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At high angular velocity, the induction motor is operated in the field weakening range due to the voltage limit of the inverter. Field oriented vector control (FOC) is unsuitable for this operation due to coupling, non-linearities, and saturation of linear current controllers. A proposed direct torque control space vector modulation (DTC-SVM) scheme using SVM does not use coordinate transforms or current controllers to achieve DTC. Control of the stator flux vector allows for dynamic change in the torque in all regions, including field weakening with the six-step operation. This paper describes the torque control dynamic in the field weakening range, using a step change in stator flux vector magnitude and it's angular velocity. The method is demonstrated experimentally. Index Terms--Constant power speed range (CPSR), direct torque control (DTC), field-weakening.

A constant switching frequency torque control method is presented in this paper, that uses flux error vector based space vector modulation (SVM) to achieve steady state and dynamic control of torque. The effect of SVM switching on torque ripple has been analyzed using 'flux ripple vectors.' This approach is used to develop an insight of torque ripple and to estimate it for any operating angular velocity. We propose a method of compensation to maintain steady state control of torque in the overmodulation region of operation. During torque dynamic, the optimum maximum switching state vector is selected. This gives a response similar to that obtained using direct torque control (DTC) and direct self control (DSC) methods. The proposed method is verified experimentally. Index Terms--Dynamic torque control (DTC), flux ripple vector, space vector modulation, torque ripple.

This paper proposes the use of iterative learning control (ILC) in designing a torque controller for switched reluctance motors (SRMs). The demanded motor torque is first distributed among the phases using a torque-sharing function. Following that, the phase torque references are converted to phase current references by a torque-to-current converter and the inner current control loop tracks the phase current references. SRM torque is a highly nonlinear and coupled function of rotor position and phase current. Hence, the phase current references for a given demanded torque can not be obtained analytically. Assumption of linear magnetization characteristics results in an invertible torque function. However, the nominal phase current references obtained using this torque function will lead to some torque error as motor enters into magnetic saturation. For a constant demanded torque, the error in the phase current references will be periodic with rotor position. Hence, we propose to use ILC to add a compensation current to the nominal phase current references so that torque error is eliminated. Similarly, current tracking for the nonlinear and time-varying system is achieved by combining a simple P-type feedback controller with an ILC controller. The proposed scheme uses ILC to augment conventional feedback techniques and hence, has better dynamic performance than a scheme using only ILC. Experimental results of the proposed scheme for an 8/6 pole, 1-hp SRM show very good average as well as instantaneous torque control. Index Terms--Current control, iterative learning control (ILC), switched reluctance motor (SRM), torque control, torque estimator.

This paper presents closed loop control of stator flux vector in a wide operating range that can be used in torque control. A predictive control achieves zero phase error at constant switching frequency. Space vector modulation based on stator flux error vector is used to achieve control of stator flux over the entire range including overmodulation and six-step. During dynamics the fastest possible flux vector change is employed similar to the direct torque control. Experimental results are provided for a wide speed range and effect of parameter variation is studied. Index Terms--Direct torque control, overmodulation, space vector modulation, stator flux control.

Parasitic torque pulsations exist in permanent magnet synchronous motors (PMSMs) due to nonsinusoidal flux density distribution around the air-gap, errors in current measurements, and variable magnetic reluctance of the air-gap due to stator slots. These torque pulsations vary periodically with rotor position and are reflected as speed ripple, which degrades the PMSM drive performance, particularly at low speeds. Because of the periodic nature of torque ripple, iterative learning control (ILC) is intuitively an excellent choice for torque ripple minimization. In this paper, first we propose an ILC scheme implemented in time domain to reduce periodic torque pulsations. A forgetting factor is introduced in this scheme to increase the robustness of the algorithm against disturbance. However, this limits the extent to which torque pulsations can be suppressed. In order to eliminate this limitation, a modified ILC scheme implemented in frequency domain by means of Fourier series expansion is presented. Experimental evaluations of both proposed schemes are carried out on a DSP-controlled PMSM drive platform. Test results obtained demonstrate the effectiveness of the proposed control schemes in reducing torque ripple by a factor of approximately three under various operating conditions. Index Terms--Frequency domain design, ILC, parasitic torque pulsations, PMSM, torque ripple minimization.

The commercial electrification of marine vessels started in the 1880s with a direct current (dc) system onboard SS Columbia. However, the popularity of the ac electrical distribution system resulted in the move towards an alternating current (ac) system onboard marine vessels. At present, there are marine vessels that operate based on a diesel-electric system. The on-board diesel engines generate ac power to a common ac bus, from which the electrical propulsion drives source their electrical power. Recently, there is an interest in a shift back to a dc-based diesel-electric system for marine vessels, due to the potential improvement in electrical performance and fuel savings. This paper evaluates the improvement obtained by moving to a dc system for marine vessels in terms of electrical performance and generator scheduling. An overview of a typical ac electrical system currently in use is provided, and modification of the system to a dc-based system is presented. The issue of multiple generator synchronization and harmonic elimination are also discussed. A discussion on the potential benefits of a shift to a dc system is provided, as well as the potential challenges that may arise. Both symmetrical and asymmetrical generator scheduling are examined and the potential fuel savings for an example vessel is calculated. [ABSTRACT FROM AUTHOR]

A new technique of wirelessly transmitting electric energy to piezoelectric components is explored. The proposed method improves energy transfer efficiency by using the strongly coupled magnetic resonance as well as the mechanical resonance of the piezoelectric component. In the design, a printed spiral receiving coil connected across the piezoelectric component is used to capture energy wirelessly from the magnetic fields generated by a source resonator. Experimentally, the transmission of electric energy to the piezoelectric components is enhanced when the operating frequency of the generated magnetic field is close to the mechanical resonance frequency of the piezoelectric component. The power delivered to the piezoelectric component depends on the driving frequency, vibration modes of the piezoelectric plate, design, and separation distance of the source and receiving coils. At the resonant frequency 772 kHz of the piezoelectric component operating in the thickness vibration mode, a maximum power of 1.26 W and energy conversion efficiency of 48% have been achieved wirelessly by the piezoelectric component with an input ac source power of 2.6 W across the source coil and 4 cm separation distance of the source and receiver coils. [ABSTRACT FROM AUTHOR]

Parasitic torque pulsations exist in permanent magnet synchronous motors (PMSMs) due to nonsinusoidal flux density distribution around the air-gap, errors in current measurements, and variable magnetic reluctance of the air-gap due to stator slots. These torque pulsations vary periodically with rotor position and are reflected as speed ripple, which degrades the PMSM drive performance, particularly at low speeds. Because of the periodic nature of torque ripple, iterative learning control (LLC) is intuitively an excellent choice for torque ripple minimization. In this paper, first we propose an ILC scheme implemented in time domain to reduce periodic torque pulsations. A forgetting factor is introduced in this scheme to Increase the robustness of the algorithm against disturbance. However, this limits the extent to which torque pulsations can be suppressed. In order to eliminate this limitation, a modified ILC scheme implemented In frequency domain by means of Fourier series expansion is presented. Experimental evaluations of both proposed schemes are carried out on a DSP-controlled PMSM thin platform. Test results obtained demonstrate the effectiveness of the proposed control schemes in reducing torque ripple by a factor of approximately three under various operating conditions. [ABSTRACT FROM AUTHOR]