Comparison of two, energy optimizing techniques for PM-machines

Two control methods for energy optimized sensorless control of permanent magnet machines (PM-machines) are studied and implemented. The control of the PM-machine is accomplished without knowledge of the absolute rotor position and therefore the control methods are well suited to low dynamic applications. Both methods use only the information in the DC link current in the frequency converter. The current information is used to control the PM-machine and only a few calculations are necessary. In the first method the average DC-link current is minimized in a stationary operating point and the impressed stator voltage is adjusted until a minimum of power occurs. The second method controls the PM-machine depending on the contour of the DC-link current, which is dependent on the power factor. The stator voltage to the PM-machine is adjusted to obtain an optimum power factor and efficiency. A test system which contains a frequency converter, a DC-link current measuring system, a PM-machine and a DC-machine acting as load is implemented. Test results show that the two control algorithms control the impressed stator voltages to the PM-machine very close to the optimum operating point in an efficiency point of view. The efficiencies for both methods are measured and they show only a slight difference in the efficiencies for the two methods. The efficiencies are measured at different loads and different speeds, The maximum efficiency is found to be approximately 77% around nominal load and nominal speed