Control device for electric power steering device

A control device for an electric power steering device comprising:

• a direct current power source configured to output direct current voltage;
• an inverter configured to convert the direct current voltage output from the direct current power source into alternating current voltage, and apply the alternating current voltage to a synchronous motor;
• and
• a controller configured to convert three-phase current flowing in the synchronous motor into d-axis current and q-axis current, perform proportional integral control for a deviation between d-axis current command and the d-axis current so that the d-axis current follows the d-axis current command, to calculate d-axis voltage command, perform proportional integral control for a deviation between q-axis current command and the q-axis current so that the q-axis current follows the q-axis current command, to calculate q-axis voltage command, convert the d-axis voltage command and the q-axis voltage command into three-phase voltage command, and control the inverter based on the three-phase voltage command,
• wherein a q-axis proportional gain Kpq′, which is used in the proportional integral control performed for the deviation between the q-axis current command and the q-axis current, is set according to a relation Kpq′=Kq/τq×dϕq/diq, where τq is a time constant of a q-axis current control system, dϕq is q-axis infinitesimal magnetic flux, diq is q-axis infinitesimal current, and Kq is a constant greater than zero and less than one, and wherein Kq is chosen such that a step response overshoot of the controller is less than ten percent.