High Step-Up Interleaved Forward-Flyback Boost Converter for Green Energy Sources

High Step-Up Interleaved Forward-Flyback Boost Converter for Green Energy Sources

1. Narsi Reddy

   Asst. Prof. & HOD, Dept of EEE Malineni Perumallu Educational Societys Group of Institutions, Guntur, A.P

   S. Nagendra Kumar, Asst. Prof, Dept of EEE

   Universal College of Engineering & Technology, Guntur, A.P

   S. Krishnarjuna Rao Asst. Prof, Dept of EEE

   Malineni Perumallu Educational Societys Group of Institutions, Guntur, A.P

   Abstract- A novel high step-up interleaved converter for high- voltage applications is proposed in this paper. High step-up conversion with high efficiency is obtained through three- winding coupled inductors. The proposed converter decreases the conduction losses and reduces the current stress on switches. In addition, due to the lossless passive clamp performance, leakage energy is recycled to the output terminal. Hence, large voltage spikes across the main switches are suppressed and the efficiency is improved. Finally MATLAB/ Simulink implementation of the proposed converter is developed for an output voltage of 380V with minimum ripple <2%.

   Keywords- High step-up, interleaved boost converter, renewable energy system.

   1. The high step-up gain that renewable energy systems require is easily obtained;

   2. Leakage energy is recycled to the output terminal, hence, large voltage spikes across the main switches are alleviated and the efficiency is improved;

   1. PROPOSED CONVERTER

      The proposed high step-up interleaved converter with three winding coupled inductors is shown in Fig. 1, where Lm1 and Lm2 are the magnetizing inductors; Lk1 and Lk2 represent the leakage inductors; S1 and S2 denote the power switches; Cs1 and Cs2 are the switched capacitors; and Co1, Co2, and Co3 are the output capacitors.

      1. INTRODUCTION

Nowadays renewable energy sources are valued and using worldwide for energy shortage and environmental contamination [1][8]. The renewable energy sources, such as fuel cells and photovoltaic cells, generate variable low- voltage energy. To connect to grid the DC voltage is converted in to AC with voltage equal to distribution grid voltage. In this process a dc/dc converter is required to maintain the output voltage constant and to step up the input low voltage. Thus, high step-up dc/dc converters have been widely employed in such renewable energy systems [9][13]. To convert low voltage from renewable sources into high voltage via a step-up conversion, and transform energy into DC-microgrid or utility through an inverter. Hence, the high step-up converter with high efficiency is seen as an important stage in such systems.

Theoretically, the conventional step-up converters, such as the boost converter and flyback converter, cannot achieve a high step-up conversion with high efficiency by extreme duty cycle or high turns ratio because of the resistances of elements or leakage inductance, also the voltage spike and stress on semiconductor devices are large.

The proposed boost/forward/flyback converter not only utilizes the switched capacitors, but also integrates three- winding characteristics well into coupled inductors, which achieves more flexible step-up regulation and voltage stress adjustment. Thus, the proposed converter is suitable as an excellent solution for high step-up conversion with high power and high efficiency. The advantages of the proposed converter are as follows:

1. The characteristics of low-input current ripple and low conduction losses, increase life-time of renewable energy sources and make it suitable for high-power applications;

   Fig. 1 Proposed Converter Configuration

   Dbs1 and Dbs2 are the diodes for boost operation; and Dfw1 and Dfw2 are the diodes for forward operation; and Dfb1 and Dfb2 are the diodes for flyback operation. When the switches turn OFF by turn, the phase whose switch is off- state operates as a flyback mode, and the other phase whose switch is on-state operates as a forward mode. The primary windings of the coupled inductors with N1 turns are employed to decrease input current ripple, and the secondary windings with N2 turns are utilized to operate forward mode, as well as the third windings with N3 turns are utilized to operate flyback mode. The turns ratios of the both coupled inductors are the same.

   The duty cycles of the power switches are interleaved with a 180°phase shift, and the key waveform of the proposed converter operating in continuous conduction mode (CCM) is depicted in Fig. 2. Fig. 3 shows the corresponding topological mode of the circuit. Due to the completely

   symmetrical interleaved structure, the operating modes I to V and VI to X are mutually symmetrical. In order to simplify the analysis of operating principle of the proposed

   iLk1 t3 iLm1 t3 KA21iDfw1 t3

   (4)

   converter, only the operating modes I to V are described.

   Mode V [t4,t5]: At t=t4, the phase 1 remains forward mode,

   and the power switches S2 remains off-state. The energy stored in leakage inductor Lk2 is totally released, and energy stored in magnetizing inductor Lm2 is still transferred to third winding.

   iLk1 t4 iLm1 t4 KA21iDfw1 t4

   iLk1 t4 0

   (5)

   (6)

   Where K represents the ratio of number of turns of secondary to primary.

   K NA2

   A21

   NA1

   (7)

   Fig. 2 Waveforms in Continuous Current Mode

   Mode I [t0,t1]: At t=t0, the power switchS1begins turning on to forward mode. The energy stored in magnetizing inductor Lm1 is still transferred to third winding. The switched capacitor Cs2, leakage inductor Lk2, and magnetizing inductor Lm2 are in charging state as shown in Fig. 3(a). The currents through leakage inductor Lk1 given by the equations

   iLk1 t0 iLm1 t0 KA31iDfb1 t0

   (1)

   Mode II [t1,t2]: At t=t1, both power switches S1 and S2 are in on-state, and both phases are in forward mode. The switched capacitors Cs1 and Cs2, leakage inductors Lk1 and Lk2 and magnetizing inductors Lm1 and Lm2 are in charging state. The currents through leakage inductor Lk1 given in equation

   iLk1 t1 iLm1 t1 KA21iDfw1 t1

   (2)

   Mode III [t2,t3]: At t=t2, the phase 1 remains forward mode, but the power switches S2 begins turning off to flyback mode. The magnetizing inductor Lm2 still stores energy, and the energy stored in leakage inductor Lk2 is naturally recycled to output capacitor Co1. The currents through leakage inductor Lk1 given by

   iLk1 t2 iLm1 t2 KA21iDfw1 t2

   (3)

   Mode IV [t3,t4]: At t=t3, the phase 1 remains forward mode, and the power switches S2 remains off-state. The energies stored in switched capacitor Cs2, magnetizing inductor Lm2, and leakage inductor Lk2 are transferred to output terminal.

   Fig. 3 Operating Modes

   1. Mode I (b) Mode II (c) Mode III (d) Mode IV (e) Mode V (f) Mode VI (g) Mode VII (h) Mode VIII (i) Mode IX (j) Mode X.

III . SIMULINK IMPLIMENTATION

The proposed converter is designed in MATLAB/ Simulnk with the specifications give in the Table. 1. The input voltage of the converter is 48V and the output voltage is 380V.

Fig. 4 Simulink Implementation of the Proposed Converter

Fig. 4 shows the simulink implementation of the proposed converter with three coupled inductors.

Table.1 Parameters of the proposed converter

1. SIMULATION RESULTS

   Input voltage to the converter is 48V DC supply. It is shown in the Fig. 5. The converter is supplied by pulses generated by PWM generator with Duty cycle of 0.6. It is seen that the output voltage of the converter is raised to a constant value 380V as shown in Fig. 6.

   Fig.5 Input DC voltage to Converter

   Fig. 6 Output Voltage of the Converter

   The voltage across the switches is increased up to 180V that is nearly half of the output voltage. From this it is evident that the stress on the switches is reduced. Fig. 7 & 8 shows the voltage across the switches.

   Fig. 7 Voltage across the switch S1

   Fig. 8 Voltage across the Switch S2

   Fig. 9 Switching pulses to Switches S1 and S2

   The converter has minimum peaks in the output voltage

   <5% so it is used to connect directly to DC Microgrid without any extra circuit. The power loss across the switches is also less.

2. CONCLUSION

   This High Step-up Interleaved Forward-Flyback Converter is having high voltage gain ratio. The disturbance in the output voltage is minimum. The voltage stress on the switches is reduced by a great extent. The power loss in the switches is very less and this converter is highly efficient for high voltage DC conversions..

3. ACKNOWLEDGEMENT

We sincerely thank Dr.Malineni Perumallu, Vice- Chairman, Malineni Lakshmaiah Engineering & Group of colleges and Dr.P.NageswaraRao Director-MPES for their keen interest and academic support.

.

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AUTHOR PROFILE

VAJRALA NARSI REDDY received his Bachelor of Technology degree in Electrical & Electronics Engineering and Master of Technology in Power Electronics from JNTU Kakinada,

A.P. in 2010 and 2012 respectively. Currently, working as an Assistant Professor & Head, Dept. of EEE in

Malineni Perumallu Educational Societys Group of Institutions, Guntur, A.P. His areas of interests are in Power Systems, Power Electronics and FACTS. He is a member of IEEE, ISTE, SSI and IAENG.

SINGAMSETTY NAGENDRA

KUMAR Bachelor of Technology degree in Electrical & Electronics Engineering and Master of Technology in Power & Industrial Drives from JNTU Kakinada, A.P. in 2012 and 2014 respectively. Currently, working as an Assistant Professor in Universal

College of Engineering & Technology, Guntur, A.P. His areas of interests are in Power Electronics and Machines. He is a member of SSI and IAENG.

SUDA KRISHNARJUNA RAO

Bachelor of Technology degree in Electrical & Electronics Engineering and Master of Technology in Power & Industrial Drives from JNTU Kakinada,

A.P. in 2012 and 2014 respectively. Currently, working as an Assistant Professor in Malineni Perumallu

Educational Societys Group of Institutions, Guntur, A.P. His areas of interests are in Power Electronics and FACTS. He is a member of IEEE, ISTE, SSI and IAENG.