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Tap chi Khoa hgc v^ C6ng ngh| 103 (2014) 007-011 Improving the Behaviors of Wind - Diesel Hybrid System in Smart Grid by Using Statcom Cai tien chat lugng dieu khien he Statcom cho he lai Diesel - Gio dirng luai dien thong minh Bui Dang Thanh Hanoi University of Science and Technology - No Dai Co Viet Str., Ha Noi, Viet Nam Received: April 15, 2014; accepted October 28, 2014 Abstract The paper presents studies of a wind-diesel hybrid system and the influence of mam factors on the quality of power in a smart grid A Statcom static compensation system is designed and simulated in Matlab in order to apply to the wind-diesel hybrid system The PI controllers are developed to compensate for the shortfall in power in the system A PSO (Particle Swarm Optimization) algorithm is used to optimize PI parameters The results obtained in tfie paper indicates the obvious effects of using Statcom in stabilizing the local smart grid In addition, the control quality of DC voltage on capacitor is improved by using the PSO method, compared with traditional methods Keywords: Statcom, PI controller, PSO, Wind- Diesel hybrid system, PWM Tom tat Bai bio trinh bay cac nghi§n cuv vi he lai Diesel-gid, inh hwang cua cic yeu to din chit lifong dien nang lu^i di$n thong mmh Mpt he bii ffnft Statcom dircfc thiit ki md phdng tr§n Matlab nhim ap dung cho h$ lai Diesel-gio Cac bd diiu khiin PI dwoc phit triin nhim bu lai cic thiiu hut cdng suit he thong Giai thu$t PSO duvyc ip dung de xac dmh b0 thdng so toi uv cho bd diiu khien PI Cic kit qui dat dum; bdi bio da chi hieu qua rd ret cua viec su" dung Statcom 6n dmh iwai di^n ci^c bg thong minh, ngoii chat luxpng diiu khiin cua dien ip DC tren ty ap dung phieang phip tdi uv PSO da dwqfc cii thien dang ki so sanh vai phuomg phap truyin thong TCF kh6a: Bii tTnh Statcom, digu khiln PI, giai thuSt PSO he lai Diesel-gio, dieu che dp rpng xung PWM Introduction c , j r n j ^ j cu J J Smart grid [ ] is deiined as a set ot hardware and sofhvare tools which are used to ttansmit power more efficiently, to reduce power in excess, and to manage information instantaneously according to the actual needs Smart grid reaches high efficiency in power monitoring, and it can ttansmit and collect data on the fransmission line According to [2], the smart grid uses the digital technology to optimize the use of energy, to match "green" and smart energy sources to customers through smart devices Nowadays, the wind energy is a natural energy source which has the largest reserve in the world The exploitation of this energy in the near future will certainly be stepped up basing on dominant advantages i-, f, J T of this renewable and green energy source In some , ,, • J ^.u J areas where there is no national grid, the wind power will be used with diesel generators, and grid ^ ,-, ^-ir u J ri i i.L- ' J J i stabilization will be done locally at this mdependent „., » - - LT^ f 11 I _ gnd Maintaining stability tor small-scale smart power systems using wind turbine is a technical challenge due • Corresponding Author: Tel: (+844) 3868 351t Email: thanh.buidang@hust.edu.vn to the instability of the source and the low inertia of generators in small power systems r J Statcom (Static Synchronous Compensator) is a solution which has high efficiency in order to enhance performance and stability of the independent system with the participation of wind power Basing on the rapid response ability of the Statcom, they allow to compensate qmckly for the temporary shortfall of reactive power as well as to improve performance and stability of wind power plants when there are problems The PSO algorithm is applied to determine the optimized parameters of PI confroUer in Statcom that we apply to the wind-diesel hybnd system — - , • ^ he paper includes sections After this _ j - ^ , , ,- , I , mtruduction, section presents the wmd-diesel hybnd ' ^ , , ^ ijuim system; section presents the synthesis of Statcom conttoller Simulation results are given and analyzed - ^„ ,, , , • auaLy£.cu in section 4, followed by the cone usion •' Tap chi Khoa hoc va Cong nghe 103 (2014) 007-011 Synthesis of Statcom controller Wind - Diesel hybrid system The wmd-diesel hybrid system is a system that combines w^nd tairbmes and diesel generators The wind-diesel hybrid system can be a new wmd-diesel electrical system or wmd turbines integrated with an available diesel electrical system contaming many generators to form a distnbution grid The purpose of using wind turbmes is to reduce the consumption of diesel fuel; therefore, we can enhance economic efficiency and envfronmental friendliness [3, 4] During the operation process, the vnnd turbine will suffer the impacts of environment such as temperature, humidity, changes m wind speed and these make the power generated unstable If the consumption loads ofthe power grid are asynchronous elecfrical machmes, when there are problems with the wmd source, these machines requires a large consumption of reactive power from the grid The lack of reactive power is the main cause of grid voltage fluctuation, reducing the power factor of the grid, affecting greatly the stability and quahty ofthe system Statcom is an effective solution to this problem When the Statcom is used to compensate for the reactive power in distribution system, it is called DStatcom (Distribution- Statcom) Fast response is one outstanding advantage ofthe D-Statcomin improving the dynamic responses ofthe system [5] 3.1 Wind-diesel hybrid model Model of Emergency Diesel Generator and Asynchronous Motor in SimPowerSystems in Matiab/ Simulink is used to simulate the wmd-diesel hybrid system in this research, which are described in Fig The electncal source in Fig.2 is 3-phase power sources of 25kV, lOOOMVA,, 3-Phase Fault and 3Phase Breaker blocks are used to simulate the moments when there are problems with the wind source and cutting the wind source having problems off the gnd; Wind source is modeled by an induction motor (asynchronous machine ASM 2250HP), supplying the grid via a 2.4 to 25kV fransformer The diesel generator is simulated by a synchronous generator SM 3125MVA using diesel engine integrating automatic speed and voltage confrollers The diesel engine model includes asynchronous motors, a speed confroUer and a load The engine will run at a speed that can be adjusted via the throttle signal The throttle signal conttols directly the output torque generated by the engine and conttols indirectly the speed at that the engine is running Simulation parameters for diesel models are selected according to [4] In our research, a D-Statcom is used to compensate for the reactive power and to adjust the gnd voltage in the wmd-diesel hybrid system in the case of 3-phase problems The simulation results show that the use of D-Statcom improve evidently the dynamic of the system In addition, the method of determining the parameters for Statcom confroUer also gives positive results Fig Wmd-diesel hybrid system Fig Wind-diesel hybnd model Tap chi Khoa hi?c va Cong nghe 103 (2014) 007-011 The muhi-variant conttol problem in the kinematic process of D-Statcom system is converted into die mvanant conttol problem, in this case they are two conttol loops VDC and |vl| In each confrol loop we use a cascade conttol with two sub-conttol loops: Adjusting the inner current and outer voltage When there are differences between the actual voltage amplitude |vl| and installed value |vl| *, PI2 conttoller generates the signal to set current iqs * to adjust the reactive power ofthe load The basic block diagram of a D-Statcom conttol system is described in Fig Fig Conttol two-loop structure of Statcom The 3-phase voltage signal Vabc, 3-phase current labc are put mto the voltage and cunent measuring system, they are calculated by abc-dq ttansformation (the synchronous reference signal sin(ojt) and cos((Dt) which is obtained from the phase locking loop PLL), the output of the measuring block is the signal with voltage amplitude Vmag and cunent components Id, Iq, the measured value Vdc is also put into the confrol system AC vohage regulator maintains AC voltage Vmag equal to the reference value Vac ref Fig Control diagram of Statcom 3.2 Designing D-STA TCOM The connection diagram of STATCOM with a typical disttibution grid shown in Fig 3: Where Vas, Vbs, Vcs are voltage levels generated by VSC, Ls characterizes the leakage inductance of coupling transformer; Rs characterizes the fransmission loss of VSC and couphng ttansformer; Re characterizes the switching loss of VSC and power loss on the capacitor; Vdc is the DC voltage across the capacitor, Rl and Ll are the local loads; Vai, Vbl, Vcl are voltage levels at the point of common coupling; and Van, Vbn, Ven, Rn, Ln are values characterizing the distribution grid Statcom is the phase angle conttoller of voltage and current, so in our designs, we need a converter to convert normal measured voltage and cunent signals to the signal components in the rotating synchronous reference system, where each cunent and voltage vector is characterized by the length (module) and the phase angle position, which are represented in an orthogonal coordinate system d-q The dynamic characteristics of D-Statcom is a multi-variant process with many input and output variables To simphfy the confrol process and to adjust easily parameters of conttollers, we build a doubleloop conttol strategy DC voltage regulator maintains the voltage across the capacitor equal to the reference value Vdc ref The iimer current conttoller contains two cunent conttollers in d axis and q axis The outputs of conttollers are Vd, Vq used to synthesize PWM voltage Cunent set point Iq ref is taken from AC voltage regulator Current set point Id is taken from DC voltage regulator The amplitude modulation index m and phase angle modulation (p calculated from the voltage component Vd, Vq is put into the PWM inverter to generate sine wave at the output For the dynamic process of D-Statcom which we are studying, the most important requirement of the confrol problem is to eliminate static errors in steady state For simplicity, the PI controller is used for cunent and voltage confrol loops [4, 5] 3.3 PSO algorithm PSO is proposed by Kennedy, Eberhart and Shi to optimize a problem by trying to improve a candidate solution with regard to a given measure of quality [6, 7] This algonthm was modeled on the foraging behavior of buds Initially, the birds fly in a random direction During operation, some individuals can fmd a food contamer Depending on the amount of food more or less those they can that send information to other individuals in the neighboring and spread Tap chi Khoa h^c va Cfing ngh$ 103 (2014) 007-011 throughout the population Based on this information, each individual will adjust flight direction and speed appropriate to look for where is the most foods PSO algorithm maintains a swarm of particles which is similar to a flock of bfrds, while each particle similar to an individual in the herd The particles move in the search space of many dimensions, in which the position of each particle is adjusted according to its own experience and that of all other particles, thereby find the best target value Setx,(t) is the position ofthe particle in the search space R„ at time I From a random position x,(0) in the search area, after each time step, the position of the particle is changed by adding to the current position a velocity vft): x,(l+!)=x,(l)+v,(l+l) (1) rMm-':.(t)] (2) where, w is the inertia weight; ci is an individual acceleration constant and ci is a global acceleration constant; ri, r2 are random values taking from an uniform distribution in the range (0, 1); yi(t) is an optimal individual position of the particle ;, ^'- •' is a global optimal position For minimizing the objective fiinction, PSO algorithm is earned out according to the steps shown in Fig 6, where Vdc is voltage on capacitor, V^^' is a set poir value 4.1 Simulation Results Simulation We assume that at / = 0.2s, wind have disturbance Until I = 0.3s, wind is left of grid 4.2 Model parameters The D-Statcom model is studied with a power ol ±3Mvar and it uses voltage PWM invertor from ports of IGBT DC voltage is applied to capacitor of I0000|iF The terminals of D-STATCOM arc connected parallel with grid by ttansformer, type 800/2400V A-Y Modulation frequency of PWM is 1.68kHz; Grid voltage: Vrms line-line = 2.4 kV; Source frequency; y^SOHz; F„ ™/=lp.u, Vdcrer2250y; F^ PI controllei parameters: KP - 0.55, i0=2500, Vdc PI conttoller parameters: Kj^ 0.001; K, = 0.15, Id, Iq PI conttoller Ki = 200 parameters: Kp = 0,8, Circuits are simulated m SIMULINK discretetime with sample time T, ^ 5ps 4.3 Simulation results By using the simulation parameters above, the results present in Fig In our study, PSO is applied to determine the PI parameter Z^[Kp K/\ following the objective fimction: /(z) = ;.''(c'-i'.c)'dt (3) nitialize a random position and velocity for particles Fig Description of disturbance in Wind-diesel system Evaluate a objective function for each p a r t i c l e / = ^ 2, , n^ If f(xj iff(yJ
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