Virtual model predictive control for virtual synchronous generators to achieve coordinated voltage unbalance compensation in islanded micro grids

Abstract

For virtual synchronous generators (VSGs) in islanded micro grids, to achieve voltage unbalance compensation, it is often necessary to deal with the positive and negative sequence components of voltage and current in parallel. The complex structure and cumbersome parameter tuning highlight the shortcomings of linear controllers. To simplify the unbalance compensation scheme, a virtual model predictive control (VMPC) for VSG is proposed in this paper. Based on the theoretical mechanism of unbalance problem and the unbalanced power sharing principle, a negative sequence virtual impedance (NSVI) is embedded in the inverter model to construct the virtual model. Then the predictive control is implemented based on this virtual model, and the voltage unbalance compensation behavior of VSG is controlled. Based on the VMPC method and the NSVI regulation method, the coordinated voltage unbalance compensation scheme is developed for parallel operation of VSGs. Experimental results show that the proposed VMPC method can effectively help reduce the burden on the processor when performing voltage unbalance compensation control algorithm. And the performance of the coordinated voltage unbalance compensation scheme is verified in parallel VSGs with the same or different capacities.