Page 60 - Energize July 2022
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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



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