Reduced switching loss based DC-bus voltage balancing algorithm for three-level neutral point clamped (NPC) inverter for electric vehicle applications

A performance comparison study for two proposed DC-bus voltage balancing algorithms is carried out, with a three-level NPC based permanent magnet synchronous machine (PMSM) drive for the electric vehicle propulsion application. Both the control algorithms are able to keep the two DC-link capacitor voltage variation within a tolerance level with wider range of speed and torque variation of the load drive cycle. However, with the second proposed control strategy inverter total switching losses can be reduced considerably, compared to the first proposed strategy. Both the losses are then compared with a conventional two-level inverter, with a wider variation in switching frequency. Results show a significant reduction in total inverter losses at higher switching frequencies with three-level inverter. Both the two- and three-level inverter control strategies are developed using space-vector pulse width modulation (SV-PWM) scheme. The switching and conduction loss distribution in different switches and diodes for both the two- and three-level inverters are also studied. Finally the total voltage harmonic distortion (%THD_v), percentage torque ripple (%T_rip), and capacitor voltage fluctuation (%V_caprip) are also compared. Switching losses are calculated in a PLECS environment using data sheet parameters from Infineon and control logics are developed in MATLAB/Simulink. For this study a 110 kW surface-PMSM is considered. A scaled down prototype is built in laboratory for both the inverters and tested with a 6.0 kW surface-PMSM. Both the simulation and experimental results show satisfactory performance of the proposed system.