Analysis and assessment of electrical and thermal performance of five-phase voltage source inverter under different modulation strategies: Comparative study under balanced and unbalanced load

This paper compares four modulation strategies applied to five-phase voltage source inverters (5PH-VSI). The modulation strategies under investigation are sine wave pulse width modulation (S-PWM), fifth-harmonic injection PWM (FH-PWM), space vector-PWM using two large vectors (2V-SVPWM), and space vector-PWM using two medium and two large vectors (4V-SVPWM). The study utilizes simulations to analyze the results based on four performance criteria: low-order harmonics (LOH), maximum modulation index (MMI), common mode voltage (CMV), and total harmonic distortion (THD) under balanced and unbalanced load. To validate the simulation results for these criteria, an experimental test-bench is employed, which includes a 5PH-VSI feeding an R-L load, and controlled by a low-cost STM32F4-DISCOVERY microcontroller board. Additionally, a mathematical approach is used to calculate the total thermal losses (TTL) then simulations are performed using Piecewise Linear Electrical Circuit Simulation (PLECS) software to assess the modulation schemes based on additional thermal performance criteria: conduction losses (CL), switching losses (SL), TTL, the efficiency, and the maximum permissible heat sink thermal resistance (MPHTR) at the steady-state regime. The results indicate that the 4V-SVPWM method demonstrates superior efficiency in terms of THD. Furthermore, it showcases the lowest TTL at high switching frequencies, allowing for the best efficiency and minimizing MPHRT, therefore providing the largest margin for the heat sink thermal resistance design. On the other hand, the 2V-SVPWM offers the highest MMI, but this comes at the cost of high TTL and some LOHs appearing. In addition, it exhibits the highest CMV for unbalanced load. S-PWM and FH-PWM offer the advantage of simpler implementation.