GATE OXIDE SELF-RECOVERY OF A POWER MODULE

Abstract

A controller closes, while a vehicle is not being driven, a switch to connect windings of an electric machine directly to a center point of a traction battery and operates an inverter system controller between the electric machine and the traction battery to maintain switches of the inverter system controller at a predefined temperature for a predefined duration.

Description

FIELD OF TECHNOLOGY

[0001] This disclosure relates to automotive power systems. GENERAL STATE OF THE ART

[0002] A motor vehicle can use electrical energy to power an electric machine. The electric machine can convert this electrical energy into mechanical energy to propel the vehicle. The motor vehicle can include various power electronics equipment to condition and store electrical energy. SUMMARY

[0003] An automotive power system includes a traction battery, an electric machine including star-connected windings, an inverter system controller connected between the traction battery and the electric machine, and a switch having a terminal directly connected to a midpoint of the traction battery and a terminal directly connected to a star point of the star-connected windings.

[0004] A method includes closing a switch during a parking mode to directly connect a midpoint of a traction battery and a star point of star-connected windings of an electric machine, and operating an inverter system controller connected between the traction battery and the electric machine to maintain switches thereof at a predefined temperature for a predefined duration.

[0005] A vehicle includes a traction battery, an electric machine, an inverter system controller connected between the traction battery and the electric machine, a switch connected between the traction battery and windings of the electric machine, and a controller that, while the vehicle is not being driven, closes the switch and operates the inverter system controller to maintain switches thereof at a predefined temperature for a predefined duration. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic diagram of an automotive power system. Fig. Figure 2 is a block diagram of a control algorithm for gate oxide self-recovery of a closed-loop power module. Fig. Figure 3 shows simulated circuit breaker current waveforms associated with the automotive power system Fig. 1 and the control algorithm for gate oxide self-recovery of a closed-loop power module from Fig. 2 are assigned. Fig. Figure 4 shows simulated circuit breaker temperature waveforms associated with the automotive power system Fig. 1 and the control algorithm for gate oxide self-recovery of a closed-loop power module from Fig. 2 are assigned. Fig. Figure 5 shows simulated circuit breaker loss waveforms associated with the automotive power system Fig. 1 and the control algorithm for gate oxide self-recovery of a closed-loop power module from Fig. 2 are assigned. Fig. Figure 6 shows simulated battery current waveforms associated with the automotive power system Fig. 1 and the control algorithm for gate oxide self-recovery of a closed-loop power module from Fig. 2 are assigned. Fig. Figure 7 shows simulated phase current and battery voltage waveforms associated with the automotive power system from Fig. 1 and the control algorithm for gate oxide self-recovery of a closed-loop power module from Fig. 2 are assigned. DETAILED DESCRIPTION

[0006] Embodiments are described herein. It should be understood, however, that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or reduced to show details of specific components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art.

[0007] Various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for particular applications or implementations.

[0008] Electric vehicles may use an inverter system controller to provide electrical power to the motor to propel the vehicle. The inverter system controller may use insulated-gate bipolar transistors or silicon carbide devices to convert DC power to AC power to power the motor and AC to DC power to charge the battery. These power devices are some of the essential components of the inverter system controller.

[0009] These devices require a certain gate voltage to be optimized for efficiency and operate properly. The threshold voltage is where the device first begins to conduct, and the gate voltage from the gate driver circuit is selected based on manufacturer specifications to be greater than the device's threshold voltage. The gate driver circuit is designed based on this and operates at one voltage to turn the device on and another voltage to turn it off. As the device ages and the gate oxide layer deteriorates, the threshold voltage for turning the device on and off also changes. This causes more losses and, in certain cases, renders the gate driver circuit unable to drive the power device at all.These types of problems may require replacing the inverter system controller. A primary cause of this problem is trapped charges in the gate oxide layer within the device. These trapped charges alter the threshold voltage, which in turn alters the device's turn-on and turn-off voltages.

[0010] The device can go through three aging stages depending on operating parameters and environmental conditions. The first stage is when the device is in normal operation and nothing has changed. The second stage may be when the threshold voltage has begun to decrease due to trapped charges. The third stage may be when Fowler-Nordheim tunneling begins and the threshold voltage begins to rise continuously. In the latter stages, greater power loss and inefficient device operation may become apparent.

[0011] Generally, one method used to restore the gate oxide involves heating to a temperature of 120°C for 30 minutes to an hour or more. This existing method uses the vehicle's positive temperature coefficient heater or heat pump. Using this method, the coolant must be heated in the circuit. Another option routes the coolant to the engine and uses the engine to heat the coolant. A third option cycles the vehicle's gasoline engine to keep the battery charged to power the positive temperature coefficient heater. In the context of an electric vehicle, this option uses a plug and electricity to allow the positive temperature coefficient heater to heat the coolant.

[0012] These techniques can have disadvantages. The positive temperature coefficient heater is inefficient and uses power from the battery to heat the coolant. The coolant must be pumped and heated throughout the glow cycle, causing unnecessary heating of other components in the circuit. Such cycling can reduce the lifespan of the positive temperature coefficient heater. The positive temperature coefficient heater may need to be enlarged, and additional cooling paths and valves may be necessary.

[0013] This disclosure contemplates strategies and components to restore the threshold voltage of the device or return it as close as possible to the stage-one threshold voltage. This includes a self-annealing process for a device to remove charges trapped within the device.

[0014] With reference to Fig. 1, a vehicle 10 includes a traction battery 12, an inverter system controller 14, an electric machine 16, a switch 18, and a controller 20. The inverter system controller 14 is connected between the traction battery 12 and the electric machine 16. The controller 20 communicates with / exerts control over the components of the vehicle 10.

[0015] The traction battery 12 includes two sets of battery cells 22, 24, which thus define a center point therebetween.

[0016] The inverter system controller 14 includes a DC link capacitor 26, current sensors 28, 30, 32 and power switches Q1, Q2, Q3, Q4, Q5, Q6 with corresponding gates G1, G2, G3, G4, G5, G6 and junction temperature sensors Tj1, Tj2, Tj3, Tj4, Tj5, Tj6. The power switches Q1, Q2 are connected in series and define a first phase branch of the inverter system controller 14, the power switches Q3, Q4 are connected in series and define a second phase branch of the inverter system controller 14, and the power switches Q5, Q6 are connected in series and define a third phase branch of the inverter system controller 14. The phase branches are connected in parallel to each other and to the DC link capacitor 26. Each of the current sensors 28, 30, 32 is arranged to detect a current associated with one of the phase branches.

[0017] The electrical machine 16 includes star-connected windings 34 and thus defines a star point.

[0018] One terminal of switch 18 taps the star point of the star-connected windings 34. Another terminal of switch 18 taps the center point of the traction battery 12 between the sets of battery cells 22, 24. When closed, switch 18 directly connects the star point and the center point.

[0019] With reference to Fig. 2, a reference temperature (e.g., 120°C) Tj_Ref and one of the junction temperatures Tji (i = 1, 2, 3, ... 6) are differentiated at operation 36. The resulting difference is provided to the proportional-integral block PI1. The output of the proportional-integral block PI1 and the output of the feedback block 38 are multiplied at operation 40. The phase currents are summed at operation 42. The resulting product of operation 40 and the resulting sum of operation 42 are differentiated at operation 44. The resulting difference is provided to a block 46, which includes a multiplication operation 48, 50, a difference operation 52, the proportional-integral block PI2, and the NOT gate 54, arranged as shown. An output from the square wave generator 56 is provided to the feedback block 38 and the block 46. An output from the block 46 and the triangle wave generator 58 is provided to the comparator 60.The resulting output is provided to AND gates 62, 64. An output from square wave generator 56 is provided to AND gate 62 and NOT gate 66. An output from NOT gate 66 is provided to AND gate 64. An output from AND gate 62 affects the control of gates G1, G3, G5. An output from AND gate 64 affects the control of gates G2, G4, G6.

[0020] When the vehicle 10 is driven, the switch 18 is open. The proposed strategy is deactivated, and the inverter system controller 14 and the electric machine 16 are controlled by conventional control strategies.

[0021] When the vehicle 10 is not being driven (e.g., while parked) and restoration of the power switches Q1, Q2, Q3, Q4, Q5, Q6 is required, the switch 18 is closed, and the gate oxide self-recovery control algorithm for a closed-loop power module is executed to maintain the junction temperatures at a predefined temperature for a predefined period of time (e.g., 120°C for 30 minutes to 1 hour, or longer if needed). This process can be repeated whenever the device threshold voltage increases or decreases from the level one threshold voltage range, which can be detected via known sensors and techniques.

[0022] Tj_Ref is the target junction temperature of the circuit breakers Q1, Q2, Q3, Q4, Q5, and Q6, which is set to 120°C in this example. Other temperatures may be required depending on the circuit breaker type, etc. The feedback temperatures come from the junction temperature sensors Tj1, Tj2, Tj3, Tj4, Tj5, and Tj6. This can be a single device temperature or the average temperature of all circuit breakers Q1, Q2, Q3, Q4, Q5, and Q6. The proportional-integral (PI) controller PI1 is used to control the actual junction temperature of the circuit breakers Q1, Q2, Q3, Q4, Q5, and Q6, and its output is the target current of the sum of the three winding currents. The second PI controller PI2 is used to cause the motor winding current to follow the reference current, with the gate control signals G1, G2, G3, G4, G5, G6 controlling the power switches Q1, Q2, Q3, Q4, Q5 and Q6 respectively.The carrier signal has a frequency fsw, which defines the switching frequency of the power switches Q1, Q2, Q3, Q4, Q5, and Q6. The square wave has a duty cycle of 50%, and its frequency fo defines the fundamental frequency of the currents of the power switches Q1, Q2, Q3, Q4, Q5, and Q6.

[0023] This strategy heats the power switches Q1, Q2, Q3, Q4, Q5, and Q6 and maintains their junction temperatures at the target temperature (e.g., 120°C), thereby restoring the device's threshold voltage (or bringing it back to the level one threshold voltage as close as possible). At the same time, the sets of battery cells 22, 24 maintain an equal state of charge to avoid affecting the performance of the traction battery 12.

[0024] The Fig. Figures 3 to 7 show simulation results when the proposed strategy works to remove trapped charges in the devices, thereby restoring them. In this example, the target junction temperature is 120 °C, switch 18 is closed, fo = 50 Hz, fsw = 10 kHz, and the coolant temperature is 70 °C. Other control parameter values can be used based on simulation or test results. As a result, all power switches Q1, Q2, Q3, Q4, Q5, and Q6 conduct currents simultaneously.

[0025] Fig. Figure 3 shows currents of the power switches Q1, Q2. These currents and the switching of the devices lead to power losses and cause the temperature of the devices to rise, as shown in Fig. 4 and Fig. 5. Each switch has a power dissipation of 416 W, which helps maintain the switch junction temperature at 120 °C. Fig. Figure 6 shows the currents of the sets of battery cells 22, 24, with positive and negative current at a frequency of 50 Hz maintaining a constant battery charge level for both. It also shows Fig. 7 battery voltages and each phase current of the star-connected windings 34.

[0026] The algorithms, methods, or processes disclosed herein may be implementable by or adapted for use by a computer, controller, or processing device, which may include any dedicated electronic control unit or programmable electronic control unit. Furthermore, the algorithms, methods, or processes may be stored in many forms as computer- or controller-executable data and instructions, including, but not limited to, information permanently stored on non-writable storage media, such as read-only memory devices, and information modifiably stored on writable storage media, such as compact discs, random access memory devices, or other magnetic and optical media. The algorithms, methods, or processes may also be implemented in software-executable objects.Alternatively, the algorithms, methods, or processes may be implemented in whole or in part using suitable hardware components, such as application-specific integrated circuits, field-programmable gate arrays, state machines, or other hardware components or devices, or a combination of firmware, hardware, and software components.

[0027] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms encompassed by the claims. The terms used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosed subject matter. For example, the terms "controller" and "controllers" may be used interchangeably throughout this specification, since the functionality of a controller may be distributed across multiple controllers / modules, all of which may communicate using standard techniques.

[0028] As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other prior art embodiments or implementations with respect to one or more desired characteristics, one of ordinary skill in the art will understand that one or more features or characteristics may be compromised to achieve desired overall system attributes depending on the specific application and implementation. These attributes may include, but are not limited to, strength, durability, marketability, appearance, installation, size, serviceability, weight, manufacturability, ease of assembly, etc.Thus, embodiments that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.

[0029] According to the present invention, there is provided a motor vehicle power system comprising: a traction battery; an electric machine including star-connected windings; an inverter system controller connected between the traction battery and the electric machine; and a switch having a terminal directly connected to a midpoint of the traction battery and a terminal directly connected to a star point of the star-connected windings.

[0030] According to one embodiment, the invention is further characterized by a controller programmed to close the switch and operate the inverter system controller to maintain switches thereof at a predefined temperature for a predefined duration during a parking mode.

[0031] According to one embodiment, the controller is further programmed to operate the inverter system controller via a closed-loop controller to maintain the switches thereof at the predefined temperature for the predefined duration.

[0032] According to one embodiment, the controller is further programmed to open the switch after the predefined period has elapsed.

[0033] According to one embodiment, the traction battery includes two sets of battery cells and wherein the center point is located between the two sets of battery cells.

[0034] According to one embodiment, the invention is further characterized by a controller programmed to close the switch and operate the inverter system controller during a parking mode to maintain switches thereof at a predefined temperature for a predefined duration such that charge states of the two sets of battery cells are equal.

[0035] According to the present invention, a method includes: closing a switch during a parking mode to directly connect a center point of a traction battery and a star point of star-connected windings of an electric machine, and operating an inverter system controller connected between the traction battery and the electric machine to maintain switches thereof at a predefined temperature for a predefined duration.

[0036] In one aspect of the invention, operation is carried out via a closed-loop control system.

[0037] In one aspect of the invention, the method includes opening the switch after the predefined period has elapsed.

[0038] In one aspect of the invention, operation is such that charge states of sets of battery cells on either side of the center point are equal.

[0039] According to the present invention, a vehicle is provided comprising: a traction battery; an electric machine; an inverter system controller connected between the traction battery and the electric machine; a switch connected between the traction battery and windings of the electric machine; and a controller programmed, while the vehicle is not being driven, to close the switch and operate the inverter system controller to maintain switches thereof at a predefined temperature for a predefined duration.

[0040] According to one embodiment, the windings are star-connected windings and the switch is connected to a star point of the star-connected windings.

[0041] According to one embodiment, the traction battery includes two sets of battery cells and a midpoint therebetween, and wherein the switch is connected to the star point.

[0042] According to one embodiment, the controller is further programmed to operate the inverter system controller to maintain the switches thereof at the predefined temperature for the predefined duration such that charge states of the sets of battery cells are equal.

[0043] According to one embodiment, the controller is further programmed to open the switch after the predefined period has elapsed.

[0044] According to one embodiment, the controller is further programmed to operate the inverter system controller via a closed-loop controller to maintain switches thereof at a predefined temperature for a predefined duration.

Claims

[1] Motor vehicle power system comprising: a traction battery; an electrical machine containing star-connected windings; an inverter system controller connected between the traction battery and the electric machine; and a switch having a terminal directly connected to a center point of the traction battery and a terminal directly connected to a star point of the star-connected windings. [2] The automotive power system of claim 1, further comprising a controller programmed to close the switch and operate the inverter system controller to maintain switches thereof at a predefined temperature for a predefined duration during a parking mode. [3] The automotive power system of claim 2, wherein the controller is further programmed to operate the inverter system controller via a closed-loop controller to maintain the switches thereof at the predefined temperature for the predefined duration. [4] The automotive power system of claim 2, wherein the controller is further programmed to open the switch after the predefined duration has elapsed. [5] The automotive power system of claim 1, wherein the traction battery includes two sets of battery cells and wherein the midpoint is located between the two sets of battery cells. [6] The automotive power system of claim 5, further comprising a controller programmed to close the switch and operate the inverter system controller during a parking mode to maintain switches thereof at a predefined temperature for a predefined duration such that charge states of the two sets of battery cells are equal. [7] Procedure comprising: Closing a switch during a parking mode to directly connect a center point of a traction battery and a star point of star-connected windings of an electric machine, and operating an inverter system controller connected between the traction battery and the electric machine to maintain switches thereof at a predefined temperature for a predefined duration. [8] Method according to claim 7, wherein the operation is carried out via a closed-loop control system. [9] The method of claim 7, further comprising opening the switch after the predefined duration has elapsed. [10] The method of claim 7, wherein said operating is such that charge states of sets of battery cells on either side of said center point are equal. [11] Vehicle comprising: a traction battery; an electrical machine; an inverter system controller connected between the traction battery and the electric machine; a switch connected between the traction battery and windings of the electric machine; and a controller programmed to close the switch and operate the inverter system control while the vehicle is not being driven to maintain switches thereof at a predefined temperature for a predefined duration. [12] A vehicle according to claim 11, wherein the windings are star-connected windings and the switch is connected to a star point of the star-connected windings. [13] A vehicle according to claim 11, wherein the traction battery includes two sets of battery cells and a midpoint therebetween, and wherein the switch is connected to the star point. [14] The vehicle of claim 13, wherein the controller is further programmed to operate the inverter system controller to maintain the switches thereof at the predefined temperature for the predefined duration such that charge states of the sets of battery cells are equal. [15] The vehicle of claim 11, wherein the controller is further programmed to operate the inverter system controller via a closed-loop controller to maintain switches thereof at a predefined temperature for a predefined duration.

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