Modeling and Analysis with Induction Generators, 3rd Edition

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7

Power Electronics for

Interfacing Induction

Generators

7.1 SCOPE OF THIS CHAPTER

Power electronics is the branch of electronics that studies application systems rang-

ing from less than a few watts to more than 2 GW. These systems encompass the

entire eld of power engineering, from generation to transmission and distribution

of electricity and its industrial use, as well as transportation, storage systems, and

domestic services. The progress of power electronics has generally followed the

microelectronic device evolution and inuenced the current technological status of

machine drives. The amount of power produced by renewable energy devices like

photovoltaic (PV) cells and wind turbines varies signicantly on an hourly, daily,

and seasonal basis due to variations in the availability of the sun, the wind, and other

renewable resources. This variation means that sometimes power is not available

when it is required and sometimes there is excess power.

Figure 7.1 shows how power electronics interfaces energy sources with loads. The

variable output from renewable energy devices also means that power conditioning

and control equipment are required to transform this output into a form (voltage,

current, and frequency) that can be used by electrical appliances. This chapter will

present power electronic semiconductor devices and their requirements for inter-

facing with renewable energy systems: ac–dc, dc–dc, dc–ac, and ac–ac, conversion

topologies as they apply to the control of induction machines used for motoring and

generation purposes.

7.2 POWER SEMICONDUCTOR DEVICES

After the transistor was invented, the emergence of thyristor also called silicon-

controlled rectier (SCR), initiated the rst generation of power electronics. In the

1960s, inverter-grade thyristors enabled the introduction of force-commutated thy-

ristor inverters like the McMurray inverter, the McMurray-Bedford inverter, the

Verhoef inverter, the ac-switched inverter, and the dc-side commutated inverter.

Many other commutation techniques were discussed in the literature. This class of

inverters gradually faced obsolescence because of the advent of self-commutated gate

turn-off thyristors (GTOs) and improved bipolar transistors, ending the rst genera-

tion of power electronics by the middle of the 1970s.

Thyristors and GTOs continue to grow in power rating (most recently 6000V,

6000 A) for multimegawatt voltage-fed and current-fed converter applications (with