Power inverter system and method of correcting supply voltage of the same

A power inverter system comprising:

• an inverter unit including first to third single-phase inverters, each of the first to third single-phase inverters comprising:
• a direct current power source;
• a smoothing circuit connected in parallel to the direct current power source;
• and
• a plurality of switching elements connected in parallel to the direct current power source;
• a reference current setting unit configured to set a first reference current command value representing a first reference current component in a first axis, and a second reference current command value representing a second reference current component in a second axis, the first axis and the second axis being orthogonal to each other;
• a reference-frequency calculating unit configured to calculate a reference frequency of each of the first to third single-phase inverters;
• a first converter configured to convert first to third output currents from the first to third single-phase inverters into a first current command value representing a first output current component in the first axis and a second current command representing a second output current component in the second axis;
• a first subtracter configured to subtract the first current command value from the first reference current command value;
• a second subtracter configured to subtract the second current command value from the second reference current component;
• a first current control amplifier configured to adjust a first voltage command value representing a first voltage component in the first axis such that the difference between the first reference current command value and the first current command value is reduced to zero based on the subtraction result by the first subtracter;
• a second current control amplifier configured to adjust a second voltage command value representing a second voltage component in the second axis such that the difference between the second reference current command value and the second current command value is reduced to zero based on the subtraction result by the second subtracter;
• a second converter configured to convert the first and second voltage command values into first-phase to third-phase voltage command values based on the reference frequency and to output the first-phase to third-phase voltage command values to the first to third single-phase inverters, respectively;
• a phase difference calculating unit configured to calculate a phase difference between an output voltage and an output current of the power inverter system based on the first and second current command values and the first and second voltage command values;
• and
• a voltage-correcting unit configured to calculate a correction voltage based on the phase difference, the reference frequency, and the first and second voltage command values and configured to add the calculated correction voltage to the first-phase to third-phase voltage commands, the correction voltage having a frequency three times as high as the reference frequency.

A method of correcting a voltage supplied to a power inverter system, the power inverter system including an inverter unit having first to third single-phase inverters, each of the first to third single-phase inverters having a direct current power source, a smoothing circuit connected in parallel to the direct current power source, and a plurality of switching elements connected in parallel to the direct current power source, the method comprising:

• calculating a reference frequency of each of the first to third single-phase inverters;
• calculating a reference voltage of each of the single-phase inverters;
• and
• adding a correction voltage to the reference voltage calculated by the reference voltage calculation step, the correction voltage having a frequency three times as high as the reference frequency.