Implementation of New Control Technique for Interleaved Flyback Inverter Based PV System

Implementation of New Control Technique for Interleaved Flyback Inverter Based PV System

V. Anandakumar1, A. Ramesp, Dr. E. Mariappane3

1. PG Scholar, M.E. Power electronics & Drives, Dr.Pauls Engineering college, Villupuram

2. Associate Professor, Dept of EEE,Dr.Pauls Engineering college, Villupuram

3. DEAN (Academics),Dr.Pauls Engineering college, Villupuram

Abstract Photovoltaic (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic (PV) power generation has become one of the main ways to use solar energy. And the renewable energy source based distributed generation (DG) system are normally interfaced to the grid through power electronic converters or inverters. An interleaved flyback inverter based photovoltaic system with an improved control strategy is discussed in this paper. A photovoltaic AC module system is considered for study. In a conventional single flyback inverter for the photovoltaic AC module system, this inverter has drawbacks of a conduction losses of each switch, transformer copper and high ripple current of capacitor. To overcome these problems, two flyback converter modules with interleaved pulse-width modulation (PWM) are connected in parallel at the input and output sides reducing the ripple current on the input and output capacitors and decrease the current stress on the transformer windings. In order to verify these, theoretical analysis and simulation are performed. The Matlab/Simulink based simulation demonstrate the betterment of the proposed scheme.

Keywords PV, PWM, DG, ILFI

1. INTRODUCTION

   Generally Photovoltaic (PV) energy has plays the major role in the renewable energy. The PV technique also grown faster even though the initial cost is high but the solar energy is available at free of cost by naturally and its efficiency also high. To obtain the sufficient power the PV system use the PV modules are connected in series or parallel.

   By means of mismatch between the modules, shadows from trees or tree branches, buildings and other things partially cover the PV module so the conventional PV system having power losses. To overcome this problem photovoltaic AC module is considered, For the photovoltaic AC module flyback inverter is the best for the grid connection because it having advantages of less components, simple in construction and provide the isolation between the PV modules and grid line.

   main switch is operate with soft switching. By using of the interleaved technique in the inverter the conduction loss of each switch can me minimized, reliability, system life is improved, the ripple current is reduced by the capacitor.

2. SYSTEM STRUCTURE AND ANALYSIS

   1. BLOCK DIAGRAM

      Fig 1. Block diagram for ILFI

   2. CIRCUIT CONFIGURATION AND DESCRIPTION

      Interleaved flyback inverter (ILFI) is basically design for to get the maximum power from the PV module. Normally the conventional flyback inverter having the voltage spike across the main switch. For reducing the voltage spike across the main switch the active clamp circuit is used. The clamp circuit is also used to reduce the switching loss because the

      Fig 2. Interleaved flyback inverter for photovoltaic AC module

      Interleaved flyback inverter for photovoltaic AC module consists of the PV module as input, decoupling capacitor, 1st phase converter, 2nd phase converter, unfolding bridge and C- L filter. For the Photovoltaic AC system, Maximum Power

      Point Tracking (MPPT) is essential to get the peak power from the PV module. Decoupling capacitor is used to remove the harmonic frequency which distorts the constant PV voltage and current. Both the flyback converters consist of main switches, active clamp circuit, Transformer and Diode.

      The active clamp circuit is used to reduce the voltage spike across the main switch which is occurring in resonance between output capacitor and leakage inductance. Transformer is used to maintaining the isolation between PV module and grid line and also boost the voltage. Unfolding bridge is used for connection between transformer and grid line.

   3. MODES OF OPERATION

      The ILFI having ten operational modes in the switching period, Based on its steady state operation. Due to simplicity of control here considered only discontinuous conduction mode (DCM).

      The following modes are shows the steady state operation of ILFI.

      1. Mode 1 [t0-t1]

         Mode 1 [t0-t1]: In a 1st flyback converter stage, main switch Sp1 is turned on and the auxiliary switch Sa1 is turned off. The energy is stored to the magnetizing inductor Lm1 and the primary current iSp1 increases linearly.

         In a 2nd flyback converter stage, the current through leakage inductance LLk2 is zero and the anti-paralleled diode of Sa2 is turned off. And, the output diode D2 is turned on. The magnetizing energy in Lm2 is transferred to the unfolding bridge stage.

      2. Mode 2 [t1-t2]

         Mode 2 [t1-t2]: The switches of 1st flyback converter stage operate in the same with earlier mode.

         In a 2nd flyback converter stage, magnetizing current iLm2 decreased to zero, and output diode D2 is turned off. A parasitic resonance occurs between Lm2 and Coss2 of Sp2.

      3. Mode 3 [t2-t3]

         Mode 3 [t2-t3]: The switches of 1st flyback converter stage operate in the same with earlier mode.

         In a 2nd flyback converter stage, auxiliary switch Sa2 is turned on. The output diode of D2 is turned on. In the absorbed leakage energy in clamp capacitor Cc2 is transferred to the unfolding bridge stage. The magnetizing current iLm2 increases reversely too, but the magnitude may be smaller than the leakage current.

      4. Mode 4 [t3-t4]

         Mode 4 [t3-t4]: In a 1st flyback converter stage, the main switch Sp1 is turned off, the output capacitor of Sp1 is charged up by the current of magnetizing inductor Lm1. The voltage vSp1 across main switch Sp1 increases linearly. The voltage vSp1 reaches the input voltage vin adds the clamp voltage (vc1 = vin+vc1). Due to the large clamp capacitor, the voltage spike caused by resonance between leakage inductance LLk1 and output capacitance across main switch Sp1 is reduced.

         In a 2nd flyback converter stage, the auxiliary switch Sa2 is turned off. The negative current iSp2 discharges the output capacitor across Sp2. When the leakage energy in LLk2 is larger than the energy in output capacitor across Sp2, the output diode D2 keeps on, the difference between iSp2 and iLm2 is fed to the unfolding bridge stage. Once the leakage energy is smaller than the output capacitor across Sp2, the magnetizing inductor Lm2 also helps to realize the soft switching. As soon as the leakage inductor current iSp2 reaches iLm2, the output diode D2 is turned off.

      5. Mode 5 [t4-t5]

         Mode 5 [t4-t5]: In a 1st flyback converter stage, the anti- parallel diode of main switch Sp1 and the output diode D1 are turned on. The energy stored in the magnetizing inductor Lm1 start to emit to the unfolding bridge stage. And the energy in the leakage inductor LLk1 is absorbed by the clamp capacitor Cc1.

         In this mode, the difference between the magnetizing current iLm1 and primary current iSp1 is transferred to unfolding bridge stage. When the current of leakage inductance iLk1 reaches zero, this mode is finished.

         In the 2nd flyback converter stage, the output capacitor voltage across main switch Sp2 decreased to zero and the anti- parallel diode across main switch Sp2 is turned on. So, the mai switch Sp2 can be turned on with the soft-switching.

      6. Mode 6 [t5-t6]

         Mode 6 [t5 -t6]:In a 1st flyback converter stage, the current through leakage inductance LLk1 is zero and the anti-paralleled diode of Sa1 is turned off. And, the output diode D1 is turned on. The magnetizing energy in Lm1 is transferred to the unfolding bridge stage.

         In a 2nd flyback converter stage, main switch Sp2 is turned on and the auxiliary switch Sa2 is turned off. The energy is stored to the magnetizing inductor Lm2 and the primary current iSp2 increases linearly.

      7. Mode 7 [t6-t7]

         Mode 7 [t6-t7]: The switches of 1st flyback converter stage, magnetizing current iLm1 decreased to zero, and output diode D1 is turned off. A parasitic resonance occurs between Lm1 and Coss1 of Sp1.

         In a 2nd flyback converter stage, operate in the same with

         earlier mode.

      8. Mode 8 [t7-t8]

         Mode 8 [t7-t8]: The switches of 1st flyback converter stage, auxiliary switch Sa1 is turned on. The output diode of D1 is turned on. In the absorbed leakage energy in clamp capacitor Cc1 is transferred to the unfolding bridge stage. The magnetizing current iLm1 increases reversely too, but the magnitude may be smaller than the leakage current.

         In a 2nd flyback converter stage, operate in the same with earlier mode.

      9. Mode 9 [t8-t9]

         Mode 9 [t8-t9]: In a 1st flyback converter stage, the auxiliary switch Sa1 is turned off. The negative current iSp1 discharges the output capacitor across Sp1. When the leakage energy in LLk1 is larger than the energy in output capacitor across Sp1, the output diode D1 keeps on, the difference between iSp1 and iLm1 is fed to the unfolding bridge stage. Once the leakage energy is smaller than the output capacitor across Sp1, the magnetizing inductor Lm1 also helps to realize the soft switching. As soon as the leakage inductor current iSp1 reaches iLm1, the output diode D1 is turned off.

         In a 2nd flyback converter stage, the main switch Sp2 is turned off, the output capacitor of Sp2 is charged up by the current of magnetizing inductor Lm2. The voltage vSp2 across main switch Sp2 increases linearly. The voltage vS2 reaches the input voltage vin adds the clamp voltage vc2 (= vin+vc2). Due to the large clamp capacitor, the voltage spike caused by resonance between leakage inductance LLk2 and output capacitance across main switch Sp2 is reduced.

      10. Mode 10 [t9-t10]

   Mode 10 [t9-t10]: In a 1st flyback converter stage, the output capacitor voltage across main switch Sp1 decreased to zero and the anti-parallel diode across main switch Sp1 is turned on. So, the main switch Sp1 can be turned on with the soft-switching

   In the 2nd flyback converter stage, the anti-parallel diode of main switch Sp2 and the output diode D2 are turned on. The energy stored in the magnetizing inductor Lm2 start to emit to the unfolding bridge stage. And the energy in the leakage inductor LLk2 is absorbed by the clamp capacitor Cc2. In this mode, the difference between the magnetizing current iLm2 and primary current iSp2 is transferred to unfolding bridge stage. When the current of leakage inductance iLk2 reaches zero, this mode is finished.

   Fig 3. Steady state operation waveform of ILFI

3. ACTIVE CLAMP CONTROL TECHNIQUE

   1. Without the active clamp circuit:

      When the main switch Sp1 is turned off, the voltage across Sp1 is sum of the input voltage, feedback voltage and voltage spike which is cause by means of resonance between the leakage inductance Llk1 and output capacitance Coss of the Sp1. When the voltage spike of Sp1 increased over the rating then the Sp1 has to fail. For reducing this voltage spike of the main switch Sp1 the active clamp circuit is used.

   2. With active clamp circuit:

   When using the active clamp circuit the leakage energy will be absorbed by the clamp capacitor Cc1. Hence the voltage spike across the main switch Sp1 can be reduced. So during the grid period the ILFI operates stable due to the small voltage across the main switch Sp1 than its rating.

4. MAXIMUM POWER POINT TRACKING MPPT charge controller is a maximum power point

   tracker which is an electronic DC to DC converter which takes the DC input from the solar panels, changes it to high frequency AC and converts it back to a different DC current to match with the batteries.

   1. DIFFERENT MPPT ALGORITHM

      The different types of algorithms which are used for finding MPPT of the solar panel are

      CONVENTIONAL ALGORITHMS

      • Perturb & Observe

      • Incremental conductance

      • Constant voltage method

      • Constant current method

   2. PRINCIPLE OF P&O

   If the operating current or, in other words, the current drawn from the PV array is perturbed in a given direction and if the power drawn from the PV array increases, the operating point becomes closer to the MPP and, thus, the operating current should be further perturbed in the same direction.

   If the current is perturbed and this results in a decrease in the power drawn from the PV array, this means that the point of operation is moving away from the MPP and therefore, the perturbation of the operating current should be reversed.

   Fig 4. Flow chart of the P&O technique TABLE I

   Design parameter of ILFI

5. ILFI SIMULINK MODEL

   PARAMETER	VALUE	UNIT
   Grid Frequency fgrid	50	Hz
   Input Capacitance Cin	11	mF
   DC link Capacitance Co	136	nF
   Leakage Inductance Llk1,Llk2	0.21	µH
   Transformer Turns Ratio	1:6	–
   Magnetizing Inductance Lm1,Lm2	8.28	µH
   Filter Capacitance Cf	25	µF
   Filter Inductance Lf	3	mH

   Fig 5. Simulation diagram for ILFI

   Fig 6. Simulation diagram for MPPT block

6. SIMULATION RESULTS

   The simulation results are produced with MATLAB 2009b. The result shows the waveforms for voltage and current across PV panel. Also, the gate pulses of each switches, voltage across the main switch and active clamp switch, DC input voltage for the inverter, inverter output voltage without filter and grid voltage, grid current.

   Fig 7. voltage and current across PV panel

   Fig 8. Gate pulses of each switches

   Fig 9. Voltage across switch Sa1, Sp1

   Fig 10. Voltage across switch Sa2, Sp2

   Fig 11. DC input voltage for the inverter

   Fig 12. Inverter output voltage without filter

   Fig 13. Grid voltage and Grid current

7. CONCLUSION

The flyback inverter has become an unavoidable component. Because it having the advantages of fewer components, simplicity in construction, Isolation between the PV modules and the grid line. By using the interleaved technique in the flyback inverter the conduction loss of each switch can be reduced. The ILFI being practice in renewable energy system. A flyback inverter based energy efficient PV system has been developed. The system consist of transformer, diode rectifier, unfolding bridge, filter, etc. The working of the system with mode diagram has been presented. The crux of the system, active clamp control technique helps in energy efficient operation through the power loss. The ILFI based PV system is modeled in the MATLAB simulink and the results are verified. In this the Perturb & Observe algorithm is used in the PV to get the maximum power. The proposed flyback inverter system characteristics are analysed with the help of waveforms.

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V.Anandakumar Is Currently Pursuing The M.E Dgree In Power Electronics & Drives From Dr.Pauls Engineering Colege, Anna University, Chennai, India. He Received His B.Tech Degree In Electrical And Electronics

Engineering In 2011 From Bharathiyar College Of Engineering And Technology, Pondicherry University, India. His Current Research Interest Include Renewable Energy Source And Flyback Inverter Based PV System.

A.Ramesh Is Working As An Associate Professor In Dr. Pauls Engineering College, Anna University, India. He Received The

B.E Degree In Electrical And Electronics Engineering In 2002 From IFET College Of Engineering, Anna University, Chennai, India

And The M.Tech Degree In Power Electronics & Drives At 2005 From SASTRA University, Tanjoor, India. He Have Nine Year Experience In Teaching. His Research Area Include Inverter and Renewable Energy Source.

Dr.E.Mariappane received his B.E degree in Electrical and Electronics Engineering and M.E degree in Power System Engineering from Annamalai University, Tamil Nadu, India, in 1996 and 2004 respectively. He completed the Ph.D

degree in Anna University, Chennai, India (2013). He has 15 years teaching experience at various reputed institutions in and around Tamil Nadu. Currently he is working as DEAN (Academics) at Dr.Pauls Engineering College, Tamil Nadu, India, and he is a life member of ISTE in India.