VSC Controllers for Multiterminal HVDC Transmission System: A Comparative Study

Voltage source converter (VSC)-based multiterminal high-voltage direct current (HVDC) systems received widespread attention throughout the world for grid integration of renewable energy resources in recent years. This paper presents a comparative performance analysis of different VSC-based outer control and inner current controllers for the multiterminal HVDC system. It employs either lead-lag (LL) or proportional-integral (PI) controllers for outer DC link voltage control, whereas it uses PI or model predictive controllers (MPCs) for inner current control. Hence, it designs four combinations of controllers (LL-MPC, LL-PI, PI-MPC, and PI-PI) to control the outer DC link voltage and inner current of the VSC-based multiterminal HVDC system. Besides, it proposes an integral time squared-error (ITSE)-based optimization technique to tune the parameters of the employed PI controllers that selects optimal parameters at minimum ITSE under extreme operating condition. The combination of the mentioned controllers forms the main control unit of the multiterminal HVDC transmission network for regulation of the DC link voltage and the power flow. Moreover, this article evaluates the controller performance in terms of maximum overshoot, steady-state error, settling time, rise time, and total harmonic distortion. It implements the proposed controllers in a typical VSC-HVDC system and multiterminal HVDC transmission system in MATLAB/SIMULINK platform. Presented results confirm the efficacy of the four-type controllers. The optimized PI-MPC controller provides overall better performance relative to other controllers.