Patent attributes
In a PWM-controlled motor, a motor rotation frequency f, lock determination frequency d, and power supply voltage E are acquired (S1 to S3). The d is compared to the f (S4). When f is not less than that of d, Max.Duty is calculated by the following equation for setting: Max.Duty=D0*Kf (S5, S6). D0 is an allowable Duty value and can be calculated by [DP0=a−bE] (a: fixed Duty value, b: Duty characteristic coefficient). Kf is a frequency adjustment coefficient. Kf corrects the allowable Duty value D0 in accordance with the motor rotation frequency f and can be calculated by the following equation: Kf=1+(f−d)/c (c: restriction start frequency, d: lock determination frequency). When f is less than d, Max.Duty=D0 is set (S7, S6). When the motor enters a locked state, the Duty value is suppressed to not more than the allowable Duty value D0 to thereby suppress a lock current. This reduces a lock current at low temperature time to prevent demagnetization of a magnet as well as reduces a load of a switching device.
