Ricardo Torquato

Analysis of the harmonic distortion impact of photovoltaic generation in Brazilian residential networks

In Brazil, in spite of the outstanding solar irradiance levels, the installed amount of photovoltaic (PV) generation was practically inexistent until two years ago. This scenario started to change with the publication of resolution #482/2012 by the Brazilian Electricity Regulatory Agency, which establishes the main technical and commercial rules for residential power generation. This paper presents an overview of the current and near future scenarios of residential PV generation in Brazil, including regulatory aspects. The largest Brazilian field project on PV integration (about to start in 2014) is described. Since PV arrays use power electronic inverters, the imminence of a high PV penetration has raised utilities attention to its potential impacts on system harmonic distortion levels. In such context, this paper also identifies, through extensive simulations, the key factors influencing PV impacts on harmonic distortion level. It is found that the most important factors are: network loading level; PV connection point; and PV power factor.

Towards a real-time Energy Management System for a Microgrid using a multi-objective genetic algorithm

This paper proposes a real-time Energy Management System (EMS) for a low voltage (LV) Microgrid (MG). The system operation consists in solving the Unit Commitment (UC) and Economic Load Dispatch (ELD) simultaneously for 24 hours ahead at every 15-minute period. This operation is formulated as a multi-objective optimization problem where the minimization of operational cost, total emissions and power losses is simultaneously pursued using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). In this algorithm, crossover and mutation operators were improved with respect to existing approaches to achieve an adequate characterization of the energy management problem and a good algorithm performance. Simulation studies have outlined that, in fact, the NSGA-II can be used as a real-time optimization tool providing a good-quality Pareto front to operate optimally the MG in a limited time of 15 minutes.

Method to assess the power quality impact of plug-in electric vehicles

This paper presents a probabilistic harmonic simulation method to study the power quality impact of electric vehicles (EV). The proposed method takes into account the random operating characteristics of the vehicles, such as random charging time, charging duration and vehicle locations. A multi- phase model of the primary and secondary systems is used to represent the study system. Extensive case studies have been conducted using the method and the measured EV data. The results reveal that the current versions of plug-in hybrid EVs have no significant harmonic impact on power systems. However, the Level 1 charger can increase the neutral to earth voltage at homes which could lead to increased stray voltage incidents.

Review of international guides for the interconnection of distributed generation into low voltage distribution networks

Technological development, energy source diversification, environment concerns, financial incentives have driven the increasing interest on the interconnection of small scale distributed generators (SSDG) into low voltage (LV) distribution networks. This practice allows homeowners and others to contribute to the energetic matrix without having to implement expensive modifications to the grid. In this context, this paper presents a review of the requirements adopted by distribution companies worldwide to facilitate the connection of SSDG units while maintaining the integrity of the public low voltage distribution network, both in terms of safety and supply quality. Issues like disconnect switch, protection, metering, and power quality are examined.

Attending small loads along a half-wavelength transmission line

This paper presents some results on a Transmission Line a little greater than the Half-Wavelength (HWL+) attending small loads. A non-conventional 800 kV line with 2600 km with natural power of 4.8 GW was analyzed. The studies consisted in analyzing the capacity of this AC-Link feeding some small loads. The results confirm that this transmission is rather robust and can operate with small load drainage along its length.

High frequency harmonic distortions measured in a Brazilian solar farm

The operation of modern power electronic switches located in photovoltaic (PV) inverters have the potential to create high frequency harmonic (HFH) distortions. This paper investigates the emission of such distortions by PV inverters installed in a Brazilian solar farm. High-resolution measurements are performed on three different commercial inverters, with 15 kVA rated capacity each. Results obtained from the specific measurements presented in this paper reveal HFH current distortions may reach up to 2% of fundamental frequency current, whereas HFH voltages remain below 0.2% of fundamental frequency voltage. Therefore, results suggest HFH distortions emitted by these specific PV inverters are unlikely to cause significant problems to the utility.

A Monte Carlo simulation platform for studying low voltage residential networks

Summary form only given. The smart grid vision has resulted in many demand side innovations such as nonintrusive load monitoring techniques, residential micro-grids, and demand response programs. Many of these techniques need a detailed residential network model for their research, evaluation, and validation. In response to such a need, this paper presents a sequential Monte Carlo (SMC) simulation platform for modeling and simulating low voltage residential networks. This platform targets the simulation of the quasi-steady-state network condition over an extended period such as 24 h. It consists of two main components. The first is a multiphase network model with power flow, harmonic, and motor starting study capabilities. The second is a load/generation behavior model that establishes the operating characteristics of various loads and generators based on time-of-use probability curves. These two components are combined together through an SMC simulation scheme. Four case studies are presented to demonstrate the applications of the proposed platform.

Event detection methods for nonintrusive load monitoring

This paper proposes two novel algorithms to detect appliance switch-ON/OFF events, which is the first key step of a Nonintrusive Load Monitoring (NILM) software. The Window with Margins method uses the left and right margins of a window running over the house power consumption curve to locate power steps, while the Shifted Sample method relies on the derivative of the power consumption curve to identify power steps. The former may achieve higher event detection rates, while the latter presents very low complexity and requires a reduced computational effort. Extensive sensitivity studies were performed with the parameters of each method, and obtained results have shown the importance of an adequate parameter setting, as successful event identification rates may be increased up to 95%. The applicability and effectiveness of such algorithms have been verified using field measurement data.

Impact assessment of the two-way operation of plugin electric vehicles on distribution networks

The increasing adoption of plug-in electric vehicles (EVs) on the market has raised a concern about the technical impacts this massive connection scenario may bring to the grid. In response to such concern, this paper presents a comprehensive analysis of plug-in EV charging impact on distribution networks. Three aspects of EV connection are addressed. Firstly, residential penetration is considered and its main technical impacts are identified. The second aspect is the use of charging stations; its operation impacts are compared with residential connections and advantages/drawbacks are pointed out. Finally, a smart vehicle-to-grid (V2G) operation mode is introduced. It is shown that, under a time-dependent tariff scenario, such operation mode is highly attractive to the EV owner, as the revenue arisen from power injection may compensate EV charging expenses, approaching a zero fuel expense vehicle. In addition, it is shown that smart V2G operation greatly increases the system load factor.

A method to determine stray voltage sources-Part II: Verifications and applications

The method to identify the sources of the neutral-to-earth voltage (NEV) rise as presented in a companion paper is verified in this paper through extensive simulation studies and field measurements. Sensitivity studies are conducted to determine factors that affect the performance of the proposed method. The results show that the NEV contribution factor index is effective in identifying load unbalance caused NEV and its contributors. The current return ratio index is effective in diagnosing poor grounding caused NEV and its contributors. An NEV troubleshooting strategy and a system-wide NEV condition monitoring strategy are proposed based on the findings.