Constant-Frequency Hysteresis Current Control of Grid-Connected VSI without Bandwidth Control

The theory, design, and implementation of a constant-frequency hysteresis current control for grid-connected voltage source inverter (VSI) is presented. The proposed control technique retains the benefit of the hysteresis control having fast dynamic response and tackles the drawback of the standard hysteresis control having variable switching frequency. The concept is based on predicting the current reference, system dynamic behavior and past time to formulate the switching function for dictating the switching times of the switches in the inverter within a pre-defined switching period. Of particular importance, no hysteresis bandwidth (a challenge in the practical implementation) is needed in the entire control method. The operating principles of proposed technique and mathematical derivation of the switching functions will be given. The proposed method is successfully applied to a 300W, 110V, 60Hz grid-connected VSI prototype with the controller implemented by a simple analog circuit. The steady-state and large-signal dynamic response of the VSI are studied. Experimental results show that the inverter can reach the steady-state in two switching actions after the inverter is subject to large-signal input and output disturbances.