New position sensor elimination techniques for the interior permanent magnet and switched reluctance motor drives

Recent advances in the development of powerful and cost-effective permanent-magnet materials, computer-aided design tools and efficient power semiconductor devices have made the use of Permanent-magnet (PM) and Switched Reluctance (SR) motors an attractive proposition for integral horse power variable speed drive applications.; A position sensor is required in Interior Permanent magnet (IPM) and Switched Reluctance (SR) motor drives in order to synchronize the phase excitation pulses to the rotor position. The position sensor constitutes a substantial portion of the total system cost and tends to reduce the system reliability. Consequently, efficient position sensor elimination schemes are of great interest.; The IPM and SR motors are characterized by the fact that their phase inductance varies appreciably as a function of the rotor position. Thus, the determination of phase inductance estimates the rotor position indirectly in these motors. Analytical equations are developed to calculate the phase inductance of an IPM motor from the phase voltage and current information. Algorithms are developed to obtain the rotor position estimate from the calculated phase inductance. Simulation results on a 3-Hp IPM motor are presented, and it is shown that the new scheme is quite robust in tracking a 10% step change in speed very effectively.; In the case of SR motors, the phase inductance cannot be calculated on a continuous basis due to the nature of the current waveform. It is shown that by using analog techniques the inductance of a non-conducting phase of an SR motor can be measured indirectly using a linear Inductance-Frequency (L-F) converter. The output of the L-F converter is transformed into a dc level by a frequency-to-voltage converter. Thus, the position sensing problem is translated to a simple dc level sensing problem. The required control to generate proper commutating instants is implemented using a low cost INTEL-8748 microcontroller. Experimental results on a 5-Hp SR motor drive demonstrate the potential practicality of this sensorless scheme.