A Lyapunov function theory‐based nonlinear control strategy for NPC ‐type three‐level unified power quality conditioner

Classic control methods commonly used for a unified power quality conditioner (UPQC) include the following: proportional integral (PI) control, proportional resonance (PR) control, and repetitive control. Generally, the main weaknesses of these control methods are poor compensation accuracy and low response speed. In this article, in order to enhance the overall performance of the system, we introduce an innovative nonlinear control strategy based on the Lyapunov function for the three-phase three-wire neutral-point clamp (NPC) type three-level UPQC. We first develop the mathematical UPQC model, then obtain from the model the control law which we use to construct the switching function by creating the Lyapunov function, thus avoiding the introduction of closed-loop feedback. The suggested strategy also achieves system stability and dynamic performance by selecting appropriate parameters, after which a carrier-based pulse width modulation control method based on the injected zero-sequence component is applied to maintain the stability and balance of the DC-side capacitor voltage. In addition, both numerical simulation and comparison of experimental results using traditional PI control, passivity-based control methods, and sliding mode control shows that the proposed nonlinear control strategy for three-phase three-wire NPC type three-level UPQC has an excellent response speed and compensation efficiency.