Multilevel inverter control

Abstract

A power inverter system can include a multi-level inverter, a motor in electrical communication with the multi-level inverter, and a controller in electrical communication with the multi-level inverter. The controller is programmed to determine a command torque for the motor. The controller is further programmed to compare the command torque to an upper torque threshold for a three-level mode of the multi-level inverter. The controller is further programmed to use the motor to generate the command torque by operating the multi-level inverter in a two-level mode in response to determining that the command torque is greater than the upper torque threshold. The controller is further programmed to use the motor to generate the command torque by operating the multi-level inverter in the three-level mode in response to determining that the command torque is less than the upper torque threshold.

Description

Technical Field

[0001] This disclosure relates to systems and methods for power inversion in electric vehicles. Background Technology

[0002] To manage power in electric vehicle applications, power inverters can be used. A power inverter is a power electronic device that typically includes controllable semiconductor switches to perform power inversion tasks, such as direct current (DC) to alternating current (AC) conversion. For example, a power inverter can be used to convert DC power from a vehicle battery into three-phase AC power to power an electric drive motor. Power inverters can also be used to achieve bidirectional power conversion in regenerative braking applications. In some examples, power inverters are implemented as two-level inverters, capable of synthesizing AC waveforms using pulse-width modulation between two voltage levels. In other examples, power inverters are implemented as multi-level inverters, capable of synthesizing AC waveforms using pulse-width modulation between three or more voltage levels. Compared to two-level inverters, multi-level inverters can improve efficiency and reduce total harmonic distortion (THD). In electric vehicle applications, improving drive system efficiency is beneficial for improving vehicle performance and driving range.

[0003] Although the systems and methods used for power inverters have achieved their intended purpose, new and improved systems and methods are still needed for power inverters for electric vehicles. Summary of the Invention

[0004] According to several aspects, a power inverter system is provided. The system may include a multilevel inverter, a motor electrically communicating with the multilevel inverter, and a controller electrically communicating with the multilevel inverter. The controller is programmed to determine a command torque of the motor. The controller is also programmed to compare the command torque with an upper torque threshold of a three-level mode of the multilevel inverter. The controller is further programmed to use the motor to generate the command torque by operating the multilevel inverter in a two-level mode in response to determining that the command torque is greater than the upper torque threshold. The controller is also programmed to use the motor to generate the command torque by operating the multilevel inverter in a three-level mode in response to determining that the command torque is less than the upper torque threshold.

[0005] In another aspect of this disclosure, the multilevel inverter may further include a direct current (DC) bus and a plurality of capacitors forming a neutral point from the DC bus. The multilevel inverter may also include an alternating current (AC) bus in electrical communication with the motor and a plurality of main semiconductor switches in electrical communication with both the DC bus and the AC bus. The multilevel inverter may also include a plurality of auxiliary semiconductor switches in electrical communication with the neutral point and the AC bus.

[0006] In another aspect of this disclosure, in order to use the motor to generate command torque by operating the multilevel inverter in a two-level mode, the controller is also programmed to operate multiple auxiliary semiconductor switches in a non-conducting state in response to determining that the command torque is greater than an upper torque threshold.

[0007] In another aspect of this disclosure, the upper torque threshold is determined at least in part based on the typical maximum command torque during typical operation of the motor. The upper torque threshold is less than the maximum rated torque of the motor.

[0008] In another aspect of this disclosure, an upper torque threshold is determined such that at least 50% of all torque commands received during the service life of the motor are less than or equal to the upper torque threshold.

[0009] In another aspect of this disclosure, the dimensions of the plurality of auxiliary semiconductor switches are designed at least in part based on the upper torque threshold.

[0010] In another aspect of this disclosure, the dimensions of the plurality of auxiliary semiconductor switches are designed to withstand a current less than or equal to the maximum current required for the motor to generate a torque equal to the upper torque threshold.

[0011] In another aspect of this disclosure, the plurality of auxiliary semiconductor switches may also include one or more monolithic bidirectional semiconductor switches.

[0012] In another aspect of this disclosure, in order to use the motor to generate command torque by operating the multilevel inverter in three-level mode, the controller is also programmed to use the motor to generate command torque by operating the multilevel inverter in three-level mode in response to determining that the command torque is less than an upper torque threshold and less than a lower torque threshold.

[0013] In another aspect of this disclosure, the lower torque threshold is determined based on the upper torque threshold and a predetermined torque hysteresis offset.

[0014] According to several aspects, a method is provided for operating a power inverter system for a vehicle. The method may include determining a command torque generated by a vehicle electric motor. The method may include comparing the command torque with an upper torque threshold in a three-level mode of a multilevel inverter of the vehicle. The multilevel inverter is in electrical communication with the electric motor. The method may include: in response to determining that the command torque is greater than the upper torque threshold, using the electric motor to generate the command torque by operating the multilevel inverter in a two-level mode. The method may also include: in response to determining that the command torque is less than the upper torque threshold, using the electric motor to generate the command torque by operating the multilevel inverter in a three-level mode.

[0015] In another aspect of this disclosure, the method may further include determining an upper torque threshold based at least in part on the typical maximum command torque during typical operation of the motor. The upper torque threshold is determined such that at least 50% of all torque commands received during the service life of the motor are less than or equal to the upper torque threshold. The upper torque threshold is less than the maximum rated torque of the motor.

[0016] In another aspect of this disclosure, using a motor to generate command torque by operating a multilevel inverter in three-level mode may further include: in response to determining that the command torque is less than an upper torque threshold and less than a lower torque threshold, using the motor to generate command torque by operating the multilevel inverter in three-level mode. The lower torque threshold is determined based on the upper torque threshold and a predetermined torque hysteresis offset.

[0017] In another aspect of this disclosure, using a motor to generate command torque by operating a multilevel inverter in three-level mode may further include: controlling multiple main semiconductor switches of the multilevel inverter to transfer energy from a direct current (DC) bus to an alternating current (AC) bus. The AC bus is in electrical communication with the motor. Using a motor to generate command torque by operating a multilevel inverter in three-level mode may further include: controlling multiple auxiliary semiconductor switches of the multilevel inverter to transfer energy from the DC bus to the AC bus.

[0018] In another aspect of this disclosure, using a motor to generate command torque by operating a multilevel inverter in two-level mode may further include: controlling multiple main semiconductor switches of the multilevel inverter to transfer energy from the DC bus to the AC bus. Using a motor to generate command torque by operating a multilevel inverter in two-level mode may further include: controlling multiple auxiliary semiconductor switches of the multilevel inverter to be in a non-conducting state.

[0019] In another aspect of this disclosure, one or more component ratings of a plurality of auxiliary semiconductor switches are selected, at least in part, based on an upper torque threshold.

[0020] In another aspect of this disclosure, one or more component ratings of a plurality of auxiliary semiconductor switches are selected to withstand a current less than or equal to the maximum current required for the motor to generate a torque equal to the upper torque threshold.

[0021] According to several aspects, a power inverter system for a vehicle is provided. The power inverter system may include a traction battery and an electric motor. The electric motor is configured to propel the vehicle. The power inverter system may also include a multilevel inverter including a direct current (DC) bus in electrical communication with the traction battery. The multilevel inverter may also include a plurality of capacitors forming a neutral point from the DC bus. The multilevel inverter may also include an alternating current (AC) bus in electrical communication with the electric motor. The multilevel inverter may also include a plurality of main semiconductor switches in electrical communication with both the DC bus and the AC bus. The multilevel inverter may also include a plurality of auxiliary semiconductor switches in electrical communication with both the neutral point and the AC bus. One or more component ratings of the plurality of auxiliary semiconductor switches are selected to withstand a current less than or equal to the maximum current required for the electric motor to generate a torque equal to an upper torque threshold. The power inverter system may include a controller in electrical communication with the multilevel inverter. The controller is programmed to determine the command torque of the electric motor. The controller is also programmed to compare the command torque with an upper torque threshold. The upper torque threshold is defined as the maximum torque of the motor when the multilevel inverter is operated in three-level mode. The controller is also programmed to generate the command torque using the motor by operating the multilevel inverter in two-level mode in response to determining that the command torque is greater than the upper torque threshold. The controller is also programmed to generate the command torque using the motor by operating the multilevel inverter in three-level mode in response to determining that the command torque is less than the upper torque threshold.

[0022] In another aspect of this disclosure, in order to operate the multilevel inverter in three-level mode, the controller is also programmed to control multiple main semiconductor switches of the multilevel inverter to transfer energy from the DC bus to the AC bus. In order to operate the multilevel inverter in three-level mode, the controller is also programmed to control multiple auxiliary semiconductor switches of the multilevel inverter to transfer energy from the DC bus to the AC bus.

[0023] In another aspect of this disclosure, in order to operate the multilevel inverter in two-level mode, the controller is also programmed to control multiple main semiconductor switches of the multilevel inverter to transfer energy from the DC bus to the AC bus. In order to operate the multilevel inverter in two-level mode, the controller is also programmed to control multiple auxiliary semiconductor switches of the multilevel inverter to be in a non-conducting state.

[0024] Further applicability will become apparent from the description provided herein. It should be understood that the descriptions and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0025] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0026] Figure 1This is a schematic diagram of a power inverter system according to an exemplary embodiment;

[0027] Figure 2 This is a schematic diagram of a multilevel inverter according to an exemplary embodiment;

[0028] Figure 3 This is a flowchart of a method for operating a power inverter system according to an exemplary embodiment; and

[0029] Figure 4 This is an exemplary torque-speed diagram of an electric motor according to an exemplary embodiment. Detailed Implementation

[0030] The following description is merely illustrative in nature and is not intended to limit the content, application, or purpose of this disclosure.

[0031] In several aspects of this disclosure, it is advantageous for the power inverter system to provide the highest possible efficiency. For example, in electric vehicles, efficient power conversion can increase the vehicle's driving range. Therefore, multilevel inverters can be used to reduce ripple and losses, thereby improving efficiency. However, multilevel inverters have a greater number of components than two-level inverters, resulting in increased size, weight, and / or resource usage. This disclosure provides a novel and improved power conversion system and method that fully utilizes the advantages of multilevel inverters while minimizing the impact of any disadvantages.

[0032] refer to Figure 1 A power inverter system is shown, generally indicated by reference numeral 10. System 10 is illustrated as an exemplary vehicle 12. Although a passenger vehicle is shown, it should be understood that vehicle 12 can be any type of vehicle without departing from the scope of this disclosure. Furthermore, it should be understood that system 10 can also be used for applications other than vehicle applications. System 10 typically includes a multilevel inverter 14, a battery 16, an electric motor 18, and a controller 20.

[0033] A multilevel inverter 14 is used to transfer energy between a battery 16 and a motor 18. Within the scope of this disclosure, a multilevel inverter is a power electronic device for converting direct current (DC) into alternating current (AC) with multiple voltage levels. Unlike a two-level inverter that produces only two output voltage levels, a multilevel inverter can produce a stepped waveform with more than two output voltage levels.

[0034] refer to Figure 2 A schematic diagram of an exemplary T-type three-level embodiment of the multilevel inverter 14 is shown. (Refer to...) Figure 2 And continue to refer to Figure 1The multilevel inverter 14 includes a DC bus 22a, an AC bus 22b, a plurality of capacitors 24 forming a neutral point 26 from the DC bus 22a, a plurality of main semiconductor switches 28a, and a plurality of auxiliary semiconductor switches 28b. The DC bus 22a supplies DC power to the multilevel inverter 14. In a non-limiting example, the DC bus 22a is electrically connected to a battery 16 via a positive DC port 30a and a negative DC port 30b. The AC bus 22b supplies AC power to a motor 18. In a non-limiting example, the AC bus 22b is electrically connected to the motor 18 via a first AC phase port 32a, a second AC phase port 32b, and a third AC phase port 32c. The plurality of capacitors 24 are used to form a neutral point 26 between the positive DC port 30a and the negative DC port 30b. In a non-limiting example, the voltage supplied at the neutral point 26 is equal to half the voltage between the positive DC port 30a and the negative DC port 30b.

[0035] Multiple main semiconductor switches 28a are electrically in communication with DC bus 22a and AC bus 22b and are configured to be controlled by controller 20 (e.g., via control terminals, such as gate terminals, base terminals, and / or similar terminals) to convert DC power from DC bus 22a into three-phase AC power at AC bus 22b, thereby providing two voltage levels for each AC phase pin. The multiple main semiconductor switches 28a may comprise any type of unidirectional or bidirectional modular or monolithic semiconductor switch made of any material, including, for example, insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate turn-off thyristors (GTOs), silicon controlled rectifiers (SCRs), MOS-controlled thyristors (MCTs), bipolar junction transistors (BJTs), electrostatic induction transistors (SITs), high electron mobility transistors (HEMTs), junction field-effect transistors (JFETs), etc. In one exemplary embodiment, the control terminal (e.g., gate terminal, base terminal, etc.) of each of the plurality of master semiconductor switches 28a is in electrical communication with the controller 20. In a non-limiting example, the plurality of master semiconductor switches 28a are sized to withstand the maximum rated current of the motor 18.

[0036] Multiple auxiliary semiconductor switches 28b are electrically communicated with neutral point 26 and AC bus 22b and are configured to be controlled by controller 20 (e.g., via control terminals, such as gate terminals, base terminals, and / or similar terminals) to convert DC power from battery 16 into three-phase AC power at AC bus 22b, thereby providing a third voltage level for each AC phase pin. The multiple auxiliary semiconductor switches 28b may comprise any type of bidirectional modular or monolithic semiconductor switch made of any material, including, for example, insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate turn-off thyristors (GTOs), silicon controlled rectifiers (SCRs), MOS-controlled thyristors (MCTs), bipolar junction transistors (BJTs), static induction transistors (SITs), high electron mobility transistors (HEMTs), junction field-effect transistors (JFETs), etc.

[0037] In a non-limiting example, the plurality of auxiliary semiconductor switches 28b include three pairs of anti-series unidirectional switches, thereby effectively forming a bidirectional switch for each AC phase leg, such as Figure 2 As shown. In another non-limiting example, the plurality of auxiliary semiconductor switches 28b includes three monolithic bidirectional semiconductor switches, one monolithic bidirectional semiconductor switch corresponding to each AC phase leg. It should be understood that any circuit that implements the plurality of auxiliary semiconductor switches 28b using any number of unidirectional and / or bidirectional switches is within the scope of this disclosure.

[0038] In one exemplary embodiment, the dimensions of the plurality of auxiliary semiconductor switches 28b are determined at least in part based on an upcurrent threshold. Within the scope of this disclosure, the upcurrent threshold is the maximum current that the multilevel inverter 14 typically supplies to the motor 18. Within the scope of this disclosure, "typically" can be understood as "in most cases" or, in other words, "at least greater than 50% of the time." In a non-limiting example, the upcurrent threshold is less than the maximum rated current of the motor 18.

[0039] In one non-limiting example, the upper current threshold is determined based on the upper torque threshold. Within the scope of this disclosure, the upper torque threshold is the typical maximum command torque during typical operation of the motor 18. In one non-limiting example, the upper torque threshold is determined such that at least 50% of all torque commands received during the service life of the motor 18 are less than or equal to the upper torque threshold. In another non-limiting example, the upper torque threshold is determined such that at least 75% of all torque commands received during the service life of the motor 18 are less than or equal to the upper torque threshold. In yet another non-limiting example, the upper torque threshold is determined such that at least 90% of all torque commands received during the service life of the motor 18 are less than or equal to the upper torque threshold. In one non-limiting example, the upper torque threshold is less than the maximum rated torque of the motor 18. It should be understood that the upper torque threshold can be determined for any proportion of the torque commands received during the service life of the motor 18.

[0040] In one exemplary embodiment, the upper torque threshold is determined through statistical analysis of simulations or measurements of vehicle performance during the execution of standardized driving cycles (e.g., Urban Dynamometer Driving Program (UDDS), Highway Fuel Economy Driving Program (HWFET), Worldwide Harmonized Light Vehicles Test Procedure (WLTP), New European Driving Cycle (NEDC), etc.). In another exemplary embodiment, the upper torque threshold is determined by statistical analysis of real-world driving data (e.g., crowdsourced data).

[0041] Then, based on the upper torque threshold, the upper current threshold is determined using, for example, the known current-torque characteristics of the motor 18. In one exemplary embodiment, the upper current threshold is equal to the maximum current required for the motor 18 to generate a torque equal to the upper torque threshold. In another non-limiting example where the motor 18 is replaced by a different type of load, the upper current threshold is determined using statistical analysis of simulations or measurements of the current consumption of the load during normal use or operation.

[0042] In a non-limiting example, one or more component ratings of the plurality of auxiliary semiconductor switches 28b (e.g., continuous current rating, peak current rating, on-resistance, temperature rating, etc.) are selected to withstand a maximum current equal to the upper current threshold. Therefore, the upper torque threshold can also be understood as the maximum torque of the motor 18, wherein the multilevel inverter 14 operates in a mode utilizing the plurality of auxiliary semiconductor switches 28b (i.e., a three-level mode, which will be discussed in more detail below).

[0043] In a non-limiting example, the plurality of auxiliary semiconductor switches 28b are smaller than the plurality of main semiconductor switches 28a. In other words, in a non-limiting example, one or more component ratings of the plurality of auxiliary semiconductor switches 28b are selected to withstand a lower maximum current than the plurality of main semiconductor switches 28a. For example, the plurality of auxiliary semiconductor switches 28b may have a lower continuous current rating than the plurality of main semiconductor switches 28a.

[0044] In an exemplary embodiment, the DC bus 22a, AC bus 22b, multiple capacitors 24, neutral point 26, multiple main semiconductor switches 28a, and multiple auxiliary semiconductor switches 28b are connected as follows: Figure 2 As shown. It should be understood that the above description of the multilevel inverter 14 is merely exemplary, and various additional multilevel inverter circuits and topologies are within the scope of this disclosure.

[0045] Refer again Figure 1 Battery 16 is used to supply DC power to multilevel inverter 14. In an exemplary embodiment, battery 16 is the traction battery of vehicle 12. It should be understood that battery 16 can be any DC power source without departing from the scope of this disclosure. As described above, battery 16 is in electrical communication with the positive DC port 30a and negative DC port 30b of DC bus 22a.

[0046] Motor 18 is used to receive alternating current from multilevel inverter 14. In an exemplary embodiment, motor 18 is a motor configured to drive vehicle 12. In a non-limiting example, motor 18 is a three-phase AC induction motor. It should be understood that other types of AC motors are also within the scope of this disclosure. It should also be understood that motor 18 may include or be replaced by any AC load without departing from the scope of this disclosure. As described above, motor 18 is in electrical communication with the first AC phase port 32a, the second AC phase port 32b, and the third AC phase port 32c of AC bus 22b.

[0047] The controller 20 is used to control the operation of the multilevel inverter 14 and implement the method 100 of the operating system 10, as described below. In an exemplary embodiment, the controller 20 is also used to control and / or monitor the operation of the battery 16 and / or the motor 18. The controller 20 includes at least one processor 40 and a non-transitory computer-readable storage device or medium 42. The processor 40 may be a custom or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among several processors associated with the controller 20, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, a combination thereof, or generally a device for executing instructions.

[0048] Computer-readable storage device or medium 42 may include volatile and non-volatile memory such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory used to store various operational variables when the processor 40 is powered off. Computer-readable storage device or medium 42 may be implemented using a variety of memory devices, such as PROM (programmable read-only memory), EPROM (electrical PROM), EEPROM (electrically erasable PROM), flash memory, or other electrical, magnetic, optical, or combined memory devices capable of storing data, some of which represent executable instructions.

[0049] Controller 20 may also include multiple controllers that are electrically communicating with each other. Controller 20 may interconnect with additional systems and / or controllers of vehicle 12, thereby allowing controller 20 to access data such as the speed, acceleration, braking and steering angle of vehicle 12.

[0050] The controller 20 communicates electrically with the multilevel inverter 14 and, in some embodiments, with the battery 16 and / or the motor 18. In an exemplary embodiment, electrical communication is established using, for example, a CAN network, a FLEXRAY network, a local area network (e.g., WiFi, Ethernet, etc.), a serial peripheral interface (SPI) network, etc. It should be understood that various additional wired and wireless technologies and communication protocols used for communicating with the controller 20 are within the scope of this disclosure. It should also be understood that, within the scope of this disclosure, electrical communication also includes the transfer of power and / or energy between electrical devices (e.g., using wired and / or wireless power transmission technologies).

[0051] In one exemplary embodiment, controller 20 is configured to execute program instructions (e.g., stored in medium 42) to operate multilevel inverter 14. In one exemplary embodiment, multilevel inverter 14 can operate in either two-level or three-level mode. In two-level mode, only multiple main semiconductor switches 28a are used. In a non-limiting example, in two-level mode, the multiple main semiconductor switches 28a are switched by controller 20 using a space vector modulation (SVM) algorithm, and multiple auxiliary semiconductor switches 28b are in a non-conducting state (i.e., each of the multiple auxiliary semiconductor switches 28b is in a "closed" or "open" state with no current conduction). In three-level mode, multiple main semiconductor switches 28a and multiple auxiliary semiconductor switches 28b are used simultaneously. In a non-limiting example, in three-level mode, both the multiple main semiconductor switches 28a and the multiple auxiliary semiconductor switches 28b are switched by controller 20 using a space vector modulation (SVM) algorithm to control current flow in multilevel inverter 14.

[0052] As described above, the dimensions of the multiple auxiliary semiconductor switches 28b are determined based on an upper current threshold (related to an upper torque threshold). Therefore, when the multilevel inverter 14 supplies a current greater than the upper current threshold, the multiple auxiliary semiconductor switches 28b should not operate. Thus, the upper current threshold (and upper torque threshold) can be understood as the upper threshold for the multilevel inverter 14 to operate in three-level mode, as will be discussed in more detail below.

[0053] Space vector modulation (SVM) is described, for example, in “Space Vector PWM Scheme for Three-Phase Three-Level T-Type NPC Inverters” by M. Sajitha and R. Ramchand (Second International Conference on Intelligent Computing, Instrumentation and Control Technology (ICICICT), pp. 523-528, July 2019), the entire contents of which are incorporated herein by reference. It should be understood that the multilevel inverter 14 can be controlled using a closed feedback loop based on data collected from sensors (e.g., current sensors, position sensors, rotational speed sensors, etc.) on / within the motor 18. It should also be understood that various additional algorithms and methods for controlling the individual semiconductor switches of the multilevel inverter 14 can be used within the scope of this disclosure. An exemplary method for determining whether the multilevel inverter 14 operates in a two-level or three-level mode will be discussed below with reference to method 100.

[0054] In addition, the controller 20 may be configured to execute program instructions to monitor and / or control other aspects or features of the vehicle 12, such as receiving input from the occupants of the vehicle 12 (e.g., accelerator pedal input, brake pedal input, steering input, etc.), generating / providing control outputs for autonomous driving and / or driver assistance features, monitoring the status and / or diagnostic information of vehicle components (e.g., electric motor 18 and / or battery 16), etc.

[0055] refer to Figure 3A flowchart of method 100 of operating system 10 is shown. Method 100 begins at block 102 and proceeds to block 104. At block 104, controller 20 determines the command torque of motor 18. Within the scope of this disclosure, command torque is the torque that motor 18 should provide. In one exemplary embodiment, controller 20 determines the command torque based at least in part on input received from the accelerator pedal of vehicle 12. In another exemplary embodiment, controller 20 determines the command torque based at least in part on commands received from the autonomous driving and / or driver assistance systems of vehicle 12 or software modules of controller 20. In yet another exemplary embodiment, controller 20 determines the command torque based on an open-loop or closed-loop feedback algorithm configured to achieve the desired vehicle speed and / or acceleration, regardless of loads caused by vehicle weight, road inclination, cargo / traction load, and / or similar factors. It should be understood that any method of determining command torque, including receiving command torque from an external system or controller, is within the scope of this disclosure. After block 104, method 100 continues to block 106.

[0056] At box 106, controller 20 compares the command torque with an upper torque threshold. The definition and determination of the upper torque threshold have been discussed in detail above. If the command torque determined at box 104 is greater than the upper torque threshold, method 100 proceeds to box 108. If the command torque determined at box 104 is less than or equal to the upper torque threshold, method 100 proceeds to box 110.

[0057] At block 108, in response to determining that the command torque determined at block 104 is greater than the upper torque threshold, controller 20 operates multilevel inverter 14 in a two-level mode. In an exemplary embodiment, to operate multilevel inverter 14 in two-level mode, controller 20 controls a plurality of main semiconductor switches 28a to transfer energy from DC bus 22a to AC bus 22b using pulse width modulation with two voltage levels, such that an approximately sinusoidal voltage waveform is generated at each of the first AC phase port 32a, the second AC phase port 32b, and the third AC phase port 32c, and controls a plurality of auxiliary semiconductor switches 28b to be in a non-conducting state, as described above. After block 108, method 100 continues to enter a standby state at block 112.

[0058] At block 110, controller 20 compares the command torque determined at block 104 with a lower torque threshold. Within the scope of this disclosure, the lower torque threshold is used to provide hysteresis to prevent jitter between two-level and three-level operating modes. In one exemplary embodiment, the lower torque threshold is determined at least in part based on an upper torque threshold and a predetermined torque hysteresis offset (e.g., five Newton-meters). In one exemplary embodiment, the predetermined torque hysteresis offset is determined through statistical analysis of simulation or experiment. In a non-limiting example, the lower torque threshold is equal to the upper torque threshold minus the predetermined torque hysteresis offset. If the command torque determined at block 104 is less than the lower torque threshold, method 100 proceeds to block 114. If the command torque determined at block 104 is greater than or equal to the lower torque threshold, the operating mode of the multilevel inverter 14 remains unchanged and method 100 continues to enter a standby state at block 112.

[0059] At block 114, in response to determining that the command torque determined at block 104 is less than a lower torque threshold, controller 20 operates multilevel inverter 14 in three-level mode. In an exemplary embodiment, to operate multilevel inverter 14 in three-level mode, controller 20 controls a plurality of main semiconductor switches 28a to transfer energy from DC bus 22a to AC bus 22b, and controls a plurality of auxiliary semiconductor switches 28b to transfer energy from DC bus 22a to AC bus 22b. The plurality of main semiconductor switches 28a and the plurality of auxiliary semiconductor switches 28b are used in series to generate voltage waveforms with low total harmonic distortion at each of the first AC phase port 32a, the second AC phase port 32b, and the third AC phase port 32c using pulse width modulation of three voltage levels. After block 114, method 100 continues to enter a standby state at block 112.

[0060] In one exemplary embodiment, controller 20 repeatedly exits standby state 112 and restarts method 100 at block 102. In a non-limiting example, controller 20 exits standby state 112 and restarts method 100 every timer (e.g., every 100 microseconds).

[0061] refer to Figure 4 An exemplary torque-speed graph 50 of the electric motor 18 is shown. The exemplary torque-speed graph 50 includes a torque axis 52a, a speed axis 52b, and an exemplary torque-speed curve 54 of the electric motor 18. Furthermore, the exemplary upper torque threshold is marked with a dashed line T. U As shown, and exemplarily, the lower torque threshold is marked with a dashed line T. L As shown. An exemplary torque-speed diagram 50 illustrates the operating range of the multilevel inverter 14 in two-level and three-level modes. U The first shaded area 56 at the top represents the operation in two-level mode according to method 100.L The second shaded area 58 below represents the operation in three-level mode according to method 100. T U and T L The third shaded area 60 represents the hysteresis region, in which the multilevel inverter 14 can operate in a two-level mode or a three-level mode according to method 100. It should be understood that the exemplary torque-speed graph 50, the exemplary torque-speed curve 54, and the exemplary upper torque threshold T... U The value and the exemplary lower torque threshold T L The value is merely exemplary and not necessarily proportional.

[0062] The system 10 and method 100 of this disclosure offer several advantages. By operating system 10 according to method 100, the dimensions of the plurality of auxiliary semiconductor switches 28b must be adapted only to conduct current thresholds, rather than the maximum rated current of the motor 18. Therefore, the plurality of auxiliary semiconductor switches 28b can be smaller, thereby reducing size, weight, and resource usage. In summary, system 10 and method 100 utilize the advantages of a three-level inverter (e.g., improved output waveform quality, reduced total harmonic distortion (THD), reduced switching losses, etc.) during most typical operating points of the motor 18, while minimizing the disadvantages typically associated with three-level inverters, such as larger size, greater weight, and increased resource usage.

[0063] The descriptions in this disclosure are merely exemplary in nature, and any modifications that do not depart from the spirit and scope of this disclosure are intended to fall within its scope. Such modifications should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A power inverter system, comprising: Multilevel inverter; An electric motor that is in electrical communication with the multilevel inverter; as well as A controller, which is in electrical communication with the multilevel inverter, wherein the controller is programmed to: Determine the command torque of the electric motor; The command torque is compared with the upper torque threshold of the three-level mode of the multilevel inverter; In response to determining that the command torque is greater than the upper torque threshold, the command torque is generated by using the motor by operating the multilevel inverter in a two-level mode. and In response to determining that the command torque is less than the upper torque threshold, the command torque is generated by using the motor by operating the multilevel inverter in the three-level mode.

2. The power inverter system of claim 1, wherein, The multilevel inverter also includes: DC bus; Multiple capacitors form a neutral point from the DC bus; An AC busbar, which is electrically connected to the motor; Multiple main semiconductor switches, which are electrically in communication with the DC bus and the AC bus; and Multiple auxiliary semiconductor switches are electrically connected to the neutral point and the AC bus.

3. The power inverter system according to claim 2, wherein, In order to generate the commanded torque using the motor by operating the multilevel inverter in the two-level mode, the controller is also programmed to: In response to determining that the command torque is greater than the upper torque threshold, the plurality of auxiliary semiconductor switches are operated in a non-conducting state.

4. The power inverter system of claim 3, wherein, The upper torque threshold is determined at least in part based on the typical maximum command torque during typical operation of the motor, and wherein the upper torque threshold is less than the maximum rated torque of the motor.

5. The power inverter system of claim 4, wherein, The upper torque threshold is determined such that at least 50% of all torque commands received during the service life of the motor are less than or equal to the upper torque threshold.

6. The power inverter system of claim 2, wherein, The dimensions of the plurality of auxiliary semiconductor switches are designed at least in part based on the upper torque threshold.

7. The power inverter system of claim 6, wherein, The dimensions of the plurality of auxiliary semiconductor switches are designed to withstand a current less than or equal to the maximum current required for the motor to generate a torque equal to the upper torque threshold.

8. The power inverter system of claim 7, wherein, The plurality of auxiliary semiconductor switches also include: One or more monolithic bidirectional semiconductor switches.

9. The power inverter system of claim 1, wherein, In order to generate the command torque using the motor by operating the multilevel inverter in the three-level mode, the controller is also programmed to: In response to determining that the command torque is less than the upper torque threshold and less than the lower torque threshold, the command torque is generated by using the motor by operating the multilevel inverter in the three-level mode.

10. The power inverter system of claim 9, wherein, The lower torque threshold is determined based on the upper torque threshold and a predetermined torque hysteresis offset.

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