Vladislav Oboskalov

A model for maximizing the profit of a HPP cascade considering hydraulic link via reservoirs

At the conditions of market relationships and economic and financial independence of power company (GENCO), these are guided by the principle of achieving maximum efficiency in their actions. For a hypothetical cascade of hydropower plants (HPPs) consisting of three HPPs, a problem formulation aimed at optimum loading of each individual HPP is used, ensuring maximum profit for the whole cascade from the sales of the generated electric power at the day-ahead market. The structural diagram of a problem solution algorithm is presented, which uses the method of statistical modeling. The results of the modeling of cascade operating regime are illustrated graphically. The results have been used to calculate the summary profit of the HPP cascade. The structural diagram of the algorithm can be basically used for an arbitrary mix of HPPs in the cascade, with a weekly regulation cycle.

Bid strategy under price uncertainty

The paper presents an algorithm for electricity market participant to obtain optimal bid under price uncertainty. The model is based on the known probability density functions of forecast prices. The problem is to estimate the parameters of blocks - values of power and their corresponding prices. The objective function is an expected value of profit for selling energy. The stochastic market clearing prices only affects the objective function, and particularly, the term corresponding to revenues. The parameters of blocks are interconnected by probability function. To determine required values the recurrent optimization procedure is developed. The criterion of procedure interruption is the required number of stairs in bidding function.

Inputing of electric regime into permissible region in PS security problem

Procedures of control actions selection are considered for the purpose of state parameters adjustment to the feasible region. The calculation procedure is divided into two stages – steady state calculation (equality constraints) and state adjustment to the feasible region (inequality constraints).

Protection design scheme of grid connected PMSG wind turbine

This paper is aimed at investigating the steady state analysis of a grid connected PMSG wind turbine in fixed and variable speed using MATLAB/SIMULINK. The case studied is Zafarana, Egypt. The average values of wind speed of month and day of Zafarana region is obtained from NASA site. Zafarana region has the highest wind speed which is greater than 12 m/sec. The transient analysis is investigated of the grid connected PMSG wind turbine during three-phase-to-ground fault at terminal of grid in different fault time and islanding mode. PMSG wind turbine is based on low-voltage ride-through (LVRT). The time required for recovering pre-fault values of voltage and current is less than 0.1 sec. LVRT is used to protect wind turbine from high fault current as well as to compensate PMSG voltage. PMSG is loaded by converter and capacitor which work as STATCOM. The current protection device is used to limit the fault current where the tripping current of relay is calculated using IEC method. The PMSG wind turbine consists of three protection devices; over speed protection, LVRT and point connection circuit breaker CEI. There are three protection zones in terms of the fault of; the protection zone of the fault of wind turbine (Zone 1), the protection zone of the fault of wind farm (Zone 2), the protection zone of the fault of grid (Zone 3).

An analytical approach for calculations of power system generation adequacy indices

Generation adequacy indices (GAI) calculations are performed not only for electrical power system development problems but also for on-line control problems. Liberalization of power and energy market along with increased focus on renewable energy sources, which is motivated by both ecological and economical incentives, has led to comprehensive changes in power systems. Practically, the main mathematical method for calculating GAI of an electrical grid with complex structure is Monte-Carlo simulation (MCS) technique. It can provide sufficiently accurate results, but the simulation consumes really huge amount of computational time, especially for large power systems. Generation capacity that has to be installed in a power system for meeting reliability criteria depends not only on system demand but also on generation mix. The problem at hand is to improve computational efficiency of the GAI calculating technique without decrease in calculations accuracy. In order to solve the problem, this paper proposes an analytical method for GAI calculations, that is referred to as supplied demand algorithm (SDA). The paper compares the MCS technique and the SDA. The analyzed methods have been developed using the C# and VBA programming language. Input data for the methods includes generation mix data, generation and load probability indices. The comparison results allow to select the proper method for the GAI calculations and show the main factors that affect the resulting GAI.

Mathematical models and optimal load shedding strategies for power system generation adequacy problem

This paper reviews general problem of generation adequacy indices (GAI) assessment and load shedding management problem in particular. Its shown that mutual power aid strategies and load shedding strategies used in GAI calculations are the main reasons for the difference in results obtained by diverse GAI calculating software packages. The paper presents several load shedding strategies including «proportional», «local», «linear» and «nonlinear» strategy. It compares these procedures and presents a mathematical description of each strategy. The article points out that proportional and nonlinear strategies are the most appropriate for practical application basing on the presented computational results.

Quantifying impact of directed elements on structural reliability indices of electrical power system

In order to take into account distinctive features of contingency and post-contingency states in structural reliability calculations, researchers divide power system failures into two types - “short-circuit” failures (SCF) and “cut-off” failures (COF). These failures differ significantly in repair time and, as a result, in analytical and mathematical models. The paper focuses mainly on the “short-circuit” failures. It presents an approach for structural reliability calculations, which takes into account the direction of power flows. In addition, it allows calculating additional structural reliability indices (SRI), for instance, SRI for simultaneous failure of several buses. The paper shows that probability of a short-circuit switching failure is one of the key indices for calculations concerning SCF. The paper proposes an integrated “exclusion-restoration” technique for SRI calculations concerning SCF. The proposed technique has been tested on several test systems.

Recursion based contingency analysis of an electrical power system

Large computational load is one of the key issues of an electrical power system security analysis. Currently, most of the researchers are trying to find out how to reduce the computational load. The contingency analysis is one of the most promising approaches for solving the problem. In fact, there are several ways to improve the effectiveness of the contingency analysis. The first way is to reduce the number of simulated situations via contingency searching or contingency screening. Another way is to increase the efficiency of power flow computations. This paper presents a novel recursion-based approach for solving the contingency analysis problem. The approach improves the effectiveness of the contingency analysis by the above-mentioned ways. It relies on a specific contingency sorting procedure based on the recursive call of the calculating procedure. The proposed approach has been tested on the 14-bus IEEE test system. The results obtained show almost a twofold increase in the computational efficiency in comparison with the conventional contingency sorting procedure.

Probabilistic reduction of generation in adequacy calculation

Problems of a generation system reduction in calculations of a power system (PS) adequacy are considered. The attention is mostly focused on mathematical models, based on the binominal and Poisson distributions, Poisson failure flows and characteristic functions of random variables. The reduction procedures result in the disturbance of integer number of units in operation. It was shown that it is appropriate to carry out rounding-off and following correction of probabilistic indices using the criteria of capacities at hand and expected values of generation tripped equality. As a result of models comparison the preference is made for models, based on the binominal and Poisson distributions. In the case of huge PS units diversification the combined distribution is assumed to be used, emphasizing units with the highest capacity and equivalent the rest, in order to perform adjusted calculations by means of computer.

Modification of supplied demand algorithm for generation adequacy indices calculations

In order to determine the indicators of the adequacy of meshed united electric power systems (EPSs), an algorithm of accelerated calculations is proposed, which is based on probabilistic equivalenting of intersystem power flows at the conditions of probabilistic demand and supply from adjacent EPSs. The conditions are considered and the fluctuant character is pointed out of the convergence of the iteration process of the formation of the resulting indicators of the nodal power imbalances. The recurrent relation is reflected algorithmically. In order to improve the convergence of the iteration process, a modification of the guaranteed demand algorithm is proposed, which takes into account the fluctuation character of the convergence by means of parabolic interpolation of the mathematical expectation of the power flow. The calculation procedure is illustrated on the basis of a three-node closed circuit of a united EPS. The algorithm has been appraised on the basis of a 42-node circuit of a meshed EPS. Ways for further refinement of the algorithm are proposed.