| 摘要 |
PURPOSE:To perform control of high efficiency by applying star connection to the motor and by switching an inverter to the V/F ratio selected properly at the time of a low-speed mode of constant torque control in an inverter driving method. CONSTITUTION:A DC power source 1 drives the induction motor 3 through the intermediary of a PWM inverter 2, while the motor 3 is provided with a star-delta connection selecting switch 4. In addition, the speed instruction of an instructing unit 5 and a switching level instruction L are compared with each other in a comparator 10 and by the output thereof the selecting switch 4 and a V/F ratio selecting switch 11 are selected. Moreover, the speed instruction is delivered to a function generator 8 and inputted in a modulator 12 through the intermediary of a selecting switch 11 and controls the inverter 2. Accordingly, the inverter 2 can be switched to the V/F ratio selected properly at the time of low-speed operation in the star connection, thereby the linear current can be reduced without giving any damage to the constant torque characteristic and thus the efficiency can be raised. |
