An Evaluation Circuit for DC-Link Capacitors Used in a Single-Phase PWM Inverter

High-power conversion systems are based not only on three-phase inverters but also on single-phase inverters because modular multilevel cascade converters (MMCC) consist of half- or full-bridge single-phase converters. Their DC-link capacitors are a major constraint on the improvement of power density as well as of reliability. Evaluation of dc-link capacitors in terms of power loss, ageing, and failure rate will play an important role in the next-generation power converters. This paper presents an evaluation circuit for dc-link capacitors used in a high-power single-phase PWM inverter. The evaluation circuit produces a practical ripple current waveform and a dc bias voltage into a capacitor under test with a downscaled voltage-rating inverter, which is equivalent to those of the full-scale inverter. Theoretical analysis and experimental results verify the effectiveness of the evaluation circuit.