M.I. McGilp

On the variation with flux and frequency of the core loss coefficients in electrical machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.

Line-start permanent-magnet motor single-phase steady-state performance analysis

This paper describes an efficient calculating procedure for the steady-state operation of a single-phase line-start capacitor-run permanent-magnet motor. This class of motor is beginning to be applied in hermetic refrigerator compressors as a high-efficiency alternative to either a plain induction motor or a full inverter-fed drive. The calculation relies on a combination of reference-frame transformations including symmetrical components to cope with imbalance, and dq axes to cope with saliency. Computed results are compared with test data. The agreement is generally good, especially in describing the general properties of the motor. However, it is shown that certain important effects are beyond the limit of simple circuit analysis and require a more complex numerical analysis method.

A General Model for Estimating the Laminated Steel Losses Under PWM Voltage Supply

The new model is based on a modified Steinmetz equation and employs a hysteresis-loss multiplicative coefficient and a combined coefficient for eddy-current and excess losses, both coefficients being variable with induction and frequency. The material model coefficients are first identified through multifrequency tests with sine-wave excitation. The iron-loss increase due to pulsewidth-modulation supply is estimated using global waveform parameters of the nonsinusoidal voltage. The study includes three different grades of non-grain-oriented electric steel. The data cover a wide range of fundamental frequency from 10 to 600 Hz and induction from 0.05 to 2 T. The errors of the computational model are small at relatively low fundamental frequency and increase thereafter. The main advantages of the model are its simplicity of use and minimal data requirements.

Assessment of torque components in brushless permanent magnet machines through numerical analysis of the electromagnetic field

For the calculation of torque in brushless (BL) AC motors a local method is proposed, based on the Maxwell stress theory and the filtered contributions due to the harmonics of the magnetic vector potential in the motor air-gap. By considering the space fundamental field only, the method can efficiently estimate the average synchronous torque for a variety or motor topologies, including concentrated winding designs. For BLDC motor analysis a global method is introduced, based on the virtual work principle expressed in terms of energy components in various motor regions. The method leads to simplifications in the average torque calculation and enables the direct identification of the cogging and ripple components. The mathematical procedures have been validated against experiments and other numerical techniques.

End Space Heat Transfer Coefficient Determination for Different Induction Motor Enclosure Types

In this paper, the determination of the end space induction motor heat transfer coefficients is presented, and the methodologies used are examined closely. Two ldquoad hocrdquo prototypes have been built and a test bench completed. This paper reports the setup of the test procedures and results obtained in detail. As the end windings are the hottest points of the motor, particular care has been devoted to the determination of the heat transfer coefficient concerning the end-winding structure. The results obtained are of fundamental importance for the determination of the thermal resistances between end windings and end caps. These can then be used in thermal networks usually adopted in thermal model analysis.

Asynchronous performance analysis of a single-phase capacitor-start, capacitor-run permanent magnet motor

This work presents a detailed analysis of the asynchronous torque components (average cage, magnet braking torque and pulsating) for a single-phase capacitor-start, capacitor-run permanent magnet motor. The computed envelope of pulsating torque superimposed over the average electromagnetic torque leads to an accurate prediction of starting torque. The developed approach is realized by means of a combination of symmetrical components and d-q axes theory and it can be extended for any m-phase AC motor - induction, synchronous reluctance or synchronous permanent magnet. The resultant average electromagnetic torque is determined by superimposing the asynchronous torques and magnet braking torque effects.

Short-Circuit Analysis of Permanent-Magnet Generators

Permanent-magnet generators (PMGs) have rapidly become important in renewable energy systems, portable and standby generating systems, and in many new applications in industrial, utility, aerospace, and automotive sectors. While there has been some discussion of “fault tolerance” and fault testing of an 8-MW machine has recently been reported [1], understanding the behavior of faulted PMGs remains far from complete. This paper addresses the important case of the sudden short circuit applied to large PMG machines. It explains key differences in short-circuit behavior between the PMG and wound-field generator. The subtransient reactances and time constants of the PMG are calculated by both analytical and finite-element methods and applied to the classical circuit-theory simulation of the short-circuit fault. The finite-element method is also used to assess in detail the risk of loss of magnetization in the magnets. The complexity of the transient magnetic field requires transient nonlinear circuit-coupled finite-element analysis in three dimensions with voltage-source excitation. This paper concludes with a review of the methods of calculation and a discussion of implications for future design and application of the PMG, including factors relevant to the application of standard tests and specifications.

A General Model of the Laminated Steel Losses in Electric Motors with PWM Voltage Supply

A procedure is described for identifying a general mathematical model of core losses in ferromagnetic steel when the voltage supply is non-sinusoidal, i.e. PWM inverter-fed type. This model has a hysteresis loss multiplicative coefficient variable with frequency and induction and a combined coefficient for eddy-current and excess losses that is also variable with frequency and induction. The effect of the PWM supply voltage over the core losses is modeled using factors that depend on the average rectified and rms voltage values. Validation was performed on a number of different samples of non-grain oriented fully and semi-processed steel alloys.

Line-start permanent magnet motor-single-phase steady-state performance analysis

The paper describes an efficient calculating procedure for the steady-state operation of a single-phase line-start capacitor-run permanent-magnet motor. This class of motor is beginning to be applied in hermetic refrigerator compressors as a high-efficiency alternative to either a plain induction motor or a full inverter-fed drive. The calculation relies on a combination of reference-frame transformations including symmetrical components to cope with imbalance, and dq axes to cope with saliency. Computed results are compared with test data. The agreement is generally good, especially in describing the general properties of the motor. But it is shown that certain important effects are beyond the limit of simple circuit analysis and require a more complex numerical analysis method.

Calculating the interior permanent-magnet motor

This paper describes the calculation of torque in a brushless permanent-magnet line-start AC motor by means of the flux-MMF diagram in combination with the finite-element method. Results are compared with measured flux-MMF diagrams, with shaft torque measurements, and with torque calculated using the classical phasor diagram.