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Electric Power Applications, IEE Proceedings -

Issue 6 • Date November 2006

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Displaying Results 1 - 20 of 20
  • Load-imposed instability and performance degradation in a regulated converter

    Page(s): 781 - 786
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (205 KB)  

    The stability and performance of a regulated converter is analysed based on its closed-loop output impedance. System theory is used to obtain a set of transfer functions that define the internal stability of an interconnected system consisting of source and load converters. The internal stability is described in terms of the ratio of the output impedance of the source converter and the input impedance of the load converter known as the minor-loop gain. Thus, the closed-loop output impedance of a source converter can be used to define safe operating areas that avoid instabilities in the load impedance. It is shown that the margins associated with the minor-loop gain (i.e. the gain and phase margins) do not generally match the margins of the output-voltage loop gain. The relationship is especially weak at frequencies close to and beyond the crossover frequency of the loop gain. This means that the margins given to the minor-loop gain should be gradually increased as the voltage-loop-gain crossover frequency is approached so as to avoid performance degradation (i.e. changes in margins and crossover frequency) in the supply converter. Experimental evidence is provided based on a buck converter under voltage- and peak-current-mode control View full abstract»

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  • Simplified control method for parallel-connected dc/ac inverters

    Page(s): 787 - 792
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (185 KB)  

    The parallel operation of several low-capacity inverters is better than a singular high-capacity inverter owing to the advantages of better extensibility and reliability. A simplified control method for parallel-connected inverters is proposed, which can balance the current distribution among the parallel-connected inverters with no interconnected communication lines. To verify the performance of the proposed control method, a prototype consisting of two inverters has been developed. The experimental results verify that the performance of the proposed control method is as desired View full abstract»

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  • Radial force density and vibration characteristics of modular permanent magnet brushless ac machine

    Page(s): 793 - 801
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The radial force density harmonics and vibrational characteristics of a three-phase modular permanent magnet brushless AC machine is investigated. It is shown that, owing to the presence of a large number of low- and high-order stator space harmonic magnetomotive forces, modular machines are more likely to exhibit higher low-frequency vibrations than conventional permanent magnet brushless machines. Experimental results support the analysis and its findings View full abstract»

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  • Classification and synthesis of power gyrators

    Page(s): 802 - 808
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (402 KB)  

    A systematic procedure to synthesise power gyrators for variable switching frequency operation is presented. Based on the gyrator equations, topological constraints are first established and two types of gyrators, i.e. G and R, are defined. A boost converter with an output filter and the Cuk converter are shown to have the unconditionally stable characteristics of G-gyrators with a controlled input current whereas a buck converter with an input filter and also the Cuk converter are shown to behave as G-gyrators with a controlled output current if damping networks are inserted and certain stability conditions are accomplished. Similarly, a boost converter with an output filter is shown to behave as a power R-gyrator with stable dynamics View full abstract»

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  • Integral variable-structure grey control for magnetic levitation system

    Page(s): 809 - 814
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (265 KB)  

    An integral variable-structure grey control for a magnetic levitation system for position tracking is presented. The sliding-mode control is insensitive to system uncertainties and disturbances when it is within expected limits. It produces chattering when uncertainty values are overestimated, or steady-state error when underestimated. The method uses a mathematically simple and computationally efficient grey compensator for the integral variable structure controller to reduce chattering and steady-state error. The stability of this magnetic levitation system is proven by using the Lyapunov function. The experimental results verify that the proposed controller is valid for a magnetic levitation system View full abstract»

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  • Mechanical-sensorless induction motor drive based only on dc-link measurements

    Page(s): 815 - 822
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (526 KB)  

    Sensor count reduction for high-performance induction motor (IM) drives is considered. A novel strategy to compute the three phase currents, based on a single current sensor and an adaptive observer, is proposed. The observer estimates the motor state variables, allowing then implementing an IM field-oriented controlled (FOC) drive with closed speed loop based only on DC-link measurements. To demonstrate the practical feasibility of this proposal, representative experimental results, obtained with a FOC experimental prototype, are presented. The FOC prototype showed results similar to those from a conventional FOC drive with individual phase current sensors. The sensor count reduction achieved represents a significant cost diminution in the implementation of low-power high-performance drives View full abstract»

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  • Adaptive controller design for a sensorless IPMSM drive system with a maximum torque control

    Page(s): 823 - 833
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    An advanced controller design for a sensorless interior permanent-magnet synchronous motor control system is proposed. A maximum torque/ampere control algorithm is used to improve the torque performance of the drive system. In addition, an adaptive controller combined with the maximum torque/ampere control is proposed to obtain a good transient response and a good load disturbance rejection capability. The proposed control method can be applied to both a sensorless adjustable speed control system and a sensorless position control system. Using the Lyapunov stability theory and Barbalat's lemma it is shown that the closed-loop sensorless control system is an asymptotical stable system. A 32-bit digital signal processor is used to execute the rotor position estimation algorithm and the control algorithm. Experimental results validate the theoretical analysis and show the correctness and feasibility of the proposed system View full abstract»

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  • Design of a multispeed winding for a brushless dc motor and its sensorless control

    Page(s): 834 - 841
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (559 KB)  

    V-belt-linked continuously variable transmissions (CVTs) find extensive use in both internal-combustion-engined and electric scooters. The CVTs are used to increase the starting torque and also extend the range of the operating speed of the vehicles. Unfortunately, the efficiency of a CVT is relatively low due to friction effects and the alternative techniques based on flux weakening control are both complex and costly to implement. To circumvent these problems a multispeed winding is designed that is able to increase the starting torque at low speeds and extend the constant-power speed ratio for small and midsized brushless DC motors. Moreover, in order to increase the reliability of the drive system, a cost-effective sensorless control algorithm is developed. The commutation signals can be directly extracted from the average terminal voltages of the motor using simple RC circuits and comparators. This means that the sensorless commutation can be implemented by simply using low-cost CPLDs or microcontrollers. The proposed approach is particularly suitable for application to cost-sensitive electric vehicles such as wheel chairs, bikes and scooters and also hybrid electric scooters. A theoretical analysis of the pattern is performed and various experiments are conducted to evaluate the effectiveness of the proposed method View full abstract»

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  • Synthesis of power gyrators operating at constant switching frequency

    Page(s): 842 - 847
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    A systematic procedure to synthesise power gyrators for constant switching frequency operation is presented. The equivalence between ideal sliding dynamics and PWM zero dynamics is used to derive the control law of the duty cycle. As a consequence, any power gyrator with stable behaviour in sliding-mode results in a stable equivalent gyrator at constant switching frequency with the same stability conditions. The design of a PWM G-gyrator with controlled output current based on a buck converter with input filter illustrates the procedure. Simulations and experiments are in good agreement with the theoretical predictions View full abstract»

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  • Detection of broken rotor bars in induction motor using starting-current analysis and effects of loading

    Page(s): 848 - 855
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (287 KB)  

    The detection of broken-rotor-bar faults based on common steady-state-analysis techniques, such as the fast Fourier transform (FFT), is known to be significantly dependent on the loading conditions of the induction motor. At light load, it is difficult to distinguish between healthy and faulty rotors because the characteristic broken-rotor-bar fault frequencies in the stator current are very close to the fundamental-frequency component and their amplitudes are small in comparison. As a result, detection of broken bar faults and classification of the fault severity under light load is very difficult. To overcome this problem, the analysis of the envelope of the transient starting-current waveform using the wavelet-transform has been investigated. The envelope extraction is used to remove the strong fundamental-frequency component, which would otherwise overshadow the characteristic differences between a healthy motor and a faulty motor with broken rotor bars. The wavelet-transform results are processed to develop a normalised parameter called the `wavelet indicator' which is sensitive to the presence of broken-rotor-bar faults. The results are verified using tests on machines with a varying number of broken bars, as well as partially broken rotor bars, over a wide range of loading conditions. The effects of initial rotor position and supply imbalance are also investigated View full abstract»

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  • Sub-envelope modulation method to reduce total harmonic distortion of ac/ac matrix converters

    Page(s): 856 - 863
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    An AC/AC matrix converter is an array of power semiconductor switches that connects directly a three-phase AC source to another three-phase load. It can convert an AC power source with certain voltage and frequency to another AC load with variable voltage and variable frequency directly without a DC-link and bulk energy storage component. Classical modulation methods such as the Venturini method and the space vector modulation method using AC-network maximum-envelope modulation, implement matrix conversion successfully. However, they also cause very high total harmonic distortion (THD). A novel approach, the sub-envelope modulation (SEM) method, is presented to reduce THD of matrix converters effectively. The approach is extended to an improved version of matrix converters and the THD can be reduced further. The algorithm of the SEM method is described in detail. Simulation and experimental results are also presented to verify the feasibility of the SEM approach. The results will be very helpful for industry applications View full abstract»

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  • Pulse converter for induction-heating applications

    Page(s): 864 - 872
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (286 KB)  

    A novel pulse-current converter topology for induction heating is introduced. The possibility and expediency of the pulse current for induction heating have been demonstrated. The converter comprises the input filter, input reactor, bridge rectifier, two power switches, two coils mutually coupled with the input reactor and the heating inductor (load), where the output power is controlled by a switching frequency. The steady-state analysis of the converter operation, its computer simulation and the experimental verifications on the converter model have been performed. The simulation on the computer and the experimental results are shown to be in good agreement with the theoretical results. The following two goals have been achieved: (a) the analysis of the heating process with the pulse current has been performed; and (b) the appropriate scheme of the pulse-current supply has been developed. The proposed scheme fulfills the requirements of modern power supplies: sine form of the input current, unity power factor, soft commutation and a wide range of output power. The proposed configuration can be used for heating, annealing, melting and hardening in the power range of 250-300 kW View full abstract»

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  • High-power-factor operation of three-phase ac-to-dc resonant converter

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (671 KB)  

    Analysis and design of a three-phase AC-to-DC resonant converter is considered. The power factor of the three-phase AC input line diode bridge rectifier is improved by injecting high-frequency current. The three-phase AC-to-DC resonant converter is operated at frequencies above the resonant frequency. The analysis of the converter is carried out using different operating modes in one switching cycle of the resonant inverter. The design of the AC-to-DC resonant converter is discussed step by step. An experimental prototype of a 3 kW, 500 V output power and operating above 300 kHz has been developed in the laboratory. The proposed three-phase AC-to-DC resonant converter has high power factor, low total harmonic distortion and high efficiency. It requires narrow variation in switching frequency to regulate the output voltage View full abstract»

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  • Numerical impulse response test to estimate circuit-model parameters for induction machines

    Page(s): 883 - 890
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    The estimation of electrical parameters of a cage induction machine is studied. First, the steady-state parameters are estimated using two-dimensional finite element analysis (FEA) with the assumption of sinusoidal time variation. Next, a numerical impulse response test using time-stepping FEA is utilised to produce the voltage-current data for the small-signal model parameter estimation. The method is based on the assumption of linear behaviour near the operating point and the choice for the suitable excitation signal is studied. To distinguish the influence of the skin effect, the impulse response test is also performed for the corresponding slip-ring machine. The parameters are estimated from the frequency response function of the stator line current using differential evolution. The results of the FE simulations are compared with measurements View full abstract»

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  • Load simulatorwith power recovery capability based on voltage source converter-inverter set

    Page(s): 891 - 897
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (557 KB)  

    A load simulator with power-recovery capability is proposed. The load simulator consists of a converter-inverter set with a DSP controller for system control and PWM pulse generation. The converter operates as a universal load to model the linear load and the nonlinear load, while the inverter feeds the energy back to the power source with harmonic compensation. The operation of the proposed system has been analysed through simulations with PSCAD/EMTDC, and the feasibility of hardware implementation confirmed through experimental work with a 20 kVA prototype. The load simulator can save the electrical energy used in testing performance of the power quality compensator and power equipment View full abstract»

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  • Induction motor performance as a function of phase number

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (175 KB)  

    An analytical and experimental comparison of the performance of multiphase induction machines as a function of the number of phases is provided. The method of generalised complex harmonic analysis is used to model the multiphase machine, including the calculation of pulsating torques. This general model is validated with experimental results. The test machine used a standard motor frame, which had been modified to bring every coil out to a patch panel. With 12 coils per pole, the machine was tested in 3, 4, 6 and 12-phase operation. Results show moderate reductions in stator losses and significant improvements in pulsating torques View full abstract»

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  • Analysing the dynamics of regulated converters

    Page(s): 905 - 910
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (350 KB)  

    The characterisation of regulated converters is addressed to enable the assessment of the stability, performance, supply and load interactions as well as transient responses. A canonical model of a converter is proposed and used to create a set of parameters that are able to fully describe the dynamics associated with a converter and therefore can be used to predict the dynamical behaviour of the converter to in changes in source and load interactions. System theory is used to develop methods to study the internal stability of cascaded subsystems such as an electromagnetic interference filter, load and converters. A framework is established that allows the evaluation of different converter topologies under different operation and control modes View full abstract»

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  • Improved flux estimation and stator-resistance adaptation scheme for sensorless control of induction motor

    Page(s): 911 - 920
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (731 KB)  

    The speed-sensorless vector-controlled induction-motor drive is superior to the conventional vector-controlled induction-motor drive in terms of drive cost and reliability. In speed-sensorless control, one common practice is to estimate the flux position from the terminal voltage and current using a stator-voltage model. The accuracy of estimated flux position decides the performance of the vector-controlled drive. However, the performance is limited by the DC-drift problems that prohibit the use of open integration of the flux-producing voltage component for flux estimation. The paper proposes a flux-estimation method that gives the effect of open integration along with an inherent error-decaying mechanism to resolve the DC-drift problem. A stator-resistance-adaptation method is also incorporated in the flux estimator, which makes the flux-position estimation independent of resistive parameters of the motor. Using this flux-estimation algorithm, a rotor-flux-oriented speed-sensorless speed-control scheme of induction motor is proposed. The scheme is both simulated and experimentally verified View full abstract»

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  • TSK-type recurrent fuzzy network for dsp-based permanent-magnet linear synchronous motor servo drive

    Page(s): 921 - 931
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (693 KB)  

    A TSK-type recurrent fuzzy network (TSKRFN) control system is proposed to control the position of the mover of a field-oriented control permanent-magnet linear synchronous motor (PMLSM) servo drive system to track periodic reference trajectories in this study. The proposed TSKRFN combines the merits of self-constructing fuzzy neural network (SCFNN), TSK-type fuzzy inference mechanism, and recurrent neural network (RNN). Moreover, the structure and the parameter learning phases are preformed concurrently and online in the TSKRFN. The structure learning is based on the partition of input space, and the parameter learning is based on the supervised gradient-descent method using a delta adaptation law. Furthermore, all the control algorithms are implemented in a TMS320C32 DSP-based control computer. The simulated and experimental results due to periodic reference trajectories show that the dynamic behaviour of the proposed TSKRFN control system is robust with regard to uncertainties View full abstract»

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  • Boost-half-bridge edge resonant soft switching PWM high-frequency inverter for consumer induction heating appliances

    Page(s): 932 - 938
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (522 KB)  

    A novel soft-switching PWM utility frequency AC to high-frequency AC power conversion circuit, incorporating boost-half-bridge inverter topology, which is more suitable and acceptable for cost effective consumer induction heating applications, is presented. The operating principle and the operation modes are described using equivalent circuits with the operating voltage and current waveforms. The operating performances are illustrated and evaluated, including the power regulation and power conversion efficiency against duty cycle characteristics based on the power dissipation as compared with those of the previously developed high-frequency inverter. The practical effectiveness of the power converter is substantially proved, based on experimental results from a practical design example View full abstract»

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