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Power Electronics, IET

Issue 2 • Date Feb. 2012

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Displaying Results 1 - 13 of 13
  • High power factor transformerless single-stage single-phase ac to high-voltage dc converter with voltage multiplier

    Page(s): 149 - 157
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (793 KB)  

    This study proposes a transformerless single-stage single-phase ac to high-voltage dc converter based on Cockcroft-Walton (CW) voltage-multiplier circuit with only adding one bi-directional switch and one boost inductor. This study also derives a new method of circuit representation for CW voltage multiplier, which simplifies the equivalent circuit and is convenient for simulation. Compared with conventional CW voltage multiplier, the proposed converter provides half-wave symmetry and low-distorted line current, improved power factor at the ac source and a regulated dc output voltage for wide load range. In addition, a current-fed analysis approach is used to derive a general expression of the output voltage ripple as function of the load to facilitate the design of the system parameters. A commercial average-current-control continuous conduction mode power factor correction integrated circuit (IC) is used to implement the control strategy of the proposed converter that does not need the multiplier and sensing of the input ac voltage; this strategy simplifies the design and reduces the control circuit components. A 500-W prototype is built for testing. Both simulation and experimental results demonstrate the validity of the proposed converter. View full abstract»

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  • Family of non-isolated zero current transition bi-directional converters with one auxiliary switch

    Page(s): 158 - 165
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (663 KB)  

    A new family of non-isolated zero current transition bi-directional converters is introduced. Basic non-isolated bi-directional DC-DC converters are derived by combining basic DC-DC converters and they are able to transfer energy between two DC sources using two main switches. In the proposed bi-directional converters, instead of using two independent auxiliary circuits for each main switch, same components with a single auxiliary switch is used to provide soft commutation at both modes of converter operation. In addition, the soft switching range in the proposed converters is not dependent on the duty cycle and the auxiliary circuit is applied only once in each switching cycle, which leads to a simple control circuit. Low weight, small volume, high efficiency and the ease of control are the most important benefits of the proposed converters. The proposed bi-directional buck and boost converter is fully analysed for both buck and boost operating modes. The validity of theoretical analysis is justified using experimental results of a 200 W, 50-100 V prototype converter. View full abstract»

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  • Time-domain identification of pulse-width modulated converters

    Page(s): 166 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    A discrete time domain-based system identification method for PWM DC-DC converters is proposed. Accurate information on the system's open-loop response is essential in the design of the system controller in order to obtain the desired closed-loop response. This is especially true in switch-mode converters where component uncertainty exists. It is conjectured in this study that an identification method that is based on time-domain signals will be relatively simple to realise with a digital processor. The method that is proposed is capable of successfully reconstructing the system model by an arbitrary excitation at the command input. In this study, a step perturbation was employed, which is simple to apply and leads to an intuitive interpretation of the output response. The effects of switching and quantisation noise have been overcome by choosing the sampling interval after the switching oscillations have decayed and by averaging the responses of synchronously perturbed sequences. The proposed method has been evaluated on Buck and Boost converters. The method was verified in two phases: Off-line ' data acquisition procedure was implemented on a TMS320F2407-DSP and the identification calculations were carried out on a PC. On-line ' The identification procedure (data acquisition plus fitting algorithm) was programmed on a TMS320F2808-DSP. View full abstract»

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  • High-efficiency bidirectional dc-dc converter with high-voltage gain

    Page(s): 173 - 184
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1415 KB)  

    The aim of this study is to develop a high-efficiency bidirectional dc-dc converter for a power storage system. The proposed converter can boost the voltage of an energy-storage module (e.g. battery) to a high-voltage-side dc bus for the load demand. When the high-voltage-side dc bus has excess energy, this energy-storage module can be charged by the dc bus. In this study, a coupled-inductor bidirectional converter scheme utilises only three power switches with the properties of voltage clamping, synchronous rectification and soft switching. As a result, the objectives of high-voltage gain, high-efficiency power conversion and bidirectional power control can be achieved. Some experimental results via a 48/360 V kW-level prototype are given to verify the effectiveness of the proposed converter in practical applications. View full abstract»

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  • Voltage-boosting converters with hybrid energy pumping

    Page(s): 185 - 195
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1515 KB)  

    Voltage-boosting converters with hybrid energy pumping are presented. Hence, the corresponding voltage conversion ratios are higher than the traditional boost converter or some existing voltage-boosting converters. Above all, by changing the circuit connection or turn-on types of switches, there are three voltage conversion ratios to be generated. Hence, there are three types of voltage-boosting converters to be presented herein. Furthermore, for any type, no isolated gate driver is needed instead of one half-bridge gate driver and one low-side gate driver, and the voltage stress on the low-side switch to magnetise the inductor and the voltage stress on the output diode can be reduced as compared to the traditional boost converter. In addition, the basic operating principles of these converters are easy to describe and analyse along with mathematical deductions. View full abstract»

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  • Analysis of the ramp compensation approaches to improve stability for buck converters with constant on-time control

    Page(s): 196 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    This study presents new sub-harmonic analysis for constant on-time control with ramp compensation. Ramp compensation of constant on-time control can be fulfilled by either directly feeding back a sensed inductor current signal as an internal ramp or using an external compensation ramp with a fixed slope during the off time and a fixed level during the on time. Based on the inductor current information and the charge variations of the output capacitor, the sub-harmonic mechanism is analysed in detail for constant on-time control with ramp compensation. Also, as well as explaining the benefits of using sensed inductor current signal, the effects of the sensed inductor current signal and the external compensation ramp are quantitatively compared. It is revealed that the external compensation ramp requires a lower ramp to avoid sub-harmonic oscillation. Based on the detailed theoretical analysis, experimental results demonstrate the stability criterion for constant on-time control with ramp compensation. View full abstract»

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  • Bit-stream-based space vector modulators

    Page(s): 205 - 214
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (946 KB)  

    Bit-stream-based control, which uses one bit wide signals to control power electronics applications, is a new approach for controller design in power electronic systems. This study presents a novel family of three-phase space vector modulators, which are based on the bit-stream technique and suitable for three-phase inverter systems. Each of the proposed modulators simultaneously converts a two-phase reference to the three-phase domain and reduces switching frequencies to reasonable levels. The modulators do not require carrier oscillators, trigonometric functions or, in some cases, sector detectors. A complete three-phase modulator can be implemented in as few as 102 logic elements. The performance of the proposed modulators is compared through simulation and experimental testing of a 6 kW, three-phase DC-to-AC inverter. Subject to limits on the modulation index, the proposed modulators deliver spread-spectrum output currents with total harmonic distortion comparable to a standard carrier-based space vector pulse width modulator. View full abstract»

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  • Input filter pre-charge scheme for high-power PWM-current source rectifiers connected to a weak utility supply

    Page(s): 215 - 220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    High-power PWM current source rectifiers are normally connected to the ac grid by means of a lightly damped LC input filter. Pre-charge schemes employing pre-insertion resistors are typically used to mitigate the over-voltage across the filter capacitors during the connection to the grid. However, noticeable distortion of the grid voltage may still occur during the insertion of the input filter to the grid. This is particularly true at low ratios of the supply fault level to the converter-rated power and cannot be avoided when conventional pre-charge schemes are used. This study proposes a pre-charge scheme that yields a smooth and controllable connection of the input filter to the grid along with total absence of both over-voltage across the input filter capacitors and voltage distortion on the grid. This is novel and it is of particular interest whenever PWM-CSRs are connected to relatively weak grids. Pre-charge is carried out by the main PWM-CSR converter, which is in turn supplied on its dc-side by a small low-power low-voltage pre-charge converter. This completely eliminates the need for any pre-charge components on the ac-side [which can be bulky and expensive at medium voltage (MV) levels]. Experimental results obtained from a 150 kW PWM-CSR are included in the study. View full abstract»

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  • Harmonic winding losses in the transformer of a forward pulse width modulated DC-DC converter for continuous conduction mode

    Page(s): 221 - 236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1177 KB)  

    This study presents general winding power loss expressions for a high-frequency (HF) three-winding forward transformer operated in continuous conduction mode (CCM), where the source of the transformer excitation is considered to be non-sinusoidal with many significant harmonics. The efficient operation of an isolated converter is dependent upon the performance of the transformer used. The expressions presented in this study take into account the eddy-current losses caused by current harmonics at HFs. The expressions are derived based on Fourier series of the winding current waveforms, and using Dowell's equation, which considers both the skin and proximity effects caused by eddy currents. Harmonic winding loss factors for the three windings are introduced. In addition to the power loss expressions, a step-by-step procedure to design a three-winding transformer used in a single-switch forward converter operated in CCM is presented using the area product (Ap) method. View full abstract»

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  • Passivity-based control of an asymmetric nine-level inverter for harmonic current mitigation

    Page(s): 237 - 247
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (865 KB)  

    In this study is approached the design problem of a control law for an asymmetric nine-level multilevel cascade inverter when it is implemented as active filter for harmonic current mitigation purposes. Two are the main features of the proposed controller, namely, its structure is defined considering at a fundamental level the precise establishment, in terms of mathematical expressions, of the steady-state converter behaviour required to achieve the control objective and its stabilisation properties, that render this desired steady-state behaviour attractive (asymptotically stable), are obtained by exploiting the energy-dissipation (passivity) properties of the circuit. These features lead to a simple controller structure that is easy to tune. The stability, high performance and robustness properties of the presented control scheme are experimentally evaluated. View full abstract»

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  • New technique for inductive power transfer using a single controller

    Page(s): 248 - 256
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (753 KB)  

    Inductive power transfer (IPT) technology has become a preferred technique for supplying `contactless` power to numerous applications, ranging from microwatt bio-engineering devices to high-power battery charging systems. Typical IPT systems employ two separate controllers, one on the powering or primary side and the other on the receiving or pick-up side of the system, to facilitate contactless power transfer across an air-gap in an efficient and controllable way. This study presents a new IPT control technique, which requires only a single controller, located on the primary side, to effectively regulate the output voltage, which in turn controls the amount of `contactless` power delivery to the pick-up side. The proposed technique uses only the variation in phasor relationship of circuit variables on the primary side to accurately regulate the output voltage or power without any wired or wireless feedback from the secondary side. Theoretical analysis and simulated results are presented, with experimental measurements of a prototype IPT system, to validate the viability of the proposed technique for IPT systems with constant magnetic coupling and single pick-ups. In contrast to existing IPT systems, the proposed IPT system with only a single controller is low in cost, more efficient, and thus can be considered as an attractive choice for many applications. View full abstract»

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  • Winding resistance of litz-wire and multi-strand inductors

    Page(s): 257 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1448 KB)  

    This study presents an approximate model for multi-strand wire winding, including litz-wire winding. The proposed model is evaluated using Dowell's equation. The model takes into account the existence of proximity effect within the litz-wire bundle between the strands and between the bundles, as well the skin effect. The expressions for optimum strand diameter and number of strands at which minimum winding AC resistance is obtained for the litz-wire windings are derived. The boundary frequency between the low-frequency and the medium-frequency ranges are given for both litz-wire and solid-round wire inductors. Hence, the low-frequency ranges of both wire windings are determined. It is shown that litz-wire is better than the solid wire only in specific frequency range. The model has been verified by the measurements, and the theoretical results were in good agreement with those experimentally measured. Comparison of the theoretical predictions of the proposed approximate litz-wire model with models proposed in other publications and with experimental results is given. View full abstract»

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  • Sensorless control of induction motors using multi-level converters

    Page(s): 269 - 279
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1303 KB)  

    This study describes a sensorless speed control scheme for induction motors supplied by a multi-level inverter. The scheme exploits the low DC link voltage used in some of the multi-level converter configurations which employ H-Bridges. The rotor position is tracked by measuring the rate of change of motor stator currents when low-voltage test vectors are applied using the H-Bridges. In this way, the motor current distortion introduced by the sensorless control scheme is reduced compared to that seen when using a two-level converter. The proposed approach could therefore be applied to high-power motor drives, and automotive drive systems. The study presents a theoretical derivation of the algorithm and experimental results which show the improvement in the motor current quality achieved using the new technique compared to sensorless techniques implemented on a two-level inverter. View full abstract»

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Aims & Scope

IET Power Electronics brings together five principal power electronics themes including: applications of power semiconductor technology; circuits; devices; techniques; and performance management.

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