2.2.5. Energy harvesting control system

Switching circuit is the crucial part of this energy harvesting system. Arduino UNO microcontroller is used in this circuit where it controls two N-type MOSFETs namely P36NF06L. For testing, LED was placed in parallel to the gate-source pin of the MOSFET. The system will continue to charge and discharge until the battery reaches up to 6 V. In the stripboard of the energy harvesting circuit, MOSFETs are placed as shown in Figure 4. Aligned with the bias voltage, two LEDs are placed to indicate the status of the circuit. When the MOSFET is turned on, the LED will glow and vice versa.

Figure 3. LCD screen of energy harvesting circuit.

Figure 4. MOSFET configurations in energy harvesting circuit.

The algorithm of the decision-making switching algorithm is illustrated in Figure 5. Here MOSFET 3 is usually turned off all the time. However, it is significant to declare that although the MOSFET does not have any role worthy of mention in the system, it is placed there if in case the battery has to be discharged manually. Therefore, unless stated otherwise, this MOSFET will be turned off all the time.

MOSFET 2 whose job is to charge the battery from supercapacitor is turned off. When Vsupercap is greater than or equal to 7.5 V, the second condition triggers which will turn off the MOSFET 1 and turn on MOSFET 2. Thus, overcharging does not occur from the wind turbine. In this time, the rechargeable battery will be charged up to rated voltage 6 V. When the supercapacitors' voltage dropped to 4 V, MOSFET 1 was switched on again. The switching circuit coding in

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The basic working principle of this part of the code is very simple. A signal "LOW" corresponding to 0 V was sent to the Arduino digital pin assigned to "MOSFET 1." As soon as the voltage across the supercapacitor bank exceeded 7.5 V, MOSFET 1 was switched off to

Arduino is given in Figure 6.

Figure 6. Arduino control coding.

Figure 7. Developed GUI panel of Labview.

As it is seen in Figure 5, the control system has mainly two conditions. First one is the supercapacitor charging circuit which occurs when Vsupercap is less than 4 V. Under this condition, MOSFET 1 is turned on; thus, it will charge the supercapacitor bank. In the meantime,

Figure 5. Flowchart of EHC control structure.

MOSFET 2 whose job is to charge the battery from supercapacitor is turned off. When Vsupercap is greater than or equal to 7.5 V, the second condition triggers which will turn off the MOSFET 1 and turn on MOSFET 2. Thus, overcharging does not occur from the wind turbine. In this time, the rechargeable battery will be charged up to rated voltage 6 V. When the supercapacitors' voltage dropped to 4 V, MOSFET 1 was switched on again. The switching circuit coding in Arduino is given in Figure 6.

The basic working principle of this part of the code is very simple. A signal "LOW" corresponding to 0 V was sent to the Arduino digital pin assigned to "MOSFET 1." As soon as the voltage across the supercapacitor bank exceeded 7.5 V, MOSFET 1 was switched off to

Figure 6. Arduino control coding.

The algorithm of the decision-making switching algorithm is illustrated in Figure 5. Here MOSFET 3 is usually turned off all the time. However, it is significant to declare that although the MOSFET does not have any role worthy of mention in the system, it is placed there if in case the battery has to be discharged manually. Therefore, unless stated otherwise, this

As it is seen in Figure 5, the control system has mainly two conditions. First one is the supercapacitor charging circuit which occurs when Vsupercap is less than 4 V. Under this condition, MOSFET 1 is turned on; thus, it will charge the supercapacitor bank. In the meantime,

MOSFET will be turned off all the time.

8 Supercapacitors - Theoretical and Practical Solutions

Figure 5. Flowchart of EHC control structure.


Figure 7. Developed GUI panel of Labview.

prevent overcharging. A signal "HIGH" which equals to 5 V was sent to Arduino digital pin "MOSFET 2" at the same time, and the rechargeable battery then was charged by the supercapacitor bank. Now, a signal "HIGH" was sent to one of the Arduino digital pins assigned "MOSFET 1" as soon as the voltage across supercapacitor bank was lesser than 4 V. A signal "LOW" equivalent to 0 V was sent to Arduino digital pin assigned to "MOSFET 2" at the same time. This charging and discharging of supercapacitor bank algorithm repeated simultaneously until battery was fully charged.

voltage, charging current of the supercapacitor, charging current of the battery when supercapacitor discharges and finally the rotational speed of the turbine. The data gathered here can also be easily exported to the spreadsheet software (Figure 8). Therefore, this enables

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The energy harvesting circuit built and the experimental setup are shown in Figure 9. The field testing was done in the Research Building, Block N, University of Nottingham Malaysia Campus.

This section gives a performance analysis of a Supercap (supercapacitor)-based energy harvesting battery charging device operated by the Maglev VAWT adopted to a 200 W PMSG as per the configuration discussed previously which was sent for fabrication. Upon arrival of the turbine, the system was set up in the laboratory, and field testing was performed to

This subchapter has two parts. First part includes one of the three cases in detail which has been compared for performance analysis. "Case A" showed a battery of 6 V, 3.2 AH, which was charged from 4.2 to 5 V through a DC/DC converter followed by a series of four supercapacitors (2.7 V, 35 F). "Case B" and "Case C" demonstrated the direct charging of the battery where "Case B" was experimented with the converter and "Case C" was without converter. All the three cases were experimented in low wind speed that ranges between 6 and 3 m/s. To keep it short, only results from wind speed 4 m/s will be discussed in detail. The remaining results have been given in a tabularized form to compare and find out the efficiency

The same procedure from the earlier section was followed, and results were graphically plotted for analysis. Following figures are the details of the charging process. It is noteworthy mentioning that both the Supercap discharge voltage and discharge current were the same as the previous value. This is because while Supercap bank discharged its charge to the battery, the turbine system was isolated through the MOSFET switch. Therefore, wind speed cannot make any impact on the discharging half cycle. Consequently, in all the three cases, the discharge voltage and current amount with respect to time were the same. Here, Figures 10 and 11 show the charging voltage and current graph with respect to time. For the discharging details, Section 4.5.1 may be reviewed as in both of the cases, the data will be the same.

At this point, 35 min were required to charge up the Supercap bank. Adding the discharging cycle time which was 2 min, the complete cycle duration was then 37 min. The starting current

the user to keep track of the system in real time of the system 9.

2.2.6. Experimental setup

3. Results

tabulate the data.

of the EHC.

3.1. At wind speed = 4 m/s

Case A: Energy harvesting through supercapacitor.

#### 2.2.5.1. DAQ and Labview

With NI-6212 device, data acquisition was implemented. A graphical user interface (GUI) was developed using LabVIEW. This GUI enables the user to easily monitor and analyze data. The LabVIEW interface is shown in Figure 7. This GUI displays supercapacitor and battery's


Figure 8. Data exported to excel spreadsheet from LabVIEW.

Figure 9. Experimental setup for the integrated system.

voltage, charging current of the supercapacitor, charging current of the battery when supercapacitor discharges and finally the rotational speed of the turbine. The data gathered here can also be easily exported to the spreadsheet software (Figure 8). Therefore, this enables the user to keep track of the system in real time of the system 9.

#### 2.2.6. Experimental setup

The energy harvesting circuit built and the experimental setup are shown in Figure 9. The field testing was done in the Research Building, Block N, University of Nottingham Malaysia Campus.
