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Stability of Remote Microgrids: Control of Power Converters
Published in Md. Rabiul Islam, Md. Rakibuzzaman Shah, Mohd Hasan Ali, Emerging Power Converters for Renewable Energy and Electric Vehicles, 2021
Mohd. Hasan Ali, Sagnika Ghosh
THD is defined as the measure of the effective value of the harmonic components of a distorted fundamental waveform. In other words, the THD is the summation of all harmonic components of the voltage or current waveform compared against the fundamental component of the voltage or current waveform [38–39], as shown in Equation (9.9). Harmonic distortion is usually caused by nonlinear loads connected to the grid by customers. Harmonics affects the shape and characteristics of a voltage and current waveform relative to fundamental frequency. These current or voltage harmonics can disrupt the quality and stability of the system. These harmonic currents can result in equipment failure, conductor failure and fires. Voltage distortion can lead to overheating of the equipment, electronic failures and maintenance difficulties.
Introduction to PV Systems
Published in Roger Messenger, Homayoon “Amir” Abtahi, Photovoltaic Systems Engineering, 2017
Roger Messenger, Homayoon “Amir” Abtahi
Many computer uninterruptible power supplies produce a five-level modified sine wave, so it is safe to say that this waveform is acceptable for use in providing backup ac power to a computer. However, IEEE Standard 1547–2003 [19] requires that any source connected to the utility line must have less than 5% total harmonic distortion (THD). For those who haven’t memorized the formula for THD from their electronics textbook, recall that THD is the percentage ratio of the sum of the rms values of all the harmonics above the fundamental frequency to the rms value of the fundamental frequency. It is unlikely that a five-level modified sine wave inverter will meet the 5% THD rule, especially if Vdc is allowed to vary while keeping Vrms constant. This is the reason for the existence of pure sine inverters. Using higher level H-bridges to approximate pure sine waves is one method. Another method is to use pulse width modulation techniques.
Electrical Systems
Published in Moncef Krarti, Energy Audit of Building Systems, 2020
Table 5.11 provides the current THD for selected but specific lighting and office equipment loads (NPLIP, 1995). Generally, it is found that devices with high-current THD contribute to voltage THD in proportion to their share of the total building electrical load. Therefore, the engineer should consider higher wattage devices before lower wattage devices to reduce the voltage THD for the entire building or facility. Example 5.7 shows a simple calculation procedure that can be used to assess the impact of an electrical device on the current THD. Thus, the engineer can determine which devices need to be corrected first to improve the power quality of the overall electric system. Typically, harmonic filters are added to electrical devices to reduce the current THD values.
Kernel Recursive Least Square Approach for Power System Harmonic Estimation
Published in Electric Power Components and Systems, 2021
Omar Avalos, Erik Cuevas, Héctor G. Becerra, Jorge Gálvez, Salvador Hinojosa, Daniel Zaldívar
The demand for power electronic devices in industrial areas has grown over the last decades. The precise control of power systems is an important research area, as its results can directly impact the industry. The presence of harmonics is one of the most recurrent issues. A simple description of harmonics characterizes them as the undesired spectral content of disrupted electrical waveforms with frequencies of integer multiples of the fundamental frequencies, 50 Hz or 60 Hz, according to the standard. The existence of harmonics is measured as the level of total harmonic distortion (THD) where a higher value on electrical systems can produce several problems such as the deterioration of electrical appliances, electrical losses, or even interferences with other equipment. As a result, harmonics have a profound impact on the quality of an electrical power system, and it is commonly regarded as a critical matter. Many standards and regulations over harmonic levels are established by recognized entities such as the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) [1, 2].
A Hybrid PPSOGSA Algorithm for Optimal Volt/VAr/THDv Control in Distorted Radial Distribution Systems
Published in Applied Artificial Intelligence, 2021
Miloš J. Milovanović, Jordan N. Radosavljević
In recent years, the widespread use of non-linear loads, such as adjustable speed drives and rectifiers, within the distribution system leads to power quality problems. One of the most important aspects of power quality is the presence of harmonics in the power system. High levels of THDV could lead to classical problems associated with harmonic distortion, such as equipment overheating, a reduction of efficiency in power generation, transmission and utilization, loss of reliability and communication interference. Although they do not generate harmonics, capacitors may have an important role in the propagation of harmonics in the systems. Addition of shunt capacitors in a harmonics polluted distribution system could lead to resonant conditions and increase the voltage distortion levels. In order to overcome these problems, in Volt/VAr control scheme it is necessary to take into consideration constraints which include voltage harmonic distortion limits in accordance with the IEEE-519 standard (1993). However, taking harmonics into account, Volt/VAr control problem becomes more complicated and difficult to solve.
Performance Investigation of Stand-Alone Hybrid Wind-Solar Home-Microgrids with Battery Storage System
Published in Smart Science, 2019
Mehdi Moradian, Rahmat Khezri, Amin Mahmoudi
Figure 13 demonstrates the output signals for configuration 1 (distributed battery) after disconnection of REGS from the H-Microgrid by circuit breaker; in which all the load should be supported by back-up battery banks until reconnection of the generating sources. In the time interval [1] second, variation in voltage level is affected by WECS starting from zero to nominal point. In this timeframe, both REGSs are connected to the system. In the second stage, the solar PV is disconnected in time 1s applied by its relevant circuit breaker (CB2 in the proposed H-Microgrid). After PV disconnection, output voltage confronted a small deviation (less than 1 V). In this stage, impact of PV system disconnection from the H-Microgrid is proportionally small on voltage level and its ripple. In third stage, the WECS is disconnected from the H-Microgrid by CB1 in time 4s. As it is shown in Figure 13(a), the voltage ripple is damped out after an overshoot by about 2 V voltage ripple. Load frequency after energy conversion from inverter to the load side is shown in Figure 13(b). Load frequency fluctuations are affected by WECS outage and the overshoot in 4s is lower than 0.02 Hz. PV system disconnection has almost no effect on the load frequency. Delivered power quality to loads are examined amount of THD, which is shown in Figure 13(c). The THD has a variation between about 0.12 and 0.35%, which is acceptable.