High-performance bi-directional Z-source inverter for locomotive drive application

Three-phase locomotives use voltage source inverter technology for the speed control of traction motors. The voltage source inverter is fed by single phase active front end converter connected in H bridge in the locomotives. Since the voltage source inverter works in buck mode, a higher DC-link voltage is required to provide the rated voltage of traction motors increasing the size and cost of system. This study proposes a high-performance bi-directional Z-source inverter instead of voltage source inverter. Analysis is performed in all regions of operation of locomotive drive-acceleration, free running and regenerative braking. Both the speed control techniques-variable voltage variable frequency and field weakening are used for the drives. Simulation study of the system shows that the DC-link voltage gets reduced by 39% which in turn lower the voltage stress. This will decrease the traction transformer output voltage. Reduction in the harmonics at the output of Z-source inverter by 16% reduces the overheating of traction motor drive. A small scale prototype of Z-source inverter fed drive is made in the laboratory to verify the performance obtained from the simulation.