Hybrid Voltage and Current Control Approach for DG-Grid Interfacing Converters With LCL filters

This paper presents a hybrid voltage and current control method to improve the performance of interfacing converters in distributed generation (DG) units. In general, current-controlled methods have been widely adopted in grid-connected converters nowadays. Nevertheless, in an islanded system, the voltage control of DG units is desired to provide direct voltage support to the loads. Due to the absence of closed-loop line current controller, the voltage control scheme can hardly regulate the DG unit´s line current harmonics. Furthermore, if not addressed properly, the transfer between the grid-connected operation and autonomous islanding operation will introduce nontrivial transient currents. To overcome the drawbacks of voltage- and current-controlled DG units, this paper develops a hybrid voltage and current control method (HCM). The proposed method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents. With the HCM, local harmonic loads of the DG unit can even be compensated without using harmonic current extraction. In addition, the HCM guarantees smooth transition during the grid-connected/islanding operation mode transfer. Simulated and experimental results are provided to verify the feasibility of the proposed approach.