Load Frequency Control

Abstract— In this paper the Artificial Neural Network (ANN) Controller for load frequency control of Multi area power system is presented. The performances of ANN Controller and conventional PI controllers are compared for Single area and Multi area power system with non-reheat turbines. The effectiveness of the proposed controller is compared by applying load disturbances. The dynamic response of the load frequency control problem is studied using MATLAB Simulink package. The results indicate that ANN Controller exhibits better performance.

The detailed block diagram modeling of two area thermal-thermal power system for load frequency control investigated is shown in figure 1. Each area is assumed to have only one equivalent generator and is equipped with governor- turbine system. The load flow controller shown in Fig. 1 is based upon tie-line bias control, where each area tends to reduce the Area Control Error (ACE) to zero. The ACE given in Eq. (1) for each area consists of a linear combination of frequency and tie-line power deviation [1]

the reactive power is shorted susceptive to change in the frequency and is mainly subordinate on the motility of the voltage magnitude. Therefore, the control of active and reactive power in the electrical power system is trade separately. So weight frequency control is mainly related to system frequency and actual power control, while the automatic voltage regulator loop controls is used to change in the reactive power and voltage appearance and magnitude. Load Frequency control is an elevated level of many promotions and advanced concepts, which governs the dimensions of the electrical power system. Load Frequency Control (LFC) has a basic control structure or arrangement, of parts of the machine and similar devices in term of power system operation and control. Load Frequency Control use to keep the uniform frequency during changing load. When system frequency is changed, the main problem is that the system output of generating units cannot be controlled with in specified limit is called load frequency control (LFC) [6-8]. The speed depends on the frequency of the alternative current power supply. These are the main situation when speed permanence is required to be higher order. Electrical chronometers are operated by synchronous motors. The precision of the chronometer do not depend only on the frequency but the integral part of the frequency error. If the normal frequency of any network is 50 hertz, and the network frequency falls below 48.5 hertz, and goes to high level 51.5

ANN is implemented to the process which is under control. Nguyen and Widrow have shown in a novel approach the use of this method for backing up a trailer in a two dimensional plane. Kong and Koskotried also the same approach, but used the truck kinematic equation instead of truck emulator as used by Nguyen. Beau- fays et al. have used this method for load frequency control in power systems. Generally, the off-line method is applicable to a process with explicit mathematical formulation.

Fig.1. shows the schematic diagram for automatic load frequency control (ALFC). In this structure turbine is fed by steam or water input. The input of the turbine can be controlled by valve. A turbine is a rotating mechanical device that extracts energy from a fluid flow and converts it into mechanical energy. A turbine is a turbo machine with at least one rotating part called a rotor, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. This turbine may be a water turbine, steam turbine, gas turbine or wind turbine. The turbine shaft is mechanically coupling to the alternator. The alternator converts mechanical energy into electrical energy. This electrical energy can be given to grid through an interfacing transformer.

Abstract: This paper describes about load frequency control problem in power systems by using multi-verse optimization algorithm (MVO). This paper compares the controlling of LFC with PID and PID+MVO controllers. In this paper four area hydrothermal networks was represented.MVO algorithm was introduced in this paper for tuning the secondary controllers. The concept of MVO is runs on white hole, black hole and warm hole. Inflation rates of universe can be calculated and implemented in PID. This paper was implemented in simulator (MATLAB/SIMULINK) software.

This paper deals with the Particle Swarm Optimisation (PSO) tuned Load Frequency Control (LFC) of single area power system, with diversified power sources. The diversified generating units considered for the purpose of LFC study are thermal, hydro and gas power plants. Hybrid power system increases the reliability of the supply and instigates economic/feasible system operation. System frequency gets affected due to real power changes, this is regulated using Load Frequency Control (LFC). The hybrid interconnected power system with various generating units imposes additional complexity in the tuning of controllers. Thus in this paper PSO based tuning is imposed to obtain sophisticated control parameters for LFC of Hybrid power system.

Abstract: With the increasing penetration of renewables in power systems, frequency regulation is proving to be a major challenge for system operators using slower conventional generation units, and alternative means to provide faster regulation are being actively sought. The participation of demand side management in ancillary service provision is proven in a number of energy markets, yet its full potential to benefit frequency regulation, including the exploitation of fast power ramping capability of some devices, is still undergoing research. In this paper, a novel approach to improve the speed of response of load frequency control, a secondary frequency control, approach is proposed. The proposed control is enabled by an effective location identification technique, is highly resilient to anticipated system changes such as reduction of inertia, and enables fully decentralized power system architectures. The effectiveness of the approach is demonstrated and compared to that of present day regulation control, by means of real-time simulations incorporating appropriate time delays conducted on a five-area reduced model of the Great Britain power system. The applicability of the method is further proven under realistic communications delays and measurements experimentally using a controller and power hardware-in-the-loop setup, demonstrating its critical support for enabling the stable operation of future power systems.

Abstract: Recently several robust control designs have been proposed to the Load- Frequency Control (LFC) problem. However, the importance and difficulties in the selection of weighting functions of these approaches and the pole-zero cancellation phenomenon associated with it produces closed loop poles. Also the order of robust controllers is as high as the plant. This gives rise to complex structure of such controllers and reduces their applicability in industry. In addition conventional LFC systems that use classical or trial-and-error approaches to tune the PI controller parameters are more difficult and time-consuming to design. In this paper, a bisection search method is proposed to design well-tuned PI controller in a restructured power system based on the bilateral policy scheme. The new optimized solution has been applied to a 3-area restructured power system with possible contracted scenarios and the results evaluation shows the proposed method achieves good performance compared with recently powerful robust controllers. Keywords: Bisection Search, Deregulated Environment, Load-Frequency Control.

A Proportional-Integral-Derivative(PID) tuning method of Power system load frequency control was proposed on a Ziegler-Nichols, Tyrens-Luyben, Internal Model Control and Direct Synthesis method. The simulation results shown in fig 5 and table 3. It confirms that the Direct Synthesis controller with simple design approach and smaller rule can provide better performance comparing with the Ziegler-Nichols tuned PID controller, Tyrens-Luyben and IMC based PID controller. In this paper load frequency control was proposed order reduction technique to reduce higher order to second order plus dead time(SOPDT) and first order plus dead time(FOPDT) and reduced model order has been obtained by resembling the coefficient from Taylor series approximation. The performance of the closed loop system has effectively improved with second order reduced system model instead of full order system with PID controller with different type of tuning techniques(Internal

Small power changes mainly depends on  or f . Moreover, frequency is also a major stability criterion for large-scale stability in multi area power systems. To provide the stability, a constant frequency is required which depends on active power balance. If any change occurs in active power demand/ generation in power systems, frequency cannot be hold as its rated value. Hence, oscillations increase in both power and frequency[7-8]. Thus, the system is subjected to a serious instability problem. To improve the stability 34 of the power networks, it is necessary to design load frequency control (LFC) systems that control the power generation and active power at tie lines of interconnected system. In interconnected power networks with two or more areas, the generation within each area has to be controlled to maintain the scheduled power interchange. Load frequency control scheme has two main control loops. These are primary control and secondary control loops. This action has been realized by using a turbine-governor system in the plant[9- 10] .

The continuous growth in size and complexity of interconnected power systems, along with both area frequency and tie-line power interchange. The main purpose of load frequency control (LFC) is to sustain frequency of the system under prescribed limits and check the fluctuations on tie-line loading in case of multi area power system. Past year Automatic generation control (AGC) system specifies an applicable way to hold a control over the frequency and tie line power flow. Different methods have been suggested for Load Frequency Control. The best common technique which is commonly used around world since few years is based Proportional Integral (PI) controllers, but with exponentially increasing electricity market essential for more progressive control techniques arises for correct effective of large numbers of interconnected multi area generating units. The control of load frequency and the operational aspect of automatic generation control for a multi area hybrid interconnected power system In the large interconnected power system the risk of network failure is increased many times as the system frequency is related to Active power. The two predictable controllers are based on the theories of PI and artificial neural network which is being tested on the three area interconnected hybrid power system which embraces thermal power plant with and without re-heater and hydro power plant with different loading. As it is apparent that frequency control is laggard control when paralleled against voltage control so it is necessary to reduce the transient time in load frequency control to boost the overall power system performance. Both the proposed controller is discussed in details with respect to their working and implementation in interconnected power system network completely replacing the present day PI controller. An iterative linear estimate built matrix algorithm is framed to linearize the system. Modern control technique based on network Fuzzy Logic based Controller (FLC),Artificial Neural Network (ANN), and genetic algorithm crafted are assessed for LFC problem. Yet bountiful exertion have been made for optimizing predictable LFC but very less exertion for designing intelligent controller for multi area power system.

In this paper, a new technique for load frequency control is adopted in general the frequency is controlled by using a dump load, whose rating is equal to the rated power output of the plant. The new scheme proposed reduces the size of the dump load by controlling input power of the hydro power plant using on/off controls. The water flowing through the penstock is rerouted in smaller pipes, two or three fitted with motor operated valves. The opening or closing of the valves is achieved by on/off controls. The on/off control linearly raises or lowers the generation. A transfer function model for the system is developed with an on/off control logic. Finally, system transient’s performance is compared for the case of two –pipe (50% dump load) and the three-pipe (30% dump load).

GWO is one of the recently obtained meta-heuristic procedures. In this paper GWO and GWO-BFO are used to explain load frequency control problem for two area thermal system. The simulation conclusion shows that gains of hybrid technique GWO- BFO are better to resolve Load frequency problem in power scheme. The algorithm is planned in MATLAB (R2009b) software package.

Abstract - In this paper an extensive literature review on load frequency control (LFC) problem in power system has been highlighted. The various configuration of power system models and control techniques/strategies that concerns to LFC issues have been addressed in conventional as well as distribution generation based power systems. Further, investigations on LFC challenges incorporating storage devices BESS/SMES, FACTS devices, wind–diesel and PV systems etc. have been discussed too.

[4] Ndubisi Samuel .N., “A single area load frequency control: a comparative study based on pi, optimal and fuzzy logic controllers”, American Journal Of Scientific And Industrial Research, pp. 748-754, Vol. - 2(5), 2011. [5] Surya Prakash and S.K. Sinha, “Load frequency control of three area interconnected hydro-thermal reheat power system using artificial intelligence and PI controllers”, International Journal of Engineering, Science and Technology, pp. 23-37, Vol. 4, No. 1, 2011.

Fig.1 shows two area non reheat thermal power systems and their rating are 2000 MW (area-1 and area-2) with a nominal load of 1000 MW. Two area non-reheat thermal system is extensively used in the literature for design and investigation of automatic load frequency control of interconnected areas [25]. Fig.1 shows different parameter classifies as B1& B2-frequency bias parameters; ACE1 & ACE2 -area control errors; u1&u2 -control outputs from controller; R1 &R2 - governor speed regulation parameters(p.u.); TG1 &TG2-speed governor time constants(seconds); ∆PV1 &∆PV2 -change in governor valve positions (p.u.); ∆PG1& ∆PG2 - governor output command (p.u.); TT1 & TT2 - turbine time constant(seconds); ∆PT1 & ∆PT2 - change in turbine output powers; ∆PD1 & ∆PD2-load demand changes; ∆Ptie -incremental change in tie line power (p.u.); KP1 &KP2 -power system gains; TP1 &TP2 - power system time constant(seconds); T12 - synchronizing coefficient and ∆F1 &∆F2 -system frequency deviations(Hz). The generation of power by Thermal power plants can be modified or changed at a specific maximum rate (2-5% per min) and this is Generation Rate Constraint (GRC). Both areas of the power system consist of the speed governing system, turbine and generator. Both areas have three inputs and two outputs. The inputs are the controller input ∆Pref (also denoted as u), load disturbance ∆PD and tie-line power error ∆Ptie the outputs are the generator frequency ∆F and Area Control Error (ACE).

In this paper, the Adaptive Neuro Fuzzy Inference System based Load Frequency Control is proposed for a two area power system in each control area. The results have been compared with conventional PI controller. The results proved that the Adaptive Neuro Fuzzy Inference System based LFC gives better response as compared to conventional controller in terms of peak overshoot, settling time and steady sate error. Proposed ANFIS controller is not only simple to design but also easy to implement. Moreover, the ability to adapt to disturbances makes the proposed controller more effective. Also the learning ability of ANFIS architecture can be used to generate mature membership functions and fuzzy rules based on training data when the human export knowledge is not reliable.

If there is a small change in load power in a single area power system operating at set value of frequency then it creates mismatch in power both for generation and demand. This mismatch problem is initially solved by kinetic energy extraction from the system, as a result declining of system frequency occurs. As the frequency gradually decreases, power consumed by the old load also decreases. In case of large power systems the equilibrium can be obtained by them at a single point when the newly added load is distracted by reducing the power consumed by the old load and power related to kinetic energy removed from the system. Definitely at a cost of frequency reduction we are getting this equilibrium. The system creates some control action to maintain this equilibrium and no governor action is required for this. Each output frequency finds the information about its own area and the tie line power deviation finds the information about the other areas. Thus the load frequency control of a multi area power system generally incorporates proper control system, by which the area frequencies could brought back to its predefined value or very nearer to its predefined value so as the tie line power, when the is sudden change in load occurs.

Large scale power systems were normally composed of control areas or regions representing coherent groups of generators. An interconnected power system is basically a large power system consisting of a number of power systems. These power systems or areas were connected by tie lines[1]. The objectives of a control strategy is to generate and deliver power to an interconnected power system as economically and reliably as possible, while maintaining the voltage and frequency within permissible limit. The Load Frequency Control (LFC) loop controls the real power and frequency, while the Automatic Voltage regulator (AVR) loop controls the reactive power and voltage. With the growth of interconnected power system, LFC has gained more importance. It should be noted that in this linearized model of the AGC, hence is based on an assumption that the frequency and tie line power deviations are small as referred in [2].