Achieving Fast Dynamic Response and Output Filter Condition Monitoring in Hybrid PWM Inverters Using a Low-Computational State Trajectory Prediction Algorithm Incorporating With Reduced-Order Switching Surfaces

This article presents a novel state trajectory prediction algorithm with reduced-order switching surfaces, designed for H-bridge inverters using hybrid pulsewidth modulation (h-PWM). h-PWM hybridizes the merits of a unipolar two-level switching scheme (U2SS) and a bipolar three-level switching scheme (B3SS), operating mainly in U2SS while temporarily transitioning to B3SS near the zero-crossing region to resolve the impact of pulse droppings. The algorithm predicts the state trajectory for the entire switching cycle, facilitating fast control and fast dynamic response. By sampling the state variable once at the beginning of each switching cycle, the duty ratios of all switching devices are established for the entire cycle. Since the effective operating frequency under h-PWM is twice the switching frequency, the values of the output filter components are minimized, and thus the power density can be increased. Furthermore, the algorithm can indirectly assess the condition of the output filter by adjusting the switching surface based on the comparison of actual and predicted state trajectories, thereby 1) ensuring that the prediction can adapt component variations, 2) identifying aging conditions, and 3) enabling preventive maintenance to avoid unexpected failures. The performance of the algorithm and the output filter parameter estimation technique are evaluated on a 1-kVA prototype.

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