Analytical closed-form expressions of DC current ripple for three-level neutral point clamped inverters with space-vector pulse-width modulation

The current ripple of the DC bus is a key factor for the DC-link capacitor parameter design of three-level neutral point clamped (NPC) inverters. It directly affects the selection of capacitor type and material. In this study, an analytical closed-form expression of DC current ripple for NPC inverters with space-vector pulse-width modulation (SVPWM) is proposed based on an analytical study of the calculation principle of capacitor current ripple and SVPWM algorithm. The closed-form expression of DC-link capacitor current ripple is given by modulation index M and power factor angle φ. The deviation of calculation and experience is within 5.7% in spite of neglecting the output current ripple. The analytical closed-form expression provides a convenient way to design the DC-link capacitor of a three-level NPC inverter.