Continuous compressor envelope protection

Abstract

A transport refrigeration system is provided with a control apparatus including an inverter and a microprocessor, with the microprocessor receiving signals representative of sensed values of the compressor discharge temperature and pressure, as well as the suction pressure, and controlling the inverter to responsively provide a selective level of electrical voltage and frequency to the compressor in order to maintain a desired compressor envelope.

1 . A control apparatus for a transport refrigeration system of the type having a generator driven by an engine with the generated electrical power being supplied to a compressor of a closed loop vapor compression system, comprising:
 a temperature sensor for sensing the discharge temperature of the compressor and generating a temperature signal representative thereof;   a first pressure sensor for sensing the suction pressure of the compressor and generating a suction pressure signal representative thereof;   a second pressure sensor for sensing the discharge pressure of the compressor and generating a discharge pressure signal representative thereof;   a microprocessor for receiving said temperature signal, said suction pressure signal and said discharge pressure signal and generating an inverter control signal in response thereto; and   an inverter for receiving said inverter control signal from said microprocessor and for receiving electrical power from the generator and for providing a level of electrical power to the compressor in response to said inverter control signal.   
     
     
         2 . A control apparatus as set forth in  claim 1  wherein said transport refrigeration system includes a box being refrigerated by said vapor compression system. 
     
     
         3 . A control apparatus as set forth in  claim 2  wherein said control apparatus includes a temperature sensor for sensing the temperature of air being returned from said box and for responsively sending a return air temperature signal to said microprocessor, with said inverter control signal then being responsive thereto. 
     
     
         4 . A control apparatus as set forth in  claim 1  wherein the electric power from said generator to said inverter is unregulated ac voltage. 
     
     
         5 . A control apparatus as set forth in  claim 1  wherein said electrical power from said inverter to said compressor is regulated ac current. 
     
     
         6 . A control apparatus as set forth in  claim 5  wherein said power is regulated by selectively varying the voltage, frequency and/or current. 
     
     
         7 . A control apparatus as set forth in  claim 1  wherein the level of electrical power to the compressor is controlled in order to maintain the saturated suction temperature of the compressor within a predetermined range. 
     
     
         8 . A control apparatus as set forth in  claim 7  wherein said saturated suction temperature is maintained within a range of −40° C. to 2° C. 
     
     
         9 . A control apparatus as set forth in  claim 1  wherein the level of electrical power to the compressor is controlled so as maintain a saturated discharge temperature within a predetermined range. 
     
     
         10 . A control apparatus as set forth in  claim 9  wherein said range is between 10° C. and 66° C. 
     
     
         11 . A control apparatus as set forth in  claim 1  wherein said microprocessor includes at least three different control modules, with each module being controlled in response to sensed values of, and operating to control, parameters of discharge pressure, discharge temperature and/or suction pressure. 
     
     
         12 . A control apparatus as set forth in  claim 11  and including a fourth control module which is responsive to sensed values of, and operates to control, a return air temperature. 
     
     
         13 . A control apparatus as set forth in  claim 11  wherein only one control module is operated at a time. 
     
     
         14 . A control apparatus as set forth in  claim 11  wherein the control module which controls the discharge temperature has priority over the other control modules. 
     
     
         15 . A method of controlling a transport refrigeration system of the type having a generator driven by an engine with the generated electrical power being supplied to a compressor of a closed loop compression system, comprising the steps of:
 sensing the discharge temperature of the compressor and generating a temperature signal representative thereof;   sensing the suction pressure of the compressor and creating a suction pressure signal representative thereof;   sensing the discharge pressure of the compressor and generating a discharge pressure signal representative thereof;   sending said temperature signal, said suction pressure signal, and said discharge pressure signal to a microprocessor and generating an inverter control signal in response thereto; and   sending said inverter control signal to an inverter for responsively providing the desired electrical voltage and frequency to the compressor.   
     
     
         16 . A method as set forth in  claim 15  wherein said transport refrigeration system includes a box being refrigerated by said vapor compression system. 
     
     
         17 . A method as set forth in  claim 16  and including the steps of sensing the temperature of air being returned from said box and for responsively sending a return air temperature signal to said microprocessor, with said inverter control signal then being responsive thereto. 
     
     
         18 . A method as set forth in  claim 15  wherein the electric power from said generator to said inverter is unregulated ac current. 
     
     
         19 . A method as set forth in  claim 15  wherein said electrical power from said inverter to said compressor is regulated ac current. 
     
     
         20 . A method as set forth in  claim 19  wherein said power is regulated by selectively varying the voltage, frequency and/or current. 
     
     
         21 . A method as set forth in  claim 15  wherein the level of electrical power voltage and frequency to the compressor is controlled in order to maintain the saturated suction temperature of the compressor within a predetermined range. 
     
     
         22 . A method as set forth in  claim 21  wherein said saturated suction temperature is maintained within a range of −40° C. to 2° C. 
     
     
         23 . A method as set forth in  claim 15  wherein the level of electrical power to the compressor is controlled so as maintain a saturated discharge temperature within a predetermined range. 
     
     
         24 . A method as set forth in  claim 23  wherein said range is between 10° C. and 66° C. 
     
     
         25 . A method as set forth in  claim 15  wherein said microprocessor includes at least three different control modules, with each module being controlled in response to sensed values of, and operating to control limited parameters of, discharge pressure, discharge temperature or suction pressure. 
     
     
         26 . A method as set forth in  claim 25  and including a fourth control module which is responsive to sensed values of, and operates to control, a return air temperature. 
     
     
         27 . A method as set forth in  claim 25  wherein only one control module operates at a time. 
     
     
         28 . A method as set forth in  claim 25  wherein the control module which controls the discharge temperature has priority over the other control modules.