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Problem statement: Conventional Proportional-Integral-Derivative (PID) controllers exhibit moderately good performance once the PID gains are properly tuned. However, when the dynamic characteristics of the system are time dependent or the operating conditions of the system vary, it is necessary to retune the gains to obtain desired performance. This situation has renewed the interest of researchers and practitioners in PID control. Self-tuning of PID controllers has emerged as a new and active area of research with the advent and easy availability of algorithms and computers. This study discusses self-tuning (auto-tuning) algorithm for control of autonomous underwater vehicles. Approach: Self-tuning mechanism will avoid time consuming manual tuning of controllers and promises better results by providing optimal PID controller settings as the system dynamics or operating points change. Most of the self-tuning methods available in the literature were based on frequency response characteristics and search methods. In this study, we proposed a method based on Taguchi's robust design method for self-tuning of an autonomous underwater vehicle controller. The algorithm, based on this method, tuned the controller gains optimally and robustly in real time with less computation effort by using desired and actual state variables. It can be used for the Single-Input Single-Output (SISO) systems as well as Multi-Input Multi-Output (MIMO) systems without mathematical models of plants. Results: A simulation study of the AUV control on the horizontal plane (yaw plane control) was used to demonstrate and validate the performance and effectiveness of the proposed scheme. Simulation results of the proposed self-tuning scheme are compared with the conventional PID controllers which are tuned by Ziegler-Nichols (ZN) and Taguchi's tuning methods. These results showed that the Integral Square Error (ISE) is significantly reduced from the conventional controllers. The robustness of this proposed self-tuning method was verified and results are presented through numerical simulations using an experimental underwater vehicle model under different working conditions. Conclusion/Recommendations: By using this scheme, the PID controller gains are optimally adjusted automatically online with respect to the system dynamics or operating condition changes. This technique found to be more effective than conventional tuning methods and it is even very convenient when mathematical models of plants are not available. Computer simulations showed that the proposed method has very good tracking performance and robustness even in the presence of disturbances. The simple structure, robustness and ease of computation of the proposed method make it very attractive for real time implementation for controlling of underwater vehicle and it offers a chance to extend the same technique to the three dimensional vehicle tracking control as well. Key words: Autonomous underwater vehicle, Taguchi's method, proportional-integral-derivative control, self-tuning, planar control, INTRODUCTION Modern developments in the field of control, sensing and communication have made increasingly complex and dedicated underwater vehicle systems a reality. Used in a highly hazardous and unknown environment, [...]

The design of gain-scheduled strictly positive real (SPR) controllers using numerical optimization is considered. Our motivation is robust, yet accurate motion control of flexible robotic systems via the passivity theorem. It is proven that a family of very strictly passive compensators scheduled via time-or state-dependent scheduling signals is also very strictly passive. Two optimization problems are posed; we first present a simple method to optimize the linear SPR controllers, which compose the gain-scheduled controller Second, we formulate the optimization problem associated with the gain-scheduled controller itself Restricting our investigation to time-dependent scheduling signals, the signals are parameterized, and the optimization objective function seeks to find the form of the scheduling signals, which minimizes a combination of the manipulator tip tracking error and the control effort. A numerical example employing a two-link flexible manipulator is used to demonstrate the effectiveness of the optimal gain-scheduling algorithm. The closed-loop system performance is improved, and it is shown that the optimal scheduling signals are not necessarily linear [DOI: 10.111511.4001335]

This paper presents the stability analysis for a distribution static compensator (DSTATCOM) that operates in current control mode based on bifurcation theory. Bifurcations delimit the operating zones of nonlinear circuits and, hence, the capability to compute these bifurcations is of important interest for practical design. A control design for the DSTATCOM is proposed. Along with this control, a suitable mathematical representation of the DSTATCOM is proposed to carry out the bifurcation analysis efficiently. The stability regions in the Thevenin equivalent plane are computed for different power factors at the point of common coupling. In addition, the stability regions in the control gain space, as well as the contour lines for different Floquet multipliers are computed. It is demonstrated through bifurcation analysis that the loss of stability in the DSTATCOM is due to the emergence of a Neimark bifurcation. The observations are verified through simulation studies. Index Terms--Distribution static compensator (DSTATCOM), floquet multiplier, Neimark bifurcation, point of common coupling (PCC), stability regions.

A new control strategy for static compensators (STATCOMs) operating under unbalanced voltages and currents is presented in this paper. The proposed strategy adopts a state observer (software sensor) to estimate ac voltages at the STATCOM connection point. This way, physical voltage sensors are not needed and the hardware gets simplified, among other advantages. Using the superposition principle, a controller is designed to independently control both positive and negative sequence currents, eliminating the risk of overcurrents during unbalanced conditions and improving the power quality at the STATCOM connection bus. Two operating modes are proposed for the computation of the reference currents, depending on whether the objective is to compensate unbalanced load currents or regulate bus voltages. The proposed observer allows positive and negative sequences to be estimated in a fraction of the fundamental cycle, avoiding the delay often introduced by filter-based methods. Overall, the STATCOM performance is improved under unbalanced conditions, according to simulation results presented in the paper. Index Terms--Load compensation, observers, power quality (PQ), sequence currents, software sensors, static compensator (STATCOM), unbalanced systems.

Thyristor-based onload tap-changing ac voltage stabilizers are cheap and robust. They have replaced most mechanical tap-changers in low voltage applications from 300 VA to 300 kVA. Nevertheless, this replacement hardily applies to tap-changers associated to transformers feeding medium-voltage lines (typically 69 kV primary, 34.5 kV line, 10 MVA) which need periodical maintenance of contacts and oil. The Electric Power Research Institute (EPRI) has studied the feasibility of this replacement. It detected economical problems derived from the need for series association of thyristors to manage the high voltages involved, and from the current overload developed under line fault. The paper reviews the configurations used in that field and proposes new solutions, using a compensating transformer in the main circuit and multi-winding coils in the commutating circuit, with reduced overload effect and no series association of thyristors, drastically decreasing their number and rating. The stabilizer can be installed at any point of the line and the electronic circuit can be fixed to ground. Subsequent works study and synthesize several commutating circuits in detail. Index Terms--AC voltage stabilizer, onload tap-changer (OLTC), power conditioning, power quality, voltage control.

Techniques for distributed generations (DGs) have attracted increasing attention due to considerations of environmental sustainability. Wind farms are one of the DGs, and they have intermittent characteristics. This paper presents a method using wind generator voltages, static compensators, and transformer taps as controllers to regulate the voltage profile for operation planning in a distribution system. Wind power generations and bus loads are modeled with random variables. Through gray-based genetic algorithms (GAs), the MW loss in the system is minimized and the operational constraints are fulfilled. Moreover, this paper uses the cumulant method to calculate the bus voltage fluctuation by using the algebraic addition and multiplication to avoid convolution. The probability density function of the voltage fluctuation can be further expressed by the Gram--Charlier series expansion. Applicability of the proposed method is verified through simulation by using a 17-bus system and an autonomous 24-bus (Penghu) system. Index Terms--Cumulant, genetic algorithm (GA), gray code, reactive power control, wind farm.

This paper proposes the performance study of the rotary power-flow controller (RPFC) operating in a two-line transmission corridor. Part I presented the RPFC model and its implementation in SPS/Matlab. This paper presents the simulation results of the RPFC operating in the corridor during the postcontingency period, when one of the two lines is out of service. From the RPFC model and the RPFC control system, derived in part I, this paper first determines the model of the electrical corridor equipped with the RPFC, and then implements the entire model, including the RPFC control system, in the SPS/Matlab. The obtained results provide the behavior of the RPFC as well as that of the corridor during the postcontingency period. This paper analyzes, among other parameters, the influence of the RPST number of poles on the RPFC performances. Finally, the utilization of the RPFC, associated with the shunt capacitive compensation, allows restoring the postcontingency power-flow conditions to be equal to those of the precontingency period. Index Terms--Phase.shifting transformer, rotary phase-shifting transformer, rotary power-flow controller (RPFC), unified power-flow controller (UPFC), variable frequency transformer, voltage regulating-transformer.

This paper (Part I) presents a model suitable for the performance analysis of a rotary power-flow controller (RPFC), which operates in a two-lines power system corridor. The RPFC consists of two transformers (one series and one shunt), and two rotary phase-shifting transformers operating in standstill. The shunt and series transformers and the two rotary phase-shifting transformers are represented by the conventional equivalent circuit of a two-winding transformer. The rotor windings of these rotary phase-shifting transformers are connected in parallel while their stator windings are in series. The resulting equipment is the RPFC whose macroscopic model is proposed. The model involves a series branch consisting of an adjustable voltage source (with its internal impedance) and a shunt branch consisting of a current source. The obtained RPFC model with the regulators, implemented in SPS/Matlab, is used for further simulations in Part H. Index Terms--Phase-shifting transformer, rotary phase-shifting transformer, rotary power-flow controller (RPFC), unified power-flow controller (UPFC), variable frequency transformer, voltage regulating-transformer.

This paper presents a novel radio-frequency identification (RFID)-based smart freezer using a new inventory-management scheme for extremely low temperature environments. The proposed solution utilizes backpressure inventory control, systematic selection of antenna configuration, and antenna power control. The proposed distributed-inventory-control (DIC) scheme dictates the amount of items transferred through the supply chain. When a high item visibility is ensured, the control scheme maintains the desired level of inventory at each supply-chain echelon. The performance of the DIC scheme is guaranteed using a Lyapunov-based analysis. The proposed RFID antenna-configuration design methodology coupled with locally asymptotically stable distributed power control ensures a 99% read rate of items while minimizing the required number of RFID antennas in the confined cold chain environments with non-RF-friendly materials. The proposed RFID-based smart-freezer performance is verified through simulations of supply chain and experiments on an industrial freezer testbed operating at -100[degrees]F. Index Terms--Inventory control, low-temperature chemical management, passive radio-frequency identification (RFID), power control.

This paper deals with the velocity control of motor drives when saturated inputs are considered. Two classes of velocity controllers guaranteeing exponential stability are introduced. The first controller allows nonlinear proportional an integral action, while the other one includes an antiwindup loop. A detailed experimental study is provided, which confirms the theoretical results. Index Terms--Antiwindup, input saturation, motor drive, proportional-integral (PI) control, velocity control.

In this paper, a high-power high-efficiency wireless-power-transfer system using the class-E operation for transmitter via inductive coupling has been designed and fabricated using the proposed design approach. The system requires no complex external control system but relies on its natural impedance response to achieve the desired power-delivery profile across a wide range of load resistances while maintaining high efficiency to prevent any heating issues. The proposed system consists of multichannels with independent gate drive to control power delivery. The fabricated system is compact and capable of 295 W of power delivery at 75.7% efficiency with forced air cooling and of 69 W of power delivery at 74.2% efficiency with convection cooling. This is the highest power and efficiency of a loosely coupled planar wireless-power-transfer system reported to date. Index Terms--Class-E, inductive coupling, magnetic induction, switch mode, wireless power transfer.

A framework that jointly optimizes the control and communication networks of network-controlled interactive power electronics networks is described in this paper. The joint optimization framework includes two coupled blocks, one whose focus is to ensure optimal performance of the power network within its stability bounds and the other whose thrust is on optimizing the information flow in a communication network. These two networks have contrasting requirements because, on the one hand, time delays are detrimental to the stability and performance of the control system, while on the other hand, allowing higher time delays leads to efficient utilization of the communication network's resources. The proposed framework leads to an optimal compromise between these two noncooperative networks. Three different implementation approaches for the integrated control--communication framework are investigated, namely, centralized, distributed, and clustered. A case illustration of a homogeneous power network is provided to demonstrate the efficacy of the joint control--communication framework and compare the performance of the three implementation approaches. Index Terms--Interactive power electronic networks (IPNs), joint optimization, Lyapunov stability, network control systems, network resource utilization.

In this paper, we analyze the queuing performance in the finite-state Markov channel (FSMC) when the single-step power control (SSPC) scheme is adopted. To start with, an SSPC model and its extended power control error (PCE) model are proposed and described in detail. Such models can emulate the behaviors of the interaction between the SSPC and an FSMC and the variation of the PCE with high accuracy. Furthermore, the packet error rate that has been recently analyzed by Lee and Chang is adopted to evaluate the service rate, the time average queuing length, and the probability mass function (PMF) of the queuing length variation. Based on these results, a queuing variation model is proposed to emulate the queuing variation in the FSMC. The flooring phenomenon of the queuing length is observed under a particular requirement of an overflow probability when the SNR value is greater than a certain value. This indicates that the trade-off among the SNR, the buffer size of the queue, and the overflow probability exists. Hence, two different approaches to select the optimal target SNR of the SSPC and the maximum buffer size of the queue under the requested queuing buffer overflow probability are proposed. The improvement of the SSPC, its impact on the system, and the validity of the proposed models are shown in this paper as well. Index Terms--Finite-state Markov channel (FSMC), queuing performance, queuing variation model, single-step power control (SSPC), SSPC model.

An algorithm based on a nonlinear interior-point method and discretization penalties is proposed in this paper for the solution of the mixed-integer nonlinear programming (MINLP) problem associated with reactive power and voltage control in distribution systems to minimize daily energy losses, with time-related constraints being considered. Some of these constraints represent limits on the number of switching operations of transformer load tap changers (LTCs) and capacitors, which are modeled as discrete control variables. The discrete variables are treated here as continuous variables during the solution process, thus transforming the MINLP problem into an NLP problem that can be more efficiently solved exploiting its highly sparse matrix structure; a strategy is developed to round these variables off to their nearest discrete values, so that daily switching operation limits are properly met. The proposed method is compared with respect to other well-known MINLP solution methods, namely, a genetic algorithm and the popular GAMS MINLP solvers BARON and DICOPT. The effectiveness of the proposed method is demonstrated in the well-known PG&E 69-bus distribution network and a real distribution system in the city of Guangzhou, China, where the proposed technique has been in operation since 2003. Index Terms--Distribution systems, genetic algorithms, interior-point methods, mixed-integer nonlinear programming, nonlinear programming, optimal switching operations, optimization solvers, reactive power control, voltage control.

Phasor measurement units (PMUs) are considered as a promising tool for future monitoring, protection and control of power systems. In this paper, a unified approach is proposed in order to determine the optimal number and locations of PMUs to make the system measurement model observable and thereby can be used for power system state estimation. The PMU placement problem is formulated as a binary integer linear programming (BILP), in which the binary decision variables (0, 1) determine whether to install a PMU at each bus, while preserving the system observability and lowest system metering economy. The proposed approach integrates the impacts of both existing conventional power injection/flow measurements (if any) and the possibility of single or multiple PMU loss into the decision strategy of the optimal PMU allocation. Unlike other available techniques, the network topology remains unaltered for the inclusion of conventional measurements, and therefore the network connectivity matrix is built only once based on the original network topology. The mathematical formulation of the problem maintains the original bus ordering of the system under study, and therefore the solution directly points at the optimal PMU locations. Simulations using Matlab are conducted on a simple testing seven-bus system, as well as on different IEEE systems (14-bus, 30-bus, 57-bus, and 118-bus) to prove the validity of the proposed method. The results obtained in this paper are compared with those published before in literature. Index Terms--Integer programming, optimal location, PMUs, state estimation.

Complexities of computer program codes for Newton--Raphson load flow (NRLF) analysis are usually enhanced during power flow modeling of an interline power flow controller (IPFC). This is due to the fact that the contributions of the series converters of the IPFC are needed to be accounted for while computing bus power injections and Jacobian matrix elements. Also, the IPFC real power injection term along with its associated Jacobian matrix call for new codes to be written. In this paper an advanced IPFC model is proposed to address this issue, wherein an existing power system installed with IPFC(s) is transformed into an augmented equivalent network without any IPFC. To obtain the solution of the original network containing IPFC(s), the augmented network can easily be solved by reusing the existing NRLF codes, as this network is now devoid of any IPFC. Consequently, the complexities of the computer program codes are reduced substantially. Various practical device limit constraints of the IPFC can also be taken into account by the proposed model. Index Terms--Flexible ac transmission systems (FACTS), interline power flow controller (IPFC), Newton power flow.

A novel control scheme for permanent-magnet synchronous generator is proposed in this paper, where a current-source converter is employed as the bridge between the generator and the grid for high-power wind energy conversion systems. In these medium voltage (2.3-13.8 kV) level applications, current-source converters not only have inherent advantages, but also present some challenges for controller design due to the dc link choke and filter capacitors. The control strategy is developed to achieve better performances with improved dynamic response. By maintaining the grid-side converter modulation index at the highest possible level, the proposed control scheme reduces the dc link current to a minimum value to reduce converter conduction loss. The system's dynamic performance is further improved by adopting generator-side power feedforward. Simulation and experimental results are provided to verify the proposed control scheme. Index Terms--Current source converter (CSC), permanent-magnet synchronous generator (PMSG), power feedforward control, wind energy conversion.

In this paper, the dynamic performance of grid connected wind energy conversion system (WECS) is analyzed in terms of rotor speed stability. The WECS considered is a fixed-speed system that is equipped with a squirrel-cage induction generator. The drive-train is represented as a two-mass model. Results show that for a particular fault simulated, the voltage at the point of common coupling drops below 80% immediately after fault application and exhibits sustained oscillations. The rotor speed of induction generators becomes unstable. In order to improve the low voltage ride-through of WECS under fault conditions and to damp the rotor speed oscillations of induction generator, various flexible ac transmission system (FACTS) controllers such as static VAR (volt ampere reactive) compensator, static synchronous compensator, and unified power flow controller (UPFC) are employed. The gains of these FACTS controllers are tuned with a simple genetic algorithm. It is observed that among the FACTS controllers considered, UPFC is superior not only in regulating the voltage but also in mitigating the rotor speed instability. [DOI: 10.1115/1.3028040] Keywords: rotor speed stability, wind energy conversion systems, SVC, STATCOM, UPFC, squirrel-cage induction generator, fixed-speed wind turbines, genetic algorithm, point of common coupling

This paper presents a new method for accurately determining all possible steady-state operating points of a switch-mode contactless power transfer (CPT) system. The method is based on a stroboscopic mapping model and accurate calculation of its fixed points corresponding to circuit zero current switching (ZCS) conditions. Four steady-state operating points are identified for, e.g., inductor--capacitor--inductor (LCL)-type CPT system. Voltage and current waveforms and switching periods are determined. Parameter influences on ZCS periods are studied by bifurcation diagrams. Both PSpice simulation and experimental results have verified the proposed method. The results provide new opportunities for a practical CPT system to operate at different soft switching frequencies. The method is very useful for analyzing switch-mode resonant circuits and designing new power flow controllers. Index Terms--Contactless power transfer (CPT), fixed points, stroboscopic map, zero current switching (ZCS).

The aim of this paper is to unify the optimal control of a switched reluctance machine in a four-quadrant drive with smooth transition between the control-mode operations. The smooth transition is attained since the firing angle conditions of one operating mode are derived from the conditions of the other operating mode. The proposed control scheme is easily implemented since the knowledge of the machine magnetization curves is not required. Experimental results on a prototype control system are presented to validate the theoretical considerations and demonstrate the effectiveness of the proposed control scheme. Index Terms--Current control, electric variables control, reluctance motor drives, torque control, variable-speed drives.

This paper proposes a novel uniform controller design approach for switching power converters. The procedure allows the deriving of both clock-driven and event-driven switching laws for controlling the stationary converter operation. A generic control scheme is introduced, which generalizes the concept of hysteresis control and executes a mode change, whenever the augmented state trajectory intersects with a switching plane in the state--time space. In contrast to previous approaches, the switching planes are systematically computed by means of results on periodic control systems. Consequently, desired loop properties such as orbital stability of a limit cycle and a fast transient response are guaranteed at least in a local neighborhood around a nominal set point. All results apply to a large class of switching converters and impose no restrictions un the number of energy storage devices or switches. Index Terms--Hybrid dynamical systems, hysteresis control, limit cycle, periodic systems, switching power converters.

A control scheme for star-connected cascade static synchronous compensators (STATCOMs) operating under unbalanced conditions is proposed. The STATCOM is assumed to be connected to an equivalent three-phase star-connected power supply. By selecting the line-to-neutral voltages of the equivalent power supply, zero average active power in each phase can be obtained under unbalanced compensation currents or unbalanced supply voltages. Furthermore, to implement a separate control for the three-phase dc-link voltages, the average active power in each phase can also be adjusted to a target value determined by the dc-link voltage control loop. Then, by forcing the converter neutral voltage to be equal to the counterpart of the equivalent power supply, the STATCOM can be decoupled into three single-phase systems and the line-to-neutral voltage of the equivalent power supply can be used as the input voltage to the corresponding phase leg. Accordingly, reference current tracking and dc-link voltage maintaining can be simultaneously achieved under unbalanced conditions. The valid operating range of the star-connected cascade STATCOM under unbalanced conditions is also analyzed. The proposed control scheme has been tested using the power systems computer-aided design/electromagnetic transient in dc system (EMTDC) simulation results and the experimental results based on a 30-kVAr cascade STATCOM laboratory prototype are proposed. Index Terms--Cascade multilevel converter, static synchronous compensator (STATCOM), unbalance operation.

The closed-loop control of an integrated dual ac drive system is presented to control two three-phase permanent-magnet motors. A five-leg inverter is employed in the drive system; three of the inverter legs are for a main traction motor, but only two are needed for a three-phase auxiliary motor by utilizing the neutral point of the traction motor. An integrated drive with reduced component count is therefore achieved by eliminating one inverter leg and its gate drivers. A modified current control scheme based on the rotor flux orientation principle is presented. Simulation and experimental results are included to verify the independent control capability of the integrated drive. Index Terms--Closed-loop control systems, component-count-reduced inverter, permanent-magnet (PM) motor drive.

A wide-range active and reactive power flow controller is designed to operate the inverter in pure leading, pure lagging, and the mix with active and reactive power conditions. The key to achieving lagging power flow control is to ensure sufficiently high enough dc bus voltage to avoid duty cycle saturation. The key to achieving precision power flow control for a wide range of power level is to adopt the quasi-proportional resonant controller for the current loop and the admittance compensator to cancel the grid-voltage-induced negative power flow. In this paper, the current loop transfer function has been systematically derived for the controller design purpose. Phasor analysis was adopted to explain the need of dc bus voltage requirement. A 5-kVA grid-tie fuel cell inverter was used as the platform to show current loop controller design and admittance compensation. The proposed controller has been simulated, and the same parameters have been used for a DSP-based controller. Both simulation and hardware experimental results agree well with the theoretical analysis. Index Terms--Admittance compensation, fuel cell power conditioning system, LCL filter, proportional-resonant compensator, reactive power control, single-phase grid-tie inverter.

This paper proposes a novel fuzzy power control (FPC) scheme to effectively improve the performance of the downlink code-division multiple-access (CDMA)-based local multipoint distribution service (LMDS) system. Conventional power control scheme is taken to reduce rain fading effects and intercell interference, and then increase the capacity of this LMDS system. To more effectively improve the system performance, three major factors (i.e., rain rate, path loss exponent depending on channel fading conditions, and number of subscribers in the interfering cell sectors) are taken as the input variables of fuzzy logic control in our proposed FPC scheme to obtain the channel quality condition and distance threshold for power control region adjustments. Simulation results show that our proposed FPC scheme performs better than the conventional scheme in terms of outage probability. Index Terms--Code division multiple access (CDMA), fuzzy, local multipoint distribution service (LMDS), power control.

Mobile terminals (MTs) in real personal communication service (PCS) environments are turned OFF due to limited battery lifetime, avoidance of unwanted incoming calls, and undesirable subscriber behaviors. Since the probability that an MT is in the OFF-state may be significant, MT power ON/OFF-state transition behavior and the effect of state management on mobile communication networks require analysis. Two MT power ON/OFF-state management schemes are introduced based on the level of location registers (LRs) for managing MT state information. Effects are investigated from the aspects of a radio interface, a network, and a database based on the modeling of the state transition behavior of an MT for varying values of MT and mobile communication network parameters. These values include the MT ON/OFF duration and the incoming call arrival rate. Although additional database processing overhead exists, the management of MT power ON/OFF-states provides a significant reduction in overhead from the aspects of the radio interface and the network. There is a tradeoff between the two management schemes as the MT ON/OFF ratio varies. Index Terms--Database, location register (LR), mobile communication networks, mobility management, modeling and analysis, network, personal communication service (PCS), power ON/OFF-state management, radio interface.

This paper tackles a power minimization problem of interleave-division multiple-access (IDMA) systems over a fading multiple-access channel. The problem is minimizing the total power received by the receiver while keeping the bit error rates (BERs) of all users below a predefined value. The original formulation of the problem has highly nonlinear and implicitly defined functions, which render most existing optimization methods incapable. A new formulation is proposed in this paper, whose solution can effectively be obtained by a branch-and-bound (B&B) technique. An algorithm is devised based on B&B, and its effectiveness is also demonstrated by numerical experiments of systems with a moderate numbers of users. Index Terms--Branch-and-bound (B&B), code-division multiple access (CDMA), interleave-division multiple access (IDMA), iterative multiuser detection (MUD), optimization, power allocation.

Hybrid electric vehicles (HEVs) have demonstrated the capability to improve fuel economy and emissions. The plug-in HEV (PHEV), utilizing more battery power, has become a more attractive upgrade of the HEV. The charge-depletion mode is more appropriate for the power management of PHEVs, i.e., the state of charge (SOC) is expected to drop to a low threshold when the vehicle reaches the trip destination. Trip information has so far been considered as future information for vehicle operation and is thus not available a priori. This situation can be changed by the recent advancement in intelligent transportation systems (ITSs) based on the use of on-board global positioning systems (GPSs), geographical information systems (GISs), and advanced traffic flow modeling techniques. In this paper, a new approach to optimal power management of PHEVs in the charge-depletion mode is proposed with driving cycle modeling based on the historic traffic information. A dynamic programming (DP) algorithm is applied to reinforce the charge-depletion control such that the SOC drops to a specific terminal value at the end of the driving cycle. The vehicle model was based on a hybrid electric sport utility vehicle (SUV). Only fuel consumption is considered for the current stage of the study. A simulation study was conducted for several standard driving cycles and two trip models using the proposed method, and the results showed significant improvement in fuel economy compared with a rule-based control and a depletion sustenance control for most cases. Furthermore, the results showed much better consistency in fuel economy compared with rule-based and depletion sustenance control. Index Terms--Dynamic programming (DP), intelligent transportation systems (ITSs), plug-in hybrid electric vehicles (PHEVs), power management.

In order to be able to successfully apply interline power flow controllers (IPFCs) for power-system transient-stability improvement and for the damping of oscillations, proper control strategies should be applied to these devices. The basis for the implementation of such a strategy that is proposed in this paper is to know the energy function of a power system that includes IPFCs. Already-known energy functions that proved to be suitable for an electric-power system do not include such a device. Therefore, in this paper an energy function that considers the IPFC's action in the form of a supplement to the already-known structure-preserving energy functions was constructed. Furthermore, the strategy for implementing the newly developed IPFC energy functions in order to ensure a globally optimum control strategy in the Lyapunov sense is presented. The results of the numerical examples show that the magnitudes of the IPFC's series-injected voltages remain set to their maximum values and that only the angles of these voltages change, similar to the 'bang-bang' control strategies proposed for some other FACTS devices. Index Terms--FACTS devices, interline power flow controller (IPFC), Lyapunov energy function, power system control, power system dynamic stability.

This paper presents new models of voltage source converters suitable for power system state estimation comprising STATCOM and VSC-HVDC applications. Both the back-to-back and the point-to-point VSC-HVDC variants are addressed. The state estimation models include dc measurements and converter control inputs resulting in an overall, seamless combination of the ac and dc devices or networks, in addition to providing for a higher degree of redundancy. Following a detailed description of all the relevant variables involved in the problem, taking into account equality constraints associated with both equipment and operation, a recommended set of state variables is proposed. These new models allow internal power losses of voltage source converters to be considered, leading to increased accuracy. The IEEE 14-bus system is used to illustrate and compare the main features of the proposed models. Index Terms--FACTS devices, STATCOM, state estimation, VSC-HVDC.

In conventional hard disk drives, a control system compensates for the mechanical resonance above the Nyquist frequency by using sampled-data control theories or multirate control techniques. However, such a control system can only avoid instability and cannot suppress disturbances above the Nyquist frequency. In response to this problem, a control system design method that suppresses disturbances beyond the Nyquist frequency is proposed. This method uses the frequency responses of a controlled object and a digital controller to calculate the gain of the sensitivity function in a sampled-data system without requiring complex calculations involving matrices. When the method was applied to the head-positioning system of a hard disk drive, the experimental results showed that the control system suppressed disturbances that had the frequencies higher than the Nyquist frequency. Index Terms--Hard disk drive, motion control, vibration control.

This paper introduces a hybrid flow controller (HFC) as a new member of flexible ac transmission system (FACTS) controllers for steady-state and power-flow control of power transmission lines. HFC is a hybrid compensator (i.e., provides series and/or shunt compensation). Structurally, an HFC unit is composed of a mechanically switched phase-shifting transformer, a mechanically switched shunt capacitor, and multimodule, series-connected, thyristor-switched capacitors and inductors. This paper describes the steady-state operation, single-phase equivalent circuit, power-flow model, and V-I and P-Q characteristics of the HFC. This paper highlights the steady-state technical features of the HFC for power-flow control of a study system and also provides a quantitative comparison of the HFC, UPFC, and PST. Index Terms--Flexible ac transmission system (FACTS), power flow, thyristor-switched series capacitor (TSSC), thyristor-switched series reactor (TSSR), unified power-flow controller (UPFC).

Self-commutating multilevel current reinjection is a potential alternative to conventional HVDC thyristor technology. An important drawback of the multilevel configurations is the interdependence of the reactive power injections at both ends of the link. This paper describes a new concept applicable to large power converters consisting of two series-connected twelve-pulse groups. It is based on the use of a controllable shift between the firings of the two twelve-pulse groups in opposite directions, a new concept that provides independent reactive power control at the sending and receiving ends. The theory is verified by EMTDC simulation. Index Terms--HVDC transmission, multilevel conversion, reactive power control.

Power-flow modeling of a unified power-flow controller (UPFC) increases the complexities of the computer program codes for a Newton-Raphson load-flow (NRLF) analysis. This is due to the fact that modifications of the existing codes are needed for computing power injections, and the elements of the Jacobian matrix to take into account the contributions of the series and shunt voltage sources of the UPFC. Additionally, new codes for computing the UPFC real-power injection terms as well as the associated Jacobian matrix need to be developed. To reduce this complexity of programming codes, in this paper, an indirect yet exact UPFC model is proposed. In the proposed model, an existing power system installed with UPFC is transformed into an augmented equivalent network without any UPFC. Due to the absence of any UPFC, the augmented network can easily be solved by reusing the existing NRLF computer codes to obtain the solution of the original network containing UPFC(s). As a result, substantial reduction in the complexities of the computer program codes takes place. Additionally, the proposed model can also account for various practical device limit constraints of the UPFC. Index Terms--Flexible ac transmission systems (FACTS), Newton power flow, unified power-flow controller (UPFC).

In this paper, we propose a novel approach to the modeling and controller design of the synchronous step-down dc-dc converter. We introduce a hybrid converter model that is valid for the whole operating regime and captures the different modes of operation. Based on this model, we formulate and solve a constrained optimal control problem. This allows a systematic controller design that achieves the regulation of the output voltage to its reference despite input voltage and output load variations while satisfying the constraints on the duty cycle and the inductor current. The resulting state-feedback control law is of piecewise affine form, which can be easily stored and implemented in a lookup table. A Kalman filter is added to account for unmeasured load variations and to achieve zero steady-state output voltage error. Experimental results demonstrate the potential advantages of the proposed control methodology. Index Terms--DC-DC converter, power electronics, model predictive control (MPC), optimal control, hybrid system, piecewise-affine (PWA) system.