Torque Ripple Mitigation Research Articles

Minimization of Torque Ripple in the DFIG-DC System Via Predictive Delay Compensation

Torque ripple caused by stator current and flux harmonics is one of the main issues in the doubly fed induction generator (DFIG)-dc system, which inherently has to operate with distorted waveforms produced by the diode commutation. This paper proposes a torque-ripple mitigation strategy based on a predictive estimation of the reciprocal of flux linkage. The predictive estimation compensates for the intrinsic delay in the actuation of the torque-ripple rejection signal through the rotor current control loops. Unlike other approaches relying on complex current regulators with selective harmonic tracking, this strategy is based on well-established proportional-integral (PI) controllers for the rotor currents. PI current controllers can then still have bandwidth values typical of usual DFIG systems. Simulations and experiments on a test-rig show that the compensation strategy achieves a strong torque ripple reduction and is very robust against stator frequency variations.

Direct Resonant Control Strategy for Torque Ripple Mitigation of DFIG Connected to DC Link through Diode Rectifier on Stator

This paper presents a torque ripple mitigation method for the doubly-fed Induction generator (DFIG) connected to the dc link through a diode rectifier on the stator winding. A resonant regulator based on torque compensator is directly added to the conventional rotor current control loop, and the sequential separations and calculations of rotor harmonic current references can be avoided. Then, a novel stator flux orientation method is achieved by indirectly controlling the q -axis stator flux linkage to be zero without calculating the stator flux linkage angle. The stator frequency is controlled by regulating the stator flux without calculating the stator frequency. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, analysis of the steady-state error, and the dynamic performance are discussed. Finally, the proposed control method is validated by the experiment results.

Torque-Ripple Mitigation for Brushless DC Machine Drive System Using One-Cycle Average Torque Control

This paper investigates the torque-ripple mitigation method for a brushless dc machine caused by nonideal trapezoidal back electromotive force (EMF) using a novel one-cycle average torque control algorithm. This algorithm can ensure that the average torque follows the reference in each switching cycle. The feedback average torque is computed using the energy flowing into the system in each control cycle. No sophisticated observer is needed since neither the back EMF nor accurate rotor position information is required. No current sensor is needed to measure the phase current. Only two sensors are used to obtain the dc-bus voltage and current information to calculate the input energy. Simulations and experimental results are demonstrated to verify that the proposed method is able to reduce the major lower harmonics of the machine torque ripple by more than 70%.

Torque Analysis of Permanent-Magnet Flux Switching Machines With Rotor Step Skewing

This paper investigates the torque characteristics of permanent-magnet flux switching (PMFS) machines with rotor step skewing. The cogging torque, torque ripple, and average output torque of a PMFS machine with a common stator and different rotor pole widths and rotor pole numbers are first established using two-dimensional (2-D) finite element analysis (FEA). A cost-effective rotor step skewing technique is then proposed to reduce the cogging torque and torque ripple of the machine with two different rotors. The results have revealed that the least step number and angle for optimal torque ripple mitigation of the PMFS machine are determined by the harmonic contents of the torque pulsation and the rotor pole number. The influences of load conditions on the machine torque characteristics are carried out by varying current excitations. The corresponding three-dimensional (3-D) FEA models are constructed and experimental prototypes are built for validations.

Loss-minimization Scheme in Modified DTC-SVM for Induction Motors with Torque Ripple Mitigation

Loss-minimization Scheme in Modified DTC-SVM for Induction Motors with Torque Ripple Mitigation

A Coupled Piezoelectric/Single-Hall-Sensor Position Observer for Permanent Magnet Synchronous Machines

In recent years, several control methods have been proposed to reduce the torque ripple produced by permanent magnet synchronous machines [sinusoidal and trapezoidal back electromotive force (EMF)]. In these approaches, a drive system is used to control current harmonics based upon measured machine parameters or measured torque ripple. In general, the methods presented have utilized high-precision position encoders and thus a common perception is that such encoders are required for successful mitigation. In this paper, a position observer is developed that is shown to be suitable for control-based torque ripple mitigation. Additional advantages of the observer are that it achieves excellent start-up performance, requires no knowledge of the machine parameters, and is applicable to machines with an arbitrary back EMF waveform and stator slot configuration.

Compensation for Asymmetries and Misalignment in a Hall-Effect Position Observer Used in PMSM Torque-Ripple Control

A Hall-effect-sensor-based position observer that is suitable for mitigation of torque ripple in permanent-magnet synchronous machines is derived. The observer includes an initial commissioning routine to compensate for the offset in the placement of Hall sensors, which is shown to be necessary for effective control of torque harmonics. Using the position observer in lieu of a high-precision encoder, the overall cost of control-based torque-ripple mitigation is reduced significantly. In addition to the observer, an enhancement is made to a recently developed torque-ripple mitigation algorithm. Specifically, the algorithm is modified to compensate for sensor delay. Proposed methods have been validated in simulation and hardware