Linear and Nonlinear Composite Control Strategy of a Three-Level Phase-Shift PWM DC-DC Converter for Electric Ship MVDC Application

A three-level (TL) phase-shift pulse width modulation (PSPWM) dc-dc converter is proposed for electric ship medium voltage direct current (MVDC) application. A dc-ac-dc topology is adopted for the converter considering galvanic isolation between input MVDC and output low voltage direct current (LVDC). Output voltage regulation of the converter is obtained by the use of PSPWM. In order to achieve fixed frequency and zero steady-state error during steady-state conditions and fast response during transient conditions for the converter, a linear and nonlinear composite control strategy is presented in this paper. The proposed composite control strategy is based on the small-signal model of the converter. To verify the feasibility of the control strategy, detailed simulations have been made. The control strategy has also been validated through the hardware-in-loop RT-LAB system. The experimental and simulation results prove the proposed composite control strategy to be superior in dynamic response over that of a conventional linear control strategy.