A High Voltage Gain Switched Capacitor based Boost DC-DC Converter

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A High Voltage Gain Switched Capacitor based Boost DC-DC Converter

Ms. Anziya Nazeer

P G Scholar

Electrical and Electronics Engineering Department Ilahia Collage of Engineering and Technology Muvattupuzha

Dr. S. Karthikumar

Professor and HOD

Electrical and Electronics Engineering Department Ilahia Collage of Engineering and Technology Muvattupuzha

Abstract:-This paper, going to propose a high voltage gain switched capacitor based boost DC to DC. For reducing the stress of the diodes, MOSFETs and conduction loss on the switches, uses small duty cycle. This converter has an advantage of high voltage gain and a simple structure. The converter can make 300V output from a 50V input with a duty cycle of 17%. MATLAB/SIMULINK R2017a is used for simulation works. From the analysis a voltage gain of 6 is obtained at 360W output. Based on the simulation results analysis is done. Arduino microcontroller is employed to produce the switching pulses for the control circuit . To verify the performance and operating principle output voltage of 300V and input voltage of 50V with output power of 360W prototype is constructed and the results are validated.

Keywords Boost converter, dual-switch, switched capacitor, non isolated DCDC converter, high voltage gain continuous conduction mode (CCM).

  1. INTRODUCTION

    DC-DC converter with high gain has increasing demands in recent days. High step-up DC-DC converter is a class of converter switch can boost a low voltage to a relatively high voltage. As we known, the output voltage of fuel cell stacks, single PV module, battery sources, or the super capacitors is relatively low; it should be boosted to a high voltage to feed the ac grid or other applications like un interruptible power supplies, new energy vehicles, and so on.Lots of research works have been done to provide a high step-up without an extremely high duty ratio. The isolated converters can boost the voltage ratio by increasing the turns ratio of the high- frequency transformer. However,the leakage inductor should be handled carefully; otherwise, it will cause voltage spike across the power switches or diodes. Moreover, isolated DC- DC converters have the shortages in system volume and efficiency due to multistage DC-AC-DC conversion

    F. L. Tofoli [2] introduced a step-up DC-DC topologies that feature high eciency, reduced stress, low cost, simplicity and robustness. W Li [3] introduced a power system for the downstream DC-AC grid-connected inverter which require a DC-DC converter to step up the low voltage of fuel cell or PV to a high bus voltage. Y. P. Siwakoti [4] introduced a new DC-DC converter, derived from the traditional Y-source network. The proposed circuit inherits all the advantages of the Y-source including very high boost capability and exibility to choose multiple circuit parameters to tune the gain. Minh-Khai Nguyen, Truong-Duy Duong, and Young-

    Cheol Lim [1] proposes boost dc-dc converter which employs the use of switched capacitor. It consists of two switches S1, S2, three diodes D0, D1, and D2 and one inductor L and three capacitors C0, C1 and C2. Vg is the input voltage and output voltage is denoted as V0. Figure 1 shows a typical arrangement of the converter. The circuit is analysed on continuous conduction mode carries some assumptions such as all devices are ideal and lossless, the capacitor values are large, the current owing through the inductor decrease or increase linearly.

    Fig. 1.Switched Capacitor Based Converter

    In mode 1, switch S1, S2 are turned on. At the same time diode D0 will conduct and diodes D1, D2 and D3, will not conduct. The inductor L gets charged and the capacitor C1 C2 will discharges its energy. D*T is the time duration taken for this mode, where T and D shows its switching period and duty cycle of the converter. Both the switches are turned o in mode 2. The diodes D1 and D2will conduct and diode D0 will not conduct. The time duration for this mode is D*(1- D).During this mode the energy stored in the inductor L will discharges , and the energy will stored in capacitors C1 and C2. In order to improve the voltage gain of the circuit pointed above modified the circuit by adding a switched inductor circuit in the input side. By adding switched inductor circuit in the input, it is observed that the gain can improved to 6. There is no any difference in designing aspects.

  2. PROPOSED CONVERTER

    Proposed high voltage gain Switched capacitor based boost DCDC converter is shown in fig.2. It consists couple of power switches (S1 and S2), two inductors (L1 and L2), three

    capacitors (C0 C2), seven power diodes (D0 D6) and a resistive load (R).

    state. D*T is the time duration taken for this mode, where T and D shows its switching period and duty cycle of the converter. By applying KVL in Fig. 3(a) the following formula is derived:

    L diL1 L

    diL2 V V

    (1)

    1 dt

    2 dt

    g C1

    V0 Vg VC1 VC 2

    (2)

    Fig. 2. Proposed converter

    The following assumptions are taken consideration while designing the converter:

    Mode 2: Figure 3(b) shows the operating mode 2. S1 and S2 switches are turned OFF at this mode. The diodesD1, D2, D3 and D6 will conduct and the diodes D0, D4 and D5 are block the current flow. (1 D)*T is the time duration taken for this mode. During this mode, the inductor L1 and L2 are discharged through the diodes D1, D2, D3 and D6 while capacitors C1 and C2 are charged through the same path, and the following formula is derived:

    1. All components are taken as ideal and lossless;

      L diL1 L

      diL2 V V

    2. To maintain the constant capacitor voltage, capacitance of

      the capacitors are made high; and

      1 dt

      2 dt

      g C1

      (3)

    3. The current in the inductor will increases or decreases

    VC1

    VC2

    (4)

    linearly.

    The circuit diagram of the high voltage gain switched

    Substitute equation (1) to equation (4) after applying volt balance law to the inductor gives the following equation:

    capacitor based boost DCDC converter in continues

    V V V

    (5)

    conduction mode is shown in figure 2.

  3. OPERATING PRINCIPLES

    The working of the circuit can be explained by 2 modes of

    C1 C2 g

    Proposed converters Output-voltage gain in the CCM can be obtained by substituting equation (5) in equation (2) and is shown in equation(6):

    operation. Figure 3(a) and 3(b) shows the operating modes of

    high voltage gain switched capacitor based boost DC DC converter in continues conduction mode .Switches S1 and S2,

    GCCM V0

    Vg

    3 2D 1 2D

    (6)

    will turned on in mode one and off in mode 2.

    The output current of the proposed converter is equal to the average current of the diode D0. By applying KCL in node A of Figure 2, average inductor current of the converter is as follows

    IL IL Iin I0

    (7)

    1 2

  4. DESIGN CONSIDERATIONS

    1. Voltage and Current Stress on the Switches

      By analyzing the operating mode, the input current is equal to the switch current (IS) in mode 1, and is equal to the inductor current in mode 2; following equation shows the average input current:

      Po

      Iin Vg DIS (1 D)IL

      (8)

      The peak current of the switches S1 and S2can find out by substituting equation (7) in (8) and is as follows:

      IS

      P0

      D3 2DVg

      (9)

      Fig. 3. Operating modes of the high gain switched capacitor based boost DC- DC converter: (a) mode 1 (b mode 2.

    2. Voltage and Current Stresses on the Diode D0

      The peak current of the diode D0 is calculated based on the operation in mode 1 shown in figure 3(a) is as follows:

      Mode 1 : Fig. 3(a) shows the circuit .diagram in mode 1. SwitchesS1 and S2 are turned ON in this mode. The

      ID0

      IS IL1 IL2

      (10)

      switches allows a path to charge the inductor L1 and L2 and

      discharge the capacitors C1 and C2.The diodes D0, D4, and D5 are forward-biased, and the diodes D1, D2 and D3 is in blocked

    3. Inductor Selection

      Using equation (1), we can calculate the peak-to-peak inductor current .By considering the ripple current of the

      inductor IL = ri%IL the value of the inductor should be as follows:

      D*1 D*3 2D*T*V2

      TABLE 1. SIMULATION PARAMETERS

      L1

      g

      ri %*1 2D*P0

      (11)

      Similarly,

      D*1 D*3 2D*T*V2

      Parameter

      Values

      Output voltage

      300 V

      Input voltage

      50 V

      Output power

      450 W

      Capacitors C1, C2

      C0

      C1, C2 22 µF/100 V 110 µF/450 V

      Inductor L1,L2

      0.5 mH

      Switching frequency

      50 kHz

      Parameter

      Values

      Output voltage

      300 V

      Input voltage

      50 V

      Output power

      450 W

      Capacitors C1, C2

      C0

      C1, C2 22 µF/100 V 110 µF/450 V

      Inductor L1,L2

      0.5 mH

      Switching frequency

      50 kHz

      L2

      g

      ri %*1 2D*P0

      (12)

    4. Capacitor Selection

    The capacitor voltage ripple is considered while designing the capacitor value. By analysing the current flow, the switch S1speak current and current flow in capacitor C1 in mode 1 is seems to be same. The peak current of the diode D0is equal to the current ow in the capacitor C2, therefore the equations be like:

    IC1

    IC2

    P0

    D 3 2DVg

    P0

    D 3 2DVg

    • IL

    (13)

    (14)

    The capacitances for the capacitor C1 and C2 of the converter is as follows: by considering capacitor peak-to-peak voltage ripple, the capacitor voltage is restricted in amount by rv%:

    1 2DTP0

    Fig. 4. Simulink model of proposed converter

    The simulation results of the high voltage gain switched capacitor based boost DCDC converter is shown in the

    C1

    C2

    r %3 2DV2

    V g

    V g

    0

    0

    1 2D2 TP

    V g

    V g

    r % 3 2DV2

    (15)

    (16)

    following gures.

    The switching frequency is 50 kHz. The gate pulse of main power device has xed duty cycle of 17%.

    It can be seen from the Figure 5(a) and Figure 5(b) and 5(c) that the output current is 1.2A, the output voltage V0 is about 300 V and output power is 360W. This allows high voltage

    The output current in mode 2 is equal to the current ow in

    output capacitor C0as shown in figure 3(b).The C0 capacitance is designed so as to reduce the ripple on the output voltage.

    1 D(1 2D)2 TP

    gain of low-stress converter. The output voltage has a ripple of 0.2%.As shown in Figs. 5(f) and 5(g), the voltage of the capacitor C1 and C2 is boosted to 129V.

    C0

    0

    V g

    V g

    r %3 2DV2

    (17)

  5. SIMULATION RESULTS

    The simulation parameters of high voltage gain switched capacitor based boost DC DC converter is given in table 1. An input voltage Vin of 50V gives an output voltage VO of 300V for an output power PO of 360W. The switches are MOSFET/Diode with constant switching frequency of 50 KHz. The duty cycle of switches is taken as D = 0.17. The high voltage gain switched capacitor based boost DC DC converter is simulated in MATLAB/SIMULINK by choosing the parameters listed in table 1 and the Simulink model is shown in figure 4

    Figure 5:(a)Output Current (b) Output Voltage (c) Output Power (d) Voltage Stress S1 (e) Voltage Stress S2 (f) Voltage across C0 (g) Voltage across C1 (h) Voltage across C2

    Figure 6: (a) Voltage across D0 (b) Voltage across D1 (c) Voltage across D2 (d) Voltage across D3 (e) Voltage across D4 (f) Voltage across D5 (g) Voltage across D6

  6. ANALYSIS

    The analysis of high voltage gain Switched capacitor based boost DCDC converter is carried out by considering parameters like voltage gain, eciency and duty cycle etc.

    Fig.7.Voltage gain Vs duty cycle

    A typical curve for the voltage gain Vs duty cycle is shown in gure 7. For a duty cycle of 17% the eciency is 97 % .

    A typical curve for the eciency Vs duty cycle is shown in gure 8. For a duty cycle of 17% the eciency is 97%. Thus the eciency of a switched Capacitor DC-DC Converter decreases with increase in the duty ratio.

    Fig. 8. Eciency Vs duty cycle

    The comparison of modified converter with conventional SCDC converter is given in table 2.

    TABLE 2. COMPARISON

    Parameter

    SCDC

    converter

    Proposed converter

    No of inductors

    1

    2

    Output current ripple

    0.2A

    0.2A

    Voltage gain

    4

    6

    Output voltage ripple

    0.4V

    0.2V

    No of capacitors

    3

    3

    Switches

    2

    2

    Output voltage

    200V

    300V

    Output Power

    200W

    360W

    Output Current

    1A

    1.2A

    Input Voltage

    50V

    50V

    A prototype of high voltage gain switched capacitor based boost dc dc converter with input voltage of 50V is implemented. The top view of the experimental setup is shown in Figure 9. It consists of control circuit, driver circuit and power circuit. Control circuit is composed of Arduino microcontroller and its power supply. The control pulses for MOSFET switches are generated using Arduino microcontroller. The pulses from microcontroller are amplified by driver circuit. It also provides isolation between control and power circuit.

    Fig.9.Experimental Setup

  7. CONCLUSION

High voltage gain Switched capacitor based boost DC DC converter boost input voltage to a very high Value, moreover it has low switch voltage stress, and conduction loss on the power switches. The switches and diodes have relatively low voltage stresses and hence the switching and conduction losses are reduced. It achieves an improved overall eciency. The input and output voltages of the converter verify the high boost voltage gain. The converter has an eciency of 97% and voltage gain of 6.A duty ratio of up to 0.17 is suitable for this converter so as to keep the voltage stress across the switches and diodes to a safe limit. The converter can be used for applications with high output voltage and can handle small output current. Moreover it can be used as LED driver and can be also used in solar system .High voltage gain Switched capacitor based boost DC DC converter can be also introduced in dc motor drives, electric automobiles ,and

marine hoists. Moreover it is used in high voltage low current applications such as accelerating purpose in cathode ray tube

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