The motivation of this research work was to develop a three level neutral point clamped (NPC) traction inverter for a permanent magnet synchronous machine drive. The three-level inverter helps to reduce the total inverter losses at higher switching frequencies, compared to a two-level inverter for electric vehicle applications. The three-level inverter has also more power switches compared to the two-level inverter. This helps to reduce the voltage stress across the switches and the machine winding. In addition, it also allows an increase in the DC-link voltage, which in turn helps to reduce the DC-link current, phase conductor size and the associated losses. Moreover, at higher DC-bus voltages the power switches will have lower thermal stress when compared to the 2-level. However, the NPC inverter topologies have an inherent problem of DC-link voltage balancing. In the initial part of this work, a novel space vector based DC-link voltage balancing strategy is proposed. This strategy can keep the two DC-link capacitor voltages balanced during transient changes in both speed and torque. The performance of the three-level inverter system is then compared with a two- level inverter based drive to validate its performance improvement. The results showed a significant reduction in total voltage and current harmonic distortions, reduced total inverter losses (by 2/3rd) and was even was able to keep the neutral point fluctuation low at all operating load power factor conditions. The second motivation was to reduce the computational time in the real-time implementation of the control logic. For this purpose, a modified carrier and hybrid-carrier based PWM strategy was proposed, which also kept the DC-link capacitor voltages balanced. The modified carrier based strategy was able to reduce the switching losses compared to the conventional strategies, while the hybrid-carrier based strategy kept the advantages of both carrier and the space vector techniques. For IPMSM in the field weakening region when the load power factor goes leading the neutral point potential fluctuation increases considerably. To reduce this fluctuation eight different space vector based strategies were proposed, which reduces the fluctuation considerably compared to the conventional strategy. Finally, a performance comparison study was carried out to compare the total harmonic distortion, switching loss distribution, and total inverter loss of all the four proposed strategies.
Abhijit Choudhury (S’11) received the B. E. degree from the National Institute of Technology, Agartala, India, in 2007, the M.Tech degree in electrical engineering from Indian Institute of Technology, Bombay, India, in 2011 and the Ph.D. degree from the Concordia University, Montreal, Canada in 2015. He is currently working as a Postdoctoral Research Fellow at the Department of Electrical and Computer Engineering, Concordia University, Montreal, QC, Canada. From 2007 to 2008, he was a management trainee at ABB, Vadodara, India and from Sept. 2011 to Dec. 2011, at General Motors, Bangalore, India as a graduate trainee. During his M.Tech studies at IIT Bombay he was also working as a research associate. His research interests include converter control techniques, electrical machine drives, renewable energy and electric vehicle architecture.