State Current Controller with Oscillatory Terms for Three-level Grid-connected PWM Rectifiers under Distorted Grid Voltage Conditions

This paper presents the design of a control system of a three-phase three-level pulse-width modulated rectifier operated under unbalanced and distorted grid voltage conditions. The developed scheme is based on a voltage-oriented control method. Instead of proportional-integral current controllers a state-feedback current controller in rotating reference frame is used. In order to achieve a zero steady-state current control error in response to step commands, integral terms are incorporated into the current control scheme. Similarly, to ensure the rejection of the sinusoidal component of current control error caused by unbalance and distortion in the grid voltage, the oscillatory terms are added to the current control system. To calculate the current controller gains, an augmented plant model is developed and linear-quadratic optimization method is applied. The physical experiments indicate that using state-feedback current control with oscillatory terms allows for notable improvement of the shape of the input currents of the converter and increases the power conversion efficiency.