No abstract is provided for this article.
With remarkable development and advance in PWM inverter technology on the basis of fast switching devices in the 1980s, active power filters which are classified into shunt and series active filters have been studied with the focus on their practical installation in industrial power systems. In 1982, a shunt active filter of rating 800kVA was put into practical use for the first time in the world. The main circuit consisted of a current source PWM inverter using GTO thyristors. In 1986, a combined system of a shunt active filter of rating 900kVA and a shunt passive filter of rating 6600kVA was practically installed to suppress the harmonics produced by a large capacity cycloconverter for steel mill drives. More than one hundred shunt active filters have been operating properly in Japan. The largest one of the shunt active filters is 20MVA, which was developed in 1990 for reactive power and harmonic compensation for an arc furnace with the help of a shunt passive filter of 20MVA. This paper presents a survey of shunt and series active filters using PWM inverters, paying attention to research and practical applications in Japan.
No abstract is provided for this article.
This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive EMI filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper
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This paper describes a brushless dc motor system without position or speed sensor. The brushless motor consists of a permanent magnet synchronous motor and a voltage‐source inverter capable of controlling the amplitude and frequency of voltage. The rectangular‐shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage similarly to chopper control of dc motors. In this paper, two sensorless position detecting methods, i.e., an “indirect method” suited for the lower‐speed range and a “direct method” suited for the higher‐speed range are proposed. The combination of the two makes it possible to detect the rotor position over a wide‐speed range. Furthermore, a speed‐sen‐sorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prototype brushless dc motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor also is discussed because it is impossible to detect the rotor position at a standstill.
This paper presents an advanced static VAr compensator (ASVC) using quad-series voltage-source inverters. The ASVC 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 to each other. Although each inverter outputs a square wave voltage, the synthesized output voltage of the ASVC has a 24-step wave shape. 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 AC reactors and the DC capacitor with the focus on practical use. Experimental results obtained from a small-rated laboratory model of 10 kVA are also shown to verify the analysis leading to the design of the DC capacitor. The experimental and analytical results agree well each other.
This paper presents dynamic control and performance of a UPFC under a fault condition in a dual-feeder transmission system. The transmission system discussed in this paper consists of two feeders in parallel, which are installed between two power stations. When interruption occurs in one of the two feeders, active and reactive power flow are reduced to half because the line impedance doubles. The UPFC is installed in one power station, and keeps the total amount of active power flowing through the dual feeder constant. In this paper, control stability and power-flow regulation under the single-feeder interrupt are theoretically discussed, and are verified by computer simulation and experiments using a 10-kVA laboratory setup. As a result, it is clarified that a conventional control scheme may cause a large amount of overshoot in active and reactive powers after single-feeder interrupt. On the other hand, "advanced control" can control the active and reactive power faster than the power fluctuations, and thus make it possible to eliminate the power variation accompanied by single-feeder interrupt.
A digital current sensor having the properties of high accuracy, high speed, and low cost for measuring the output current of a pulse-width-modulated (PWM) inverter is described. The digital current sensor forms a closed-loop current sensor with a tracking-type analog-to-digital converter. A prototype digital current sensor of 12 bits is developed and excellent experimental results are shown in the case when an input current of an induction motor (2.2 kW) driven by a PWM inverter is measured by the digital current sensor. >
This paper deals with a computer simulation method, which can realize high-speed and high-accuracy. The proposed method is characterized by both introducing the so-called discrete-time system with variable-sampling time and treating the digital control system as the discrete-time system with constant-sampling time. The proposed method is applied to a position-sensorless IPM motor drive system, which has been proposed by the authors. Simulated results show that the proposed method achieves more accurate and efficient simulation than conventional methods do.
This paper discusses the 6.6-kV BTB (back-to-back) system combining bidirectional isolated dc/dc converters with modular multilevel cascade PWM converters. The system consists of multiple converter cells connected in cascade per phase at both front ends. Each converter cell consists of a bidirectional isolated high-frequency dc/dc converter and two voltage-source H-bridge PWM converters. Extremely low voltage steps bring a significant reduction in harmonic voltage and current to the supply (line) current. This paper designs, constructs and tests a single-phase downscaled model rated at 120 V and 3.3 kW to verify the viability and effectiveness leading to the 6.6-kV actual system.
This paper deals with a dynamic voltage restorer (DVR) characterized by installing the shunt converter at the load side. The DVR can compensate for the load voltage when a voltage sag appears in the supply voltage. An existing DVR requires a large capacitor bank or other energy-storage elements such as double-layer capacitors or batteries. The DVR presented in this paper requires only a small dc capacitor intended for smoothing the dc-link voltage. Moreover, three control methods for the series converter are compared and discussed to reduce the series-converter rating, paying attention to the zero-sequence voltages included in the supply voltage and the compensating voltage. Experimental results obtained from a 200-V, 5-kW laboratory system are shown to verify the viability of the system configuration and the control methods.
The authors describe a 50 kHz 5 kVA voltage-source inverter using insulated gate bipolar transistors (IGBTs), a series-resonant circuit including a step-up transformer of turn ratio 1:10, and a corona surface treater. The series-resonant circuit is used as a matching circuit between the inverter of output voltage 250 V and the corona surface treater of input voltage 10 kV. Experimental results obtained from the prototype inverter system are shown to verify the stable inverter operation and proper corona discharge irrespective of load conditions. The estimated inverter efficiency is 95%, and the measured overall efficiency of the system is 74%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper describes an effect of a passive EMI filter on preventing bearing current from flowing inside an inverter-driven motor. Motor-bearing damages are often caused by bearing currents resulting from breakdown of grease films in the motor bearing. The high-frequency common-mode voltage generated by the PWM inverter induces a shaft voltage between the rotor and the frame. When the shaft voltage exceeds a breakdown voltage of the grease films, a destructive instantaneous discharge current with a peak value of about 1A flows through the motor bearing. The passive EMI filter, that is unique in access to the motor neutral line, can reduce the shaft voltage as a result of eliminating the high-frequency common-mode voltage from the motor terminals. Hence, no breakdown occurs in the grease film, so that no bearing current flows. The viability and effectiveness of the passive EMI filter is verified by experimental results obtained from a 400-V, 3.7-kW laboratory system.
No abstract is provided for this article.
This paper discusses automatic gain adjustment in fully-digital-controlled shunt active filters. This is the first step in cooperative control of the active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, an optimal control gain is equal to the characteristic impedance of a distribution line. However, it is difficult to know circuit parameters of a real distribution line, that is, feeder connections, shunt capacitors and loads. Therefore, the main purpose of the gain adjustment is to make each active filter damp out harmonic propagation without considering the circuit parameters. Moreover, the gain adjustment can reduce the compensating currents and losses in each active filter. The two active filters with constant or automatic-adjustable gains are experimentally compared. Experiment results verify the effectiveness of the active filter with automatic gain adjustment.
