2. Methodology

The novel idea we introduce in this research does not include the conventional DC/DC converter between turbine supercapacitor. Therefore, the converter voltage loss is removed. What had been done is, just after the supercapacitor gets fully charged by the turbine directly, the supercapacitor gets disconnected from the turbine by smart MOSFET switching using Arduino. Then, the fully charged supercapacitor gets connected with the battery by the MOSFET switch, which will charge the battery through a DC/DC converter by self-discharging and the process go on. In this method, voltage as small as 3–4 V can charge up a 6 V/12 V battery.

VAWT Wind speed 5 m/s

PMSG Phase 3-Phase

Table 1. System configuration for energy harvesting circuit.

Figure 1. Schematic diagram of system architecture of energy harvesting system.

Height 60 cm Radius 14.5 cm Number of blades 9

Rated power 200 W Rated voltage 12 V Diameter 16 cm Weight 12.5 kg

Open circuit voltage • 8 V (wind speed 5 m/s)

Supercapacitor-Based Hybrid Energy Harvesting for Low-Voltage System

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• 6.5 V (wind speed 4 m/s) • 3.5 V (wind speed 3 m/s)

### 2.1. System architecture

For harvesting energy from the wind, MagLEV VAWT with PMSG is used, and its specifications are as follows.

From Table 1, it can be seen that for low wind speed configuration, voltage ranges from 3.5 to 8 V. As the whole configuration is in low voltage, the battery choice we have is either 6 or 12 V. In low voltage settings, stepping up low input voltage as low as 3–12 V will result in stepping down current by even a smaller amount. Considering the facts stated, 6 V battery was chosen, which was to be charged by the turbine. Between the turbine and battery, a supercapacitor bank is placed which will be charged up by the turbine at first. Then subsequently it will be discharged through the battery. Since a constant voltage is needed for battery to be charged up properly, a DC/DC boost converter is needed between supercapacitor and the battery which will ensure constant stepped-up voltage to the battery when supercapacitor discharges. The field testing was done in the laboratory.

Figure 1 is the schematic diagram of the system architecture. As seen in Figure 1, few LED lights along with a 434 Ohm resistor were inserted as loads to discharge the battery.

#### 2.2. Hardware architecture

Initially, supercapacitors are used to store the charges as a part of the hybrid energy harvesting. In this chapter, to construct a supercapacitor bank, four supercapacitors rated 35 F–2.7 V each by Cooper Bussmann are used, which were connected in series. Therefore, a supercapacitor bank rated 8.75 F–10.8 V is formed. Battery choice is a tough one as there are many variations and specifications. For example, for rechargeable or nonrechargeable, different types such as lithium-ion, lead-acid, nickel-metal hybrid, and so on exist, which ultimately lead to confusion. In the research laboratory, there were few good quality batteries but they were rejected due to cost effectiveness and maintenance issues. For instance, Li-ion batteries are omitted because it needs extra circuitry for protection even though it has high efficiency and life cycle. Therefore, considering all these facts lead-acid battery was chosen to be fit for the research for having the optimum characteristics. For this project, a three-cell lead-acid battery manufactured by Yokohama rated 6 V (3.2 AH/20HR) was chosen.

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Table 1. System configuration for energy harvesting circuit.

2. Methodology

4 Supercapacitors - Theoretical and Practical Solutions

2.1. System architecture

field testing was done in the laboratory.

2.2. Hardware architecture

tions are as follows.

battery.

The novel idea we introduce in this research does not include the conventional DC/DC converter between turbine supercapacitor. Therefore, the converter voltage loss is removed. What had been done is, just after the supercapacitor gets fully charged by the turbine directly, the supercapacitor gets disconnected from the turbine by smart MOSFET switching using Arduino. Then, the fully charged supercapacitor gets connected with the battery by the MOSFET switch, which will charge the battery through a DC/DC converter by self-discharging and the process go on. In this method, voltage as small as 3–4 V can charge up a 6 V/12 V

For harvesting energy from the wind, MagLEV VAWT with PMSG is used, and its specifica-

From Table 1, it can be seen that for low wind speed configuration, voltage ranges from 3.5 to 8 V. As the whole configuration is in low voltage, the battery choice we have is either 6 or 12 V. In low voltage settings, stepping up low input voltage as low as 3–12 V will result in stepping down current by even a smaller amount. Considering the facts stated, 6 V battery was chosen, which was to be charged by the turbine. Between the turbine and battery, a supercapacitor bank is placed which will be charged up by the turbine at first. Then subsequently it will be discharged through the battery. Since a constant voltage is needed for battery to be charged up properly, a DC/DC boost converter is needed between supercapacitor and the battery which will ensure constant stepped-up voltage to the battery when supercapacitor discharges. The

Figure 1 is the schematic diagram of the system architecture. As seen in Figure 1, few LED

Initially, supercapacitors are used to store the charges as a part of the hybrid energy harvesting. In this chapter, to construct a supercapacitor bank, four supercapacitors rated 35 F–2.7 V each by Cooper Bussmann are used, which were connected in series. Therefore, a supercapacitor bank rated 8.75 F–10.8 V is formed. Battery choice is a tough one as there are many variations and specifications. For example, for rechargeable or nonrechargeable, different types such as lithium-ion, lead-acid, nickel-metal hybrid, and so on exist, which ultimately lead to confusion. In the research laboratory, there were few good quality batteries but they were rejected due to cost effectiveness and maintenance issues. For instance, Li-ion batteries are omitted because it needs extra circuitry for protection even though it has high efficiency and life cycle. Therefore, considering all these facts lead-acid battery was chosen to be fit for the research for having the optimum characteristics. For this project, a three-cell lead-acid

lights along with a 434 Ohm resistor were inserted as loads to discharge the battery.

battery manufactured by Yokohama rated 6 V (3.2 AH/20HR) was chosen.

Figure 1. Schematic diagram of system architecture of energy harvesting system.

A DC/DC boost converter was used to give a constant voltage of 7.5 V to the 6 V battery as per the schematic diagram of the hardware architecture. As the setup environment is for smallscale and low voltage system, the "LT1303" micropower step-up high-efficiency DC/DC converter was selected. There is another version of LT1303, that is, LT13035, which has added features like it can supply output voltage up to 25 V and also it is adjustable.

2.2.3. Anemometer

2.2.4. Liquid crystal display

2.2.5. Energy harvesting control system

on, the LED will glow and vice versa.

Figure 3. LCD screen of energy harvesting circuit.

Figure 4. MOSFET configurations in energy harvesting circuit.

To measure wind speed, an anemometer was used as shown in Figure 2. The device gives

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To display power and most importantly the current flow through the load in real time, a '16

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

measurements in miles per hour (mph); therefore, conversion to m/s was required.

2 LCD' was used as shown in Figure 3. LCD screen was controlled by Arduino.

To smartly control the charging and discharging of the supercapacitor bank and the battery, two N-channel MOSFETs were used as a switch, which are controlled by Arduino.
