Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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doi:10.21311/001.39.10.01

Current Sharing in Parallel Connected Converters with Indirect

Duty Ratio Adjustment for Photovoltaic System

M.R.Geetha1*

, T.Ahilan2 and R.Suja Mani Malar

3

1Department of ECE, Ponjesly College of Engineering, Alamparai,Nagercoil,Tamil Nadu,India

2Principal, Immanuel Arasar JJ College of Engineering, Marthandam, Kanyakumari District,Tamil Nadu,India

3Principal, Narayanaguru Siddhartha College of Engineering, Marthandam, Kanyakumari District,Tamil Nadu, India

Corresponding author (Email: geethamr029@rediffmail.com)

Abstract: This paper focuses current sharing on renewable energy photovoltaic (PV) system in standalone

model. Power generated from solar array is delivered to load through positive super lift Luo converters

(PSLLCs). To achieve higher output current two equal rated PSLLCs are connected in parallel at the output.

Unequal sharing of load current takes place in paralleled connected converters if parameters of converter

modules are different. In order to ensure equal sharing of load current a new current sharing scheme is proposed.

In the proposed system converter duty ratio is adjusted indirectly to regulate load current and to share the load

current correctly between parallel connected converters. Hence no dedicated current sharing controller is

needed. Due to this system complexity is reduced when compared to existing current sharing schemes that regulate converter output by direct selection of duty ratio. Regulation of output voltage is implemented using

(Adaptive Neuro Fuzzy Inference system) ANFIS controller in MATLAB- Simulink and its performance is

compared with Type III compensator. Simulation and experimental results are presented to prove the possibility

of proposed system.

Key words: Closed Loop System, Current Control, Dc-Dc Converter, Photovoltaic Cells

1. INTRODUCTION

Photovoltaic power generation systems produce pollution free electrical power by conversion of solar

energy into electricity. Solar Photovoltaic (SPV) is an efficient technique to use solar energy. It can build

anywhere, the sun irradiation is available. It plays a vital role in both small scale and large scale applications

(Green et al.,2010; Poshtkouhi, Varley, Popuri and Trescases, 2010; Banu, Benuiga and Istrate,2012).

Due to nonlinear characteristics of photovoltaic system (Sera,Mathe,Kerekes and Spataru,2013;Arun,

Banerjee, and Bandyopadhyay,2009), it is essential to operate it at its maximum operating point. Many

Maximum power point tracking (MPPT) methods are available. In this paper ANFIS based MPPT is used to

track maximum power. Integration of solar array (Wu, Xiao, Wu, Zhang and Wang, 2011), with input parallel output parallel

(IPOP) connected PSLLCs can be used for generation of higher output current. Since two equal rated converters

may not be identical practically, the output currents of two converters may not share equally. To ensure equal

sharing of output current, a new current sharing scheme is used.

There exist many current sharing techniques for paralleled connected converters. Among them, the simplest

one is droop method. The disadvantage associated with droop method is for achieving good current sharing,

voltage regulation has to be degraded (Johnsy,2014; Abu-Qahouq,2010; Li and Liu,2016). The drawback of

droop method was overcome by active current sharing method. Active current sharing methods achieve good

current sharing by means of feedback control. But the expense is more and the circuit is complex ( Sha, Guo

andLi,2011).

A three loop control scheme which required a dedicated current sharing controller for current sharing was

implemented (Sha,Guo and Li,2010). An average current sharing control with loop gain measurement has been presented (Yuri Panov & Milan.M.Jovanovic., 2008). For measuring gain of current sharing loop, dedicated

injection sources were needed which was implemented by excitation transformer with two secondary windings

that have same number of turns.

Two loop control schemes have been implemented for current sharing (Sha, Gu and Liao,2010). It needed a

dedicated current sharing controller. A three loop control scheme with fixed and common duty cycle was

presented (Sha, Guo and Liao,2010).

Control scheme with common duty ratio for an IPOP connected converters was presented

(Shi, Zhouand Xiangning,2012). Automatic current sharing was implemented (Shi et al.,2015; Cheng et

al.,2012).Common duty ratio control scheme gives stable operation but perfect current sharing takes place for

converter modules with well-matched parameters.

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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In active current sharing schemes a dedicated current sharing controller is needed which increases

complexity of system. In case of common duty ratio control scheme, current sharing takes place without a

dedicated current controller. But the drawback is no perfect current sharing takes place if parameter mismatches

are more between converter modules.

In this paper duty ratio of IPOP connected converters is adjusted indirectly for perfect load regulation and

current sharing. The adjustment of duty ratio depends on converter inductor currents, capacitor voltages and power input voltage of IPOP connected PSLLCs. This helps in eliminating the need of dedicated current sharing

controller.

In the following, circuit configuration and control scheme is described, Luo converter operation, its

mathematical model and controller model is given and the design of Lag-Lead compensator and ANFIS

controller are presented. The design of controllers is then verified by MATLAB simulation and hardware

prototype.

2. CIRCUIT CONFIGURATION AND CONTROL SCHEME

2.1. Circuit Configuration The proposed block diagram with current sharing scheme is shown in Fig. 1. It consists of two sections. The

first section is for obtaining maximum power from solar array. The second section is to deliver maximum power

from solar array to load. Power deliver from solar array is stored in battery (𝑣𝑔 ) and given to load using IPOP

connected PSLLCs. The input current𝑖𝑔generated due to𝑣𝑔 flows through IPOP connected PSLLC modules.

Currents 𝑖𝐿1 and 𝑖𝐿2

are input currents through inductances 𝐿1and𝐿2respectively. The output current due to 𝑖𝐿1

and 𝑖𝐿2 is𝑖𝑜 .This output current𝑖𝑜may or may not be shared equally between IPOP connected PSLLCs. To share

the load current equally between IPOP connected PSLLCs a new current sharing scheme is proposed.

Figure 1. Proposed block diagram with new current sharing scheme

2.2.Proposed Control Scheme

Based on the error difference between reference signal (𝑣 𝑟𝑒𝑓 ) and the actual output voltage (𝑣 𝑜) the control

signal (𝑖 𝑐)is generated. It acts as a reference signal for inner current loop. The error difference between control

signal ( 𝑖 𝑐) and input current of converter modules (𝑖𝐿1) and (𝑖𝐿2

) generates control signal (𝑖 𝐿1) and (𝑖 𝐿2

) .

Thiscontrol signals along with loop gains (𝐻𝑔1 ,𝐻𝑣1for module 1 and 𝐻𝑔2 ,𝐻𝑣2

for module 2) adjusts the duty ratio

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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of IPOP connected PSLLC modules for equal sharing of load currents (𝑖 𝑜1) and (𝑖 𝑜2

) in presence of parameter

mismatches. Thus by sensing input currents, output currents are shared equally between parallel connected

converter modules.

3. SMALL SIGNAL MODELLING OF PSLLC

Positive Super Lift Luo Converter is shown in Fig. 2.

Figure 2.Circuit of PSLLC

It consists of an input supply voltage𝑉𝑖𝑛 , capacitors C1 andC2, inductorL1, power switch S, freewheeling

diodes D1 and D2and load resistance R.Assume that PSLLC operates in Continuous conduction mode (CCM).

Two modes of operation are there for PSLLC. Under mode 1 the switch is closed and switch is open under mode

2.

Let iL be the inductance current and Vc1 and Vc2

be the voltage across capacitances C1 andC2. The modeled

transfer function of PSLLC under mode 1 and mode 2 for direct adjustment of duty ratio (Joseph Basanth,

Natarajan and Sivakumaran, 2013; J.Barsana Banu, Dr.M.Balasingh Mosesand S.Rajarajacholan,2016) and

indirect adjustment of duty ratio is given in Table.1.

Table 1. Transfer function of PSLLC for direct and indirect adjustment of duty ratio

Transfer function of PSLLC with

direct adjustment of duty ratio

Transfer function of PSLLC

with indirect adjustment of

duty ratio

Line to output transfer function

𝐺𝑉𝑔 𝑠 =

𝑣 (𝑠)

𝑣 𝑔(𝑠)

= (−𝐷

𝐷′)

1

1 +𝐿

𝐷′2 𝑆 +𝑅𝐿(𝐶1+𝐶2 )𝑆

2

𝐷′2

Line to output transfer

function

𝐺𝑉𝑔 𝑠 = −

𝐷2

𝐷′𝑅(

1

1 +𝑆𝑅𝐶

1+𝐷

)

Control to output transfer function 𝐺𝑣𝑑

𝑠

= (−(𝑉1 − 𝑉2)

𝐷′)

[1 + 𝑆𝐿𝐼𝑜

𝐷′ 𝑉1−𝑉2 ]

[1 +𝐿

𝑅𝐷′2 𝑆 + 𝑆2𝐿 𝐶1+𝐶2

𝐷′2 ]

Control to output transfer function

𝐺𝑉𝑔 𝑠 = −

𝐷2

𝐷′𝑅(

1

1 +𝑆𝑅𝐶

1+𝐷

)

A. Modelling of controller for indirect regulation of converter

As shown in Fig.2(a) the maximum value of inductor current (𝑖𝐿(𝑡)) vary from control input signal current

( 𝑖𝑐(𝑡)) by 𝑚𝑎𝑑𝑇𝑠 at time 𝑡 = 𝑑𝑇𝑠 where 𝑚𝑎𝑑𝑇𝑠 is the magnitude of artificial ramp waveform. When the

response changes, the inductor current ripples magnitude during 𝑡 = 𝑑𝑇𝑠 and 𝑑′𝑇𝑠 sub intervals are 𝑚1𝑑𝑇𝑠

2 and

𝑚2𝑑 ′𝑇𝑠

2.

𝑅

𝑆

𝑉𝑖𝑛 𝐿1 𝐶1 𝐶2

𝐼𝑖𝑛 𝐼𝑜

𝑉𝑜

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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Figure 2(a). Inductor current waveform of PSLLC

The mean value of inductor current ripple is

𝑑 𝑚1𝑑𝑇𝑠

2 + 𝑑′(

𝑚2𝑑 ′𝑇𝑠

2) (1)

The inductor current at its average can be expressed as

< 𝑖𝐿 𝑡 > 𝑇𝑠 =< 𝑖𝑐 𝑡 > 𝑇𝑠 −𝑚𝑎𝑑𝑇𝑠 − 𝑑 𝑚1𝑑𝑇𝑠

2 − 𝑑′(

𝑚2𝑑 ′𝑇𝑠

2) (2)

< 𝑖𝐿 𝑡 > 𝑇𝑠 =< 𝑖𝑐 𝑡 > 𝑇𝑠 −𝑚𝑎𝑑𝑇𝑠 − 𝑚

1𝑑2𝑇𝑠

2 − (

𝑚2𝑑 ′2𝑇𝑠

2) (3)

After perturbation and linearization equation (3) can be rewritten as

𝐼𝐿 + 𝑖 𝐿 𝑡 =𝐼𝑐 + 𝑖 𝑐 𝑡 -𝑀𝑎𝑇𝑠 𝐷 + 𝑑 𝑡 −𝑇𝑠

2 𝑀1 + 𝑚 1 𝑡 𝐷 + 𝑑 t 2 −

𝑇𝑠

2 𝑀1 + 𝑚 1 𝑡 𝐷

′ + 𝑑 t 2 (4)

Eliminating higher order terms from equation (4),

𝑖 𝐿 𝑡 =𝑖 𝑐 𝑡 -(𝑀𝑎𝑇𝑠 + 𝐷𝑀1𝑇𝑠 − 𝐷′𝑀2𝑇𝑠)𝑑 t −𝐷2𝑇𝑠

2𝑚 1 𝑡 −

𝐷 ′2𝑇𝑠

2𝑚 2 𝑡 (5)

Assuming 𝐷𝑀1 = 𝐷′𝑀2

𝑖 𝐿 𝑡 =𝑖 𝑐 𝑡 -𝑀𝑎𝑇𝑠𝑑 t −𝐷2𝑇𝑠

2𝑚 1 𝑡 −

𝐷 ′2𝑇𝑠

2𝑚 2 𝑡 (6)

Simplifying equation (6) gives

𝑑 t =1

𝑀𝑎𝑇𝑠[𝑖 𝑐 𝑡 − 𝑖 𝐿 𝑡 −

𝐷2𝑇𝑠

2𝑚 1 𝑡 −

𝐷 ′2𝑇𝑠

2𝑚 2 𝑡 (7)

Equation (7) indicates 𝑑 t depends 𝑖 𝐿 𝑡 , 𝑖 𝑐 𝑡 ,𝑚 1 𝑡 𝑎𝑛𝑑𝑚 2 𝑡 . The slope variation for PSLLC is given by

𝑚1 =𝑣 𝑔

𝐿 and 𝑚2 =

−𝑣

𝐿

Therefore equation (7) can be rewritten as

d t = Hm [i c t − i L t − Hgv g t − Hv v t ] (8)

Where

Hm =1

Ma Ts (9)

Hg =D2Ts

2L (10)

Hv = −D ′2 Ts

2L (11)

Hm , 𝐻𝑔 and 𝐻𝑣 are gains of PSLLC

Assume the control input to current loop in Fig 1 as (𝑖𝑐(𝑡)). From the relation between average inductor

currents 𝑖 𝐿1 𝑡 ,𝑖 𝐿2

𝑡 and control input (𝑖𝐿(𝑡)) the expression of duty ratio for PSLLC module 1 and PSLLC

module 2 are given by

𝑑 1 t = Hm [𝑖 𝑐 𝑡 − 𝑖 𝐿1 𝑡 − 𝐻𝑔1

𝑣 𝑔 𝑡 − 𝐻𝑣1𝑣 𝑡 ] (12)

Where Hm =1

𝑀𝑎𝑇𝑠,𝐻𝑔1

=𝐷2𝑇𝑠

2𝐿1,𝐻𝑣1

= −𝐷 ′2𝑇𝑠

2𝐿1

𝑣𝑔

𝐿

𝑣

𝐿

0 d𝑇𝑠 𝑑′𝑇𝑠 𝑡

𝑖𝐿(𝑡)

𝑖𝑐

𝑚1

−𝑚2

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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and

d 2 t = Hm [i c t − i L2 t − Hg2

v g t − Hv2v t ](13)

Where Hm =1

𝑀𝑎𝑇𝑠,𝐻𝑔2

=𝐷2𝑇𝑠

2𝐿2,𝐻𝑣2

= −𝐷 ′2𝑇𝑠

2𝐿2

𝐻𝑔1 and 𝐻𝑣1

are gains of PSLLC 1 and 𝐻𝑔2 and 𝐻𝑣2

are gains of PSLLC 2.

Figure 3.Transfer Function Model of PSLLC with proposed control scheme.

Based on equations (12) and (13) PSLLC module 1 and PSLLC module 2 gets regulated and perfect

current sharing takes place between IPOP connected PSLLC modules. From equation (13) the equivalent

transfer function model of PSLLC module 1 is obtained and is shown in Fig 3.

4. DESIGN OF CONTROLLERS

4.1.Type III Compensators

Generally compensator acts as a controller. It is used to adjust system parameters in order to achieve desired

specifications. Type I (Lead) compensator reshape frequency response curve to obtain enough phase lead angle.

It acts as a high pass filter. Transfer function of Type I compensator has its zero closer to the origin.

Type II(Lag) compensator acts as a low pass filter. It has its pole closer to the origin and increase system

order by one. It has more gain at high frequencies which helps to improve steady state accuracy. Type III (Lag-

Lead) Compensator combines the characteristics of both Type I compensator and Type II compensator.

Figure 4. Open loop response of PSLLC

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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In the proposed system from open loop response of PSLLC, Type III voltage compensator is designed. Fig 4

gives the open loop response of PSLLC. The designed voltage compensator from open loop response of PSLLC

is shown in Table 2.

4.2.ANFIS Controller For learning and tuning parameters in a fuzzy inference system (FIS), ANFIS has 5 layers. It uses hybrid

learning model (Buragohain and Mahanta, 2008). ANFIS are fuzzy Sugeno models put in the framework of

adaptive systems to facilitate learning and adaptation. This framework makes FLC more systematic and less

dependent on expert knowledge.

Based on a first order Sugeno model, consider two-fuzzy rules

Rule 1: if(𝒂 is 𝑷𝟏)and(𝒃 is 𝑸𝟏)) then(𝒇𝟏=𝑷𝟏 𝒂 +𝒒𝟏 𝒃 +𝒓𝟏)

Rule 2:if(𝒂 is 𝑷𝟐)and(𝒃 is 𝑸𝟐)) then(𝒇𝟐=𝑷𝟐 𝒂 +𝒒𝟐 𝒃 +𝒓𝟐)

For implementing these two rules, the ANFIS architecture is shown in Fig.5.

Layer 1: Each and every node of layer 1 is an adaptive node. Layer 1 outputs are the fuzzy membership grade

of the inputs. Layer 1 outputs are given by:

𝑂𝑖1 = µ𝐴𝑖 𝑎 𝑓𝑜𝑟 𝑖 = 1,2

𝑂𝑖1 = µ𝐵𝑖−2 𝑏 𝑓𝑜𝑟 𝑖 = 3,4

Where 𝑎 and 𝑏 are the inputs to node 𝑖 , µ𝐴𝑖 𝑎 , µ𝐵𝑖−2 𝑏 are fuzzy membership function.

Layer 2: It is a rule layer. Its output is expressed as:

𝑂𝑖2 = 𝑤𝑖 = µ𝐴𝑖 𝑎 µ𝐵𝑖 𝑏 𝑓𝑜𝑟 𝑖 = 1,2

Figure 5. ANFIS Architecture

Layer 3: It’s a layer for normalization. It’s node is marked as a circle labelled N.

𝑂𝑖3 = 𝑤 𝑖 =𝑤𝑖

𝑤1 + 𝑤2

𝑓𝑜𝑟 𝑖 = 1,2

Layer 4: Fourth layer is for defuzzification. It’s output is the combination of the normalized firing strength and

a first order polynomial.

𝑂𝑖4 = 𝑤 𝑖𝑓𝑖 𝑓𝑜𝑟 𝑖 = 1,2

𝑓𝑖 = 𝑝𝑖𝑎 + 𝑞𝑖𝑏 + 𝑟𝑖𝑓𝑜𝑟 𝑖 = 1,2

Layer 5: This node computes output as the sum of all input signals

𝑂 = 𝑤 𝑖𝑓𝑖 𝑓𝑜𝑟 𝑖 = 1,2

𝐴1

𝐴2

𝐵1

𝐵2

𝜋

𝜋

𝑁

𝑁

∑ 𝑓

𝑤1

𝑤2

𝑤 1

𝑤 2

𝑤 1𝑓1

𝑤 2𝑓2

Table 2.Voltage Compensator

Type III

compensator

𝟑. 𝟓𝒆 − 𝟔𝑺𝟐 + 𝟏. 𝟑𝟕𝒆 − 𝟑𝑺 + 𝟏

𝟑. 𝟓𝒆 − 𝟔𝑺𝟐 + 𝟏. 𝟓𝒆 − 𝟑𝑺 + 𝟏

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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Figure 6. Block Diagram of proposed system using ANFIS

The block diagram of proposed system with ANFIS based voltage regulation for paralleled connected

PSLLCs is shown in Fig 6. The development of control strategy to regulate output voltage of paralleled

connected PSLLCs using ANFIS is presented here.

The neuro - fuzzy method represents knowledge using fuzzy and uses neural network for optimizing

parameters. FIS under consideration has two inputs. In the proposed paper, inputs to ANFIS considered are error

(𝑒) which is the difference between (𝑉𝑜 ) and (𝑉𝑟𝑒𝑓 ) and change in error.

(∆𝑒).Fig.7 shows ANFIS structure for designed Neuro Fuzzy controller.

Figure 7.ANFIS structure for thedesigned Neuro Fuzzy controller

5. RESULTS AND DISCUSSIONS

A prototype of solar integrated IPOP system consisting of two modules, as shown in Fig. 1, has been built

to verify the effectiveness of proposed current sharing scheme.

The parameters of solar panel are Peak power voltage (𝑉𝑃𝑉)of 16V, Current at peak power (𝐼𝑃𝑉)of 5A,

Open circuit voltage(𝑉𝑜𝑐 )of 0.9V and Short circuit current (𝐼𝑠𝑐 )of 5A.

The specifications of PSLLC are given as follows: 1) the input dc voltage of 12–15 V; 2) output voltage of

36 V, directly regulated by closed-loop controller and 3) maximum output current of 0.72A.

The component values for power stage are designed as follows: primary and secondary are all equal to 30μF; input-filter inductances of L1and L2are same at 100 μH; and duty ratios D1and D2are between 0.3 to 0.9. The

switching frequencies for individual converter modules are 100 kHz.

A. Simulation Results

This section discusses MATLAB based simulation results of paralleled connected PSLLCs. Fig.9 shows

simulation waveforms of IPOP connected PSLLC converter modules whose regulation and current sharing takes

place by direct choice of duty ratio. The voltage regulation of IPOP connected converter modules are compared

- +

𝑣𝑟𝑒𝑓 -

+ ANFIS

𝐻𝑣1

𝑖𝑐

𝐻𝑔2

𝐻𝑣2

Luo

Converter1 Load

𝑣𝑜

𝑑2

𝑣𝑔

𝑖𝑖1

Luo

Converter2

𝑖𝑖2

𝐻𝑚

𝐻𝑚

𝑑1

+

+ +

+

+ +

- +

𝐻𝑔1

Input 1

Input 2

Aggregated Output

Input 1 MF in 1mf1

Input 1 MF in 1mf2

Input 1 MF in 1mf3

Input 2 MF in 2mf1

Input 2 MF in 2mf2

Input 2 MF in 2mf3

Output MF1

Output MF2

Output MF3

Output MF4

Output MF5

Output MF6

Output MF7

Output MF8

Output MF9

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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using ANFIS controller and Type III compensator. The capacitances of PSLLC 1 and PSLLC 2 are chosen

as𝐶11 = 30µ𝐹 and 𝐶21 = 40µ𝐹. It indicates that perfect current sharing takes place in presence of parameter

mismatches. Here line disturbance is given at t=0.05s and load disturbance is given at t=0.07s. Line disturbance

affects response of load current while using Type III compensators. For ANFIS controller line disturbance is

totally rejected. But response of load current using ANFIS controller has highly oscillatory start-up transient.

Figure 9. Current sharing among each PSLLC converter module with 𝐶11 = 30µ𝐹 and 𝐶21 = 40µ𝐹 using compensator and ANFIS for direct adjustment of duty ratio

Figure 10. Current sharing among each PSLLC converter module with L1 = 100µH and L2 = 110µH using

compensator and ANFIS for indirect adjustment of duty ratio

Fig.10 shows simulation waveforms of current sharing among each PSLLC converter module with 𝐿1 =100µ𝐻 and 𝐿2 = 110µ𝐻using Type III compensator and ANFIS for indirect adjustment of duty ratio.

In fig 10 perfect current sharing takes place in presence of parameter mismatches. Both Type III

compensators and ANFIS controller reject line disturbance from𝑉𝑔 = 12𝑉to𝑉𝑔 = 8𝑉 to at t=0.05s. Similarly

Type III compensators and ANFIS controller settles correctly for change in load from R=50 Ω to R=40 Ω at

t=0.07s. Here the startup transient is totally rejected while using ANFIS controller. Also for Type III

compensator the peak overshoot is reduced when compared to direct adjustment of duty ratio.

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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Table 3. Comparison between direct adjustment and indirect adjustment of duty ratio Parameters Indirect adjustment of duty ratio Direct adjustment of duty ratio.

Dedicated current sharing controller

Not needed Needed

Complexity Less More

Settling time Very less More

Overshoot Totally reduced present

Transistor Protection Protect transistor against excessive current during transient and fault condition

No such protection takes place

Stability Can be enhanced by adding ramp

signal to input current

Can be accessed using phase

margin test. Inadequate phase margin leads to ringing and overshoot

From Fig 9 and 10 it is inferred that for transfer function of paralleled connected PSLLCs using indirect

adjustment of duty ratio, the response settles faster and peak overshoot is totally reduced.

In addition no dedicated current sharing controller is needed. It helps in reducing complexity of the system.

Hence the proposed system is implemented in real time using PIC16F877A controller based on indirect

adjustment of duty ratio. Table 3 shows the difference between direct adjustment of duty ratio and indirect adjustment of duty ratio. Table 4 shows performance of PSLLCs with ANFIS controller and Type III

compensator as a voltage regulator.

B. Experimental Results

The parameter used in simulation is used to obtain experimental results.Prototype of solar integrated IPOP

connected PSLLCs has been built as shown in Fig 6. Control scheme of IPOP connected PSLLCs has been

implemented in real time using PIC16F877A.

The signals output voltage (𝑉𝑜), input voltage (𝑉𝑔), input current of PSLLC(𝐼𝑖𝑛1)and input current of

PSLLC2 (𝐼𝑖𝑛1)are sensed using IC741.

These signals are then processed using PIC16F877A controller based on the control scheme shown in Fig 6. The control signals from PIC16F877A adjust the duty ratio of PSLLC1 and PSLLC2 for ensuring equal sharing

of load current.

Controller and Type III compensator

Fig 11 shows the output voltage from buck boost converter after MPPT. Fig.12 shows output voltage and

input voltage waveform of IPOP connected PSLLCs in presence of solar radiation and with mismatches in

individual capacitancesC11 = 30µF and C21 = 40µF.

Table 4. Performance of PSLLCs with ANFIS

Line/Load

Variations

ANFIS controller Type III compensator

Vo Io Io1 Io2 Vo Io Io1 Io2

Vin=12V 36 .72 .36 .36 35.94 .718 .359 .359

50Ω 36 .72 .36 .36 35.94 .718 .359 .359

40Ω 36 0.9 0.45 0.45 35.94 .898 .449 .449

It indicates that in presence of solar radiation and in presence of parameter mismatches perfect load voltage

regulation takes place.

Figure 11. Output Voltage from buck boost converter after MPPT

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Fig.13 shows waveform of output current of IPOP connected PSLLCs with mismatches in individual

capacitances 𝐿1 = 100µ𝐻 and 𝐿2 = 110µ𝐻. It indicates that proposed control scheme results in perfect load

current regulation even in presence of parameter mismatches and without any dedicated current sharing

controller.

Figure 12. Input voltage and output voltage of IPOP connected PSLLCs with 𝐶11 = 30µ𝐹 and 𝐶21 = 40µ𝐹

Fig.14 shows waveform of output current 1 and 2 of IPOP connected PSLLCs with mismatches in

individual capacitancesC11 = 30µF and C21 = 40µF.

Figure 13. Output current of IPOP connected PSLLCs with 𝐿1 = 100µ𝐻 and 𝐿2 = 110µ𝐻

Figure 14. Output current 1 and 2 of IPOP connected PSLLCs with 𝐶11 = 30µ𝐹 and 𝐶21 = 40µ𝐹

Figure 15. Output current 1 and output current 2 of IPOP connected PSLLCs for change in load from R=50Ω to

R=40Ω

Rev. Téc. Ing. Univ. Zulia. Vol. 39, Nº 10, 01 - 12, 2016

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Fig.14 indicates that in presence of solar radiation and even in presence of parameter mismatches and

without any dedicated current sharing controller perfect sharing of load current takes place. Output current 1 and

2 of IPOP connected PSLLCs for change in load from R=50Ω to R=40Ω is shown in Fig 15.It indicates that

even without any dedicated current sharing controller good current sharing takes place in presence of load

changes.

6. CONCLUSION

This paper has proposed a new current sharing scheme for IPOP connected PSLLCs which generate higher

output current for standalone photovoltaic system. The proposed current sharing scheme gives perfect current

sharing without a dedicated current sharing controller, (i.e.) indirect adjustment of duty ratio takes place.

Simulation and experimental results shows that perfect current sharing takes place for the proposed current

sharing scheme .The proposed system find its application in satellite communication, uninterrupted power

supplies etc.

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