The uncertainty of high-permeability renewable energy output brings about great challenges to the operation control in distribution network. The traditional control mode has lower reliability, higher calculation and greater communication pressure. It is more difficult to realize the technical requirements of “plug and play” of power components. Therefore, a bi-level coordinated control model is proposed for the operation and energy management optimization of active distribution network with multi-microgrid in this paper. The consensus algorithm which exists in the multi-agent system is applied in the upper-level model and the capacity utilization ratio of the different microgrids is set as the consistent variable because the ratio of resistance and reactance is usually larger in distribution network and the interests in the different microgrid entities should be distributed fairly. Moreover, in the lower-level model, the lowest operating cost is the final goal and the model predictive control rolling optimization is utilized to reasonably allocate the output of the equipments in the microgrid according to the changing trend of renewable energy. Thereby the tracking of the upper-level control commands is realized. Finally, the simulations are conducted in the IEEE-33 nodes distribution system connected to a multi-microgrid to verify the feasibility and effectiveness of the proposed method, in which a reference for the optimal operation of higher penetration renewable energy to distribution network is provided.

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Research on the Bi-Level Optimization Model of Distribution Network Based on Distributed Cooperative Control

The vibration signal of hydraulic generator is non-stationary. Features of the early fault signal are weak and thus are difficult to be extracted. In this paper, features of the bearing vibration signal for fault diagnosis are extracted by using the variational mode decomposition (VMD) and singular value. Fault diagnosis is carried out by using the support vector machine (SVM). Firstly, several intrinsic mode functions (IMFs) are obtained by performing VMD on the bearing vibration signal. Then, singular values of the modal component matrix constituted by the intrinsic mode functions are calculated, which are regarded as the feature vector input to the support vector machine. Finally the fault classification and recognition are done by the support vector machine. The proposed method is verified by analyzing the rolling bearing experimental data. The vibration data of the near Wake Island Hydropower Station in Hunan province are used to test the accuracy of the proposed method in practical application.

Fault Diagnosis of Hydraulic Generator Bearing by VMD-Based Feature Extraction and Classification

Passive intermodulation (PIM) is a niggling phenomenon that debilitates the performance of modern communications and navigation systems. PIM products interfere with information signals and cause their nonlinear distortion. The sources and basic mechanisms of PIM have been studied in the literature but PIM remains a serious problem of signal integrity. In this paper, the main sources and mechanisms of PIM generation by joints of good conductors are discussed. It is shown that the passive electrical, thermal and mechanical nonlinearities are intrinsically linked despite their distinctively different time scales. The roughness of the contact surfaces plays an important role in PIM generation by conductor joints. A review of the PIM phenomenology at the contacts of the good conductors suggests that novel multiphysics models are necessary for the analysis and reliable prediction of PIM products generated by several concurrent nonlinearities of a diverse physical nature.

/pdf/passive-intermodulation-at-contacts-of-rough-conductors-sf7yk9nl.pdf

Passive Intermodulation at Contacts of Rough Conductors

This paper proposes a new method to comprehensively predict the passive intermodulation (PIM) distortion in loose contact coaxial connectors by the time-domain reflectometry (TDR) test. The proposed approach treats the insulating film current and the electrothermal (ET) coupling as PIM sources. An ET coupling model is introduced to analyze the generating process of the PIM caused by the ET coupling in the loose contact coaxial connectors. The simulation and measurement results show good agreement. The proposed method is a cost-effective approach for the evaluation of the PIM distortion, because it uses a common TDR method to replace professional PIM test instruments. The proposed method can also be extended to all the loose metallic contact cases.

TDR Prediction Method for PIM Distortion in Loose Contact Coaxial Connectors

A design method is proposed in this article for on-line (online measurement: measurement when producing devices) and on-site (on-site measurement: measurement when using devices) passive intermodulation (PIM) measurement with a small-size anechoic chamber. In a PIM measurement, the role of an anechoic chamber is to shield extraneous electromagnetic signal and reduce reflection, so that an accurate measurement result can be obtained. However, the chamber itself may introduce new PIM sources due to the nonlinearity in absorbing material and shielding enclosure. The traditional method to lower the influence of chamber to PIM measurement is to design a large-size PIM test chamber in order to reduce the PIM level by path loss. In this article, an innovative design concept of the PIM test chamber is presented by controlling the PIM source level of the anechoic chamber instead of increasing the size of the chamber. It can significantly reduce the chamber size using this method, particularly suitable for on-line and on-site PIM measurement. To implement the concept, absorbing material and shielding enclosure structure with extremely low PIM are developed. The design concept includes defining the worst-case reflection level, estimating the PIM level due to reflected signals, and determining the smallest size of the chamber that meets the design specifications. Finally, two PIM test chambers are built to demonstrate the design concept. PIM measurement results are given to verify the theoretical analysis.

Small Anechoic Chamber Design Method for On-Line and On-Site Passive Intermodulation Measurement

The mechanism of the passive intermodulation (PIM) distortion caused by the loose contact in coaxial connectors is of great importance in wireless communication systems. This paper focuses on the effect of the additional impedance on PIM levels in coaxial connectors. First, the additional impedance and PIM levels of the loose contact coaxial connectors are measured. Then, the S-parameters and the additional impedance with three different loose contact cases are simulated. Finally, a modified coaxial connector with different values of conductive tapes is designed to verify the additional impedance impacts on the PIM level. It is shown that the increase of the additional impedance of the metal–metal loose contact will lead to the deterioration of PIM levels in the coaxial connector.

Measurement and Analysis of Passive Intermodulation Induced by Additional Impedance in Loose Contact Coaxial Connector

With emerging wireless communication technology, undesired interference caused by passive intermodulation (PIM) becomes a major obstacle to the network efficiency and the electromagnetic compatibility (EMC) of the devices. Accurate measurement techniques for PIM are fundamental to identify and characterize the electromagnetic interferences (EMIs). Anechoic chambers are commonly used in the antenna PIM test. The noise of PIM test chamber usually determines the accuracy of PIM measurement. The additional PIM sources caused by the chamber can be classified into three classes: those due to the absorbers, those due to the design of the shielded enclosure, and those due to the extraneous signals caused by an ineffective shielding. In this paper, a measurement method is proposed for the performance verification of PIM test chamber. The proposed method has two key points. One is adjusting the measurement distance between antenna and absorbers for gain compensation, which can evaluate the maximum measurable antenna gain of the PIM test chamber. The other is choosing the multiple measurement points according to the beamwidth of antenna, which can define the PIM level in worse case of the chamber. Theoretical analysis of the proposed method and measured results for two PIM chambers by the method are given in this paper.

Feng Gao

Papers

Measurement and Analysis of Passive Intermodulation Induced by Additional Impedance in Loose Contact Coaxial Connector

Notice of Retraction: A Measurement Method for Passive Intermodulation Chamber Performance Evaluation

A Measurement Method for Passive Intermodulation Chamber Performance Evaluation