| 摘要 |
PURPOSE:To improve an overload capacity, by lowering the carrier frequency of a pulse width modulation when the load of a motor is increased, through changing the pulse width modulation frequency according to the output of the thermal-model circuit approximating the temperature-rise curves of power semiconductors. CONSTITUTION:In a circuit 28 for setting a carrier frequency, the output frequency of the triangular wave to be outputted by a circuit 25 for generating a triangular wave, is set according to the approximate value of the temperature-rise coefficient of a part 27 for converting an electric power, which is indicated by a signal Qa outputted from a thermal-model circuit 24. Also, at the same time, in a circuit 29 for setting gains, the gains of a U and V phase current amplifier 14 and 15 are set according to the signal Qa outputted from the thermal-model circuit 24. In this manner, the output frequency of the triangular wave outputted from the circuit 25 for generating a triangular wave, and the gains of the U and V phase current amplifier 14 and 15 are changed according to the temperature-rise coefficient of the part 27 for converting an electric power. As a result, the heat-generation quantities of power semiconductors in the part 27 for converting an electric power are reduced, and the temperature rise of the part 27 for supplying an electric power is suppressed too. |
