This paper discusses a shunt active filter intended for installation on a power distribution system. The active filter has an additional capability to regulate the distribution-line voltage by means of adjusting reactive power. Theoretical analysis investigates the dynamic performance of combined harmonic damping and voltage regulation. As a result, harmonic damping makes it possible to improve the stability of the control loop for voltage regulation, and the combined harmonic damping and voltage regulation lead to good voltage regulation performance. Experimental results are shown to verify the effectiveness of the combined harmonic damping and voltage regulation
This paper presents a comparative analysis between results from applications of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-q</i> and the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-q-r</i> theories in shunt active power filters for three-phase four-wire systems, discussing aspects related to the influence of the system voltage in the control methods that calculate the compensating currents. It is shown that in some cases, a preprocessing of the system voltage is required if the goal is to achieve sinusoidal compensated currents. On the other hand, when the goal is to compensate zero-sequence current, the need of energy storage elements in the active filter is discussed. In this case, if zero-sequence components are present simultaneously in the system voltage and load current, they produce zero-sequence power flow, and the control methods based on both theories must contain additional calculations to allow the elimination of energy storage elements in the active filter. A control strategy based on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-q</i> theory is proposed to eliminate the neutral current without the need of energy storage elements, with the advantage of avoiding the extra transformation from alphabeta0 to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pqr</i> coordinates that is needed in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-q-r</i> theory. Simulation results are presented for the purpose of comparing the performance of both control methods.
No abstract is provided for this article.
This paper presents an intensive discussion on conducted electromagnetic interference (EMI) emissions from an inverter-driven air conditioner. The common-mode voltages produced by the pulse-width-modulation (PWM) inverter may cause a high-frequency leakage current. The use of a spectrum analyzer and a line-impedance stabilization network (LISN) makes it possible to refer the leakage current in the time domain to the conducted-EMI emissions in the frequency domain, which are prescribed by the EMI regulations. Estimating the conducted-EMI emissions by means of computer simulation in advance is beneficial for engineers who try to efficiently design a cost-effective EMI-filter intended for meeting the regulations. This paper achieves modeling of common-mode voltages, leakage-current propagation paths, and an EMI-filter for an inverter-driven air conditioner. The simulation circuit based on the developed models makes it possible to predict conducted-EMI emissions. Simulated results agree well with experimental ones in both cases of the EMI-filter being connected and disconnected.
This paper describes a bi-directional isolated dc/dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc/dc converter is intended to use power switching devices based on SiC and/or GaN, which will be available on the market in the near future. A 350-V, 10-kW and 20-kHz dc/dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate Si-IGBTs and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive circuit and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. The loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc/dc converter. As a result, the overall efficiency may reach 99% or higher.
No abstract is provided for this article.
This paper describes a bi-directional isolated dc/dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc/dc converter is intended to use power switching devices based on SiC and/or GaN, which will be available on the market in the near future. A 350-V, 10-kW and 20kHz dc/dc converter is designed, constructed and tested in this paper. It consists of two single-phase full-bridge converters with the latest trench-gate Si-IGBTs and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive circuit and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. The loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc/dc converter. As a result, the overall efficiency may reach 99% or higher.
A measured contact-loss ratio is used to estimate current-collection performance. There are two types of methods used to estimate the contact-loss ratio. One is to measure all the contact losses, including small ones; the other is to measure only contact losses that are greater than 5 ms in duration. The extent of wear of a contact strip caused by arc discharges varies as a function of the amount of electric charge. This fact makes it possible to manage the wear on a contact strip. This paper shows a calculation method for the amount of electric charge based on the output of a contact-loss measurement as well as the expected lifetime of the contact strip and the creation of a maintenance threshold level for of the contact strip.
No abstract is provided for this article.
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. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 73–82, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20460
This paper describes a DC micro‐grid system interconnecting distributed power generators. The system consists of five generation and control units: a solar‐cell generation unit, a wind‐turbine generation unit, a battery energy‐storage unit, a flywheel power‐leveling unit, and an AC grid‐interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the DC grid voltage. This method brings high reliability, high flexibility, and maintenance‐free operation to the system. The method pays attention to DC output voltage performance of each unit. Each of the power control units and the energy‐storage unit is controlled to act as a voltage source with imaginary impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power‐leveling unit is controlled to act as a current source having the function of frequency selectivity like a high‐pass filter. A 10‐kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the DC‐grid system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 86–93, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20603
Arc discharges increase the mass of the anode in a contact field. However, contact losses decrease the mass of the cathode, which is made of current-collecting materials in a rail field. Conducting careful experiments with the focus on proper changes in arc duration make it possible to notice clear differences among the volumes of the molten material, the surface concave of contact wire on the anode, and the molten-metal bridge. The authors analyzed the differences because the mechanism in the rail field is not the same as that in the contact field but the mechanism is related to the material decrease in the rail field. The Phenomena observed between the anode and the cathode from the start to approximately 10ms during the arc duration can be clarified by taking the aforementioned differences into account. Understanding the phenomena makes it possible to explain the decrease in the current-collecting materials. The paper presents the concave measurement results of the contact wire and the phenomena observed between the electrodes from the start to approximately 10ms during the arc duration.
This paper describes an autonomous-control method for a DC microgrid system having distribution power generators. This system consists of following five generation and control units; a solar-cell generation unit, a wind-turbine generation unit, a battery energy-storage unit, a flywheel power-leveling unit, and an AC grid-connected power control unit. The proposed control method intended for suppression of circulating current detects only the DC grid voltage. Each unit could be controlled autonomously without communicating each other. This method brings high reliability, high-flexibility and maintenance-free operation to the system. Experimental results from a 10 kW-prototype system verify the validity and effectiveness of the proposed control method.
A modular multilevel cascade inverter based on double-star bridge cells (MMCI-DSBC) is expected to be one of the next-generation medium-voltage pulsewidth modulation (PWM) inverters intended for grid connections. This inverter is formed by six modular arms, each of which consists of a cascaded stack of multiple full-bridge converters. The DSBC is different from the traditional two-level PWM inverter in that the ac voltages are independent of the dc link voltage. Hence, the DSBC is suitable for a grid-connected inverter with a time-varying dc link voltage. This paper describes the DSBC with a focus on its operating principles and performance. The validity of the inverter is confirmed by experiments using a three-phase, 200-V, and 10-kW downscaled system.
