Twice frequency waves occurred in voltage of capacitor at DC side of D-STATCOM under unbalanced voltage,which results in negative sequence and 3 times harmonics in AC voltage,therefore,an improved switching function modulation was proposed to improve voltage output performance of D-STATCOM and to suppress 3 times harmonic current.

According the problem above, improved switching function modulation is proposed to improve voltage output performance of D-STATCOM and suppress 3 times harmonic current.

By utilizing the auxiliary ordinary differential equation and its solutions,the first kind and second kind of KdV equation with variable coefficients were investigated by means of the extended tanh-function method,and abundant new exact solitary wave solutions were obtained under certain conditions.

Based on the needs of system control strategy and with the output of the active inverter considered,a switch function method was adopted to build The average model of switch cycle for the active inverter.

Based on the needs of system control strategy and taking the output of active power filter into consideration,a switch function method was adopted to build the mathematical model of parallel hybrid active power filter.