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Control of AC Machines
Published in Iqbal Husain, Electric and Hybrid Vehicles, 2021
In the case of PM BLDC motors, the rotor position sensor and power electronic converter replace the mechanical commutators and brushes of DC motors; these components work in synchronism to maintain the orthogonality between the stator current space vector i→s(t) and the rotor flux vector λ→r(t) on an average basis. The back-emfs in these machines are trapezoidal, and not sinusoidal; hence, vector control is not possible. Torque ripple is a problem in PM BLDC motors, since square wave currents are used for torque production in synchronism with the trapezoidal back-emfs. In contrast, the orthogonality between armature and field mmfs is continuously maintained in DC commutator machines that help deliver a smoother torque. However, in the case of PM synchronous machines, the back-emfs are sinusoidal, and using vector control, smooth torque control can be achieved like that in an induction machine.
Introduction to Electric Machines and Drive Systems
Published in R. Krishnan, Entrepreneurship in Power Semiconductor Devices, Power Electronics, and Electric Machines and Drive Systems, 2020
Two major issues have been identified with the SRM drive system and they are: Torque Ripple: A simple control technique such as mentioned above resulted in significant torque ripple which may not be acceptable in few high-performance applications. They mainly resulted from the inherent nonlinear feature of the machine. Control techniques to overcome this issue have been demonstrated both in theory and practice to the tune of controlling the torque ripple to less than 1% of the rated torque.Acoustic Noise: Regular control resulted in higher acoustic noise which was unacceptable. This is primarily due to vibration induced by the resonance of switching or operating at speeds near natural frequencies of the machines and many other phenomena such as forces created by the interaction of two salient magnetic parts of a structure such as in SRMs, load-induced noise, cooling related, etc. Ways to control and manage both in the motor design and its realization, and in addition by nonlinear control techniques have been demonstrated by some startups among others.
T
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
touch screen torque the product of a force acting at a distance. The output of an electric motor. torque angle the displacement angle between the rotor and rotating magnetic flux of the stator due to increases in shaft load in a synchronous machine. See also power angle. torque pulsation oscillating torque produced by the interaction between the air gap flux, consisting mainly of the fundamental component, and the fluxes produced by harmonics in the rotor. Torque pulsations can stimulate complex mechanical vibrations that can flex and damage rotor and turbine elements. torque ripple in variable speed motor drives, refers to the torque not being smooth as the rotor moves from one position to another. Torque ripple may be produced from space harmonics within the machine or time harmonics generated by the supply. torque servo a servo where the output torque is the controlled variable and the operating speed depends on the load torque. See also servo. torus a donut-shaped magnetic core used in electric transformers. total demand distortion (TDD) an index that quantifies the amount of distortion in the voltage or current waveform with respect to the maximum 60-Hz demand load current I M L over a 15-30 minute demand period. Ih
Proportional-integral-proportional control and compensation design for low-speed motions of permanent magnet synchronous motor driven servomechanism with position-dependent disturbance
Published in Journal of the Chinese Institute of Engineers, 2022
Torque ripple can be suppressed by modifications to the hardware design and the control approach. The hardware design mainly modifies the motor stator and rotor structure (Zhu and Liu 2018; Hwang et al. 2014; Fei and Luk 2012). Lan et al. (2018) analyzed a permanent magnet synchronous machine design and evaluated the unbalanced magnetic force induced by asymmetric designs. Ishak, Rezal, and Tiang (2018) discovered that a PMSM with ideal Halbach magnetization presents almost zero cogging torque and sinusoidal phase back-emf waveform; moreover, parallel and radial magnetization will generate more trapezoidal phase back-emf waveforms, which will induce larger torque ripples. Asgari and Mirsalim (2019) indicated that the dual-stator permanent magnet synchronous machine design can have minute torque ripples and sinusoidal air-gap flux density waveforms. Liu et al. (2017) used the magnet shifting method to reduce the torque ripple and discussed the effect of magnet shifting on cogging torque, reluctance torque, and total torque. Abdelmoula et al. (2017) used the two-dimensional finite element method to analyze the effect of a surface-mounted PMSM’s design on torque ripple and back-emf and discussed the design method of slot opening and skewing the stator laminations for reducing torque ripple.
Comparative Analysis of Torque Ripple for Direct Torque Control based Induction Motor Drive with different strategies
Published in Australian Journal of Electrical and Electronics Engineering, 2022
Pravinkumar D. Patel, Saurabh N. Pandya
Torque pulsations contribute to noise and vibrations. Torque pulsations caused by supply current ripple, phase current commutation and from machine cogging effect. In electrical machines, torque ripple is due to cogging effect, distortion of the sinusoidal distribution of the magnetic flux density in the air gap and unequal permeance in the d and q axis (Bimal 2002). Torque pulsations become especially noticeable at low frequency (fs = 0–5 Hz) thus putting the limit on the range of speed control. Low torque harmonics can be damped by stator current PWM. Electromagnetic torque pulsating components with frequency six times of supplied (6fs) whose amplitude is independent of the motor load. The sixth harmonic amplitude is proportional to the square of the flux. Therefore, flux weakening may considerably reduce torque pulsations. For low frequencies (fs ≤5 Hz), the effect of stator resistance voltage drop on the stator voltage becomes remarkable. The increase of the frequency of pulsating torque components may be effectively damped by rotor inertia without causing any fluctuation of its speed (Kazmierkowski 1994). Torque pulsation is produced due to air gap flux at one frequency interacting with rotor MMF at a different frequency. The general torque expression as a function of air-gap flux, rotor current, and the phase angle between the air gap flux and rotor current (Bimal 2002).
Harmonic current suppression method with adaptive filter for permanent magnet synchronous motor
Published in International Journal of Electronics, 2021
Zhe Song, Jun Yang, Xuesong Mei, Tao Tao, Muxun Xu
Permanent magnet synchronous motor (PMSM) has been widely used in CNC machine tools, aerospace, industrial robots and other fields because of its small size, high efficiency, large electromagnetic torque, easy maintenance and control (Guo et al., 2015; Kommuri et al., 2016; Shao & Sun, 2007). In the process of its operation, besides the fundamental component, the current waveform also contains a large number of high order harmonic components. According to the nature of harmonic current, it can be divided into time harmonic and space harmonic. Among them, time harmonics are mainly caused by the non-linear characteristics of inverters due to dead-time and switching tube voltage drop, while space harmonics are mainly caused by the slot effect, winding distribution and magnetic circuit saturation, etc (Kim & Park, 2007; Murai et al., 1987). The characteristic of time harmonics is time dependent, while the characteristic of space harmonics is position dependent. The existence of harmonic current makes the current waveform of the PMSM seriously distorted, increases the loss of the motor and causes the motor to heat up. At the same time, it also produces torque ripple, which affects the stability operation and deteriorates the output quality of the motor (AI-Nabi et al., 2012; Schwager et al., 2014).