Refrigeration cycle device and control method

Abstract

A refrigeration cycle device includes a refrigerant circuit and a control device to control an expansion valve. The control device includes a supercooling level controller, a discharge temperature controller and a first maximum selector. The supercooling level controller calculates a first opening degree of the expansion valve such that a supercooling level of the refrigerant follows a target value and to output a calculation result. The discharge temperature controller calculates a second opening degree of the expansion valve such that temperature of a refrigerant discharged from a compressor follows a predetermined upper limit and to output a calculation result. The first maximum selector outputs a maximum value out of the output of the supercooling level controller and the output of the discharge temperature controller. The control device controls the expansion valve by using the value outputted from the first maximum selector.

1 . A refrigeration cycle device comprising:
 a refrigerant circuit to make a refrigerant flow in a compressor to compress a refrigerant, a condenser, an expansion valve to regulate a flow rate of a refrigerant, an evaporator, and an accumulator to supply a refrigerant to the condenser in this order; and   a control device to control the expansion valve,   wherein the control device includes:   a supercooling level controller to calculate a first opening degree of the expansion valve such that a supercooling level of a refrigerant follows a target value and to output a calculation result:   a discharge temperature controller to calculate a second opening degree of the expansion valve such that temperature of a refrigerant discharged from the compressor follows a predetermined upper limit and to output a calculation result; and   a first maximum selector to output a maximum value out of the output of the supercooling level controller and the output of the discharge temperature controller,   wherein the control device controls the expansion valve by using the value outputted from the first maximum selector.   
     
     
         2 . The refrigeration cycle device according to  claim 1 , wherein
 the supercooling level controller is a first PI controller,   the discharge temperature controller is a second PI controller, and   a parameter of each of the first PI controller and the second PI controller is calculated by using a result of system identification based on a step response.   
     
     
         3 . The refrigeration cycle device according to  claim 1 , wherein
 each of the supercooling level controller and the discharge temperature controller has an anti-reset windup function, and   integral values calculated by the supercooling level controller and the discharge temperature controller do not diverge.   
     
     
         4 . The refrigeration cycle device according to  claim 1 , wherein
 the control device includes a switch to receive the output from the supercooling level controller,   the switch determines whether a state of a refrigerant existing at an outlet of the condenser is a liquid phase or a two-phase state on a basis of the supercooling level, the switch outputs a value equal to the output of the supercooling level controller when the state of the refrigerant existing at the outlet of the condenser is determined to be the liquid phase,   the switch outputs an invalid signal when the state of the refrigerant existing at the outlet of the condenser is determined to be the two-phase state, and   when the invalid signal is received by the first maximum selector, the first maximum selector outputs a maximum value out of the outputs inputted to the first maximum selector excluding the invalid signal.   
     
     
         5 . The refrigeration cycle device according to  claim 1 , wherein the discharge temperature controller makes the temperature of the refrigerant discharged from the compressor follow a predetermined target value other than the upper limit. 
     
     
         6 . The refrigeration cycle device according to  claim 1 , further comprising an outlet temperature sensor placed at an outlet of the evaporator,
 wherein the control device includes:   an evaporator differential temperature controller to calculate a third opening degree of the expansion valve such that an evaporator differential temperature follows a predetermined upper limit and to output a calculation result, the evaporator differential temperature being calculated as a difference between temperature of the refrigerant exiting from the evaporator and temperature of the refrigerant entering the evaporator:   a discharge superheating level lower limit controller to calculate a fourth opening degree of the expansion valve such that a discharge superheating level follows a lower limit and to output a calculation result:   a discharge superheating level upper limit controller to calculate a fifth opening degree of the expansion valve such that a discharge superheating level follows an upper limit and to output a calculation result:   a minimum selector to output a minimum value out of the output of the first maximum selector and the output of the discharge superheating level lower limit controller: and   a second maximum selector to output a maximum value out of the output of the minimum selector, the output of the discharge superheating level upper limit controller, and the output of the discharge temperature controller, wherein   the first maximum selector outputs a maximum value out of the output of the supercooling level controller and the output of the evaporator differential temperature controller, and   the control device controls the expansion valve by using the value outputted from the second maximum selector.   
     
     
         7 . A control method for controlling an expansion valve in a refrigeration cycle device including a compressor to compress a refrigerant, a condenser, the expansion valve to regulate a flow rate of a refrigerant, and a control device to control the expansion valve, the control method comprising:
 calculating a first opening degree of the expansion valve such that a supercooling level of a refrigerant follows a target value:   calculating a second opening degree of the expansion valve such that temperature of a refrigerant discharged from the compressor follows a predetermined upper limit: and   controlling the expansion valve by using a maximum value out of the first opening degree and the second opening degree.   
     
     
         8 . The refrigeration cycle device according to  claim 2 , wherein
 each of the supercooling level controller and the discharge temperature controller has an anti-reset windup function, and   integral values calculated by the supercooling level controller and the discharge temperature controller do not diverge.