Harmonic Energy Regulation for Grid Current Quality Improvement in Electrolytic Capacitorless PMSM Drives
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When the grid impedance changes, the performance of active damping strategies for electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives may decay. A novel harmonic energy regulation strategy for grid currents is proposed to improve the robustness to the grid impedance. The quality of grid currents can be improved when the DC-link capacitors and the motor inductance serve as the main harmonic energy storage elements. Based on this concept, the harmonics in the DC-link voltage are extracted to reconstruct the sampled DC-link voltage in Space Vector Pulse Width Modulation (SVPWM) for harmonic energy regulation. Specifically, the phase and amplitude processing units are applied to regulate the harmonics in the motor current and DC-link voltage based on system model to achieve the theoretical harmonic energy exchange state. By comparing the stability criterion of the cascaded system with the active damping strategy, the proposed method shows better robustness to the grid impedance. Finally, experiments are carried out on a platform of 5.5kW electrolytic capacitorless PMSM drive to verify the effectiveness of the proposed control strategy.Keywords:
Harmonic
Robustness
Harmonic Analysis
Given the growing number of interactive nonlinear loads in power distribution systems, some techniques to monitor the spread of harmonics through the system need to be developed. This paper examines the nature of harmonics in a naval power distribution system and develops a harmonic model using the CYMHARMO package to monitor current sources and the interaction that can occur in the Canadian Patrol Frigate (CPF) power distribution system. The results indicate that a significant level of harmonics can exist in the CPF system due to 43 identified harmonic current sources. The presence of any capacitive loads will only serve to increase the level of distortion if resonance occurs. With shipboard testing to confirm equipment loading and identify capacitive elements, the model will be a useful tool for naval engineers to examine and modify the CPF system.
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A periodic wave having a frequency that is an integral multiple of the fundamental power line frequency component is harmonics. They are the byproducts of modern electronics devices so it is necessary to mitigate the harmonics and offer techniques to mitigation of harmonics. This paper provides an explanation of the various harmonic mitigation techniques available to solve harmonic problems in three phase power systems. Included are the advantages and disadvantages of each method, their normal circuit connection as well as typical performance that can be expected when each method is properly employed.
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Power quality, and harmonics in particular, is a major issue in any isolated power system due to extensive use of non-linear power electronic devices. The harmonic problem in an isolated system is even more magnified because of the absence of an external grid, which is a basic characteristic of all isolated systems (like that of a ship). Harmonic studies are, therefore, conducted on a fairly regular basis to analyze and rectify the problems associated with harmonics. In order to conduct such studies in any electrical system, it is important to accurately model its components. As there is no transmission network or "system equivalent," the generator(s) represents a major portion of an isolated power system. Within this paper, appropriate models of synchronous generators for low-frequency harmonic studies are presented. These models are developed using detailed "dq0" representations of the synchronous machine.
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Power system harmonics
Transmission system
Synchronous motor
Fundamental frequency
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Inter-harmonics are defined as the spectrum components that have frequencies between two harmonics. This letter points out that these fractional-harmonic components are not always the result of actual inter-harmonic sources. The signal sampling window size and position for Fourier analysis, as well as the time-varying characteristic of the signals, can all be factors leading to the so-called inter-harmonic components. Case studies illustrate that the inter-harmonic definition can be misleading and needs to be improved.
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Traditional voltage quality control devices do not consider the harmonic factors in the regulation,but excessive harmonics may cause great damages in the actual project.An integrated VQC power quality regulating devices with harmonic suppression is proposed,the causes of harmonic amplification and suppression strategies are discussed.Furthermore,a multi-objective optimal control model is designed,considering power quality,reactive power,power losses and harmonics at the same time.Simulation and experimental results prove the effectiveness of the device and the control strategy.
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Many articles have been written about the growing harmonic problems in present day power systems. The topics range from the fundamentals of harmonics to specific case studies showing harmonic cause and effect relationships. The articles follow a common theme: they describe harmonic problems and recommend possible solutions after the problems occurs. This article describes how computer simulations can be used to predict harmonic problems before they occur, and evaluate corrective alternatives prior to implementation. A case study demonstrates a computer simulation used to eliminate harmonic problems at a cement plant. The study involves: (1) initial data collection and harmonic measurement; (2) computer simulation of the initial plant to compare measured harmonics with predicted harmonics; (3) computer simulation to evaluate the proposed addition of capacitors and design corrective harmonic filters; and (4) installation of the corrective filters and final data collection to verify the design effectiveness.
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To resolve the harmonics pollution of medium frequency electric furnace in a steelwork, power quality monitoring is conducted for power source in steelwork and substation. By the analysis of test data, the 11th, 13th, 17th harmonic are the main reason for the pollution of power quality. The effective measures were put forward for users to prevent harmonics pollution, Effectiveness of the measures was verified by the comparison data before and after treatment.
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The paper presents levels of voltage harmonics with low-voltage (LV) customers in 2020. Measurements are obtained from an open power quality (PQ) data base (PQube- Live World Map of Power Quality) where measurements from two different PQ monitors (PQube and PQube3) show data from different sites around the world. In this paper, only harmonic voltage data from four countries in Europe will be considered and particularly, higher odd harmonic orders (above 15th order) and even harmonics. Those levels will be compared to the limits at standards as EN-50160 and IEC 61000-2-2. The motivation is some reported cases concerning the increasing voltage levels at higher harmonic orders, even reaching standard limits. These PQ monitors are placed in different LV-networks so that, giving an overview of voltage levels. The aim of the paper is not to verify whole of EU network compliance, but to give an overview of harmonic levels during several months from different LV sites in Europe.
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Harmonic Analysis
Power system harmonics
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Harmonic on a power system refers to the voltages and currents imposed on a system that has frequencies which are a multiple of the fundamental frequency. It is the main index and the most important parameters of power quality. Harmonics generated by nonlinear loads cause harmonic pollution. Because this pollution can cause problems within power systems that can range from the false operation of protection devices to the physical damage of power system components and loads, it is urgent to eliminate harmonics. First, this paper lists a variety of harmonic sources and their impact on the power system. Second, based on the harmonic pollution characteristics, this paper suggests some management remedies for harmonic problems.
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In order to limit the amount of harmonic content on an electrical network, information about harmonic levels and their source is required. The aim of this paper is to investigate the correlation between the measured harmonics on the electrical network of an isolated mine site, and the modelled predictions based on equipment information. Measurements were performed by a power quality monitoring equipment, and simulations were performed using a sophisticated power systems design package EDSA. The availability of harmonic filters and other methods for the reduction of harmonics makes the need for accurate harmonic modelling of a network imperative. This paper concludes with the explanations for the major differences between the measured parameters and the modelled predictions.
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