A METHODOLOGY FOR MODELING POWER SUPPLY SYSTEMS

Subject of research: power quality indicators, non-sinusoidal modes in power supply systems. Purpose of research: assessment of power factor components under non-sinusoidal modes for the conditions of industrial power supply systems with linear and nonlinear loads. Methods and objects of research: simulation modeling of electrical systems in the Matlab Simulink environment, analysis of complex non-sinusoidal modes. Main results of research: а computer simulation model of an industrial power supply system with linear and nonlinear loads, as well as the presence of harmonic distortions from the supply network, has been developed. The dependences of the power factor components in non-sinusoidal modes on variations in the resistance of the power system and the length of the supply line connecting the source and the load node were obtained.

Computer simulation is a method resorted to more and more frequently for the development of the prospective power supply systems, in particular the vessel power supply system. It provides valuable insights into the transient processes and indicators of electric power quality in the system without building its physical model, thus significantly improving the efficiency and quality of the physical model.Nowadays MathLab package with Simulink application is used with increasing frequency for simulation of such systems.The paper presents a model of the power supply system of small hydrographic vessel ‘Vaygach’ built in MatLab environment. The system vulnerabilities and their remedies have been identified. Changes in sinusoid before and after the non-linear load on the network have been demonstrated and solutions for improving the non-linear distortion factor are proposed. The model developed for the vessel power supply system can be used for building models of different vessels.

The article is devoted to choosing ways to improve the technological reliability of regional electric network (REN) to ensure reliable power supply. At the operational stage, the task of increasing operational reliability is assigned to the enterprise asset management system of the territorial network organization (TNO), as a REN operator. Technological reliability is ensured by an operational dispatch control system, which uses the existing reserves in the network to support the technological process of electricity supply to electricity consumers in case of network equipment failures. The relevance of improving the technological and operational reliability of power supply system (PSS) requires the development and improvement of methods for analyzing and assessing the TNO's readiness to provide power transmission services. The indicators adopted in Russia reflect the level of technological reliability of PSS. However, these indicators do not reflect the technical condition of the equipment, or identify causal relationship between an equipment failure and an interruption of power supply. The research is aimed at identifying “bottlenecks” from the technological reliability standpoint and substantiating maintenance and repair, and technical re-equipment and reconstruction measures to improve operational reliability. A PSS model is proposed reflecting the technical condition of the network equipment, the operational readiness of automation systems, the availability of structural, functional and load redundancy in the REN. A method is suggested for calculating the PSS reliability indicators, where the developed indices reflect the degree of development of the network technical potential and the role of the aforesaid nodes in the PSS. The method makes it possible to identify the network parts, where it is necessary to introduce new technologies. In contrast to a well-known method, which is based on expert estimates of probabilities of different circuit-mode states of the network and on the calculation of normal and post-emergency modes, a less timeconsuming formalized procedure for analyzing and evaluating the network structural and functional reliability is proposed. The results obtained allow to increase the validity of the decisions made both at the operational stage and the design stage.

The article discusses the issues of ensuring the quality of electricity in power supply systems. It is shown that during the operation of power supply systems in certain cases the quality of electrical energy can be violated, including due to the uneven load of the electrical network phases, that leads to a significant asymmetry of voltages in this network. The emergence of a large difference between the voltages in the phases of the electrical network inevitably leads to negative effects on various electrical equipment of both power supply organizations and consumers' electrical equipment, thereby creating conditions for the occurrence of technological and electromagnetic damage, which are the reasons for the appearance of financial losses and other negative consequences in case of electricity quality violations. The results of voltage unbalance measurements obtained by the authors of the article while monitoring the power quality are presented. These results show that during the operation of power supply systems, modes arise in which the voltage asymmetry in the zero sequence significantly exceeds the permissible values. It is shown on a computer model of the simplest power supply system that reducing the resistance of the neutral conductor can serve as a rather effective measure to reduce voltage unbalance, especially when inductive load prevails in the composition of consumers.

The parameters of complex power supply schemes of tram lines, which are required for simulation modeling, were studied: statistical characteristics of traction loads of feeders and voltage on the tires of traction substations. It was established that the distribution function of the feeder feeding the tram depot corresponds to the logarithmic normal law, the distribution function of the modules of the idle voltage deviation and the angles between the idle voltages of adjacent traction substations to the truncated normal law. It is proposed to modernize the information bases of electric traction network parameters with complex power schemes to increase the efficiency of modeling the modes of operation of sections of urban electric transport. A method of calculating instantaneous schemes has been developed, which allows to create algorithms that do not depend on the degree of complexity of the scheme. A method of simulation modeling of complex power supply systems of electric transport based on the synthesis of the matrix method of calculating instantaneous circuits and the method of statistical tests for modeling the organization of traffic of trams and trolleybuses is proposed. Algorithms and simulation models of traction power supply systems of urban electric transport have been developed, taking into account the modes of operation of power systems. A single simulation complex has been created that takes into account the traffic schedules of trams and trolleybuses, power flows in power supply systems, which makes it possible to obtain generalized dependences of power flows and energy losses, and to increase the accuracy of calculations of electrical parameters to 5–7%. Adequacy of the simulation model to the real process was verified by experimental data on a number of two-track, single-track sections of electric traction networks and complex power supply schemes of traction substations. The error in determining the integral indicators of costs and energy losses does not exceed 5%, and the rms currents – 3%. The use of simulation modeling in the design of traction power supply systems allows to improve the quality of electrical engineering calculations of complex power supply schemes and to propose energy-efficient power supply modes.

This paper analyzes the advantages of bilateral power supply systems for electrified railway. Firstly, the equilibrium current is analyzed under different external power supply conditions. A method of reducing the equilibrium current is proposed, and the voltage loss of the traction substation caused by this method is solved. Next, the electrical performances of traction power supply system are analyzed, including current distribution, impedance and voltage loss. Finally, the model of bilateral power supply system was built, and the theoretical analysis was simulated and verified by Matlab/Simulink.

China's high-speed railway adopts a single-phase AC power supply system. In order to balance the three-phase load on the grid side, the railway traction power supply system sets up a phase-separated area every 30km for commutation power supply. At present, most of the phase-separated areas of China's railways use automatic power-off and over-power phase mode. Before the train enters the neutral section, it will receive a signal to automatically disconnect the on-board circuit breaker to cut off the connection between the catenary and the train load. When the train passes through the articulated electrical phase separation, after on-site observation, the voltage drop between the pantograph and the catenary will break down the air when the pantograph slides on the neutral line and begins to gradually separate from the left branch catenary, resulting in repeatedly burning pantograph arcs. Since the on-board circuit breaker has been opened, the high-voltage cables on the train have no load current. The current through the arc in this process can only come from the stray capacitance of the neutral line, the voltage transformer on the high-voltage side of the train, the on-board cables to the car body and so on, this arc current will cause the overvoltage of the catenary. Combined with the Mayr arc model and the Cassie arc model, an improved Habedank arc correction model was built, and the distributed parameter line model of the traction power supply system and the pantograph-catenary multiple arcing model were jointly established. The influencing factors of split-phase overvoltage are derived from the multiple transient processes of the circuit caused by repeated arcing, and the variation law of split-phase overvoltage is obtained.

There is the risk of subsynchronous oscillations when wind-thermal-bundled power supply delivered through AC transmission line with series capacitance compensation and high voltage DC system. However, the current researches are all aimed at the subsynchronous oscillation of wind-thermal-bundled power supply or AC-DC hybrid transmission, without considering the subsynchronous oscillation of wind farms, thermal power plants, AC transmission system with series capacitance compensation and DC transmission system at the same time. The linearized model of wind-thermal power supply and extreme high voltage (EHV) AC-DC hybrid transmission system is built firstly in this paper and then subsynchronous oscillation mode of system is analyzed by factors related with characteristic values. This study uses characteristic values sensitivity make sure the main influencing factors of subsynchronous oscillation and then analyze the influence of AC-DC transmission power distribution, thermal power and wind power output allocation, wind power control parameters and DC transmission control parameters on subsynchronous oscillation. The correctness of theoretical analysis is verified by the simulation results.1

The economic profit of investment in energy storage systems are investigated with a regional-type grid as the research object. Firstly, the economic operation model of power supply and Energy Storage System (ESS) within the local grid is established, and the optimization model is solved by using hybrid particle swarm algorithm based on heuristic adjustment strategy. In order to reasonably assess the feasibility of the investment scheme, the equivalent net benefit method is designed to discount the economic benefits and investment costs of the ESS to a dispatch cycle based on the discount rate of life of the ESS and cost-benefit analysis. The algorithm gives the equilibrium return mean value point of ESS investment and performs a sensitivity analysis for the impact of investment unit price and price of electricity purchasing on the investment in ESS.

Modeling of power supply systems of stationary railway objects

According to various estimates, railways account for about 15 % of all transportation in the agro-industrial complex. At the same time, railway transport has a relatively low cost, good adaptability for transporting different types of cargo under any weather conditions, and the ability to deliver goods over long distances without intermediate storage. Ensuring the required train schedule, reliability and safety of transportation on both electrified and non-electrified sections of railways largely depends on the proper functioning of railway automation and telemechanics devices, primarily signals and interlocking systems. The main features influencing the equivalent circuit diagrams of individual power transmission elements in the MatLAB Simulink software package have been examined. Recommendations are provided for calculating transformer parameters, as well as cable and overhead line segments in the task of modeling transverse asymmetry. It is determined that the developed model is not suitable for simulating single-phase ground fault conditions. Software products used for simulation modeling of power supply systems often have technical and software limitations on the number of elements within an object. Therefore, there is a need to simplify the model of signals and interlocking overhead lines while maintaining sufficient accuracy in modeling. The conducted research led to conclusions regarding the necessity of accounting for step-down transformers and wire transposition in overhead line sections. Recommendations are given for developing a model of a 6–10 kV signals, and interlocking overhead line in the MatLAB Simulink software package, intended for simulation modeling of two-phase, two-phase-to-ground, and three-phase short circuits.

To simulate the process of electrode operation, a dynamic model describing the electrode system of three-phase electric arc furnace was developed. This new model can be divided into three submodels in terms of the practical situation. They are the power supply system model the electric arc model and the hydraulic actuator system model. According to the basic circuit theory, the power supply system model where the high voltage transmission circuit and mutual inductances were considered, was set up. The electric arc model, which was novel for the electrode control, served as the electrical load and was connected to the power supply system model. The hydraulic actuator system model consists of the proportional valve part that is modeled to capture the dead-zone nonlinear characteristics and the hydraulic cylinder part where the impact of the load force is taken into account. By comparing simulation data and actual data, the results show that the electrode system model is proved to be accurate.

Using the multiple-module coupling algorithm, this contribution presents a model of a concrete power supply system operating in the normal state and the fault state of its module single-circuit high-voltage three-phase power transmission line. The corresponding digital real-time simulation is carried out on a PC. The real-time results of the model show that the model of the multiple-module coupling algorithm presented here is in good agreement with practical experience and suited to meet the demand of real-time simulation.

It is known that the occurrence and existence of ferroresonant oscillations at the subharmonic frequency (SHC) in power transmission lines (TL) and in power supply systems is extremely undesirable, since they cause ferroresonant overvoltages at different frequencies. At the same time, there is a wide class of nonlinear electrical circuits, in which the excitation of autoparametric oscillations (AIC) at the frequency of the SHC forms the basis of frequency converting devices serving as secondary power sources. It is shown that three-phase nonlinear systems are in one way or another equivalent circuits for power transmission lines, the main elements of which are: longitudinal compensation capacitors, transverse compensation reactors, and transformers with a nonlinear characteristic. To study the regularities of the excitation and maintenance of SHC at a frequency in three-phase electro-ferromagnetic circuits (EFMC), theoretical and experimental studies of an equivalent model of a three-phase circuit with nonlinear inductance were carried out. For the analysis of the steady-state mode of the SHC at the frequency, the method of a small parameter (averaging) was applied. A shortened differential equation of motion for a three-phase nonlinear circuit is obtained. By solving them, the regions of existence of the SHC and the critical parameters of the chain were determined. The obtained results of theoretical research are confirmed by experimental studies.

Due to the increasing need for intelligent systems, the adaptive neuro-fuzzy inference system (ANFIS) has recently attracted the attention of researchers in various scientific and engineering areas. The purpose of this work is to present the modeling of a photovoltaic power supply (PVPS) system using an ANFIS. For the modeling of the PVPS system, it is required to find suitable models for its different components (ANFIS PV-generator, ANFIS battery and ANFIS regulator) under variable climatic conditions. A database of measured weather data (global radiation, temperature and humidity) and electrical signals (photovoltaic, battery and regulator voltage and current) of a PVPS system installed in Tahifet (south of Algeria) has been recorded for the period from 1992 to 1997 using a data acquisition system. These data have been used for the modeling and simulation of the PVPS system. The ANFIS for the PV-generator, battery and regulator have been trained by using 10 signals recorded from the different components of the PVPS system. Each signal is represented by 365*5 values (complete 5-years). A set of data for 4-years have been used for the training of the ANFIS and data for 1-year has been used for the testing of the ANFIS. In this way, the ANFIS was trained to accept and handle a number of unusual cases. The comparison between actual and estimated values obtained from the ANFIS gave satisfactory results. The correlation coefficient between measured values and those estimated by the ANFIS gave good prediction accuracy of 98%. In addition, test results show that the ANFIS performed better than the artificial neural networks (ANN). Predicted electrical signals by the ANFIS can be used for several applications in PV systems.