Transient response improvement of buck converter
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Transient response improvement of buck converter

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  • 1. INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME & TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 1, January- February (2013), pp. 131-138 IJEET© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2012): 3.2031 (Calculated by GISI) ©IAEMEwww.jifactor.com TRANSIENT RESPONSE IMPROVEMENT OF BUCK CONVERTER # * # Arun Kumar Pandey , Prof. S. K. Misra , Sumit Kumar Misra # P.G Student (Power Electronics & Control) (Department of Electrical Engineering, HarCourt Butler Teconological Institute Kanpur-208002, India) * Professor (Department of Electrical Engineering, HarCourt Butler Teconological Institute Kanpur-208002, India ABSTRACT Sliding mode (SM) and Proportional-integral-derivative (PID) controller are implemented for Buck converter in a continuous conduction mode. A closed-loop controller system is implemented and goes through the transient time response of buck converter. Sliding mode controller is worked as robust controller and can be used to reduce the Delay time and settling time of the system. In power drives controller are required to be of faster transient response to increase the synchronization of the system. The closed-loop system and the transients of the closed loop system are analyzed for various circuit parameters. Under a large range of operating points, the buck converter under the SM controller has a output voltage accuracy upto ± 0.02V and operating frequency of 5 MHz (approx). The merits of the SM controller are compared with some other controller. Keywords: Transient response, sliding mode control, buck converter, settling time, simulation. 1. INTRODUCTION Direct current converters are used to convert source voltage to other voltage level by varying the duty cycle of the switches in circuit. As they are non linear systems it is difficult to implement their control design. Since traditional control methods are designed by taking one reference operating point, they did not give the proper transient response and parameter variation responses. 131
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEThe buck dc-dc converters are used were the required output voltage signal should be lowerthan the source voltage signal. In buck converter, an extremely high speed switching devicesare placed and the better efficiency of power conversion with the steady state is to be achieve.This is achieved by a appropriate switching process of the circuit. Hence the motive of theswitching control in buck converter is to implement high power transfer efficiency and sharptracking of output voltage. In this paper transient performance of buck converter is analyzed.For better transient response in DC-DC converter settling time and overshoot should beminimum. For this different types of controllers are used. Like as linear controller PI, PIDand in nonlinear controllers SMC (sliding mode controller), neural network and fuzzycontrol. To design the switching characteristic of converters, any nonlinear control methodscan be used, like neural network, fuzzy control and slide mode control. The implementationof a PID controller is based on the Bode plot or tuned with Ziegler-Nichols techniques. Dueto the highly nonlinear characteristics of the DC-DC converters, the PID control does notallow disturbances rejection and fast transient response time. Hence it is very interesting aswell as difficult to develop more nonlinear and advanced non-conventional robust controlstructures to improve the performance of the DC-DC converters. Sliding mode controllers arewell known for their robustness and stability but this kind of controller operate at very large(infinite) switching frequency so-called chattering phenomenon [2].PWM DC-to-DC converters are very popular for the last three decades, and that are widelyused at all power levels. Since switching converters constitute a case of variable structuresystems, the sliding mode (SM) control technique can be a possible option to control this kindof circuits [5]. Sliding Mode (SM) controllers are well known for their robustness andstability. The nature of the controller is to ideally operate at an infinite switching frequencysuch that the controlled variables can track a certain reference path to achieve the desireddynamic response and steady-state operation [3]. This requirement for operation at highswitching frequency, create challenges in the feasibility of applying SM controllers in powerconverters. This is because extreme high speed switching in power converters results inexcessive switching losses, inductor and transformer core losses, and electromagneticinterference (EMI) noise issues.Different control programs are applied to design the DC-DC converters for getting a robustoutput voltage. As DC-DC converters are time variant and nonlinear systems. The use oflinear control techniques to control these converters is not appropriate. A multi-loop controltechnique, like current mode control, will greatly improve the dynamic behaviour, but thecurrent mode control is not fully non linear control. So it does not support the large signaldisturbances and it remains difficult for the implementation of higher order convertertopologies.In this paper we had implemented the buck converter using non linear controller i.e. slidingmode controller for the faster transient response of the system. We had also implementedbuck converter using conventional linear controller and provide the simulated results for thecomparison of the transient responses of both the converters with change in differentparameters. 132
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME2. BUCK CONVERTER The buck converter in Fig. 1 is powered from a constant DC source through a dioderectifier and uses a controlled switch to govern unidirectional power flow from input tooutput. The converter includes one capacitor and one inductor to store and transfer energyfrom the input to output. A filter is used to smooth the voltage and current waveforms. Thecircuit is assumed to be operating in the steady state continuous conduction mode. Thecapacitor is large enough to filter the AC component and provide a constant output voltage. Fig.1. DC-DC buck converter Fig.2. Turn on switch Fig.3. Turn off switch 133
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEWhen the switch S1 is on and D is reverse biased, the dynamics of inductor current iL and thecapacitor voltage Vc are (1)When the switch S1 is off and D is forward biased, the dynamics of the are (2)When the switch S1 is off and D is also not conducting, (3)The state space representation for converter circuit configuration can be expressed as (4)Where (5)Here x is the state vector and A’s and B’s are system matrices. The state matrices and theinput vectors for the ON and OFF periods are (6)2.1 Controller DesignIn SM control, the switching function is employed to decide the input states u to the system (7) where α is the sliding coefficient to be designed. For stability concern, the value of α shouldbe greater than zero [4]. The basic control law is expressed as (8)The basic control law in (8) determines the switching state u and directs the phase trajectorytoward the sliding surface (S= 0) in phase plane. 134
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME (9)However, to maintain the phase trajectory on the sliding surface and force it toward the origin,the Lyapunovs second method must be obeyed [4].3. BUCK CONVERTER USING PID CONTROLLER After studying the following results we can that the conventional controllers may beused in power circuits where sharp parameter changes does not govern the system stability aswell or lesser settling time doesn’t effect the performance of the system. Fig.4. SIMULINK Model of buck converter using PID ControllerFig.5. SIMULINK Result with Vin = 24V, Vref. = 12V and Settling Time = 1.25 X 10-3 sec (PID Controller). 135
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME Fig.6. SIMULINK Result with Vin = 24V, Vref. = 12V and Settling Time = 1.65 X 10-3 sec (PID Controller).4. BUCK CONVERTER USING SM CONTROLLER Here some experimental results are presented to explain the lesser settling time ofsiliding mode controller with variable input-output conditions. Fig.7. SIMULINK Model of buck converter using SM Controller 136
  • 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME Fig.8. SIMULINK Result with Vin = 50V, Vref. = 24V and Settling Time = 1.5 X 10-4 sec (SM Controller). Fig.9. SIMULINK Result with Vin = 24V, Vref. = 12V and Settling Time = 1.4 X 10-4 sec (SM Controller).5. TRANSIENT RESPONSE COMPARISON BETWEEN PID AND SM CONTROLLER TABLE I SIMULATION RESULTS FOR DIFFERENT CONTROLLERS Controller Settling Input Output Type time(sec) voltage(V) voltage(V) SMC 1.4 X 10-4 24 12 SMC 1.5 X 10-4 50 24 PID 0.75 X 10-3 200 120 PID 1.6 X 10-3 24 12 PID 1.25 X 10-3 50 24 137
  • 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEBy comparing the results of fig.5,6 (output of PID controller) and fig.8,9 (output of SMcontroller), now it can be concluded that the transient response of SM controller is fasterthan PID controller and the SM controller output is more stable than PID controller output.Hence for getting greater voltage accuracy in short duration we have to use SM controller.6. CONCLUSIONS After analyzing the performance comparison result of the paper it can be concludedthat the settling time of sliding mode controller is lesser than conventional PID controller.The simulation results shows high accuracy of the SM controller for achieving a referencevoltage with fast transient responses and strong system robustness. But when we have toreduce the cost of a system by compromising with less accuracy and complexity, than PIDcontroller can be used.7. ACKNOWLEDGMENT The authors would like to acknowledge the contribution by Department of ElectricalEngineering, HBTI Kanpur for their support and guidance.REFERENCES[1] Zengshi Chen, “PI and Sliding Mode Control of a Cuk Converter,” IEEE Transactions on Power Electronics, vol. 27, no. 8, August 2012, pp. 3695-3703[2] S. C. Tan, Y. M. Lai, C. K. Tse, and M. K. H. Cheung, “A fixed-frequency pulse-width- modulation based quasi sliding mode controller for buck converters,” IEEE Trans. Power Electron., vol. 20, no.6, pp.1379–1392, Nov. 2005.[3] S. C. Tan, Y. M. Lai, C. K. Tse, “General design issues of sliding-mode controllers in dc-dc converters,” IEEE Trans. Industrial Electronics., vol. 55, no. 3, pp. 1160–1174, Mar. 2008.[4] M. Castilla, “L. G. de Vicuna, J.M. Guerrero, J. Miret, and N. Berbel, Simple low- cost hysteretic controller for single-phase synchronous buck converter,” IEEE Transactions on Power Electronics, Vol. 22, No. 4, pp.1232–1241, Jul. 2007.[5] V. M. Nguyen and C. Q. Lee, “Tracking control of buck converter using sliding-mode with adaptive hysteresis,” in IEEE Power Electronics Specialists Conf. Rec. (PESC), 1995.[6] S. C. Tan, Y. M. Lai, M. K. H. Cheung, and C. K. Tse, "On the practical design of a sliding mode voltage controlled buck converter," IEEE Trans. Power Electron., vol. 20, no. 2, Mar. 2005, pp. 425-437.[7] V.I.Utkin, “Sliding modes and their application in variable structure systems,” MIR Publishers, Moscow, 1978.[8] P. Mattavelli, L. Rossetto, G. Spiazzi, and P. Tenti, “General-purpose sliding-mode controller for dc/dc converter applications,” in IEEE Power Electronics Specialists Conf. Rec. (PESC), 1993, pp. 609–615.[9] Jadhav Sumedh Damodhar and Phatale Aruna Prashant, “Microcontroller Based Photovoltaic Battery Charging System With Buck Converter” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp. 123 - 130, Published by IAEME. 138