DC-Link Capacitor Lifetime Extension for Two-Level Back-to-Back Converters Based on Zero-Sequence Voltage Injection

To increase the lifetime of DC-link capacitors in two-level three-phase back-to-back converters, this paper presents a novel root-mean-square (RMS) current reduction method utilizing zero-sequence voltage injection. The core concept involves optimizing the RMS current of the capacitor by modulating the overlapping intervals between the currents on the rectifier and inverter sides. By analyzing the voltage references and phase currents on both sides, an optimal zero-sequence voltage is determined and injected into either the rectifier or the inverter side. Simulation results validate the efficacy of the proposed method, demonstrating a significant reduction in the RMS value of the capacitor current, thereby extending the capacitor lifetime. Moreover, the proposed method has a minimal impact on current quality.