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Electric Power Applications, IEE Proceedings -

Issue 1 • Date 7 Jan. 2005

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Displaying Results 1 - 15 of 15
  • Modelling of switched mode power converters using bond graph

    Page(s): 51 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    Modelling of the switched mode power converter (SMPC) involves obtaining the large signal, steady-state and small signal representations. Transfer functions and state equations are used for mathematical representation of the SMPC. Obtaining these dynamic models using a mathematical or graphical approach sometimes lead to loss of an intuitive understanding of the system dynamics. A unified graphical method of modelling SMPC using bond graphs is presented. Only the PWM DC-DC converters are considered. The concept of switched power junctions is used for modelling of switching phenomenon in the SMPC. This approach uses a logical process of graphical reduction, which ultimately results in the state equations of the large signal and small signal AC models of the SMPC including the steady-state equations of the SMPC. This method is applicable to SMPC, in both continuous conduction mode and discontinuous conduction mode The proposed modelling approach is illustrated by a few examples. View full abstract»

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  • Optimal area control of AC railway systems via PWM traction drives

    Page(s): 33 - 40
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    The latest generation of AC-fed traction drives, employing high-speed switching devices, is able to control the reactive power drawn by each locomotive or train from the overhead line. If the conditions at each train could be fed back to a central control point, it would be possible for a centrally located controller to calculate optimal values for the reactive power in each drive and to send these commands back to the individual equipments. A scheme is proposed whereby the AC power flows are analysed in real time and the results used to optimise some particular system objective via control of the PWM equipments as mobile reactive power compensators. The system voltage profile can be improved and the overall power factor at the feeder substation made nearer to unity. Computational verification is presented with results obtained from a multi-train simulator with the power network optimisation operating in several test case scenarios. The test results are compared with those obtained without compensation and with classical trackside Var compensation methods. The scheme is shown to give the best improvement where an existing fleet of diode or thyristor equipments is partially replaced with PWM front-end equipments. From these results, the potential for PWM locomotives to improve overall system performance is clearly confirmed. View full abstract»

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  • Critical review of the analytical approaches accounting for interbar currents and experimental study of ageing in two-speed asynchronous motors for elevator drives

    Page(s): 72 - 80
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    The existence of interbar currents in induction motors is well known and has received serious attention in the technical literature, mainly in connection with additional losses and their impact on motor efficiency. Much less known is the fact that these currents may have critical industrial importance on the working cycle of some machines, for instance, in two-speed elevator motors, where they may cause changes in the braking torque of 100% and over when compared with motors with isolated rotor bars. However, the difficulties and uncertainties in iron current analysis together with the strong variations of the iron to bar resistance, both locally and over the motor's lifetime, seriously limit the utility of analytical studies. In view of these facts, an extended and critical review of the proposed approaches to the analytical determination of interbar currents is first presented and thereafter a deep and physical insight into the phenomenon of interbar currents is given and emphasised. The different causes of motor ageing are then described and finally the results of an experimental study into thermal ageing of two-speed elevator motors with skewed and straight rotor bars are given. View full abstract»

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  • Ultra-lift Luo-converter

    Page(s): 27 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (557 KB)  

    The voltage-lift (VL) technique has been successfully applied in the design of power DC/DC converters. Good examples are the three series Luo-converters. Using the VL technique can give high-voltage transfer gain. The super-lift technique has been given much attention since it yields high-voltage transfer gain. The ultra-lift Luo-converter is introduced as a novel approach to the new technology, ultra-lift technique, which produces even higher voltage transfer gain. Analysis and calculation illustrate the advanced characteristics of this converter. View full abstract»

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  • A simple method for acquiring the conducting angle in a multilevel cascaded inverter using step pulse waves

    Page(s): 103 - 111
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    In recent years, the multilevel inverter synthesising the output voltage with a step pulse, has been widely used in high power and high voltage applications. To acquire the conducting angles of switches, the conventional method needs to solve simultaneous equations, corresponding to the fundamental and harmonic components, by the use of a Fourier series. Since they are calculated by an iterative method, the process is requires with a large amount of calculation and time. Moreover, they are calculated by means of an off-line operation. To overcome these drawbacks, this paper proposes a simple method of obtaining the conducting angles. This method reduces the amount of calculation needed to obtain the conducting angles and determines them through an on-line operation. It makes use of the voltage-second areas of the divided reference voltage according to the output voltage levels of the inverter. It does not solve the set of nonlinear transcendental equations, but calculates several trigonometric functions. The validity of the proposed method is demonstrated according to each modulation index through simulation and experiment results. The results indicate that the harmonic components obtained by the proposed method are similar to those from the conventional one in the high modulation index. However, in the low modulation index, the proposed method includes more harmonics than the conventional one. View full abstract»

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  • Current sharing for synchronised DC/DC converters operating in discontinuous conduction mode

    Page(s): 119 - 127
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (993 KB)  

    A new approach for active current sharing in parallel-connected power converters, based on filtering capacitor current properties, is presented in the paper. Due to the total autonomy of the module, the current sharing bus is eliminated. In addition, the proposed method ensures a significant reduction of switching currents flowing through the output interconnections, as well as reduction of accompanying EMI. The implementation of the proposed method is simple, reliable and cost effective. View full abstract»

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  • Single-phase switching-mode rectifier with capacitor-clamped topology

    Page(s): 9 - 16
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1501 KB)  

    A single-phase switching-mode rectifier with capacitor-clamped topology is presented to achieve power factor correction, eliminate current harmonic, draw a sinusoidal line current from the AC source and maintain the DC-link voltage constant. The proposed switching-mode rectifier has the capability of bidirectional power flow. Six active switches and one clamping capacitor are used in the rectifier to achieve the three-level pulse-width-modulated operation. A carrier-based current controller is adopted in the inner loop to track the reference line current. To regulate the DC bus voltage constant, a voltage controller based on a proportional-integral scheme is used in the outer loop. A voltage self-balancing technique is adopted in the control scheme to balance the capacitor voltages. Based on the proposed control scheme, a three-level pulse-width-modulated waveform is generated on the AC terminal of the rectifier. The proposed control algorithm illustrates its validity and effectiveness through computer simulation and experimental results. View full abstract»

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  • A Theoretical minimum DC-link capacitance in PWM converter-inverter systems

    Page(s): 81 - 88
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    In the PWM converter-inverter system, if the converter current control is fast enough to match the inverter power at all instants, then no current flows through the DC-link capacitor, making the DC-link voltage constant, even with a very small DC-link capacitance. A matching control method making the capacitor current zero suggests the possibility of using a tiny DC-link capacitor. However, in practice, a certain amount of capacitance is required, since the matching control itself is not perfect and there are one-step delays in the PWM. In this work, the authors investigate a theoretical low bound of the DC-link capacitance, considering an extreme case in which the DC-link voltage rises to a maximum value in a single PWM period. Utilising the optimisation technique, the theoretical minimum capacitance is found to be the one that limits the voltage rise below a certain threshold value. Analytical calculation results are compared with MATLAB simulation results. View full abstract»

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  • Full expandable model of parallel self-excited induction generators

    Page(s): 96 - 102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (669 KB)  

    Self-excited induction generators (SEIG) offer many advantages as variable-speed generators in renewable energy systems. Small hydro and wind generating systems have constraints on the size of individual machines, and several induction generators must be paralleled in order to access fully the potential of the site. SEIGs connected in parallel may lose excitation momentarily owing to large transient currents caused by differences in individual instantaneous voltages and frequency. This phenomenon cannot be easily simulated using the conventional models because it has such a fast transient nature. An innovative and automatic numerical solution for steady-state and transient analysis of any number of SEIGs operating in parallel is presented. Experimental results confirm the accuracy of the proposed model and open new possibilities for incorporating advanced control to monitor and optimise a parallel installation of SEIGs. The proposed SEIG model is applied to a two-turbine case, which can be extended to simulate a wind generating system. View full abstract»

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  • Single-stage dimmable electronic ballast with high power factor and low EMI

    Page(s): 89 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1193 KB)  

    A novel fixed-frequency electronic ballast that consists of a single-stage balanced type asymmetrical half-bridge inverter, a load resonant tank and a switched-capacitor dimming control circuit is proposed for driving fluorescent lamps. High efficiency and unity power factor are achieved by the proposed single-stage topology. The switched-capacitor dimming control technique and the balanced topology in the studied high-frequency electronic ballast provide better EMI features. The steady-state operating principle and design procedure for the proposed single-stage dimmable electronic ballast are analysed and discussed in detail. A ballast prototype has been implemented in the laboratory. The experimental results verify the feasibility of the proposed method. View full abstract»

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  • Modelling and analysis of cascade step-down converters

    Page(s): 41 - 50
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (686 KB)  

    Signal flow graph nonlinear modelling of N-cell cascade step-down buck converters is presented. General rules useful for drawing the signal flow graphs are evolved. A systematic procedure for developing a unified flow graph model of the cascade buck converters operating in synchronous control is discussed. A simplified procedure is given to deduce large, small-signal and steady-state models from the unified signal flow graph of the converter. A straightforward algorithm is developed to draw the unified graph model of the N-cell cascade buck converter. The unified nature of the proposed method is discussed by taking illustrative examples. Converter performance expressions, small-signal transfer functions and steady state, are derived taking the two-cell buck converter as an example. A large-signal model is developed and has been programmed in a TUTSIM simulator. Large-signal responses against supply and load disturbances are obtained. The validity of the proposed signal flow graph modelling of the cascade buck converters is verified and compared through PSIM simulator results. A few experimental large-signal responses results are provided to verify the proposed method. View full abstract»

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  • Rotor flux linkage oriented control of induction motor with included magnetic saturation

    Page(s): 112 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    The vector control of an induction motor in the rotor flux linkage oriented reference frame, with magnetic saturation included, is considered. The magnetic saturation is represented by the non-linear magnetising curve of the iron core. The rotor flux linkage model and the voltage decoupling in the traditional vector control scheme are modified to account for the magnetic saturation of the iron core. The mixed stator current - rotor flux linkage' model of the saturated induction machine is used in the control design, simulation and experimental realisation. Experimental results show that the proposed control with the included saturation offers a number of benefits, such as reduced stator current and smaller speed tracking error. View full abstract»

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  • Modular hysteresis current control of hybrid multilevel inverters

    Page(s): 1 - 8
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    The cascading of H-bridges, with different DC-link potentials and power devices, to implement modular hybrid binary, quasilinear and trinary multilevel inverters has been a recent research area. To achieve true modular implementation of a hybrid inverter, it is important to design each H-bridge as a stand-alone power bridge with its own integrated controller. Various three-level hysteresis controllers suitable for integrating with an H-bridge inverter to form a stand-alone power bridge are presented. The hysteresis current controllers on multiple power bridges can be co-ordinated to implement a modular hysteresis-controlled hybrid multilevel inverter with robust reference tracking and fast dynamic performance. Digital logic synthesised to ensure equal switch utilisation within each of the power bridges is also presented. Simulation and experimental results verify the performance and practicality of the proposed modular hysteresis control of hybrid multilevel inverters. View full abstract»

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  • Optimisation of inverter placement for mass rapid transit systems by immune algorithm

    Page(s): 61 - 71
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    Optimal inverter substation planning is solved by minimising the overall cost of power consumption and inverter investment for mass rapid transit power systems with immune algorithm (IA). The objective function and constraints are expressed as antigens, and all feasible solutions are expressed as antibodies in the IA simulation process. The diversity of antibodies is then enhanced by considering the proximity of antigens so that the global optimisation during the solution process can be obtained. It is found that energy regeneration, which results from the braking operation of train sets approaching the next station, can be restored effectively by the optimal planning of inverters using the proposed immune algorithm. View full abstract»

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  • Lightweight ironless-stator PM generators for direct-drive wind turbines

    Page(s): 17 - 26
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1233 KB)  

    A permanent-magnet electrical machine that employs lightweight spoked structures for both rotor and stator is described. The stator is ironless so that there is no direct magnetic attraction between rotor and stator. The lightweight structures are sufficient to carry the small forces due to the interaction of the permanent magnet field with the stator winding current. Despite the absence of stator iron and a large airgap, rare-earth magnets are able to create a working flux density of about 0.25 T at the winding. This is sufficient for an effective generator design because the lightweight structures offer the opportunity to build generators of unprecedented diameter. The outcome is a generator that has a mass typically 20-30% of equivalent designs based on iron-cored magnetic circuits, and with efficiency greater than 90%. View full abstract»

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