Le Anh Tuan

Competitive framework for procurement of interruptible load services

This paper deals with optimal procurement of interruptible load services within secondary reserve ancillary service markets in deregulated power systems. The proposed model is based on an optimal power flow framework and can aid the independent system operator (ISO) in real-time selection of interruptible load offers. The structure of the market is also proposed for implementation. Various issues associated with procurement of interruptible load such as advance notification, locational aspect of load, and power factor of the loads are explicitly considered. It is shown that interruptible load market can help the ISO maintain operating reserves during peak load periods. Econometric analysis reveals that a close relationship exits between the reserve level and amount of interruptible load service invoked. It was also found that at certain buses, market power exists with the loads, and that could lead to unwanted inefficiencies in the market. Investing in generation capacity at such buses can mitigate this. The CIGRE 32-bus system appropriately modified to include various customer characteristics is used for the study.

Effects of Plug-in Electric Vehicles on distribution systems: A real case of Gothenburg

The electric power system is changing and, especially, the electrical distribution system will meet new features. One of the large changes is a transformation of the transportation sector with the use of electricity, with introduction of Plug-in Electric Vehicles (PEVs). This will pose new challenges and opportunities for the electric distribution companies. This paper analyzes the effects of PEVs charging on the local 400 V and 10 kV electric distribution systems in the city of Gothenburg, Sweden, using steady-state power flow analysis. Two different areas representing residential area and commercial area have been simulated for the worst-case scenario, which is simultaneous charging of all the vehicles during the peak load period. The number of PEVs used has been estimated based on the load level at each customer location. The study results have shown that overloading of lines and transformers would occur when simultaneous charging of the vehicles during the peak load period. There would, however, be no problem with the voltage drop at the customers location during PEVs charging. An iterative method is proposed to estimate the maximum number of possible vehicles charging in the distribution system without resulting in any congestion. This method is also applied when one of the feeders is on outage to ensure the N-1 reliability criterion.

Distributed routing algorithms to manage power flow in agent-based active distribution network

The current transition from passive to active electric distribution networks comes with problems and challenges on bi-directional power flow in the network and the uncertainty in the forecast of power generation from grid-connected renewable and distributed energy sources. The power flow management would need to be distributed, flexible, and intelligent in order to cope with these challenges. Considering the optimal power flow (OPF) problem as a minimum cost flow represented with the graph, this paper applies a cost-scaling push-relabel algorithm in order to solve the OPF in a distributed agent environment. The algorithms performance is compared with the successive shortest path algorithm developed in our previous work. The simulation is implemented for both meshed and radial networks. The simulation results show the advantages of the cost-scaling push-relabel algorithm over the shortest path algorithm in the radial networks with respect to significantly reduced number of exchanged messages on the agent platform, and thus the reduced time for calculation. This will be of great importance if the method is to be applied to a large system.

On the analysis of the dc dynamics of multi-terminal VSC-HVDC systems using small signal modeling

In this paper, an analysis of the dc dynamics of multiterminal VSC-HVDC systems using the small signal modeling method is presented. Usually, the VSC controllers are designed under the consideration that they operate independently of each other. However, the possible interactions among them and the dc grid should be studied, especially in multi-terminal topologies. In this paper, three VSC-HVDC systems are modeled and, after linearization, the eigenvalues of the system are calculated for different loading conditions. The results from this analysis are compared to those obtained from more detailed models using PSCAD. It is shown that the operating point, the gains of the direct-voltage controller and the cable dynamics have an impact on the system performance.

Medium-term electricity price forecasting

Medium-term price forecasting plays an important role in electricity markets. Obtaining reasonably accurate medium-term electricity price predictions is critical in many applications, such as maintenance scheduling, generation expansion planning, and bilateral contracting. Medium-term price forecasting is a complex task because of the long forecasting horizon, dependence of medium-term electricity prices to various variables, and limited availability of explanatory data. In this paper, different aspects of a medium-term electricity price forecasting are discussed, and several data-driven 12-month-ahead approaches are developed. The presented approaches are applied to Nord Pool and the Ontario electricity market to examine their performance and effectiveness.

Medium-term electricity market price forecasting: A data-driven approach

Medium-term electricity price forecasting is necessary for several applications in electricity markets, such as pricing derivatives, maintenance scheduling for generation companies, and budgeting and fuel contracting. However, this is a complex task because of the inherent dependence of price to other sometimes unpredictable variables, such as variations in availability of different supply resources. This paper presents two regression-based linear forecasting models to predict the monthly average of electricity spot prices in deregulated electricity markets, with specific focus on systems with large penetration of hydro generation units. The forecasting horizon is a full year, i.e., the models are used to generate 12-month-ahead forecasts. Numerical results are provided for Nord Pool market.

Risk and reliability assessment for electrical distribution systems and impacts of regulations with examples from Sweden

The introduction of performance based tariff regulations, and higher media and political pressure have increased the need for well-performed asset management in the operation and planning of electrical distribution systems. In this paper quantitative reliability assessment methods are proposed as a tool to meet these new incentives. Electrical distribution systems have compared to other technical systems several special characteristics which are important to take into consideration when introducing reliability analysis methods. Moreover, the paper gives a brief discussion on the effects and the importance of customer participation in improving system reliability by providing additional system operating reserve from the market perspective. Finally, the paper discusses the reliability analysis with the reliability test systems, and stresses the usefulness of generally known test systems for such assessments. The ideas of future work on development of these test systems to address the changing power systems are presented.

Optimal load management of electric heating and PEV loads in a residential distribution system in Sweden

The electrical distribution system is facing major challenges in the near future related to increased electricity consumption, increased amount of distributed generation (DG) and the introduction of plug-in electric vehicles (PEVs). These could require large investments in the distribution system to maintain and operate the system in a secure way. However, the need to reinforce the distribution system can be avoided or postponed if the loads could be managed and controlled in order to reduce the peak load in the system. This paper examines the possibility for such a load management scheme in a residential part of the distribution system in the city of Gothenburg, Sweden. The load management scheme aims to minimize the losses in the system by shifting the heat loads and PEV charging in time without reducing the comfort level of the customers. In addition, a price-based optimal strategy is proposed, assuming dynamic electricity rates, that aims to minimize the electricity cost for the customers. The results indicate that the peak load can be decreased by the proposed load management scheme and that the number of PEVs that can be handled by the distribution system increases. However, dynamic electricity rates can cause increased peak power demand, indicating that either an aggregator or more advanced approaches for the electricity tariffs are needed to cope with the peak power.

A cost-benefit analysis of transmission network reinforcement driven by generation capacity expansion

This paper assesses the effects of the future European power generation system with strict CO2 emission reduction targets on the planning of cross-border interconnection lines. Results from a techno-economic energy systems model have been used as input to this work, regarding the development of the European power generation system until the year 2050, meeting the EU 2020 CO2 target and a 85% emissions reduction until the year 2050. A simplified UCTE power system model was developed in order to analyze how the cross-border interconnections in continental Europe are affected by the generation plans using an iterative method. The paper also attempts to identify the congestion points and proposes solutions based on nodal price modeling. A cost-benefit analysis (CBA) is used to evaluate the appropriate transmission planning strategy, with the costs being the long-term investment costs and the benefits being both the avoided environmental costs and the total congestion costs. The effects of new investments on the nodal prices are also studied. The results show that the profitability of the investments is influenced by the available production mix and the forecasted CO2 prices. The avoided congestion costs participate rather insignificantly in the CBA, which means that congestions are not relieved, showing that many interconnections are insufficient for nodal pricing market structure.

A combined zone-3 relay blocking and sensitivity-based load shedding for voltage collapse prevention

A typical power system voltage collapse scenarios is often ended with the undesirable operation of the Zone-3 distance relay of the transmission lines. This paper presents a protection scheme to avoid power system voltage collapse using a combined method of distance relays Zone-3 blocking scheme and a sensitivity-based load shedding selection. The Zone-3 distance relay blocking is based on the proper differentiation between transmission line overloading and line faulted conditions, using a fast estimation of power flow based on Line Outage Distribution Factor (LODF) and Generation Shift Factor (GSF). The Zone-3 distance relay of the transmission line would be blocked if the power flow change over the line is determined to be due to an overload so that more time would be available for the system to take necessary control actions. One of the important control actions is the emergency load shedding. A method based on the calculated sensitivities GSF to identify the most effective load shedding positions and amounts is proposed. The proposed method has been implemented in the Advanced Real-Time Interactive Simulator for Training and Operation (ARISTO) software with the Nordic 32-bus test system. ARISTO offers the possibility to test the proposed scheme since it can be seen as the virtual power system with all live information. The analyses of power system voltage collapse scenarios with and without the proposed scheme implemented have shown the effectiveness of the scheme to prevent the voltage collapses.