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Power Electronics, IET

Issue 4 • Date July 2010

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Displaying Results 1 - 17 of 17
  • Simple method for measuring the equivalent series inductance and resistance of electrolytic capacitors

    Page(s): 465 - 471
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (758 KB)  

    A simple equivalent series inductance (ESL) and equivalent series resistance (ESR) measurement technique for capacitors is presented. A low-cost square waveform voltage source coupled with a reference resistor can be used to measure the ESL, ESR and capacitance of an electrolytic capacitor. By connecting a capacitor in series with a reference resistor, the equivalent output step response of the capacitor voltage reveals the ESL and ESR of the capacitor. To effectively capture the output step response, a square input waveform is used instead. The square waveform voltage source can easily be realised using a DC voltage source and simple switching devices. Experimental results are included to demonstrate the effectiveness of the proposed scheme. View full abstract»

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  • AC-DC-DC isolated converter with bidirectional power flow capability

    Page(s): 472 - 479
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (865 KB)  

    A novel AC-DC-DC isolated converter with bidirectional power flow capability is proposed and studied. The proposed structure consists of a three-phase current source converter and a special DC-DC isolated converter. In this DC-DC converter, the primary side of the high-frequency transformer is a current source converter and the secondary side is a voltage source converter. Based on this novel topology, a simple and efficient control strategy using the voltage of the inductor in the DC-side to control the current of the AC-side is presented. The feature of the bidirectional power flow allows the converter to provide energy as a power source or to regenerate power back to the AC power grid with high overall energy efficiency. Another feature of this converter is that the DC-side current and voltage can be regulated in a wide range from zero to the rating value. Furthermore, the AC-side current and voltage have low total harmonic distortion and unit power factor in a wide output power range. The operation of the proposed topology and control scheme are confirmed by the experimental results on a 10-kW design example. View full abstract»

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  • Novel single-phase five-level voltage-source inverter for the shunt active power filter

    Page(s): 480 - 489
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1054 KB)  

    To achieve five-level pulse width modulation (PWM) operation, a single-phase voltage-source inverter is proposed. A shunt active power filter based on the proposed inverter is implemented to achieve harmonics elimination, reactive power compensation and dc-link voltage regulation. Whereas eight power switches are used in the conventional five-level inverter, only six power switches are needed in the proposed inverter. The proposed voltage-source inverter achieves five-level PWM operation without clamping diodes and flying capacitors. The proposed inverter functions as a controllable current source to supply the necessary active power for compensating for inverter losses, to suppress the current harmonics and to compensate for the reactive power drawn by the non-linear loads. The current commands are tracked using the hysteresis current controller. Simulation and experiments based on a laboratory prototype are carried out to verify the effectiveness of the proposed topology and its control scheme. View full abstract»

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  • Low-cost microprocessor-based alternating current voltage controller using genetic algorithms and neural network

    Page(s): 490 - 499
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1003 KB)  

    A low-cost, high-performance microprocessor-based pulse width modulated (PWM) AC voltage controller with a novel harmonic reduction technique is proposed. Genetic algorithm is adopted to evaluate the optimal turn-on and turn-off angles in the PWM pattern such that the total current harmonic distortion is minimised. The evolved angles are only optimised at a desired output voltage. In the proposed design, an artificial neural network trained by sets of optimal angles is utilised, making the designed system applicable to all operating points. The simulation and experimental results verify that the proposed technique is a suitable technique, and its performance is comparable to the conventional techniques. View full abstract»

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  • Five-level Z-source diode-clamped inverter

    Page(s): 500 - 510
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (857 KB)  

    This study proposes a five-level Z-source diode-clamped inverter designed with two intermediate Z-source networks connected between the dc input sources and rear-end inverter circuitry. By partially shorting the Z-source networks, new operating states not previously reported for two-level Z-source inverter are introduced here for operating the proposed inverter with voltage buck-boost energy conversion ability and five-level phase voltage switching. These characteristic features are in fact always ensured at the inverter terminal output by simply adopting a properly designed carrier modulation scheme, which always inserts two partial shoot-through states per half carrier cycle for smooth balanced operation. Theoretical findings and practical issues identified are eventually verified by constructing a scaled down laboratory prototype for testing. View full abstract»

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  • Parallelling three-phase AC to DC converter using CUK rectifier modules based on power balance control technique

    Page(s): 511 - 524
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1457 KB)  

    The analysis and design of a paralleling three-phase ac to dc converter using CUK rectifier modules for DC Distributed Power System (DPS) applications are presented. The proposed control technique is used to obtain the three-inductor current compensators and to improve the dynamic response of the rectifier without affecting its steady-state performance and also to minimize total harmonic distortion (THDi) in the source current. As a result, the output voltage of the converter can withstand the variations of the dc load current and input voltage. The control method is employed in the voltage feedback loop. The implementation of this control circuit uses only analog circuitry. The experimental prototype has been built with a DC output voltage -48 V and output power 1.5 kW. Each converter operates in Continuous Conduction Mode together with hysteresis current control. The experimental results indicate that such scheme is effective and offers the good dynamic transient response. The results obtained are: power factor higher than 0.99 and THDi less than 3%. The system offers 88% efficiency and provides good inductor current sharing among the converter modules. The simulation and experimental results are presented to verify the feasibility of the control strategy. View full abstract»

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  • Autoconnected transformer-based 18-pulse ac-dc converter for power quality improvement in switched mode power supplies

    Page(s): 525 - 541
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1871 KB)  

    Switched mode power supplies (SMPS) are commonly used in telecommunication towers and welding equipments. In medium capacity SMPS, power quality at the utility interface is a major concern. A new autoconnected transformer is presented for power quality improvement in 18-pulse AC-DC converter fed SMPS with least magnetic rating. Various autoconnected transformers are studied for 18-pulse AC-DC rectification and a new autoconnected transformer is selected to improve the power quality of the supply current. The effect of load variation on SMPS is studied to demonstrate the performance and effectiveness of the proposed 18-pulse AC-DC converter-based SMPS in the wide operating range of the power supply system. A set of power quality indices at input AC mains and magnetic rating of various autoconnected transformers are presented to compare their performance. Laboratory prototype of the proposed autoconnected transformer-based 18-pulse AC-DC converter is developed and test results are presented to validate the proposed design and developed model of the converter system. View full abstract»

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  • Protection of unified power quality conditioner against the load side short circuits

    Page(s): 542 - 551
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (858 KB)  

    This study presents a protection scheme for protecting the series inverter of a unified power quality conditioner (UPQC). The proposed scheme protects the series inverter from overcurrents and overvoltages, which appear during short-circuit faults on the load side of the UPQC. The main protection element is a crowbar connected across the secondary of the series transformer and consists of a pair of antiparallel connected thyristors, which is governed by a simple Zener diode-based control circuit. In the case of an overvoltage, the crowbar short circuits the secondary of the transformer, thus removing the overvoltage and diverting the fault current from the series inverter. An additional circuit is used to disable the inverters in overcurrent conditions. The effectiveness of the proposed protection scheme is demonstrated both through simulation and experimentation. View full abstract»

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  • Dc voltage sensorless control method for three-phase grid-connected inverters

    Page(s): 552 - 558
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    A novel dc-link voltage sensorless technique for a three-phase grid-connected inverter is presented. Based on predictive and real-time sampling schemes, the required pulse width modulation (PWM) output voltage vector is accurately predicted by measuring the grid voltage and the inverter output current. A q-axis current proportional-integral (PI) controller is also used. The controller forces the output current to accurately follow its reference, and is also used to derive the dc-link voltage. By using this method, the dc-link voltage is not obtained from a voltage sensor, but instead is obtained from inverter output current information. Test results show that the output current of the resultant inverter is of high quality at steady state and can follow its reference quickly in dynamic states as well. View full abstract»

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  • Analysis and implementation of a softswitching converter with reduced switch count

    Page(s): 559 - 570
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1288 KB)  

    This study presents a reduced switch dual-converter to implement the features of zero-voltage switching (ZVS), load current sharing, high output current and low output ripple current. There are two converter modules in the proposed converter. These two modules share the same power switches and provide the balance load current. The active-clamping circuit is used to realise the ZVS turn-on such that the switching losses on power switches are reduced. The current output rectifier is adopted in the output side to realise the higher output current with reduced ripple current such that the sizes of the output chokes and capacitor are reduced. Compared with the conventional ZVS parallel-connected converter with four power switches, only two switches are used in the proposed converter to accomplish parallel operation. Thus, the proposed converter has less circuit components. Finally, the experimental results based on a laboratory prototype (12 V/50 A) are provided to demonstrate the effectiveness of the proposed converter. View full abstract»

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  • Resonant inverting-buck converter

    Page(s): 571 - 577
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (605 KB)  

    This study presents a new resonant inverting step-down DC-DC converter. A half-bridge inverter and an LC resonant tank are employed. The resonant tank is the medium of energy transfer and provides soft-switching conditions at turn-on and turn-off switching instants for all active elements. The voltage conversion ratio is adjustable, and the converter is automatically shut down at output short circuit. Its characteristics are very similar to half-bridge series-resonant converter, except that input and output terminals possess common ground and voltage gain up to unity can be achieved at discontinuous conduction mode. Practical results from a laboratory prototype verify the presented theoretical analysis. View full abstract»

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  • New approach in back-to-back m-level diodeclamped multilevel converter modelling and direct current bus voltages balancing

    Page(s): 578 - 589
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    Multilevel power converter structures have been introduced as the solution for high-power high-voltage applications and also for grid interface connection of renewable energy sources systems, where they have several advantages, namely low distortion voltages and currents and low switching losses resulting in higher efficiency. As a consequence of increasing interest on the multilevel converter applications, accurate models of these power converters are essential to be used in computer simulation studies. This study presents a new systematic modelling approach suitable to obtain global generalised models for back-to-back m-level diode-clamped multilevel converters connecting AC loads. Using the proposed converter modelling, an advantageous generalised method to balance the (m - 1) DC bus capacitors, based on the DC bus average power flow is also presented. The generalised proposed model is particularised to the back-to-back multilevel structure for m = 5. This back-to-back converter is studied working with bidirectional power flow, connecting an induction machine (in motor or self-excited generator mode) to the power grid as a flexible AC transmission system. View full abstract»

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  • Simple controller for single-phase power factor correction rectifier

    Page(s): 590 - 600
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1626 KB)  

    This study proposes a simple low-cost modulating duty cycle analogue controller to reduce line frequency harmonics for high power factor boost rectifier. The proposed method eliminates the need for current sensing, and simultaneously offers the performance results comparable to those of continuous conduction mode (CCM). This scheme also maintains the simplicity comparable to that of discontinuous conduction mode (DCM). Only the output voltage and the rectified input voltage are monitored to vary the duty cycle of the boost switch within a line cycle so that the third-order harmonic, which is the lowest order harmonic of the input current, is reduced. As a result, the total harmonic distortion (THD) of the line current and thus the input power factor is improved. Moreover, the rectifier shows a good transient performance where the converter's output voltage overshoots during input voltage/load transients is reduced. The proposed method is developed for constant switching frequency boost rectifier. Simulation and experimental results are presented to verify the effectiveness of the proposed control method. View full abstract»

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  • Voltage vector control of a hybrid three-stage 18-level inverter by vector decomposition

    Page(s): 601 - 611
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1083 KB)  

    This study presents a three-stage 18-level inverter design and its innovative control method. The inverter consists of a series-connected main high-, medium- and low-voltage stages. The high-voltage stage is made of a three-phase, six-switch inverter. The medium- and low-voltage stages are made of three-level inverters constructed by H-bridge units. The proposed control strategy assumes a reference input voltage vector and aims to operate the inverter in one state per sampling time to produce the nearest vector to that reference. The controller operates to reach the desired state with minimum switching actions, giving the priority in switching reduction to the higher voltage stage. The approach of the proposed control strategy has been presented, a set of related terms has been defined and the implementation process has been described. The test results verify the effectiveness of the proposed strategy and the capability of the inverter to produce low-voltage distortion and switching losses. View full abstract»

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  • Switched mode power supplies for charge-up, discharge and balancing dc-link capacitors of diode-clamped five-level inverter

    Page(s): 612 - 628
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2276 KB)  

    Inductor switch mode power supplies (SMPS) operated in a discontinuous inductor current mode are used to balance the dc-link capacitor voltages of a diode-clamped five-level inverter. The SMPS concept is extended to charge up and discharge the four dc-link capacitors. Complete diode-clamped five-level inverter operation is implemented, from start-up, charge-up, balance dc-link capacitors in normal operation, discharge, to shut-down, which have not been presented before. Ramped start of a controlled rectifier sourcing a boost converter limits the lowest dc-link capacitor inrush current and control its charging time. SMPS in conjunction with the boost converter are used to control the dc-link capacitor charge-up and discharge times. The proposed inverter complete operation is validated by simulation and practically. View full abstract»

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  • Modified PWM switch model for continuous conduction mode DC-DC converters with coupled inductors

    Page(s): 629 - 636
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (539 KB)  

    A modified PWM switch model for DC-DC converters operating in continuous conduction mode (CCM) is proposed in this study. The modified model is based on the conventional PWM switch model. Compared to other modelling methods, the conventional model is versatile and easy to implement. However, it is typically restricted to a few topologies only. Therefore in this study, the proposed modified model expands the application fields, which includes the DC-DC converter with the coupled inductor; it can also be used in basic converters as a conventional topology. A high step-up buck-boost converter was built for this investigation to verify the accuracy of the modified model. The experimental results show that this modified model can accurately predict the characteristics of the system. View full abstract»

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  • Five-level inverter scheme for an open-end winding induction machine with less number of switches

    Page(s): 637 - 647
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    Higher level of inversion is achieved with a less number of switches in the proposed scheme. The scheme proposes a five-level inverter for an open-end winding induction motor which uses only two DC-link rectifiers of voltage rating of Vdc/4, a neutral-point clamped (NPC) three-level inverter and a two-level inverter. Even though the two-level inverter is connected to the high-voltage side, it is always in square-wave operation. Since the two-level inverter is not switching in a pulse width modulated fashion and the magnitude of switching transient is only half compared to the convention three-level NPC inverter, the switching losses and electromagnetic interference is not so high. The scheme is experimentally verified on a 2.5 kW induction machine. 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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