PROJECT 6

Title: Modified Model Predictive Control of Bidirectional AC-DC And Isolated DC-DC Converters for Energy Storage System

Abstract: Energy storage systems have been increasingly employed in utility and transport applications as well as in renewable energy sources to ensure power reliability, active power control, load leveling, frequency control and grid synchronization. This research presents a modified model predictive algorithm to control bidirectional AC-DC and high frequency-linked isolated DC-DC converter, which have been used in energy storage system for power transferring between the three-phase AC supply and energy storage devices. The modified model predictive control (MMPC) algorithm utilizes the discrete behavior of the power converter and predicts the future variables of the system by defining cost functions for all possible switching states. Subsequently, the switching state that corresponds to the minimum cost function is selected for the next sampling period for firing the switches. The proposed model predictive control scheme allows bidirectional power flow with instantaneous mode change capability and fast dynamic response. The performance of the proposed MMPC controlled bidirectional AC-DC converter is simulated with MATLAB/Simulink and further verified with 3.0 kW experimental prototypes. Both the simulation and experimental results show that, the AC-DC converter is operated with unity power factor, acceptable THD (3.3% during rectifier mode and 3.5% during inverter mode) level of AC current and very low DC voltage ripple. Moreover, the proposed MMPC controlled bidirectional DC-DC converter is also simulated with MATLAB/Simulink, which shows that the proposed MMPC algorithm of the DC-DC converter reduces reactive power by avoiding the phase-shift between primary and secondary sides of the high frequency transformer and allow power transfer with unity-power-factor. Finally, the efficiency comparisons have been performed between the proposed MMPC algorithm and conventional MPC method for both the bidirectional AC-DC and high frequency-linked isolated DC-DC converter which ensures the effectiveness of the MMPC controller.