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Interfacing DC sources to load/power grid requires DC converters that produce minimum level of current ripples. This is to limit the losses and hence increase the life span of these sources. This article proposes a simple inter-leaved boost converter that interfaces PhotoVoltaic (PV) module into a common DC-link. The article also addresses the faulty mode operation of the proposed circuit while advising the appropriate remedy actions. A MATLAB and Simulink dynamic platform are used to simulate the transient performance of the proposed converter. The results revealed the effectiveness and the viability of the proposed converter in reducing the ripples in the PV current without employing bulky input inductors or increasing the switching frequency.

PV industry gains more intention recently, due to the salient advantages of PV modules as size variability, environmental compatibility and modularity. PV in general requires mechanical and electronic tracking for producing maximum output power at different levels of solar irradiance and temperature. Mechanical tracking could be efficient large-scale PV circuits as in utility scale PV installations. However, in residential and small-scale PV arrangements, usually mechanical tracking is ignored. This is to optimize the complexity and implementation costs. However, electronic tracking is mandatory for all scales of PV installations [

Tracking of Maximum Power Point (MPP) usually is realized via a DC-DC converter; the control methodology is to increment/decrement PV voltage/current such that MPP is realized. In other approaches, PV voltage/current is forced to follow a predetermined reference. This reference is extracted from actual PV voltage and current [

Basic DC-DC boost converter is the preferred for PV applications. This is due to topology of this converter. The inductor in the input side reduces the ripple in the current drawn from PV and hence its losses. Moreover, the diode in the basic cell protects the PV module from reverse current. However, for reduced ripple level in the PV current, a volumetric inductor has to be used [

Interleaved boost DC-DC converter consists of two cells of basic converter operating parallel. It is able to reduce the ripples in PV current without requirements of sizable inductor or high switching frequency. This is accomplished via introducing phase shift between the switching signals of the switches in the parallel cells. Moreover, the interleaved boost converter reduces efficiently the Electromagnetic Interference (EMI). The application of non-isolated interleaved boost converter was investigated in the literature for PV field [

The limitations of the interleaved boost converter are highlighted in this research, while conditions for ripple-free input current operation are identified [

Different variety of MPP Tracking (MPPT) algorithms are reported in the literature [

The reliability of power electronic components decreases with aging; therefore, there is considerable probability of faulty operation of interleaved boost converter. Less is reported in the literature about faulty mode of interleaved boost converter in PV applications. This results in decreasing the harvest power under such conditions as there is no comprehensive analysis or valuable remedy strategy [

Elaborate remedy strategies are advised for different faults in the operation of interleaved boost converter driving PV module, which are not widely reported [

This article analyzes comprehensively the operation of interleaved DC-DC boost converter for PV applications. The limitations on the output voltage of the converter are derived. An annotative implementation scheme for the modulation strategy ensuring equal value of switches’ duty cycles is proposed. The article directs more emphasis on the faulty mode of the proposed converter operation. Different fault scenarios are investigated while advising the appropriate remedy strategy. This article has the following contributions:

1) Defining the upper limit of the duty cycle and hence output voltage for interleaved boost converter.

2) Proposing a simple modulation strategy ensuring equal values for the switches’ duty cycles.

3) Investigating the operation of interleaved boost converter while a switch develops short/open circuit fault and advising the appropriate remedy scheme.

4) Proposing intelligent remedy scenario while the interleaved boost converter operating with open diode fault.

The system under concern is composed of PV generator, interleaved boost converter and DC-link, as shown in

1) Interleaved boost converter has lower ripple level in the PV output current than the basic boost cell, which reduces the losses in the PV module and hence lengths its lifespan.

2) The interleaved boost converter has inherent short-circuit protection.

3) The interleaved boost converter has the same output voltage boosting ability as the basic cell.

Different models are advised for stimulating PV cell, these models differ in accuracy and complexity. Moderate model is advised here, the PV cell is modeled

as a solar irradiation and temperature dependent current source I_{ph} in parallel with diode as shown in

Basically, the PV cells are grouped in series to deliver a reasonable voltage/power, these structures as mentioned before are themed modules. The module has an equivalent circuit similar to that of the cell.

The relation between the terminal current I and voltage V of a PV module is expressed by [

I = I p h − I o ( e V + I R s V t h − 1 ) (1)

where I_{o}, I_{ph}, I and V are saturation current, photo current, current and voltage of the module. V_{th} = nN_{s}kT/q is thermal voltage of the module; n, N_{s}, K, T and q are ideality factor, number of cells in series, Boltz’s man constant and electron charge respectively. The PV modules under concern are from Kyocera KC200GT type. The parameters of KC200GT module are given in

The value of series resistance R_{s} calculated by iterative method in [

The PV modules are grouped in series-parallel arrangement to form array, which is termed here as PV generator. Each PV generator is consisting of 30 Kyocera KC200GT modules. The relation between the PV array/generator terminal voltage V_{pv} and current I_{pv} could be expressed by a relation similarly to (1), however, it is more meaningful to express the PV array/generator current in

No. of cells | 54 |
---|---|

Short circuit current | 8.21 A |

Open circuit voltage | 32.9 V |

Current at MPP | 7.61 A |

Voltage at MPP | 26.3 V |

Maximum power | 200.143 W |

Voltage coefficient | −0.1230 V/K |

Current coefficient | 0.0032 A/K |

terms of the voltage V_{pv}, short-circuit current I_{sc} and open-circuit voltage V_{oc} of the module, as these data are commonly supplied by the manufacturers at standard test conditions [

I p v = M s s I s c ( 1 − exp ( V p v − N s s V o c + N s s I p v R s / M s s N s s V t h ) ) (2)

where M_{ss} and N_{ss} are number of shunt and series connected modules respectively. The current I_{pv} and the voltage V_{pv} of the PV array/generator under concern calculated at 25˚C and different radiation levels are given in

_{mpp} and I_{sc} could be given by,

I m p p = k m p p s c I s c (3)

where K_{mppsc} is equal to 0.9286,

The interleaved boost converter as shown in

around 180˚ phase shift between the ripples in the input current inductor of the two boost cells as shown in _{L}, is the summation of currents I_{L}_{1} and I_{L}_{2}. Therefore, the input current I_{L} is nearly ripple free for 50% duty cycle.

Assume ΔI_{L}_{1} and ΔI_{L}_{2} are peak to peak ripples in the currents I_{L}_{1} and I_{L}_{2} respectively. Calculating ΔI_{L}_{1} and ΔI_{L}_{2} following the procedure in [

Δ I L 1 = V s L 1 D 1 T s (4)

Δ I L 2 = − V s L 2 D 2 T s (5)

Assuming that L_{1} and L_{2} are equal, L_{1} = L_{2} = L. The ripples in the input current I_{L} is given by,

Δ I L 1 + Δ I L 2 = V s L T s ( D 1 − D 2 ) (6)

Equation (6) shows that zero ripple in the input current IL could be realized if D_{1} = D_{2}. However, this condition places a limit on the maximum value of the duty cycles D_{1} and D_{2}. As, the two cells operate in cascaded pattern; therefore, D_{1} + D_{2} = 1.0. Therefore, for zero ripple in the inductor current D_{1} = D_{2} = D, and the duty cycle of each boost cell is limited by,

0 < D ≤ 0.5 (7)

Equation (7) indicates that maximum value of a cell duty cycle is 0.5; this set the maximum output voltage of interleaved boost converter to twice input voltage. This considers a major deficiency in the interleaved boost converter. There is no limitation on the output voltage of basic boost converter as compared to the interleaved boost chopper.

The slope of power-voltage curve of a PV generator,

Δ I p v Δ V p v > − I p v V p v , leftMPP Δ I p v Δ V p v = − I p v V p v , atMPP Δ I p v Δ V p v < − I p v V p v , rightMPP (8)

where I_{PV}, V_{PV} and P_{PV} are PV module current, voltage and power respectively.

The slope of power-voltage curve of a PV module,

E = Δ I p v Δ V p v + I p v V p v (9)

MPP is tracked by continuously comparing the incremental and instantaneous conductance and incrementing/decrementing the PV voltage/current until MPP is reached. This technique is reported in the literature under ICC [

An innovative implementation for ICC is proposed here under the theme of Modified Incremental Conduction Controller (MICC). According to (9), the sum of the incremental and instantaneous conductance is equal to zero at MPP; therefore, employing a sufficiently fast PI controller ensures that sum is settled at zero.

E = Δ I p v Δ V p v + I p v V p v (10)

This article proposes an innovative approach to ensure equal duty cycle for the switches of the converter. This is the condition for zero ripple, which is extracted from (6). Sawtooth of a switch is inversion for the other switch as shown in

To tune the proposed PI controller, the large signal model of the system under

Inductors L_{1} | L_{1} = 100 μH |
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Inductors L_{2} | L_{2} = 100 μH |

Input capacitance C_{in} | C_{in} = 50 μF |

Output capacitance C_{o} | C_{o} = 100 μF |

concern has to be obtained [

1) The input/output capacitors C_{in} and C_{o} are sufficiently large, so that the PV module output voltage V_{pv} and output voltage V_{o} are constant.

2) The converter input current is ripple free.

The dynamic performance model of the interleaved boost converter is similar to the basic boost topology. Averaging over a switching cycle, the dynamic performance of the interleaved boost chopper could be depicted by [

L d i L d t = V p v − V o ( 1 − D ) (11)

C o d V o d t = − V o R L + i L ( 1 − D ) (12)

where i_{L}, V_{o}, R_{L} and C_{o} are respectively inductor current, output voltage, load resistance and output capacitance respectively. D is the duty cycle.

Perturbing (11)-(12) and linearizing around a steady-state operating point and transforming into Laplace Transform [

s L I L ( s ) = − V o ( s ) ( 1 − D o ) + D ( s ) V o s (13)

s C o V o ( s ) = − V o ( s ) R L + I L ( s ) ( 1 − D o ) − I L a v D ( s ) (14)

where D_{o}, I_{Lav} and V_{os} are steady-state values of duty cycle, average inductor current and output voltage. Rearranging (13) and (14), solving for V_{o}(s); then substituting V_{o}(s) in terms of I_{L}(s) and D(s), the transfer function between inductor input current and duty cycle is given by,

V o ( s ) D ( s ) = G v ( s ) = − s L R L ( 1 − D o ) V o s + V o s ( 1 − D o ) ( s 2 C L + s L R L ) + ( 1 − D o ) 2 (15)

A PI controller with parameters given in

The open loop transfer function has two complex poles and one right hand zero. Therefore, the PI controller has to ensure the stability while achieving reasonable bandwidth. The proposed PI controller, ^{5} rad/sec bandwidth. This bandwidth is sufficient high such that the rapid

Proportional gain k_{p} | 5 |
---|---|

Integral gain k_{i} | 20 |

fluctuation in the solar irradiance are efficiently tracked. The proposed PI produce 52 dB and 89˚ gain and phase margin.

MATLAB and its dynamic platform, Simulink, are used to stimulate the system under concern with the proposed control methods and MPPT technique. A solar irradiance that varies according to daytime is considered for validating the system under concern. This pattern of solar irradiance is shown in

The ICC successfully forces the PV generator to operate at MPP at different solar irradiance,

Faulty mode of the interleaved boost under concern considers only the defects in

power electronic elements. The failure of input/output capacitors is out of scope of this research. There are three scenarios under concern. They are:

1) Scenario#1 a switch open-circuit fault.

2) Scenario#2 a switch short-circuit fault.

3) Scenario#3 a diode open-circuit fault.

Appropriate remedy strategies are identified for each scenario.

If a switch in a boost cell develops open-circuit fault, the current in this switch diminishes to zero. Moreover, the diode of this cell would be reveresbias, therefore the current in the inductor of the faulty cell drops to zero. However, as the interleaved boost converter consists of two cells. The other cell still operates and fulfills the load. This scenario is illustrated in ^{2} during the simulation time span.

Short-circuit switch fault is the severest, as the PV generated would operate at short-circuit operating point, where the output power is zero and the current is maximum. This scenario is illustrated in ^{2} over the simulation time span.

generator. The DC-link voltage decreases to zero after the fault. The effect of the energy stored in the output capacitor is clear in

The proposed remedy is interfaced the interleaved boost converter to the PV generator via a switch. This switch would be continuously on during normal operation. However, it disconnects the circuit if the PV input current equals to the short-circuit current value.

This scenario investigates the open-circuit diode fault that develops in a converter cell. This scenario is illustrated in ^{2} over the simulation time span.

The proposed remedy strategy is permantely to open the switch of the defected cell. This could be accomplished via continuous sensing of the inductors’ currents.

Efficient interleaved boost converter is proposed to interface a PV module into common DC-link. The article also identifies the condition for zero ripple in the interleaved boost converter input current. The limitations of the interleaved boost chopper are highlighted. An innovative implementation of the control circuit of interleaved boost converter is advised such that the two switches have

equal value of the duty cycle.

The proposed control method of the interleaved boost converter enjoys the simplicity and flexibility [

In general, the following conclusions could be extracted:

1) The interleaved boost converter has a maximum limit on the output voltage, as the output voltage is restricted to twice the input voltage. This limitation is not there in the basic boost cell.

2) The interleaved boost chopper could have ripple free input current, if the duty cycles of the two switches are equal and they are equal to 50%.

An innovative implementation of switching strategy is advised to ensure equal value of duty cycles under varying levels of solar irradiance and temperature.

Hafez, A.A., Hatata, A.Y., Alsubaihi, M.I., Alotaibi, R.M., Alqahtani, F.T., Alotaibi, S.O., Alhusayni, A.M. and Alharbi, M.D. (2018) High Power Interleaved Boost Converter for Photovoltaic Applications. Journal of Power and Energy Engineering, 6, 1-17. https://doi.org/10.4236/jpee.2018.65001