A control system configured to provide commands to a source-side converter and a line-side converter of a power conversion system for balancing a neutral point voltage on a DC link between the source-side converter and the line-side converter, the control system comprising: a first fundamental control unit configured to generate a first fundamental command to implement fundamental power conversion operation for the source-side converter; a second fundamental control unit configured to generate a second fundamental command to implement fundamental power conversion operation for the line-side converter; and characterized by: a compensation control unit comprising: a comparator configured to compare a first modulation index (MI_source) of the source-side converter and a second modulation index (MI_line) of the line-side converter; a first calculation element configured, when the first modulation index (MI_source) is less than the second modulation index (MI_line), to receive a fundamental compensation command (Vdcoffset) and to generate a first source-side compensation command (Vdcoffset S1) for injection into the first fundamental command and, when the first source-side compensation command is not sufficient to balance the neutral point voltage, to further generate a first line-side compensating command (Vdcoffset_L1) for injection into the second fundamental command; and a second calculation element configured, when the first modulation index (MI source) is greater than the second modulation index (MI_line), to receive the fundamental compensation command (Vdcoffset) and to generate a second line-side compensation command (Vdcoffset_L2) for injection into the second fundamental command and, when the second line-side compensation command is not sufficient to balance the neutral point voltage, to further generate a second source-side compensating command (Vdcoffset_S2) for injection into the first fundamental command. a first fundamental control unit configured to generate a first fundamental command to implement fundamental power conversion operation for the source-side converter; a second fundamental control unit configured to generate a second fundamental command to implement fundamental power conversion operation for the line-side converter; and characterized by: a compensation control unit comprising: a comparator configured to compare a first modulation index (MI_source) of the source-side converter and a second modulation index (MI_line) of the line-side converter; a first calculation element configured, when the first modulation index (MI_source) is less than the second modulation index (MI_line), to receive a fundamental compensation command (Vdcoffset) and to generate a first source-side compensation command (Vdcoffset S1) for injection into the first fundamental command and, when the first source-side compensation command is not sufficient to balance the neutral point voltage, to further generate a first line-side compensating command (Vdcoffset_L1) for injection into the second fundamental command; and a second calculation element configured, when the first modulation index (MI source) is greater than the second modulation index (MI_line), to receive the fundamental compensation command (Vdcoffset) and to generate a second line-side compensation command (Vdcoffset_L2) for injection into the second fundamental command and, when the second line-side compensation command is not sufficient to balance the neutral point voltage, to further generate a second source-side compensating command (Vdcoffset_S2) for injection into the first fundamental command. a comparator configured to compare a first modulation index (MI_source) of the source-side converter and a second modulation index (MI_line) of the line-side converter; a first calculation element configured, when the first modulation index (MI_source) is less than the second modulation index (MI_line), to receive a fundamental compensation command (Vdcoffset) and to generate a first source-side compensation command (Vdcoffset S1) for injection into the first fundamental command and, when the first source-side compensation command is not sufficient to balance the neutral point voltage, to further generate a first line-side compensating command (Vdcoffset_L1) for injection into the second fundamental command; and a second calculation element configured, when the first modulation index (MI source) is greater than the second modulation index (MI_line), to receive the fundamental compensation command (Vdcoffset) and to generate a second line-side compensation command (Vdcoffset_L2) for injection into the second fundamental command and, when the second line-side compensation command is not sufficient to balance the neutral point voltage, to further generate a second source-side compensating command (Vdcoffset_S2) for injection into the first fundamental command.