A study of decoupling with skeleton matrix in two‐degree‐of‐freedom generalized minimum variance control

There are many multi‐input multi‐output (MIMO) systems in chemical plants, and they have multiple time delays of different length in each input and output pair. This paper explains a two‐degree‐of‐freedom (2DOF) control system based on generalized minimum variance control (GMVC) for MIMO systems. It can improve the tracking performance with respect to the reference signals and the response properties for the disturbance. The states between the sampling period can be expressed by using the modified z transform to take account of multiple time delays. Additionally, a tracking controller is designed to decouple the plant. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 28–36, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21046     

Two‐degree‐of‐freedom model matching control of shift‐by‐wire system with emergency mechanical link

A new shift‐by‐wire system having a standby mechanical link with backlash is proposed. The link directly connects the select lever and the manual lever of the automatic transmission in case of emergency. Thus, it is necessary to keep the backlash free during normal operations without generating a force. The angles of the manual lever driven by an actuator should follow the angles of the select lever exactly and quickly. A two‐degree‐of‐freedom model matching control is developed to meet this requirement. It is shown that the backlash is kept free during the range select operation. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 45–52, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21049     

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     

Realization of precise force control using both 2‐DOF control and learning control

Recently, two degrees‐of‐freedom (2DOF) control has been widely recognized to be efficient. The major merit of 2DOF control is independence between tracking performance and the feedback performance. However, there is a limitation on tracking performance in the 2DOF control system. In this paper, we propose a new control system that consists of a conventional 2DOF controller and a learning controller. The role of the learning controller is to realize high tracking performance, which cannot be realized alone by the 2DOF controller. The learning controller can be designed by using only information specifying a 2DOF controller, and it does not need information about the controlled plant. We show some experimental results to verify the effectiveness of the proposed system. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 102–110, 1999     

采用超级电容器供电的功放电源系统设计

为了解决功放变压、整流、滤波式电源的直流电压不稳定和便携式蓄电池电源充电时间长、使用寿命短等问题,分析研究了超级电容器储能系统的优点,提出一种采用超级电容器供电的功放电源系统。采用四个超级电容器组构成两组正负电源,通过智能控制使两组电源轮流充放电,能够很好地解决上述问题,具有良好的使用前景。     

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 study of a two‐stage maximum power point tracking control of a photovoltaic system under partially shaded insolation conditions

A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current–voltage (I–V) characteristic. Therefore, Maximum Power Point Tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current–power (I–P) curve sometimes shows multi‐local maximum power points mode under nonuniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output power point which is not the real maximal output point on the I–P curve. Some papers have tried to avoid this difficulty. However, most of those control systems become rather complicated. The two‐stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under nonuniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 39–49, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20188     

A novel slip‐power recovery system using a PWM boost rectifier

A novel compact slip‐power recovery system having sinusoidal rotor currents is proposed. In this system, a PWM boost rectifier is used as a substitute for a diode rectifier and a boost chopper in a conventional compact slip‐power recovery system. The conventional compact system has the disadvantage that it has a rectangular rotor current, and a motor torque with large ripple, because a diode rectifier remains in the system. Also, the rotor current cannot reach the current reference value near the synchronous speed, because the voltage drop caused by the resistance of the semiconductor devices and so on cannot be neglected when the rotor voltage becomes smaller near the synchronous speed. The use of the system proposed in this paper has solved these problems. The effectiveness of the proposed system was verified through computer simulations and experiments. As a result, the proposed system brings the sinusoidal rotor current, the small torque ripple, and wide controllable range near the synchronous speed. © 2002 Scripta Technica, Electr Eng Jpn, 139(2): 52–60, 2002; DOI 10.1002/eej.10012     

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     

Control using joint torque sensor of robot arm with two‐inertia resonance: Comparison with control using state‐estimation observer

Most industrial robots are driven through reduction gears such as Harmonic Drives and RV gears. Due to the flexibility of the drive system, vibratory behavior occurs during operation. When flexibility is considered, the drive system of the robot joint can be modeled as a resonant mechanical system called a two‐inertia system. Conventionally, studies of two‐inertia system have discussed semiclosed‐loop control using only motor information and a state observer. On the other hand, joint torque sensing of robots has been studied in the harmonic drives that are widely used in robot joints. The joint torque sensor is becoming available with higher performance. In this paper, we consider the control of a robot arm having two‐inertia resonance by using the joint torque sensor. The performance of the torque sensor and that of the observer are compared. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(2): 75–84, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20226     

Configuration of a voltage sag compensator by use of a micro‐SMES and experimental results

A voltage sag compensating using a micro‐SMES is presented. Based on previous works, we have carried out experiments for voltage sag compensation on the laboratory‐built system in order to validate the proposed minimum energy injection voltage sag compensation algorithm. To improve the compensating performance of the system, two‐degree‐of‐freedom voltage control is proposed. In this paper, the circuit configuration and feedback voltage control system of the compensator are described and the experimental results are reported. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 84–92, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10267     

A design method for robust model matching control of nonminimum‐phase discrete‐time systems

This paper presents a design method for robust model matching control of nonminimum‐phase discrete‐time systems. This scheme can robustly control the nominal model in the presence of unmodeled dynamics and can achieve the desired model matching simultaneously. Furthermore, the sufficient condition for stabilizing the nominal model in the presence of the unmodeled dynamics is derived and the existence of bounds for all signals is proved. Finally, computer simulation results are presented to illustrate the effectiveness of the proposed method. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 36–44, 1999     

A matching transformer‐less inrush current suppressor for transformers using a series‐connected small‐rated voltage‐source PWM converter—consideration of the control gains and required ratings of the PWM converter

This paper proposes a new inrush current suppressor using a series‐connected small‐rated PWM converter for a transformer. The PWM converter is directly connected in series between the source and transformer without a matching transformer. The inrush phenomena of the matching transformer, thus, can be avoided. The control gain and required ratings of the series‐connected small‐rated PWM converter are discussed in detail. The capacity of the DC capacitor of the PWM converter is also discussed considering the active power flows into the PWM converter. The PSCAD/EMTDC is used to verify the validity of the proposed inrush current suppressor. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed suppressor can perfectly overcome the inrush phenomena of transformers. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 45–55, 2007; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20374     

Development of a city‐type compact wind power generation system

It is necessary to use renewable energy, such as photovoltaic, wind power, and biomass energy, from the viewpoint of CO₂ regulation and environmental protection of the Earth. In recent years, the tendency is toward larger wind power generation systems to achieve cheaper electricity. Generators having capacities of 1500 kW to 2000 kW tend to dominate the market. However, a large wind power generation system has limitations in terms of location and can be installed only in the suburbs. At the same time, a city‐type compact wind power generation system, designed for city needs, has more flexibility and can be installed in the residential areas of a city. In this paper, we introduce an original control operation system called a “pump‐up” operation system, designed to effectively use the city wind, and report the results of its field test. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 56–63, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20440     

New digital control and protection equipment using multiprocessor architecture of distributed functions for power system

Control and protection of equipment in power systems generally require a high-information processing capability to cope with today's power system requirements. Then, new digital control and protection equipment have been developed using high-speed and high-precision processors. Essential requirements for the new control and protection equipment are a multiprocessor architecture of distributed functions to retain sufficient computing power (fast and high-precision operations), and flexible and expandable hardware with high reliability. In multiprocessor architecture, it is important to determine how the distributed processors share the functions. By analysis and synthesis of relaying and control processings, we divided them into six processing circuits. This paper proposes a multiprocessor architecture of distributed functions, using 32-bit floating-point and 16-bit microprocessors depending on the computational requirements. In addition a digital filter for fast sampled data is described along with performance of a digital relay.     

Control schemes and transient characteristics of a high‐speed phase shifter for power flow control in power transmission systems

In recent years, attention has been paid to the concept of FACTS (Flexible AC Transmission Systems), along with significant progress in power electronic technology. A high‐speed phase shifter, which is one of the most promising devices in the FACTS concept, has the potential of power flow control and/or voltage stability in power transmission systems. In this paper, theory and experiment reveal that conventional high‐speed phase shifters may cause power swings in a transient state as a result of coupling between instantaneous active and reactive power control loops. Thus, two new control schemes for a high‐speed phase shifter are proposed to achieve both power flow control and power swing damping. The second proposed control scheme is based on the control scheme of an already proposed series active filter. Simulated and experimental results agree well with analytical results, not only in steady states but also in transient states. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 74–82, 1999     

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     

Resolution of a digital servo control system using single‐bit digital signal processing

The application of single‐bit digital signal processing to mechanical control systems has already been proposed by the authors. Multibit A/D converters have been improved to a high level. But it is difficult to improve high‐resolution A/D by the latest semiconductor technologies. A single‐bit digital signal can be generated by a delta‐sigma modulator. Single‐bit digital signal has a small quantized error at low frequency. Then with this single‐bit digital signal processing, high resolution on controlling such a narrow‐bandwidth mechanical system will be realized. In this paper, resolution of analog, multibit, and single‐bit control systems is estimated via simulation. According to the results of simulations, a single‐bit control system has a higher resolution than a multibit system under conditions of equal bit rates. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 94–101, 1999     

An improved method of voltage utility factor for PWM control of a five‐leg inverter in two induction motor drives

This paper presents an improved method of voltage utility factor (VUF) from 50 to 86.6% for a five‐leg inverter when two induction motors are driven in vector control and in a condition where the frequencies of the two motors are not very different, and the improved method of voltage utility is theoretically shown. Many modulation methods for the five‐leg inverter have been proposed, but the voltage utility factor is 50% in these methods. The voltage utility factor of the five‐leg inverter is lower than that of the three‐leg inverter as maximum voltage utility factor of the three‐leg inverter is 100%. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fault analysis of the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system

Fault analyses are performed for the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system through a line‐commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short‐circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single‐line ground fault and of a three‐phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design‐point flow of the MHD generator. Phase‐control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001