| 摘要 |
PURPOSE: To reduce stress acting on the switching element in an inverter circuit. CONSTITUTION: When a low speed command 'Slow' is generated from a low speed command generator 24a in response to an operation stop command, a frequency reference switching means 24b and a voltage reference switching means 24c are turned on to deliver a frequency reference 'Flow' and a voltage reference 'Vlow' to a PWM signal generator 19. Based on both reference 'Flow' and 'Vlow', the PWM signal generator 19 generates a switching pattern for an inverter circuit 13 which operates an induction motor 14 at a constant low speed, based on the switching pattern. Since the conduction switching elements in the inverter circuit 13 vary with time in order to sustain the low speed state, the regenerative energy is distributed to switching elements when the low speed operation is started. Consequently, stress acting on the switching element can be reduced when DC brake power is applied after low speed operation. |
