Energy Efficiency Improvement in AC/DC/AC Diode-Clamped Multilevel Conversion Systems

An analysis of the efficiency of AC/DC/AC diode-clamped multilevel converters is presented, where commanded and suitable variations of the DC-link voltages are proposed in order to decrease the energy losses. The study is carried out also aiming at the correct DC-link capacitor voltage balance, obtained with additional chopper stages together with a new PWM technique, considering both inverter and line-side converter behaviour in different working points. The minimum losses and the correct operation of the system are then obtained by combining the optimal operating conditions of the converters. A detailed explanation of the efficiencies evaluation and the main results are reported.