ABSTRACT

At the end of this chapter you should be able to: • appreciate typical applications of the maximum power transfer theorem

• appreciate the conditions for maximum power transfer in a.c. networks

• apply the maximum power transfer theorems to a.c. networks

• appreciate applications and advantages of impedance matching in a.c. networks

• perform calculations involving matching transformers for impedance matching in a.c. networks

35.1 Maximum power transfer theorems

As mentioned in Section 13.9 on page 152, the maximum power transfer theoremhas applications in stereo amplifier design, where it is necessary to maximise power delivered to speakers, and in electric vehicle design, where it is necessary to maximise power delivered to drive a motor. A network that contains linear impedances and one

or more voltage or current sources can be reduced to a Thévenin equivalent circuit as shown in Chapter 33.When a load is connected to the terminals of this equivalent circuit, power is transferred from the source to the load. A Thévenin equivalent circuit is shown in Figure 35.1

with source internal impedance, z= (r + jx) and complex load Z = (R+ jX).