J.M.D. Murphy

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

The recommended practice for electric vehicle battery charging using inductive coupling (SAE J-1773), published in January 1995 by the Society of Automotive Engineers, Inc., outlines values and tolerances for critical vehicle inlet parameters which must be considered when selecting a coupler driving topology. The inductive coupling vehicle inlet contains a significant discrete capacitive component in addition to low magnetizing and high leakage inductances. Driving the vehicle interface with a variable-frequency series-resonant power converter results in a four-element topology with many desirable features: unity transformer turns ratio; buck/boost voltage gain; current-source operation; monotonic power transfer characteristic over a wide load range; throttling capability down to no load; high-frequency operation; narrow modulation frequency range; use of zero-voltage-switched MOSFETs with slow integral diodes; high efficiency; inherent short-circuit protection; soft recovery of output rectifiers; and secondary d/spl nu//dt control and current waveshaping for the cable, coupler and vehicle inlet, resulting in enhanced electromagnetic compatibility. In this paper, characteristics of the topology are derived and analyzed using two methods. Firstly, the fundamental mode AC sine-wave approximation is extended to battery loads and provides a simple, yet insightful, analysis of the topology. A second method of analysis is based on the more accurate, but complex, time-based modal approach. Finally, typical experimental results verify the analysis of the topology presented in the paper.

Torque ripple minimization in switched reluctance drives using self-learning techniques

The nonlinear torque-production mechanisms in the doubly salient, switched reluctance motor drive are both current and position dependent. It is shown that the shape of the static torque-angle-current characteristics of this drive can be fully determined by a series of measurements performed with the drive in a self-learning mode, without the need for an external loading device. These measurements consist of static tests, in which the torques produced by currents in different phases are balanced, and dynamic measurements, in which the relative currents required to produce the same torque at different positions are ascertained. The controller can then achieve very smooth low-speed performance by determining the current required to obtain the optimum torque contribution from each phase, at each rotor position.<<ETX>>

A BIFRED converter with a wide load range

In this paper, the boost integrated flyback rectifier energy DC-DC (BIFRED) power converter which incorporates power factor correction, output voltage hold-up and input-to-output isolation is examined. The particular problem of high bulk capacitor voltage at light loads is addressed and it is shown how this may be resolved if the boost and flyback sections of the power converter are allowed to operate discontinuously. The criteria for ensuring correct operation in the discontinuous mode are investigated. It is shown that operating in this mode places no restrictions on the minimum load and simplifies the control loop design.<<ETX>>

Neural network based torque ripple minimisation in a switched reluctance motor

This paper presents an artificial neural network (ANN) solution to torque ripple reduction in a switched reluctance motor. Magnetic saturation together with salient stator and rotor poles give rise to a highly nonlinear torque/current/angle characteristic. The approach in this paper allows the neural network to be used to its full potential, that is, learning the nonlinear flux linkage characteristic while also incorporating a priori analytical knowledge of the torque production mechanism of the machine. This combination of neuro-learning and analytical insight results in a greatly simplified controller. Simulation results are presented to illustrate the performance of the proposed technique. Experimental results based on a floating point DSP processor are included.<<ETX>>

The effects of quantization noise and sensor nonideality on digital differentiator-based rate measurement

This paper focuses on the nature of the rate error which arises when a first-order digital differentiator is applied to the output of a uniform quantizer for the purpose of rate estimation. The quantizer input is assumed to be a constant-rate signal which is subject to a uniformly distributed noise source. New formulae are presented for the corresponding rms and spectral error characteristics. The results are applicable to the signal processing of sensor outputs, exemplified by the shaft encoder-based velocity estimation of an almost uniformly rotating mass. Both computer-generated finite data sets and experimental data derived from encoder-based shaft velocity measurements are utilized to verify the theoretical results. The results described are also applicable to a more general class of systems which involve the digital differentiation of quantized, noise-affected signals, such as first-order sigma-delta modulators with nominally constant input.

Analysis and design of a practical discontinuous-conduction-mode BIFRED converter

Impending international standards on harmonic current levels drawn by single-phase mains-operated equipment have created a need for low-cost off-line power-factor-corrected switched-mode power supply topologies in the power range up to a few hundred watts. The boost integrated/flyback rectifier/energy storage/DC-DC converter (BIFRED) is one such topology which shows promise in this regard. In particular, the discontinuous-conduction-mode (DCM) BIFRED avoids the light-load high-voltage stress problem associated with the continuous-conduction-mode design, while still achieving the combined advantages of a low-cost single-stage topology with high displacement factor and low total harmonic distortion. In this paper, a practical DCM BIFRED converter with integrated low-loss snubber is investigated from both power and small-signal control perspectives. Design equations are given to ensure DCM operation under closed-loop output voltage control, in which switch duty cycle is varying. Experimental results on a prototype converter are also presented.

The application of state observers in current regulated PM synchronous drives

The application of state observer structures in digital current controllers for permanent magnet synchronous motors (PMSM) is considered. A predictive observer algorithm is developed to overcome the intrinsic sampling delay of the digital controller. The resultant control structure is shown to have larger stability margins, higher closed loop bandwidth, superior dynamic performance and better disturbance rejection capabilities than the more conventional controller. Practical results from a prototype controller are presented which illustrate these effects and quantify the possible improvements in system capability. The paper also considers the effects of parameter variations on the performance of the observer-based controller and suggests means by which such effects may be minimised.<<ETX>>

Reduction of quantisation noise in position servosystems

The performance of a digital position servo system is analyzed. In particular, the bandwidth limitation due to finite position resolution (or quantization) is discussed. The principal consequences of finite position resolution are: (1) torque pulsation and attendant speed ripple; (2) excessive current ripple leading to additional machine and power converter losses; and (3) acoustic noise in the machine. Two controller structures are presented which minimize these objectionable effects: the oversampling digital filter and the state observer. The oversampling digital filter is proposed as a simple, parameter-free, cost-effective solution. The state observer offers potentially superior performance but is parameter dependent and more complex. Simulation and measurement results are presented for both methods, and potential pitfalls in their implementation are discussed.<<ETX>>

Modular approach to parameter estimation in geared and linear resonant systems

Abstract This paper proposes a unified approach to the estimation of the physical parameters defining both geared and linear resonant systems, namely the dead-zone, inertia, stiffness and damping parameters. Although the technique is based on discrete-time models, it allows extraction of the continuous-time parameters from the discrete coefficients. This is facilitated by a modular procedure, involving separate locked- and unlocked-load measurements. The difference equation coefficients associated with the discrete model become trivial functions of the physical system parameters, which are computed using predetermined polynomial approximations. The reduced-order estimation modules improve noise immunity and simplify the estimation routines. Very accurate experimental results verify the utility of the approach.

Digital simulation of adjustable-frequency ac motor drives

Simulation techniques are very useful in designing static adjustable-frequency ac drive systems and in evaluating alternative control strategies for them. This paper outlines the basic principles of the modern dc-link static frequency converter, and then describes the implementation of a digital simulation of a complete drive system. The principal components of the drive are programmed as FORTRAN subroutines. The main program uses the IBM Continuous System Model ing Program (CSMP), which is translated into FORTRAN and combined with the FORTRAN subroutines. Harmonics in the output waveform of the frequency converter can cause design and operating problems under steady-state as well as transient conditions. These problems are discussed and illustrated by results from simulation runs.