Current fluctuations reduction strategy based on optimal three-space-vector pulse-width modulation for service-life improvement of DC-link electrolytic capacitors in three-phase voltage-source inverter system

The authors propose a current fluctuation reduction strategy based on optimal three-space-vector pulse-width modulation (TSVPWM), which is used to improve the service-life of the dc-link electrolytic capacitors in two-level three-phase voltage-source inverter (VSI) system. Differing from the typical SVPWM-based method that employs two adjacent active voltage vectors and zero voltage vectors to synthesise the reference voltage, the proposed strategy selects the required voltage vectors based on the minimum dc-link electrolytic capacitor current fluctuation. With the proposed strategy, an objective function for the root-mean-square value of dc-link electrolytic capacitor current is first constructed under the constraint of eight permissible voltage vectors. And then, by solving the minimum of the objective function through the piecewise linear programming, the optimal three voltage vectors under the different modulation ratios and load power factors are obtained accordingly, so as to achieve the minimum dc-link electrolytic capacitor current fluctuations during each switching period. Meanwhile, a PWM implementation scheme based on positive-negative double carrier signals is presented, which not only simplifies the implementation process but also effectively reduces the switching losses of power devices. Finally, the experimental results demonstrate that the proposed strategy can minimise the dc-link electrolytic capacitor current fluctuation under different working conditions. Based on space voltage vector, a voltage vector combination was derived to minimise the capacitor current within a single switching cycle. Compared to the traditional SVPWM, experimental results have shown that the rms value of capacitor current can be reduced by up to 37%.image