Grid-Connected Control Strategy of VSG under Complex Grid Voltage Conditions

Under complex grid conditions,the grid voltage usually has an imbalance,low order harmonics,and a small of DC bias.When the grid voltage contains low order harmonics and a small amount of DC bias component,the inverter’s output current cannot meet the grid connection requirements,and there is a three-phase current imbalance in the control strategy of common VSG under unbalanced voltage.A theoretical analysis of non-ideal power grids is carried out,and a VSG control strategy under complex operating conditions is proposed.Firstly,the third-order generalized integrator(TOGI)is used to eliminate the influence of the DC component of grid voltage.An improved delay signal cancellation(DSC)method is proposed to control the balance current and power fluctuation under unbalanced voltage based on the method of common VSG positive and negative sequence separation,It also eliminates the harmonic of command current.Then,the improved quasi proportional resonant controller(QPR)cascaded PI is used to suppress the harmonic current further so that the harmonic content of grid-connected current can meet the grid-connected requirements and achieve the three-phase current balance.Finally,the proposed strategy is verified by simulation under the control objectives of the current balance,active power,and reactive power constant.

Surface Geophysical Methods used to Verify the Karst Geological Structure in the Built-up Area:A Case Study of Specific Engineering-Geological Conditions

This article presents a research study of complex limestone karst engineering-geological conditions in the municipality Valaskanear Banska Bystrica in Slovakia.The aim of the study is to demonstrate the impossibility of spatial identification of cave spaces using surface geophysical methods due to the specific engineering-geological conditions of a thick surface layer of anthropogenic fill containing highly heterogeneous anthropogenic material.Its maximum thickness is 3 m.Another specificific condition of the study area is its location in the built-up area,due to which the applicability of geophysical methods was limited.The article contains methodological recommendations to be used in analogous geological conditions with karst structures topped with anthropogenic fill,which complicates the identification of cave spaces.The recommended solution herein is the identification of the cave system using underground mapping of the karst and its projection onto the surface for which surface geophysical methods have been combined.

Simulation of operation of neural network with purpose of utilisation of hydraulic actuators in complicated technical conditions

Application of neural network technologies is becoming more extensive every year,especially in the economic field.New methods are being discovered;new models of neural networks are being created.Currently,the main application of neural networks in the economy is the prediction of markets,optimization of commodity-money flows,analysis and generalization of various social surveys,prediction of the dynamics of political ratings,optimization of the production process,comprehensive diagnostics of product quality,etc.Utilisation of the hydraulic equipment makes it possible to design systems of automatic operation in the conditions,where minimal human participation and maximum speed of response are required.It is possible to state that such conditions exist in the regions with the permanent access of repair teams or technicians,who perform monitoring of the complex technical objects.Therefore,it is necessary to develop automated systems of operation and monitoring of various equipment components,which are intended for operation in the complicated technical conditions.Authors of this article have selected the hydraulic equipment as the object under investigation due to the fact that it is widely distributed equipment,as well as due to possibilities of this equipment to function or to be adapted for operation in practically any environmental conditions.At the same time,quantity of the state-of-the-art equipment,which is used,as well as complexity of this equipment increase very quickly,therefore process of making decision concerning utilisation of this equipment must be made very quickly.Authors analyse the sphere of automation,where utilisation of a human decision is required.The novelty of this article is connected with the assumption that further direction of operation of such equipment in the complicated technical conditions must be implemented in the sphere of guessing of the user’s actions.Authors review neural networks as the toolkit,and they believe that these networks can make decisions in the proactive mode,practically without participation of a user.This article includes description of the model,which can be used as the basis for the system,which is planned to design.In addition,methodological toolkit for assessment of efficiency of this model is proposed.