Distribution Network Mixed-harmonic Separation Method Based on Characteristic Vector

The penetration of distributed generation (DG) scheme in modern power system is progressively increasing because of the call for environmental friendly energy resources. Photovoltaic (PV) has been identified as one of such energy resources which can provide reliable and efficient power supply when integrated with distribution network. The installation of a single site PV module is modelled in a bus bar of the 31-bus 330kV network of Power Holding Company of Nigeria (PHCN) to characterize and predict harmonic pattern therein and also to assess bus voltage disturbance in the network due to increase in harmonic emission level. The simulation results obtained using PCFLO version 6 programme platform indicates that the system voltage variation is dependent on harmonic emission level. In a bus bar the highest and constant non-sinusoidal current Total Harmonic Distortion (THD) of 29% flows in the neutral of the apparatus in the candidate bus where the non-linear load is installed irrespective of harmonic current source magnitude.

Due to the widespread applications of new energy and the power electronic residential loads in the distribution network, it is very necessary to assess the harmonic current emission level since the impact of the collective harmonics cannot be ignored. The calculation of the harmonic impedance is a crucial task to determine the harmonic responsibilities at the point of common coupling (PCC). This paper presents a method to quantify the harmonic current responsibilities of the system side and customer side based on the impedance gathering trend, and then to calculate the emission level of the residential loads. This study has a sparked phenomenon on the evaluation of current emission level of the residential loads and can reflect the residential load harmonic emission characteristic precisely.

Accurate harmonic emission level evaluation is the basis of distinguishing the responsibility of harmonic pollution between power supply system and consumer. A new harmonic emission level evaluation method based on principal component analysis (PCA) regression is proposed in this paper. Firstly, the principle of principal component analysis regression method is stated. Secondly, harmonic impedance of supply system is evaluated by principal component analysis regression method. Finally, harmonic emission level of supply system and consumer is calculated according to the harmonic impedance of supply system. This method has a high accuracy in harmonic emission level evaluation. The effectiveness of the proposed method was verified by computer simulation results.

In this paper, a method for estimating the system harmonic impedance and harmonic emission level based on the pan-normal impedance cloud is presented. First of all, based on the basic principle of fluctuation method, it can be obtained that the key to estimate the system harmonic impedance is how to identify fluctuation ratio samples closer to the true value through theoretical analysis; Secondly, through the study of the probability distribution of fluctuation ratio, this paper proposes the characteristic of the pan-normal distribution meets the applicable conditions of normal cloud model, which can be used to calculate the digital features of impedance cloud by backward cloud generator; Finally, based on the 3En' Rules of cloud model, the filtering threshold of impedance is determined, then the system harmonic impedance and harmonic emission level can be estimated by filtering qualified samples. It proves the accuracy and effectiveness of the proposed method by the simulation of theoretical model and calculation of practical engineering examples.

Phasor-based assessment for harmonic sources in distribution networks

With the rapid growth of urban power transmission cable scale, the harmonic pollution in the high-voltage power grid is more transmitted to other power grids of different voltage levels, which makes the harmonic transmission more complicated, increases the harmonic emission level, and makes it difficult to quantitatively analyze and study the allowable value of users’ electrical pollution emission. Therefore, in this paper, by establishing the harmonic conduction model of the urban high-voltage power grid and considering the equivalent circuit of transformer and transmission cable in the urban power grid, the parameters of transmission cable harmonic transfer coefficient and the allowable emission value of power quality pollution of the urban power grid are deduced and quantitatively analyzed. Then the harmonic transmission and mutual influence of urban power network harmonics in power transmission cable are analyzed through examples, which is helpful to determine the allowable value of harmonic pollution emission scientifically and reasonably.

Although good application effect of locating faulty section in complex distribution network can be attained by applying ant colony algorithm, however there are also disadvantages such as too long search time and computation time. For this reason, traditional ant colony algorithm should be improved. Firstly, a switching function that can dynamically adapt to topological structure of distribution network is constructed; then a method to set the initial values of ant colony's pheromone and the disturbance rule of the solution are led in; finally the method to apply the improved ant colony in fault section location of distribution network with multi power supplies is determined. The advantages of the improved ant colony algorithm in calculation speed and error tolerance are verified by results of calculation example.

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.

With the widespread application of distributed energy resources in the distribution network, the traditional single-power-source radial distribution network is gradually transforming into a complex multi-source distribution network. The traditional fault handling strategies have been unable to meet the requirements of modern distribution networks for efficient and rapid power restoration. Therefore, it is of great practical significance to study fault elimination strategies applicable to multi-source distribution networks. This paper proposes a multi-stage fault elimination strategy for multi-source distribution networks based on real-time risk perception. During the fault handling process, this strategy adopts a multi-stage fault elimination method. In the early stage of the fault occurrence, the fault point is quickly located, and the fault area is isolated. On the basis of isolating the fault area, the strategy gradually optimizes the recovery path of the fault area according to the real-time operating status of the distribution network and the availability of distributed energy, reasonably allocates the output of distributed energy and traditional power sources, and introduces distributed reactive power compensation. The research results show that the multi-source distribution network multi-stage fault elimination strategy based on real-time risk perception proposed in this paper can significantly improve the fault handling efficiency, achieve a response within one cycle, and effectively enhance the reliability and stability of the distribution network.

The precise location of voltage sag sources plays an important role in formulating a voltage sag governance plan and clarifying the responsibility for the accident. The traditional location method of voltage sag sources is difficult to establish a precise mathematical model and locate the complex voltage sag sources accurately in the complex distribution network. In order to solve these problems, a location method for complex voltage sag sources based on random matrix theory is proposed in this paper. Firstly, the augmented matrix is constructed based on the influence factor data and the operation state data of the distribution network as the data source matrix, and the statistical characteristics of each data are analyzed by using the random matrix theory to determine the suspicious area of voltage sag source. Then, the disturbance signal of each node in the suspicious area of voltage sag source is analyzed by using the atomic algorithm and disturbance active power method, and it can determine the location of each disturbance source in the complex voltage sag event and the cause of voltage sag at each node. Compared with the existing model-based methods, the proposed method in this paper is a data-driven approach, which does not need the physical model and topology information. Furthermore, it can reduce the amount of data and improve the analysis efficiency on the basis of determining the suspicious area of the voltage sag source. Finally, the examples are given to show that the proposed method can accurately locate the disturbance sources in complex voltage sag events.

This paper presents a Norton model for modelling distribution networks where the system configuration is not fully known. Traditionally harmonic studies use complex distribution networks modelled by harmonic current sources for specific frequencies. Although this model has been proved to be adequate for some studies, this may not be adequate for other applications. When changing the operating conditions of the supply-side system, the harmonic currents injected by the distribution network might change and to investigate these harmonic currents, the Norton model is used. The change of operating condition is obtained by switching shunt capacitors. The estimated model can be used to analyze, for example, the effect of harmonic filters under different supply system configurations or operating conditions. The method of estimating the Norton models is illustrated on a test system, simulated on the well-known simulation program EMTP-ATPDraw. Key words : Norton model; Distribution network; Operating conditions; Harmonic currents and voltages

A severe interference problem caused by a large rectifier installation is studied. The interaction between harmonic emission level and power system impedance matching is described. An elegant solution involving corrective measures on each of the plants???customer, power system and communication circuits???are proposed. The dangers of creating new problems with single approaches are stressed, and the use of power current phase angles is illustrated in the analysis.

This study addresses constructing Minimum Spanning Trees (MST) in stochastic weighted distribution networks, where edge costs have inherent uncertainties with known means and variances. Traditional deterministic methods often fail, and existing stochastic approaches are frequently unstable or computationally complex under high uncertainty. A novel variance-based deterministic transformation algorithm is proposed. Its core feature is transforming stochastic edge costs into robust deterministic equivalents by computing an aggregate variance term from the largest (n – 1) edge variances, enabling MST construction via classical algorithms. This method fundamentally enhances stability and ensures feasibility, particularly in high-variance scenarios, improving upon traditional confidence interval-based techniques. The algorithm’s efficacy was rigorously validated. Its performance was compared against a probabilistic Qij-based method under moderate variance, demonstrating consistent and accurate MSTs. It was then applied to a complex 21-edge distribution network with high variance parameters. Results confirm the algorithm’s broad applicability, precision, and capability to construct reliable spanning trees under both moderate and substantial uncertainty. The algorithm demonstrates significant computational efficiency (O(r log r)), ensuring practicality and scalability across varying uncertainty levels. Unlike iterative or constraint-heavy models, this algorithm simplifies optimization while preserving uncertainty representation. This makes it well-suited for large-scale networks and real-world systems where cost variability is critical. Future research includes expanding this approach to multi-objective optimization or dynamic networks

The characteristics of electrical noise and power harmonics from power converters and other harmonic sources, as well as the effects of such noise and harmonics on distribution system equipment and operation are described. Power system surges and their effects on converter equipment are also described. Field tests were conducted on two different distribution systems. Measurements were made of harmonic voltage and current magnitudes, capacitor-switching transients, and impulsive electromagnetic noise in the frequency range of 3 kHz to 300 kHz. Test methodology and instrumentation are described, and the measured results are presented. The implications of this high-frequency noise on power line communication systems are discussed. A computer program was developed to aid in analyzing distribution system response to harmonic sources on the system. Simulations performed for the two distribution systems tested are described, and comparisons between simulation results and measured harmonic magnitudes are presented. The project also addressed methods of controlling harmonics on distribution systems. The different methods for harmonic control, principally the filtering and/or phase cancellation of harmonics, are described.

The high cabled rate of urban power grid aggravates the risk of resonance and harmonic amplification. In addition, the system side of DC receiving end urban power grid contains converter station high-power harmonic sources, while the user side contains other nonlinear user harmonic sources. There are two-way conduction characteristics of harmonics in transmission lines. The problem of resonance and harmonic amplification in distribution network is aggravated by high cable ratio. Therefore, the response of the system side injected harmonic voltage at the end of the line and the potential harmonic amplification problem after the user side injected harmonic current are studied respectively. The influence of key factors (line type, length, load rate and power factor) on harmonic propagation is analyzed. The characteristic harmonic of converter station is not amplified and the most severe condition of amplification is summarized. The harmonic limit of the harmonic injection terminal is also proposed.