| 摘要 |
PROBLEM TO BE SOLVED: To improve life time of a main circuit element, without deteriorating its controllability. SOLUTION: In a PWM power converting device, the state of a load is monitored. When the load is light, a carrier frequency for PWM is increased, the switching frequency of a main circuit element is increased, the switching loss is increased, and a junction temperature of the element is increased. When the load is heavy, however, the carrier frequency is decreased, the switching frequency of the main circuit element is decreased, the switching loss is decreased and the junction temperature of the element is decreased. The difference in the junction temperatures in the case of a light load and in the case of a heavy load becomes small, so that the power cycle and thermal fatigue life time are improved. The carrier frequency may be changed only when the load is light. |
