A new analog technique is proposed in order to track the maximum power point (MPP) of PV panels. The proposed technique uses the well-known simple functions of electronic circuits. The proposed technique is validated by applying it to boost based off grid PV system. The simulation of the PV system was done on the circuit oriented simulator Proteus-ISIS. A good efficiency of the analog technique (more than 98%) was registered. The variation of irradiation was introduced in order to study the robustness of the proposed analog MPPT technique.
Currently, the production of domestic and industrial energy is based, in large part, on a limited resource: oil. Oil sources are becoming more and more rare, while the energy demands of the world rise continually. Since this form of energy covers a large part of the current energy production, it is necessary to find another solution to take over. The imposed constraint is to use an energy source that is economical and less polluting because the protection of the environment has become an important point [
The search for alternative energy resources has therefore become a crucial issue these days. Many scientific researches have been carried out, not only in the field of nuclear energy production, but also in the sector of unlimited energy sources, such as wind power generation and energy transformation. In the latter case, the design, optimization, and realization of photovoltaic systems are topical issues since they lead to a better exploitation of solar energy [
These photovoltaic powers generating systems can be operated in different places: electrification of isolated sites, installation in buildings or direct connection to network of electricity, and so on.
A major problem with PV systems is to realize transfer of maximum power from PV generator to load. For several years, many MPPT control methods have been developed and implemented, like Fuzzy Logic Method [
Alternatively, the MPPT can be implemented by analog circuits [
In this paper, a new analog MPPT technique suitable for PV system applications is presented and validated by simulations.
Solar cell is the main building block of PV arrays, which consist of many photovoltaic cells linked in parallel/series manner for each module. A PV cell can be modeled from the equation defining the static behavior of the PN junction of a conventional diode. Thus, Figure
Equivalent circuit of solar PV cell.
The primary solar cell equivalent circuit can involve a current source in parallel with a diode and a shunt relatively large resistance (
The current
The PV module characteristic has a current boundary called short-circuit current
The PV module can also be characterized by the maximum power point where the product of its voltage (
The goal for a solar direct electricity generation system or photovoltaic system is to provide high quality, reliable, and green electrical power. Usually a number of PV modules are arranged in series and/or parallel combinations to meet the output energy requirements. The series connection increases the module’s voltage whereas the parallel connection increases its current [
At the temperature 25°C and irradiation of 1000 W/m2, Table
Typical electrical characteristics of a PV module, JA SOLAR.
Characteristics | Specifications |
---|---|
Maximum power rating | 265 W |
Open circuit voltage ( |
38.38 V |
Short-circuit current ( |
8.8 A |
Maximum power voltage ( |
31.24 V |
Maximum power current ( |
8.48 A |
Maximum Power Point Tracking (MPPT) is the important factor in PV systems to maintain maximum power output. It is the component that tracks the maximum power point of the PV panel’s curve.
The problem addressed by MPPT techniques is to maintain the output voltage
Figure
Here, the design of a photovoltaic system equipped with a new analog Maximum Power Point Tracking (MPPT) technique is studied. Its main parts are the switch-mode DC-DC converter, the control system, and the tracking system. Proteus-ISIS simulation tool was used to show proposed analog technique performance [
The two main categories of PV systems are grid tie and stand alone. In our case, we have chosen to develop the analog MPPT controller on a simple and classical stand-alone PV system. Specific equipment is required to control, transfer, distribute, and store the energy produced by the PV arrays. Figure
Block diagram of the proposed photovoltaic system.
The different blocks constituting the system are as follows: The PV panels. Load; in our case a simple impedance. DC-DC boost power converter. In this case the output voltage is higher than the one delivered by the PV panel. The converter involves one controlled switch (Mosfet or IGBT). The semiconductor device controlled by a variable frequency and duty cycle ( Analog MPPT controller. It allows the track of the maximal power point of the PV array, which depends on climate conditions [
The detailed diagram of the photovoltaic technique is presented in Figure A shunt resistor ( A voltage divider composed by two resistors “ An analog multiplier is used to calculate the instantaneous output power delivered by the PV panels. The block Comparator (2) compares the really generated power ( Hysteresis (2) is used to detect the maximum power point and to control the hold circuit, its output commutes to (+15 V) when the comparator (2) output reaches A hold circuit can block the value of the reference signal ( An RC cell generates a pulse when the maximum power is reached (define the values of The summation block produces Comparator (1) calculates the difference between Hysteresis (1) is used to control the real power
The detailed synoptic diagram of the whole photovoltaic technique.
Figure
The transfer function of hysteresis (1) and hysteresis (2).
The transfer function of hysteresis 1 block, for example, is given by the following equations:
Figure
The proposed analog MPPT technique circuit.
Different power waveforms evolutions and the corresponding panel operating point in
The majority of MPPT techniques attempt to vary PV current
Figure
If the power magnitude is able to increase usually (from zero and initially from open circuit condition of the
When the reference signal
The hold circuit is just necessary to block the “
The signal which has a variable magnitude and allows the regulation of the real power is the signal “
In the above situation, the real power cannot be regulated to the blocked value which is slightly higher than the maximum power
In order to avoid the above behavior of the operating point, the
The regulated real power pursues
The hysteresis bands and first-order pulse magnitude are chosen so that the operating point (E) is below the operating point (B) in the right side of the
At the end of (
The band 1 of “hysteresis 1” block (defined by
The value of
This condition is necessary to be sure that the operating point of the PV panels is kept in the right side of the maximum point of the
The used circuit of the RC cell block is given by Figure
The RC cell block circuit and its output voltage waveform.
The proposed MPPT technique, power converter, and PV arrays models are implemented in the Proteus-ISIS circuit oriented simulator. For different irradiance conditions, the different voltage waveforms corresponding to the above-mentioned power are registered and shown in Figure
Tracked maximum power under variable solar radiation.
Figure
Image of the PV panels current and voltage.
The efficiency of the proposed MPPT technique was computed for different
New MPPT technique efficiencies for unipolar input reference
We notice that in the input of the boost converter there is no filtering capacitance added and this in order to control instantaneously the real current in PV panels. This is considered as an advantage of the proposed MPPT technique. The choice of the value of storage inductance of the boost and hysteresis 1 band defines the variable switching frequency of the power device. This value is in general limited by maximum junction temperature in the active device.
In order to increase the efficiency of the proposed analog MPPT technique a bipolar (+15 V/−15 V)
Proposed MPPT technique efficiency as a function of irradiation when the reference power signal (
Beyond
In the proposed analog MPPT technique, we obtained a good efficiency of the technique compared to the analog techniques proposed in literature [
For this purpose, the boost converter is realized, and the used semiconductor devices are the STGW30V60F N-channel IGBT Transistor and the STTA3006P Diode.
The realized analog MPPT circuit is shown in Figure
Photo of the realized analog PMMT control circuit.
A PV panels (JA SOLAR) generating a maximum power around 580 W, at the temperature 25°C and irradiation of 1000 W/m2, are used.
The open circuit voltage of the PV panels is equal to 105 V.
We notice that, in the experimental waveform shown in Figure
A new technique to track the maximum power point operation using analog MPPT controller is proposed in this paper. The proposed MPPT control strategy has the ability of fast tracking of the MPP for PV systems. It uses DC-DC boost converter. Through simulation by Proteus-ISIS and experiments, the accuracy and feasibility of the proposed method were validated. The idea proposed showed its accuracy to detect the optimal generated power by the PV panels. An improvement of the technique efficiency, by using a bipolar voltage of the reference
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This paper contains the results and funding of a research project that is funded by King Abdulaziz City for Science and Technology (KACST) Grant no. 35-130.