Linear Control Functions Research Articles

Robust Parametric Programming for Adaptive Piecewise Linear Control of Photovoltaic Inverters to Regulate Voltages in Power Distribution Systems

This paper proposes a robust parametric programming (RPP) method to adaptively obtain piecewise linear control functions of photovoltaic (PV) inverters for real-time voltage regulation in distribution systems. First, the voltage regulation problem is designed as a multi-parameter programming problem, which is transformed into single-parameter linear programming (sp-LP) problems for realizing local control of a PV inverter while considering the maximum voltage deviation caused by other PV units. Second, an alternating iterative algorithm is developed to solve the sp-LP problem of each PV unit and obtain the control functions of all the PV units. Third, considering the information on PV power correlation, a two-level parametric programming problem is established to enhance the voltage regulation performance of PV inverters. A geometric method is developed to solve the inner-level problem, and breakpoint reduction with robust interpolation is developed to improve the computational efficiency in solving the outer-level problem. Four distribution systems integrated with PV units are used to validate the effectiveness of the proposed method. Numerical results show that the performance of the proposed PV inverter control strategy is close to that of the ideal optimal solution and superior to existing piecewise linear control strategies.

ANALYTICAL DESIGN OF A QUASIOPTIMAL REGULATOR FOR THE ELECTRIC FEED DRIVE OF STRAW CHOPPER

The use of control systems for feed drives of straw chopper using of frequency inverters allows to ensure the stability of the load of the main motor of system, to ensure high-quality grinding of components. At the same time, a feature of the control system is the significant asymmetry of regulator output characteristic, which significantly complicates the synthesis procedure of the control law, accordingly. Existing regulators often do not provide the ability to adjust the load in a wide range and require reconfiguration when the operating parameters of straw are changed. An urgent task is the realization of the synthesis procedure of the control law, which provides a close to optimal behavior of load stabilization of the straw chopper main electric drive. The aim of the work is to solve the problem of analytical design of a quasioptimal feed regulator in the presence of significant asymmetric nonlinearity of control output. The method of dynamic programming for linearized systems and quadratic quality functional to solve the problem of synthesis of the feed regulator was used. To linearize significant nonlinearity, the "instant linearization" method was used. Using this method the nonlinear characreristic was replaced by a linear one, where the linearization coefficient is a control function. The transition from a linear control function to an adaptive one using the Pearson method was carried out. Using concept of Pearson's method allowed replacing the original non-linear problem of synthesis with a linear one, which is solved in each calculation cycle of the programmable logic controller. Using of modified minimization quality functional proposed by O.A. Krasovsky, made it possible to significantly simplify the procedure for finding the coefficients of the optimal regulator. Investigation the dynamic characteristics with proposed control system by the method of digital modeling was made. Comparison of the transients performance of the synthesized regulator with a linear one was made, and the advantages of the proposed approach were determined. The prospects for the further development of optimal control systems are formulated and the features of the practical implementation of the control algorithm are defined. Thus, the use of a synthesized regulator made it possible to improve the quality of drive load control; the proposed approach can be used for electromechanical systems in which the drive load by programmable logic controllers is controlled.

Hello, I am calling to ask for some money: mobile phones and credit uptake in rural Ethiopia

PurposeIt is widely believed that ICT has a significant influence on the daily life of the poor and has positive spillover effects in their livelihoods. Mobile phones are one of the few ICT innovations that have found their way into the hands of the poor residing in remote and rural areas. In Ethiopia, mobile phones are recently introduced but got an acceptance from everyone including the rural poor; in five years’ time, mobile phones subscription has increased from less than 4% to more than 40%. Empirical evidence generally documents the positive role mobile phones play in facilitating the development efforts of poor households. However, using panel data from Ethiopia, the current paper explores a less investigated issue of the possible effects of mobile phone adoption on the credit uptakes of the rural poor who are mostly neglected from the formal credit markets but finance their credit demand from informal sources including relatives/friends.Design/methodology/approachTo investigate the relationship between mobile phones and credit uptake and/or loan size, one can use different empirical strategies. For partly unleashing the endogeneity problem, an instrumental variable estimation approach is adopted in this paper. To deal with the endogeneity problem, one may consider using the linear IV approach or the control function. But the outcome variable and the endogenous variable are binary in nature, and the usual trend is to use the linear IV models or control functions, which do not consider these binary natures of the variables. To this end, a special regressors estimator is adopted, mostly used when both the dependent and the endogenous variables are binary in nature.FindingsThe econometric results suggest mobile phones are positively associated with the credit uptake of rural households, especially credit uptake from informal sources. Households with mobile phones are found to have 4%–14% higher probabilities of credit uptake and about 6%–17% in the case of credit from informal sources. Besides, households with mobile phones are found to have about ETB 65 (USD 3.42) higher loan size and about ETB 78 (USD 4.11) higher amount of loan in the case of a loan from the informal sources. Thus, policy-makers and financial providers working on providing credit in rural areas need to exploit the use of mobile phones in reaching out to the rural poor.Originality/valueThe author attests the fact that the work described has not been published previously and that it is not under consideration for publication elsewhere. Besides, it is the original work of the author.

Numerical Solution of the Problem of Determining the Number and Locations of State Observation Points in Feedback Control of a Heating Process

The problem of optimizing the number and locations of state observation points in the feedback control of heating a rod in a furnace is considered. The weighting coefficients determining the importance of each observation point in the current linear control function are also optimized. The synthesis of control functions is reduced to the problem of optimizing parameters for a pointwise loaded parabolic equation, which is solved by applying first-order optimization methods.

Exact Boundary Controllability for Free Traffic Flow with Lipschitz Continuous State

We consider traffic flow governed by the LWR model. We show that a Lipschitz continuous initial density with free-flow and sufficiently small Lipschitz constant can be controlled exactly to an arbitrary constant free-flow density in finite time by a piecewise linear boundary control function that controls the density at the inflow boundary if the outflow boundary is absorbing. Moreover, this can be done in such a way that the generated state is Lipschitz continuous. Since the target states need not be close to the initial state, our result is a global exact controllability result. The Lipschitz constant of the generated state can be made arbitrarily small if the Lipschitz constant of the initial density is sufficiently small and the control time is sufficiently long. This is motivated by the idea that finite or even small Lipschitz constants are desirable in traffic flow since they might help to decrease the speed variation and lead to safer traffic.

Optimality of robust disturbance-feedback strategies

In this paper, robust disturbance-feedback strategies for finite time-horizon problems are studied. Linear discrete-time systems subject to linear control, state constraints, and quadratic objective functions are considered. In addition, persistent disturbances, which enter the system additively and are contained in a polytopic set, act on the system. The synthesis of robust strategies leads in the case of the traditional robust state-feedback and open-loop min–max strategies to, respectively, nonconvex problems or conservatism. However, robust disturbance-feedback problems can easily be reformulated as convex problems and solved by tractable linear matrix inequalities. Hence this approach bypasses the nonconvexity issue while maintaining the advantages of feedback strategies. As a key result, it is shown that both sources of conservatism attributed to this approach, namely, the relaxation method and the affine parametrization, can be removed at the expense of an increase in computational effort. Copyright © 2015 John Wiley & Sons, Ltd.

Partisan Imbalance in Regression Discontinuity Studies Based on Electoral Thresholds

Many articles use regression discontinuity designs (RDDs) that exploit the discontinuity in “close” election outcomes to identify various political and economic outcomes of interest. One of the most important types of diagnostic tests in an RDD is checking for balance in observable variables within the window on either side of the threshold. Finding an imbalance raises concerns that an unobservable variable may exist that affects whether a case ends up above or below the threshold and also directly affects the dependent variable of interest. This article shows that imbalance in RDDs exploiting close elections are likely to arise even in the absence of any type of strategic sorting. Imbalance may arise simply due to variation in the underlying distribution of partisanship in the electorate across constituencies. Using both simulated and actual election data, the study demonstrates that the imbalances driven by partisanship can be large in practice. It then shows that although this causes a bias for the most naive RDDs, the problem can be corrected with commonly used RDDs such as the inclusion of a local linear control function.

Development of optimal and robust predictive guidance technique for Mars aerocapture

The paper discusses a predictive guidance technique for the optimal aerocapture maneuver accomplished by a high-mass Mars orbiter to achieve the targeted circular parking orbit with minimal fuel consumption. Unlike the majority of investigated algorithms of the “predictor–corrector” family with a time-invariant control, the guidance algorithm considered in the paper computes a time-dependent control function which, being a reference profile of the angle of attack, provides a minimum to the post-aerocapture propulsive ΔV at the apoapsis of a transfer ellipse. Initially, the two-parametric bounded linear control function has been used, and the algorithm developed found an optimal solution directly by “descending” in a control parameters space. The simulation has shown that an optimum is achieved when the slope of the linear function tends to infinity, i.e., the bounded linear control is being transformed into a one-parametric step function. Such a result proved to be in conformity with the earlier “indirect” optimal solution, namely, derived from Pontryaginʼs maximum principle for a slightly simplified motion model. Thus, the final version of algorithm providing “direct” optimization by solving a nonlinear eigenvalue problem needs to determine only one parameter – switching time of angle of attack. The solution obtained satisfies the terminal condition – a target apoapsis, as well as it is close to optimum. Another issue the paper focuses on is an improvement of robustness of the algorithm under unpredictable model disturbances, especially variations of atmospheric density. The new model adaptation algorithm is developed, which estimates density errors and updates the density profile during the descent phase to be used for control corrections in the ascent phase. Testing the example simulation model with angular motion has shown the runtime effectiveness and high targeting accuracy provided by the proposed predictive technique.

CHAOS MULTISCALE-SYNCHRONIZATION BETWEEN TWO DIFFERENT FRACTIONAL-ORDER HYPERCHAOTIC SYSTEMS BASED ON FEEDBACK CONTROL

In this paper, the chaos multiscale-synchronization between two different Fractional-order Hyperchaotic System (FOHCS)s have been investigated. The Lü-like and its FOHCS are also studied. The Lü-like FOHCS is controlled to be multiscale-synchronization with Liu FOHCS and new Lorenz FOHCS, respectively. The analytical conditions for the multiscale-synchronization of these pairs of different FOHCSs are derived by utilizing Laplace transform. Furthermore, multiscale-synchronization between two different FOHCSs is achieved by utilizing the different linear and nonlinear feedback control method in a short period and both remain in chaotic states. Numerical simulations are used to verify the theoretical analysis using different values of the fractional-order parameter and the different linear and nonlinear control functions.

LED BLU의 최적 소비전력을 위한 선형적 피드백 제어기능을 가지는 드라이버 설계

As demands for green industry increase, this paper proposes a power control technique that can substitute pre -existing CCFL(Cold Cathode Fluorescent Lamp) and optimize power consumption of LED BLU. This techique is designing LED driver circuit that make a DC-DC output voltage(VLED) to have a linear control function for a supply voltage of LED string. The proposed LED driver have an advantage that can increase or decrease a DC-DC output voltage compared with conventional LED driver. The designed LED driver circuit was designed using 0.35um CMOS technology. And its operation was verified through simulation.

Optimal control in trajectory planning for a re-entry vehicle

The objective of this paper is to establish a desired trajectory for the Alflex reentry vehicle using stepwise and linear control functions, so that the oscillations of the pitch, roll and yaw rates are minimized. For the variations of the attack angle and pitch angle we find control functions for which the computed results are in a good agreement with those recorded experimentally.

Periodic motion suppression based on control of wing rock in aircraft lateral dynamics

Wing rock prevention is an important objective for an aircraft that needs to fly and maneuver at moderate to high angles of attack. This phenomenon is characterized as a periodic motion (or limit cycle), and needs to be avoided at all costs. A candidate mechanism for the wing rock limit cycle is the inertia coupling between an unstable lateral-directional (Dutch roll) mode with a stable longitudinal (Short period) mode. The coupling mechanism is provided by the nonlinear interaction of motion related terms in the complete set of motion equations. A methodology for preventing the limit cycle accomplished by adding a control function to the original equation of wing rock motion is presented in this paper. To analyze the state variables of the system, the complete set of nonlinear equations of motion including effective linear control function was solved. Numerical model constructed for A-4D and a Mig-21 Aircraft is solved to illustrate the results. The numerical results show that it was sufficient to use a linear control function including both roll attitude and roll rate for suppressing wing rock motion without any error in desired time. A good agreement between the numerical results and the published work is obtained for limit cycle oscillation existence at different values of damping ratio for almost the same roll angle.

A method of analytical solution of dynamic optimization tasks

In the article a method of possibility evaluation of obtaining of analytical solution of optimization tasks is proposed on the basis of sufficient conditions for optimality by V. F. Krotov for functionals with the linear control function and functions of power polynomials on phase coordinates with coefficients that are any time functions

Dynamic queue control functions for ATM ABR switch schemes: design and analysis

The main goals of a switch scheme are high utilization, low queuing delay and fairness. To achieve high utilization the switch scheme can maintain non-zero (small) queues in steady state which can be used if the sources do not have data to send. Queue length (delay) can be controlled if part of the link capacity is used for draining queues in the event of queue build up. In most schemes a simple threshold function is used for queue control. Better control of the queue and hence delay can be achieved by using sophisticated queue control functions. It is very important to design and analyze such queue control functions. We study step, linear, hyperbolic and inverse hyperbolic queue control functions. Analytical explanation and simulation results consistent with analysis are presented. From the study, we conclude that inverse hyperbolic is the best control function and to reduce complexity the linear control function can be used since it performs satisfactorily in most cases.

The control parameterization enhancing transform for constrained optimal control problems

AbstractConsider a general class of constrained optimal control problems in canonical form. Using the classical control parameterization technique, the time (planning) horizon is partitioned into several subintervals. The control functions are approximated by piecewise constant or piecewise linear functions with pre-fixed switching times. However, if the optimal control functions to be obtained are piecewise continuous, the accuracy of this approximation process greatly depends on how fine the partition is. On the other hand, the performance of any optimization algorithm used is limited by the number of decision variables of the problem. Thus, the time horizon cannot be partitioned into arbitrarily many subintervals to reach the desired accuracy. To overcome this difficulty, the switching points should also be taken as decision variables. This is the main motivation of the paper. A novel transform, to be referred to as the control parameterization enhancing transform, is introduced to convert approximate optimal control problems with variable switching times into equivalent standard optimal control problems involving piecewise constant or piecewise linear control functions with pre-fixed switching times. The transformed problems are essentially optimal parameter selection problems and hence are solvable by various existing algorithms. For illustration, two non-trivial numerical examples are solved using the proposed method.

Evaluation beschäftigungspolitischer Maßnahmen in Ostdeutschland / An Evaluation of Employment Measures in Eastern Germany

Zusammenfassung Untersucht werden die Beschäftigungseffekte von in Ostdeutschland angewandten Maßnahmen. Gebrauch gemacht wird von ökonometrischen Methoden, die Korrelationen berücksichtigen zwischen Bestimmungsgründen für die Teilnahme an Beschäftigungsmaßnahmen und Determinanten, die die Beschäftigungswahrscheinlichkeit beeinflussen, d.h. lineare Kontrollfunktionen, Instrumentalvariablenschätzer, Random-effects-Schätzer, Pre-Programm-Tests, und Matched-sampling-Methoden sowie eine Kombination finden Berücksichtigung. Die Ergebnisse, die auf Daten des Arbeitsmarkt-Monitors basieren, zeigen, daß die traditionellen Instrumente nach AFG wenig erfolgreich waren. Positive Beschäftigungseffekte lassen sich von Weiterbildungsmaßnahmen, die von Betrieben veranlaßt wurden, identifizieren. Fortbildung und Umschulung, die von den Arbeitsämtern finanziert wird, führt zu keinen einheitlichen Resultaten. Es zeigen sich zunächst negative und später positive Beschäftigungseffekte. Bei Trennung zwischen Frauen und Männern läßt sich dieses Muster nur für letztere feststellen. Auch bei betriebsinterner Fortbildung treten geschlechtspezifische Unterschiede auf. Innerhalb von drei Jahren nach der Maßnahme nehmen bei Männern die positiven Effekte tendenziell zu. Bei Frauen ist der Einfluß am Ende des Zeitraums statistisch nicht mehr gesichert.

A new adaptive LQG control algorithm

AbstractA new control algorithm is developed for the discrete time, finite horizon adaptive LQG problem. In the new algorithm, randomization over linear control functions is performed at future stages to find a deterministic desired control U(k) at the current stage. This randomized linear control policy, which is U(k)‐dependent and non‐linear in measurements, incorporates explicitly the knowledge available about the unknown parameter at future stages in terms of the posterior distribution. At the same time it enables us to obtain a closed form expression of an approximation of the optimal control‐cost function. Numerical examples comparing the new solution with the optimal are also provided.

A General Methodology for Bilinear System Stability with Output Feedback

New results are derived for the stability analysis of bilinear systems (BLS) with output feedback of a general form which includes linear control functions, quadratic functions, all functions which satisfy Lipschitz condition and others. Theorems and applications are obtained for time-variant, continuous and discrete BLS. The results form a base for adaptive trajectory-tracking controllers.The sufficient conditions which are derived can be applied directly to the range of admissible controller gains for given plant parameters, or there is a trade off between controller and plant design parameters. The method does not depend on the computation of a Liapunov function and indirect stability analysis as do most techniques which are available in the literature. In the continuous case, certain necessary conditions also are derived. A field-controlled, electric motor example is presented.

Computation of Open-Loop Solutions for Zero-Sum Differential Games by Parameterization

Given a dynamical system controlled by two parties aiming at diametrically opposite goals and a initial state, regard the time histories of the controls when both parties do the best they can do. In this paper an algorithm is presented to compute them. Mathematically, this conflict situation can be formulated as Zero-Sum Differential Game with terminal payoff and some terminal (equality and/or inequality) constraintsminumaxvΦxtf(P1)subjecttox˙=fx,u,v,O≤t≤tf,x0=xOu∈Uv∈VΨxtf≥¯¯O Restricting the search for the “optimal” opan-loop controls u¯=u¯t,v=v¯t for given xo to a prespecified class of parameterized control functions u = u(t, α), v = v(t, β), α∈RP,β∈Rq, (e.g. The class of continuous and piecewise linear control functions), the following saddlepoint problem in the parameter-space associated with is obtained:minα∈Amaxβ∈BΦxtf,α,β(P2)subjecttoΨxtf,α,β≥¯¯0where x(tf,α, β) is the value of the solution ofx˙=fx,ut,α,vt,β,x0=xOattimetf>o. A⊂RP,B⊂Rqare to be chosen such that ut,α∈U,vt,β∈v for α∈A,β∈B,O≤t≤tf. The algorithm to solve (p2) uses an implementation of the iterative method with quadratic programming of Han-Wilson-Powell for solving general nonlinear optimization problems doing some iteration steps alternating between a and 3. This procedure is continued until both optimizations are completed and thus ends up with a saddlepoint in the parameter space, at least a local one. The partials of Φxtf,α,β,xtf,α,β with respect to α or β needed for each iteration may be computed by forward differences or by the technique of impulsive response functions using solutions of the adjoint variational equations. To demonstrate the feasibility of the algorithm it is used to operate solutions for the “Homicidal Chauffeur”, a classical pursuit-evasion problem in the plane, which can be solved by hand. A second example will be a rather complex and realistic aircraft pursuit-evasion problem, where an exact analytical solution is not found.

Parallel Resonance Synthesizer for Speech Research

This paper describes the development of a parallel terminal analog speech synthesizer designed for the needs of a nontechnically oriented user who has minimal engineering support. Salient features considered are reasonableness of cost, ease of maintenance and calibration, flexibility of configuration, and compatibility with various input devices. Four vowel resonances, a nasal resonance, and two fricative resonances are included. Resonance bandwidths are manually adjustable over a wide range. The excitation may be either pulses, noise, or a mixture of both. The synthesizer requires 10 time-varying parameter inputs and one two-bit state control. A parameter switch steers the parameter inputs to 14 synthesizer control points according to the synthesizer state. Integrated circuit operational amplifiers are used extensively to provide linear control functions.