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 with 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.
This paper presents the modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC), which is intended for installation on the 6.6-kV Japanese industrial and utility distribution systems without using line-frequency transformers. The converter is characterized by an arm structure based on the module consisting of cascade connection of multiple bidirectional PWM chopper-cells and floating dc capacitors per arm. This arm structure requires voltage-balancing control for all the chopper-cells. However, the voltage control combining averaging- with individual-balancing controls imposes certain limitations on operating conditions. This paper proposes an arm-balancing control to achieve voltage balancing in all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is confirmed by computer simulation.
No abstract is provided for this article.
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.
An active power filter using quad-series voltage-source PWM converters is used to suppress ac harmonics by injecting PWM modulated currents to the ac side. In this paper, the calculation circuits for the harmonic currents to be injected, the compensation characteristics, and the capacity of the dc capacitor are discussed. A new control circuit for the dc capacitor voltage is proposed. These discussions focus on transient states and are on the basis of the instantaneous reactive power theory. Finally, a passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the ac side. Some experiments to illustrate the details of the study are shown.
This paper presents a battery energy storage system with a modular push-pull PWM converter (MPC), which is intended for grid connection to medium-voltage or high-voltage power systems. The converter is equipped with a center-tapped transformer and two arms consisting of a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, to achieve voltage balancing of all the floating capacitors. Moreover, a comparison is made between the MPC and a modular multilevel converter (MMC) as the battery energy storage system. The validity of the concept and control method developed in this paper is confirmed by computer simulations using the “PSCAD/EMTDC” software package.
A voltage-source PWM inverter produces common-mode and normal-mode currents flowing through stray capacitors inside an ac motor every switching. Therefore, the currents may cause radiational EMI to electronic equipment, e.g., AM radio receivers, because its oscillation frequency ranges from 100kHz to several MHz. However, few technical papers related to the radiational EMI have been reported although attention has paid to the EMI.This paper discusses relationships between radiational electromagnetic noises and the commom-mode and normal-mode currents. Reduction methods of both the commom-mode and normal-mode currents are also discussed on the basis of a motor model including the stray capacitors. It is shown theoretically and experimentally that both the currents can be damped by the combination of the common-mode transformer which has already been proposed by the authors and normal-mode filters proposed in this paper. Radiational EMI of a vector-controlled induction motor drive system of 3.7kW is measured according to the VDE 0877. Experimental results show not only that the radiational EMI results from the high-frequency oscillatory currents, i.e., the common-mode and normal-mode currents, but also that the combination of the common-mode transformer and the normal-mode filters is an effective, practical way of reducing the EMI.
This article presents an advanced method for power-loss breakdown of a high-power bidirectional isolated dual-active-bridge (DAB) dc-to-dc converter using SiC-<small>mosfet</small>/SBD H-bridge modules. This method is so simple and practical as to extract a switching loss from accurately measured overall losses. A test bench designed and built in this article is characterized by cascading the two identical 750-V 100-kW 16-kHz DAB converters equipped with the two identical unity-turns-ratio transformers. The test bench allows power-loss breakdown at buck and boost operation. When a dc-input voltage of 750 V is different from a dc-output voltage of 850 V at 100 kW and 16 kHz, “hybrid” phase-shift control makes the overall power loss lower by 158 W than “pure” phase-shift control.
The authors describe a brushless DC motor without a position sensor. Variable speed is achieved by adjusting the average motor voltage, just like chopper control of DC motors. The position sensorless drive proposed is based on detection of the conducting interval of free-wheeling diodes connected in antiparallel with power transistors. This approach makes it possible to detect the rotor position over a wide speed range, especially at a lower speed. Experimental results obtained from a prototype brushless DC motor of 300 W rating are shown to confirm the validity of the sensorless drive from 45 to 2300 r/min. A starting procedure of the motor is also discussed because it is impossible to detect the rotor position at standstill.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
No abstract is provided for this article.
Over the last five to ten years, significant progress has been made in high-power semiconductor devices and in their practical applications to power systems. This comes not only from sophisticated semiconductor technology but also from the demand for a higher degree of frequency and voltage stability, and for greater reliability in power systems. This paper deals with an adjustable speed rotary condenser capable of not only reactive power control but also active power control based on a flywheel effect of the rotor. The behavior of a power system consisting of the adjustable speed rotary condenser, a synchronous generator, and a transmission line is subjected to a set of nonlinear differential equations. The set of nonlinear equations can be linearized by limiting attention to small perturbations around a reference state, thus leading to the so-called Heffron–Phillips model of the power system. The Heffron–Phillips model derived is effective in analyzing effects of the adjustable speed rotary condenser on power system stabilization. The validity of the analysis is confirmed by computer simulation based on EMTDC. Finally, it is discussed how well power system stabilization is achieved by the rotary condenser. As a result, the rotary condenser has the function of decoupling reactive power control from active power control, thus producing a good effect on power system stabilization which would not be achieved by a conventional inverter-based static var compensator. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 31–42, 2000
No abstract is provided for this article.
Converters or rectifiers using semiconductor switching devices generate harmonics caused by the behavior of switching. Harmonic currents generated by a rectifier are almost constant even if a source impedance varies, because the impedance on the dc side is much larger than the source impedance on the ac side. Therefore, the equivalent circuit of the rectifier can be considered as an ideal current source for harmonics. However, the theoretical derivation of the equivalent circuit has not been reported as long as the authors know.In this paper, some problems of the conventional equivalent circuit are pointed out, and a new equivalent circuit of the rectifier for harmonics which can solve the problems of the convenional equivalent circuit is derived theoretically. As a result, the applicable limitation of the new equivalent circuit is revealed quantitatively. To clarify the validity of the new equivalent circuit, it is appied to the analysis of anti-resonance between the source impedance and the LC filter connected on the ac side of a rectifier. An accurate explanation of the harmonic amplification in the source is done by using the new equivalent circuit proposed in this paper.
