An IGBT based current flow controller for use in meshed HVDC grids

Abstract

The continuous installation of offshore wind farms in the North Sea area in the past few years has resulted in the installation of numerous point to point HVDC links. As a result, the idea of forming Multi-Terminal Direct Current (MTDC) grids by interconnecting these links emerged along with its challenges. Power (current) flow control is one of few challenges that need to be solved to realize reliable operations of these MTDC grids. This paper presents an IGBT based Current Flow Controller (CFC) for power flow and current limiting applications in MTDC grids. Moreover, two control strategies based on PID controllers and a Hysteresis band Current Control (HCC) technique are proposed for the CFC. The theory of operation and control of the CFC are demonstrated. Key features of the proposed controller including the balancing of cable currents, limiting of cable current, current nulling and automatic switching mode detection and changing are discussed. A MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, low power prototype is built for a CFC to experimentally validate its performance under steady state and sudden load change condition. Simulation and experimental studies indicate fast dynamic response and precise results. The proposed controller offers a promising solution for power flow control challenges in MTDC.