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- 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 74 UNIFIED POWER QUALITY CONDITIONER FOR COMPENSATING POWER QUALITY PROBLEM: ADAPTIVE NEURO-FUZZY INTERFERENCE SYSTEM (ANFIS) Mr. M. Vishnu vardhan1* , Mr. N.M.G.Kumar1 , Dr. P. Sangameswararaju2 1 (EEE, SV University, Tirupati, India) 2 (EEE, SV University, Tirupati, India) ABSTRACT Nowadays, the power quality related issues are more concentrating in power electronic devices. Hence, the electronic devices are affected by the PQ disturbances. Various power devices are used for compensating the PQ disturbances. Unified power quality conditioner (UPQC) is one of the power electronics devices that are used for enhancing the PQ. It consists of two voltage source inverters (VSIs) and sharing with one DC link capacitor. The discharging time of DC link capacitor is very high, and so it is the main problem in UPQC device. In this paper, an enhanced Adaptive Neuro-fuzzy Inference System (ANFIS) based UPQC is proposed to eliminate this problem. Main Objective of this paper is to improve the power quality problem compensating performance of UPQC. The purpose of ANFIS is use to generate the discharging dc link voltage by bias voltage generator. ANFIS permits the combination of numerical and linguistic data. The generated fuzzy rules are then trained by using the neural network and we get a desired output from the interference system. The output of ANFIS is injected to the line by the proposed UPQC system. Then, the power quality problem compensating performance of proposed ANFIS based UPQC is analyzed. The analyzed results are compared with Neuro-fuzzy controller (NFC), artificial neural network (ANN), fuzzy logic controller (FLC) based UPQC system. Keywords: ANFIS, UPQC, Neural Network, Fuzzy Logic controller and Power Quality Disturbance. 1. INTRODUCTION PQ studies have emerged as a significant topic because of the extensive use of sensitive electronic equipments [6]. A broad definition of power quality that includes the definitions of technical quality and supply continuity states that the limits specified in the standards and regulations should not be exceeded by electrical PQ or in other words frequency, number and interval of INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), pp. 74-92 © IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2013): 5.5028 (Calculated by GISI) www.jifactor.com IJEET © I A E M E
- 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 75 interruption, interruption in voltage, sine waveform and voltage unbalance [13]. Nowadays power quality is definitely a big issue and the inclusion of advanced devices, whose functioning is extremely sensitive to the quality of power supply, makes it especially important [17]. Due to the increasing anxiety over supplying pure electrical energy to the consumers in the availability of non- sinusoidal waveforms, PQ has gained much interest in recent years. [9]. Huge number of non-linear loads and generators on the grid, especially systems based on power electronics like variable speed drives, power supplies for IT-equipment and high efficiency lighting and inverters in systems producing electricity from renewable energy sources have made electrical energy systems, voltages and specifically currents extremely irregular [8]. Degradation or impairment can occur in the electrical equipments connected to the system as a result of poor PQ [12]. The increased anxiety has resulted in measurement of changes in PQ, analysis of power disturbance characteristics and generation of solutions to the PQ problems [4]. Any apparent problem in voltage, current that gives rise to any frequency variations leading to breakdown or malfunction of customer equipment is termed as the PQ problem [1] [10]. A PQ problem can be caused by several events. As a switching operation within the facility to a power system may be associated with the cause of a fault event located hundreds of miles away from that place, analysis of these events is frequently difficult [2]. PQ problems include short disruptions, long disruptions, voltage sags and swells, harmonics, surges and transients, unbalance, flicker, earthing defects and electromagnetic compatibility (EMC) problems [5]. Undesirable effects like extra heating, intensification of harmonics because of the existence of power factor correction capacitor banks, decrease of transmission system efficiency, overheating of distribution transformers, disoperation of electronic equipment, improper functioning of circuit breakers and relays, incorrectness in measuring device, interference with communication and control signals etc are caused by these PQ problems [7] [11]. Lessening the PQ problems and supporting the functioning of sensitive loads are possible because of Power Electronics and Advanced Control technologies [3]. The quality and reliability of electric power distribution systems are reported to be improved by Custom Power Devices (CPDs). Three major CPDs are D-statcom, DVR and UPQC [18]. One of the foremost custom power devices that are competent of alleviating the consequence of power quality problems at the non linear load is the UPQC [14] [15]. In addition to removal of harmonics, recompense for reactive power, load current unbalance, source voltage sags, source voltage unbalance and power factor correction are provided by UPQCs [16] [20]. In power distribution systems or industrial power systems, UPQC has the outstanding potential to enhance the quality of voltage and current at the position of installation [19]. Generally, an UPQC is comprised of two voltage source inverters (VSIs) sharing with one DC link capacitor. Here, the main problem is that the discharging time of DC link capacitor is very high. To mitigate this problem, an enhanced ANFIS based UPQC is proposed and detailed in Section 4. Prior to that, a concise review about the recently available related works are given in Section 2. Section 3 discusses problem formulation of the proposed technique. Section 5 discusses and analyzes the results of the proposed controller and the Section 5 concludes the paper. 2. RELATED RECENT RESEARCHES: A BRIEF REVIEW Numerous research works already exist in the literature that compensate power quality problem in power operating system. Some of them are reviewed here. A. Ananda Kumar and J. Srinivasa Rao [21] have proposed a novel method to improve the power quality at the point of common coupling (PCC) for a 3-phase 4- wire DG system using fuzzy logic control for grid interfacing inverter. The grid interfacing inverter is effectively utilized for power conditioning. Their proposed method eliminates the additional power
- 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 76 conditioning equipment to improve power quality at PCC. They use fuzzy logic to handle rough and unpredictable real world data. Their proposed method results show that, high accuracy of tracking the DC-voltage reference, and strong robustness to load parameter variation. Miss Sobha rani Injeti and K. Ratna Raju [22] have presented a new compensation strategy implemented using an UPQC type compensator. Their proposed compensation scheme enhances the system power quality, exploiting fully DC–bus energy storage and active power sharing between UPQC converters, features not present in DVR and D–Statcom compensators. The internal control strategy is based on the management of active and reactive power in the series and shunt converters of the UPQC, and the exchange of power between converters through UPQC DC–Link. They have proved that their proposed algorithm was efficient and stability. Accurate, and robust in comparing with the commonly used backward/forward sweep method for weakly meshed networks. Lachman et al. [23] have proposed a Wavelet Transform technique for studying PQ disturbances. They have discussed and deliberated Waveform distortion type of PQ disturbances. Diverse kinds of signals have been created and diverse frequency bands have been acquired in the calculation process. It has been observed that identification of PQ disturbances necessitates selection of appropriate mother. It has been concluded that detection of PQ disturbances is made easier by the use of approximate coefficients and scaling. Wavelet Transform has been proved to be an appropriate tool for examining PQ disturbances, when time-frequency information is needed simultaneously by means of computational results. Radhakrishnan et al. [24] have proposed a Fuzzy logic controller (FLC) for improving the power quality indices of an AC–AC Conversion System as well as controlling its steady state and transient state output voltage. The Fuzzy response verified by means of PI action has been proved to be appropriate for utilization in Power Converters. The merits of the individual methods have been illustrated by comparing the performance of three firing schemes. The applicability of Sinusoidal Pulse Width Modulation (SPWM) over a wide range of applications has been demonstrated by sufficiently emphasizing the fact that it inherits numerous exclusive merits. As Random PWM (RPWM) considerably reduces the magnitude of harmonic components in addition to decreasing the filtering necessities it adapts itself for high power applications by its ability of spread its harmonic power. They have anticipated that such an analysis together with the advantages of the proposed FLC will go a long distance in nourishing new applications for AC-AC conversion systems although the option of a specific scheme could only be determined by specific needs. Darly Sukumar et al. [25] have discussed a fuzzy algorithm based new method for attenuating the current harmonic contents in the output of an inverter. Ride-through capability amidst voltage sags, decreased harmonics, better power factor and high reliability, reduced electromagnetic interference noise, reduced common mode noise and increased output voltage range have been provided by the inverter system that uses fuzzy controllers. A model of three-phase impedance source inverter designed and managed based on the proposed considerations has been constructed and a practicable test has been implemented. The improved effectiveness and suitability of these new methods to reduce harmonics and increase the power quality have been verified from the practical point of view. A compromise between cost and performance has been frequently required in the realization because of the complexity of the algorithm. Variable-frequency DC-AC inverters, UPSs, and AC drives have applications for the proposed optimizing strategies. 3. PROBLEM FORMULATION From the review of the research work shows that, an intelligent technique which is adopted in various electrical and electronics applications. In the previous paper this intelligent technique is being used for improving the power quality problem compensating performance of UPQC. This
- 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 77 technique combines the properties of both the neural network and the fuzzy logic which makes it more robust and efficient. A neural network suggests the possibility of solving the problem of tuning. Even though a neural network is capable of learning from the given data, the trained neural network is generally understood as a black box. Neither it is possible to extract structural information from the trained neural network nor can we integrate special information into the neural network in order to simplify the learning procedure. Alternatively, a fuzzy logic controller is designed to work with the structured knowledge in the form of rules and nearly everything in the fuzzy system remains highly transparent and easily interpretable. However, there exists no formal framework for the choice of various design parameters and generally the optimization of these parameters is done by trial and error method. Hence, a combination of neural networks and fuzzy logic presents the possibility of solving tuning problems and design difficulties of fuzzy logic. The resulting network will be more flexible and can be easily recognized in the form of fuzzy logic control rules or semantics. This new approach combines the well established advantages of both the methods and avoids the drawbacks of both. In this paper, adaptive neural-fuzzy controller architecture is proposed, which is an improvement over the existing Neuro fuzzy controllers. 3.1. Need for Advancement of Proposed Adaptive Technique As of now, various researches have been performed by researchers in the power quality maintenance and enhancement sector. Some devices such as dynamic voltage restorer (DVR), uninterruptible power supplies (UPS) and many others are used for maintaining the quality power supply. But, these devices are capable of maintaining only the symmetrical or unsymmetrical power supplies, so the power quality is not maintained at all time. To avoid these problems, an enhanced Neuro fuzzy controller has been proposed [1] which is capable of maintaining the quality power supply in the distribution network. But the system designed by [1] has a main drawback i.e. it can only be applied to small networks and cannot work effectively in case of complex and wider operating conditions. Hence to overcome this issue in this paper, we have proposed an intelligent technique called the Adaptive Neuro Fuzzy Inference System (ANFIS) which is nothing but an advanced version of the Nero fuzzy controller (NFC) or is a kind of neural network that is based on Takagi–Sugeno fuzzy inference system. Since, it integrates both neural networks and fuzzy logic principles, it has a potential to capture the benefits of both in a single framework. The fuzzy part of the ANFIS device generally works with five steps which will be illustrated later. ANFIS also permits the combination of numerical and linguistic data. Its inference system corresponds to a set of fuzzy IF–THEN rules that have learning capability to approximate nonlinear functions. The generated fuzzy rules are then trained by using the neural network and we get a desired output. 4. PROPOSED ADAPTIVE NEURO FUZZY INFERENCE (ANFIS) BASED UPQC UPQC is power electronics based power conditioning device, designed to compensate both source current and load voltage imperfections. This device combines a shunt active filter together with a series active filter in a back to back configuration, to mitigate any type of voltage and current fluctuations and power factor correction in a power distribution network. UPQC is able to compensate current harmonic reactive power, voltage distortions and control load flow but cannot compensate voltage interruption because of not having sources. Hence in this paper we have proposed a hybrid technique called the adaptive Neuro fuzzy inference system (ANFIS). By adding an ANFIS device to the UPQC system the discharging time of the DC link capacitor is maintained at a lower level. Accordingly the system performance is enhanced dramatically.
- 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 78 The general structure of proposed ANFIS based UPQC consists of two inverters and it is connected with a bias voltage generator. The inputs of the bias voltage generator are reference voltage Vref and the calculated voltage Vcal, which is calculated from ANFIS. The Inverter II is connected in series with an inductance that is denoted by LSLC. The purpose of the synchronous link inductor is to generate a voltage with respect to PQ disturbance. The inverter I is connected in series with a low pass filter and the purpose of the filter is to pass the low frequency component, and to reduce the high frequency component of the specific voltage signal. Then, the output of low pass filter is applied to the voltage injection transformer. Hence, the obtained output from injection transformer maintains PQ in the operating system. The injected line voltage, voltage source, current source and load current are denoted as Vinj, Vk, Ik, Iload . The Vinj can be determined as follows, 1 2 2 2 2 inj k kV V V= − (1) injV = 1 2 2 2 k kV V− (2) injV = 2 2 dcnV (3) Where, 1kV is the pre voltage variation, 2kV is the post voltage variation, ‘n’ is the modulation index, dcV is the normal rated DC voltage. 4.1. ANFIS based bias voltage generator The bias voltage generator is used for eliminating the high discharging time of the D.C link capacitor. The ANFC is a hybrid technique which combines Fuzzy Inference System (FIS) and NN. The fuzzy logic is operated based on fuzzy rule and NN is operated based on training data set. The neural network training datasets are generated from the fuzzy rules and the error and change in error voltage of the device is determined which is shown below, Figure 1. Schematic diagram of proposed UPQC controller
- 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 79 ( ) ( ) ( ) ( )1 dc dcE k V ref V E E k E k = − ∆ = − − Where, E (k-1) is the previous state error. The error voltage and change of error voltage are calculated by using the above formula and the value are applied to the input of ANFIS. From the output of NFC, the Vout is determined. The function of ANFIS is explained in t he below section. 4.2. Working Procedure of ANFIS Step-1: At first the initialization of the input variables called the parameters is done which is in a binary form and the input variables are fuzzy field. Step-2: After input fuzzification, output fuzzification is done by applying fuzzy operators like AND, OR operators. Step-3: Membership functions are defined and are computed to track the given input/output data. Step-4: The parameters associated with the membership function changes through the learning process. Step-5: Fuzzy rules are created basing on the input output relationship of the system. Step-6: After creating rules, aggregation of various outputs is done and then the resulted functions are defuzzyfied to get an optimal output. Step-7: The obtained output is then trained by applying it to the Neural network through the back propagation method. Step-8: The error is minimized by performing various iterations in the Neural network and we get an optimized output. 4.3. ANFIS Architecture One of the most popular hybrid methods called the adaptive Neuro-fuzzy method is nothing but an advanced version of the Neuro-Fuzzy method. The ANFIS combines both the neural network and the fuzzy logic controller methods. The basic structure of the type of fuzzy inference system could be seen as a model that maps input characteristics to input membership functions. Then it maps input membership function to rules and rules to a set of output characteristics. Finally it maps output characteristics to output membership functions, and the output membership function to a single valued output or a decision associated with the output. It has been considered only fixed membership functions that were chosen arbitrarily. Fuzzy inference is applied only to modeling systems whose rule structure is essentially predetermined by the user's interpretation of the characteristics of the variables in the model. ANFIS uses a combination of least squares estimation and back propagation for membership function parameter estimation. The suggested ANFIS has several properties: 1. The output is zeroth order Sugeno-type system. 2. It has a single output, obtained using weighted average defuzzification. All output membership functions are constant. 3. It has no rule sharing. Different rules do not share the same output membership function, namely the number. 4. It has unity weight for each rule. To explain the ANFIS architecture, two fuzzy if-then rules based on a first order Sugeno model are considered. Rule 1: If ( E is C1) and ( E∆ is D1) then (f1= p1 E + q1 E∆ + r1) Rule 2: If ( E is C2) and ( E∆ is D2) then (f2= p2 E + q2 E∆ + r2) Where, E and E∆ are the error and the change in error signals respectively, which are applied as inputs to the ANFIS network, Ci and Di are the fuzzy sets, fi is the corrected and rectified signal which we get as an output of the fuzzy region specified by the fuzzy rule, ip , iq and ir are the
- 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 80 design parameters that are determined during the training process. The bell shaped curves which are having a maximum value of 1 and minimum value of 0 is shown below. fig.3. Shows the generalized ANFIS architecture which is formed by the combination of adaptive neural network and adaptive fuzzy controller. The ANFIS operation is carried out by the five layers and the processing of the five layers is explained below, The network diagram and functioning of the ANFIS is explained through the five layers of the above shown structure, Layer 1: - The outputs of layer 1 are the fuzzy membership grade of the inputs which are all adaptive nodes and are given by: 1 ( )i iO C Eµ= , for i = 1, 2 Or 1 2 ( )i iO D Eµ −= ∆ , for i = 3, 4 Where, E is the error and ∆E is the change in error, given as input to node-i, and Ci is the linguistic label associated with this node function. In other words, O1 i is the membership function of Ci and it specifies the degree to which the given E satisfies the quantifier Ci. Usually µCi(E) is chosen to be bell-shaped with a maximum value of 1 and a minimum value as 0, such as the generalized bell function: 2 1 ( ) 1 iC n i i E E C m µ = − + (4)
- 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 81 Layer 2: - In this layer every node is a circle node labeled ‘M’ which multiplies the incoming signals and sends the product out. For instance, 2 ( ) ( ),i i iO w C E E D Eµ µ= = ∆ for i= 1,2 Each node output represents the firing strength of a rule. (In fact, other T-norm operators that performs generalized AND can be used as the node function in this layer.) Layer 3: - In the 3rd layer every node is a circle node labeled ‘N’ which represents normalization. The ith node calculates the ratio of the ith rule’s firing strength to the sum of all rules firing strengths: 3 1 2 ,i i w O w w w = = + for i= 1,2 For convenience, the output of this layer will be called as normalized firing strengths. Layer 4: - This layer consists of square nodes I which encloses certain transfer functions in it. 4 ( )i i i i i iO wf w p E q E r E= = + + where, iw is the output of layer 3, and { ip , iq , ir } is the parameter set. Parameters in this layer will be referred to as consequent parameters. Layer 5: - In the final layer a single circle node is present which is labeled as ‘Σ’ that computes the overall output as the summation of all incoming signals, i.e., 5 i i iO w f= ∑ After evaluating the five layers of the ANFIS we get an error free signal which is our desired output. By using the output of ANFIS, the DC-link voltage of UPQC is varied according to the variation in load voltage. The ANFIS controller based regulating system, uses neural network for optimizing the membership function of fuzzy controllers. The bias voltage generator is used for eliminating the high discharging time of the D.C link capacitor. The inputs of the bias voltage generator are taken as reference voltage Vref and the calculated voltage Vcal , which is calculated from ANFIS. Initially, the load end and source end voltage of the system is applied to the neural network. Then, the interference system is generated from the optimized output of neural network. Accordingly, the performance of the ANFIS based UPQC device is evaluated and the D.C link regulated voltage is determined. Then, the determined D.C link voltage is applied to the voltage regulation system of UPQC and the PQ problem is compensated effectively. 5. RESULTS AND DISCUSSION The proposed ANFIS based UPQC controller is simulated in MATLAB platform. Then, the performance of the proposed controller is tested with PQ problem. The testing performance of the proposed controller is analyzed. The proposed ANFIS simulated diagram is illustrated below. The parameters chosen for implementation are tabulated in Table I.
- 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 82 Table I: Parameters Chosen for implementation Parameters Values DC Voltage (Vdc) V230± Reference Voltage (Vref) V230± Error Voltage (e(n)) -230V to +230V Change of Error voltage ( e) -230V to +230V From the ANFIS based UPQC simulation model, the following performances are obtained. The reference Voltage and Line Voltage at different instants, are determined. PQ affected the line voltage has been enhanced using the proposed controller ANFIS, N.N and Fuzzy. However the performance of the technique is analyzed by the process of ANFIS, NN-based controller and then with FL. The reference voltage, line voltage with PQ problem at the defined time instants (T= 0.03,0.06,0.13,0.15,0.17 sec) and line voltage with enhanced PQ are illustrated in Fig 4,6,7,8,9, 10 and 11. Here, The PQ problems are occurring in NN, FLC and NFC at 0.03 seconds then clearing at 0.061, 0.062 and 0.061 seconds respectively. In the proposed controller, the PQ problems are occurring at 0.03 seconds and clearing at 0.06 seconds. So, the total PQ problem duration is 0.03seconds. . Fig 4: Reference Voltage Fig 5: Line voltage with PQ problem at T=0.03 sec
- 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 83 Fig 6(a): Line voltage with PQ problem at T=0.03 sec Fig 6(b): Line voltage with PQ problem at T=0.03 sec Fig 6(c): Line voltage with PQ problem at T=0.03 sec Fig 6(d): Line voltage with PQ problem at T=0.03 sec Fig 7: Line voltage with PQ problem at T=0.06 sec
- 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 84 Fig 7(a): Line voltage with PQ problem at T=0.06 sec Fig 7(b): Line voltage with PQ problem at T=0.06 sec Fig 7(c): Line voltage with PQ problem at T=0.06 sec Fig 7(d): Line voltage with PQ problem at T=0.06 sec From the above illustrations, the PQ problem arises at Time instant T=0.06 sec defined by using ANFIS, NN and FLC methods. The PQ problems are occurring in NN, FLC and NFC then clearing at 0.13, 0.14 and 0.14 respectively. In the proposed controller, PQ problems are clearing at 0.08 seconds. So, the total PQ problem duration is 0.02seconds.
- 12. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 85 Fig 8: Line voltage with PQ problem at T=0.13 sec Fig 8(a): Line voltage with PQ problem at T=0.13 sec Fig 8(b): Line voltage with PQ problem at T=0.13 sec Fig 8(c): Line voltage with PQ problem at T=0.13 sec
- 13. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 86 Fig 8(d): Line voltage with PQ problem at T=0.13 sec Here, the PQ problem arises at Time instant T=0.13 sec, and that are occurring in NN, FLC and NFC then clearing at 0.16, 0.162 and 0.161 respectively. In the proposed controller, the PQ problems are clearing at 0.16 seconds. So, the total PQ problem duration is 0.03seconds. Similarly, all the different time instants, the proposed controller performance are calculated. Fig 9: Line voltage with PQ problem at T=0.15 sec Fig 9(a): Line voltage with PQ problem at T=0.15 sec Fig 9(b): Line voltage with PQ problem at T=0.15 sec
- 14. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 87 Fig 9(c): Line voltage with PQ problem at T=0.15 sec Fig 9(d): Line voltage with PQ problem at T=0.15 sec Fig 10: Line voltage with PQ problem at T=0.17 sec Fig 10(a): Line voltage with PQ problem at T=0.17 sec
- 15. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 88 Fig 10(b): Line voltage with PQ problem at T=0.17 sec Fig 10(c): Line voltage with PQ problem at T=0.17 sec Fig 10(d): Line voltage with PQ problem at T=0.17 sec From the above illustrations, the performance of the proposed controller has been observed. So, the time taken to solve the PQ problem by ANFIS based UPQC system is very low when compared to the NFC, FLC and NN. Therefore, the proposed controller is improved for solving the PQ problems. The Root Mean Square (RMS) voltage (Vrms) is calculated as follows. 2 p rms V V = where, Vp is the peak voltage value. Then, PQ affected the line voltage has been enhanced using the proposed controller. Hence, achieved RMS voltages of ANFIS, NN-based controller and FLC for different time instants are tabulated in TABLE II.
- 16. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 89 Table II: RMS Voltages From ANFIS, NFC, NN-Based Controller And FLC Time instant in sec at which the PQ error occurs RMS Voltage (in Volts) when PQ issue occurs RMS Voltage ( in Volts) after PQ enhancement ANFIS NFC NN FLC 0.03 95 77 28 49 63 0.06 91 88 31 53 81 0.13 91 81 53 53 56 0.15 70 162.63 74 75 76 0.17 88 81 31 40 77 The proposed controller enhances the PQ and brings the line RMS voltage to the reference voltage level. But when the PQ problem is occurring in the defined time instants, the RMS voltage gets decreased. 5.1 Performance Deviation The performance deviation of the proposed controller is analyzed with NFC, FLC and NN- based controller. The performance deviation between ANFIS and NFC based controller can be calculated as follows ANFIS rms NFC rms ANFIS rms V VV Deviation 100*)( (%) − = Similarly, the performance deviation can also be calculated between ANFIS and FLC, NN for different instances of occurrence of PQ issues and that are chosen for implementing the proposed controller are tabulated in TABLE III. The performance deviation of ANFIS controller represented in fig 11. It can be deviates positively at a rate of 18.18% rather than FLC, 63.63% rather than NFC and 36.36% rather than NN-based controller at T=0.03sec. And the time instant (T=0.06 sec), the proposed controller deviates at a rate of 7.95% rather than FLC, 39.77% rather than NN and 64.77% rather than NFC. Similarly, the performance deviation of the proposed technique achieves a positive rate in solving the defined instants. It can be shown that, the proposed controller can achieve a better performance of PQ issues compared with the FLC, NFC and NN. Table III. Performance deviation of ANFIS with NFC, NN and FLC Time (in sec) Performance Deviation of ANFIS NFC NN FLC 0.03 63.63% 36.36% 18.18% 0.06 64.77% 39.77% 7.95% 0.13 34.57% 34.57% 30.86% 0.15 55.72% 52% 53% 0.17 61.73% 50.62% 4.94%
- 17. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME 90 Fig 11: Performance analysis of ANFIS with NFC, FLC and NN-based controller 6. CONCLUSION In this paper, an ANFIS based UPQC controller was proposed for compensating the PQ problem. The proposed controller was implemented and the results were evaluated with NFC, NN and FLC methods. Here, the voltage sag PQ problems were considered for analyzing the performance of the ANFIS controller. The voltage sag issues were represented at different time instants of the line voltage. The proposed controller has compensated the PQ problem that is specified with the waveform. The PQ problem compensated by ANFIS with 0.03seconds compared with NN, NFC and FLC methods. The performance deviations were evaluated in the proposed controller with the NFC, NN and FLC techniques. The performance deviation of the proposed technique achieves a positive rate in solving all the defined instants of occurrences of PQ issues. The comparative results showed that the proposed controller can achieve a better performance of PQ issues compared with the FLC, NFC and NN based controllers. REFERENCES [1] S.Deepa and S.Rajapandian, "Voltage Sag Mitigation Using Dynamic Voltage Restorer System", International Journal of Computer and Electrical Engineering, Vol.2, No.5, pp.821- 825, October 2010 [2] Thomas E. Grebe, "Application of Distribution System Capacitor Banks and Their Impact on Power Quality", IEEE Transaction on Industry Applications, Vol.32, No.3, pp.714-719, 1996 [3] S.Sadaiappan, P.Renuga and D.Kavitha, "Modeling and Simulation of Series Compensator to Mitigate Power Quality Problems", Vol.2, No.12, pp.7385-7394, 2010 [4] M.A. Hannan, A. Mohamed, A. Hussain and Majid al Dabbay, "Development of the Unified Series-Shunt Compensator for Power Quality Mitigation", American Journal of Applied Sciences, Vol.6, No.5, pp.978-986, 2009 [5] R.Valarmathi and A.Chilambuchelvan, "Harmonic Analysis of Distributed PV System Under High and Low Irradiance", International Journal of Engineering and Technology, Vol.2, No.3, pp.190-193, 2010
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