| 摘要 |
PROBLEM TO BE SOLVED: To protect a switching device from overheating in a low frequency operation. SOLUTION: The characteristics such as the normally-on loss, the switching loss and the overheat impedance of the switching device of an inverter 1 and a switching device loss calculation formula are stored in the memory device of a control unit 3. By using a detected current whose waveform is close to a rectangular wave, a control factor and an output frequency as variables, the stored normally-on loss, switching loss, etc., are taken into the stored formula to obtain the loss of the switching device by the CPU of the control unit. By using the loss and the overheat impedance in the memory, a device junction temperature is calculated and the output current of the inverter is so controlled as to have the calculated junction temperature within a set temperature. |
