Load Balancing Method for Two Compressors

Abstract

A load balancing method for two compressors. The two compressors are used in a refrigeration system and are driven coaxially by the same driving device. The method comprises the steps of obtaining parameters, determining balance, and controlling start/stop states. The parameters in the step of obtaining parameters are parameters related to the two compressors, such as a compressor suction side flow rate, or exhaust side flow rate, or suction side temperature; the step of determining balance comprises determining, on the basis of the obtained parameters related to the two compressors, whether load is balanced between the two compressors; the step of controlling start/top states comprises controlling the start/stop states of the two compressors according to whether the load is balanced. The method can monitor the load balance state of two compressors that are coaxially driven, thereby effectively avoiding failure of the refrigeration system caused by unbalanced loads of the compressors.

1 . A load balancing method for two compressors, the two compressors being used in a refrigeration system, comprising a first compressor ( 101 ) and a second compressor ( 102 ), wherein the first compressor ( 101 ) and the second compressor ( 102 ) are driven coaxially by the same driving device, suction sides of the first compressor ( 101 ) and the second compressor ( 102 ) are both connected with the same evaporator ( 103 ) via a pipeline, and exhaust sides of the first compressor ( 101 ) and the second compressor ( 102 ) are both connected with the same condenser ( 104 ) via a pipeline, characterized in that the method comprises:
 obtaining parameters, the parameters being related to the first compressor ( 101 ) and the second compressor ( 102 );   determining balance, comprising determining whether a balance is achieved between the first compressor ( 101 ) and the second compressor ( 102 ) according to the obtained parameters related to the first compressor ( 101 ) and the second compressor ( 102 ); and   controlling start/stop states, comprising controlling start/stop states of the first compressor ( 101 ) and the second compressor ( 102 ) according to whether the balance is achieved.   
     
     
         2 . The method according to  claim 1 , characterized in that,
 the suction side of the first compressor ( 101 ) and the suction side of the second compressor ( 102 ) are respectively provided with a pre-rotation guide vane ( 105 ), the pre-rotation guide vanes ( 105 ) are used for regulating the flow rate of a refrigerant flowing into the first compressor ( 101 ) and the second compressor ( 102 ), and the imbalance between the first compressor ( 101 ) and the second compressor ( 102 ) is caused by the pre-rotation guide vanes ( 105 ).   
     
     
         3 . The method according to  claim 2 , further comprising:
 obtaining an operating mode, wherein operating modes of the first compressor ( 101 ) and the second compressor ( 102 ) are obtained according to current load demands of the first compressor ( 101 ) and the second compressor ( 102 ), the operating modes comprise a hot gas bypass operating mode, a speed operating mode, and a PRV operating mode, and when the first compressor ( 101 ) and the second compressor ( 102 ) are running in the speed operating mode and the PRV operating mode, the steps of determining balance and controlling start/stop states are carried out.   
     
     
         4 . The method according to  claim 3 , characterized in that,
 the step of obtaining parameters comprises:
 obtaining the flow rate Q A  at the suction side of the first compressor ( 101 ) and the flow rate Q B  at the suction side of the second compressor ( 102 ); or 
 obtaining the flow rate Q C  at the exhaust side of the first compressor ( 101 ) and the flow rate Q D  at the exhaust side of the second compressor ( 102 ); and 
   the step of determining balance comprises:
 obtaining a flow rate deviation value δQ according to the flow rate Q A  and the flow rate Q B  or according to the flow rate Q C  and the flow rate Q D . 
   
     
     
         5 . The method according to  claim 4 , characterized in that the step of obtaining balance further comprises:
 when the first compressor ( 101 ) and the second compressor ( 102 ) are running in the PRV operating mode, determining whether the flow rate deviation value δQ is greater than or equal to a first preset value, and if yes, preliminarily determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state.   
     
     
         6 . The method according to  claim 5 , characterized in that the step of obtaining balance further comprises:
 after preliminarily determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state, continuously monitoring the flow rate Q A  and the flow rate Q B  or monitoring the flow rate Q C  and the flow rate Q D  within a first preset time, determining whether the flow rate deviation δQ is continuously greater than or equal to the first preset value according to the monitored flow rate Q A  and flow rate Q B  or the monitored flow rate Q C  and flow rate Q D , and if yes, determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state.   
     
     
         7 . The method according to  claim 6 , characterized in that
 the method further comprises adjusting the compressors, wherein the step of adjusting the compressors comprises adjusting the opening degree of the pre-rotation guide vanes ( 105 ), and the step of adjusting the compressors is carried out after determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state;   the step of controlling start/stop states comprises: waiting for a second preset time after the step of adjusting the compressors, re-obtaining the flow rate Q A  and the flow rate Q B  or re-obtaining the flow rate Q C  and the flow rate Q D  after the second preset time elapses, and determining the adjusted flow rate deviation value δQ according to the flow rate Q A  and the flow rate Q B  or according to the flow rate Q C  and the flow rate Q D ; determining whether the flow rate deviation value δQ is greater than or equal to a second preset value, and if yes, shutting down, wherein the second preset value is greater than the first preset value.   
     
     
         8 . The method according to  claim 4 , characterized in that
 the step of determining balance further comprises: when the first compressor ( 101 ) and the second compressor ( 102 ) are running in the speed operating mode, determining whether the flow rate deviation δQ is greater than or equal to a third preset value, and if yes, determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state; and   the step of controlling start/stop states comprises: after determining that the first compressor ( 101 ) and the second compressor ( 102 ) are in an unbalanced state, obtaining a shutdown time according to the flow rate deviation δQ, and shutting down when the shutdown time elapses.   
     
     
         9 . The method according to any one of  claims 4-8 , characterized in that
 the flow rate Q A  at the suction side of the first compressor ( 101 ) is measured on a bypass pipeline at one side of the main pipeline between the first compressor ( 101 ) and the evaporator ( 103 ), and the flow rate Q B  at the suction side of the second compressor ( 102 ) is measured on a bypass pipeline at one side of the main pipeline between the second compressor ( 102 ) and the evaporator ( 103 );   the flow rate Q C  at the exhaust side of the first compressor ( 101 ) is measured on a bypass pipeline at one side of the main pipeline between the first compressor ( 101 ) and the condenser ( 104 ), and the flow rate Q D  at the exhaust side of the second compressor ( 102 ) is measured on a bypass pipeline at one side of the main pipeline between the second compressor ( 102 ) and the condenser ( 104 ).   
     
     
         10 . The method according to any one of  claims 4-8 , characterized in that
 the flow rate deviation value δQ=2|Q A −Q B |/(Q A +Q B ), or the flow rate deviation value δQ=2|Q C −Q D //(Q C +Q D ).   
     
     
         11 . The method according to  claim 1 , characterized in that
 the step of obtaining parameters comprises:
 obtaining the temperature T A  at the suction side of the first compressor and the temperature T B  at the suction side of the second compressor; and 
   the step of determining balance comprises:
 determining whether the temperature T A  at the suction side of the first compressor or the temperature T B  at the suction side of the second compressor is greater than a first preset temperature, and if yes, carrying out the step of controlling start/stop states to shut down the first compressor and the second compressor. 
   
     
     
         12 . The method according to  claim 11 , characterized in that
 the top of the evaporator ( 103 ) and the top of the condenser ( 104 ) are in communication with each other through a hot gas bypass pipeline, and a hot gas bypass valve ( 106 ) is provided in the hot gas bypass pipeline;   the step of determining balance further comprises:
 after determining that neither the temperature T A  at the suction side of the first compressor nor the temperature T B  at the suction side of the second compressor is greater than the first preset temperature, obtaining the degree of superheat ΔT A  at the suction side of the first compressor and the degree of superheat ΔT B  at the suction side of the second compressor; determining whether the degree of superheat ΔT A  at the suction side of the first compressor or the degree of superheat ΔT B  at the suction side of the second compressor is greater than a second preset temperature, and if yes, determining whether the hot gas bypass valve ( 106 ) is open; 
 if determining that the hot gas bypass valve ( 106 ) is open, determining whether it is the degree of superheat ΔT A  at the suction side of the first compressor or the degree of superheat ΔT B  at the suction side of the second compressor that is greater than the second preset temperature; if it is the degree of superheat ΔT A  at the suction side of the first compressor that is greater than the second preset temperature, obtaining the degree of superheat ΔT C  at the exhaust side of the first compressor, and determining whether the degree of superheat ΔT C  at the exhaust side of the first compressor is lower than a third preset temperature; if yes, carrying out the step of controlling start/stop states to shut down the first compressor and the second compressor; if it is the degree of superheat ΔT B  at the suction side of the second compressor that is greater than the second preset temperature, obtaining the degree of superheat ΔT D  at the exhaust side of the second compressor, and determining whether the degree of superheat ΔT D  at the exhaust side of the second compressor is lower than the third preset temperature; if yes, carrying out the step of controlling start/stop states to shut down the first compressor and the second compressor; 
 if determining that the hot gas bypass valve ( 106 ) is closed, carrying out the step of controlling start/stop states to shut down the first compressor and the second compressor. 
   
     
     
         13 . The method according to  claim 11 , characterized in that the step of determining balance further comprises:
 determining whether the rotational speeds of the first compressor and the second compressor are greater than a predetermined rotational speed, and carrying out, only when the determination result is yes, the step of determining whether the temperature T A  at the suction side of the first compressor or the temperature T B  at the suction side of the second compressor is greater than the first preset temperature.   
     
     
         14 . The method according to  claim 12 , characterized in that:
 the degree of superheat ΔT A  at the suction side of the first compressor is a temperature difference between the temperature at the suction side of the first compressor and the saturation temperature of the evaporator ( 103 ); and   the degree of superheat ΔT B  at the suction side of the second compressor is a temperature difference between the temperature at the suction side of the second compressor and the saturation temperature of the evaporator ( 103 ).   
     
     
         15 . The method according to  claim 12 , characterized in that:
 the degree of superheat ΔT C  at the exhaust side of the first compressor is a temperature difference between the temperature at the exhaust side of the first compressor and the saturation temperature at the exhaust side of the first compressor; and   the degree of superheat ΔT D  at the suction side of the second compressor is a temperature difference between the temperature at the exhaust side of the second compressor and the saturation temperature at the exhaust side of the second compressor.