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" is 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper deals with digital control of a series active filter integrated with a diode rectifier where the series active filter is controlled to function as a current source. A predictive current regulator is considered for the series active filter to achieve good ripple characteristics and predictable switching losses. The operating conditions, and the effect there of on the current regulator are considered and oversampling and prediction of the load voltage is suggested to improve the active filtering performance without increasing the switching frequency.
A neutral-point-clamped voltage source inverter (NPC-VSI), which is one of double series connected inverters, is able to output 5 level step-shaped line to line voltage without output transformers or reactors, thus reducing harmonic currents. The NPC-VSI is suitable to high voltage applications, because the required voltage rating of the switching devices used in the NPC-VSI is only 1/2 of the DC link voltage. However, the DC link voltage may be applied to the switching devices in the worst case if the potential of neutral point the DC link varies because of the flow-in or flow-out of the neutral point current.In this paper, the authors discuss the variation of the neutral point potential theoretically, and propose a suppression method of the variation. This is based on the control of a zero-sequence voltage that is a voltage difference between the center of the DC link and the neutral point of a load. The analysis is done for the vector control drive system of an induction machine without or with the proposed suppression method. Consequently, it is shown that the variation of the potential can be completely suppressed by the method except for a special operating condition. Moreover, the relation between the potential variation and the capacity of the DC capacitor is clarified to lead to the desing of the DC capacitor.
The paper describes a new family member of the modular multilevel cascade converter (MMCC), with the given name, triple-star bridge-cells (TSBC). It is a direct ac-to-ac power converter with the capability of bidirectional power flow with three-phase sinusoidal input and output currents. Therefore, it is suitable to a medium-voltage motor drive requiring regenerative braking. This paper has an intensive discussion on a general control of the TSBC intended for the motor drive. Theoretical analysis and computer simulation confirm the effectiveness and viability of the TSBC.
This article, based on modeling and scaling as well as simulation and experiment, provides a comprehensive discussion on a real-time real-power emulator for a medium-voltage, high-power, high-speed motor drive. A three-phase modular multilevel double-star chopper-cell (DSCC) inverter under test is connected in front-to-front (FTF) with the emulator. The DSCC inverter is the same in circuit configuration as the DSCC rectifier. This emulator is characterized by integrating mechanical dynamics of both motor and load into it. The power-electronic circuit of the emulator consists of a three-phase DSCC rectifier, three ac inductors, and a single two-winding common-mode inductor at the dc side. This article starts with modeling and scaling of a three-phase 6.6-kV 10.9-MW four-pole 9000-r/min induction motor drive. Then, the authors design, build, and test a three-phase 200-V 10-kW downscaled test bench. Experimental waveforms from the 10-kW test bench, as well as simulated waveforms from the 10.9-MW full-scale and 10-kW downscaled systems, lead to the following conclusion: The emulator can reproduce both electrical and mechanical dynamics of the three-phase 200-V, 10-kW, four-pole, 9000-r/min induction motor coupled with a centrifugal compressor.
A modular multilevel cascade inverter based on double-star chopper-cells (MMCI-DSCC) is expected to be used as one of the next-generation medium-voltage PWM inverters suitable to motor drives for energy savings. This three-phase inverter is formed by six modular arms, each of which consists of a cascaded stack of multiple bidirectional chopper-cells. It suffers from ac-voltage fluctuation in the dc-capacitor voltage of each chopper-cell at low speed. The frequency of the fluctuation is equal to the stator-current frequency. This paper attempts to suppress the fluctuation by injecting a common-mode voltage of 45 Hz and circulating currents among the three legs. Experimental results obtained from a 400-V 15-kW downscaled system verify that stable operation is achieved at an ultra-low speed of 17 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with a load torque of τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> = 40%, as well as "three-phase" dc-current feeding operation. Moreover, the motor can start up from a standstill without producing any overvoltage or overcurrent.
A feeding circuit for a superconducting magnetic levitation train system, or the so-called "maglev" consists of feeder cables and armature coils which show characteristics of a distributed-parameter line. Electric power is supplied to the cables and coils by PWM inverters whose output voltage contains a large amount of harmonics. As a result, a harmonic resonance may occur in the feeding circuit. Besides the above characteristics, the connecting point of sections (groups of armature coils) or the feeder cables length changes according to the movement of a maglev train, thus causing changes in the harmonic-resonance characteristics of the feeding circuit.This paper describes analytical results of the harmonic resonance in the feeding circuit for the maglev, with the focus on changes in the connecting point of sections and the feeder cables length.
Since electric vehicles (EVs) suffer from a long charging time and a short mileage, they have not yet formed a full-scale market. A dynamic wireless power transfer system that can supply electric power to the vehicles during driving has been expected as an effective means to solve the above issues. When the primary coils are connected in series, the dynamic wireless power transfer system becomes the same in equivalent circuit as a stationary wireless power transfer system. As a result, the dynamic system is of great advantage for the common use of the secondary coils for parking and driving. This paper provides a fundamental discussion on the dynamic wireless power transfer system with focus on the secondary coils, along with experimental results.
This paper deals with a self-commutated BTB (Back-To-Back) 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 trans-formers. 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.
This paper proposes a new dc-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive with a three-phase diode rectifier used as the front end. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically isolated windings. The inductor produces no net dc magnetic flux because the individual dc magnetic fluxes generated by the two windings are canceled out with each other. This makes the inductor compact by a factor of six, compared with the balancing circuit including two noncoupled inductors. Moreover, introducing phase-shift control to the new balancing circuit makes it possible to adjust the midpoint voltage. As a result, the dc mean voltages of all the four split dc capacitors can be balanced, independent of inverter control. Experimental results obtained from a 200-V 5.5-kW downscaled model verify the effectiveness of the new balancing circuit.
The combined system of a series active filter and a shunt passive filter has been proposed by the authors. It has the ability to eliminate such a disadvantage of a shunt passive filter as a harmonic amplifying phenomina. The series active filter needs much smaller kVA rating than a conventional shunt active filter does. As a result, the combined system shows good filtering characteristics and high efficiency.This paper presents an optimum design of the shunt passive filter for a great reduction of the required kVA rating of the series active filter. It can minimize the peak voltage across the series active filter, and reduce the required kVA rating of the series active filter to 60%. The optimized system is compared in compensation characteristics with the combined system using a conventional shunt passive filter by digital computer simulation, paying attention to practical applications to large rated three-phase twelve-pulse thyristor rectifiers. Experimental results obtained by a laboratory model are shown to verify the design theory.
This paper discusses a 6.6-kV next-generation BTB system in which bidirectional isolated dc/dc converters are combined with modular multilevel cascade converters. The system consists of N converter cells cascaded in each phase at both front ends. Each converter cell consists of a bidirectional isolated dc/dc converter and two voltage-source H-bridge PWM converters. This circuit configuration can be adopted to significantly reduce harmonic voltages and currents because the voltage steps are extremely low. In a conventional power conversion system, bulky line-frequency transformers are employed. On the other hand, in the present system, light and compact high-frequency transformers are used for providing galvanic isolation. Thus, the overall physical size and weight are reduced. The authors design, construct, and test a single-phase 120-V, 3.3-kW downscaled model with N=3, in order to verify the feasibility and effectiveness. The downscaled model helps to develop an operable 6.6-kV system with focus on control and performance.
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