Multi-level inverter powered by multi-level direct-current power source

Abstract

A multi-level inverter control system includes a power storage system having a high voltage terminal, a low voltage terminal, and an intermediate voltage terminal. The intermediate voltage terminal is at a voltage between the high voltage terminal and the low voltage terminal. The multi-level inverter includes a plurality of switches, a high voltage input connected to a high voltage terminal, a low voltage input connected to a low voltage terminal, and an intermediate voltage input connected to an intermediate voltage terminal. A controller is controllably coupled to the multi-level inverter. The controller includes at least a processor and a memory. The memory stores instructions configured to cause the controller to operate the multi-level inverter in a three-level inverter mode, a full-power two-level inverter mode, a first part-power two-level inverter mode, and a second part-power two-level inverter mode.

Description

Technical Field

[0001] The subject disclosure relates to a multilevel inverter configured to draw power from a direct current (DC) power source having a multilevel output, and a control system for the multilevel inverter. Background Art

[0002] Electric vehicles and hybrid electric vehicles include power storage systems that store electrical power and output DC power. However, the drive motors and other mechanical features of the vehicle require alternating current to operate. To facilitate the conversion of DC power into alternating current (AC) power, the vehicle includes one or more inverters. The inverter uses actively controlled switches (e.g., transistors) to convert DC power into a sinusoidal or nearly sinusoidal AC power output.

[0003] Two-level (and higher) voltage source inverters include limitations related to efficiency driven by high switching losses and current ripple, reliability degradation due to dv / dt (voltage change over time) variations, di / dt (current change over time) variations, electromagnetic interference, and power density degradation due to capacitance variations. Existing systems attempt to address some of these issues by utilizing multi-level inverters. Summary of the invention

[0004] In an exemplary embodiment, a multilevel inverter control system includes: a power storage system having a high voltage terminal, a low voltage terminal and an intermediate voltage terminal, wherein the intermediate voltage terminal is at a voltage between the high voltage terminal and the low voltage terminal; a multilevel inverter including a plurality of switches, a high voltage input connected to the high voltage terminal, a low voltage input connected to the low voltage terminal and an intermediate voltage input connected to the intermediate voltage terminal; and a controller controllably coupled to the multilevel inverter, the controller including at least a processor and a memory storing instructions configured to cause the controller to operate the multilevel inverter in a three-level inverter mode, a full-power two-level inverter mode, a first partial power two-level inverter mode and a second partial power two-level inverter mode.

[0005] In addition to one or more features described herein, the power storage system is a battery comprising a plurality of battery cells, and the battery cells are divided into a first group of battery cells and a second group of battery cells, wherein the voltage difference between the low voltage terminal and the intermediate voltage terminal is the voltage of the first group of battery cells, and the voltage difference between the intermediate terminal and the high voltage terminal is the voltage of the second group of battery cells.

[0006] In addition to one or more features described herein, the voltage difference of the first group of battery cells and the voltage difference of the second group of battery cells are the same.

[0007] In addition to one or more features described herein, the memory also includes instructions for identifying a battery cell fault in a battery cell in one of the first group of battery cells and the second group of battery cells, and instructions for responding to the identified battery cell fault by operating the multilevel inverter in a first partial power two-level inverter mode when the identified battery cell fault is in the first group of battery cells and operating the multilevel inverter in a second partial power two-level inverter mode when the battery cell fault is in the second group of battery cells.

[0008] In addition to one or more features described herein, the multilevel inverter is a T-type inverter topology having a first capacitor connecting the high voltage input to the intermediate voltage input, a second capacitor connecting the intermediate voltage input to the low voltage input, a first switch connecting the high voltage terminal to the AC output, a pair of second switches connecting the intermediate voltage terminal to the AC output, and a third switch connecting the low voltage input to the AC output.

[0009] In addition to one or more features described herein, the first partial power two-level inverter mode includes maintaining the first switch open, thereby electrically removing the first switch and the first capacitor from the multi-level T-type inverter topology, and operating the pair of second switches and third switches as a two-level inverter.

[0010] In addition to one or more features described herein, the second partial power two-level inverter mode includes keeping the third switch open, thereby electrically removing the third switch and the second capacitor from the multi-level T-type inverter topology, and operating the pair of the second switch and the first switch as a two-level inverter.

[0011] In addition to one or more features described herein, the controller is configured to operate the multilevel inverter in a first partial power mode while discharging a first group of battery cells within the power storage system until a charging threshold is reached, and is configured to alternately operate between a first partial power two-level inverter mode and a second partial power two-level inverter mode to maintain a balance between the first group of battery cells and the second group of battery cells.

[0012] In yet another exemplary embodiment, a method of operating an inverter within a vehicle power system includes operating the inverter in a multi-level operation mode when the vehicle power system is in a nominal mode; operating the inverter in one of a full-power two-level inverter mode, a first partial-power two-level inverter mode, and a second partial-power two-level inverter mode when the power system is in a non-nominal mode, and wherein the inverter is a T-type inverter topology having a first capacitor connecting a high voltage input to an intermediate voltage input, a second capacitor connecting the intermediate voltage input to a low voltage input, a first switch connecting the high voltage terminal to an AC output, a pair of second switches connecting the intermediate voltage terminal to the AC output, and a third switch connecting the low voltage input to the AC output.

[0013] In addition to one or more features described herein, the inverter operates in a full power two-level inverter mode, and the non-nominal mode is an identified fault in a pair of second switches of the inverter.

[0014] In addition to one or more features described herein, operating in the full power two level inverter mode includes maintaining at least one switch of the pair of second switches in an open state for the entire duration of operating in the full power two level inverter mode.

[0015] In addition to one or more features described herein, the inverter operates in a first partial power two-level inverter mode, and the non-nominal mode is a fault in at least one of a first group of power battery cells of the connected DC battery, a fault in the first capacitor, and a fault in the first switch, and wherein the inverter operates in a second partial power two-level inverter mode, and the non-nominal mode is a fault in at least one of a second group of power battery cells of the connected DC battery, a fault in the second capacitor, and a fault in the third switch.

[0016] In addition to one or more features described herein, operating in a first partial power two-level inverter mode includes maintaining the first switch in an open state for the duration of the first partial power two-level inverter mode, and wherein operating in a second partial power two-level inverter mode includes maintaining the third switch in an open state for the duration of the second partial power two-level inverter mode.

[0017] In addition to one or more features described herein, the power system includes a DC battery having a plurality of battery cells divided into a first group of battery cells and a second group of battery cells, and wherein the first group of battery cells is connected between a high voltage input and an intermediate voltage input, and the second group of battery cells is connected between the intermediate voltage input and a low voltage input.

[0018] In addition to one or more features described herein, a first partial power two-level inverter mode is entered in response to a fault detected in a first group of battery cells, and a second partial power two-level inverter mode is entered in response to a fault detected in a second group of battery cells.

[0019] In addition to one or more features described herein, a first partial power two-level mode is entered in response to at least one condition that negatively impacts inverter thermal characteristics, inverter efficiency, and inverter life.

[0020] One or more features described herein also include balancing a battery system connected to an inverter, the battery system including a plurality of battery cells, and the battery cells are divided into a first group and a second group, wherein a voltage difference between a low voltage terminal and an intermediate voltage terminal is a voltage of the first group, and a voltage difference between an intermediate terminal and a high voltage terminal is a voltage of the second group, by placing the inverter in a first partial power two-level inverter mode and discharging the first group until a charging threshold is reached, placing the inverter in a second partial power two-level inverter mode and discharging the second group until a charging threshold is reached, and alternating between the first partial power mode and the second partial power mode, thereby maintaining a balance between the first group of battery cells and the second group of battery cells.

[0021] In yet another exemplary embodiment, a vehicle includes a power storage system having a high voltage terminal, a low voltage terminal, and an intermediate voltage terminal, wherein the intermediate voltage terminal is at a voltage between the high voltage terminal and the low voltage terminal, at least two electric motors configured to convert AC power into mechanical rotation, a multilevel inverter connected to the power storage system and configured to output AC power, the multilevel inverter including a plurality of switches, a high voltage input connected to the high voltage terminal, a low voltage input connected to the low voltage terminal, and an intermediate voltage input connected to the intermediate voltage terminal, and a controller controllably coupled to the multilevel inverter, the controller including at least a processor and a memory, the memory storing instructions configured to cause the controller to operate the inverter in a three-level inverter mode, a full-power two-level inverter mode, a first partial power two-level inverter mode, and a second partial power two-level inverter mode.

[0022] In addition to one or more features described herein, the multilevel inverter is a T-type inverter topology having a first capacitor connecting the high voltage input to the intermediate voltage input, a second capacitor connecting the intermediate voltage input to the low voltage input, a first switch connecting the high voltage terminal to the AC output, a pair of second switches connecting the intermediate voltage terminal to the AC output, and a third switch connecting the low voltage input to the AC output.

[0023] In addition to one or more features described herein, a first partial power two-level inverter mode includes maintaining the first switch open, thereby electrically removing the first switch and the first capacitor from the multi-level T-type inverter topology, and operating the pair of second switches and third switches as a two-level inverter, and wherein the second partial power two-level inverter mode includes maintaining the third switch open, thereby electrically removing the third switch and the second capacitor from the multi-level T-type inverter topology, and operating the pair of second switches and the first switch as a two-level inverter.

[0024] The above features and advantages and other features and advantages of the present disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other features, advantages and details appear, by way of example only, in the following detailed description, which refers to the accompanying drawings, in which:

[0026] Figure 1 is an exemplary vehicle including a direct current (DC) power storage system and a pair of alternating current (AC) driven drive motors;

[0027] Figure 2 is an illustrative multilevel inverter for converting DC power from a power storage system into AC power for driving a motor;

[0028] Figure 3 is an example single-phase leg of a T-type multilevel inverter topology configured to interface with direct midpoint terminals;

[0029] Figure 4 Shows Figure 3 The single-phase branch of the T-type multilevel inverter topology is operated in a two-level mode without a midpoint;

[0030] Figure 5 shows operation in a first two-level partial power mode of operation Figure 3 A single-phase branch of a T-type multilevel inverter topology; and

[0031] Figure 6 Shows the use of Figure 3 The full T-type multilevel inverter topology of the phase legs operates in a second two-level partial power operation mode. DETAILED DESCRIPTION

[0032] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or use. It should be understood that in all figures, corresponding reference numerals represent the same or corresponding parts and features. As used herein, the term module refers to a processing circuit, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit and / or other suitable components that provide the described functions.

[0033] According to some exemplary embodiments, the multilevel inverter system described herein generally utilizes an intermediate voltage node having a voltage level lower than the high voltage terminal and higher than the low voltage (zero voltage) terminal. The intermediate voltage node is directly connected to an intermediate voltage tap within a corresponding power supply. In some examples, the intermediate voltage tap is at a split in a split battery pack, wherein the battery pack includes a plurality of battery cells, and the voltage at the split is the combined voltage of the subgroup battery cells in the battery. Providing a direct connection to the intermediate voltage tap allows the multilevel inverter to operate more efficiently and allows the inverter to continue to operate as a two-level inverter in an additional operating mode during one or more fault conditions.

[0034] Figure 1 An embodiment of a motor vehicle 10 is shown that includes a body 12 that at least partially defines an occupant compartment 14. The body 12 also supports various vehicle subsystems, including a propulsion system 16, a battery system 22, and other subsystems to support the functions of the propulsion system 16 and other vehicle components, such as a braking subsystem, a suspension system, a steering subsystem, a fuel injection subsystem, an exhaust subsystem, etc.

[0035] The vehicle 10 may be an internal combustion vehicle, an electric vehicle (EV), or a hybrid vehicle. In one embodiment, the vehicle 10 is a hybrid vehicle that includes an internal combustion engine system 18 and at least one electric motor assembly. For example, the propulsion system 16 includes a first electric motor 20 and a second electric motor 21. The motors 20 and 21 may be configured to drive wheels on opposite sides of the vehicle 10. In addition, any number of motors located at different locations around the vehicle 10 may be used.

[0036] The battery system 22 may be electrically connected to the motors 20 and 21 and / or other components, such as vehicle electronics. The battery system 22 may be configured as a rechargeable energy storage system (RESS) and include a plurality of battery cells divided into a plurality of sections, and a plurality of voltage outputs (taps).

[0037] Continue to refer Figure 1 , Figure 2An exemplary inverter system 200 is shown, which includes a multi-level inverter 210 for converting DC power from a battery system 22 to an AC power output 216 of one or more phases of an electric motor 20, 21. The AC power output 216 provides drive power to the motor 20, 21 to which the AC power output 216 is connected. The battery system 22 includes a high voltage output terminal 202 and a low voltage output terminal 204, each of which is connected to a corresponding input terminal 212, 214 of the multi-level inverter 210 topology. The connection between the high voltage output terminal 202 and the high voltage input 212, and the switch 344 (such as the switch 344) connecting the high voltage input 212 to the AC output 216. Figure 3-6 4, also referred to as the first switch) is referred to as the high voltage branch 404. Similarly, the connection between the low voltage output terminal 204 and the low voltage input 214 and the switch 346 (as shown) connecting the low voltage input to the AC output 216 Figure 3-6 The direct connection between the intermediate input 228 and the intermediate terminal 208, and the two switches 340, 342 (as shown) connecting the input 228 to the AC output 216 are referred to as the low voltage branch 406. Figure 3-6 As shown, also referred to as a pair of second switches) is referred to as the middle branch 402.

[0038] As used herein, "high voltage" refers to the voltage potential when the battery system 22 is fully charged, "low voltage" refers to a voltage potential of zero or approximately zero, and "intermediate voltage" refers to a voltage potential between the high voltage and the low voltage. The switches within the inverter 210 are actively controlled by an active inverter controller 260 to convert the DC power to an AC power output at the AC power output 216. The inverter controller 260 can be a dedicated inverter controller, a module within a power system controller, a module within a general controller, a distributed control architecture, or any similar control system within the vehicle 10.

[0039] A pair of capacitors 222, 224 arranged in series are connected across the terminals 212, 214. The capacitors 222, 224 are connected at an intermediate voltage node 228. The intermediate voltage node 228 is directly connected to the corresponding intermediate voltage output terminal 208 of the battery system 22. The intermediate voltage output node 208 can be set at the midpoint between each group of battery cells 22', 22", modules or battery packs within the battery system 22. In an alternative example, the intermediate voltage output 208 can be a node connecting two battery systems 22 arranged in series or any electrically similar power storage system. The two groups of battery cells 22', 22" can have the same potential, the first group of battery cells 22' can be higher than the second group of battery cells 22", or the second group of battery cells 22" can have a higher potential than the first group of battery cells 22'. As used herein, the potential of a group of battery cells 22', 22" or other similar components refers to the voltage difference output by the group of battery cells 22', 22" when the group of batteries 22', 22" is at full capacity.

[0040] The direct connection between the intermediate voltage node 228 and the intermediate voltage terminal 208 provides three stable voltage levels to power the inverter 210, wherein the intermediate voltage levels are independent of the charge state of the capacitors 222, 224. The three stable voltage levels in turn allow the capacitors 222, 224 to operate individually as high frequency ripple current filters. Limiting the ripple filtering function allows a significant reduction in the physical size, volume, capacitance, and weight of the capacitors 222, 224.

[0041] Continue to refer Figure 2 , Figure 3 Shows that it can be used as Figure 2 A single phase leg of an exemplary multi-level inverter topology 310 of the inverter 210 of the system 200 is shown, the topology 310 being a T-type inverter. In the three-phase example, the phase legs shown are repeated once for each phase. It should be understood that during operation of a complete three-phase assembly, the operation of the single phase shown here is repeated simultaneously on each phase. The phase legs shown in the topology 310 are repeated once for each phase. Figure 2 The inverter system 200 is provided in the context of an inverter system 200 and is actively controlled by a controller within the vehicle to produce AC power at an AC output 216 according to known control processes.

[0042] Specific reference Figure 3The phase leg 310 of the T-type inverter includes a first MOSFET switch 340 including a drain connected to the intermediate voltage node 228 and a source connected to the source of a second MOSFET switch 342. The drain of the second MOSFET switch 342 is connected to the power output 216. In addition, the phase leg 310 includes a third MOSFET switch 344 having a drain connected to the high voltage output terminal 202 and a source connected to the AC power output 216. The fourth MOSFET switch 346 includes a drain connected to the power output 216 and a source connected to the low voltage output terminal 204.

[0043] Each of switches 340, 342, 344, 346 is controlled and provided to a respective gate via a control signal originating from controller 260. Controller 260 sets the control signals and switching rates to achieve desired AC power output characteristics at power output 216 according to known inverter control methods.

[0044] In addition to the increased voltage stability at the intermediate node 228 due to the direct connection to the intermediate voltage output of the battery system 22, the multi-tap connection to the battery system 22 allows additional modes of operating the T-type inverter 310 to be combined in response to various possible operating conditions (such as short circuit, overcurrent, charging requirements, capacitor temperature, etc.), thereby improving the operation of the vehicle power system.

[0045] Continue to refer Figure 3 , Figure 4-6 shows different additional modes of operation, Figure 4 , 5 Each of 6 shows a different mode.

[0046] In some cases, the fault may occur at one or more points within the battery system 22 and the inverter 210. Depending on the location and type of the fault, the required response range may range from immediate cessation of operation to continued operation indefinitely in two-level mode and monitoring. When such a fault occurs, the controller 260 electrically removes a portion of the inverter 210 from the topology, and operates the remaining portion as a two-level inverter at full capacity or partial capacity, depending on the location and type of the fault or the purpose of entering the two-level mode. By keeping one or more switches 340, 342, 344, 346 within the removed portion disconnected, the portion is electrically removed, thereby preventing current from flowing through the portion.

[0047] refer to Figure 1-3 , Figure 4The operation of the T-type inverter phase branch 410 as a two-level inverter without a midpoint is shown by keeping one or both of the pair of switches 344, 346 on the middle branch 402 open, thereby electrically removing the middle branch 402 from the circuit. This operation can be selected when a fault occurs on the middle branch 402. When this type of fault occurs, the controller 260 switches the inverter 210 to a two-level inverter without a midpoint. The remaining two switches 344, 346 are operated by the controller 260 together with the capacitors 222, 224 as a conventional two-level inverter providing an AC output 216.

[0048] Figure 4 The operating mode shown in allows the inverter 210 to continue to operate at full power level, but as a two-level inverter, until the fault is corrected or can be resolved in other ways. In another example, in response to a problem with branch 402, a Figure 4 Two-level inverter shown without midpoint operating mode. In certain situations, this mode may be entered if conventional two-level inverter operation is desired to achieve an efficiency, speed or torque operating point.

[0049] In an alternative example, when there is a fault in the high branch 404 or the low branch 406, or when there is a fault condition in one or more groups of battery cells 22', 22" of the battery system 22, the controller 260 can place the inverter 210 in Figure 5 The first part of the power two-level inverter mode shown or Figure 6 The second partial power two level inverter mode is shown. The partial power two level inverter mode phase legs 510, 610 shown operate in a substantially similar manner due to the similar composite circuit structure.

[0050] When a fault occurs in the high branch 404 or the low branch 406, the controller 260 electrically removes the portion of the inverter 210 where the fault has occurred and transfers the operation to the corresponding partial power two-branch inverter mode phase branch 510, 610. When a fault occurs in the first group of battery cells 22', the first capacitor 222 or the third switch 344, the controller 260 keeps the third switch 344 open, thereby preventing current from flowing through the high voltage input branch 202 and Figure 5 The partial two-level inverter mode shown in FIG. 5 is operated in the phase branch 510. In contrast, when a fault occurs in the second group of battery cells 22', the second capacitor 224 or the fourth switch 346, the controller 260 keeps the fourth switch 346 disconnected, thereby preventing current from passing through the low voltage input branch 406. The electrical disconnection of the third switch 344 or the fourth switch 346 ensures zero current in one direction. However, under a positive bias, the switches 344, 346 can still be turned on. Appropriate gate control of the active switch prevents such a positive bias from occurring and can be implemented according to known conventional methods.

[0051] In the specific case of a fault within a battery cell 22', 22" in a group of battery cells 22', 22" in the battery system 22, the partial power two-level inverter mode phase leg 510, 610 electrically removes the corresponding group of battery cells 22', 22", thereby allowing the vehicle 10 to continue to operate without the risk of the fault in the battery cell 22 propagating to other battery cells 22', 22" or potential further damage to the vehicle. The severity and cause of the battery cell fault can affect the inverter 210 in detail. Figure 5 and 6 Relatedly, if one of capacitors 222, 224 fails, keeping the corresponding switch open removes the faulty capacitor from the circuit and prevents the fault from causing further damage to the inverter.

[0052] While described above with respect to detected fault conditions, it should be appreciated that sensing techniques exist to identify other conditions that may benefit from temporarily switching to a two-level operating mode. For example, the controller 260 may include a sensor input corresponding to the temperature of the capacitors 222, 224, or otherwise determine the temperature of a portion of the inverter 210. When such information is available, the controller 260 may switch to a two-level operating mode 510, 610, which electrically removes the overheated capacitors 222, 224 from the inverter 210 until the temperature of the capacitors 222, 224 has cooled, and when the capacitor 222 is overheated, use Figure 5 mode, used when capacitor 224 is overheated Figure 6 The length of time for cooling can be predetermined or based on a measured or derived temperature threshold. A similar process can be applied to any thermal detection within the inverter 210 and is not limited to the specific example of capacitors 224, 222.

[0053] In yet another example, while the vehicle 10 is operating, the controller 260 may determine that there is an imbalance in the battery system 22. When the imbalance is due to a battery cell 22" having a high charge, the controller 260 first places the vehicle 10 in a Figure 5 The first partial power two-level inverter mode phase branch 510 is connected to discharge the first group of battery cells 22' in the battery system 22. Then, once a sufficient charging threshold and balance between the top and bottom sides are reached, the charge state of each group of battery cells 22', 22" is balanced as a whole. When the imbalance is due to the battery cell 22' having a higher charge, the controller 26 puts the vehicle 10 into Figure 6 mode shown, and balance is achieved in the same manner.

[0054] In yet another example, the controller 260 can determine a saturation state in one of the switches 340, 342, 344, 346 and allow the inverter 210 to continue operating in one of the two-level inverter mode phase legs 410, 510, 610 if one of the switches 340, 342, 344, 346 inadvertently becomes desaturated. The mode selected depends on the particular switch that becomes desaturated. Figure 4 The mode corresponds to the desaturation of switches 340 and 342, Figure 5 The mode corresponds to the desaturation of switch 344, while Figure 6 The mode corresponds to desaturation of switch 346. As in the previous example, when a desaturation fault occurs, controller 260 detects the desaturation and places inverter 210 in a corresponding operation mode that electrically removes the switch experiencing the saturation fault, and inverter 210 can continue to operate.

[0055] In some cases, a two-level partial power mode can be entered ( Figure 5 and Figure 6 ) operation to achieve higher efficiency in low speed operation of the motors 20, 21. When the motors are running at low speed, half of the battery 22 with a smaller DC bus voltage can still be used to power the motors 20, 21. Applying a lower DC voltage can improve inverter and motor efficiency. In an alternative control embodiment, a two-level partial power mode can be entered to avoid overheating of the inverter switches due to aging or fault behavior.

[0056] In an alternative example, the multi-level inverter 210 may include up to N intermediate voltage connections for N-level inverters, where N is the total available voltage output from the battery system 22. In such an example, the controller 260 may employ an extended form of the above method to switch the operating mode of the N-level inverter to the N-1-level inverter in response to a similar fault or condition.

[0057] The terms "one" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced items. The term "or" means "and / or", unless the context clearly indicates otherwise. References to "an aspect" throughout the specification mean that a particular element (e.g., feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in various aspects.

[0058] When an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0059] Unless otherwise indicated herein, all test standards are the most recent standards in effect as of the filing date of the present application or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0060] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0061] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope thereof. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the disclosure without departing from the essential scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A multi-level inverter control system, comprising: a power storage system having a high voltage terminal, a low voltage terminal, and an intermediate voltage terminal, wherein the intermediate voltage terminal is at a voltage between the high voltage terminal and the low voltage terminal; a multilevel inverter including a plurality of switches, a high voltage input connected to the high voltage terminal, a low voltage input connected to the low voltage terminal, and an intermediate voltage input connected to the intermediate voltage terminal; as well as A controller controllably coupled to the multilevel inverter includes at least a processor and a memory storing instructions configured to cause the controller to operate the multilevel inverter in a three-level inverter mode, a full-power two-level inverter mode, a first partial-power two-level inverter mode, and a second partial-power two-level inverter mode.

2. The multilevel inverter control system according to claim 1, wherein: The power storage system is a battery including a plurality of battery cells, and the battery cells are divided into a first group of battery cells and a second group of battery cells, wherein the voltage difference between the low voltage terminal and the intermediate voltage terminal is the voltage of the first group of battery cells, and the voltage difference between the intermediate voltage terminal and the high voltage terminal is the voltage of the second group of battery cells.

3. The multilevel inverter control system according to claim 2, wherein: The voltage difference of the first group of battery cells and the voltage difference of the second group of battery cells are the same; and wherein the memory also includes instructions for identifying a battery cell fault in a battery cell in one of the first group of battery cells and the second group of battery cells, and instructions for responding to the identified battery cell fault by operating the multilevel inverter in a first partial power two-level inverter mode when the identified battery cell fault is in the first group of battery cells and operating the multilevel inverter in a second partial power two-level inverter mode when the battery cell fault is in the second group of battery cells.

4. The multilevel inverter control system according to claim 1, wherein: The multilevel inverter is a T-type inverter topology having a first capacitor connecting the high voltage input to the intermediate voltage input, a second capacitor connecting the intermediate voltage input to the low voltage input, a first switch connecting the high voltage terminal to an AC output, a pair of second switches connecting the intermediate voltage terminal to the AC output, and a third switch connecting the low voltage input to the AC output.

5. The multilevel inverter control system according to claim 4, wherein: The first partial power two-level inverter mode includes keeping the first switch open, thereby electrically removing the first switch and the first capacitor from the multi-level T-type inverter topology, and operating the pair of second switches and the third switch as a two-level inverter, and wherein the second partial power two-level inverter mode includes keeping the third switch open, thereby electrically removing the third switch and the second capacitor from the multi-level T-type inverter topology, and operating the pair of second switches and the first switch as a two-level inverter.

6. The multilevel inverter control system according to claim 1, wherein: The controller is also configured to operate the multilevel inverter in the first partial power mode while discharging a first group of battery cells within the power storage system until a charging threshold is reached, and is configured to alternately operate between the first partial power two-level inverter mode and the second partial power two-level inverter mode to maintain a balance between the first group of battery cells and the second group of cells.

7. A method of operating an inverter in a vehicle power system, comprising: operating the inverter in a multi-level operation mode when the vehicle power system is in a nominal mode; operating the inverter in one of a full power two-level inverter mode, a first partial power two-level inverter mode, and a second partial power two-level inverter mode when the power system is in a non-nominal mode; and Wherein, the inverter is a T-type inverter topology, having a first capacitor connecting the high voltage input to the intermediate voltage input, a second capacitor connecting the intermediate voltage input to the low voltage input, a first switch connecting the high voltage terminal to the AC output, a pair of second switches connecting the intermediate voltage terminal to the AC output, and a third switch connecting the low voltage input to the AC output.

8. The method according to claim 7, wherein: The inverter operates in the full power two level inverter mode, and the non-nominal mode is an identified fault in the pair of second switches of the inverter, and wherein operating in the full power two level inverter mode includes maintaining at least one of the pair of second switches in an open state for the entire duration of operating in the full power two level inverter mode.

9. The method according to claim 7, wherein: The inverter operates in the first partial power two-level inverter mode, and the non-nominal mode is a fault in at least one of a first group of power battery cells of a connected DC battery, a fault in the first capacitor, and a fault in the first switch, and wherein the inverter operates in the second partial power two-level inverter mode, and the non-nominal mode is a fault in at least one of a second group of power battery cells of a connected DC battery, a fault in the second capacitor, and a fault in the third switch, wherein operating in the first partial power two-level inverter mode includes maintaining the first switch in an open state for the duration of the first partial power two-level inverter mode, and wherein operating in the second partial power two-level inverter mode includes maintaining the third switch in an open state for the duration of the second partial power two-level inverter mode.

10. The method according to claim 7, further comprising balancing a battery system connected to the inverter by: The voltage difference between the low voltage terminal and the intermediate voltage terminal is the voltage of the first group, and the voltage difference between the intermediate terminal and the high voltage terminal is the voltage of the second group: placing the inverter in the first partial power two-level inverter mode and discharging the first group until a charging threshold is reached; placing the inverter in the second partial power two-level inverter mode and discharging the second group until a charging threshold is reached; as well as Operation is alternated between the first partial power mode and the second partial power mode to maintain a balance between the first group of battery cells and the second group of battery cells.

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