Elham Foruzan

Hybrid system modeling and supervisory control of a microgrid

A new approach to designing a microgrid supervisory controller based on a hybrid automaton is described. A microgrid is defined as a small-scale local grid, comprised of various distributed energy resources (DERs), loads, and energy storage systems. Due to the intermittency of renewable generation, microgrid controllers play a vital role maintaining microgrid stability and integrity in case of an energy shortage (surplus) or when subjected to any disturbances. These controllers should be designed to provide proper control of voltage and frequency. Supervisory controllers are high level control systems that perform optimization, faults detection, protection, and energy management based on their observation from the microgrid. Supervisory controllers define set points to the local controllers for DERs and loads. In this paper, the joint continuous and discrete behavior of the supervisory controller is addressed using a hybrid controller. A complete model of the hybrid automaton (HA) is formalized and tested through one case study of a microgrid using DIgSILENT PowerFactory software. According to the results, the controller can thoroughly manage the load flow within and outside the microgrid.

A comparative study of different machine learning methods for electricity prices forecasting of an electricity market

Generally, it is difficult to accurately forecast electricity prices because they are unpredictable. Yet, accurate price forecasting is expected to provide crucial information, needed by power producers and consumers to bid strategically, thereby decreasing their risks and increasing their profits in the electricity market. In this paper, two models using artificial neural networks (ANN) and support vector machines (SVM) were developed for electricity price forecasting. In addition, ant colony optimization (ACO) was used to reduce the feature space and give the best attribute subset for ANN model. Using ACO for feature selection significantly reduced the training time for ANN-based electricity price forecasting model while the results were almost as accurate as those from ANN model.

The investigation of dielectric barrier impact on the breakdown voltage in high voltage systems by modeling and simulation

Nonpressurized air is used extensively as a basic insulation medium in medium/high voltage equipment. An inherent problem of air-insulated designs is that the systems tend to become physically large. Application of dielectric barriers can increase the breakdown voltage and thereby decrease the size of the equipment. In this paper, the impact of polytetrafluoroethylene (PTFE) and polyvinyl chloride (PVC) as dielectric barriers on breakdown voltage for DC and AC voltages were investigated by developing two geometric models. In the first model, it was assumed that a U-shaped electrode was covered with PVC dielectric. In the second model, it was assumed that PTFE dielectric was inserted in the air gap between electrodes. Both models were simulated using COMSOL Multiphysics software. The simulation results were verified by experimentation in the lab. The results show that a layer of PTFE and PVC dielectrics behaved as a mechanical obstacle, and they increased the voltage breakdown channel. In addition, the residual charges over the barrier changed the electric field distribution, resulting in a significant increase in the breakdown voltage.

Decentralized controller design for microgrids in islanded and grid-connected modes

Microgrids are key elements for integrating renewable resources as well as distributed energy storage systems as green sources of electricity. However, the presence of controllers is indispensable in confronting the intermittency and variable operation of renewable resources. This paper explores the control of active and reactive power flow through two modes of microgrid operations, namely islanded and grid-connected modes. A distributed primary-secondary controller was proposed to dynamically share power between parallel distributed energy resources (DERs). Additionally, a tertiary controller was implemented to make full use of renewable generation and optimal power flow inside the microgrid. The studies were conducted in the time-domain, using the DIgSILENT PowerFactory software environment. The study results demonstrate the accuracy of the proposed approach for sharing loads inside a microgrid.

Fuzzy cost-based FMECA for wind turbines considering condition monitoring systems

This paper discusses a fuzzy cost-based failure modes, effects, and criticality analysis (FMECA) approach for wind turbines. Conventional FMECA methods use a crisp risk priority number (RPN) as a measure of criticality which suffers from the difficulty of quantifying the risk. One method of increasing wind turbine reliability is to install a condition monitoring system (CMS). The RPN can be reduced with the help of a CMS because faults can be detected at an incipient level, and preventive maintenance can be scheduled. However, the cost of installing a CMS cannot be ignored. The fuzzy cost-based FMECA method proposed in this paper takes into consideration the cost of a CMS and the benefits it brings and provides a method for determining whether it is financially profitable to install a CMS. The analysis is carried out in MATLAB® which provides functions for fuzzy logic operation and defuzzification.

On the performance of forecasting models in the presence of input uncertainty

Nowadays, with the unprecedented penetration of renewable distributed energy resources (DERs), the necessity of an efficient energy forecasting model is more demanding than before. Generally, forecasting models are trained using observed weather data while the trained models are applied for energy forecasting using forecasted weather data. In this study, the performance of several commonly used forecasting methods in the presence of weather predictors with uncertainty is assessed and compared. Accordingly, both observed and forecasted weather data are collected, then the influential predictors for solar PV generation forecasting model are selected using several measures. Using observed and forecasted weather data, an analysis on the uncertainty of weather variables is represented by MAE and bootstrapping. The energy forecasting model is trained using observed weather data, and finally, the performance of several commonly used forecasting methods in solar energy forecasting is simulated and compared for a real case study.

Low-voltage ride-through simulation for microgrid systems

In contrast to the previous generation of power grid codes, recent standards require that distributed energy resources (DERs) provide low-voltage ride-through (LVRT) capabilities during grid faults. Consequently, the high penetration of DERs in todays power system requires an efficient method of controlling the active and reactive power of those resources during normal as well as abnormal voltage conditions. Coordinated selection of different combinations of DERs in a microgrid can maximize the ability of these resources to ride through low voltage faults. In this paper, a microgrid system is developed as a key element for combining different types of DERs so that the true ride-through capability of the entire system can be assessed. A simulation of this model was conducted using DIgSILENT PowerFactory software. The proposed combination of distributed energy resource types, and their controls, improve the LVRT capability of microgrid system.

Towards a voltage regulation market

In this work, we propose a possible voltage support or voltage regulation market in which voltage service providers (VSPs) will compete for an opportunity to provide voltage support or regulation by using voltage support devices. We assume that voltage regulation market is a separate but complementary market to existing energy markets (day-ahead and real time markets). An independent system operator (ISO) will decide when the voltage regulation market is to be launched. ISO will determine the required voltages (in p.u) at some nodes and clear the market based on the submitted bids and offers by the voltage service providers. ISO can anticipate the low-voltage situation ex-ante at some locations and can initiate the voltage regulation market. The voltage regulation market problem was formulated as nonlinear AC-OPF model and was solved using improved differential evolutionary algorithm. We used an IEEE 14 bus system as a test system in which the voltage regulation market clears. We showed that the development of voltage regulation market is of practically possible and can improve both social welfare and system condition.

Reliability assessment of distribution system using fuzzy logic for modelling of transformer and line uncertainties

Reliability assessment of distribution system, based on historical data and probabilistic methods, leads to an unreliable estimation of reliability indices since the data for the distribution components are usually inaccurate or unavailable. Fuzzy logic is an efficient method to deal with the uncertainty in reliability inputs. In this paper, the ENS index along with other commonly used indices in reliability assessment are evaluated for the distribution system using fuzzy logic. Accordingly, the influential variables on the failure rate and outage duration time of the distribution components, which are natural or human-made, are explained using proposed fuzzy membership functions. The reliability indices are calculated and compared for different cases of the system operations by simulation on the IEEE RBTS Bus 2. The results of simulation show how utilities can significantly improve the reliability of their distribution system by considering the risk of the influential variables.

Simulation and modeling of dielectric barrier impact on heterogeneous electric field

Non-pressurized air is extensively used as basic insulation medium in medium/high voltage equipments. An inherent property of air-insulated design is that the systems tend to become physically large. Application of dielectric barrier can increase the breakdown voltage and therefore decrease the size of the equipment. In this paper, the impact of dielectric barrier on breakdown voltage enhancement is investigated under both dc and ac applied voltages. For this purpose, two different kinds of dielectric materials as barrier are examined in high voltage electrode structures. Several simulations are carried out to investigate the effect of electric field uniformity factor on breakdown voltage enhancement with dielectric barrier in different structures. The impact of different parameters such as inter-electrodes gap, shape of electrodes, and dielectric materials on the break-down voltage are investigated with simulations and experiments for applied ac and dc voltages. Simulation studies and experimental results illustrate the effectiveness of dielectric barrier in the system.