Battery Charging System with Three-level ANPC Converter Operating at Variable Bipolar DC-link

Three-level converters are an interesting solution for the input stage of EV charging systems as a number of advantages over two-level counterparts can be found, only to mention the better quality of the processed energy (lower harmonic distortion and EMI level). On the other hand, higher element count and power loss may be recognized as disadvantages. In such systems switching losses represent a significant part of the overall losses even if modern SiC power devices are applied. To resolve this issue, this paper focuses on the single-phase (1/3 PWM) modulation of the three-level Active Neutral-Point-Clamped (ANPC) converter. The system also contains a three-level DC/DC converter connected to the energy storage, which delivers variable DC-link voltage. A simulation study compares variable DC-link approach to other PWM strategies: carrier-based sinusoidal with 3rd harmonic component and two-phase discontinuous modulation. For the investigated 20 kW charging system with the 1/3 modulation the semiconductor losses of the ANPC converter drop by 184 W (0,92% of nominal power). Operating conditions of the DC/DC converter are challenging due to required variable DC-link voltage but with a lower average value. This also leads to decreased switching loss. All in all, the total loss in selected SiC MOSFETs (C3M0015065K) semiconductors are reduced by 0,96% of nominal power.