Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Daming of local and inter-area oscillation for multi machine power system with considered renewable energy Homayon Ebrahimian1, Alireza Noruzi2, Mehdi Mirzaey1, Tohid Banki2 1- Department of Electrical Engineering, Ardabil Branch, Islamic Azad university, Ardabil, Iran 2- Department of Electrical Engineering, Bilesuvar Moghan Branch, Islamic Azad university, Bilesuvar Moghan, Iran Abstract In this paper a robust Power System Stabilizer (PSS) is proposed based on inverse additive perturbation in a power system with wind farms. The proposed controller designed by new modified Honey Bee Mating optimization namely Honey Bee Mating Optimization (IHBMO) to achieve robustness of this strategy where the optimization process is formulated based on an enhancement of system robust stability margin. The designed optimal PSS is based on Fuzzy Logic Controller (FLC). The effectiveness of the proposed technique is tested over ten macine 39 buses New England power system. Obtained results demonstrate the superiority of proposed technique over conventional PSS. Keywords: IHBMO, Fuzzy controller, PSS, Multi-machine. NUMENCLUTURE δ ω Pm Pe E'q Efd Te T'do KA TA vref v Rotor angle Rotor speed Mechanical input power Electrical output power Internal voltage behind x'd Equivalent excitation voltage Electic torque Time constant of excitation circuit Regulator gain Regulator time constant Reference voltage Terminal voltage I. INTRODUCTION Some of the earliest power system stability problems included spontaneous power system oscillations at low frequencies. These Low Frequency Oscillations (LFOs) are related to the small signal stability of a power system and are detrimental to the goals of maximum power transfer and power system security. Once the adjustment of using damper windings on the generator rotors and turbines to control these oscillations was found to be satisfactory, the stability problem was thereby disregarded for some time [1]. But, as power systems began to be operated closer to their consistency limits, the weakness of a synchronizing torque among the generators was distinguished as a major cause of system instability [2]. Automatic Voltage Regulators (AVRs) helped to improve the steady-state stability of the power systems, but transient stability started a concern for the power system operators. With the development of large, interconnected power systems, another concern was the transfer of large amounts of power across extremely long transmission lines. The addition of a supplementary controller into the control loop, such as the introduction of Power System Stabilizers (PSSs) to the AVRs on the generators, supplies the means to reduce the inhibiting effects of low frequency oscillations [3]. Most of the time the PSSs and AVRs are locally controlled; which means that, the controller is designed to act on measurements such as bus voltage, generator shaft speed, or rotor angle of the associated machine’s controls as 293 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com presented in Fig. 1. Figure 1. Local Feedback Controller In the recent years, renewable electrical energy such as wind power generations, have achieved a significant level of penetration in the power systems due to infinite availability and low impact to environment. However, wind power generation is staggering in nature. Matching the supply and the demand is often a problem. The power output fluctuations from wind power generations cause a problem of low frequency oscillation, deteriorate the system stability and make the power system operation more difficult. The power frequency and the tie-line power deviations persist for a long term. In this status, the governor system may no longer be capable to absorb the frequency fluctuations due to its slow response [4]. Actually, several plants prefer to employ conventional lead-lag structure PSSs, due to the ease of online tuning and reliability [5]. However, the revenue of these controllers doesn’t have good behavior in different load conditions. For this reason, a lot of intelligent algorithms have been introduced to optimal tuning of the PSSs parameters such as Ant Colony (AC) [6], Genetic Algorithm (GA) [7], Particle Swarm Optimization [8], Artificial Bee Colony [9] and etc. The proposed algorithms are strong in optimization procedure but, they have some advantages and disadvantages. For instance, GA is a powerful optimization technique, independent on the complexity of problems where no prior knowledge is available. Also GA is very sufficient in finding global or near global optimal solution of the problem, it requires a very long run time that may be several minutes or even several hours depending on the size of the system under study [10-11]. The HBMO is a relatively new technique that has been empirically shown to perform well on many of these optimization problems [5]-[7]. This optimization method has been widely applied to solve different problems especially the locating problems in power system. Unfortunately, the standard HBMO algorithm often converges to local optima, especially while handling problems with more local optima and heavier constraints. This work presents the interactive strategy by considering the universal gravitation between queen and drone bees for the standard HBMO algorithm to retrieve the disadvantages, which is called the IHBMO. In the other word, the IHBMO introduces the concept of universal gravitation into the consideration of the affection between drone bees and the queen bee within a honey bee colony. By assigning different values of the control parameter, the universal gravitation should be involved for the IHBMO when there are various quantities of drone bees and the single queen bee. The inverse additive perturbation is applied to represent unstructured system uncertainties. For tuning the optimal rule base of fuzzy controller, the concept of enhancement of system robust stability margin is formulated as the optimization problem. Also, the proposed IHBMO is considered as a solution technique to problem. The obtained simulation results over ten machine-39 bus New England power system demonstrate the robustness of the proposed strategy. The remaining parts of the paper are organized as follows. In the second section, the formulation of power system modeling is presented. The proposed controller structure is introduced in section three. The proposed IHBMO and its application for the solution of the low oscillation problem with wind are presented in section four. Obtained numerical results from New England power system are presented in section five and compared with the other recently published methods. Section six concludes the paper. II. PROBLEM STATEMENT In this paper a multi-machine power system is considered as a test case where the third order model is presented in [12]. Actually, the proposed power system consists of ten generators and the electrical and mechanical part of ith generator is modeled as follow: 294 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com . i (t ) w i (t ) w0 w0 D ( Pmi Pei (t )) i ( w i (t ) w0 ) Mi Mi . 1 E qi (t ) ' ( E fi (t ) Eqi (t )) Tdoi . wi (t ) Eqi (t ) E 'qi (t ) ( xdi xdi' ).I di (t ) Vti (t ) 1 2 2 [ xsi Eqi Vsi2 xqi2 2 xsi xdi xdsi Pei cot i ]1/2 xdsi n Pei (t ) Eqi' (t ) Eqj' (t )( B ij sin( ij (t )) Gij cos( ij (t ))) j 1 n Qei (t ) Eqi' (t ) Eqj' (t )(G ij sin( ij (t )) Bij cos( ij (t ))) j 1 n I di (t ) Eqj' (t )(G ij sin( ij (t )) Bij cos( ij (t ))) j 1 n I qi (t ) Eqj' (t )( B ij sin( ij (t )) Gij cos( ij (t ))) j 1 Qei (t ) Eqi' (t ) Pei (t ) Eqi' (t ) Eqi (t ) xadi I fi (t ) Also, it can be presented after mathematical transformers where, ΔPe, Δw and ΔVt are quantities; S Ei SVi . T' S Pei di Vi . w0i wi Hi . Vti S S Vi Ei' Tdi RVi SVi RVi S Ei REi' Tdi' SVi Pei Td 0i E fdi Where, 0 wi 0 R' Ei S Vti Td 0i RVi ' Ei Tdi SVi S Ei' Di Hi S Ei' SVi RVi ΔPei is the state deviation in generator electromagnetic power for the ith subsystem Δωi is the state deviation in rotor angular velocity for the ith subsystem, ΔVti is the state deviation in the terminal voltage of the generator for the ith subsystem S Ei S ' Ei EqiU si X d i cos i U si2 E 'qiU si X 'd i X d i X q i cos i U si2 REi U si sin i X d i REi' U si sin i X 'd i SVi S Ei RVi X d i X q i cos 2 i X 'd i X q i X 'd i X q i cos 2 i U ti V , RVi S Ei / ti i Eqi A. Mechanical Oscillation Frequency The linearized rotor motion equation for synchronous generator can be described as: TJ d w Tm Te TD dt Where, ΔTm is the mechanical input torque ΔTe is the electromagnetic torque and ΔTe =K1Δδ+ K2Δδ, By neglecting the K2ΔE’q the formulation can be described as; ΔTe =K1Δδ+ ΔTD 295 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com D is the natural damping constant Accordingly the above equation after Laplace transformer and Δw=sΔδ/w0 can be described as; TJ s 2 s K1 D w0 w0 Which can be described as; TJ s 2 Ds w0 K1 0 OR s 2 2 n wn s wn2 0 Accordingly, we can achieve the following equation from above equations; n D / 2 w0TJ K1 wn w0 K1 / TJ Where, ξn is the damping factor wn is the undamped mechanical oscillation frequency Usually the value of D is small, so the system damping is low. In order to enhance the system damping for suppressing the low frequency oscillation, the positive damping term is added by PSS. B. Power System Model A 10-machine 39-bus power system with wind farms is considered as a test case for this paper which is presented in Fig. 2. To assess the effectiveness and robustness of the proposed method over a wide range of loading conditions, different operation conditions are considered. Details of the system data and operating condition are given in Ref. [13]. The proposed power system is divided to four area with connected wind farm as shown in Fig. 2. Zone 1 Zone 3 G8 G10 28 8 29 10 PW3 26 25 9 31 G9 27 39 18 24 32 16 17 G6 G1 15 33 21 12 34 1 6 14 35 22 23 36 11 2 37 13 19 20 30 G2 7 38 3 PW1 4 5 G7 G4 G3 G5 Zone 2 PW2 PW4 Zone 4 Figure 2. Structure of power system with wind farms C. Wind power model It is clear that the output power of wind generator depends on wind velocity. The wind speed model chosen in this study consists of four-component model [14], that is defined as; VW VWB VWG VWR VWN 296 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Where WB V = Base wind velocity WG V = Gust wind component WR V = Ramp wind component WN V = Noise wind component The base wind velocity component is represented in literature as: VWB K B Where KB is a constant and assumed to presenting the wind power. The gust wind velocity can be defined as; VWG 0 t T1G Vcos T1G t T1G TG t T1G TG 0 Where, Vcos (MAXG / 2) 1 cos 2 (t / TG ) (T1G / TG ) MAXG is the gust peak TG is the gust period T1G is the gust starting time (1-cosine) gust is an essential component of wind velocity for dynamic studies The ramp wind velocity component is described as: VWG 0 t T1R Vramp T1R t T2 R t T2 R 0 Where, Vramp MAXR[1 (t T2G ) / (T1R T2 R )] MAXR is the ramp peak T1R is the ramp start time T2R is the ramp maximum time This component may be used to approximate a step change with T2R >T1R. Also, the random noise component can be described as: N VWN 2[ SV (i ) ]1/2 cos(i t i )t 0 i 1 Where, i (i 1/ 2) i is a random variable with uniform probability density on the interval 0 to 2π and the spectral density function can be defined as: 2 K N F 2 [i ] SV (i ) 2 [1 ( Fi / )2 ]4/3 Where KN is the surface drag coefficient which is considered 0.004 and F is turbulence scale which is considered 2000, and μ is the mean speed of wind at reference height. Various study have shown that values of N=50, and Δω = 0.5-2.0 rad/s provide results of excellent accuracy. D. Characteristic of wind generator output power The output power of studied wind generator is expressed by a nonlinear function of the power coefficient Cp as function of blade pitch angle, β, and tip speed ratio, γ. The tip speed ratio is presented as follow: R blade Blade VW The power coefficient can be presented as: 297 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com ( 3) CP (0.44 0.0167 )sin 0.0184( 3) 15 0.3 At the end, the output of mechanical power for wind generator is: PW 1 Ar CPVW3 2 Where, ρ (=1.25 kg/m3) is the air density and Ar (=1735 m2) is the swept area of blade. III. FUZZY LOGIC CONTROLLER In classical control, the value of control is determined in relation to a number of data inputs using a set of equations to express the entire control process. Expressing human experience in the form of a mathematical formula is a very difficult task, if not an impossible one. Accordingly, Fuzzy Logic Controller (FLC) provides a simple tool to interpret this experience into reality [15]. FLCs are rule-based controllers with resembles structure with a knowledge based controller except that the FLC utilizes the principles of the fuzzy set theory in its data representation and its logic. The classic structure of FLC can be simply presented in Fig. 3. Knowledge Base Decision Making Logic Slip Figure 3. Defuzzificatio n Interference Actual Control Non Fuzzy Process Output and State Fuzzification Interference Multi-machine Power System Model The conventional fuzzy controller structure A set of fuzzy rules represents the FLC mechanism for adjusting the effect of certain system stimuli. Thus, the aim of fuzzy control systems is to replace a skilled human operator with a fuzzy rules-based system. The FLC also provides an algorithm which can convert the linguistic control strategy, based on expert knowledge, to automatic control strategies. Thus, to reduce fuzzy system effort cost, in this paper proposed an intelligent technique for optimal tuning of fuzzy controller. Fig. 4, shows the structure of the proposed IHBMO-FPSS to improve power system stability. IV. THE IHBMO TECHNIQUE This section the standard HBMO briefly reviewed. For better illustration see ref [16]. At the start of the flight, the queen is initialized with some energy content and returns to her nest when her energy is within some threshold from zero or when her spermatheca is full. In developing the algorithm, the functionality of workers is restricted to brood care, and therefore, each worker may be represented as a heuristic which acts to improve and/or take care of a set of broods. A drone mates with a queen probabilistically using an annealing function as: prob (Q , D ) e ( f ) S (t ) (7) Where Prob (Q, D) is the probability of adding the sperm of drone D to the spermatheca of queen Q (that is, the probability of a successful mating); ∆( f ) is the absolute difference between the fitness of D (i.e., f (D)) and the fitness of Q (i.e., f (Q)); and S(t) is the speed of the queen at time t. It is apparent that this function acts as an annealing function, where the probability of mating is high when both the queen is still in the start of her mating–flight and therefore her speed is high, or when the fitness of the drone is as good as the queen’s [17]. After each transition in space, the queen’s speed, S(t), and energy, E(t), decay using the following equations: S t 1 HBMO S t (8) E t 1 E t γHBMO (9) 298 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Where αHBMO(t) is speed reduction factor and γHBMO is the amount of energy reduction after each transition (α, γ ϵ [0,1]). Thus, HBMO algorithm may be constructed with the following five main stages: Step 1: The algorithm starts with the mating flight, where a queen (best solution) selects drones probabilistically to form the spermatheca (list of drones). A drone is then selected from the list at random for the creation of broods. Step 2: Creation of new broods by crossoverring the drones’ genotypes with the queen’s (Breeding process). The breeding process can transfer the genes of drones and the queen to the jth individual based on the Equation (10). child parent i HBMO ( parent k parent i ) (10) Where βHBMO is the decreasing factor (βHBMO ~U (0, 1)). Step 3: Use of workers (heuristics) to conduct local search on broods (trial solutions). Step 4: Adaptation of workers’ fitness based on the amount of improvement achieved on broods as follows: Brood ik Brood ik ( HBMO HBMO )Brood ik HBMO [0,1],0 HBMO 1 (11) Step 5: Replacement of weaker queens by fitter broods. The standard HBMO technique has a flexible and well-balanced mechanism to enhance the global and local exploration abilities. The main disadvantage of the HBMO algorithm is the fact that it may miss the optimum, not strong enough to maximize the exploitation capacity and provide a near optimum solution in a limited runtime period. Nonetheless, the standard HBMO method is prosperous for finding best answer in optimization problem. However, the algorithm makes use of an independent random, βHBMO ~U (0, 1). This factor used to affect the stochastic nature of the standard HBMO algorithm, as shown in equation (14). In the other word, the original Breeding process design of the drone bee’s movement only considers the relation between the queen bee, which is selected by the mating wheel selection, and the one selected randomly. Hence, it is not strong enough to maximize the exploitation capacity. In order to overcome this drawback, the Interactive Honey Bee Mating Optimization (IHBMO) algorithm is proposed based on the structure of original HBMO algorithm. In the other word, by employing the Newtonian law of universal gravitation described in the equation (12), the universal gravitations between the queen bee and the selected drone bees are exploited. The gravitational force between two particles (F12) with the mass of the first and second particles (m1 and m2), and the distance between them (r12) can be expressed as: F12 G m1 m 2 ^ r21 r212 (12) Where, G is gravitational constant. ˆr21 denotes the unit vector in the equation (13): ^ r21 r2 r1 | r2 r1 | (13) In the optimization procedure with IHBMO algorithm, the mass 𝑚1 is replaced by the symbol, F(parenti), which is the fitness value of the queen bee that picked by applying the mating wheel selection. The mass, 𝑚2, is replaced by the fitness value of the randomly selected drone bee and is denoted by the parameter, F(parentk). The universal gravitation in the equation (12) is formed in the vector format. Therefore, the quantities of it on different dimensions can be considered separately. Hence, 𝑟21 is calculated by taking the difference between the objects only on the concerned dimension currently and the universal gravitation on each dimension is calculated separately. In other words, the intensity of the gravitation on different dimensions is calculated one by one. Therefore, the gravitation on the jth dimensions between parenti and parentk can be expressed in the equation (14). Finally, the equation (14) can be modified in iteration interval t with the equation (15): Fik j G F ( parent i ) F ( parent k ) parent kj parent ij . ( parent kj parent ij )2 | parent kj parent ij | (14) child ij (t 1) parent ij (t ) Fik j .[ parent ij (t ) parent kj (t )] (15) Extending the consideration of the universal gravitation between the drone bees, which is picked by the queen bee, and more than one drone bees is achievable by adding different Fik.[ parentk – parenti] into the equation (15). Thus, the gravitation Fik plays the role of a weight factor controlling the specific weight of [parentk – parenti]. The normalization process is taken in order to ensure that Fik ~U (0, 1). Through the normalization of 299 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Fik the gravitational constant (G) can be deleted. In general, the whole process of IHBMO algorithm can be summarized at the five main steps as follows: 1. Generate an initial population: In this step, an initial population based on state variable is generated, randomly. That is formulated as: D [D1 , D 2 , D3 ,..., D n ] Di (d i1 , d i2 ,..., d im ) (16) Where, dij is the jth state variable value of ith drone bee. For each individual (Di) the objective function values are evaluated. The queen was chosen according to the best solution (minimum objective function value). The other solutions which were generated during this phase became the drones to be used during the mating flight (trial solutions). The speed of queen at the start and the end of a mating flight is generated in this step. 2. Flight matting: At the start of the flight mating, the queen flies with her maximum speed and energy. A drone is selected from the population of drones with the largest prob(Q, D). The mating probability is calculated based on the objective function values of the queen and the selected drone. If the mating is successful (i.e., the drone passes the probabilistic decision rule), the drone's sperm is stored in the queen's spermatheca and the queen’s speed and energy decay is reduced by Eqs. (12)-(13). Otherwise, the flight matting is continues until the speed S(t) is less than a threshold d or the queen's spermatheca gets full. 3. Breeding process: In this step, a population of broods is generated based on mating between the queen bee and the drone bees stored in the queen's spermatheca. The generation of new broods is occurred by crossoverring the drones’ genotypes with the queen’s. The jth brood is generated by using the equation (15). 4. Adaptation of worker‘s fitness: In this step, after new broods are generated, an attempt is made to improve both the new solutions and the best solution by using of a mutation procedure as equation (10): 5. Replacement of weaker queens by fitter broods and Check the termination criteria: If the new brood is better than the current queen, it takes the place of the queen. If the brood fails to replace the queen, then this brood will be one of the drones in the next flight mating of the queen. Meanwhile, if the termination criterion is satisfied then finish the algorithm. Otherwise, it discards all of the previous trial solutions (brood set) then the generation of new drones is set and goes to stage 2. FIX FIX Rule base Slipi Membership functions + yrefi d/dt KI Membership functions Inference engine Membership functions 1/S Defuzzier _ Fuzzification Rule base Membership functions d/dt Membership functions S Defuzzier Rule base Fuzzification Membership functions KD Membership functions Inference engine Inference engine Fuzzification Membership functions IHBMO KP Defuzzier Fuzzy PID Controller Figure 4. Proposed Fuzzy Controller Structure 300 Efd PSS Excitation ∆ Generator i Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com V. SIMULATION RESULTS In this paper, an IHBMO-FPSS is proposed, which combines the advantage of the IHBMO and fuzzy control techniques to achieve good robust performance. It should be mentioned that obtaining the optimal decisionmaking logic for the proposed IHBMO fuzzy control strategy is very important to achieve the desired level of robust performance [9], because it is a computationally expensive combinatorial optimization problem. Usually, the rule-base sets are determined by experience and control knowledge of a human expert. However, experts may not always be available and even when available it is a trial-and-error process that takes much time and cost [9]. The results of the fuzzy rule-base sets are listed in Tables 1-3. In the proposed rule-base optimization problem, the membership function sets for the KPi, KIi and Kdi are defined as triangular partitions with five segments from 0 to 1 [18]. In this study the controllers are connected to G2 – G10 in the test system. Evaluation of the Integral of the Time multiplied Absolute value of the Error (ITAE) and Figure of Demerit (FD) based on the system performance characteristics are defined as [19]: FD (500 OS )2 (8000 US )2 0.01T s2 ITAE 100 t sim t (| |).dt 0 Where, Overshoot (OS), Undershoot (US) and settling time of the rotor angle deviation of the machine is considered for evaluation of the FD. “Fig. 5”, shows the plot of obtained fitness function value. OPTIMAL RULE-BASE FOR KII NB NS PS PB NB NM PB ZO PB NS NM NB ZO ZO Z PM NM PM PM PS NS PM NS NM PB PM NB NS NS TABLE II. OPTIMAL RULE-BASE FOR KDI NB NS PS PB NB NS NS PB NM NS PM ZO NB ZO Z NM NB ZO ZO PS NS PM PM NB PB NM NB PM NS TABLE III. OPTIMAL RULE-BASE FOR KPI NB NS PS PB NB NS NS PB NM NS PM ZO NB ZO Z NM NB ZO ZO PS NS PM PM NB PB NM NB PM NS TABLE I. Fitness 0.7 0 Iteration Figure 5. 100 Variations of the fitness functions 301 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com The wind velocity in four area is presented in Fig. 6. Also, wind power generations are presented in Fig. 7, and Fig. 8-10 shows tie-line power deviation in nominal load condition. 7.2 PW1 PW2 PW3 PW4 7 PW1 Wind Velocity (m/s) 6.7 6.3 6 5.7 5.5 5.2 5 50 100 200 Figure 6. 300 400 Time (sec) 500 600 700 Wind velocity 5.2 PW1 PW2 PW3 PW4 Wind power generation (pu) 4.6 PW1 4 3.2 2.6 2 1.4 0.8 0.2 50 100 Figure 7. 200 300 400 Time (sec) 500 600 700 Wind power generations Scenario 1 In this paper two scenarios are presented to test the proposed control strategy in New England power system. For the first scenario, it is very important that, the performance of the proposed controller is tested under transient conditions by applying a 6-cycle three-phase fault or increasing the mechanical torque. So, in this scenario a 6-cycle three-phase fault is applied in line 26-29 and bus 29. The responses of generators 1, 3, 7 and 9 are presented in Fig. 11. Also the numerical results of FD and ITAE are presented in Table 4. Tie-line power deviation (pu) 1-2 0.07 0 -0.06 Figure 8. 50 100 200 400 300 Time (sec) 500 600 700 System response in first scenario under nominal load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) 302 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Tie-line power deviation (pu) 1-3 0.07 0 -0.06 Figure 9. 50 100 200 400 300 Time (sec) 500 600 700 System response in first scenario under heavy load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) Tie-line power deviation (pu) 1-4 0.07 0 -0.06 Figure 10. 50 100 200 400 300 Time (sec) 500 600 700 System response in first scenario under light load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) 303 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com -3 x 10 1 Speed Division G1 0 -2 0 2 4 6 8 10 6 8 10 Time (sec) -3 x 10 Speed Division G3 2 0 -2 0 2 x 10 2 Speed Division G7 4 Time (sec) -3 0 -2 0 2 4 Time (sec) 6 8 10 2 4 Time (sec) 6 8 10 -3 x 10 Speed Division G9 1 0 -1 0 Figure 11. Generators response at first scenario under nominal load condition (Solid: Proposed, Dashed: CPSS) Scenario 2 In the second scenario a 0.1 step is applied over the torque of generators. The tie-line response of power system is presented in Fig. 13-15. Also, the responses of 1, 3, 7 and 9 generators are presented in Fig. 12-15. The numerical results of FD and ITAE are presented in Table 5. 304 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com Tie-line power deviation (pu) 1-2 0.07 0 -0.06 Figure 12. 50 100 200 400 300 Time (sec) 500 600 700 System response in second scenario under nominal load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) Tie-line power deviation (pu) 1-3 0.07 0 -0.06 Figure 13. 50 100 200 400 300 Time (sec) 500 600 700 System response in second scenario under heavy load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) Tie-line power deviation (pu) 1-4 0.07 0 -0.06 Figure 14. 50 100 200 400 300 Time (sec) 500 600 700 System response in second scenario under light load condition (Solid: Proposed, Dashed: CPSS, Doted: No-PSS) 305 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com x 10 -4 Speed Division G1 2 0 - 0 2 x 10 4 6 8 10 6 8 10 6 8 10 6 8 10 Time (sec) -4 Speed Division G3 5 0 - 0 2 4 Time (sec) x 10 -4 Speed Division G7 5 0 -5 0 x 10 2 4 2 4 -3 Time (sec) Speed Division G9 1 0 -1 0 Time (sec) Figure 15. Generators response at first scenario under nominal load condition (Solid: Proposed, Dashed: CPSS) TABLE. 4. CALCULATE OF FD AND ITAE FOR DIFFERENT LOAD CHANGES. IHBMO CPSS Change load ITAE FD ITAE FD 25% 2.8293 1.6251 9.656 8.455 20% 1.1093 1.2543 8. 856 8.490 15% 1.1110 1.0137 8.890 8.466 10% 1.0123 1.0225 8.265 8.349 5% 1.0313 1.0129 8.853 8.763 Nominal 1.0113 1.2421 8.876 8.223 -5% 1.2413 1.2663 8.243 8.324 -10% 1.1542 1.2514 8.866 8.365 -15% 1.1652 1.2665 8.234 8.387 -20% 1.1334 1.1322 8.734 8.376 306 Applied mathematics in Engineering, Management and Technology 3(3) 2015:293-308 www.amiemt-journal.com -25% 2.1542 1.1652 9.029 8.376 TABLE. 5. CALCULATE OF FD AND ITAE FOR DIFFERENT LOAD CHANGES. IHBMO CPSS Change load ITAE FD ITAE FD 25% 2.3411 1.0321 9.6947 8.3109 20% 1.0193 1.0302 8. 4771 8.0382 15% 1.0232 1.0203 8.4571 8. 6898 10% 1.0133 1.0243 8.4539 8.0117 5% 1.0322 1.0421 8. 5404 8.0446 Nominal 1.0244 1.0321 8.5069 8.0488 -5% 1.1093 1.0445 8.5294 8.0551 -10% 1.1034 1.0421 8.4432 8.0621 -15% 1.1033 1.1342 8.5570 8.0726 -20% 1.1045 1.1034 8.7436 8.1157 -25% 1.1135 1.1211 12.6553 8. 0117 IV. CONCLUSION In this paper, a design scheme of robust PSS ten-machine New England power system using by considering inverse additive perturbation in a power system with wind farms is presented through hybrid technique of fuzzy controller and improved HBMO. By proposed IHBMO, the rule based of fuzzy controller is optimized to damp power system oscillation where. The proposed technique is tested in various load condition for the solution of the low frequency oscillation problem in power system. 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