Mass flow interpolation systems and methods for dynamic compressors
A method for determining a mass flow of a dynamic compressor that does not include a mass flow sensor while the compressor is operating to compress a working fluid includes determining, by a processor, a current operating point of the compressor. If the current operating point is the same as one in a map of a plurality of predetermined operating points stored in a memory, the mass flow of that predetermined operating point is retrieved as the mass flow of the current operating point. Otherwise, the processor calculates the mass flow at the current operating point from the mass flows of a subset of the predetermined operating points nearest the current operating point. The dynamic compressor continues to operate to compress the working fluid based at least in part on the calculated mass flow rate for the current operating point.
1. A system for use in a heating ventilation and air conditioning (HVAC) system comprising:
a dynamic compressor operable to compress a working fluid, the dynamic compressor comprising a motor and a variable inlet guide vane (VIGV); and
a controller connected to the dynamic compressor, the controller comprising a processor and a memory, the memory storing:
a map of a plurality of predetermined operating points of the dynamic compressor, each predetermined operating point including a mass flow and a VIGV position of the dynamic compressor at that predetermined operating point; and
instructions that program the processor to:
operate the dynamic compressor to compress the working fluid;
determine, while operating the dynamic compressor, a current operating point including a current VIGV position of the dynamic compressor;
determining a mass flow for the current operating point by:
retrieving the mass flow for the current operating point from the map when the current operating point and the current VIGV position correspond to one of the predetermined operating points; and
calculating the mass flow for the current operating point from the mass flows of a first subset of the predetermined operating points nearest the current operating point at a first VIGV position below the current VIGV position and a second subset of the predetermined operating points nearest the current operating point at a second VIGV position above the current VIGV position when the current operating point and the current VIGV position do not correspond to one of the predetermined operating points; and
continue to operate the dynamic compressor to compress the working fluid based at least in part on the determined mass flow for the current operating point,
wherein the instructions stored in the memory program the processor to calculate the mass flow for the current operating point from the mass flows of the first and second subsets of the predetermined operating points nearest the current operating point by:
identifying the first and second subsets of the predetermined operating points nearest the current operating point by:
identifying the first subset of the predetermined operating points nearest the current operating point, the first subset of predetermined operating points having the same first VIGV position less than the current VIGV position of the current operating point; and
identifying the second subset of the predetermined operating points nearest the current operating point, the second subset of predetermined operating points having the same second VIGV position greater than the current VIGV position of the current operating point;
determining distances between the current operating point and the first and second subsets of the predetermined operating points nearest the current operating point by:
determining distances between the current operating point with the current VIGV position replaced with the first VIGV position and the predetermined operating points in the first subset; and
determining distances between the current operating point with the current VIGV position replaced with the second VIGV position and the predetermined operating points of the second subset; and
calculating the mass flow of the current operating point as a function of the determined distances and the mass flow of each predetermined operating point of the first and second subsets of the predetermined operating points nearest the current operating point by:
calculating a first intermediate mass flow of the current operating point with the current VIGV position replaced with the first VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the first subset;
calculating a second intermediate mass flow of the current operating point with the current VIGV position replaced with the second VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the second subset; and
calculating the mass flow of the current operating point as a function of the first intermediate mass flow, the second intermediate mass flow, and distances between the current VIGV position and the first and second VIGV positions.
2. The system of claim 1 , wherein the dynamic compressor comprises a centrifugal compressor.
3. The system of claim 1 , wherein the instructions stored in the memory program the processor to input the determined mass flow for the current operating point into a control algorithm for operation of the dynamic compressor.
4. The system of claim 1 , wherein the memory further stores a map of a plurality of predetermined surge points, a surge point mass flow for each predetermined surge point, a plurality of predetermined choke points, and a choke point mass flow for each predetermined choke point, and the instructions stored in the memory program the processor to:
determine a current surge point for the current operating point based on the map of the plurality of predetermined surge points;
determine a current choke point for the current operating point based on the map of the plurality of predetermined choke points;
retrieve the mass flow for the current surge point from the map when the current surge point is one of the predetermined surge points;
retrieve the mass flow for the current choke point from the map when the current choke point is one of the predetermined choke points;
calculate a surge point mass flow for the current surge point from the mass flows of a subset of the plurality of predetermined surge points nearest the current surge point when the current surge point is not one of the predetermined surge points; and
calculate a choke point mass flow for the current choke point from the mass flows of a subset of the plurality of predetermined choke points nearest the current choke point when the current choke point is not one of the predetermined choke points.
5. The system of claim 1 , wherein the dynamic compressor does not include a mass flow sensor.
6. A controller for a dynamic compressor without a mass flow sensor in a heating ventilation and air conditioning (HVAC) system, the dynamic compressor including a motor and a variable inlet guide vane (VIGV), the controller comprising:
a processor, and
a memory, the memory storing:
a map of a plurality of predetermined operating points of the dynamic compressor, each predetermined operating point including a mass flow and a VIGV position of the dynamic compressor at that predetermined operating point; and
instructions that program the processor to:
operate the dynamic compressor to compress a working fluid;
determine, while operating the dynamic compressor, a current operating point including a current VIGV position of the dynamic compressor;
determining a mass flow for the current operating point by:
retrieving the mass flow for the current operating point from the map when the current operating point and the current VIGV position corresponds to one of the predetermined operating points;
calculating the mass flow for the current operating point from the mass flows of a first subset of the predetermined operating points nearest the current operating point at a first VIGV position below the current VIGV position and a second subset of the predetermined operating points nearest the current operating point at a second VIGV position above the current VIGV position when the current operating point and the current VIGV position do not correspond to one of the predetermined operating points; and
continue to operate the dynamic compressor to compress the working fluid based at least in part on the determined mass flow for the current operating point,
wherein the instructions stored in the memory program the processor to calculate the mass flow for the current operating point from the mass flows of the first and second subsets of the predetermined operating points nearest the current operating point by:
identifying the first and second subsets of the predetermined operating points nearest the current operating point by:
identifying the first subset of the predetermined operating points nearest the current operating point, the first subset of predetermined operating points having the same first VIGV position less than the current VIGV position of the current operating point; and
identifying the second subset of the predetermined operating points nearest the current operating point, the second subset of predetermined operating points having the same second VIGV position greater than the current VIGV position of the current operating point;
determining distances between the current operating point and the first and second subsets of the predetermined operating points nearest the current operating point by:
determining distances between the current operating point with the current VIGV position replaced with the first VIGV position and the predetermined operating points in the first subset; and
determining distances between the current operating point with the current VIGV position replaced with the second VIGV position and the predetermined operating points of the second subset; and
calculating the mass flow of the current operating point as a function of the determined distances and the mass flow of each predetermined operating point of the first and second subsets of the predetermined operating points nearest the current operating point by:
calculating a first intermediate mass flow of the current operating point with the current VIGV position replaced with the first VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the first subset;
calculating a second intermediate mass flow of the current operating point with the current VIGV position replaced with the second VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the second subset; and
calculating the mass flow of the current operating point as a function of the first intermediate mass flow, the second intermediate mass flow, and distances between the current VIGV position and the first and second VIGV positions.
7. The controller of claim 6 , wherein the instructions stored in the memory program the processor to input the determined mass flow for the current operating point into a control algorithm for operation of the dynamic compressor.
8. The controller of claim 6 , wherein the memory further stores a map of a plurality of predetermined surge points, a surge point mass flow for each predetermined surge point, a plurality of predetermined choke points, and a choke point mass flow for each predetermined choke point, and the instructions stored in the memory program the processor to:
determine a current surge point for the current operating point based on the map of the plurality of predetermined surge points;
determine a current choke point for the current operating point based on the map of the plurality of predetermined choke points;
retrieve the mass flow for the current surge point from the map when the current surge point is one of the predetermined surge points;
retrieve the mass flow for the current choke point from the map when the current choke point is one of the predetermined choke points;
calculate a surge point mass flow for the current surge point from the mass flows of a subset of the plurality of predetermined surge points nearest the current surge point when the current surge point is not one of the predetermined surge points; and
calculate a choke point mass flow for the current choke point from the mass flows of a subset of the plurality of predetermined choke points nearest the current choke point when the current choke point is not one of the predetermined choke points.
9. The controller of claim 6 , wherein the dynamic compressor comprises a centrifugal compressor.
10. A method of determining a mass flow of a dynamic compressor that is compressing a working fluid in a heating ventilation and air conditioning (HVAC) system and does not include a mass flow sensor, the dynamic compressor including a motor and a variable inlet guide vane (VIGV), the method comprising:
operating the dynamic compressor to compress the working fluid;
determining, while operating the dynamic compressor, a current operating point including a current VIGV position of the dynamic compressor;
determining the mass flow for the current operating point by:
retrieving the mass flow for the current operating point from a map of predetermined operating points stored in a memory when the current operating point and the current VIGV position correspond to one of a plurality of predetermined operating points of the dynamic compressor in the map, each predetermined operating point in the map including a mass flow and a VIGV position of the dynamic compressor at that predetermined operating point; and
calculating the mass flow for the current operating point from the mass flows of a first subset of the predetermined operating points nearest the current operating point at a first VIGV position below the current VIGV position and a second subset of the predetermined operating points nearest the current operating point at a second VIGV position above the current VIGV position when the current operating point and the current VIGV position do not correspond to one of the predetermined operating points in the map; and
continuing to operate the dynamic compressor to compress the working fluid based at least in part on the determined mass flow for the current operating point, wherein calculating the mass flow for the current operating point from the mass flows of the first and second subsets of the predetermined operating points nearest the current operating point comprises:
identifying the first and second subsets of the predetermined operating points nearest the current operating point by:
identifying the first subset of the predetermined operating points nearest the current operating point, the first subset of predetermined operating points having the same first VIGV position less than the current VIGV position of the current operating point; and
identifying the second subset of the predetermined operating points nearest the current operating point, the second subset of predetermined operating points having the same second VIGV position greater than the current VIGV position of the current operating point;
determining distances between the current operating point and the first and second subsets of the predetermined operating points nearest the current operating point by:
determining distances between the current operating point with the current VIGV position replaced with the first VIGV position and the predetermined operating points in the first subset; and
determining distances between the current operating point with the current VIGV position replaced with the second VIGV position and the predetermined operating points of the second subset; and
calculating the mass flow of the current operating point as a function of the determined distances and the mass flow of each predetermined operating point of the subset of the predetermined operating points nearest the current operating point by:
calculating a first intermediate mass flow of the current operating point with the current VIGV position replaced with the first VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the first subset;
calculating a second intermediate mass flow of the current operating point with the current VIGV position replaced with the second VIGV position as a function of the determined distances and the mass flow of each predetermined operating point of the second subset; and
calculating the mass flow of the current operating point as a function of the first intermediate mass flow, the second intermediate mass flow, and distances between the current VIGV position and the first and second VIGV positions.
11. The method of claim 10 , further comprising
determining a current surge point for the current operating point based on a map of a plurality of predetermined surge points, wherein the map includes a surge point mass flow for each predetermined surge point;
determining a current choke point for the current operating point based on a map of a plurality of predetermined choke points, wherein the map includes a choke point mass flow for each predetermined choke point;
retrieving the mass flow for the current surge point from the map when the current surge point is one of the predetermined surge points;
retrieving the mass flow for the current choke point from the map when the current choke point is one of the predetermined choke points;
calculating a surge point mass flow for the current surge point from the mass flows of a subset of the plurality of predetermined surge points nearest the current surge point when the current surge point is not one of the predetermined surge points; and
calculating a choke point mass flow for the current choke point from the mass flows of a subset of the plurality of predetermined choke points nearest the current choke point when the current choke point is not one of the predetermined choke points.
12. The method of claim 10 , wherein the dynamic compressor comprises a centrifugal compressor.
13. The method of claim 10 , further comprising inputting the determined mass flow for the current operating point into a control algorithm for operation of the dynamic compressor.