Research On DC Balance Control Strategy For Cascaded SAPF Based On PD-SFO-PWM

Harmonic problems are caused by large-capacity power electronic devices and nonlinear loads in medium-high voltage networks.Cascaded H-Bridge(CHB)shunt active power filters(SAPF)are relatively easy to use.The characteristics of realization,high reliability,and ease of modular expansion in the structure make it an APF that is widely used in high-power and high-voltage applications.However,because H-bridges are independent modules of the cascaded H-bridge SAPF,the loss of series losses and parallel losses of each H-bridge have different factors and cause the unbalanced generation of the SAPF DC side.This will affect the compensation effect of SAPF harmonic currents,and may even cause SAPF to paralyze.Based on the PD-PWM strategy and SFO-PWM strategy,this paper proposes a Phase Disposition-Switching Frequency Optimal-PWM(PD-SFO-PWM)strategy.Both the carrier wave in-phase stacked modulation good line voltage harmonic elimination effect,and the switching frequency optimization PWM modulation reduces the switching loss capability,while reducing the multiple in-phase carrier to one channel carrier.For the cascaded H-bridge SAPF,there is a phenomenon of dc voltage imbalance.Starting from the topology and principle of SAPF,on the basis of analyzing the unbalance on the DC side,in order to stabilize the DC voltage,balance the DC voltage among phases and balance the DC voltage of each unit,this paper presents a three-stage balance strategy of DC voltage based on phase disposition-switching frequency optimal-PWM(PD-SFO-PWM).When a DC-side voltage imbalance occurs,the three-stage strategy plays a regulatory role.Compared with the traditional balancing strategy,the strategy is simple and easy to implement.At the same time,the modulation strategy also has the modulating function and the strategy of balancing the DC voltage of each unit,which avoids the design of an additional strategy of balancing the DC voltage of each unit,which greatly reduces the The complexity of the DC-side balancing strategy.Finally,seven-level SAPF simulations and experiments were conducted to verify the feasibility of a balancing strategy that can achieve a balanced effect with smaller overshoot and ripple,and ensure the stable operation of SAPF.