Discontinuous Pulse Width Modulation for Simultaneous Thermal Stress Reduction in Power Devices and DC-link Capacitors of NPC Inverter

In three-level NPC inverters, power devices and DC-link capacitors are the most reliability-critical components. Pulse width modulation (PWM) methods significantly influence the thermal performance of these components. Space vector pulse width modulation (SVPWM) provides low output current total harmonic distortion (THD) but results in high power device switching loss compared with Discontinuous PWM (DPWM). DPWM reduces the power device losses through phase clamping but increases power loss in DC-link capacitors due to low-frequency ripple currents. This paper proposes DPWM that reduces thermal loadings in both power devices and DC-link capacitors. The proposed DPWM subdivides each sector into four regions and strategically minimizes the use of small voltage vectors that cause large neutral point currents. Simulation results demonstrate that the proposed DPWM maintains power loss of the power devices comparable to DPWM while substantially reducing capacitor power losses compared to both SVPWM and DPWM.