A Low-Distortion Voltage Control Strategy Based on Digital ΔΣ PWM-P-PI for Voltage-Source Inverters

Transportation electrification leads to a growing demand for low-distortion voltage control algorithms in auxiliary inverters in electric trains, uninterruptible power supply (UPS) inverters in ships, and vehicle-to-load (E2L) inverters. However, conventional PWM-based methods impose extremely high hardware and design requirements. To address these challenges, we apply $\Delta \Sigma $ PWM techniques from microelectronics to power inverters, focusing on sampling, analysis, and improvements to achieve a low-distortion voltage source. Specifically, we propose a relatively simple digital solution using an isolated $\Delta \Sigma $ ADC with certain optimizations to capture nonlinearities of the pulses. Then, by developing the $\Delta \Sigma $ PWM model that considers the dead time effect in inverters, this study analyzes its precision advantages and discovers the problem of a lower damping ratio than PWM. Furthermore, implementing $\Delta \Sigma $ PWM in a multilevel topology mitigates distortion caused by unbalanced neutral-point voltage, though resonance may occur after level shifting. Subsequently, $\Delta \Sigma $ PWM-P-PI is proposed to suppress the resonance and enhance precision. An analytical approach is also provided to address the unique stability challenge. Experiments on a 1-kW hybrid five-level active neutral-point-clamped (5L-ANPC) inverter can achieve voltage total harmonic distortions (THDs) of less than 0.2% under various conditions, which offers a low-distortion and robust voltage control solution for the aforementioned wide-ranging transportation electrification applications.