Aimed at the control problem of cascade static synchronous compensator (STATCOM) in three-phase voltage imbalance condition

this paper analyzes the operating characteristics of the cascade STATCOM in three-phase voltage imbalance condition

and points out that the cascade STATCOM output negative sequence voltage can be made to ensure access point voltage balance. The decoupled control equation of the system is derived in detail in the positive and negative sequence environment

a new control method of positive-negative sequence decoupling pulse-width modulation (PWM) is put forward

and the two kinds of work mode within the method are analyzed

namely the reactive power compensation mode and voltage control mode. At the upper layer

the positive-negative sequence decoupling control is adopted; at the lower layer

the energy balance control strategy is adopted to ensure capacitor voltage at direct current side of each module is balanced. Simulation and experiment results show that this method can effectively solve the problem of the cascade STATCOM safe operation in unbalanced conditions. While coping with definite unbalanced voltage

it has fast reactive compensating features

and achieves maximum utilization.