Linear motor
First Claim
1. A method for driving and controlling the amplitude of the piston in a free piston vapor compressor wherein said piston reciprocates in a cylinder and wherein the vibrating system of piston, spring and the pressure of said vapor has a resonant frequency which varies with vapor pressure, said method using a linear brushless DC motor having at least one winding and comprising the steps of:
- electronically commutating said at least one winding from a DC supply to reciprocate said piston, with computations timed to drive said piston at the resonant frequency of said vibrating system, limiting the amount of current in said at least one winding by limiting the value of a parameter which determines current supply during commutation to a value which is a function of said resonant frequency.
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Accused Products
Abstract
The present invention provides an improved design of linear motor as well as an improved control strategy. The design allows for a shorted stator, where the armature magnets are controlled to reciprocate to a greater maximum displacement that for a equivalent conventional linear motor. The control strategy is such that a minimum of external sensors are required. The linear motor is driven at its resonant frequency ensuring optionally efficient operation. A determination of the maximum current is made based on a relationship with the resonant frequency and the evaporating temperature/pressure of the vapor entering the compressor. The current is then limited to control the maximum displacement to avoid damage.
77 Citations
13 Claims
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1. A method for driving and controlling the amplitude of the piston in a free piston vapor compressor wherein said piston reciprocates in a cylinder and wherein the vibrating system of piston, spring and the pressure of said vapor has a resonant frequency which varies with vapor pressure, said method using a linear brushless DC motor having at least one winding and comprising the steps of:
electronically commutating said at least one winding from a DC supply to reciprocate said piston, with computations timed to drive said piston at the resonant frequency of said vibrating system, limiting the amount of current in said at least one winding by limiting the value of a parameter which determines current supply during commutation to a value which is a function of said resonant frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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