A Technique for Enhancement of Power System Dynamic Stability

Transcription

1 International Journal of Engineering Science Invention arch. 3 A Technique for Enhancement of Power System Dynamic Stability Dr. Ramesh Kumar, ithilesh Das, R.K.andal 3, Ruchita 4 National Institute of Technology Patna, Associate Professor, Department of Electrical Engineering Ashok Rajpath, Patna-85, Bihar, India National Institute of Technology Patna, Department of Electrical Engineering Ashok Rajpath, Patna-85, Bihar, India 3 National Institute of Technology Patna, Associate Professor, Department of Electrical Engineering Ashok Rajpath, Patna-85, Bihar, India 4 B.Tech IVth year, Department of Electronics & Communication Engineering, Rajasthan Institute of Engineering & Technology Jaipur ABSTRACT:This paper presents a technique for power system dynamic stability enhancement. This technique consists of IPFC with Lead-Lag Controller. Low power frequency oscillation has been kept into mind for Power system dynamic stability prospect. SIB System and Phillip Heffron model of equivalent SIB System are being used for modelling and analysis purposes respectively.atlab Simulation provides the time domain analysis of the System. Keywords: IPFC, SIB, Lead-Lag Controller and Phillip Heffron odel I. INTRODUCTION Power system may be subjected to low frequency disturbances that might cause loss of synchronism and an eventual breakdown of entire system. The oscillations, which are typically in the frequency range of. to 3. Hz, mightbe excited by the disturbances in the system or in some cases, might evenbuild up spontaneously. These oscillations limit the power transmissioncapability of a network and sometimes, even cause a loss of synchronism and an eventual breakdown of the entire system. For this purpose, Power System Stabilizers (PSS) are used to generate supplementary control signals for the excitation system in order to damp these low frequency power systemoscillations. The use of power system stabilizers has become popular in the form of POD controller. By the virtue of advancement in technology, FACTScontroller replaces the Conventional Power System Stabilizer []. In this work, we deal with damping out the low power frequency oscillation. Small deviation (.p.u.) in the mechanical power (echanical Torque) has taken into consideration for the purpose of analysis. A model of Power System named as Phillip Heffron odel has been implemented for the time domain analysis. An Interline Power Flow Controller (IPFC) and Lead- Lag controller have been used as a FACTS controller and supplementary controller respectively. POWER SYSTE ODELLING Fig. shows a single machine infinite bus installed with Interline Power Flow Controller [3] which consists of two, three phase GTO based voltage source converters, each providing a series compensation for the two lines incorporated in the system. VSCs are connected to the transmission line through their series coupling transformers. Hence the configuration allows the control of real and reactive power flow of line. Here m & mare the amplitude modulation ratio and δ and δ are phase angle of the control signal of each VSCs respectively, which are the input control signals of IPFC.V s, V b, V pq, and V pq are the terminal voltage of generator, voltage of infinite bus, and voltage of VSCs respectively.

2 Fig.: Single achine Infinite Bus installed with IPFC Linearized model of SIB installed with IPFC [] can be represented as: δ = ω ω ω = P e D ω E q = E q + E fd T d E fd = E fd + K A V t () Where, P e = K δ + K E q + K pv V DC + K pm m +K pδ δ + K pm m + K pδ δ E q = K 4 δ + K 3 E q + K qv V DC + K qm m +K qδ δ + K qm m + K qδ δ V t = K 5 δ + K 6 E q + K vv V DC + K vm m +K vδ δ + K vm m + K vδ δ () (3) (4) V DC = K 7 δ + K 8 E q + K 9 V DC + K cm m +K cδ δ + K cm m + K cδ δ (5) By substituting (-5) with (), we can obtain the state variable equation of SIB Power system installed with IPFC: ω δ ω E q E fd VDC = (6) K K 4 T d K AK 5 K 7 D K K 3 T d K AK 6 K 8 T d K pv K qv T d K AK vv K 9 δ ω E q E fd V DC + K pm K qm T d K vm K cm K pδ K qδ T d K pm K qm T d K vδ K vm K cδ K cm K pδ K qδ T d K vδ K cδ The PH model of the corresponding linearized model is shown in fig.. In this fig, there are so many constants. These constants are functions of the system parameters and initial operating condition. The controlled vector u is defined as: u= m δ m δ T Where m, δ, m, δ represent the linearization of the input control signals of the IPFC. Under this work,only one input control signal is taken into consideration at a time for the analysis purpose, viz either we take U = m or U = δ, U = m or U = δ. And K p, K q, K v and K c are the row vectors defined as: K p = K pm K pδ K pm K pδ m δ m δ

3 K q = K qm K qδ K qm K qδ (7) K v = K vm K vδ K vm K vδ K c = K cm K cδ K cm K cδ A Technique for Enhancement of Power System Dynamic Stability K + + P _ s + D + + ω δ ω s Kp K K4 K5 Kpv K6 _ K E q + A T d s + K 3 + s K8 Kq Kvv Kv Kvv + Kc u + + K 9 + s V dc K7 Fig. : PH model of SIB system installed with IPFC DESIGN OF DAPING CONTROLLER Damping Controllers are designed to produce an electrical torque in phase with the speed deviation that damp out the power system oscillations. For using IPFC as damping controller, there is a requirement of supplementary damping controller. We have usedlead- Lagcontroller as supplementary controller. In this supplementary controller either ω or δ is taken as input. ω / δ u SUPPLEENTARY CONTROLLER Fig. 3: Block diagram of Supplementary controller Lead Lag Controller: To get fast response and good steady-state accuracy, a Lead-Lag controller is used. It also increases the low frequency gain and system bandwidth. In general, the phase lead portion of this compensator provides large bandwidth and hence has shorter rise time and settling time, while the phase lag portion provides the major damping of the system. In the lead-lag controller, phase lead and lag occur at different frequency regions. The phase lag occurs in a low frequency region, whereas phase lead occurs in a high frequency region. ω u K DC st w + st w + st + st Fig. 4: structure of lead-lag as supplementary controller Steps for calculating supplementary controller parameters:. Computation of natural frequency of oscillation ω n by using relation ω n = K ω K is the constant of model, computed for operating condition and system parameters. ω is frequency of operating condition (rad/sec) ω n is natural frequency of oscillation (rad/sec)

4 . Computation of GEPA (phase angle between u and P) at s=jω n 3. Design of Phase lead lag compensator: the phase lead/lag compensator is designed to provide the required degree of phase compensation. for % compensation, G c (jω n ) + GEPA (jω n ) = Assuming one lead-lag network at T = T, the transfer function becomes, G c s = +s T +st Where α = +sin γ sin γ T = ω n a 4. Computation of optimum gain K DC The value of gain setting to achieve the required amount, damping torque D IPFC can be provided by IPFC supplementary damping controller. The signal washout is the high pass filter that prevents steady changes in the speed from modifying the IPFC input parameter. The value of the washout time constant T w should be high enough to allow signals associated with oscillations in rotor speed to pass unchanged.tw is not yet critical, may range from s to s. II. SIULATION AND RESULT To analyse the performance of IPFC controller, simulation work is done for circuit given in fig.. All the simulation is done for a step change (i.e.. p.u.) in mechanical power. All the constant values are mentioned in the Appendices. Simulation work is divided in two parts:-. Without any supplementary controller. With Lead-Lag controller 3 x Fig. 5: Response of speed deviation ( ω) without any supplementary controller.5. deviation in rotor angle (p.u) Fig. 6: Response of Rotor angle deviation ( δ) without any supplementarycontroller

5 4 x Fig. 7: Response of speed deviation ( ω) for m of IPFC controller with Lead-Lag controller..9.8 deviation in rotor angle (p.u) Fig. 8: Response of Rotor angle deviation ( δ) for m of IPFC controller with Lead-Lag controller x Fig. 9: Response of speed deviation ( ω) for δ of IPFC controller with Lead-Lag controller

6 .4. deviation in rotor angle(p.u) Fig. : Response of Rotor angle deviation ( δ) for δ of IPFC controller with Lead-Lag controller 3.5 x Fig. : Response of speed deviation ( ω) for m of IPFC controller with Lead-Lag controller 9 x deviation in rotor angle (p.u) Fig. : Response of Rotor angle deviation ( δ) for m of IPFC controller with Lead-Lag controller

7 .5 x Fig. 3: Response of speed deviation ( ω) forδ of IPFC controller with Lead-Lag controller.6.4 deviation in rotor angle (p.u) Fig. 4: Response of rotor angle deviation ( δ) for δ of IPFC controller with Lead-Lag controller.5 x -4 del Controller del Controller m Controller m Controller Rotor speed deviation(p.u) Fig. 5: Response of speed deviation ( ω)

8 .6.4. del Controller del Controller m Controller m Controller Rotor angle deviation(p.u) Fig. 6: Response of rotor angle deviation ( δ) III. CONCLUSION Responses shown in fig.5,6 are of IPFC withoutusing supplementary controller. Responses shown in fig. 7-4 areobtained using Lead-Lag controller for all the four input (m, m, δ and δ ) of IPFC controller respectively. From the response of fig 5 and 6, we observe that m input parameter of IPFC controller gives best among all. Hence, it can be concluded that using Lead-Lag as supplementary controller, IPFC controller gives better damping capability thanipfc controller only. IV. APPENDICES A: Parameters of SIB System with IPFC =8. T do =5.44s X d =. pu Generator J/VA X q =.6pu X d =.3pu D= Reactances X s =.5pu X t =.pu X t =.pu X t =.pu X L =.5pu X L =.5pu X L =.5pu IPFC parameters m =.5 m =. δ =8. δ =-. Excitation K A =5 =.5s System DC link V DC =.pu C DC =.pu IPFC Controller Input B: Constant for Lead- Lag Controller Lead-lag controller Parameters K DC T w (s) T (s) T (s) m m δ δ

9 C: Constant value of PH odel installed with IPFC Constant Value Constant Value K.586 K vm.44 K.793 K cm.37 K K pδ.43 K K qδ.53 K 5 -. K vδ -.88 K 6.55 K cδ.88 K K pm.57 K K qm.4 K K vm -.96 K pv K cm -.75 K qv -.6 K pδ. K vv -.3 K qδ.46 K pm.5344 K vδ -.7 K qm K cδ -.63 REFERENCES []. Narain G. Hingorani, Laszlo Gyugyi, Understanding FACTS : concept and technology of flexible AC transmission system, John Wiley & Sons, INC., Publication, 999. []. Wang, H. F, Phillips heffron model of power system installed with STATCO and applications, IEEE Proc. Generation Transmission Distribution, 999, 45 ( ), pp [3]. Jitendra Veeramalla and Sreerama Kumar, Application of Interline Power Flow Controller for Damping Low Frequency Oscillation in Power System, EPS, Wroclaw, Poland.