Voltage-Hertz Strategy for Synchronous Motor with Controlled Exciting Field

The classical constant volt/hertz = ct. scalar control procedure applied to the induction motors historically was the first method which ensured loss-less operation. It is an indirect flux control method, which maintains the stator flux constant at its rated value. This can be achieved by adjusting in a proper way the stator-voltage amplitude according to the imposed stator-frequency. The method is applied with success for the induction and also for the synchronous motor drives. In case of the excited synchronous motors there is possible to increase the drive performances by controlling the excitation, too. It introduces an additional degree of freedom from the control point of view that offers one more possibility for flux or power factor control. In this paper there is presented a simple procedure, which ensures an improved dynamic behaviour of the synchronous motor. It consists of the exciting field control which is correlated with the volt-hertz control procedure, in order to maintain the simplicity of the control structure. Simulation and implementation results are also presented for validation.