Long horizon linear MPC of grid-connected VSIs: Regulation problems and a plug-in solution

This work investigates a linear model predictive control (MPC) in conjunction with a voltage source inverter with a grid-interfacing passive filter. In an ideal grid, standard linear MPC demonstrates fast transient and excellent steady-state performance while respecting the imposed constraints. Nevertheless, its direct application onto the grid-connected converters operating with a distorted grid (e.g. islanded microgrid and marine vessel grid) or with applications that require harmonic current injection would encounter steady-state tracking error [1, 2], leading to unfulfilled application objectives. This shortfall is first demonstrated here using simulation, and then a solution based on plug-in repetitive control (RC) is proposed and investigated. With some assumptions simplifying this investigation, the resulted linear MPC with RC plug-in successfully mitigates the steady-state tracking errors while preserving the applicability of the multi-parametric quadratic-programming — the explicit implementation method that makes the linear MPC feasible in fast sampling applications. It is worth noting here that the notable features of MPC such as simple tuning, fast current response close to the physical limits of the system, and constraints consideration are retained and this makes the proposed control method a powerful alternative to the established grid-converter control techniques.