Patent ID: 12244245

DETAILED DESCRIPTION

Referring toFIG.1, a transport refrigeration system20includes a refrigeration unit22. The refrigeration unit22functions, under the control of a controller30, to establish and regulate a desired product storage temperature within a refrigerated cargo space wherein a perishable product is stored during transport and to maintain the product storage temperature within a specified temperature range. The refrigerated cargo space may be the cargo box of a trailer, a truck, a seaboard shipping container or an intermodal container wherein perishable cargo, such as, for example, produce, meat, poultry, fish, dairy products, cut flowers, pharmaceuticals, and other fresh or frozen perishable products, is stowed for transport.

The refrigeration unit22includes a refrigerant compression device32, a refrigerant heat rejection heat exchanger34, an expansion device36, and a refrigerant heat absorption heat exchanger38connected in refrigerant flow communication in a closed loop refrigerant circuit and arranged in a conventional refrigeration cycle. The refrigeration unit22also includes one or more fans40associated with the refrigerant heat rejection heat exchanger34and driven by fan motor(s)42and one or more fans44associated with the refrigerant heat absorption heat exchanger38and driven by fan motor(s)46. The refrigeration unit22may also include an electric resistance heater48associated with the refrigerant heat absorption heat exchanger38. The electric resistance heater48may be used, for example, for defrost or temperature control. It is to be understood that other components (not shown) may be incorporated into the refrigerant circuit as desired, including for example, but not limited to, a suction modulation valve, a receiver, a filter/dryer, an economizer circuit.

The refrigerant heat rejection heat exchanger34may, for example, comprise one or more refrigerant conveying coiled tubes or one or more tube banks formed of a plurality of refrigerant conveying tubes extending between respective inlet and outlet manifolds. The fan(s)40are operative to pass air, typically ambient air, across the tubes of the refrigerant heat rejection heat exchanger34to cool refrigerant vapor passing through the tubes. The refrigerant heat rejection heat exchanger34may operate either as a refrigerant condenser, such as if the refrigeration unit22is operating in a subcritical refrigerant cycle or as a refrigerant gas cooler, such as if the refrigeration unit22is operating in a transcritical cycle.

The refrigerant heat absorption heat exchanger38may, for example, also comprise one or more refrigerant conveying coiled tubes or one or more tube banks formed of a plurality of refrigerant conveying tubes extending between respective inlet and outlet manifolds. The fan(s)44are operative to pass air drawn from the temperature controlled cargo box across the tubes of the refrigerant heat absorption heat exchanger38to heat and evaporate refrigerant liquid passing through the tubes and cool the air. The air cooled in traversing the refrigerant heat rejection heat exchanger38is supplied back to the temperature controlled cargo box. It is to be understood that the term “air” when used herein with reference to the atmosphere within the cargo box includes mixtures of air with other gases, such as for example, but not limited to, nitrogen or carbon dioxide, sometimes introduced into a refrigerated cargo box for transport of perishable produce.

The refrigerant compression device32may comprise a single-stage or multiple-stage compressor such as, for example, a reciprocating compressor or a scroll compressor. The compression device32has a compression mechanism (not shown) driven by an electric motor50. In an embodiment, the motor50may be disposed internally within the compressor with a drive shaft interconnected with a shaft of the compression mechanism, all sealed within a common housing of the compression device32.

The refrigeration system20also includes a controller30configured for controlling operation of the refrigeration system20including, but not limited to, operation of various components of the refrigerant unit22to provide and maintain a desired thermal environment within the cargo box of the truck or trailer, that is within the temperature controlled space in which a perishable product is stowed. The controller30may be an electronic controller including a microprocessor and an associated memory. The controller30controls operation of various components of the refrigerant unit22, such as the refrigerant compression device32and its associated drive motor50, the fan motors42,46and the electric resistance heater48.

The refrigeration unit22has a plurality of power demand loads, including, but not limited to, the compression device drive motor50, the drive motor42for the fan40associated with the refrigerant heat rejection heat exchanger34, and the drive motor46for the fan44associated with the refrigerant heat absorption heat exchanger38. In the depicted embodiment, the electric resistance heater48also constitutes a power demand load. The electric resistance heater may be selectively operated by the controller30whenever a control temperature within the temperature controlled cargo box drops below a preset lower temperature limit, which may occur in a cold ambient environment. In such an event the controller30would activate the electric resistance heater48to heat air circulated over the electric resistance heater by the fan(s)44associated with the refrigerant heat absorption heat exchanger38.

The compression device32and its associated drive motor50, the fan motors42,46and the electric resistance heater48represent loads of the transport refrigeration unit22. One or more of the loads is powered by AC power generated by an inverter assembly52. The inverter assembly52includes a plurality of inverters that convert DC power from a DC power source17into AC power to power one or more loads of the transport refrigeration unit22. The DC power source17may be a battery or may be an AC-DC converter that converts an AC input (e.g., from grid power and/or a generator) to DC power. One or more sensors37are installed at the inverter assembly52to monitor a load on the one or more operating inverters in the inverter assembly52. The sensor(s)37may monitor load on an inverter by measuring electrical parameters (e.g., current, voltage, power) and/or physical parameters (e.g., temperature).

FIG.2depicts the inverter assembly52in further detail in an example embodiment. The inverter assembly52includes at least two inverters601-60Nhaving an input connected to the DC power source17and an output connected to at least one load of the refrigeration unit22. Example loads shown inFIG.2include the compression device32, fan motors42and46and heater48. The outputs of the inverters601-60Nare connected in electrical parallel to a common AC output62. A sensor37is shown associated with inverter N, but it should be understood that a sensor37may be associated with each individual inverter60. The sensor(s)37may monitor load on an inverter60by measuring electrical parameters (e.g., current, voltage, power) and/or physical parameters (e.g., temperature). The inverters601-60Nmay all have a similar power rating and may be identical devices in an example embodiment.

In operation, the controller30is in communication with the inverters601-60Nand the sensor(s)37. The controller30sends commands to each of the inverters601-60Nto enter an active state (i.e., produce AC power) or an inactive state (i.e., do not produce AC power). The controller30determines how many inverters601-60Nshould be in an active state in response to parameters measured by one or more sensors37.

FIG.3is a flowchart of a process for controlling the inverters601-60Nin an example embodiment. The process begins at500where the refrigeration unit22begins operation and a single inverter601is set to the active state to produce AC power at502. At504, the controller30determines if the load on each inverter in the active state is greater than an upper threshold. At this point, only one inverter601is in the active state. The load on each inverter in the active state may be determined based on sensors37associated with the inverters601-60N. The sensor(s)37may monitor load on an inverter60by measuring electrical parameters (e.g., current, voltage, power) and/or physical parameters (e.g., temperature). The upper threshold may be represented as a percentage (e.g., 90% electrical limit or 90% of temperature limit) or as a numerical value (e.g., current greater than 8 Amps or temperature greater than 120 degrees Fahrenheit).

If at504, the controller30determines that the load on each inverter in the active state is less than the upper threshold, the refrigeration unit22continues to operate with the current number of inverters60in an active state. If at504, the controller30determines that the load on each inverter in the active state is greater than the upper threshold, flow proceeds to506where the number of active inverters60is increased by 1, until all the inverters al in use. The controller30send a command to another inverter602to enter an active state. At this stage, the two inverters601and602provide AC power to supply the loads of the refrigeration unit22.

At508, the controller30determines if the load on each inverter60in the active state is less than a lower threshold. The lower threshold may be represented as a percentage (e.g., 25% electrical limit or 30% of temperature limit) or as a numerical value (e.g., current less than 1 Amp or temperature less than 40 degrees Fahrenheit).

If at508, the controller30determines that the load on each inverter60in the active state is not less than the lower threshold, flow proceeds to504and the number of inverters60in the active state remains the same. If at508, the controller30determines that the load on each inverter60in the active state is less than the lower threshold, flow proceeds to510. At510, the controller30sends a command to decrease the number of inverters60in the active state, unless there is only one inverter in the active state. For example, if two inverters601and602are operating at a load less than the lower threshold (e.g., each producing less than 1 Amp), there is no need to have both inverters601and602in the active state. At510, one of inverters601and602would be changed to the inactive state.

A number of techniques may be used to control the AC output of each inverter601-60Nso that the AC outputs can be effectively paralleled at common AC output62. In general, the controller30and/or the inverters601-60Ncommunicate to synchronize the AC outputs of each inverter601-60Nin frequency and phase so the AC outputs can be effectively paralleled at common AC output62. Each inverter601-60Nmay include a local controller to enable communications between inverters601-60N. During operation, a first inverter601communicates to the second inverter602when a reference point has occurred in a pulse width modulation (PWM) signal from controller30. The second inverter602then determines when the reference point occurs in its PWM signal from controller30. If there is a difference between when the reference point occurs in the first PWM signal at the first inverter601and when the reference point occurs in the second PWM signal at the second inverter602, then one or both of the first inverter601and the second inverter602may adjust the period of the PWM signals such that the reference points occur at the same time. The first inverter601and the second inverter602may use known techniques to adjust the period of the PWM signals, such as a phase locked loop technique to reduce error between when the reference points occurs in control signal and when the reference point occurs in control signal. This improves synchronization of the control signals between first inverter601and the second inverter602. The control signal synchronization as described may be used with any number of inverters60.

The inverters601-60Nmay be multiphase inverters, producing multiphase AC outputs. In this configuration, each individual phase from each inverter601-60Nwould be paralleled at the common AC output62.

Embodiments of the disclosure allow the use of multiple inverters601-60N, connected in electrical parallel. This allows a single inverter design to be used, which reduces complexity in using a single inverter customized for a specific refrigeration unit loads. For high power loads, embodiments can simply use additional inverters arranged in parallel, rather than a customized high power inverter.

As described above, embodiments can be in the form of processor-implemented processes and devices for practicing those processes, such as a processor in controller30. Embodiments can also be in the form of computer program code containing instructions embodied in tangible media, such as network cloud storage, SD cards, flash drives, diskettes, CD ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes a device for practicing the embodiments. Embodiments can also be in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into an executed by a computer, the computer becomes an device for practicing the embodiments. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.

While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.