Novel Variable Switching Frequency PWM Strategy for a SiC-MOSFET-Based Electric Vehicle Inverter to Increase Battery Usage Time

Abstract

In this study, a novel variable switching frequency pulse width modulation (VSFPWM) strategy is proposed to achieve improved electric vehicle inverter efficiency. The silicon carbide (SiC) MOSFET inverter has excellent switching characteristics, thus enabling pulse width modulation control with a high switching frequency. The high switching frequency can reduce the voltage ripples in DC-link capacitors, which enables their use at a reduced capacitance. The switching frequency is typically set to a level that is within the limits of the voltage ripple in the maximum output region. Given that the same switching frequency is applied to the entire operating region, there is a sufficient margin with respect to the limits of the voltage ripple in the low-to-medium output range. The proposed method is designed to consider the real-time minimum switching frequency by considering the voltage ripple of the capacitor during operation under loaded conditions, thereby minimizing the switching loss. In addition, the method is suitable for high-switching frequency control because the calculation time is short. Because it does not require additional hardware, it is easy to apply to the existing inverter. The validity of the proposed method was verified based on simulations and experiments.