**1. Introduction**

**Chapter 3:** This chapter focuses on the sequential harmonic elimination method employed for multimodule multilevel converters. The principles of the sequential selective harmonic elimi‐

**Chapter 4:** This chapter introduces a general model modified from the conventional control structure diagram for analysis of the harmonic generation process for photovoltaic (PV) instal‐ lations. Causes of the current harmonics and their relationships with output power levels are

**Chapter 5:** This chapter presents a case study about harmonic measurements in high-voltage networks. The measurements are analyzed and temporal harmonic profiles are studied in detail.

**Ahmed Zobaa**

Cairo, Egypt

**Murat Erhan Balci**

Balikesir University Balikesir, Turkey

College of Engineering Design and Physical Sciences Brunel University London Uxbridge, United Kingdom **Shady H. E. Abdel Aleem**

15th of May Higher Institute of Engineering

Mathematical and Physical Sciences

Electrical and Electronics Engineering

nation for MMC topology and amplitude control are described with examples.

summarized and analyzed.

VIII Preface

Nowadays, electrical utilities and consumers are paying much attention to enhance the quality of the generated and distributed electrical energy. The main aims are to produce clean electrical power and to distribute it to the end customers with acceptable power quality performance in a cost-effective manner. Nowadays, the importance of power quality aspects has increased due to the booming developments in power-electronic devices and renewable energy resources under the umbrella of smart grids. Besides, the deregulation of the electricity market resulted in a competitive market in which multiple utility companies try to deliver the best products (generated electrical energy) for the customers who have the chance to choose the utility company that provides them with electrical energy with the highest quality level. In consequence, power quality will play an essential role in modern electrical power systems. However, there are also difficulties before wider applicability is possible for the power quality performance limits. One difficulty is that, to date, there is no single commonly approved definition of power quality because of the various power quality perspectives and phenomena [1]. As well, power quality has dissimilar interpretations for people in various electric entities. Some express power quality as the voltage quality, others express it as the current quality, and some practice power quality as the system reliability. Furthermore, IEEE Std. 1100 [2] defines power quality as "the concept of powering and grounding sensitive electronic equipment in a manner suitable for the equipment." One can say that everyone describes it from his own perspective.

© 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 reproduction 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.

On one side, voltage quality focuses on variations of voltage from its ideal waveform (i.e., characterized by a sine wave of constant magnitude and frequency), while current quality is concerned with the deviation of the current from the ideal sinusoidal waveform. On the other side, discrimination of power quality as a voltage quality or current quality is an ambiguous way of thinking as a deviation in voltage can result in a deviation in current and vice versa. Thus, in order to keep generality, and as the power is mathematically the voltage times current, power quality should be the combination of both voltage and current qualities [3] and is signified by a set of electrical limitations (reference boundaries/margins) that enable an equipment to operate in its planned manner without major operating losses [4, 5] to long live as possible.

To generalize, power quality issues cover many power system problems like impulsive and oscillatory transients, different types of interruptions, voltage sags and swells, imbalance, under and over voltages, notching, noise, harmonics and interharmonics, voltage fluctuations and flickers, and power frequency variations [6]. In the following sections, these power qual-

Introductory Chapter: Power System Harmonics—Analysis, Effects, and Mitigation Solutions…

http://dx.doi.org/10.5772/intechopen.76628

3

Over voltages are defined as any voltage greater than the equipment nominal operating voltage when the equipment is specified to operate at for a time period that exceeds 1 min. While, the under voltage can be defined as any voltage below the nominal operating voltage of the

Over-voltage phenomenon has many causes in power system networks such as sudden changes in the system operating settings, abrupt load rejection, series/parallel harmonic resonance cases, sudden line-to-ground faults, improper earthing schemes, poor voltage regulation throughout the system, and overcompensation of the reactive power support provided by capacitor banks. Under voltages can result from improper power cables sizing, long feeder

Over voltage has a serious impact on electrical equipment and power systems as it stresses the equipment's insulation and may damage it, in addition to protective devices tripping because of dielectric failure. Also, over voltage may lead to flashover between line and ground at the weakest point in the system and can cause breakdown of the equipment insulation. On the other hand, under voltage causes an increase in the system losses and results in voltage stability problems. Also, different operational problems may arise due to under voltages such as

Voltage flickers are defined as a continuous rapid variation of input supply voltage sustained for an appropriate period to enable visual recognition of a variation in electric light intensity. Flicker is a power quality problem in which the magnitude of the voltage or frequency changes at a rate that is to be noticeable to the human eye [6]. The main causes of the voltage flicker are the loads that draw large starting currents during initial energization such as elevators, arc furnaces, and arc welders. If load starting cases are rapidly repeated, then light flicker effects can be quite noticeable. The severity of voltage flickers is measured using short-term and long-term flicker severity terms, where an expected flicker severity over a short duration (typically 10 minutes) is known as *Pst*, and that evaluated over a long duration (typically 2

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

surveillance period. By definition, a value of one for *Pst* expresses a visible disturbance, a level

(0.0314 <sup>×</sup> *Pa*) <sup>+</sup> (0.0525 <sup>×</sup> *Pb*) <sup>+</sup> (0.0657 <sup>×</sup> *Pc*) <sup>+</sup> (0.28 <sup>×</sup> *Pd*) <sup>+</sup> (0.08 <sup>×</sup> *Pe*) (1)

are the surpassed flicker levels during 0.1, 1, 3, 10, and 50% of the

routes with high loading capacities, and large motor starting conditions.

motor starting problems and protection relay tripping [7].

hours) is known as *Plt*. Thus, *Plt* is a combination of 12 *Pst* values.

ity problems are presented.

**2.2. Voltage flickers**

*Pst* = √

*, Pb , Pc , Pd*

*,* and *Pe*

where *Pa*

**2.1. Over voltages and under voltages**

equipment for a time period that exceeds 1 min.
