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High Performance Driver P7

It has been assumed so far in all the considerations of induction machine and SPMSM vector control that a speed (or position) sensor is available and that it provides the required feedback signal for closed loop speed control (and the speed/position information for co-ordinate transformation, where required). Sensors mounted on the machine shaft are in general not desirable for a number of reasons. First of all, their cost is substantial. Secondly, their mounting requires a machine with two shaft ends available - one for the sensor, and the other one for the load coupling. . | HIGH PERFORMANCE DRIVES 100 6. SPEED ESTIMATION FOR SENSORLESS HIGH PERFORMANCE VECTOR CONTROL 6.1. INTRODUCTION It has been assumed so far in all the considerations of induction machine and SPMSM vector control that a speed or position sensor is available and that it provides the required feedback signal for closed loop speed control and the speed position information for co-ordinate transformation where required . Sensors mounted on the machine shaft are in general not desirable for a number of reasons. First of all their cost is substantial. Secondly their mounting requires a machine with two shaft ends available - one for the sensor and the other one for the load coupling. Thirdly electrical signals from the shaft sensor have to be taken to the controller and the sensor needs a power supply and these require additional cabling. Finally presence of a shaft sensor reduces mechanical robustness of the machine and decreases its reliability. It is for all these reasons that substantial efforts have been put in recent past into possibilities of eliminating the shaft mounted sensor. However the information regarding actual speed and or position of the rotor shaft remains to be necessary for closed loop speed and or position control and co-ordinate transformation if applicable even if the shaft sensor is not installed. Hence the speed and or position has to be estimated somehow from easily measurable electrical quantities in general stator voltages and currents . All the schemes of vector control introduced in Chapters 3 and 4 are valid regardless of whether the machine speed and or position is measured or estimated. This Chapter therefore discusses only issues related to speed estimation. An induction machine is under consideration at all times although the same approaches as those explained in what follows are in general applicable with some modifications to permanent magnet synchronous machines as well. A drive in which the speed position sensor is absent is usually