Control system for refrigeration compressor

Claim 2

A refrigeration system including an evaporator, a compressor, a condenser and an expansion device, all intercoupled in a closed vapor cycle refrigeration circuit, with a control system for providing a modulating signal to regulate compressor operation, which control system comprises: a first circuit, including a first sensor positioned adjacent the evaporator input to provide a first signal which varies as a function of the evaporator inlet temperature, a second sensor positioned adjacent the evaporator output to provide a second signal which varies as the evaporator outlet temperature, and means for combining the first and second signals to provide a superheat signal which varies as a function of the temperature difference between the inlet and outlet portions of the evaporator; a second circuit, comprising an adjusting means for establishing a temperature set point signal, a third sensor disposed in the controlled space to provide a third signal which varies as a function of the actual space temperature, and means for combining the set signal and the third signal to provide a control signal which varies as a function of the difference in temperature denoted by the set point signal and the third signal; and an all-electrical comparator stage, having a first input connection for receiving the superheat signal, a second input connection for receiving the control signal, and an output connection to provide the modulating signal required to regulate compressor operation and control the temperature of the space as a function of the difference between the superheat and control signals.

Claim 3

A control system as claimed in claim 1, and further comprising a resistor coupled in series with a capacitor between the first input connection and the output connection of the comparator stage, such that said capacitor affords an integrating function to stabilize the refrigeration control system, and a unidirectional current conduction means coupled in parallel with said resistor, connected in a sense to afford rapid charging of said capacitor as the superheat value decreases and the amplitude of the superheat signal increases by effectively bypassing said resistor, thus providing a capacity increase change rate of the entire control system which is substantially less than the capacity decrease change rate of the system.

Claim 4

A control system as claimed in claim 1 and further comprising a trigger circuit, having a first input connection connected to receive the signal related to the evaporator coil inlet temperature, a second input connection connected to receive a reference signal, and an output connection coupled to said first input connection of the comparator stage, to effectively override the superheat signal during start-up when there is no temperature difference across the evaporator coil.

Claim 5

A control system as claimed in claim 1 and further comprising a limiter stage, having a first input connection connected to receive said control signal, a second input connection for receiving a reference signal, and an output connection for applying an override signal to the second input connection of the signal combining means in the second circuit, to override the control signal under predetermined conditions and allow a zero capacity output indication when the superheat signal indicates zero superheat.

Claim 6

A refrigeration system including an evaporator, a compressor, a condenser and an expansion device, all intercoupled in a closed vapor cycle refrigeration circuit, a motor coupled to the compressor, and an inverter connected to energize the motor, with a control system for providing a modulating signal to regulate inverter operation, which control system comprises: a first circuit, including a first thermistor positioned adjacent the evaporator inlet to provide a first signal which varies as a function of the evaporator inlet temperature, a second thermistor positioned adjacent the evaporator outlet to provide a second signal which varies as the evaporator outlet temperature, and a first operational amplifier connected to combine the first and second signals to provide a superheat signal which varies as a function of the temperature difference between the inlet portions of the evaporator; a second circuit, comprising a potentiometer for establishing a temperature set point signal, a third thermistor disposed in the controlled space to provide a third signal which varies as a function of the actual space temperature, and a second operational amplifier connected to combine the set point signal and the third signal to provide a control signal which varies as a function of the difference in temperatures denoted by the set point signal and the third signal; and a comparator stage, including a third operational amplifier having a first input connection for receiving the superheat signal, a second input connection for receiving the control signal, and an output connection to provide the modulating signal required to regulate inverter operation and control the temperature of the space as a function of the difference between the superheat and control signals.

Claim 7

A refrigeration system including an evaporator, a compressor, a condenser and an expansion device, all intercoupled in a closed vapor cycle refrigeration circuit, a motor coupled to the compressor, and an inverter connected to energize the motor, with a control system for providing a modulating signal to regulate inverter operation, which control system comprises: a first circuit, including a first thermistor positioned adjacent the evaporator inlet to provide a first signal which varies as a function of the evaporator inlet temperature, a second thermistor positioned adjacent the evaporator outlet to provide a second signal which varies as the evaporator outlet temperature, and a first operational amplifier connected to combine the first and second signals to provide a superheat signal which varies as a function of the temperature difference between the inlet portions of the evaporator; a second circuit, comprising a potentiometer for establishing a temperature set point signal, a third thermistor disposed in the controlled space to provide a third signal which varies as a function of the actual space temperature, and a second operational amplifier connected to combine the set point signal and the third signal to provide a control signal which varies as a function of the difference in temperatures denoted by the set point signal and the third signal; and a comparator stage, including a third operational amplifier having a first input connection for receiving the superheat signal, a second input connection for receiving the control signal, and an output connection to provide the modulating signal required to regulate inverter operation and control the temperature of the space as a function of the difference between the superheat and control signals.

Claim 8

A control system as claimed in claim 5, and further comprising a resistor and capacitor coupled in series between the first input connection and the output connection of the third operational amplifier, such that said capacitor affords an integrating function to stabilize the refrigeration control system, and a diode coupled in parallel with said resistor, which diode is connected in a sense to afford rapid charging of said capacitor as the level of superheat decreases and the amplitude of the superheat signal increases by effectively bypassing said resistor, thus providing a capacity decrease change rate of the entire control system when the superheat decreases which is substantially greater than the capacity increase change rate of the control system when the superheat increases.

Claim 9

A control system as claimed in claim 5 and further comprising a trigger circuit, including a fourth operational amplifier having a first input connection connected to receive the signal related to the evaporator coil inlet temperature, a second input connection connected to receive a reference signal, and an output connection coupled to said first input connection of the third operation amplifier, to effectively override the superheat signal during start-up when there is no temperature difference across the evaporator coil.

Claim 10

A control system as claimed in claim 5 and further comprising a limiter stage, comprising a fifth operational amplifier having a first input connection connected to receive said control signal, a second potentiometer connected in a voltage divider circuit to provide a reference signal, a second input connection for receiving said reference signal, and an output connection for applying an override signal to the second input connection of the second operational amplifier, to override the control signal under predetermined conditions and allow a zero capacity output indication when the superheat signal indicates zero superheat.