Automatic Voltage Regulator with Series Compensation

Transcription

1 Automatic Voltage Regulator with Serie Compenation 1 Neethu Sajeev, 2 Najeena K S, 3 Abal Nabi 1 M.Tech Student, 2, 3 Aitant Proffeor, Electrical and Electronic Dept ILAHIA College of Engineering and Technology Muvattupuzha, India Abtract An Automatic voltage regulator (AVR) baed erie compenation i decribed in thi paper. An AC chopper i ued here for producing the compenation voltage. The AC chopper i baed on pule width modulation technique (PWM).The witching pattern of AC chopper will reduce the commutation problem. The direct AC-AC converion preent here will reduce the requirement of energy torage device. It ha the ability to compenate both voltage ag a well a the pike. The control ection i developed uing artificial neural network. Keyword - Component, AVR, Serie compenation, PWM I. INTRODUCTION In recent year, there ha been an increaed emphai on, and concern for, the quality of power delivered to factorie, commercial etablihment, and reidence [1]. Thi i due to the preponderance of harmonic-creating ytem in ue. Adjutable-peed drive, witching power upplie, arc furnace, electronic fluorecent lamp ballat, and other harmonic-generating equipment all contribute to the harmonic burden the ytem mut accommodate. In addition, utility witching and fault clearing produce diturbance that affect the quality of delivered power. Much of the equipment in ue today i uceptible to damage or ervice interruption during poor powerquality. Power quality problem are mitigated by equipment like power conditioner.. By employing power conditioning equipment uch a voltage regulator and uninterruptible power upplie, problem at the utility ide may be prevented from ditorting the voltage at the load ide[1]. There are variou power quality problem on the utility ide: Voltage ag, voltage well, tranient, voltage interruption, etc. Power quality i quite frequently decribed a voltage quality. Alo, power quality can be defined with repect to clean power. Clean power refer to power that ha inuoidal voltage without any ditortion and which i at the deired magnitude and frequency. Power quality i important and neceary epecially for enitive electronic device deigned and manufactured in tate-of-the-art technology. Non-electronic equipment ued in the pat uch a motor, incandecent light, and reitance heater could tolerate voltage diturbance of ±5 % of nominal voltage. Power line diturbance can caue eriou problem to enitive equipment uch a computer, communication equipment and proce control ytem. With an increae in the ue of enitive equipment, voltage ag and well have been identified a important power quality problem facing indutrial cutomer today. The ource of 85% of all voltage event, caued by inadequate upply, underized wiring, or an overloaded circuit, originated within a facility, not on the electric utility ytem. Frequently, problem arie when equipment turn on or off on the ame circuit. Environmental change, uch a lightning torm, high wind, flooding, phyical damage, utility operation, or neighboring facilitie, alo can affect voltage. II. OPERATING PRINCIPLE The electric circuit of the automatic voltage regulator i hown in Figure 1. The AVR generate the compenation voltage Vco uing the buck topological operation.s1, S2, S3 and S4 are witche of the AVR. T i a three winding tranformer ued for erie compenation according to the input voltage Vi and i alo tabilize the output voltage v o. N P1 and N P2 are the number of primary winding turn, where N P1 =N P2, and N S i the number of econdary winding turn. The primary winding of the tranformer ha a centre tap. The filter capacitor voltage V C i tranformed into V CO through T. V r i the chopper modulated voltage and V L i the inductor voltage. The AVR ytem ue PWM controller to generate and modulate the PWM ignal, and control the output of the AC chopper. Here two TRIAC S b1 and S b2 or back-to-back connected thyritor are ued for erie compenation according to the polarity of input voltage. It offer a bidirectional current flow. If a hort circuit condition occur, a large current may be paing through the primary of the tranformer and may affect the operation of automatic voltage regulator. Alo thi high current hould pae through the ac chopper ection and reulting a high witching tre, ometime it may detroy the witche. So additional bypa witche are provided for afe operation of AVR. ISSN: Page 121

2 Fig.1. Automatic voltage regulator When a hort circuit occur, the bypa circuit compoed of bypa witche carrie the econdary current of the tranformer. Thu, the hort-circuit current circulate through the bypa witche. Uing the bypa witche, the propoed AVR can compenate not only for the ag but alo for the well of the input voltage. When the ag i detected, the AVR operate under the voltage ag condition. Under the voltage ag condition, the voltage Vco i in phae with V in. S b1 i turned on and S b2 i turned off. Then, V CO i added to the input voltage, o the AVR can compenate the voltage ag. When the well i detected, the AVR operate under the voltage-well condition. Under the voltagewell condition, the voltage Vco i out of phae with Vin.S b1 i turned off and S b2 i turned ON. So the injection voltage i injected through S b2. The electric circuit of the ac chopper ued in the propoed AVR i hown in Figure 2. Thi AC chopper conit of four witche, an inductor and capacitor. The output voltage can be controlled by the duty ratio of the chopping pule. The low-pa filter i ued to filter the harmonic component of the output of the AC chopper. L i the filter inductance, i the filter capacitance and R L i the equivalent reitance of the AC chopper. Owing to the energy tored in the inductance, input filter capacitor C b are added directly to power emiconductor witche and aborb the energy. Fig.2. Electric circuit of the ac chopper The AC chopper provide direct AC AC converion without energy torage element uch a a moothing inductor or a moothing capacitor. Thu, the ize and cot of the AVR are reduced. The AC chopper compenate for only the deviation from the required voltage, o the witche have reduced rating and tree compared with AVR that handle 100% of the ytem power capability. A. Operating Mode The output voltage i controlled by changing the duty ratio of the drive ignal. The witching pattern are decided by the polarity of the input voltage in the AVR. The drive ignal for the witche are hown in table 1. Table1: The drive ignal for the witche Input State Mode S1 S2 S3 S4 1 ON ON OFF ON Vi > 0 2 OFF ON OFF ON 3 OFF ON ON ON 4 OFF ON OFF ON 1 ON ON ON OFF Vi < 0 2 ON OFF ON ON 3 ON OFF ON OFF 4 ON OFF ON OFF During the poitive emi cycle of the input voltage, witche S2 and S4 are et to conduct, and witche S1 and S3 are driven by PWM. During the ISSN: Page 122

3 negative emi-cycle of the input voltage, witche S1 and S3 are et to conduct, and witche S2 and S4 are driven by PWM. If all witche are on, a hort circuit occur, and if all witche are off, voltage pike damage the witche in the AVR. Thu, a witching cycle ha a dead time to avoid current pike of the witche. There are mainly four mode of operation. Mode 1 Thi mode i defined when witche S1 and S2 are turned on, a hown in Figure 3. The inductor current i L conduct through S1 and the diode acro S2 for i L > 0a hown in figure 3.3. The inductor current i L conduct through S2 and the diode acro S1 for i L < 0a hown in figure 3.4.i L conduct through the input and output ide, providing energy to the output. A the v i i higher than the V c, the current paing through the inductor i increaed and energy of the inductor i charged in thi mode. output ide during thi period. During the poitive half cycle of input voltage, the inductor current freewheel through S4 and diode acro S3. Thu, the current paing through the inductor i decreaed and the energy tored in the inductor L i dicharged. Mode 3 Thi mode i complementary to Mode 1. The inductor current i L conduct through S2 and the diode acro S1 for i L >0a hown in Figure 5. I L conduct through the input and output ide, providing energy to the output. A the V i i higher than then V c, the current paing through the inductor i increaed and energy of the inductor i charged in thi mode. Thu current through the inductor i increaed in negative half cycle. Thi mode i the active mode of negative half cycle. Mode 2 Fig.3.Operating Mode 1:I L >0 Thi mode i defined a the Freewheeling mode of poitive emi cycle of input voltage which i hown in fig 4. Mode 4 Fig.5.Operating Mode 3:Vi<0 I L >0 Thi mode i complementary to Mode 2. The inductor current i L conduct through S3 and the diode acro S4 for i L <0a hown in Figure 6.In thi mode the inductor energy i dicharged through the output ide. Fig 4.Operating Mode 2 V i >0; I L <0 Thi mode can be called a freewheeling mode. Thi allow freewheeling action of tored charge in the inductor. The inductor current freewheel through the Fig.6.Operating Mode 4:Vi>0 I L <0 ISSN: Page 123

4 B. Gating Pattern propagation algorithm i ued for layered feed forward network. The input ignal are ending forward and the error are backward. The network receive input from the neuron preent in the input layer, and output of network i given to the output layer. Between thi input and output layer, there will be number of hidden layer. The Back propagation algorithm ue upervied learning. The error i computed in each tep and the ultimate goal of Back propagation i to adjut the weight and eliminate the error. a. Poitive half cycle, b. Negative half cycle Fig.7.Gating Pattern The witche are triggered in accordance with the polarity of the input ine wave. The duty cycle adminitered by the controller make the converter to produce the chopped AC voltage, which in turn i filtered and paed through TRIAC S. Fig.9.Artificial neuron Here the output hould be maintained contant at a range of input voltage. The duty ratio for witch control at different time i given by the ANN. The ignal correponding to the output voltage i given to the input layer, correponding duty ratio for witch control are produced at the output layer of ANN. When defining an ANN, it i explained by uing the term perceptron a the baic unit intead of a neuron. The perceptron can take everal weighted input and ummarize them, if the combined input exceed a threhold, it will activate and ent an output. The larger and complex network lead to complex computation. The bet approach i to arrange neuron in layer. Thee multi layer network ha been proven to have capabilitie beyond thoe of ingle layer Fig.8. Input, Output and Switching waveform for voltage well mode It may be noted that the polarity of the compenation voltage V CO differ in polarity in both ag and well mode. Thi compenation voltage i injected uing the erie tranformer to form the compenate voltage at load terminal of rated magnitude. C. Control trategy The control cheme for the AC chopper i implemented uing Artificial neural network. It i a computational model inpired by human brain in which the ytem ued for control i trained by ANN.An Artificial neural network conit of number of artificial neuron that are arranged in layer. Here the duty ratio correponding to the output voltage i need to be controlled. So optimum angle in each output voltage i trained uing Back propagation algorithm. The Back Fig.10. Back propagation algorithm The imulation wa conducted in MATLAB platform.ann functional block in the MATLAB i ued for training the control ytem of AVR. ISSN: Page 124

5 III. THEORETICAL ANALYSIS A Deign Equation The turn ratio of tranformer depend on input voltage.the turn ratio i baed on percentage of compenation voltage N N 100 Pco n N N P p1 p2 Where the percentage of compenation voltage P co given by P co V i,min V nom co Ripple of inductor current i L; vc (1 D) il Lf Ripple of capacitor voltage il vc (1 D) v c 2 Cf 8LCf 8 Fig.11. Matlab imulation model for Automatic voltage regulator with erie compenation IV. SIMULATION AND RESULTS The automatic voltage regulator uing erie compenation i done by uing matlab. The model conit of an AC to AC converter named a Ac chopper,two TRIAC Which are connected to a three winding injection tranformer.so that it can inject the compenating voltage according to the ag and well.the triac provide a correct polarity to the injection proce.switching pule for ac chopper awell a for the TRIAC are generated.there are two controlling cheme are preent for each.an artificial neural network control cheme i adopted for providing triggering pule for witche in ac chopper.simulation model of Automatic voltage regulator with erie compenation i hown in fig 11 and the ub model for gating pule are hown in fig 12 and fig 13. Fig.12. Matlab imulation ub model of artificial neural network for producing gating pule. Fig.13. Matlab imulation ub model of TRIAC for producing gating pule. ISSN: Page 125

6 input voltage, while the pule of witch S2 are complementary to S1 and S4complementary to S3. The magnitude of the output pule from the microcontroller 5 V. The expanded view of the witching pule are hown. Fig.14. Input voltage and correponding gating pule Fig.15. Output voltage and input voltage Fig 14 how the witching waveform of the chopper witche which are determined by the polarity of the input voltage. In fig 15, the input voltage i hown along with output voltage. The input voltage i egmented and then paed through the output filter to get the voltage required for compenation. Fig 17.Chopper Waveform V. HARDWARE RESULTS The hardware unit i hown in Figure 16.The hardware etup i connected to a wire wound reitive load of 100Ω, and the reult are taken a hown below. Fig 18.output Waveform Fig.16. Hardware Unit The hardware reult for the converter are preented in thi ection.figure 17 indicate the chopper output wave form.figure 18 how the microcontroller derived pule to how the matching of the pule with the theoritical and imulation waveform. It can be een that the wiche S1 and S3 are driven by pule width modulation ignal during the poitive half cycle of the Fig 19.Gating pule for S1 and S3 ISSN: Page 126

7 Fig 19.Gating pule for S2 and S4 on Indutry Application, Vol. 29, No.2, pp ,March [5] Jimichi, T., Fujita, H., Akagi, H. Deign and Experimentation of a Dynamic Voltage Retorer Capable of Significantly Reducing an EnergyStorageElement,IEEE Tranaction on Indutry Application, Vol. 44, No. 3, pp , [6] Torrico-Bacopé, R. P., Oliveira,D. S., Branco,C. G. C., Antune,F. L. M., Cruz,C. M. T., A High Frequency Tranformer Iolation 110 V/220 V Input Voltage UPS. [7] Vincenti, D., Jin, H., Zioga, P.D., Deign and Implementation of a 25-kVA Three-Phae PWM AC Line Conditioner,IEEE Tran. Power Electron., Vol. 9, pp , [8] Min, B.D., Kwon, B.H., Novel PWM Line Conditioner with Fat Output Voltage Control, IEE Proc. Electr. Power Appl., Vol. 145, No. 2, pp , V CONCLUSION Thi paper propoed an AVR baed on erie voltage compenation with an ac chopper. The propoed AVR include a PWM ac chopper and a tranformer for erie voltage compenation. The ac chopper provide direct ac ac power converion. Owing to thi feature, the AVR doe not require the energy torage element, o the ize and cot of the AVR are reduced. The ac chopper compenate for only the deviation from the required voltage, o the rating and tree of the witche have reduced. In the witching pattern, the hort circuit i prevented by uing dead time. Beide, the current path for the inductor current alway exit whatever the current direction, o the commutation problem i olved by witching pattern. Alo, uing the bypa witche, the propoed AVR can compenate not only for the voltage ag but alo for the voltage well of the input voltage. REFERENCES [1] IEEE Recommended Practice for Emergency and Standby Power Sytem for Indutrial and Commercial Application, IEEE Standard (Orange Book), [2] Rahul Rahulanker, Dhirendra Tiwari, Preent Scenario of Voltage Regulator in India Available from: [3] Shindo, T.,Hayahi, T. Current Statu and Preventing Method of Voltage Sag, IEEJ Tran. Power Energy, Vol. 123-B, No. 6, pp ,2003. [4] McGranaghan, M. F., Mueller, D.R., Samotyj, M.J. Voltage Sag in Indutrial Sytem, IEEE Tranaction ISSN: Page 127