Control system for regulating large capacity rotating machinery

• US 4,151,725 A
• Filed: 07/18/1977
• Issued: 05/01/1979
• Est. Priority Date: 05/09/1977
• Status: Expired due to Term

• Current Assignee: York International Corporation (Johnson Controls International plc)
• Original Assignee: BorgWarner Incorporated
• Inventors: Kountz, Kenneth J., Erth, Richard A., Bauman, Bruce K.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US05/816,428
• Time in Patent Office: 652 Days
• Field of Search: 62/228, 62/229, 62/230, 62/182, 62/209, 417/25, 417/19, 417/32, 417/47
• US Class Current: 62/182
• CPC Class Codes: F04D 27/0246 by varying geometry within the pumps, e.g. by adjusting vanes
• CPC Class Codes: F04D 27/0261 by varying driving speed
• CPC Class Codes: F04D 27/0284 Conjoint control of two or more different functions
• CPC Class Codes: F25B 1/053 of turbine type
• CPC Class Codes: F25B 2339/047 Water-cooled condensers
• CPC Class Codes: F25B 25/005 using primary and secondary systems
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: F25B 2600/026 by controlling unloaders
• CPC Class Codes: F25B 2700/21163 of the refrigerant at the outlet of the condenser
• CPC Class Codes: F25B 2700/21173 at the outlet
• CPC Class Codes: F25B 2700/21175 of the refrigerant at the outlet of the evaporator
• CPC Class Codes: F25B 49/022 Compressor control arrangements
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

The control system of the invention regulates a centrifugal compressor having inlet guide vanes adjustable as one means for varying the compressor capacity. A variable speed motor is connected to drive the compressor, and provides another means for regulating the compressor capacity. The control system regulates the motor speed alone over one portion of the load variation curve, and regulates the motor speed jointly with the inlet guide vane opening over another portion of the load variation curve, to achieve the most energy-efficient operating condition while avoiding the surge condition. This optimum control path is realized by utilizing a signal which is a measure of the compressor head value. Compressor surge or instability is avoided by deriving a critical Mach number (speed indication) for any given operating condition, as a function of the compressor head and vane position, and preventing the motor speed from going below that Mach number under the specific operating conditions. The control system of the invention is useful both with existing equipment, by way of retrofit, and with newly manufactured and installed equipment.

Claims

1. A control system for a refrigeration system including a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit, which compressor includes an adjustable capacity control means, means for regulating the adjustable capacity control means, and an electrical prime mover connected to drive the compressor, which control system comprises:

means for providing a timing signal;

means for providing a position signal which varies as a function of the setting of the adjustable capacity control means; and

a drive control circuit, having a first input coupled to the means for providing a timing signal, a second input coupled to the means for providing the position signal, and an output coupled to the means for regulating the adustable capacity control means, which drive control circuit produces an output drive signal having at least one characteristic which varies as a function of the position signal, thus driving the means for regulating the adjustable capacity control means as a function of the position of the adjustable capacity control means.

2. A control system as claimed in claim 1, in which a logic circuit is coupled between the drive control circuit and the means for regulating the adjustable capacity control means, and the output control signal is a pulse-width modulated signal having a pulse duration which varies as a function of the position signal.

3. A control system as claimed in claim 1, in which the adjustable capacity control means comprises a plurality of inlet guide vanes, the means for regulating the adjustable capacity control means is an electrical motor which is coupled to the inlet guide vanes, and the output control signal is applied to the electrical motor to adjust the position of the inlet guide vanes and correspondingly regulate the capacity of the compessor.

4. A control system as claimed in claim 3, in which an oscillator is the means for supplying a timing signal, and the means for providing the position signal includes a potentiometer having a movable arm, which potentiometer is mechanically connected such that the potentiometer arm position is a function of the position of the inlet guide vanes.

5. A control system for a refrigeration system including a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit, which compressor includes a plurality of adjustable inlet guide vanes, a motor connected to regulate the inlet guide vanes position, and an electrical prime mover connected to drive the compessor, which control system comprises:

an oscillator for providing a timing signal;

means including a potentiometer connected to provide a position signal which varies as a function of the setting of the inlet guide vanes; and

a drive control circuit, having a first input coupled to the oscillator, a second input coupled to the potentiometer which provides the position signal, and an output coupled to the motor which regulates the inlet guide vanes, which drive control circuit includes an integrator, a comparator, and a NOR gate, all intercoupled to produce an output drive signal having a pulse duration which varies as a function of the vane position signal, thus regulating the drive signal to the motor as a function of the position of the inlet guide vanes.

6. A control system for a refrigeration system including a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit, which compressor includes an adjustable capacity control means, means for regulating the adjustable capacity control means, and an electrical prime mover connected to drive the compressor, which control system comprises:

means for providing a timing signal;

means for providing a position signal which varies as a function of the setting of the adjustable capacity control means;

a drive control circuit, having a first input coupled to the means for providing a timing signal, a second input coupled to the means for providing the position signal, and an output coupled to the means for regulating the adjustable capacity control means, which drive control circuit produces an output signal having at least one characteristic which varies as a function of the position signal, thus regulating the adjustable capacity control means as a function of the position of the adjustable capacity control means; and

a prime mover control circuit, including means for deriving a signal which varies as the compressor head, and means for utilizing the head-indicating signal to regulate the speed of the electrical prime mover such that combined control of the prime mover speed and the adjustable capacity control means is effected in an energy-conservation manner and without sending the compressor into surge.

7. A control system for a refrigeration system including a compressor, a condenser and an evaporator, all connected in a closed refrigeration circuit, which compressor includes an adjustable capacity control means, means for regulating the adjustable capacity control means, an electrical prime mover connected to drive the compressor, and means for regulating the speed of the prime mover, which control system comprises:

a first circuit connected to provide a signal which connotes the head of the compressor, a second circuit connected to provide a signal to the means for regulating the electrical prime mover speed as a function of the head-connoting signal, and a third circuit connected to provide a signal to the means for regulating the adjustable capacity control means, such that combined control of the prime mover speed and the adjustable capacity control means is effected in an energy-conservation manner and compressor surge is avoided.

8. A control system as claimed in claim 7, in which the first circuit includes a first sensing means positioned to provide a first signal related to the refrigerant condensing temperature, a second sensing means positioned to provide a second signal related to the refrigerant evaporating temperature, and means for combining the first and second signals to provide the head-connoting signal.

9. A control system as claimed in claim 7, and further comprising means, coupled to the adjustable capacity control means, for providing an electrical signal which indicates the physical position of the capacity control means, and means for applying the position-indicating signal to the third circuit, to produce a drive signal for the means for regulating the adjustable capacity control means as a function of the capacity control means position.

10. A control system as claimed in claim 7, and further comprising a temperature sensing means positioned to provide a signal related to the chilled water discharge temperature from the evaporator, adjustable means for establishing a temperature set point signal, and means for combining the chilled water temperature signal and the temperature set point signal to produce a temperature error signal which is applied to the second circuit and the third circuit for use in controlling the operation of the refrigeration system, to assist in regulating both prime mover speed and the adjustable capacity control means.

11. A control system as claimed in claim 10, and further comprising a dead band circuit, coupled between the means for producing the temperature error signal and the second and third circuits, to avoid hunting and excessive switching in the control system.

12. A control system as claimed in claim 9, and further comprising a network, connected to modify the position-indicating signal and produce a modified signal for use in regulating the electrical prime mover.

13. A control system as claimed in claim 12, and further comprising means for combining the modified signal and the head-connoting signal to produce a combined signal, means for providing a signal related to the actual speed of the electrical prime mover, and means for combining the combined signal and the actual speed signal to produce a signal for regulating the speed of the electrical prime mover.

14. A control system as claimed in claim 10, and further comprising an unload control circuit, coupled to the adjustable means for establishing the temperature set point signal, operable to change the temperature set point, thus changing the load on the compressor and reducing the rate at which energy is consumed.

15. A control system for a refrigeration system including a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit, which compressor includes adjustable inlet guide vanes, a position-controlling motor mechanically coupled to the inlet guide vanes, an a-c motor mechanically coupled to the compressor, an inverter connected to supply an a-c voltage to the a-c motor, and a logic circuit connected to regulate the frequency of the inverter output voltage as a function of a received speed control signal, which control system comprises;

a first circuit, connected to provide a minimum Mach number signal, related to the compressor head, as a function of the difference between the condensing refrigerant temperature in the condenser and the evaporating refrigerant temperature in the evaporator;

an inverter speed logic circuit, connected to provide said speed control signal to the inverter logic circuit;

a PRV control logic circuit, connected to supply drive signals to the inlet guide vanes; and

circuit means for utilizing said minimum Mach number signal in deriving control signals for the inverter speed logic circuit and the PRV control logic circuit.

16. A control system as claimed in claim 15, and further comprising a second circuit including a component coupled to the inlet guide vanes, for providing a functional signal related to the instantaneous position of the inlet guide vanes;

and

means for combining the functional signal with the minimum Mach number signal, to provide a signal for use in regulating the speed of the a-c motor.

17. A control system as claimed in claim 16, in which the component in the second circuit is a potentiometer having a movable arm, and the second circuit further comprises a network having a plurality of stages intercoupled to provide said functional signal as the potentiometer arm is displaced as a result of movement of the inlet guide vanes.

18. A control system as claimed in claim 16, and further comprising means for providing a signal which varies as a function of the actual speed of the a-c motor, and means for combining this motor-speed-indicating signal with the resultant of the functional and minimum Mach number signals, to provide a speed boost signal for use in regulating the inverter speed logic circuti and thus controlling the speed of the a-c motor driving the compressor.

19. A control system as claimed in claim 18, and further comprising means for providing a signal related to the temperature of chilled water discharged from the evaporator, adjustable means for establishing a temperature set point signal, and means for combining the chilled water temperature signal with the temperature set point signal, to produce a temperature error signal for application to the inverter speed logic circuit.

20. A control system as claimed in claim 18, and further comprising means for combining the actual motor speed signal with the minimum Mach number signal, to produce a logical signal for application to the inverter speed logic circuit and to the PRV control logic circuit.

21. The method of controlling a refrigeration system having a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit, which compressor includes adjustable inlet guide vanes to vary the compressor capacity, and an electrical adjustable speed motor connected to drive the compressor, such that motor speed adjustment also varies the capacity, comprising the steps of:

continually establishing a compressor head signal as a function of the condensing refrigerant and evaporating refrigerant temperatures;

deriving a functional signal related to the instantaneous position of the inlet guide vanes;

combining the head-indicating signal and the functional signal to produce an intermediate signal;

providing a signal related to the actual motor speed;

combining the actual motor speed signal and the intermediate signal to provide a first signal for use in regulating the speed of the compressor drive motor; and

deriving a temperature error signal, related to the difference in temperature between the cooling medium at the evaporator outlet and the desired temperature set point, and employing the temperature error signal as a second signal for use in regulating both the speed of the compressor drive motor and the position of the inlet guide vanes.

22. The method of control described in claim 21, in which the compressor drive motor speed and the inlet guide vanes position are regulated to reduce system capacity, in accordance with the following steps taken in sequence;

reducing the compressor drive motor speed, while the inlet guide vanes remain wide open, from a first operating condition, through a second operating condition to a third operating condition;

gradually closing the inlet guide vanes, and simultaneously increasing the compressor drive motor speed, to reach a fourth operating condition;

continuing to close the inlet guide vanes while simultaneously reducing the drive motor speed, to reach a fifth operating condition; and

thereafter continuing to close the inlet guide vanes while simultaneously increasing the drive motor speed, until a sixth operating condition is reached.

23. The method of control described in claim 22, and further comprising the following steps, taken in sequence, to again restore capacity to the system;

gradually opening the inlet guide vanes while decreasing the compressor drive motor speed as the system moves from the sixth operating condition to the fifth operating condition;

continuing to open the inlet guide vanes while simultaneously increasing the motor speed, while the system moves from the fifth operating condition to the fourth operating condition;

continuing to increase the opening of the inlet guide vanes, and simultaneously increasing the compressor drive motor speed, as the system moves from the fourth operating condition directly to the second operating condition without going through the third operating condition, with the inlet guide vanes being fully open at the second operating condition; and

continuing to increase the compressor drive motor speed to increase the system capacity, until the first operating condition is reached.

24. The method of regulating a refrigeration system including a compressor having adjustable guide vanes and driven by a variable speed motor, in which the position of the inlet guide vanes and the speed of the compressor drive motor are jointly regulated substantially according to the functional variations illustrated in FIG. 4 and described in the specification, to avoid surge while operating in an energy-efficient manner.