A Comparison of a Discrete-Time PI and an Indirect MPC Current Controllers for a Single-Phase Grid-Connected Inverter Operating with Distorted Grid and Significant Computation Feedback Delay

In this paper, one technical gap related to the indirect model predictive control (MPC) is discussed. This technical gap corresponds to the performance of such a controller to deal with distorted grid voltages and a significant computation delay through the feedback regulation loop. A basic case study involving a traditional 3-level h-bridge and a first-order output filter was considered in order to magnify the effect of time horizon prediction and voltage over the regulated grid current waveform. A comparison related to the covered MPC controller (in two different forms) and a classical discrete-time proportional-integral (PI) controller is performed by means of the achieved total harmonic distortion (THD) values. Simulation results from a model built on PSIM/Powersim are presented and discussed. It can be concluded that the MPC controller offers a wider operating range with stable conditions and lower measured values of THD from regulated grid current. And such kind of special feature becomes even more evident if a significant computation delay at the feedback control loop must be overtaken.