 Open Access
 Total Downloads : 2625
 Authors : Y.Mrudula, B.Subbareddy, T.Devaraju
 Paper ID : IJERTV1IS4211
 Volume & Issue : Volume 01, Issue 04 (June 2012)
 Published (First Online): 01072012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
A High Step Up DCDc Converet With PV Cell For Distributed Generation System
Y.Mrudula
PG student,
Dept of EEE SVEC AP.INDIA
B.Subbareddy,
Assistant professor
Dept of EEE, SVEC A.P,India.

evaraju,
HOD Dept of EEE, P.Hd SVEC A.P, India.
Abstract
During the first decade of the 21st century, the world wide photovoltaic (PV) markets have experienced a tremendous expansion. One reason for installing distributed generation in general of which distributed PV is a special case is to locate power generation closer to the load. A high stepup converter with PV cell for a distribution generation system is this paper. The concept is combined of two capacitors, two diodes and one coupled inductor and photovoltaic cell. Two capacitors are charged in parallel and are discharged in series by the coupled inductor. The high step up voltage gain can be get with an appropriate duty ratio. The voltage stresses on the main switch and output diode are reduced by a passive clamp circuit. Therefore, low resistance RDS(ON) for the main switch can be adopted to reduce conduction loss. In addition, the reverse recovery problem of the diode is alleviated and thus, the efficiency can be further improved. The operating principle and steadystate analyses of the voltage gain are also discussed in detail. Finally, a 24volts input voltage, 400volts output voltage and 400Watts output power prototype circuit of the proposed converter are implemented in the simulink to verify the performance.
Keywords – PV system, IGBT ,distributed generation system, high stepup dcdc converter, coupled inductors

INTRODUCTION
In a micro grid system, all system components such as battery inverter, diesel generator, PV solar array, wind turbine, hydroturbine etc. are connected together via the acnetwork [15]. This allows these components to be placed on any location on the property and also allows for easy expansion of the system. A system can start as a simple 5kW single phase stand alone system and grow into a large 3phase network with multiple houses, multiple PV arrays and multiple windturbines connected. Micro grid systems are used as standalone power systems or as distributed generation systems that are connected to the public grid at one common point. These distributed generation systems can be a cost effective solution for sub divisions with limited capacity from the public grid. Fig.1 shows a photovoltaic distributed system have the solar energy source is low dc input voltage. Photovoltaic sources are connected in series to produce a sufficient dc
voltage for generating ac utility voltage. However it is difficult to realize a series connection of the photovoltaic source without incurring a shadow effect [67]. The photovoltaic source produce very low voltage, I want high dc voltage, we are using high step up dcdc converters. The low voltage (1214V) to high voltage(380400V)[8]. The high step up dcdc converters wanted high conversion ratio, high efficiency and small size [914]. The dcdc converters are two types. They are isolated and non isolated dcdc converters. The nonisolated dcdc converters are buck, boost, buckboost. These are low voltage gain are produces. But any time fault occurs on the load side directly effects on the supply side, finally the system will collapse. So we are going to the isolated converters. They are fly back, forward, pushpull, sepic, cuk converters. These are high stepup voltage gain produced by adjusting the transformer windings. However,
Figure. 1 Photovoltaic distributed system
the main switches of these converters are suffering a heavy voltage spike and high power loss from the leakage inductor of the transformer [15]. To decrease these disadvantages, the nondissipative snubber circuits and active clamp circuits are employed. However the cost increases accordingly due to the extra power switch and high side driver[16].
Theoretically, the non isolated converters can be added to provide high stepup voltage gain with extremely high duty cycle [17]. However, the stepup voltage gain certain range by the effect of the semiconductor switches, rectifier diodes and equivalent series resistance of the inductors and capacitors. The extreme duty cycle operation may also result in serious reverserecovery problem and electromagnetic interference problem [18].
To improve the conversion efficiency and get high stepup voltage gain, much topography has been proposed [1726].
High stepup gain can be gained by the use of the switched capacitor technique [2023].A coupled inductor is used in a boost or buckboost converter instead of the input inductor. However, the main switch will suffering high transient current and conduction loss is high. Another method for achieving high stepup gain is the use of the voltagelift technique [2426]. However, it is the same disadvantage. The converters designing the coupled inductor technique to get high stepup gain by adjusting the turns ratio[27].
The system analysis, design consideration, and implementation of a softswitching zetafly back converter to achieve zerovoltage switching (ZVS). In proposed converter the zeta and flyback topologies are adopted in the output side to achieve the following features: to share the power components in the transformer primary side, to achieve the partial magnetizing flux reset, and to share the output power .The buckboost type of active clamp is connected in parallel with the primary side of the isolation transformer to recycle the energy stored in the leakage inductor of isolated transformer and to limit the peak voltage stress of switching devices due to the transformer leakage inductor when the main switch is turned off. The active clamp circuit can make the switching devices to turn on at ZVS [2829].An integrated boostfly back converter is presented, in which the secondary side of the coupled inductor is used as a flybacktype[3031]. The proposed converter topology can promote the voltage gain of a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetization of transformer for a coupledinductor based converter [3234].A new type of nonisolated step up converter with high voltage gain is proposed on this work. It is suitable for applications with a high voltage gain between the input and the output stages. In this converter, the output to input voltage ratio, for a given duty cycle, can be raised by adding voltage multiplier stages of capacitors (mc) [3536].The sepicfly back converter with the coupled inductor and output stacking techniques has been proposed [37]. Additionally, a high stepup boost converter that uses multiple coupled inductors with output stacking has been proposed [3839].
A special type of power FET that has the function of a BJT with its base driven by a FET. Faster than a BJT of similar ratings, and easy to use. Ratings from 10 to
>600 A, with voltages of 600 to 1700V. The IGBT is popular in inverters from 1 to 100kW or more. It is found almost exclusively in power electronics applications.
This paper proposes a high efficiency, high stepup voltage gain, and clampmode converter. The proposed converter adds two pairs of additional capacitors and diodes to achieve high stepup voltage gain. The coupled inductor is used as both a forward and flyback type; thus, the two capacitors can be charged in parallel and discharged in series via the coupled inductor. The transit current does not flow through the main switch compared
with earlier studies [2026]. Thus, the proposed converterhas low conduction loss. Additionally, this converter allows significant weight and volume reduction compared with other converters [27[38]. Another benefit is that the voltage stresses on the main switch and output diode are reduced. However, the leakage inductor of the coupled inductor may cause high power loss and voltage spike. Thus, a passive clamping circuit is needed to recycle the leakageinductor energy of the coupled inductor and to clamp the voltage across the main switch. The reverse recovery problems in the diodes are alleviated, and thus, high efficiency can be achieved.

OPERATION FOR THE DCDC PROPOSED CONVERTER

Figure 2: Circuit of proposed converter
Fig. 2 shows the circuit topology of the proposed converter. This converter consists of PV cell as input source consists of modeling of PV cells power switch S, coupled inductors Np and Ns, one clamp diode D1, clamp capacitor C1, two blocking capacitors C2 and C3, two blocking diodes D2 and D3, output diode Do, and output capacitor Co. The coupled inductor is modeled as the magnetizing inductor Lm and leakage inductor Lk .Fig 3 shows the example of the circuit analysis with dc as input source
To simplify the circuit analysis, the following conditions are assumed.

Capacitors C2 , C3 , and Co are large enough that Vc 2, Vc 3 and Vo are considered to be constant in one switching period.

The power MOSFET and diodes are treated as ideal, but the parasitic capacitor of the power switch is considered

The coupling coefficient of coupled inductor k is equalto Lm/(Lm+Lk ) and the turns ratio of coupled inductor n is equal to Ns /Np period.

ContinuousConduction Mode (CCM) Operation
In CCM operation, there are six operating modes in one switching period of the proposed converter. Fig.
4shows the typical waveforms and Fig. 5 shows the currentflow path of the proposed converter for each modes. The operating modes are described as follows.
Figure.4 The waveforms of the proposed converter operation in CCM
(a)
(b)
(c)
(d)
(e)
(f)
Figure.5 In CCM operation the current flowing in operating modes (a) Mode I (b) Mode II (c) Mode III
(d) Mode IV (e)Mode V (f) Mode VI

Mode I [t0, t1 ]: During this time interval, S is turned on. Diodes D1, D2, and D3 are turned off, and Do is turned on. The currentflow path is shown in Fig. 5(a). The primaryside current of the coupled inductor iLk is increased linearly. The magnetizing inductor Lm stores its energy from dc source Vin. Due to the leakage inductor Lk
, the secondaryside current of the coupled inductor I s is decreased linearly. The voltage across the secondary side winding of the coupled inductor VL 2 , and blocking voltages Vc2 and Vc3 are connected in series to charge the output capacitor Co and to provide the energy to the load
R. When the current is becomes zero, dc source Vin begins to charge capacitors C2 and C3 via the coupled inductor. When iLk is equal to iLm at t = t1 this operating mode ends.

Mode II [t1, t2 ]: During this time interval, S is still turned On. Diodes D1 and Do are turned off, and D2 and D3 are turned on. The currentflow path is shown in Fig. 5(b). The magnetizing inductor Lm is stored energy from dc source Vin Some of the energy from dc source Vin transfers to the secondary side of the coupled inductor to charge the capacitors C2 and C3. Voltages Vc2 and Vc3 are approximately equal to nVin. Output capacitor Co provides the energy to load R. This operating mode ends when switch S is turned off at t = t2 .

Mode III [t2, t3 ]: During this time interval, S is turned off. Diodes D1 and Do are turned off, and D2 and D3 are turned on. The currentflow path is shown in Fig. 5(c). The
energies of leakage inductor Lk and magnetizing inductor Lm are released to the parasitic capacitor Cds of switch S. The capacitors C2 and C3 are still charged by the dc source Vin via the coupled inductor. The output capacitor Co provides energy to load R. When the capacitor voltage Vin+Vds is equal to Vc1 at t = t3 , diode D1 conducts and this operating mode ends.

Mode IV [t3, t4]: During this time interval, S is turned off. Diodes D1, D2, and D3 are turned on and Do is turned off. The currentflow path is shown in Fig. 5(d). The energies of leakage inductor Lk and magnetizing inductor Lm are released to the clamp capacitor C1. Some of the energy stored in Lm starts to release to capacitors C2 and C3 in parallel via the coupled inductor until secondary current is equals to zero. Meanwhile, current iLk is decreased quickly. Thus, diodes D2 and D3 are cut off at t
= t4, and this operating mode ends.

Mode V [t4 , t5 ]: During this time interval, S is turned off. Diodes D1 and Do are turned on, and D2 and D3 are turned off. The currentflow path is shown in Fig. 5(e). The energies of leakage inductor Lk and magnetizing inductor Lm are released to the clamp capacitor C1. The primary and secondary windings of the coupled inductor, dc sources Vin, and capacitors C2 and C3 are in series to transfer their energies to the output capacitor Co and load
R. This operating mode ends when capacitor C1 starts to discharge at t = t5 .

Mode VI [t5, t6 ]: During this time interval, S is still turned off. Diodes D1 and Do are turned on, and D2 and D3 are turned off. The currentflow path is shown in Fig. 5(f). The primaryside and secondaryside windings of the coupled inductor, dc sources Vin, and capacitors, C1, C2, and C3, transfer their energies to the output capacitor Co and load R. This mode ends at t = t6 when S is turned on at the beginning of the next switching period.
B. DiscontinuousConduction Mode (DCM) Operation
In order to simplify the analysis for DCM operation, leakage inductor Lk of the coupled inductor is neglected. Fig. 6 shows the typical waveforms when the proposed converter is operated in DCM, and Fig. 7 shows the currentflow path of the proposed converter for each mode. There are three modes in DCM operation. The operating modes are described as follows.
(a)
(b)
(c)
Figure .6 In DCM operation the current flowing in operating modes (a) Mode I (b) Mode II (c) Mode III
Fig.6 The wave forms of the proposed converter in DCM

Mode I [t0, t1]: During this time interval, S is turned on. The currentflow path is shown in Fig. 7(a). The part energy of dc source Vin transfers to magnetizing inductor Lm. Thus, iLm is increased linearly. The dc source Vin also transfers another part energy to charge capacitors C2 and C3 via the coupled inductor. The energy of the output capacitor Co is discharged to load R. This mode ends when S is turned off at t = t1.

Mode II [t1, t2]: During this time interval, S is turned off. The currentflow path is shown in Fig. 7(b). The energy of the magnetizing inductor Lm is released to the capacitor C1. Similarly, capacitors C2 and C3 are discharged in a series with dc source Vin and magnetizing inductor Lm to the capacitor Co and load R. This mode ends when the energy stored in Lm is depleted at t = t2.

Mode III [t2, t3]: During this time interval, S remains turned off. The currentflow path is shown in Fig. 7(c). Since the energy stored in Lm is depleted, the energy stored in Co is discharged to load R. This mode ends when S is turned on at t = t3.

II. STEADYSTATE ANALYSIS OF THE DCDC CONVERTER

CCM Operation
At modes IV and V, the energy of the leakage inductor Lk is released to the clamped capacitor C1 . According to previous work [13], the duty cycle of the released energy can be expressed as
The schematic of the voltage gain versus the duty ratio under various coupling coefficients of the coupled inductor is shown in Fig. 9. It is seen that the voltage gain is not very sensitive to the coupling coefficient. When k is equal to 1, the deal voltage gain is written as Fig. 9 shows the voltage gain versus the duty ratio of the proposed converter as compared with the converters in previous work [33] and [34] at CCM operation under k = 1 and n =
3. One can see that the voltage gain of the proposed converter is higher than those of the converters in [33] and [34]. According to the description of the operating modes, the voltage stresses on the active switch S and diodes D1,D2, D3 , and Do are given as
(10)
(1)
where Ts is the switching period, Dc 1 is the duty ratio of the switch, and tc 1 is the time of modes IV and V. By applying the voltagesecond balance principle on Lm, the voltage across the capacitor C1 can be represented by
(2)
Since the time durations of modes I, III, and IV are significantly short, only modes II, V, and VI are considered in CCM operation for the steadystate analysis. In the time period of mode II, the following equations can be written based on Fig.5(b):
Figure. 8. Voltage gain versus duty ratio at CCM operation under n = 3 and various k.
(3)
(4)
Thus, the voltage across capacitors C2 and C3 can be written As
(5)
During the time duration of modes V and VI, the following equation can be formulated based on Fig.5(f):
(6)
Thus, the voltage across the magnetizing inductor Lm can be derived as
(7)
Using the voltsecond balance principle on Lm, the following equation is given:
Figure. 9. Voltage gain versus duty ratio of the proposed converter, the converters in [33] and [35] at CCM operation under n = 3 and k = 1.
(11)
(12)
(13)
(8)
Substituting (2), (3), (5), and (7) into (8), the voltage gain is
Obtained as
(9)
Equations (11)(13) mean that with the same specifications, the voltage stresses on the main switch and diodes can be adjusted by the turns ratio of the coupled inductor.

DCM Operation
In DCM operation, three modes are discussed. The key waveform is shown in Fig. 7. During the time of mode I,
the switch S is turned on. Thus, the following equations can be formulated based on Fig. 7(a):
(14)
(15)
The peak value of the magnetizing inductor current is given
as
The curve of the voltage gain, shown in Fig. 9, illustrates the voltage gain versus the duty ratio under various Lm.
(16)
Furthermore, the voltage across capacitors C2 and C3 can be
written as
(17)
In the time interval of mode II, the following equations can
be expressed based on Fig. 6(b):
(18)
(19)
During the time of mode III, the following equation can be derived from Fig. 6(c):
Figure. 10. Voltage gain versus duty ratio at DCM operation under various Lmand at CCM operation under n = 3 and k = 1.
(20)
Applying the voltagesecond balance principle on Np , Ns
of
the coupled inductor, the following equations are given as
(21)
(22)
Substituting (14), (15), (17), (18), (19), and (20) into (21) and (22), the voltage gain is obtained as follows:
Figure. 11. Boundary condition of the proposed converter under n = 3.
(23)
(24)
According to (24), the duty cycle DL can be derived as
(25)
From Fig. 5, the average current of ico is computed as
(26)
Since Ico is equal to zero under steady state, (16), (25), and
Ico = 0 into (26) yield
(27)
Then, the normalized magnetizinginductor time constant is
defined as

Boundary Operating Condition Between CCM and DCM
If the proposed converter is operated in boundary condition mode, the voltage gain of CCM operation is equal to the voltage gain of DCM operation. From (10) and (29), the boundary normalized magnetizinginductor time constant LmB can be derived as Applying the voltagesecond balance principle on Np, Ns of the coupled inductor, the following equations are given as
(30)
The curve of LmB is plotted in Fig. 11. If Lm is larger than
LmB , the proposed converter is operated in CCM.
where fs is the switching frequency.
(28)
IV MATLAB/SIMULINK MODELING AND SIMULATION RESULTS
Substituting (28) into (27), the voltage gain is given by
(29)
A simulation modeling of a PV distributed system with high step up dc dc converter is showed bellow
Figure 12. Simulink modeling of PV distributed system
PV connect in series to DCDC converter obtain sufficient dc voltage for generating ac utility voltage. IGBT which is connected to the load .PWM generator generates the pulse to the diode .The internal structure of the DCDC converter as shown below
Figure13:Internal structure of the DCDC converter
Fig 13 shows the internal structure of the dcdc converter with input as photovoltaic cell of voltage of(15V17V)and getting output of 240v .The below fig shows the ouptput of the dcdc conveter
Figure 14: Output response of the DCDC converter The Fig 14 shows that the output response of the dcdc converter With 240V . The IGBT which is a special type of power FET that has the function of a BJT with its base driven by a FET. Faster than a BJT of similar ratings, and easy to use. Ratings from 10 to >600 A, with voltages of 600 to 1700V. The IGBT is popular in inverters from 1 to 100kW or more. It is found almost exclusively in power electronics applications Focusing on PV systems, a typical
12 Volt PV module or panel has 36 series connected solar cells with a maximum power point (MPP) of approximately 15V at normal operating temperatures (approx 50Â°C). These system voltages are appropriate for lower power systems, but beyond powers of a few hundred Watts, these panels themselves are placed in series strings PV arrays to maintain lower currents and higher efficiencies.
A problem occurs when even a single cell in the array is shaded or obscured. The photocurrent generated in a shaded cell may drop to perhaps 20% of the other cells. The shaded cell will be reverse biased by the remaining cells in the string, but current will continue to flow through it causing large localized power dissipation.
Figure 15: Modeling of solar array
The overall efficiency of the array is reduced to the efficiency of this module. For similar reasons PV panels in a string should be given the same orientation, and be of identical size. This is not always possible or desirable for ascetic or other architectural reasons.
The first order filter output sinwave voltage used in the simulink model of the proposed circuit is shown in the below wave form of the PV distributed system
Figure 17: Response of the PV distributed system with filter
Fig 17 shows that the output response of the PV distributed system using the filter we get the sinusoidal output voltage as shown

CONCLUSION
This paper proposed a high gain and high efficiency using PV cell for a distributed system. By using the PV cell in series and discharged in a series to the DcDc converter to
achieve high stepup voltage gain and high efficiency. The steadystate analyses of voltage gain and boundary operating condition are discussed in detail. Prototype circuit of the proposed converter is built in the laboratory. Experimental results confirm that high efficiency and high stepup voltage gain can be achieved. The efficiency is 95.5%. The voltage stress on the main switches is 90 V; thus, low voltage ratings and low onstate resistance levels RDS(ON) switch can be selected. Moreover, the proposed converter has simple structure. It is suitable for renewable energy systems for the distributed generation system applications.

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