A Novel Zero Sequence Injection Method for Three-Phase Energy Storage Systems in Time-Varying Amplitude-Frequency Conditions

The study focuses on the interphase power imbalance problem in the cascaded multilevel energy storage inverter for ultra-high-speed linear motor propulsion (UHSLMP) systems. The traditional interphase energy balancing methods, which rely on fixed frequency and amplitude, are limited due to the continuous variation of supply voltage amplitude and frequency, traditional zero-sequence voltage injection methods with constant values are inadequate. To address this challenge, this paper analyzes power calculation and definition considering the time-varying AC supply and establishes a phasor model that accounts for the time-varying amplitude and frequency. Based on this model, a novel zero-sequence voltage injection method is proposed to tackle the interphase energy balance problem under varying amplitude and frequency conditions. Simulation results demonstrate the effectiveness of the proposed method.