Showing papers on "Three-phase published in 1998"

Current control techniques for three-phase voltage-source PWM converters: a survey

Abstract: The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

A new control approach to three-phase active filter for harmonics and reactive power compensation

Abstract: This paper deals with a new control scheme for a parallel 3-phase active filter to eliminate harmonics and to compensate the reactive power of the nonlinear loads. A 3-phase voltage source inverter bridge with a DC bus capacitor is used as an active filter (AF). A hysteresis based carrierless PWM current control is employed to derive the switching signals to the AF. Source reference currents are derived using load currents, DC bus voltage and source voltage. The command currents of the AF are derived using source reference and load currents. A 3-phase diode rectifier with capacitive loading is employed as the nonlinear load. The AF is found effective to meet IEEE-519 standard recommendations on the harmonics level.

Statcom controls for operation with unbalanced voltages

Abstract: Voltage sourced static VAr compensators such as the Statcom need to be able to handle unbalanced voltages. Mild imbalance can be caused by unbalanced loads while severe short-term imbalance can be caused by power system faults. A synchronous frame voltage regulator is presented that works even when three phase symmetry is lost. This regulator addresses voltage imbalance by using separate regulation loops for the positive and negative sequence components of the voltage. The proposed regulator allows the Statcom to ride through severe transient imbalance without disconnecting from the power system and, further, to assist in rebalancing voltages. The regulator maintains sufficient bandwidth to perform flicker compensation. The controller's performance is simulated for a Statcom in a model distribution system where it is subjected to a severe single line to ground fault and a rapidly varying three phase load.

Lyapunov-based control for three-phase PWM AC/DC voltage-source converters

Abstract: The three-phase pulsewidth modulation (PWM) AC/DC voltage-source converter with the control laws proposed so far is not only unstable against large-signal disturbances, but also has the problem that its stability depends on the circuit parameters such as the DC-output capacitance. This paper describes a new control law based on Lyapunov's stability theory. It is shown that the converter can be stabilized globally for handling large-signal disturbances. The resulting closed-loop system not only guarantees a sufficient stability region (independent of the circuit parameters) in the state space, but also exhibits good transient response both in the rectifying and regenerating modes. Also, a new simulation technique is introduced which increases the speed of the simulation process considerably. Computer simulations are presented to confirm the effectiveness of the proposed control strategy and the validity of the simulation technique. Experimental results are also presented to verify the theoretical and simulation studies.

DC bus voltage balancing and control in multilevel inverters

Abstract: A multilevel inverter system having four or more levels of output voltage on each inverter output line. The voltage across each of three or more series connected DC bus capacitors is provided to an inverter which is formed to have redundant switching states, such as a plurality of controlled switching devices and diodes connected in a diode-clamped multilevel inverter configuration. The switching of the switching devices is controlled to provide a selected output voltage waveform utilizing redundant switching states, when such states are available on each voltage transition, by selecting a one of the available switching states that serves to provide the desired phase-to-phase voltages and to tend to equalize the voltages across the DC bus capacitors. Active or passive rectifiers may be used to provide the DC voltage across the DC bus lines and across the DC bus capacitors. Separate rectifiers may be provided for each capacitor which are supplied from secondaries of transformers connected to the three phase input lines to provide isolation and voltage level adjustment. The multilevel inverter system provides output voltage waveforms with lower total harmonic distortion that conventional two or three level inverters, while maintaining voltage balance across the several DC bus capacitors.

Design and performance of active power filters

Abstract: This article has demonstrated the feasibility of a three phase active filter based on a half-bridge topology. Design guidelines for the power circuit have been derived and applied to a 5 kVA IGBT laboratory prototype. In the single phase mode, the active filter can reduce the low frequency harmonic content in the AC line to below 1% excluding the harmonics due to switching action of the converter. In the three phase mode, line currents are corrected under balanced and unbalanced conditions. The neutral current is reduced significantly.

Harmonic cancellation by mixing nonlinear single-phase and three-phase loads

Abstract: The voltage on the distribution line is, in most cases, distorted even at no load of the transformer. This is due to the "background" distortion on the medium-voltage line caused by the large number of single-phase nonlinear loads, such as PCs, TVs, VCRs, etc. This paper proposes a method to mix single-phase and three-phase nonlinear loads and reduce the harmonic currents significantly. The dependence of the phase angle of the harmonic currents as a function of the short-circuit impedance is investigated using SABER for the three-phase and the single-phase diode rectifier both with and without DC-link inductance. The phase angle of the fifth harmonic current of a three-phase diode rectifier is always in counterphase with the fifth harmonic current of a single-phase diode rectifier. This leads to the conclusion that adding three-phase rectifier load can actually improve the power quality at the transformer. This is also validated by a number of on-site measurements in several applications of three-phase adjustable-speed drives.

Harmonic impedance measurement using three-phase transients

Abstract: In this paper, a technique is presented for measuring the harmonic impedances of an unbalanced three-phase distribution feeder. The technique uses transients in bus voltages and feeder currents generated by several close-trip operations of the shunt capacitor bank. The work is based on the assumption that the impedance of the feeder does not change over time during which the switching operations are performed. Mathematical development of the technique is verified with the laboratory and the field tests. The technique provided good measurements of the harmonic impedances up to 1.5 kHz for the given capacitor sizes. Statistical indices were developed to assess the accuracy of the estimated impedance values.

Variable frequency drive noise attenuation circuit

Abstract: A noise attenuation circuit is used in a motor drive system. The motor drive system includes a variable frequency drive having a pulse width modulated inverter converting DC power from a DC bus to three-phase power output on three-phase conductors for driving a motor. The noise attenuation circuit comprises a common-mode transformer including a common mode choke having a core, with first, second and third choke windings on the core, each connected in series with one of the three phase conductors, and a fourth winding on the core. A three-phase iron core transformer creates a neutral point representing common mode voltage. The iron core transformer has three primary windings connected in a "wye" configuration to the three phase conductors. The fourth winding has a start connected to the neutral point and an end operatively connected to the DC bus to force a current, dependent on the voltage of the neutral point relative to the DC bus, in the fourth winding of the common mode transformer in an opposite direction to cancel main common mode current.

Optimal current programming in three-phase high-power-factor rectifier based on two boost converters

Abstract: Current programming in a three-phase high-power-factor rectifier based on two boost converters is discussed in this paper. It is shown that the converter currents can be expressed in terms of two mutually related auxiliary functions. The auxiliary functions are related to the input current spectrum. Optimal auxiliary functions that eliminate harmonics of the input currents are derived. A method to generate reference signals for the optimal current programming is proposed. Experimental results confirming the proposed concepts are presented.

New single-switch three-phase high-power-factor rectifiers using multiresonant zero-current switching

Abstract: A new family of single-switch three-phase high-power-factor rectifiers, which have continuous input and output currents, is introduced. By using a multiresonant scheme, the transistor operates with zero-current switching (ZCS), and the diodes operate with zero-voltage switching (ZVS). These multiresonant rectifiers with a single transistor are capable of drawing a higher quality input-current waveform at nearly unity power factor and lower stresses than quasi-resonant rectifiers. Buck-type converters are used for the power stage, and, hence, the output voltage is lower than the input voltage. Moreover, these rectifiers have a wide load range and low stresses on semiconductor devices. From the analysis, normalized characteristics of the rectifier are derived. The design and breadboard implementation of the rectifier delivering 147 V/sub dc/ at 6 kW from a 3/spl phi/ 240-V/sub rms(LL)/ input is described. The total harmonic distortion (THD) of the line current is less than 5%, and the system efficiency is about 94% at the full load.

Two-stage, three phase boost converter with reduced total harmonic distortion

Abstract: For use with a three-phase split boost converter having a primary stage with a primary rectifier and first and second primary boost switches coupled between an input and first and second outputs of the three-phase split boost converter, an auxiliary stage interposed between the input and the first and second outputs, a method of reducing input current total harmonic distortion (THD) and a converter incorporating the auxiliary stage or the method. In one embodiment, the auxiliary stage includes: (1) first, second and third auxiliary boost inductors coupled to corresponding phases of the input and (2) an auxiliary boost network interposed between the first, second and third auxiliary boost inductors and the first and second outputs and including (2a) an auxiliary three phase full-wave rectifier, (2b) first and second auxiliary boost diodes, and (2c) first and second auxiliary boost switches, coupled between the auxiliary three phase full-wave rectifier and the first and second auxiliary boost diodes, that cooperate to conduct currents through the first, second and third auxiliary boost inductors to reduce input current total harmonic distortion (THD) at the input of the three-phase split boost converter.

Analysis and design of a three-phase LCC-type resonant converter

Abstract: A three-phase dc-to-dc LCC-type resonant converter with high-frequency transformer isolation is proposed. The operation and a simple analysis of the converter are presented. Design curves are obtained and a design example is given. SPICE simulation and experimental results are presented to verify the performance of the proposed converter for varying load conditions. The converter proposed has several advantages, e.g., operation in lagging PF mode for the entire load range, requires a narrow variation required in switching frequency, reduced component size and stresses, etc.

Eliminating output distortion in four-switch inverters with three-phase loads

Abstract: A new space vector switching strategy for four-switch inverters driving three-phase induction motors is described. The technique allows a full range of operation, compensating for both DC link ripple and imbalance to eliminate torque and speed pulsations under all operating conditions, while allowing the largest possible voltages to be produced. The paper presents theoretical expectations and compares these with measured values obtained from an inverter operating off a single phase AC supply corresponding to worst case conditions.

A comparative study of single-switch, three-phase, high-power-factor rectifiers

Abstract: Three three-phase, single-switch, high-power-factor rectifier implementations were evaluated on a comparative basis. Specifically, the discontinuous-conduction-mode boost rectifier with a 5/sup th/-harmonic-trap filter, the discontinuous-conduction-mode boost rectifier with a harmonic-injection circuit, and the multi-resonant, zero-current-switching buck rectifier were compared with respect to their efficiencies, compliance with the IEC555-2 specifications, volumes, weights, and costs. The comparisons were done for the three-phase, line-to-line input voltage of 380 V/sub rms//spl plusmn/20% and for 0-6 kW output-power range.

A comparative study of single-switch three-phase high-power-factor rectifiers

Abstract: Three three-phase single-switch high-power-factor rectifier implementations were evaluated on a comparative basis. Specifically, the discontinuous-conduction-mode (DCM) boost rectifier with a 5th-harmonic-trap filter, the DCM boost rectifier with a harmonic-injection circuit, and the multiresonant, zero-current-switching buck rectifier were compared with respect to their efficiencies, compliance with the IEC555-2 specifications, volumes, weights and costs. The comparisons were done for the three-phase line-to-line input voltage of 380 V/sub rms//spl plusmn/20% and for 0-6 kW output power range.

Implementation of three-phase power factor correction circuit with less power switches and current sensors

Abstract: A three-phase ac to dc converter employing a new control scheme is presented. Only four power switches and two current sensors are required in this system. By using the proposed control scheme, just two of the switches are active to approach the desired waveform at any timer, hence the switching numbers can be reduced, compared with the conventional six switches converter. Furthermore, the local average method is presented to verify that the instantaneous power between ac source and dc source is balanced. Finally, simulated and experimental results are presented to verify the characteristics of unity power factor, sinusoidal input current, and bidirectional power flow capability.

A novel and simple current controller for three-phase PWM power inverters

Abstract: A new feedback current controller for three-phase pulsewidth modulation (PWM) power inverters is presented. To achieve robustness, fast dynamical response, reduced switching frequency, and simple hardware implementation, an improved three-level hysteresis sliding-mode controller is used. All voltage vectors are accurately selected in order to minimize the current error.

Single phase to three phase converter

Abstract: A converter for providing three phase power to a three phase load from a single phase supply includes an inverter connected to single phase input power lines and a bi-directional switch connected in series with one of the input power lines. The converter has three output lines, one connected to the inverter output, another connected to an input power line between the bi-directional switch and the inverter, and the third connected directly to the other input power line. The inverter switching devices are controlled to provide a signal on the output of the inverter to provide balanced three phase power on the converter output lines. This is preferably accomplished by pulse width modulation of an inverter output voltage reference signal derived by phase shifting the single phase input voltage signal by 60°. The inverter is preferably also controlled to phase shift the inverter output signal when necessary to ensure that the net power flow into the inverter is zero under light load conditions. During load start-up, the bi-directional switch is phase controlled to adjust the amplitude of the converter output current to thereby adjust the load current to limit inrush current levels and provide a soft starter by ramping up the current in the load.

Single channel apparatus for on-line monitoring of three-phase AC motor stator electrical faults

Abstract: An on-line monitor for electrical faults in the stator of an ac motor has a single di/dt current transformer or three separate di/dt current transformers coupled to the three phase conductors of the ac supply. The windings of the transformer, or transformers, are selected to generate a single sensed signal containing a linear combination of components of current in the three phase conductors weighted relatively so that algebraic differences between components from any two phase conductors is non-zero, such as preferably 2A+B-C or 3A+2B+C. The single sensed current signal is bandpass filtered to generate a pulse signal which is applied to an analyzer. The analyzer, preferably implemented by a microcontroller, generates an output based upon a combination of the amplitude and frequency of occurrence of the current pulse signal including a time attenuated accumulation of the pulses. A similar pulse signal is generated from a single sensed voltage signal and compared to the pulse signal generated from the current sensor to verify that the detected events originate in the motor and not from upstream in the ac supply. The monitor is coupled to the phase conductors between the local disconnect switch and the motor, and preferably, is mounted in the disconnect housing.

Improved three-phase load flow using phase and sequence components

Abstract: The single-phase load flow is efficiently optimised for the rapid solution of power flow and voltages in large systems. The three-phase load flow, at present treated simply as an extension of the single-phase load flow, is primarily used to calculate asymmetry at fundamental frequency throughout the transmission system. A new three-phase load flow, radically different from the single-phase load flow, is proposed. The new load flow is more suited to the analysis of power quality problems in the transmission system. A mixed combination of sequence and phase component mismatches is used, with emphasis on robust convergence rather than speed. It is shown that the three-phase load flow will find one of two solutions at each load busbar, one of which corresponds to abnormal levels of zero sequence voltage. The abnormal solution can be avoided by ensuring a path for zero-sequence current from the load.

The circulating current in paralleled three-phase boost PFC rectifiers

Abstract: This paper presents modeling, simulation, and experimental results of paralleled three-phase boost PFC rectifiers. The first part of the paper describes the overall system set-up and control schemes of the PFCs. Although individual modules work as expected, a low frequency oscillation between the paralleled units was observed. Because the conventional model of the three-phase rectifier cannot predict this kind of interaction, an average model is developed for system simulation. From this model, it is shown that the interleaved discontinuous space vector modulation produces a periodic disturbance on the zero axis. Because the conventional control in a balanced three-phase system with only dq channels cannot reject this disturbance, a circulating current will flow between the paralleled modules. Based on this observation, a space vector modulation with control in the third axis is proposed for the parallel operation of the rectifiers. Simulations are done to show the feasibility of this scheme.

New medium voltage PWM inverter topologies for adjustable speed AC motor drive systems

Abstract: In this paper new PWM voltage source inverter topologies suitable for adjustable speed operation of medium voltage (690 V, 2300 V, 3300 V, 4160 V) induction motor drives are introduced. The new inverter topologies are derived from an optimum combination of several three phase and single phase PWM inverter modules. These modules employ low voltage high current IGBT devices and can be viewed as power electronic building blocks (PEBBs). The proposed medium voltage inverters exhibit high quality PWM output with low dv/dt, modular construction with built-in redundancy, lower DC-link capacitive energy storage compared to other structures and are flexible for different medium voltage ASD applications. A method to eliminate bulky input transformers is shown. Issues of input current quality are also addressed. Simulation results are presented to validate the concepts.

A new space-vector-modulated control for a unidirectional three-phase switch-mode rectifier

Abstract: A unidirectional three-phase switch-mode rectifier that delivers sinusoidal input currents in phase with the corresponding input phase voltages is proposed and analyzed in this paper. In the proposed topology, three AC switches are placed before the bridge rectifier and, respectively, across two power lines. A simple control scheme combing space-vector modulation and hysteresis current control is presented. Sinusoidal input line currents are observed in experimental results.

Controller for ac motor

Abstract: There is provided a controlling device for an AC motor having a structure in which a current of a three phase brushless DC motor is detected and then converted to a rotor coordinate system, to separately control a torque split current (q axis) and an exciting split current (d axis), wherein an offset is estimated with a DC component of a multiplied value of the values corresponding to a d axis voltage command which is an output of an exciting split current controller and an electrical angle, and the detected current is compensated for, so that an offset of a current detector may be estimated and compensated for during its operation without stopping its rotation and the motor can rotate smoothly without a torque ripple, even in the case in which the current detector has an offset error or in the case in which an offset changes due to a temperature drift.

Control of a complete digital-based component-minimized single-phase to three-phase AC/DC/AC converter

Abstract: This paper proposes a new control strategy for a complete digital-based component minimized single- to three-phase AC/DC/AC power converter where it is possible by proper control to reduce the capacitor size in the DC-link. The power converter offers four quadrant operation including unity power factor and it uses only six transistors and six diodes. Control is done completely digitally with a high bandwidth input current controller and a lower bandwidth DC-link voltage controller. The modulation of the inverter compensates for the voltage variation in the DC-link. The proposed methods are validated through simulation and experimental work. It is concluded that the capacitor-size can be reduced significantly in a B4-inverter by the control method but a load dependent sub-harmonic current is injected into the grid.

How to include the dependency of the R/sub DS(on/) of power MOSFETs on the instantaneous value of the drain current into the calculation of the conduction losses of high-frequency three-phase PWM inverters

Abstract: In this paper, the conduction losses of power MOSFETs are calculated analytically for application in three-phase voltage DC-link pulsewidth modulation (PWM) power converter systems. Contrary to a conventional calculation, the dependency of the turn-on behavior on the drain current is considered in terms of a quadratic approximation. The derived relationships are represented graphically; they can be included directly into the dimensioning of the power transistors.

Symmetrical space vector PWM DC-AC converter controller

Abstract: A control apparatus for controlling a three phase load apparatus. The control apparatus includes a voltage source inverter having a first pair of transistors, a second pair of transistors, and a third pair of transistors. Each such pair of transistors is connected serially between the terminals of a voltage source. The activation of a first transistor in each such pair of such transistors is effected by the application thereto of a first activation voltage, a second activation voltage and a third activation voltage, respectively, causing a first phase voltage, a second phase voltage and a third phase voltage, to be applied to a respective one of the three parts of the three-phase load apparatus. The selection and duration of activation of such first transistors during each of a continuing series of equal time periods T p is symmetrical about the mid-point of each of the time periods, and is represented by six non-zero vectors and two zero vectors. The control apparatus also includes a processor, and a bus coupled to the processor for communicating data between the processor and other control apparatus elements. The control apparatus also includes a counter coupled to the bus for providing a counter value counting from zero up to a value of one half of T p and then counting down to zero, for each of the equal time periods T p . A compare unit is also included, coupled to the bus, having a plurality of registers for the storage of transition count values corresponding to the transition times between the activations of the first transistors in accordance with predetermined space vectors, for comparing the counter value against the transition count values and providing respective transition timing signals when the counter value is the same as the transition count values. Finally, a state machine is included, coupled to the bus and to the compare unit for generating the first activation voltage, the second activation voltage and the third activation voltage and providing them to the voltage source inverter in response to the respective transition timing signals.

Battery charger apparatus

Abstract: A battery charger which supplies charging current for a high voltage, high current battery in accordance with a charge profile which preferably includes both a charge pulse sequence as well as a discharge pulse sequence. Charging power is obtained from a three phase power line the voltage of which is reduced by an isolation transformer. Conversion of ac to dc is accomplished by a switching transistor power converter having a control for supplying transistor switching signals. The control is responsive to the angle of line voltage, the actual line current and a reference signal indicative of desired charge current, to generate the transistor switching signals. Any deviation between actual and desired current is then corrected by modification of the transistor switching signals.