摘要:

The application of self excitation in dynamic braking of induction machines using one or three equal excitation capacitors is discussed. Analytical expressions are derived to determine boundary values of the excitation capacitor as functions of the machine parameters as well as speed for different configurations. Various factors which influence braking performance are examined. Guidelines are proposed for the proper selection of excitation capacitor for dynamic braking of induction machines. Theoretical results are verified experimentally using a laboratory machine.

DOI:10.1049/ip-b.1993.0001

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A small battery energy storage (BES) system is proposed. The power circuit of this BES system is simple, since only one current-forced subharmonic PWM switching converter is used. The precise current control is achieved by applying feedforward control. If the utility power is off, the BES system operates in the inverter mode to supply power to the load. A sinusoidal output voltage with low distortion and good regulation is obtained by using instantaneous voltage control and average voltage control techniques. When the utility power recovers, the BES system minimises the power from the utility to the load in the peak load period. Conversely, the power from the BES system is minimised in the medium load period. During the off-peak load period, the utility supplies power to the load and also charges the battery bank. In addition to real power conditioning, the BES system can also compensate the load reactive and harmonic powers. Thus the current waveform and the power factor on the utility grid are much improved. The modelling, design and implementation of the proposed controllers are described and some experimental results are given to show the performance of this BES system.

DOI:10.1049/ip-b.1993.0002

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A special machine, an electromagnetic vibration damper, is designed to create an attractive rotating force, in synchronism with the rotor. It consists of a laminated slotted stator and a massive, smooth, passive rotor. The aim of the paper is the computation of magnetic-flux density and iron losses by means of Fourier-Bessel and Fourier-Laurent series. The proposed analytical method assumes the stator currents to be surface located on the smooth airgap-stator boundary, and the machine is divided into three areas of constant permeability. Maxwell equations, with vector potential, lead to different solutions, including Fourier-Bessel or Fourier-Laurent series for space unknowns (radius and angle), where time appears as another Fourier series. Magnetic-flux density and iron losses come, respectively, from spatial and time derivatives. Iron losses, due to slot field pulsation losses, are added by means of a classical analytical formula.

DOI:10.1049/ip-b.1993.0003

出版商:IEE    

年代:1993

数据来源: IET

摘要:

This paper considers brushless DC position control systems with unknown external load disturbance and plant parameter variations. Since the dynamic characteristics of such systems are very complex and highly nonlinear, a conventional linear controller design may not assure satisfactory requirements. To improve the dynamic response of such systems, an integral-compensated variable structure control (IVSC) has been proposed. The approach comprises an integral controller for achieving a zero steady-state error response under step input, and a variable structure controller for enhancing the robustness. Simulation results show that the proposed approach gives a rather accurate servo tracking result and is fairly robust to plant parameter variations and external load disturbance.

DOI:10.1049/ip-b.1993.0004

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A new PWM AC-DC convertor with only one switching device is proposed. The control of the AC-DC convertor based on the PWM strategy to make the source current in phase with the source voltage is described, and a simple and practical input filter design is proposed. A comparative study between two proposed types of PWM AC-DC convertors and a new PWM AC-DC convertor with only one switching device, is carried out. The waveforms of voltage and current, the input and output characteristics, and the dynamic characteristics of the new PWM AC-DC convertor with only one switching device, are discussed and verified.

DOI:10.1049/ip-b.1993.0005

出版商:IEE    

年代:1993

数据来源: IET

摘要:

This study attempts to determine the steady-state performance of an isolated, self-excited, induction generator when a single capacitor is connected across one phase or between two lines. The work is concentrated on the case when the machine is supplying one or two loads. With the aid of the equivalent circuit, an analytical technique has been used to obtain nonlinear algebraic equations for operation frequency and magnetising reactance. A numerical solution method is applied to solve the nonlinear equations. Performances for different load configurations, and different load conditions have been considered. Where possible, computed results have been confirmed with experimental results.

DOI:10.1049/ip-b.1993.0006

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The authors show that the resistance and leakage reactance of the end rings of a rotor cage can be evaluated from the impedance of an identical ring which carries a circulating current of the appropriate frequency. Two mathematical methods for calculating end-ring impedance using this physical model are described, the first based on the use of modal currents together with the method of images, and a second employing finite elements. The influence of skin effect is investigated, as is the proximity of the rings to the shaft and to the core-pack end. The method is also applied to the consideration of the impedance of the end rings in a double-cage machine.

DOI:10.1049/ip-b.1993.0007

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The paper introduces the concept of using a fully pitched winding in a switched-reluctance or stepping motor. It is demonstrated that such a winding configuration results in more efficient use of the electric circuit, with each phase contributing to torque for more than half of the cycle of rotation. As a result, for many machine configurations significantly greater torques are predicted for a given frame size. In contrast to the short-pitched windings conventionally employed in such machines, the new configuration is shown to derive virtually all its torque from the rate of change of mutual inductance between phases. A number of different idealised current-excitation patterns are investigated, using both unipolar and bipolar excitation, and the mean output torques produced by the various configurations are compared.

DOI:10.1049/ip-b.1993.0008

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The problem of estimating the currents in the windings of a three phase brushless DC machine from measurements of a single drive input current is discussed in this paper. The proposed solution involves the application of a state observer, which uses errors between the actual and estimated drive input currents to update its estimates of winding currents. Such estimation is possible only if the winding currents are observable (i.e. knowledge of the drive input currents is sufficient to derive the winding currents), and it is shown that observability depends on drive operating condition, PWM switching strategy and machine winding connection. All of these factors are discussed for the case of current measurement in the DC link and a novel measurement strategy involving the measurement of total switching device current. An important advantage of the single current measurement method is that measurements are made equally on all three phases of the machine, so that the effects of sensor imbalance are eliminated.

DOI:10.1049/ip-b.1993.0009

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Rotor-position detection either directly or indirectly is essential for SR motors operating in variable-speed drive applications. Direct rotor-position sensors provide stable operation of the drive system. However, the use of direct sensors leads to reliability problems in certain industrial environments e.g. high-temperature conditions or where electromagnetic interference is present. Additionally, for fractional horse power drives the cost of the position sensors becomes a significant part of the overall drive system cost. Indirect rotor-position sensing is an attractive alternative in such applications. In this part of the paper the waveform detection technique is analysed using computer simulation with back EMF taken into account. Simulation is carried out to find which parameter, out of the current chop rise and fall-times in the active and inactive phases, is best suited to rotor-position detection under various operating conditions. It is concluded that the current chop falltime in the inactive phase provides reliable position detection under varying operating conditions. The simulation is based on a 4 kW 4-phase SR motor.

DOI:10.1049/ip-b.1993.0010

出版商:IEE    

年代:1993

数据来源: IET