Three-phase induction motors have a widespread use in industry, and starting of loaded induction motors is an important matter. However, there are few studies on motor starting using variable-frequency drives (VFDs). The existing control schemes, described by these studies, have disadvantages such as dependence on derived characteristics, adjustment of settings, design of controllers, or burden of calculations on the control processor. In this paper, a simple and effective control scheme of VFDs to start loaded motors is proposed. In this scheme, there is no dependence on any characteristic, adjustment of settings, controllers, and rotor speed sensor. By this scheme, the motor is controlled to give the required acceleration rate, provided that the maximum-torque limit is not violated. Also, this leads to keep the starting current at satisfactory values. The proposed scheme is appropriate when a high starting torque is required and /or when the starting is repeated many times per hour. |
