Standby variable frequency compressor drive

Abstract

A transport refrigeration system is provided with a variable speed compressor which is operated only in the low capacity perishable range of operation. In this way, the line voltage and frequency power can be used during high capacity operation and a relatively small inverter can be used to provide variable voltage and frequency for the variable speed operation. The variable voltage and frequency can also be provided to a variable speed condenser motor to provide additional condensing capacity during economized operation. It can also be used to provide DC voltage to the compressor for heating purposes.

1 . A method of operating a transport refrigeration system of the type having a compressor and associated vapor compression circuitry, an economizer circuit, and an evaporator flow control apparatus, comprising the steps of:
 providing a variable speed capability to the compressor;   providing an inverter for selectively providing either line voltage and frequency or variable voltage and variable frequency power to said compressor;   operating said compressor at fixed speeds during high capacity operation to pull down the load to the perishable range; and   operating said compressor at variable speeds during low capacity operation in the perishable range.   
   
   
       2 . A method as set forth in  claim 1  wherein, during fixed speed operation, the vapor compression circuit is used in combination with the economizer circuit. 
   
   
       3 . A method as set forth in  claim 1  wherein, during fixed speed operation, the vapor compression circuit is used without the economizer circuit. 
   
   
       4 . A method as set forth in  claim 1  wherein, during fixed speed operation, the vapor compression circuit is used in combination with the evaporator flow control apparatus. 
   
   
       5 . A method as set forth in  claim 1  wherein, during low capacity operation, line voltage and frequency power is provided to the compressor. 
   
   
       6 . A method as set forth in  claim 5  wherein the evaporator flow control apparatus is used until the temperature demand is stable. 
   
   
       7 . A method as set forth in  claim 6  wherein, when the evaporator flow control apparatus valve starts to close, the line voltage and frequency power will be switched to variable frequency voltage and frequency power to drive the compressor at variable speed. 
   
   
       8 . A method as set forth in  claim 1  and including the further step of providing a variable speed condenser fan motor and selectively applying variable voltage and frequency power thereto when operating with the economizer. 
   
   
       9 . A method as set forth in  claim 1  and including the step of using the variable frequency and voltage power to provide a DC voltage to the compressor for heating purposes. 
   
   
       10 . A method of operating a transport refrigeration system of the type having a vapor compression circuit with an economizer, an evaporator flow control apparatus, and a compressor receiving power from a power source by way of controller and adapted to operate, at times, under part load conditions comprising:
 providing an inverter for receiving a fixed voltage and frequency from the power source and converting it to a variable voltage and frequency power output;   providing a compressor that is capable of operating at either fixed or variable speed operation;   providing a switch to selectively include or exclude said inverter from the circuit to provide either a fixed voltage and frequency or a variable voltage and frequency to said variable speed compressor; and   using said variable voltage and frequency only during periods of part load operating conditions.   
   
   
       11 . A method as set forth in  claim 10  wherein, during fixed speed operation, the vapor compression circuit is used in combination with the economizer circuit. 
   
   
       12 . A method as set forth in  claim 10  wherein, during fixed speed operation, the vapor compression circuit is used without the economizer circuit. 
   
   
       13 . A method as set forth in  claim 10  wherein, during fixed speed operation, the vapor compression circuit is used in combination with the evaporator flow control apparatus. 
   
   
       14 . A method as set forth in  claim 10  wherein, during low capacity operation, fixed voltage and frequency power is provided to the compressor. 
   
   
       15 . A method as set forth in  claim 14  wherein the evaporator flow control apparatus is used until the temperature demand is stable. 
   
   
       16 . A method as set forth in  claim 15  wherein when the evaporator flow control apparatus starts to close, the line voltage and frequency power will be switched to variable frequency voltage and frequency power to drive the compressor at variable speed. 
   
   
       17 . A method as set forth in  claim 10  and including the further step of providing a variable speed condenser fan motor and selectively applying variable voltage and frequency power thereto when operating with the economizer. 
   
   
       18 . A method as set forth in  claim 10  and including the step of using the variable frequency and voltage power to provide a DC voltage to the compressor for heating purposes.