SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

CHAPTER 7 - Concluding Remarks
As stated in Chapter 1, this report summarizes a present state of understanding. As each topic was
brought to a close, comments were given regarding the issues that deserve further study and lists
of potentially-useful references were given. A few of the topics are mentioned again here, along
with some addition ones.
The focus of this report has been the sinusoidal BPMS motor. Torque production was examined
in Chapter 2, and Appendix C investigated the nature of the sinusoidal machine. However, the
study of torque in that appendix concluded with the single-phase case. Thus the next step would
be to study torque in terms of current harmonics for the three-phase machine.
As mentioned in Chapter 5, the coupling in the dq model is likely to be negligible because of the
low synchronous reactance of BPMS motors, but it may be worth a more detailed look, especially
in conjunction with the synchronous regulator. Similarly, the subject of current measurement
needs further study, and this should be done in conjunction with the synchronous regulator or
FOC topology as well. For example, it would be useful to understand why synchronous sampling
of the current requires no filtering [62, p.34-40], [98]. There are many practical limitations to
consider when using shunts in the legs of the inverter. It would be useful to determine if some of
those limitations could be eliminated by inline current sensors (either shunt or Hall-effect) or if
inline schemes have limitations of their own.
The area most lacking in this report is the sensorless operation of FOC. Unlike the other topics
covered, the author has come across relatively little literature on the structure of observer
presented here. There are many articles on the sensorless control of a BPMS motor but many
require an advanced understanding of modern control techniques. Of considerable interest would
be the sensitivity of observer’s “DC” accuracy (steady-state error) to parameter changes.
Concerning sensorless operation, it would be useful to find a startup technique that is more robust
than the “forced commutation” (open-loop) that is often used. Techniques exist to determine the
initial position of the rotor, but that is only half of the problem—the other half of the problem is
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