Efficient IEC permanent-magnet motor (3kW)

Efficient permanent-magnet motors achieve in the area up to 100kW a higher efficiency than induction machines (standard motors). A simple and fast energy saving option is the exchange of inefficient standard motors. The objective of this work is to install a 3kW permanent-magnet motor in a standard IEC housing and the optimization of the design for high efficiency. Another objective is the development and the realization of an efficient variable speed control. The efficiency of the motor and the inverter with the control system must be demonstrated by tests. These tasks have been split between Circle Motor AG and the universities of applied sciences Wallis and Lucerne.

Considering high-efficiency and low manufacturing cost, a Brushless DC solution was adopted. This resulted in an optimum design of the motor and the control system realized with a three-phase rectifier, a buck converter with variable DC voltage, and a three-phase inverter feeding full positive and negative current to two of the legs simultaneously.

The maximum measured efficiency is about 96.5% for the inverter and 92% for the motor.

With the advantage of the variable speed operation, the efficiency of the realized 3kW permanent magnet motor together with the control system is always higher than the efficiency of a measured class EFF1 induction motor, even with a direct connection to the grid. The permanent-magnet motor is also about 10 kg lighter. The cost calculation shows that the permanent-magnet motor can be competitive with the induction motor when speed control is desired. This is also the domain with the largest potential for energy savings from variable speed pumps, compressors, fans.