Patent Publication Number: US-2021180598-A1

Title: Method of improved control for variable volume ratio valve

Description:
FIELD 
     This disclosure is directed to methods and systems for controlling valves governing the volume ratio of a variable volume ratio compressor. Particularly, this disclosure is directed to controlling the volume ratio of a compressor based on compressor mass flow, determined through inputs such as suction density and compressor speed. 
     BACKGROUND 
     Compressors can incorporate hardware allowing the volume ratio of the compressor to be adjusted. Changing the volume ratio of a compressor affects the conditions at the discharge of the compressor. Changes to the volume ratio can affect compressor performance under partial load conditions, increasing or decreasing the efficiency of the compressor at partial and full loads depending on whether the volume ratio is properly selected for a set of operating conditions of the compressor. 
     SUMMARY 
     This disclosure is directed to methods and systems for controlling valves governing the volume ratio of a variable volume ratio compressor. Particularly, this disclosure is directed to controlling the volume ratio of a compressor based on compressor mass flow, determined through inputs such as suction density and compressor speed. 
     Variable volume ratio compressors allow the volume ratio to be changed between at least two settings, which can improve matching of compressor discharge conditions to pressure conditions at a condenser of a refrigerant circuit that includes the compressor so as to increase efficiency. 
     Under some conditions, for example when the compressor is operating close to the switching conditions, automated switching of volume ratios may occur at high frequencies. Such high-frequency switching could create additional wear on the variable volume ratio system components. Delay periods may be incorporated into determining and implementing changes to the volume ratio, providing more consistent operation over time and reducing potentially excessive changes in the volume ratio of the compressor. 
     In an embodiment, a compressor system includes a variable volume ratio compressor configured to be operated at one of a plurality of different volume ratios and having a suction. The compressor system also includes a controller. The controller is configured to obtain a speed of operation of the variable volume ratio compressor and a refrigerant density at the suction of the variable volume ratio compressor. The controller is also configured to determine a switching parameter based on the speed of operation and the refrigerant density. The controller is further configured to determine whether to change a volume ratio of the variable volume ratio compressor based on a switching condition and the switching parameter. When the controller determines that the volume ratio is to be changed, the controller directs a change in the volume ratio that the variable volume ratio compressor is operated at. 
     In an embodiment, the plurality of different volume ratios is two different volume ratios. 
     In an embodiment, the compressor system includes one or more sensors located at the suction of the variable volume ratio compressor, and the controller obtains the refrigerant density based on outputs from the one or more sensors. 
     In an embodiment, the outputs from the one or more sensors include a suction pressure and a suction temperature. 
     In an embodiment, the switching parameter determined by the controller is a product of the speed of operation and the refrigerant density. 
     In an embodiment, the switching condition is a linear function of the speed of operation and the refrigerant density. 
     In an embodiment, the compressor system includes a piston, a first valve, and a second valve. The first valve is configured to communicate the piston with a first pressure, the second valve is configured to communicate the piston with a second pressure, different than the first pressure, and the piston is configured to be positioned by a received pressure. In an embodiment, the first pressure is a pressure at the suction of the variable volume ratio compressor and the second pressure is a pressure at an intermediate point of the variable volume ratio compressor. In an embodiment, the controller directs the change in the volume ratio that the variable volume ratio compressor is operated at by directing each of the first valve and the second valve to change positions. 
     A method embodiment for controlling a variable volume ratio compressor includes obtaining a suction density and an operating speed of the variable volume ratio compressor. The method further includes determining a switching parameter based on the suction density and the operation speed. The method also includes determining whether to change a volume ratio of the variable volume ratio compressor, and changing the volume ratio of the variable volume ratio compressor when it is determined to that the volume ratio of the variable volume ratio compressor is to be changed. In an embodiment, the switching parameter is a function of a suction density of the variable-volume ratio compressor and an operation speed of the compressor. 
     In an embodiment, determining the switching parameter includes determining the switching parameter at a first time, waiting a switching parameter delay period, and determining the switching parameter at a second time, and determining whether to change the volume ratio of the variable volume ratio compressor is based on the switching parameter determined at the second time. In an embodiment, the switching parameter delay period is approximately five (5) minutes. 
     In an embodiment, the method includes waiting a volume ratio change delay period after changing a volume ratio of the compressor. In an embodiment, the volume ratio change delay period is approximately fifteen (15) minutes. 
     In an embodiment, the switching parameter is a product of the suction density and the operating speed of the variable volume ratio compressor. 
     In an embodiment, the switching condition is a linear function of the product of the suction density and the operating speed of the variable volume compressor. 
     In an embodiment, changing the volume ratio of the variable volume ratio compressor includes switching the variable volume ratio compressor from a first volume ratio to a second volume ratio by changing the position of each of a first and a second valve, where the first valve is in fluid communication with a first pressure and the second valve is in fluid communication with a second pressure, different from the first pressure. In an embodiment, the first pressure is a suction pressure of the variable volume ratio compressor, and the second pressure is an intermediate pressure within the variable volume ratio compressor. In an embodiment, the first valve and the second valve are configured to provide one of either the first pressure or the second pressure to a piston within the variable volume ratio compressor. 
    
    
     
       DRAWINGS 
         FIG. 1  shows a compressor system and a refrigerant circuit according to an embodiment. 
         FIG. 2  shows a flowchart of a method for controlling a compressor system according to an embodiment. 
         FIG. 3  shows a flowchart of an embodiment for controlling a compressor system. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is directed to methods and systems for controlling valves governing the volume ratio of a variable volume ratio compressor. Particularly, this disclosure is directed to controlling the volume ratio of a compressor based on compressor suction density and speed. 
       FIG. 1  shows a compressor system  100  according to an embodiment. Compressor system  100  includes variable-volume compressor  102 , one or more sensors  104  at or near suction  108  of compressor  102 , and controller  106 . Compressor  102  is incorporated into a refrigerant circuit including condenser  110 , expansion device  112 , and evaporator  114 . In an embodiment, controller  106  is operatively connected to solenoid valves  116 ,  118 , that control whether pressure from compressor suction  108  or intermediate point  120  act on piston  122  of compressor  102  to adjust the volume ratio of compressor  102 . 
     Compressor  102  is a variable volume compressor configured to be operated at a plurality of different volume ratios. The variable volume ratio compressor  102  is operated at a volume ratio that may be determined by controller  106 . The volume ratio may be changed by a variable volume ratio system. In an embodiment, compressor  102  is configured to be operated at two different volume ratios. In an embodiment, compressor  102  switches between the two volume ratios by movement of piston  122 . In an embodiment, piston  122  is controlled by varying the pressure applied to the piston  122  between either a suction pressure of the compressor as suction  108  or an intermediate oil pressure at an intermediate point  120  within the compressor. While the embodiment shown in  FIG. 1  is directed to piston  122  controlled by application of suction or intermediate pressure, it is appreciated that other variable volume ratio systems of compressors may be used. In an embodiment, compressor  102  is configured to change between different volume ratios by operation of a slide valve. In an embodiment, the volume ratio of compressor  102  is changed by operation of a stepper motor. In an embodiment, the volume ratio of compressor  102  is continuously variable across a range of volume ratio states. 
     The one or more sensors  104  are configured to obtain the density of refrigerant at the suction  108  of compressor  102 , alone or in combination with controller  106 . The one or more sensors  104  may be located at or near suction  108  of compressor  102 . 
     Controller  106  is configured to determine a switching parameter based on the density of refrigerant at suction  108  and the speed at which compressor  102  is operated. Controller  106  may obtain the density of the refrigerant, for example, from the one or more sensors  104 , or by determining the suction density from values reported by the one or more sensors  104 . The suction density is a density of the refrigerant at the suction  108  of compressor  102 . Controller  106  may obtain the compressor speed from a sensor included in compressor  102 , or from a controller directing the operation of compressor  102 . Controller  106  may be configured to determine the switching parameter multiple times, implement delays between determination of the switching parameter, implement delays between changing the volume ratio of the compressor and determining the switching parameter, or other such operations affecting the frequency at which volume ratio changes may be performed. The switching parameter may be a product of the suction density and the speed of compressor  102 . 
     Controller  106  is further configured to determine whether to change a volume ratio of compressor  102  based on the switching parameter and the switching condition. The switching condition may be, for example, a pressure ratio criterion. The pressure ratio criterion may provide a threshold value used to determine whether to switch the volume ratio of compressor  102 . The pressure ratio criteria may be specific to components of the compressor system  100 , such as compressor  102 , and the refrigerant used in the refrigeration circuit of the compressor system  100 . In an embodiment, the pressure ratio criterion is a linear function of the product of the suction density and the compressor speed. The switching parameter may be compared to the switching condition at controller  106 , and whether to change the volume ratio of the compressor  102  may be determined via that comparison. 
     Controller  106  is further configured to direct compressor  102  to change a volume ratio. Controller  106  may be configured to direct compressor  102  to change the volume ratio based on the switching parameter and the switching condition. In an embodiment, controller  106  is operatively connected to a first solenoid valve  116  and a second solenoid valve  118  and configured to direct their operation. The first solenoid valve  116  may be a valve in fluid communication with the suction of the compressor and is capable of applying the pressure at suction  108  of compressor  102  to the piston  122  of compressor  102 . The second solenoid valve  118  may be a valve in fluid communication with an intermediate point  120  within compressor  102 , and capable of providing the pressure at that intermediate point  120  to the piston  122 . The pressure at suction  108  or intermediate point  118  drive the piston to a particular position, changing the volume ratio of the compressor  102 . The controller  106  may switch the first solenoid valve  116  to a closed position and the second solenoid valve  118  to an open position, or vice versa, to switch the compressor  102  between two different volume ratios. 
     Compressor  102  may be included in a refrigerant circuit including condenser  110 , expansion device  112 , and evaporator  114 . Refrigerant compressed and discharged by compressor  102  may be directed to condenser  110 , then from condenser  110  to expansion device  112 . Expansion device  112  is a device configured to expand and lower a pressure of a fluid, such as an expansion valve, an orifice, or the like. Refrigerant expanded at expansion device  112  passes to evaporator  114 , then returns to compressor  102  at compressor suction  108 . The refrigerant circuit may use any refrigerant, such as, for example, refrigerant R134(a), refrigerant R1234ze(E), or any other suitable refrigerant. 
       FIG. 2  shows a flowchart of a method  200  for determining when to switch a volume ratio of a compressor according to an embodiment. Method  200  includes obtaining a suction density and a compressor speed  202 , determining a switching parameter based on compressor speed and suction density at  204 , determining whether to switch a volume ratio of the compressor based on the switching parameter and a switching condition  206 , and changing the volume ratio of the compressor when it is determined that the volume ratio of the compressor is to be switched  208 . 
     A suction density and the compressor speed are obtained  202 . The suction density is the density of the refrigerant at the suction port of the compressor. The suction density may be obtained from one or more sensors located at or near a suction port of the compressor. The suction density may be measured directly, or computed from the outputs of the one or more sensors. In an embodiment, the suction density is computed based on a suction pressure and a suction temperature measured by sensors, and the particular refrigerant used with the compressor. For each refrigerant, the suction pressure and temperature are related to the suction density by a function specific to that refrigerant, for example due to differences in the properties of the refrigerant and its behavior as a gas. The compressor speed may be obtained from a controller of the compressor, a drive of the compressor such as a variable-frequency drive, or measured at the compressor. 
     The switching parameter is determined based on the compressor speed and the suction density  204 . The switching parameter is a function of both the compressor speed and the suction density. In an embodiment, the switching parameter is a product of the compressor speed and the suction density. In an embodiment, the switching parameter is a mass flow rate. The mass flow rate may be determined based on the volume flow rate of the compressor and the suction density. 
     The switching parameter and a switching condition are used to determine whether to change the volume ratio of the compressor  206 . The switching condition may be, for example, a pressure ratio criterion. The pressure ratio criterion may provide a threshold value used to determine whether to switch the volume ratio of compressor. The pressure ratio criteria may be specific to the compressor, and the refrigerant used in the refrigeration circuit including the compressor. The pressure ratio criteria may be a function of the mass flow rate through the compressor. In an embodiment, the pressure ratio criterion is a linear function of the product of the suction density and the compressor speed. In an embodiment, the pressure ratio criterion is a linear function of the mass flow rate. In an embodiment, the mass flow rate is the product of the suction density and the compressor speed. In an embodiment, the mass flow rate is a product of the suction density and a volume flow rate. The switching parameter may be compared to the switching condition to determine whether to change the volume ratio of the compressor  206  via that comparison. The method  200  may be used with a variety of refrigerants in variable volume ratio compressor systems. In an embodiment, the refrigerant is refrigerant 134a (R134a). In an embodiment, the refrigerant is refrigerant 513A (R513A). In an embodiment, the refrigerant is refrigerant 1234ze (R1234ze). Parameters of the function such as constants may be determined by testing compressor efficiency over states of a variable volume ratio setting of the compressor across the operating map of a particular compressor. 
     The volume ratio of the compressor is changed at  208  when it is determined at  206  that the volume ratio is to be changed. The volume ratio can be changed from a first volume ratio to a second volume ratio. In an embodiment, the first and second volume ratios are two of multiple volume ratios. In an embodiment, the compressor switches from one of two volume ratios to the other of the two volume ratios. In an embodiment, the switching of compressor volume ratios occurs by operating one or more valves to change a source of pressure applied to a piston of the variable volume ratio system included in the compressor. In an embodiment, the source of pressure may be switched between an intermediate oil pressure of the compressor and a suction pressure of the compressor. In an embodiment, the volume ratio of the compressor is changed at  208 , for example by operation of a stepper motor or by operation of a slide valve. 
     In compressor operations, the method  200  may further include, for example, delays to avoid constant switching and to confirm when to perform switching of the volume ratio. An example of such compressor operations is provided in  FIG. 3 . 
       FIG. 3  shows a flowchart of an example method  300  for controlling a compressor system according to an embodiment. In the method  300  shown in  FIG. 3 , the switching parameter is determined a first time  302 . A delay period is allowed to pass  304 . The switching parameter is determined a second time  306 . It is determined, using the switching parameter determined at  306 , whether the volume ratio of the compressor is to be changed  308 . When it is determined at  308  that the volume ratio of the compressor is to be changed, the volume ratio of the compressor is changed  310 . After the volume ratio of the compressor is changed at  310 , a second delay period is allowed to pass  312  before returning to  302  or  304  and iterating method  300 . 
     A switching parameter is determined at  302 . The switching parameter may be a function of the compressor suction density and the compressor speed. The suction density and compressor speed may be obtained according to  202  described above and shown in  FIG. 2 . The switching parameter may be determined according to  204  described above and shown in  FIG. 2 . 
     After the switching parameter is determined at  302 , a switching parameter delay period is allowed to pass  304 . The switching parameter delay period is a period between a first determination of the switching parameter at  302  and a second determination of the switching parameter at  306 . The switching parameter delay period of  304  may be used to prevent excessive switching frequencies, for example by reducing the number of switching events triggered by outlier results or transient conditions (e.g. erroneous sensor readings, spikes in temperature or pressure, or the like) for suction density. In an embodiment, the switching parameter delay of  304  is a period of time for an accumulating value to meet a target, for example integrating the compressor speed and suction density over time and ending the switching parameter delay period of  304  when that value meets a threshold. In an embodiment, the switching parameter delay period of  304  is approximately five (5) minutes. 
     Once the switching parameter delay period has passed  304 , the switching parameter is determined a second time  306 . The switching parameter is determined in the same manner as at  302 , including obtaining the suction density and compressor speed according to  202  and determining the switching parameter according to  204 . 
     The second determination of the switching parameter at  306  may be used to determine whether the volume ratio of the compressor is to be changed  308 . Determining whether the volume ratio of the compressor is to be changed at  308  may be performed according to  206  described above and shown in  FIG. 2 , comparing the switching parameter as obtained at  306  to the switching condition. 
     When it is determined that the volume ratio of the compressor is to be changed at  308 , the volume ratio of the compressor is changed at  310 . The volume ratio of the compressor may be changed at  310  according to  208  described above and shown in  FIG. 2 . 
     Following the changing of the volume ratio at  310 , the method  300  includes allowing a volume ratio change delay period to pass  312 . In an embodiment, the volume ratio change delay period of  312  is a period between the implementation of the change to the volume ratio at  310  and determining the switching parameter for a first time at  302  in a subsequent iteration of method  300 , for example, when the compressor speed and suction density values are obtained continuously. In an embodiment, the volume ratio change delay period may be variable based on, for example, the number of times the volume ratio has been changed according to  310  within a predefined time period. In an embodiment, the volume ratio change delay period is within a range from at or about one (1) minute to at or about one (1) hour. In an embodiment, the volume ratio change delay period of  312  is approximately fifteen (15) minutes 
     Aspects: 
     It is understood that any of aspects 1-9 may be combined with any of aspects 10-19. 
     Aspect 1. A compressor system, comprising: 
     a variable volume ratio compressor configured to be operated at one of a plurality of different volume ratios and having a suction; and 
     a controller configured to: 
     obtain a speed of operation of the variable volume ratio compressor and a refrigerant density at the suction of the variable volume ratio compressor;
 
determine a switching parameter based on the speed of operation and the refrigerant density;
 
determine whether to change a volume ratio of the variable volume ratio compressor based on a switching condition and the switching parameter; and
 
     when it is determined to change the volume ratio, direct a change in the volume ratio that the variable volume ratio compressor is operated at. 
     Aspect 2. The compressor system according to aspect 1, wherein the plurality of different volume ratios is two different volume ratios. 
     Aspect 3. The compressor system according to any of aspects 1-2, further comprising one or more sensors located at the suction of the variable volume ratio compressor, and wherein the controller obtains the refrigerant density based on outputs from the one or more sensors. 
     Aspect 4. The compressor system according to aspects 3, wherein the outputs from the one or more sensors include a suction pressure and a suction temperature. 
     Aspect 5. The compressor system according to any of aspects 1-4, wherein the switching parameter determined by the controller is a product of the speed of operation and the refrigerant density. 
     Aspect 6. The compressor system according to any of aspects 1-5, wherein the switching condition is a linear function of the speed of operation and the refrigerant density. 
     Aspect 7. The compressor system according to any of aspects 1-6, further comprising a piston, a first valve, and a second valve, wherein the first valve is configured to control fluid communication between the piston and a first pressure source, the second valve is configured to control fluid communication between the piston and a second pressure source, different than the first pressure source, and the piston is configured to be positioned by a received pressure. 
     Aspect 8. The compressor system according to aspect 7, wherein the first pressure source is the suction of the variable volume ratio compressor and the second pressure source is intermediate point of the variable volume ratio compressor. 
     Aspect 9. The compressor system according to any of aspects 7-8, wherein the controller directs the change in the volume ratio that the variable volume ratio compressor by directing each of the first valve and the second valve to change positions. 
     Aspect 10. A method for controlling a variable volume ratio compressor, comprising: 
     obtaining a suction density and an operating speed of the variable volume ratio compressor; 
     determining a switching parameter based on the suction density and the operation speed; 
     determining whether to change a volume ratio of the variable volume ratio compressor based on the switching parameter and a switching condition; and 
     when it is determined to change then volume ratio of the variable volume ratio compressor, changing the volume ratio of the variable volume ratio compressor, 
     wherein the switching parameter is a function of a suction density of the variable-volume ratio compressor and an operation speed of the compressor. 
     Aspect 11. The method according to aspect 10, wherein determining the switching parameter includes: 
     determining the switching parameter at a first time; 
     waiting a switching parameter delay period; and 
     determining the switching parameter at a second time, and 
     wherein determining whether to change the volume ratio of the variable volume ratio compressor is based on the switching parameter determined at the second time. 
     Aspect 12. The method according to aspect 11, wherein the switching parameter delay period is approximately five (5) minutes. 
     Aspect 13. The method according to any of aspects 10-12, further comprising waiting a volume ratio change delay period after changing a volume ratio of the compressor. 
     Aspect 14. The method according to aspect 13, wherein the volume ratio change delay period is approximately fifteen (15) minutes. 
     Aspect 15. The method according to any of aspects 10-14, wherein the switching parameter is a product of the suction density and the operating speed of the variable volume ratio compressor. 
     Aspect 16. The method according to any of aspects 10-15, wherein the switching condition is a linear function of the product of the suction density and the operating speed of the variable volume compressor. 
     Aspect 17. The method according to any of aspects 10-16, wherein changing the volume ratio of the variable volume ratio compressor includes switching the variable volume ratio compressor from a first volume ratio to a second volume ratio by changing the position of each of a first and a second valve, where the first valve is in fluid communication with a first pressure and the second valve is in fluid communication with a second pressure, different from the first pressure. 
     Aspect 18. The method according to aspect 17, wherein the first pressure is a suction pressure of the variable volume ratio compressor, and the second pressure is an intermediate pressure within the variable volume ratio compressor. 
     Aspect 19. The method according to any of aspects 17-18, wherein the first valve and the second valve are configured to provide one of either the first pressure or the second pressure to a piston within the variable volume ratio compressor. 
     The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.