Self‐sensing active magnetic bearings with zero‐bias‐current control

A zero‐bias‐current self‐sensing active magnetic bearing is proposed. One degree‐of‐freedom (DOF) of the rotor is controlled by a pair of electromagnets which are alternatively energized by the proposed circuit. The rotor position of the one DOF is measured by using both electromagnets: the nonenergized electromagnet also contributes to the position sensing. The proposed method gives good linearity in the position estimation. The controller of the magnetic levitation consists of a digital signal processor, DSP, which compensates the nonlinearity of the magnetic force and achieves good damping. In the experiment, the rotor can run at 45,000 min^‐1. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 69–76, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20616     

A robust decentralized approach to the multiarea frequency control of power systems

It is an important problem in multiarea power systems to attenuate the frequency deviation due to load change. Since power systems are spatially dispersive, decentralized control is more practical than lumped control. In this paper, we propose two robust decentralized control schemes for this problem. The difficulty with this problem is that the linearized model of a multiarea power system with frequency deviations as outputs is a MIMO system that has a transmission zero at s = 0. They key idea is to change the output of one subsystem so that the resulting new plant does not have any zero at s = 0. The new outputs are chosen carefully so that the regulation of the new outputs can guarantee the regulation of all frequency deviations and tieline power. Further, parameter uncertainty is taken into account in the controller design to achieve robustness. Simulation shows that the proposed methods are effective. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 68–76, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10004     

A new position‐sensorless position control method for high‐speed spindle systems

This paper proposes a new position‐sensorless position control method for high‐speed spindle drive systems. Mechanical vulnerability of position sensors such as an encoder mounted on a spindle motor is becoming a serious problem as required speed increases. For high speeds above 1500 rad/s, sensorless drive is preferred. It is possible for current technologies to control spindle motor in speed control mode without the sensor, but not in position control mode without the sensor. In the example of high‐speed spindle systems of automatic machine tools, implements must be automatically attached to and removed from the spindle at standstill. Automation necessitates position control, for which current technologies require a sensor. The proposed method makes it possible to realize pure sensorless high‐speed spindle systems performing in both speed and a position control modes. The method can attain a position control performance with quick settling from speed control and a repetitive positioning precision of 0.006 rad, 0.4°, which is comparable to that achieved by current sensor‐based methods. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 58–69, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10059     

Low‐frequency noise analysis and minimization in Gilbert‐cell‐based mixers for direct‐conversion (zero‐IF) low‐power front‐ends

Low‐frequency (flicker) noise is one of the most important issues in the design of direct‐conversion zero‐IF front‐ends. Within the front‐end building blocks, the direct‐conversion mixer is critical in terms of flicker noise, since it performs the signal down‐conversion to baseband. This paper analyzes the main sources of low‐frequency noise in Gilbert‐cell‐based direct‐conversion mixers, and several issues for minimizing the flicker noise while keeping a good mixer performance in terms of gain, noise figure and power consumption are introduced in a quantitative manner. In order to verify these issues, a CMOS Gilbert‐cell‐based zero‐IF mixer has been fabricated and measured. A flicker noise as low as 10.4 dB is achieved (NF at 10 kHz) with a power consumption of only 2 mA from a 2.7 V power supply. More than 14.6 dB conversion gain and noise figure lower than 9 dB (DSB) are obtained from DC to 2.5 GHz with an LO power of ?10 dBm, which makes this mixer suitable for a multi‐standard low‐power zero‐IF front‐end. Copyright © 2008 John Wiley & Sons, Ltd.     

Double resonant tank LLC‐DCX based two‐stage power supply for magnetic levitation control system applications

Magnetic levitation train power supply systems, or Maglev, are most commonly powered by 330‐V high‐voltage direct current power systems. The power supply for maglev control system is used to provide a stable voltage to the suspension control circuit, which is the key part of Maglev trains. The suspension control power supply is typically a DC–DC converter with a high voltage input and multiple low voltage outputs. The traditional solutions typically lead to the following issues, such as uncontrolled duty ratio, poor cross‐regulation capability, and low reliability. In order to solve these problems, a novel two‐stage solution employing a double resonant tank LLC DC transformer (LLC‐DCX) is proposed and developed in this paper. The proposed solution not only increases the overall conversion efficiency significantly because of the achieved soft‐switching over the entire operation range, but also realizes the low input current ripple and high reliability owing to a uniform thermal distribution. A 210‐W, 220–380‐V input laboratory prototype with four outputs is fabricated and tested, and the experimental results are presented in this paper. The declared features of the proposed solution are well demonstrated by the experimental results. Copyright © 2015 John Wiley & Sons, Ltd.     

Impact of stray inductances of the power loop on false trigger‐on in the zero‐voltage‐switching full‐bridge converter

Here, we propose an exhaustive theoretical investigation and experimental verification of the false trigger‐on phenomenon, which would lead to the interaction between the upper and lower devices during the switching transient, in the zero‐voltage‐switching (ZVS) full‐bridge converter. An equivalent model of the converter, which takes not only the parasitic capacitors of the metal–oxide–semiconductor field‐effect transistors into account but also the stray inductances of the main circuit, is presented. Based on the model, a comprehensive study of the false trigger‐on phenomenon is carried out. According to the analysis results, the stray inductances of the metal–oxide–semiconductor field‐effect transistors have negligible influence on the false trigger‐on phenomena since the soft‐switching is realized. The false trigger‐on phenomenon is induced by the stray inductances of the main circuit. Moreover, the arrangement of the switching sequence would cause significant discriminations in the false trigger‐on phenomena because of the specific working mode of the ZVS full‐bridge converter. According to the investigation results, optimization methods are presented to suppress the induced voltage. At last, the theoretical investigations are verified by tests of a ZVS full‐bridge converter. Copyright © 2016 John Wiley & Sons, Ltd.     

Parallel operation of four‐switch full‐bridge power amplifiers and a unique digital control scheme for advanced magnetic resonance imaging

In recent years, magnetic resonance imaging (MRI) systems have been in demand to diagnose moving parts in the human body such as the heart or the blood in angiography, where images should be taken in milliseconds instead of minutes. Gradient power amplifiers, which are small but vital components for advanced MRI, require higher output power capacity as well as faster rise/fall dynamic response characteristics under a variety of specified current reference signals. This paper presents a novel switch‐mode gradient power amplifier using IGBTs which are connected in parallel to a conventional four‐switch full‐bridge power conversion circuit at their inputs/outputs in order to realize a higher power density. To satisfy the design specifications, which require minimized ripple and improved rise/fall dynamic response characteristics of the current in the gradient coil, a unique digital control scheme based on an optimal type 1 servo system is proposed and described in detail. The effectiveness of the above is discussed and evaluated through computer‐aided analysis. It is expected that the proposed techniques will greatly expand the diagnostic targets and improve the image quality of MRI. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 64–72, 2000     

Augmented automatic choosing control of filter type for nonlinear systems and its application to power systems

This paper deals with a feedback control using automatic choosing control and nonlinear filter for nonlinear systems with noise measurement. The state estimation of plants is carried out by the nonlinear filter. The control is designed by piecewise linear controls which are smoothly integrated into a single nonlinear feedback control by the automatic choosing functions. This is called an augmented automatic choosing control of filter type (AACCF) for nonlinear noisy measurement systems. This controller is applied to a transient stability problem of power systems, whose simulation results show that the new controller enables the expansion of the stable region well. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于零动态理论PSS参数与STATCOM协调设计及其在含风电机组系统中的应用

励磁系统和FACTS装置的不协调设计会导致电网的鲁棒性变差。基于多输入多输出系统的励磁控制装置和STATCOM数学模型,利用零动态设计原理对系统PSS参数与STATCOM进行协调设计,分别在PSS与STATCOM协调和不协调两种情况下,应用DIgSILENT/PowerFactory软件对系统进行仿真,根据仿真结果得出,零动态设计原理可以显著提升含风电多机系统的动态稳定性且具有优良的品质。     

A new approach to an individual‐phase reactive power compensator for nonsinusoidal and unbalanced three‐phase systems

Many researchers have attempted to clarify the definitions of active power, reactive power, active current, reactive current, etc. for unbalanced and nonsinusoidal three‐phase situations. The so‐called pq theory has given a new definition of instantaneous reactive power, and it has been discussed and developed by many authors. In this paper, the merits and demerits of the instantaneous reactive power compensator are discussed. It is shown theoretically that applying instantaneous reactive power compensation to unbalanced three‐phase systems has a serious disadvantage in that it causes third‐order harmonic currents on the source side, which problem cannot be avoided. To overcome this problem the authors propose a new approach, and name it the “quasi‐instantaneous” reactive power compensator. It compensates individual‐phase reactive currents. The basic principles of the quasi‐instantaneous reactive current compensator are discussed in detail, and its validity is confirmed using digital simulation. In particular the authors show that the power factor of each phase becomes unity on the source side, but the source currents remain unbalanced when the proposed method is applied. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 73–81, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1162     

Matching capacitance and transfer efficiency of four wireless power transfer systems via magnetic coupling resonance

Matching capacitance determines the resonance and resonant frequency for a given wireless power transfer (WPT) system. Theoretical solutions for matching capacitance are essential to designing and controlling a coupling system in resonant status and to ensuring that the system operates under high power transfer efficiency. This paper deduced all the analytical expressions of matching capacitance to achieve magnetic resonance for four classical circuitries when considering the coils' resistances. Our results showed that there are several kinds of capacitance matching methods for each circuitry to achieve resonance. Matching capacitances, different from those in the existing literatures, make the system really operate under the magnetic coupling resonance. In literatures, the capacitance at the receiver side compensated only the self‐inductance of the receiver coil and the system except series to series did not operate in the resonance state. Furthermore, the resonance conditions in applications were then given. Accordingly, the expressions of resonant WPT efficiency were presented. These expressions revealed how the underlying factors besides matching capacitance affect the power transfer efficiency, and provided easy access optimizing circuit parameters for high transfer efficiency. Four kinds of circuits were compared through theoretical analysis, calculations and experiments. Experimental results verified the theoretical solutions. Copyright © 2016 John Wiley & Sons, Ltd.     

Location and design of stabilizers in multimachine power systems

A new procedure for the design of decentralized power system stabilizers (PSS) in multimachine power systems (MMPS) is presented in this paper. In the proposed approach, the generators most effective for stabilizer applications are first identified using participation factors and mode controllability matrix. The method determines the parameters of stabilizers by assigning mechanical modes at desired locations. The algorithm uses transfer function matrix between inputs and outputs, to assign the mechanical modes.     

Online concurrent reinforcement learning algorithm to solve two‐player zero‐sum games for partially unknown nonlinear continuous‐time systems

Online adaptive optimal control methods based on reinforcement learning algorithms typically need to check for the persistence of excitation condition, which is necessary to be known a priori for convergence of the algorithm. However, this condition is often infeasible to implement or monitor online. This paper proposes an online concurrent reinforcement learning algorithm (CRLA) based on neural networks (NNs) to solve the H _∞ control problem of partially unknown continuous‐time systems, in which the need for persistence of excitation condition is relaxed by using the idea of concurrent learning. First, H _∞ control problem is formulated as a two‐player zero‐sum game, and then, online CRLA is employed to obtain the approximation of the optimal value and the Nash equilibrium of the game. The proposed algorithm is implemented on actor–critic–disturbance NN approximator structure to obtain the solution of the Hamilton–Jacobi–Isaacs equation online forward in time. During the implementation of the algorithm, the control input that acts as one player attempts to make the optimal control while the other player, that is, disturbance, tries to make the worst‐case possible disturbance. Novel update laws are derived for adaptation of the critic and actor NN weights. The stability of the closed‐loop system is guaranteed using Lyapunov technique, and the convergence to the Nash solution of the game is obtained. Simulation results show the effectiveness of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.     

Excitation and steam‐valving coordinated robust controller design for multi‐machine power systems based on the multi‐index nonlinear robust control approach

This paper proposes a novel multi‐index nonlinear robust control (MNRC) approach for multi‐machine power systems. The MNRC approach combines multi‐index nonlinear control with the control theory. With the multi‐index nonlinear control, which selects the output functions as arithmetic combination of state variables, multiple performance indices of the controlled system can be achieved simultaneously in the nonlinear control framework. The control is able to ensure that the system possess the desired robust performance during disturbance. Then, excitation and steam‐valving coordinated robust controllers are developed based on the MNRC approach for multi‐machine power systems. The effectiveness of the proposed robust controller is evaluated by a six‐machine power system simulation. Simulation results show that the expected dynamic and steady‐state performances of power system can be achieved with the MNRC approach. Meanwhile, it is able to achieve the prescribed system performance despite the presence of disturbances. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A wavelet‐based piecewise approach for steady‐state analysis of power electronics circuits

Simulation of steady‐state waveforms is important to the design of power electronics circuits, as it reveals the maximum voltage and current stresses being imposed upon specific devices and components. This paper proposes an improved approach to finding steady‐state waveforms of power electronics circuits based on wavelet approximation. The proposed method exploits the time‐domain piecewise property of power electronics circuits in order to improve the accuracy and computational efficiency. Instead of applying one wavelet approximation to the whole period, several wavelet approximations are applied in a piecewise manner to fit the entire waveform. This wavelet‐based piecewise approximation approach can provide very accurate and efficient solution, with much less number of wavelet terms, for approximating steady‐state waveforms of power electronics circuits. Copyright © 2006 John Wiley & Sons, Ltd.     

电力系统静态安全分析中的校正控制算法

系统运行过程中,以消除运行约束越限为目标的校正控制策略可能导致系统的静态电压稳定裕度不满足要求。提出一种直接消除系统运行约束越限,间接提高静态电压稳定裕度的校正控制算法。该方法首先消除系统运行约束越限现象,然后通过潮流方程的切向量识别系统的薄弱节点,并利用电压幅值优化来间接地提高系统的静态电压稳定裕度。IEEE24节点和我国西北682节点系统的仿真算例表明,方法简单有效,计算速度快。     

光伏并网发电与电能质量调节统一控制系统

结合光伏并网系统与有源电力滤波器在控制结构和控制策略上的相似性,研究了一种既能实现光伏并网发电又能实现电能质量调节的统一控制系统。对传统的光伏电池最大功率跟踪(Maximum Power Point Tracking,MPPT)方法进行了改进,给出了流程图。针对统一控制系统特点,在PI控制基础上,提出了准PIR控制策略,从理论上分析了其优势,并给出了各参数的计算方法。在Matlab环境下,搭建了系统的仿真模型,仿真结果证明了该系统结构和控制策略的有效性。     

Applications of the passive systems approach to the stability analysis of adaptive controllers for robot manipulators

Utilizing the fact that a manipulator composed of rigid links is a passive system, an approach based on the properties of interconnected passive systems is proposed for the analysis and synthesis of fixed and adaptive controllers for robot manipulators. This approach clarifies the rationale behind the various fixed and adaptive control laws synthesized using Lyapunov functions and provides new adaptation algorithms.     

An augmented automatic choosing control of observer type for nonlinear systems with linear measurement and its application to power systems

This paper deals with a feedback control using automatic choosing functions and the observer-control design procedure for nonlinear systems with linear measurement. A constant term which arises from linearization of a nonlinear equation is treated as a coefficient of a stable zero dynamics. A given nonlinear system is linearized piecewise so as to be able to design the linear optimal controllers with the linear observers. By the automatic choosing functions, these controllers are smoothly united into a single nonlinear feedback controller, which is called an augmented automatic choosing control of observer type. This controller is applied to a transient stability of power systems, whose simulation results show that the new controller enables to expand the stable region well. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.