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Just a word to explain what electrical interconnections in EMC and Power Electronics applications are. It is a set of metallic conductors that link electronic components, i.e. to allow the electric current to flow from one component to the others. Unfortunately, the electromagnetic behavior of such wiring conductors is not an ideal short-circuit, which means that there is a voltage drop between two different points of the interconnection. In the device or system under consideration, some undesirable effects crop up, like extra-losses, overvoltages on components, dissymmetry on currents flowing in parallel paths, common-mode couplings, etc.
All these phenomena degrade the device performances and need to be kept under control by designers during the development of an electronic product; in other words, parasitic effects (resistive,
inductive and capacitive) of electrical interconnections need more and more to be taken into account by ad-hoc simulations. Flux PEEC environment (integration of previously InCa3D software) is the new software covering such necessity.
Examples of “cabling” systems
The figure below lists some examples of devices where connecting conductors are significant and where Flux PEEC simulations are useful: they are positioned on a two-dimensional graph with working frequency and power on the abscissa and ordinate axes, respectively. At low frequency (hundreds of Hz), systems can drive higher power, while energy quantities are lower inside devices that work at high frequencies (hundreds of kHz).
Even though the borderline is really ephemeral, it is interesting to organize the devices into two families because the technical points and issues the designer faces are not the same. The first group, which we can call Electrical Connections, includes elements like cables, distribution bars, switchboards, busbars and grounding systems where skin and proximity effects have a strong impact on device performance. Parasitic phenomena to be assessed are essentially resistive and inductive, whereas physical quantities to control include current distributions, power losses and electrodynamic forces.
The aim of this article is mainly focused on the second family, namely EMC – Power Electronics, since the new version of the Flux PEEC software provides a key functionality for the analysis of devices like power modules, power converters and adjustable speed drives: computation of the capacitive couplings between conductors.
In fact, when working frequencies are higher and harmonic distortions (tens of MHz) need to be assessed, the effects of parasitic capacitances are no longer hidden by the inductive behavior of the interconnection, but they can become the main cause of malfunction.
“Common-mode currents, flowing for example between the power/ground conductors and the heat sink, are one of the main reasons behind EMC failures.”
Benefits of the new Flux PEEC release
Flux 2018 PEEC environment opens the door to these investigations, since it provides all the elements of the capacitance matrix between the conductors, possibly separated by dielectric substrates. The power electronics designer can easily find out where most critical parasitic capacitances are and judge – in the early stages of product development – whether or not risks are acceptable.
Once the capacitance matrix is obtained, the Flux PEEC user can – in the same software environment, thus cutting down working time – build and solve the global models composed by these capacitances and the resistive-inductive behavior of the structure. Several interesting results are produced by this RLC computation. The so-called “Conductor Impedances” application provides the engineer with a feature to plot 2D curves of the impedances as a function of frequency and consequently to reveal the values of the system’s electrical resonances. This analysis allows the engineer to check whether critical harmonics of the switching signals are in this band and, if necessary, to adjust the design to shift them.
To go into greater depth on the study of harmonic distortions, time-domain simulations are sometimes necessary: within circuit-level tools, the functional scheme of the power module or converter is thus supplemented by the parasitic behaviors of the interconnections. Flux PEEC also fulfills this need, since it has the ability to extract accurate equivalent RLC circuits in the most common standard languages (SPICE, VHDL-AMS). This enables the power electronics designer to evaluate the amplitude of the overvoltages that can damage the switching components or cause premature aging.
The other Flux PEEC application, namely “Supplied Conductors”, is historically dedicated to – amongst other things – the study of current distribution flowing inside conductors. Since global RLC models are developed in the new version, this Flux PEEC application also provides the user with the value of the current inside all the parasitic capacitances for each frequency.
These currents, flowing between the power/ground conductors and the heat sink for example, are the origin of common-mode noise which is often difficult to investigate by measurement and which is one of the main reasons behind EMC failures during final qualification tests of power electronics devices. Being able to explore such behaviors by simulation is a great benefit: it reduces
development time for the product and makes it possible to respect time-to-market constraints.
A post by Dr. Enrico Vialardi – Flux PEEC Expert – Altair