Pablo Frías

Assessment of the Impact of Plug-in Electric Vehicles on Distribution Networks

Plug-in electric vehicles (PEVs) present environmental and energy security advantages versus conventional gasoline vehicles. In the near future, the number of plug-in electric vehicles will likely grow significantly in the world. Despite the aforementioned advantages, the connection of PEV to the power grid poses a series of new challenges for electric utilities. This paper proposes a comprehensive approach for evaluating the impact of different levels of PEV penetration on distribution network investment and incremental energy losses. The proposed approach is based on the use of a large-scale distribution planning model which is used to analyze two real distribution areas. Obtained results show that depending on the charging strategies, investment costs can increase up to 15% of total actual distribution network investment costs, and energy losses can increase up to 40% in off-peak hours for a scenario with 60% of total vehicles being PEV.

An Aggregate Model of Plug-In Electric Vehicles for Primary Frequency Control

Summary form only given. The penetration level of plug-in electric vehicles (PEVs) has the potential to be notably increased in the near future, and as a consequence, power systems face new challenges and opportunities. In particular, PEVs are able to provide different types of power system ancillary services. The capability of storing energy and the instantaneous active power control of the fast-switching converters of PEVs are two attractive features that enable PEVs to provide various ancillary services, e.g., primary frequency control (PFC). However, concurrently, PEVs are obliged to be operated and controlled within limits, which curbs the grid support from PEVs. This paper proposes a new model for PEV using a participation factor, which facilitates the incorporation of several PEV fleets characteristics such as minimum desired state of charge (SOC) of the PEV owners, drive train power limitations, constant current and constant voltage charging modes of PEVs. In order to reduce computational complexity, an aggregate model of PEVs is provided using statistical data. In the end, the performance of PEVs for the provision of PFC is evaluated in a power system. Results show that PEV fleets can successfully improve frequency response, once all the operating constraints are respected.

A Novel Rotor Ground-Fault-Detection Technique for Synchronous Machines With Static Excitation

This paper presents a novel ground-fault-detection technique for synchronous machines. This technique is suitable for synchronous machines with static excitation systems, whose excitation field winding is fed by rectifiers through an excitation transformer. The main contribution of this new technique is that it can detect and discriminate both ac- and dc-side ground faults in the excitation system, without the need for traditional power injection sources. This detection technique is based on the frequency analysis of the voltages or currents at a grounding impedance placed at the excitation transformer neutral terminal. This technique has been validated through computer simulations and experimental laboratory tests.

Regulation of distribution system operators with high penetration of distributed generation

The increase of distributed generation (DG) in distribution networks is an important challenge for distribution system operators (DSOs). DG integration not only impacts on DSO short-term costs but also involves new risk uncertainty regarding system reliability, security and network planning. Therefore, because DSO is mainly a regulated business, it is clear that new regulatory mechanisms should be designed. This paper analyzes how the traditional model of DSO regulation is impacted by increasing penetration of DG. A set of proposals on how this model can be improved are presented. Finally, some guidelines on regulatory improvements for the transition between the current and future situation with high penetration of DG are recommended.

Influence of Rotor Position in FRA Response for Detection of Insulation Failures in Salient-Pole Synchronous Machines

Frequency response analysis (FRA) is a very common test for the diagnosis of power transformers. This paper presents some relevant results on the application of FRA to the diagnosis of rotating machines. First, a reference rotor position for obtaining the reference FRA response of a rotating machine is proposed. Then, FRA with the proposed rotor position is used to identify faults in the stator of the machine. This paper studies turn-to-turn and ground faults in the stator for different fault resistance values. Several laboratory tests demonstrate the applicability and value of the use of FRA in the diagnosis of rotating machines.

Calculation of the Elastic Demand Curve for a Day-Ahead Secondary Reserve Market

The level of secondary reserve needed in a power system is traditionally settled by system operators according to engineering criteria. This paper proposes a novel methodology to determine the optimum level of secondary reserve based on both engineering and economic criteria. Within the proposed approach a price elastic-quantity demand curve for the secondary reserve is built. This approach assumes that the provision of secondary reserve is made under a competitive market. In this market, the supply curve that collects the bids from generators providing secondary reserve is matched with the calculated elastic demand cost curve. The cross of the supply and demand curves determines the optimal level of secondary reserve and the price for provision of the service. The developed approach is illustrated with a case study based on the current day-ahead secondary reserve market in Spain.

An Aggregate Model of Plug-in Electric Vehicles Including Distribution Network Characteristics for Primary Frequency Control

Summary form only given. In the future, the number of plug-in electric vehicles (PEVs) that will participate in the primary frequency control (PFC) is likely to increase. In our previous research, the computational complexity of the PFC problem for a large number of PEVs was reduced using aggregate models of PEVs. However, in the literature on the PFC, the distribution network characteristics have not been included in the aggregate models of PEVs for the PFC, despite the fact that PEVs will be dispersedly connected to the distribution network. This paper proposes an aggregate model of PEVs for the PFC that further incorporates distribution network characteristics, i.e., the distribution network power loss (DNPL) and the maximum allowed current (MAC) of the lines and transformers. The DNPL variation is formulated according to the line and transformer impedance, spatial distribution of PEVs and loads, and active power variation of PEVs. Then, DNPL variation together with the MAC of the lines and transformers are incorporated in the proposed model of PEVs. Finally, the simulation results show an excellent agreement of 98% between the detailed model and the proposed aggregate model of PEVs.

New On-Line Rotor Ground Fault Location Method for Synchronous Machines With Static Excitation

This paper presents a novel on-line rotor ground fault location method for synchronous machines, which, combined with rotor ground fault protection, can detect and locate faults in the rotor. This method is suitable for synchronous machines with static excitation systems, whose excitation field winding is fed by rectifiers through an excitation transformer. The main contribution of this new technique is that it can locate the position of a ground fault in the rotor winding online, reducing the repair time. The proposed technique is based on the analysis of the ac and dc components of the excitation voltage and the voltage measured in a grounding resistance located in the neutral terminal of the excitation transformer. This technique has been validated through computer simulations and experimental laboratory tests.

A Reactive Power Capacity Market Using Annual Auctions

This paper presents a new approach to design reactive power capacity markets. Under this approach annual auctions to procure reactive power capacity are conducted by the system operator. Two products are defined, reactive power generation and absorption capacity, which can be supplied by different independent VAR sources, such as generators, SVCs, capacitor banks and shunt reactors. Reactive power capacity is allocated using an optimization algorithm that matches capacity bids and system reactive power needs, for peak and low demand hours. The reactive power requirements are calculated taking into account system contingencies and the dynamic performance of the VAR sources under these situations. Another key proposal of the paper is the distribution of costs of the reactive power capacity market to the agents responsible for contingencies according to the use of the service by each market participant. This remuneration approach provides fair and efficient economic signals to all market participants. The applicability of the approach is illustrated with two case studies.

Reference Network Models: A Computational Tool for Planning and Designing Large-Scale Smart Electricity Distribution Grids

Reference Network Models (RNMs) are large-scale distribution network planning tools. RNMs can be used by policy makers and regulators to estimate efficient distribution costs. This is a very challenging task, particularly being network planning a combinatorial problem, which is especially difficult to solve due to the vast size of the distribution areas, and the use of several voltage levels. This chapter presents the main features of RNMs developed by the authors, including high performance requirements related to the type and size of the problem. The model can be used to plan distribution networks either from scratch or incrementally from existing grids. Different case studies illustrate the applicability of these models to the assessment of the impact of massive deployment of renewable distributed generation, demand response actions, and plug-in electric vehicle penetration on distribution costs. The results obtained provide valuable information to guide strategic policy-making decisions regarding the implementation of renewable energy programs and smart grid initiatives.