Impedance-Based Stability Characterization of Extended Finite Control Set MPC Under Realistic Switching Constraints

Advances in digital processing have made finite control set Model predictive control (MPC) increasingly viable for real-world power electronics applications. However, the maximum switching frequency of FCS-MPC is determined by the controller sampling time, which leads to a maximum switching frequency in the range from tens of kHz to hundreds of kHz. The finite switching capabilities of semiconductor devices limit the achievable switching frequency in practical power converter implementations. To address this, an extended finite control set MPC (FCS-MPC) is proposed, which effectively limits the maximum switching frequency without explicitly modifying the cost function. To assess the impact of introducing these realistic switching constraints on the system's behavior, a smallsignal stability analysis of the proposed MPC is performed. An impedance-based analytical model of the proposed MPC is developed, verified, and analyzed to evaluate its stability characteristics. Furthermore, since MPC lacks tunable parameters typically available in conventional PI-based control, an analytical equivalence between MPC and PI-based current controller is established to provide a reference framework and to understand their differences in converter impedance. It is shown through the analysis that the impedance of the FCS-MPC controlled converter is an intrinsic property of the controller, inherently exhibiting a stable profile and serving as a benchmark for PI-based designs, as it inherently achieves a wider stability margin corresponding to the optimal bandwidth attainable at a given switching frequency. The theoretical findings and stability assessments are validated experimentally using a Control-Hardware-in-the-Loop setup .