Method for operating a variable displacement compressor and system with a variable displacement compressor

A system comprising

• a variable displacement compressor,
• an evaporator in operational connection with an inlet of the compressor,
• a condenser in operational connection with an outlet of the compressor,
• wherein the compressor is coupled to a control unit arranged to operate the compressor according to a method that causes a compressor torque to be provided depending on a calculated compressor displacement, wherein, in the compressor a volume of a compression chamber of at least one cylinder is varied during a compression cycle and during the cycle the at least one cylinder is alternately coupled to a low pressure side and a high pressure side of the compressor, the method comprising
• estimating a first thermodynamic state of the low pressure side using a temperature (Tevap) characteristic of a temperature (Tin) of a fluid at an inlet of the compressor and estimating a second thermodynamic state of the high pressure side using a pressure value (Pout) of the fluid at an outlet on the high pressure side of the compressor,
• estimating a current compression ratio (specific volume in/specific volume out
• (
• v
• in
• v
• out
• )
• )
• of the compressor,
• calculating, a compressor displacement (D) as a function of the compression ratio
• (
• v
• in
• v
• out
• )
• ,
• estimating, a compressor torque (M) depending on the calculated displacement (D) and the estimated first and second thermodynamic states,
• providing the estimated compressor torque (M) to the control unit for operating the compressor or an engine coupled to the compressor, and
• controlling operation of the compressor or the engine coupled to the compressor as a function of the estimated compressor torque (M).

A non-transitory computer program product stored on a computer readable medium, comprising a program code for use in a method comprising at least the steps of

• estimating a first thermodynamic state of the low pressure side using a temperature (Tevap) characteristic of a temperature (Tin) of a fluid at an inlet of the compressor and estimating a second thermodynamic state of the high pressure side using a pressure value (Pout) of the fluid at an outlet on the high pressure side of the compressor,
• estimating a current compression ratio (specific volume in/specific volume out
• (
• v
• in
• v
• out
• )
• )
• of the compressor,
• calculating, a compressor displacement (D) as a function of the compression ratio
• (
• v
• in
• v
• out
• )
• ,
• estimating, a compressor torque (M) depending on the calculated displacement (D) and the estimated first and second thermodynamic states,
• providing the estimated compressor torque to a control unit for operating the compressor or an engine coupled to the compressor, and
• controlling operation of the compressor or the engine coupled to the compressor as a function of the estimated compressor torque.