Direct current bus voltage control

An apparatus comprising:

• a voltage regulator that generates a q-axis reference current from a Direct Current (DC) voltage error comprising a DC voltage input modified by a DC bus voltage in a closed outer loop and generates a d-axis reference current from the DC voltage error, wherein the second-order harmonic in the d-axis reference current is delayed from that in q-axis reference current by 90 degrees;
• a second inner-loop current control that generates a q-axis current iq from the q-axis reference current;
• and
• a first inner-loop current control that generates a d-axis current id from the d-axis reference current, wherein the second-order harmonic in d-axis current is offset from the second-order harmonic in q-axis current by 90 degrees, the first and second inner-loop current controlling the DC bus voltage of a voltage control plant to mitigate a second-order harmonic in the DC bus voltage with the second-order harmonics in the q-axis current and the d-axis current.

A computer program product comprising a computer readable storage medium having program code embodied therein, the program code readable/executable by a processor to:

• generate a q-axis reference current from a Direct Current (DC) voltage error comprising a DC voltage input modified by a DC bus voltage in a closed outer loop;
• generate a d-axis reference current from the DC voltage error, wherein the second-order harmonic in the d-axis reference current is delayed from that in q-axis reference current by 90 degrees;
• generate a q-axis current from the q-axis reference current;
• generate a d-axis current from the d-axis reference current, wherein the second-order harmonic in d-axis current is offset from the second-order harmonic in q-axis current by 90 degrees;
• and
• control the DC bus voltage of a voltage control plant to mitigate a second-order harmonic in the DC bus voltage with the second-order harmonics in the q-axis current and the d-axis current.