Global interest in environmentally friendly ships has surged as a result of greenhouse gas reduction policies and the demand for carbon neutrality. Despite growing demand for electric propulsion systems, there is a lack of research and development on crucial components. Efficiency and stability are primarily influenced by the performance of inverters, which are essential for driving propulsion motors. Existing inverter control techniques can be of two types: continuous-PWM (pulse width modulation) methods for harmonic performance enhancement and discontinuous-PWM methods for efficiency improvement by reducing losses. However, there are limitations in that each PWM method exhibits substantial variations in inverter performance based on its operating conditions. To address these challenges, this study proposes the hybrid pulse-width-modulation (HPWM) method for optimal inverter operation. By analyzing the inverter’s operating conditions, the proposed HPWM method adopts various pulse-width-modulation (PWM) strategies based on a modulation index to achieve harmonic improvement and loss reduction. Our focus is on comparing and analyzing diverse PWM techniques under varying modulation indices and frequency conditions to attain the optimal operating conditions. Experimental validation of the proposed method was conducted using a 2.2 kW dynamometer. In comparison with existing PWM methods, the proposed method demonstrated superior performance.

This study proposes a novel fault diagnosis algorithm based on Equivalent Series Resistance (ESR) estimation to enhance the accuracy of capacitor life diagnosis techniques for the DC link in marine electric propulsion systems. Accurate ESR estimation is critical for maintaining the reliability and efficiency of DC-Link capacitors, which play a key role in stabilizing voltage, reducing harmonics, and ensuring the smooth operation of electric propulsion systems. By preventing capacitor failures, this algorithm contributes to reducing the risk of catastrophic damage to entire systems. The ESR value is determined by extracting AC voltage and current data within the frequency range of 10 kHz to 30 kHz using a band-pass filter. To improve reliability, the algorithm compensates for input errors based on the modulation index and switching pattern, with error data stored in a lookup table. By addressing limitations in existing ESR estimation techniques, the proposed method reduces estimation errors across the entire range and enhances fault diagnosis accuracy. Experimental results validate the algorithm’s improved accuracy, reliability, and stability, demonstrating its effectiveness in preventing damage to power conversion devices.