Abstract: A direct current powered, linear resonant cryocooler having a compressor in which the piston is reciprocated by a linear motor at substantially resonant frequency and the length of stroke of the piston is varied as a direct function of cryocooler temperature. There are two control loops, a temperature control loop and a voltage control loop which is independent of the temperature control loop. In the temperature control loop, temperature is sensed at the cryocooler or expander and the temperature signal is compared with a reference temperature signal to produce a temperature error signal or voltage. The voltage control loop controls motor voltage. As input to the voltage control loop, the linear motor voltage is fed back and compared with the temperature error voltage V.sub.TE to produce a voltage level signal V.sub.L in the input of the voltage control loop, representative of the correction required to obtain and then to maintain the cryocooler temperature represented by the reference temperature voltage.

Abstract: A refrigeration control apparatus especially adapted for use in conjunction with cryogenic coolers includes a brushless variable speed drive motor for powering a mechanical cooler-compressor and electronic control circuitry coupled to the motor allowing motor speed and hence cooling rate to be responsive to changes in the temperature of the volume sought to be cooled. A signal corresponding to sensed temperature is compared to a reference signal derived from motor speed. The difference therebetween used to vary the duty cycle of a high frequency pulse train. The pulse train is used to modulate the drive current applied to the motor through pulse position switching circuitry to vary the speed of the drive motor. High and low motor speed limits are provided along with sensor failure protection circuitry to insure continuous motor operation between chosen limits.

Abstract: A control system for controlling a direct current powered motor in which the direct current voltage, which may not be constant, is reversibly commutated across the coil or winding of the motor during the predetermined commutation time intervals and chopped at high frequency during each commutation time interval by a variable duty cycle, pulse width modulated voltage, in which the width of each voltage pulse, determined by a reference voltage, is varied as an inverse function of the magnitude of the direct current voltage which exists during each voltage pulse interval.