Speed Control of Induction Motor Using DTC- SVM & Monitoring Using PLC with Motor Protection

Transcription

1 Internatinal Jurnal f Engineering Research in Electrical and Electrnics Engineering (IJEREEE) Vl 1, Issue 1, February 2015 Speed Cntrl f Inductin Mtr Using DTC- SVM & Mnitring Using PLC with Mtr Prtectin [1] Arun S Dev, [2] Aleena Maria Isaac, [3] Aswathi R, [4] Atheena Francis, [5] Vrinda V R, [6] Mrs. Saritha M [1][2][3][4][5] B.TechSchlars, Cllege Of Engineering Perumn, Kllam. [6] Assistant Prfessr, EEE Dept, Cllege Of Engineering Perumn, Kllam. Abstract: This paper examines the speed cntrl f inductin mtrs and mnitring f its parameters alng with verlad and vercurrent prtectin; prpsing a single unit t execute the mentined functins. The speed cntrl f inductin mtrs is necessary t reach the best efficiency f high speed electric drives besides its rbustness and cheapness. Mnitring presents the result f cmplicated analysis t the user in a simple way by prviding detailed diagnstic infrmatin fr verlad and vercurrent prtectin. Speed cntrl is dne using Direct Trque Cntrl Space Vectr Mdulatin (DTC-SVM) and mnitring using Prgrammable Lgic Cntrl (PLC). This paper prvides a vectrial representatin f speed cntrl algrithm using SVM and a high accuracy mnitring cntrl system by PLC incrprated with verlad and vercurrent prtectin. This prpsed system increases the versatility f existing cnventinal systems. Index Terms DTC, SVM, Vltage vectrs, PLC, H-Bridge. I. INTRODUCTION I. INTRODUCTION With the cntinuus develpments in the industrial sectr, AC mtrs have nw becme a pre-requisite fr mst applicatins. On such AC mtr is the inductin mtr which is widely used nwadays due t is numerus advantages like simple and extremely rugged cnstructin, lw cst, high reliability, minimum maintenance csts, and high efficiency. But the main disadvantage that prmted the use f DC mtrs, despite their demerits in cmparisn with inductin mtrs in the lden days was that, the speed cntrl f inductin mtrs had t be dne at the cst f efficiency. Als, its speed decreases with the increase in lad. Inductin mtrs are cmmnly knwn as cnstant speed mtrs and hence its speed cntrl is in fact inevitably significant. The equatin gverning the speed f an inductin mtr is given by, N s = 120f P Where, Ns is the synchrnus speed f the machine f is the supply frequency and, P is the number f ples. The methds t cntrl speed f inductin mtrs may be mainly gruped as fllws: 1. Cntrl frm statr side: (a)by changing the applied vltage (b)by changing the applied frequency (c)by changing the number f statr ples 2. Cntrl frm rtr side: (a)rtr rhestat cntrl (b)by injecting an emf in the rtr circuit (c)by perating tw mtrs in cascade But these cnventinal methds f speed cntrl are less efficient and quite difficult. The factrs that must be taken int accunt fr chice f new methds f speed cntrl are: 1. Affrdable cst 2. Imprvement in efficiency 3. Ease f implementatin 4. Adaptability t incrprate cmplex algrithms The advancement in the pwer electrnics field increased the availability f thyristrs, pwer transistrs, IGBTs and GTOs which in turn gave better chances f inventing effective speed drives fr inductin mtrs. The speed cntrl algrithm presented in this paper is Direct Trque Cntrl Space Vectr Mdulatin (DTC-SVM) which will be discussed in detail later n. It is nt just necessary t emply speed regulatin in mtrs but als make sure that the system perates efficiently at all times. This can be achieved by real time mnitring f the parameters f the inductin mtr like speed, temperature, mtr current, mtr vltage etc. The mnitring system aids in the preventin f prblems and keeps track f the peratins that are perfrmed by the system. All Rights Reserved 2015 IJERCSE 9

2 Internatinal Jurnal f Engineering Research in Cmputer Science and Engineering (IJERCSE) Vl 2, Issue 1, January 2015 Several applicatins utilize sequential industrial prcesses that depend n use f relays, stepping drum, timers and cntrls. But cnsiderable difficulties are experienced in reprgramming necessitated, due t change in the nature f prductin. Often the whle system has t be redesigned as required. T vercme these prblems, Prgrammable Lgic Cntrl (PLC) System was intrduced. II. DIRECT TORQUE CONTROL (DTC) The trque cntrl f inductin mtr was presented by I. Takahashi and T. Nguchi as Direct Trque Cntrl andprved t be a prmising methd f speed cntrl ffering simple structure and gd dynamic behavir. As discussed earlier, the speed f the inductin mtr can be maintained at a cnstant value as lng as the magnitude and frequency f the vltage driving the inductin mtr is mdified accrdingly. This mdificatin shuld be a functin f the errr between the actual mtr speed and the desired mtr speed. A.Overview f the System Frm fig.1 it can be seen that the main elements f a DTC system are as fllws: (a)flux Estimatr The statr flux varies with the change in applied statr vltage with time. Therefre, the statr flux maybe cntrlled if a prper chice f the statr vltage is made. The estimated statr flux is decreased r increased t be made equal t the desired r reference statr flux. The flux errr which is the difference between the estimated and desired statr flux is fed t the hysteresis cmparatr which in turn prduces the flux errr status. (b)trque Estimatr The instantaneus value f trque is a sinusidal functin f the angle between the statr and rtr fluxes given by the relatin, T. I 2. Csθ Where, T is the trque f the mtr is the statr flux I 2 is the rtr current at standstill and, θ is the angle between statr and rtr fluxes. This angle will change t a great extent, if the statr flux changes quickly, causing a large variatin in the utput trque. Thus, the vltage vectrs f the inverter must be prperly chsen in rder t btain a cnstant speed s that the desired perfrmance is achieved. Similar t the flux cntrl, trque is cntrlled within the tlerance band. (c)vltage Surce Inverter A vltage surce inverter (VSI) cnverts the DC t AC thrugh pwer electrnic devices such as an IGBT. In rder t get the desired statr flux, the technique f space vectr mdulatin is applied. It is this inverter that carries ut the cmmand frm the switching algrithm t vary the statr vltage as required in rder t cntrl the speed The value f statr flux and trque calculated are cmpared with the desired values in the hysteresis cmparatrs. This utput is then fed t a switching table t select an apprpriate vltage vectr at the inverter. The switching table determines the vltage vectr t be applied, which depends n the required changes in statr flux and trque. The selected vltage vectr will be applied t the inductin mtr t run the machine at the required speed. Fig.1. Blck Diagram f DTC Methd B.Main Features f DTC Direct cntrl f flux and trque. Indirect cntrl f statr currents and vltages. Apprximately sinusidal statr fluxes and statr currents. High dynamic perfrmance even at standstill. C.Why DTC Alne Is Nt Sufficient In the basic frm f DTC, nly ne vectr is applied fr a particular sampling perid. This may cause the statr flux and trque t g beynd their tlerance limits which intrduces high trque ripples and distrtins in the statr flux and current. This is the main disadvantage f the cnventinal DTC methd. Anther algrithm that can be used in cnjunctin with the basic DTC system is the Space Vectr Mdulatin, which eliminates the cmmn disadvantages f the cnventinal DTC methd. III. DIRECT TORQUE CONTROL SPACE VECTOR MODULATION (DTC-SVM) The alteratin f the vltage wavefrms t maintain the mtr at cnstant speed is dne by emplying SVM algrithm in a Vltage Surce Inverter (VSI) but the extent f the alteratin is determined by the DTC algrithm. In the vltage surce inverter, cnversin f DC pwer t AC pwer is perfrmed in the switched mde. The actual pwer flw in each mtr phase is cntrlled by the duty cycle f the respective switches. T btain a suitable duty cycle All Rights Reserved 2015 IJERCSE 10

3 Active Vectrs Internatinal Jurnal f Engineering Research in Cmputer Science and Engineering (IJERCSE) Vl 2, Issue 1, January 2015 fr each switch, the technique f Pulse Width Mdulatin (PWM) is used. zer vectrs. Table I. Switching Table in SVM Space Vectrs Switching State ON-State Switches Zer Vectrs V0 [0 0] S4 S2 V3 [1 1] S1 S3 V1 [0 1] S4 S3 V2 [1 0] S1 S2 The vltage surce inverter here is an H-bridge inverter that cnsists f several pwer electrnic switches. The switching pwer devices can be cnstructed using pwer BJTs, GTOs, IGBTs, etc.the chice f switching devices is based n the desired perating pwer level, required switching frequency, and acceptable inverter pwer lsses. The ON and OFF states f the lwer switches are cmplementary t the upper nes. Tw switches n the same leg cannt be clsed r pened at the same time. The switch cmbinatins can be represented as binary cdes that crrespnd t the equivalent switches and the eight inverter states can transfrmed int eight crrespnding space vectrs. Fig.3. Reference Vltage Vectr Synthesis Thus, SVM defines a space vectr table that represents the states (ON r OFF) f the individual switches. In a three phase system, eight vltage vectrs maybe defined, ut f which tw are null vectrs and six are active vectrs. In a single phase system there wuld be nly fur vltage vectrsas shwn in table 1. The space vectr table r the switching table is shwn in table 1. The reference vltage vectr is realized by the sequential switching f active and Fig.2. Schematic Diagram f Vltage Surce Inverter The statr vltage vectrs are selected frm the switching table t minimize the errr signal that cmes frm the DTC sectin. Once the vltage vectrs are selected, the switches f the inverter are switched ON and OFF with the required duty cycle such that the average utputvltage f the inverter is btained by using a weighted average f the three clsest switching states. This way, a sine wave f the right magnitude and frequency t bring the mtr t its nrmal speed is made by a series f DC pulses. The first pulse has a very shrt ON time, fllwed by lnger ON perid until the widest pulse appears at the centre f the sine wave. Cmparisn between SPWM and SVPWM SVPWM has lesser Ttal Harmnic Distrtin (THD) cmpared t SPWM. SVPWM ffers better DC bus utilizatin cmpared t SPWM (by abut 15.4%). SVPWM gives enhanced fundamental utput with better quality. IV. PLC MONITORING SYSTEM Prgrammable Lgic Cntrllers (PLCs) have becme an integral part f the industrial envirnment. APrgrammable Lgic Cntrller(PLC) is a cmpact cmputer based electrnic system that uses digital r analg input/utput mdules t cntrl machines, prcesses, and ther cntrl mdules. A PLC is able t receive (input) and transmit (utput) varius types f electrical and electrnic signals and use them t cntrl and mnitr practically any kind f mechanical and electrical systems. A.Overview f the System Fig.4 shws the blck diagram f a PLC based mnitring system. (a)data Acquisitin System (DAS) The data acquisitin system takes infrmatin signals frm sensr utputs. All the mtr parameters like temperature, speed, vltage and current are physical quantities which are in the frm f analg signals. T be read by the prcessr, these analg signals are changed t its digital value which maybe further prcessed. (b)input and Output Mdules All Rights Reserved 2015 IJERCSE 11

4 Internatinal Jurnal f Engineering Research in Cmputer Science and Engineering (IJERCSE) Vl 2, Issue 1, January 2015 The input and utput mdules are used t interface the input devices (sensrs) with the micrprcessr and the micrprcessr with the utput devices. The input and utput infrmatin is transferred frm the sensrs t the prcessr and frm the prcessr t the utput devices f the PLC system. These als prvide islatin t the PLC frm any fluctuatins in the signal vltages r current. (c)prcessr The prcessr is the heart f the PLC system. It can be a 1 bit prcessr fr lgical peratins r a wrd prcessr t invlve texts, numerical etc. It accepts input data frm the Data Acquisitin System. Then, executes the user prgram n the data and sends the apprpriate utput cmmands t the cntrl devices as required. Fig.4. Blck Diagram f PLC Mnitring System (d)keybard and Display Keybard and display allws the user t set values, t read current values f prcessed variables and issue cmmands. (e)digital t Analg Cnverter In applicatins where a PLC system is t drive an analg circuit, it becmes necessary t cnvert the prcessed digital values int cntinuus signals. This functin is carried uthere PLC takes input instructins in the frm f ladder diagram r cmputer sftware instructins. Ladder lgic is a prgramming language that represents a prgram by a graphical diagram and is widely used t prgram PLCs, where sequential cntrl f a prcess r manufacturing peratin is required. The name is based n the bservatin that prgrams in this language resemble ladders, with tw vertical rails and a series f hrizntal rungs between them. A "rung" in the ladder represents a rule. When implemented in PLC, the rules execute sequentially by sftware in a cntinuus lp. The fllwing are the majr advantages f using PLCs ver cnventinal mnitring systems: Fig.5. Blck Diagram f Mtr Prtectin System V. MOTOR PROTECTION Mtr prtectin safeguards the mtr, the supply system and persnnel frm varius perating cnditins f the driven lad, the supply system r the mtr itself. Mtr prtectin categries in this paper include: Overcurrent Prtectin Overlad Prtectin Overcurrent prtectin interrupts the electrical circuit t the mtr upn excessive current demand n the supply system frm either shrt circuits r grund faults. It is required t prtect the mtr branch circuit cnductrs and cntrl equipment frm these large currents. Overlad prtectin is installed in the mtr circuit t prtect the mtr frm damage frm mechanical verlad cnditins when it is perating. The effect f an verlad is an excessive rise in temperature in the mtr windings due t current higher than full lad current. The larger the verlad, the mre quickly the temperature rises t a pint that damages the insulatin and lubricatin f the mtr. The blck diagram f the mtr prtectin system is as shwn in fig.5. After the single phase AC supply is steeped dwn using a transfrmer, it is cnverted int DC using a rectifier and prevented frm any variatins using a vltage regulatr. A current sensr keeps track f the mtr current, which when ges beynd the limit, makes the micrcntrller t trigger ff the relay driver. At the time f verlad r vercurrent, the respective relay discnnects the mtr frm supply and thus prtectin is ensured. After the situatin is taken care f, the mtr regains its state f peratin. Flexibility Ease f trubleshting Space efficiency Lw cst Testing Visual peratin CONCLUSION In this paper, a mst cnvenient industrial cntrl scheme fr vltage surce inverter-fed inductin mtr drives was presented with reference t the cnventinal DTC methd. The DTC-SVM has a simple structure and it can be analyzed and implemented in a simple way. This is a All Rights Reserved 2015 IJERCSE 12

5 Internatinal Jurnal f Engineering Research in Cmputer Science and Engineering (IJERCSE) Vl 2, Issue 1, January 2015 very imprtant feature f DTC-SVM. This methd wuld prvide peratin in a wide pwer range. Industrial system designers f PLCs cntinue t push fr higher perfrmance and functinality relying n its prmising features. PLC mnitring wuld ensure a highly accurate mnitring system. A simplified peratinal blck diagram f the PLC based mnitring system was discussed, pinting ut the advantages as well. Als, the need fr mtr prtectin and the methd t vercme the cnditins f dwntimes was examined. Thus this paper prpses a reliable, all in ne mtr cnditining system using micrcntrllers that is capable f replacing cmplicated circuits by a single, efficient unit. Jurnal Of Systems Applicatins, Engineering & Develpment,Issue 3, Vlume 2, REFERENCES [1] CristianLasc u, In Bldea,, and FredeBlaabjerg, A Mdified Direct Trque Cntrl fr Inductin Mtr Sensrless Drive, IEEE Transactins On Industry Applicatins, VOL. 36, NO. 1, January/February [2] Hsni Hiba, Hmidet Ali and HasnauiOthmen, DTC-SVM Cntrl fr Three Phase Inductin Mtrs. [3] K. Vinth Kumar, Prawin Angel Michael, Jseph P. Jhn and Dr. S. Suresh Kumar, Simulatin And Cmparisn Of SPWM And SVPWM Cntrl Fr Three Phase Inverter, VOL. 5, NO. 7, ARPN Jurnal f Engineering and Applied Sciences, July [4] Drin O. Neacsu, Space Vectr Mdulatin An Intrductin, IECON'01: The 27th Annual Cnference f the IEEE Industrial Electrnics Sciety. MªÁngeles Martín Prats, L. G. Franquel,, R. Prtill, J. I. León, E. Galván, and J. M. [5] Carrasc, A 3-D Space Vectr Mdulatin Generalized Algrithm fr Multilevel Cnverters, IEEE Pwer Electrnics Letters, VOL. 1, NO. 4, December [6] Alnasir. Z.A, Almarhn. A.H, Design f Direct Trque Cntrller f Inductin Mtr (DTC), Alnasir, Z.A. et al. / Internatinal Jurnal f Engineering and Technlgy (IJET). [7] Maria G. Iannides, Design and Implementatin f PLC-Based Mnitring Cntrl System fr Inductin Mtr, IEEE Transactins n Energy Cnversin, VOL. 19, NO. 3, September [8] YasarBirbir, H.SelcukNgay, Design and Implementatin f PLC- Based Mnitring Cntrl System fr Three-Phase Inductin Mtrs Fed by PWM Inverter, Internatinal All Rights Reserved 2015 IJERCSE 13