Research on Multi-Scale Modeling of Grid-Connected Distributed Photovoltaic Power Generation

The complexity of distribution network model mainly depends on the model scale of grid-connected distributed photovoltaic (PV) power generation. Therefore, the simulation performance of multi-scale PV model is the key factor of the simulation accuracy in the specific operating scenarios of distribution network. In this paper, a multi-scale model of grid connected PV distributed generation system is proposed based on the mathematical model of grid-connected distributed PV power generation. It is analyzed that differences of simulation performance, such as adaptability of simulation step size, accuracy of output and the effect on voltage profile of distribution network, between PV models with different scales in IEEE 33 node example. Simulation results indicate that the multi-scale model is effective in improving the accuracy and efficiency of simulation under different operating conditions of distribution network.

Research on Power Quality Disturbance Signal Classification Based on Random Matrix Theory

In this paper, a method of power quality disturbance classification based on random matrix theory (RMT) is proposed. The method utilizes the power quality disturbance signal to construct a random matrix. By analyzing the mean spectral radius (MSR) variation of the random matrix, the type and time of occurrence of power quality disturbance are classified. In this paper, the random matrix theory is used to analyze the voltage sag, swell and interrupt perturbation signals to classify the occurrence time, duration of the disturbance signal and thedepth of voltage sag or swell. Examples show that the method has strong anti-noise ability.

Transient Stability Analysis and Design of VSGs with Different DC-Link Voltage Controllers

Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.

Simultaneous photocatalytic degradation and SERS detection of tetracycline with self-sustainable and recyclable ternary PI/TiO_(2)/Ag flexible microfibers

Facile and efficient photocatalysts using sunlight,as well as fast and sensitive surface-enhanced Raman spectroscopy(SERS)substrates,are urgently needed for practical degradation of tetracycline(TC).To meet these requirements,a new paradigm for PI/TiO_(2)/Ag organic‒inorganic ternary flexible microfibers based on semiconducting titanium dioxide(TiO_(2)),the noble metal silver(Ag)and the conjugated polymer polyimide(PI)was developed by engineering a simple method.Under sunlight,the photocatalytic characteristics of the PI/TiO_(2)/Ag flexible microfibers containing varying amounts of Ag quantum dots(QDs)were evaluated with photocatalytic degradation of TC in aqueous solution.The results demonstrated that the amount of Ag affected the photocatalytic activity.Among the tested samples,PI/TiO_(2)/Ag-0.07(93.1%)exhibited a higher photocatalytic degradation rate than PI/TiO_(2)(25.7%),PI/TiO_(2)/Ag-0.05(77.7%),and PI/TiO_(2)/Ag-0.09(63.3%).This observation and evaluation conducted in the present work strongly indicated a charge transfer mechanism.Moreover,the PI/TiO_(2)/Ag-0.07 flexible microfibers exhibited highly sensitive SERS detection,as demonstrated by the observation of the Raman peaks for TC even at an extremely low concentration of 10–10 moles per liter.The excellent photocatalytic performance and SERS detection capability of the PI/TiO_(2)/Ag flexible microfibers arose from the Schottky barrier formed between Ag and TiO_(2)and also from the outstanding plasmonic resonance and visible light absorptivity of Ag,along with immobilization by the PI.The successful synthesis of PI/TiO_(2)/Ag flexible microfibers holds significant promise for sensitive detection and efficient photocatalytic degradation of antibiotics.

Two-dimensional flow vector measurement based on all-fiber laser feedback frequency-shifted multiplexing technology

The decomposition and identification of signals are crucial for flow vector acquisition in a multi-dimensional measurement. Here, we proposed a two-dimensional(2D) flow vector measurement system based on all-fiber laser feedback frequency-shifted multiplexing technology. The reliable performance of the system is characterized by experimental verification and numerical simulation. An orthogonal dual-beam structure is employed to eliminate the impact of an unknown incident angle in the practical application. Meanwhile, the vector velocity signals in 2D can be decomposed into one-dimensional(1D) scalar signals by adopting the frequency-shifted multiplexing,which makes it easy to obtain the vector information and velocity distribution of fluid motion through the self-mixing interference frequency spectrum.

Collaborative Fault Recovery and Network Reconstruction Method for Cyber-physical-systems Based on Double Layer Optimization

For fault characteristics of cyber-physical-systems(CPS)based distribution network,a spatiotemporal incidence matrix to represent correlation of concurrent faults on cyberspace and physical space is proposed,and strategies of fault location,removal,and recovery of concurrent faults are analyzed in this paper.Considering the multiple objectives of minimum network loss,voltage deviation,and switching operation times,a collaborative power supply restoration model of a CPS-based distribution network with the strategy that restoration of the communication layer is prior to the physical layer is constructed using the Dijkstra’s dynamic routing algorithm and second-order cone relaxation distribution network reconfiguration method,to realize orderly recovery of a distribution network during CPS concurrent faults.Related investigations are made based on the DCPS-160 case,and the accuracy and effectiveness of the proposed model are also verified.

Cyber-physical Test Case for Distribution Grid Operation and Control

In the CPS-oriented power distribution system,a large number of the existing test cases cannot be accessed and reused.That is not conducive to the continuity of the CPS research of the distribution network.In response to above problem,based on an actual distribution network and considering the mapping relationship between cyber systems and physical systems,a computation test case that covers multiple power sources,and multiple types of load is proposed in this paper,and it is suitable for the simulation of multiple types of information system scenarios.In order to satisfy the specific needs of researchers for system topology and data,how to perform cyber contingency analysis,vulnerability assessment and distributed control are also discussed based on the existing topology and data.Researchers can utilize the test case presented in this paper to test their innovative methods in operational analysis,optimization control,and safety analysis for distribution networks.They can also utilize the published topologies and data to design their own test cases based on the methods in this paper.

A Novel Frequency-changer Control Strategy Based on a Virtual Synchronous Motor

The use of frequency-changers is widespread in daily electric power generation.If a frequency-changer could automatically adjust its power output according to the load status and power network operation,it would have a positive impact on power system stability.To achieve this a novel control strategy based on virtual synchronous motors(VSM)is proposed in this paper.The frequency-changer consists of two main parts:the rectifier and the inverter.In the rectifier part,a UDC-Q control strategy is adopted to control the DC-link voltage and the reactive power.In the inverter part,a VSM control strategy is used;it includes a power-frequency controller and an excitation controller,and can change the inverter’s output frequency and voltage with the variation of load,can adjust the active power with change of the power system frequency.The proposed control strategy is simulated using Simulink/Matlab.The simulation results show that the proposed control strategy can follow the mechanical inertia and electrical characteristics of the synchronous moto and can effectively improve the system power quality and system stability.

Novel Affine Power Flow Method for Improving Accuracy of Interval Power Flow Data in Cyber Physical Systems of Active Distribution Networks

A large number of load power and power output of distributed generation in an active distribution network(ADN)are uncertain,which causes the classical affine power flow method to encounter problems of interval expansion and low efficiency when applied to an AND.This then leads to errors of interval power flow data sources in the cyber physical system(CPS)of an ADN.In order to improve the accuracy of interval power flow data in the CPS of an ADN,an affine power flow method of an ADN for restraining interval expansion is proposed.Aiming at the expansion of interval results caused by the approximation error of non-affine operations in an affine power flow method,the approximation method of the new noise source coefficient is improved,and it is proved that the improved method is superior to the classical method in restraining interval expansion.To overcome the decrease of computational efficiency caused by new noise sources,a novel merging method of new noise sources in an iterative process is designed.Simulation tests are conducted on an IEEE 33-bus,PG&E 69-bus and an actual 1180-bus system,which proves the validity of the proposed affine power flow method and its advantages in terms of computational efficiency and restraining interval expansion.