Heat pump apparatus using expander

Abstract

A heat pump apparatus includes a compressor, a motor, an expander, a generator, and a variable-speed converter. The variable-speed converter is connected to the generator and converts alternating current generated by the generator into direct current. The variable-speed converter continues to control driving of the generator after an operation stop trigger occurs for lowering the speed of the motor and stopping the operation of the heat pump apparatus at least until a value of current flowing through the generator becomes equal to or less than a predetermined value. The variable-speed converter stops the working of the generator after the value of current flowing through the generator becomes equal to or less than the predetermined value.

1 . A heat pump apparatus, comprising: 
 a compressor for compressing a working fluid;    a motor for driving the compressor;    an expander for expanding the working fluid;    a generator connected to the expander, for converting mechanical power into electric power, the mechanical power being recovered by the expander when the working fluid expands; and    a variable-speed converter connected to the generator, for converting alternating current generated by the generator into direct current, wherein the variable-speed converter continues to control driving of the generator after an operation stop trigger occurs for lowering rotational speed of the motor and stopping the operation of the heat pump apparatus at least until a value of current flowing through the generator becomes equal to or less than a predetermined value, and stops the working of the generator after the value of current flowing through the generator becomes equal to or less than the predetermined value.    
     
     
         2 . The heat pump apparatus according to  claim 1 , wherein after the operation stop trigger occurs, the variable-speed converter continues to control the driving of the generator until the value of current flowing through the generator becomes equal to or less than the predetermined value in such a manner that the generator is driven at a speed that is equal to or less than the speed at the time when the operation stop trigger has occurred.  
     
     
         3 . The heat pump apparatus according to  claim 1 , further comprising: 
 means (A) for determining whether or not the value of current flowing through the generator is equal to or less than the predetermined value in response to the occurrence of the operation stop trigger, or wherein the variable-speed converter comprises the means (A), and    the variable-speed converter continues to control the driving of the generator until the value of current flowing through the generator becomes equal to or less than the predetermined value if the value of current flowing through the generator exceeds the predetermined value, and the variable-speed converter stops the working of the generator if the value of current flowing through the generator becomes equal to or less than the predetermined value.    
     
     
         4 . The heat pump apparatus according to  claim 3 , wherein; 
 the means (A) further assesses whether or not the generator is performing a powering operation; and    if the generator is performing the powering operation, the variable-speed converter immediately finishes controlling the driving of the generator.    
     
     
         5 . The heat pump apparatus according to  claim 1 , wherein the variable-speed converter is connected to the generator by a three-phase power line, and the variable-speed converter performs a DC excitation for phase windings of the generator when stopping the working of the generator.  
     
     
         6 . The heat pump apparatus according to  claim 5 , wherein the predetermined value is determined so that the electric current flowing through the generator does not exceed a capacity of the variable-speed converter when the DC excitation is performed for the phase windings.  
     
     
         7 . The heat pump apparatus according to  claim 5 , wherein the predetermined value is determined according to the state in which the speed of the generator reduces when the DC excitation is performed for the phase windings.  
     
     
         8 . The heat pump apparatus according to  claim 5 , wherein: 
 the generator is a permanent magnet synchronous generator; and    the predetermined value is determined so that electric current flowing through the permanent magnet synchronous generator does not exceed a demagnetization current of the permanent magnet synchronous generator when the DC excitation is performed for the phase windings.    
     
     
         9 . The heat pump apparatus according to  claim 1 , further comprising: 
 an inverter connected to the motor, for converting direct current into alternating current and for controlling the driving of the motor, wherein    the inverter lowers the speed of the motor in response to the occurrence of the operation stop trigger so as to reduce a high pressure/low pressure difference of the working fluid, and continues to control the driving of the motor to consume regenerative power until the electric current flowing through the generator becomes equal to or less than the predetermined value.    
     
     
         10 . The heat pump apparatus according to  claim 1 , further comprising: 
 a protection circuit connected to the variable-speed converter, for consuming or storing regenerative power generated by the generator in place of the motor.    
     
     
         11 . The heat pump apparatus according to  claim 10 , wherein: 
 the protection circuit comprises a first switch provided on a DC power line connected to the variable-speed converter, a second switch connected to the DC power line between the first switch and the variable-speed converter and in parallel to the variable-speed converter, and a load or an electricity storage unit connected to the DC power line in series with the second switch; and    by turning the first switch off and turning the second switch on, the regenerative power is consumed by the load or the regenerative power is stored in the electricity storage unit.    
     
     
         12 . A heat pump apparatus, comprising: 
 an expander for expanding a working fluid;    a generator connected to the expander, for converting mechanical power into electric power, the mechanical power being recovered by the expander when the working fluid expands;    a variable-speed converter connected to the generator, for converting alternating current generated by the generator into direct current; and    a protection circuit connected to the variable-speed converter, wherein the protection circuit is supplied with a control signal while the expander is being driven, and consumes or stores regenerative power generated by the generator when the supply of the control signal stops.    
     
     
         13 . The heat pump apparatus according to  claim 12 , wherein: 
 the protection circuit comprises a first switch provided on a DC power line connected to the variable-speed converter, a second switch connected to the DC power line between the first switch and the variable-speed converter and in parallel to the variable-speed converter, and a load or an electricity storage unit connected to the DC power line in series with the second switch; and    if the supply of the control signal stops, the first switch is turned off and the second switch is turned on.