Since a direct drive motor (DDM) does not require a reduction
gear, the drive system can be made simple, and therefore it is used in
high-precision robot and machine tool applications. However, without
reduction gear, a disturbance torque is directly reflected to the motor
shaft, and a torque ripple generated by the motor is directly
transmitted to the load, causing poor speed control characteristics. An
improved torque control system for DDM with a permanent magnet rotor,
equipped with a torque observer implemented by digital signal software,
is proposed. The speed fluctuation can be fully removed with a torque
"Even if such methods perform well in ripple minimization, machine design techniques additionally complicate the production process and increase the final machine cost , . The methods belonging to the latter family try to minimize the torque ripple using an additional control effort to correct for non-ideal characteristics of the machine (see ,  for example). In the case of time-varying motor parameters, on-line estimation techniques have been widely investigated . "
[Show abstract][Hide abstract] ABSTRACT: Permanent magnet motors are largely employed due to their high performances in terms of efficiency, power factor and power density. However, non-uniformity into the generated torque may heavily limit their use. In this paper a novel approach is proposed to cancel torque ripple when motor parameters are unknown. The cancellation scheme is based on the frequencies estimation of periodic disturbances acting on the generated motor torque. The estimation process makes use of an adaptive frequency-locked loop system driven by speed measurements. A fractional-order controller is designed to guarantee the stability of the closed-loop system.
"Reference  gives an overview of torque ripple minimization techniques of permanent magnet ac motors, the authors have pointed out many control-based ripple minimization algorithms. Among these techniques, two interesting strategies are presented respectively in  . The first one consists on optimal currents injection determined by finite element method and the second one is based on a load torque observer and online torque ripple compensation. "
[Show abstract][Hide abstract] ABSTRACT: The paper deals with modeling of synchronous reluctance motor (SynRM) accounting for all phenomena responsible for torque ripple. Based on winding function approach, the proposed model consists in computing self and mutual inductances considering no sinusoidal distribution of stator windings, slotting effect and no sinusoidal reluctance variation caused by the rotor saliency. Then, optimal current waveforms are determined for each rotor position by solving a second order equation to reduce torque ripple. These currents are used within a vector control scheme. Satisfactory agreement between simulation and experimental results is obtained.
Mathematics and Computers in Simulation 10/2010; DOI:10.1016/j.matcom.2010.07.024 · 0.95 Impact Factor
"These parameters were then used to develop a nonlinear control strategy. Other researchers developed dynamical torque controllers by using either a torque observer or a flux observer to compensate torque ripple , , , . The torque control problem is radically simplified when the motor's excitation currents are considered as inputs. "
[Show abstract][Hide abstract] ABSTRACT: Accurate torque control of a brushless motor requires the motor's torque characteristics, which follows a periodic function of motor angle. This brief presents a direct adaptive controller for torque control of brushless motors, which estimates the Fourier coefficients of this periodic function based on the measurements of motor phase voltage and angle. It will be analytically shown that the proposed adaptive controller achieves torque tracking regardless of the trajectories of input signals. Moreover, the adaptive controller does not rely on the modeling of the mechanical load, so that control implementation is simple and modular. Experimental results obtained from the McGill/MIT motor have demonstrated that motor torque converges to the command torque.
IEEE Transactions on Control Systems Technology 04/2008; 16(2-16):356 - 364. DOI:10.1109/TCST.2007.908213 · 2.47 Impact Factor
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