General Torque Enhancement Approach for a Nine-Phase Surface PMSM With Built-In Fault Tolerance

Abstract

The paper investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine (PMSM) with a reduced magnet span, which causes production of highly nonsinusoidal back-EMF. It contains a high third and fifth harmonics, which can be used for the torque enhancement, using stator current harmonic injection. Optimal magnet span is studied first and it is shown that with such a value the machine would be able to develop an insignificantly lower maximum torque than with the full magnet span. Next, field-oriented control (FOC) algorithm, which considers all non-fundamental EMF components lower than the machine phase number, is devised. Using maximum-torque per Ampere (MTPA) principles, optimal ratios between fundamental and all other injected components are calculated and then used in the drive control. The output torque can be in this way increased up to 45% with respect to the one obtainable with fundamental current only. Alternatively, for the same load torque, stator current RMS value can be reduced by 45%. Last but not least, a method for position sensor fault mitigation is introduced. It is based on the alternative use of a back-EMF harmonic for rotor position estimation, instead of the torque enhancement. Experimental verification is provided throughout for all the relevant aspects.

A Novel Matrix Transformation for Decoupled Control of Modular Multiphase PMSM Drives

“…5), allowing its control using only a pair of resonant regulators [17], [43]. Therefore, in a nonsinusoidal PMSM, this approach is the most suitable one for performing the torque enhancement using the harmonics above the time-fundamental [48]. With regard to the DMS differential-mode subspaces, it is noted how the same timeharmonics map into them (see Fig.…”

Third Harmonic Current Injection in Different Operating Stages of Five-Phase PMSM With Hybrid Single/Double Layer Fractional-Slot Concentrated Winding

“…Five-phase brushless permanent-magnet (PM) machine with trapezoidal back electromotive force (EMF) supplied by third harmonic current injection achieves better performance compared with both brushless dc machine and PMSM, due to vector decoupling control of d 1 -q 1 and d 3 -q 3 harmonic space [7]. With constant rms harmonic injection, nine-phase machine with PM whose pole arc coefficient is only 0.389 generates almost the same torque compared with machine with full-pitch PM [8], [9]. The optimal injection ratio of harmonic current for maximizing output torque of multiphase machine has been analyzed, which is related with the ratio of the corresponding harmonics contained in the back EMF of multiphase PMSM [9], [10].…”

“…With constant rms harmonic injection, nine-phase machine with PM whose pole arc coefficient is only 0.389 generates almost the same torque compared with machine with full-pitch PM [8], [9]. The optimal injection ratio of harmonic current for maximizing output torque of multiphase machine has been analyzed, which is related with the ratio of the corresponding harmonics contained in the back EMF of multiphase PMSM [9], [10].…”

Permanent Magnet Reduction by Current Harmonics Injection for Surface Permanent Magnet Machines

“…The third current harmonic injection is investigated also for a nine-phase machine with high nonsinusoidal BEMF in [16]. Genetic algorithms are implemented in [18] in order to maximize the torque per ampere and optimize the iron utilisation by an optimum flux distribution by harmonic injection. This work is analysing in detail the effects of the permanent magnet span, of SPM machines, on the spatial harmonics distribution.…”

“…The proposed method permits to maintain the RMS current constant with respect to the current control with the only fundamental component, thus the Joule losses are not affected by harmonics injection. A similar approach has been used in [18], where a ninephase SPM machine is studied via FE for different PM span to increase the torque performance by harmonic injection. However, the investigation is based on the injection until the seventh harmonic.…”