New Publications are available for Stability in control theory
http://dl-live.theiet.org
New Publications are available now online for this publication.
Please follow the links to view the publication.Evaluation of reactive power control concepts for PV inverters in low-voltage grids
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0892
The proportion of renewable energies in power generation has increased significantly in recent years according to the political aims. In low-voltage grids, these are mostly distributed intermittent generation systems such as photovoltaic systems that are connected through inverters to the grid. Thus, the distribution networks have to meet hitherto unfamiliar technical challenges. A temporary reversal of the power flow can cause overvoltage problems. Traditional voltage regulation strategies cannot solve this problem. Consequently, regenerative sources need to be turned off temporarily or on the long term the grid infrastructure has to be extended by the network operator. Therefore, the distributed generation has to take part in the voltage regulation. With the help of reactive power, which is generated by the solar inverters, power capability and voltage quality of the networks can be increased. Thus, grid extension can be delayed or even avoided in many times. This paper presents a new approach to the evaluation of reactive power control strategies. Different reactive power control concepts are simulated and evaluated concerning their efficiency, effectiveness and stability. (4 pages)Voltage regulation (MV) by means of Q(U) - Simulation and measurement on a 12 MVA PV power plant
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0841
Open loop reactive power (Q) control function of the local voltage (U) measured at the inverter's terminals is one possibility to comply with the BDEW's MV grid regulations [1] in Germany, while other countries are considering to apply this solution as well. A better understanding of the stability limits for such a control algorithm is required when applying it to large PV plants or PV dominated grids. A dynamic RMS simulation model of a big PV plant including Q(U) control is developed. The model is compared with real life measurements in the PV plant and the local laboratory. Various study cases are further on performed in order to assess the voltage stability. An upper stability limit can be found depending on the grid connection parameters in the point of common coupling (PCC). (4 pages)Robust stability of solar-power wireless network control system with stochastic time delays based on H2 norm
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0605
In this paper, the robust stability analysis of Solar Wireless Networked Control Systems (SWNCSs) with stochastic time delays and packet dropout is investigated. The Robust Model Predictive Controller (RMPC) technique for the SWNCS is discussed using the linear matrix inequality (LMI) technique. Based on the SWNCS model, the RMPC (a full state feedback controller) can be constructed by using the Lyapunov functional method. Both sensor-to-controller and controller-to-actuator time delays of the SWNCS are considered as stochastic variables controlled by a Markov chain. A discrete-time Markovian Jump Linear System (MJLS) with norm bounded time delay is presented to model the SWNCSs. Sufficient conditions for stochastic stability based on H_2-norm and stabilization of the fundamental systems are derived via LMIs formulation. Finally, an illustrative numerical example is given to demonstrate the effectiveness of the proposed techniques. (6 pages)Control of an AC brushless permanent-magnet machine using long supply cables
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0265
The use of a long cable between an inverter and motor is recognised as problematic and a cause of insulation failure in motors. The cable also introduces a voltage drop and phase shift in the fundamental voltage at the motor terminals, reducing the available motor torque in open-loop control, and affecting the stability of a closed-loop controller. This paper investigates the performance of a brushless, permanent magnet motor in order to determine the maximum operating distance between the motor and its inverter. The study develops simulation models of the motor in open and closed-loop modes, with and without the inclusion of a line filter. The ability to track changes in reference speed and reject torque disturbances is shown to depend on the resistance of the damper circuits in open-loop control, but is not an issue in closed-loop control. The maximum operating distance depends on cable resistance, and a practical operating limit of 2km is given for the motor-cable combination studied. (6 pages)Effect of MPP-tracking DC/DC converter on VSI-based photovoltaic inverter dynamics
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0334
The utility-grid connection of a photovoltaic (PV) generator can be implemented by using a single or double-stage inverter. The single-stage inverter is connected directly to the PV generator, which is observed to significantly change the control dynamics of the inverter depending on the operating point. In the double-stage scheme, a dc/dc converter - operating either at open loop or under input-voltage-feedback control - is connected between the PV generator and the inverter. This paper investigates the effect of the dc/dc converter on the interfacing effects of the PV generator. The investigations show that the input-voltage-feedback control has clearly a stabilizing effect on the DC-link-voltage feedback control but the open-loop converter does not change the situation. (6 pages)Decentralized coordinated robust controller design for multimachine power system based on multi-agent system
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0084
A decentralized coordinated control is researched based on multi-agent structure for transient stability improvement of large-scale power system in this paper. First, a multi-agent system (MAS) model is structured based on the wide-area measurement system (WAMS), which consists of both upper and lower level agents. The upper level coordinated agents are mainly responsible for coordinating and controlling the lower level agents via sending coordinated control signals into local decentralized control loops in order to damp lower frequency oscillations between regions. And the main function of lower level agents is to continuously regulate generator unit through excitation controller to overcome small disturbances. Then, the focal task of this paper is to design a decentralized coordinated controller based on the MAS model. To eliminate the nonlinearities and interconnections of multimachine models, a direct feedback linearization (DFL) compensator is designed through the decentralized excitation control loop. Besides, taking consideration of the effects of uncertainty introduced by transient process, the H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> robust control method integrating with linear matrix inequality (LMI) technology is used to seek the solutions of the decentralized coordinated controller. Finally, simulation demonstrates that the MAS based decentralized coordinated robust controller has better transient stabilization performance than the conventional PSS. (6 pages)Frequency-Domain Control Design for High-Performance Systems
http://dl-live.theiet.org/content/books/ce/pbce078e
<p xmlns="http://pub2web.metastore.ingenta.com/ns/">This book serves as a practical guide for the control engineer, and attempts to bridge the gap between industrial and academic control theory. Frequency domain techniques rooted in classical control theory are presented with new approaches in nonlinear compensation that result in robust, high-performance closed-loop systems. Illustrative examples using data from actual control designs are included.</p>Application of measurement noise decoupling for a robust multiple models adaptive controller (RMMAC) to improve the damping of power system inter-area oscillation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0513
The electric power system is a non-linear dynamic system, with continuous condition changes during normal operation. Therefore, it is required to have a special control strategy to cover different operating points. One of the proposed techniques to solve such problem is the use of a multiple model adaptive control (MMAC), allowing that the controller updating to represent the actual system properly. The use of a MMAC strategy is based on a physical system output measurement for system model estimation. So any noise from the output sensor measurement leads to a significant increase in the residual (the error in the output signal between the physical system and the designed model),[1]. So the weight computation block uses this residual to calculate the weights for all controllers in the controller bank. The highest residual model means that the model is far from the true system. Therefore, it is important to remove the noise from the residual calculations. In this work the new observer is installed to provide the full state estimation and noiseless output. So the effect of measurement noise is avoided and is independent of the type of noise. The system is tested by adding unknown noise to the system output measurement. The design of the local controller is based on different linear control techniques to achieve both local and global system stabilities. The damping improvements are verified using the Matlab software. (5 pages)Design of robust power system stabilizer using mixed sensitivity based H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> output-feedback control in LMI framework
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0397
This paper presents the design of robust power system stabilizer (PSS)for damping low frequency oscillations. The proposed damping controller design is formulated as mixed sensitivity based H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> output-feedback control with pole placement constraints. The synthesis problem can be formulated into a standard linear matrix in equalities (LMIs) framework which can be tractable numerically. A single generator, 3-bus system is used to demonstrate the effective ness and robustness of the designed controller at different system operating conditions. The MATLAB simulation result shows good damping and robustness.Enhancement of voltage stability by coordinated control of multiple FACTS controllers in multi-machine power system environments
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0328
This paper presents the implication of adding various FACTS controllers in multi-machine power system environment in coordinated control manner for enhancement of voltage stability requires an appropriate mathematical model of the power system and the FACTs controllers such as a Static Var Compensator (SVC) and Thyristor Controlled Series Capacitor (TCSC). The DAE (Differential Algebraic Equation) methodology for multi-machine system has been is used in this paper. Event tough the SVC model has been incorporated in DAE model, TCSC model has not been incorporated. So the purpose of this paper is to derive a TCSC model such that it can be incorporated in DAE model of power system. Further in a large power system there may be more than one FACTS controllers, therefore it is important to develop a combination of series and shunt FACTS controllers that can be incorporated in the DAE model in Modular fashion. The models developed have been utilized for eigen-value analysis of IEEE 9-bus 3-machine power systems. There are many commercial packages available for transient simulation and analysis of power systems. The transient simulation packages (e.g. EMTDC/PSCAD) allow incorporation of FACTS controller models. This facility is however not available in the small signal stability analysis packages. The objective of this paper is to develop a methodology to incorporate FA CTS controllers in a modular fashion to facilitate eigen-value and voltage stability analysis using MATLAB toolbox.Dynamic behaviour of hill-climbing MPPT algorithms at low perturbation rates
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0108
Hill-climbing algorithms are the most commonly utilized maximum power point tracking (MPPT) control schemes in photovoltaic (PV) applications. Two techniques have been adopted in the literature for implementing such hill-climbing algorithms: reference voltage perturbation where a reference value for the PV generator output voltage is used as the control parameter and direct duty ratio perturbation where the duty ratio of the MPPT converter is used directly as the control parameter. This paper presents a detailed comparison between these two techniques on the basis of system stability. Practical results obtained using a 540Wp PV experimental setup with a resistive load show very good agreement with the theoretical analysis and numerical simulations. (6 pages)Optimal corrective control for the stability enhancement of power systems considering wind penetration
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0180
This paper proposes an optimal corrective control method to enhance the small signal stability of power systems considering grid-connected wind penetration. The proposed method can optimally compute the amount of generator decreasing and load shedding at selected buses to damp the oscillation. The optimal corrective control procedure for small signal stability enhancement has been present. An eigenvalue sensitivity based optimal corrective control problem with linearized small signal stability constraint is introduced and solved in an iteration manner. Effectiveness of the proposed method is demonstrated by numerical simulation on a modified example of 16-machine power system with 3 grid-connected wind farms. (6 pages)Power oscillation damping capabilities of wind power plant with full converter wind turbines considering its distributed and modular characteristics
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0130
Wind power plants (WPP) are for power system stability studies often represented with aggregated models, where several wind turbines (WT) are aggregated into a single up scaled model. The advantage is a reduction in the model complexity and the computational time, and for a number of study types the accuracy of the results has been found acceptable. A large WPP is, however, both modular and distributed over a large geographical area, and feasibility of aggregating the WTs, thus, have to be reassessed when new applications are introduced for WPPs. Here, the power oscillation damping capabilities are investigated for a WPP, which includes the full layout of the collector grid and where the WTs are represented individually. With this approach, the influence of the WT control in terms of impact on oscillatory modes is assessed for the WTs individually. This will, furthermore, give input to whether park level control is possible. (6 pages)Multi-control strategy for the operation of microgrid based on the interior-point method
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0178
As for the control of microgrid, this paper studied multi control strategy of microgrid based on the nonlinear prime dual method. Objective function of the model is minimization of micro sources' cost and cost of purchased power from grid when microgrid is connected to grid while satisfying a series of constraints. Minimization of load shed is the objective function when microgrid is isolated when keeps load as much as possible and ensures the stable of voltage and frequency. Simulation is done with a distributed system. Results indicate that proposed method can ensure the stability of microgrid when it is connected to or isolated from grid. (6 pages)Sensorless maximum wind energy capture based on input output linearization and sliding mode control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0198
This paper proposes a new sensorless direct power control (DPC) for wind turbine system driven by doubly fed induction generator (DFIG) in order to track maximum absorbable power in different wind speeds. A generalized regression neural network is used to estimate wind speed and tip speed ratio. Then the desired optimum power is determined online as a function of tip speed ratio for per wind speed. Finally new direct power control (DPC) employs input output linearization and sliding mode nonlinear controller for robust control of active and reactive power and obtaining maximum power from wind turbine. Also constant switching frequency is achieved by using space vector modulation. Simulation results on 660-kw wind turbine are provided and compared with those of classic stator-flux oriented vector control. Results show that the proposed controller using the new algorithm has low error for tracking maximum power in compression with the existing controller in presence machine parameters variation. (6 pages)An innovated nonlinear voltage regulator for DC/DC converters: theoretical and experimental results on PV applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0132
In this paper, a nonlinear dynamic controller is proposed for regulating the dc bus voltage of a DC/DC boost power converter in a stand-alone photovoltaic system. The controller is proven to achieve the desired voltage regulation independently from the PV source voltage, the converter parameters and the kind of the load. Extended mathematical analysis shows that the proposed control scheme guarantees damping characteristics (passivity) of the closed-loop system, which represents a fundamental property for achieving stability at the desired equilibrium. Simulation and experimental results verify the controller efficiency for a single resistance-inductance load case and for a nonlinear load consisted of a three-phase voltage source inverter and a three-phase resistance-inductance. (6 pages)Small-signal probabilistic stability of power systems considering the stochastic uncertainty of grid-connected wind farm
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0206
The impact of stochastic uncertainty brought about by the grid-connected wind farm penetration on power system small-signal stability is investigated in this paper. An analytical method to carry out the probabilistic analysis is proposed. The cumulants and central moments of the system critical eigenvalues are computed on the basis of the normal probabilistic distribution of wind power generation. The Gram-Charlier expansion is employed to obtain the probabilistic distribution of the eigenvalues. All the conclusions gained by the analytical method proposed have been confirmed by Monte Carlo simulations in the case study presented in the paper. (6 pages)Voltage stability assessment for radial distribution power system with wind power penetration
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0209
Integration of wind power may enhance the performance of power systems. This paper presents the impacts of wind power penetration on the operation of a radial distribution power system. A 37-bus radial system is studied. Continuation power flow (CPFLOW) is performed on the system without wind power and with gradually increasing a rate of wind power penetration. The wind turbine is connected to bus 35 which is the weakest bus. The wind turbine is modelled in as PQ generator, as the wind park is typically regulated with constant power factor. Voltage stability for the radial power system is determined by the corresponding PV curves for each bus with and without wind power. The effects of wind power penetration on the active power losses of the whole system as well as the voltage collapse with loading parameters are investigated. Changing the power factor by connecting a parallel capacitor is also considered. The simulation analysis was performed by PSAT/MATLAB simulation package. The analysis shows the benefits of introducing wind power to radial distribution systems by decreasing the active power losses and hence increasing the system efficiency. Voltage collapse was found to occur at higher loading factor which enhances the voltage stability of the system. Finally, the steady state bus voltages became higher than without wind penetration. (6 pages)Robust control of a wind turbine
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0906
The wind turbine is represented as an uncertain plant whose parameters depend on the wind speed. A two degree-of-freedom turbine speed controller is designed by using the technique of μ-synthesis. The frequency responses and time responses of the closed-loop system show a satisfactory performance of the linearized system. It is demonstrated that by relaxing the robustness requirements it is possible to achieve acceptable performance of the nonlinear closed-loop system as well. (5 pages)Fuzzy generalized synchronization between non-smooth-air-gap and smooth-air-gap PMSM chaotic systems with channel delay
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0785
The generalized synchronization problem between non-smooth-air-gap and smooth-air-gap PMSM chaotic systems is studied in this paper. In addition, the channel delay is considered in the realization of the chaotic synchronization. Firstly, the nonsmooth-air-gap PMSM chaotic system and the smooth-air-gap PMSM chaotic system are represented by the T-S fuzzy models without any modeling error. Then, a simple fuzzy state feedback controller is designed based on the parallel distributed compensation technique. By virtue of the definition of lag synchronization and fuzzy control idea, the asymptotical synchronization is realized by choosing appropriate controller gain matrices. Finally, an illustrative example is presented to demonstrate the effectiveness of the proposed fuzzy synchronization method.Image-guided position and height estimation for unmanned helicopter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0599
Helicopter is a nimble vehicle with flight property. It can take off or land vertically, move in any direction and hover. Because of the innate instability and highly nonlinear property, designing autonomous flight control system of helicopter is of much difficulty. The main consideration in helicopter flying control is to hover and to land. In this paper, we consider the case that a CCD is hanged on helicopter as an auxiliary sensor. The CCD can get the image of H-type hard-stand on the ground and calculate the horizontal shift error and height of helicopter by PC. It can apply to observe the river, disaster area, science and military detection. In order to get the information about aerial photography and observation, we add the function of taking picture and video recording.PSO optimized PID parameters for coupled HVDC control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0483
High Voltage Direct Current (HVDC) systems are used in power systems for the efficient transfer of energy over long distances and can improve the stability and performance of electrical networks. Using the internal node representation, the dynamics of a system with HVDC links can be represented in terms of the internal currents of the generators of the system and this representation can be used to control the system frequency. Here the control of a multiple HVDC link system, modelled using this representation, is improved using Particle Swarm Optimization, PSO.Conception of robust neural networks for hybrid control of asynchronuous motor drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0069
It is well known that the combination between Neural networks and fuzzy controllers are considered as the most efficient approximators of different functions and also proves their capability of controlling nonlinear dynamical systems So, in this paper, the authors introduce a novel technique of control called" hybrid control" which is Based on Feedback Linearization and Field Oriented Control of an Induction Motor, in order to replace the sliding mode controllers (speed and flux ones). In fact, the objectives required by the introduction of neural networks (RANNCs) is to perform the control which is shown by simulation results. (7 pages)Sliding mode observation of capacitor voltage in multilevel power converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0014
In this paper a sliding mode observer is designed and applied to a two-port multi-cellular power converter topology in order to observe the DC-link capacitor voltages. Among different sliding mode observers, the Sliding Mode Observer (SMO) using equivalent control approach has been selected for use because of its robustness against uncertainties in system equations. Simulation is carried out using SABER software. For practical results the controller is implemented on a TMS320C6713 DSP and two ACTEL FPGAs. The observer equations are implemented on an FPGA using a fixed-point system programmed in VHDL. (6 pages)On a variation of the Gershgorin circle theorem with applications to stability theory
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1687
The conclusions of the Gershgorin circle theorem are significantly extended for the special case of real matrices. The extended result is applied to the problem of the absolute stability of both continuous- and discrete-time Lur'e systems containing sector nonlinearities. Specifically necessary conditions for the existence of common unic Lyapunov functions are presented in the form of constraints upon the root locus of the linear, time-invariant component. (5 pages)Transient stability analysis of Gadong Power Station
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1750
Transient stability analysis is very important to find the behavior of the synchronous machines under faulted condition. In this paper, IPSA simulation software is used to study the transient stability analysis of Gadong Power Station. Three-phase faults are considered at the busbar 1415LPS and 2829GPS1 with different fault clearing times. From the location at 1415LPS busbar, it is found that the generators of the Gadong I power station are stable for the fault clearing times of 0.1 s and 0.3 s and becomes unstable for the fault clearing time of 0.6 s and 0.7 s. At the other location of the busbar 2829GPS1, the generators of the Gadong I power station becomes unstable for the fault clearing time 0.7 s. (4 pages)String stability analysis of homogeneous linear unidirectionally connected systems with nonzero initial conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1694
This paper investigates string stability issues in homogeneous strings of strictly proper feedback control systems. We consider initial condition problems with unidirectional nearest neighbour communications, using only linear systems with two integrators in the loop. We define string stability as a type of stability that is uniform with respect to the string length. We show conditions under which the L<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>-norm and the L<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub>-norm of states are bounded and derive a formula for the minimal time headways required to guarantee string stability. (6 pages)Stability and damping performance analysis of induction motor
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1831
This paper presents the stability and damping performance analysis of induction motor driven by open-loop constant V/Hz control. Based on linearized mathematical model, the unstable ranges of induction motor are illustrated, which involve with the motor parameters and the frequencies of applied voltage. Then the well-known concept of damping ratio is adopted to give further analyses on damping performance, it is found that the variation of motor parameters can improve the stability but at the same time deteriorate the damping ratio at critical frequency. Time-domain simulations are used to validate these frequency-domain analytical results. The stability of induction motor with different motor parameters is also investigated. (6 pages)Research on trajectory tracking control of nonholonomic wheeled mobile service robots
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1523
Nonholonomic wheeled mobile service robot's posture error model denoted by Cartesian coordinates in local coordinates is established. A novel nonlinear state feedback trajectory tracking control law is proposedL which causes closed-loop system state space equation of robot to have isolated euqilibrium state at origin.Through analysing the local uniform asymptotical stability at origin and the instability of isolated boundary equilibrium state at non-origin under the proposed trajectory tracking control lawL the scale of control parameters is confirmed. By Lyapunov candidate function methodL this paper concludes that the elosed-loop system is globally uniformly asymptotically stable at origin. Simulation results show the effectiveness of the proposed control law. (5 pages)Proximal time-optimal control of flexible systems made robust though feedback
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1685
The paper presents a new robust acceleration limited time-optimal law for flexible system control by combining the well known open loop time-optimal solution and wave-based control. Using the time optimal solution a new launch wave input to the wave based controller is designed, allowing it to recreate the time optimal solution when the system model is exactly known. If modelling errors are present, or a real actuator is used, the residual vibrations which normally remain when using the time optimal solution alone are quickly suppressed, due to the additional robustness provided by the wave based controller. A proximal time optimal response is still achieved. A robustness study is undertaken and shows significant improvements can be achieved using wave based control in conjunction with the time optimal solution. (6 pages)Analysis of a closed loop control for current unbalance compensation based on AC/AC converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0674
In this paper a stability analysis method for unbalance compensation system based on AC-chopper is proposed. Employing AC-choppers and Steinmetz theory it's possible to obtain a dynamic compensation system. This system's performance and stability are not depending only on the cause of unbalance but also on grid parameters such as line impedances and other connected loads. If a quasi-static sinusoidal steady-state approximation is hypothesized, through the multivariable control theory it's possible to study the compensation system stability propriety in relation with grid parameters. (4 pages)Driver model simulation for railway brake systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_20080332
This study proposes an essential issue to construct a driver model for a railway in order to keep a safe and integral society throughout the world. As of now, no study has been made on the transfer function of train drivers and brake systems as to safety of a railway. This paper describes the stability and safety of railway vehicles controlled by train drivers. The driver model used the model as proposed by Iguchi et al., and used the transfer function that consisted of the proportion, differentiation and the integrated operation. This study describes the frequency characteristics: transfer function from a braking command to error between the reference velocity and real velocity. Moreover, overrun distances against driver model parameters are shown. According to the simulation results, an integral gain of the transfer function of the driver model is important in the brake and vehicle dynamics. (6 pages)Operation of brushless doubly-fed machine for drive applications
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080539
This paper presents dynamic and steady-state performance of the Brushless Doubly-Fed Machine (BDFM) operating as a variable speed drive. A simple closed-loop control system is used which only requires a speed feedback. The controller is capable of stabilising the machine when changes in speed and torque are applied. The machine starts in cascade mode and then makes a transition to the synchronous mode to reach the desired speed. This will allow a uni-directional converter to be used. The experiments included in this paper were carried out on a 180 frame size BDFM.Distributed power control technique for 802.15.4 wireless sensor networks, based quantitative feedback theory
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080673
This paper presents a novel, practically implementable, frequency domain solution to the question of robust dynamic power control (PC) for wireless sensor networks. Following the definition of the challenging issues regarding wireless sensor technology, the PC framework is constructed based on tracking a target received signal strength achieving minimal outage probability and transmission power. A systematic design procedure based on quantitative feedback theory is then presented which is intuitively appealing from an engineering perspective. The proposed controller is extensively tested experimentally on a fully complaint 802.15.4 testbed where mobility is introduced using fully autonomous robots. A benchmark comparison is made between this approach and a number of proven strategies.Analysis and design of QFT-based robust control of a boost power converter
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080579
The application of quantitative feedback theory (QFT) to design robust controller for a DC-DC boost converter operating in continuous conduction mode (CCM) is investigated in this paper. The controller is designed to provide good attenuation of the load disturbances in spite of practical limitations on the achievable closed-loop performance (i.e. right-half-plane zero) and in the presence of other design constraints including closed-loop tracking and robust stability. A prefilter is subsequently designed in order to improve the transient and steady state control responses. Tracking control characteristics are analyzed through computer simulation for a peak-current-mode (PCM) controlled boost converter in order to demonstrate the effectiveness of the proposed control methodology.Application of the discrete-time structured singular value for DC-DC converters
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080644
This paper considers the application of the discrete-time structured singular value to assess the robustness of systems subject to real parametric uncertainties. Since the associated uncertainty set is strictly real, the resulting μ bounds may be discontinuous irrespective of the fineness of the frequency sweep. It is therefore necessary to seek other more reliable methods of test. One such method detailed is a discrete robust stability state-space test that is not dependent on a frequency sweep. It is shown that this is a discrete skewed structured singular value problem. For illustration purposes, a robustness analysis using both a frequency sweep and state-space transformation is performed on a forward converter with a real parameter uncertainty. The results are detailed and critically assessed.Variable frequency adaptive selective compensation for active power filters
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080475
This paper investigates an adaptive current controller for active power filters for aeronautic applications, which compensate selected load current harmonics. The attention is focused on the load current harmonic compensation when the fundamental frequency varies over a wide range (typically between 400 Hz and 800 Hz) and the harmonics produced by distorting loads (such as the 5<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">th</sup> and the 7<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">th</sup>) are above the achievable current loop bandwidth. Compared to previously reported resonant controllers, this paper proposes an adaptive leading angle compensation in the resonant filter, which - by compensating the variable process delay -is potentially able to guarantee the theoretical current control stability when the selected frequency is up to the Nyquist frequency. However, the presence of intermodulation, i.e. distortion introduced due to the compensation of frequencies approaching the Nyquist limit, introduces an additional distortion, which limits the maximum compensation frequency. Experimental results are also presented.Control of a highly non-linear multi-variable thermal processing furnace
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080642
Tuning a controller's parameters can sometimes be a very complex and challenging task. Many methods have been used through the years to try and overcome this difficult challenge. In this paper we investigate the linear quadratic regulator (LQR) as a method for giving robust control for the non-linear multiple input multiple output system discussed in this paper. The system is a thermal processing furnace used to anneal 150 mm wafer batches in the 250°C to 450°C range in high vacuum. A plant model was developed which is a hybrid of a physical-law heat-transfer model and measurement data based model of the system. Numerical optimization was used to minimize the difference between measured data and model predicted outputs. Then, multiple linearized models were obtained. LQR was applied to one such model. It achieved the required specifications over the specified temperature range. The important specifications in this application are rise time, steady state accuracy and overshoot which are critical to the process.A modified bumpless transfer technique for seamless handoff in mobile ad-hoc 802.15.4 wireless sensor networks
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080674
In this paper a modified anti-windup-bumpless-transfer (AWBT) power control technique is proposed, to enable seamless handoff in mobile ad-hoc wireless sensor networks, that are subject to hardware limitations. The approach adopts an intuitively appealing two step design procedure where firstly a linear controller is designed ignoring the inherent nonlinearities in the system. Quantitive feedback theory is used in this regard and provides pre-specified levels of robust stability and performance. In the second stage of the design process an AWBT controller is designed to account for hardware saturation constraints. This scheme is subsequently modified to account for feedback discrepancies due to a varying propagation environment, ensuring smooth handoff in the network. The proposed method is extensively tested on a fully compliant 802.15.4 wireless sensor testbed.Stable MRAS-based sensorless scheme design strategy for high power traction drives
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080584
- A model reference adaptive system (MRAS) based observer is the dominant speed estimation scheme for sensorless induction motor drives. The main drawback of fundamental model based estimation techniques is instability in the low speed region under regenerating conditions. Furthermore, accuracy and estimation stability is especially influenced by stator resistance thermal variation in this region. The main novelty of the proposed sensorless control scheme lies in its flexibility for ease of use in both stator flux and conventional rotor flux control drives. Both degrees of freedom of stator currents errors are used for speed and stator resistance estimation in parallel whilst the speed estimation adaptive function is reconfigured for assuring stability in the whole speed region. Overall stability is analyzed by linear adaptive control theory methods such as closed-loop system Bode and poles placement.A STATCOM with supercapacitors for enhanced power system stability
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080490
STATCOMs have been widely used for voltage support over the past decade, to improve power quality and voltage stability. However STATCOMs are limited in their ability to improve the system stability margin due to their restricted capability for delivering real power. Supercapacitors are devices which can store significant amounts of energy, and are able to quickly release it. The aim of this work is to investigate how supercapacitor based energy storage technology can be used to enhance the capability of STATCOM units to maintain a high quality of distribution voltage and improve the system stability.State-space averaging, closed loop analysis, and stability studies of a step up positive output switched-capacitor DC-DC converter
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070608
This paper presents the closed loop analysis and design of a positive output switched capacitor DC-DC converter controlled using a PID controller. The state-space averaging approach is used for obtaining linear model of the converter circuit. Closed loop stability analysis for the converter is investigated using root locus technique. Using the combined operation of the switched capacitor and voltage lift-techniques, a converter of small size, high power density, high-voltage transfer gain, high power efficiency and low electromagnetic interference is constructed and tested. The distinctive feature of this converter is on chip power integrator. The simulation results are validated and verified with the experimental hardware results.Fuzzy gain scheduled pole placement based state feedback control of CSTR
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070588
CSTR plays a vital role in almost all the chemical industries. Continuous stirred tank reactor (CSTR) is a highly nonlinear process exhibiting stable and unstable steady state at different regions. Control of CSTR in the complete range is a mind boggling problem. In this paper, a fuzzy scheduled pole placement based state feedback control of CSTR is investigated. The entire region is divided into three regions; low, middle and the high region. The low and the high region have stable steady state and the middle region have unstable steady state. Initially, the gain matrix of the state feedback controller is computed for each region using pole placement technique. Then using fuzzy gain scheduler, the complete controller is formed. The result shows the feasibility of using the proposed controller for the control of CSTR. In this chapter optimal control of CSTR is investigated for the tracking and regulatory problems.Genetically optimized neuro-fuzzy PSS for damping modal oscillations of power system
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070601
An integrated approach of Takagi-Sugeno (TS) fuzzy scheme with a genetic optimization of their parameters has been developed in this paper to design intelligent adaptive controllers for improving the dynamic and transient stability performance of power systems. This concept is applied to power system stabilizer (PSS) connected to a nine bus three machine power system. The rules of the TS-fuzzy scheme are derived from the speed error and their derivatives. Further, to implement this combined scheme only one coefficient in the TS-fuzzy rules needs to be optimized. The optimization of this coefficient as well as the coefficient for auxiliary signal generation is performed through genetic algorithm. The performance of the new controller is evaluated in multimachine power systems subjected to various dynamic and transient disturbances. The new genetic-neuro-fuzzy control scheme exhibits a superior damping performance as well as a greater critical clearing time in comparison to the existing PI and supplementary controller with updating of its parameters through lag-lead compensation. Its simple architecture reduces the computational burden, thereby making it attractive for real-time implementation.Power system stabilizer using fuzzy logic controller in multimachine power systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070599
In general, Power Systems are subjected to wide ranges of transient instability and the dynamic instability. By using fast acting high gain excitation systems the transient stability limit of a synchronous machine has been significantly improved, but impair the dynamic stability. The dynamic instability is damped by using the Power System Stabilizers (PSS). The Power System Stabilizer means a supplementary excitation control which is capable of providing additional damping torque to the rotor angle oscillations of the synchronous machine without affecting its synchronizing torque. The Power System Stabilizer is developed by using the conventional and non conventional controller. In the conventional controller a Phase Lead Compensation technique is used and in the non conventional controller fuzzy set theory is used. The proposed Power System Stabilizer is designed for a Multi-Machine connected to an infinite bus system. The generator speed deviation and acceleration is taken as inputs to the controller. Simulation of Multi-Machine Power Systems with and without using Power System Stabilizers subjected to various disturbances and operating conditions are presented. These simulation results are plotted as a function of time. On comparing simulation results with and without using Power System Stabilizers it is observed that the fuzzy set theory based Power System Stabilizer for Multi-Machine power system has better performance than other.Closed loop stability analysis for the particle swarm optimization dynamics
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070589
The paper presents an alternative formulation of the PSO dynamics by a closed loop control system, and analyzes the stability behavior of the system by using Jury's test and root locus technique. Previous stability analysis of the PSO dynamics was restricted because of no explicit modeling of the non-linear element in the feedback path. In the present analysis, the model of the nonlinear element is considered for closed loop stability analysis. Unlike the previous works on stability analysis, where the acceleration coefficients have been combined into a single term, we in this paper consider their separate existence to determine their suitable range to ensure stability of the dynamics. The range of parameters of the PSO dynamics, obtained by Jury's test and root locus technique are also confirmed by computer simulation of the PSO algorithm.Interconnection and damping assignment approach for reliable PM synchronous motor control
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070036
The goal of this paper is to design a high performance speed controller for a PMSM drive. The controller is passivity based using the energy shaping technique namely interconnection and damping assignment. Under some assumptions, a linear controller is derived associated to a non linear observer to estimate the load torque which is unknown. The important point developed in this paper is the proof of the global stability, which is mandatory in a drive especially in embedded or transportation applications where reliability is a key issue. Simulation and experimental results prove the feasibility of the approach. (6 pages)Model reference adaptive control using quadratic and non-quadratic Lyapunov functions - Part I
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070806
In the design of model reference adaptive control (MRAC) schemes, adaptive laws have been developed based on Lyapunov stability theory. Over the past few decades it has been a common practice to use Quadratic Lyapunov Functions (QLF) and recently, in a similar spirit, Non-Quadratic Lyapunov Functions (NQLF) have been used. This paper, using a new Lyapunov Function based on both QLF and NQLF, presents new adaptive laws for MRAC. These new laws have been shown to overcome the drawbacks of the laws based on either QLF or NQLF alone. Finally, this paper also presents simulation results supporting the arguments.Stability analysis and control synthesis of affine fuzzy systems
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070688
This paper presents an approach to stability analysis and control synthesis of affine fuzzy systems. The analysis is based on quadratic Lyapunov functions. The approach considers the nonlinear offset terms in affine fuzzy systems as non-vanishing perturbations added to the corresponding nominal linear blending systems. The affine fuzzy system is bounded by an ultimate limit if the corresponding linear blending system is exponentially stable. A state feedback controller with an extra term is designed with guaranteed global stability. The ultimate bounds are determined for both the open loop system and the compensated system.Multi-rate sampled-data systems with decentralized control structure
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070691
This paper presented the mathematical formulation of the decentralized multi-rate controller design problem based on a lifting technique, taking account of stability and input-output performance. The design procedure includes both the analysis of the overall system and the controller synthesis for individual subsystems. Also an approach to the optimal stabilization via a decentralized control law is proposed and the main result presents a scheme for constructing a class of decentralized controllers, which stabilizes the system and is optimal with respect to a quadratic performance index.