DESIGN AND ANALYSIS OF DC-DC BOOST CONVERTER BY USING MATLAB SIMULINK Pund Sunil Kacharu*1,Vivek Kumar Yadav*2 *1(PG Scholar, Assistant Professor, RKDF Bhopal (M.P.)) Sunilpund25@gmail.com,ee.rkdf@gmail.com Abstract: DC-DC converters are electronic devices used to change DC electrical power efficiently from one voltage level to another. Operation of the switching devices causes the inherently nonlinear characteristic of the DC-DC converters including one known as the Boost converter. This thesis is proposed to provide the designer with a method of boosting DC voltage from 5 Volts to 15 Volts, by using a boost converter designed specifically for this task. All aim, calculations, tests, data and conclusions have been documented within this report. Results of simulation show that the switching converter will boost voltage from 5 volts to 15 volts with power conversion efficiency of 93.97 percent. The evaluation of the output has been carried out and compared by software simulation using MATLAB software between the open loop and closed loop circuit. The simulation results are shown that voltage output is able to be control in steady state condition for DC-DC boost converter by using this methodology. Index Terms: AC Module, High Step-Up Voltage Gain, Switch. Single 1Introduction : In many technical applications, it is required to convert a set voltage DC source into a variablevoltage DC output. A DC-DC switching converter converts voltage directly from DC to DC and is simply known as a DC Converter. A DC converter is equivalent to an AC transformer with a continuously variable turns ratio. DC converters are widely used for traction motor control in electric automobiles, trolley cars, marine hoists, forklifts trucks, and mine haulers. They provide high efficiency, good acceleration control and fast dynamic response. They can be used in regenerative braking of DC motors to return energy back into the supply. This attribute results in energy savings for transportation systems with frequent steps. DC converters are used in DC voltage regulators; and also are used, with an inductor in conjunction, to generate a DC current source, specifically for the current source inverter. 2.1 Boost Converter: DC to DC is an electronic circuit which converts a source of direct current (DC) from one voltage level to another. In other word, converting the unregulated DC input to controlled DC output with a desired voltage level. Dc to dc converter are widely used in switched-mode power supplies (SMPS), battery chargers, adjustable speed drives, uninterruptible power supplies and many other applications to change the level of an input voltage to fulfil required operating conditions. There are typically three types of dc to dc converters, which are :- i. Buck converter ii. Boost converter iii. Buck-Boost converter 2.2Boost Converter A boost converter (step-up converter), steps up the input DC voltage value and provides at output. It consists of an inductor L, capacitor C, controllable semiconductor switch S, diode D, and Load resistance R as depicted by Figure 2-1. Capacitors are generally added to output so as to perform the function of removing output voltage ripple. The boost converter is one of the most important nonisolated step-up converters. Published in 1
The inductor voltage V L =V s = = (2.4) Fig 2.1 Boost converter operates, assume that the inductor is charged in the previous cycle of operation and the converter is at the steady state operation and CCM Condition. Fig 2.2 Define Duty Cycle (D) which depends on ton and switching frequency fs D = = t on f s (2.1) During steady state operation the ratio between the output and input voltage is, the ouput voltage is controlled by varying the duty cycle. Range of Duty Cycle: 0 < D < 1. = Since the derivative of il is a +ve constant, therefore il must increase linearly; = Δ Δ = Δ DT = closed =.DT (2.5) Figure 2-3 The Equivalent Circuit of Boost Converter When the Switch S is closed Published in =(1 ) (2.3) 2.2.1 Analysis for switch closed (On):Start with the power switch S is closed. Now the diode will be reversed-biased by the capacitor voltage, hence it will act as open. The equivalent circuit is shown in Figure 2-3 (Keynani, 2011). Diode is reverse-biased. Input is disconnected from the output, no energy flows from input to output, output gets energy from capacitor, V LON = Vs. Figure 2-4 Analysis for switch closed(on) 2.3.2 Analysis for switch open (off) For the next cycle, the power switches S open. The condition is depicted in Figure 2-5. Because the inductor fully charged in the previous cycle, it will continue to force its current through the diode D to the output circuit and charge the capacitor. Inductor is discharging, diode is forward-biased, and Input is connected to the output, energy flows from input to output while capacitor s energy is replenished. The 2
output stage receives energy from the input as well as from the inductor, VLOFF = Vs Vo. Inductor current: Input power = Output power Figure 2-5 The Equivalent Circuit of Boost Converter When the Switch S Open Figure 2-6 Analysis for switch opened (off) The inductor voltage V L =V s -V o = = (2.6) Since the derivative of i L is a -ve constant, therefore i L must decrease linearly. = Δ Δ = Δ (1 ) = opened = (1 D)T (2.7) Steady-state operation closed + opened =0 = = () (2.8) In steady state the average inductor voltage is zero over one switching period known as Volt Second Balance, V LON t ON + V LOFF t OFF =0 =V S DT+( )(1 D)T = () (2.9) From the equation (2.9) average output voltage is higher than input voltage. I L =.() (2.10) Average inductor current V S I S = V S I L =.() (2.11) 2.3.3 Boost Converter modes of operation: The DC-DC converters can have two distinct modes of operation: Continuous conduction mode (CCM) and discontinuous conduction mode (DCM). In practice, a converter may operate in both modes, which have significantly different characteristics. However, for this project only consider the DC-DC converters operated in CCM. CCM IS for efficient power conversion and Discontinuous Conduction Mode DCM for low power or stand-by operation. Continuous Conduction Mode (CCM) when inductor current > 0 Discontinuous Conduction Mode (DCM) when inductor current goes to 0 and stays at 0 for some time. Published in 3.2. Boost converter: 3.2.1. Operating phases The boost converter circuit is illustrated in figure 8a. The principle of the switch control is described in figure 5b Three operating phases are counted (figure 8c) : - T state-on and D state-off - T state-off and D state-on - T and D state-off 3
The variation of the voltage across the inductance L (equation 14) and the current through the capacity (equation 15) depend on the operating phase. V L (t) = V i (t)*f+[ V i (t) ()]* F *sign(i L ) (14) i C (t) =- i o (t)*f+ i L (t)*f * sign(i L ) (15) = ()dt = [ ().+ i L *F * sign (i L )]dt (16) 3.2.2. Open-loop operation: Simulink model of a open-loop boost converter is shown in figure 9a. The Boost block isillustrated in figure 9b. Equation (14), (15) and (16) are modeled by addition blocks multiplication blocks and logic blocks. The structure of the converter requires a current il necessarily positive or zero. Also, the inductance current is modeled by an integrator block that limits the minimum value of il to zero. The PWM control block is illustrated in figure b.in the case of a resistive load, the load block is constituted by a gain block (value 1/R). Simulation example: The parameters used for of an open-loop simulation are : V i = 12 V L = 200 µh C = 50 µf R = 5 Ω f t = 50 khzcontrol blok: V t max = 1 V V t min = - 1 V V m = 0. The simulation of the open-loop boost converter is illustrated in figure 9c. The list ofconfiguration parameters used is: Start time:0 Stop time : 7 e-3 Type:Variable-step Solver : ode15s (stiff/ndf) Max step size : 1e-6 Relative tolerance :1e-3 Min step size : auto absolute tolerance : auto Knowing that v t varies from 1 V to + 1 V and v m = 0, we deduce that the duty cycle is equal to 0.5. In steady-state, we deduce theoretical value of V o : V o steady state = = 24V (17) Published in Simulation is in good agreement with theoretical value. From figure 9c, we deduce that the transient state last roughly 2.5 ms. a) Open-loop Boost block diagram 4
Simulink Model: Result: 7. Conclusion: This chapter has shown that it is possible to simulate many electrical power converters onlyusing Simulink toolbox of Matlab, thus avoiding the purchase of expensive and complexdedicated software. The simulation method is based on the variable topology approachwhere switching conditions of semiconductor are realized by switching functions. All of the specifications stated previously have been met by this boost converter design. MATLAB simulations using calculated parameters were performed and corresponding waveforms were obtained. The output voltage across the output capacitor is 15V with a maximum output ripple of 1.6%. The power efficiency of the circuit exceeds 93.97 %. Hardware design of BOOST CONVERTER was done. It is observed, by varying duty cycle output voltage also changes. References: [1] F. Terrien, M. F. Benkhoris and R. Le Doeuff, "An Approach for Simulation of Power Electronic Systems," Electrimacs' 99, Saint Nazaire, France, vol. 2, pp 201-206. [2 ]C. Batard, F. Poitiers and M. Machmoum, "An Original Method to Simulate Diodes Rectifiers Behaviour with Matlab-Simulink Taking into Account Overlap Phenomenon," IEEE International Symposium on Industrial Electronics 2007, ISIE 2007, pp 971-976, Vigo,Spain, 4-7 June 2007. [3] Muhammad H. Rashid, (2004): Power Electronics Circuits, Devices, and Applications Electrical computer Engineering University of west Florida. Published in [4] T.Gupta&R.Boudreax, (1997): Implementation of a Fuzzy Controller for DC-DC Converters Using an Inexpensive 8-Bit micro controller, IEEE Trans. on Industrial Electronics, vol. 44, no.5, pp.661-667. Figure 9.Boost converter described in Simulink [5] Wang, M.; Power supply design with fast transient response using V2 control scheme, International IC 99 Conference Proceedings-,Page(s): 189 199. 5