Method for operating a converter, converter and computer program product

A converter, comprising

• Z modular-multilevel converters that are coupled in a parallel circuit, wherein each modular-multilevel converter of the Z modular-multilevel converters comprises M branches, each branch comprises cells with a capacitor and respective semiconductor switches, each modular-multilevel converter of the Z modular-multilevel converters is configured to accept or provide a three-phase AC voltage, corresponding inputs of each of the Z modular-multilevel converters are connected together, corresponding outputs of each of the Z modular-multilevel converters are connected together, and Z and M are each an integer greater than one;
• and
• a control arrangement configured to:
• generate Z first voltage reference signals as a function of a DC voltage reference and Z measured signals gained at the Z modular-multilevel converters;
• generate a second voltage reference signal as a function of a first terminal reference;
• generate an inner voltage reference signal as a function of an average DC voltage reference and of branch capacitor voltage signals generated by detecting capacitor voltages of the capacitors of the cells of each branch;
• combine the Z first voltage reference signals, the second voltage reference signal and the inner voltage reference signal into a branch control signal for each branch of each modular-multilevel converter;
• generate cell control signals as a function of the branch control signals, wherein each cell control signal of the cell control signals is a function of the Z first voltage reference signals, the second voltage reference signal and the inner voltage reference signal;
• and
• provide the cell control signals to each of the respective semiconductor switches of each of the cells of each of the M branches of each of the Z modular-multilevel converters.

A non-transitory computer readable medium comprising instructions to cause a converter to execute a method, the converter comprising Z modular-multilevel converters that are coupled in a parallel circuit, wherein each of the Z modular-multilevel converters comprises M branches, each branch comprises cells with a capacitor and respective semiconductor switches, each modular-multilevel converter of the Z modular-multilevel converters is configured to accept or provide a three-phase AC voltage, corresponding inputs of each of the Z modular-multilevel converters are connected together, corresponding outputs of each of the Z modular-multilevel converters are connected together, and Z and M are each an integer greater than one, the method comprising:

• generating Z first voltage reference signals as a function of a DC voltage reference and Z measured signals gained at the Z modular-multilevel converters;
• generating a second voltage reference signal as a function of a first terminal reference;
• generating an inner voltage reference signal as a function of at least an average DC voltage reference and of branch capacitor voltage signals generated by detecting capacitor voltages of the capacitors of the cells of each branch;
• combining the Z first voltage reference signals, the second voltage reference signal and the inner voltage reference signal into a branch control signal for each branch of each modular-multilevel converter;
• generating cell control signals as a function of the branch control signals, wherein each cell control signal of the cell control signals is a function of the Z first voltage reference signals, the second voltage reference signal and the inner voltage reference signal;
• and
• providing the cell control signals to each of the respective semiconductor switches of each cell of each of the M branches of each of the Z modular-multilevel converters.