Apparatus and method for controlling delta-connected cascaded multilevel converter

A method for controlling a delta-connected cascaded multilevel converter, comprising:

• receiving current signals indicating phase currents flowing through respective phase arms of the converter;
• determining a harmonic current signal indicating a circulating current of the converter from the current signals;
• generating, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
• receiving a phase voltage reference signal associated with a load electrically coupled to the converter;
• and
• generating, by combining the harmonic voltage signal with the phase voltage reference signal, a control signal for controlling the converter to cause a peak amplitude of the phase currents to be a first amplitude,
• wherein the first amplitude is associated with a second amplitude of the circulating current in the phase currents.

An apparatus for controlling a delta-connected cascaded multilevel converter, comprising:

• a converter controller configured to:
• receive current signals indicating phase currents flowing through respective phase arms of the converter;
• determine a harmonic current signal indicating a circulating current of the converter from the current signals;
• generate, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
• determine a first DC component of the harmonic current signal from the current signals;
• compare the first DC component with a first reference DC component of the reference current signal to generate a first DC difference;
• determine a second DC component of the harmonic current signal from the current signals;
• compare the second DC component with a second reference DC component of the reference current signal to generate a second DC difference;
• and
• generate the harmonic voltage signal based on the first DC difference and the second DC difference,
• wherein the converter controller is configured to generate the harmonic voltage signal based on a comparison of the harmonic current signal and the reference current signal.

A method for controlling a delta-connected cascaded multilevel converter, comprising:

• receiving current signals indicating phase currents flowing through respective phase arms of the converter;
• determining a harmonic current signal indicating a circulating current of the converter from the current signals;
• generating, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
• controlling, based on a cell control signal generated from the control signal, one of a plurality of converter cells in the phase arm to cause the amplitude of the circulating current to be the predetermined amplitude;
• receiving a DC voltage value indicating a DC voltage across a capacitor in the one of the plurality of converter cells;
• comparing the DC voltage value with a nominal value to generate a compensation factor;
• and
• controlling the one of the plurality of converter cells based on the generated compensation factor and the cell control signal,
• wherein generating the compensation factor comprises generating the compensation factor by dividing the DC voltage value by the nominal value.