2014 INTERNATIONAL CONFERENCE ON COMPUTATION OF POWER, ENERGY, INFORMATION AND COMMUNICATION (ICCPEIC)
Nonlinear DSTATCOM Controller using Passivity- Based Sliding Mode Control Pooja Lal1 , S. Krishna Kumar2 1
2
M.E, Department of EEE, Assistant Professor, Department of EEE Prathyusha Institute of Technology and Management, Thiruvallur-602 025, Chennai,Tamil Nadu, India 1
2
Email id:
[email protected],
[email protected]
Abstract-This paper presents a non-linear DSTATCOM Controller designed by using a passivitybased sliding mode control. The designed controller aims at achieving the compensation of reactive power and voltage regulation to provide an improved power factor and stable voltage during linear and non-linear load conditions. The passivity-based sliding mode controller is separated into inner and outer loop control. It employs the passivity-based control in the inner loop to achieve regulation of voltage and current. The outer loop employs the sliding mode control in order to improve the dynamic response and to eliminate the steady state errors. Keywords:Distributive Static Synchronous Compensator (DSTATCOM), Passivity-based Control, Sliding Mode Control
I. INTRODUCTION In distribution system, a major portion of power is consumed by reactive loads. Since these loads draw a low power factor, it therefore generates the reactive power burden for the distribution system. The DSTATCOM controller aims to compensate the reactive power, to achieve a good power factor and to eliminate the current harmonics. Distribution STATCOM (DSTATCOM) exhibits faster control of reactive power to provide dynamic voltage control, transient stability, voltage flicker control, and other types of system control.Among all the Flexible AC Transmission Systems(FACTS), Distribution STATCOM (DSTATCOM) shows an important role in achieving the reactive power compensation and voltage regulation because of its operating characteristics and steady state performance. The power flow in a power system must be controlled carefully within acceptable voltage limits. The reactive power flow in the system can give rise to voltage changes across the system, and therefore it is necessary to maintain the reactive power balances between the sources of generation and demanding points.The most widely used conventional control scheme with DSTATCOM is PI controllers. But as the DSTATCOM model is a complete non linear system, a linear approach does not lead to the better dynamic decoupling. In order to overcome this limitation Passivity- Based non-linear Sliding Mode Control (PBSM) scheme is presented in this paper to achieve the
reactive power compensation and voltage regulation for the system. The Sliding Mode Controller (SMC) is a nonlinear control method that can be used for a non linear system to alter its dynamics by the application of a discontinuous control signal. The sliding mode controller is used to improve the overall dynamic response of the system and to eliminate the steady state errors. This nonlinear controller model considers the operation under a changeable load condition. The controller design is given as inner and outer loop control.
II. PRINCIPLE OF DSTATCOM The voltage regulation and the power quality in the distribution feeder is improved by installing a shunt compensator. The STATCOM is a shunt connected device used for reactive power compensation. When the STATCOM is applied in distribution system it is called DSTATCOM (Distribution-STACOM). It exhibits faster control of reactive power to provide dynamic voltage control, flicker control, and other types of system control. The DSTATCOM is modeled to achieve the correction of power factor and for voltage regulation along with current compensation, elimination of harmonics and load balancing with linear loads and non-linear loads. A coupling transformer can be used between the distribution system and the DSTATCOM for isolation. In addition, the device needs to be installed as close to the sensitive load as possible to maximize the compensating capability. Being a shunt connected device, the DSTATCOM mainly injects reactive power to the system. The structure of DSTATCOM along with its operating modes is given in Figure 1.
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POOJA LAL, et.al.: NONLINEAR DSTATCOM CONTROLLER USING PASSIVITY- BASED SLIDING MODE CONTROL
coupling transformer. The DC side terminal of the converter is connected to a DC capacitor. This capacitor carries the input ripple current of the converter and is also the main storage element of the reactive energy. This capacitor can be charged by using a battery source, or can be charged by using the converter itself. If the output voltage of the converter (VSC) is equal to the terminal voltage, no reactive power exchange takes place. If the output voltage of the converter is greater than the terminal voltage, the DSTATCOM generates the capacitive reactive power for the ac system. If the output voltage of the converter is less than the terminal voltage, the DSTATCOM absorbs the inductive reactive power from the ac system. The reactive power flow in the system is proportional to the difference in the two voltages. If a DSTATCOM is used for voltage regulation at the point of common coupling then the compensation can be done when the supply currents leads the supply voltages whereas, for the power factor Correction, the supply currents should be in phase with the supply voltages. Figure 1: Operating modes of DSTATCOM The basic principle of DSTATCOM is to generate the ac voltage source by using voltage source converter (VSC) connected to a energy storage device mainly a capacitor. The DSTATCOM is connected with the transmission line at the Point of common coupling, by a coupling reactance which gives active and reactive power exchange between the power system and the DSTATCOM. Under ideal conditions, the output voltage of the VSC is in phase with source voltage. A DSTATCOM includes a Voltage Source Converter (VSC) and a DC link capacitor connected in shunt, capable of generation and absorption of reactive power.
III. PASSIVITY BASED SLIDING MODE CONTROL (PBSM) The Passivity Based Controller (PBC) aims at achieving the current and voltage regulation .The PBC uses the energy shaping and damping injection techniques to generate proper switching function for VSC-based DSTATCOM.The Sliding Mode Control( SMC), is a nonlinear control method that alters the dynamics of a nonlinear system by application of a discontinuous control signal that forces the system to "slide" along a cross-section of the system's normal behaviour, it can switch from one continuous structure to another based on the current position in the state space and hence the sliding mode control is a variable structure control method. The Sliding Mode Control (SMC) is employed in order to improve the dynamic response of the system and to eliminate the steady state error. The sliding mode control is the one of the efficient way to design the robust controllers for highly nonlinear complex dynamic systems operating with uncertain conditions or changeable loads. Sliding-mode control (SMC) is one of the robust and nonlinear control methods. The systematic design procedure of this method provides a straight forward solution for the control input. A few advantages for SMC can be given such as robustness against matched external disturbances and unpredictable parameter variations.
Figure2. Basic Structure of DSTATCOM The VSC AC side terminals are connected to the Point of Common Coupling (PCC) by an inductance, which can be a filter inductance or the leakage inductance of the
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2014 INTERNATIONAL CONFERENCE ON COMPUTATION OF POWER, ENERGY, INFORMATION AND COMMUNICATION (ICCPEIC)
A. PBSM BLOCK DIAGRAM
Figure 4. PBSM block diagram
Figure 3. Graphical representation of sliding-mode control
The first step in the sliding-mode control solution is to determine a sliding manifold which is also called sliding surface or sliding function, s(t) being a function of the tracking error, e(t), e(t) ϵ R that is the difference between set point and output measurement, as
( )
(
)
e(t)
(1)
Where n denotes the order of uncontrolled system, λ is a positive constant. λ is the tuning parameter which determines the slope of sliding manifold. When the system is in sliding-mode, The control law u(t) is determined to make the tracking error and its derivative to converge to zero from any initial state to the equilibrium point in a finite time. U (t) consists of two additive signals switching (discontinuous) signal, usw(t), and equivalent (continuous) signal, usw(t),is determined separately. ( )
( )
(t)
The Passivity-Based Sliding Mode (PBSM) control block diagram as given is separated into two loops, the inner and the outer loop controller. The outer loop in the sliding mode controller will generate the appropriate d-q reference current fed for the inner loop whereas, the passivity based outer loop controller will produce the switching functions Uh,d and Uh,q to inject the appropriate current for ac grid. The is,dq, iL,dq, ih,dq represents the source, load, and DSTATCOM current. The Passivity based control aims to achieve the signal regulation which can be obtained by proper energy control of the closed loop system, and adding the required damping. In order to improve the dynamic response and to eliminate the steady state error, the outer loop employs the sliding mode control to determine the appropriate reference currents Is*,dq.
IV. SIMULATION MODEL The model shown below is 3-phase system of 415v; 50Hz is connected to a non-linear load (3-phase unbalanced). By injecting the compensation voltage the reactive power compensation is done.
(2)
The Sliding Mode Controller (SMC) provides the following advantages: (1) The low sensitivity to system parameter variations and disturbances. (2) It enables the overall system motion to be independent component. Figure5.Simulink model with DSTATCOM
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POOJA LAL, et.al.: NONLINEAR DSTATCOM CONTROLLER USING PASSIVITY- BASED SLIDING MODE CONTROL
and voltage regulation for VSC-based DSTATCOM. The dynamic response and the steady state errors of the system are improved by employing the sliding mode control for the VSC-Based DSTATCOM by generating d-axis and qaxis reference current.
V. REFERENCES [1]
Figure6. Three phase load voltage and current waveform
Figure7. Power factor simulation results before and after compensation
Figure8. dqo-axis, Sin and Cos References, Iabc Waveform
Figure8. Harmonic analysis for load voltage V. CONCLUSION
Bhattacharya Sourabh NIIIST Bhopal, MP, INDIA, “Applications of DSTATCOM Using MATLAB/Simulation in Power System”, Research Journal of Recent Sciences Vol. 1(ISC2011), 430-433 (2012). [2] Rodda Shobha Rani1, B. Jyothi2, “VSC Based DSTATCOM & Pulse-width modulation for Power Quality Improvement”, International Journal of Engineering Trends and Technology, Volume2Issue2- 2011. [3] Mahesh K. Mishra1, Member, IEEE and K. Karthikeyan2, “A Three phase DSTATCOM compensating ac and dc loads with fast dynamic response” Department of Electrical Engineering, Indian Institute of Technology Madras, India. [4] Bhim Singh, Senior Member IEEE, P. Jayaprakash*, Student Member IEEE, D. P. Kothari, Senior Member IEEE, “Isolated HBridge VSC Based 3-Phase 4-Wire DSTATCOM for Power Quality Improvement”, ICSET 2008 IEEE. [5] A. Elnady, Student Member, IEEE, and Magdy M. A. Salama, Fellow, IEEE, “ Unified Approach for Mitigating Voltage Sag and Voltage Flicker Using The DSTATCOM”, IEEE transactions on power delivery, vol. 20, no. 2, April 2005. [6] Parag Nijhawan1*, Ravinder Singh Bhatia2, and Dinesh Kumar Jain3, “Application of PI controller based DSTATCOM for improving the power quality in a power system network with induction furnace load” Songklanakarin J. Sci. Technol.34 (2), 195-201, Mar. - Apr. 2012. [7] Su Chen, Géza Joós, Department of Electrical and Computer Engineering, Concordia University, “Direct Power Control of DSTATCOMs for Voltage Flicker Mitigation” 2001 IEEE. [8] I. PapiE, Associate Member, IEEE Faculty of Electrical Engineering University of Ljubljana, “Power Quality Improvement Using Distribution Static Compensator with Energy Storage System”, 2000IEEE. [9] Alpesh Mahyavanshi1, M. A. Mulla2, R. Chudamani3, Electrical Engineering Department, “Reactive Power Compensation by Controlling the DSTATCOM”, International Journal of Emerging Technology and Advanced Engineering, (ISSN 2250-2459, Volume 2, Issue 11, November 2012). [10] A.H.Norouzi and A.M.Sharaf, “Two control scheme to enhance the dynamic performance of the STATCOM and SSSC.“IEEE Trans. On Power Delivery. [11] Q. Song and W. Liu, “Control of a cascade STATCOM with star configuration under unbalanced condition,IEEE Trans. Power Electron., vol. 24, no. 1, pp. 45–58, Jan. 2009. [12] H. Akagi, S. Inoue, and T. Yoshii, “Control and performance of a transformerless cascade PWM STATCOM with star configuration,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1041–1049, Jul./Aug. 2007. [13] Xiao-pingYang, FanFeng, Xian-Feng Duan, Lu-Lin Tian, “Research on the control strategy of the Transformer-isolated Multilevel H-bridges DSTATCOM for three-phase unbalanced load Compensation”,IEEE Xplore. [14] Bhim Singh, Senior Member, IEEE and Jitendra Solanki, “A Comparative Study of Control Algorithms for DSTATCOM for Load Compensation”,1-4244-0726-5/06/$20.OO '2006 IEEE. [15] Vincent George, Student Member, IEEE, Mahesh K. Mishra, Member, IEEE, and Srikanthan Sridharan, “A novel constant switching frequency strategy for a three-leg DSTATCOM”, CCECE/CCGEI May 5-7 2008 Niagara Falls. Canada 978-14244-1643-1/08/$25.00 _ 2008 IEEE. [16] A. Elnady, Student Member, IEEE, and Magdy M. A. Salama, Fellow, IEEE, “Unified Approach for Mitigating Voltage Sag and Voltage Flicker Using The DSTATCOM”, ieee transactions on power delivery, vol. 20, no. 2, april 2005.
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[17] P.K.Dhal and C.Christober Asir Rajan, “Transient Stability Improvement using Hybrid Controller Design for STATCOM”, International Journal of Soft Computing and Engineering (IJSCE) ISSN: 2231-2307, Volume-2, Issue-1, March 2012. [18] K. Anuradha, B.P.Muni, and A. D. Raj Kumar, “Control of Cascaded H-Bridge Converter based DSTATCOM for High Power Applications”, 0-7803-9772-X/06/$20.00 (©2006 IEEE. [19] A. Rahmati, A. Abrishamifar and E. Abiri, “Sensorless direct power control for a DSTATCOM”, from IEEE Xplore. [20] K. Anuradha1 B. P. Muni 2 A. D. RajKumar 3, “Simulation of Cascaded H-Bridge Converter based DSTATCOM”, 0-7803-9514X/06/$20.00 ©2006 IEEE
Pooja Lal received her B.E degree in Electrical and Electronics Engineering from Meenakshi Academy of Higher Education and Research, Chennai in 2008.She is currently pursuing her M.E degree in specialization Power Electronics and Drives from Prathyusha Institute of Technology and Management, Chennai. Her area of interest includes Power Electronics and Applications of Power Electronics in Power Systems.
S. Krishna Kumar received his B.E degree in Electrical and Electronics Engineering from Madras University in 1996. He received his M.E degree in specialization Power Electronics and Drives from College of Engineering, Guindy (CEG), Anna University in 2007.He is currently pursuing his PhD degree from CEG, Anna University. His area of interest includes Power Quality and Power Electronics.
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