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Microgrids are characterized as weak systems with poor power quality due to significant variations in frequency and/or voltage that can occur during sudden changes in load demand. This problem is exacerbated in cases where one of the power sources is tied to the microgrid through a grid-interactive inverter which is designed to trip when deviations in frequency and voltage exceed well-defined thresholds...
The relative amount of distortion in the current generated by a PV system under low solar irradiance is known to be quite significant. This paper analyzes such distortion on the utility-side of the interconnection transformer thus including its excitation current. An approximate method that reveals the imbalance and distortion of both the phase and line currents in a 3-legged transformer is presented...
Power quality is becoming a concern in installations with significant photovoltaic (PV) generation systems. This article analyses the low-order harmonic currents that are generated by a 12 kW photovoltaic system. Field measurements are taken under different levels of solar irradiance as well as under different power factor operation of the inverter. The impact of the quality of the utility supply...
The recent amendment to the IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems (IEEE Std. 1547a-2014) is unleashing the application of advanced inverter functionalities to help mitigate voltage regulation problems commonly encountered in areas with high levels of PV penetration. This paper describes the experimental testing of some of the important autonomous functionalities...
The recent exponential growth of utility-interconnected PV systems has led to changes to IEEE 1547 - the standard for interconnecting distributed resources with electric power systems. IEEE 1547a and IEEE 1547.8 are unleashing the application of advanced inverter functionalities, or grid support functions, for the purpose of minimizing adverse distribution system effects that are commonly encountered...
Conductors for most buildings in the United States are sized using the National Electrical Code (NEC). The 2014 NEC now requires that a value be added to the ambient temperature used to determine the ampacity of conductors installed on rooftops. This paper reports the results of a related experimental test (on both energized and non-energized cables) that is conducted on a rooftop of a building located...
Grid-tied photovoltaic inverter manufacturers rarely reveal the type of power electronic circuit topology and the type of technique used to track maximum power, control of power injected into the grid, and method used to avoid islanding operation. In this paper, an attempt is made to gain such information on a commercial 2.5 kW inverter by measuring the voltage and current waveforms under normal operation...
Partial shading on a solar photovoltaic (PV) array is known to have a significant impact on its energy yield. This paper presents experimental measurements on a 2 kW grid-tied PV array under different shading profiles that are caused by structures of various shapes at different times of the year. A simulation method that provides an accurate description of shadow movement of the simpler structure...
It is a known fact that when an AC motor operates below its rated load, its efficiency can be improved by reducing the supply voltage to an appropriate level. This paper proposes an automatic voltage controller that optimizes the efficiency of fractional-horsepower motors when operating under variable load conditions. The scheme is based on perturbing the supply voltage (by controlling the firing...
Electric utility companies curb their system peak power demand through numerous Demand Response (DR) programs, such as the Time-Of-Use (TOU) rates where the cost of energy is typically much higher during the peak period and lower for the rest of the time relative to the standard flat rate. Meanwhile, a vertically installed West-facing bifacial PV array is expected to provide an advantage over a conventional...
This paper proposes a new strategy to meet the controllable heating, ventilation, and air conditioning (HVAC) load with a hybrid-renewable generation and energy storage system. Historical hourly wind speed, solar irradiance, and load data are used to stochastically model the wind generation, photovoltaic generation, and load. Using fuzzy C-Means (FCM) clustering, these data are grouped into 10 clusters...
This paper evaluates the performance of a 1 kW bifacial grid-connected PV system. The array is mounted vertically facing west on a building roof for the purpose of generating power during the late afternoon hours, thus assisting with peak load demand. Simulated solar irradiance received by both sides of the array and power production are compared to measured values. The need for better models to estimate...
Numerous methods are known for grid-tie photovoltaic inverters to track the maximum power point and to avoid islanding operation, but the inverter manufacturers generally do not publish which of these methods they have implemented in their products. This paper reviews the most common maximum power point tracking and anti-islanding methods and points out to power quality signatures they may leave in...
This paper presents a calculation of voltage sag magnitude, area of vulnerability spectrum and method for SARFI-indices due to a fault in distribution system of Provincial Electricity Authority of Thailand. Voltage sag is related to power quality problems and reliability of utility. Analysis of voltage sag will help utilities to determine and predict the area of vulnerability in distribution system...
Operation of power systems with high wind penetration is significantly influenced by wind variability and uncertainty. This paper examines the potential impact of distributed wind generation on ramping requirements in the IEEE 24-bus system. Wind generation and load are modeled probabilistically using actual data and curve fitting. Probabilistic unit commitment (UC) based on unit de-commitment method...
Operation of the power systems with high wind penetration is significantly influenced by wind variability and uncertainty. This paper examines the potential impact of distributed wind generation on operating reserve requirements in the IEEE 24-bus system. Wind and load are stochastically modeled using actual data from a balancing authority. Probabilistic optimal power flow based on the two point estimate...
Electrochemical batteries are rapidly gaining wide-spread application in transportation systems as well as in the electric utility sector, and accurate battery models are need during the design stage of such systems to forecast future performance. This paper proposes a simple and yet accurate model of a sealed AGM battery. The model takes into account the nonlinear characteristics of the discharge...
Cloud-induced transients induced in photovoltaic (PV) power are considered as a potential barrier to further expansion when the penetration of this renewable generation resource reaches a high level in distribution systems. Such transients can cause voltage flicker or excessive operation of the voltage regulating equipment. This article studies these effects on part of a local distribution substation...
The increasing amount of wind power generation in Thailand power systems requires stability analysis considering interaction between wind-farms and transmission systems. Dynamics introduced by dispersed wind generators at the distribution level can usually be neglected. However, large wind farms have a considerable influence to power system dynamics and must definitely be considered for analyzing...
This article evaluates the method of reducing power loss due to 3rd harmonic currents in a building that contains a significant level of electronic loads, by placing a passive filter in the neutral path. The initial power loss is obtained through current measurements in the phase and neutral conductors and knowledge of the resistance of these conductors and that of the transformer serving the facility...
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