Janusz Bialek

Topological generation and load distribution factors for supplement charge allocation in transmission open access

This paper introduces a simple novel method of transmission supplement charge allocation based on topological analysis of power flows in the network. The method uses the MW-MILE methodology but analyses the share, not the impact of, individual loads and generators in line flows. This results in positive contributions from all the users hence rescinding the problem of counterflows.

Smart Operation of Smart Grid: Risk-Limiting Dispatch

The drastic reduction of carbon emission to combat global climate change cannot be realized without a significant contribution from the electricity sector. Renewable energy resources must take a bigger share in the generation mix, effective demand response must be widely implemented, and high-capacity energy storage systems must be developed. A smart grid is necessary to manage and control the increasingly complex future grid. Certain smart grid elements-renewables, storage, microgrid, consumer choice, and smart appliances-increase uncertainty in both supply and demand of electric power. Other smart gird elements-sensors, smart meters, demand response, and communications-provide more accurate information about the power system and more refined means of control. Simply building hardware for renewable generators and the smart grid, but still using the same operating paradigm of the grid, will not realize the full potential for overall system efficiency and carbon reduction. In this paper, a new operating paradigm, called risk-limiting dispatch, is proposed. It treats generation as a heterogeneous commodity of intermittent or stochastic power and uses information and control to design hedging techniques to manage the risk of uncertainty.

Approximate model of European interconnected system as a benchmark system to study effects of cross-border trades

Research into transmission pricing and congestion management in interconnected power systems, such as those found in USA and Europe, requires an appropriate benchmark system to test different methodologies. Creation of a realistic benchmark system is difficult as utilities are often unwilling to disclose details of their own systems because of commercial sensitivity and security reasons. This paper presents development of an approximate model of a European interconnected system which could be used to study the effects of cross-border trades. In creating the load-flow model, only publicly available information was used. Comparison of simulation results conducted on the test system with the published cross-border flows and power transfer distribution factors showed a very good correlation, exceeding 90%.

Allocation of transmission supplementary charge to real and reactive loads

This paper has applied the MW-MILE methodology to allocate the transmission supplementary charge to real and reactive power loads. The charge for usage of an individual transmission asset is split into a nonlocational component, due to the unused capacity of the asset, and a locational component, due to the actually used capacity of the asset. The latter is allocated, using the previously proposed electricity tracing method, to individual real and reactive loads in the network.

Optimal power flow as a tool for fault level-constrained network capacity analysis

The aim of this paper is to present a new method for the allocation of new generation capacity, which takes into account fault level constraints imposed by protection equipment such as switchgear. It simulates new generation capacities and connections to other networks using generators with quadratic cost functions. The coefficients of the cost functions express allocation preferences over connection points. The relation between capacity and subtransient reactance of generators is used during the estimation of fault currents. An iterative process allocates new capacity using optimal power flow mechanisms and readjusts capacity to bring fault currents within the specifications of switchgear. The method was tested on a 12-bus LV meshed network with three connection points for new capacity and one connection to an HV network. It resulted in significantly higher new generation capacity than existing first-come-first-served policies.

Supervisory Control of a Wind Farm

This paper presents a scheme for supervisory control of wind farms. We concentrate on reduction of power output variation, but the proposed scheme can also be used for system-wide controls that are related to power variation, such as frequency control or damping of power swings. The scheme may utilize either a separate (external) energy storage device or a power reserve achieved through part-loading of one or more turbines in a wind farm. The proposed supervisory control scheme has been validated on a model of a wind farm with four turbines. Simulations have confirmed the usefulness of the scheme. The proposed control system is general and could also be used for other types of intermittent generators such as wave or solar.

Direct incorporation of fault level constraints in optimal power flow as a tool for network capacity analysis

The aim of this paper is to present a method for the direct incorporation of fault level constraints (FLCs) in the optimal power flow (OPF) as a tool for network capacity analysis, i.e., optimal generation expansion planning within an existing network. A mathematical methodology to convert constraints imposed by fault levels to simple nonlinear inequality constraints is developed. No new variables are introduced in the OPF formulation to describe the additional constraints. Most common OPF-solving engines already have the computational capacity to handle numerous nonlinear constraints, such as the ones described by the power balance equations on buses. Therefore, once FLCs are converted to nonlinear constraints described by OPF variables, they can be directly introduced to any optimization process performing the OPF. A 12-bus/15-line test case demonstrates the advantages of the new method in comparison with a previously proposed iterative method that converted them to restrictions on new capacity. It also proves that when FLCs are ignored, the capacity of the network to absorb new generation is overestimated.

Opportunity Cost Bidding by Wind Generators in Forward Markets: Analytical Results

Wind generation must trade in forward electricity markets based on imperfect forecasts of its output and real-time prices. When the real-time price differs for generators that are short and long, the optimal forward strategy must be based on the opportunity costs of charges and payments in real-time rather than a central estimate of wind output. We present analytical results for winds optimal forward strategy. In the risk-neutral case, the optimal strategy is determined by the distribution of real-time available wind capacity, and the expected real-time prices conditioned on the forward price and wind out-turn; our approach is simpler and more computationally efficient than formulations requiring specification of full joint distributions or a large set of scenarios. Informative closed-form examples are derived for particular specifications of the wind-price dependence structure. In the usual case of uncertain forward prices, the optimal bidding strategy generally consists of a bid curve for wind power, rather than a fixed quantity bid. A discussion of the risk-averse problem is also provided. An analytical result is available for aversion to production volume risk; however, we doubt whether wind owners should be risk-averse with respect to the income from a single settlement period, given the large number of such periods in a year.

Decentralized stability-enhancing control of synchronous generator

This paper describes new structures for stability-enhancing excitation controllers designed using a nonlinear multi-machine system model and Lyapunovs direct method. Two control structures are presented: a hierarchical structure In which the AVR is the master controller and the PSS the slave controller and a traditional structure in which the PSS constitutes a supplementary loop to the main AVR. Both controllers are shown to be robust, as the damping they introduce into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralized approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system are presented that confirm the above and show that the two control structures are very effective in damping both local and inter-area power swings.

Efficient Secure AC OPF for Network Generation Capacity Assessment

This paper presents a novel method for determining the capacity of a network to accommodate new generation under network security constraints. The assessment is performed by maximizing the total generation capacity in an optimal power flow model; this is solved by gradually adding limited numbers of line outage contingencies, until a solution to the complete problem is obtained. The limit on the number of contingencies added is key to the methods efficiency, as it reduces the size of the optimization problems encountered. Moreover, varying this limit on contingencies added provides a simple and highly efficient means of searching for multiple local optima of the nonlinear optimization problem. The method has been tested on a modified version of the highly meshed IEEE Reliability Test System with N-1 security, where a significant reduction in the systems capacity for new generation is seen when security constraints are imposed. The method is generic and may be applied at any voltage level, for other security models and for other similarly structured problems such as the analysis of multiple resource availability scenarios.