Showing papers on "Three-phase published in 2005"

Comparative evaluation of three-phase high-power-factor AC-DC converter concepts for application in future More Electric Aircraft

Abstract: A passive 12-pulse rectifier system, a two-level, and a three-level active three-phase pulsewidth-modulation (PWM) rectifier system are analyzed for supplying the dc-voltage link of a 5-kW variable-speed hydraulic pump drive of an electro-hydrostatic actuator to be employed in future More Electric Aircraft. Weight, volume, and efficiency of the concepts are compared for an input phase voltage range of 98-132 V and an input frequency range of 400-800 Hz. The 12-pulse system shows advantages concerning volume, efficiency, and complexity but is characterized by a high system weight. Accordingly, the three-level PWM rectifier is identified as the most advantageous solution. Finally, a novel extension of the 12-pulse rectifier system by turn-off power semiconductors is proposed which allows a control of the output voltage and, therefore, eliminates the dependency on the mains and load condition which constitutes a main drawback of the passive concept.

Active filtering function of three-phase PWM boost rectifier under different line voltage conditions

Abstract: Slight hardware and algorithm modifications as well as a higher power ratio of a three-phase pulsewidth-modulation (PWM) rectifier make compensation of neighboring nonlinear power load possible. The active filtering function enlarges the functionality of PWM rectifiers, which decreases the cost of additional installation of compensating equipment. It gives a chance to fulfill both shunt active filter (SAF) and PWM rectifier tasks in a multidrive system by one advanced converter. Thanks to the idea of virtual flux, the direct power control space-vector-modulated (DPC-SVM) and new synchronous double reference frame phase-locked loop approach, the control system is resistant to a majority of line voltage disturbances. This assures proper operation of the system for abnormal and failure grid conditions. Simulation and experimental results have proven excellent performance and verify the validity of the proposed system.

Application of a sinusoidal internal model to current control of three-phase utility-interface converters

Abstract: Three-phase voltage-source converters are used as utility interfaces. In such a case, the converter line currents are required to track sinusoidal references synchronized with the utility grid without a steady-state error. In this paper a current control method based on a sinusoidal internal model is employed. The method uses a sine transfer function with a specified resonant frequency, which is called an S regulator. The combination of a conventional proportional-integral (PI) regulator and an S regulator is called a PIS regulator. The PIS regulator ensures that the steady-state error in response to any step changes in a reference signal at the resonant frequency and 0 Hz reduces to zero. An experiment was carried out using a 1-kVA prototype of three utility-interface converters, a voltage-source rectifier, an active power filter, and static synchronous compensator. Almost perfect current-tracking performance could be observed.

Online capacitance estimation of DC-link electrolytic capacitors for three-phase AC/DC/AC PWM converters using recursive least squares method

Abstract: A novel online capacitance estimation method for a DC-link capacitor in a three-phase AC/DC/AC PWM converter is prepared. At no load, a controlled AC current with a lower frequency than the line frequency is injected into the input side, which then causes AC voltage ripples at the DC output side. By extracting the AC voltage and current components on the DC output side using digital filters, the capacitance can then be calculated using the recursive least squares method. The proposed method can be simply implemented with only software and no additional hardware. Experimental results confirm that the estimation error is less than 0.26%.

A three-phase ZVS PWM DC/DC converter with asymmetrical duty cycle for high power applications

Abstract: This paper proposes the application of the asymmetrical duty cycle to the three-phase dc/dc pulse-width modulation isolated converter. Thus, soft commutation is achieved for a wide load range using the leakage inductance of the transformer and the intrinsic capacitance of the switches, as no additional semiconductor devices are needed. The resulting topology is characterized by an increase in the input current and output current frequency, by a factor of three compared to the full-bridge converter, which reduces the filters size. In addition, the rms current through the power components is lower, implying the improved thermal distribution of the losses. Besides, the three-phase transformer allows the reduction of the core size. In this paper, a mathematical analysis, the main waveforms, a design procedure, as well as simulation and experimental results obtained in a prototype of 6 kW are presented.

Independent field-oriented control of two split-phase induction motors from a single six-phase inverter

Abstract: Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n/spl plusmn/1 (n=1,3,5...) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n/spl plusmn/1 (n=0,1,2,3...)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper.

Continuous and discrete variable-structure controls for parallel three-phase boost rectifier

Abstract: We describe three nonlinear control schemes for a parallel three-phase boost rectifier consisting of two modules. The basic idea, however, can be extended to a system with N modules. All of the control schemes are developed in a synchronous frame. Moreover, each of the closed-loop power-converter modules operates asynchronously without any communication with the other module. Based on the dynamical equations of the parallel converter, we find that independent control of both of the modules on the DQ axes is not necessary and possible. Consequently, we develop control schemes that stabilize the dq axes and limit the zero-axis disturbance by preventing the flow of the pure zero-sequence current. One of the control schemes is developed purely in the discrete domain. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance. The performances of the other control schemes are also satisfactory.

Application of a sinusoidal internal model to current control of three-phase utility interface converters

Abstract: Three-phase voltage-source converters are used as a utility interface. In such a case, the converter line currents are required to track sinusoidal references synchronized with the utility grid without steady-state error. In this paper a current control method based on a sinusoidal internal model is employed. The method uses a sine transfer function with a specified resonant frequency, which is called an S compensator. The combination of a conventional PI compensator and an S compensator is called a PIS compensator. The PIS compensator ensures that the steady-state error in response to any step changes in a reference signal at the resonant frequency and zero hertz reduces to zero. An experiment was carried out using a 1-kVA prototype of three utility interface converters, a voltage-source rectifier, an active power filter, and STATCOM. Almost perfect current tracking performance can be observed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 54–61, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20064

Comparison of three phase current source inverters and voltage source inverters linked with DC to DC boost converters for fuel cell generation systems

Abstract: Three phase current source inverters (CSI) and voltage source inverters linked with a DC to DC boost converter (VSI+BC) are appropriate solutions to convert electrical energy for distributed fuel cell generation systems. The performance of CSI's and VSI+BC's in this application is shown and both topologies are compared to each other concerning their power semiconductor design rating and their semiconductor power losses

Unity power factor control for three phase three level rectifiers without current sensors

Abstract: Three level rectifiers with reduced number of switches (such as the Vienna rectifier) have been receiving wide interest in the past years to improve the input power quality of rectifier systems. In this paper, a new carrier-based pulse width modulation (PWM) control algorithm is proposed for such converters to eliminate the low frequency harmonics in the line current while achieving unity power factor at the rectifier input terminals. The operating constraints of the Vienna rectifier with the carrier-based modulation strategy are examined carefully and the proposed control algorithm ensures that appropriate voltage/current directional constraints are met. A promising cost reduction opportunity can be seen with elimination of input current sensing to operate the Vienna rectifier. The control algorithm is verified via Saber simulation and experimental results.

A DSP-based implementation of a nonlinear model reference adaptive control for a three-phase three-level NPC boost rectifier prototype

Abstract: In this paper, the design and the implementation of a model reference adaptive control (MRAC) applied to a three-phase three-level neutral-point-clamped (NPC) boost rectifier are presented. This control strategy is developed with a view to regulate dc output and neutral point voltages and to reduce the influence of parameter variations while maintaining unity power factor. A nonlinear multiple-input multiple-output (MIMO) state space model of the rectifier is then developed in dq0 reference frame. The proposed controller is based on the use of a feedback linearization technique followed by a robust MRAC scheme allowing the design of a suitable controller applied to the plant. The control law is designed in Simulink/Matlab and applied to the converter via a 1920-Hz pulse width modulator both executed in real time using the DS1104 DSP of dSPACE. A 1.25 kW laboratory prototype is developed for validation. The experimental results are given for different operating conditions: nominal power operation, balanced and unbalanced dc load steps, boost inductor variation, and reactive power control. The proposed control law performs perfectly in a wide operation range giving low output voltage ripple, low line-current THD, a small overshoot and a fast settling time under system parameters variation.

Implementation issues of a fuzzy-logic-based three-phase active rectifier employing only Voltage sensors

Abstract: Switch-mode rectifiers are becoming more and more interesting in those applications where bidirectional power flow, power-factor correction, and electromagnetic interference reduction are required. Typical active rectifiers include current or voltage sensors, however, in order to obtain low-cost systems, their number should be reduced. In this paper, a current-sensorless active rectifier with feedforward fuzzy logic control is presented and discussed. The mathematical description of the system and the design of the fuzzy logic controller are introduced and analyzed; moreover the implementation on a SH7047 microcontroller is presented with emphasis on the most significant implementation issues. Experimental results are reported and discussed.

A novel hysteresis current control for three-phase three-level PWM rectifiers

Abstract: A novel hysteresis current control concept for three-phase three-level PWM rectifiers is presented. The proposed control is based on a virtual connection of the output center point and the mains star point and achieves a decoupling of the three phases. This control technique, besides having the advantages of a classical hysteresis control, provides a more regular switching of the power transistors and an intrinsic stability of the output center point voltage, and allows a full utilization of the modulation range. The novel control concept is discussed and compared to conventional current control techniques. Furthermore, the current control is digitally implemented and experimental results for controlling a Vienna rectifier are presented.

A novel control concept for reliable operation of a three-phase three-switch buck-type unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains condition

Abstract: In this paper the reliable operation of a three-phase three-switch buck-type pulsewidth-modulation unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains, i.e., mains voltage unbalance, loss of one phase, short circuit of two phases, or earth fault of one phase is investigated theoretically and experimentally. A brief description of the principle of operation and the most advantageous modulation method are given. The analytical calculation of the relative on-times of the active switching states and of the dc-link current reference value is treated in detail for active and deactivated boost output stage. Based on the theoretical considerations a control scheme which allows for controlling the system for any mains condition without changeover of the control structure is described. Furthermore, digital simulations as well as experimental results are shown which confirm the proposed control concept for different mains failure conditions and for the transition from balanced mains to a failure condition and vice versa. The experimental results are derived from a 5-kW prototype (input voltage range (280...480) V/sub rms/ line-to-line, output voltage 400 V/sub DC/) of the rectifier system, where the control is realized by a 32-bit digital signal processor.

Modelling and control of three-phase/switch/level fixed-frequency PWM rectifier: state-space averaged model

Abstract: A new and simple state model of a three-phase, three-switch, three-level, fixed-frequency pulse-width-modulated rectifier is presented. The modelling approach uses the state-space averaging technique in continuous current mode. The averaging process is applied on two time intervals: the switching period for average current evaluation, and the mains period for average voltage computation. A basic mathematical model of the converter is first established. A simplified time-invariant model is then deduced using the rotating Park transformation. The steady-state regime is analysed on the basis of the model obtained, and converter design criteria consequently discussed. The proposed modelling approach is then verified numerically through a digital implementation of the converter in the Matlab/Simulink framework, using the switching function approach. The numerical results show the reliability of the proposed model that would be then easily applied to the design of suitable duty-cycle-based control schemes.

A DSP-based implementation of a new nonlinear control for a three-phase neutral point clamped boost rectifier prototype

Abstract: This work presents the design and implementation of a nonlinear control strategy for a three-phase three-level neutral-point-clamped boost rectifier. The adopted control consists of nonlinear feedback linearization technique. The nonlinear state-space model of the rectifier was obtained in the dq0 reference frame. The input/output feedback linearization is then applied and the linearizing control law is derived. Therefore, the resulting model is linearized and decoupled in three independent subsystems. Afterwards, the stabilizing controllers are designed based on linear techniques to control line currents, output, and neutral point voltages. The control law is designed using Simulink/Matlab and applied to the converter via a 1.8-kHz pulsewidth modulator (PWM). Both control law and PWM signals are executed in real time using the DS1104 DSP of dSPACE. A 1.2 kW laboratory prototype is built for validation purposes. The proposed control law robustness is validated for diverse severe load and system parameter variations. It shows robust performance in terms of high power factor, low total harmonic distortion and output voltage ripples, small overshoot, and short settling time.

A three-phase ZVS PWM DC/DC converter with asymmetrical duty cycle associated with a three-phase version of the hybridge rectifier

Abstract: This paper proposes the use of a three-phase version of the hybridge rectifier in the three-phase zero-voltage switch (ZVS) DC/DC converter with asymmetrical duty cycle. The use of this new rectifier improves the efficiency of the converter because only three diodes are responsible for the conduction losses in the secondary side. The current in the secondary side of the transformer is half the output current. In addition to this, all the advantages of the three-phase DC/DC converter, i.e., the increased frequency of the output and input currents, the improved distribution of the losses, as well as the soft commutation for a wide load range, are preserved. Therefore, the resulting topology is capable of achieving high efficiency and high power density at high power levels. The theoretical analysis, simulation, and experimental results obtained from a 6-kW prototype, and also a comparison of the efficiency of this converter with the full-bridge rectifier are presented.

Variable speed electric drive options for electric ships

Abstract: Variable speed electric propulsion motors are operated from a variable frequency drive (VFD), which supplies power to motors at a frequency appropriate to the desired speed. These VFD's are normally very heavy and large in size. A variety of designs are commercially available but they have characteristics unsuitable for ship applications. The objective of this study was to evaluate various options for shipboard applications and to recommend designs that meet navy performance, weight and size constraints. It is possible to dramatically reduce the size and weight of the VFD by optimizing the VFD and the motor as a system, utilizing an optimal distribution voltage, eliminating distribution frequency transformers, and utilizing the weight and size reductions available with liquid cooling. Three systems were studied in detail: cycloconverters, series connected low voltage inverters, and multi-level medium voltage inverters using 6 kV class IGBT's or similar switching devices. On the basis of this evaluation, a multi-level diode-clamped pulse width modulated (PWM) drive topology is recommended for navy ships. A three phase distribution voltage of 6 to 9 kV RMS minimizes the number of series semiconductors and control complexities of the drive.

Three phase buck power converters having input current control

Abstract: A three phase buck power converter having input power control is described. The power converter uses a three input buck converter comprising switches for each phase, a catch rectifier, an inductor and an output capacitor. The duty cycle of the three switches is constrained to have a sine function relationship that may be derived from the input voltage wave form or from a reference oscillator. When so constrained, the input currents have high power factor. The output is a precise, high quality dc voltage, comparable to the output of a dc—dc buck converter, and the dynamic response is comparable. Voltage mode and current mode controls are shown, as is a precise line regulation feed forward for the voltage mode embodiment. The three phase buck power converter may be operated in reverse as a three phase boost converter, as they are reciprocal. A three phase ac—ac converter may have a three phase buck converter as its input and a three phase boost converter as its output.

Precise derating of three-phase induction motors with unbalanced voltages

Abstract: Performance analysis of three-phase induction motors under supply voltage unbalance conditions is normally carried out using the well-known symmetrical components analysis. In this analysis, the voltage unbalance level at the terminals of machine is assessed by means of the NEMA or IEC definitions. Both definitions lead to a relatively large error in predicting the performance of a machine. A method has recently been proposed in which, in addition to voltage unbalance factor (VUF), the phase angle has been accounted. This means that the voltage unbalance factor is regarded as a complex value. This paper shows that although the use of the complex VUF reduces the computational error considerably, it is still high. This is proven by evaluating the derating factor of a three-phase induction motor. A method is introduced to determine the derating factor precisely using the complex unbalance factor for an induction motor operating under any unbalanced supply condition. A practical case for derating of a typical three-phase squirrel-cage induction motor supplied by an unbalanced voltage is studied in the paper.

Predictive Control of a Three-Phase Neutral Point Clamped Inverter

Abstract: A new predictive strategy for current control of a three-phase neutral point clamped inverter is presented. It is based on a discrete-time model of the system, used to predict future values of the load current and voltage of the capacitors in the DC-link, for each possible switching state generated by the inverter. The state that minimizes a given quality function "g" is selected to be applied during the next sampling interval. Several compositions of g are proposed, including terms dedicated to achieve reference tracking, balance in the DC-link and reduction of the switching frequency. The algorithm uses the redundancy of switching states, typical of a three-level inverter, by means of a simple strategy. In comparison with classic PWM current control, the strategy presents a remarkable performance. The proposed method achieves comparable reference tracking with lower switching frequency per semiconductor and a slightly improved transitory behavior. It requires a greater sampling frequency, which should not be a problem, considering the present technologies available in digital signal processors. The main advantage of the method is that it does not require any kind of linear controller or modulation technique, achieving a different approach to control a power converter

Study of advanced current control strategies for three-phase grid-connected pwm inverters for distributed generation

Abstract: Three-phase PWM voltage-source inverters (VSI) are widely employed for distributed generation (DG) systems. Since the voltage at the point of common coupling should not be regulated by DGs, the current control strategy of grid-connected inverters plays a dominant role in providing high quality power to electric grids. The authors have proposed two advanced SVPWM-based current controllers to improve the performance of grid-connected VSIs for DG systems. Three current control strategies, namely hysteresis current control, SVPWM-based PI control and SVPWM-based predictive control, have been developed, implemented, and studied on a 30kW three-phase grid-connected PWM VSI. Effective compensation for the grid harmonics and for the system nonlinearity due to control delay and switching dead time are investigated. The results of computer simulations and experimental tests are provided to verify and compare the performances of these three current control strategies

Capacitor placement in three-phase distribution systems with nonlinear and unbalanced loads

Abstract: The problem of choosing optimal locations and sizes for shunt capacitors in distribution systems is addressed. The objective of the capacitor placement procedure is not only to minimise the power losses along distribution feeders, but also to make sure that these capacitors will have the minimum possible impact on the harmonic distortion of bus voltages in the system. Furthermore, the fact that distribution systems can operate under unbalanced loading conditions, means that the optimisation will have to account for any unbalances in the system. An optimisation program, which successfully solves the problem is developed and tested. Results obtained by simulation of a distribution test system under various operating conditions, are presented to validate the proposed solution methods.

Analysis and control of three-phase self-excited induction generators supplying single-phase AC and DC loads

Abstract: An approach employing genetic algorithm (GA) has been evolved for the analysis of single-phase operation of three-phase self-excited induction generators. Using symmetrical components, the circuit equations have been written and an impedance matrix has been derived, which can be straightaway solved using this method. The lengthy derivations of nonlinear equations required for the unknown variables, in the earlier methods, are thus not required in the present method. Apart from single-phase AC loads, feeding of DC loads through a controlled rectifier has also been considered and the analysis has been extended for this combined loading. For maintaining a desired DC voltage on the rectifier output side, symmetrical and extinction angle control techniques have been adopted. These techniques are shown to be better compared to the conventional phase angle control, in improving voltage regulation of the generator. The suitability of each of these control schemes for specific load conditions is discussed with examples. A biomass gasifier-based diesel engine has also been used as a prime-mover and the experimental results obtained on two generators with AC as well as DC loads, closely agree with the values predetermined using the GA approach.

A survey of output filter topologies to minimize the impact of PWM inverter waveforms on three-phase AC induction motors

Abstract: Three-phase output filters have been developed to a mature level with improved power quality in terms of over voltage transients at motor terminals when using long cables and high switching frequencies, high frequency common-mode voltages, which induce high shaft voltages leading to bearing currents and a very fast voltage rise in the PWM wave causing EMI problems including high leakage currents. This paper presents an exhaustive survey of output filter topologies to minimize the impact of PWM inverter waveforms on AC induction motors by using output filters. It is aimed at presenting a state of the art on the improved power quality of PWM inverter to researchers, designers, and application engineers dealing with three-phase output filters

Advanced Synchronous Reference Frame Controller for Three-phase UPS Powering Unbalanced and Nonlinear Loads

Abstract: This paper describes a high performance voltage controller for 3-phase 4 wire UPS (uninterruptible power supply) system, and proposes a new scheme of synchronous reference frame controller in order to compensate for the voltage distortions due to unbalanced and nonlinear loads. Proposed scheme in this paper is able to completely eliminate the negative sequence voltage distortion due to unbalanced loads and also reduce the harmonic voltage distortion due to non-linear loads, even if the bandwidth of voltage control loop is a very narrow. Therefore, the proposed scheme is especially appropriate for a fully digital controlled UPS or a high power UPS with limited voltage control bandwidth. In order to compensate for the effects of unbalanced loads, the synchronous reference frame controller with the positive and negative sequence computation block is proposed, and the synchronous frame controller with a bandpass filter is proposed to compensate for the selected harmonic frequency of output voltage. The effectiveness of the proposed scheme has been investigated and verified through computer simulations and experiments by a 30 kVA UPS

A three-phase unity-power-factor diode rectifier with active input current shaping

Abstract: This paper proposes a new three-phase diode rectifier that actively shapes the input current by means of two direct current dc-dc converters operating at continuous conduction mode. The proposed approach draws sinusoidal input current at unity power factor and has output voltage regulation capability. The size and weight of the magnetic devices is reduced since a low-kilovolt-ampere three-phase autotransformer is incorporated and dc outputs of two bridges are directly connected without using low-frequency interphase transformers (IPTs).

Three-phase single-stage four-switch PFC buck-boost-type rectifier

Abstract: This paper proposes a new three-phase single-stage power-factor corrector buck-boost-type rectifier topology. The typical topology uses a bridge configuration with six switches. This new topology only requires four switches, improving the rectifier efficiency as only one reverse-blocking power semiconductor conducts at any time. A vector-based sliding-mode control method for the three-phase input currents is also proposed. This fast and robust technique uses sliding mode to generate /spl alpha//spl beta/ space-vector modulation, which forces the input line currents to track a suitable sinusoidal reference. A near-unity power-factor operation of the rectifier is obtained using a sinusoidal reference in phase with the input source voltages. A proportional-integral controller is adopted to regulate the output voltage of the converter. This external voltage controller modulates the amplitude of the current references. The characteristics of the new rectifier are verified with experimental results.

Apparatus for controlling three-phase AC motor on two-phase modulation technique

Abstract: An apparatus is provided to control a three-phase AC motor and comprises an inverter and a controller. The inverter powers the motor in response to a three-phase PWM command. The control circuit controls the inverter based on two modulation techniques selectively switched from one the other depending on information indicative of an operation state of the motor. One modulation technique gives the PWM command a first two-phase modulation allowing each phase voltage to be fixed at a predetermined voltage level in turn at intervals of an electrical angle of 2π/3. The other modulation technique gives the PWM command a second two-phase modulation allowing each phase voltage to be fixed at a predetermined voltage in turn at intervals of an electrical angle of π/3. The switchover can be made between the two-phase and three-phase modulations or can be made with consideration of temperature at switching elements.

Apparatus and method for determining a faulted phase of a three-phase ungrounded power system

Abstract: Provided is an apparatus and method for determining a faulted phase resulting from a fault in a three-phase ungrounded power system. The method includes comparing a phase angle of an operating phasor to a phase angle of a fixed reference phasor. The operating phasor is derived from a digitized signal sample of a plurality of measured signals of the power system. The method also includes comparing a phase angle difference between the operating phasor and the fixed reference phasor to at least one threshold to determine the faulted phase. The fixed reference phasor may be a phase-to-phase voltage or a positive sequence voltage of the plurality of measured signals of the power system. The operating phasor may be a zero sequence current, a zero sequence voltage or a combination of a zero sequence current and a zero sequence voltage of the plurality of measured signals of the power system.