Design and Implementation of On-board Electrical Power ... - OUFTI-1

Figure 5.21: Measured Bode diagram of Z in (f).However, some values of L and C used on the “breadboard” prototypes were modifiedwhile designing the engineering model (the engineering model uses the values given in thisdocument). The plot measured on the breadboard model can be adapted to the situation ofthe engineering model.Adaptation to new convertersThe shape of a Z in (s) curve is composed of three main parts:1. At low frequency, it is nearly constant. This part is essentially influenced by the loadR.2. At mid frequencies, the curve has a slope of -20dB/decade. This corresponds to theinfluence of C.3. At high frequencies, the curve has a slope of +20dB/decade. There L has the moreinfluence.The impedance of a circuit composed of an inductor in series with a condensator anda resistor that are in parallel would have a similar shape (Z L (s) = sL, Z C (s) = 1sC , andZ R (s) = R, where Z L (s) is the impedance of an inductor with a inductance L, Z C (s) theimpedance of a capacitor with a capacitance C, and Z R (s) the impedance of a resistor witha resistance R). In the case of a converter, the shape of Z in (s) is determined by R, L, andC seen from the input through the converter. The observed curve is in fact αL + (βR//γC)with α, β, and γ depending on the characteristics of the converter (Fig. 5.26).74