Preface

This edited volume is a collection of reviewed and relevant research chapters, concerning the developments within the *Supercapacitors - Theoretical and Practical Solutions* field of study. The book includes scholarly contributions by various authors and is edited by a group of experts pertinent to electronic devices and materials. Each contribution comes as a separate chapter complete in itself but directly related to the book's topics and objectives.

The book contains eight chapters.

The target audience comprises scholars and specialists in the field.

**IntechOpen**

**Chapter 1**

Provisional chapter

**Supercapacitor-Based Hybrid Energy Harvesting for**

DOI: 10.5772/intechopen.71565

This research provides a platform for a novel innovative approach toward an off-grid energy harvesting system for Maglev VAWT. This stand-alone system can make a difference for using small-scale electronic devices. The configuration presents a 200 W 12 V 16 Pole AFPMSG attached to Maglev VAWT of 14.5 cm radius and 60 cm of height. The energy harvesting circuit shows better efficiency in charging battery in all aspects compared to direct charging of battery regardless with or without converter. Based on analysis and results carried out in this research, all feasibility studies and information are provided

Keywords: supercapacitor, hybrid energy harvesting, low voltage, VAWT, MOSFET

Supercapacitors have started to gain attention and are widely used for energy storage in recent years especially in the renewable energy sector. The advantages such as fast charging time, unlimited life cycle, low equivalent series resistance (ESR) and robust and high power density make it attractive and have been used to replace battery in a number of applications [1]. However, supercapacitors are greatly affected by temperature as an increase in temperature will produce negative effects to the electrolyte in the supercapacitor, thus reducing the lifespan. Charge balancing of supercapacitors has always been an issue, and it is important to minimize it in order to improve the performance and reliability. Analysis of few existing

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Supercapacitor-Based Hybrid Energy Harvesting for

**Low-Voltage System**

Low-Voltage System

MD Shahrukh Adnan Khan,

MD Shahrukh Adnan Khan,

Anas Syed

Abstract

for the next barrier.

switch, PMSG

1. Introduction

Anas Syed

Rajprasad Kumar Rajkumar, Wong Yee Wan and

Rajprasad Kumar Rajkumar, Wong Yee Wan and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71565

#### **Supercapacitor-Based Hybrid Energy Harvesting for Low-Voltage System** Supercapacitor-Based Hybrid Energy Harvesting for Low-Voltage System

DOI: 10.5772/intechopen.71565

MD Shahrukh Adnan Khan, Rajprasad Kumar Rajkumar, Wong Yee Wan and Anas Syed MD Shahrukh Adnan Khan, Rajprasad Kumar Rajkumar, Wong Yee Wan and Anas Syed

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71565

#### Abstract

This research provides a platform for a novel innovative approach toward an off-grid energy harvesting system for Maglev VAWT. This stand-alone system can make a difference for using small-scale electronic devices. The configuration presents a 200 W 12 V 16 Pole AFPMSG attached to Maglev VAWT of 14.5 cm radius and 60 cm of height. The energy harvesting circuit shows better efficiency in charging battery in all aspects compared to direct charging of battery regardless with or without converter. Based on analysis and results carried out in this research, all feasibility studies and information are provided for the next barrier.

Keywords: supercapacitor, hybrid energy harvesting, low voltage, VAWT, MOSFET switch, PMSG

#### 1. Introduction

Supercapacitors have started to gain attention and are widely used for energy storage in recent years especially in the renewable energy sector. The advantages such as fast charging time, unlimited life cycle, low equivalent series resistance (ESR) and robust and high power density make it attractive and have been used to replace battery in a number of applications [1]. However, supercapacitors are greatly affected by temperature as an increase in temperature will produce negative effects to the electrolyte in the supercapacitor, thus reducing the lifespan. Charge balancing of supercapacitors has always been an issue, and it is important to minimize it in order to improve the performance and reliability. Analysis of few existing

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

charge balancing circuits along with their pros and cons have been taken into consideration. By placing passive resistors across each capacitor, there is a high power loss from the resistors, which causes the circuit to be inefficient. Another concept of using DC/DC converters across two supercapacitors, on the other hand, results in high efficiency as no other losses occur besides from the converters itself. However, this circuit requires a large amount of components which adds to the cost.

devices is to connect them in parallel. Although this way of harvesting energy maintains the same voltage in both storage banks, yet it restricts the power delivered by the supercapacitor. The role of an electronic control unit in a 'battery supercapacitor hybrid energy storage system' under different load conditions with the aid of various sensors have been previously studied [9, 10]. Here, the DC/DC converter permits the supercapacitor to supply extra power required by the load. However, in low wind speed, it will not be possible for the turbine to charge a hybrid storage system where both the supercapacitors and battery are connected in parallel. Because at low wind speed the turbine rotates at a very low RPM resulting in a low output voltage at the generator terminal, which is not sufficient to charge the hybrid storage in

Supercapacitor-Based Hybrid Energy Harvesting for Low-Voltage System

http://dx.doi.org/10.5772/intechopen.71565

3

Also areas with low wind do not require a system that includes a generator of mega watt range. Coming back to the energy harvesting circuit, this investigation discovers a novel hybrid circuit with a combination of a battery and supercapacitor bank. In 2010, Worthington proposed a novel circuit that combines the synchronous switched harvesting technique, which was connected to a load capacitor directly to harvest energy [11]. This allowed the capacitor to act as a reservoir that would be disconnected when fully charged and then would discharge to a load. The circuit was connected with a charge pump tire circuit [11]. Experiment results showed that this idea was capable of harvesting three times more the amount of energy compared to the usual bridge rectifier circuit. However, this idea has not yet been implemented into the off-grid wind energy sector. Although Lee [12] implemented a hybrid energy harvesting storage in 2008 for wind power application, it was meant for grid connection and again was of high power range. Hence, it was impossible for the energy storage system to be implemented for the off-grid system. This study brings the supercapacitor-based hybrid energy harvesting for first time into the off-grid low wind power application. A supercapacitor bank is used in this experiment that charges up from the turbine and discharges through the

Batteries have relatively high energy density compared to supercapacitors; however, they do not have the characteristics of supercapacitors, that is, instantaneous charging and discharging [13, 14]. Even though batteries can store more energy, it requires longer time to discharge and recharge. Moreover, batteries require constant voltage for charging. If the current exceeds battery rating, it may get heated up and voltage fluctuation reduces life span of the battery. In order to give a constant voltage from the generator, a DC/DC converter has to be used. However, the internal voltage drops in DC/DC converter together with low voltage at generator output does not make a vertical axis wind turbine worthy of charging a battery in low wind speed. Therefore, this research proposes a balancing circuit which introduces the supercapacitor to act as a buffer between the turbine and a battery. The supercapacitor would get charged up from the turbine and discharge through the battery in two separate processes by using MOSFET control switching system. In this research, the proposed hybrid supercapacitor-based battery charging circuit has been implemented into a vertical axis wind turbine in low wind speed and compared with direct charging of battery from the turbine with or without a DC/DC converter. Finally, the proposed system has also been compared with

current existing systems of rural Malaysia in terms of cost-effectiveness.

parallel configuration.

battery with the use of power electronics.

Liyan Qu, Wei Qiao (2011) proposed a novel two-layer constant power control (CPC) scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbines [3], where each wind turbine generator (WTG) is equipped with a supercapacitor energy storage system (ESS). The ESS serves as either a source or a sink of active power to control the generated active power of the DFIG wind turbine. Results have shown that the proposed CPC scheme enabled the wind farm to effectively participate in unit commitment and active power and frequency regulations of the grid [2–4]. The proposed system and control scheme provide a solution to help achieve high levels of penetration of wind power into electric power grids. Output power of wind turbine fluctuates constantly, which may cause grid frequency variations, and imposes a high risk on system stability. In order to smoothen power output of wind turbine, the proposed system was used. By using a supercapacitor-based energy storage, the effects of frequency fluctuation and deviation on system during fault condition were minimized. This was one of the early examples of using supercapacitors in wind turbine. However, our research deals with off-grid wind energy harvesting; therefore, Lian Qu's model cannot be used. Moreover, our research aims to charge a DC battery, whereas Lian Qu worked with three-phase grid connection.

Battery and supercapacitors are used together to form a hybrid system. As discussed earlier, battery and supercapacitor have their own advantages and disadvantages. Supercapacitors have high-power density but low energy density, whereas batteries have low power density and high energy density. Besides, battery also has higher ESR which results in high internal loss, thus less efficient compared to supercapacitors. Therefore, both devices are often integrated so that they can complement each other. This system known as hybrid energy storage system (HESS), which is widely used now in order to prolong the lifespan of each device and improve stand-alone systems [5]. For example, Babazadeh et al. [6] implemented an HESS system into a PMSG wind turbine with a large variable wind speed between 6 and 21 m/s. The HESS system helps to smoothen and regulate the output caused by peaks generated due to variation in the wind speed by using a control system to disconnect the battery from wind turbine. This successfully proved that the battery life is able to last longer as the battery experiences lesser stress. The average urban driving patterns that require rapid discharging of battery banks when accelerating and charging of banks when decelerating will reduce the battery banks' lifespan; thus, supercapacitors are beneficial in this case. Since supercapacitors are able to charge and discharge at a fast rate, it is able to provide a boost of power during acceleration and absorbs power during regenerative braking [7, 8].

One of the problems of establishing the hybrid storage system is the different voltage level of the supercapacitor and battery bank. The most common way of coupling the two storage devices is to connect them in parallel. Although this way of harvesting energy maintains the same voltage in both storage banks, yet it restricts the power delivered by the supercapacitor. The role of an electronic control unit in a 'battery supercapacitor hybrid energy storage system' under different load conditions with the aid of various sensors have been previously studied [9, 10]. Here, the DC/DC converter permits the supercapacitor to supply extra power required by the load. However, in low wind speed, it will not be possible for the turbine to charge a hybrid storage system where both the supercapacitors and battery are connected in parallel. Because at low wind speed the turbine rotates at a very low RPM resulting in a low output voltage at the generator terminal, which is not sufficient to charge the hybrid storage in parallel configuration.

charge balancing circuits along with their pros and cons have been taken into consideration. By placing passive resistors across each capacitor, there is a high power loss from the resistors, which causes the circuit to be inefficient. Another concept of using DC/DC converters across two supercapacitors, on the other hand, results in high efficiency as no other losses occur besides from the converters itself. However, this circuit requires a large amount of components

Liyan Qu, Wei Qiao (2011) proposed a novel two-layer constant power control (CPC) scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbines [3], where each wind turbine generator (WTG) is equipped with a supercapacitor energy storage system (ESS). The ESS serves as either a source or a sink of active power to control the generated active power of the DFIG wind turbine. Results have shown that the proposed CPC scheme enabled the wind farm to effectively participate in unit commitment and active power and frequency regulations of the grid [2–4]. The proposed system and control scheme provide a solution to help achieve high levels of penetration of wind power into electric power grids. Output power of wind turbine fluctuates constantly, which may cause grid frequency variations, and imposes a high risk on system stability. In order to smoothen power output of wind turbine, the proposed system was used. By using a supercapacitor-based energy storage, the effects of frequency fluctuation and deviation on system during fault condition were minimized. This was one of the early examples of using supercapacitors in wind turbine. However, our research deals with off-grid wind energy harvesting; therefore, Lian Qu's model cannot be used. Moreover, our research aims to charge a DC battery, whereas Lian Qu worked

Battery and supercapacitors are used together to form a hybrid system. As discussed earlier, battery and supercapacitor have their own advantages and disadvantages. Supercapacitors have high-power density but low energy density, whereas batteries have low power density and high energy density. Besides, battery also has higher ESR which results in high internal loss, thus less efficient compared to supercapacitors. Therefore, both devices are often integrated so that they can complement each other. This system known as hybrid energy storage system (HESS), which is widely used now in order to prolong the lifespan of each device and improve stand-alone systems [5]. For example, Babazadeh et al. [6] implemented an HESS system into a PMSG wind turbine with a large variable wind speed between 6 and 21 m/s. The HESS system helps to smoothen and regulate the output caused by peaks generated due to variation in the wind speed by using a control system to disconnect the battery from wind turbine. This successfully proved that the battery life is able to last longer as the battery experiences lesser stress. The average urban driving patterns that require rapid discharging of battery banks when accelerating and charging of banks when decelerating will reduce the battery banks' lifespan; thus, supercapacitors are beneficial in this case. Since supercapacitors are able to charge and discharge at a fast rate, it is able to provide a boost of power during

One of the problems of establishing the hybrid storage system is the different voltage level of the supercapacitor and battery bank. The most common way of coupling the two storage

acceleration and absorbs power during regenerative braking [7, 8].

which adds to the cost.

2 Supercapacitors - Theoretical and Practical Solutions

with three-phase grid connection.

Also areas with low wind do not require a system that includes a generator of mega watt range. Coming back to the energy harvesting circuit, this investigation discovers a novel hybrid circuit with a combination of a battery and supercapacitor bank. In 2010, Worthington proposed a novel circuit that combines the synchronous switched harvesting technique, which was connected to a load capacitor directly to harvest energy [11]. This allowed the capacitor to act as a reservoir that would be disconnected when fully charged and then would discharge to a load. The circuit was connected with a charge pump tire circuit [11]. Experiment results showed that this idea was capable of harvesting three times more the amount of energy compared to the usual bridge rectifier circuit. However, this idea has not yet been implemented into the off-grid wind energy sector. Although Lee [12] implemented a hybrid energy harvesting storage in 2008 for wind power application, it was meant for grid connection and again was of high power range. Hence, it was impossible for the energy storage system to be implemented for the off-grid system. This study brings the supercapacitor-based hybrid energy harvesting for first time into the off-grid low wind power application. A supercapacitor bank is used in this experiment that charges up from the turbine and discharges through the battery with the use of power electronics.

Batteries have relatively high energy density compared to supercapacitors; however, they do not have the characteristics of supercapacitors, that is, instantaneous charging and discharging [13, 14]. Even though batteries can store more energy, it requires longer time to discharge and recharge. Moreover, batteries require constant voltage for charging. If the current exceeds battery rating, it may get heated up and voltage fluctuation reduces life span of the battery. In order to give a constant voltage from the generator, a DC/DC converter has to be used. However, the internal voltage drops in DC/DC converter together with low voltage at generator output does not make a vertical axis wind turbine worthy of charging a battery in low wind speed. Therefore, this research proposes a balancing circuit which introduces the supercapacitor to act as a buffer between the turbine and a battery. The supercapacitor would get charged up from the turbine and discharge through the battery in two separate processes by using MOSFET control switching system. In this research, the proposed hybrid supercapacitor-based battery charging circuit has been implemented into a vertical axis wind turbine in low wind speed and compared with direct charging of battery from the turbine with or without a DC/DC converter. Finally, the proposed system has also been compared with current existing systems of rural Malaysia in terms of cost-effectiveness.
