Investigation of rotor position detection schemes for PMSM drives based on analytical machine model incorporating nonlinear saliencies
- Publication Type:
- Thesis
- Issue Date:
- 2011
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This thesis presents the essential and new improvements of the machine modelling and
drive-strategies for permanent magnet synchronous machines (PMSMs), including the
rotor position sensorless drive schemes. Many important issues about PMSM drive
schemes, from the modelling to drive design have been investigated from the machine
model point of view. A comprehensive PMSM model incorporating both structural and
magnetic saturation saliencies has been developed and expressed numerically and
analytically. Highly efficient rotor position detection method has been developed based
on the new machine model.
The traditional mathematical model of PMSM is investigated at the beginning of this
thesis for the conventional PMSM drive schemes, including six-step control, field
oriented control (FOC) and direct torque control (DTC). The fundamental principles and
improvements of the drives are summarized based on the machine model. Performance
companson is conducted for djfferent schemes and an improved DTC scheme is
developed.
PMSM drive without rotor position sensor, or so called sensorless drive, is a desired
feature for the electrical servo systems and automotive applications. The Jack of
accurate nonlinear machine model L the bottle neck for highly efficient sensorless drive
development. Experiment trial and error attempts have to be employed to design rotor
position detection schemes. On the other hand, there is not a comprehensive machine
model to assess the sensorless drive performance.
The inaccuracies associated with the conventional PMSM model have been discussed in
this thesis. The saliencies in PMSM utilized for rotor position tracking are classified as
two types, the structural saliency and the magnetic saturation saliency. The nonlinear
saturation saliency cannot be modelled in the conventional PMSM model. However, it
is essential for the rotor position estimation, especially the initial rotor position
detection. A composite function is designed to express the inductances of PMSM,
incorporating the nonlinear saturation saliency. Experimentally collected inductance
data are used to regress the parameter matrix and a numerical PMSM model is
developed.
It is then proved that the structural and saturation saliencies can be decoupled
analytically and expressed separately. The concepts, structural saliency ratio and
saturation saliency ratio are defined to indicate the magnetic saliency in PMSMs. The
analytical mathematic machine model incorporates the nonlinear behaviour of the
magnetic field of PMSMs. The proposed model is validated by the experimentally
collected data.
Based on the developed analytical nonlinear machine model, a DC voltage pulse
injection based initial rotor position detection scheme is designed and implemented.
Thanks to the comprehensive machine model, improved injection scheme is designed to
minimize the rotor vibration and increase the estimation speed. Simulation and
experiment of the novel detection method are conducted to verify the estimation
accuracy.
Finally the proposed model is applied to analyse the sensorless drive schemes for
PMSMs. The investigation focuses on high frequency signal injection based sensorless
methods. A new inj ection method is proposed based on the machine model, in which the
carrier signal is injected on a fixed stator spatial direction. The proposed sensorless
method and other reported sensorless schemes are compared based on both machine
model and simulation. According to the non1inear machine model, generalized
indicators are defined to express the drive performance, computing cost and estimation
efficiency, which provide a comprehensive assessment for sensorless drive schemes of
PMSM.
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