Predictive control algorithm for capacitor-less inverters with fast dynamic response

This paper presents a scheme to improve the input current ripple of capacitor-less inverter system using a predictive control algorithm. The capacitor-less inverter, which is using small capacitor in the dc-link, has several advantages such as competitive cost, compact size, enhanced reliability, and elimination of initial charging circuit. However, the dc-link voltage shows instability because the energy storage capability of the small capacitor is not sufficient. Therefore, DC-link shunt compensator (DSC) should be used in capacitor-less inverter to stabilize the dc-link voltage and nullify the negative impedance by injecting the compensation current. However, the general proportional integral (PI) current controller, which has wide bandwidth to track the compensation current having a sinusoidal waveform, is weak for the noise and disturbance. This paper proposes a model predictive control (MPC) algorithm to improve the performance of DSC. Given the optimal duty cycle calculated by estimating the next state current, the proposed algorithm has a fast dynamic response and accuracy. The proposed method is verified through PSIM simulations.