Optimization of the Current Operating State of Induction Machines Based on Electrical Quantities, Rated Data and Temperatures

Inhalt:
This paper describes a method for optimizing the current operating state of induction machines based on electrical quantities and rated data. In the process, the temperature dependence of ohmic resistances is taken into account. The objective is to maximize efficiency or minimize total losses at any speed and torque without measuring the mechanical quantities. The total losses of the induction machine consist of two significant parts. On the one hand, the load-independent losses are composed of the iron losses, the ventilation and friction losses. On the other hand, the load-dependent losses include the stator winding losses and the rotor winding losses. Load-dependent additional losses are also taken into account. All these loss components are differently dependent on the operating parameters voltage, current, frequency, torque, speed and temperatures in the respective machine part. Induction machines show a drop in efficiency and temperatures especially during partial load operation at low torques. The motor model, proposed in this paper, is used to estimate the temperatures in the respective machine parts and to calculate the optimum values of stator voltage and stator frequency at any speed and torque. Lowering the stator voltage or the main magnetic flux is accompanied by a reduction in total losses, especially in partial load operation, which allows better efficiency to be achieved.