Improved Model Predictive Control for High-Power Current-Source Rectifiers Under Normal and Distorted Grid Conditions

This article proposes an improved model predictive control (MPC) method for high-power current-source rectifiers (CSR). Instead of introducing the virtual impedance based active damping notion into MPC framework, the predefined cost function directly takes grid-side current and capacitor voltage as the regulating objectives to suppress the $LC$ resonance and grid current distortions. The relationship and differences between the proposed cost function and its form with active damping function are analyzed in detail under normal grid conditions. Moreover, the number of discrete candidate vectors during each predictive horizon in the proposed scheme is reduced from nine to five by considering the constraint of switching states transition. Therefore the computational burden is relieved compared with conventional MPC under normal grid conditions. Finally, in order to keep sinusoidal grid current for CSR even working under severe distorted supply voltage, specific harmonic orders of grid current suppression items are added into the proposed cost function subsequently. The performance of proposed methods at low switching frequency ($\leq$1kHz) under normal and distorted grid conditions are tested through both simulation and experiments. For the implementation of all MPC methods, capacitor voltage is estimated by an observer to save hardware expense instead of using transducers.