J.G. Kettleborough

Fast calculation of harmonic torque pulsations in a VSI/induction motor drive

The authors present a frequency-domain model for the accurate and efficient prediction of harmonic torque pulsations in three-phase VSI/induction motor drives, which enables rapid consideration to be given to their potentially harmful effects in producing uneven shaft rotation. A detailed analysis is provided for both quasi-square wave (QSW) and optimal pulse-width modulated (PWM) modes of switching operation, with the latter technique designed to improve the low-speed drive performance by eliminating low-order harmonic components. A comparison is made with practical results obtained from an experimental 0.56 kW drive and from a comprehensive time-domain model using a numerical solution of the machine equations. It is shown that accurate prediction of the actual performance is provided. >

Permanent-magnet linear actuator for static and reciprocating short-stroke electromechanical systems

With the rapid progress in permanent-magnet technology, through the use of high-energy-density rare-earth materials a range of compact and high-performance linear actuators is now available. The paper presents simulated and experimental results from an investigation into the performance of such a device, in which the internal operating conditions are first modeled using a finite-element approach. Information obtained from this investigation is used, together with equations for both the electrical circuit and the mechanical motion, to enable both the static and the dynamic characteristics to be predicted. The most significant parameters affecting the performance of the actuator are identified, and an optimized design is produced.

Performance evaluation for a limited-angle torque motor

Describes the performance evaluation of a limited-angle torque motor, using a simple piecewise analytical approach to overcome system nonlinearities. A block-diagram model developed from a combination of measurement and manufacturers data is shown to be capable of accurately predicting both the steady-state and the dynamic performance. The approach described is of valuable assistance in the design of a complex multiloop nonlinear controller that is needed for a drive system containing the motor.

Generalized model of brushless DC generator

A generalized model is described for a brushless DC machine consisting of a multiphase synchronous machine with a full-wave bridge rectifier connected to its output terminals. The state-variable equations for the machine are suitable for numerical integration on a digital computer, and are assembled in a form which permits investigations to be made on the effects of different numbers of armature phase windings and different winding connections. The model has been used in both steady-state and transient studies on a number of generating units, with the detailed information which is provided being beneficial to design engineers. Comparisons presented between predicted and measured results illustrate the validity of the model and the mathematical techniques adopted, and confirm that accurate information on the performance of a brushless generator may be obtained prior to manufacture. >

A stand alone induction generator model producing a constant voltage constant frequency output

Mathematical modelling, design and development of ldquoa variable speed constant frequency self-excited induction generator (IG)rdquo using field-oriented techniques for its voltage and frequency control is described. A space-phasor model for the generator is developed to implement Indirect Field Oriented Control. To study the generator dynamic response the machine was driven by a separately-excited DC motor simulated as a variable speed turbine and a 2.2kW wound rotor IM as an IG. The excitation current for the wound rotor induction generator (variable frequency, 3-phase sinusoidal current) was provided by a current-controlled voltage-source inverter (CCVSI). The generator closed-loop control performance has been studied under varying load and wind speed conditions. Simulated results are compared with experimental data to validate the proposed control system.

Simplified modelling and dynamic analysis of a Laws' relay actuator

Abstract This paper presents results from an extensive investigation into the modelling and experimental performance evaluation of a Laws’ relay actuator. Ideally, the actuator is analyzed through the solution of the partial differential equations that describe the electro-magnetic interaction and the mechanical movement, and this requires the use of information not normally provided in the manufacture’s design data. The paper describes an alternative and much simplified approach, using a combination of experimental and analytical techniques, that, although including the significant nonlinearities present in the actuator, avoids the need for a complex finite-element and numerical solution. Measured results from an experimental actuator demonstrate the effectiveness of the model, which is of considerable value when designing a complex control loop of which the actuator forms part.

Microprocessor-based DC motor drive with spillover field weakening

A microprocessor-based speed control scheme for a separately excited DC motor fed from a DC source, which incorporates both armature-voltage control and spillover field weakening to provide smooth and precise control from standstill to speeds well above the base value, is described. Armature-current limitation during transient operation is achieved using an interventionist system external to the microprocessor controller, thereby simplifying considerably the overall system design. Experimental results obtained from a prototype 5 kW drive are presented to illustrate the excellent dynamic behavior of the scheme. >

MATHEMATICAL MODELING OF ANALOG CONTROLLED VOLTAGE SOURCE CONVERTERS FOR IMPROVED DYNAMIC RESPONSE

Increases in the occurrence of nonlinear loads have resulted in the need to reduce or minimize the levels of harmonic currents being injected into the power supply. As a consequence, active current waveshaping and pulse-width modulation have now replaced conventional phase-controlled and diode bridge rectifiers in many applications. In this paper, mathematical models are developed for the power circuits of analog controlled single-phase and three-phase voltage source converters, and then used to analyse the performance of current- and voltage-control loops for the converters. Analytical expressions are derived for the gains and time constants of the current and voltage controllers, and it is shown that the bandwidth of the current-loop is a function of the switching frequency, and that of the voltage-loop is a function of the DC-busbar capacitance and the voltage filter cut-off frequency. To illustrate the application of the models, simulation results are presented from investigations into the control of a 5 kW single-phase voltage-source converter and a 100 kW three-phase boost converter.

Accurate Tracking Control of a Limited Angle Torque Motor

This paper presents a novel control scheme that was developed and implemented to provide accurate tracking control of a limited angle torque motor following a 50 Hz sawtooth reference waveform. The approach could be extended to other limited motion actuators which require high tracking accuracy, but are subject to a single dominant nonlinear element, such as magnetic stiffness, which may be defined experimentally. One example is the variable reluctance linear actuator, used in the aerospace industry for control of aerodynamic surfaces. Despite the significant nonlinearities inherent in the torque motor, a complex nonlinear controller can be designed using simple linear design techniques, and it is demonstrated that the motor is then able to track the reference signal with a very high accuracy. The hybrid scheme uses a multicompensator, multiloop linear controller to reshape substantially the motor response characteristics, which have both inherent time-lag and oscillatory dynamics and an additional nonlin...

An integrated non-fossil fuel electrical power system

The authors describe an integrated nonfossil-fuel electrical power system (NFFPS) developed on a farm at Loughborough, England. They investigates the performance and economic viability of the system, both for electrical energy consumption on the farm and for export to the national electricity grid for supply to other consumers. The performance of the system was monitored over a one-year period, to take account of climatic variations during the different seasons. Results obtained are discussed, together with the economics of the system and the development of control strategies to optimize the profit/energy ratio. The NFFPS described uses well-proven items of plant. No significant teething problems were encountered, and, of the 60 MWh of energy produced annually, almost 80% is exported to the national grid.