Charles Pollock

Analysis and reduction of vibration and acoustic noise in the switched reluctance drive

This paper describes the results of an extensive study into the production and reduction of acoustic noise and vibration in the switched reluctance drive. Time domain analysis has been used to draw conclusions about the effects of changing the operating parameters of the power electronic controller on the vibration and acoustic noise. Experimental results have been taken from a four-phase switched reluctance drive with one-, two-, or four-phase excitation. The results of this time domain study reveal important information about the stator vibration which would not be apparent from frequency spectra. The results have been used to derive operational concepts for the power electronic controller to reduce the acoustic noise and vibration produced by the drive. A new control technique has been developed to cancel the stator vibration. Using this novel control method, experimental results show that the vibration and acoustic noise produced by a switched reluctance drive can be reduced dramatically without affecting the performance of the drive.The authors describe the results of an extensive study into the production and reduction of acoustic noise and vibration in the switched reluctance motor drive. Time domain analysis has been used to draw conclusions about the effects of changing the operating parameters of the power electronic controller on the vibration and acoustic noise. Experimental results have been obtained on a four-phase switched reluctance drive with one, two, or four phase excitation. The results of this time-domain study reveal important information which would not be apparent from frequency spectra. The results have been used to derive operational concepts for the power electronic controller to reduce the acoustic noise and vibration produced by the motor. Based on these results, a successful control technique has been developed. Using this control method, the vibration and acoustic noise can be dramatically reduced without affecting the performance of the drive.<<ETX>>

Acoustic noise cancellation techniques for switched reluctance drives

The levels of acoustic noise emitted by the switched reluctance drive are noted as being above those of competing variable speed drives. In other respects the switched reluctance drive offers distinct advantages. In a previous paper, the authors described a new technique for the cancellation of radial vibrations of the stator. This new technique was limited to power converters offering a zero voltage freewheel path. This paper describes further development of the technique which allows noise cancellation to be achieved with all types of power converter. The techniques disclosed in this paper include a smoothing method, a three stage commutation method for converters with one switch per phase and a noise cancellation technique suitable for switched reluctance drives incorporating an extended zero voltage freewheel period for improved efficiency. The techniques are all compared, with experimental and simulated results.

Power electronic converters for switched reluctance drives

A number of power electronic converter circuits exist for switched reluctance motor (SRM) drives which are generally applicable to most loads. A larger number of circuits exist which are suitable for particular niche applications, but which have the potential to be the most cost-effective within that niche. Due to the variable methods of operation of these circuits and the rapid progress in this field, comparisons of these circuits have so far been limited. This paper attempts to bring together the sum total of power converter topologies so far published for SRM drives. A novel classification methodology is presented. The power converters are compared using a straightforward total semiconductor VA per phase sum, and the relative cost of the drive system elements is considered.

Reduction of noise and vibration in switched reluctance motors: new aspects

This paper describes recent work of the authors on an active noise cancellation techniques for switched reluctance drives. This work goes beyond the research previously published in the literature, in that vibration cancellation can now be equally effective at any motor speed. The proposed method focuses on the reduction of acoustic noise by inducing two minor stator vibrations that oppose each other. In order to achieve a significant reduction in acoustic noise, the magnitude of the two opposing vibrations must be approximately equal. This is achieved by adopting a two stage commutation method with an average negative voltage, V/sub n/. At the commutation instant, a step change from the average chopping voltage, V/sub c/, to V/sub n/ is initiated and a resulting vibration is induced. Half a mechanical resonant cycle of the stator later, a second step change in voltage from V/sub n/ to the negative supply voltage, -V/sub s/, is induced. The resulting second vibration is 180/spl deg/ out of phase with the first vibration. The two opposing vibrations of equal magnitude almost completely cancel each other out. The level of the average negative voltage, V/sub n/, must be continuously monitored and adjusted, depending on the motor running and base speeds in order to keep the magnitude of the two opposing vibrations equal. Experimental results demonstrate the effectiveness of the proposed method.

Forward converters for dual voltage switched reluctance motor drives

A new circuit is presented which allows a switched reluctance motor to operate from AC mains or a low voltage battery supply. In addition the AC mains can be used to charge the battery. The switched reluctance motor is used as the voltage-changing transformer, potentially reducing the cost of the system. The operation of the drive is explained, and results of an experimental prototype are presented.

Rotor position detection techniques for brushless permanent-magnet and reluctance motor drives

The basic principles of sensorless rotor position detection in brushless permanent magnet and reluctance motor drives are discussed. Techniques for sensorless rotor position detection from the literature are reviewed. All the methods proposed in the literature extract the rotor position information from measurements on the phase winding circuits. Such techniques therefore eliminate the connections of the sensor to the motor and controller, simplifying the system construction. Furthermore, continuous rotor position information can be obtained for optimal control.<<ETX>>

Short flux paths optimise the efficiency of a 5-phase switched reluctance drive

A new configuration of switched reluctance drive is proposed in which the windings of a five-phase motor are configured to encourage short flux paths within the motor. The five-phase prototype motor can be fed from a new power converter which uses only six switching devices in a shared switch configuration. Experimental results demonstrate that the five-phase prototype achieves higher efficiency than prior art switched reluctance and induction drives constructed in the same frame size, and with the benefit of the new electronic circuit it is very cost effective.

A new magnetic flux pattern to improve the efficiency of the switched reluctance motor

A novel configuration of the switched reluctance motor is proposed in which the windings are arranged to provide short flux paths within the motor. This decreases the current required to establish the flux in the airgap. The motor has an odd number of phase windings with five or seven predicted to be the optimum. A novel power converter has also been developed which makes the control of these motors possible without excessive numbers of power switches. Finite-element analysis was used to model the effects of the short flux loops. A prototype seven-phase motor was designed and built. Test results are presented which indicate the improvements in performance offered by the new design.<<ETX>>

A rechargeable and portable AC power supply with the minimum of electronic components

The development of a rechargeable portable power supply is presented. A novel topology is proposed which combines the function of rectifier, inverter, step-up and step-down converter into a single circuit, reducing components used, resulting in a unit that is compact, lightweight, reliable, and cheap. The concept of a variable voltage DC link between the power conversion stages and a new inverter switching scheme have been proposed and realized. The concepts presented have been amply verified and are also applicable to uninterruptible power supplies and stand-by power systems.<<ETX>>