the system stabilitywhen the system’s parameters change. This method could precisely calculate theparameters of inner and outer loop controller when system parameters are given, andsome system performance and robustness can be obtained. On the basis of theoreticalresearch, the hardware system and software system of energy storage system aredesigned, including the calculation of the main circuit parameters, the design ofDC/DC control system and DC/AC control system, the design of peripheral circuit forcontrol system, the design of control system software and the design of man-machineinterface. Detailed hardware circuit designs are given about sampling, signalconditioning, IPM interface, timing control, protection, status indication,communication interface, auxiliary power system; Detailed workflows of the softwaresystem are given about main program, main interruption, communication interruption, start and stop timing, according to different phase start, software phase-locked loopbase on single synchronous coordinate system, sampling processing, digital PIDcontroller, SVPWM modulation algorithm base on parameters normalized. Finally, a10kW bidirectional converter for vanadium redox flow battery energy storage systemprototype has been built according to the designs. System were continuouslyoptimized and upgraded in the process of debugging, and a series of experiments havebeen carried out.Feasibility and effectiveness of the control strategy and design method arevalidated by simulation and experimental results. Energy storage converter systemcan run stably on grid-connected inverter mode, isolated inverter mode andgrid-connected rectifier mode, and the basic functions of the system are achieved.