HIGH STEP UP SWITCHED CAPACITOR INDUCTOR DC VOLTAGE REGULATOR

Transcription

1 INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India ISSN (Print) ISSN (Online) Volume 5, Issue 2, December (204), pp IAEME: Journal Impact Factor (204): (Calculated by GISI) IJEET I A E M E HIGH STEP UP SWITCHED CAPACITOR INDUCTOR DC VOLTAGE REGULATOR SHAHANA JABAR, Mr. JOSE SEBASTIAN T.K Dept. of Electrical & Electronics Eng., Government Engineering College Thrissur, Kombanaparambil (H), Thodupuzha, Idukki, kerala, India, 2 Dept. of Electrical & Electronics Eng., Government Engineering College Thrissur, Thalakkottur(H), Aiswaria nagar, West fort,india ABSTRACT A new converter using a switched-inductor cell integrated with a switched-capacitor cell within a boost-like structure is proposed. The converter can achieve a very high dc conversion ratio. It can serve as the front-end dc-dc converter for a voltage regulator system. The inductors and capacitors are switched in a parallel-series configuration. The charging circuit of the inductors from the source is separated from the load. A dc analysis of the new circuit leading to the formula of the dc gain and a breakdown calculation of the losses are given. The proposed Switched Capacitor Inductor (SCI) converter circuit can meet the high efficiency requirement and simple structure. A small resonant inductor is used in these converters to limit the current peak caused by switched capacitor. Therefore, the SCI converters have good performance and high efficiency as well the voltage stress of the converter is reduced. In order to verify the proposed Switched Capacitor Inductor (SCI) dc-dc converter, modeling and simulation was carried out by using MATLAB. Keywords: High Voltage Gain, Switched Capacitor, Switched Inductor. INTRODUCTION The need for a DC/DC converter of this caliber is a great one. The future is looking towards alternative power sources all of which will need to be regulated in one Form or another. To make this possible, a highly efficient low cost product will have to be designed. Among all the different converter designs only a few are capable of providing high power with high efficiency. The basic switched-mode dc dc converters including buck, boost, buck-boost, cuk, zeta, and sepic have been used in various electronic applications due to their numerous advantages such as simple structure, good performance, high efficiency, easy design, and simple control circuit []. The resonant converters such as single-ended and bridge type are also very popular in the last decade [2], [3]. And the basic switched-capacitor (SC) converters also have wide application as their advantages of nonmagnetic components employed and small size and high power density [4], [5]. A small resonant inductor has been added in SC converters to eliminate the current peak and achieve soft switching in [6] and, therefore, the SC Converters have good performance and high step up as well. In recent years, many researchers are trying to take these types of converters aforementioned into a new type of combination converters to obtain high step-up voltage gains. Even though these converters have different structures and can provide different voltage conversion ratios, they have a characteristic in common which is that all of them are multistage combination of switched-inductor cells and SC cells. Like other cascaded high step-up converters, in which energy is transferred from one unit to next unit and gradually to output stage, their efficiency is therefore generally not promising and is equal to the product of Efficiency. 26

2 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India In this paper, a high efficiency Switched Capacitor Inductor DC-DC converter is proposed. The converter composed of the following components: include two energy transfer components, i.e., one Switched Capacitor C and one switched inductor L, a small resonant inductor L r that is employed to limit the current peak caused by SC, three active or passive switches and one output filter capacitor. The greatest feature of these converters is that energy flowing from input power sources is directly transferred to the two energy transfer components (C and L ) and then directly released to output terminal, i.e., these converters are actually single-stage dc dc converters rather than like aforementioned converters obtained high voltage gain by using different cascading methods. When the two energy transfer components operate in parallel manner during a charging process and then in series manner during a discharging period, the higher output level can be produced. Similarly, this principle is not only suitable for deriving single-input converters, but can also be extended to dual-input dc-dc converters that are popularly used in dual-level dc distributional and renewable energy system. To distinguish the proposed family of converters from conventional SC/SI converters introduced in literatures, the proposed converters are hence named high gain switched capacitor inductor (SCI) converters. This paper is organized as follows: Section II introduces the block diagram of proposed voltage regulator system. Section III introduces the proposed SCI dc-dc converter, which consists the detailed analysis of the operating principle and oscillation amplitude along with design consideration of SCI converter. Section IV introduces the proposed high step up SCI dc voltage regulator. Section V introduces the simulation and experimental result discussion of SCI dcdc converter. Finally, this paper is concluded in Section VI. 2. PROPOSED VOLTAGE REGULATOR SYSTEM High step up SCI converter can be used for verity of applications including Battery charger, UPS System with Renewable Energy Source, Voltage regulator.switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge is transferred to the load. This is controlled by a similar feedback mechanism as in a linear regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives the switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input, or of opposite polarity something not possible with a linear design. 3. SCI DC-DC CONVERTERS FIG.. PROPOSED VOLTAGE REGULATOR SYSTEM The proposed SCI dc-dc converter circuit is shown in Figure 2. The circuit uses only one active switch Q and a very small resonant inductor L r which is employed to limit the current peak caused by capacitor C when the switch Q is turned ON. The two energy storage components C and L are alternately connected in parallel and series according to different switching states. Voltage transfer relationship can be derived and expressed as follows, 2 d V0 = Vin () d 262

3 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India FIG. 2. HIGH STEP UP SCI CONVERTER There are two inductors employed in this converter, the energy transfer inductor L and the resonant inductor Lr. The function of L is to transfer energy while Lr is just used to limit the current peak caused by the capacitor C when the switch Q is turned ON. Specifically, when switch Q is turned ON, the capacitor C begins to be charged or to discharge, the charging or discharging current will soar to a very high peak at the moment of Q being ON if there are not any measures to limit it. For this reason, a small inductor Lr is added and connected in series with C to form a resonant tank with the resonant frequency fo = /2π LrC during the switching ON period. With the resonant inductor, the charging or discharging current of C gradually increases from zero when switch Q is turned ON. In order to ensure that the current changes back to zero before switch Q is turned OFF, the switch conduction time should be longer than half of a period of the resonant frequency, i.e., dts > π LrC(where TS and d are the switching cycle period and duty ratio, respectively). 3.. Mode of Operation of the Converter For the SCI converter shown in Fig. 2, there are three working states in one period of switching cycle. Fig. 3 shows its three state circuits and its idealized waveforms are shown in Fig. 4. The following detailed analysis is based on the assumptions that: all components are ideal, i.e., there are no voltage drop and on-resistance; the inductor L operates in continuous current mode; the output filter capacitor C2 is so large such that the output voltage ripple is ignorable and it can therefore be seemed as a constant voltage source VO State I (t0 t) When the switch Q is turned ON, diode D2 is reversely biased. D is forward biased and the resonant inductor Lr is connected in series with C to form a resonant tank. The input voltage V is developed across the resonant tank that causes the resonant current ic gradually increases from zero in a sinusoidal manner; C begins to be charged and its voltage increases from its minimum value. FIG. 3. STATE CIRCUITS FOR CONVERTER (A) STATE I (T0 T). (B) STATE II (T T2). (C) STATE III (T2 T3). 263

4 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India Meanwhile, input voltage is developed across inductor L causing a linear increase in current il. The state circuit is shown in Fig. 3(a) and the idealized waveforms are shown in Fig. 4. This status can also be mathematically described as: ic = Ic sin ω0( t t0) (2) Vc Vc = V cos ω0( t t0) 2 (3) V il = I L min + ( t t0) L (4) Where ω 0 resonant angular frequency I C and V C are oscillation amplitudes of the current and voltage of capacitor C, respectively, and both are related to the output current; IL min is the minimum value of the current flowing through L. After Lr and C resonate for half of a cycle, the resonant current i C falls back to zero and then diode D is reversely biased. The resonance stops and the capacitor voltage reaches to its maximum value at time t, i.e., V V 2 c c max = V + (5) State II (t t2) After the resonance stops, the switch Q continues to conduct and the inductor current il continues to rise linearly as given by (4).There is no current flowing though C and its voltage is maintained the maximum value. The state circuit is shown in Fig. 3(b).This state continues until the switch is turned OFF as shown in Fig. 4 time from t to t2, and then the inductor current il rises to its maximum value. V i = I + dt (6) L max L min s L FIG. 4. SOME IDEALIZED WAVEFORMS FOR A HIGH STEP-UP CONVERTER 264

5 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India State III (t2 t3) After switch Q is turned OFF, diode D2 is forward biased and D is reversely biased. The capacitor C, the inductor L, and input source are connected in series and discharge to VO as shown in Fig. 3(c).The currents flowing though C and L are therefore the same and can be expressed as: V V V i = i = I ( t t ) (7) 0 c L c L min 2 L Based on the assumption that the switching frequency is high enough the changes of capacitor voltage VC and discharging current il can be approximated as linear with time, i.e., V V V i = i I ( t t ) (8) 0 c L c L min 2 L I V V ( t t ) 0 c c max 2 ( d) C (9) At the end of this state, i.e., time t 3, the loop current il and the capacitor voltage VC both decrease to their minimum values. And then, the switch Q is turned ON again and the three states will be repeated Design Considerations Based on the previous analysis, the values ofc and Lr can be determined by the design requirements of the resonant current and voltage. And the value of L can be determined by the design requirements of its current ripple. The design process therefore can be divided into the following steps: ) Determine the values of the duty ratio and the switching frequency, and then calculate the resonant frequency according to the condition that the switch conduction time should be longer than half of a period of resonant frequency, i.e., f 0 = > (0) 2dT 2π LrC s 2) The value of the capacitor C can be calculated by, i.e, C I T 0 s = () VC 3) The resonant inductor Lr hence can be determined by the value of C and the resonant frequency, i.e., L r 4π f C = (2) ) The value of inductor L can be determined by, i.e., L V dt s = (3) I L Where IL is the design requirement of the current ripple flowing through L. 4. SWITCHED CAPACTOR INDUCTOR DC VOLAGE REGULATOR. Switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. A feedback circuit (voltage sensor circuit) measures or monitors the output voltage and compares it with a reference voltage, which shown in the block diagram Fig:. serves this purpose. When it is lower than the desired voltage, it turns on the switch. When the output voltage is above the desired voltage, it turns off the switch. The advantage of using switching regulators is that they offer higher efficiency than linear regulators. The complete system overview of high gain SCI DC voltage regulator is shown in Fig 5. Switching pulses to mosfet is produced using The 265

6 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India Atmel AVR ATmega8.AVR is made to operate in Fast PWM Mode (WGM:0 =3). It is used to create high resolution PWM waveforms with same frequency, different duty cycle. FIG. 5. TOTAL SYSTEM OVERVIEW Three distinct steps used for programming process are writing the code, debugging the code, programming in AVR. The programming language for microcontrollers is Flowcode V5 for AVR. The flowchart of program for high gain SCI DC voltage regulator is shown in Fig 6. FIG. 6. FLOWCHART OF THE PROGRAM 5. SIMULATION AND EXPERIMENTAL RESULTS 5.. Simulation parameter for the Proposed High Step-Up Regulator The Closed loop simulation of High step up Switched capacitor inductor converter is made and a prototype of the converter with closed loop voltage control is made. The following TABLE I shows the component details of simulation model and prototype circuit of high step up SCI converter which is calculated using equations in design consideration with Vc=0.03V and IL=0.8A. 266

7 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India TABLE I. SIMULATION PARAMETER Input Voltage Maximum output Power Switching Frequency (2-5)V DC 5W 28kHz Capacitor C 2µF Capacitor C2 400µF Inductor L 450µH Resonant Inductor Lr Resistor R 2.7µH kω 5.2.Closed loop simulation of high step up SCI converter (DC voltage regulator) Figure 7 shows the simulink model of the closed loop high step up SCI converter. Closed loop provides regulated output voltage for input voltage variation. In closed loop control, the output voltage of converter is compared with required constant output voltage. The error is given to the PI controller. PI controller parameters are obtained by trial and error method. The output of PI controller is combined with ramp signal for the main switch. FIG. 7. SIMULINK MODEL OF THE CLOSED LOOP CONVERTER. 267

8 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India FIG. 8. INPUT & OUTPUT VOLTAGE OF CLOSED LOOP HIGH STEP UP SCI CONVERTER 5.3. Experimental set up and Results discussions for the proposed High step up regulator A prototype circuit of the closed loop high step-up converter has also been built as shown in Fig. 9 to confirm the theoretical analysis and simulation results, the experimental results are shown in Fig. 8 when the output is connected to a -kω pure resistor load. It is evident that the results agree to and are supported by the preceding analysis and simulation results. Output voltage V o of the converter with input voltage of 2.4V simulated in MATLAB is show in fig 0. The corresponding experimental result is shown in fig.. As can be seen, the output voltage is 74V.The resonant switching techniques introduced to this converter further improved the performance of converter. When the input powers V=0V, load is a -kω pure resistor, and the switch Q is operated at 28-kHz switching frequency, the output voltage is 74 V. FIG. 9. EXPERIMENTAL SETUP FIG. 0. SIMULATED OUTPUT VOLTAGE FIG.. EXPERIMENTAL OUTPUT VOLTAGE WITH VIN=2.4V, OUTPUT VOLTAGE VO=74V), UPPER TRACE: OUTPUT VOLTAGE; LOWER TRACE: INPUT VOLTAGE 268

9 Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM4) 30-3, December, 204, Ernakulam, India 6. CONCLUSION In this project work, a high step up SCI DC voltage regulator is designed simulated and a hardware prototype is made. High step up SCI DC converter without feedback and High step up SCI inverter circuit are also simulated.the SCI dc-dc converter give high step up and efficiency compared with conventional SC converter, hence we can apply this converter for making UPS system with renewable energy sources, voltage regulator etc. The proposed converters employ two energy transfer components (one SC and one inductor) and do not use the cascade method like conventional SC/switched-inductor converters. The energy stored in the two components both directly come from input power sources and then directly been released to output terminal. This design can meet the high efficiency requirement with a simple structure. A resonance method is used in this paper to limit the current peak caused by the SC. Detailed analysis and design considerations are also introduced. Compared with traditional switched-mode converters, the proposed converters can provide higher voltage gains and the switch stress is lower. The SC converter voltage stress is high because of using more number of switches. In SCI converter used one switch therefore voltage stress of the converter is reduced. The renewable energy sources can give more efficient power by using SCI dc-dc converter. The complete circuit including the high step up SCI converter with microcontroller based voltage control has been tested to demonstrate the claimed features. This project work has described the basic circuit operating principle, device selection, and passive component design procedure to achieve the desired high voltage ratio. REFERENCES Journal Papers [] K. W. E. Cheng, Classical Switched Mode and Resonant Power Converter. Kowloon, Hong Kong: Hong Kong Polytechnic Univ., 2002, pp W. Williams, Basic DC-to-DC converters, IEEE Trans. Power Elec-tron., vol. 23, no., pp , Jan [2] Y. Ren, M. Xu, J. Sun, and F. C. Lee, A family of high power density unregulated bus converters, IEEE Trans. Power Electron., vol. 20, no. 5, , [3] K. W. E. Cheng and P. D. Evans, Parallel-mode extended-period quasi resonant convertor, IEE Proc.-B, vol. 38, no. 5, pp , Sep. 99. K. Tse, S. C. Wong, and M. H. L. Chow, On lossless switched-capacitor power converters, IEEE Trans. Power Electron., vol. 0, no. 3, , May 995. [4] K. K. Law, K. W. E. Cheng, and Y. P. Benny Yeung Design and Analysis of Switched-Capacitor-Based Step-Up Resonant Converters IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I: REGULAR PAPERS, VOL. 52, NO. 5, MAY 2005 [5] J. M. Henry and J. W. Kimball, Switched-capacitor converter state model generator, IEEE Trans. Power Electron., vol. 27, no. 5, pp , May 202. [6] Y. Yuanmao and K. W. E. Cheng, Level-shifting multiple-input switched-capacitor voltage-copier, IEEE Trans. Power Electron., vol. 27, no. 2, , Feb Books [] Bert Van Dam Microcontroller system engineering and Atmel bit-AVR-microcontroller-ATmega8 datasheet. 269