The invention discloses a method for controlling the balance of a 
direct current side of a cascaded grid-connected 
inverter based on zero sequence and negative sequence 
voltage injection. The method is based on the combination of zero sequence 
voltage and negative sequence 
voltage injection; and the method comprises the following steps of (1) integrally controlling the 
direct current voltage by using a control method of positive sequence current decoupling, and correcting the unbalance of the 
system on the basis of positive sequence decoupling, and decomposing network voltage and the positive and negative sequence of the current by using a second 
harmonic filtering method; and (2) controlling the 
phase balance of the 
direct current side, respectively calculating the zero sequence voltage component and the negative sequence voltage component needing injecting, starting the zero sequence voltage injection method under a normal condition, and using the negative sequence voltage injection method when the 
power difference of each phase is large according to switching conditions. Furthermore, when the zero sequence voltage injection is used, the condition that the maximum output phase voltage does not exceed the maximum value provided by the 
inverter needs to be satisfied. Through the method, three phases can be comprehensively combined; the voltage of different phase sequences can be injected under different conditions, the output performance and 
interphase power adjustment ability of the device are both considered; and for the application of three-phase cascaded grid-connected 
inverter matched 
renewable energy sources large-scale synchronization and large-scale 
energy storage, the method has an important value.