Umberto Grasselli

Satellite power system simulation

Abstract In order to furnish a useful tool for the power system preliminary sizing, a satellite power system simulator was developed. The simulator has a modular structure where each module implements the mathematical model of the system components (solar array, battery, voltage regulators etc.). The software allows both the verification of the rating co-ordination of all those parts composing the power system itself, once the mission is assigned, and the analysis of the time behavior of the electronic regulators during transients. Therefore, by using this simulator, any power system architecture can be easily analyzed. In this paper only the electrical preliminary sizing of the components is treated without considering power system mass and battery thermal calculations. As example of the capabilities of the tool the results of two simulations are reported; in the first, the transient behavior of a sequential switching shunt regulator (S3R) is analyzed. In the second simulation the power system of a LEO satellite is simulated in order to verify the rating co-ordination in case of unregulated bus voltage. The tool was developed within MATLAB/SIMULINK environment.

The arc-fault circuit protection

In electrical power systems bolted short-circuits are rare and the fault usually involves arcing and burning; mostly the limit value of minimum short-circuit depends on arcing-fault. In AC low voltage systems, the paper examines the arcing-fault branch circuits as weak points. Different protection measures are available against the arc-faults. A first measure that can guarantee a probabilistic protection is allowed by the adoption of overcurrent protective devices (OCPD), optimizing the design of the structure of the system and/or the coordination of protection. A well known complete protection is allowed by adopting arc-fault circuit interrupters (AFCI) for the protection of branch circuits. The authors suggest a new complete protection allowed wiring of the branch circuits, particularly including extension cords, with special power cables, protected by ordinary ground fault protective devices (GFPD). The suggested design for single-core or multi-core power cables is that each insulated core has a concentric conductor shield. Converting the line-to-line fault into a line to ground fault or into a mixed type is the goal of this special cable type faults ground-forced cable (FGFC).

Time-varying harmonics of single-phase nonlinear appliances

The paper deals with the time-variant behavior of harmonic currents produced by single-phase nonlinear (NL) appliances. The harmonic currents have been monitored in a broad field measurement activity that has concerned several samples of the more widespread appliance types in a power demand range up to hundreds of Watts. For the measurement activity a custom system allowing the continuous harmonic monitoring of voltage and current signals has been used. The results obtained show that for almost all the investigated appliances a not negligible variation of harmonic currents with time can be found. The possible causes of the observed behavior are discussed in detail. Finally, the utility of specific statistical and graphical tools for approaching the problem is discussed.

Robust LCC compensation in wireless power transfer with variable coupling factor due to coil misalignment

The paper provides an investigation of a possible application of wireless power transfer (WPT) technology to recharge the battery of a short-distance electric vehicle. The performance of the WPT system working at 85 kHz is first investigated by simulations. A robust LCC compensation network suitably tuned is then investigated with the goal to analyze the influence of design parameters on the compensation strategy. Particular attention is addressed to evaluate the deterioration of the WPT system performance due to coil misalignment. Finally, the WPT performances are evaluated demonstrating the feasibility of the proposed WPT technology.

Assessment of a practical model to estimate the cell temperature of a photovoltaic module

AbstractInstantaneous solar irradiance profiles or solar irradiation data collected with small time intervals (e.g., minutes) are usually required for the energy simulation of photovoltaic systems, especially as concerns the estimation of the cell temperature. However, meteorological stations and technical standards often provide just monthly average values of the horizontal daily solar irradiation; extensive climate databases which make available up to date hourly observation data, or satellite-derived data are seldom available. The goal of the present paper is to investigate the suitability and the accuracy of a methodology aimed at estimating the time profile of the cell temperature of a photovoltaic system on the basis of only the monthly mean values of the daily global irradiation on a horizontal surface. The methodology consists of a chain of well-established models which are applied one after another, in a step-by-step procedure, in order to derive the cell temperatures from the solar radiation data. In particular, we selected different models as possible candidates for each step of the methodology and compared their predictions with measured data to identify the most suitable ones. In addition, we tried several combinations of models in order to identify the most accurate combination. Comparisons with data measured in Rome confirm the suitability of the proposed approach and give information about its accuracy.

A planning study on power systems of metro-transit transportation system

A simulation program, implementing a deterministic-probabilistic methodology, has been applied to an Italian railway line (Roma - Ostia Lido), whose operation is going to be changed from railway to metropolitan service. The application tasks are to point out possible critical issues of the present supplying power systems and to provide proposal about their future optimal upgrading. In order to get the real values of the main electrical parameters of electrical sub-stations (ESS) of the railway line for the simulation, an experimental survey has been performed. The paper reports the main experimental and simulation results.

Harmonics monitoring survey on office LV appliances

The paper reports some experimental measurement results concerning current harmonics and power consumptions associated to some single phase non-linear loads supplied in low voltage. In particular some office equipments and florescent lamps have been monitored during their typical operation phases. For the purpose a custom monitoring system has been used. The harmonic monitoring survey has permitted an interesting characterization of harmonic spectrum variability that is very useful for penetration studies based upon a bottom-up approach.

Simplified conservative measurements of touch and step voltages

Protection against electric shock requires grounding systems that must be designed primarily to keep touch voltage (E/sub t/) and step voltage (E/sub s/) to a safe value. Testing of the efficiency of a grounding system is mandatory to verify the capability to satisfy the protection requirements at the end of the construction and periodically in the following. With urban development and buildings growth adjacent to power systems, grounds systems that are not metallically connected may often be found. They are thus significantly interdependent as they are located in each others area of influence and particularly it is useful to consider ground potential difference (GPD). It becomes increasingly difficult to choose suitable locations for test probes to make resistance, E/sub t/ and E/sub s/ tests of a grounding system. Accuracy of tests requires reaching remote earth and for large grounds the spacing required may not be practical or even possible. Unfortunately accurate measurement is often unfeasible, owing to the additional difficulty to measure both the hazardous voltages of the ground system, where test ground current flows, and the hazardous voltages of influenced ground systems. Since the rigorous measure can result too much laborious or too much expensive, a simplified conservative testing method of the behavior of ground electrodes can be favorable. This paper discusses an approach to the above-simplified testing method, which relies on single, or multiple auxiliary electrodes placed at short distance from the grounding system. By means of this approach, a conservative test can be made of both E/sub t/ and E/sub s/ GPD.Protection against electric shock requires grounding systems that must be designed primarily to keep touch voltage (E/sub t/) and step voltage (E/sub s/) to a safe value. Testing of the efficiency of a grounding system is mandatory to verify the capability to satisfy the protection requirements at the end of the construction and periodically in the following. With urban development and buildings growth adjacent to power systems, grounds systems that are not metallically connected may often be found. They are thus significantly interdependent as they are located in each others area of influence and particularly it is useful to consider ground potential difference (GPD). It becomes increasingly difficult to choose suitable locations for test probes to make resistance, E/sub t/ and E/sub s/ tests of a grounding system. Accuracy of tests requires reaching remote earth and for large grounds the spacing required may not be practical or even possible. Unfortunately accurate measurement is often unfeasible, owing to the additional difficulty to measure both the hazardous voltages of the ground system, where test ground current flows, and the hazardous voltages of influenced ground systems. Since the rigorous measure can result too much laborious or too much expensive, a simplified conservative testing method of the behavior of ground electrodes can be favorable. This paper discusses an approach to the above-simplified testing method, which relies on single, or multiple auxiliary electrodes placed at short distance from the grounding system. By means of this approach, a conservative test can be made of both E/sub t/ and E/sub s/ GPD.

Lighting systems: Power consumptions and harmonics monitoring survey

The paper reports some experimental measurement results concerning energy consumptions and Power Quality in lighting. Therefore, the power consumptions and harmonic absorptions of several types of lamps are analyzed. The recorded power consumptions put in evidence the different lamps impact related to the used luminaire technologies. Moreover the recorded harmonic absorptions show an interesting characterization of harmonic spectrum variability of the lamps.

Small scale ESS for LV prosumers: An economic feasibility and sensitivity analysis

In a framework of fast evolving power systems in terms of structure and operation, the implementation of energy storage systems (ESSs) is a key element. The aim of the present work is to identify economic conditions for the effective application of ESSs for LV residential prosumers, i.e. consumers with local power generation. An economic feasibility and sensitivity analysis is performed. Three cases are considered, basing on current Italian incentive policy. Each case study is analyzed in two conditions in reference to the derating and replacement of ESS. The comparison of the two conditions gives a measure of the impact of technology on economic effectiveness of its application. Another analysis is reported, based on introduction of support policies as the German ones. Results show that implementation of a residential ESS could be advantageous in case of introduction of suitable support policies or decreasing ESS costs.