Abstract
Information obtained about magnetic anisotropy via neutral point voltage measurements can be used to estimate the position of synchronous and induction machines at all speeds including standstill. Due to its usually high signal-to-noise ratio, this estimation method can be an attractive alternative to approaches that acquire anisotropy information via current measurements. The position estimation method looked at in this paper relies on anisotropy information in the form of position-dependent inductance ratios. These are obtained through measurement of the voltage between the machine's neutral point and an artificial neutral point during the application of different voltage vectors via a two-level switching inverter. We analyze the conditions placed on and the consequences of implementing necessary modifications to a standard space vector modulation. Five different modified modulation strategies are compared and investigated, including two newly proposed strategies which use only a minimal set of active and zero voltage vectors for measurement of the inductance ratios and therefore allow high utilization of available voltage and a high update rate of the estimated position. Experimental results for three low-power three-phase permanent magnet synchronous machines are presented which suggest that modulation strategies that use active measurement vectors in all three instead of only two axes of the machine are less susceptible to systematic deviations in the position estimation that presumably result from nonlinear machine properties. As part of the machine model, a normalizing inductance variation ratio is introduced, which simplifies expressions and supports the comparison of motors.
Highlights
E STIMATING position and speed of synchronous and inductance machines from electrical quantities instead of using mechanical sensors offers opportunities to save space and cost and to increase reliability
Experimental results for three low-power threephase permanent magnet synchronous machines are presented which suggest that modulation strategies that use active measurement vectors in all three instead of only two axes of the machine are less susceptible to systematic deviations in the position estimation that presumably result from nonlinear machine properties
This work showed that modified space vector modulation (SVM) strategies are necessary when estimating the rotor position from twodimensional anisotropy information obtained via neutral point voltage measurements
Summary
E STIMATING position and speed of synchronous and inductance machines from electrical quantities instead of using mechanical sensors offers opportunities to save space and cost and to increase reliability. The use of magnetic anisotropies has been strongly investigated over the past three decades in order to complement methods based on induced voltages and allow estimation at very low speeds and standstill. While the voltage induced by rotor movement is proportional to speed, estimation via magnetic anisotropy is based on machine inductances varying with position. To acquire information related to the position dependent machine inductances, the machine phases must be excited with AC signals such as sinusoidal or pulsed signals. There exists a wide variety of approaches to exploit the anisotropy information using different forms of excitation, measurement, signal processing and methods to determine position and speed [1], [2]. We focus only on estimation approaches that use the discrete voltage vectors from a two-level switching inverter as the source of excitation to obtain information about the varying inductances in the machine. The following advantages can be identified: applying pulses with the highest
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