Active discharge of dc bus

Abstract

An active discharge system and method includes an inverter circuit including a plurality of inverter branches, the plurality of inverter branches including a first inverter branch and a second inverter branch, each branch including first and second power switches. In response to a first active discharge event, first and second power switches of the first inverter leg are operated to discharge a high voltage bus connected to the inverter. In response to a subsequent or second active discharge event, the first and second power switches of the second inverter leg are operated to discharge a high voltage bus connected to the inverter.

Description

Background Art

[0001] In certain power circuits, especially high voltage direct current (HVDC) power electronic systems such as those used in vehicle applications, various high voltage energy storage elements (HVESE) are used on the direct current (DC) link. Such HVESE may include high voltage batteries and high voltage DC bus capacitors. Components such as DC bus capacitors are discharged after the associated inverter system is shut down for various reasons (e.g., passenger safety, emergency systems, etc.).

[0002] Active discharge is used in various situations, including internal fault response, HVDC overvoltage, HVDC voltage sensor problem, low voltage power loss, shutdown events, etc. Summary of the invention

[0003] According to some aspects of the present disclosure, an active discharge method includes providing an inverter circuit including a plurality of inverter branches / bridge arms, the plurality of inverter branches including a first inverter branch and a second inverter branch, each branch including a first and a second power switch. In response to a first active discharge event, the first and second power switches of the first inverter branch are operated to discharge a high voltage bus connected to the inverter. In response to a subsequent or second active discharge event, the first and second power switches of the second inverter branch are operated to discharge the high voltage bus connected to the inverter.

[0004] According to another aspect of the present disclosure, a high-voltage DC active discharge system includes a DC power supply connected between a first and a second power rail, and a DC bus capacitor connected between the first and second power rails. An inverter circuit has a first inverter branch, a second inverter branch, and a third inverter branch. Each of the first, second, and third inverter branches includes a first and a second power switch connected in series between the first and second power rails. The controller is configured to selectively operate the first and second power switches of the first, second, and third inverter branches to excite / energize the windings of the motor. The controller is also configured to operate the first and second power switches of a selected one of the first, second, or third inverter branches in response to a first active discharge event to discharge the DC bus capacitor.

[0005] According to another aspect of the present disclosure, an inverter circuit includes a first inverter branch, a second inverter branch, and a third inverter branch, the first inverter branch includes a first and a second power switch connected in series between a first power rail and a second power rail, the second inverter branch includes a first and a second power switch connected in series between the first power rail and the second power rail, and the third inverter branch includes a first and a second power switch connected in series between the first power rail and the second power rail. The controller is configured to selectively operate the first and the second power switches of the first, second, and third inverter branches to excite the windings of the motor. The controller is also configured to select one of the first, second, or third inverter branches based on a predetermined parameter, and in response to a first active discharge event, operate the first and the second switches of the selected inverter branch to actively discharge the DC bus capacitor connected between the first and second power rails. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A and 1B A circuit diagram showing an example of an active discharge system according to aspects of the present disclosure.

[0007] Figure 2 It shows Figure 1A and 1B A block diagram of other aspects of the active discharge system is shown in FIG.

[0008] Figure 3 A portion of an exemplary control signal for a gate driver is shown to Figure 2 and Figure 3 An active discharge process is implemented in the system shown.

[0009] Figure 4 Shows Figure 3 Other aspects of the control signals are shown.

[0010] Figure 5 is a flow chart illustrating aspects of an active discharge method according to the present disclosure.

[0011] Figure 6 is a flow chart illustrating aspects of another active discharge method according to the present disclosure. DETAILED DESCRIPTION

[0012] In the following detailed description, reference is made to the accompanying drawings, which form a part of the detailed description, and in which specific embodiments of the present invention can be practiced are shown by way of illustration. In this regard, directional terms such as top, bottom, front, back, etc. are used with reference to the orientation of the (multiple) accompanying drawings described. Because the components of the embodiments can be positioned in a plurality of different orientations, the directional terms are used for illustrative purposes and are by no means intended to be limiting. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description should not be construed as limiting.

[0013] High voltage direct current (HVDC) power electronic systems, such as those used in vehicle applications, include various high voltage energy storage elements used on the direct current (DC) link. Components of such systems are discharged after the associated inverter system is shut down for various reasons, such as passenger safety, emergency systems, etc. Active discharge is used in various situations, including internal fault reactions, HVDC overvoltage, HVDC voltage sensor problems, loss of low voltage power, shutdown events, etc.

[0014] Some conventional HVDC discharge systems include dedicated discharge circuits for dissipating and / or otherwise discharging the charge stored in the system, which can add cost and complexity to the system. According to aspects of the present disclosure, the same circuit is used in the normal operating mode and also in the discharge mode to provide safe discharge of the stored energy, while eliminating the need for a dedicated discharge circuit.

[0015] For example, a three-phase inverter circuit may be used in a high voltage power electronic system to dissipate energy stored in the high voltage DC bus capacitors through components of the inverter in addition to the normal operation of the inverter to excite motor windings.

[0016] Figure 1A An example of a high voltage power electronics system 100 according to the present disclosure is shown. The system 100 includes an inverter 110. The example system 100 can be used for motor control to provide power and control to one or more electric motors and support, for example, one or more powertrain topologies. The circuit 100 can convert energy stored in a high voltage battery system 120 into instantaneous multi-phase alternating current (AC) power for traction drive, etc.

[0017] Figure 1AThe example also includes a high voltage battery 120 and a high voltage bus capacitor 130 connected between the upper and lower power rails 122A and 122b. A charger and a battery management system (BMS) 180 are connected to the battery system 120. The inverter 110 is configured to convert direct current from the battery 120 into alternating current to generate a rotating magnetic field for an electric machine such as a motor 140. In some examples, the motor 140 can also be used as a generator. In some examples, the motor speed, phase voltage, and phase current are sensed to achieve closed-loop control of motor variables such as speed and torque. The encoder 160 can provide motor position information to the controller 200, and the phase current information can be output to the isolator 170, which sends the phase current information to the controller 200. Based on this, the operation of the power switch is controlled to achieve the desired operation of the motor 140.

[0018] Figure 1B Other aspects of the system 100 are shown. The inverter 110 includes three branches or legs 102a, 102b and 102c (collectively referred to as inverter legs 102), each branch or leg having two power switches 150a, 150b (collectively referred to as power switches 150) connected in series between the upper power rail 102a and the lower power rail 102b. The switches may include, for example, bipolar transistors, IGBTs, MOSFETs, SiC, etc. In order to control the current and voltage applied to the motor 140, the motor controller generates a PWM signal, which is applied to the gate terminal of the switch 150 so that the switch 150 in the branch of the motor is PWM controlled to provide the desired motor voltage and current.

[0019] The controller 200 is connected to a vehicle controller area network (CAN) bus 162 to communicate with a vehicle electronic control unit (ECU) 164. The controller 200 is also connected to a low voltage portion 166, which is connected to a low voltage battery 168.

[0020] Figure 22 is a block diagram illustrating other aspects of the system 100. As described above, the motor controller 200, which may include a microcontroller 202 and / or a programmable device 204, is configured to control a gate driver 210 connected to a gate terminal of a corresponding power switch 150. The gate driver 210 is configured to provide an input signal to the gate terminal of the corresponding power switch 150 to turn the corresponding power switch on or off. The controller 200 is connected to a logic circuit 220, which is configured to apply a control signal to the gate driver 210 of the desired or selected branch 150a, 150b, 150c of the inverter 110. In some embodiments, the controller 200 controls the gate driver 210 to operate in an "ON" mode (i.e., controlling the corresponding switch so that it remains in an on or conducting state), an "OFF" mode (i.e., controlling the corresponding switch so that it remains in an off or non-conducting state), or a pulse width modulation (PWM) mode in which a PWM signal is applied to the gate terminal of the corresponding power switch 150.

[0021] Refer to Figure 1 and Figure 2 In the example of the first and second power switches 150a, 150b (also referred to herein as upper power switch 150a and lower power switch 150b) are IGBTs with respective diodes connected in parallel. The node between the upper switch 150A and the lower switch 150b of each branch 102A, 102b, and 102c is connected to a rotating machine, such as a three-phase motor generator 140.

[0022] The power switch 150 is operated by a control signal from the motor controller 200 to convert the direct current supplied from the battery 120 into three-phase alternating current. For example, the converted power is supplied to the armature winding of the motor 140. The inverter circuit 110 is thus configured as a three-phase bridge circuit in which the series-connected upper and lower power switches 150a, 150b of each branch 102a, 102b, 102c are connected in parallel between the upper and lower power rails 122a, 122b. The capacitor 130 suppresses the fluctuation of the DC voltage generated by the switching operation of the power switch 150.

[0023] When configured to operate the motor 140 , the motor controller 200 provides control signals based on various variables such as desired torque, speed, etc. The PWM signal is output to the gate driver 210 to control the power switch 150 to apply the desired waveform to the windings of the motor 140 .

[0024] In regenerative operation, the motor 140 acts as a generator. The power switch is controlled in a predetermined manner so that the current generated in the motor windings by the rotation of the rotor of the motor 140 can be used to charge the battery 120, for example.

[0025] In some examples, the power switch (ie, IGBT) 150 is additionally used for active discharge of the capacitor 130, so that no additional active discharge circuit is required. This can result in reduced PCB size and optimized component count.

[0026] The controller provides a gate drive signal to the gate terminal of the power switch 150 to perform active discharge of the capacitor 130. For each half-bridge of the inverter 110, the power switch 150, the gate driver 210 and the controller 200 operate synchronously together to perform active discharge and ensure that the DC bus capacitor 130 is discharged as required.

[0027] The gate voltage of the power switch 150 is controlled to limit the current flowing through the inverter branch 102 in the event of an active discharge event. By controlling the gate voltage, the power switch 150 operates in a "safe" operating region of the component to avoid faults and thermal runaway events. For example, the DC bus discharge can be determined based on various factors, such as the operating frequency, the on-time of the power switch 150, the associated gate voltage level, etc. In order to achieve a complete energy discharge of the inverter 110, the number of PWM pulses to be excited within a given duration span must be determined based on the requirements of the switch manufacturer. During the active shutdown process, the power switch 150 may be heated due to the discharge current flowing through it. As discussed further below, parameters such as the temperature of the component can be monitored to ensure that the component operates within the desired parameters.

[0028] Figure 3 The control signal portion for the gate driver 210 is shown to implement the active discharge process. For the controlled current "through", the desired branch (one or more) 102 of the inverter 110 is used. The logic circuit 220 can be configured to output the control signal from the controller 200 to the desired branch 102 of the inverter 110. One of the power switches 150 of a given inverter branch (e.g., the high-side switch 150a) is kept turned on by the corresponding gate driver 210, while the relative power switch is controlled (i.e., turned on / off) according to the PWM signal Fpwm generated by the "safety logic" of the controller 200 and / or the gate driver 210. The controlled through method provides a safe active discharge operation by applying a closed-loop strategy to the PWM signal duration and the gate voltage finally applied. The generated PWM signal is clamped within the duration T_EXCITE that can be programmed into the controller 200. Alternatively, the controlled through can also be performed by keeping the low-side switch 150b turned on while providing a PWM signal to the high-side switch 150a.

[0029] Figure 4150 . Other aspects of the active discharge logic are shown. When the PWM positive edge is applied to the gate terminal of the desired power switch 150, the switch output VO begins to charge, and as a result, the gate-source voltage begins to rise. The active discharge control technique is based on the power switch threshold voltage V_threshold and the programmable T_EXCITE time (e.g., 0ns to 70ns). The gate driver 210 is configured to continuously monitor the gate-to-source (or gate-to-emitter, depending on the type of power switch 150 applied) voltage / gate-source voltage. When the gate-source voltage is greater than the threshold voltage V_threshold, an internal timer is started, and after reaching the programmed T_EXCITE duration, the gate driver 210 turns off the gate voltage.

[0030] In some examples, the gate driver 210 includes an internal comparator configured to determine the T_EXCITE duration. The internal comparator is further configured with a fixed time delay T_internal filter to increase the total on-time, thereby allowing the T_EXCITE time to be reduced, thereby reducing the total on-time of the external FET. By controlling the threshold voltage V_Threshold and T_EXCITE, the through current can be controlled.

[0031] As described above, it is often desirable to implement active discharge of the HVDC bus and associated bus capacitors 130, typically in applications such as vehicles and power electronics units. After "normal" operation of the inverter 110 (i.e., converting DC power from the battery 120 to AC power for the motor 140), it may be necessary to shut down the inverter. Active shutdown is also used in some applications, such as for system faults, HVDC overvoltage conditions, HVDC voltage sensor failures, LV power loss, and safety shutdown events (e.g., flameout). The disclosed examples use components of the inverter 110 for active shutdown and discharge of the HVDC bus including the DC bus capacitors 130, rather than employing a separate dedicated discharge circuit including components such as a high voltage resistor array.

[0032] Some examples avoid thermal runaway by performing a polling method on each half-bridge of the inverter 110 for each active discharge event. In addition, the specific inverter branches 102 used for active discharge can be "rotated" from one branch to the next to account for the continued thermal rise of the inverter branches, thereby avoiding reliability issues of the inverter components. This "rotation" of the inverter branches 102 can be reflected in Figure 5In the method 260 shown, in response to a first active discharge event (i.e., system failure, flameout, etc.) at operation 262, the power switch 150 of the first inverter branch 102a is controlled at operation 264 to discharge the capacitor 130. In response to a second active discharge event at operation 266, the power switch 150 of the second inverter branch 102b is controlled at operation 268 to discharge the capacitor 130. In other words, different inverter branches 102 are used for each active discharge operation in succession. Therefore, in response to a third active discharge event shown at operation 270, the third inverter branch 102c is used to perform active discharge of the capacitor 130 at operation 272. Further, in response to a fourth active discharge event at operation 274, the first inverter branch 102a is used again at operation 264 to actively discharge the capacitor 130.

[0033] Figure 6 3 is a flow chart illustrating an example of a polling method 300 for active discharge operation. At operation 310, gate driver components (e.g., gate drivers 210 and power switches 150) of each inverter branch are checked for faults. If a fault is found in a component of one or more of the inverter branches 102 at operation 310, active discharge is performed by operating the gate driver 210 and switch 150 of the "next" or adjacent inverter branch and the inverter branch with the component fault. For example, if a gate driver fault of the gate driver 210 of the first branch 102a is determined at operation 310, active discharge is performed at operation 302, wherein the gate driver 210 of the first branch 102a controls the corresponding switch 150 to be in a conducting mode (i.e., the switch 150 remains in a conducting state), and the gate driver 210 of the second branch 102b (i.e., the adjacent branch) operates one or both of the corresponding switches 150 in a PWM mode.

[0034] If it is determined at operation 310 that there is no fault, then an active discharge is performed using the first inverter branch 102a at operation 312. During the active discharge process, a diagnostic test is performed at operation 314. For example, at operation 316, the high voltage DC level of the inverter branch is determined and compared to a predetermined voltage level. If it is determined at operation 316 that the HVDC level is less than a predetermined level (e.g., 60V), the active discharge operation is complete.

[0035] If the HVDC level determined at operation 316 is greater than the predetermined level, the temperature of the associated power switch 150 is compared to a predetermined temperature level (e.g., 175° C.) at operation 318. If the temperature level does not exceed the predetermined temperature level, at operation 312, the active discharge process continues in the first branch 102a of the inverter 110.

[0036] If it is determined at operation 318 that the temperature of the power switch 150 exceeds the predetermined temperature, an error flag is set at operation 320, and an active discharge operation is performed using the second branch 102b of the inverter 110 at operation 330. A diagnostic check of the second inverter branch is performed at operation 332. If it is determined at operation 334 that the HVDC voltage level does not exceed the predetermined level, the active discharge operation is completed using the second branch 102b of the inverter 110.

[0037] If the HVDC level determined at operation 334 is greater than the predetermined level, the temperature of the associated power switch 150 of the second branch of the inverter 110 is compared to a predetermined temperature level at operation 336. If the temperature level does not exceed the predetermined temperature level, at operation 330, the active discharge process continues in the second branch of the inverter 110.

[0038] If it is determined at operation 336 that the temperature of the power switch 150 exceeds the predetermined temperature, then an error flag is set at operation 338, and an active discharge operation is performed using the third branch 102c of the inverter 110 at operation 340. A diagnostic check on the third inverter branch 102c is performed at operation 342. If it is determined at operation 346 that the HVDC voltage level does not exceed the predetermined level, then the active discharge operation is completed on the third branch 102c of the inverter 110.

[0039] If the HVDC level determined at operation 346 is greater than the predetermined level, the temperature of the associated power switch 150 of the third branch 102c of the inverter 110 is compared to a predetermined temperature level at operation 348. If the temperature level does not exceed the predetermined temperature level, the active discharge process continues in the third branch 102c of the inverter 110 at operation 340. If it is determined at operation 348 that the temperature exceeds the predetermined level, the process returns to operation 310 to check again whether the gate driver 210 is faulty.

[0040] The features of the exemplary embodiments are summarized above so that those skilled in the art can better understand the various aspects of the present disclosure. Those skilled in the art should understand that they can easily use the present disclosure as a basis to design or modify other processes and structures for performing the same purpose and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and various changes, substitutions and modifications may be made to this without departing from the spirit and scope of the present disclosure.

Claims

1. An active discharge method, comprising: Providing an inverter circuit, the inverter circuit comprising a plurality of inverter branches, the plurality of inverter branches comprising a first inverter branch and a second inverter branch, each branch comprising a first and a second power switch; In response to a first active discharge event, operating first and second power switches of the first inverter branch to discharge a high voltage bus connected to the inverter; as well as In response to a second active discharge event, first and second power switches of the second inverter leg are operated to discharge the high voltage bus connected to the inverter.

2. The method according to claim 1, wherein: The plurality of inverter branches further include a third inverter branch, and the method further includes: In response to a third active discharge event, the first and second power switches of the third inverter branch are operated to discharge the high voltage bus connected to the inverter.

3. The method according to claim 2, further comprising: In response to a fourth active discharge event, the first and second power switches of the first inverter branch are operated to discharge the high voltage bus connected to the inverter.

4. The method according to claim 1, wherein: Discharging the high-voltage bus connected to the inverter includes: discharging a high-voltage DC bus capacitor connected to the inverter.

5. The method according to claim 1, wherein: Operating the first and second power switches of the first inverter leg includes maintaining the first power switch of the first inverter leg turned on while applying a pulse width modulation (PWM) signal to the second power switch of the first inverter leg.

6. The method according to claim 5, wherein: The pulse width modulation signal is determined based on a gate-source voltage of a first power switch of the first and second power switches.

7. The method according to claim 1, wherein: The first active discharge event includes an internal fault.

8. The method according to claim 1, wherein: The first active discharge event includes a key-off condition.

9. The method according to claim 1, wherein: Each inverter branch includes first and second gate drivers connected to respective first and second power switches, the method further comprising: In response to determining that a fault exists in at least one of the first and / or second gate drivers of a first inverter branch among the plurality of inverter branches, the first and second power switches of the first inverter branch are kept turned on, while a pulse width modulation (PWM) signal is applied to at least one of the first and / or second power switches of the second inverter branch to discharge the high voltage bus.

10. The method according to claim 1, wherein: Operating the first and second power switches of the first inverter branch to discharge the high voltage bus connected to the inverter includes comparing a voltage level of the high voltage bus to a predetermined voltage level.

11. The method according to claim 1, wherein: Operating the first and second power switches of the first inverter branch to discharge the high voltage bus connected to the inverter includes comparing a temperature of at least one of the first and / or second switches to a predetermined temperature.

12. A high voltage direct current active discharge system, comprising: a DC power supply connected between the first power rail and the second power rail; a DC bus capacitor connected between the first power rail and the second power rail; an inverter circuit comprising a first inverter branch, a second inverter branch, and a third inverter branch, each of the first inverter branch, the second inverter branch, and the third inverter branch comprising first and second power switches connected in series between a first power rail and a second power rail; a controller configured to selectively operate first and second power switches of the first inverter leg, the second inverter leg, and the third inverter leg to energize windings of the motor; as well as The controller is further configured to operate first and second power switches of a selected one of the first inverter branch, the second inverter branch and the third inverter branch in response to a first active discharge event to discharge the DC bus capacitor.

13. The system according to claim 12, wherein: The inverter circuit further includes a plurality of gate drivers, each of the first switch and the second switch of the first inverter branch, the second inverter branch, and the third inverter branch having a corresponding gate driver connected thereto.

14. The system according to claim 13, wherein: The gate driver is configured to selectively operate its respective first and second switches in an on mode, an off mode, and a pulse width modulation mode.

15. The system of claim 14, wherein: The gate driver is configured to selectively operate a first switch of the first inverter leg in a conducting mode and a second switch of the first inverter leg in a pulse width modulation mode in response to a first active discharge event to actively discharge the DC bus capacitor.

16. The system of claim 15, wherein: The gate driver is configured to selectively operate the first switch of the second inverter leg in a conducting mode and the second switch of the second inverter leg in a pulse width modulation mode in response to a second active discharge event to actively discharge the DC bus capacitor.

17. The system of claim 15, wherein: The gate driver is configured to clamp the pulse width modulated signal based on threshold voltages of the first and second power switches.

18. An inverter circuit comprising: a first inverter branch including first and second power switches connected in series between a first power rail and a second power rail; a second inverter branch including first and second power switches connected in series between the first power rail and the second power rail; a third inverter branch comprising first and second power switches connected in series between the first power rail and the second power rail; a controller configured to selectively operate first and second power switches of the first inverter leg, the second inverter leg, and the third inverter leg to energize windings of the motor; as well as The controller is further configured to select one of the first inverter branch, the second inverter branch and the third inverter branch based on predetermined parameters in response to a first active discharge event, and operate the first and second switches of the selected inverter branch to actively discharge the DC bus capacitor connected between the first power rail and the second power rail.

19. The inverter circuit according to claim 18, wherein: The predetermined parameter includes a voltage level of the selected inverter branch.

20. The inverter circuit according to claim 18, wherein: The predetermined parameters include temperatures of first and second power switches of the selected inverter branch.

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