The Voltage Support and Power Balance Control Method of Three-phase Four-wire Cascaded Multilevel Inverter

Three-phase four-wire cascaded multilevel inverter can be utilized in lithium battery cascade utilization and other fields. However, the conditions of power balance control may conflict with the voltage support conditions, which may cause the failure of the control strategy. To solve the problems existed in the three-phase three-wire system, a split-capacitor three-phase four-wire system is adopted in this paper with the dc side midpoint connected to the neutral line which can provide access to zero-sequence components. Thus the new constraint equations are formed from the power generated by zero sequence components to achieve power balance and voltage support simultaneously. A new control strategy with peak current limitation for three-phase four-wire cascaded multilevel inverter under asymmetrical grid fault is proposed in this paper. The control strategy proposed in this paper ensures that the inverter operates safely during voltage sags, limiting the injected current to the maximum allowed by the inverter. Simulation and experiment results verified the effectiveness of the strategy.