Renewable energy source currently have possibilities of performing a huge role in electrical power generation. Today, solar panel technology is a popular renewable energy resource. Therefore extracting highest possible energy from solar panel is crucial. To be able to improve the output from a solar panel maximum peak power tracker (MPPT) must be brought in.
This microcontroller MPPT circuit for final year project explains the structure and progress affordable MPPT circuit for extracting maximum power from the solar panel and using it to charge a storage battery. The developed circuit is made up of microcontroller (PIC16F72) that produces high frequency pulse transmission various widths relative to the output of solar panel and electrical attributes from the load to run the panel at maximum power point. The produced pulse signal operates a DC-DC Buck-Boost converter that offers constant voltage of 15V to the battery pack guaranteeing the best possible power getting extracted from the solar panel. The microcontroller regulates the procedure of the program based on the codes emebeded inside, which in turn was formulated in MPLAB IDE.
Introduction
In this contemporary time of intensified improvement of science and technology the growing requirement of power generation has turned into a substantive concern. Renewable energy sources possess prospective of enjoying crucial role in electricity generation aiding pollution free, less noise creating and reduced upkeep energy manufacturing. Solar panels hold the pointed out strengths and can easily be traditionally used anywhere sunshine is obtainable. The output power coming from a solar panel is held in rechargeable battery, from where it is delivered to common home appliances. Even so, the output voltage along with MPPT of the panel may differ with various aspects such as sun irradiation, dirt, heat, etc. which in turn lead to less effective battery charging process. As a result, to acquire maximum energy through solar panel we'd like a maximum power point tracker (MPPT) technique. MPPT adjusts the electrical operating point of the PV panel simply by complementing the solar panel output as well as the input of the storage battery pack. The sychronisation is as a result of a microcontroller (PIC16F72), that looks after the PHOTOVOLTAIC panel and battery situations and produce necessary command signals to offer maximum power to the battery regardless of the output voltage connected with solar panel.
Fundamental Functioning
Fig. 1 exhibits the basic block diagram of the MPPT program. To charge the battery at constant voltage, a DC-DC buck-boost converter is actually powered through the square pulse created from the microcontroller. If output charging voltage for the battery is no more than particular voltage, subsequently duty cycle of the pulse is elevated through the microcontroller to lift the output voltage and conversely. The microcontroller detects output voltage of solar power via path A. This specific sample is commonly employed to discover whether or not the MPPT program must supply charging current for the battery. When the voltage produced through the solar panel is lesser compared to limit in that case the MPPT circuit doesn't provide any kind of charging current or voltage to the battery. Feedback through the input of the battery obtained via feedback path B is utilized to modify the duty cycle of the pulse produced in the microcontroller in ways that the device receive maximum feasible energy from PV panel to offer the battery.
Our offered program includes the important thing contraptions of sampling path, feedback path and blocks as demonstrated in Fig. 1. The in depth schematic diagram for the recommended strategy is highlighted in Fig. 2. They are additionally talked about beneath the individual sub-headings.
Buck-Boost Converter
A power MOSFET and an inductor (as proven in Fig. 2) are classified as the most critical areas of the MPPT circuit. Considering that the output from IO pins of the microcontroller are not able to push the MOSFETat high frequency, an n-p-n power transistor (BD437) is employed in common emitter arrangement to operate the input to the gate of MOSFET.
The output of Buck-Boost converter can easily generate output voltage possibly greater or below the input voltage. This boosts the output voltage in case the voltage through PHOTOVOLTAIC panel is lesser compared to specific charging voltage of the battery; and decreases the voltage in case it is over a expected level enhancing the charging current. The outcome of Buck-Boost converter delivers negative voltage since it functions in inverting topology, i.e. if your input is positive the outcome is going to be negative and the other way round.
The Buck-Boost converter was created for continuous-current function procedure. Picking out switching frequency and inductance to offer steady current throughout the inductor is granted through the following formula Lmin = (1 - D)2R/2f Considering that the ferrite core inductor which was utilized functioned most effective at 100kHz frequency, working frequency (f) had been established at 100kHz. Supposing the resistance (R) in the battery 22Ω, the best charging current 800mA and voltage of 15V and lowest duty-cycle (D) to be 0.01 as authorized within this layout; the lowest inductance required had been determined being 108uH. Nonetheless, an increased inductance (465uH) utilized to make sure that the circuit would not work in discontinuous conduction mode. Different parts employed in this segment tend to be high power P-channel MOSFET (IRF9530), fast recovery switching diode along with a 470uF capacitor.
Sampling Path A
Sampling Path A is a straightforward voltage divider that ranges the voltage coming from solar panel to reduced degree (under 5V) suitable for applying as an input to microcontroller. Given that highest output voltage coming from solar panel will be 22V, utilizing voltage divider the outcome will be lowered to 20% to make certain that the maximum voltage in no way get across 5V, establishing the resistors value R3 and R4 to 4.7kΩ and 1.2kΩ correspondingly, the microcontroller transforms this specific sampled voltage to electronic digital value and analyzes this together with the reference of 1.62V (equivalent to 8V) to determine whether or not to maintain the MPPT circuit on or off. In case the sampled voltage through the solar panel is lesser compared to limit (1.62V) then your MPPT circuit would not offer any charging current or voltage to the battery.
Feedback Path B
A straightforward voltage divider can't be employed in this feedback route since the cutting down of negative voltage might furthermore generate negative voltage that is not appropriate for applying as an input to microcontroller. Therefore, a minimal power p-n-p transistor (BC178) had been accustomed to invert and sample the voltage inside the functioning array of PIC microcontroller. The value of resistors R5 as well as R6was established at 10MΩ and 10kΩ correspondingly to ensure that the transistor had been running at linear section.
Microcontroller
The microcontroller is paramount device of the proposed Microcontroller MPPT Circuit for Final Year Project that analyzes feedback principles with the pre-set principles to tailor-make the duty-cycle of the pulse signal intended for generating the necessary result. The microcontroller functionality is actually determined through the codes developed inside it. The flowchart in Fig. 3 exhibits the format of the software that regulates the operations of the microcontroller. This system have been composed in assembly language making use of the MPLAB software and the in depth program is offered in the file. The sampled voltages through path A and B within the analog input pins tend to be transformed into digital value and weighed against the reference principles to figure out the transformation required in the duty-cycle of the pulse created. These reference values as well as the border restraints of duty-cycle are outlined at the start of this software. A standard register (INITIATION_CHECK) is additionally fixed at low logic during the onset, utilized for process examine.
