PUBLICATIONS

This dissertation proposes a method to ensure the reliability of critical and frequently failing components—the electrolytic capacitor and the high-power switching device, IGBT (Insulated Gate Bipolar Transistor)—in motor drive parallel operation systems. Although the parallel operation system, which drives a single motor using multiple parallel-connected inverters, is suitable for high efficiency and scalability, system stability is compromised by capacitor degradation and output current unbalance caused by circulating currents between the inverters.

To address these issues, this research proposes comprehensive methods for capacitor and IGBT protection. First, the structure and limitations of a single, large-capacity inverter are discussed, followed by an explanation and comparison of three different system configurations for implementing large-capacity motor drive using inverter parallel operation.

Furthermore, a method is presented for diagnosing the replacement timing of the DC link smoothing capacitor by estimating its current capacitance and calculating its usage rate against the initial design capacity, thereby ensuring capacitor reliability.

To minimize the output current unbalance between parallel-connected inverters, the PCUC (Phase Current Unbalanced Compensator) technique is proposed. The PCUC ensures uniform control of the common-mode output current of the parallel inverters, preventing IGBT overcurrent damage resulting from output current unbalance caused by circulating currents between the inverters, thereby enhancing system stability. The effectiveness of the proposed technique is verified through simulation and experimental validation using a parallel operation system configured with three inverters.

This proposes novel diagnostic and control methodologies that simultaneously secure the reliability of both the capacitor and the IGBT in a parallel operation system. The proposed approach enables stable system operation by pre-detecting component faults and effectively controlling the system. This approach is expected to contribute to the enhanced stability and extended lifetime of future high-power motor drive systems.