Grid independent operation control unit, power conditioner, and grid independent operation control method

A grid independent operation control unit incorporated in a distributed power supply that includes an inverter configured to convert a received DC bus voltage Vdc to an AC output voltage, and an LC filter configured to remove a harmonic component from output of the inverter, and is configured to execute grid connected operation or grid independent operation,

• the grid independent operation control unit comprising:
• a load current estimator configured to estimate a load current iload supplied to stand-alone power system in accordance with a following mathematical expression on and an output current iinv of the inverter and an output voltage esd;
• and
• a feedback controller configured to PWM control the inverter at a duty ratio feedback calculated to cause the inverter to output an output voltage command value e*sd in accordance with the output voltage esd and the load current iload, wherein
• the feedback controller is configured to PWM control the inverter at a duty ratio u*d feedback calculated for output of a normalized output voltage command value x*sd obtained by normalizing the output voltage command value e*sd with the DC bus voltage Vdc in accordance with a normalized output voltage xsd obtained by normalizing the output voltage esd with the DC bus voltage Vdc and a normalized load current xload obtained by normalizing the load current iload with the DC bus voltage Vdc;
• {
• i
• load
• =
• i
• inv
• -
• i
• c
• 
• i
• c
• =
• sC
• f
• sR
• c
• 
• C
• f
• +
• 1
• ·
• e
• sd
• .
• [
• Expression
• 
• 
• 1
• ]

A grid independent operation control method executed by a grid independent operation control unit incorporated in a distributed power supply that includes an inverter configured to convert a received DC bus voltage Vdc to an AC output voltage and an LC filter configured to remove a harmonic component from output of the inverter and is configured to execute grid connected operation or grid independent operation,

• the grid independent operation control method comprising:
• a load current estimation step of estimating a load current iload supplied to stand-alone power system in accordance with a following mathematical expression, and an output current iinv of the inverter and an output voltage esd;
• and
• a feedback control step of PWM controlling the inverter at a duty ratio feedback calculated to cause the inverter to output an output voltage command value e*sd in accordance with the output voltage esd and the load current iload, wherein
• the feedback control step includes PWM controlling the inverter at a duty ratio u*d feedback calculated for output of a normalized output voltage command value x*sd obtained by normalizing the output voltage command value e*sd with the DC bus voltage Vdc in accordance with a normalized output voltage xsd obtained by normalizing the output voltage esd with the DC bus voltage Vdc and a normalized load current xload obtained by normalizing the load current iload with the DC bus voltage Vdc;
• {
• i
• load
• =
• i
• inv
• -
• i
• c
• 
• i
• c
• =
• sC
• f
• sR
• c
• 
• C
• f
• +
• 1
• ·
• e
• sd
• .
• [
• Expression
• 
• 
• 4
• ]