| 摘要 |
PROBLEM TO BE SOLVED: To provide technique with which a direct current for applying preheat to a motor is measured with ease. SOLUTION: A current sensor 47 is provided with a function of measuring the sum of currents passed through phase U negative side, phase V negative side, and phase W negative side. A resistor made into a modular together therewith and normally installed to protect transistors 41 to 46 against overcurrents can be adopted as a shunt resistor as the current sensor 47. The current measured by the current sensor 47 is pule current I1 passed between the positive side and the negative side of an inverter 4. By repeatedly applying the pulse current I1 in an appropriate cycle, a direct current I2 with the peak of the pulse current I1 substantially maintained is passed through the motor 6 because of the inductor component of the motor 6. In other words, the value 9b of the direct current passed through the motor 6 can be grasped as the peak of the pulse current I1. |
