Design and Development of an Efficient Multilevel DC/AC Traction Inverter for Railway Transportation Electrification

This paper presents a new trend in the transportation industry to adopt the multilevel inverter-based propulsion systems and gives the design procedure of a new DC/AC three-phase six-level inverter for powering the rail metro cars. The proposed inverter is based on the multilevel converter as it possesses much lower component voltage stress compared with the pulsewidth-modulated (PWM) topologies. Space vector pulsewidth modulation (SVPWM) with back-to-back clamped diode voltage modulation operation is used to achieve voltage regulation and high efficiency at any loading condition. Zero-current-switching operation is achieved without using an auxiliary circuit, which leads to minimum switching losses. The novelty of the proposed inverter lies within the proposed control methodology, which uses a new switching pattern that guarantees a modified SVPWM to eliminate the unwanted harmonics from the output voltage. The new algorithm is developed using numerical iterative solution using the Newton-Raphson technique that was downloaded to the processor using digital signal processing developed code. The mathematical model is simple but proven to be effective. As a result, a higher operating efficiency at full load of 98.5% is achieved as compared to previous efficiency of 97%. Analytical, simulation, and experimental results of a 1500 Vdc/700 Vac 400-kW converter are presented to offer the proof of concept. The converter provides real estate savings for the train under floor layout, higher operating efficiency as well as better cost price than the conventional two-level PWM hard-switched converters.