|
New methods of carrying out homeland security and antiterrorist operations call for the development of a new generation
of mechanically cooled, portable, battery powered infrared imagers, relying on micro-miniature Stirling cryogenic
coolers of rotary or linear types. Since split Stirling linearly driven micro-miniature cryogenic coolers have inherently
longer life spans, low vibration export and better aural stealth as compared to their rotary driven rivals, they are more
suitable for the above applications. The performance of such cryogenic coolers depends strongly on the efficacy of their
electronic drivers. In a traditional approach, the PWM power electronics produce the fixed frequency tonal driving
voltage/current, the magnitude of which is modulated via a PID control law so as to maintain the desired focal plane
array temperature. The disadvantage of such drivers is that they draw high ripple current from the system's power bus.
This results in the need for an oversized DC power supply (battery packs) and power electronic components, low
efficiency due to excessive conductive losses and high residual electromagnetic interference which in turn degrades the
performance of other systems connected to the same power bus. Without either an active line filter or large and heavy
passive filtering, other electronics can not be powered from the same power bus, unless they incorporate heavy filtering
at their inputs.
The authors present the results of a feasibility study towards developing a novel "pumping" driver consuming essentially
constant instant battery power/current without making use of an active or passive filter. In the tested setup, the driver
relies on a bidirectional controllable bridge, invertible with the driving frequency, and a fast regulated DC/DC converter
which maintains a constant level of current consumed from the DC power supply and thus operates in input current
control mode. From the experimental results, the steady-state power consumed by the linear compressor remains the
same as compared with the traditional sine wave driver, the voltage and current drawn from the battery pack is
essentially free of low frequency ripple (this without use of any kind of filtering) and the overall coefficient of
performance of the driver is in excess of 94% over the entire working range of supply voltages. Such a driver free of sine
forming PWM stage and have reduced power peaks in all power conversion components.
|
