Optimal bus voltage and switching frequency strategy

Abstract

A transport refrigeration system is provided and includes a trailer refrigeration unit (TRU), a battery for providing power to the TRU, an electrical system, and a controller. The electrical system includes a direct current (DC) bus electrically interposed between the battery and the TRU. The electrical system also includes an inverter and a boost converter disposed on the DC bus. The controller includes: a memory unit that stores a first efficiency table, a second efficiency table, and a third efficiency table for the TRU, the inverter, and the boost converter, respectively; and a processor. The processor sets an operation target of the TRU and controls the inverter and the boost converter to achieve the operation target according to a voltage of the battery, the first efficiency table, the second efficiency table, and the third efficiency table, and real-time operation conditions.

Description

Technical Field

[0001] This disclosure relates to compressor systems, and more specifically, to optimal DC bus voltage and switching frequency strategies for compressor systems. Background Technology

[0002] Refrigerated vehicles transport perishable or temperature-sensitive goods within logistics networks. Refrigerated vehicles typically include a trailer refrigeration unit (TRU), which regulates the environment within the storage area (e.g., container or trailer) of the vehicle storing goods during transport. The TRU includes a refrigeration system powered by an energy source. Traditionally, in tractor-trailer systems where the storage area is located within a trailer, the trailer has been equipped with an internal combustion engine to power the TRU. The TRU's internal combustion engine is separate from the internal combustion engine of the tractor that provides the power.

[0003] In recent years, electric power sources have been used to power the tractor unit (TRU) instead of an internal combustion engine. Such electric power sources can include batteries that are charged using electrical energy derived from the grid and / or coupled to a generator on the tractor's axle. This increases the fuel consumption of the tractor's internal combustion engine but allows for the use of smaller batteries. Summary of the Invention

[0004] According to an aspect of this disclosure, a transport refrigeration system is provided, comprising a trailer refrigeration unit (TRU), a battery for supplying power to the TRU, an electrical system, and a controller. The electrical system includes a direct current (DC) bus electrically inserted between the battery and the TRU. The electrical system also includes an inverter and a boost converter disposed on the DC bus. The controller includes: a memory unit storing a first efficiency table, a second efficiency table, and a third efficiency table for the TRU, the inverter, and the boost converter, respectively; and a processor. The processor sets an operating target for the TRU and controls the inverter and the boost converter to achieve the operating target based on the battery voltage, the first efficiency table, the second efficiency table, the third efficiency table, and real-time operating conditions.

[0005] According to one or more additional and / or alternative embodiments, the controller is distributed between the inverter and the boost converter.

[0006] According to one or more additional and / or alternative embodiments, the controller controls the inverter and the boost converter by issuing a first signal and a second signal to the inverter and the boost converter, respectively.

[0007] According to one or more additional and / or alternative embodiments, the first signal and the second signal include pulse width modulation (PWM) signals.

[0008] According to one or more additional and / or alternative embodiments, the first efficiency table, the second efficiency table, and the third efficiency table are based on historical data and are updatable.

[0009] According to one or more additional and / or alternative embodiments, the operational target includes compressor speed.

[0010] According to one or more additional and / or alternative embodiments, the real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU, temperature and pressure characteristics of the container to be regulated by the TRU, pressure and flow rate characteristics of the TRU, and additional electrical characteristics of the electrical system.

[0011] According to one or more additional and / or alternative embodiments, the processor is configured to: determine the maximum efficient voltage requirement for the compressor speed and the voltage difference between the battery voltage and the voltage requirement; modulate the switching frequency of the boost converter to compensate for the voltage difference with maximum efficiency; and modulate the switching frequency of the inverter to construct a sinusoidal voltage output from the boost converter output with maximum efficiency.

[0012] According to an aspect of this disclosure, a transport refrigeration system is provided, comprising a trailer refrigeration unit (TRU), a load, a battery for providing power to the TRU and the load, an electrical system, and a controller. The electrical system includes a direct current (DC) bus electrically inserted between the battery and the TRU and the load. The electrical system also includes an inverter for each TRU and each load, and a boost converter for a subset of the inverters disposed on the DC bus. The controller includes: a memory unit storing a first efficiency table, a second efficiency table, and a third efficiency table for the TRU and the load, the inverters, and the boost converters, respectively; and a processor. The processor sets operational targets for the TRU and the load and controls the inverters and the boost converters to achieve the operational targets based on the battery voltage, the first efficiency table, the second efficiency table, the third efficiency table, and real-time operating conditions.

[0013] According to one or more additional and / or alternative embodiments, the first efficiency table, the second efficiency table, and the third efficiency table are based on historical data and are updatable.

[0014] According to one or more additional and / or alternative embodiments, the operating target of the TRU includes compressor speed.

[0015] According to one or more additional and / or alternative embodiments, the real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU and the load; temperature and pressure characteristics of the container to be regulated by the TRU and the load; pressure and flow rate characteristics of the TRU and the load; and additional electrical characteristics of the electrical system.

[0016] According to one or more additional and / or alternative embodiments, the processor is configured to: determine the maximum efficient voltage requirement for the compressor speed and the voltage difference between the battery voltage and the voltage requirement; modulate the switching frequency of the boost converter to compensate for the voltage difference with maximum efficiency; and modulate the switching frequency of the inverter to construct a sinusoidal voltage output from the boost converter output with maximum efficiency.

[0017] According to an aspect of this disclosure, a method for operating a transport refrigeration system is provided, the transport refrigeration system including a trailer refrigeration unit (TRU) and a battery for providing power to the TRU. The method includes: setting a compressor speed of the TRU for a target temperature of the container; determining a voltage requirement for the compressor speed by referring to an efficiency table of the TRU; determining a voltage difference between the battery voltage and the voltage requirement; and compensating for the voltage difference to achieve the target temperature by controlling the inverter and the boost converter, which are disposed on a direct current (DC) bus of an electrical system electrically inserted between the battery and the TRU, according to an efficiency table of an inverter and a boost converter and real-time operating conditions.

[0018] According to one or more additional and / or alternative embodiments, control of the inverter and the boost controller includes issuing pulse width modulation (PWM) signals to the inverter and the boost converter.

[0019] According to one or more additional and / or alternative embodiments, the method further includes the PWM signal modulated onto the inverter and the boost converter.

[0020] According to one or more additional and / or alternative embodiments, the PWM signal modulated onto the inverter changes the duty cycle of the inverter to construct a sinusoidal voltage output from the boost converter output.

[0021] According to one or more additional and / or alternative embodiments, the PWM signal modulated onto the boost converter changes the duty cycle of the boost converter to obtain a desired output voltage.

[0022] According to one or more additional and / or alternative embodiments, the method further includes generating the efficiency table of the TRU, the inverter, and the boost converter based on historical data, and updating the efficiency table of the TRU, the inverter, and the boost converter.

[0023] According to one or more additional and / or alternative embodiments, the real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU, temperature and pressure characteristics of the container to be regulated by the TRU, pressure and flow rate characteristics of the TRU, and additional electrical characteristics of the electrical system.

[0024] Additional features and advantages are achieved through the technology of this disclosure. Other embodiments and aspects of this disclosure are described in detail herein and are considered part of the claimed technical concept. Reference is made to the specification and drawings for a better understanding of the advantages and features of this disclosure. Attached Figure Description

[0025] To gain a more complete understanding of this disclosure, reference is now made to the following brief description in conjunction with the accompanying drawings and detailed description, wherein similar reference numerals denote similar parts: Figure 1 This is a schematic diagram of a transport refrigeration system with a battery and a TRU according to an embodiment; Figure 2 According to the embodiments Figure 1 A graphical representation of the efficiency table of the transportation refrigeration system; Figure 3 According to the embodiments Figure 1 A schematic diagram of the controller for the transport refrigeration system; Figure 4 This is a schematic diagram of a transport refrigeration system having a battery, multiple TRUs, and a load according to an embodiment; Figure 5 According to the embodiments Figure 4 A schematic diagram of the controller for the transport refrigeration system; and Figure 6 This is a flowchart illustrating a method of operating a transport refrigeration system according to an embodiment, the transport refrigeration system including a TRU and a battery for providing power to the TRU. Detailed Implementation

[0026] Recently, there has been considerable effort to electrify truck and trailer products. These efforts involve replacing diesel generators with electric drive units to operate TRU motors using electricity from batteries. However, a problem with such arrangements is their tendency towards inefficiency. This inefficiency can stem from a lack of DC bus voltage and switching frequency management capabilities, which in turn can lead to energy losses, poor system performance, and shortened component lifespan.

[0027] Therefore, as will be described below, a method is provided for dynamically adjusting the DC bus voltage level and switching frequency of a compressor system including an electric drive for operating a TRU motor using electrical energy from a battery based on real-time operating conditions, load demand, and other relevant parameters. By employing advanced algorithms that consider various factors, including but not limited to the compressor system's temperature, pressure, flow rate, and electrical characteristics, this method ensures optimal efficiency across a wide range of operating conditions by providing a self-adjusting mechanism that responds to changing conditions without human intervention, thereby maintaining peak performance while reducing energy consumption.

[0028] refer to Figures 1-3 A transport refrigeration system 101 is provided and includes a TRU 110, a battery 120 for supplying power to the TRU 110, an electrical system 140, and a controller 160. The electrical system 140 includes a DC bus 141 electrically inserted between the battery 120 and the TRU 110. The electrical system 140 also includes an inverter 142 and a boost converter 143, both disposed on the DC bus 141. The inverter 142 includes multiple switches 1421, such as transistor elements. The switching frequency of the switches 1421 can be influenced and controlled, as described below. The boost converter 143 includes multiple switches 1431, such as transistor elements. The switching frequency of the switches 1431 can also be influenced and controlled, as described below.

[0029] To understand this, the total efficiency of the transport refrigeration system 101, 𝜂_𝑡𝑜𝑡𝑎l, is equal to the efficiency of the boost converter 143, 𝜂_𝑏𝑜𝑜𝑠𝑡 multiplied by the efficiency of the inverter 142, 𝜂_𝑖𝑛𝑣 multiplied by the efficiency of the TRU 110, 𝜂_𝑢𝑛𝑖𝑡.

[0030] The controller 160 includes a processor 201, a memory unit 202, and an input / output (I / O) unit 203. The processor 201 receives voltage information and real-time operating conditions from the battery 120 through the I / O unit 203, and also sends signals to the TRU 110, inverter 142, and boost converter 143 through the I / O unit 203. The memory unit 202 has executable instructions stored thereon that are readable and executable by the processor 201, and also has a first efficiency table 181 for the TRU 110, a second efficiency table 182 for the inverter 142, and a third efficiency table 183 for the boost converter 143 stored thereon for access by the processor 201 (see, for example...). Figure 2(Example efficiency table 201). Each of the first efficiency table 181, the second efficiency table 182, and the third efficiency table 183 can be generated based on historical data and can be updated as new data is received and analyzed.

[0031] The first efficiency table 181, the second efficiency table 182, and the third efficiency table 183 can each associate maximum efficiency with certain combinations of optional variables. As an example, such as... Figure 2 As shown, efficiency table 201 indicates that maximum efficiency is achieved at a 50% duty cycle for a voltage of 400V and at a 55% duty cycle for a voltage of 500V.

[0032] When the executable instructions are read and executed by the processor 201, the processor 201 generally operates as described herein. That is, when the executable instructions are read and executed by the processor 201, the processor 201 sets an operational target for the TRU 110 (i.e., a first optional variable) and achieves the operational target with maximum efficiency by controlling the inverter 142 (i.e., a second optional variable for the inverter 142) and the boost converter 143 (i.e., a third optional variable for the boost converter 143) based on the voltage of the battery 120, based on the reads of the first efficiency table 181, the second efficiency table 182, and the third efficiency table 183 by the processor 201, and based on real-time operating conditions received by the processor 201. According to an embodiment, the operational target may be the compressor speed of the compressor motor of the TRU 110, and the real-time operating conditions may include at least one or more of the following: ambient temperature and pressure characteristics around the TRU 110, temperature and pressure characteristics of the container to be regulated by the TRU 110, pressure and flow rate characteristics of the TRU 110, and additional electrical characteristics of the electrical system 140.

[0033] According to an embodiment, processor 201 determines the maximum efficient voltage requirement for compressor speed and the voltage difference between the voltage of battery 120 and the voltage requirement, modulates the switching frequency of switch 1431 of boost converter 143 to compensate for the voltage difference with maximum efficiency, and modulates the switching frequency of switch 1421 of inverter 142 to construct a sinusoidal voltage output from the output of boost converter 143 with maximum efficiency.

[0034] The first efficiency table 181, the second efficiency table 182, and the third efficiency table 183 can be modified (i.e., automatically) according to real-time changes in operating conditions. That is, for the first efficiency table 181 of TRU 110, a specific compressor speed may exist at a specific voltage on DC bus 141, which is associated with the maximum efficiency of TRU 110 under given real-time operating conditions. However, if those real-time operating conditions change, the first efficiency table 181 can indicate the maximum efficiency achieved at different compressor speeds under the same voltage on DC bus 141. A similar effect may occur for the second efficiency table 182 and the third efficiency table 183.

[0035] Control of the inverter 142 and the boost converter 143 can be achieved by the processor 201 sending signals S1 and S2 to the inverter 142 and the boost converter 143, respectively. According to an embodiment, signals S1 and S2 can be provided as pulse width modulation (PWM) signals, which determine the switching frequency of the switch 1431 of the boost converter 143 and the switching frequency of the switch 1421 of the inverter 142.

[0036] The boost converter 143 effectively controls the bus voltage of the DC bus 141, which serves as its output. Ideally, the output voltage of the boost converter 143 is Vout - Vin(1-D), where Vout is the voltage output of the boost converter 143, Vin is the voltage of the battery 120, and D is the duty cycle of the PWM signal 2. For example, when D = 0.5 (50%), This makes Vout twice as large as Vin. Processor 201 commands the signal S2PWM with a duty cycle to obtain the desired output voltage of boost converter 143.

[0037] Using PWM control of inverter 142, inverter 142 generates a 3-phase AC output voltage based on the voltage of DC bus 141 (which may or may not be boosted by boost converter 143). Processor 201 continuously changes the PWM duty cycle to construct a sinusoidal voltage output, which controls the speed of the compressor motor of TRU 110 to achieve the desired compressor speed.

[0038] The controller 160 may be at least one or more independent computing devices, remote computing devices, and / or embodied as computing resources distributed between at least the inverter 142 and the boost converter 143, as well as the battery 120 and the TRU 110.

[0039] Continue to refer to Figures 1-3 And refer to other sources. Figure 4 and Figure 5 A transport refrigeration system 401 is provided. The transport refrigeration system 401 is typically similar to... Figures 1-3 The transport refrigeration system 101 includes TRUs 4101 and 4102 and loads 4151 and 4152, a battery 420 for providing power to TRUs 4101 and 4102 and loads 4151 and 4152, an electrical system 440, and a controller 460. The electrical system 440 includes a DC bus 441 electrically inserted between the battery 420 and TRUs 4101 and 4102 and loads 4151 and 4152, and also includes an inverter 442 for each of TRUs 4101 and 4102 and each of loads 4151 and 4152. 1-4 And some inverters 442 for setting on DC bus 441 1-4 The boost converters 4431 and 4432.

[0040] The controller 460 includes a processor 501, a memory unit 502, and an I / O unit 503. The processor 501 receives voltage information and real-time operating conditions from the battery 420 through the I / O unit 503, and the processor 501 also communicates with the TRUs 4101 and 4102, loads 4151 and 4152, and inverter 442 through the I / O unit 503. 1-4 Signals are emitted by boost converters 4431 and 4432. Memory unit 502 has executable instructions stored thereon that are readable and executable by processor 501, and also has a first efficiency table 481 for TRUs 4101 and 4102 and loads 4151 and 4152, and for inverter 442. 1-4 The second efficiency table 482 and the third efficiency table 483 for boost converters 4431 and 4432. Each of the first efficiency table 481, the second efficiency table 482 and the third efficiency table 483 can be generated based on historical data and can be updated as new data is received and analyzed.

[0041] When the executable instructions are read and executed by processor 501, processor 501 typically operates as described herein. That is, when the executable instructions are read and executed by processor 501, processor 501 sets the operational targets for TRUs 4101 and 4102 and loads 4151 and 4152, and controls inverter 442 based on the voltage of battery 420, read from the first efficiency table 481, the second efficiency table 482, and the third efficiency table 483 by processor 501, and based on real-time operating conditions received by processor 501. 1-4 The 4431 and 4432 boost converters are used to achieve the operational goal with maximum efficiency.

[0042] refer to Figure 6A method 600 for operating a transport refrigeration system, the transport refrigeration system including a TRU, a battery for providing power to the TRU, and an inverter and boost converter disposed on a DC bus of an electrical system, the electrical system being electrically inserted between the battery and the TRU, the transport refrigeration system being, for example... Figures 1-3 The transport refrigeration system 101 and Figure 4 and Figure 5 The transport refrigeration system 401. Method 600 initially includes generating an efficiency table of the TRU, inverter, and boost converter based on historical data (block 601) and updating the efficiency table of the TRU, inverter, and boost converter (block 602). Method 600 also includes setting the compressor speed of the TRU for a target temperature of the container (block 603) and determining the voltage requirement for the compressor speed by referring to the efficiency table of the TRU (block 604). Method 600 also includes determining the voltage difference between the battery voltage and the voltage requirement (block 605) and compensating for the voltage difference by controlling the inverter and boost converter according to the efficiency table of the inverter and boost converter and according to real-time operating conditions to achieve the target temperature (block 606). Real-time operating conditions may include at least one or more of the following: ambient temperature and pressure characteristics around the TRU, temperature and pressure characteristics of the container to be regulated by the TRU, pressure and flow rate characteristics of the TRU, and additional electrical characteristics of the electrical system. Control of the inverter and boost controller in block 606 may include sending PWM signals to the inverter and boost converter (block 6061), and modulating the PWM signals to the inverter and boost converter by changing the duty cycle of the inverter to construct a sinusoidal voltage output from the boost converter output and by changing the duty cycle of the boost converter to obtain the desired output voltage (block 6062).

[0043] The technical effects and benefits of this disclosure are to provide an optimal DC bus voltage and switching frequency strategy for a compressor system including an electric drive for operating a TRU motor powered by battery energy. This strategy improves overall efficiency by intelligently managing the DC bus voltage and the switching frequency of the power electronic switch involved in operating the TRU motor powered by battery energy. This strategy minimizes energy loss, improves system performance, and extends the lifespan of components within the compressor system.

[0044] All components or steps plus functional elements in the following claims are intended to include corresponding structures, materials, actions, and equivalents for performing functions in conjunction with other claimed elements as specifically claimed. The description of this disclosure has been presented for illustrative and descriptive purposes, but it is not intended to be exhaustive or limited to technical concepts in the form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure. These embodiments have been chosen and described in order to best explain the principles and practical application of this disclosure and to enable others skilled in the art to understand this disclosure with various modifications suitable for the particular purpose contemplated.

[0045] While preferred embodiments of this disclosure have been described, it will be understood that various modifications and enhancements can be made by those skilled in the art now and in the future, all of which fall within the scope of the appended claims. These claims should be construed as maintaining appropriate protection for the disclosure first described.

Claims

1. A transport refrigeration system, comprising: Trailer refrigeration unit (TRU); Batteries used to provide power to the TRU; An electrical system comprising a direct current (DC) bus electrically inserted between the battery and the TRU, and further comprising an inverter and a boost converter disposed on the DC bus; as well as Controller, the controller includes: A memory unit stores a first efficiency table, a second efficiency table, and a third efficiency table for the TRU, the inverter, and the boost converter, respectively. as well as The processor is configured to set the operating target of the TRU and control the inverter and the boost converter to achieve the operating target based on the battery voltage, the first efficiency table, the second efficiency table, the third efficiency table, and real-time operating conditions.

2. The transport refrigeration system according to claim 1, wherein, The controller is located between the inverter and the boost converter.

3. The transport refrigeration system according to any one of claims 1 or 2, wherein, The controller controls the inverter and the boost converter by sending a first signal and a second signal to the inverter and the boost converter, respectively.

4. The transport refrigeration system according to claim 3, wherein, The first signal and the second signal include pulse width modulation (PWM) signals.

5. The transport refrigeration system according to any one of claims 1-4, wherein, The first efficiency table, the second efficiency table, and the third efficiency table are based on historical data and are updatable.

6. The transport refrigeration system according to any one of claims 1-5, wherein, The operational target includes compressor speed.

7. The transport refrigeration system according to claim 6, wherein, The real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU, temperature and pressure characteristics of the container to be regulated by the TRU, pressure and flow rate characteristics of the TRU, and additional electrical characteristics of the electrical system.

8. The transport refrigeration system according to claim 6, wherein, The processor is configured to: Determine the maximum high-efficiency voltage requirement for the compressor speed and the voltage difference between the battery voltage and the voltage requirement. The switching frequency of the boost converter is modulated to compensate for the voltage difference with maximum efficiency. The switching frequency of the inverter is modulated to construct a sinusoidal voltage output from the boost converter output with maximum efficiency.

9. A transport refrigeration system, comprising: Trailer refrigeration unit (TRU); load; Batteries used to provide power to the TRU and the load; An electrical system comprising a direct current (DC) bus electrically inserted between the battery and the TRU and the load, and further comprising an inverter for each TRU and each load, and a boost converter for some of the inverters disposed on the DC bus; as well as Controller, the controller includes: A memory unit stores a first efficiency table, a second efficiency table, and a third efficiency table for the TRU and the load, the inverter, and the boost converter, respectively. as well as The processor is configured to set the operating targets of the TRU and the load, and control the inverter and the boost converter to achieve the operating targets based on the battery voltage, the first efficiency table, the second efficiency table, the third efficiency table, and real-time operating conditions.

10. The transport refrigeration system according to claim 9, wherein, The first efficiency table, the second efficiency table, and the third efficiency table are based on historical data and are updatable.

11. The transport refrigeration system according to any one of claims 9 or 10, wherein, The operating target of the TRU includes compressor speed.

12. The transport refrigeration system according to claim 11, wherein, The real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU and the load; temperature and pressure characteristics of the container to be regulated by the TRU and the load; pressure and flow rate characteristics of the TRU and the load; and additional electrical characteristics of the electrical system.

13. The transport refrigeration system according to claim 11, wherein, The processor is configured to: Determine the maximum high-efficiency voltage requirement for the compressor speed and the voltage difference between the battery voltage and the voltage requirement. The switching frequency of the boost converter is modulated to compensate for the voltage difference with maximum efficiency. The switching frequency of the inverter is modulated to construct a sinusoidal voltage output from the boost converter output with maximum efficiency.

14. A method of operating a transport refrigeration system, the transport refrigeration system comprising a trailer refrigeration unit (TRU) and a battery for providing power to the TRU, the method comprising: Set the compressor speed of the TRU for the target temperature of the container; The voltage requirement for the compressor speed is determined by referring to the efficiency table of the TRU; Determine the voltage difference between the battery voltage and the voltage requirement; as well as The voltage difference is compensated to achieve the target temperature by controlling the inverter and the boost converter, which are located on the DC bus of the electrical system electrically inserted between the battery and the TRU, according to the efficiency table of the inverter and the boost converter and the real-time operating conditions.

15. The method according to claim 14, wherein, Control of the inverter and the boost controller includes sending pulse width modulation (PWM) signals to the inverter and the boost converter.

16. The method according to claim 15, wherein, The method also includes the PWM signal modulated onto the inverter and the boost converter.

17. The method according to claim 16, wherein, The PWM signal modulated onto the inverter changes the inverter's duty cycle to construct a sinusoidal voltage output from the boost converter output.

18. The method according to claim 16, wherein, The PWM signal modulated onto the boost converter changes the duty cycle of the boost converter to obtain the desired output voltage.

19. The method according to any one of claims 14-18, further comprising generating the efficiency table of the TRU, the inverter, and the boost converter based on historical data, and updating the efficiency table of the TRU, the inverter, and the boost converter.

20. The method according to any one of claims 14-19, wherein, The real-time operating conditions include at least one or more of the following: ambient temperature and pressure characteristics around the TRU, temperature and pressure characteristics of the container to be regulated by the TRU, pressure and flow rate characteristics of the TRU, and additional electrical characteristics of the electrical system.

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