Showing papers on "Three-phase published in 1997"

A new mathematical model and control of a three-phase AC-DC voltage source converter

Abstract: A new mathematical model of the power circuit of a three-phase voltage source converter (VSC) was developed in the stationary and synchronous reference frames. The mathematical model was then used to analyze and synthesize the voltage and current control loops for the VSC. Analytical expressions were derived for calculating the gains and time constants of the current and voltage regulators. The mathematical model was used to control a 140-kW regenerative VSC. The synchronous reference-frame model was used to define feedforward signals in the current regulators to eliminate the cross coupling between the d and q phases. It allowed the reduction of the current control loops to first-order plants and improved their tracking capability. The bandwidths of the current and voltage-control loops were found to be approximately 20 and 60 times (respectively) smaller than the sampling frequency. All control algorithms were implemented in a digital signal processor. All results of the analysis were experimentally verified.

Three-phase four-wire shunt active filter control strategies

Abstract: This paper describes a three-phase four-wire shunt active power filter using a conventional three-leg converter, without the need of power supply at DC bus Two approaches have been developed to control the active filter Both control strategies consider harmonics and zero sequence components in the voltage and current simultaneously The first one provides constant power and the second one sinusoidal current to the source, even under unbalanced voltage conditions Simulation results from a complete model of shunt active filter are presented to validate and compare the control strategies

A novel control to actively damp resonance in input LC filter of a three-phase voltage source converter

Abstract: The voltage source converter (VSC) provides constant/controllable DC bus voltage, regenerating capability, controllable power factor, and nearly sinusoidal input current. If an input LC filter is added, it prevents pollution of the utility by the current ripple due to the pulsewidth modulation (PWM) switching. A novel control strategy for actively damping high-frequency resonance (above 1.5 kHz) in the input LC filter is presented. No additional sensors are required for the standard VSC. Theoretical results of the analysis and simulation are experimentally verified.

Implementation of single-phase boost power-factor-correction circuits in three-phase applications

Abstract: A three-phase rectifier employing three single-phase boost power-factor-correction circuits is analyzed. Each converter operates in the continuous conduction mode (CCM), which allows a high power factor and a small EMI filter. Current sharing is ensured by a common voltage loop driving the individual current loops of the three converters. A suitable circuit arrangement is devised to limit phase interaction. The zero-voltage-transition technique (ZVT) is successfully applied to each converter, in order to obtain zero turn on losses and soft turnoff of the freewheeling diodes. Results of a 1800-W 100-kHz experimental prototype are reported, which confirm the theoretical forecasts.

Variable speed wind turbine generator with zero-sequence filter

Abstract: A variable speed wind turbine generator system to convert mechanical power into electrical power or energy and to recover the electrical power or energy in the form of three phase alternating current and return the power or energy to a utility or other load with single phase sinusoidal waveform at sixty (60) hertz and unity power factor includes an excitation controller for generating three phase commanded current, a generator, and a zero sequence filter. Each commanded current signal includes two components: a positive sequence variable frequency current signal to provide the balanced three phase excitation currents required in the stator windings of the generator to generate the rotating magnetic field needed to recover an optimum level of real power from the generator; and a zero frequency sixty (60) hertz current signal to allow the real power generated by the generator to be supplied to the utility. The positive sequence current signals are balanced three phase signals and are prevented from entering the utility by the zero sequence filter. The zero sequence current signals have zero phase displacement from each other and are prevented from entering the generator by the star connected stator windings. The zero sequence filter allows the zero sequence current signals to pass through to deliver power to the utility.

Identification and modelling of a three phase arc furnace for voltage disturbance simulation

Abstract: This paper presents a new arc furnace model which copes with the two main voltage disturbances normally associated with arc furnaces: voltage fluctuations; and harmonics. The model is based on the stochastic nature of the electric arc current-voltage characteristic. The model has been estimated from measurements made in two actual electric plants. Although a single-phase model has been normally proposed, this paper develops a three-phase model in order to fully represent the unbalances that are present in real industrial plants and which play a central role in the behavior of compensation devices such as SVCs. The model has been implemented using the SIMULINK environment in order to facilitate later simulation of advanced disturbance control systems. Finally, the simulation results are compared with actual data in order to validate the accuracy of the model.

Performance analysis of a self-regulated self-excited single-phase induction generator using a three-phase machine

Abstract: A performance analysis of a modified self-regulated self-excited single-phase induction generator is presented. This generator consists of a three-phase squirrel-cage induction machine and three capacitors connected in series and parallel with a single-phase load. By utilizing this three-phase system as a single-phase generator, in addition to improved voltage regulation, the inherent vibration and noise in the generator can be significantly reduced. Using an equivalent circuit model, the generator steady-state characteristics are theoretically predicted, and confirmed through experiment. These results are useful in optimizing generator performance.

New current control concept-minimum time current control in the three-phase PWM converter

Abstract: In this paper, a new current controller that guarantees the fastest transient response is proposed. The basic concept is to find the optimal control voltage for tracking the reference current with minimum time under the voltage limit constraint. Though this minimum time control concept is also applicable to all the machine drive systems, this paper focuses on the current regulation in the three-phase pulse width modulation (PWM) converter. In the simulation and experimental results, it is observed that the proposed controller has much less transient time than the conventional synchronous PI regulator and the performance of the DC link voltage control is also greatly improved with the proposed current controller.

Three-phase matrix converter and method for operation thereof

Abstract: A three-phase matrix converter for converting AC voltages of predetermined amplitude and frequency into AC voltages of any amplitude and frequency and a method for operating the same, include four-segment switches as main switches which are combined into three switch groups. A resonance capacitance is connected in parallel with each main switch, or an output capacitance of power semiconductors of the main switches acts as a resonance capacitance. An auxiliary commutation device which is provided between three-phase output connections of each switch group has an auxiliary switch constructed as a four-segment switch and a resonance inductance connected in series therewith.

Method of and apparatus for power management and distribution in a medical imaging system

Abstract: An apparatus for energizing a large scale medical imaging system, preferably in the form of a CT scanner so that the scanner operates off an uninterruptable power supply in the event that the external power falls below sufficient power to operate the system so that system operation remains uninterruptable. The system is designed to operate off a broad range and types of external power supplies including those providing DC, single or three phase AC power. The system therefore can operate from a common single phase AC outlet. In addition, power factor correction is provided so that the system can correct for phase differences between the voltage and current at the input line created by the input impedance of the system.

A transformer-less static synchronous compensator employing a multi-level inverter

Abstract: This paper examines the application of a high voltage multi-level invertor in a 13.8 kV distribution system static synchronous compensator (SSC). Equations are developed for the component MVA of the multi-level inverter. Trends in component MVA as a function of the number of inverter voltage levels and the modulation strategy are identified. Control of the DC bus capacitor voltages during phase voltage imbalance is identified as a problem. A method is described whereby the multi-level inverter's DC bus capacitor voltages are actively controlled without using additional power components. The operation of the capacitor voltage control loop is demonstrated through EMTP simulations of an SSC responding to single phase and three phase load variations in a model distribution system.

The instantaneous power theory based on mapping matrices in three-phase four-wire systems

Abstract: Characteristics of the instantaneous active/reactive powers and zero-sequence current/voltages are analyzed in three-phase four-wire systems. Control strategy for an active filter without energy storage components is proposed on the basis of mapping matrices. It can compensate for the zero-sequence current, irrespectively of whether or not a zero-sequence voltage exists in three-phase four-wire systems.

A novel, robust, harmonic injection method for single-switch, three-phase, discontinuous-conduction-mode boost rectifiers

Abstract: This paper describes a new robust low-cost harmonic-injection method for single-switch three-phase discontinuous-conduction-mode (DCM) boost rectifiers. In the proposed method, a periodic voltage is injected in the control circuit to vary the duty cycle of the rectifier switch within a line cycle so that the fifth-order harmonic of the input current is reduced to meet the IEC555-2 requirement. Since the injected voltage signal, which is proportional to the inverted AC component of the rectified three-phase line-to-line input voltages, is employed, the injected duty-cycle variations are naturally synchronized with the three-phase line-to-neutral input voltages. In addition, the injected harmonic signal naturally contains desirable higher order harmonics, such as sixth, twelfth, eighteenth, etc., which are more effective in improving total harmonic distortions (THDs) than harmonic-injection methods based on the sixth-order harmonic only.

Improved simulation of HVDC converter transformers in electromagnetic transient programs

Abstract: In electromagnetic transient simulation HVDC converter transformers are normally represented as magnetically independent single-phase units. However, three-limb converter transformers are often used in HVDC schemes. Single-phase and three-limb three-phase transformer models are derived using a unified magnetic equivalent circuit concept. The new models are verified with laboratory and field data. Also, a comparison is made between the transient performance of HVDC converters with conventional and proposed transformer models.

Control of unbalanced voltage PWM converter using instantaneous ripple power feedback

Abstract: The voltage unbalance can impair a PWM converter system because the input active and reactive power ripples are generated by the cross products of line currents and unbalanced voltages. In this paper, effects of voltage unbalance in a three phase PWM converter are analyzed and a new control scheme to suppress input power ripple and DC link voltage ripple caused by unbalances is presented. The proposed method is based on the instantaneous power theory to compute compensation currents which cancel the power ripple. The simulation and experimental results are presented to verify the feasibility and effectiveness of the proposed method.

A.c. electrical machine and method of transducing power between two different systems

Abstract: A structure for an a.c. electrical machine and method of transducing power between two different systems. The machine comprises two electrically balanced transformers which are generally, but not exclusively, three phase. Initially the transformers are in balance and no currents flow in the secondary windings of the transformers. An electrical or mechanical imbalance is introduced between the transformers causing current to circulate in the secondary windings. The secondary windings in one embodiment are provided on a rotor in which case the currents induced in the secondary windings cause a torque to be exerted on the rotor. It is also possible to arrange the machine as a transformer or alternator.

Distribution system voltage regulation under fault conditions using static series regulators

Abstract: Power quality and availability are becoming important issues for critical and sensitive loads. Many of the disturbances are caused by faults on the utility distribution system in one or more phases, resulting in voltage dips and sags. This paper presents a viable alternative to UPS solutions to three phase load support in the form of practical series compensator structures. The compensators consist of transformer coupled voltage source inverters fed from a single diode rectifier connected to the faulted AC supply. The balancing and regulating algorithms are developed and applied to partial and total single phase to three phase type of faults. The compensation capability of the proposed schemes are derived. Practical issues, such as design, converter rating and the relative merits of each topology are considered. The paper also provides experimental results for a 2 kVA prototype power conditioner.

A novel three-phase three-switch three-level high power factor SEPIC-type AC-to-DC converter

Abstract: In this paper, the topology of a new three-phase three-switch three-level PWM rectifier system is derived based on the basic structure of a DC-to-DC SEPIC power converter. The system is characterized by full controllability of the power flow (independent of the level of the output voltage) and by a sinusoidal mains current shape in phase with the mains voltage. The operating principle of the power converter is explained based on the conduction states of a bridge leg within a pulse period. The stationary operating behavior is analyzed by digital simulation based on the control of the mains phase currents by independent ramp-comparison controllers. Furthermore, a mathematical description of the operating behavior of the three-phase system including the coupling of the phase current controllers (given due to the floating mains star point) is discussed. Finally, results of an experimental investigation of a laboratory model of the power converter are presented.

Three phase rectifier using three single phase converters and a single DC/DC converter

Abstract: A power converter for converting three phase input power to DC output power and a method of effecting such conversion. The power converter includes: (1) three single phase DC converters, each having outputs, that receive the three phase input power, (2) a DC/DC converter coupled to the outputs of the three single phase DC converters and (3) a converter selection circuit, associated with the three single phase DC converters, that selects a selected subset of the three single phase DC converters as a function of an electrical characteristic of each phase of the three phase input power to conduct a portion of the three phase input power to the DC/DC converter, the converter selection circuit permitting the power converter to operate on the three phase power with less than three DC/DC converters.

The use of three phase bridge inverters with switched reluctance drives

Abstract: Switched reluctance motors are virtually always supplied with unipolar current pulses: this requirement is substantially different from all other AC motor drives, and has led to the development of alternative power electronic converter configurations. It is generally perceived that it is not sensible to operate an SRM from a standard three-phase converter. Such conclusions arise from the assumption that it is not possible to excite one phase at a time when operating from a three-phase bridge. This paper first explores the problems of using three-phase bridge power converters driving standard star and delta machine configurations. It then demonstrates how, with a minor modification, it is possible to operate an SRM with unipolar currents, fed from a conventional three-phase bridge. The new circuit configuration presented permits the use of standard power converters without any significant loss of performance.

Modelling and design of a reversible three-phase switching mode rectifier

Abstract: A reversible three-phase switching mode rectifier consisting of a four-active-switch and without current sensor is proposed. To achieve controllable power factor, clean sinusoidal input current, adjustable DC output voltage, and bidirectional power flow capability, a closed-form pulse width modulation (PWM) duty cycle function is derived. The popularly used state space averaging technique is extended for modelling the reversible three-phase four-active-switch rectifier. The space vector representation technique is then used to simplify the modelling process without sacrificing accuracy and valid frequency range. Both steady-state and small signal analyses are made. Results show that the proposed closed-form control law for the rectifier can indeed achieve the desired property. Moreover, the rectifier also possesses a bidirectional power flow capability, which is useful for many applications. Finally, a prototype hardware circuit was constructed and experimental results are presented for demonstration. Guidelines for determining the LC parameters and the PI controller gains are described briefly in the text.

Determination of induction motor parameters by using neural network based on FEM results

Abstract: A neural network (NN) is introduced for making model-building between design variables and equivalent circuit parameters in designing three phase induction motors. Some equivalent circuit parameters are calculated by finite element method (FEM) at each slip conditions and various design variables. From these results, a self-organized distributed network (SODN) is trained, then combined with per-phase equivalent circuit method. The use of the proposed method is evaluated from the results that a rapid execution time compared with original FEMs in design procedures. This method is useful for nonlinear problems and model-building problems such as parameter determination.

Line voltage sensorless three phase PWM converter by tracking control of operating frequency

Abstract: Much research about a power line voltage sensorless PWM converter has been presented from the view points of the simplicity and the reliability of the control system. Most schemes need some calculations to estimate the power line voltage using circuit parameters. In this paper, we propose a novel control strategy of the three phase PWM converter by tracking control of the operating frequency based on the power balance of the converter. The system is composed of the direct PWM control loop of the instantaneous active and reactive current. The features of the proposed PWM control system are simplicity without sensing the line voltage, high reliability with poor dependence of the circuit parameters, high efficiency and fast response etc.

A three-phase model for surge distribution studies in electrical machines

Abstract: This paper describes a computer model for surge distribution studies in the windings of electrical machines. The computer model takes the coil as the basis for the analysis and uses multiconductor transmission line theory to obtain the transference matrix for the winding. Several practical formulations based on machine design characteristics are used for calculating electrical parameters. Flux penetration into the iron core and mutual coupling between coils in different phase windings are incorporated into the analysis. The model was validated by a comparison of predicted and calculated results in a high voltage motor.

Parallel connection of single-switch three-phase power-factor correction converters for interleaved switching

Abstract: A circuit for the parallel connection of multiple high-frequency three-phase power-factor-correction converters is proposed which enables their input and output current ripple to be interleaved. Such interleaved operation substantially improves the composite power factor, line-current ripple and output-voltage ripple. The improvement is investigated by developing solutions to circuit state equations which allow the high-frequency content of the line current, as well as the low-order line-frequency harmonics, to be computed. Conclusions drawn from the computed results are verified experimentally using a 1 kW, two-stage, interleaved converter.

A novel three-phase sinusoidal PWM voltage source inverter and its application for photovoltaic power generation system

Abstract: In this paper, a novel three-phase sinusoidal PWM voltage source inverter (VSI) is proposed. The inverter has an additional arm to the normal PWM three-phase bridge circuit. The additional arm contributes to reduce the ripple in the AC output current. As an example of the application of this VSI, a utility-connected photovoltaic power generation system is shown. In the system, smooth DC current without pulsation is supplied from a PV array, and the VSI provides sinusoidal AC current for domestic loads and the utility line.

A simple three-phase power factor corrector with improved harmonic distortion

Abstract: The theoretically optimal duty-cycle modulation for the lowest possible input current distortion of a single-switch three-phase power factor corrector is analyzed. A simple control strategy which achieves results which are very close to the theoretical optimum is presented. Furthermore problems that arise when an isolation transformer is introduced are explored and a solution is proposed.

Harmonic current reduction in three-phase bridge-rectifier circuits using controlled current injection

Abstract: This paper describes the further development of the novel current-injection scheme devised by the authors for attenuating line current harmonics in bridge-rectifier circuits. The previous passive filters are replaced by controlled filters connected between the bridge-rectifier output and the star point of the power transformer secondary. These filters are used to inject controlled third harmonic currents into the transformer windings. Variations in bridge working conditions, due to changes in either load or bridge delay angle, lead to corresponding changes in the filter operating conditions if the harmonic attenuation is to remain optimal. The control law for the filters has been derived and the effectiveness of the new method confirmed by both simulation and laboratory tests.

Three phase high power factor converter using phase selection circuit

Abstract: For use in a DC/DC converter fed by a three phase rectifier, an active circuit and method for delivering an inner phase of three phase AC input power provided to the rectifier and a power converter employing the active circuit or the method. The active circuit includes: (1) a phase selection switching circuit, coupled to the rectifier, that selects an inner phase of the three phase AC input power and (2) a switching network, coupled to the phase selection switching circuit, that controls a waveshape of at least the inner phase to the DC/DC converter thereby to reduce harmonics associated with the three phase AC input power.

A multi axis space phasor based current hysteresis controller for PWM inverters

Abstract: In conventional three-phase current hysteresis controllers, the current error along the three phase axes are independently controlled. This will result in random selection of switching vectors causing high inverter switching losses. In this paper, a space phasor based multi axis current hysteresis controller is proposed, in which the current error along the orthogonal axes (jA, jB, jC) are monitored. The current error boundary is a hexagon. The proposed control scheme can be implemented using simple look up tables. The advantages of the proposed current hysteresis controlled PWM scheme, when compared to other multi level current hysteresis controllers, is that only the adjacent vectors close to the motor back EMF space phasor voltage, is only used for the inverter switching, for the entire speed range (optimum PWM switching). In the present scheme, the selection of the inverter voltage vectors for optimum PWM switching is achieved without any computation of the machine voltage space phasor, for the full speed range of the drive system. The proposed scheme is self-adapting, as far as the motor space phasor voltage is concerned, and also maintains the controller simplicity and quick response features of a hysteresis current controller. The scheme is simulated and also experimentally verified.