Search

This paper deals with integrating a small-sized passive electromagnetic interference (EMI) filter with a voltage-source pulse-width modulated (PWM) inverter. The purpose of the filter is to eliminate both high-frequency common-mode and normal-mode voltages from the three-phase output voltages of the inverter. A laboratory system consisting of a 5-kVA inverter, a 3.7-kW induction motor, and a specially-designed passive EMI filter was constructed to verify the viability and effectiveness of the filter. As a result, both line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter were an ideal three-phase variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in a complete solution to serious EMI issues related to high-frequency common-mode and normal-mode voltages produced by the PWM inverter. Index Terms--Common-mode voltage, electromagnetic interference (EMI) filters, shaft voltage, three-phase voltage-source pulse-width modulated (PWM) inverters.

This paper proposes a small-sized passive electromagnetic interference (EMI) filter for the purpose of eliminating high-frequency shaft voltage and ground leakage current from an ac motor driven by a voltage-source pulsewidth-modulation inverter. The filter requires access to the neutral point of the motor. A common-mode inductor is connected between the inverter and the motor. The neutral point of the motor is connected to the dc-bus midpoint via a resistor. The dc-bus midpoint is created by using two capacitors in series across the dc positive and negative buses. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. The validity and effectiveness of the EMI filter is verified by experimental results obtained from a 5-kVA laboratory system. Index Terms--Common-mode voltage, electromagnetic interference (EMI), ground leakage current, inverter-driven motors, shaft voltage.

Recently, static var generators (SVGs) or static synchronous compensators based on self-commutated converters have been put into practical use for the purpose of compensation for reactive power, power swings damping, and/or voltage control in power systems. The SVGs have also been applied to reduce voltage fluctuations appearing at high-speed train substations. When parallel resonance occurs between passive filters installed at a point of common coupling (PCC) and the power-system impedance existing upstream of the PCC, voltage/current harmonics are significantly amplified in the power system. This paper describes the control and performance for a self-commutated gate-turn-off (GTO) converter operating in parallel with conventional line-commutated thyristor converters. This hybrid power conversion system rated at more than dozens of MVA has an inductive load at the dc side. A bank of passive filters is connected not only for harmonic compensation of the line-commutated converters, but also as a constant leading reactive-power source. The GTO converter can control either leading or lagging reactive power so as to achieve unity power factor operation. In addition, it has the capability of damping out parallel resonance between the passive filters and the power-system impedance. This paper confirms the viability and effectiveness of the hybrid system by means of theory and computer simulation. Index Terms--Harmonics, line-commutated converters, parallel resonance, self-commutated converters, static synchronous compensator (STATCOM), static var generator (SVG).

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. These motors are characterized by integration of switched reluctance motors and magnetic bearings. It is essential for a control system to consider magnetic saturation in real time in order to realize stable operation at a full torque load. Thus, this paper proposes a method for fast calculation of radial force and torque of a bearingless switched reluctance motor operating in a region of magnetic saturation. It is shown experimentally that the proposed method is effective in calculating the radial force and the torque under conditions of magnetic saturation. Index Terms--Bearingless motors, magnetic saturation, magnetic suspension, switched reluctance motors.

The integration of a series active filter with a 12-pulse diode rectifier can provide a cost-effective and efficient means of supply current harmonic-free ac/dc conversion. Controlling the series active filter as a frequency-selective impedance requires low delays and is not well suited for digital control. This paper suggests a current-mode control strategy to allow full digital control of the active filter. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally. Index Terms--Digital control, diode rectifier, harmonics, series active filter.

This paper deals with transient analysis of a series active filter integrated with a double-series diode rectifier. A dc model is developed with the help of the p-q coordinates transformation. It can be used to accurately and simply analyze transient characteristics around the fundamental frequency of the integrated system. The analysis using the dc model tells us that either increasing the active filter gain or decreasing the cut-off frequency of low-pass filters used in the harmonic detector results in a slow response, and causes a large and long transient of the dc voltage. Simulation results using a software package 'EMTDC' and experimental results verify the validity of the proposed dc model. Index Terms--DC mode, diode rectifiers, power converters, series active filters, transient analysis.

This paper proposes a 3.3-kV transformerless ac-to-dc power conversion system consisting of a three-phase six-pulse diode rectifier and a shunt hybrid filter. The hybrid filter is formed by a single tuned LC filter per phase and a small-rated three-phase active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter be. In addition, no additional switching-ripple filter is required for the hybrid filter because the LC filter functions not only as a harmonic filter tuned at the seventh harmonic frequency but also as a switching-ripple filter around 10 kHz. Experimental results obtained from a 200-V 5-kW laboratory system and simulation results of a 3.3-kV 300-kW system confirm the validity and effectiveness of the system. Index Terms--Active filters, diode rectifiers, harmonics, hybrid filters, passive filters, power conversion.

This paper proposes cooperative control of multiple active filters based on voltage detection for harmonic damping throughout a power distribution system. The arrangement of a real distribution system would be changed according to system operation, and/or fault conditions. In addition, shunt capacitors and loads are individually connected to, or disconnected from, the distribution system. Independent control might make multiple active filters produce unbalanced compensating currents. This paper presents hardware and software implementations of cooperative control for two active filters. Experiment results verify the effectiveness of the cooperative control with the help of a communication system. Index Terms--Active filters, cooperative control, digital control, harmonic damping, harmonic propagation, power distribution systems.

This paper deals with a self-commutated back-to-back (BTB) high-voltage direct-current (HVDC) link system for the purpose of power flow control and/or frequency change in transmission systems. Each BTB unit consists of two sets of 16 three-phase voltage-source converters, and their ac terminals are connected in series each other via 16 three-phase transformers. Hence, the BTB unit uses totally 192 switching devices capable of achieving gate commutation. This results in a great reduction of voltage and current harmonics without performing PWM control. Simulation results verify the validity of the proposed system configuration and control scheme not only under a normal operating condition but also under a single-line-to-ground fault condition. Index Terms--BTB HVDC link, multiconverters, power flow control, single-line-to-ground fault, unit capacitance constant.

This paper develops a systematic and mathematically formal study of the balancing theory of series-stacked multilevel converters. It is shown that the dc bus voltages of these converters balance naturally, provided that the switching frequency is chosen high enough. Two balancing mechanisms, one associated with losses and the other with the load impedance, are identified. A single phase of a 2 MVA series-stacked power quality device was constructed and the theoretical results were verified experimentally. Index Terms--Balancing theory, multilevel converter, series-injection device, series-stacked converter.

This paper deals with a curious phenomenon referred to as the 'whack-a-mole' that may occur in a long-distance distribution feeder having many capacitors for power-factor correction. The idea of whack-a-mole is that installation of an active or passive filter on the feeder makes voltage harmonics increase on some buses, whereas it makes voltage harmonics decrease on other buses, especially at the point of installation. The distributed-parameter representation is applied to a simplified feeder, thus making it possible to perform analysis of the whack-a-mole. As a result, this analysis yields such a basic way as to avoid the whack-a-mole. Moreover, both theory and experiment clarify that installation of the active filter acting as a harmonic terminator on the end bus of the feeder can damp out harmonic propagation throughout the feeder without causing any whack-a-mole. Index Terms--Distributed-parameter representation, harmonic damping, harmonic propagation, power distribution systems, shunt active filters.

This paper discusses automatic gain adjustment in a fully-digital-controlled shunt active filter. This is the first step in cooperative control of the multiple active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, the active filter should be equipped with an optimal control gain corresponding to the characteristic impedance of a distribution line. However, it is difficult to know circuit parameters of a real distribution line having various shunt capacitors and loads. Therefore, a main purpose of the gain adjustment is to make the active filter damp out harmonic propagation without considering the circuit parameters. In addition, the gain adjustment can reduce the compensating currents and losses in the active filter, and moreover it can avoid over-damping performance. Experiment results obtained from a 200-V, 20-kW laboratory system verify the effectiveness of the active filter equipped with automatic gain adjustment. Index Terms--Active filters, digital control, harmonic damping, harmonic propagation, power distribution systems.

This paper deals with a harmonic current-free ac/dc power conversion system which is characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The stability of the active filter based on feedback control is discussed theoretically, taking into account delay time in the control circuit. As a result, it is revealed that the delay time may produce a bad effect on stability, especially when the power conversion system is installed on a stiff power system with low system inductance. The authors propose a viable way of reducing the effect of delay time on the system stability. Analysis in the frequency domain enables us to know how much the system stability is improved in terms of gain and phase margins. A switching-ripple filter is designed to obtain good filtering performance without affecting the system stability. Experimental results obtained from a 20-kW laboratory system verify the validity of the developed theory, and confirm the viability and effectiveness of the proposed control circuit. Index Terms--Diode rectifier, harmonics, series active filter, stability.

A large-capacity low-speed flywheel energy storage system based on a doubly-fed induction machine basically consists of a wound-rotor induction machine, and a cycloconverter or a voltage-source pulse width modulation (PWM) rectifier-inverter which is used as an ac exciter. Adjusting the rotor speed makes the machine either release the kinetic energy to the power system or absorb it from the utility grid. Thus, the machine has the capability of achieving not only reactive-power control, but also active-power control based on the flywheel effect of the rotating parts. This paper proposes a new control strategy for a doubly-fed induction machine intended as a flywheel energy storage system, which is characterized by the combination of vector control and decoupling control. The control strategy enables the induction machine to perform active-power control independent of reactive-power control even in transient states. The validity of the theory developed in this paper, along with the effectiveness and viability of the control strategy, is confirmed by computer simulation. In addition, this paper discusses a transient behavior of a magnetizing current in the induction machine. Index Terms--Decoupling control, doubly-fed induction machine, flywheel energy storage system, vector control.

This paper presents a fully-digital-controlled shunt active filter for harmonic termination of a power distribution system. The main purpose of the active filter based on voltage detection is not to compensate for current harmonics but to damp out harmonic propagation caused by line inductors and shunt capacitors for power factor correction. However, time and phase delays inherent in digital controllers might lead to unsatisfactory harmonic-damping performance although digital controllers are preferable to analog controllers. This paper deals with the design and implementation of a digital controller for a shunt active filter based on voltage detection. Experimental results obtained from a laboratory system developed in this paper verify the viability and effectiveness of the fully-digital-controlled active filter. Index Terms--Active filters, delays, digital control, DSP, harmonics, power distribution systems.

This paper presents control and performance of a pulse-density-modulated (PDM) series-resonant voltage-source inverter developed for corona discharge processes. The PDM inverter produces either a square-wave ac-voltage state or a zero-voltage state at its ac terminals to control the average output voltage under constant dc voltage and operating frequency. This results in a wide range of power control from 0.5% to 100%, even in the corona discharge load with a strong nonlinear characteristic. A 30-kHz 6-kW surface treatment system consisting of a voltage-source PDM inverter, a step-up transformer, and a corona discharge treater shows the establishment of a stable corona discharge in an extremely wide range of power control and, therefore, succeeds in performing both strong and weak surface treatment processes for film. Index Terms - Corona discharge, power control, pulse-density modulation, series-resonant inverter.

This paper is focused on a shunt active filter based on detection of harmonic voltages at the point of installation. The objective of the active filter is to attenuate harmonic propagation resulting from series/parallel resonance between capacitors for power factor correction and line inductors in a power distribution line. The active filter acts as a low resistor to the external circuit for harmonic frequencies, and it is installed on the end bus of the power distribution line, just like a 50-[ohms] terminator installed on the end terminal of a signal transmission line. Therefore, the function of the active filter is referred to as 'harmonic termination' in this paper. Experimental results obtained from a laboratory system rated at 200 V and 20 kW verify that the active filter for the purpose of harmonic termination has the capability of harmonic damping throughout the power distribution line. Index Terms - Harmonic termination, power distribution systems, pulsewidth modulation inverters, shunt active filters, voltage detection.

A third-order resonant circuit was designed to provide fast switching operation for a voltage-source series-resonant inverter that uses four metal oxide semiconductor field effect transistors (MOSFET's). With this resonant circuit, charging and discharging of MOSFET's output capacitance will be easy. Hence, the commutation period needed to turn the MOSFET on and off will be decreased. The third-order resonant circuit was tested in a 2-MHz 2-kW voltage source inverter, which is used for low-temperature plasma generators, and found to be effective.

This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7-kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage. Index Terms - Active common-noise canceler (ACC), bearing current, EMI/EMC, ground current, PWM inverter, shaft voltage.

This paper describes position-sensorless control of an interior permanent magnet synchronous (IPM) motor, which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm detects motor current harmonics and determines the inductance matrix, including rotor position information. An experimental system consisting of an IPM motor and a voltage-source pulsewidth modulation inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms. Index Terms - Interior permanent magnet synchronous motor, magnetic saliency, position control, sensorless drive.

Since the late 1950's, power electronics has been developing by leaps and bounds without saturation to become the key technology essential to modern society and human life as well as to electrical engineering. This paper mainly focuses on the state-of-the-art of power electronics technology and its medium to high-power applications because the author cannot survey the whole spectrum of power electronics ranging from a 5-W switching regulator to a 2.8-GW high-voltage dc transmission system now under construction in Japan. This paper also presents prospects and directions of power electronics in the 21st century, including the personal views and expectations of the author. Index Terms - AC motor drives, active filters, power converters, power devices, power electronics.

This paper deals with unified power quality conditioners (UPQC's), which aim at the integration of series-active and shunt-active filters. The main purpose of a UPQC is to compensate for voltage flicker/imbalance, reactive power, negative-sequence current, and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. This paper discusses the control strategy of the UPQC, with a focus on the flow of instantaneous active and reactive powers inside the UPQC. Experimental results obtained from a laboratory model of 20 kVA, along with a theoretical analysis, are shown to verify the viability and effectiveness of the UPQC. Index Terms - Active filters, harmonics, power conditioners, power quality, voltage flicker, voltage imbalance.

This paper presents a magnetic saliency-based position estimation approach for a permanent magnet (PM) motor fed by a voltage-source pulsewidth modulation (PWM) inverter. The proposed real-time estimation algorithm detects motor current harmonics and calculates the inductance matrix, including rotor position information. Position estimation can be performed every period of PWM or carrier cycle. An experimental system using an interior permanent magnet (IPM) synchronous motor has been constructed. Experimental results verify that position estimation within 10 [degrees] in electrical angle is obtained at standstill and at speeds as low as 1 r/min by the proposed approach. Index Terms - Interior permanent magnet synchronous motor, magnetic saliency, sensorless drive.

This paper proposes a new harmonic current-free ac/dc power conversion system characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The dc terminals of the active filter are directly connected in parallel with those of the diode rectifier, thereby forming a common dc bus. The active filter enables the diode rectifier to draw three-phase sinusoidal currents from the utility. In addition, it can provide the supplementary value-added function of regulating the common de-bus voltage to a limited extent of [+ or -]5%, slightly increasing the rms voltage rating, but not increasing the peak voltage rating. Experimental results obtained from a 5-kW laboratory system verify the practical viability and cost effectiveness of the proposed system. Index Terms - Diode rectifiers, harmonic currents, PWM inverters, series active filters.

This paper presents theoretical and experimental relationships between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source pulsewidth modulation (PWM) inverter. A method of reducing both currents is proposed, based on an equivalent model, taking into account parasitic stray capacitors inside an induction motor. Electromagnetic interference (EMI) radiated by a 3.7-kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3 mi. Experimental results verify that the combination of the already proposed common-mode transformer (CMT) and the normal-mode filters (NMF's) being proposed in this paper is a practically viable and effective way to reduce EMI resulting from both common-mode and normal-mode currents. Index Terms - Common-mode transformer, electromagnetic interference (EMI), normal-mode filter.

This paper deals with a shunt active filter which will be installed by an electric utility, putting much emphasis on the control strategy and the best point of installation of the shunt active filter on a feeder in a power distribution system. The objective of the shunt active filter is to damp harmonic propagation, which results from harmonic resonance between many capacitors for power factor improvement and line inductors in the feeder, rather than to minimize voltage distortion throughout the feeder. Harmonic mitigation is a welcome 'by-product' of the shunt active filter, which comes from damping of harmonic propagation. This paper concludes that the shunt active filter based on detection of voltage at the point of installation is superior in stability to others, and that the best site selection is not the beginning terminal but the end terminal of the primary line in the feeder. Computer simulation is performed to verify the validity and effectiveness of the shunt active filter by means of an analog circuit simulator, which is characterized by installing it on a feeder of a radial distribution system in a residential area.

Attention has been paid to active filters for power conditioning which provide the following multifunctions: reactive power compensation, harmonic compensation, flicker/imbalance compensation, and/or voltage regulation. Active filters in a range of 50 kVA-60 MVA have been practically installed in Japan. In the near future, the term 'active filters' will have a much wider meaning than it did in the 1970's. For instance, active filters intended for harmonic solutions are expanding their functions from harmonic compensation of nonlinear loads into harmonic isolation between utilities and consumers, and harmonic damping throughout power distribution systems. This paper presents the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st century, including the personal views and expectations of the author. Index Terms - Active filters, harmonics, passive filters, power conditioning, power quality, power systems, PWM inverters

This paper presents an equivalent circuit for high-frequency leakage currents in pulsewidth modulation (PWM) inverter-fed ac motors, which forms a series resonant circuit. The analysis based on the equivalent circuit leads to such a conclusion that the connection of a conventional common-mode choke or reactor in series between the ac terminals of a PWM inverter and those of an ac motor is not effective to reduce the rms and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transformer which is different in damping principle from the conventional common-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the rms value of the leakage current to 25%, where the core used in the common-mode transformer is smaller than that of the conventional common-mode choke.

This paper presents a dc voltage-controlled static var compensator (SVC) using quad-series voltage-source non-PWM inverters. The SVC consists of four three-phase voltage-source inverters having a common dc capacitor and four three-phase transformers, the primary windings of which are connected in series with each other. Although each inverter outputs a square wave voltage, the synthesized ac voltage of the SVC has a 24-step waveshape. This results not only in a great reduction of harmonic currents and dc voltage ripples but also in less switching and snubbing losses. This paper develops the analysis of the transient response and the resonance between the ac reactors and the dc capacitor, with the focus on practical use. Experimental results obtained from a 10-kVA laboratory system are shown to agree well with the analytical results, thus verifying the analysis and leading to the design of dc capacitance value.

This paper presents a 4 kW, 450 kHz voltage-source inverter with a series resonant circuit for induction melting applications, which is characterized by the power control based on pulse density modulation (PDM). The pulse-density-modulated inverter makes an induction melting system simple and compact, thus leading to higher efficiency. A modulation strategy is proposed to realize the induction melting system capable of operation at the frequency and power level of interest. Some interesting experimental results are shown to verify the validity of the concept.

This paper presents a new method of harmonic power detection based on the instantaneous active power in three-phase circuits, and its applications to search for dominant harmonic sources in power systems. The proposed method requires only band elimination filters and a three-phase active power meter to detect the harmonic active power, and it is able to deal with harmonic power flow more easily and precisely than a conventional one which is based on Fourier series of single-phase circuits. In addition, measurement errors of the harmonic power are discussed theoretically. The validity of the proposed method is demonstrated by digital simulation.

This paper proposes a new power line conditioner consisting of two small rating series active filters and a shunt passive filter. The power line conditioner aims at a general filtering system which will be installed at the point of common coupling in a power system feeding harmonic-sensitive loads and unidentified harmonic-producing loads. One of the two active filters is connected in series with the supply, while another is in series with the shunt passive filter. The purpose of the power line conditioner is to reduce voltage distortion at the connection point, and is to eliminate harmonic currents escaping into the system upstream of the connection point. A control scheme of the two series active filters which play an important role is described in this paper. Its filtering characteristics are discussed with the focus on voltage and current distortion. A prototype model of 20kVA is constructed to verify the functionality and performance of the power line conditioner.

Active power line conditioners, which are classified into shunt and series ones, have been studied with the focus on their practical installation in industrial power systems. In 1986, a combined system of a shunt active conditioner of rating 900 kVA and a shunt passive filter of rating 6600 kVA was practically installed to suppress the harmonics produced by a large capacity cycloconverter for steel mill drives. More than one hundred shunt active conditioners have been operating properly in Japan. The largest one is 20 mVA, which was developed for flicker compensation for an arc furnace with the help of a shunt passive filter of 20 mVA. In this paper, the term of 'active power line conditioners' would be used instead of that of 'active power filters' because active power line conditioners would cover a wider sense than active power filters. The primary intent of this paper is to present trends in active power line conditioners using PWM inverters, paying attention to practical applications.

A combined system of shunt passive and small rated series active filters has already been proposed by the authors. The operating principle and steady compensation characteristics have been presented as well. The combined system can greatly reduce problems of using only shunt passive or shunt active filters and is suitable for harmonic compensation for large VA rated loads in power systems because the required VA rating of the series active filter used is considerably smaller than that of a conventional shunt active power filter.In this paper, transient compensation characteristics and stability of the system are discussed and analyzed theoretically and experimentally in detail. A new control method, which enables application of the combined system to compensation for cyclo converters, is proposed. Some results obtained from the experimental model using the new control method are presented to demonstrate and confirm its validity.