摘要:

The paper describes a small autonomous wind energy conversion system that has been designed and implemented as a prototype unit for the demonstration of wind-electricity generation. A simple, closed-loop control system assures maximum-power transfer by the aid of a lookup table which relates the electrical power output of the system to the shaft speed. The lookup table is deduced from the turbine and generator data and corrected by field tests. A directly-coupled, wound-rotating field synchronous generator is used for energy conversion. The generator speed in this system is variable while the terminal voltage is substantially constant. The terminal voltage is kept under control by varying the field current to meet various load and battery conditions. In the paper a new criterion for determining optimum dimensions of a generator for wind energy conversion system applications is introduced. This criterion envisages a maximisation of the energy output for the chosen wind regime while keeping the generator cost at a minimum. To obtain the optimum solution of the cost minimisation problem, the constrained optimisation problem is first converted to the unconstrained form by using the external penalty approach and then solved using the Devidon-Fletcher-Powel method. Results of the optimisation are presented and evaluated in the paper.

DOI:10.1049/ip-b.1992.0052

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper covers the steady-state analysis of a wound-rotor induction generator operated at varying shaft speeds in the subsynchronous and supersynchronous regions, by control of both the magnitude and direction of slip power. A modified equivalent circuit is used in the analyses in which core losses and harmonics are ignored. The resulting nonlinear algebraic equations are solved numerically. An optimum control strategy, which maximises the total electrical power output of the double output induction generator is determined, and theoretical results are verified experimentally with particular emphasis on the system including naturally commutated convertors. The limitations of naturally commutated convertor circuits and their effects on the output power characteristic of the system are also discussed. This system shows considerable advantage in the field of wind-energy conversion. Its performance is optimised on the basis of annual energy production by calculating optimum values of gear ratio and generator size for the given turbine characteristic and site wind regime. Also, a comparison is made among optimised versions of alternative induction generator schemes used in wind-energy conversion systems, on the bases of annual energy production and transfer characteristic for the same site and turbine.

DOI:10.1049/ip-b.1992.0053

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Corrosion prevention of buried metallic facilities (i.e. piping, armoured cables etc.) by means of cathodic protection is currently practised in both civil and industrial fields. The design of adequate cathodic protection for an individual conductor is rather simple. However, for the case of several conductors forming complex and extended nets, where the theoretical prediction of the potentials distribution consequent to the cathodic protection currents injection may be a hard task, the design of cathodic protection is rather more problematical. This paper proposes a method, based on the electrical linear net equations, that allows a solution to the problem. Experimental results to vindicate the method are also reported

DOI:10.1049/ip-b.1992.0054

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A class-D zero-voltage-switching (also called soft-switching) inverter with only one capacitor in parallel with either transistor, along with an approximate analysis and experimental results, is introduced. The inverter offers both zero turn-on and zero turn-off switching losses, yielding high efficiency at high frequencies. In addition, soft switching reduces switching noise associated with the high-frequency ringing at the switching instants. The transistor voltage stresses are low, similar to those in conventional class-D and pulse-width-modulated inverters. This permits the use of low-on-resistance MOSFETs, reducing the conduction losses. A 50 W class-D inverter was built and tested. The theoretical and experimental results were in good agreement. The inverter combines, low transistor peak voltages and low conduction losses, as in PWM converters, with low switching losses and low noise as in single-ended resonant convertors.

DOI:10.1049/ip-b.1992.0055

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper examines a three-phase hysteretic-control algorithm, applicable to a voltage-source inverter for real-time implementation of power systems active power filtering. Special features of the proposed scheme are: coordinated hysteretic controller operating on the radial and tangential components of the busbarvoltage error, and the use of a microcontroller to implement the co-ordinate frame transformation, setting the switching parameters required by the hysteretic comparators, and monitoring the inverter-synthesised switching frequency. Provision for real-time tailoring of the tangential hysteresis band has been made to supplement the co-ordination scheme. The proposed algorithm is experimentally verified on a low-power prototype circuit. The experimental results have shown that the hysteretic controller can approach to the generation of a fully optimised and uniform three-phase switching pattern with a corresponding reduction in residual harmonic distortion. The results also showed the desired regularity of the radial/tangential error trajectory with nearly constant average switching frequency. The supporting hardware and software have been designed such that the control algorithm is used for active power filtering in a potentially resonant system bus condition.

DOI:10.1049/ip-b.1992.0056

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In this paper, a single phase AC to DC convertor consisting of a front end diode rectifier, an active switch and without a current sensor is proposed to achieve high performance and simple control logic. The familiar state-space averaging technique for discontinuous operation mode DC to DC convertors is extended to model the proposed AC to DC convertor with excellent accuracy. Unlike the existing model, which is valid only for very low frequency range(i.e. below line frequency), the proposed model is applicable up to half switching frequency theoretically. Design of the convertor is detailed and some selected experimental results are presented to verify the theory.

DOI:10.1049/ip-b.1992.0057

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The design of high speed permanent magnet machines needs to address conflicting requirements arising from the requirements of high electromechanical efficiency and mechanical strength and smoothness of running. This paper investigates the use of canning material surrounding the rotor, to give it mechanical strength, and investigates its consequences with regard to the electromagnetic performance of the motor at high speeds. Two designs are investigated in detail. The performance of a high-field magnet configuration is assessed experimentally, and compares well with the results predicted from finite-element computations.

DOI:10.1049/ip-b.1992.0058

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper proposes a practical new method for calculating the harmonic currents of a three-phase bridge controlled rectifier under unbalanced supply conditions. Analytical equations for the harmonic currents are derived, taking into account the effects of DC current ripple and overlap angle. The proposed method is based on the frequency domain method and the rectifier switching functions. All the calculations are conducted only by algebraic calculations, and the accuracy is within 1.1% and 2.6% for the DC and AC side harmonics, respectively. The validity of the proposed method is demonstrated by comparison with the results of digital simulation.

DOI:10.1049/ip-b.1992.0059

出版商:IEE    

年代:1992

数据来源: IET