Yahia Baghzouz

Practical definitions for powers in systems with nonsinusoidal waveforms and unbalanced loads: a discussion

Existing definitions for power terms in alternating current systems work well for single-phase and three-phase systems where both voltages and currents are sinusoidal with respect to time. This paper clarifies and proposes definitions for power terms that are practical and effective when voltage and/or currents are distorted and/or unbalanced. It also suggests definitions for measurable values that may be used to indicate the level of distortion and unbalance.

Shunt capacitor sizing for radial distribution feeders with distorted substation voltages

An algorithm for optimizing shunt capacitor sizes on radial distribution lines with nonsinusoidal substation voltages such that the RMS voltages and their corresponding total harmonic distortion lie within prescribed values is presented. The problem is formulated as a combinatorial optimization problem with inequality constraints. A simple heuristic numerical algorithm that is based on the method of local variations is proposed to determine an optimal solution. An example shows that optimal capacitor sizes found by neglecting the harmonic components may result in unacceptable voltage distortion levels. >

Genetic-Algorithm-Based Optimization Approach for Energy Management

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 of days with similar data points to account for seasonal variations. In order to minimize cost and increase efficiency, we use a GA-based optimization approach together with a two-point estimate method. Minimizing the cost function guarantees minimum PV and wind generation installation as well as storage capacity selection to supply the HVAC load. Different scenarios are examined to evaluate the efficiency of the system with different percentages of load shifting. The maximum capacity of the storage system and excess energy are calculated as the most important indices for energy efficiency assessment. The cumulative distribution functions of these indices are plotted and compared. A smart-grid strategy is developed for matching renewable energy generation (solar and wind) with the HVAC load.

Time-varying harmonics. I. Characterizing measured data

This paper represents Part I of a two-part article which summarizes the probabilistic aspects of harmonics in electric distribution systems. This first part reviews the problems associated with direct application of the fast Fourier transform to compute harmonic levels of nonsteady state distorted waveforms, and various ways to describe recorded data in statistical terms. Each statistical description is applied to a set of recorded data for illustration purposes.

Effects of nonlinear loads on optimal capacitor placement in radial feeders

The nonlinear portion of electrical loads has increased significantly in recent years. Harmonic currents injected by these loads into the distribution system should be considered when solving the capacitor placement problem in order to assure that the optimal solution does not result in excessive harmonic distortion. A voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies. Computer simulations show that the optimal capacitor sizes and locations depend heavily on the load model used at fundamental frequency and on harmonic signals, especially when limits are imposed on voltage waveforms. >

Time-varying harmonics. II. Harmonic summation and propagation

This paper represents the second part of a two-part article reviewing the state of the art of probabilistic aspects of harmonics in electric power systems. It includes tools for calculating probabilities of rectangular and phasor components of individual as well as multiple harmonic sources. A procedure for determining the statistical distribution of voltages resulting from dispersed and random current sources is reviewed. Some applications of statistical representation of harmonics are also discussed.

Battery Storage System sizing in distribution feeders with distributed photovoltaic systems

This paper presents a procedure for sizing a Battery Energy Storage System (BESS) for the purposed of shaving the peak demand of a residential distribution feeder. The BESS power and energy storage rating are determined from actual load demand data and desired level of peak reduction using the load following method. The impact of distributed photovoltaic (PV) power generation (to be installed by residential customers) on the feeder load curve, and on the BESS sizing is explored. It is determined that while PV installations have no impact on the BESS power rating, they reduce its energy storage capacity in proportion with the PV penetration level.

Probabilistic Modeling of Power System Harmonics

A generalized procedure to obtain the probabilistic model of power system harmonic current injection and propagation is presented. The model takes into account random variations of both the operating modes as well as the configuration of nonlinear loads connected to a distribution feeder. The method is illustrated by an example of a bus having linear as well as nonlinear loads of different types. Potential applications of the model are also discussed.

Impact of high PV penetration on voltage regulation in electrical distribution systems

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. Actual transformer load and solar irradiance data based on 1-minute interval are used to simulate the impact of 20% PV penetration on the feeder voltage during a time period that covers both clear and cloudy skies. Based on some specified conditions, the simulations indicate that voltage flicker is not a concern, but the tap changer operates excessively even when using a 5-minute time delay.

On the voltage profile of distribution feeders with distributed generation

This paper derives simple analytical expressions of voltage profile along radial distribution feeders containing distributed generation (DG) units. The analysis assumes fixed substation voltage by LTC transformer is based on uniformly distributed loads. DG active and reactive power generation limits constrained by permissible voltage levels are also expressed as a function of DG location along the feeder. The method is extended to more practical feeders with concentrated loads and line segments with different conductor size and geometry. The analysis is illustrated by a numerical example that shows that the analytical expressions derived are quite accurate.