International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN 2250-155X Vol. 3, Issue 4, Oct 2013, 43-50 TJPRC Pvt. Ltd. CONVERSION OF MULTI INPUTS TO MULTI OUTPUTS USING SWITCHED CAPACITOR G. BHARATHI & V. S. VIJAYA DURGA SVECW, Bhimavaram, West Godavari, Andhra Pradesh, India ABSTRACT Recent developments in sustainable energy sources such as fuel cells and photo voltaic (PV) have brought challenges to the design of power conversion systems. These power systems will require interfacing of various energy sources. To enable multi-source technology, a multi-input power converter is of practical use. An ideal multi-input power supply could accommodate a variety of sources and combine their advantages. Traditionally transformer based or inductor based Multi port networks have been used, but they occupy more space and losses are also high. So to overcome this, in this paper, a switched capacitor voltage copier (SCVC) is introduced, which has less number of components. So, this SCVC requires less space and the losses are also less. But, if the voltages are high, then the switches will be operated in hard switching and electromagnetic interference will be introduced in the circuits. In order to avoid this, resonant circuits are implemented. The simulation results verify the performance of voltage copier. KEYWORDS: Electromagnetic Interference, Multiport Network, Resonant Inductor, Switched Capacitor, Voltage Copier INTRODUCTION Recently, demand for versatile energy management systems capable of capturing energy from diverse sustainable and/or conventional energy sources, along with energy storage elements, is increasing because of their potential applications in hybrid electric vehicles (HEVs) and fuel cell vehicles (FCVs), renewable energy generation systems, and uninterruptible power supplies. The voltage levels and the voltage-current characteristics of energy sources and storage devices are normally different from those of loads. Therefore, a multi-port converter interfacing sources, storages and loads need to be incorporated into the entire energy management system [1]. The Demand for multiport converters is increasing because of their potential application in renewable energy generation systems, hybrid electric vehicles and fuel cell vehicles, uninterruptible power supplies [1]. Conventionally, the transformer-based or inductor-based multiport dc dc converters are widely employed [2]-[4]. However, the drawbacks of these types of converters include the high component count, large circuit size, and higher electromagnetic interference (EMI). Switched-capacitor (SC) DC-DC power converters are a subset of DC-DC power converters that use a network of switches and capacitors to efficiently convert one voltage to another. Unlike traditional inductor-based DC-DC converters, SC converters do not rely on magnetic energy storage. This fact makes SC converters ideal for integrated implementations, as common integrated inductors are not yet suitable for power electronic applications [5]. In this paper a switched capacitor voltage copier (SCVC) is introduced which has two voltage levels as input to get eight different output voltage levels. The SCVC consists of five kinds of conversion circuits. They are summation [6], subtraction [6], double [7], half [7] and inverting circuits [7]. In all these circuits we have two switches, two diodes, one switched capacitor and one output filter
44 G. Bharathi & V. S. Vijaya Durga capacitor to convert two voltage levels to eight voltage levels. So, as the components are less in number, this SCVC consumes less power and occupies less space. The size of the circuits is also very small. If the voltage is high, the switching currents are very high and oscillatory, and the devices are operated at hard switching. It not only induces large electromagnetic interference, but also shortens the life of a converter and more switching loss [8], [9]. Reduction of size and weight of converter systems require higher operating frequencies, which would reduce sizes of inductors and capacitors. However, stresses on devices are heavily influenced by the switching frequencies accompanied by their switching losses. It is obvious that switching-aid-networks do not mitigate the dissipation issues to a greater extent. Turn-on snubbers are rarely used. Even if used, it would not be able to prevent the energy stored in the junction capacitance to discharge into the transistor at each turn-on. Soft switching techniques use resonant techniques to switch ON at zero voltage and to switch OFF at zero current [10]. There are negligible switching losses in the devices, though there is a significant rise in conduction losses. There is no transfer of dissipation to the resonant network which is non-dissipative. So the resonant inductor is added in the above circuits in series with switched capacitor so that it forms a resonant circuit and ensures soft switching [11]. THE SWITCHED CAPACITOR VOLTAGE COPIER (SCVC) This SCVC consists of five types of conversion circuits as shown in the below Figure 1. They are summation, subtraction, double, half and inverting circuits. The summation circuit utilizes two inputs and gives the output which is the sum of the two inputs. The subtraction circuit also uses two inputs and gives the output which is the difference of the two inputs. The double, half and inverting circuits utilizes only one input voltage. The double circuit gives the output which is double the input. The half circuit gives the output which is half the input. And also the inverting circuit gives the output which is inversion of the input. The figure 1 shows the block diagram of SCVC. Figure 1: Block Diagram of Voltage Copier The non resonant circuits are discussed in the reference [6], [7]. WORKING OF THE RESONANT CIRCUITS circuit. To ensure soft switching a resonant inductor is added in series with the capacitor C 1 so that it forms the resonant
Conversion of Multi Inputs to Multi Outputs Using Switched Capacitor 45 Resonant Summation Circuit Figure 2: Resonant Summation Circuit The Resonant summation circuit is as shown above Figure 2.The resonant summation circuit has four modes of operation. In mode-i, Q1 is on, Q 2 is off, D 1 is on, and D2 is off. The capacitor C1 is charging to the voltage V S1. After conducting for some time the diode D 1 stops conducting and comes to off position. In mode-ii, Q 1 is on, Q 2 is off, D 1 is off, D 2 is off. And the voltage across the capacitor C 1 remains constant. In mode-iii, Q 1 is off, Q 2 is on, D 1 is off, and D 2 is on. And C 1 is discharging and capacitor C 2 is charging to voltage V C1 +V S2. After conducting for some time the diode D 2 stops conducting and comes to off position. In mode-iv, the voltage across the capacitor remains constant. The output voltage of resonant summation circuit is V S1 +V S2. Resonant Subtraction Circuit Figure 3: Resonant Subtraction Circuit The Resonant subtraction circuit is as shown above Figure 3. The resonant subtraction circuit has four modes of operation. In mode-i, Q1 is on, Q 2 is off, D 1 is on, and D2 is off. The capacitor C1 is charging to the voltage V S1 - V S2. After conducting for some time the diode D 1 stops conducting and comes to off position. In mode-ii, Q 1 is on, Q 2 is off, D 1 is off, D 2 is off and the voltage across the capacitor C 1 remains constant. In mode-iii, Q1 is off, Q2 is on, D1 is off, and D 2 is on and C 1 is discharging and capacitor C 2 is charging to voltage V S1 - V S2. After conducting for some time the diode D 2 stops conducting and comes to off position. In mode-iv, the voltage across the capacitor remains constant. The output voltage of resonant summation circuit is V S1 - V S2. Resonant Double Circuit Figure 4: Resonant Double Circuit The Resonant double circuit is as shown above Figure 4. The resonant double circuit has four modes of operation. In mode-i, Q 1 is on, Q 2 is off, D 1 is on, and D 2 is off. The capacitor C1 is charging to the voltage V S. After conducting for
46 G. Bharathi & V. S. Vijaya Durga some time the diode D 1 stops conducting and comes to off position. In mode-ii, Q 1 is on, Q 2 is off, D 1 is off, D 2 is off and the voltage across the capacitor C 1 remains constant. In mode-iii, Q 1 is off, Q 2 is on, D1 is off, and D 2 is on and C 1 is discharging and capacitor C 2 is charging to voltage V C1 +V S. After conducting for some time the diode D 2 stops conducting and comes to off position. In mode-iv, the voltage across the capacitor remains constant. The output voltage of resonant summation circuit is 2V S. Resonant Half Circuit Figure 5: Resonant Half Circuit The Resonant half circuit is as shown above Figure 5. The resonant half circuit has four modes of operation. In mode-i Q1 is on, Q 2 is off, D 1 is on, and D 2 is off. The capacitor C1 and C 2 is charging equally to the voltage 0.5V S. After conducting for some time the diode D 1 stops conducting and comes to off position. In mode-ii Q 1 is on, Q 2 is off, D 1 is off, D 2 is off and the voltage across the capacitor C 1 remains constant. In mode-iii Q1 is off, Q 2 is on, D 1 is off, and D 2 is on and the voltage across the capacitor C 2 is remains constant i.e. 0.5 V S. After conducting for some time the diode D 2 stops conducting and comes to off position. In mode-iv the voltage across the capacitor remains constant. The output voltage of resonant summation circuit is 0.5 V S. Resonant Inverting Circuit Figure 6: Resonant Inverting Circuit The Resonant inverting circuit is as shown above Figure 6. The resonant inverting circuit has four modes of operation. In mode-i Q1 is on, Q 2 is off, D 1 is on, and D 2 is off. The capacitor C 1 is charging to the voltage V S. After conducting for some time the diode D 1 stops conducting and comes to off position. In mode-ii Q 1 is on, Q 2 is off, D 1 is off, D 2 is off and the voltage across the capacitor C 1 remains constant. In mode-iii Q1 is off, Q 2 is on, D 1 is off, and D 2 is on and C 1 is discharging and capacitor C 2 is charging to voltage V C1 with reverse polarity. After conducting for some time the diode D 2 stops conducting and comes to off position. In mode-iv the voltage across the capacitor remains constant. The output voltage of resonant inverting circuit is -V S. SIMULATION OF THE NON RESONANT AND RESONANT CIRCUITS The simulation of the resonant circuits is done in MATLAB SIMULINK. The values for the capacitors and resistors are given below in Table 1. For resonant circuits the switching frequency is taken as 100 khz. The resonant
Conversion of Multi Inputs to Multi Outputs Using Switched Capacitor 47 inductor value for the resonant circuits is taken as 0.27µf. RESULTS Table 1: Circuit Parameters for Resonant Circuits Resonant Input Circuit Voltages(v) C 1 (µf) C 2 (µf) R(Ω) Summation 24,12 10 10 10 Subtraction 24,10 20 10 10 Double 24 10 10 10 Half 24 40 40 10 inverting 12 40 40 10 Figure 7: Output Waveforms of Resonant Summation Circuit Figure 8: Output Waveforms of Resonant Subtraction Circuit Figure 9: Output Waveforms of Resonant Double Circuit Figure 10: Output Waveforms of Resonant Half Circuit
48 G. Bharathi & V. S. Vijaya Durga Figure 11: Output Waveforms of Resonant Inverting Circuit CONCLUSIONS In this paper a level shifting switched capacitor voltage copier (SCVC) is introduced to convert two voltage levels to eight voltage levels. This SCVC is the new family of multiport networks. In this SCVC we have five kinds of conversion circuits. They are summation, subtraction, double, half and inverting circuits. In all these circuits only two switches (MOSFET), two diodes, one switching capacitor and one output filter capacitor is used. So the size of the circuits is very less as it doesn t employ any transformers unlike conventional multiport networks. So the power loss is very small as there are only small switching losses. If we employ these circuits for high voltages the switches will be operated at hard switching which is undesirable condition. An inductor is introduced in the circuits in series with the switched capacitor to ensure soft switching. In this soft switching the switches are on and off at current zero. Because of this soft switching, both the losses and the EMI were eliminated.the simulation of the resonant circuits was done in MATLAB SIMULINK and the output performance of the circuits is verified. The non resonant circuits will employ up to 20w. And the resonant circuits will employ up to 500w. This SCVC is efficient as both power consumption and cost are low. In this paper the resonant voltage copier was discussed and the results were verified. In the resonant circuits, the Switching frequency was 100 khz. In non resonant circuits the output performance was improved for the switching frequency of 200 khz. These non resonant circuits will be extended to the switching frequency of 200 khz for the better output results. REFERENCES 1. Chuanhong Zhao, Johann W. Kolar, An Isolated Three-Port Bidirectional DC-DC Converter with Decoupled Power Flow Management IEEE transactions on power electronics, vol. 23, no. 5, September 2008. 2. Y.-C. Liu and Y.-M. Chen, A systematic approach to synthesizing multi input dc dc converters, IEEE Trans. Power Electron., vol. 24, no. 1, pp. 116 127, Jan. 2009. 3. Y.-K. Lo, S.-C. Yen, and T.-H. Song, Analysis and design of a double output series-resonant dc dc convertor, IEEE Trans. Power Electron., vol. 22, no. 3, pp. 952 959, May 2007. 4. A. Nami, F. Zare, A. Ghosh, and F. Blaabjerg, Multi output dc dc converters based on diode-clamped converters configuration: Topology and control strategy, IET Power Electron., vol. 3, no. 2, pp. 197 208, Mar. 2010. 5. Michael Douglas Seeman, A Design Methodology for Switched-Capacitor DC-DC Converters, EECS Department, University of California, Berkeley, May 21, 2009.
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