Sensorless control of brushless permanent magnet motors

In this thesis, a sensorless control method of permanent magnet synchronous machines (PMSMs), whose machine neutral points are accessible, for all speeds and at standstill is proposed, researched and developed. The sensorless method is called Direct Flux Control (DFC). The different voltages between a machine neutral point and an artificial neutral point are required for the DFC method. These voltages are used to extract flux linkage signals as voltage signals, which are necessary to approximate electrical rotor positions by manipulating the flux linkage signals. The DFC method is a continuous exciting method and based on an asymmetry characteristic and machine saliencies. The DFC method is validated by implementing on both software and hardware implementation. A cooperative simulation with Simplorer for the driving circuit and programming the DFC and Maxwell for doing finite element analysis with the machine design is selected as the software simulation environment. The machine model and the DFC method are validated and implemented. Moreover, the influences of different machine structures are also investigated in order to improve the quality of the measured voltages. The hardware implementation has been employed on two test benches, i.e. for small machines and for big machines. Both test benches use a TriCore PXROS microcontroller platform to implement the DFC method. There are several PMSMs, both salient poles and non-salient poles, which are used to validate the DFC method. The flux linkage signals are also analyzed. The approximation of the flux linkage signal is derived and proposed. A technique to remove the uncertainty of the calculated electrical rotor position based on the inductance characteristics has been found and implemented. The electrical rotor position estimation method has been developed based on the found flux linkage signal approximation function and analyzed by comparing with other calculation techniques. Moreover, the calculated electrical rotor position is taken into account to either assure or show the relation with the exact rotor position by testing on the hardware environment. The closed loop speed sensorless control of PMSMs with DFC is presented and executed by using the assured calculated electrical rotor position to perform the DFC capability. This thesis has been done in the Electric Machines, Drives and Power Electronics Laboratory, South Westphalia University of Applied Sciences, Soest, Germany