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Electromagnetic Compatibility in Power Electronics von Costa, Francois (eBook)

  • Erscheinungsdatum: 17.01.2014
  • Verlag: Wiley-ISTE
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Electromagnetic Compatibility in Power Electronics

Scientists largely attribute the recent deterioration of the electromagnetic environment to power electronics. This realization has spurred the study of methodical approaches to electromagnetic compatibility designs as explored in this text. The book addresses major challenges, such as handling numerous parameters vital to predicting electro magnetic effects and achieving compliance with line-harmonics norms, while proposing potential solutions.

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 290
    Erscheinungsdatum: 17.01.2014
    Sprache: Englisch
    ISBN: 9781118863077
    Verlag: Wiley-ISTE
    Größe: 7534 kBytes
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Electromagnetic Compatibility in Power Electronics

Chapter 2

Fundamental Principles

2.1. Sources of noise: the switching cell and its control

The static conversion of electrical energy (switch-mode power supply, inverter, rectifier, etc.) is based on the principle of the switching cell: it is the connection of two switches, which enables the management of energy between an input source of voltage and an output source of current ( Figure 2.1 ). The main switch is controlled by a periodic modulation function fm ( t ), with a binary value and a variable cyclic ratio ( α = ton / Td ), which regulates the transfer of power according to the value of this cyclic ratio α . The notion of source must be understood in the sense that it is capable of imposing a near-constant quantity (of voltage or current) at the time-scale of the switching period. This characteristic is generally due to the presence of reactive components (input capacitor Ce or output smoothing inductance).

Thus, it is noteworthy to see that the external parameters of the switching cell ( E and Io ) are constants, whereas the internal parameters ( ie and vk ) are variables, regulated by the function fm ( t ).

Figure 2.1 . Switching cell and its corresponding wave shapes

It is possible to express the variable voltages and currents of the switching cell as a function of those that are constant:

[2.1]

[2.2]

From these relations, we deduce the law of converted power control:

[2.3]

Thus, by this principle, all static conversion functions can be undertaken. We sometimes add a transformer to the structure when a galvanic insulation is required.
2.1.1. Origin of conducted and radiated perturbations in static converters

The electrical quantities are very much variable in the switching cell. Indeed, in order to reduce losses during commutation (simultaneous presence of the voltage and the current in the switches), it is essential that the commutations be very quick. Currently, the size of switching gradients is on the scale of 100 - 1,000 A/μs for dI / dt and of 5 - 50 kV/μs for dV / dt .

To illustrate, Figure 2.2 outlines these phenomena in a chopper connected to a line impedance stabilization network (LISN): in the mesh surrounding the hatched area, the current Ie undergoes very quick high-frequency variations. The resulting loop connects to a magnetic radiative dipole: the input decoupling capacitor Ce , limited in its operation due to its imperfections (resistance and inductance in series lp), is generally not sufficient to prevent the propagation of an impulsive parasitic current Ip onto the network.

Figure 2.2 . Origin and coupling mode of electromagnetic perturbations of a static converter

Moreover, the conductors shown in grey bold lines in Figure 2.2 endure the strong variations of the voltage VK . They constitute an electric radiative dipole and can transmit impulsive currents Imc to the earth via the parasitic capacitance denoted by Cp between the device and the earth.
2.2. Modeling

2.2.1. Simple model of the switching cell

We can now provide a model of the switching cell, representing the effects of perturbation [COS 93]. The input current of the cell is presented as a current generator creating the parasitic differential-mode current by means of coupling through a common impedance (input capacitor). The voltage of the switch is presented as a voltage generator generating the common-mode current via capacitive couplings. The switching cell can then be represented by one of the two models in Figure 2.3 , where the sources of current Ie/em

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