Control system for regulating large capacity rotating machinery

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.

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.

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.

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.