_{1}

This paper presents improvement tests based in a feedback-current controller designed to Tracking Maximum Power Point in photovoltaic system (MPPT-PV). Previously, a version was developed exhibiting results satisfactory in simulation and through of a low cost prototype. Now, using a sophisticated physical model of solar cell available in PSIM program is shown other cases, considering variations both irradiation and temperature to evaluate successfully the controller. The results show that its system is suitable under dynamical changing atmospheric conditions operating with effectiveness acceptable.

A MPPT (Maximum Power Point Tracking) controller is most effective solution used to maximize the power extracted from PV modules under atmospheric conditions [

DC/DC converter is modeled using controlled sources of voltage VCVSV1 and current IVCCSV1. Both configurations depend on the duty cycle signal provided by the MPPT regulator. Its unit only requires measurement of the current I_{sal} which is proportioned for solar cells array. The controller structure is based on the model equations explained in a next section.

Connecting adequate sources on S and T terminals available of solar cell module is feasible simulate changing conditions of irradiation and temperature respectively. Either S or T can be configured independently using different profiles: fixed, staircase-ramp type, piecewise linear and with triangular variations.

Acquiring and comparing P_{max} and P_{out} signalsis possible evaluate the tracking method proposed under different operational conditions.

Although physical and functional models are available in PSIM, the first option can simulate the behavior of the solar module more accurately, and can take into account the light intensity and temperature variation. Some parameters required are: number of cells, maximum power, voltage and current in maximum power, open-circuit voltage, short-circuit current, standard light intensity, reference temperature, internal resistances, bang energy, ideality factor, temperature and light coefficients.

Both light intensity and ambient temperature are incoming externally. Default parameters used in simulations test are listed in

The node S refers to the light intensity input (W/m^{2}), and the node T is the ambient temperature input (˚C). The node on the top is theoretical maximum power given the operating conditions. While the positive (+) and negative (−) terminal nodes are power circuit nodes.

Manufacturer Datasheet | Parameter | Specified Valued | Unit |
---|---|---|---|

Number of Cells Ns | 36 | ||

Maximum Power Pmax | 60 | W | |

Voltage at Pmax: | 17.1 | V | |

Current at Pmax: | 3.5 | A | |

Open-Circuit Voltage Voc: | 21.1 | V | |

Short-Circuit Current Isc: | 3.8 | A | |

Temperature Coeff. of Voc: | −0.38 | %/˚C | |

Temperature Coeff. of Isc: | 0.065 | %/˚C | |

Model Parameters (Defined) | Parameter | Specified Valued | Unit |

Band Energy Eg: | 1.12 | eV | |

Ideality Factor A: | 1.2 | ||

Shunt Resistance Rsh: | 1000 | Ω | |

Coefficient Ks: | 0 | ||

Model Parameters (Calculated) | Parameter | Specified Valued | Unit |

Series Resistance Rs: | 0.008 | Ω | |

Short Circuit Current Isc0: | 3.8 | A | |

Saturation Current Is0: | 2.16e−8 | A | |

Temperature Coefficient Ct: | 0.00247 | A/K |

^{a}PSIM tutorial. How to use solar module physical model.

The equations that describe a solar cell are:

where

and

Defining q: electron charge (q = 1.6 × 10^{−19} C); N_{s}: corresponding to solar cells connected in series; C_{t}: temperature coefficient (˚C); k: Boltzmann constant (k = 1.3806505 × 10^{−23}); R_{s}: series resistance of each solar cell (Ω); A: ideality factor; R_{sh}(Ω): shunt resistance of each solar cell; S_{0}: light intensity under standard test conditions; E_{g}: band energy of each solar cell (eV); T_{ref}: temperature under standard test conditions (˚C); v_{d} is the voltage that appears on R_{sh}; v(V)/N_{s} is the across the entire solar module; and i(A) is the current flowing out of the positive terminal of solar module [

MPPT strategy works as follows. The proposed MPPT based on output current measurements taking into account the theoretical straight line connecting the maximum power points in the PV panel characteristics. Specifically considering a couple points of power and voltage given by p_{1}: 11.12W, v_{1}: 15.31V and p_{2}: 69.38W, v_{2}: 16.32 V, is possible establish the load power as:

According MPPT strategy previously presented [_{control} or duty cycle expression is determined by:

where D_{max} is a constant; and I_{sal} is the current generated according to Equation (1).

A first test is focused to evaluate MPPT behavior under temperature variations. When T_{a} is adjusted, tracker function is kept close such to PV power available as is illustrated in

A second evaluation is realized to verify the possible impact when solar irradiance changes linearly, simulated through triangular waveform with amplitude range between 100 to 1100 W/m^{2}, applied as input signal to “S” terminal of solar cell model.

Regarding to dynamic test, the MPPT controller respond quickly under step change of solar irradiance as is showed in

Finally, is considered a staircase function as irradiation over solar cell but adjusting simultaneously a temperature range between 25˚C to 45˚C.When upper temperature is reached, the theoretical maximum available power is 60.648W, the extracted power is 58.292W, and therefore the MPPT efficiency is 96.11%, such as showed in

Because significant modifications are not required, the control system can be implemented with conventional PWM regulators [

MPPT controller reveals that it operates satisfactorily during each test realized. The controller is efficient but also optimizes energy production of PV array. However, just like any off-line techniques, it requires manufacturer data sheet of solar cell connected.

Under conditions considered, it is feasible to install the MPPT controller in isolated locations although atmospheric perturbations persist.

Although the design does not require a compensation stage, nevertheless, a simple network could be added to adapt the circuit to temperature changes.

The author would like to thank support provided by the team VG Metals, especially to Mrs. María Mendoza and Mr. Jesús Vergara.

Herman Enrique Fernandez Hernandez, (2016) Upgrading Tests Using PSIM Tool of MPPT-PV Feedback-Current Controller. Energy and Power Engineering,08,236-241. doi: 10.4236/epe.2016.84022