Suppression of Overvoltage and Oscillation in Three-Level ANPC Converter Using Duty-Decreased PWM and Saturable Ferrite Cores

In the three-level active neutral point clamped (3L-ANPC) converter operating in the outer-mode, there are severe overvoltage and oscillation across the inner switches. They are caused by the oscillation between the large parasitic inductance within the low-frequency (LF) commutation loop, and the nonlinear output capacitances of SiC MOSFETs. This article proposes a method including two measures to suppress the overvoltage and the oscillation respectively. The first measure is an improved modulation strategy called duty-decreased pulse width modulation (DDPWM), which reduces the overvoltage while avoiding steady-state voltage drift. The second measure is utilizing saturable ferrite cores (FC) to suppress the subsequent oscillation without increasing losses. Finally, the suppression effects of the proposed measures are validated through double pulse tests (DPT).