The issue of power system stability is becoming more crucial. In deregulated power systems, competition could push the system near its security limit. The governing controls of generator play an important role in improving the dynamic and transient stability of power system. In this paper, we present an interval type-2 fuzzy logic based method for governing control. Interval type-2 Fuzzy logic is applied to generate compensating signals to modify the controls during system disturbances. The oscillation of internal generator angles is observed to indicate the good performance of proposed control scheme, very over a wide range. In this work, development of Interval Type-2 Fuzzy based Model of steam turbine Governing System of Power Plant is proposed. The power system transient terminal voltage and frequency stability enhancement have been well investigated and studied through the following efforts. Membership functions in interval type-2 fuzzy logic controllers are called footprint of uncertainty (FOU), which is limited by two membership functions of adaptive network based fuzzy inference systems; they were upper membership function (UMF) and lower membership function (LMF). The performances of the proposed controllers were evaluated and discussed on the basis of the simulation results. An experiment set up of power system governing system was built and used to verify the performance of IT-2FLC controller.
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Expensive proportional valves are dominantly used in pneumatic positioning systems even with low demanding accuracy positioning tasks, which deprive pneumatic systems from its economical advantages. Thereby, using low cost on/off solenoid valves instead of proportional valves has been a topic of research in the last decades. In this paper, a parametric study is conducted to investigate the effect of using low-cost 3/2 internally pilot on/off solenoid valves to control a double acting cylinder and study the system nonlinear response to on/off and PWM input signal. Matlab ® Simscape library is used to model and simulate the system. The model is validated though experimental measurements of the system behavior. The model is used to study and decrease the nonlinear pressure response associated with the cylinder chambers in addition to the evaluation of the dead zone and operating range of the on/off solenoid valve when operated with PWM signal. The results show that using a meter-in flow control and having a near constant cylinder back pressure can reduce the nonlinearity. An orifice of 1e-6 m2 can reduce the pressure variation by 80% but increase the transient time. Connecting an accumulator with 1 liter volume can result in 50% reduction in rod side pressure variation. The model has been used to predict the PWM parameters as well. It has been found that the most suitable parameters for this valve are 20 Hz and duty cycle from 12 to 65%. These results encourage going further with controlling a pneumatic position system using low-cost control valves and a simple controller.
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The control concept on the electro-hydraulic servovalve system focuses on the pressure control, position control and velocity control. The servovalve and the system components are needed to be considered in the proposed control strategy. The control concepts on the electro-hydraulic servovalve systems in this work are divided into two parts: 1. Theoretical and experimental investigation for pressure control on the electro-hydraulic servovalve systems. The pressure control study in this work is concerned with the modeling and controlling of the hydraulic fluid pressure value at the end of long transmission line (TL) by using the electro-hydraulic servovalve. The input voltage signals to the amplifier, designed by C++ program, are used to control the pressure reference signal at the end of TL. The electrical analogy method is used to simulate the effect of the TL, as well as the first order transfer function to simulate the servovalve effect. Therefore, the whole system is represented mathematically in MATLAB m-file program. The mathematical model is seen as a good simulation approach compared with the experimental open loop control test. The on-line adjustable control strategy, Ziegler & Nichols method and Astrom & Hagglund method, can be used experimentally to find the proportional and integral control gain values for acceptable control system behavior. The servovalve succeeds to reduce and overcome the negative effect of the TL on the hydraulic fluid pressure value at the chosen control point. 2. Theoretical and experimental investigation for velocity and position control by the electro-hydraulic servovalve system. The C++ language programs are designed to control the position and velocity of the road simulator (single-rod, double acting linear cylinder actuator) with variable load (quarter car suspension system). The whole system is analyzed mathematically and experimentally. The mathematical model of the electro-hydraulic servovalve system is represented and analyzed successfully by designing the SIMULINK program. The dynamics modeling of the servovalve and the single road cylinder actuator under variable load which are controlled as a closed loop position control method with existence of the actuator internal leakage is done successfully by using the SIMULINK environments. So, the transfer function and the state-space model of the system in open and closed loop control are presented. Also, the Bode diagram is done for the system as well as the stability characteristics are found for the system by the Nyquist Diagram. The on-line adjustable PID control tuning is employed experimentally to find the best control gain values which are applied to the system. In the mathematical SIMULINK program, the PID gains values are tuned manually and automatically by computing a linear model of the plant. The tuning strategies are done automatically for the P, PI and PID strategies for three different response time values. The comparison figures in the P strategy show that the simulation programs give a good and accurate prediction results and enhance the system behavior. On the other hand, the PI strategy shows incompatible results between the actual test and the simulation program. The PID strategy shows a good prediction results. To analyze the actual fully system behaviors for a large spectrum frequency, the numbers of sinusoidal voltage input signal are used with unity compensator to create actual Bode plot. The tracking closed loop control method is done experimentally by designing C++ program and it is done theoretically by the SIMULINK simulation program for the system. The comparison result with the previous research clarifies that the mathematical solution method proposed in this dissertation shows that the prediction of the system behavior is acceptable and improve the system behavior.
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The awareness and concern of our environment together with legislation have set more and more tightening demands for energy efficiency of non-road mobile machinery (NRMM). Integrated electro-hydraulic energy converter (IEHEC) has been developed in Lappeenranta University of Technology (LUT) /1/. The elimination of resistance flow, and the recuperation of energy makes it very efficient alternative. The difficulties of IEHEC machine to step to the market has been the requirement of one IEHEC machine per one actuator. The idea is to switch IEHEC between two actuators of log crane using fast on/off valves. The control system architecture is introduced. The system has been simulated in co-simulation using Simulink/Mevea. The simulated responses of pump-controlled system is compared to the responses of the conventional valve-controlled system. KEYWORDS: IEHEC pump/motor, pump-controlled system, non-road mobile machinery, fast on/off valve.
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