*5.1.8 Storaging of harvested energy by supercapacitors*

Regardless of the source of clean renewable energy, it is necessary to have a circuit to store the energy generated from the energy harvesting source. When a DC voltage is

*Supercapacitors: The Innovation of Energy Storage DOI: http://dx.doi.org/10.5772/intechopen.106705*

**Figure 18.** *Thermoelectric device principle [40].*

applied to a discharged supercapacitor, it is charged, and thus stores electrical energy. Since these are small consumers (sensors, transmitters, and IoT), today's supercapacitor can often replace batteries and be more durable and environmentally friendly.

Most consumers require a higher operating voltage than a single supercapacitor can provide. In systems requiring higher voltages, supercapacitors are usually connected in series. In series-connected supercapacitors, however, a balancing circuit such as this, is required to distribute the voltages across the individual elements equally. There are two types of balancing circuits: passive balancing and active balancing [43].

A team of scientists from the American UCLA and the University of Connecticut [44] designed a system that is powered by electrical impulses from the human body. It is a "biological supercapacitor" that uses charged particles and ions, from the fluids in the human body. The device is not dangerous for the body and it can be used in pacemakers and other implants that require a power supply (**Figure 19**).

The block diagram of a system for collecting the energy of light radiation (natural or artificial) is shown in **Figure 20**. A supercapacitor with a capacity of 400 mF was used.

Another example of ultra-low power management, with a supercapacitor for energy storage (1.5 F) is shown in **Figure 21**. MOSFETs are used to rectify the output voltage of a wind energy harvester exposed to low wind. The proposed algorithm enables the monitoring of the maximum output power at time-varying wind speeds. A microcontroller was used to provide a source and sink impedance matching [46].

#### **5.2 Smart cities**

Following the smart city concept, supercapacitors have the potential to be involved in the creation of greener, sustainable, and efficient powering systems. One of the

#### **Figure 19.**

*Energy harvesting power management [44].*

#### **Figure 20.**

*Energy harvesting power management [45].*

most prominent examples is public transport. By using the distributed energy sources in the urban smart environments, the power sources become DC based including the photovoltaics cell, and fuel cell, etc. As the urban environments are designed with many distributed power sources connected to the distribution lines, energy storage takes a significant place in the system. Battery energy storage systems and

*Supercapacitors: The Innovation of Energy Storage DOI: http://dx.doi.org/10.5772/intechopen.106705*

supercapacitor energy storage systems, as well as hybrid ones, may be installed both on large and small scales, which makes them the ideal fit for the smart city concept [47].

The smart city concept cannot be imaginable without sensor networks and Internet of Things devices and applications. As the energy requirement in sensor devices is increasing, the energy has to be stored for the blackout periods. Considering that the batteries are not a permanent solution, the supercapacitors serve as a solution for high-energy storage applications that require high-voltage and high-current drive [48]. Recent studies show that the supercapacitors are well suited for a wide range of applications, such as IoT, consumer products, white goods, office automation, longterm battery backup, and energy harvesting [48]. In order to overcome the powering issues that may occur at the remote nodes, as well as in the extreme weather conditions, fully functional IoT devices have been designed based on energy harvesting with supercapacitors and batteries as storage elements [47].

#### **5.3 Smart grid**

In recent years, the economic trends have been dictating the renewable energy sources generation of electric power. Therefore, the concept of the microgrid has been introduced as an off-grid or grid-connected energy system that can work independently or collaboratively with other microgrids [49]. In general, such a system can provide electric power either from a single source or multiple sources, such as wind and solar energy, adding energy storage to the system [50, 51].

The supercapacitors are being used to regulate the microgrid voltage and to improve the system stability. In recent studies, the supercapacitor provides the error component of the battery current in the proposed control scheme. This is an addition to the microgrid, as it improves the microgrid voltage regulation capability, as well as extends the battery lifetime [52, 53].

#### **5.4 Energy systems**

Supercapacitors are increasingly used in both AC power systems (EES) and DC power sources. With the development of the voltage balancing technique of serially connected SCs, a great improvement in the HVDC transmission system is expected. The large capacity of SC provides enough energy storage for small consumers in a short time, and their main advantage in energy systems is high power density, so they can cover large consumption peaks. In combination with power electronics circuits, SCs can inject energy into the EES at the right moment, thus opening a whole new field of development of circuits and control algorithms. A large field of application of SC in DC power supplies is low-pass filters with previously unimaginable parameters.

#### *5.4.1 Quality of electricity in AC systems*

Experts realized a long time ago that the quality of electricity affects the quality of work and life. Many norms from that area were applied, but the real progress started at the end of the last century. The problem began to be approached globally. CENELEC (European Committee for European Standardization) was established [54]. Most European countries have accepted the CENELEC standard EN 50160 [55] for voltage monitoring at the point of delivery to the consumers under normal conditions.

The LEM corporation (NORMA, ELMES, ELSIS, and HEME) developed a series of measuring devices MEMOBOX for monitoring the quality of electricity, and thus, began a new practice supported by the EN 50160 standard, but also by newly created standards (e.g., IEC 1000-3-6/71).

As connecting the national and European power systems is a necessity, it is also necessary to adapt local legislation and standardization in this area. The specificity of electricity is that its quality is influenced to a greater extent by consumers (non-linear loads) than by producers. That is why the consumer is, to a considerable extent, a partner of the supplier in ensuring the quality of electricity. At the same time as electrical energy becomes dirty, the consumer is also sensitive to this kind of contamination. From the point of view of the application of supercapacitors for the elimination of short-term disturbances, the following terms should be highlighted [55]:

#### *5.4.2 Frequency change*

Under normal operating conditions in the distribution network connected to the power system, the ten-second mean value of the frequency during 99.5% of each week must be within 50 Hz 1% and 50 Hz + 4% / - 6% in the remaining 0.5% of the week.

In disconnected (island) networks, the limits are 50 Hz 2% during 95% of the week and 50 Hz 15% during the remaining 5% of the week.

#### *5.4.3 Flicker*

The need to define and measure that parameter is created from the fact that the change in light intensity in the working or living environment negatively affects people's health, that is, their work and other efficiencies. Headaches, nervousness, depression, and vision impairment, etc. occur. Flicker is defined as follows: If there are 100 people in a room under equal conditions, and if the light intensity changes so much that 50 of the 100 people notice it, the flicker is said to have an intensity of 1. Flicker is a consequence of amplitude modulation supply voltage with frequencies in the range from 1 to 33 Hz, where the amplitude is a direct function of that frequency. For example, at a frequency of 8 Hz, the nominal voltage fluctuation amplitude is about 0.256 % of the nominal value (e.g., 0.59 V from 230 V).

#### *5.4.4 Voltage failure*

Voltage failures occur most often due to faults in the consumer's facilities or in the public distribution network. They are defined as follows: failure (partial loss of voltage) is sudden (unpredicted), short-lived (from 10 ms, up to 1 minute) reducing the supply voltage to one of the values in the range of 90%, and up to 1% of the nominal voltage, after which the nominal voltage is restored. The permissible guideline number of voltage drops during one year is ranged from 10 to 1000. Most of them must have a duration of less than 1s and an amplitude of less than 60% of the nominal voltage.

#### *5.4.5 Power failure*

It is a state in which the voltage at the point of transmission is less than 1% of the nominal voltage. The following power interruptions are distinguished:


The following random interruptions are distinguished:


**Figure 22** shows an example of a short-term power failure.

**Figure 23** shows the configuration of the system supercapacitor in the control area of the power system. The converter (VSC) consists of a rectifier/inverter with 6-pulse control and pulse width modulation (PWM) with an IGBT bridge. The PWM converter and the DC-DC converter (chopper) are connected by a DC link capacitor. A bidirectional DC-DC converter operates in step-up mode if electrical power is supplied to the supercapacitor bank from the power system. Smoothing inductance is used for current transfer and filtering [56].

**Figure 22.** *Example of a short-term power failure [54].*

**Figure 23.** *Configuration of supercapacitor bank in the control area [56].*
