A Switching-Gain Controller for Grid-Connected MMC Complying with Voltage Ride-Through Requirements

Abstract

Connecting high-power Renewable Energy Sources (RESs) to the utility grid has to be secured considering international standards to guarantee the efficiency, reliability, and stability of the power system. Redundancy, modularity, and scalability of the Modular Multilevel Converter (MMC) make it a proper option for high-power RESs such as offshore wind energy and PV systems. In this paper, the control of grid-connected MMC is investigated in order to comply with low voltage ride-through requirements. The modeling of MMC is achieved in this study using the Average Value Model (AVM). Grid integration through LCL-filter is explored since an LCL-filter may be required for Quasi two-level (Q2L) PWM operation of MMC and/or MMC with a relatively low-level order. A switching-gain integral state feedback with full-order observer controller is designed, evaluated, and verified for LCL-filter connecting MMC to the utility grid. Low Voltage Ride Through (LRVT) capability using Reactive Power Compensation (RPC) technique for grid voltage sag based on international codes such as German code is considered with the designed controller.