16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER,

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1 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 86 Steady State Assessment o -φ SEIG with Noel LVARC and Alleiation o Harmonics with Shunt Actie Power Filter E.Vargil Kumar, P.V.R.L.Narasimham, A.V.R.S. Sarma, Department o EEE, Gudlaalleru Engineering College, Gudlaalleru, A.P. 6, INDIA Department o Electrical Engineering, Uniersity College o Engg., Osmania Uniersity, Hyderabad, INDIA Abstract Sel Excited Induction Generator (SEIG) is identiied as isolated power source, whose terminal oltage and requency are controlled by arying speed, excitation capacitance or load impedance. Since load changes rom time to time, the output parameters mostly are controlled by either speed or by arying excitation capacitance. To reduce the complexity in assessing, the speed o a primemoer driing the induction generator is kept constant. For proper oltage built-up suitable alue o excitation capacitance is necessary. This paper put orward a method or calculating the minimum excitation capacitance using the equialent circuit approach. Change in load impedance orces alteration in the alue o excitation capacitance which is diicult to be implemented. A noel leading VAR controller (LVARC) consisting o uncontrolled conerter, inerter and a series LCR resonance circuit, is introduced in between the load and source to take care o reactie power disparity thereby eeding the reactie power to the inductie loads and absorbing reactie power or capacitie loads, which also acts as a Load Balancer. The LVARC happened to be an open loop; a closed loop operation o SEIG was deeloped using Shunt Actie Power Filter (SAF) along with it a Hysteresis Current Controller (HCC) is used or generating appropriate iring angle or inerter circuit. MATLAB based simulation and experimental results are presented and compared or VAR controller operated with linear loads. Simulation study is made or Non-Linear loads with respect to SAF s. The simulation results show the eectieness o Voltage built-up and harmonic reduction in Wind based Power Generation. Key words: SEIG, Leading VAR Controller (LVARC), Shunt Actie Power Filter (SAF), Hysteresis current controller (HCC), Harmonics. I INTRODUCTION The depleting Energy resources had made the present society to rethink about the Power generation procedures and paed a path or utilizing Non-renewable energy resources []. One such resource is Wind Energy, where the generated output power aries as the cube o wind speed shown in Fig.. P C p A () Where is the air density, C p is the power coeicient and A is the rotor swept area and is the wind speed Fig. Speed and Power Characteristic Basically the wind generation schemes inole induction generators, not only o its usage in large numbers but also due to aried modes o operation both under steady and dynamic states. Increased use o Power Electronic controllers with such machines makes appropriate modeling and parameter identiication crucial, or both working control strategies and perormance predictions. Induction Generator (IG) is not able to start on its own and sustain electrical oscillations. To sustain the electrical oscillations, reactie magnetization current should be completely compensated by appropriate reactie current [, ]. It is well known that a suitable capacitor is compulsory to be connected at the output terminals o induction machine while working as generator, which raises a problem in designing the alue o capacitor. This paper coners a simple neertheless open methodical procedure to perceie the steady state condition using the operational equialent circuit o the machine [, 6]. SEIG has to supply both the linear and non-linear loads. As a result, the reactie power oscillation has to take place between the source and the load, which enorces the VAR control, enisaging the usage o power electronic switching deices and passie energystorage-circuit elements inductors or capacitors. These elements can be used or controlling current harmonics at the low or medium-oltage distribution leels or or controlling reactie power, and oltage [7-]. In a capacitance excited SEIG, the terminal oltage and its requency are dependent on exciting capacitance, speed and load impedance. The required exciting capacitance calculation or load impedance is estimated through a MATLAB program, by keeping the prime moer speed as constant.

2 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 87 II THEORY OF PROPOSED VAR CONTROLLER With the designed capacitance, and constant primemoer speed the terminal oltage o IG reaches to required oltage. The current lowing in the loop PQRS can be written as I. () loop Z eq Fig. Equialent circuit o SEIG with proposed controller. Fig. Proposed VAR controller with SEIG The controller consists o three parts the ront end uncontrolled rectiier, the SPWM inerter and the LCR circuit shown in Fig.. The VAR controller circuit is used in conjunction with the ixed minimum capacitance, which is permanently connected to the machine terminals. With increase in load the capacitance required to sustain the terminal oltage increases, this increase in the reactie power requirement. Change in the load current will insist to change AC/DC/AC resonance circuit current in opposite direction. The total generator current should be maintained at the rated current. At any instant o time AC/DC/AC conerter is operated to balance the load current to maintain the generator current constant. The ariable requency operation o series resonance LCR circuit eectiely takes care o VAR ariation in load, which is supplied by the VAR controller by operating the inerter either below or aboe the resonant requency. The operation o SEIG along with series LCR circuit can be renowned as a Load Balancer Because o proposed VAR controller, the power actor ariation o SEIG is minimized. The mathematical approach in relation to aboe discussion is gien in the commencing section. III MODELING OF PROPOSED VAR CONTROLLER The adantage in this scheme is that only, ixed minimum capacitance is needed to be connected to the SEIG, and also this scheme proides smooth terminal oltage regulation. The per phase equialent circuit gien in Fig., is taken to derie the expression or terminal capacitance. Here core losses are being ignored. For the minimum capacitance requirement, the machine must operate at the threshold o saturation. All the parameters except X m magnetizing reactance are assumed constant. The loop impedance Z eq o SEIG with proposed controller is gien by R l R sh jxcsh jxct Rs Rr jx ll// jxlsh // jxs jxr //jx m () On soling and combining similar terms in eq. a complex equation in requency is obtained as X ct ( j A A ja A ) A j A (A X ct A ) j (A X ct A ) A Z 9 X ct eq B jb ()EjE + E j()e () Under steady state sel excitation the loop current is not be zero, I loop, so equialent impedance is assumed zero. Z eq [6]. Or both the real and imaginary parts o Z eq are zeros on urther rearranging the terms o eq. gets conerted to an equation in X ct. X [AN]* [ED ] [B jb ][AD X AD ] * ED ct ct [ ( )E je ][AD X AD ] Z ct eq [AD X AD ](ED ) ct () From eq. separating the real and imaginary parts o the terminal capacitance X ct are obtained as 7 M 6 M M M M M X 6 ctreal (6) M 7 M 8 M 9 M M X ctimag 6 I I I I I (7) I 6 I 7 I 8 I 9 Since a alue or C t which satisies both eq.6 and eq.7 is obtained by equating both o them, resulting in a th Order equation in.

3 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 88 X ctl J J J J J J6 J7 J8 J9 (8) Since the solution o the eq.8 is tedious and lengthy a MATLAB m-ile program was written and soled. By conducting suitable tests, and using the basic equations o induction machine the proposed VAR controller is designed, and open loop operation is being assessed or linear loads and nonlinear loads, by eriying the theoretical and experimental results and are presented in section VIII. Operation o LVARC happened to an open loop system is eectie with respect to linear, but coming to nonlinear loads the harmonic current are not properly taken care because o presence o ast acting nonlinear switching deices (results o Fig., Fig. 8 can be compared). So a closed loop system based on shunt actie power ilter is designed, the discussion ollows. IV CLOSED LOOP SAF DESIGN FOR SEIG When SEIG supplies a non-linear load, the load draws a undamental component o current and harmonic current rom the generation systems, which are to be properly controlled. The shunt APF can compensate the harmonic current by continuously tracking the changes in harmonic content. APF s consists o a oltage ed conerter with a PWM current controller and an actie ilter controller that realizes an almost instantaneous control algorithm shown in Fig.. V MATHEMATICAL MODELING OF SAF-SEIG The source oltages in all the three phases are combined with currents and by using Clarke Transormation are conerted to V α,v β, and I α,i β respectiely. These space ectors are easily transormed into a three coordinates as ollows: α β / / a b c ia iα / / i i b β ic The conentional instantaneous power on the three phase circuit can be deined as ollows p.i.i () Instantaneous reactie power is deined by q.i.i () The conentional instantaneous power, p and the Instantaneous imaginary power q, are expressed by p i q i () Ater determining the actie and reactie power signals, they are passed through ilter, so that the ariation is conerted into the desired range by selecting the ilter order. Later they are conerted back to three phase reerence currents and made aailable or comparison with actual currents. Both are ed to hysteresis current controller, which generates the iring angle corresponding to the dierence o the two signals and are ed to Inerter shown in Fig. 6. (9) Fig. Block Diagram o APF The SAF works in a closed loop manner, continuously sensing the load current and calculating the instantaneous alues o the compensating current reerence I c * or the PWM conerter. In an ideal case, the PWM conerter may be considered as a linear power ampliier, where the compensating current I c tracks correctly its reerence I c *. The PWM conerter should hae high switching requency in order to reproduce accurately the compensating currents. p-q theory orms a ery eicient basis or designing actie ilter controllers. Fig. 6 A Three phase, Three-wire, Current Compensation SAF The inerter is enabled to act as a ilter and the use o inductie and capacitie elements can be anished out, thereby reducing the cost inoled on them (as in case o

4 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 89 LVARC). And this ilter design promises the closed loop control and proides better eicient harmonic elimination, which is alidated by simulation results. Hysteresis current control method is used or producing compensating currents. Fig.7 shows the switching scheme o the IGBT s. Now assume that the reerence compensating current i Ca * is positie. A Switch T r, is turned on when i Ca is equal to the lower limit o i Ca *. Fig. 8 Simulation o SEIG with proposed VAR controller Fig. 7 Hysteresis Current controller and its waeorm On the contrary, T r is turned o when i Ca is equal to the upper limit o i Ca *. The switching operation o the power Switch automatically orces the compensating currents i Ca, i Cb, and i Cc to ollow their respectie reerence compensating currents i Ca *, i Cb *, and i Cc *. Thereore the power circuit can be considered as a kind o three phase current ampliier. VI SIMULATION METHODOLOGY The required capacitance alue (C =. µfd) o SEIG has been calculated rom the steady state equialent circuit, using MATLAB m-ile program by soling a th order equation in terminal capacitance X ct, and simulation o SEIG with proposed VAR controller and the closed loop operation with SAF is being done using SimPowerSystems block-set o MATLAB/Simulink. The Simulink models o SEIG with LVARC and SAF is shown in Fig.8, Fig.9 and results o LVARC are presented in Fig. to Fig. or linear loads and Fig. to Fig. or Nonlinear loads. SEIG with LVARC as a Load Balancer in Fig., The results o SAF with Non-linear loads are presented in Fig. 9 or Voltage built-up;; and Pulse Generation using HCC in Fig.. VII RESULTS A -φ, KVA, V, 7A alternator is connected across R-L load, and a drop o about V is calculated to be controlled. For conenience the oltage waeorm in the graphs below is scaled by, in order to get a better iew o oltages and currents. Source Controller Fig. 9 Simulation o SEIG with Actie Power Filter and Hysteresis Current Controller with non-linear Load Load Fig. Lagging VAR Control o proposed Controller

5 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 9 Source Controller Load Source C ontroller Load O u tp u t Fig. In-phase VAR Control o proposed Controller simulation Fig. Leading VAR Control o proposed Controller Source Voltage o Phase 'a' o LVARC Current in phase 'a' o LVARC P-Source P-Load P -C o n tro lle r Fig. Stator Voltages currents in phase A o LVARC with non linear loads Time Time Fig. SEIG with LVARC as a Load Balancer VIII POWER QUALITY ANALYZER RESULT The obsered phasors are obtained using the FLUKE power quality analyzer and are gien in Fig.6 to Fig.8. The ariable impedance eect o the LCR circuit with the change in inerter output requency was obsered. Q-Source Q-Load Q-Controller Controller Load Fig. Leading VAR Control o proposed Controller with Nonlinear Loads Fig. 6 UPF eect at requencies equal to resonant requency

6 6th NATIONAL POWER SYSTEMS CONFERENCE, th-7th DECEMBER, 9 Current in 'A' phase Distoted Current Error Current Hysteresis Puleses Fig. 7 Lagging eect at requencies greater than resonant requency Fig. 8 Leading eect at requencies greater than resonant requency Fig. 9 Voltage built-up in all the three phases o SEIG-SAF Fig. Waeorms o Reerence currents, Controller Current, Error current, and Hysteresis pulse Generation IX CONCLUSION It can be accomplished that the minimum excitation capacitance calculated rom the design equations was ound to be.µf, which aided proper oltage built-up in an SEIG. The noel LVARC introduced between SEIG and load has taken care o the reactie power disparity by proiding a reactie power ranging rom % to % o the rated capacity on an aerage, eeding linear and non-linear loads. An improement in the oltage magnitude and power actor is possible by changing the operating requency o the inerter in multiples o Hz, and the by arying LCR component ratings aboe and below mh and 9 µf. SEIG along with LVARC also acts as an eectie Load Balancer at leading and lagging VAR s. The shunt actie power ilter with the aid o hysteresis current controller had taken care o the uneen distortion in current thereby smooth oltage characteristic at the output is achieed in comparison with LVARC technique. The Shunt actie power ilter eliminated the harmonics by enabling the inerter to act as a ilter, ading away the usage o inductors and capacitors, reducing the cost inoled on them. The simulation and experimental results proes the eectieness o VAR controller, and Shunt Actie Power Filter in Wind based Power System. APPENDIX By perorming arious tests on a φ squirrel cage induction machine possessing a rating o.7kw, V, Hz the stator resistance and inductances were ound to be.7, and. p.u., and Rotor. and. p.u., and magnetizing reactance o.9 p.u. is preerred. REFERENCES. Iulian Munteanu Antoneta Iuliana Bratcu, Nicolaos-Antonio Cutululis Emil Ceang Optimal control o Wind Energy Systems, Springer Edn., 7.. P.Vas, Electrical Machines and Dries A Space Vector Approach, Oxord: Clarendon Press, R.Rabinoici, Autonomous excitation o induction generators, IEEE transactions on Mag.,., pp , May G.R.Slemon, Electric Machines and Dries, Reading, MA: Addison-Wesley Publishing Company, Inc., 99.. Kh. Al Jabari and Alolah Limits on the perormance o the Three Phase Sel-excited Induction Generators, IEEE Transaction on energy Conersion, ol.,, No., Page -6,June Kh. Al Jabari and Alolah, Capacitance requirement or Selexcited Induction Generator, IEE Proceeding, Vol.7, pt. C, No., Page -9,May S. Singaraelu, S. Velusami, Capacitie VAR requirements or wind drien sel-excited induction generators, Energy Conersion and Management 8 (7) Hiroumi Akagi, Yoshihira Kanazawa, and Akira Nabae.: Instantaneous Reactie Power Compensators Comprising Switching Deices without Energy Storage Components, IEEE Transactions on Industry Applications, Vol. IA-, No., June Jayant K. Chatterjee, B.Venkatsa Perumal, and Naeen Reddy Gopu Analysis o Operation o a Sel Excited Induction Generator with Generalized Impedance Controller, IEEE Trans. Power App. Sys., ol. No., pp. 7-, 6.. Bhim Singh, S.S. Murthy, and Sushma Gupta, Analysis and Design o Electronic Load Controller or Sel-Excited Induction Generators, IEEE Trans. On Energy Conersioon, Vol., No., Page 8-9, March 6.