The Effect Of Switching Frequency On Switching

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Fig. 10 compares the switching instances between – (i) CSFSVPWM and VSFSVPWM, and (ii) CSFDPWM2 and VSFDPWM2. It also shows the shape of the switching frequency variation for each sector. The following can be noted: - The VSFSVPWM reduces 3 switching instances per cycle compared to CSFSVPWM, a 13.6 % reduction. - The VSFDPWM reduces 2 switching instance per cycle compared to CSFDPWM, a 12.5% reduction. Hence, the proposed variable switching frequency PWM reduces the switching instances within a fundamental cycle by lowering the effective switching frequency, while maintaining the output current ripple within a pre-defined range. To study the impact of VSFPWM on switching loss reduction over the entire modulation index range, the simulations were carried out different speeds (modulation indices) for a constant load torque. Table II and Table III compares the current ripple, and the percentage change in the current distortion and the switching losses for CSFSVPWM-VSFSVPWM and CSFDPWM2-VSFDPWM2 techniques respectively. Similar to the analytical results at section II, there is higher switching loss reduction capability at higher speed due to higher variation in current ripple at higher speeds (modulation indices). For example, with VSFSVPWM, around 15% switching loss reduction is obtained, whereas with VSFDPWM2, around 7.2% switching loss reduction is obtained. The difference in switching loss reduction capability in comparison to analytical results is attributed to the
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