Quality monitoring of electrical power to evaluate the operational reliability of power equipment and active–adaptive voltage control in distribution power grids

Monitoring systems of power quality and operation mode parameters are currently being developed and widely introduced. These systems make it possible to receive needed information in different nodes of a grid in real time, as well as build up data archives over a long period of time. The presence of such information makes it possible to change the approach to short- and long-term control by distribution grids. This paper describes the possibilities of application of information obtained from a monitoring system to control distribution power grids using the example of reliability evaluation of power equipment to schedule the repairs, and active–adaptive voltage control system. The dependences are shown of probability of failure of power equipment on operation time under different types of load curves and power quality. The conclusion is drawn that the wear of main equipment significantly increases when it is operated in conditions of low power quality. The dependence is shown of changing repair and inspection frequency of equipment on operation time and operating conditions. This paper describes the structure and principles of operation of an active–adaptive voltage control system. As a test example, the amount of violations upon steady-state voltage deviations of power consumers in a distributed grid using different methods of voltage control in a power supply center are compared. It is shown that, at nonuniform load in the grid, the required voltage level cannot be provided by the counterload regulation method. The ease of use of a monitoring system of the power quality of operation mode parameters of power consumers makes it possible to use the control system providing a required voltage level for the greatest number of power consumers.     

Active–reactive power approaches for optimal placement of charge stations in power systems

Electric Vehicles (EVs) have been suggested as alternatives to conventional vehicles for reducing petrol consumption and carbon dioxide (CO₂) emissions. When a large number of EVs connect to the grid, they can cause a large amount of power loss. Where to install multiple charge stations in the grid, so as to mitigate losses caused by EVs when providing energy to those EVs, is becoming vitally important. In this paper, a distribution test-network model is described. A new analytical method is proposed, using the stations’ cooperation in terms of optimal active and reactive power dispatch as well as power flow analysis for locating the optimal placement of charge stations, so as to reduce power losses. This method is compared with the previously developed current density method for single charge stations using system simulation results. It was demonstrated that the methods proposed in this paper are more accurate than the current density method, and that 17% of the average active power loss can be saved for three different types of load profile. In addition, 27% of the average active power loss was saved by installing two charge stations rather than no charge stations in the test-line. It is shown that this could represent a 2.6% annual yield above inflation for investing in installing and running such charge stations.     

Practical application of the benchmarking technique to increase reliability and efficiency of power installations and main heat-mechaniс equipment of thermal power plants

Data on the comparative analysis variants of the quality of power installations (benchmarking) applied in the power industry is systematized. It is shown that the most efficient variant of implementation of the benchmarking technique is the analysis of statistical distributions of the indicators in the composed homogenous group of the uniform power installations. The benchmarking technique aimed at revealing the available reserves on improvement of the reliability and heat efficiency indicators of the power installations of the thermal power plants is developed in the furtherance of this approach. The technique provides a possibility of reliable comparison of the quality of the power installations in their homogenous group limited by the number and adoption of the adequate decision on improving some or other technical characteristics of this power installation. The technique provides structuring of the list of the comparison indicators and internal factors affecting them represented according to the requirements of the sectoral standards and taking into account the price formation characteristics in the Russian power industry. The mentioned structuring ensures traceability of the reasons of deviation of the internal influencing factors from the specified values. The starting point for further detail analysis of the delay of the certain power installation indicators from the best practice expressed in the specific money equivalent is positioning of this power installation on distribution of the key indicator being a convolution of the comparison indicators. The distribution of the key indicator is simulated by the Monte-Carlo method after receiving the actual distributions of the comparison indicators: specific lost profit due to the short supply of electric energy and short delivery of power, specific cost of losses due to the nonoptimal expenditures for repairs, and specific cost of excess fuel equivalent consumption. The quality loss indicators are developed facilitating the analysis of the benchmarking results permitting to represent the quality loss of this power installation in the form of the difference between the actual value of the key indicator or comparison indicator and the best quartile of the existing distribution. The uncertainty of the obtained values of the quality loss indicators was evaluated by transforming the standard uncertainties of the input values into the expanded uncertainties of the output values with the confidence level of 95%. The efficiency of the technique is demonstrated in terms of benchmarking of the main thermal and mechanical equipment of the extraction power-generating units T-250 and power installations of the thermal power plants with the main steam pressure 130 atm.     

State extension in adequacy evaluation of composite power systems—concept and algorithm

The number of possible system contingency states can be extremely large for practical composite generation and transmission systems. It is therefore not feasible or even possible to investigate all the contingencies in adequacy evaluation of composite power systems. Only those system states which are credible or usually given as up to certain contingency level are investigated in practical calculations. Although the probabilities of the ignored high level system contingency states are individually very small, the total value can be significant as the number of these high level system states is very large, especially for large size composite systems. This paper presents a state extension algorithm, which effectively includes the effects of high level contingencies without increasing the computational effort. The algorithm can, therefore, effectively and efficiently provide improved estimates of the adequacy indices. The accuracy improvement applies to the basic failure probability, frequency and duration (F&D) indices, determined for both the overall system and the individual load points. The technique also provides exact error estimates for the three adequacy indices. The concepts associated with the technique are developed and illustrated using simple networks. A numerical example is presented in the paper to illustrate the effectiveness of the proposed algorithm.     

The power flow algorithm for balanced and unbalanced bipolar multiterminal ac–dc systems

Bipolar dc terminals are used for hvdc transmission in an ac–dc system. The sequential ac–dc power flow algorithm has been proposed for an ac–dc system consisting of balanced and unbalanced bipolar multiterminal in this paper. The algorithm has two superiority. Firstly, as dc system variables are not included in Jacobian matrix the convergence time of the algorithm and necessity of computer memory is little. Secondly, both this algorithm has been developed for (balanced and unbalanced) bipolar system (not only monopolar) and this algorithm also can be run with current controlled, voltage controlled and power controlled terminals without making any changes in proposed method.     

A robust SMES controller strategy for mitigating power and voltage fluctuations of grid-connected hybrid PV–wind generation systems

Electrical Engineering - Recently, hybrid generation systems (HGSs) are considered to be the optimal solution for supplying remote areas with the required electrical power. HGSs contain two or more...     

Preventive and corrective control applications in power systems via Big Bang–Big Crunch optimization

This paper proposes a new method of optimization, the Big Bang–Big Crunch (BB–BC) method, for the optimization of preventive and corrective control actions to enhance the dynamic security of a power system against transient instabilities. The control actions, generation rescheduling and load shedding, are considered as constrained optimization problems with static and dynamic security constraints. These optimization problems are solved through the BB–BC method to minimize some operational costs related to the control actions. To reduce the size of the search spaces and the computational burden, decision trees and correlation coefficients are used as feature selection tools, which determine the most effective generators and loads for shaping the system’s transient stability. The proposed method is applied to a test system and compared with genetic algorithms, particle swarm optimization, differential evolution and active set method. The BB–BC method is promising since it gives comparable results with the other population based optimization methods.     

Quadratic models of AC–DC power flow and optimal reactive power flow with HVDC and UPFC controls

Quadratic models of power flow (PF) and optimal reactive power flow (ORPF) for AC–DC power systems are proposed in the paper. Voltage magnitudes at the two sides of ideal converter transformers are used as additional state variables to build the quadratic models. Effects of converter controls on equality constraints are considered. The quadratic expression of unified power flow controller (UPFC) is also developed and incorporated into the proposed models. The proposed PF model retaining nonlinearity has a better convergence feature and requires less CPU time compared to traditional PF models. The Hessian matrices in the quadratic AC–DC ORPF model are constant and need to be calculated only once in the entire optimization process, which speeds up the calculation greatly. Results obtained from the four IEEE test systems and an actual utility system indicate that the proposed quadratic models achieve a superior performance than conventional models.     

Estimation of interarea electromechanical modes during ambient operation of the power systems using the RDT–ITD method

An accurate awareness of the properties of the interarea electromechanical oscillation modes is essential for the secure operation of the power systems. Previously, the Ibrahim time domain (ITD) method has been applied to estimate the interarea oscillation modes using ring-down signals caused by major disturbances (such as three phase faults). In this paper, through the combination of the random decrement technique (RDT) and the ITD method, the RDT–ITD method is proposed to estimate the interarea modes during ambient operation of the power systems, using random responses caused by random changes of the loads. The estimated parameters include the frequencies, damping ratios and mode shapes. Considering the fact that both the ambient excitations and the measurement noise are stochastic in nature, Monte Carlo simulations were conducted to evaluate the performances of the RDT–ITD method in a statistical way. Simulation results in the 16 machine nonlinear power system model, as well as comparison results with the RDT-Prony method, the NExT-ERA method and the Subspace method realized by N4SID (Numerical algorithm for Subspace State Space System Identification) show that the RDT–ITD method is promising in estimating the interarea modes during ambient operation conditions. The RDT–ITD method was also validated using real PMU measurements from Sichuan power grid of China.     

On the storage batteries used in solar electric power systems and development of an algorithm for determining their ampere–hour capacity

Storage batteries are indispensable in all stand alone solar electric systems (PV power systems). Their efficiencies and life times affect significantly the overall PV system performance and economics. Batteries specified especially for use in PV systems have to be distinguished with standing of very deep discharge rate and high cycling stability.Ordinary batteries being marketed world wide for use in automobile, are mostly not appropriate for PV power systems. The most important characteristics of lead–acid batteries are presented and discussed in this paper. Moreover, the paper illustrates an experimental procedure for developing an algorithm for determining the ampere–hour capacity of batteries operating in PV systems. This algorithm enables determining the state-of-charge of a battery by measuring voltage and electrolyte-specific gravity at definite temperature and is applicable also for large battery storage systems.     

A parallel distributed computing framework for Newton–Raphson load flow analysis of large interconnected power systems

This paper proposes a simple parallel and distributed computing framework for the conventional Newton–Raphson load flow (NRLF) solution of large interconnected power systems. The proposed approach is based on message-passing distributed-memory architecture with separate workstations, and involves the piecewise analysis of power systems utilizing the network tearing procedure. The NRLF solution method, applied to each torn system at the selected buses, employs the matrix inversion lemma consisting of the factorization, forward elimination and back substitution procedures. The computational requirements of the state-of-the art parallel algorithm to obtain the correction vector involved in the back substitution procedure is reduced with the proposed approach in which the back substitution is carried out in parallel taking into account the split buses, rather than the order in which the forward elimination is performed. The investigations are carried out on the IEEE 118 bus standard test system in a Redhat Linux based 100 Mbps Ethernet LAN environment. The investigations reveal that the proposed method is significantly faster than the conventional NRLF and also the NRLF based on the state-of-the-art parallel algorithm, and thus finds potential applications for the real-time load flow solution of both regulated and deregulated power systems distributed over large geographical areas.     

Novel chaos game optimization tuned-fractional-order PID fractional-order PI controller for load–frequency control of interconnected power systems

In this work, chaos game optimization (CGO), a robust optimization approach, is employed for efficient design of a novel cascade controller for four test systems with interconnected power systems (IPSs) to tackle load–frequency control (LFC) difficulties. The CGO method is based on chaos theory principles, in which the structure of fractals is seen via the chaotic game principle and the fractals’ self-similarity characteristics are considered. CGO is applied in LFC studies as a novel application, which reveals further research gaps to be filled. For practical implementation, it is also highly desirable to keep the controller structure simple. Accordingly, in this paper, a CGO-based controller of fractional-order (FO) proportional–integral–derivative–FO proportional–integral (FOPID–FOPI) controller is proposed, and the integral time multiplied absolute error performance function is used. Initially, the proposed CGO-based FOPID–FOPI controller is tested with and without the nonlinearity of the governor dead band for a two-area two-source model of a non-reheat unit. This is a common test system in the literature. A two-area multi-unit system with reheater–hydro–gas in both areas is implemented. To further generalize the advantages of the proposed scheme, a model of a three-area hydrothermal IPS including generation rate constraint nonlinearity is employed. For each test system, comparisons with relevant existing studies are performed. These demonstrate the superiority of the proposed scheme in reducing settling time, and frequency and tie-line power deviations.     

Global method for time–frequency analysis of harmonic distortion in power systems using the wavelet packet transform

The paper proposes a method based on the use of the wavelet packet transform for the time–frequency analysis of harmonic distortion in power systems. The magnitude of harmonic and interharmonic groups, as defined in Standard IEC 61000-4-7, the magnitude of the subharmonic group, defined as an extension of the standard method, and the time evolution of odd harmonics in voltage and current waveforms can be simultaneously computed using different levels of the same wavelet decomposition tree applied to the samples of the input signal. The paper shows the performance of the method proposed in different measurement conditions and the comparison of the results with those obtained applying the standard method.     

A comparison of time-average power losses in insulated-gate bipolar transistors and hybrid SIT–MOS–transistors

Switching of equivalent silicon insulated-gate bipolar transistors, such as carrier-stored trenchgate bipolar transistors (CSTBTs) and hybrid static induction transistor/metal–oxide–semiconductor (SIT–MOS) thyristors (HSMTs), from a blocking state to a conducting state and vice versa is numerically simulated in two dimensions. It is shown that on–off switching losses in an HSMT are greater than in a fully equivalent CSTBT. Thus, time-average power P that dissipates in an HSMT becomes smaller than the power in the equivalent CSTBTh only at a long current pulse duration. However, a decrease in lifetime τ₀ of nonequilibrium charge carriers in an SIT makes it possible to significantly reduce HSMT switching losses while maintaining its advantage in the on state. Consequently, for each set of CSTBT parameters, such τ₀, it can be selected in the almost equivalent HSMT that power P dissipating in the HSMT will be smaller than the power in the equivalent CSTBT in any given range of amplitude J _a and duration T _on of the current pulses.     

Novel chaos game optimization tuned-fractional-order PID fractional-order PI controller for load–frequency control of interconnected power systems

In this work, chaos game optimization (CGO), a robust optimization approach, is employed for efficient design of a novel cascade controller for four test systems with interconnected power systems (IPSs) to tackle load–frequency control (LFC) difficulties. The CGO method is based on chaos theory principles, in which the structure of fractals is seen via the chaotic game principle and the fractals’ self-similarity characteristics are considered. CGO is applied in LFC studies as a novel application, which reveals further research gaps to be filled. For practical implementation, it is also highly desirable to keep the controller structure simple. Accordingly, in this paper, a CGO-based controller of fractional-order (FO) proportional–integral–derivative–FO proportional–integral (FOPID–FOPI) controller is proposed, and the integral time multiplied absolute error performance function is used. Initially, the proposed CGO-based FOPID–FOPI controller is tested with and without the nonlinearity of the governor dead band for a two-area two-source model of a non-reheat unit. This is a common test system in the literature. A two-area multi-unit system with reheater–hydro–gas in both areas is implemented. To further generalize the advantages of the proposed scheme, a model of a three-area hydrothermal IPS including generation rate constraint nonlinearity is employed. For each test system, comparisons with relevant existing studies are performed. These demonstrate the superiority of the proposed scheme in reducing settling time, and frequency and tie-line power deviations.     

Robust optimisation for self-scheduling and bidding strategies of hybrid CSP–fossil power plants

This paper describes a profit-maximisation model for a hybrid concentrated solar power (CSP) producer participating in a day-ahead market with bilateral contracts, where there is no correlation between the electricity market price and the solar irradiation. Backup system coordination is included between the molten-salt thermal energy storage (TES) and a fossil-fuel backup to overcome solar irradiation insufficiency, but with emission allowances constrained in the backup system to mitigate carbon footprint. A robust optimisation-based approach is proposed to provide the day-ahead self-schedule under the worst-case realisation of uncertainties due to the electricity market prices and the thermal production from the solar field (SF). These uncertainties are modelled by asymmetric prediction intervals around average values. Additionally, a budget parameter is used to parameterise the degree of conservatism of the decision. The decision provides the optimal bidding strategies consisting in supply functions built not only for different budget parameter values, but also for different emission allowance levels. Finally, a realistic case study is presented to show the effectiveness of the proposed approach.     

Physical and dielectric properties of BaTiO3–fluoride–glass systems for nitrogen-fireable embedded capacitors

BaTiO₃-based dielectrics containing the selective additive combinations from Pb-free glasses and fluoride compounds such as AlF₃, BaF₂, CaF₂, LiF and ZnF₂ were studied mainly for a potential N₂-fireable embedded capacitor in printed circuit board with Cu metallization. The physical and dielectric properties, such as dielectric constant (k), loss tangent (tanδ) and T _c, strongly depended on the choice of additive combination. A bismuth borosilicate glass was most promising in terms of the degree of densification and dielectric constant. The samples containing LiF and ZnF₂ and sintered at 950 °C looked most beneficial in that these additives produced high k of >1,200 and low tanδ of < 0.022 at room temperature regardless of sintering atmosphere. As an example, the 95BaTiO₃–2LiF–3(Bi borosilicate) sample exhibited k?~?1,340 and tanδ?~?0.022 at room temperature when fired at 950 °C in N₂.     

Full and reduced-order H∞ filtering of Takagi–Sugeno fuzzy time-varying delay systems: Input–output approach

This article addresses the issue of delay-dependent H_∞ filtering design for TakagiŮSugeno fuzzy time-varying delay systems using the input–output approach. A three-term approximation model has been used to transform the original system into two interconnected subsystems. Since the nonquadratic Lyapunov–Krasovskii functional requires to deal with the membership function's (MF) time derivative, upper-bound inequalities have been added to the obtained conditions. Based on the scaled small gain theorem, nonquadratic Lyapunov–Krasovskii functional approach and considering the bounds of the MF time-derivative, the H_∞ full- and reduced-order filters are designed and then formulated in terms of linear matrix inequalities. Finally, illustrative examples are presented to demonstrate the validity of the proposed methods.     

Development of and experience using the Del’Tek computerized automation system for furnishing thermal power facilities with automated process control systems

Basic principles of constructing the Russian Del’Tek computerized automation system intended for development of modern process control systems for thermal power engineering facilities are considered. Informational-computation systems and full-scale process control systems built around the Del’Tek computerized automation system, as well as test results and experience gained from their operation, are described.