Performance Comparison of Multi Input Capacitor Converter Circuits

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 8, No. 5, October 2018, pp. 3471~3483
ISSN: 2088-8708, DOI: 10.11591/ijece.v8i5.pp3471-3483  3471
Journal homepage: http://iaescore.com/journals/index.php/IJECE
Performance Comparison of Multi Input Capacitor Converter
Circuits
Sreejith S1
, Karthik Balasubramanian2
1
School of Electrical Engineering, Vellore Institute of Technology, Vellore, India
2
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore
Article Info ABSTRACT
Article history:
Received Jun 18, 2018
Revised Sep 2, 2018
Accepted Sep 9, 2018
This paper analyze the operation of a multi input switched capacitor (MIC)
converters using a couple of switches, diodes and capacitors for several
levels. With two input sources it is possible to obtain 8 output voltage levels.
Here, 5 topologies of switched capacitor circuits namely summation,
subtraction, inverting, double and half circuits are simulated and their
performances are analyzed. Multi Input Converters have a high regard for
multiple renewable energy sources used in smart grid systems, especially for
distributed generators. The effects on output voltage with variation in load
for different frequencies are also analyzed. Hardware implementation of
summation and subtraction circuit is carried out and the results are compared
with the simulated results
Keyword:
Inverting circuit
Multi Input Converters
Summing circuit
Switched capacitor circuits
Copyright © 2018 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Sreejith S,
Department of Energy and Power Electronics,
School of Electrical Engineering,
Vellore Institute of Technology,
Vellore,Tamil Nadu, India.
Email: sreejith.s@vit.ac.in
1. INTRODUCTION
Inductors and capacitors are the main energy storage for the switched-mode power supplies (SMPS).
The sizes are usually dominated by the inductor and transformer [1]. DC-DC converters play a vital role in
renewable energy based applications [2], [3]. Resonant converters based on this SMPS can operate at high
switching frequencies to decrease the size of the converters, however, their switching frequencies are not
constant and hence the electromagnetic interference (EMI) filter cannot be optimized. Extended period
quasiresonant converters have been introduced in [4], [5]. These converters are able to operate at constant
switching frequencies and all the switching devices are switched at zero-current or zero-voltage. The
requirement of magnetic components restricts the application and increases the difficulty in designing the
converters. These difficulties were replaced with switched capacitor circuits. Switched-capacitor (SC) DC-
DC power converters [6] are a subset of DC-DC power converters, using only switches and capacitors that
can efficiently convert one voltage to another. Since SC converters does not have any inductors, they are
ideal for integrated implementations, as common integrated inductors are not suitable for power electronic
applications. The main advantage of this kind of converter is that no magnetic component is required for
storing energy, making it possible to fabricate a smaller size and lighter weight converter in an integrated
circuit [7]. There are very mature theories and techniques to design variety of DC–DC converters with single-
input. Buck converter can for lower voltage than input [8], boost converter output higher voltage [9], boost-
buck converter and Cuk converter can obtain the output voltage with step up or down ratio [10] In addition,
Half-mode, Double-mode [11], step-up and step-down converter based on switched-capacitor can output half,
twice and multiple and fractional voltage ratios [12], [13]. In recent years, with the continuous development

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 8, No. 5, October 2018 : 3471 – 3483
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of new energy technologies and the production of complex electrical equipment, multi-input DC–DC
converter has aroused significant attention. A few topologies of multi input converters (MICs) have been
presented in [14]-[21]. Due to the advantages of multiport converter, recently there have been extensive
researches that resulted in a wide variety of topologies. One simple approach is to interface several converter
stages to a common dc bus with independent control for each converter stage. A multi input boost-type
converter [22] was designed for hybrid electric vehicles using such loose structure.
2. MULTILEVEL CONVERSION CIRCUITS
Figure 1 shows the diagram of a multilevel dc conversion from two different voltage levels. Two
voltage levels as input, it is anticipated that the two voltage levels can be converted to other voltage levels in
order to suit different voltage needs for other electronic appliances. With these five conversion circuits
namely summation circuit, subtraction circuit, double circuit, half circuit, inverting circuit it is possible to
convert two input voltages into eight levels of voltage. With only one input source Vs , the family of
switched-capacitor converter can transform it into 0.5VS , −Vs, or 2Vs . With two input supplies Vs1 and
Vs2, it can transform them into Vs1 + Vs2 or Vs1–Vs2. So, using the switched-capacitor converter and three
distribution lines, two voltage levels can be converted into eight voltage levels. It includes Vs1+Vs2
(Summation) , Vs1-Vs2 (Subtraction), 2Vs1 (Double) , 2Vs2 (Double) , 0.5Vs1 (Half), 0.5Vs2 (Half), -Vs1
(Inverting) and –Vs2 (Inverting). Each of the circuits uses only two switches, two diodes and two capacitors.
Therefore, the size of the circuits is very small and simple enough to handle. A pair of complementary pulses
is given to two switches with fixed duty ratio of 0.5 for all the five circuits.
Figure 1. Multilevel converter
2.1. Summation circuit
The basic circuit diagram of a summation circuit is shown in Figure 2. Here, when Q1 is turned ON
and Q2 is turned OFF, diode D1 is forward biased and D2 is reverse biased. Vs1, C1, Q1, and D1 forms a
closed loop. Vs1 charges C1 and the voltage across C1 is the same voltage as Vs1, i.e., Vc1 = Vs1. When,
Q1 is turned OFF and Q2 is turned ON, D2 is forward biased and D1 is reverse biased, Vs2, C1, Q2, D2, and
C2 form a closed loop. C1 is connected in series with Vs2 and delivers the total voltage to C2, so the voltage
across C2 is Vs2 + Vc1. As Vc1 = Vs1, the output voltage Vo = Vs1 + Vs2. Figure 3 shows the output
voltage of summation circuit. Here Vs1 and Vs2 are 24V and 12 V respectively, the output voltage across
load is 33.87V.

Int J Elec & Comp Eng ISSN: 2088-8708 
Performance Comparison of Multi Input Capacitor Converter Circuits (Sreejith S)
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Figure 2. Summation Circuit Figure 3. Output voltage and capacitor voltage of
Summation Circuit
2.2. Subtraction circuit
The circuit diagram of a subtraction circuit is shown in Figure 4. When Q1 is turned ON and Q2 is
turned OFF, D1 is forward biased and D2 is reverse biased. Vs1, Vs2, C1, Q1, and D1 form a closed loop,
and Vs1 is connected in series with –Vs2 and charges C1, so the voltage across C1 is Vs1-Vs2. Next, when
Q1 is turned OFF and Q2 is turned ON, D2 is forward biased and D1 is reverse biased, C1, Q2, D2, and C2
form a closed loop. C1 is connected in series with C2, so the voltage across C2 is equal to Vc1. The output
voltage Vo = Vs-Vs. Figure 5 shows the output of a subtraction circuit. Here Vs1 and Vs2 are 24V and 12 V
respectively, Vo = 12.27V.
Figure 4. Subtraction circuit Figure 5. Output voltage and capacitor voltage of
Subtraction circuit
2.3. Double circuit
The circuit diagram of double circuit is shown in Figure 6. During mode 1, when Q1 is ON, Q2 is
OFF, D1 is forward biased and D2 is reverse biased, Vs1, D1,C1,Q1 forms a closed loop and capacitor C1
charges to voltage Vs. This is known as charging state. In mode 2 Q2 is ON, Q1 is OFF, D2 is forward biased
and D1 is reverse biased, Vs, Q2, C1, D2, RL forms a closed loop. Capacitor C1 discharges now and
capacitor C2 is now charging to voltage Vc1+Vs.This is known as discharging state. The output of double
circuit becomes Vo = 2Vs. Figure 7 shows the output of double circuit. Here Vs1 and Vs2 are 24V and 12 V
respectively, the output voltage Vo = 45.67V.

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Figure 6. Double circuit Figure 7. Output voltage and capacitor voltage of double
circuit
2.4. Half circuit
The diagram of half circuit is shown in Figure 8. In mode 1 Q1 is ON, Q2 is OFF, D1 is forward
biased and D2 is reverse biased, Vs, Q1, C1, D1, C2 forms a closed loop. Capacitor C1and capacitor C2
equally charges to voltage 0.5Vs. In mode 2 Q2 is ON, Q1 is OFF, D2 is forward biased and D1 is reverse
biased. The voltage across capacitor C2 remains constant. The output of half circuit is Vo = 0.5Vs2.
Figure 9 shows the output of half circuit. Here Vs2 is 24V, the output voltage Vo = 11.14V.
Figure 8. Half circuit
Figure 9. Output voltage and capacitor voltage of half circuit

3475
2.5. Inverting circuit
The inverting circuit is shown in Figure 10. In mode 1 Q1 is ON, Q2 is OFF, D1 is forward biased
and D2 is reverse biased,Vs,Q1,C1,D1 forms a closed loop and capacitor C1 charges to voltage Vs .This is
known as charging state. In mode 2 Q2 is ON, Q1 is OFF, D2 is forward biased and D1 is reverse biased, Q2,
C1, D2, C2 forms a closed loop and capacitor C1 starts discharging. Capacitor C2 is now charging to voltage
Vs with reverse polarity. This is known as discharging state. The output of inverting circuit Vo = -Vs. The
output voltage of an inverter circuit is shown in Figure 11. The input voltage is 12V and output voltage is
-12V.
Figure 10. Inverting circuit
Figure 11. Output voltage and capacitor voltage of inverting circuit
3. VARIATION OF LOAD AND FREQUENCY ON CONVERSION CIRCUITS
The performance of the above said circuits are analyzed under different loads and frequencies. The
results obtained are shown in Figure 11 (a) to Figure 11(e). The input voltages considered are 24V and 12V.
The frequency chosen are 50 kHz and 100 kHz. The load is varied from 1 to 500Ω. It is clear that, the
performance of the circuit is independent of the switching frequency. The initial voltage shoot increases with
frequency, finally settle down to a constant value.

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3476
(a) (b)
(c) (d)
(e)
Figure 12. (a) Summing circuit under variable load and frequency, (b) subtracting circuit under variable load
and frequency, (c) double Circuit under variable load and frequency, (d) half circuit under variable load and
frequency, (e) inverting circuit under variable load and frequency

3477
4. HARDWARE REULTS AND DISCUSSION
To validate the simulation findings a hardware prototype for summation and subtraction circuit are
fabricated. The circuit is tested for the frequencies of 50 kHz, 100 kHz and loads of 100Ω and 330 Ω.
Figure 13. Hardware set up for summation circuit
Figure 13 shows the experimental setup for summation circuit. For a load of 330Ω and switching
frequency of 100 kHz, the input voltages given to the summation converter are 24V and 12 V respectively.
The output voltage obtained is 32.1V and is shown in Figure 14. This is similar to the values obtained in
simulation.
Table 1. Summation Circuit Results for 100 kHz
Figure 14. Output voltage for summation circuit
4.1. Variable load with fixed frequency of 100 kHz
When C1 and f are fixed, the variation in frequency is shown in Figure 15(a) and Figure 15(b).
indicates the influence of a varying load on Vo. The output voltages for resistances of 100Ω and 330 Ω are
shown. It is clear that, the output voltage changes with variation in load resistance. The comparison between
Load
(Ω)
Calculated output voltage (V) Simulated output voltage (V) Experimental output voltage(V)
100 33.09 31.52 30.3
330 34.1 33.46 32.1
430 34.23 33.67 32.4

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simulated and hardware results are furnished in Table 2.
(a)
(b)
Figure 15. (a) Output voltage for 100Ω, (b) Output voltage for 330Ω
Table 2. Summation Circuit Results for Variable Load
Load
(Ω)
Calculated output voltage (V) Simulated output voltage(V) Experimental output voltage(V)
100 33.83 32.88 30.9
330 34.36 33.91 32.1
430 34.4 34.02 32.6

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4.2. Variable load with fixed frequency of 50 kHz
The hardware output for 50 kHz for variable resistance is shown in Figure 16(a) and Figure 16(b).
The output varies with the change in load resistance.
(a)
(b)
Figure 16. (a.) Output voltage for 100Ω, (b) output voltage for 330Ω
4.3. Variable frequency with fixed of load 100 Ω
For a fixed load of 100 Ω, the switching frequency is varied for 50 kHz and 100 kHz and the results
obtained are shown in fig 17.a and 17.b. The simulated and hardware results are furnished in Table 3. It is
clear that, the output depends on both load resistance and frequency.

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(a) (a)
Figure 17. (a) Output voltage for 50 kHz, (b) output voltage for 100 kHz
Table 3. Summation Circuit Results for Variable Frequencies
Frequency
(kHz)
Calculated output voltage (V) Simulated output voltage (V) Experimental output voltage (V)
50 33.09 31.52 30.3
100 33.83 32.88 30.9
4.4. Subtraction circuit
For a load of 330Ω and switching frequency of 100 kHz, the input voltages given to the subtraction
converter are 24V and 10 V respectively. The output voltage obtained is 12.2V and is shown in Figure 18.
Figure 18. Output voltage for subtraction circuit

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Figure 19(a) to Figure 19(b) shows the output voltage at 100 kHz and100Ω, output voltage at
100 kHz and 330Ω, output voltage at 50 kHz and 100Ω, and the output voltage at 50 kHz and 330Ω. Table 4
shows the subtraction circuit results for variable frequencies.
(a) (b)
(c) (d)
Figure 19. (a) Output voltage at 100 kHz and100Ω, (b) Output voltage at 100 kHz and 330Ω, (c) Output
voltage at 50 kHz and 100Ω, (d) Output voltage at 50 kHz and 330Ω
Table 4. Subtraction Circuit Results for Variable Frequencies
Load
(Ω)
Frequency = 100 kHz Frequency = 50 kHz
Calculated
output voltage
(V)
Simulated
output voltage
(V)
Experimental
output voltage
(V)
Calculated
output voltage
(V)
Simulated
output voltage
(V)
Experimental
output voltage
(V)
100 12.32 12.11 11.6 12.02 11.85 11.2
330 12.5 12.32 12.2 12.42 12.26 11.8
430 12.53 12.36 12.2 12.46 12.33 12.2

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5. CONCLUSION
The performance of various multi input switched capacitor converters are analyzed in this paper.
Various topologies namely summation, subtraction, inverting, double and half circuits are simulated under
variable load and variable frequencies. The variation in outputs with variable load and frequencies are
illustrated. With different switched capacitors topologies mentioned here a multi converter can convert two
input voltages can be used to obtain 7 different voltage levels. The results have been experimentally verified
for summation and subtraction converters for different loads under different frequencies. These results have
been compared with the theoretical and simulated value. This can be extended to three input converters also.
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BIOGRAPHIES OF AUTHORS
Sreejith S received his Bachelor's degree in Electrical and Electronics Engineering from M.S
University. He completed his Master’s in Power Electronics and Drives from Anna University
Chennai. He completed his Doctoral research in Electrical Engineering at National Institute of
Technology, Trichy, India. Presently he is working as an Associate Professor at VIT university,
Vellore. His areas of interest include FACTS, Power Electronics & Drives and Power Electronics
Applications to Power Systems.
Karthik Balasubramanian. Completed B. Tech in Electrical and Electronics Engineering with
Minor in Industrial Automation from VIT University, Vellore, India, in 2014. He is currently
working as an Electrical Engineer in Saipem India Projects Pvt. Ltd. He has published many research
papers in various national and international journals. His area of research interest are Power
engineering, Fuel cell system design, PV system design and applications of Power electronics in
Renewable Energy systems

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