Patent Publication Number: US-11383584-B2

Title: Device and method for controlling operation of transport refrigeration unit

Description:
FIELD 
     The embodiments disclosed herein relate generally to devices and methods directed to controlling an operation of a transport refrigeration unit (“TRU”). 
     BACKGROUND 
     Transport refrigeration systems (“TRS”s) are used to cool a container (typically referred to as a refrigerated transport unit or “TU”). The TU can be used to transport perishable items such as produce and meat products. In such a case, the TRS can be used to condition the air inside a cargo space of the TU, thereby maintaining desired temperature and humidity during transportation or storage. Different perishable items can require different desired temperatures during transport. A TRU is attached to the TU to facilitate a heat exchange between the air inside the cargo space and the air outside of the TU. Some TRUs have a compressor which is directly coupled to an engine (e.g., the engine of a vehicle connected to the TU). The engine coupled to the compressor transfers power to the compressor to provide cooling or heating capacity to the TU (e.g., to the volume of space inside the TU). Generally, the engine provides the compressor with two operation modes: (1) a low speed operation mode, and (2) a high speed operation mode. The low speed operation mode is used to control the temperature when the TU has reached a setpoint temperature (e.g., desired temperature) and thus requires low refrigeration system capacity. The high speed operation mode is used during pull-down or pull-up situations when the TU is far away from the setpoint temperature, and thus higher refrigeration system capacity is necessary to change the temperature of the TU to the setpoint temperature. The engine uses more fuel when the compressor is operating in the high speed operation mode than operating in the low speed operation mode. Generally, when the TRS is in operation, the TU can switch between the two discrete speed operation modes (i.e., the low speed operation mode and the high speed operation mode) several times based on the setpoint temperature and the temperature of the TU because the temperature of the TU can change due to the ambient temperature changes and other factors. 
     SUMMARY 
     Generally, because the TRU is coupled to the engine, the lowest possible engine speed is considered to provide the best fuel consumption. It has been found that using only the lowest possible engine speed is not necessarily “optimal” because running the engine at the lowest possible engine speed can require a very long time for the temperature inside the TU to reach the setpoint or desired temperature (e.g., temperature required for a particular cargo) in the TU. Accordingly, operating the engine at the lowest engine speed can result in a high amount engine operation hours (e.g., engine duty cycle) for a given amount of temperature control hours. High engine duty cycle can result in poor resale value of the TRU (e.g., much like a car having a high mileage reading on the odometer). 
     Further, there are situations when it is desirable to bring the temperature inside the TU to a desired or setpoint temperature quickly (sometimes, even as soon as possible, for example, to prevent spoilage of cargo stored in the TU). In such situations, the engine can be operated at the highest possible engine speed to bring the temperature inside the TRU to the setpoint, but such operation can result in very poor fuel consumption. 
     Accordingly, it has been found that the engine which provides the compressor with only two operation modes (a low speed operation mode, and a high speed operation mode) cannot optimize fuel consumption in real world transport refrigeration applications. 
     According to an embodiment, the TRU includes a controller device. The controller device refers to an electronic device, which includes a processor component and a non-transitory computer-readable medium (e.g., memory, computer-readable storage, etc.). The controller device commands, directs and/or regulates the operation of a compressor of the TRU. An embodiment of the controller device of the TRU operates the compressor of the TRU to have a continuously-variable speed mode which allows the compressor to run continuously but with a smooth gradient range of speed variations. Thus, the compressor can be operated in continuously have varying speeds instead of the discrete two speeds (i.e., the low speed operational mode, and the high speed operational mode). Thus, the TRU can have several operating stages, such as, for example, start-stop operation stage, continuous run operation stage, and/or a cycle-sentry operation stage. 
     According to an embodiment, the compressor does not have only the two operating modes (low speed and high speed). That is, the compressor, according to an embodiment, can be operated at variable speeds of more than two speeds. 
     The compressor, according to an embodiment, can be operated at continuously variable speeds (e.g., not discrete speeds). 
     Further, the compressor, according to an embodiment, can be operated at a range of speeds that is greater than the range of speed of the engine to which the compressor is coupled to. 
     The engine directly coupled to the compressor, according to an embodiment, can be operated at continuously variable speeds (e.g., not discrete speeds). 
     Further, according to an embodiment, the engine that is directly coupled to the compressor does not drive the compressor to have only the two operating modes (low speed and high speed). That is, the engine drives the compressor so that the compressor operates at variable speeds of more than two speeds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic drawing of an embodiment of a transport refrigeration system including a TRU and a TU. 
         FIG. 2  shows a schematic drawing of an embodiment of a controller device which controls an operation of a TRU. 
         FIG. 3  shows a schematic flowchart for an embodiment of a method for controlling an operation of the compressor of the TRU according to computer-readable and computer-executable instructions stored in a non-transitory computer-readable memory which can be executed by a processor. 
         FIG. 4  shows a schematic flowchart for another embodiment of a method for controlling the operation of the compressor of the TRU according to computer-readable and computer-executable instructions stored in the non-transitory computer-readable memory which can be executed by the processor. 
     
    
    
     DETAILED DESCRIPTION 
     The fuel efficiency of the TU when the TRS is in operation can be improved by controlling the TU to operate according to the embodiments disclosed herein. 
       FIG. 1  shows an embodiment of a TRS  100 . The TRS  100  includes a TRU  102 , and a TU  104  (e.g., a container) to which the TRU  102  is connected to for controlling the environment inside the TU  104 . 
     An engine  106  is connected to the TRU  102  for powering the TRU  102 , and a controller device  110  is in communication with the engine  106  and the TRU  102  for operating the TRU  102 . The TRU  102  includes a compressor  108  which is directly coupled to the engine  106 . The compressor  108  is a part of the refrigerant fluid circuit  112  of the TRU  102 , wherein the refrigerant fluid circuit  112  includes a condenser and an evaporator through which a refrigerant fluid flows. The flow of the refrigerant fluid through the refrigerant fluid circuit  112  is provided by, at least, the compressor  108 . The refrigerant fluid circuit  112  includes a capacity limiting device  114 , which can be for example, an electronic throttling valve (ETV). 
     The controller device  110  is in communication with the engine  106  for controlling the operation of the engine  106 . Because the engine  106  is coupled to the compressor  108 , the controller device  110  can control the operation of the compressor  108  by controlling the engine  106 . 
     The TRU  102  directs the flow of heat between the outside of the TU  104  and the inside of the TU  104  (e.g., flow of heat shown as arrows  116 ,  118  in  FIG. 1 ). That is, the refrigerant fluid circuit  112  of the TRU  102  can direct the flow of heat  116 ,  118  from the outside of the TU  104  to the inside of the TU  104 , or from the inside of the TU  104  to the outside of the TU  104 . 
     The controller device  110  is in communication with the capacity limiting device  114  (e.g., ETV) and controls the opening and/or closing of the capacity limiting device  114 . In certain situations, as described below in regards to  FIG. 4 , the controller device  110  opens the capacity limiting device  114 , as much as 100% (which means completely open). In certain situations, as described below in regards to  FIG. 4 , the controller device  110  opens the capacity limiting device  114 , as little as 0% (which means the capacity limiting device  114  is completely closed). Accordingly, the controller device  110  can be configured to control the capacity limiting device  114  to be open in the range of 0% (completely closed) to 100% (completely open). 
     The controller device  110  is in communication with one or more sensor devices  120 ,  122  and receives data from the sensor devices  120 ,  122 . Based on the data received, the controller device  110  controls the operation of the engine  106  and thus the compressor  108  for affecting the environment conditions inside the TU  104 . For example, one of the sensor devices  120  can detect and/or measure the ambient temperature outside of the TU  104 . Another one of the sensor devices  122  can detect and/or measure the temperature inside the TU  104 . Accordingly, the controller device  110  can control the operation of the engine  106 , which drives the compressor  108 , based on the received data from the sensor devices  120 ,  122 , wherein the received data include the ambient temperature outside of the TU  104  (“Tamb”) and the temperature inside the TU  104  (“Tbox”). 
     The controller device  110  controls the operation of the engine  106  (thus, the compressor  108  of the TRU  102 ) so that the compressor  108  has a continuously-variable speed mode which allows the compressor  108  to run continuously but with a smooth gradient range of speed variations. Thus, the compressor  108  operates in continuously varying speeds, and can provide continuously varying temperature control rates to the TU  104 . 
       FIG. 2  shows an embodiment of the controller device  200  which is similar to the controller device  110  shown in  FIG. 1 . The controller device  200  includes, but is not necessarily limited by, a processor component  202  in communication with an interface component  204  for communicating with other components, such as for example, the engine (e.g.,  106  shown in  FIG. 1 ), the sensor devices (e.g.,  120 ,  122  shown in  FIG. 1 ), and the capacity limiting device (e.g.,  114  shown in  FIG. 1 ). Although not shown, the interface component  204  can also be in communication with the compressor (e.g.,  108  shown in  FIG. 1 ) so that the processor component  202  can send and/or receive data to and/or from the compressor (e.g.,  108  shown in  FIG. 1 ) via the interface component  204 . The controller device  200  also includes a non-transitory computer-readable memory  206  that is in communication with the processor component  202 . The non-transitory computer-readable memory  206  has stored therein computer-readable and computer-executable instructions  208  that can be executed by the processor component  202  to control the TRU (e.g.,  102  shown in  FIG. 1 ) according to one or more of the embodiments of the methods shown in  FIGS. 3 and 4 . Accordingly, the computer-readable and computer-executable instructions  208  can be instructions for carrying out one or more of the methods shown in  FIGS. 3 and 4 . Thus, the processor component  202  can execute the computer-readable and computer-executable instructions  208  for carrying out one or more of the methods shown in  FIGS. 3 and 4 . 
       FIG. 3  shows a flowchart  300  for an embodiment of a method in computer-readable and computer-executable instructions (e.g.,  208  shown in  FIG. 2 ) stored in a non-transitory computer-readable memory (e.g.,  206  shown in  FIG. 2 ) which can be executed by a processor component (e.g.,  202  shown in  FIG. 2 ) for controlling an operation of the compressor (e.g.,  108  shown in  FIG. 1 ) of the TRU (e.g.,  102  shown in  FIG. 1 ). Accordingly, when computer-readable and computer-executable instructions are executed by the processor component (e.g.,  202  shown in  FIG. 2 ) of the TRU, the following method is performed by the controller device (e.g.,  110  shown in  FIG. 1, and 200  shown in  FIG. 2 ) for controlling the operation of the compressor (e.g.,  108  shown in  FIG. 1 ) of the TRU. The process shown in  FIG. 3  includes examples of a start-stop operation stage of the TRU and a cycle-sentry operation stage of the TRU. 
     In step  302 , the TRU is set to a “NULL” mode, wherein the controller device is on and operational, but the refrigeration system is off (e.g., the compressor is not operating to control the temperature in the TU). Thus, at this stage, the TRU is at a “stop” of the start-stop operation stage of the TRU. 
     In step  304 , which is prior to the refrigeration system is turned on for controlling the temperature in the TU, the controller device receives or collects temperature data from one or more of the sensor devices (e.g.,  120 ,  122  shown in  FIG. 1 ) that the TRU is in communication with. For example, as shown in  FIG. 1  and described above, the controller device receives ambient temperature data (Tamb) and the temperature inside the TU (Tbox) from the respective sensor devices. The controller device also receives an input of the temperature setpoint (“Tsetpoint”), which is the desired temperature inside the TU. The Tsetpoint is stored in the non-transitory computer-readable memory. 
     In step  306 , the processor component of the controller device determines the target compressor speed to be reached based on the Tamb, Tbox, and Tsetpoint information stored in the non-transitory computer-readable memory. For example, the controller device&#39;s computer-readable memory has stored therein a look-up table or database which has a correlation of the compressor speed based on the three variables, Tamb, Tbox, and Tsetpoint. The processor component operates with information which associates the target compressor speed to an expected rate of change to Tbox with respect to time based on Tamb. Thus, the controller device can determine the target compressor speed and/or expected rate of change to Tbox with respect to time based on the look-up table or database. As another example, the processor component of the controller device can determine the target compressor speed on the fly based on the three variables, Tamb, Tbox, and Tsetpoint. Accordingly, the processor component can also be configured to determine the expected rate of change to Tbox with respect to time. Then the refrigeration system is turned on and the controller device controls the engine speed in order to achieve the target compressor speed (and thus, the expected rate of change to Tbox with respect to time). The expected rate of change to Tbox with respect to time can be called the “target rate” and the TRU at this stage is at the “start” in the start-stop operation stage of the TRU. 
     Steps  308  to  320  shown in  FIG. 3  is an example of a cycle-sentry operation of the TRU as performed by the controller device. 
     In step  308 , the controller device receives, continuously or frequently, Tbox data from the sensor device (e.g.,  122  shown in  FIG. 1 ) and an actual rate of change to Tbox with respect to time is determined by the processor component of the controller device. The processor component of the controller device makes a determination of whether the actual rate of change to Tbox with respect to time is higher than the target rate determined in step  306 , or whether the actual rate of change to Tbox with respect to time is lower than the target rate determined in step  306 . From step  308 , the controller device can proceed to either step  310  or step  316 . 
     In step  310 , when the controller device determines that the actual rate of change to Tbox with respect to time is higher than the target rate. 
     Then, in step  312 , the controller device decreases the compressor speed (e.g., by controlling the engine to slow the speed of the engine) in order to reduce the magnitude of the actual rate of change to Tbox with respect to time. 
     In step  314 , after the change to the compressor speed, the controller device receives Tbox data from the sensor device (e.g.,  122  shown in  FIG. 1 ) and another actual rate of change to Tbox with respect to time is determined by the processor component of the controller device. The controller device determines a new target rate based on some of the variables from the following: Tamb, Tbox, Tsetpoint, and the most recently determined actual rate of change to Tbox with respect to time. This new target rate is likely different from the target rate determined in step  306 . For example, the magnitude of the new target rate can be less than the magnitude of the target rate determined in step  306 . Then, based on the new target rate, the controller device determines a new target compressor speed and controls the operation of the compressor to achieve the new target compressor speed via controlling the speed of the engine. From step  314 , the controller device proceeds to step  322 . 
     Alternative to step  310 , in step  316 , the controller device determines that the actual rate of change to Tbox with respect to time is lower than the target rate. 
     Then, in step  318 , the controller device increases the compressor speed (e.g., by controlling the engine to increase the speed of the engine) in order to increase the magnitude of the actual rate of change to Tbox with respect to time. 
     In step  320 , after the change to the compressor speed, the controller device receives Tbox data from the sensor device (e.g.,  122  shown in  FIG. 1 ) and another actual rate of change to Tbox with respect to time is determined by the processor component of the controller device. The controller device determines a new target rate based on some of the variables from the following: Tamb, Tbox, Tsetpoint, and the most recently determined actual rate of change to Tbox with respect to time. This new target rate is likely different from the target rate determined in step  306 . For example, the magnitude of the new target rate can be greater than the magnitude of the target rate determined in step  306 . Then, based on the new target rate, the controller device determines a new target compressor speed and controls the operation of the compressor to achieve the new target compressor speed via controlling the speed of the engine. From step  320 , the controller device proceeds to step  322 . 
     Once the Tbox has reached the Tsetpoint, in step  322 , the TRU is set to a “NULL” mode, wherein the controller device is on and operational, but the refrigeration system is off (e.g., the compressor is not operating to control the temperature in the TU, similar to in step  302 ). Then, the controller device proceeds to step  304  to continue the operation cycle. It is expected that the controller device according to this method can lead to about 15% to 20% improvement in the fuel efficiency for the engine coupled to the compressor of the TRU. And again, at this stage, the TRU is at a “stop” of the start-stop operation stage of the TRU. 
     Further, the method for controlling the TRU via variable speed can also provide a range for the speed of the compressor that is broader than the range for the speed of the engine. Accordingly, a range for refrigeration capacity (e.g., mass flow) can be made broader than the range of the compressor speed, thus also broader than the range for the speed of the engine. 
     In another embodiment, the continuously variable speed control of the compressor speed is replaced by a multi-stage (e.g., more than two speeds), quantized speed control. 
       FIG. 4  shows a flowchart  400  for an embodiment of a method in computer-readable and computer-executable instructions (e.g.,  208  shown in  FIG. 2 ) stored in a non-transitory computer-readable memory (e.g.,  206  shown in  FIG. 2 ) which can be executed by a processor component (e.g.,  202  shown in  FIG. 2 ) for controlling an operation of the compressor (e.g.,  108  shown in  FIG. 1 ) of the TRU (e.g.,  102  shown in  FIG. 1 ). Accordingly, when the computer-readable and computer-executable instructions are executed by the processor component of the TRU, the following method is performed by the controller device (e.g.,  110  shown in  FIG. 1, and 200  shown in  FIG. 2 ) for controlling the operation of the compressor (e.g, by controlling the operation of the engine  106  shown in  FIG. 1 ). The process shown in  FIG. 4  includes an example of a continuous operation stage of the TRU. 
     In step  402 , the TRU is already on, and Tbox has reached the Tsetpoint. Thus, the step  402  likely follows the method shown in  FIG. 3 . The controller device controls the operation of the engine so that the compressor of the TRU runs at the lowest permissible speed. In an embodiment of the TRU, the controller device can control the continuously variable speed compressor to operate at an ultra-low speed operation mode, which leads to even greater fuel efficiency. This step can be in either COOL or HEAT mode, depending on whether the Tbox is above or below Tsetpoint, and whether Tamb is above or below Tsetpoint. Further, the TRU includes a capacity limiting device (e.g., an electronic throttling valve (ETV)) which is open 100% at this step. From step  402 , either step  404  or step  410  is possible. 
     In step  404 , the controller device detects that the Tbox is drifting away from Tsetpoint in the same direction of the temperature control mode of the TRU, for example, the Tbox drift direction is going below Tsetpoint when in COOL mode, or the Tbox drift direction is going above Tsetpoint when in HEAT mode. Then, in step  406 , the controller device recognizes that the TRU has more capacity than required to hold Tbox at Tsetpoint. Then, in step  408 , the compressor is still operating at the lowest permissible speed (preferably at the ultra-low speed operation mode), but the capacity limiting device (e.g., the ETV) closes to maintain Tbox at or near Tsetpoint. That is, the ETV can be closed to stop the Tbox drifting further away from the Tsetpoint. 
     In step  410 , the controller device detects that the Tbox is drifting away from Tsetpoint in the opposite direction of the temperature control mode of the TRU, for example, the Tbox drift direction is going above Tsetpoint when in COOL mode, or the Tbox drift direction is going below Tsetpoint when in HEAT mode. Then, in step  412 , the controller device recognizes that the TRU does not have enough capacity to hold Tbox at Tsetpoint. Then, in step  414 , the controller device increases the engine speed to compensate for the temperature drift in order to bring Tbox back to Tsetpoint. The capacity limiting device (e.g., the ETV) is still open 100% at this stage. 
     Accordingly, the controller device operates to improve temperature control by providing only the TRU output capacity necessary to maintain Tbox at Tsetpoint. Fuel consumption can be improved because the TRU is not required to cycle between low and high engine speeds or cycle between COOL and HEAT modes to maintain Tbox at Tsetpoint. 
     From either steps  408  or  414 , the method  400  proceeds to step  416  of exiting the modulation control (either ETV modulation of  408  or the engine modulation of  414 ) when the controller device determines that Tbox exceeds the modulation control band range (e.g., in situations such as when a door of the TU is opened, Tsetpoint has been changed, etc.). Then, the controller device changes operating mode from continuous operating mode in  FIG. 4  to the start-stop operating mode in  FIG. 3  to bring Tbox to Tsetpoint. Then, the process can switch to the continuous operating mode by proceeding to step  402 . 
     Further, it is expected that the methods shown in  FIGS. 3 and 4  can advantageously and surprisingly improve fuel efficiency by about 10% in the cycle-sentry operation stage (e.g.,  FIG. 3 ), and by about 15-20% in continuous run operation stage (e.g., see  FIG. 4 ). 
     Aspects 
     Any of the elements in the following Aspects can be combined together. 
     Aspect 1. A controller device for controlling an operation of a transport refrigeration unit, wherein the controller device operates the compressor of the transport refrigeration unit to have a variable refrigeration capacity. 
     Aspect 2. The controller device according to Aspect 1, wherein the controller device operates the compressor of the transport refrigeration unit to have a variable speed mode which allows the compressor to run continuously with a gradient range of speed variations to have the variable refrigeration capacity.
 
Aspect 3. The controller device according to any one or more of Aspects 1-2, wherein the variable speed mode includes a continuously-variable speed mode, and the gradient range of speed variations includes a continuously-variable speed mode.
 
Aspect 4. The controller device according to any one or more of Aspects 1-3, wherein the compressor does not operate in discrete speeds.
 
Aspect 5. The controller device according to any one or more of Aspects 1-4, wherein compressor does not operate in discrete speeds consisting of a low speed and a high speed.
 
Aspect 6. The controller device according to any one or more of Aspects 1-5, wherein the transport refrigeration unit includes a start-stop operation stage.
 
Aspect 7. The controller device according to any one or more of Aspects 1-6, wherein the transport refrigeration unit further includes a cycle-sentry operation stage.
 
Aspect 8. The controller device according to any one or more of Aspects 1-7, wherein the transport refrigeration unit further includes a continuous run operation stage.
 
Aspect 9. The controller device according to any one or more of Aspects 1-8, wherein the transport refrigeration unit includes one or more of a start-stop operation stage, a cycle-sentry operation stage, and a continuous run operation stage.
 
Aspect 10. The controller device according to any one or more of Aspects 1-9, wherein the controller device receives temperature data from one or more sensor devices; and the controller device determines a target compressor speed to be reached based on the temperature data.
 
Aspect 11. The controller device according to any one or more of Aspects 1-10, wherein the controller device controls the compressor speed in order to achieve the target compressor speed.
 
Aspect 12. The controller device according to any one or more of Aspects 1-11, wherein the controller device determines an expected rate of change to a temperature inside a transport unit with respect to time; the controller device determines an actual rate of change to the temperature inside the transport unit with respect to time based on temperature data from one or more sensor devices; and the controller device performs a comparison of the expected rate of change to the actual rate of change and controls the compressor speed based on the comparison of the expected rate of change to the actual rate of change.
 
Aspect 13. The controller device according to any one or more of Aspects 1-12, wherein the controller device receives a temperature of an inside a transport unit; the controller device compares the temperature inside the transport unit to a preset setpoint temperature; and when the controller device determines that the temperature inside the transport unit is equal to the preset setpoint temperature, the controller device controls the compressor to operate a lowest speed in the continuously variable speed mode.
 
Aspect 14. The controller device according to any one or more of Aspects 1-13, wherein the controller device determines the temperature inside the transport unit drifting away from the preset setpoint temperature, and a direction of temperature drift; and the controller device controlling a capacity limiting device of the transport refrigeration unit for modulating refrigeration capacity of the transport unit.
 
Aspect 15. The controller device according to any one or more of Aspects 1-14, wherein the controller device determines the temperature inside the transport unit drifting away from the preset setpoint temperature, and a direction of temperature drift; and the controller device controlling the compressor speed for modulating refrigeration capacity of the transport unit.
 
Aspect 16. A method for electronically controlling a transport refrigeration unit, comprising:
 
     a controller device receiving temperature data from one or more sensor devices; and 
     the controller device determining a target compressor speed to be reached based on the temperature data; and 
     the controller device controlling a compressor to achieve the target compressor speed. 
     Aspect 17. The method according to Aspect 16, further comprising: 
     the controller device determining an expected rate of change to a temperature inside a transport unit with respect to time; 
     the controller device determining an actual rate of change to the temperature inside the transport unit with respect to time based on temperature data from one or more sensor devices; 
     the controller device performing a comparison of the expected rate of change to the actual rate of change; and 
     the controller device controlling the compressor speed based on the comparison of the expected rate of change to the actual rate of change. 
     Aspect 18. The method according to any one or more of Aspects 1-17, further comprising: 
     the controller device receiving a temperature inside a transport unit; 
     the controller device comparing the temperature inside the transport unit to a preset setpoint temperature; 
     the controller device determining that the temperature inside the transport unit is equal to the preset setpoint temperature; and 
     the controller device controlling the compressor to operate a lowest speed in the continuously variable speed mode. 
     Aspect 19. The method according to any one or more of Aspects 1-18, further comprising: 
     the controller device determining that the temperature inside the transport unit is drifting away from the preset setpoint temperature, and a direction of temperature drift; and 
     the controller device controlling a capacity limiting device of the transport refrigeration unit for modulating the variable refrigeration capacity of the transport unit. 
     Aspect 20. The method according to any one or more of Aspects 1-19, further comprising: 
     the controller device determining the temperature inside the transport unit is drifting away from the preset setpoint temperature, and a direction of temperature drift; and 
     the controller device controlling the compressor speed for modulating the variable refrigeration capacity of the transport unit. 
     Aspect 21. A transport refrigeration unit, comprising: 
     a compressor connected to a refrigeration fluid circuit; and 
     a controller device for controlling an operation of the compressor according to any one or more of Aspects 1-15. 
     Aspect 22. The transport refrigeration unit according to Aspect 21, wherein the controller device operates the compressor to have one or more of a start-stop operation stage, a cycle-sentry operation stage, and a continuous run operation stage. 
     Aspect 23. A transport refrigeration unit, comprising: 
     a compressor connected to a refrigeration fluid circuit; and 
     a controller device, wherein a method of operation performed by the controller device is according to any one or more of the methods in Aspects 16-20. 
     With regard to the foregoing description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size and arrangement of the parts without departing from the scope of the present invention. It is intended that the specification and depicted embodiment to be considered exemplary only, with a true scope and spirit of the invention being indicated by the broad meaning of the claims.