Page 60 - Energize July 2022
P. 60
TECHNICAL
Linear generators: A new standby
generation option
Today’s mechanically driven generators are rotating machines and all mechanical energy
sources are rotational. By comparison, a linear generator is an electromechanical device
which converts linear motion (i.e., movement along a straight line) into electricity using
chemical or thermal energy.
by Mike Rycroft, Energize
state-of-the-art linear generator uses a low temperature flexible, and dispatchable onsite power generation can be uniquely
reaction of air and fuel to drive magnets through copper delivered by linear generators.
c
A oils to efficiently produce electricity. With incorporation
of adaptive control software, a linear generator can reach high Linear internal combustion powered generators have several
efficiency levels, near-zero NOx emissions, full dispatchability, advantages over rotary generators of the same capacity.
and seamless switching between fuels. 3 • Lower size and weight for the same output
Gas-, steam- and water-driven turbines used to generate • Fewer machinery parts
electricity deliver energy by means of a rotating shaft. • Simpler generator construction
The generator consists of a rotating rotor and a stationary • Lower fuel consumption and higher efficiency
stator, and relative movement through the rotor and stator • Less pollution
fields produces electricity. The rotating generator provides • Fuel flexibility without changes to components
a convenient means of generating a continuous periodic
waveform of fixed shape and constant frequency, in generally a Linear alternators are typically driven by wave energy converters,
pure sine wave form. free piston engines, and linear sterling engines. This article will focus
Internal combustion or reciprocating engines, however, on the free piston driven version, which is the most common fuel-
deliver energy in a linear motion, which is converted to rotation driven version, and the term linear generator will be used to refer to
by means of crankshafts and flywheels. This process is inefficient a combination of free piston engines (FPE) and linear alternator.
and requires complex machinery to accomplish. An ideal
system would use linear power directly, an idea which has been The linear alternator
pursued for decades. Modern materials such as high grade Most of the research into linear alternators has come from the
permanent magnets are now making this goal achievable. wave energy sector. A simplified layout is shown in Figure 1.
The concept of the linear generator follows on that of the A linear alternator consists of two parts, the fixed part known
linear motor, and the idea has been pursued extensively in the as the stator, and the internal movable part, known variously as
field of wave energy converters (WEC) with numerous designs the slider, translator, oscillator or mover. For the purposes of this
emerging. Recent developments of internal combustion free article, the moveable part will be referred to as the rotor. The rotor
piston engines (FPE) and the availability of advanced materials contains the device that generates the magnetic field, in this case
and control technologies has made the fuel-driven linear an assembly of permanent magnets, while the stator contains the
generator a possibility, and several models have appeared on coils that collect the electrical energy.
the market. This all makes the linear generator a candidate
for small- to medium-sized standby generators. Recent
1
developments in the automobile industry have produced free
piston linear generators intended for use with hybrid electric
vehicles (EVs).
With the prospect of tapping renewable biogas and green
hydrogen in the future, linear generators can significantly
reduce carbon and costs now, while serving as a transition
from natural gas to a permanent source of net zero carbon
and reliable electricity. The extraordinary value of clean, fuel- Figure 1: Cylindrical linear alternator
energize | July 2022 | 58