Volume 117 No. 21 2017, 231-241 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu ijpam.eu A Fuzzy based MC-DPFC for Enhancement of Power Quality in Transmission Line 1 G. Bharat Reddy, 2 K.B. Madhu Sahu, 3 C.H. Krishna Rao and 4 K.B. Saikiran 1 Department of EEE, AITAM Engineering College, AP, India. reddy.bharat21@gmail.com 2 Department of EEE, AITAM Engineering College, AP, India. kbmadhusahu@gmail.com 3 Department of EEE, AITAM Engineering College, AP, India. krishna.challa@gmail.com 4 Department of EEE, IIT Patna, Bihar, India. kbsaikiran94@gmail.com Abstract A new control scheme to improve and maintain the power quality of an electrical power system by design of distributed power flow controller. Generally, In case of modern power utilities have problems like challenges in growth of electricity in case of non-linear loads in grid connected systems. In this paper, we introduced a new series-shunt type FACTS controller called as distributed power flow controller. This DPFC method is same as the UPFC used to compensate the sag and swell voltage based power quality problems. In DPFC, we eliminate the common dc link capacitor and instead of single three phase series converter it has three individual single phase converters. In this paper the control circuit is designed by using series referral voltages, branch currents. The evaluated values are obtained by using MATLAB/SIMULINK. Key Words:DPFC, voltage sag and swell, power quality. 231
1. Introduction Because of power demand grows dramatically, and extension in transmission and generation is restricted with the rigid environmental constraints and the limited availability of resource. By considering the transmission i.e., the transmission of electrical energy form generating stations to consumer points, the term power quality is used to measure the quality of power and how the system effected by transmission elements. From consumer side, the power quality issue is concentrated about how the transmission line parameters such as voltage, current and other are effected and deviated from their actual values due to occurrence of disturbance. For solving such type of power quality problem in literature point of view the method based on the power electronic based equipment s such as custom power devices i.e. dynamic voltage regulator are used in both transmission and distribution system. However, the majority of power quality problems occurred in transmission and distribution system are deviations in voltage such as sag and swell, and harmonics generated in currents due to non-linear loads. For compensating these problems compared all other devices the Flexible AC Transmission System provides the efficient work. These are classified as Static compensator, series-shunt controllers. Out of all these methods, this paper we presents a new controller under series-shunt controller called as distributed power flow controller. Basically, the distributed power flow controller is a combination of one parallel converter in combination with more number of series converters which is used to compensate the problems in transmission line parameters. Working of DPFC The structure of DPFC system has following modification as compared with UPFC i.e. common dc link capacitor is eliminated and it used for individual converter using 3 rd harmonic currents are injected in transmission for exchanging active power exchange. The DPFC is a combination of one parallel and multiple series converters. The parallel converter is considered as STATCOM, while the series converters is considered from the concept of DVR. Illustration. 1 shows the structure of single machine system with DPFC. The control capability of the Unified power flow controller such as back-toback combination of shunt and the series converters with a common DC link, which is used for exchanging the power. To make that the DPFC also have the same control capability like UPFC, i.e it doesn t have common dc link capacitor. Therefore, it is allows to exchange the active power through the AC terminals of the converters. 232
Figure 1: Basic Configuration of DPFC Advantages of DPFC The Distributed Power Flow Controller has the following advantages in comparison with UPFC, such as: 1) High reliable to control The distributed power flow controller has only alone to control all transmission parameters such as line impedance, load angle and deviations in voltage. 2) More efficiency The series converters redundancy increases the DPFC reliability during converters operation [10]. It means, if one of series converters fails, the others can continue to work. 3) Least Economy 2. Control Circuit for DPFC According to illustration 2 the control strategies of Distributed Power Flow Controller are classified in to mainly three types: i.e. 1) Main controller, 2) DVR controller and 3) Static controller. Figure 2: Control Diagram of DPFC 233
These three controllers are explained as follows: Central Controller The central controller is used to control dvr and static controllers by generation of referral signals (like series voltages and currents). Series Controller The main purpose of this series control technique is used to compensate the voltage quality problems by maintain the voltage of capacitor in rated value. This controller is operated based on the reference signals generated by capacitor voltages in both direct and quadrature frame. Generally, these series controllers has first order low pass and third order band pass filters to create natural and 3 rd order harmonic currents. The control structure for series controller is shown in figure 3. Figure 3: Block Diagram for Series Controller Parallel Controller The control structure for the shunt converter is as shown in figure 4. Main aim of the shunt control is to inject a 3 rd order harmonic current into the transmission line to generate suitable active power to DVR converter. The static converter is basically a three phase based converter and is back to back connected with another single phase converter. 234
Figure 4: Control Diagram for Shunt Controller 3. Fuzzy Logic Controller Fuzzy controllers are normally built with the use of fuzzy rules. Fuzzy rules are conditional statement that specifies the relationship among fuzzy variables. These rules help us to describe the control action in quantitative terms and have been obtained by examining the output response to corresponding inputs to the fuzzy controller. The basic block diagram of Fuzzy Logic Controller is shown below. Figure 5: Block Diagram of Fuzzy Logic Controller The Fuzzy Logic Controller is applied in Load Frequency control of Two area system, this analysis is done using different Fuzzy based rules using Linguistic variable. 235
4. Experimental Verification In this we consider a case study such as creating a voltage dip condition by implementing a three phase fault implemented in a single machine system and analyzed observations are shown below. The experimental diagram is implemented by basic diagram which is shown in figure 5. Figure 6: Structure of DPFC In this system the fault occur between the time 500ms to 1500ms. During this fault time the voltage is goes to sag position as shown in figure 6. The magnitude of this voltage is reduced by 0.65 percent of its nominal value during this fault time. Figure 7: Simulation Results for Voltage Sag Condition Figure show the simulation result for output voltage by considering DPFC in order to mitigate the or compensate the voltage sag problems. 236
Figure 8: Simulation Results for Mitigation of Voltage Sag with DPFC system During this fault time the load current rises its magnitude around 1.2% per unit. The simulation results of load current in case of swell condition and mitigation of load current problems are shown in figure 8 and figure 9. Figure 9: Simulation Results for Current Swell Condition Figure 10: Simulation Results for Mitigation of Current Swell with DPFC System 237
Figure 11: Simulation Results for Active and Reactive Powers Figure 12: THD of Load Voltage in Line2 Figure.12 shows the THD performance load voltage in line2. By using FFT analysis, in DPFC, the odd harmonics are minimized in line2. Table.1explains the difference between the THD values of current and voltage without fuzzy and with fuzzy controller. Table 1: THD Comparison Without and with Fuzzy Parameters Without fuzzy With fuzzy Current 17.19 6.79 Voltage 6.75 4.59 238
5. Conclusion In this paper we implemented a new concept for controlling power quality problems by Distributed Power Flow Controller device. The proposed concept of the DPFC approach is mathematically formulated and analyzed for voltage dips and their mitigations for a three phase source with linear load. In this paper we also proposed a concept of fuzzy logic controller for better controlling action. As compared to all other facts devices the DPFC based Fuzzy has effectively control all power quality problems and with this technique we get the THD as 4.59% and finally the simulation results are shown above. References [1] Ahmad Jamshidi S., Masoud Barakati, Moradi Ghahderijani M., Presented a paper on Impact of Distributed Power Flow Controller to Improve Power Quality Based on Synchronous Reference Frame Method, At IACSIT International Journal of Engineering and Technology 4 (5) (2012). [2] Srinivasa Rao K., Madhu Sahu K.B., Krishna Rao C.H., A New Simplified Symmetrical Multilevel Inverter Topology with PV Applications, Scopus 10 (12) (2015). [3] Jamshidi A., Barakati S.M., Ghahderijani M.M., Power quality improvement and mitigation case study using distributed power flow controller, IEEE International Symposium on Industrial Electronics (ISIE) (2012), 464-468. [4] Santhosh Kumar B., Madhu Sahu K.B., Krishna Rao C.H., Sai Kiran K.B., Enhancement Of Power Quality Using FUZZY Controlled D-STATCOM in Distribution System, TRANS STELLAR (IJEEER) 7 (3) (2017), 1-12. [5] Enslin J.R., Power mitigation problems, In Proc. IEEE Int. Symp. Industrial Electronics (ISIE 98) (1998), 8 20. [6] Phalguna Rao P., Madhu Sahu K.B., Krishna Rao C.H., Performance Evaluation of High step-up DC-DC Converter Working Under Closed Loop Control Scheme, Scopus 10 (15) (2015). [7] Hannan M.A., Mohamed A., PSCAD/EMTDC simulation of unified series-shunt compensator for power quality improvement, IEEE Transactions on power delivery 20 (2) (2005), 1650-1656. [8] Manaswini B., Vathsal S., Prasad S.S., Enhancement of Power Quality in Multi Feeders by using MC-DPFC, IJRCCT 3(10) (2014), 1165-1169. 239
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