Patent ID: 8598738

Claim:
A power assist apparatus for assisting a load power with an inverter connected with an AC power source and a power storage device which is connected with a DC circuit of the inverter and which includes a chopper and an electricity storage device, the power assist apparatus comprising: an instantaneous output power calculating section including a power calculating section configured to detect a voltage and a current between the inverter and a load, to transform the voltage and current by a coordinate transformation into a q-axis voltage and a q-axis current, and to calculate a power on the basis of the transformed voltage and current, and a correction calculating section to receive the calculated power, and to correct an input-output power characteristic of the inverter; and a chopper control circuit including voltage control sections configured to calculate a value of a charge command and a value of a discharge command, respectively, by receiving a deviation signal between a preset value of an upper limit voltage and the detected DC circuit voltage of the inverter and a deviation signal between a preset value of a lower limit voltage and the detected DC circuit voltage of the inverter, limiter sections to receive the signals, respectively, from the voltage control sections, and PWM control sections to produce PWM signals, respectively, by receiving signals from the limiter sections, the instantaneous output power calculating section and the limiter sections of the chopper control circuit being so arranged that a signal of the power calculated by the instantaneous output power calculating section is supplied to each of the limiter sections, and thereby each of the limiter sections varies a limiter value.