Compressor unit for cryocooler and cryopump system

Abstract

A compressor unit includes a flow control valve controlling a flow rate of a bypass pipe according to a valve command signal, a compressor inverter, and a controller. A range of operation frequency values is limited to a first operation frequency interval from a lower limit value to a first value and a second operation frequency interval from a second value to an upper limit value. When a target flow rate is between a first discharge flow rate and a second discharge flow rate, the controller generates an inverter command signal such that the operation frequency is set to the second operation frequency interval, and generates the valve command signal such that the flow rate of the bypass pipe coincides with a differential flow rate obtained by subtracting the target flow rate from a discharge flow rate of a compressor body obtained by the inverter command signal.

What is claimed is: 
     
         1 . A compressor unit for a cryocooler, comprising:
 a compressor structure portion which includes
 a compressor body configured to compress a working gas and discharge the working gas into the cryocooler, 
 a compressor motor which has a variable operation frequency and is configured to operate the compressor body, 
 a high-pressure pipe which is connected to the compressor body such that the working gas is discharged from the compressor body through the high-pressure pipe, 
 a low-pressure pipe which is connected to the compressor body such that the working gas is sucked into the compressor body through the low-pressure pipe, 
 a bypass pipe which bypasses the compressor body and connects the high-pressure pipe to the low-pressure pipe, which allows working gas to flow from the high-pressure pipe to the low-pressure pipe bypassing the compressor body, and 
 a flow control valve which is provided in the bypass pipe to control a flow rate of the bypass pipe according to a valve command signal; 
   a compressor inverter configured to control an operation frequency of the compressor motor according to an inverter command signal; and   a compressor controller configured to generate the valve command signal and the inverter command signal such that the working gas is supplied from the compressor unit to the cryocooler at a target flow rate,   wherein a range of operation frequency values is limited to a first operation frequency interval from a lower limit value larger than zero to a first value and a second operation frequency interval from a second value to an upper limit value,
 wherein the second value is larger than the first value, 
 wherein the first value and the second value are defined such that a frequency interval from the first value to the second value includes at least one natural frequency for at least a portion of the compressor structure portion, and 
 wherein the lower limit value, the first value, the second value, and the upper limit value of the operation frequency correspond to a lower limit discharge flow rate, a first discharge flow rate, a second discharge flow rate, and an upper limit discharge flow rate of the compressor body, respectively, and 
   wherein, in a case where the target flow rate is between the first discharge flow rate and the second discharge flow rate, the compressor controller generates the inverter command signal such that the operation frequency is set to be in the second operation frequency interval, and generates the valve command signal such that the flow rate of the bypass pipe coincides with a differential flow rate obtained by subtracting the target flow rate from a discharge flow rate of the compressor body obtained according to the inverter command signal.   
     
     
         2 . The compressor unit according to  claim 1 ,
 wherein, in the case where the target flow rate is between the first discharge flow rate and the second discharge flow rate, the compressor controller generates the inverter command signal such that the operation frequency is the second value.   
     
     
         3 . The compressor unit according to  claim 1 ,
 wherein, in a case where the target flow rate is between the lower limit discharge flow rate and the first discharge flow rate, the compressor controller generates the inverter command signal such that the operation frequency is set to be in the first operation frequency interval and generates the valve command signal such that the flow control valve is closed, and   wherein, in a case where the target flow rate is between the second discharge flow rate and the upper limit discharge flow rate, the compressor controller generates the inverter command signal such that the operation frequency is set to be in the second operation frequency interval and determines the valve command signal such that the flow control valve is closed.   
     
     
         4 . The compressor unit according to  claim 1 ,
 wherein, in a case where the target flow rate is between zero and the lower limit discharge flow rate, the compressor controller generates the inverter command signal such that the operation frequency is the lower limit value, and generates the valve command signal such that the flow rate of the bypass pipe coincides with the differential flow rate.   
     
     
         5 . The compressor unit according to  claim 1 ,
 wherein the compressor controller performs a smoothing process on the valve command signal or the inverter command signal when the operation frequency is switched from the first value to the second value.   
     
     
         6 . A cryopump system comprising:
 a cryopump which includes a cryopanel and a cryocooler configured to cool the cryopanel;   a compressor unit having a compressor structure portion including
 a compressor body configured to compress a working gas and discharge the working gas into the cryocooler, 
 a compressor motor which has a variable operation frequency and is configured to operate the compressor body, 
 a high-pressure pipe which is connected to the compressor body such that the working gas is discharged from the compressor body though the high-pressure pipe, 
 a low-pressure pipe which is connected to the compressor body such that the working gas is sucked into the compressor body through the low-pressure pipe, 
 a bypass pipe which bypasses the compressor body and connects the high-pressure pipe to the low-pressure pipe, which allows working gas to flow from the high-pressure pipe to the low-pressure pipe bypassing the compressor body, and 
 a flow control valve which is provided in the bypass pipe to control a flow rate of the bypass pipe according to a valve command signal; 
   a compressor inverter configured to control an operation frequency of the compressor motor according to an inverter command signal; and   a controller configured to generate the valve command signal and the inverter command signal such that the working gas is supplied from the compressor unit to the cryocooler at a target flow rate,   wherein a range of operation frequency values is limited to a first operation frequency interval from a lower limit value larger than zero to a first value and a second operation frequency interval from a second value to an upper limit value,   wherein the second value is larger than the first value,   wherein the first value and the second value are defined such that a frequency interval from the first value to the second value includes at least one natural frequency for at least a portion of the compressor structure portion, and   wherein the lower limit value, the first value, the second value, and the upper limit value of the operation frequency correspond to a lower limit discharge flow rate, a first discharge flow rate, a second discharge flow rate, and an upper limit discharge flow rate of the compressor body, respectively, and   wherein, in a case where the target flow rate is between the first discharge flow rate and the second discharge flow rate, the controller generates the inverter command signal such that the operation frequency is set to be in the second operation frequency interval, and generates the valve command signal such that the flow rate of the bypass pipe coincides with a differential flow rate obtained by subtracting the target flow rate from a discharge flow rate of the compressor body obtained according to the inverter command signal.