Showing papers on "Three-phase published in 1992"

Active filtering of harmonic currents in three-phase, four-wire systems with three-phase and single-phase nonlinear loads

Abstract: A novel active harmonic-neutralizing filter is proposed which eliminates current harmonic effects, caused by any configuration of nonlinear loads in a three-phase, four-wire systems. The authors present proposed filter topologies and simulation results verifying the concept. Theoretical analysis of the circuit is included to facilitate a detailed converter design. The proposed topology is shown to have distinct advantages over traditional approaches to the problem, particularly over the three single-phase inverter approach. >

Analysis and design of a series voltage unbalance compensator based on a three-phase VSI operating with unbalanced switching functions

Abstract: Voltage unbalance in AC supply systems is typically corrected by means of a shunt connected thyristor-controlled static VAr compensator. This approach has the disadvantage of slow response, harmonic injection into the AC system, and the requirement for large passive components. The proposed system consists of a three-phase PWM voltage source inverter, connected in series with the line through a three-phase transformer. The unbalance compensation is achieved by canceling the negative sequence component of the line-to-line voltages of the source. It is also shown that by having the inverter operate with unbalanced switching functions, it is possible to balance the load voltage and to control the amplitude of the positive sequence component in order to perform load voltage regulation. A complete mathematical description of the method is presented, demonstrating that the compensation can be achieved with low kVA inverters and low harmonic injection. Implementation procedures, design equations, and a design example are also included in order to illustrate the proposed method. Experimental results of a 1.5 kVA laboratory prototype system confirm the feasibility of the technique. >

A single transistor three phase resonant switch for high quality rectification

Abstract: Three new classes of low-cost 3 phi AC-DC high-power-factor/low-harmonic controlled rectifiers are derived from parent DC-DC power converter topologies containing boost-type inputs, buck-type inputs, and quasi-resonant zero-current-switch (ZCS) buck-type inputs. With a single active switch in addition to the diode bridge rectifier, the converters are capable of drawing a high-quality input-current waveform naturally at nearly unity power factor. Thus a simple 3 phi AC-DC high power factor rectifier is obtained. Simulation and experimental results are supplied to demonstrate the validity of the concept. >

Third-harmonic modulated power electronics interface with three-phase utility to provide a regulated DC output and to minimize line-current harmonics

Abstract: A novel approach to achieving nearly sinusoidal line current rectification of three-phase utility voltages is presented. The scheme incorporates two step-up DC-DC power converters to modulate the DC link currents at the third harmonic frequency. The modulated currents are then reinjected on the AC side of the diode bridge rectifier. Simulation results for a three-phase, 208 V (line-to-line), 3 kW system are presented. The sensitivity of the interface to unbalances in various system parameters is included. Results from experimental investigations on a small-scale laboratory model are presented. >

A three-phase active power filter operating with fixed switching frequency for reactive power and current harmonic compensation

Abstract: The performance and dynamic characteristics of a three-phase active power filter operating with fixed switching frequency are presented and analysed. The proposed scheme employs a pulse width modulation voltage source inverter and has two important characteristics. First, it operates with fixed switching frequency, and, second, it can compensate the reactive power and the current harmonic components of nonlinear loads. Reactive power compensation is achieved without sensing the computing the reactive component of the load current, thus simplifying the control system. Current harmonic compensation is done in the time domain. The principles of operation of the proposed active power filter along with the design criteria of the power and control circuit components are discussed in detail. Experimental results obtained from a 5 kVA prototype confirm the feasibility and the features of the proposed system. >

Analysis of a new power electronics interface with approximately sinusoidal 3-phase utility currents and a regulated DC output

Abstract: A three phase rectification scheme that draws line currents with reduced distortion and provides a regulated DC output voltage is analyzed. The scheme employs two boost DC-DC converters to modulate the DC link currents. The modulation current is injected into the AC side through an impedance network consisting of series tuned L-C branches. The theoretical analysis and the basic simulation results, which can be used to carry out the design of a system based on this approach, are presented. >

Direct field orientation controller using the stator phase voltage third harmonic

Abstract: This paper presents the development and implementation of a direct field orientation controller (DFOC) for induction machines based on determination of the spatial position of the air gap flux from the third harmonic component of the stator phase voltages. The control utilizes spatial saturation harmonic components rotating at synchronous frequency that are generated in the air gap flux when the machine operates in a saturated condition. When the machine is wye connected, the sum of the three phase voltages results in a signal dominated by the third harmonic and a high frequency component due to the rotor slot ripple. It is shown that the third harmonic voltage component can be effectively used to estimate both amplitude and position of the air gap flux. Two methods for estimation of the air gap flux from the third harmonic voltage are discussed in the paper. A complete induction motor direct field orientation control is designed and implemented in the laboratory. Extensive experimental results showing the DFOC drive system performance are presented and discussed. >

Performance analysis of three-phase inverters controlled by synchronous delta-modulation systems

Abstract: Synchronous delta-modulation systems are used to control resonant voltage link inverters, where switching has to be synchronized with the zero crossings of the link voltage. This paper shows that output current harmonic distortion and average switching frequency of such systems can be calculated analytically in spite of the quasistochastic behavior of the modulators output. Under the assumption of constant link frequency and large ratio of link to output frequency, results are derived for three-phase sigma-delta modulation, space-vector based sigma-delta modulation, and current-regulated delta modulation. The results hold for any shape of the inverter input voltage (including DC). The output current harmonic distortion of resonant link inverters is compared with conventional hard switching PWM inverters. >

Three-phase active filter utilizing rotating axis transformation

Abstract: A three-phase active filter for connection into a three-phase power distribution system to compensate undesirable harmonic deviations. A converter is electrically connected between the power distribution system and a DC energy storage element. The converter is selectively controlled by control means to effectuate a flow of energy between the system and the storage element to offset the harmonic deviations. To improve the dynamic response of the filter, the control means utilize vector control principles. Specifically, a synchronous fundamental vector of AC energy waveforms in the power distribution system is derived in a rotating reference frame. Fundamental reference signals are then produced in a stationary reference frame which are compared with corresponding actual condition signals. Error signals thus produced are then utilized to operate the converter. To compensate losses in the storage element and inverter, the control means preferably further comprise loss compensation means also utilizing vector control principles.

Current detection method for DC to three-phase converters using a single DC sensor

Abstract: A current detection method for a direct-current (DC) to three-phase alternating-current (AC) converter can utilize only a single DC sensor to detect and calculate the three-phase alternating currents. The method can detect a direct current value of one phase at each of six different gate states of three pairs of transistors in the DC to three-phase AC converter by means of the DC sensor. In the two-level pulsewidth modulation control, the control signal includes a plurality of carrier periods each being subdivided into three intervals. The three pairs of transistors are switched to the zero state in one interval of each carrier period, and to two different gate states respectively in the two other intervals. The method can detect two current values of different phases respectively in the two other intervals of each carrier period, and then calculate the current value of the other phase in accordance with the principle that the sum of the three-phase currents is always equal to zero.

Minimization of torque ripple in permanent magnet motors: a closed form solution

Abstract: A closed-form solution for minimizing torque pulsations or ripple in three-phase permanent magnet motors by the appropriate weighting of input current harmonics is presented. First, an analysis of torque ripple is presented by using the complex exponential Fourier series. In addition, a method to design the optimal weighting of current harmonics is developed by using constrained optimization techniques. In contrast to iterative approaches, the proposed design method determines the current harmonic weights in closed form; the procedure is especially easy to perform. Steps in the design procedure are demonstrated by a numerical example. Application of the optimal current should reduce torque-induced motor vibration and noise, as well as improve accuracy in servo applications. >

Calculation of harmonic currents in a three-phase convertor with unbalanced power supply conditions

Abstract: The paper proposes a practical new method for calculating the harmonic currents of a three-phase bridge controlled rectifier under unbalanced supply conditions. Analytical equations for the harmonic currents are derived, taking into account the effects of DC current ripple and overlap angle. The proposed method is based on the frequency domain method and the rectifier switching functions. All the calculations are conducted only by algebraic calculations, and the accuracy is within 1.1% and 2.6% for the DC and AC side harmonics, respectively. The validity of the proposed method is demonstrated by comparison with the results of digital simulation.

Analysis and implementation of a grey-noise PWM technique based on voltage space vectors

Abstract: The grey noise pulse width modulation (GNPWM) technique for three-phase, voltage-controlled inverters is described. It is shown that the GNPWM combines the best features of the deterministic space-vector PWM and the random PWM techniques. The GNPWM technique is characterized by: the highest DC/AC voltage conversion; high-quality output current at a low switching frequency of the inverter; varying switching patterns and spread, grey-noise, harmonic spectra of the output voltage and current, beneficial for the noise/vibration characteristics of a drive system supplied from the inverter; and simplicity of the hardware implementation using an integrated microcontroller system. Theoretical background, simulations, and experimental results are presented. >

PWM control and input characteristics of three-phase multi-level AC/DC converter

Abstract: The authors discuss the current control and pulse width modulation (PWM) pattern generation of a multilevel power converter which is capable of producing three levels of phase voltage. In the proposed current control, fast response is realized by introducing a converter model in the control algorithm and the effect of parameter difference between the model and an actual system is compensated for through proportional-plus-integral control of current difference. In PWM pattern generation, the balance of two capacitor voltages is taken into account. For the same sampling period, the current distortion factor of the proposed system can be approximately reduced to 60% of that of a conventional two-level power converter. The prototype was made using a digital signal processor, and simulation and experimental results were compared. >

Analysis and design of a series voltage compensator for three-phase unbalanced sources

Abstract: Voltage unbalance typically present in three-phase AC supply systems adversely affects power system components, static converters, drive systems, electric machines, etc., connected to the system. A method to eliminate this unbalance by means of a voltage compensator connected in series with the supply through transformers is described. The technique is based on extracting the negative sequence voltage component of the supply and canceling it in order to obtain balanced voltages. The positive sequence component is then adjusted to achieve voltage regulation. It is shown that the compensation can be achieved with low kilovolt-ampere inverters and that harmonic injection is reduced to a minimum. The authors include implementation principles, design equations, and a design example. Simulated and experimental results confirm the theoretical concept and feasibility of the proposed system. >

Minimisation of unbalanced and reactive currents in three-phase asymmetrical circuits with nonsinusoidal voltage

Abstract: Asymmetry of three-phase loads causes deterioration in the power factor and power quality of a circuit. Waveform distortion aggravates these unfavourable effects even more. A method of improving the power factor and the loading symmetry in a three-phase unbalanced circuit under nonsinusoidal conditions is presented. The method discussed is based on the source current orthogonal decomposition into the active, scattered, unbalanced, and reactive components, developed for three-phase asymmetrical systems. The author shows that this current decomposition provides the fundamentals for the design of passive compensators which can effectively reduce the unbalanced and reactive components of the source current under nonsinusoidal conditions. >

Real-time multi-DSP control of three-phase current-source unity power factor PWM rectifier

Abstract: The design of a real-time multi-DSP controller for a high-quality, six-valve, three-phase, current-source, unity power factor, PWM rectifier is discussed. With the decoupler preprocessor and the dynamic trilogic PWM trigger scheme, each of the three input currents can be controlled independently. Based on the a-b-c frame system control and the fast parallel computer control, the pole placement control method is implemented successfully to achieve fast response in the AC currents. The low frequency resonance in the AC filter LC networks has been damped effectively. The experimental results are obtained from a 1 kVA bipolar transistor current-source PWM rectifier with a real-time controller using three TMS320C25 DSPs. >

Fast estimation of symmetrical components in real time

Abstract: Methods for online calculation of the phasors of symmetrical components from the complex space-phasor in three phase power systems are presented. In this way the number of numerical operations can be cut by one third. The methods combine the suppression of higher frequencies and the separation of symmetrical components. Transfer functions obtained from the developed filter algorithms for the complex input and output signals are investigated and compared. The proposed approach with a variable sampling window enables a faster estimation of the desired components under transient conditions compared to the method using a constant sampling window.< >

A brushless self-exciting three-phase synchronous generator utilizing the 5th-space harmonic component of magneto motive force through armature currents

Abstract: A novel brushless self-exciting three-phase synchronous generator is proposed. It consists of three-phase armature windings on the stator, one field winding and one exciting winding with five times as many poles as that of the armature winding on the rotor, and a three-phase reactor connected to the terminal of the armature windings. By utilizing the 5th-space harmonic component of armature electromotive force, small voltage regulation for various loads and no oscillatory tension occurring at the rotor shaft were realized. The basic constitution, principle of operations, and exciting characteristics are described. The experimental results obtained from using a trial generator demonstrated its practical usefulness. >

A simple and self-adapting high-performance current control scheme for three phase voltage source inverters

Abstract: An adaptive optimized regulator (AOR) for three-phase voltage source inverters is presented. The zero-voltage vectors are used systematically to reduce the switching frequency and can be reached by switching only one inverter leg. In the steady stage the controller applies to the machine only those three voltage vectors which are directly adjacent to the machine voltage (similar to pulse width modulation). Adaptive identification of position and amplitude of the determining machine voltage vector is realized by multilevel hysteresis comparators and a switching table. The dynamic performance is as excellent as for the three-phase bang-bang controller, and the hardware implementation is very simple. >

Finite-element simulation of a generator on load during and after a three-phase fault

Abstract: A two-dimensional, time-stepped, finite-element technique for the simulation of the electrical and mechanical transient response of a turbine generator to system faults is presented. The stator winding is modeled directly in phase bands, rather than as an equivalent sinusoidal distribution, and rotor torque is calculated by the Maxwell stress tensor method. The method is validated by a comparison of calculated results with test data for the case of a sudden three-phase short-circuit applied to a generator operating at full load, followed by fault clearance and reconnection to the power system. >

Finite element computation of eddy current losses in nonlinear ferromagnetic sheaths of three-phase power cables

Abstract: A novel method for the finite element computation of the losses in a three-phase power cable is presented. The phase conductors carry sinusoidal, steady-state, and balanced currents, and the sheath is made of a nonlinear ferromagnetic material. A concept for an effective equivalent magnetic permeability is introduced that allows calculations in the complex domain. Sheath losses are presented and discussed for a symmetrical configuration. >

Active power line conditioner with a derived load current fundamental signal for fast dynamic response

Abstract: An improved active power line conditioner with fast dynamic response is disclosed. The active power line conditioner includes a series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a three phase load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. The load current fundamental signal is derived and is multiplied by a derived voltage output/input ratio to render a current reference product. The current reference product may be further modified by a user-set displacement power factor correction ratio. The current reference product is applied to the series inverter for fast dynamic response within the active power line conditioner.

A unity power factor current-regulated SPWM rectifier with a notch feedback for stabilization and active filtering

Abstract: A stand-alone, unity power factor, current-regulated sinusoidal pulsewidth modulated (SPWM) rectifier is described. The topology is based on the series connection of three four-valve single-phase bridges, which allows the conventional two-stage logic SPWM strategy to be used without interphase interference. The problems of stability and low harmonic waveform distortion are identified. Solutions are found by using a simple local notch filter feedback circuit that fulfils the dual function of stabilizing and active filtering. From the clarification given by this more expensive but less constrained topology, the stage is set for the next step in incorporating the lessons learned to the more economical topology based on the six-valve, three phase parallel bridge, which requires a tristate logic for PWM control when operating in the current-source configuration. >

Delta connected three phase AC-DC converter with power factor correction circuits

Abstract: A three phase power conditioner. The inventive power conditioner (10) converts an alternating current input signal from a three phase source (12) into a direct current output signal and includes a first circuit (20) for converting a first phase of the input signal into a first direct current output signal. A second circuit (22) is included for converting a second phase of the input signal into a second direct current output signal. Likewise, a third circuit (24) converts a third phase of the input signal into a third direct current output signal. A control circuit (30) regulates the power supplied by the first, second and third circuits to balance the loads (26) for all load values dynamically. In an illustrative implementation, the first, second and third circuits (20, 22, and 24) are implemented with boost converters and the controller (30) is implemented with a load share controller. The inventive power conditioner is adapted for use with Wye and Delta configured three phase power sources.

Mains-isolated three=phase asynchronous rotary electrical machine speed monitor e.g. for door - has two=channel processing circuits for delivering bit signals to coupling circuit, which generates output signal when speed is above or below limits, if bit signal changes from rest to active within time window

Abstract: The monitor detects machine speed above or below a given limit value and uses a dual-channel evaluation circuit (11) coupled to the three machine winding phases (5,6,7). Each channel (12,13) of the evaluated circuit has two inputs (15,16;21,22) coupled to two different phases and a single digital output (17,23) providing a binary signal. The two binary signals are combined to provide an output signal which changes from a rest value to an active value when the limit value is exceeded. Pref. each channel of the evaluation circuit contains a voltage amplifier with a variable amplification and a precision rectifier. USE/ADVANTAGE - For asynchronous motor drive indicating abnormal speed to prevent overloading, without noise problems and without structural interference in or at machine.

Apparatus and three phase induction motor starting and stopping control method

Abstract: The invention refers to an apparatus and starting and stopping control method of three phase induction motors and consists of carrying out the striking of the static switches simultaneously two by two, establishing a synchronization with a determined point of the compound voltage wave corresponding to the phases that are struck, cyclically repeating in the three phases, determining the operating condition in discontinuous conduction, with instants without current in any phase. The apparatus basically comprises some voltage transducers connected between the input and output terminals of the static switches placed in each phase. At least in one of the phases there is a passing by zero detector connected, a striking control device, an electromotive power detector and an intensity transducer connected to the corresponding converter.

Predicting the level of airgap eccentricity in operating three-phase induction motors, by Park's vector approach

Abstract: The authors report on a study carried out to predict the level of airgap static eccentricity in operating three-phase induction motors by Park's vector approach. Two kinds of normalized severity factor are introduced, their values being calculated by means of postprocessing computational algorithms of the stator current Park's vector data. Experimental results demonstrate that strong eccentricity levels are easily predicted for different load values, either with a delta or a wye connection of machine stator windings. >

A study of single-phase to three-phase cycloconverters using PSPICE

Abstract: A single-phase-to-three-phase cycloconverter system operating from a 50 Hz input has been simulated under various loading conditions using a PSPICE circuit simulator. The Giacolleto SCR model has been modified. Detailed waveforms of load voltage, load current, and current of various semiconductor-controlled rectifiers (SCRs) have been plotted. It has been demonstrated that for low and medium L/R loads a simple constant firing angle sequence works well, whereas the cosine wave crossing method (CWCM) seems to be optimum for high L/R loads. Theoretical results are validated with the experimental results. >