K.J. Bradley

Conducted electromagnetic emissions in induction motor drive systems. II. Frequency domain models

For pt.I see ibid., vol.13, no.4, p.757-67 (1998). Predicting conducted emissions in pulsewidth modulation (PWM) inverter induction motor drive systems requires various frequency-dependent effects to be considered. A frequency domain method has advantages in such cases compared to a time domain approach. Based on the modal analysis presented in Part I, this paper develops frequency domain models to evaluate the spectra of the conducted emissions directly. The common and differential mode excitation sources are modeled in the frequency domain and related to the switching functions of the PWM inverter. Network models are established where the induction motor is represented using its frequency-dependent impedance characteristics, which can be obtained from measurements. The influences of system unbalances and of transmission-line effects due to long cables are investigated. Predicted emission spectra are compared with laboratory measurements and those derived from the time domain simulation. It is found that the agreement is good. The proposed method allows emission spectra to be predicted without recourse to specialist circuit simulators.

Conducted electromagnetic emissions in induction motor drive systems. I. Time domain analysis and identification of dominant modes

Stray components distributed in a pulsewidth modulation (PWM) drive system form parts of resonant circuits which can be excited to produce radio frequency (RF) noise driven by the pulsed switching action of the power devices. The dynamic response of such circuits is complex. It is essential to identify the dominant oscillation modes in the system so that electromagnetic interference (EMI) reduction techniques can be effectively implemented. This paper (Part I) investigates the mechanisms of conducted EMI emissions associated with a typical PWM inverter induction motor drive system. A numerical model, which includes the high-frequency effects within the machine, is established to evaluate the emissions in the time domain. The dominant high-frequency current paths are identified, and this allows the oscillation frequencies to be predicted from knowledge of the component values. The analysis is confirmed using laboratory measurements. Simplified frequency domain methods for direct calculation of the emission spectra based on the dominant high-frequency current paths are discussed in Part II.

Reliability comparison of matrix and other converter topologies

Several rectifier-inverter and matrix converter topologies suitable for aerospace applications are compared, and their reliability is predicted. The military handbook MIL-HDBK-217F guidelines have been used to predictreliability. The matrix converter has several attractive features for aerospace applications such as potential size and weight savings. Although the matrix converter has a higher number of semiconductor switches, they are subjected to a lower voltage stress, which decreases their failure rate. This results in the reliability indicators of the different converter topologies being very similar

Suppression of saturation saliency effects for the sensorless position control of induction motor drives under loaded conditions

This paper presents an automated commissioning procedure used for the elimination of the saturation saliency effects in the sensorless position control of field-orientated cage induction motor drives. The position control itself is based on extracting a rotor position estimate from a high-frequency signal injection interacting with natural or engineered rotor position saliencies within the machine. The paper shows that this estimate cannot be robustly or accurately obtained if saturation saliencies are present. The paper introduces a method for suppressing the effects of the saturation saliency through information gained in a prior commissioning procedure. The effectiveness of the procedure is demonstrated through experimental results showing both good suppression of the saturation harmonics and true sensorless position control under high load torques.

Integrated PM Machine Design for an Aircraft EMA

This paper looks at the requirements and challenges of designing a permanent-magnet (PM) motor for a directly driven electromechanical actuator for aerospace applications. Having a directly driven system, the intermediate gearbox is eliminated, bringing advantages in terms of lower component count and reduced jamming probability. The design of a low-speed high pole number PM motor will be investigated as a potential solution. The main goals of the design are a high level of actuator integration in order to minimize weight and volume, fault tolerance, and high reliability. The design will be tailored to the requirements of a typical midspoiler actuation system for a large civil aircraft.

Analysis and suppression of high-frequency inverter modulation in sensorless position-controlled induction machine drives

This paper focuses on the modulation of high-frequency (HF) currents required for sensorless position control of induction machine drives. Such drives can be realized by using the modulating effect of the rotor slots or from an engineered rotor saliency. Distortion due to saturation is known to cause a deterioration in the rotor position estimate. This paper reports a hitherto unreported distortion arising from inverter deadtime that will affect all sensorless drives using HF injection techniques. The deadtime distortion behaves in a similar way to that of saturation but has some specific characteristics that are presented in this work. Standard deadtime compensation techniques reduce but do not eliminate the distorting modulation. The residual distortion should be suppressed for good position estimation. The paper presents a new compensation strategy termed space modulation profiling which is effective in suppressing the HF modulations due to inverter deadtime and saturation saliencies. Experimental results show the sensorless drive under heavy load for zero-speed and transient operation.

The effect of rotor design on sensorless speed estimation using rotor slot harmonics identified by adaptive digital filtering using the maximum likelihood approach

Adaptive digital filtering has been demonstrated as an effective technique for extracting a real-time, sensorless, speed signal from rotor slot harmonics (RSHs) embedded in the line current waveform of induction motor drives. It is known that sensorless speed estimation techniques using RSHs may exhibit poor performance with certain motor designs. This paper examines the reasons for that poor performance which reflects differences in the magnitude of the slot harmonic signals consequent upon rotor design. Experimental results for a 30 kW motor with 6 different rotors are presented. The significant parameters are the number of rotor slots, skew and the accuracy of construction. It is clearly shown how inferior performance can arise. Conversely, improvements in reliability of speed estimation and transient response can be obtained by recognising those aspects which provide an enhanced signal, by minimising the background noise of the inverter/machine, or by enhancing the adaptive filter. The recursive maximum likelihood technique is presented as an improved algorithm for tuning the digital filter which aids transient response and reliability of speed estimation. Real time, experimental transient performance is demonstrated for the different rotors used in this paper and the performance failure of a particular slot combination demonstrated.

Design Aspects of High-Speed High-Power-Density Laminated-Rotor Induction Machines

This paper deals with the considerations associated with the design of high-speed high-power-density laminated-rotor induction machines (IMs). The considerations discussed are described by the design of an actual 10-kW machine, which runs at speeds of up to 75 kr/min with a rated power density of 28 MW/m3 for an electrically assisted turbocharger. Using a developed multidomain design environment which puts equal weight on the electromagnetic, mechanical, and thermal aspects, the rotor split ratio, electric and magnetic loadings, lamination material, rotor-bar material, and rotor-bar shape are identified as important and sensitive parameters in the design of high-speed IMs. Finally, general guidelines for designing high-speed high-power-density IMs are presented.

An FFT-based novel approach to noninvasive speed measurement in induction motor drives

A novel sensorless speed detection method based on the fast Fourier transform (FFT) spectral analysis is described. The main concern is the extraction of the speed information contained in the rotor slot-ripple harmonics created in the airgap of the induction motor using digital signal-processing techniques. A nonintrusive all-digital speed detector suitable for steady-state operation has been designed around an Intel/80386-based microcomputer equipped with a 80387 coprocessor. The detector performance with and without load over a wide range of speeds is described. >

Harmonic Loss Due to Operation of Induction Machines From Matrix Converters

This paper quantifies the extra harmonic losses in an induction motor that are associated with the use of a matrix converter topology as a motor drive. These extra losses are compared to the harmonic losses associated with an inverter-based motor drive. The technique employed in the determination of the harmonic losses is described. For the matrix converter, the extra harmonic losses associated with two commonly used modulation techniques are calculated and compared. The impact of these extra losses on the cooling requirements and operation of the motor is considered.