Performance estimation of interior permanent-magnet brushless motors using the voltage-driven flux-MMF diagram

Abstract

The flux-magnetomotive force (flux-MMF) diagram, or "energy conversion loop," is a powerful tool for computing the parameters of saturated interior permanent-magnet brushless motors, especially when the assumptions underlying classical dq theory are not valid, as is often the case in modern practice. Efficient finite-element computation of the flux-MMF diagram is possible when the motor current is known a priori, but in high-speed operation the current regulator can lose control of the current waveform and the computation becomes "voltage-driven" rather than "current-driven." This paper describes an efficient method for estimating the motor performance-average torque, inductances-by solving the voltage-driven problem. It presents experimental validation for a two-pole brushless interior permanent-magnet motor. The paper also discusses the general conditions under which this method is appropriate, and compares the method with alternative approaches. . It is well known that when the magnets are embedded inside the rotor iron, as in the "interior permanent-magnet motor" (IPM), calculations based on classical theory can be unreliable, mainly because of the variation of parameters due to saturation. IndexFor example in such machines can vary by at least 700% between no-load and full-load, while cross saturation influences the -axis parameters in a complex manner [1]- [7], [9]. The difficulties are increased by the use of fractional-slot windings with small numbers of slots/pole (even less than 1), non-circular laminations, and other departures from the ideal machine, so that neither the EMF waveform nor the variation of inductance with rotor position is sinusoidal. , and although they allow for cross-saturation effects they restrict themselves to steady-state operation and ignore the effect of rotor position on the -axis parameters.As long as the current waveform is known a priori, these problems can be overcome in an efficient computation in which the finite-element method is used to determine one cycle of the flux-linkage waveform, which is then plotted against the current waveform to establish a "loop" whose area gives the average electromagnetic torque. This loop diagram is known as the "flux-MMF diagram" or "i-psi loop" or "energy conversion loop" [9]. Bearing in mind that finite-element formulations are fundamentally always "current-driven," the computation is efficient because of the foreknowledge of the current waveform, so that a series of current values can be used as inputs to the finite-element process. This method does not necessarily rely on theory. At higher speeds it is normal for the current-regulator to lose control of the current waveform, and ultimately at the highest speeds the drive may operate in six-step mode. In this case, the applied voltage waveform is known but the current waveform is not. Similarly, if the machine is generating into a rectifier, the applied voltage at the machine terminals is known or calculable, whereas the current waveform is unknown.The accuracy of the finite-element m...

A High-Fidelity Computationally Efficient Transient Model of Interior Permanent-Magnet Machine With Stator Turn Fault

“…It is well known that in order to accurately model behavior of a healthy IPM machine, a mapping of flux-linkages to current is needed [38], [28]. This non-linear flux linkage map can capture most of the behavior of the machine including the magnetic saturation, spatial saliency and harmonics [28]-[31].…”

“…In [10] and [27] an inductance based model was proposed for inter-turn fault detection in PM synchronous machines. However, IPM machines with buried magnets exhibits high level of magnetic saturation and cross-saturation effects and therefore separation of armature reaction flux linkage from the total flux linkage will incur large error and hence compromises model accuracy [28]- [33]. Moreover the method of extraction of inductances reported in [27] and [34] by energy-perturbation is computationally more demanding requiring twice as many FE computations [32].…”

“…This non-linear flux linkage map can capture most of the behavior of the machine including the magnetic saturation, spatial saliency and harmonics [28]- [31]. 3-dimensional (3d) effects such as overhang fringe fields, iron losses and rotor eddy currents may also be included.…”

The Numerical Calculation and Experimental Measurement of the Inductance Parameters for Permanent Magnet Synchronous Motor in Electric Vehicle

“…Numerical calculation can be achieved by using static magnetic field or transient magnetic field. Experimental measurement can be done by using off-line measurement, such as direct load method, voltage integration method and current decay method, as well as on-line identification [6][7].…”

Torque Estimation Using Precise Calculations of Inductance and Iron loss Mathematization

“…If a calculation of nonlinear parameters was exactly performed, it is known as a efficient method [1]- [2].…”