Centrifugal compressor controller for minimizing power consumption while avoiding surge

Claim 2

For use with a variable capacity centrifugal compressor driven by an electric motor, a controller for adjusting the capacity of the compressor to satisfy a demand, minimize electric power consumption and avoid a surge condition, comprising: a. means for sensing an operating parameter that is indicative of the capacity of the compressor; b. means for setting a selected setpoint that represents a desired value of the operating parameter; c. surge sensing means for detecting an impending surge by sensing fluctuation in the electric current supplied to the compressor motor, wherein an impending surge is detected whenever fluctuations in excess of a predetermined amplitude occur in excess of a predetermined frequency; and d. control means, responsive to the operating parameter sensing means, the setpoint setting means, and the surge sensing means, for controlling the compressor, such that its capacity is minimally above a level that would cause a surge condition yet is sufficient to maintain the operating parameter at the setpoint.

Claim 3

The controller as recited in claim 1, wherein each current fluctuation indicative of an impending surge condition includes a first and second current pulse, wherein the first pulse is a decrease in motor current and the second pulse is an increase in motor current.

Claim 4

A controller as recited in claim 1 wherein the compressor is used in a temperature conditioning system for conditioning the temperature of a fluid, and wherein the operating parameter is the temperature of the fluid and the setpoint is the desired temperature of the fluid.

Claim 5

A controller as recited in claim 3, wherein the compressor is driven by a variable speed motor and includes adjustable inlet guide vanes, and wherein the controller further comprises: a. means for sensing the speed of the compressor; b. position feedback means for sensing the position of the inlet guide vanes; and wherein the control means include a microprocessor and in response to the temperature of the fluid, the setpoint, the surge sensing means, the speed sensing means, and position feedback means, are further operable to: i. reduce the speed of the compressor when: (1) the inlet guide vanes are not substantially fully open, (2) the temperature of the fluid is less than the setpoint, and (3) a surge condition is not impending; and ii. increase the speed of the compressor when: (1) a surge condition is impending, or (2) the temperature of the fluid is greater than the setpoint and the inlet guide vanes are substantially fully open.

Claim 6

The controller as recited in claim 4, further comprising means, responsive to the output sensing means, for variably positioning the inlet guide vanes between an opened and closed position.

Claim 7

The controller as recited in claim 4, wherein the motor is driven by a variable frequency inverter and the control means are further operable to control the speed of the motor by varying the inverter frequency.

Claim 8

The controller as recited in claim 4, wherein the temperature conditioning system includes a condenser cooled by a second fluid and the controller further comprises a temperature sensor for sensing the temperature of the second fluid, wherein the control means, in further response to the temperature sensor, derive a target speed for making coarse reductions in compressor speed.

Claim 9

The controller as recited in claim 4, wherein said microprocessor, in response to an impending surge condition, increases the speed of the compressor in increments with time delays therebetween.

Claim 10

In a system for temperature conditioning a fluid using a variable capacity centrifugal compressor which has adjustable inlet guide vanes and which is driven by a variable speed motor, a controller for adjusting the capacity of the compressor to satisfy a demand, minimize electric power consumption, and avoid a surge condition, comprising: a. a temperature sensor for sensing the temperature of the fluid; b. means for setting a desired fluid temperature set-point; c. means for sensing the speed of the compressor; d. position feedback means for sensing the position of the inlet guide vanes; e. surge sensing means for detecting an impending surge by sensing fluctuation in the RMS value of the electric current supplied to the compressor motor, wherein an impending surge is detected whenever fluctuations in excess of a predetermined amplitude occur in excess of a predetermined frequency; and f. control means, including a microprocessor responsive to the temperature sensor, the temperature setpoint setting means, the compressor speed sensing means the position feedback means, and the surge sensing means, for positioning the inlet guide vanes so that the temperature of the fluid is maintained at the setpoint and for controlling the compressor speed to a minimum level which is still sufficient to avoid a surge.

Claim 11

In a system for temperature conditioning a fluid using a variable capacity centrifugal compressor which has adjustable inlet guide vanes and which is driven by a variable speed motor, a controller for adjusting the capacity of the compressor to satisfy a demand, minimize electric power consumption, and avoid a surge condition, comprising: a. a temperature sensor for sensing the temperature of the fluid; b. means for setting a desired fluid temperature set-point; c. means for sensing the speed of the compressor; d. position feedback means for sensing the position of the inlet guide vanes; e. surge sensing means for detecting an impending surge by sensing fluctuation in the RMS value of the electric current supplied to the compressor motor, wherein an impending surge is detected whenever fluctuations in excess of a predetermined amplitude occur in excess of a predetermined frequency; and f. control means, including a microprocessor responsive to the temperature sensor, the temperature setpoint setting means, the compressor speed sensing means the position feedback means, and the surge sensing means, for positioning the inlet guide vanes so that the temperature of the fluid is maintained at the setpoint and for controlling the compressor speed to a minimum level which is still sufficient to avoid a surge.

Claim 12

The controller as recited in claim 9, wherein each current fluctuation indicative of an impending surge condition includes a first and second current pulse, wherein the first pulse is a decrease in motor current and the second pulse is an increase in motor current.

Claim 13

The controller as recited in claim 10, wherein the control means varies the position of the inlet guide vanes to maintain the fluid temperature at the setpoint and varies the speed of the compressor by: i. reducing the speed of the compressor when: (1) the inlet guide vanes are not substantially fully open, (2) the temperature of the fluid is less than the setpoint, and (3) a surge condition is not impending; and ii. increasing the speed of the compressor when: (1) a surge condition is impending, or (2) the temperature of the fluid is greater than the setpoint and the inlet guide vanes are substantially fully open.

Claim 14

The controller as recited in claim 11, wherein the motor is driven by a variable frequency inverter and the control means are further operable to control the speed of the motor by varying the inverter frequency.

Claim 15

The controller as recited in claim 11, wherein the temperature conditioning system includes a condenser cooled by a second fluid and the controller further comprises a second temperature sensor for sensing the second fluid temperature, and wherein the control means, in further response to the second temperature sensor, derives a target speed for making coarse reductions in compressor speed.

Claim 16

The controller as recited in claim 11, wherein said microprocessor, in response to an impending surge condition, incrementally increases the speed of the compressor in increments with time delays therebetween.

Claim 17

In a system for temperature conditioning a fluid, having an evaporator, a condenser, and a variable capacity centrifugal compressor with adjustable inlet guide vanes and driven by a variable speed motor, a controller for adjusting the capacity of the compressor to satisfy a temperature conditioning demand, minimize electric power consumption, and avoid a surge condition, comprising: a. a temperature sensor for sensing the temperature of said fluid; b. means for sensing the speed of said compressor; c. position feedback means for sensing the position of said inlet guide vanes; d. surge sensing means for detecting an impending surge by sensing fluctuation in the RMS value of the electric current supplied to the compressor motor, wherein an impending surge is detected whenever fluctuations in excess of a predetermined amplitude occur in excess of a predetermined frequency; e. means for setting a fluid temperature setpoint; f. inlet guide vane positioning means for variably positioning the inlet guide vanes between an opened and closed position; and g. control means that include a microprocessor responsive to the temperature sensor, the setpoint setting means, the speed sensing means, the position feedback means, and the surge sensing means, for controlling the position of the inlet guide vanes by providing a control signal to the inlet guide vane positioning means and for: i. reducing the speed of the compressor when: (1) the inlet guide vanes are not fully open, (2) the temperature of the fluid is less than the setpoint, and (3) a surge condition is not impending; and ii. increasing the speed of the compressor when: (1) a surge condition is impending, or (2) the temperature of the fluid is greater than the setpoint and the inlet guide vanes are substantially fully open.

Claim 18

In a system for temperature conditioning a fluid, having an evaporator, a condenser, and a variable capacity centrifugal compressor with adjustable inlet guide vanes and driven by a variable speed motor, a controller for adjusting the capacity of the compressor to satisfy a temperature conditioning demand, minimize electric power consumption, and avoid a surge condition, comprising: a. a temperature sensor for sensing the temperature of said fluid; b. means for sensing the speed of said compressor; c. position feedback means for sensing the position of said inlet guide vanes; d. surge sensing means for detecting an impending surge by sensing fluctuation in the RMS value of the electric current supplied to the compressor motor, wherein an impending surge is detected whenever fluctuations in excess of a predetermined amplitude occur in excess of a predetermined frequency; e. means for setting a fluid temperature setpoint; f. inlet guide vane positioning means for variably positioning the inlet guide vanes between an opened and closed position; and g. control means that include a microprocessor responsive to the temperature sensor, the setpoint setting means, the speed sensing means, the position feedback means, and the surge sensing means, for controlling the position of the inlet guide vanes by providing a control signal to the inlet guide vane positioning means and for: i. reducing the speed of the compressor when: (1) the inlet guide vanes are not fully open, (2) the temperature of the fluid is less than the setpoint, and (3) a surge condition is not impending; and ii. increasing the speed of the compressor when: (1) a surge condition is impending, or (2) the temperature of the fluid is greater than the setpoint and the inlet guide vanes are substantially fully open.

Claim 19

The controller as recited in claim 15, wherein each current fluctuation indicative of an impending surge condition includes a first and second current pulse, wherein the first pulse is a decrease in motor current and the second pulse is an increase in motor current.

Claim 20

The controller as recited in claim 15, further comprising, a second temperature sensor for sensing the temperature of a second fluid used to cool the condenser and wherein the control means, in further response to the second temperature sensor, derive a target speed for making initial coarse reductions in compressor speed.

Claim 21

The controller as recited in claim 15, wherein said microprocessor, in response to an impending surge condition, increases the speed of the compressor in increments with time delays therebetween.

Claim 22

The controller as recited in claim 15, wherein the motor is driven by a variable frequency inverter and the control means are further operable to control the speed of the motor by varying the inverter frequency.