Harmonic Current Emission Research Articles

Coupled Harmonic Admittance Identification Based on Least Square Estimation

Norton equivalent circuit is a commonly used model in estimating harmonic current emissions of harmonic sources. It however cannot reflect the mutual coupling relationships among voltage and current in different harmonic orders. This paper proposes a new method to identify parameters in a coupled harmonic admittance model. The proposed method is conducted using voltage and current measurements and is based on least square estimation technique. The effectiveness of the method is verified through time-domain simulations for a grid-connected converter and also through field data obtained from a ±800 kV converter station. The experimental results showed that the proposed method presents higher accuracy in terms of harmonic current emission estimation compared with three Norton-base methods.

Measurement-based harmonic current modeling of mobile storage for power quality study in the distribution system

Abstract Electric vehicles (EVs) can be utilized as mobile storages in a power system. The use of battery chargers can cause current harmonics in the supplied AC system. In order to analyze the impact of different EVs with regardto their number and their emission of current harmonics, a generic harmonic current model of EV types was built and implemented in the power system simulation tool PSS®NETOMAC. Based on the measurement data for different types of EVs three standardized harmonic EV models were developed and parametrized. Further, the identified harmonic models are used by the computation of load flow in a modeled, German power distribution system. As a benchmark, a case scenario was studied regarding a high market penetration of EVs in the year 2030 for Germany. The impact of the EV charging on the power distribution system was analyzed and evaluated with valid power quality standards.

Assessment of Prevailing Harmonic Current Emission in Public Low-Voltage Networks

The total harmonic current emission in a public low-voltage (LV) network is mainly determined by the large number of electronic devices, which use different circuit topologies with different harmonic emission characteristics. Consequently, the total harmonic current measured at the LV busbar can provide valuable qualitative information, for example, about dominating circuit topologies. This paper describes and applies a methodology to characterize the harmonic current emission of an LV network by a prevailing phasor. Using measurements from 130 German public LV networks, the “prevailing” location of 3rd and 5th harmonic current is analyzed with respect to different types of consumers. The results are compared with initial measurements received from other countries. Based on the prevailing phasor, a simplified method for an approximate estimation of the impact (cancellation potential) of a particular LV network or a new equipment technology (e.g., electric-vehicle charging) on the harmonic levels in a public distribution network is proposed.

Improving the Summation Law for Harmonic Current Emissions of Parallel Operated PV Inverters by Considering Equivalent Grid Impedance

Improving the Summation Law for Harmonic Current Emissions of Parallel Operated PV Inverters by Considering Equivalent Grid Impedance

Harmonic current emission level assessment of residential loads based on impedance-gathering trend

Summary Because of the widespread application of new energy and power electronic–based residential loads in distribution networks, the impact of collective harmonics cannot be ignored. The harmonic impedance should be evaluated when determining the harmonic responsibilities at the point of common coupling. This paper presents a new noninvasive method to quantify the harmonic current responsibilities of the utility side and customer side on the basis of impedance-gathering trend. The method is compared with another noninvasive resistance-sign–based method. In addition, the emission level of the residential loads is calculated. The presented results of a field test conducted in a typical residential apartment in Shanghai, China, prove that the method works well in practical conditions.

Light intensity variation (flicker) and harmonic emission related to LED lamps

This paper discusses two power-quality aspects of LED lamps: harmonics and flicker. Measurements have been performed of 24 different LED lamps: the harmonic current spectrum and light intensity variations have been measured. To enable an objective comparison, the light intensity variations were measured for all the lamps when exposed to the same voltage magnitude variations. Results show a large variety in harmonic emission between different LED lamps indicating that different technologies or different components are being used within the LED lamps. Moreover the results show a large variety in light intensity variations when different LED lamps are subjected to the same voltage fluctuations. A clear correlation was found between harmonic emission and sensitivity to voltage magnitude variations. Lamps with low light intensity variations are also the ones with the highest harmonic current emission. No clear relation between active power or price and sensitivity to voltage magnitude variations was found.

Harmonic Emissions of Three-Phase Diode Rectifiers in Distribution Networks

Harmonic emissions have been changed in distribution networks, with respect to frequency range and magnitude, due to the penetration of modern power electronics systems. Two new frequency ranges 2–9 and 9–150 kHz have been identified as new disturbing frequency ranges affecting distribution networks. This paper presents the effects of grid-connected three-phase systems with different front-end topologies: conventional, small dc-link capacitor, and electronic inductor. A power converter with a small dc-link capacitor can create a resonant frequency with the line impedance below and above 1 kHz depending on the grid configurations. The resonant effects depend on many factors, such as load power levels, filter types, and the number of parallel drives. These issues can affect the grid current harmonics and power quality of the distribution networks. Analyses and simulations have been carried out for three different topologies and the results have been verified by experimental test at system level. Current harmonic emissions have been considered for 0–2, 2–9, and 9–150 kHz frequency ranges.

Challenges Facing PFC of a Single-Phase On-Board Charger for Electric Vehicles Based on a Current Source Active Rectifier Input Stage

This paper aims to study the power factor (PF) correction scheme for a single-phase on-board charger of electric vehicles. The topology is based on a unidirectional current source active rectifier (CSAR) consisting of four insulated-gate bipolar transistors in series with four diodes followed by a boost converter. Buck-type rectifiers inject low-order input current harmonics into the ac mains. Thus, an inductor–capacitor ( LC ) input filter is employed. The capacitor's reactive energy results in a leading grid current. In order to achieve a unity displacement power factor, a phase shift control is implemented. However, the LC filter is prone to series and parallel resonances coming from the grid disturbances and the converter harmonics, respectively. Therefore, the phase shift control strategy combined with the topology of the CSAR results in a periodical resonance of the input filter. This phenomenon is studied in detail. In order to reduce the grid current's distortion level, an active damping control with resonance frequency tracking that achieves a good PF while meeting the IEC's international standards on harmonic current emissions is presented. An experimental test bench is developed to validate the simulations’ theoretical findings. Compliance with the standards is achieved and system limitations are discussed.

MODELING OF FREQUENCY-DEPENDENT IMPEDANCE OF VOLTAGE SOURCE INVERTER

Growing popularity of renewable energy brings about negative effects for the power quality especially for harmonic levels of supply voltage. Voltage source inverters being inevitable for operation of renewable energy can produce significant amounts of current harmonics in power grids. This paper provides the analysis of current harmonic sources within the inverter and then introduces the Simulink model of three-phase inverter. Derived model defines the current harmonic levels of inverter in regard to the supply voltage distortion. The model validation is done by comparing the modeling results with measurement data. Finally, the analysis of frequency-dependent characteristics of voltage source inverter reveals factors with critical impact on current harmonic emission of inverter.

Future Drives of Home Appliances: Elimination of the Electrolytic DC-Link Capacitor in Electrical Drives for Home Appliances

This article describes the next step in the development of the home appliance motor drive-the elimination of the electrolytic dc-link capacitor and the substitution of one with a small film. A small film capacitor increases total device reliability and improves the spectrum of the input current so the power factor corrector (PFC) used to satisfy existing standards on harmonic current emission can be omitted, which decreases the size and cost of the appliances. This article also proposes simple modifications to the standard vector control scheme, making operation with pulsating dc-link voltage possible.

Impact of supply voltage distortion on the current harmonic emission of non-linear loads

<p>Electronic devices have a non-linear characteristic and emit harmonics into the low voltage grid. Different harmonic studies analyze their impact on the grids based on different types of harmonic models. The most used model is the constant current source. Measurements have shown that the harmonic currents emitted by electronic devices depend on the circuit topology and the existing supply voltage distortion. This paper quantifies the impact of supply voltage distortion on the harmonic current emission of individual devices and the summation of multiple devices. After a classification of the commonly used circuit topologies a time-domain model is developed for each of them. Then the individual and combined impact of voltage harmonics on the harmonic current emission of the modeled devices is analyzed based on simulations. Finally the impact of voltage distortion on the summation of multiple devices is analyzed and the accuracy of constant current source models is evaluated.</p>

Study of resonance in wind parks

Wind turbine harmonic current emissions are a well-known power quality problem. These emissions flow through wind park impedances, leading to grid voltage distortion. Parallel resonance may worsen the problem because it increases voltage distortion around the resonance frequency. Hence, it is interesting to analyze the parallel resonance phenomenon. The paper explores this phenomenon in wind parks and provides analytical expressions to determine parallel resonances.

Compact Fluorescent Lamp Modeling for Large-Scale Harmonic Penetration Studies

Low-watt compact fluorescent lamps (CFLs) may account for significant energy consumption of power distribution feeders in future years. This can lead to power-quality concerns because these devices consume highly distorted currents. In order to predict CFL harmonic current emissions into networks, CFL models capable of predicting these emissions accurately are being studied. On the other hand, these models require great computational effort in large-scale CFL penetration studies. This paper presents and discusses several approximate CFL models based on the harmonic-coupled admittance matrix model which reduces the computational effort while maintaining reasonable accuracy. The performance of the models is validated with CFL laboratory measurements.

Harmonic Modeling of Electric Vehicle Chargers in Frequency Domain

Fully electric cars will be increasingly used in the near future in many countries. They are commonly known as electric vehicles (EVs) and use power electronic-based rectifiers for charging their batteries, which may significantly impact power quality in LV and MV distribution grids. Of particular importance are harmonic emissions of EV chargers, which are strongly influenced by the distortion of the supply voltage. This paper presents the results of testing and analyzing harmonic current emission of eight different single-phase EV chargers, with respect to supply voltage distortion. The analysis is based on extensive measurements performed at a test stand, capable of accurately reproducing supply voltage waveforms with desired distortion. The harmonic model consists of a constant part and a part that depends on the level of harmonics in the supply voltage. In order to characterize each EV charger in a general model, some characteristic indices are introduced, which quantify the sensitivity and linearity of harmonic currents of EV chargers to harmonics present in the supply voltage. The paper presents and discusses results for each individual EV charger, as well as a comparison of them.

Low Frequency Conducted Emissions of Grid Connected Static Converters

Pulse-width modulated rectifiers are nowadays commonly used for AC to DC power conversion. PWM rectification technology is very effective and allows for bidirectional power flow with the possibility of power factor improvement and low-order harmonic emission limitation. Unfortunately, employed PWM boost topology results with generation of input current harmonic distortions in a frequency range tightly correlated to modulation frequency. PWM carrier frequency and its harmonic components in typical applications are usually located in frequency range from single kHz up to hundreds of kHz. Increase of harmonic emission in this particular frequency range can be disturbing for other sensitive systems, therefore can cause lack of electromagnetic compatibility. Interferences in low frequency range are increasingly frequent EMC issue because of extensive use of low power PWM rectifiers and significant increase of rated power of individual converters, which already reach several MW. Presented comparison of current harmonic emission spectra of PWM rectifiers with relation to classic diode rectifiers is focused on frequency range of 2 to 9 kHz, for which emission limitation rules are currently under development. New class of EMC problems arising in low frequency range in power system are underlined as a result of increased harmonic emission in frequency range of 2 to 9 kHz.

Harmonic modelling of PV systems for probabilistic harmonic load flow studies

SummaryProbabilistic harmonic load flow (HLF) is currently enjoying renewed popularity. This is not surprising since in the near future, thousands of photovoltaic (PV) systems will be integrated into distribution systems. However, as yet, there is no model capable of explaining PV harmonic current behaviour in probabilistic HLF studies. To fill this gap, the harmonic modelling of PV systems proposed in this paper has three key points. First, it provides an effective model of the relationship between PV harmonic current emission and background harmonic voltages. Second, it statistically characterises PV harmonic currents (relative magnitude and phase angle) at different fundamental‐frequency current output intervals using historical time‐series data. In this statistical characterisation, the first fifth moments of each PV harmonic current are used to accurately approximate the raw probability density function (PDF) by means of the Legendre series. Finally, the third key point of this harmonic modelling is a method capable of determining the distribution functions of PV harmonic currents (absolute magnitude and phase angle), based on the statistical characterisation and a fundamental‐frequency probabilistic PV model. The numerical results obtained confirm the effectiveness of this PV model. Copyright © 2014 John Wiley & Sons, Ltd.

Parameter estimation procedure for the equivalent circuit model of compact fluorescent lamps

The spreading use of compact fluorescent lamps (CFLs) in utility distribution systems is leading to increased concerns over power quality because CFLs consume highly distorted currents, which may account for significant power consumption of distribution feeders. For this reason, CFL models and estimation procedures of CFL model parameters must be studied in order to predict CFL harmonic current emissions into networks. This paper describes estimation procedures of CFL model parameters and presents estimation algorithms based on least-square techniques and actual measurements. The estimation procedures are validated with extensive laboratory measurements.

Model of Electronic Ballast Compact Fluorescent Lamps

The use of compact fluorescent lamps (CFLs) in utility distribution systems is spreading due to energy consumption concerns. This can damage system power quality because CFLs are nonlinear harmonic injecting loads. For this reason, CFL modeling must be studied to predict their harmonic current emissions into networks. This paper presents a CFL model for calculating these emissions, as well as a simple estimation algorithm for determining the model parameters from experimental measurements. They are both validated with laboratory tests.

Harmonic Propagation and Interaction Evaluation between Small-Scale Wind Farms and Nonlinear Loads

Distributed generation is a flexible and effective way to utilize renewable energy. The dispersed generators are quite close to the load, and pose some power quality problems such as harmonic current emissions. This paper focuses on the harmonic propagation and interaction between a small-scale wind farm and nonlinear loads in the distribution grid. Firstly, by setting the wind turbines as P – Q(V) nodes, the paper discusses the expanding Newton-Raphson power flow method for the wind farm. Then the generalized gamma mixture models are proposed to study the non-characteristic harmonic propagation of the wind farm, which are based on Gaussian mixture models, improved phasor clustering and generalized Gamma models. After the integration of the small-scale wind farm, harmonic emissions of nonlinear loads will become random and fluctuating due to the non-stationary wind power. Furthermore, in this paper the harmonic coupled admittance matrix model of nonlinear loads combined with a wind farm is deduced by rigorous formulas. Then the harmonic propagation and interaction between a real wind farm and nonlinear loads are analyzed by the harmonic coupled admittance matrix and generalized gamma mixture models. Finally, the proposed models and methods are verified through the corresponding simulation models in MATLAB/SIMULINK and PSCAD/EMTDC.

Statistical characterisation of harmonic current emission for large photovoltaic plants

SUMMARY Harmonic current emission of photovoltaic (PV) systems is a well-known problem. However, its quantitative characterisation, which requires the compilation and use of abundant statistical data, had never been satisfactorily dealt with. This paper discusses the multifaceted statistical characterisation of these emissions in a large PV plant. The topics addressed are harmonic current magnitude and its phase angle in relation to PV power output level and background harmonic voltages. Harmonic current emission in PV systems should be recorded during any single 1-week period throughout a full year. Because power quality metres are expensive, it is more economical to measure this type of emission with simple, cost-effective equipment. This paper thus presents a new assessment method for harmonic emission based on PV power output level, which is the main parameter affecting the emission, and which is easily monitored by most PV inverters. This new method uses statistical data to define a dependence model for the PV power output of PV harmonic current emissions. Such a model is rarely provided by PV inverter manufacturers. However, the simpler dependence model required for this method can be obtained by inexpensive power quality metres. This new method also produces accurate results at low process costs. Copyright © 2013 John Wiley & Sons, Ltd.