Design of an efficient multilevel inverter for a 1500V railway propulsion system applications

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 3-phase 7-level inverter for powering rail metro cars. The novelty of the proposed inverter lies within the proposed control methodology, which uses a new switching pattern that guarantees a modified space vector pulse with modulation (SVPWM) to eliminate the unwanted harmonics from the output voltage. The new algorithm is developed using numerical iterative solution using a modified Newton-Raphson technique that was downloaded to the processor using digital signal processing (DSP) 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. Analytical, simulation and experimental results of a 1500Vdc/700Vac 400kW 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 than the conventional two level pulse width modulated (PWM) hard switched converters.