This paper presents a robust control approach to enhance the participation of Variable Speed Wind Turbines (VSWTs) in the primary frequency regulation during network disturbances. The proposed control system utilizes an H∞ Linear Matrix Inequality (H∞ LMI) based scheme to improve the closed-loop performance. In order to demonstrate the effectiveness of the proposed control scheme, it is compared with two classical control systems: the Inertial Control (IC) and the Modified Inertial Control (MIC). Several simulations on a multi-machine test system were performed in Matlab/Simulink environment. The H∞ LMI controller optimizes the trade-off between frequency deviation smoothing and wind turbine (WT) speed deviation after the disturbance. Results show a considerable improvement in frequency deviation smoothing, optimal speed recovery and power injection, during a sudden variation in the system load, compared with the two traditional approaches. A desirable robust performance was also obtained with the proposed scheme after variations in the system parameters.

In this paper, a robust proportional-integral-derivative (PID) feedback compensator is designed for a low power radio-frequency (RF) amplifier, using Kharitonov’s theorem. The robust D-stability concept is used to achieve robust performance by clustering the characteristic polynomial equation roots of the closed loop system in a specified angular region. Then, the controller is realized and the obtained results demonstrate a desirable amplification over the operating frequency band. It is shown that the designed feedback compensator guarantees the robust stability and robust performance for a wide range parameter variation.

Frequency regulation in interconnected networks is one of the main challenges posed by wind turbines in modern power systems. The wind power fluctuation negatively contributes to the power imbalance and frequency deviation. This paper presents an intelligent agent based load frequency control (LFC) for a multi-area power system in the presence of a high penetration of wind farms, using multi-agent reinforcement learning (MARL). Nonlinear time-domain simulations on a 39-bus test power system are used to demonstrate the capability of the proposed control scheme.

A new intelligent agent based control scheme, using Bayesian networks (BNs), to design automatic generation control (AGC) system in a multi-area power system is addressed. Model independency and flexibility in specifying the control objectives, make the proposed approach as an attractive solution for AGC design in a real-world power system. The proposed control scheme is tested in simulation on a three areas power system and shows desirable performance. The results are also compared with the multi-agent reinforcement learning based AGC design technique.

Frequency regulation in interconnected networks is one of the main challenges posed by wind turbines in modern power systems. The wind power fluctuation negatively contributes to the power imbalance and frequency deviation. This paper presents an intelligent agent based load frequency control (LFC) for a multi-area power system in the presence of a high penetration of wind farms, using multi-agent reinforcement learning (MARL). Nonlinear time-domain simulations on a 39-bus test power system are used to demonstrate the capability of the proposed control scheme.

As the use of renewable energy sources (RESs) increases worldwide, there is a rising interest on their impacts on power system operation and control. An overview of the key issues and new challenges on frequency regulation concerning the integration of renewable energy units into the power systems is presented. Following a brief survey on the existing challenges and recent developments, the impact of power fluctuation produced by variable renewable sources (such as wind and solar units) on system frequency performance is also presented. An updated LFC model is introduced, and power system frequency response in the presence of RESs and associated issues is analysed. The need for the revising of frequency performance standards is emphasised. Finally, non-linear time-domain simulations on the standard 39-bus and 24-bus test systems show that the simulated results agree with those predicted analytically.

Frequency deviation can be used as an indicator of imbalance between supply and demand. When generation is insufficient, it can cause frequency decline in a power system operation. Implementing under frequency load shedding (UFLS) is one of the common methods to overcome this problem. This paper proposes a novel approach for adaptive load shedding. The concept is an extension of shared and targeted load shedding using reserve margin. The optimal system configuration is then selected from those candidates to fulfill operational objectives. Operational constraints related to system parameters, threshold frequency, total of load shed and control area including line capacity are considered. An example using four sub-areas connected to an external system shows that the proposed regional coordination as an adaptive UFLS is feasible.

This paper addresses a new intelligent based emergency power system control strategy. To design an optimal load shedding scheme, both system frequency and voltage characteristics are considered. A new tool for post-contingency dynamic behavior and stability analysis is introduced. The proposed methodology is supplemented by nonlinear simulations to examine the effectiveness against serious contingencies.

This paper proposes a more realistic model for automatic generation control (AGC) design in an interconnected power system by considering the generation rate constraint (GRC), dead band, and time delays. These physical constraints imposed to power system by governor-turbine, filters, thermodynamic process, and communication channels. The simplicity of structure and acceptable response of the well-known integral controller make it attractive for power system AGC issue. In this paper, a genetic algorithm (GA) approach is employed to calculate the controller parameters to achieve an optimal performance. Importance of considering the physical constraints is demonstrated by examination of the closed loop performance in a 3-control area power system. It is shown that neglecting above physical constraints, simultaneously or in part, leads to impractical and invalid results. Taking to account the advantages of the GA besides considering a more complete dynamic model provides a flexible and more realistic AGC system in comparison of existing conventional schemes.

In this paper, A new load frequency control (LFC) using the model predictive control MPC technique is presented. The MPC technique has been designed such that the effect of the uncertainty due to governor and turbine parameters variation and load disturbance is reduced. A simplified frequency response model is introduced, and physical constraints of the governor and turbine are considered in this model. The model was employed in the MPC structure. Digital simulations for a single control area are provided to validate the effectiveness of the proposed scheme. The results show that, with the proposed MPC technique, the system performance has a good robustness in the face of uncertainties due to governor and turbine parameters variation and load disturbance. A performance comparison between the proposed controller and a conventional integral control scheme is carried out confirming the superiority of the proposed MPC technique.

A robust controller for a quadratic buck converter is designed using Kharitonov’s theorem. Then, the controller is implemented and experimental results are given for a low power switching quadratic buck converter. The robust D-stability concept is used to achieve robust performance by clustering the roots of closed loop system characteristic polynomial equation in a specified angular region. The obtained results demonstrate a desirable reference voltage tracking, line disturbance rejection and show that the designed controller guarantees the robust stability and robust performance for a wide range of line voltage and load variation.

Optimal load shedding (LS) design as an emergency plan is one of the main control challenges posed by emerging new uncertainties and numerous distributed generators including renewable energy sources in a modern power system. This paper presents an overview of the key issues and new challenges on optimal LS synthesis concerning the integration of wind turbine units into the power systems. Following a brief survey on the existing LS methods, the impact of power fluctuation produced by wind powers on system frequency and voltage performance is presented. The most LS schemas proposed so far used voltage or frequency parameter via under-frequency or under-voltage LS schemes. Here, the necessity of considering both voltage and frequency indices to achieve a more effective and comprehensive LS strategy is emphasized. Then it is clarified that this problem will be more dominated in the presence of wind turbines.

This paper quantifies the impact of providing a shortterm excess active power support of a variable speed wind turbine (VSWT) and effect of super magnetic energy storage (SMES) unit on frequency control, particularly temporary minimum frequency (TMF) term. To demonstrate the effect of these factors on the power system frequency, a three-area power system is considered as a test system.

In a power network, when a propagation energy wave caused by a disturbance hits a weak link, a reflection has appeared and some of energy is transferred across the link. In this work, an analytical descriptive methodology is proposed to study the dynamical stability of a large scale power system. For this purpose, the measured electrical indices (angle, or voltage/frequency) following a fault in different points among the network are used, and the behaviors of the propagated waves through the lines, nodes and buses are studied. This work addresses a new tool for power system stability analysis based on a descriptive study of electrical measurements. The proposed methodology is also useful to detect the contingency condition and synthesis of an effective emergency control scheme.

In a power network, when a propagation energy wave caused by a disturbance hits a weak link, a reflection is appeared and some of energy is transferred across the link. In this work, an analytical descriptive methodology is proposed to study the dynamical stability of a large scale power system. For this purpose, the measured electrical indices (angle, or voltage/frequency) following a fault in different points among the network are used, and the behaviors of the propagated waves through the lines, nodes and buses are studied. This work addresses a new tool for power system stability analysis based on a descriptive study of electrical measurements. The proposed methodology is also useful to detect the contingency condition and synthesis of an effective emergency control scheme.

A survey on coordinated design of automatic voltage regulator and power system stabilizer

International Review of Automatic Control (IREACO)

The most load shedding (LS) schemas proposed so far used voltage and frequency parameters via under-frequency (UFLS) and under-voltage (UVLS) LS schemes, separately. The under-frequency and under-voltage relays are working in the power system without any coordination. In this paper, the necessity of considering both of voltage and frequency indices to achieve a more effective/adaptive and comprehensive LS strategy is illustrated. It is also clarified that this problem will be more dominated in the presence of wind turbines. Finally, an effective LS scheme considering both system frequency and voltage characteristics is addressed.

Fuzzy rule base and inference engine

The load–frequency control (LFC) problem has been one of the major subjects in a power system. In practice, LFC systems use proportional–integral (PI) controllers. However since these controllers are designed using a linear model, the non-linearities of the system are not accounted for and they are incapable of gaining good dynamical performance for a wide range of operating conditions in a multi-area power system. A strategy for solving this problem because of the distributed nature of a multi-area power system is presented by using a multi-agent reinforcement learning (MARL) approach. It consists of two agents in each power area; the estimator agent provides the area control error (ACE) signal based on the frequency bias (β) estimation and the controller agent uses reinforcement learning to control the power system in which genetic algorithm optimisation is used to tune its parameters. This method does not depend on any knowledge of the system and it admits considerable flexibility in defining the control objective. Also, by finding the ACE signal based on β estimation the LFC performance is improved and by using the MARL parallel, computation is realised, leading to a high degree of scalability. Here, to illustrate the accuracy of the proposed approach, a three-area power system example is given with two scenarios

As the use of wind power turbines increases worldwide, there is a rising interest on their impacts on power system operation and control. Frequency regulation in interconnected networks is one of the main challenges posed by wind turbines in modern power systems. The wind power fluctuation negatively contributes to the power imbalance and frequency deviation. Significant interconnection frequency deviations can cause under/over frequency relaying and disconnect some loads and generations. Under unfavorable conditions, this may result in a cascading failure and system collapse.This chapter presents an overview of the key issues on frequency regulation concerning the integration of wind power units into the power systems. Following a brief survey on the recent developments, the impact of power fluctuation produced by wind units on system frequency performance is presented. An updated frequency response model is introduced, and the inertia contribution of wind turbine in the overall system inertia is properly considered. The need for the revising of frequency performance standards is emphasized, and an intelligent agent based load frequency control (LFC), using multi-agent reinforcement learning (MARL) is proposed. Finally, nonlinear time-domain simulations on a 39-bus test power system are used to demonstrate the capability of the proposed control structure, and to analyze the system frequency performance in the presence of high wind power penetration and associated issues.

The most load shedding (LS) schemas proposed so far used voltage and frequency parameters via under-frequency (UFLS) and under-voltage (UVLS) LS schemes, separately. The under-frequency and under-voltage relays are working in the power system without any coordination. In this paper, the necessity of considering both of voltage and frequency indices to achieve a more effective / adaptive and comprehensive LS strategy is illustrated. Then it is clarified that this problem will be more dominated in the presence of wind turbines. Finally, a general LS scheme considering both system frequency and voltage characteristics is addressed.

In this paper, we present a new Call Admission Control (CAC) for IEEE 802.16 broadband wireless networks considering Quality of Service (QoS) constraint. With the assumption that there is a scheduling algorithm to allocate total bandwidths, our proposed CAC algorithm accepts new request for some slot times temporary. In this algorithm, during certain time slots, departure rate for ongoing connections will be decreased and for new connection will increase. After this period, if QoS for ongoing connections and new request is satisfied, new request will be accepted permanently and otherwise it will be rejected. We study the results in two phases, first we show that our algorithm works well with some routine scheduling algorithms and second we show the performance of our algorithm in comparison to some other CAC algorithms. We simulate our algorithm with Matlab tools, and the results show proposed algorithm is quite efficient.

Re-evaluation of emergency control and protection schemes for distribution and transmission networks are one of the main problems posed by wind turbines in power systems. Change of operational conditions and dynamic characteristics influence the requirements to control and protection parameters.Introducing a significant wind power into power systems leads to new undesirable oscillations. The local and inter-modal oscillations during large disturbances can cause frequency and voltage relays to measure a quantity at a location that is different to the actual underlying system voltage and frequency gradient. From an operational point of view, this issue is important for those networks that use the protective voltage and frequency relays to re-evaluate their tuning strategies.In this chapter, an overview of the key issues in the use of high wind power penetration in power system emergency control is presented. The impact of wind power fluctuation on system frequency, voltage and frequency gradient is analyzed, the need for the revising of tuning strategies for frequency protective relays, automatic under-frequency load shedding (UFLS) and under-voltage load shed-ding (UFLS) relays are also emphasized.In the present chapter, necessity of considering both system frequency and voltage indices to design an effective power system emergency control plan is shown. Then, an intelligent artificial neural network (ANN) based emergency control scheme considering the dynamic impacts of wind turbines is proposed. In the developed algorithm, following an event, the related contingency is determined by an appropriate ANN using the online measured tie-line powers. A suitable set of voltage sensitivity indices based on a comprehensive voltage stability analysis in the presence of the wind turbines is proposed. Another intelligent ANN is used to examine the stability margin by estimating the system power-voltage (P-V) curves. Finally, the system frequency gradient, voltage sensitivity indices and stability information are properly used by an effective load shedding algorithm. The proposed emergency control scheme and discussions are supplemented by computer nonlinear simulations on the IEEE 9-bus test system.

The authors consider network utility maximisation problem in orthogonal frequency division multiple access (OFDMA) networks to study cross-layer, fair and efficient resource allocation. Assuming knowledge of the instantaneous channel gains, this problem is decomposed into rate control and scheduling problems at the transport and medium access control/physical layers, respectively. In contrast to the rate control problem that is solved using subgradient method, the scheduling problem has high computational complexity owing to optimising integer and continuous variables simultaneously. Based on the results from analysing the integer relaxed scheduling problem, computationally efficient adaptive scheduling (CEAS) and opportunistic time division multiple access (Opp-TDMA) scheduling schemes are proposed to joint subcarrier assignment and power allocation. Simulation results demonstrate that aggregate utility achieved in the network with the cooperation between rate control and proposed scheduling schemes outperforms those of previously proposed joint channel-aware and queue-aware scheduling schemes. Also, through comparison with the optimal solution, the authors conclude that CEAS is applicable for OFDMA real-time scheduling due to low computational complexity and high performance.

We consider the utility-maximization problem in the downlink of wireless mesh networks with orthogonal frequency-division multiple access (OFDMA). We formulate this problem as a cross-layer design of joint rate control and OFDMA scheduling to efficiently utilize the scarce radio resources. The problem is decoupled into a rate-control problem at the transport layer and a channel-aware and queue-aware scheduling problem at the Media Access Control/physical layer (MAC/PHY). The rate-control problem adjusts arrival rates to the base station (BS) queues, and the scheduling problem determines link rates, i.e., departure rates from the BS and other network nodes, through subcarrier and modulation rate assignment. Although the rate-control problem is locally solved at the BS, we propose a greedy algorithm that solves the scheduling problem in a distributed manner, at network nodes. Furthermore, we propose a heuristic algorithm for fast execution of the scheduling scheme at individual nodes. Numerical results show that the heuristic algorithm performs comparably with the greedy algorithm, whereas it has lower computational complexity. In addition, our proposed scheduling scheme, when it cooperates with the rate-control mechanism, improves the network performance in terms of end-to-end delay, aggregate utility, and fairness.

We have analysed the output pulse characteristics of semiconductor optical amplifier (SOA). They can be modified due to the variation of input parameters, such as, gain, input pulsewidth and internal loss imposed by the medium. In our model, the effect of self-phase modulation (SPM) has taken into consideration to improve the accuracy of simulation results. The proper output pulse characteristics can be achieved by controlling the mentioned parameters. We used a simplified nonlinear Schrodinger equation (SNSE) to model the behaviour of SOAs. The SNSE is solved using the finite-difference beam propagation method (FDBPM).

We have numerically analysed the effects of SOA’s medium length on four-wave mixing (FWM) characteristics in semiconductor optical amplifier (SOA). We have studied the shape, spectrum, full width at half maximum (FWHM), timebandwidth product, peak shift and frequency shift of the FWM signal for weak and strong input pump and probe pulses. We have used the nonlinear propagation equation taking into account gain spectrum dynamic gain saturation which depends on carrier depletion, carrier heating, spectral hole-burning, group velocity dispersion, self phase modulation and two photon absorption. We have used finite-difference beam propagation method (FD-BPM) to simulate the wave evolution both in time and spectral domain in the SOA. From this simulation, it has become clear that the FWM signal characteristics are dependent to the length of SOA. In high power regime, nonlinear phenomena in SOA have more influences on the FWM signal characteristics.

In this paper, we present a numerical model to study counter pulse propagation in semiconductor optical amplifiers. An improved finite-difference beam propagation method for solving the modified nonlinear Schrodinger equation is applied for the first time in the counterpropagation regime. In our model, group velocity dispersion, two-photon absorption, ultrafast nonlinear refraction, and the change in the gain peak wavelength with carrier density are included, which have not been considered simultaneously in previous counterpropagation models. The model is applied to demonstrate how a subpicosecond and picosecond probe pulse shape and spectrum can be modified by a counterpropagating pump pulse. Based on the results obtained by this model, while subpicosecond probe pulses can be compressed by in this scheme, their time-bandwidth product are also improved significantly. Furthermore, the effects of several parameters are analyzed to obtain the proper probe spectral peak shift using counterpropagating probe pulses. The accuracy and computational efficiency of the new scheme are assessed through numerical examples and are shown to be superior to previously published approaches.

An efficient pulse shaping method using counter-propagating pulses in the femtosecond regime is proposed and investigated. The effects of pump pulse power and pulsewidth on probe pulse are studied in counter-propagation scheme. It is shown that, with the proposed method, output probe pulse temporal and spectral peak shift due to femtosecond nonlinearities can be compensated, while the output pulse is amplified sufficiently. Furthermore, in relatively high power regime, the probe pulsewidth and time-bandwidth product are improved using counter-propagating pump pulse.

Larger width of P-cladding layer in p-i-n waveguide of traveling wave electroabsorption modulator (TWEAM) results in lower resistance and microwave propagation loss which provides an enhanced high speed electro-optical response. In this paper, a full-vectorial finite-difference-based optical mode solver is presented to analyze mushroom-type TWEAM. The important parameters in the high-frequency TWEAM design such as optical effective index and transverse mode confinement factor are calculated. The modulation response of mushroom-type TWEAM is calculated by considering interaction between microwave and optical fields in waveguide and compared with conventional ridge-type TWEAM. The calculated 3dB bandwidths for ridge-type and mushroom-type TWEAM are about 139 GHz and 166 GHz for 200 mum and 114 GHz and 126 GHz for 300 mum waveguide length, respectively.

Optical ultra-short pulse compression and amplification using semiconductor optical amplifier (SOA) is presented. Using pump-probe pulse configuration, we present an SOA model which includes the nonlinear effects such as, spectral hole burning (SHB), carrier heating (CH), two-photon absorption (TPA) and group velocity dispersion (GVD) taking into account gain spectrum effect. Then by adjusting time delay between the pump pulse and probe pulse we use the model for simultaneous compression and amplification of probe pulse. We also analyze the four wave mixing (FWM) signal during pulse compression process. It is shown that dispersive effect of GVD on output probe pulse becomes more important for larger cavity length and probe-pump pulses relative time delays.

Boost dc-to-dc converters have very good source interface properties. The input inductor makes the source current smooth and hence these converters provide very good EMI performance. On account of this good property, the boost converter is also the preferred converter for off-line UPF rectifiers. One of the issues of concern in these converters is the large size of the storage capacitor on the dc link. The boost converter suffers from the disadvantage of discontinuous current injected to the load. The size of the capacitor is therefore large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is quite demanding. This is specially so in the emerging application areas of automotive power conversion, where the input voltage is low (typically 12V) and large voltage boost (4 to 5) are desired. The first part of this thesis suggests multi-phase boost converter to overcome the disadvantages of large size storage capacitor in boost converter. Comparison between the specification of single stage and multi-stages is thoroughly examined. Besides the average small signal analysis of N converters in parallel and obtaining an equivalent second order system are discussed. By paralleling the converters the design of closed loop control is a demanding task. To achieve proper current sharing among the stages using current control method is inevitable. Design and implementation of closed loop control of multi-phase boost converter both in analog and digital is the topic of next part of the thesis. Comparison between these two approaches is presented in this part and it will be shown that digital control is more convenient for such a topology on account of the requirement of synchronization, phase shifted operation, current balancing and other desired functions, which will be discussed later in detail. A new direct digital control method, which is simple and fast, is developed. Two different realizations with DSP controller and FPGA controller are considered. In the last part of the thesis a novel soft switching circuit for boost converter is presented. It provides Zero Voltage Switching (ZVS) for the main switch and Zero Current Switching (ZCS) for the auxiliary switch. The paper presents the idealized analysis giving all the circuit intervals and the equations necessary for the design of such a circuit. The proposed soft switching circuit is particularly suited for the tapped-inductor boost circuit with a minimum number of extra components. Extension of the method to tapped inductor boost converter addresses the application of Zero Voltage Transition (ZVT) to high conversion ratio converters. Extension of the method to multiphase boost converter shows that with less number of auxiliary switches soft switching operation can be achieved for all interleaved switching devices. Several laboratory prototype boost converters have been built to confirm the theoretical results and design methods are matching with both simulation and experimental results.

Larger width of P-cladding layer in p-i-n waveguide of traveling wave electroabsorption modulator (TWEAM) results in lower resistance and microwave propagation loss which provides an enhanced high speed electro-optical response. In this paper, a full-vectorial finite-difference-based optical mode solver is presented to analyze mushroom-type TWEAM. The important parameters in the high-frequency TWEAM design such as optical effective index and transverse mode confinement factor are calculated. The modulation response of mushroom-type TWEAM is calculated by considering interaction between microwave and optical fields in waveguide and compared with conventional ridge-type TWEAM. The calculated 3dB bandwidths for ridge-type and mushroom-type TWEAM are about 139 GHz and 166 GHz for 200 mum and 114 GHz and 126 GHz for 300 mum waveguide length, respectively.

The use of counter-propagating sub-picosecond pulses to modify the temporal shape and spectrum of a probe pulse in an SOA is investigated using a modified nonlinear Schroumldinger equation (MNLSE), which includes all of the dynamical processes relevant to the sub-picosecond range. The MNLSE is solved using a novel numerical method based on trapezoidal integration and central difference techniques. It is shown that by using the counter propagation scheme besides amplification, both time and spectral profile of the propagated pulse are compressed. Furthermore, the output pulse distortion caused by nonlinear phenomena in SOA is improved.

In this paper, we present a numerical model to study counter pulse propagation in semiconductor optical amplifiers. An improved finite-difference beam propagation method for solving the modified nonlinear Schrödinger equation is applied for the first time in the counterpropagation regime. In our model, group velocity dispersion, two-photon absorption, ultrafast nonlinear refraction, and the change in the gain peak wavelength with carrier density are included, which have not been considered simultaneously in previous counterpropagation models. The model is applied to demonstrate how a subpicosecond and picosecond probe pulse shape and spectrum can be modified by a counterpropagating pump pulse. Based on the results obtained by this model, while subpicosecond probe pulses can be compressed by in this scheme, their time-bandwidth product are also improved significantly. Furthermore, the effects of several parameters are analyzed to obtain the proper probe spectral peak shift using counterpropagating probe pulses. The accuracy and computational efficiency of the new scheme are assessed through numerical examples and are shown to be superior to previously published approaches.

This paper proposes a blind reversible watermarking approach for medical images based on histogram shifting in wavelet domain. An integer wavelet transform is applied to map the integer host image components to integer wavelet coefficients. The watermark information is inserted into the high frequency subband regions of the transformed image. According to the capacity required for the watermark, two thresholds, T ₁ and T ₂ , are selected, one in the begging part and the other in the end part of the histogram of the high frequency subbands of the transformed image. Two zero-points, Z ₁ and Z ₂ are also created by properly shifting the beginning and the end parts of the histogram. The part of the histogram located between the two thresholds remains unchanged. The binary watermark data are inserted in the thresholds and zero-points locations. The high PSNR (above 53 dB) obtained for several watermarked medical images, indicates imperceptibility of the approach. Experimental results also show superiority of the proposed approach in compare to some other methods that are based on histogram shifting in spatial as well as integer wavelet domains. Enabling lossless reconstruction of both watermark and host image, beside providing the high quality for the watermarked image, make the proposed approach attractive for medical image watermarking applications.

This paper addresses a control methodology to enhance power system dynamic stability and voltage regulation by augmenting existing generator controls (conventional PSS and AVR) using an optimal static gain vector. The control design problem is reduced to finding a new control loop including a simple fixed gain vector. In order to optimal tune gain elements, the problem is formulated via an H_∞ static output feedback (H_∞-SOF) control technique, and the solution is easily found using an iterative linear matrix inequalities (ILMI) algorithm. Real-time experiments have been performed for a longitudinal four-machine infinite-bus system on the Analog Power System Simulator at the Research Laboratory of the Kyushu Electric Power Co. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances.

In this paper we calculate the spatial dependency of the spontaneous emission in semiconductor laser cavity using a model based on transmission line laser method (TLLM). Results show that in the simple ridge laser structure, the major part of the spontaneous emission occurs at the middle of the cavity and so uniform spontaneous emission can’t be assumed

In this paper, two robust decentralized proportional-integral (PI) control designs are proposed for load frequency control (LFC) with communication delays. In both methodologies, the PI-based LFC problem is reduced to static output feedback (SOF) control synthesis for a multiple delay system. The first one is based on the optimal H1 control design using a linear matrix inequalities (LMI) technique. The second control design gives a suboptimal solution using a developed iterative linear matrix inequalities (ILMI) algorithm via the mixed H2/H1 control technique. The control strategies are suitable for LFC applications that usually employ PI control. The proposed control strategies are applied to a three control area power system with time delays and load disturbance to demonstrate their robustness. 2007 Elsevier Ltd. All rights reserved.

In this paper, two robust decentralised proportional integral (PI) control designs are proposed for load frequency control (LFC) with communication delays. In both methodologies, the PI based LFC problem is reduced to a static output feedback (SOF) control synthesis for a multiple delay system. The first one is based on the optimal H_∞ control design using a linear matrix inequalities (LMI) technique. The second control design gives a suboptimal solution using a developed iterative linear matrix inequalities (ILMI) algorithm via the mixed H₂/H_∞ control technique. The control strategies are suitable for LFC applications that usually employ PI control. The proposed control strategies are applied to a three control area power system with time delays and load disturbance to demonstrate their robustness.

Frequency regulation in off-normal conditions has been an important problem in electric power system design/operation and is becoming much more significant today due to the increasing size, changing structure and complexity of interconnected power systems. Increasing economic pressures for power system efficiency and reliability have led to a requirement for maintaining power system frequency closer to nominal value. This paper presents a decentralized frequency control framework using a modified low-order frequency response model containing a proportional-integral (PI) controller. The proposed framework is suitable for near-normal and emergency operating conditions. An H∞ control technique is applied to achieve optimal PI parameters, and an analytic approach is used to analyse the system frequency response for wide area operating conditions. Time-domain simulations with a multi-area power system example show that the simulated results agree with those predicted analytically.

In this paper, we propose and analyze a different channel allocation scheme in mobile cellular networks which not only gives priority to handoff calls but also tries to protect originating calls. We use channel reservation to protect handoff calls and in contrast, to protect originating calls, we set a maximum reservable channel, NG, in our scheme. In channel reservation schemes, there are some periods that reserved channels are not actively utilized. In this paper, these periods are defined as dead time. Some new performance measures of the system such as the distribution and the mean dead time of a reserved channel are obtained. The main contribution of this work is to find optimum NG so as to maximize the service providerpsilas revenue while customerspsila satisfaction (in term of connection continuity) and system utilization (in term of system capacity and less dead time) are justified jointly. We assume a general cost structure which is due to blocking of handoff calls, blocking of originating calls and unutilized periods of reserved channels. Based on the total cost, we investigate the trade-off between the service utilization and customerspsila satisfaction.

The dynamic performance of differential Symmetric Mach Zehnder Interferometer (SMZI) switch based on semiconductor optical amplifier (SOA) phase shifter is analyzed. For the first time, we investigate the effect of two photon absorption (TPA) as a nonlinear effect of SOA on the push-pull MZ switching scheme where SOAs are placed in each arm. It is shown that our switch is easily affected by TPA phenomena in SOA-SMZI. We use finite difference beam propagation (FD-BPM) method for analysis and solve nonlinear modified Schrödinger equation. In our results we take into account all nonlinear effects relevant to subpicosecond regime in SOA such as group velocity dispersion (GVD), Kerr effect, carrier heating and spectral hole burning (SHB).

In this paper we investigate joint channel-aware and queue-aware scheduling to downlink subcarrier allocation in the context of Orthogonal Frequency Division (OFDM) networks. The objectives are to provide users with high throughputs and queues with high degree of stability that decreases the service discontinuity of non-real-time applications. The term stability for a queue is defined as the ratio of average departure rate to the average arrival rate. To achieve this, Multi Carrier Opportunistic Stability Queue (MC-OSQ) scheduling scheme is proposed and multi carrier implementation of well-known MLWDF scheduling scheme is extended. Comparing throughput and degree of stability performance of these schemes with queue-ware scheduling scheme demonstrates that joint channel-aware and queue-aware scheduling schemes perform absolutely well. Furthermore, simulation results reveal that MC-OSQ scheme, by taking the stability degree of queues into account performs the same as multi carrier implementation of MLWDF.

In this paper, a nonlinear model predictive control (NMPC) based on a piecewise linear Wiener model is applied to a polymerization reactor. The static nonlinear part of the applied Wiener model is approximated using the piecewise linear functions and its dynamic linear element is identified using a state-space description. Due to the nonlinear gain of model, for gathering data, a generalized multiple-level noise (GMN) test has been used. This test demonstrates the response of the system to a range of amplitude changes. The predictive control based on this model retains all the interested properties of the classical linear MPC. This approach leads to a quadratic programming problem due to the canonical structure of the nonlinear gain. The control scheme has been applied to a polymerization reactor as a MIMO process. Results show that the used Wiener model is able to identify the nonlinear processes effectively. The nonlinear predictive control based on this model is compared to the linear MPC. The parameters of both linear and nonlinear model predictive controllers are tuned and the performances of both methods are compared. It is shown that the nonlinear controller has a better performance, having short settling time and without any overshoot compared to its linear one. Moreover, this controller has a good performance and rejects unmeasured disturbances effectively.

In this paper performance of dynamic bandwidth allocation in broadband wireless networks under dynamic arrival process and channel SNR is evaluated using queuing analysis framework. Adaptive modulation and coding rate based on IEEE 802.16 standard is used to adjust the transmission rate adaptively in each frame time according to channel quality in order to obtain multi-user diversity gain. Arrival process is considered to be discrete-time Markov chain which is modeled by the Markov modulated Poisson process (MMPP) as the traffic source. Quality of service parameters are evaluated under several allocated bandwidths to a single queue in the case of two scenarios: 1) different arrival traffic intensity, and 2) different channel quality. As expected, dynamic bandwidth allocation according to channel variations improves quality of service parameters.

 Online Manuscript Access

Transfer matrix method (TMM) has been applied to analyze characteristics of semiconductor laser optical amplifiers. The input signal is sinusoidal modulating wave and we do not assume the modulating bias signal as well. We have shown that the distortion arises from gain modulation at low modulation frequencies, but in microwave modulation frequencies, the gain takes an average value and the response becomes linear.

This paper addresses a new method for robust decentralized design of proportional‐integral‐based load–frequency control (LFC) with communication delays. In the proposed methodology, the LFC problem is reduced to a static output feedback control synthesis for a multiple delays power system, and then the control parameters are easily carried out using robust H_∞ control technique. To demonstrate the efficiency of the proposed control strategy, an experimental study has been performed on the Analog Power System Simulator at the Research Laboratory of the Kyushu Electric Power Co. in Japan. Copyright © 2007 John Wiley & Sons, Ltd.

 Many real world control systems usually track several control objectives, simultaneously. At the moment, it is desirable to meet all specified goals using the controllers with simple structures like as proportional-integral (PI) and proportional-integral-derivative (PID) which are very useful in industry applications. Since in practice, these controllers are commonly tuned based on classical or trial-and-error approaches, they are incapable of obtaining good dynamical performance to capture all design objectives and specifications. This paper addresses a new method to bridge the gap between the power of optimal multiobjective control and PI/PID industrial controls. First the PI/PID control problem is reduced to a static output feedback control synthesis through the mixed H2/H∞ control technique, and then the control parameters are easily carried out using an iterative linear matrix inequalities (ILMI) algorithm. Numerical examples on load-frequency control (LFC) and power system stabilizer (PSS) designs are given to illustrate the proposed methodology. The results are compared with genetic algorithm (GA) based multiobjective control and LMI based full order mixed H2/H∞ control designs.

This paper addresses a control methodology to enhance power system dynamic stability and voltage regulation by augmenting existing generator controls (conventional PSS and AVR) using an optimal static gain vector. The control design problem is reduced to find a new control loop including a simple fixed gain vector. In order to optimal tuning of gain elements, the problem is formulated via an H∞ static output feedback (H∞-SOF) control technique, and the solution is easily carried out using an iterative linear matrix inequalities (ILMI) algorithm. It is shown that we can easily remove the conventional PSS and AVR and replace those by the mentioned simple H∞-SOF controller. Real-time experiment has been performed for a longitudinal four-machine infinite-bus system on the Analog Power System Simulator at the Research Laboratory of the Kyushu Electric Power Co*. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances.

Automatic Generation Control (AGC) problem has been one of the major subjects in electric power system design operation and is becoming much more significant today in accordance with increasing size, changing structure and complexity of interconnected power systems. In practice, AGC systems use simple proportional-integral (PI) controllers. However, since the PI controller parameters are usually tuned based on classical or trial-and-error approaches, they are incapable of obtaining good dynamical performance for a wide range of operating conditions and various load changes scenarios in a multi-azea power system.In this paper, in order to design a robust PI controller for the AGC in a multi-area power system, fast the problem is formulated as an 1-h static output feedback control problem, and then it is solvedusing a developed iterative linear matrix inequalities algorithm to get an optimal performance index. A three control area power system example with a wide range of load changes is given to illustratethe proposed approach and the results are compazed with Ih dynamic output feedback control design.

This paper addresses a new robust control methodology to enhance the power system stability and voltage regulation as an integrated design approach. The automatic voltage regulation (AVR) and power system stabilizer (PSS) design problems are reduced to solve a single H∞ based static output feedback control problem. To determine the optimal gains, an iterative linear matrix inequalities (LMI) algorithm is used. A four-machine infinite-bus system example is given to demonstrate the efficiency of developed approach. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances, properly.

The present short paper reports a real-time nonlinear simulation, which performed on the Analog Power System Simulator at the Research Laboratory of the Kyushu Electric Power Co., to demonstrate the efficiency of a proposed robust control methodology to design of proportional-integral (PI) based load-frequency control (LFC) with communication delays.

This paper addresses a new robust control methodology to enhance the power system stability and voltage regulation as an integrated design approach. The automatic voltage regulation (AVR) and power system stabilizer (PSS) design problems are reduced to solve a single H∞ based static output feedback control problem. To determine the optimal gains, an iterative linear matrix inequalities (LMI) algorithm is used. A four-machine infinite-bus system example is given to demonstrate the efficiency of developed approach. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances, properly.

This paper addresses a control methodology to enhance stability and voltage regulation for the existing power systems with conventional PSS and AVR equipments. The control design problem is reduced to find a new control loop including a simple fixed gain vector. In order to optimal tuning of gain elements, the problem is formulated via an H _infin static output feedback ( H _infin -SOF) control technique, and the solution is easily carried out using a developed iterative linear matrix inequalities (ILMI) algorithm. A single-machine infinite-bus system example is given to illustrate the developed approach. The results of the proposed control strategy are compared with conventional PSS design. The robust controller is shown to maintain the robust performance and minimize the effect of disturbance properly

This research work addresses a new robust control strategy to synthesis of robust proportional-integral-derivative (PID) based power system stabilizers (PSS). The PID based PSS design problem is reduced to find an optimal gain vector via an H∞ static output feedback control (H∞-SOF) technique, and the solution is easily carried out using a developed iterative linear matrix inequalities algorithm. To illustrate the developed approach a real-time experiment has been performed for a longitudinal four-machine infinite-bus system on the Analog Power System Simulator at the Research Laboratory of the Kyushu Electric Power Co. The results of the proposed control strategy are compared with full order H∞ and conventional PSS designs. The robust PSS is shown to maintain the robust performance and minimize the effect of disturbances properly.

This paper addresses an LMI (linear matrix inequalities) based robust control methodology for designing of power system stabilizers (PSS) using mixed H2/Hinf control technique. A single-machine infinite-bus (SMIB) system example is given to illustrate the developed approach. The robust PSS is shown to maintain the robust performance and minimize the effect of disturbance and specified uncertainties.

This paper addresses a new method to bridge the gap between the power of optimal multiobjective control and PI/PID industrial controls. First the PI/PID control problem is reduced to a static output feedback control synthesis through the mixed H2/H∞control technique, and then control parameters are easily carried out using an iterative linear matrix inequalities (ILMI) algorithm. Numerical examples on load-frequency control (LFC) design in a multi-area power system are given to illustrate the proposed methodology. The results are compared with genetic algorithm (GA) based multiobjective control and LMI based full order mixed H2/H∞ control designs.

This paper addresses a new systematic method to design a robust proportional-integral (PI) controller for a three-phase sinusoidal active power rectifier based on H∞ control technique. The control design problem is reduced to solve an H∞ based static output feedback control problem. To determine the optimal gains, an iterative linear matrix inequalities algorithm is used. A classical power active rectifier example is given to demonstrate the efficiency of developed approach. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances, properly.

A new approach based on artificial Flexible Neural Networks (FNNs) is proposed to design of load frequency controller for a large scale power system in a deregulated environment. In this approach, the power system is considered as a collection of separate control areas under the bilateral Load Frequency Control (LFC) scheme. Each control area which is introduced by one or more distribution companies, can buy electric power from some generation companies to supply the area-load. The control area is responsible to perform its own LFC by buying enough power from pre-specified generation companies, which equipped with a FNNs based load frequency controller. The proposed control strategy is applied to a 3-control area power system. The resulting controllers are shown to minimize the effect of disturbances and achieve acceptable frequency regulation in the presence of load variations and line disturbances.

Boost d.c.-d.c. converters have very good source interface properties. The input inductor makes the source current smooth and hence these converters provide very good EMI performance. On account of this good property, the boost converter is also the preferred converter for off-line UPF rectifiers. One of the issues of concern in these converters is the large size of the storage capacitor on the dc link. The boost converter suffers from the disadvantage of discontinuous current injected to the load. The size of the capacitor is large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is demanding. This paper presents the polyphase boost converter, which overcomes the problem of high ripple current in the tank capacitor, which has not been discussed earlier. Comparison between the specifications of single stage and multistage is thoroughly examined. Digital control is more convenient for such a topology on account of the requirement of synchronization, phase shifted operation and current balancing. The control method is simpler and faster than its original form [10]. It does not depend on the previous duty ratio and it has been tested on four boost converters in parallel. Each is a 35W unit switched at 200 kHz. Experimental results in digital control, synchronization operation and current sharing are presented. The control method is implemented using a TI’s general purpose Digital Signal Processor eZdspF2812. This control scheme is applicable for PFC rectifiers as well.

Converter circuits-Polyphase Boost Converter with Digital Control

JPEG-LS standard is a context-based lossless image compression scheme, which uses 180° type modeling contexts in one pass scanning of an image. In this paper, for capturing high-order dependencies, statistical features and spatial configuration of an image, the three-pass JPEG-LS scheme with 360° type modeling contexts is proposed. For context determination, local gradients of intensity capturing the level of activity (smoothness, edginess) surrounding a pixel, is employed. For images with small dimensions, three-pass scheme and for large dimensions one-pass scheme result in higher compression ratios.

Auxiliary Switch Commutated ZVS Multiphase Boost Converter with Coupled Inductor

As the use of renewable energy sources (RESs) increases worldwide, there is a rising interest on their impacts on power system operation and control. This report presents an overview of the key issues and new challenges on frequency regulation concerning the integration of renewable energy units (especially wind turbine generators) into the power systems. Following a brief survey on the existing challenges and recent developments, the impact of power fluctuation produced by variable renewable sources (such as wind and solar units) on system frequency performance is presented. An updated LFC model is introduced, and power system frequency response in the presence of RESs and associated issues is analyzed. The need for the revising of frequency performance standards is emphasized. Finally, nonlinear time-domain simulations on a nine-bus test system show that the simulated results agree with those predicted analytically.

This paper addresses an LMI (linear matrix inequalities) based robust control methodology for designing of power system stabilizers (PSS). The PSS design problem is considered as a multi-objective control problem and formulated via a mixed H2/Hinf control technique, then for a given power system it is easily carried out to synthesis the desired robust controller by solving standard LMI. A single-machine infinite-bus system example is given to illustrate the developed approach. The results of the proposed control strategy are compared with conventional PSS design. The robust PSS is shown to maintain the robust performance and minimize the effect of disturbance and specified uncertainties.

In this paper a nonlinear model predictive control (NMPC) based on a piecewise linear Wiener model is presented. The nonlinear gain of this particular Wiener model is approximated using the piecewise linear functions. This approach retains all the interested properties of the classical linear model predictive control (MPC) and keeps computations easy to solve due to the canonical structure of the nonlinear gain. The presented control scheme is applied to a pH neutralization process and simulation results are compared to linear model predictive control. Simulation results show that the nonlinear controller has better performance without any overshoot in comparison with linear MPC and also less steady-state error in tracking the set-points