ISSN Vol.07,Issue.04, June-2015, Pages:

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1 ISSN Vol.07,Issue.04, June-2015, Pages: Closed Loop Control of Induction Motor by using Sparse AC-Link Buck Boost Inverter M. SURESH 1, S. V. SIVANAGARAJU 2 1 PG Scholar, Dept of EEE (PE & ED), SVCET, Chittoor, Andhrapradesh, India. 2 Associate Professor, Dept of EEE, SVCET, Chittoor, Andhrapradesh, India. Abstract: This paper proposes a modified configuration for the dc ac and ac-dc power conversion, which reduces the number of switches without changing the principles of operation. This converter which is named sparse ac-link buck boost inverter reduces the number of switches from 20 to 18. Regardless of reducing the number of switches, the partial resonant time, during which no power is transferred, is as short as the original configuration. An important feature of this inverter that it can be fabricated by IGBT modules, which are more compact and more cost effective compared to the discrete devices. The operation of this configuration, and compares the efficiency and failure rate, and the current rating of the switches in the proposed and original inverters. It is revealed that the failure rates of the sparse configuration are lower than the original configuration. Therefore, they have longer lifetime. The bidirectional and unidirectional three-phase inverter configurations for battery utility and photovoltaic applications were presented. The efficiency of sparse configuration is slightly lower than that of the original configuration. However, by using reverse blocking IGBTs in the sparse configuration, the efficiency of the proposed inverter will be improved significantly. When we use this inverter to control of induction machine without using sensor control. Here we taken voltage and current of stator winding, the controller are FUZZY LOGIC and MRAS controllers. A detailed simulation comparison between the traditional designs is carried out closed loop control methods of operation when a vector control drive is working under load and no load separately. The performance of the proposed system is verified by simulation using MATLAB / Simulink experiment. unidirectional three-phase inverter configurations for battery utility and photovoltaic applications were presented and thoroughly studied.the soft-switching ac-link universal power converter has several ad-vantages over the other types of converters. This converter is an extension of the dc dc buck boost converter. Therefore, unlike matrix converters and three-phase voltage source inverters; it is capable of both stepping up and stepping down the voltage. Fig.1. Conventional bidirectional inverter (two-stage). Fig.2. AC-link buck boost inverter introduced. Keywords: Bidirectional, Buck Boost Converter, Inverter, Soft-Switching, Model Reference Adaptive System, Fuzzy Logic Controller. I. INTRODUCTION Soft-switching ac-link universal power converter also called partial resonant ac-link converter. Being universal, the input and output of this converter may be dc, ac, singlephase, or multiphase. Therefore, it can appear as dc dc, dc ac, ac dc, or ac ac configurations. In the ac ac and ac dc configurations were studied in detail. The bidirectional and 2015 IJATIR. All rights reserved. It can also change the frequency in a wide range. By adding the complementary switches and by modifying the switching scheme, the link inductor, which is the main energy storage element in this converter, can have alternating current instead of the direct current. This approach improves the performance of the converter and significantly increases the utilization of the link inductor. In this converter, the frequency of the link current and voltage is only limited by the characteristics of the switches and the sampling time of the microcontroller. Therefore, the frequency can be very high, which results in compact link and filter components. By placing a small capacitor in

2 parallel with the link inductor, the converter benefits from the soft switching. Therefore, the LC pair has small reactive ratings; and there is low power dissipation in the link. The alternating link current and voltage of the soft-switching aclink universal. Fig.3. proposed inverter. In this converter, unlike the resonant converters introduced in the link resonates just for a short time in each link cycle. power converter, eliminates the need for the dc electrolytic capacitors at the link. Electrolytic capacitors are integral parts of the conventional dc-link ac ac converters and the two-stage bidirectional inverters, which are formed by bidirectional dc dc converters and voltage source inverters to pro-vide the possibility of regulating the dc-side current, as shown in Fig. 1. The main problem with the electrolytic capacitor is its high-failure rate, especially at high temperatures. Therefore converters containing electrolytic capacitors are expected to have shorter lifetime. Another advantage of the ac-link converters is the possibility of having galvanic isolation with a single-phase high-frequency transformer added to the link. In a threephase voltage source inverter, galvanic isolation is provided by a bulky three-phase low-frequency transformer. Considering the aforementioned merits, the soft-switching ac-link universal power converter is expected to be more compact and more reliable than conventional converters. B DIVYA, K BALAJI NANDA KUMAR REDDY, V RADHIKA The schematic of the dc ac configuration, called ac-link buck boost inverter in this paper, is represented in Fig. 2. Although this inverter is still a new technology, it has a very promising future. Despite all the advantages of the ac-link buck boost inverter, it requires more switches compared to the other inverters, which makes the control process more complicated. In this paper, a modified configuration that has all the advantages of the ac-link buck boost inverter but requires fewer switches is proposed. Despite reducing the number of switches, the principles of the operation in the proposed converter, which is named the sparse ac-link buck boost Inverter, is the same as the original converter. This inverter, shown in Fig. 3, offers higher reliability compared to the ac-link buck boost inverter. Another important feature of the sparse configuration is that due to using unidirectional switches, it can be fabricated by switch modules. These modules are more compact and more costeffective, compared to the discrete devices. Hence, the sparse configuration is expected to be less expensive, less complicated, and more compact compared to the ac-link buck boost inverter. Despite using unidirectional switches, the sparse ac-link buck boost inverter can support bidirectional flow of power. As seen in Fig. 3 this method of switch reduction has not led to any switch count reduction at the dc side. Therefore, we may keep the dc side as the original converter, as shown in Fig. 4. As seen in Figs. 3 and 4, there is a diode in series with each IGBT. Since conventional IGBTs cannot block the reverse voltage, a diode is connected in series with each IGBT. In case reverse-blocking IGBTs are used, the sparse configuration can be simplified further, as represented in Fig. 5.In the next part, the principles of the operation in the sparse ac-link buck boost inverter will be studied in detail. Section III compares the proposed inverter with the ac-link buck boost inverter, to show the advantages and the disadvantages of this configuration. Simulation and experimental results will be presented in Section IV, and Section V summarizes the paper. II. PROPOSED CONFIGURATION AND PRINCIPLES OF OPERATION As mentioned earlier, in the ac-link buck boost inverter, shown in Fig. 2, the complementary switches are added to pro-vide the link with alternating current. In the sparse configuration, the complementary switches are removed; however, the link cur-rent is still alternating. Fig.3 represents this configuration, and as seen in this figure, the number of switches is reduced from 20 to 18. The input and Fig. 4. Proposed inverter when keeping the dc side similar to the ac-link buck boost inverter. output switch bridges contain unidirectional switches, and, in order to provide the link with alternating current, the intermediate cross-over switching circuits have been added to both the input side and the output side. Switches Si7,Si8, Si9, and Si10, which form the input-side intermediate crossover switching circuit, and switches So7, So8, So9, and So10, which form the output-side intermediate cross-over switching circuit, permit the partially resonant circuit to operate bidirectionally, which affords the advantages discussed earlier. The performance of the proposed configurations is similar to that of the ac-link buck boost

3 Closed Loop Control of Induction Motor by using Sparse AC-Link Buck Boost Inverter inverter. The link current and voltage are exactly the same as that of the original configuration, and the partial resonance time is as short as in the original converter. As mentioned earlier the method used for reducing the number of switches does not lead to any switch count reduction at the dc side. In order to improve the efficiency, the dc side may be kept similar to the original configuration. Therefore, in this paper, we will mainly focus on the configuration shown in Fig. 4. during which no power is transferred and the link resonates. Before the start of mode 1, the incoming switches, which are supposed to conduct during mode 1, are turned ON (S3 and S8 in Figs. 6 and 7); however they do not conduct immediately, because they are reverse-biased. Once the link voltage, which is resonating before mode 1, becomes equal to the voltage across the dc side, proper switches (S3 and S8) are forward biased initiating mode 1. This implies that the turn ON of the switches occurs at zero voltage as the switches transition from reverse to forward bias. Therefore, the link is connected to the dc source via switches which charge it in the positive direction. The link charges until the dc-side current averaged over a cycle time, meets its reference value. Input-side switches are then turned OFF. Fig.5. Proposed inverter with reverse-blocking IGBTs. Before studying the principles of the operation of the proposed configuration, a brief overview of the principles of operation in the ac-link buck boost inverter is presented. Detailed information may be found in [2] [6]. Both converters transfer power entirely through the link inductor, which is charged through the input phases and then discharged into the output phases. The frequency of charge/discharge is called the link frequency and is typically much higher than the output line frequency. Between each charging and discharging there is a resonating mode during which none of the switches conduct, and the LC link resonates to facilitate the soft-switching of the switches. In the ac-link buck boost inverter, charging and discharging of the link in a reverse direction is feasible through complimentary switches located at each leg, which leads to an alternating current in the link. In this inverter, there are three output phases and one charged link to be discharged into these phases. In order to have more control on the currents and minimized harmonics, the link discharging mode is split into two modes. Although there are three phase-pairs in a three-phase system, considering the polarity of the current in each phase, only two of these phase-pairs can provide a path for the current when connected to the link. Again between each charging or discharging mode there is a resonating mode, which facilitates zero voltage turn ON of the switches and their soft turn OFF. The basic operating modes of the ac-link buck boost inverter and the relevant waveforms are represented in Figs. 6 and 7, respectively. Each link cycle is divided into 12 modes, with 6 power transfer modes and 6 partial resonant modes taking place alternately. The link is energized through the input phase pairs during modes 1 and 7 and is deenergized to the output phase pairs during modes 3, 5, 9, and 11. Modes 2, 4, 6, 8, 10, and 12 are resonating modes Fig.6. Behavior of the ac-link buck boost inverter in different modes of operation: (a) Mode 1. (b) Mode 2, 4, and 6. (c) Mode 3. (d) Mode 5. During mode 2 none of the switches conduct. The link resonates and the link voltage decreases until it reaches zero. At this point, the incoming switches that are supposed to conduct during modes 5 and 7, are turned ON (S13, S14,

4 and S18 in Figs 6 and 7); however being reverse-biased they do not conduct immediately. Once the link voltage reaches VAC O (assuming VAC O is lower than VABO ) switches S14 and S18 become forward biased and they start to conduct initiating mode 3. During mode 3, the link is discharged into the chosen phase pair until the current of phase C at the output-side averaged over a cycle meets its reference. At this point S14 will be turned OFF initiating another resonating mode. During mode 4, the link is allowed to swing to the voltage of the other output phase pair chosen during Mode 2. For the case shown in Figs. 6 and 7, it swings from VC AO to VBAO. Once the link voltage becomes equal to the voltage across the output phase pair AB, switches S13 and S18 become forwardbiased, initiating mode 5. During mode 5, the link discharges to the selected output phase pair until there is just sufficient energy remained in the link to swing to a predetermined voltage (V max ), which is slightly higher than the maximum input and output line-to-line voltages. At the end of mode 5, all the switches are turned OFF allowing the link to resonate during mode 6. During mode 6, the link voltage swings to V max, and then its absolute value starts to decrease. Modes 7 through 12 are similar to modes 1 through 6, except that the link charges and discharges in the reverse direction. For this, the complimentary switch on each leg is switched when compared to the ones switched during modes 1 through 6. B DIVYA, K BALAJI NANDA KUMAR REDDY, V RADHIKA are the same as those of the ac-link buck boost inverter, shown in Fig. 7. Modes 1 6 in the modified configuration are similar to those of the original converter, except other than turning on the proper switches on the output switch bridges; So7 and So8, on the output intermediate cross-over switching circuit, should be turned ON during modes 3 5. Although the output switch bridge contains unidirectional switches, So7 So10 (referenced above as intermediate cross-over switching circuit) enable the link to conduct both positive and negative currents. Therefore, during modes 7 12, the same output switches as modes 1 6 will be conducting; however, instead of So7 and So8, switches So9 and So10 conduct during modes Fig.7. Link current, link voltage, and unfiltered input and output currents in the ac-link buck boost inverter. For the ac dc mode of operation, the link is charged from the output phase pairs during modes 1 and 3, and then it is discharged into the dc side during mode 5.Fig. 8 represents the behavior of the sparse ac-link buck boost inverter. The current/voltage waveforms at different modes Fig. 8.Behavior of the sparse ac-link buck boost inverter during different modes of operation: (a) Mode1. (b) Mode 2, Mode 4, and Mode 6. (c) Mode 3.(d) Mode 5, (e) Mode11.

5 Closed Loop Control of Induction Motor by using Sparse AC-Link Buck Boost Inverter Fig.9. Sparse ac-link buck boost inverter with galvanic isolation. sparse configuration should with-stand is twice the average current passing through the ac-side switches in the ac-link buck boost inverter. Because the con-ducting switches are involved during both first and second half cycles of the link. The average current that the switches/diodes located at the output intermediate cross-over switching circuit in the sparse configuration tolerate is three times the current passing through the ac-side switches in the ac-link buck boost inverter. These switches conduct either during the first half cycle or the second half cycle of the link. When they conduct, the maximum current of the three phases passes through these switches. The average current of the ac-side switches in the ac-link buck boost inverter configuration is By adding a single-phase, high-frequency transformer to the link, the sparse ac-link buck boost inverter can provide galvanic isolation, as shown in Fig. 9. In practice, due to leakage inductance of the transformer, the link capacitor needs to be split into two capacitors placed at the primary and the secondary of the transformer. Otherwise at the end of the charging or discharging mode, depending on which side the capacitor is located at, the current of the leakage inductance will have an instantaneous change, which results in voltage spike. III. COMPARISON OF THE AC-LINK BUCK BOOST INVERTER AND THE SPARSE AC-LINK BUCK BOOST INVERTER A detailed design procedure of the ac-link buck boost inverter may be found in [5]. Designing the link parameters is the same in the sparse and original ac-link buck boost inverter. However, due to the unequal number of switches at the ac side, and consequently different switch conduction periods in these converters, the ac-side switch ratings will be different. The link current is the same in both converters. Therefore, the peak current each switch should tolerate is the same, whereas, the average currents passing through the switches in the original and the sparse ac-link buck boost inverters are different. The peak current of the switches, which is equal to the link peak current, is a function of the average input current and the output peak current as follows [5]: (1) In the above equation, I dc and I o,peak are the average dc side current and the peak of the filtered ac side current, respectively. The average current of the dc-side switches, I si, in both ac-link converters is half the average dc-side current (2) Four of the dc-side switches conduct only during the dc ac mode of operation and the other four switches conduct during the ac dc mode of operation. In the conventional dclink con-figuration, shown in Fig. 1, the average current of the dc-side switch is twice that of the sparse and regular aclink buck boost inverters. The average current that the switches/diodes located on the output switch bridge in the (3) where I so and I o,avg are the average current of the ac-side switches and the average rectified output current, respectively. The average current of the switches/diodes located on the out-put switch bridge (I So sw b sparse ) and the average current of the switches/diodes located on the output intermediate cross-over switching circuit as follows as (5) As shown, the average current of the switches in the sparse configuration is higher than the average current of the switches in the original configuration. However, in both converters, the peak current of the switches is usually much higher than their average currents. Consequently, the peak current may become the limiting factor in choosing the switches. Therefore, the higher average current of the switches in the sparse configuration may not play any role in choosing high current rating and consequently, more expensive switches. In the voltage source inverter, the acside currents are continuous; whereas in the ac-link buck boost converters (both the original and sparse configurations) the ac-side currents are discontinuous, which result in higher peak currents. In order to show the advantages and disadvantages of the sparse configuration its failure rates and efficiency will be com-pared with those of the ac-link buck boost inverter. IV. CONTROLLERS A. Design of the Fuzzy Logic Controller Various applications of FL have shown a fast growth in the past few years. Also FL has become popular in the field of industrial control applications for solving control, estimation, and optimization problems. In this section, FL is proposed to replace the PI controller used for error minimization. FL technique has been applied to solve optimization problems for induction motor drives. It has been proposed to replace PI controllers in different error minimization applications. Therefore, FL can replace the conventional PI controller to solve the optimization problem. The proposed FL is a Mamdani-type rule base (4)

6 where the inputs are the speed tuning signal ε ω and its change Δ εω, which can be defined as; The structure of fuzzy logic system is shown in Fig.10 B DIVYA, K BALAJI NANDA KUMAR REDDY, V RADHIKA (6) V. SIMULATION RESULTS Simulation results of this paper is shown in Bellow Figs.12 to 21. A. Simulation Circuit Diagram DC to AC Mode Operation: Fig.10. Structure of fuzzy logic controller. These two inputs are multiplied by two scaling factors k 1 and k 2, respectively. The output of the controller is multiplied by a third scaling factor k3 to generate the actual value of the rate of change of the optimized speed. Fig.12. Simulink model of DC to AC mode of sparse aclink buck-boost inverter. AC to DC Mode Operation: B. MRAS in Motor Control Applications In the MRAS method, the motor speed is estimated using a reference model and adaptive model. The reference model, which is independent of the rotor speed, calculates the state variable from the terminal voltage and current. Then the adaptive model, which is dependent on the rotor speed, estimates the state variable. The difference between these state variables is then used to drive an adaptation mechanism which generates the estimated speed ω r. Fig.13. Simulink model of AC to DC mode of sparse aclink buck-boost inverter. Closed Loop Control Induction machine with Withoutload and With Load Operation: Fig.11. Structure of MRAS. The generalized structure of MRAS is shown in Fig.11. The reference model and adaptive model have the same input. x and are respectively the state variable of the reference model and adaptive model. Given performance index x is set by the reference model, which is compared with the corresponding performance of adaptive model. The difference value is the input of adaptation mechanism. The variable in adaptive model is modified by adaptation mechanism, in order to make its state variable draw near x which also means the difference value approaches zero. Fig.14.Close loop control of induction machine.

7 Closed Loop Control of Induction Motor by using Sparse AC-Link Buck Boost Inverter B. Simulation Waveforms AC to DC Mode Operation: DC to AC Mode Operation: Fig.15. DC input voltage. Fig.18. ac side link current and voltage. Fig.19. DC Output voltage and current. Fig.16. Link Current and Voltage. Speed Control Of Induction Machine With Load & Without Load Operation: Fig.17. AC Output Current. Fig.20. speed of induction machine with no-load condition.

8 Fig.21. Speed of induction machine with load condition. VI. CONCLUSION The proposed converter, named sparse ac-link buck boost inverter, is a modification of the ac-link buck boost inverter that requires fewer switches. Despite reducing the number of switches, the proposed inverter has all the advantages of the ac-link buck boost inverter, including zero voltage turn on and soft turn-off of the switches, alternating link current, and the possibility of having galvanic isolation with the addition of a single-phase high-frequency transformer. It was shown that the switches in the proposed configuration should withstand higher average current; however, the peak current they tolerate is the same as the peak current switches in the ac-link buck boost inverter tolerate. Therefore, the proposed configuration does not necessarily lead to high current switches. The efficiency of the sparse ac-link buck boost inverter is about 2% lower than that of the ac-link buck boost inverter. By using reverse-blocking IGBTs its efficiency will be increased 4%. It was also shown that the failure rates of the sparse ac-link buck boost inverter are about 12% lower than that of the original configuration. When the sensorless control was carried out on induction machine based on MRAS and FUZZY CONTROLLER. In this performance of the proposed inverter was verified through simulations and experiments. VII. REFERENCES [1]A. Balakrishnan, H. A. Toliyat, and W. C. Alexander, Soft switched ac link buck boost converter, in Proc. Twenty-Third Ann. IEEE Appl. PowerElectron. Conf. Expo., Feb. 2008, pp [2]M Amirabadi, H. A. Toliyat, and W. Alexander, Battery-utility interface using soft switched AC link supporting low voltage ride through, in Proc.IEEE Energy Convers. Congr. Expo. Conf., 2009, pp [3]M.Amirabadi, A. Balakrishnan, H. Toliyat, and W. Alexander, High frequency ac-link PV inverter, IEEE Trans. Ind. Electron., vol. 61, no. 1, pp , Jan [4]M.Amirabadi, Soft-switching high-frequency ac-link universal power converters with galvanic isolation, Ph.D. dissertation, Texas A&M Uni-versity, College Station, TX, USA, B DIVYA, K BALAJI NANDA KUMAR REDDY, V RADHIKA [5]T. A. Lipo, Resonant link converters: A new direction in solid state power conversion, presented at Second Int. Conf. Electrical Drives, Eforie Nord, Romania, Sep [6]P. K. Sood, T. A. Lipo, and I. G. Hansen, A versatile power converter for high frequency link systems, IEEE Trans. Power Electron., vol. 3, no. 4, pp , Oct [7]F. C. Schwarz, An improved method of resonant current pulse modula-tion for power converters, IEEE Trans. Ind. Electron. Control Instrum., vol. 23, no. 2, pp , May [8]Y. Murai and T. A. Lipo, High-frequency seriesresonant DC link power conversion, IEEE Trans. Ind. Appl., vol. 28, no. 6, pp , Nov./Dec [9]D. M. Divan, The resonant DC link coverter A new concept in static power conversion, in Proc. IEEE IAS Annu. Meet., pp [10]S. Chakraborty, B. Kramer, and B. Kroposki, A review of power electron-ics interfaces for distributed energy systems towards achieving low-cost modular design, Renewable Sustainable Energy Rev., vol. 13, pp , [11]G. Grandi, C. Rossi, D. Ostojic, and D. Casadei, A new multilevel con-version structure for grid-connected PV applications, IEEE Trans. Ind.Electron., vol. 56, no. 11, pp , Nov [12]T. Kerekes, R. Teodorescu, P. Rodriguez, G. Vazquez, and E. Aldabas, A new high-efficiency single-phase transformerlesspv inverter topology, IEEE Trans. Ind. Electron., vol. 58, no. 1, pp , Jan Author s Profile: M.Suresh received B.Tech in Electrical & Electronics Engineering in 2013 from KMM Institute of Technology and Science, Tirupati, Affiliated to Jawaharlal Nehru Technological University (JNTUA), Anantapur, India. He is pursuing M.Tech in Power Electronic and Electrical Drives from Sri Venkateswara College of Engineering & Technology (Autonomous), Chittoor and Affliated to Jawaharlal Nehru Technological University (JNTUA), Anantapur, India. Mr.S.V.Sivanagaraju, Received Bachelor s Degree in Electrical & Electronics Engineering from Sree Vidyanikethan Engineering College, Tirupati, A.P affiliated to JNTU Anantapur University in 2002,the Masters Degree in Electrical Power Engineering fom JNTCEH, affiliated to JNTU Hyderabad University in He has 11 years of experience in Teaching and 02 years experience in Industry. Currently he is working as Associate Professor, Dept. of EEE, Sri Venkateswara College of Engineering & Technology (Autonomous), Chittoor, AP, India.