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Reluctance Electric Machines
An Introduction
1.1Electric Machines: Why and Where?
Electric machines provide the conversion of electric energy (power) into mechanical energy (power) in motor operation, and vice versa in generating operation. This dual energy conversion presupposes energy storage in the form of magnetic energy located mainly in the airgap between the stator (fixed) and rotor (rotating) parts and in the permanent magnets (if any).
Energy is the capacity of a conservative system to produce mechanical (useful) work. As all we do in industry is, in fact, temperature and motion control, we may reduce it to energy control for better productivity and energy savings for a given variable useful output.
The main forms of energy are mechanical (kinetic and potential), thermal, electromagnetic (and electrostatic), and electrochemical.
According to the law of energy conservation, energy may not be created or disappear but only converted from one form to another. In addition, each form of energy has its own fundamental laws that govern its conversion and control, all discovered experimentally over the last three centuries.
Energy conversion starts with a primary source:
ā¢Fossil fuels (coal, gas, petroleum, nuclear, waste)
ā¢Solar thermal irradiation (1 kW/m2, average)
ā¢Solar photovoltaic source
ā¢Wind (solar, ultimately) source
ā¢Geothermal source
ā¢Hydro (potential or kinetic) sources: potential (from water dams) and kinetic (from rivers, marine currents, and waves)
In the process of energy conversion, electric machines are used to produce electric power, which is very flexible in transport and rather clean, and allows for fast digital control. Only in solar photovoltaic energy conversion (less than 1% of total) are electric machines not involved.
Electric machines are ubiquitous: there is one in every digital watch; three (the loudspeaker, microphone, and ring actuator) in a cellular phone; tens in any house (for various appliances) and in automobiles; and hundreds on trains, streetcars, subway systems, ships, aircraft, and space missions, not to mention most industrial processes that imply motion control to manufacture all the objects that make for our material prosperity.
So far, the more electricity (installed power) used per capita (Norway leads the way), the higher the material living standard. Environmental concerns are shifting this trend toward an optimal (limited) installed electric power (kW/person) in power plants per citizen, which, through distributed systems that make use ...
