Refrigerant system with multi-speed pulse width modulated compressor

Abstract

A refrigerant system is provided with a compressor having a motor that is operable at least at two distinct speeds. The pulse width modulation control is provided to cycle a compressor motor operation between its at least two speeds at a specific rate to exactly match thermal load demands in a conditioned space. The present invention reduces cycling and other efficiency losses as have been experienced in the prior art, as well as minimizes cost and may improve reliability. Also, the present invention can be utilized in conjunction with other known unloading techniques.

1 . A refrigerant system comprising:
 a compressor for compressing a refrigerant and delivering this refrigerant to a downstream condenser, refrigerant passing through said condenser, through an expansion device, through an evaporator, and returning from said evaporator to said compressor;   a motor for driving said compressor, said motor being operable at at least two speeds; and   a pulse width modulation control for said motor, said pulse width modulation control operating said motor between a higher speed and a lower speed at a certain cycling rate to vary the refrigerant system capacity.   
   
   
       2 . The refrigerant system as set forth in  claim 1 , wherein said motor has only two speeds, with said pulse width modulation control cycling said motor between a higher speed and a lower speed. 
   
   
       3 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system is also provided with an economizer function, and said economizer function being selectively actuated to assist in achieving a desired system capacity. 
   
   
       4 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system is also provided with an unloader function, and said unloader function being selectively actuated to assist in achieving a desired system capacity. 
   
   
       5 . The refrigerant system as set forth in  claim 1 , wherein said compressor is a scroll compressors. 
   
   
       6 . The refrigerant system as set forth in  claim 5 , wherein a flow control device is provided for controlling the amount of refrigerant passing to a back pressure chamber for holding orbiting and non-orbiting scroll members of said scroll compressor in contact with each other, and said flow control device being selectively and periodically closed to block flow of compressed fluid to the back pressure chamber to assist in achieving a desired system capacity. 
   
   
       7 . The refrigerant system as set forth in  claim 1 , wherein a suction modulation valve is placed on a suction line leading to said compressor, and is controlled to limit the amount of refrigerant reaching said compressor to assist in achieving a desired system capacity. 
   
   
       8 . The refrigerant system as set forth in  claim 1  wherein a cycling rate is adjustable. 
   
   
       9 . The refrigerant system as set forth in  claim 1  wherein the cycle time can vary from 1 second to 30 seconds. 
   
   
       10 . The refrigerant system as set forth in  claim 1  wherein the cycling rate is defined by at least one of reliability, temperature control, and efficiency considerations. 
   
   
       11 . The refrigerant system as set forth in  claim 1  wherein a time period at the lower speed is defined by lubrication consideration of the compressor elements. 
   
   
       12 . The refrigerant system as set forth in  claim 1 , wherein said compressor is selected from a set consisting of a screw compressor, a reciprocating compressor and a rotary compressor. 
   
   
       13 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system is one of an air-conditioning system, a heat pump system, a container refrigeration system, a tractor-trailer refrigeration system and a supermarket refrigeration system. 
   
   
       14 . The refrigerant system as set forth in  claim 1 , wherein said motor is positioned outside a compressor shell. 
   
   
       15 . The refrigerant system as set forth in  claim 1 , wherein said motor is positioned inside a compressor shell. 
   
   
       16 . The refrigerant system as set forth in  claim 1 , wherein said motor operation between a high and low speed is accomplished by solid state contactors. 
   
   
       17 . A method of operating a refrigerant system comprising the steps of:
 a) providing a compressor for compressing a refrigerant and delivering refrigerant to a downstream condenser, refrigerant passing through said condenser, through an expansion device, through an evaporator, and returning from said evaporator to said compressor;   providing a motor for driving said compressor, said motor being operable at least at two speeds; and   cycling said motor between a higher speed and a lower speed at a certain rate in a pulse width modulation manner to vary the refrigerant system capacity.   
   
   
       18 . The method as set forth in  claim 17 , wherein said motor has only two speeds, with said pulse width modulation control cycling said motor between a higher speed and a lower speed. 
   
   
       19 . The method as set forth in  claim 17 , wherein said refrigerant system is also provided with an economizer function, and said economizer function being selectively actuated to assist in achieving a desired system capacity. 
   
   
       20 . The method as set forth in  claim 17 , wherein said refrigerant system is also provided with an unloader function, and said unloader function being selectively actuated to assist in achieving a desired system capacity. 
   
   
       21 .- 32 . (canceled)