TABLE OF CONTENTS Nearly all systems in power electronics rely on feedback control systems for their operation. This chapter presents the basic analog analysis of such systems because, in this author's opinion, it offers a more intuitive understanding of their behavior than can be obtained from modern control theory with digital techniques.
Fig. 4.1 shows the simplest feedback control system. A command signal is received by a summing junction and compared to a feedback signal of opposite polarity. The difference signal is sent to an ampli-fier that produces the system output with a feedback signal derived from the amplifier output. Both the amplifier characteristic and the feedback characteristic are functions of frequency and are shown as G(s) and H(s), respectively.
The performance of such system can be derived from an equation that relates output to input. The equation is developed as follows:
e = ec ef
eo = e G(s)
ef = eo H(s)
eo = G(s) [ ec eo H(s)]
eo/ec = G(s)/[1 + G(s) H(s)] = A
where eo/ ec is the closed-loop system gain as a function of frequency.
If the feedback is disconnected from the summing junction, then A = G(s) H(s), the open-loop gain. Simple systems such as the one shown in Fig. 4.1 can be analyzed for stability and performance by an...
