Understanding the Impact of Supraharmonics on Power Grid Stability.
Supraharmonics in Power Grid: Identification, Standards, and Measurement Techniques
If you are interested in the power quality of electric power distribution systems, you may have heard of a new phenomenon called supraharmonics (SH). SH are emissions in the frequency range of 2-150 kHz, which are caused by the increasing use of power electronics devices in renewable energy systems (RES) and smart grids. These devices, such as inverters, converters, and controllers, use high switching frequencies to convert, control, or transfer electric power from RES to the power grids. However, these switching frequencies also generate unwanted signals that can interfere with other devices and equipment connected to the same grid.
SH can have negative impacts on the power quality of electrical distribution systems, such as:
- Increasing losses and heating in transformers, cables, and motors
- Reducing the efficiency and lifetime of power electronics devices
- Causing malfunction or damage to sensitive equipment, such as communication devices, meters, relays, and protection systems
- Disturbing the operation of power line communication (PLC) systems
- Affecting the accuracy of power quality measurements and analysis
Therefore, it is important to identify, measure, and mitigate SH emissions in power grids. However, this is not an easy task, as SH have some characteristics that make them different from the conventional harmonics in the range of 50/60 Hz to 2 kHz.
For example:
- SH are highly variable and stochastic, depending on the load conditions and switching patterns of power electronics devices
- SH are not integer multiples of the fundamental frequency, but rather depend on the switching frequency and its harmonics
- SH can propagate in both directions along the power grid, creating complex interactions and resonances
- SH can be affected by the impedance of the grid and the load, which can vary with frequency
- SH can have different waveforms and spectra, depending on the modulation techniques and topologies of power electronics devices
To address these challenges, several methods have been developed and proposed in the literature for identifying, measuring, and setting new standards for SH. However, there is no consensus or uniformity among these methods, and some of them have limitations or drawbacks. Moreover, there is a lack of comprehensive and comparative reviews on this topic, which makes it difficult for researchers and practitioners to understand the state-of-the-art and the current research gaps.
In this blog post, we aim to provide an extensive overview of the existing techniques and standards for identifying, measuring, and mitigating SH emissions in power grids. We also highlight some of the recent developments and trends in this field, as well as some important recommendations for future research. We hope that this blog post will help you gain a better understanding of SH and their impacts on power quality.
The rest of this blog post is organized as follows:
- Section 1: Identification of SH sources and characteristics
- Section 2: Standards and regulations for SH emissions
- Section 3: Measurement techniques and instruments for SH
Section 1: Identification of SH sources and characteristics
One of the first steps to deal with SH is to identify their sources and characteristics. This can help to locate the origin of SH emissions, to quantify their magnitude and frequency spectrum, to evaluate their impacts on power quality, and to design appropriate mitigation solutions.
There are two main approaches for identifying SH sources and characteristics: analytical methods and experimental methods.
Analytical methods use mathematical models and simulations to describe the behavior and operation of power electronics devices and their interactions with the grid. These methods can provide insights into the generation mechanisms and influencing factors of SH emissions. However, they also have some limitations, such as:
- They require accurate parameters and assumptions for the models
- They may not capture all the nonlinearities and uncertainties in real systems
- They may not account for all the possible scenarios and conditions in complex grids
Experimental methods use measurements and tests to observe and analyze the actual SH emissions from power electronics devices and their impacts on the grid. These methods can provide realistic data and evidence for validating or improving analytical models. However, they also have some challenges, such as:
- They require specialized equipment and instruments for measuring SH
- They may be affected by noise and interference from other sources
- They may be limited by time or space constraints
Some examples of analytical methods for identifying SH sources are:
- Fourier analysis: This method uses Fourier series or transforms to decompose a periodic or non-periodic signal into its frequency components. It can reveal the amplitude and phase of each harmonic component in a signal. However, it may not be suitable for signals with high variability or non-stationarity.
- Wavelet analysis: This method uses wavelets or basis functions that can vary in scale (frequency) and position (time) to analyze a signal. It can provide a time-frequency representation of a signal, which can capture the transient and dynamic features of SH. However, it may require a large amount of computation and memory.
- Prony analysis: This method uses a parametric model to fit a signal with a sum of exponentially damped sinusoids. It can estimate the frequency, amplitude, damping factor, and phase of each sinusoidal component in a signal. However, it may be sensitive to noise and initial conditions.
Some examples of experimental methods for identifying SH sources are:
- Spectrum analyzer: This device measures the frequency spectrum of a signal by using a filter bank or a fast Fourier transform (FFT). It can display the magnitude and frequency of each harmonic component in a signal. However, it may have limited resolution or bandwidth for measuring SH.
- Power quality analyzer: This device measures the power quality parameters of a signal, such as voltage, current, power, power factor, harmonics, flicker, etc. It can provide information about the impacts of SH on power quality. However, it may not comply with the standards or specifications for measuring SH.
- Oscilloscope: This device measures the waveform of a signal by using a sampling technique. It can display the shape and time domain features of a signal. However, it may not provide enough information about the frequency domain features of SH.
Section 2: Standards and regulations for SH emissions
Another important aspect of dealing with SH is to follow the standards and regulations for SH emissions. These are rules or guidelines that define the acceptable levels or limits of SH emissions in power grids. They can help to ensure the compatibility and interoperability of power electronics devices and equipment connected to the grid. They can also help to protect the grid and its users from harmful effects of SH.
There are two main types of standards and regulations for SH emissions: international standards and national standards.
International standards are developed and adopted by international organizations or committees that represent different countries or regions. They aim to harmonize the requirements and specifications for SH emissions across different markets and jurisdictions. However, they may not reflect the specific needs or conditions of each country or region.
National standards are developed and adopted by national authorities or agencies that regulate the power sector in each country or region. They aim to address the local issues or challenges related to SH emissions in their own grids. However, they may not be consistent or compatible with other standards.
Some examples of international standards for SH emissions are:
- IEC 61000-4-7: This standard specifies the general requirements for measuring harmonics and interharmonics in power systems, including SH. It defines the measurement methods, instruments, settings, and procedures for measuring harmonics and interharmonics. However, it does not specify the limits or thresholds for harmonics and interharmonics.
- IEC 61000-4-19: This standard specifies the specific requirements for measuring SH in public low-voltage power systems. It defines the measurement methods, instruments, settings, and procedures for measuring SH in the range of 2-150 kHz. However, it does not specify the limits or thresholds for SH.
- IEC 61000-4-30: This standard specifies the methods for measuring power quality parameters in power systems, including harmonics and interharmonics. It defines the measurement methods, instruments, settings, and procedures for measuring power quality parameters. However, it does not specify the limits or thresholds for power quality parameters.
Some examples of national standards for SH emissions are:
- EN 50160: This standard specifies the voltage characteristics of electricity supplied by public distribution systems in Europe. It defines the limits or thresholds for voltage parameters, including harmonics and interharmonics up to 95 kHz.
- IEEE 519: This standard specifies the practices and limits for harmonic control in electric power systems in North America. It defines the limits or thresholds for harmonic distortion at different points of common coupling (PCC) between different users or suppliers.
- GB/T 14549: This standard specifies the quality requirements and assessment methods for electric energy supplied by public grids in China. It defines the limits or thresholds for power quality parameters, including harmonics up to 2 kHz.
Section 3: Measurement techniques and instruments for SH
A crucial step to deal with SH is to measure their magnitude and frequency spectrum in power grids. This can help to monitor and evaluate their impacts on power quality, to identify their sources and characteristics, and to design appropriate mitigation solutions.
There are two main categories of measurement techniques and instruments for SH: conventional techniques and instruments and advanced techniques and instruments.
Conventional techniques and instruments are based on well-established methods and devices that have been widely used for measuring harmonics and interharmonics in power systems. They include spectrum analyzers, power quality analyzers, oscilloscopes, etc. These techniques and instruments have some advantages, such as:
- They are relatively simple and easy to use
- They are relatively cheap and available
- They are relatively reliable and accurate
To learn more here
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Ammar Ahmed Alkahtani
Ali Q. Al-Shetwi
FBSU
Ali Saadon Al-Ogaili
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