Showing papers on "Three-phase published in 2010"

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

Abstract: This paper presents a nonlinear control technique for a three-phase shunt active power filter (SAPF). The method provides compensation for reactive, unbalanced, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently nonlinear SAPF system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the SAPF output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that significantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the SAPF reference currents, is proposed. The first step is to extract the SAPF reference currents from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase diode bridge rectifier with R-L load is taken as the nonlinear load, and then, the reference currents are modified, so that the delay will be compensated. The converter, which is controlled by the described control strategy, guarantees balanced overall supply currents, unity displacement power factor, and reduced harmonic load currents in the common coupling point. Various simulation and experimental results demonstrate the high performance of the nonlinear controller.

Modulation Techniques to Eliminate Leakage Currents in Transformerless Three-Phase Photovoltaic Systems

Abstract: In some photovoltaic (PV) applications, it is possible to remove the transformer of a system in order to reduce losses, cost, and size. In transformerless systems, the PV module parasitic capacitance can introduce leakage currents in which the amplitude depends on the converter topology, on the pulsewidth modulation, and on the resonant circuit comprised by the system components. Based on the common-mode voltage model, modulation techniques are proposed to eliminate the leakage current in transformerless PV systems without requiring any modification on the converter and any additional hardware. The main drawback is that the proposed modulation technique for two-level inverters can only be used with 650-V dc link in the case of a 110-V (rms) grid phase voltage. Comparisons among the modulation techniques are discussed, and it is proven that the proposed modulation for two- and three-level inverters presents the best results. To validate the models used in the simulations, an experimental three-phase inverter is used.

Impact of Interleaving on AC Passive Components of Paralleled Three-Phase Voltage-Source Converters

Abstract: This paper presents a comprehensive analysis studying the impact of interleaving on harmonic currents and voltages on the ac side of paralleled three-phase voltage-source converters. The analysis performed considers the effects of modulation index, pulsewidth-modulation (PWM) schemes, and interleaving angle. Based on the analysis, the impact of interleaving on the design of ac passive components, such as ac line inductor and electromagnetic interference (EMI) filter, is discussed. The results show that interleaving has the potential benefit to reduce ac passive components. To maximize such a benefit, the interleaving angle should be optimized according to the system requirements, including total harmonic distortion limit, ripple limit, or EMI standards, while considering operating conditions, such as modulation index and PWM schemes. Experimental results have verified the analysis results.

Parameter design principle of the arm inductor in modular multilevel converter based HVDC

Abstract: This paper describes two distinctive functions of the arm inductor in the modular multilevel converters (MMC): suppressing the circulating current and limiting the fault current rise rate. Based on the equality of the instantaneous power, the characteristics of the circulating current are analyzed and demonstrated that it flows through the three phase of the converter in negative sequence at double-fundamental frequency. The relationship between the amplitude of the circulating current and the value of the arm inductor is discussed, and the first principle to design the parameters is proposed. The second principle to design the parameters is based on the calculation of the fault current rise rates, with different values of the arm inductors. A detailed PSCAD/EMTDC model of MMC is developed. Steady state simulation proves the existence of the circulating current at double fundamental frequency. Simulation results show a close agreement with the calculation of the circulating current, with different arm inductor parameters. The fault between the DC terminals of the converter is investigated; the results verify the above parameter design principles of the arm inductor.

Grid-Fault Control Scheme for Three-Phase Photovoltaic Inverters With Adjustable Power Quality Characteristics

Abstract: The power quality of a three-phase photovoltaic (PV) inverter drastically deteriorates in the presence of grid faults with unbalanced voltages. A ripple in the injected power and an increase in the current harmonic distortion are the main noticeable adverse effects produced by this abnormal grid situation. Several grid-fault control schemes are nowadays available for operating under unbalanced grid voltage. These control schemes usually have extreme power quality characteristics. Some of them have been conceived to completely avoid power ripple during unbalanced voltage sags, but at an expense of high current harmonic distortion. With other schemes, the harmonic distortion is totally eliminated but at an expense of high ripple in the injected power. This paper further explores the performance of PV inverters under unbalanced voltage sags. It has three theoretical contributions: 1) a generalized control scheme, which includes the aforementioned grid-fault controllers as particular cases; 2) a control strategy based on the use of continuous values for the control parameters. This original approach gives adjustable power quality characteristics that cannot be achieved with the previous control schemes; 3) three different control algorithms for calculating the continuous values of the control parameters. These contributions are experimentally validated with a digital signal processor-based laboratory prototype.

Three-Phase Cascaded Multilevel Inverter Using Power Cells With Two Inverter Legs in Series

Abstract: In this paper, a modular three-phase multilevel inverter specially suited for electrical drive applications is proposed. Unlike the cascaded H-bridge inverter, this topology is based on power cells connected in cascade using two inverter legs in series. A detailed analysis of the structure and the development of design equations for the load voltage with n levels are carried out using pulsewidth-modulation phase-shifted multicarrier modulation. Simulations and experimental results for a 15-kW three-phase system, with nine voltage levels, validate the study presented.

Implementation of the Three-Phase Switched Reluctance Machine System for Motors and Generators

Abstract: This paper presents two three-phase switched reluctance machine systems. One is the dual motors drive for the electric locomotive traction; the other is the variable-speed generator system for wind power applications. The principles of the switched reluctance machine system operated at four quadrants, the scheme of the symmetrical traction at quadrant I and quadrant III, and the scheme of the symmetrical regenerative braking control at quadrant II and quadrant IV, are given. The transient phase current analysis and the energy analysis of the switched reluctance machine system at the operational state of braking or generating are evaluated, and the rotor position and the peak value of the phase current at three different conditions are given. The closed-loop rotor speed control of the main motor, synchronization of the rotor speed, and balance distribution of loads between the main motor and the subordinate motor have been implemented by the fuzzy logic algorithm. The closed-loop output power control of the switched reluctance wind power generator system implemented by regulating the turn-on angle of the main switches with fuzzy logic algorithm and fixed turn-off angle of the main switches is also presented. The major components of the two prototypes are explained in detail. The experimental results of the dual 7.5-kW three-phase 6/4 structure switched reluctance motors (SRMs) parallel drive system prototype are included. It is shown that the maximum difference in the output torque of the two motors at the same given rotor speeds is within 10.00% and the maximum difference in the practical rotor speed of the two motors is within 5.00%. The tested results of three-phase 12/8 structure switched reluctance variable-speed wind power generator system show that the error of the closed-loop output power control is within 2.2%, while the rotor speed range is close to the ratio of 1:3 with the low rotor speed 405 r/min. The average dc line current of the power converter can be utilized as a feedback signal for the actual output torque of SRM drive or a feedback signal for the actual output power of switched reluctance generator system.

Simulation and comparison of spwm and svpwm control for three phase inverter

Abstract: A voltage source inverter is commonly used to supply a three-phase induction motor with variable frequency and variable voltage for variable speed applications. A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage in the line side of the inverter. The different methods for PWM generation can be broadly classified into Triangle comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The highest possible peak phase fundamental is very less in sine triangle PWM when compared with space vector PWM. Space Vector Modulation (SVM) Technique has become the important PWM technique for three phase Voltage Source Inverters for the control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet Synchronous Motors. The study of space vector modulation technique reveals that space vector modulation technique utilizes DC bus voltage more efficiently and generates less harmonic distortion when compared with Sinusoidal PWM (SPWM) technique. In this paper first a model for Space vector PWM is made and simulated using MATLAB/SIMULINK software and its performance is compared with Sinusoidal PWM. The simulation study reveals that Space vector PWM utilizes dc bus voltage more effectively and generates less THD when compared with sine PWM.

Circulating current suppressing controller in modular multilevel converter

Abstract: A circulating current suppressing controller (CCSC) is presented to eliminate the inner balancing currents in modular multilevel converter (MMC) Based on the double-fundamental-frequency, negative-sequence rotational frame, the three phase alternative circulating currents are decomposed to two DC components, and are limited to a low level by a pair of proportional integral controllers This control strategy does not affect the MMC outer dynamics in the ac side Simulation results based on PSCAD/EMTDC demonstrated the circulating current suppressing effect of the proposed CCSC and proved that the distortion of the arm current is mitigated significantly

Direct-Matrix-Converter-Based Drive for a Three-Phase Open-End-Winding AC Machine With Advanced Features

Abstract: This paper describes how matrix converters (MCs), one at each side of a three-phase open-end-winding ac machine, achieve the following features simultaneously: 1) machine phase voltage up to 1.5 times the input phase voltage in the linear modulation mode, therefore extending the rated torque operation region to 150% of the rated speed of the machine; 2) peak voltage stress across the slot insulation which is limited to the peak of input phase voltage, i.e., a factor of at least √3 lower as compared to the conventional back-to-back converter; 3) controllable grid power factor to be leading, lagging, or unity; and 4) elimination of the instantaneous common-mode voltage at the machine terminals, therefore eliminating the bearing current due to switching common-mode voltage and reduction in the conducted electromagnetic interference. To simultaneously achieve the aforementioned capabilities, a space vector pulsewidth modulation technique is described in which the MCs are modulated using only rotating space vectors. A hardware prototype of the drive system is built. Experimental results from this hardware prototype verify the operation and claims of the drive system.

Three phase tooth-concentrated multiple-layer fractional windings with low space harmonic content

Abstract: The possibility of obtaining lower space harmonic content for the fractional-slot, tooth-concentrated windings by multiplying the number of coils, leading to bigger number of layers in the armature slots is presented. By using multiple layer windings it is possible to reduce or even to cancel some space sub-harmonics having as final result lower eddy current losses induced by the armature reaction in the iron structure of the rotor. The general method of doubling (or trebling) the winding and relatively shifting by one (or more) slots is presented in the paper. Two examples of three phase concentrated windings are presented and analyzed as primitive windings, 12 slots/10poles and 9 slots/8 poles. In the first case the only existing space sub-harmonic is reduced firstly from 35.9% (from fundamental wave) to 9.6% and finally it is canceled by using different number of turns per coils. In the second case the two existing sub-harmonics are reduced and balanced by using the developed method.

Design of a Plug-In Repetitive Control Scheme for Eliminating Supply-Side Current Harmonics of Three-Phase PWM Boost Rectifiers Under Generalized Supply Voltage Conditions

Abstract: This paper presents a digital repetitive control (RC) scheme to minimize the even-order harmonics at the dc link voltage and odd-order harmonics in the line-side currents under distorted and unbalanced supply voltage conditions. The proposed current control scheme consists of a conventional PI and a plug-in repetitive controller. On the basis of the mathematical model of the three-phase pulsewidth-modulated (PWM) boost rectifier under the generalized supply voltage conditions, the control task is divided into: 1) dc-link voltage harmonics control and 2) line-side current harmonics control . In the voltage harmonics control scheme, a reference current calculation algorithm has been derived accordingly to ensure that the dc link voltage is maintained constant at the demanded value and the supply-side power factor is kept close to unity. In the line-side current harmonics control scheme, a plug-in repetitive controller is designed to achieve low total harmonic distortion (THD) line-side currents of the three-phase PWM boost rectifier. The experimental test results obtained from a 1.6-kVA laboratory-based PWM rectifier confirm that the proposed control scheme can reduce the line-side current THD from 16.63% to 4.70%, and improve the dc-link voltage tracking accuracy substantially over the conventional PI-based controller.

Analysis and Tests of a Dual Three-Phase 12-Slot 10-Pole Permanent-Magnet Motor

Abstract: In order to increase the fault tolerance of a motor drive, multiphase systems are adopted. Since custom solutions are expensive, machines with dual three-phase windings supplied by two parallel converters seem to be more convenient. In the event of a fault, one of the two three-phase windings (the faulty winding) is disconnected, and the motor is operated by means of the healthy winding only. A fractional-slot permanent-magnet (PM) motor with 12 slots and 10 poles is considered with two different rotor topologies: the interior PM (IPM) rotor and the surface-mounted PM rotor. Various winding configurations of dual three-phase windings are taken into account, comparing average torque, torque ripple, mutual coupling among phases, overload capability, and short-circuit behavior. Considerations are given regarding the winding arrangements so as to avoid excessive torque ripple and unbalanced radial forces in faulty operating conditions. An IPM motor prototype has been built, and experimental results are carried out in order to verify the numerical predictions.

A Three-Phase High-Frequency Semicontrolled Rectifier for PM WECS

Abstract: This paper proposes the use of a three-phase high-frequency semicontrolled rectifier for wind energy conversion systems based on permanent magnet generators. The main advantages of the topology are: simplicity, since all active switches are connected to a common point, robustness, as short-circuit through a leg is not possible, and high efficiency due to reduced number of elements. As a disadvantage, higher but acceptable total harmonic distortion of the generator currents results. The complete operation of the converter and theoretical analysis are presented. Additionally, a single-phase pulsewidth modulation inverter is also employed in the grid connection. Experimental results on 5-kW prototype are presented and discussed.

Control of Three-Phase Boost-Type PWM Rectifier in Stationary Frame Under Unbalanced Input Voltage

Abstract: In the last decade, many methods for control of three-phase boost-type pulsewidth modulation (PWM) rectifier under unbalanced input voltage conditions have been studied and presented. These methods use the sequential components of input voltages, pole voltages, and input currents of the rectifier to analyze and control the instantaneous powers, of which dual (positive-sequence and negative-sequence rotating) frame control is the most common structure. Anyway, this paper analyzes the instantaneous powers of the PWM rectifier in two-phase stationary frame. Based on this analysis, the input-power-control, input-output-power-control, and output-power-control methods for PWM rectifier under unbalanced voltage conditions are proposed in single stationary frame. Compared with the existing methods, simplicity may be the major advantage of the method in this paper. Rotating transformation and phase detection of the input voltages are both eliminated. Moreover, sequential component extraction of the control variables is also not necessary, leading to much reduced time delay to the control system. Experimental results on a 9-kVA PWM rectifier show validity and effectiveness of the proposed methods.

Architecture for power plant comprising clusters of power-generation devices

Abstract: Various techniques are employed alone or in combination, to reduce the levelized cost of energy imposed by a power plant system. Solar energy concentrators in the form of inflated reflectors, focus light onto photovoltaic receivers. Multiple concentrators are grouped into a series-connected cluster that shares control circuitry and support structure. Individual concentrators are maintained at their maximum power point via balance controllers that control the flow of current that shunts this series connection. DC current from clusters is transmitted moderate distances to a centralized inverter. The inductance of transmission lines is maximized using an air-spaced twisted pair, enhancing the performance of boost-type three phase inverters. Cluster outputs are separate from individual inverters in massively interleaved arrays co-located at a central location. Step-up transformers convert inverter voltages to grid voltages, and small transformers provide isolation and voltage step-up only on receiver-to-receiver imbalance currents, typically <20% of the total current.

New Stationary Frame Control Scheme for Three-Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions

Abstract: A new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple This paper's novelty is the development of a new current-reference generator implemented directly in stationary reference frame This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme A comparison with two other existing control techniques is also performed Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating conditions

Predictive control of a three-phase UPS inverter using two steps prediction horizon

Abstract: A Model Predictive Control scheme is used for voltage control in a three-phase inverter with output LC filter. The controller uses a model of the system to calculate predictions of the future value of the system variables for a given voltage vector sequence. A cost function considering the voltage errors is defined and the voltage vectors that minimize it are selected and applied in the converter. The effect of considering different number of prediction steps is studied in this work in terms of THD. Simulation results for one and two prediction steps are presented and compared.

A Proportional ${\bm +}$ Multiresonant Controller for Three-Phase Four-Wire High-Frequency Link Inverter

Abstract: A new solution for unbalanced and nonlinear loads in terms of power circuit topology and controller structure is proposed in this paper. A three-phase four-wire high-frequency ac-link inverter is adopted to cater to such loads. Use of high-frequency transformer results in compact and light-weight systems. The fourth wire is taken out from the midpoint of the isolation transformer in order to avoid the necessity of an extra leg. This makes the converter suitable for unbalanced loads and eliminates the requirements of bulky capacitor in half-bridge inverter. The closed-loop control is carried out in stationary reference frame using proportional + multiresonant controller (three separate resonant controller for fundamental, fifth and seventh harmonic components). The limitations on improving steady-state response of harmonic resonance controllers is investigated and mitigated using a lead-lag compensator. The proposed voltage controller is used along with an inner current loop to ensure excellent performance of the power converter. Simulation studies and experimental results with 1 kVA prototype under nonlinear and unbalanced loading conditions validate the proposed scheme.

Direct Control Strategy for a Four-Level Three-Phase Flying-Capacitor Inverter

Abstract: A direct predictive control strategy is proposed for a three-phase four-level flying-capacitor (FC) inverter in this paper. The balancing of the FC voltages, a challenge in applications with small capacitors and low switching frequencies, is done without any modulation, simply using tables calculated offline. These allow the realization of fast-dynamics output currents with reduced dv/dt in the output voltages and reduced switching frequencies. Moreover, no interharmonics are created when operating at low switching frequencies and with reference currents containing multiple harmonic components, which is a key feature for active power filters. Simulations and experimental results are presented to demonstrate the excellent performance of the direct control strategy in comparison with a conventional pulsewidth-modulation control technique, mostly for operation at low switching frequencies.

A Three-Phase Adaptive Notch Filter-Based Approach to Harmonic/Reactive Current Extraction and Harmonic Decomposition

Abstract: This paper introduces a new three-phase adaptive notch filtering approach for the extraction of harmonic and reactive current components for use in grid-connected converters. The main function of this phase-locked loop-less method is to provide synchronized harmonic and reactive current components for control purposes. Moreover, this method is capable of detecting a selective order of harmonics. This feature is useful where elimination of certain harmonics is of concern. The theoretical analysis is presented and the performance of the method is experimentally evaluated. The methodology is applicable for a wide range of equipment like regenerative converters, distributed generation systems, as a basis for detection of the reference signals.

Voltage oriented control of three‐phase boost PWM converters

Abstract: In a plug‐in hybrid electric vehicle, the utility grid will charge the vehicle battery through the battery charger. For a three‐phase grid supply voltage, three‐phase boost rectifiers are a commonly used scheme for chargers. Bi‐directional power transfer capability and unit power factor operation are interesting features that can be achieved by the method proposed in this thesis. Different control strategies have been proposed to control the converter. The Voltage Oriented Control is one of these methods based on high performance dq‐coordinate controllers. The Voltage Oriented Control method for a three‐phase boost rectifier have been designed and simulated. Moreover, an implementation of the system has been started. The system simulation has been done using Matlab/Simulink software. Feedforward decoupled current controller has been designed along with Pulse Width Modulation scheme to control the battery charging. The controller, that is, a current controller and a DC‐link voltage controller, have been designed using a method called Internal Model Control. The simulation results have been presented and the control system performance evaluated in response to the load and dc‐bus voltage step changes. dSpace system have been used for practical implementation. The system is directly running a Simulink model as a controller. The Simulink files have been developed for this purpose. A brief explanation of the system configuration has been provided for the experimental system.

Dynamic Hysteresis Current Control to Minimize Switching for Three-Phase Four-Leg VSI Topology to Compensate Nonlinear Load

Abstract: This letter presents a dynamic hysteresis current control algorithm for a three-phase four-leg voltage-source inverter (VSI) topology. In order to improve the performance and life of the power switches of VSI, we require an optimized control technique that reduces its switching frequency. Proposed hysteresis current control method is a generalized control method that minimizes switching operations to compensate nonlinear load under both balanced and unbalanced supply voltages. It is shown that this control scheme is able to reduce the switching frequency by more than 50% compared to conventional hysteresis current control method and retain the quality of load compensation. The effectiveness of the proposed control scheme is illustrated through simulations using Power Systems Computer-Aided Design (PSCAD) 4.2.1.

Improved Three-Phase Current Reconstruction for Induction Motor Drives With DC-Link Shunt

Abstract: This paper aims to reveal an offset jitter-like waveform error, which is usually present in all three-phase current signals reconstructed from dc-link current samples. This paper also presents a method for the cancellation of that error, which could be useful in low-cost shaft-sensorless drives. A combination of two samples' time displacement and the line current pulse-width modulation (PWM) ripple produces a distinctive shape of the reconstructed current error, which is offset jitter like, and is always at the current ripple level. This unusual waveform distortion is often masked by other jitters and noise sources and therefore is typically not given in the relevant literature. However, the distortion is difficult to filter out, and it may be harmful, particularly in applications with low rated motor current. The proposed waveform correction scheme uses the readily available motor states in shaft-sensorless drives and does not require major computational effort. Experimental results show that the scheme recovers the α-β current waveforms and, as a result, prevent the increase in the sixth harmonic ripple in the d-q currents, which is inherent to the PWM inverter-controlled drives. Consequently, drives with the dc shunt will neither have current signal offset problems nor the need for d-q current signal prefilters with order significantly higher than usual.

Multi-phase multi-level AC motor drive based on four three-phase two-level inverters

Abstract: A novel multi-phase multi-level ac motor drive is analyzed in this paper. The proposed scheme is based on four conventional 2-level three-phase voltage source inverters (VSIs) supplying the open-end windings of a dual three-phase motor (asymmetric six-phase machine), quadrupling the power capability of a single VSI with given voltage and current ratings. The proposed control algorithm is able to generate multi-level voltage waveforms, equivalent to the ones of a 3-level inverter, and to share the total motor power among the four dc sources within each switching period. The proposed ac motor drive has been numerically implemented and a complete set of simulation results is given to prove the effectiveness of the whole scheme.

Adjustable Flux Three-Phase AC Machines With Combined Multiple-Step Star-Delta Winding Connections

Abstract: In this paper, a complete theory and analysis method for combined star-delta three-phase windings from the point of view of magnetomotive force spatial harmonics content and equivalent winding factors calculation is developed. The method allows for any spatial angle and any coils percentage distribution between star and delta balanced winding systems. It is proven that connecting the inner delta in the clockwise or counterclockwise direction leads to two different space angles between the star and delta systems and two different steps in the flux level control. It means that, compared to what is known and applied up to now, using n winding sections in each phase, it is possible to obtain 2 n steps (instead of n + 1) in the flux level. To check the analysis validity, two experimental tests are reported on both squirrel-cage, integer-winding, induction motor, and permanent magnet, low-speed, fractional-winding, synchronous generator with a specially designed stator winding, allowing multiple-step air-gap flux regulation.

A Novel Three-Phase to Five-Phase Transformation Using a Special Transformer Connection

Abstract: The first five-phase induction motor drive system was proposed in the late 1970s for adjustable speed drive applications. Since then, a considerable research effort has been in place to develop commercially feasible multiphase drive systems. Since the three-phase supply is available from the grid, there is a need to develop a static phase transformation system to obtain a multiphase supply from the available three-phase supply. Thus, this paper proposes a novel transformer connection scheme to convert the three-phase grid supply to a five-phase fixed voltage and fixed frequency supply. The proposed transformer connection outputs five phases and, thus, can be used in applications requiring a five-phase supply. Currently, the five-phase motor drive is a commercially viable solution. The five-phase transmission system can be investigated further as an efficient solution for bulk power transfer. The connection scheme is elaborated by using the simulation and experimental approach to prove the viability of the implementation. The geometry of the fabricated transformer is elaborated in this paper.

A Three-Phase Zero-Voltage and Zero-Current Switching DC–DC Converter for Fuel Cell Applications

Abstract: In spite of having many advantages, such as low switch voltage and easy implementation, the voltage-fed dc-dc converter has been suffering from problems associated with large transformer leakage inductance due to high transformer turn ratio when it is applied to low-voltage, high-current step-up application such as fuel cells. This paper proposes a new three-phase voltage-fed dc-dc converter, which is suitable for low-voltage, high-current applications. The transformer turn ratio is reduced to half owing to ?-Y connection. The zero-voltage and zero-current switching (ZVZCS) for all switches are achieved over wide load range without affecting effective duty cycle. A clamp circuit not only clamps the surge voltage but also reduces the circulation current flowing in the high-current side, resulting in significantly reduced conduction losses. The duty cycle loss can also be compensated by operation of the clamp switch. Experimental waveforms from a 1.5 kW prototype are provided.

Direct Self-Control for BLDC Motor Drives Based on Three-Dimensional Coordinate System

Abstract: In this paper, a new control algorithm for brushless dc (BLDC) motor drives is presented. Direct self-control, which has been widely applied on induction motor drives in high-power low-frequency traction, is introduced to BLDC drives. The Cartesian coordinate system is selected with three coordinate axes X, Y, and Z mutually at right angle to each other with three phase axes a, b, and c being movable. A two-phase conduction scheme is selected with the axis of the exciting phase located in the X-Y plane or, otherwise, along the direction of the Z -axis during unexcited (i.e., the unexcited phase axis is always directed along the Z-axis). The tracks of stator flux and voltage vectors are all three-dimensional, as a result of a variable voltage of unexcited phase and commutation every 60 electrical degrees. However, projections on the X-Y plane of these three-dimensional tracks are concise. The projection of flux vector is a hexagonal path, whereas the voltage vector projections are six active vectors. The projection of stator flux is controlled by the projections of voltage vectors. The newly proposed algorithm can be implemented with relatively low cost hardware and concise software, presenting fast torque transient response in 0.1 ms. The sensorless control is also implemented by flux estimation once in one sector. The validity and effectiveness of the proposed scheme are verified with simulated and experimental results.

A Soft Switching Scheme for Multiphase DC/Pulsating-DC Converter for Three-Phase High-Frequency-Link Pulsewidth Modulation (PWM) Inverter

Abstract: This paper outlines a switching scheme to improve the energy efficiency for an isolated high-frequency multiphase dc/pulsating-dc converter, which is the front end of a three-phase rectifier-type high-frequency-link inverter. Without using any auxiliary circuit, the proposed switching scheme achieves zero-current or zero-voltage switching for the power switches on the front-end multiphase dc/pulsating-dc converter. Moreover, on the back-end pulsating-dc/ac converter, the proposed soft-switching scheme reduces the switching frequency requirements for the associated switchers, which need high-frequency switching. In conjunction with the back-end pulsating-dc/ac converter, operating with a patent-filed hybrid modulation scheme, the proposed switching scheme leads to reduced overall switching loss as compared with other existing schemes. It is more suitable for isolated low-voltage dc to three-phase high-voltage ac applications from the standpoints of cost, efficiency, and footprint.