Angelo Brambilla

Model of Photovoltaic Power Plants for Performance Analysis and Production Forecast

A photovoltaic (PV) plant model is presented. It is based on a detailed electrothermal description of the panels forming strings that, in turn, form the power plant. It accounts for environmental working conditions, such as temperature and wind speed, and specific plant configuration, such as plant topology and power losses due to interconnections. The input variables of the model are the ambient temperature, irradiance, and wind speed. The model derives the working temperature of the panel taking into account also the power conversion performed by the panel; the electrical operating point is determined by simulating the actions done by the maximum power point tracker that operates at plant level. This model has been tested using a large database of experimental data from industrial PV plants characterized by power levels ranging from 250 kW to 1 MW. As shown, the model is capable to predict power production when “fed” by forecast irradiance, ambient temperature, and wind speed data.

Steady State Computation and Noise Analysis of Analog Mixed Signal Circuits

Steady state simulation and noise analysis are two essential tools for circuit designers. The algorithms currently available in commonly used simulators are basically limited to the analysis of analog circuits that can be modeled by Lipschitz continuous functions. This is a strong restriction, since current applications are often naturally described by mixed analog-digital models; these models are only piece-wise continuous and Lipschitz condition is not satisfied in the breakpoints. In this paper we propose a method to overcome this limitation by showing how circuits in this class, and, in general, circuits showing discontinuities, can be modeled as hybrid systems. Conventional steady state and noise analysis methods are then extended to this class of circuits. A method to identify the discontinuity points, that, in general, are not known a priori in circuit analysis, is also proposed. With this last addition the method is fully automated and does not require any user intervention.

Measurements and extractions of parasitic capacitances in ULSI layouts

This paper deals with the extraction of parasitic capacitances of interconnects in submicron layouts. It is well known that, in integrated circuits, the signal delay due to interconnects is comparable to that of gates. This aspect becomes particularly important, for example, during the design of clock trees in high-speed applications. In general, capacitance extraction is carried out with software tools but they should be validated on a set of geometrical structures, which have been accurately characterized and that are representative of the circuit layouts. Experimental characterization of these structures and their set up in a golden set of measures is still a challenging task. In this paper, we first describe some experimental approaches to measure capacitances of structures from the golden set and in particular we identify a high accuracy transducer based on pass-gate transistors. We then propose a software implementation of the floating random walk algorithm that solves the drawbacks in the extraction of capacitances of interconnects in a nonhomogeneous medium as an industrial layout. Finally, experimental and simulation results are presented, validating the adopted approach.

Envelope following method for the transient analysis of electrical circuits

An envelope following method (EFM) that allows efficient transient simulations of electrical circuits is here presented. Its mathematical and electrical bases are considered and the influence of some general properties, such as stability and truncation error of integration methods employed by EFM, are studied. Furthermore, we present a new state variable prediction algorithm that improves previously reported ones, since it better adapts to fast dynamics of the solution. A set of power switching circuits is employed as a benchmark and numerical results of our algorithm are compared to those of conventional integration and of previous EFM versions. Remarkable results are obtained in the electrothermal simulation of power converters where the efficiency gain rises up to some magnitude orders with respect to conventional integration.

Computation of period sensitivity functions for the simulation of phase noise in oscillators

Accurate phase noise simulation of circuits for radio frequency applications is of great importance during the design and development of wireless communication systems. In this paper, we present an approach based on the Floquet theory for the analysis and numerical computation of phase noise that solves some drawbacks implicitly present in previously proposed algorithms. In particular, we present an approach that computes the perturbation projection vector directly from the Jacobian matrix of the shooting method adopted to compute the steady-state solution. Further, we address some problems that arise when dealing with circuits whose modeling equations do not satisfy the Lipschitz condition at least from the numerical point of view. Frequency-domain aspects of phase noise analysis are also considered and, finally, simulation results for some benchmark circuits are presented.

Improved Small-Signal Analysis for Circuits Working in Periodic Steady State

This paper considers the formulation of the variational model (VM) of autonomous circuits (oscillators) working in periodic steady-state conditions. The shooting method, which is largely used to compute the solution in the time domain when the VM is forced by a small-signal perturbation, is studied. The proposed analytical approach can be exploited to improve accuracy in the simulation of the effects of noise sources. In particular, we justify from an analytical standpoint the adoption of a suitable periodicity constraint in the shooting method. We exploit the properties of block circulant matrices that naturally arise in the description of the problem. We prove that the frequency of the small-signal perturbation must be different from that of the unperturbed oscillator to avoid inaccuracy of the shooting method due to the existence of singularities in the VM formulation, and derive a method that allows us to get closer to the singularity.

Frequency warping in time-domain circuit simulation

Time-domain simulation of dynamic circuits and, in general, of any physical model characterized by ordinary differential equations or differential algebraic equations, implies the use of some numerical integration method to find an approximate solution in a discrete set of time points. Among these methods, the class known as linear multistep includes many well-known formulas such as the backward Euler method, the trapezoid method, and the implicit backward differentiation formulas used in most circuit simulators. All these methods introduce a very subtle effect that is, here, called the warping error. As shown, it is equivalent to a perturbation of the eigenvalues of the linearized ordinary differential problem. The perturbation introduced depends on the integration time step; it is often very small and in most cases irrelevant or even not noticeable. Nevertheless an exception to this situation is found when simulating high-quality factor circuits where even very small warping errors can lead to qualitatively wrong solutions. In this paper, we demonstrate that higher order linear multistep methods, while characterized by weaker stability properties, introduce less of a warping error and are well suited to the simulation of high-quality factor circuits.

A statistical algorithm for 3D capacitance extraction

This letter deals with the problem of parasitic capacitance extraction in deep suhmicron layouts having general geometries. The presented extraction method is based on the statistical floating random walk algorithm. It employs a suitable spherical Greens function that, in a charge free region, relates the electrical field in the sphere center to the surface electrical potential.

Periodic Small Signal Analysis of a Wide Class of Type-II Phase Locked Loops Through an Exhaustive Variational Model

Phase-locked loops are important building blocks for several different applications. Modern design and implementation of these circuits is largely advantaged by a mixed analog/digital simulation approach since phase locked loops are stiff systems and a full analog representation is in general too large to simulate in reasonable time. Even though current algorithms, based on a mixed analog/digital representation, lead to models characterized by outstanding properties, they do not allow efficient simulations of important periodic and small signal features such as modulation/demodulation or noise effects. In this paper a novel, reliable and efficient method is proposed that overcomes those limitations and makes possible to evaluate both modulation/demodulation and noise effects in the widely adopted class of type-II phase-locked loop circuits based on a digital three-state phase-frequency detector.

Statistical method for the analysis of interconnects delay in submicrometer layouts

In deep-submicrometer layouts, the determination of the signal delay due to interconnects is a main aspect of the design. Usually, on-chip interconnects are modeled by a distributed resistance-capacitance (RC) line. Key aspects of the interconnect modeling are the extraction of parasitic capacitances and the determination of reduced lumped models suited for electrical simulation. This paper addresses both these aspects. The parasitic capacitance extraction problem of layouts is efficiently carried out by means of the floating random walk (FRW) algorithm. It is shown how the employment of the Monte Carlo integration jointly to an extended version of the FRW algorithm allows to directly synthesize an accurate reduced-order RC equivalent net. The new method can deal with very complex geometries in an efficient way and needs neither fracturing of the original layout into subregions nor discretization of interconnects.