Loop power system control by high-speed phase shifter

Recently, power systems have become larger and more complex. Particularly, the looping of power systems is becoming highly desirable to improve the stability. The main features of such looped power systems are: (i) comparatively fewer losses; and (ii) improved angle stability as well as voltage stability. However, these systems have demerits, such as, in case of route off fault in a loop power system, power disturbances increase more and more, etc. If these demerits are overcome, the loop power systems are going to be more beneficial. In an attempt to obtain a solution to such problems, this paper describes several results of applying a high-speed phase shifter in the control system of a loop power system.     

A robust power flow model for active power flow control via thyristor‐controlled series compensator

In this paper, a new power flow model for active power flow control through a thyristor‐controlled series compensator (TCSC) in an AC network system is proposed. The proposed power flow model is based on the Newton–Raphson method. In this model, TCSC's admittance effect is included as a state variable into the Jacobian matrix to avoid the divergence problem. Unlike similar studies in the literature, TCSC's admittance is ignored in the bus admittance matrix, and the need for rebuilding the bus admittance matrix in each power flow iteration caused by the change of TCSC's admittance is prevented. So, faster convergence for power flow calculation is achieved. For this aim, new power equations are obtained. Also, in the proposed approach, we need not consider each terminal of TCSC as an individual bus in the power flow calculation. Thus, increasing the Jacobian and bus admittance matrixes sizes caused by the total bus number is prevented. The proposed approach is tested on an IEEE 57‐bus test system. The obtained results prove that this approach provides efficient, reliable, and fast convergence. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Unbalanced power flow calculation of a power system containing a variable‐speed generator

There are some factors that render a power system network unbalanced: UHV transmission lines in which three‐phase transmission lines are not transposed, an unbalanced transformer, unbalanced load as well as sustained unbalanced faults. On the other hand, the number of variable‐speed generators used in pumping‐up power stations has recently been increasing in Japan. This paper presents a new means of calculating unbalanced power flow of a power system which contains variable‐speed pumping‐up generators. This new technique is based on the phase coordinate method, because a power system which has elements of unsymmetrical impedance can easily be analyzed by using it. In this paper, phase coordinate models of the variable‐speed generator and its secondary exciting circuit, composed of a GTO converter/inverter, are analyzed first. Procedures of power flow calculation of unbalanced power systems follow. © 2000 Scripta Technica, Electr Eng Jpn, 134(3): 34–43, 2001     

A novel strategy for a high‐power utility interactive inverter with a series active filter

High‐power utility interactive inverters used for large‐capacity energy storage systems are composed of multiple connected inverters, in order to realize high efficiency and high performance of the harmonic elimination characteristic simultaneously. Some disadvantages of multiple connected inverters, such as harmonic current flowing from an inverter unit to the other one, and increase of the number of inverter units, cannot be overcome easily. This paper presents a novel strategy for a high‐power utility interactive inverter, which is composed of a large power with low‐switching‐frequency PWM inverter (high‐power PWM inverter), an LC passive filter, and a series active filter (series AF). Because harmonic components contained in the utility line current are absorbed by the series AF, the switching frequency of the PWM inverter can be selected to about 1 kHz. In addition because the power capacity and the output voltage of the series AF can be suppressed lower than 10% of the power capacity and the output voltage of PWM inverter, low‐voltage and high‐speed power devices can be applied to the series AF. Consequently, high power, high efficiency, and high harmonics elimination performance can be realized without increasing the number of inverter units. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 57–66, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10048     

Proposal of current control method of high‐speed AC motor system

In this paper, a current control method for a high‐speed AC motor system is proposed. In high‐speed driving operation, the current controller tends to lose stability because of the dead time caused by computational delay and electromagnetic coupling included in the AC motor model. The main purpose of the proposed method is reduction of the dead time on the current controller. The proposed method is based on model predictive control and optimization of the start timing. The effectiveness of the proposed method is confirmed by simulation results. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 37–45, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21083     

An accurate power delivery system (PDS) design methodology for high‐speed digital systems

The trend in high‐speed digital circuits is to increase speed and density and to operate at lower voltage. This fast increase in the switching speed combined with the decrease of the operating voltage causes the allowable absolute voltage variations to decrease, which makes the PDS design a more challenging task than ever. Moreover, the complex 3D nature of the modern PDS causes it to be more sensitive to capacitors' placement as well as capacitance value. In this paper, we introduce an efficient complete solution for the design of high‐speed digital PDS. This solution (a) takes the effects of the decoupling capacitor placement into consideration through a 3D electromagnetic simulation of the PDS, (b) defines a more‐realistic PDS design target, and (c) presents a clear capacitor value selection methodology. Finally, we applied our methodology to an industrial test case, compared its results with that of industrial design, and showed its advantages. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of a new adaptive LQG system generator for high‐speed damping control techniques of power system oscillation

With the advent of interconnection of large‐scale electric power systems, many new dynamics power system problems have emerged, which include low‐frequency intersystem oscillations and many others. To date, most major generators in trunk electric power systems in Japan are equipped with supplementary excitation control, commonly referred to as the conventional single and two input PSS. However, low‐frequency oscillations still occur. It is difficult for these conventional PSS to improve the additional damping of power system oscillation, because of the hardware and design of fixed PSS control constants from a one‐machine infinite‐bus model. It has therefore become necessary to develop a new adaptive LQG system generator. This paper explains the development of the new adaptive LQG system and the simulation of low‐frequency and local mode oscillation for this new adaptive LQG system. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 30–40, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10109     

Power system stabilizing control by a superconducting magnetic energy storage with a high-speed phase shifter

Electric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated. On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously. This paper proposes a combination of SMES with a high-speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically.     

Series resonant ZCS‐PFM DC‐DC power converter with high‐frequency high‐voltage transformer link for high‐power magnetron drive

This paper presents a single lossless inductive snubber‐assisted ZCS‐PFM series resonant DC‐DC power converter with a high‐frequency high‐voltage transformer link for industrial‐use high‐power magnetron drive. The current flowing through the active power switches rises gradually at a turned‐on transient state with the aid of a single lossless snubber inductor, and ZCS turn‐on commutation based on overlapping current can be achieved via the wide range pulse frequency modulation control scheme. The high‐frequency high‐voltage transformer primary side resonant current always becomes continuous operation mode, by electromagnetic loose coupling design of the high‐frequency high‐voltage transformer and the magnetizing inductance of the high‐frequency high‐voltage transformer. As a result, this high‐voltage power converter circuit for the magnetron can achieve a complete zero current soft switching under the condition of broad width gate voltage signals. Furthermore, this high‐voltage DC‐DC power converter circuit can regulate the output power from zero to full over audible frequency range via the two resonant frequency circuit design. Its operating performances are evaluated and discussed on the basis of the power loss analysis simulation and the experimental results from a practical point of view. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 79–87, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20126     

A high‐speed reclosing method to improve the stability in a power system

This paper proposes a high‐speed reclosing operating method to improve the stability in a power system. The proposed method calculates the reclosing time, taking a standard case in which the reclosing is not done using the generator phase angle δ, and the angular velocity ω, and the field system voltage ed′. Also, the execution of reclosing time is calculated, while taking into consideration the acceleration/deceleration energy of the generator during a fault. It can be expected that δ is suppressed by this optimum reclosing operation. Therefore, the system stability can be expected to improve by carrying out high‐speed reclosing when a fault occurs. At present, it has been set at a value which seems to be optimal considering various problems in the reclosing time. However, in those methods, the system stability improvement effect cannot be expected. It was demonstrated that the high‐speed reclosing method serves to depress δ in the computer simulation. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 13–21, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10317     

Application of unified voltage analysis for high‐ and low‐voltage distribution systems by power flow calculation using indication method between nodes

It has been noted that the voltage of connection points rises according to the reverse power flow when grid‐connected photovoltaic systems are concentrated in distribution systems in residential areas. When this happens, the photovoltaic system may control the power generation output to maintain a suitable voltage for the connection point. Designing a demand area power system aiming at free access to a distributed power supply for energy‐effective practical use requires a precise understanding of this problem. When analyzing photovoltaic systems mainly connected to low‐voltage systems, we looked for a method of analysis in which the high‐voltage systems and the low‐voltage single‐phase three‐wire systems are unified. This report concerns use of the indication method between nodes using power flow calculation, for the purpose of developing a technique of analyzing unified high‐voltage systems and low‐voltage single‐phase three‐wire systems. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 49–62, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10255     

Improvement of power system stability by high-speed power control of adjustable speed machines

Large-capacity adjustable speed machines (ASMs) at pumped storage power stations have been put into full operation and their operating characteristics have been highly evaluated from the viewpoint of power system operation. The output power (input power) of ASMs can be controlled very quickly by applying a vector control scheme to the excitation control. This quick responsive feature of ASMs can make it possible to improve the stability of the neighbor subpower system. For improvement of transient stability, the output power of ASMs is reduced very quickly in order to control the acceleration of neighbor generators during and after transmission line faults. For improvement of dynamic stability, the output power of ASMs is modulated in accordance with the stabilizing signals detected from the swing of generator rotor or the power flow fluctuation on the transmission line. This paper describes the design concepts and method of control system for improving the transient and dynamic stability and proposes a power system stabilizing control system. The effects of the proposed stabilizing control system have been verified by a power system simulator. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 27–36, 1997     

A three‐phase,active power filter with a predictive‐instantaneous‐current PWM controller

One of the most emphasized problems to be solved in power systems in recent years is the line‐current harmonics problem. This is due to the use of diode rectifiers, PWM converters, nonlinear loads, and so on. To reduce or eliminate such current harmonics, an active power filter (APF), which is a sophisticated power electronic converter, has been studied and used in some practical applications. In this paper, we propose and discuss two new control methods for three‐phase shunt APFs: the sinusoidal line‐current control method and the instantaneous‐reactive‐power compensation control method. They are based on pulsewidth prediction control, or a predictive‐instantaneous‐current PWM control. Neither any instantaneous power information nor coordinate transformation is necessary for control. In the sinusoidal line‐current control scheme, the controller governs the switching devices of the APF by using the pulse width that is optimally predetermined at the beginning of every switching period with the sinusoidal current reference. The line currents flow sinusoidally and are in phase with the voltage accordingly. In the instantaneous‐reactive‐power compensation control, the control is performed so that the resultant circuit of the load and the APF is regarded as a time‐variant conductance circuit model. The APF with this control scheme can cancel effectively the instantaneous reactive component produced by the load though the controller is simple. This paper discusses the performance characteristics of the APFs when a three‐phase diode rectifier and an unbalanced load are connected to the line. The practicability of the proposed methods is verified by experiment. © 1999 Scripta Technica, Electr Eng Jpn, 130(3): 68–76, 2000     

A novel robust current control approach using adaptive line enhancer for three‐phase current‐source active power filter

An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014     

电力潮流灵活控制技术应用综述

统一潮流控制器(unified power flow controller, UPFC)、静止同步串联补偿器(static synchronous series compensator, SSSC)、可控串联补偿装置(thyristor controlled series compensation, TCSC)和移相器(phase-shifting trans former, PST)能够调节线路参数、灵活控制潮流变化,均已在国内外电网中实现工程应用,对均衡输电通道潮流、提升供电能力有重要作用。文中对UPFC、SSSC、TCSC和PST的理论研究和工程实践进行了综述。首先,分析了4种潮流控制装置的基本结构和控制原理,并介绍了国内外已投运工程的运行情况;其次,从结构、换流器技术、选址定容、控制策略、故障保护5个方面对潮流控制装置的关键技术研究现状进行概述;最后,展望了潮流控制装置在未来电网中的典型应用场景,并对潮流控制技术的研究方向进行了分析。     

Autonomous decentralized system for torque control of high‐power permanent magnet synchronous motor

An autonomous decentralized system (ADS) for the control of a high‐power permanent magnet synchronous motor (PMSM) presented in this paper. The system decentralizes a centralized control system into several autonomous subsystems. Thus the power supply and power electronic devices of the control system can be replaced by smaller ones, thereby obtaining better fault tolerance of the system. The subsystems are connected only through the data field, which, in this paper consists of feedback elements and communication modules. This structure enables the autonomous controllability and autonomous coordinability of the system. The mathematical model of the PMSM with decentralized stator coils is proposed. This model takes into account the self‐ and mutual inductance of the coil, as well as the effect of the stator slot‐pitch angle. In addition, an autonomous algorithm for the torque control of the PMSM with decentralized stator coils is proposed, and the fault‐tolerance design is developed. Experimental results of the torque control and fault‐tolerance control confirm the validity of the proposed system. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Stabilization of a large‐capacity,long‐distance transmission system by an adjustable‐speed flywheel generator

An adjustable‐speed flywheel generator (FWG) can control both active power and reactive power rapidly. We have studied the effect of FWG installation on a large‐ capacity, long‐distance transmission system, especially when the system includes loops. In this paper, we describe the selection of FWG location, the selection of stabilizing control input signal, and the required quantities of FWG. FWG location is selected by a PQ‐sensitivity method, calculation of which is simple and permits easy understanding of the effect of both FWG's active and reactive power. As a stabilizing control input signal, we use bus voltage frequency instead of power flow because the flow changes stepwise by opening three‐phase single‐circuit. Additionally, we clarify the FWG quantities that must be designed, such as FWG's active power and reactive power. We considered FWG's slip to determine the quantity because the capacity of the exciter depends on slip. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 32–41, 1999     

A decentralized control system for stabilizing multimachine power systems

A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.     

Active‐terminated transmitter and receiver circuits for high‐speed low‐swing duobinary signaling

In this work, we propose transmitter and receiver circuits for high‐speed, low‐swing duobinary signaling over active‐terminated chip‐to‐chip interconnect. In active‐termination scheme port impedance of transmitter and receiver is matched with characteristic impedance of the interconnect. Elimination of the passive terminators helps in reducing the transmitted signal level without degrading the 0signal detectability of the receiver. High‐speed current‐mode receiver and transmitter circuits are designed, so that the input port impedance of the receiver and the output port impedance of the transmitter are matched with characteristic impedance of the link. These Tx–Rx pair is used to validate the proposed active‐termination scheme. We also propose a duobinary precoder architecture suitable for high‐speed operation and a low‐power broadband equalizer topology for compensating the lossy long interconnect. The duobinary transmitter and receiver circuits are implemented in 1.8 V, 0.18 µm Digital CMOS technology. The designed high‐speed duobinary Tx/Rx circuits work up to 8 Gb/s speed while transmitting the data over 29.5 in. FR4 PCB trace for a targeted bit error rate (BER) of 10^?15. The power consumed in the transmitter and receiver circuits is 42.9 mW at 8 Gb/s. Copyright © 2010 John Wiley & Sons, Ltd.     

Maximum output power control system of variable‐speed small wind generators

This paper proposes a maximum output power control system for variable‐speed small wind generators. The proposed control system adjusts the rotational speed of a single‐phase AC generator to the optimum rotational speed, which yields the maximum output power according to the natural wind speed. Since this adjustment is performed on‐line in order to adapt to variations in wind speed, the rotational speed of the single‐phase AC generator is adjusted by controlling the generated current flowing in an FET (field‐effect transistor) device, serving as the generated power brake, which is linked directly to the single‐phase AC generator. In order to reduce heat loss from the FET device, a PWM (pulse width modulation) controller is introduced. An experimental model of the proposed control system was built and tested, and the validity and practicality of the proposed control system were confirmed by the experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 9–17, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20692