A deadbeat controller for bidirectional high-frequency link inverter

Abstract

This thesis presents a Deadbeat controller for Bidirectional High-Frequency Link (BHFL) inverter. Deadbeat control technique is applied as it exhibits fast dynamic response. The proposed controller consists of inner current loop, outer voltage loop and a feedforward controller. The feedforward controller, which imposes a gain scheduling effect according to the reference signal, is used to compensate steady-state error of the system. The main property of the controller is that the current loop controller and the voltage loop controller have the same structure, and uses the same sampling period. This simplifies design and implementation of the controller. To improve overall performance of the system, disturbance decoupling networks are employed. The design takes into account the model discretisation effect. As such, accurate disturbance decoupling can be achieved. The robustness of the inverter towards load variations is thus increased. To avoid transformer saturation due to low frequency voltage envelope, an equalised Pulse Width Modulation (PWM) technique is proposed. The performances of the BHFL inverter with the proposed controller are investigated using MATLAB/Simulink. The simulation results are compared with the conventional Proportional-Integral (PI) controller and the multirate digital controller. The feasibility of the controller is further validated by a 1kVA laboratory prototype. The DS1104 Digital Signal Processor (DSP) from dSPACE is used to implement the control algorithm. The results show that the BHFL inverter with the proposed Deadbeat controller has excellent dynamic response and low output voltage distortion (1.5%). It also performs well under cyclic step load variations, and good steady-state response under highly nonlinear loads.