Variable geometry diffuser having extended travel and control method thereof

A method for controlling refrigerant flow in a centrifugal compressor, comprising the steps of:

• providing a variable geometry diffuser configured to control a capacity of the centrifugal compressor without prerotation vanes, wherein the variable geometry diffuser comprises:
• a drive ring rotatably mounted and movable between a first position and a second position, the drive ring including a cam track positioned on a circumference of the drive ring;
• an actuator attached to the drive ring to move the drive ring from a first position to a second position;
• a drive pin connected to the drive ring;
• a cam follower connected to the drive pin, the cam follower mounted into the cam track of the drive ring;
• a nozzle base plate disposed adjacent to the drive ring, wherein the drive pin extends through an opening in the nozzle base plate;
• a diffuser ring connected to the drive pin, the diffuser ring mounted to move axially within a groove of the nozzle base plate as the drive ring rotates, the diffuser ring movable within a diffuser gap, wherein the diffuser ring further includes a first flange extending from a first surface of the diffuser ring in the direction of the diffuser gap toward a diffuser plate cross-wise to a gas flowing in the diffuser gap, wherein the diffuser ring has an L-shaped cross section formed by the first flange and a second flange, wherein a first radial thickness of the first flange is less than a second radial thickness of the second flange, wherein the second flange has the first surface and a second surface opposite the first surface, and wherein the gas is configured to fill a gap between the groove and the second flange to surround the second flange and contact the first surface and the second surface of the second flange;
• a removable cover plate coupled to the nozzle base plate, wherein the removable cover plate extends partially into the groove of the nozzle base plate to enable the first flange to extend from within the groove and into the diffuser gap;
• and
• a controller determining a position of the diffuser ring within the diffuser gap;
• determining a width of the diffuser gap at the first flange of the diffuser ring with the first flange of the diffuser ring fully retracted into a nozzle base plate and storing the width in the controller;
• calibrating the position of the diffuser ring within the diffuser gap by activating the actuator to move the drive ring from the first position corresponding to the first flange of the diffuser ring being fully extended across the width of the diffuser gap and to a second position corresponding to the first flange of the diffuser ring being fully retracted into the nozzle base plate and storing the position of the actuator when the first flange of the diffuser ring is fully extended and fully retracted in the controller;
• and
• determining the opening of the diffuser gap based on the stored width of the diffuser gap and a current position of the actuator, the position of the first flange of the diffuser ring calculated by the controller based on the current position of the actuator.