Igor Kuzle

Capacity Optimization of Renewable Energy Sources and Battery Storage in an Autonomous Telecommunication Facility

This paper describes a robust optimization approach to minimize the total cost of supplying a remote telecommunication station exclusively by renewable energy sources (RES). Due to the intermittent nature of RES, such as photovoltaic (PV) panels and small wind turbines, they are normally supported by a central energy storage system (ESS), consisting of a battery and a fuel cell. The optimization is carried out as a robust mixed-integer linear program (RMILP), and results in different optimal solutions, depending on budgets of uncertainty, each of which yields different RES and storage capacities. These solutions are then tested against a set of possible outcomes, thus simulating the future operation of the system. Since battery cycling is inevitable in this application, an algorithm that counts the number of cycles and associated depths of discharges (DoD) is applied to the optimization results. The annual capacity reduction that results from these cycles is calculated for two types of battery technologies, i.e., valve-regulated lead-acid (VRLA) and lithium-ion (Li-ion), and treated as an additional cost. Finally, all associated costs are added up and the ideal configuration is proposed.

Yearly Maintenance Scheduling of Transmission Lines Within a Market Environment

Within a yearly horizon, a transmission system operator needs to schedule the maintenance outages of the set of transmission lines due for maintenance. Facing this task, two conflicting objectives arise: on one hand, the transmission system adequacy should be preserved as much as possible, and, on the other hand, market operation should be altered in the least possible manner. To address this scheduling problem, a bilevel model is proposed whose upper-level problem schedules line maintenance outages pursuing maximum transmission capacity margin. This upper-level problem is constrained by a set of lower-level problems that represent the clearing of the market for all the time periods considered within the yearly planning horizon. This bilevel model is conveniently converted into a nonlinear mathematical program with equilibrium constraints (MPEC) that can be recast as a mixed-integer linear programming problem solvable with currently available branch-and-cut techniques.

The mixed-integer linear optimization model of virtual power plant operation

The concept of virtual power plant is developed for two prime reasons. First, to diversify the risk of not meeting the long-term electricity delivery contracts, and secondly to achieve better results on the electricity market. This paper regards the case in which a wind power plant and a solar power plant are joint together with a conventional gas power plant to act on the electricity market as a single agent. The problem is formulated as a mixed-integer linear programming model which incorporates long-term bilateral contracts with weekly forecasted hourly market prices. The aim of the optimization is to maximize the profit of the virtual power plant. The efficiency of the proposed model is rendered through two case studies and detailed analysis is provided.

Virtual power plant dispatch optimization using linear programming

Since renewable sources, such as wind and solar power plants, suffer from their stochastic nature, their behavior on market is very delicate. In order to diversify the risk, a concept of virtual power plant is developed. The virtual power plant is consisted of several renewable energy sources and at least one conventional power plant. The production of renewable energy sources cannot be perfectly forecasted, and in order to create a stabile market agent, a conventional power plant is used to produce the electricity when necessary. Therefore, an optimal dispatch schedule within the virtual power plant is needed. To address this problem, a mixed-integer linear programming model is created with goal of minimizing the costs of conventional power plant. It is assumed that virtual power plant has to satisfy the bilateral contracts of electricity delivery within a weekly time horizon on hourly basis. The focus of this paper is the influence of the conventional power plant technical minimum value to overall virtual power plant production costs.

An adaptive approach to setting underfrequency load shedding relays for an isolated power system with private generation

The problem of frequency load shedding in an isolated power system is considered. A proper design of the load shedding scheme should minimize consumer disruption in the case of the load excess and help balance the load to the remaining generation in a system. An adaptive strategy, which can reduce total amount of shed close to the theoretical minimum, is proposed and compared to conventional load shedding scheme.

Undervoltage load shedding using global voltage collapse index

Increasingly higher demand in power created problems in power system operation since the growth of the transmission system is restricted. System often function close to their stability limits and sometimes loads need to be shed in order to prevent system from collapsing. In this paper one undervoltage load shedding (UVLS) method to prevent voltage collapse is presented. This method is based on a global index, which indicates voltage collapse proximity and voltage magnitudes on critical buses. Global index for voltage collapse proximity determination is calculated based on power flow Jacobian matrix operations. Considering that on the voltage stability limit Jacobian matrix becomes singular, it cannot be inverted. Therefore method involving eigenvalue calculation is used here. IEEE 14 bus system was used as a numerical example, which showed how loads and system in general can be saved from voltage collapse using UVLS.

Energy storage operation in the day-ahead electricity market

This paper considers market operation of an energy storage unit. The goal is to assess the potentials for revenue and impact of a profit-maximizing storage unit on market prices in the day-ahead electricity market. It also analyzes the impact of a storage unit on market performance of conventional generators. A bilevel profit maximization model is proposed in which the upper-level problem is a storage operation and bidding decision problem, while the lower level problem simulates market clearing. The proposed model is applied to the 24-bus IEEE test system.

An overview of ancillary services in an open market environment

The worldwide restructuring of the electrical energy industry is followed by processes like deregulation, liberalization and commercialization. These changes introduce new paradigms such as competition in generation and the concept of electricity supply as a commodity market and creates a new set of transactions among utilities and new agents and end users. An important aspect is the role of competitive markets stressed by the new regulation in procurement and remuneration of ancillary services. These services are required to provide stability and security of supply. Ancillary services have a variety of terms used through the world to name them (e.g. system services, support services) and it is not easy to define or classify them. The objective of this paper is to give a possible classification scheme for ancillary services to allow an easier identification of the roles of suppliers and buyers. Also, means by which the costs of various services can be measured, quantified and allocated are discussed and one method for cost allocation is proposed.

Zonal reactive power market model based n optimal voltage scheduling

Zonal reactive power market model with implementation of optimal voltage scheduling is described in this paper. Proposed model is characterized by splitting the power system or a control area of an interconnected power system into autonomous voltage zones with sufficient reactive power reserves. Zones are selected using electrical distance method. In every zone a short-term auction based reactive power market is established. Based on the generators cost functions for reactive power production/consumption the optimal power flow problem is solved respecting the economic criteria and power system security constraints. The result of optimization algorithm is optimal voltage plan. Minimization of transmission losses is respected in second optimization step where final dispatching decision is made according to active and reactive energy prices and planned power system conditions.

Nonlinear digital simulation model of hydroelectric power unit with Kaplan turbine

Mathematical and simulation models enable hydroelectric power unit dynamic behavior analysis using computers. To approximate the power unit dynamics as accurate as possible, nonlinear high-order model is required. This paper describes a hydroelectric power unit with double regulated Kaplan turbine. The runners of such turbines permit the blades angle to be varied on the run depending on operating conditions. This ensures maximum turbine efficiency under all operating conditions. Detailed mathematical and digital simulation model of the hydroelectric power unit with double regulated turbine was presented for turbine control system analysis. Simulation model developed for Varazdin HPP (power unit 1) is verified by several comparisons with real measurement results.