Page 113 - Modern Control of DC-Based Power Systems

Small-Signal Analysis of Cascaded Systems 77

Figure 2.53 Bode plot of the identified output impedance of the source converter
compared to the analytic transfer function with the Wideband System Identification
technique.

2.7 SUMMARY
In this chapter a dynamic modeling of power converters in a cas-
caded arrangement based on small-signal properties was presented; this
helps drawing conclusions for DC distribution systems. The terminal
characteristics of tightly controlled power converters are an important fac-
tor for stability analysis and controller design. They were modeled taking
into account the conventional averaging approach for DC DC conver-
ters, which requires negligible current ripple and takes basically the DC
term of the Fourier series [11].
Furthermore, the authors in [15] investigated the terminal characteris-
tics such as the impedance for different converters looking at two aspects.
The first aspect is that the control loop (VMC or PCMC) changes the
input and output impedances of the converters, therefore the closed-loop
impedances should be used. The second aspect is that the loading effect
of the load is overlooked as it alters the dynamics of the upstream con-
verter. The influences of different load models were presented.