Development Of Dynamic Voltage Restorerfor Microgrid And Optimization Of Its Compensation Control Strategy

In recent years, more and more distributed generation systems connect into the power grid in the form of microgrid, the exposed power quality problems also become increasingly prominent, moreover, the voltage sag is the most frequently and dangerous kind among the power quality problems. Dynamic Voltage Restorer(DVR) can solve the problem of voltage sag effectively, so it is widely used in microgrid systems.To begin with, this paper presents a microgrid model that contains DVR, and uses DVR for voltage sag mitigation of microgrid feeders in order to maintain the normal operation of sensitive loads. On the basis of introducing DVR working principle, this paper analyzed and designed its composition modules. In order to output the load reference voltage quickly and accurately and obtain better compensation result, the compound control strategy using the grid voltage feed-forward control and the load voltage and capacitor current double closed-loop feedback control is proposed, and then verify the performance of compound control strategy by simulation in different instances.On the basis of the theoretical simulation, hardware is designed such as the main circuit of DVR prototype, DSP main controller, measurement circuit for voltage and current, fault-secure circuit and optocoupler driver and separation circuit, the flowchart design for DVR software is given, and then three phase voltage sag experiment was carried out on the DVR prototype, the experimental results show that the DVR prototype gives quick response speed, the output compensation voltage is stable and the load voltage has small distortion, thus the compensation effect is good.Then the traditional compensation strategies are analyzed and compared in view of the DVR economic performance. On the theoretical derivation basis of maximal compensation time, an improved compensation control strategy is advocated, which has combined the strengths of traditional compensation strategies while effectively avoiding their weaknesses, so that the DVR compensation control strategy can optimize its effect. The simulation results have shown that under the same capacity of the energy storage device, the improved compensation control strategy can reach the small distortion to load voltage and obtain longer compensation time, thus being able to more efficiently use DC side energy storage and improving DVR’s economic performance.