Method for active short circuit control for NPC type two-level inverter

Abstract

The invention provides an active short circuit control method for an NPC type three-level inverter, the inverter comprises three phases of bridge arms, each phase of bridge arm comprises two upper bridge arm switch elements and two lower bridge arm switch elements, and the method comprises the following steps: receiving an active short circuit protection trigger signal; under the condition of receiving an active short-circuit protection trigger signal, controlling two upper bridge arm switch elements of each phase bridge arm of the inverter to be fully conducted and two lower bridge arm switch elements to be fully turned off, or controlling the two lower bridge arm switch elements of each phase bridge arm of the inverter to be fully conducted and the two upper bridge arm switch elements to be fully turned off; for at least one phase of bridge arm, the outer switching element of the two upper bridge arm switching elements to be switched on or the two lower bridge arm switching elements to be switched on is switched on in a delayed manner compared with the inner switching element at least in some cases. The invention also provides a control device for the inverter and a computer program product.

Description

Technical Field

[0001] This invention relates to a method for active short-circuit control of an NPC-type three-level inverter, and also to a control device and a computer program product for an NPC-type three-level inverter. Background Technology

[0002] When an electric drive system malfunctions, it is crucial that the motor quickly enters a safe state. Active Short Circuit (ASC) provides an effective safety mechanism that achieves safe isolation between the motor, controller, and power battery by short-circuiting the three-phase stator windings of the motor, ensuring the high-voltage safety of the entire vehicle.

[0003] NPC-type three-level inverters are widely used in power electronics due to their low switching losses and superior output waveform quality. Currently, when controlling such inverters into ASC mode, two switching devices in the upper or lower segment of the same bridge arm often operate simultaneously, which poses a certain risk. In extreme cases, the outer switching element in the upper or lower bridge arm may turn on before the inner switching element, causing uneven voltage distribution. This can lead to excessive voltage stress on individual devices, or even system failure.

[0004] Therefore, existing technologies still have shortcomings in the active short-circuit control of NPC-type three-level inverters. Summary of the Invention

[0005] The purpose of this invention is to provide a method for active short-circuit control of an NPC-type three-level inverter, a control device for an NPC-type three-level inverter, and a computer program product, so as to at least solve some of the problems in the prior art.

[0006] According to a first aspect of the present invention, a method for active short-circuit control of an NPC-type three-level inverter is provided, the NPC-type three-level inverter comprising three-phase bridge arms, each phase bridge arm comprising two upper bridge arm switching elements and two lower bridge arm switching elements, the method comprising the following steps:

[0007] Receive active short-circuit protection trigger signal;

[0008] Upon receiving an active short-circuit protection trigger signal, the two upper bridge arm switching elements of each phase bridge arm of the NPC-type three-level inverter are controlled to be fully turned on and the two lower bridge arm switching elements are fully turned off, or the two lower bridge arm switching elements of each phase bridge arm of the NPC-type three-level inverter are controlled to be fully turned on and the two upper bridge arm switching elements are fully turned off. For at least one phase bridge arm, in at least some cases, the outer switching element of the two upper bridge arm switching elements to be turned on or the outer switching element of the two lower bridge arm switching elements to be turned on is delayed compared to the inner switching element.

[0009] This invention includes the following technical concept: It proposes optimizing the time-sharing conduction sequence of switching elements in the same bridge arm when triggering ASC mode. This prevents the entire DC bus voltage from being applied to a single switching element when entering ASC mode, providing a safer solution for the application of NPC-type three-level inverters in active short-circuit protection mode.

[0010] According to a second aspect of the present invention, a control device for an NPC-type three-level inverter is provided, wherein the control device includes: a microcontroller unit configured to generate switching signals for controlling the switching elements of the NPC-type three-level inverter to perform switching operations by executing a software program; an active short-circuit protection circuit, implemented as a hardware logic circuit, configured to, when no active short-circuit protection trigger signal is received, directly relay the switching signals output by the microcontroller unit to the NPC-type three-level inverter or to the drive circuit of the NPC-type three-level inverter; and, upon receiving an active short-circuit protection trigger signal, control the NPC-type three-level inverter to enter an active short-circuit protection mode according to the method of the first aspect of the present invention. The hardware circuit provides immediate fault response, ensuring that active short-circuit protection measures can be quickly activated when an abnormal situation is detected, reducing system response time.

[0011] According to a third aspect of the present invention, a computer program product having program code units is provided, the program code units being configured to cause the computer to perform the method according to the first aspect of the present invention when the computer program product is run on a computer or stored on a computer-readable storage medium. Attached Figure Description

[0012] The invention will now be described in more detail with reference to the accompanying drawings, which will provide a better understanding of its principles, features, and advantages. The drawings include:

[0013] Figure 1 A schematic diagram of a control device for an NPC-type three-level inverter according to an exemplary embodiment of the present invention is shown;

[0014] Figure 2A flowchart of an active short-circuit protection control method for an NPC-type three-level inverter according to an exemplary embodiment of the present invention is shown;

[0015] Figure 3 It shows Figure 2 A flowchart of one method step of the method shown;

[0016] Figure 4 It shows Figure 2 A flowchart of one method step of the method shown;

[0017] Figure 5 It shows Figure 2 A flowchart of one method step of the method shown;

[0018] Figures 6A to 6E A schematic diagram of the commutation path of one phase arm is shown when the NPC-type three-level inverter is controlled to enter the lower active short-circuit protection mode.

[0019] Figures 7A to 7E A schematic diagram of the commutation path of one phase arm is shown when the NPC-type three-level inverter is controlled to enter the upper active short-circuit protection mode.

[0020] Figure 8A A schematic diagram is shown of the drive signals applied to the two lower arm switching elements of one phase arm when controlling an NPC-type three-level inverter to enter active short-circuit protection mode, according to an exemplary embodiment.

[0021] Figure 8B A schematic diagram is shown of the drive signals applied to the two lower arm switching elements of one phase arm when controlling an NPC-type three-level inverter to enter active short-circuit protection mode, according to another exemplary embodiment. Detailed Implementation

[0022] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0023] Figure 1 A schematic diagram of a control device for an NPC-type three-level inverter according to an exemplary embodiment of the present invention is shown.

[0024] The active short-circuit protection control method of this invention is applicable to various motor drive systems employing NPC-type three-level inverters. For example, this method can be widely used in motor control systems in the field of new energy vehicles, including but not limited to pure electric vehicles, range-extended electric vehicles, hybrid vehicles, and fuel cell electric vehicles, to achieve efficient protection of the motor.

[0025] like Figure 1 As shown, the DC input terminals P and N of the NPC-type (Neutral-Point-Clamped) three-level inverter 3 are connected to the battery, and the AC output terminals A, B, and C of its three-phase bridge arms 3a, 3b, and 3c are connected to the three-phase motor 5. The inverter 3 also includes two capacitors C1 and C2 connected in series between the positive and negative DC input terminals P and N. These capacitors divide the DC bus voltage Vdc, thereby generating a DC intermediate voltage at the midpoint terminal O between the two capacitors C1 and C2. This DC intermediate voltage provides the necessary voltage support and potential balance for the operation of the inverter 3.

[0026] The inverter 3 is equipped with three-phase bridge arms 3a, 3b, and 3c. Each bridge arm 3a consists of four switching elements T1, T2, T3, and T4 connected in series. Each switching element is equipped with freewheeling diodes D1, D2, D3, and D4 connected in reverse parallel. In each bridge arm 3a, the first switching element T1 and the second switching element T2 form the upper bridge arm, while the third switching element T3 and the fourth switching element T4 form the lower bridge arm. These switching elements T1, T2, T3, and T4 are responsible for regulating the current flowing to the three-phase motor 5 and are typically composed of insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or other power switching devices. By precisely controlling the on and off states of these switching elements T1, T2, T3, and T4, the inverter 3 can precisely control the operation of the three-phase motor 5, thereby achieving efficient and precise motor drive control.

[0027] Within each phase arm 3a, the switching elements T1, T2, T3, and T4 are defined as "inner" and "outer" based on their position relative to the DC bus. "Inner switching elements" are relatively farther from the DC bus, while "outer switching elements" are relatively closer to the DC bus. For example... Figure 1 As shown, the outer and inner switching elements of the upper bridge arm are the first switching element T1 and the second switching element T2, respectively; correspondingly, the inner and outer switching elements of the lower bridge arm are the third switching element T3 and the fourth switching element T4, respectively.

[0028] Each phase arm 3a also includes a first clamping diode D5 and a second clamping diode D6, which are connected in parallel across the series branch of the two inner switching elements T2 and T3 in each phase arm 3a, and connected at the midpoint to the midpoint terminal O. The clamping diodes D5 and D6 clamp the potential of the midpoint terminal of the inverter DC side to half of the DC bus voltage through clamping action.

[0029] In addition, Figure 1 The diagram also shows a control device 50 for the NPC-type three-level inverter 3, which controls the switching elements of the inverter 3. In the event of a fault in the inverter 3 or other components of the electric drive system, the control device 50 can automatically execute active short-circuit protection control to ensure the safety of the electric drive system. The control device 50 is communicatively connected, for example, to various monitoring sensors of the inverter 3 and / or the vehicle's electronic control unit (ECU) to receive fault detection signals (which correspond to active short-circuit protection trigger signals). These faults may include overcurrent, overvoltage, drive circuit abnormalities, communication failures between the ECU and the control device 50, and faults in other components of the electric drive system besides the inverter 3. Once these fault detection signals are received, the control device 50 will automatically implement active short-circuit protection control.

[0030] Alternatively, the control device 50 is connected to the drive circuit 20. The drive circuit 20 converts the switching signal generated by the control device 50 into a drive signal that can drive each switching element T1, T2, T3, T4, and applies the corresponding drive signal to the control terminals (e.g., the gate terminals of IGBT power transistors) of each switching element T1, T2, T3, T4 of the inverter 3, so as to realize independent control of each switching element T1, T2, T3, T4.

[0031] In this embodiment, the control device 50 includes a microcontroller unit 51 and an active short-circuit protection circuit 52. The microcontroller unit 51 relies on software programs to control its operation; these programs can be programmed into the microcontroller's non-volatile memory and executed by the processor during operation. The microcontroller unit 51 is configured to generate switching signals for controlling the switching elements of the inverter 3. In one embodiment, the microcontroller unit 51 is configured only to control the switching elements of the inverter 3 in normal operating mode to achieve the conversion of DC input voltage to multiphase AC voltage. In another embodiment, the microcontroller unit 51 may also receive fault detection signals from external devices (such as monitoring sensors or a vehicle ECU) and generate an operating signal upon receiving the fault detection signal to cause the inverter 3 to enter an active short-circuit protection mode.

[0032] The active short-circuit protection circuit 52, implemented as hardware logic, directly relays the switching signals output by the microcontroller unit 51 to the inverter 3 or the drive circuit 20 of the inverter 3 when no active short-circuit protection trigger signal, such as a fault detection signal, is received. Once a fault signal, such as an active short-circuit protection trigger signal, is detected, the active short-circuit protection circuit 52 immediately takes over control. It blocks signals from the microcontroller unit 51 and no longer relays these signals to the inverter 3 or its drive circuit 20. At this time, the active short-circuit protection circuit 52 directly generates control signals to cause the inverter 3 to enter the active short-circuit protection mode. These control signals are then provided to the drive circuit 20 and, after appropriate voltage conversion, are applied to the switching elements T1, T2, T3, and T4 of the inverter 3.

[0033] In an exemplary embodiment, the active short-circuit protection circuit 52 is further divided into a trigger circuit and a delay circuit (not shown specifically for simplicity). The trigger circuit is responsible for generating a pair of control signals, namely PWM1 and PWM2, or PWM3 and PWM4, for each phase arm 3a. The generated pair of control signals are synchronous rising edge signals, used to turn on the upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 together. The delay circuit is responsible for delaying the rising edge of the pair of control signals PWM1 and PWM2, or PWM3 and PWM4 generated by the trigger circuit. The delayed control signal is used to control the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 of one phase arm 3a to turn on. Optionally, the delay circuit can further receive signals from the microcontroller unit 51 and extract the state information or current direction information of each switching element T1, T2, T3, T4 when the active short-circuit protection trigger signal is received. Based on this state information, the delay circuit can determine whether it is necessary to implement delayed conduction control of the corresponding external switching element T1 or T4.

[0034] Figure 2 A flowchart illustrating an active short-circuit protection control method for an NPC-type three-level inverter according to an exemplary embodiment of the present invention is shown. In this embodiment, Figure 2 The method shown includes steps S1 to S4, and can be used in... Figure 1 The control device 50 shown is implemented in this case.

[0035] In step S1, it is checked whether an active short-circuit protection trigger signal is received. If no trigger signal is received, this monitoring continues in step S1. The active short-circuit protection trigger signal may include an overcurrent fault signal and / or a voltage fault signal in the inverter circuit, which can be detected by preset monitoring sensors in the inverter circuit. The overcurrent fault signal indicates that the current at the AC output terminal of at least one phase arm of the inverter exceeds a preset operating range. This preset operating range corresponds to the maximum current that the motor can withstand during stable operation, and in some cases, this range can be adjusted according to the actual application. The voltage fault signal indicates that the deviation between the drive signal of the inverter's switching element and a preset voltage exceeds a set threshold. This deviation may originate from an internal fault in the drive circuit, such as component damage, connection problems, or other abnormalities, causing the drive signal to fail to correctly reflect the required voltage level. Within a normal operating range, the drive signal should switch between two specific levels, such as +15V and -8V. If the drive signal deviates from these preset voltage values, it may cause the switching element to be incorrectly turned on or off, leading to system control errors.

[0036] In addition, the active short-circuit protection trigger signal can also come from at least one external control unit, such as the vehicle's electronic control unit (ECU). During the operation of the electric drive system, the vehicle ECU outputs a status signal representing the motor speed or vehicle stability. For example, when the vehicle ECU detects a loss of vehicle control or abnormal motor speed, it will generate a status abnormality signal. Upon receiving such a signal, the active short-circuit protection mode can also be triggered to generate reverse torque, ensuring that the vehicle can brake and stop safely.

[0037] In step S2, upon receiving an active short-circuit protection trigger signal, the two upper bridge arm switching elements T1 and T2 of each phase bridge arm of the NPC-type three-level inverter 3 are controlled to be fully turned on and the two lower bridge arm switching elements T3 and T4 are fully turned off; or, the two lower bridge arm switching elements T3 and T4 of each phase bridge arm of the NPC-type three-level inverter are controlled to be fully turned on and the two upper bridge arm switching elements T1 and T2 are fully turned off. For at least one phase bridge arm 3a, at least in some cases, the outer switching element T1 or T4 of the two upper bridge arm switching elements T1 and T2 to be turned on or the inner switching element T2 or T3 of the two lower bridge arm switching elements T3 and T4 to be turned on is delayed compared to the inner switching element T2 or T3.

[0038] As in Figure 1As explained earlier, the switching elements T1 and T4 closest to the DC bus in each phase arm can be defined as "outer switching elements," while the switching elements T2 and T3 furthest from the DC bus can be defined as "inner switching elements." For example, in the upper arm, the first switching element T1, directly connected to the positive DC bus (or positive DC input terminal), is an outer switching element, while the second switching element T2, directly connected to the AC output terminal A, is an inner switching element. Similarly, in the lower arm, the fourth switching element T4, directly connected to the negative DC bus (or negative DC input terminal), is an outer switching element, while the third switching element T3, directly connected to the AC output terminal A, is an inner switching element.

[0039] Active short-circuit protection modes include, for example, a lower active short-circuit protection mode and an upper active short-circuit protection mode. Inverter 3 can be controlled to enter the lower active short-circuit protection mode by fully turning on the lower bridge arm switching elements T3 and T4 of each phase bridge arm 3a, 3b, and 3c, and fully turning off the upper bridge arm switching elements T1 and T2 of each phase bridge arm 3a, 3b, and 3c. For at least one phase bridge arm 3a, and especially for each phase bridge arm, the outer switching element T4 of the lower bridge arm switching elements T3 and T4 can be turned on later than the inner switching element T3 to avoid the DC bus voltage being entirely applied to a single switching element. Correspondingly, inverter 3 can be controlled to enter the upper active short-circuit protection mode by fully turning on the upper bridge arm switching elements T1 and T2 of each phase bridge arm 3a, 3b, and 3c, and fully turning off the lower bridge arm switching elements T3 and T4 of each phase bridge arm 3a, 3b, and 3c. For at least one phase arm 3a, and especially for each phase arm, the outer switch element T1 of the upper arm switching elements T1 and T2 can be turned on later than the inner switch element T2.

[0040] "At least in some cases" means that delayed turn-on control is executed every time the inverter enters active short-circuit protection mode, or only sometimes. By executing delayed turn-on indiscriminately in all cases, the control logic can be simplified, and circuit complexity and data processing volume can be reduced. Alternatively, delayed turn-on control can be selectively implemented based on at least one conditional factor, which may include: the current switching state of each switching element in at least one phase arm when the active short-circuit protection trigger signal is received, the current direction at the AC output of at least one phase arm, the inverter's fault response speed requirements, and / or system computational overhead, etc.

[0041] The turn-on delay time of the outer switching element can be precisely set to be greater than the longest turn-on delay time of a single switching element (especially the inner switching element), which typically refers to the longest time required for the switching element to fully turn on after receiving a trigger signal. For example, this turn-on delay time is set to at least 3 microseconds. This effectively ensures that the outer switching element turns on only after the inner switching element is fully turned on, thereby further reducing the risk of the outer switching element turning on alone. The maximum value of the turn-on delay time can be determined according to the fastest requirements of the system's active short-circuit protection mode, ensuring that the system can quickly and accurately enter a safe state under different operating conditions. In practical applications, the turn-on delay time can also be dynamically adjusted according to the real-time operating status and performance requirements of the inverter.

[0042] By delaying the turn-on of the external switching elements, the voltage stress on the internal switching elements of the inverter can be balanced, preventing damage to the devices due to voltage stress concentration. A more detailed explanation of the operating mechanism and its effects will be provided below. Figures 6A to 6E and Figures 7A to 7E In-depth discussion.

[0043] In optional step S3, during the active short-circuit protection mode activation, it is checked whether an active short-circuit protection exit signal has been received. For example, the status of the inverter and motor can be monitored in real time in this step, and once the fault is detected to have been cleared, the active short-circuit protection exit signal can be confirmed. If no active short-circuit protection exit signal is received, the inverter is controlled to remain in active short-circuit protection mode.

[0044] In optional step S4, upon receiving the active short-circuit protection exit signal, the two upper bridge arm switching elements T1 and T2 of each phase bridge arm 3a, 3b, and 3c of the inverter 3 that have been turned on are completely turned off, or the two lower bridge arm switching elements T3 and T4 of each phase bridge arm 3a, 3b, and 3c that have been turned on are completely turned off. This allows the NPC-type three-level inverter 3 to exit the active short-circuit protection mode. During the turn-off process of at least one phase bridge arm 3a, in at least some cases, the inner switching element T2 or T3 of the two upper bridge arm switching elements T1 and T2 to be turned off, or the inner switching element T3 or T4 of the two lower bridge arm switching elements T3 and T4 to be turned off, is delayed compared to the outer switching element T1 or T4. In this way, the system can not only respond safely and quickly when entering the safe mode, but also ensure the stability and safety of the system when exiting the safe mode. After optional step S4, the inverter can be restored from the fully turned-off state to the normal operating mode (i.e., the standard PWM waveform mode).

[0045] In another embodiment, after the active short-circuit protection mode ends, the inverter does not need to execute the delayed shutdown strategy in step S4, but can directly start normal PWM wave generation from the switching state in the active short-circuit protection mode.

[0046] In one embodiment, when the NPC-type three-level inverter 3 is controlled to enter the active short-circuit protection mode, each phase arm 3a, 3b, and 3c are controlled synchronously. For example, if delayed conduction control is implemented for the outer switching elements of at least two phase arms 3a and 3b, the delayed conduction time of the outer switching element in at least one phase arm 3a is the same as the delayed conduction time of the outer switching element in at least another phase arm 3b. Similarly, if delayed conduction control is implemented for all three phase arms 3a, 3b, and 3c, the outer switching element to be turned on in each phase arm 3a will be turned on later than the inner switching element in that phase, and the delayed conduction time of the three phases will be the same. This synchronous control strategy helps to ensure the coordinated operation of each phase arm 3a, 3b, and 3c, ensuring a fast and consistent overall response of the inverter 3 to faults, and reducing system oscillations caused by asynchrony.

[0047] Figure 3 It shows Figure 2 A flowchart of one method step of the method shown is provided. In this embodiment, Figure 2 Step S2 of the method shown further includes steps S21 and S22.

[0048] In step S21, upon receiving an active short-circuit protection trigger signal, at least one phase arm 3a of the inverter is first switched to a transitional state where all switching elements T1, T2, T3, and T4 are turned off. This transitional state effectively avoids arm shoot-through and ensures system safety.

[0049] When performing a full shutdown operation, for example, the shutdown sequence of "outer first, then inner" can be followed, that is, the outer switching element T1 or T4 is shut down first, and then the inner switching element T2 or T3 is shut down, in order to prevent the inner switching element from being shut down too early due to line delay or device differences, thereby avoiding it from being subjected to overvoltage.

[0050] The duration of the transition state should generally be shorter than the delayed turn-on time of the external switching elements when entering the active short-circuit protection mode, to prevent the back current generated by the motor's back EMF from overcharging the DC-side capacitor during the transition state. This ensures that after the fault condition is handled, the inverter can quickly and safely exit the transition state and enter the active short-circuit protection mode, protecting the system from the back EMF backflow.

[0051] In step S22, starting from the transition state, the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 of at least one phase bridge arm 3a are controlled to turn on. When controlling the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 of at least one phase bridge arm 3a to turn on starting from the transition state, a delayed turn-on control of the outer switching element T1 or T4 is implemented in all cases.

[0052] The phrase "implemented in all cases" clarifies that as long as bridge arm 3a has been placed in the transition state, the subsequent conduction operation of the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 will always follow the delayed conduction control strategy of the outer switching element T1 or T4.

[0053] For example, when entering the lower active short-circuit protection mode, the operating sequence of at least one phase arm 3a is: first, control the inner switching element T3 of the lower arm (such as...). Figure 1 The third switching element in the middle is turned on, and then the outer switching element T4 of the lower bridge arm (such as...) is turned on. Figure 1 The fourth switching element in the circuit is turned on.

[0054] Accordingly, when entering the upper active short-circuit protection mode, the operating sequence of at least one phase arm 3a is: first control the inner switching element T2 of the upper arm (such as... Figure 1 The second switching element in the middle is turned on, and then the outer switching element T1 of the upper bridge arm (such as...) is turned on. Figure 1 The first switching element in the circuit is turned on.

[0055] Figure 4 It shows Figure 2 A flowchart of one method step of the method shown is provided. In this embodiment, Figure 4 Step S2 of the method shown further includes steps S210 to S240.

[0056] Based on the current switching states of each switching element T1, T2, T3, and T4 in at least one phase bridge arm 3a when the active short-circuit protection trigger signal is received, the outer switching element T1 or T4 of the two upper bridge arm switching elements T1 and T2 to be turned on, or the outer switching element T3 or T4 of the two lower bridge arm switching elements to be turned on, is selectively delayed compared to the inner switching element T2 or T3. Specifically, for at least one phase bridge arm 3a, when the active short-circuit protection trigger signal is received:

[0057] In step S210, when an active short-circuit protection trigger signal is received, the current switching state of each switching element T1, T2, T3, and T4 in at least one phase bridge arm 3a is obtained.

[0058] In subsequent steps S220 to S240, based on the current switching state of each switching element T1, T2, T3, T4 in at least one phase bridge arm 3a when the active short-circuit protection trigger signal is received, the outer switching element T1 or T4 of the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 to be turned on is selectively delayed compared to the inner switching element T2 or T3.

[0059] Specifically, in step S220, it is checked whether, upon receiving the active short-circuit protection trigger signal, at least the innermost switching element among the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 in at least one phase bridge arm 3a that is to be turned on is already in a conducting state. Here, for the case of entering the upper active short-circuit protection mode, for each phase, the two upper bridge arm switching elements are "to be turned on". For the case of entering the lower active short-circuit protection mode, for each phase, the two lower bridge arm switching elements are "to be turned on".

[0060] "At least the inner switching element is in the on state" can specifically include the following situations:

[0061] a) Both upper bridge arm switching elements T1 and T2, which are to be turned on, are already turned on, or

[0062] b) Both lower bridge arm switching elements T3 and T4, which are to be turned on, are already turned on, or

[0063] c) Of the two upper bridge arm switching elements T1 and T2 to be turned on, the inner switching element T2 is already turned on, and the remaining switching elements T1, T3, and T4 in this phase bridge arm 3a are all in the off state, or

[0064] d) The inner switch element T3 of the two lower bridge arm switching elements T3 and T4 to be turned on has been turned on, and the remaining switching elements T1, T2 and T4 in the phase bridge arm 3a are all in the off state.

[0065] e) One inner switch element T2 or T3 in each of the upper bridge arm switch elements T1 and T2 and the lower bridge arm switch elements T3 and T4 is turned on, that is, the second switch element T2 and the third switch element T3 in one phase bridge arm 3a are both turned on.

[0066] If, in step S220, it is determined that at least the inner switch element T2 or T3 of the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 to be turned on is already in a conducting state, then delayed turn-on control may not be applied to the corresponding outer switch element T1 or T4. Specifically:

[0067] For cases a) and b), the current on state of the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 can be directly maintained in step S230.

[0068] For cases c) and d), the outer switching element T1 or T4 to be turned on in the upper or lower bridge arm can be directly turned on in step S230.

[0069] For scenario e), in step S230, the corresponding switching element T2 or T3 can be turned off first, and then the outer switching element T1 or T4 can be turned on. For example, if the inverter 3 is to be controlled to enter the lower active protection mode, in step S230, the second switching element T2 can be turned off first, while the third switching element T3 remains on, and then the fourth switching element T4 in the lower bridge arm can be turned on after the second switching element T2 is turned off. If the inverter 3 is to be controlled to enter the upper active protection mode, in step S230, the third switching element T3 can be turned off first, while the second switching element T2 remains on, and then the first switching element T1 in the upper bridge arm can be turned on after the third switching element T3 is turned off.

[0070] If, in step S220, it is determined that the two upper bridge arm switching elements T1 and T2 to be turned on, or the two lower bridge arm switching elements T3 and T4 to be turned on, are both in a non-conducting state, then in step S240, delayed turn-on control of the outer switching element T1 or T4 can be implemented. Specifically, this may involve first switching the phase bridge arm 3a to a transition state where all switching elements T1, T2, T3, and T4 are fully off, and then implementing delayed turn-on control of the outer switching element T1 or T4 based on this. The specific process can be referred to... Figure 3 The relevant descriptions will not be repeated here.

[0071] Figure 5 It shows Figure 2 A flowchart of one method step of the method shown is provided. In this embodiment, Figure 2 Step S2 of the method shown further includes steps S201 to S204.

[0072] In step S201, the current direction in at least one phase arm 3a is obtained when the active short-circuit protection trigger signal is received.

[0073] In step S202, it is determined whether the current direction meets a predetermined condition. Only if the current direction meets the predetermined condition is a delayed conduction control implemented in step S203 on the outer switch element T1 or T4 among the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 to be turned on. Conversely, if it is determined in step S202 that the current direction does not meet the predetermined condition, the delayed conduction control is not implemented on the corresponding outer switch element T1 or T4 in step S204. Therefore, based on the current direction in at least one phase bridge arm 3a when the active short-circuit protection trigger signal is received, the outer switch element T1 or T4 among the two upper bridge arm switching elements T1, T2 or the two lower bridge arm switching elements T3, T4 to be turned on can be selectively delayed compared to the inner switch element T2 or T3.

[0074] In one embodiment, consider the scenario where inverter 3 enters the lower active short-circuit protection mode. In step S202, if the initial current direction in phase arm 3a is negative, i.e., current flows from the AC output terminal A of at least one phase arm 3a into the at least one phase arm 3a, then it is determined that the current direction meets the preset condition. In this case, if the outer switching element T4 (fourth switching element) of the lower arm is turned on alone, the inner switching element T3 (third switching element) may face the risk of overvoltage. This process will be described in detail below. Figures 6A to 6E A more detailed explanation follows. Conversely, if it is determined in step S202 that the initial current direction is positive, i.e., if the current flows out of bridge arm 3a from AC output terminal A, then the current direction is determined not to meet the preset conditions. Based on the characteristic that the current direction cannot change instantaneously, even if the outer switching element T4 (the fourth switching element) turns on first, there is no risk of excessive voltage in the inner switching element T3 (the third switching element). Therefore, in this case, there is no need to implement delayed turn-on control.

[0075] In another embodiment, consider the scenario where the inverter enters the upper active short-circuit protection mode. In step S202, if the current direction in the phase bridge arm 3a is initially positive, i.e., if the current flows out of bridge arm 3a from the AC output terminal A, it is determined that the current direction meets the preset condition. In this case, if the outer switching element T1 (first switching element) of the upper bridge arm is turned on alone, the inner switching element T2 (second switching element) may face the risk of overvoltage. This process will be described in detail below. Figures 7A to 7E To elaborate further. Conversely, if it is determined in step S202 that the initial current direction is negative, i.e., if current flows from AC output terminal A into bridge arm 3a, then the current direction does not meet the preset conditions. Based on the characteristic that the current direction cannot change instantaneously, even if the outer switching element T1 (the first switching element) turns on first, there is no risk of excessive voltage in the inner switching element T2 (the second switching element). Therefore, in this case, there is no need to implement delayed turn-on control.

[0076] pass Figure 4 and Figure 5 The demonstrated selective control strategy with delayed turn-on can avoid unnecessary delays, ensuring that the inverter enters active short-circuit protection mode faster in more situations, thereby improving the system's fault response speed.

[0077] It should be understood that Figure 3 , 4 and Figure 5Although the embodiments shown are presented separately, this does not imply a contradiction in their determination of whether to implement delayed conduction control or that they cannot be applied simultaneously. Those skilled in the art should understand that these embodiments are listed separately to illustrate different control strategies. In practical applications, the switching states and current directions of each switching element can be flexibly considered in combination as needed. For example, the need to enter a transition state and whether delayed conduction control needs to be implemented on the outer switching elements can also be comprehensively determined based on the switching states of the switching elements in the bridge arm and the actual current flow. This comprehensive determination method also falls within the scope of protection of this invention.

[0078] Figures 6A to 6E This diagram illustrates the commutation path of one phase arm when the NPC-type three-level inverter is controlled to enter the lower active short-circuit protection mode.

[0079] Figure 6A The diagram shows the initial circuit state of the inverter before entering the lower active short-circuit protection mode. At this time, the first switching element T1 and the second switching element T2 are turned on, and the current direction in this phase bridge arm is negative. In this case, the current flows from the AC output terminal A into this phase bridge arm and flows sequentially to the positive DC bus via two freewheeling diodes D2 and D1 connected in parallel with the second switching element T2 and the first switching element T1.

[0080] exist Figure 6B The diagram illustrates the transition state before entering the lower active short-circuit protection mode. At this time, both the first switching element T1 and the second switching element T2 are turned off, and the third switching element T3 and the fourth switching element T4 remain off, with the current direction being negative. In this case, the current still flows from the two freewheeling diodes D2 and D1 connected in parallel with the second switching element T2 and the first switching element T1 to the positive DC bus.

[0081] exist Figure 6C The diagram illustrates how inverter 3 enters the lower-side active short-circuit protection mode by controlling the conduction of two switching elements T3 and T4 (i.e., the third and fourth switching elements) in the lower bridge arm. Ideally, if the two lower bridge arm switching elements T3 and T4 are controlled to conduct simultaneously, they should theoretically conduct at the same time. However, in practice, due to differences in device manufacturing processes, the outer switching element T4 may conduct before the inner switching element T3. Figure 6CThis situation is illustrated in the diagram. When the fourth switching element T4, located on the outer side of the lower bridge arm, is turned on, the third switching element T3, located on the inner side of the lower bridge arm, is not yet turned on. The current direction in the bridge arm remains from the AC output terminal A through the two freewheeling diodes D1 and D2 to the positive DC bus. At this time, the collector of the third switching element T3 is at the positive DC bus potential, while its emitter is at the negative DC bus potential. The entire bus voltage Vdc is applied across the unconducted third switching element T3, which may cause the third switching element T3 to be subjected to excessive voltage stress and damaged.

[0082] exist Figure 6D The diagram also illustrates how the inverter enters the lower-side active short-circuit protection mode by controlling the conduction of two switching elements T3 and T4 (i.e., the third and fourth switching elements) in the lower bridge arm. Figure 6C The situation shown is different, in Figure 6D Delayed turn-on control was implemented on the outer switching elements. Therefore, in Figure 6D The third switching element T3, located on the inner side of the lower bridge arm, is the first to turn on. At this time, current flows from the AC output terminal through the third switching element T3 and the second clamping diode D6 before being injected into the midpoint terminal. In this configuration, the collector of the fourth switching element T4 is clamped to the intermediate bus voltage at the midpoint terminal O, while the emitter is at the negative DC bus potential. Under this configuration, the voltage applied across the fourth switching element T4 is only half of the total bus voltage, Vdc / 2, with the other half shared by the first switching element T1 and the second switching element T2 in the upper bridge arm. This switching state achieves a more even distribution of the total bus voltage Vdc across the multiple switching elements T1, T2, and T4, preventing any single switching element from experiencing excessive voltage stress, thereby reducing the risk of device damage and improving system reliability.

[0083] exist Figure 6E In this configuration, both switching elements T3 and T4 of the lower bridge arm are turned on, while the two switching elements T1 and T2 of the upper bridge arm remain off. Under these conditions, current flows from the AC output terminal A through the third switching element T3 and the fourth switching element T4, ultimately reaching the negative DC bus. Combined with the other lower bridge arm switching elements that are also turned on in other phases, a closed loop is formed in the motor stator windings. The establishment of this current path signifies that the inverter has successfully entered the lower-side active short-circuit protection mode.

[0084] The above analysis of the commutation path and voltage division shows that, in order to effectively achieve voltage equalization control of the devices, when the third switching element T3 and the fourth switching element T4 located in the lower bridge arm are turned on to enter the lower active short-circuit protection mode, the inner third switching element T3 should be turned on before the outer fourth switching element T4. Therefore, a reasonable delay time must be set between the turn-on times of the third switching element T3 and the fourth switching element T4.

[0085] Figures 7A to 7E This diagram illustrates the commutation path of one phase arm when the NPC-type three-level inverter is controlled to enter the upper active short-circuit protection mode.

[0086] Figure 7A The diagram shows the initial circuit state of the inverter before entering the upper active short-circuit protection mode. At this time, the third switching element T3 and the fourth switching element T4 are turned on, and the current direction in this phase bridge arm is positive. In this case, the current flows sequentially through the two freewheeling diodes D4 and D3 connected in parallel with the fourth switching element T4 and the third switching element T3, and finally flows out of this phase bridge arm from the AC output terminal A.

[0087] exist Figure 7B The diagram illustrates the transition state before entering the upper active short-circuit protection mode. At this time, both the third switching element T3 and the fourth switching element T4 are turned off, while the first switching element T1 and the second switching element T2 remain off, and the current direction is positive. In this situation, current still flows out of the AC output terminal A from the freewheeling diodes D4 and D3.

[0088] exist Figure 7C The diagram illustrates how the inverter enters the upper-side active short-circuit protection mode by controlling the conduction of two switching elements T1 and T2 (i.e., the first and second switching elements) in the upper bridge arm. Ideally, if the two upper bridge arm switching elements T1 and T2 are controlled to conduct simultaneously, they should theoretically conduct at the same time. However, in practice, due to differences in device manufacturing processes, the outer switching element T1 in the upper bridge arm may conduct before the inner switching element T2. Figure 7C This situation is illustrated in the diagram. When the first switching element T1, located on the outer side of the upper bridge arm, is turned on, the second switching element T2, located on the inner side of the upper bridge arm, is not yet turned on. The current direction in the bridge arm remains from the negative DC bus through the two freewheeling diodes D4 and D3 connected in parallel with the fourth and third switching elements T4 and T3 to the AC output terminal. At this time, the collector of the second switching element T2 is at the positive DC bus potential, while its emitter is at the negative DC bus potential. The entire bus voltage Vdc is applied across the unconducted second switching element T2, which may cause the second switching element T2 to be subjected to excessive voltage stress and damaged.

[0089] exist Figure 7D The diagram also illustrates how the inverter enters the upper-side active short-circuit protection mode by controlling the conduction of two switching elements T1 and T2 (i.e., the first and second switching elements) on the upper bridge arm. Figure 7C The situation shown is different, in Figure 7D Delayed on-time control was implemented on the outer switching element T1 in the upper bridge arm. Therefore, in Figure 7D In the upper bridge arm, the innermost second switching element T2 turns on first, while the outermost first switching element T1 remains off. Current flows from the midpoint terminal O through the first clamping diode D5 and the second switching element T2 to the AC output terminal A. In this configuration, the emitter of the first switching element T1 is clamped to the intermediate bus voltage, while its collector is at the positive DC bus potential. Under this configuration, the voltage applied across the first switching element T1 is only half of the total bus voltage, Vdc / 2, with the other half shared by the two switching elements T3 and T4 in the lower bridge arm. This switching state achieves a more even distribution of the total bus voltage Vdc across the multiple switching elements T1, T3, and T4, preventing any single switching element from experiencing excessive voltage stress, thereby reducing the risk of device damage and improving system reliability.

[0090] exist Figure 7E In this configuration, both switching elements T1 and T2 of the upper bridge arm are turned on, while the two switching elements T3 and T4 of the lower bridge arm remain off. Under these conditions, current flows from the positive DC bus through the first and second switching elements T1 and T2 to the AC output terminal A. Combined with the other upper bridge arm switching elements that are also turned on in other phases, a closed loop is formed in the motor stator windings. The establishment of this current path signifies that the inverter has successfully entered the upper-side active short-circuit protection mode.

[0091] Figure 8A A schematic diagram is shown of the drive signals SW3 and SW4 applied to the two lower arm switching elements of one phase arm when controlling an NPC-type three-level inverter to enter active short-circuit protection mode, according to one embodiment.

[0092] exist Figure 8AIn the illustrated embodiment, before time t1, the switching elements T1, T2, T3, and T4 of phase bridge arm 3a are exactly in the "0010" state, meaning the first, second, and fourth switching elements T1, T2, and T4 are all in the off state, while the third switching element T3 is in the conducting state. At time t1, the control device receives the active short-circuit protection trigger signal and then controls all switching elements T1, T2, T3, and T4 of phase bridge arm 3a to switch to the off state, entering the so-called "transition state." This transition state lasts from time t1 to time t2. Subsequently, at time t2, the third switching element T3 on the inner side of the lower bridge arm is first controlled to conduct to begin establishing a current path. Then, at time t3, the fourth switching element T4 on the outer side of the lower bridge arm is controlled to conduct, completing the entry into the active short-circuit protection mode. Through this sequential control strategy, the three-level inverter can safely and effectively respond to the active short-circuit protection requirements.

[0093] Depend on Figure 8A It can be seen that the duration Δt0 of the transition state is significantly less than the delayed turn-on time Δt1 of the outer switching element T4. This design is based on the following considerations: it is an undesirable state for all switching elements T1, T2, T3, and T4 to be in the off state. It is only used as a transition when necessary. If the open-circuit state lasts too long, it may cause adverse problems such as back EMF backflow.

[0094] Figure 8B A schematic diagram is shown of the drive signals applied to the two lower arm switching elements of one phase arm when controlling an NPC-type three-level inverter to enter active short-circuit protection mode, according to another exemplary embodiment.

[0095] exist Figure 8B In the illustrated embodiment, before time t1, the switching elements T1, T2, T3, and T4 of phase bridge arm 3a are also exactly in the "0010" state, that is, the first, second, and fourth switching elements T1, T2, and T4 are all in the off state, and the third switching element T3 is in the independently conducting state. At time t1, an active short-circuit protection trigger signal is received. Figure 8A Unlike the illustrated embodiment, not all switching elements T1, T2, T3, and T4 are placed in the off state. When the active short-circuit protection trigger signal is received, since the innermost third switching element T3 is already in the on state, there is no need to implement delayed conduction control for the fourth switching element T4. Therefore, the fourth switching element T4 can be directly turned on at time t1 or at a time slightly later, thereby completing the entry into the active short-circuit protection mode.

[0096] This specification discloses specific circuit elements and their specific connection methods in several embodiments. However, it should be noted that those skilled in the art, guided by the teachings of this specification, can use more, fewer, or different circuit elements and combinations thereof to implement modules with the same or similar functions, all of which fall within the scope of protection of this invention.

[0097] It should be understood that the methods of the various embodiments of this disclosure can be implemented by computer programs / software. This software can be loaded into the processor's working memory and, when run, is used to execute the methods according to the various embodiments of this disclosure.

[0098] It should be understood that the same or similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on describing the differences from other embodiments. In particular, for the apparatus embodiments, since their control logic basically corresponds to that of the method embodiments, the description is relatively brief, and relevant parts can be referred to the description of the method embodiments.

[0099] According to another embodiment of this disclosure, a computer program product having program code units configured to perform methods according to embodiments of this disclosure when the computer program product is run on a computer or stored on a computer-readable storage medium (such as a CD-ROM). The machine-readable storage medium is, for example, an optical storage medium or a solid-state medium supplied together with or as part of other hardware.

[0100] Although specific embodiments of the invention have been described in detail herein, they are given for illustrative purposes only and should not be construed as limiting the scope of the invention. Various substitutions, alterations, and modifications may be conceived without departing from the spirit and scope of the invention.

Claims

1. A method for active short-circuit control of an NPC-type three-level inverter, the NPC-type three-level inverter comprising three-phase bridge arms, each phase bridge arm comprising two upper bridge arm switching elements and two lower bridge arm switching elements, the method comprising the following steps: Receive active short-circuit protection trigger signal; Upon receiving an active short-circuit protection trigger signal, the two upper bridge arm switching elements of each phase bridge arm of the NPC-type three-level inverter are controlled to be fully turned on and the two lower bridge arm switching elements are fully turned off, or the two lower bridge arm switching elements of each phase bridge arm of the NPC-type three-level inverter are controlled to be fully turned on and the two upper bridge arm switching elements are fully turned off. For at least one phase bridge arm, in at least some cases, the outer switching element of the two upper bridge arm switching elements to be turned on or the outer switching element of the two lower bridge arm switching elements to be turned on is delayed compared to the inner switching element.

2. The method according to claim 1, wherein, The delayed turn-on time of the outer switching element is greater than the longest turn-on delay time of the inner switching element. The delayed conduction time of the outer switching element is at least 3 microseconds; The delayed conduction time of the external switching element is less than the minimum response time required for the NPC-type three-level inverter to enter the active short-circuit protection mode.

3. The method according to claim 1 or 2, wherein, Before controlling the two upper bridge arm switching elements or the two lower bridge arm switching elements of the at least one phase bridge arm to turn on, the at least one phase bridge arm is controlled to switch to a transitional state in which all switching elements are off, wherein, when controlling the two upper bridge arm switching elements or the two lower bridge arm switching elements of the at least one phase bridge arm to turn on from the transitional state, delayed turn-on control of the outer switching elements is implemented in all cases.

4. The method according to claim 3, wherein, The duration of the transition state is less than the delayed turn-on time of the outer switching element.

5. The method according to any one of claims 1 to 4, wherein, Based on the current switching state of each switching element in at least one phase arm when the active short-circuit protection trigger signal is received, the outer switching element of either of the two upper bridge arm switching elements to be turned on or the outer switching element of either of the two lower bridge arm switching elements to be turned on is selectively delayed compared to the inner switching element, wherein, for at least one phase arm, when the active short-circuit protection trigger signal is received: If both upper bridge arm switching elements to be turned on or both lower bridge arm switching elements to be turned on are in a non-conducting state, then delayed turn-on control is implemented for the outer switching elements. If at least the innermost switching element of either of the two upper bridge arm switching elements to be turned on or the two lower bridge arm switching elements to be turned on is in the on state, then no delayed turn-on control is implemented for the outer switching elements.

6. The method according to any one of claims 1 to 5, wherein, Based on the current direction in at least one phase arm when the active short-circuit protection trigger signal is received, the outer switching element of either of the two upper bridge arm switching elements to be turned on or the outer switching element of either of the two lower bridge arm switching elements to be turned on is selectively delayed compared to the inner switching element, wherein, for at least one phase arm, when the active short-circuit protection trigger signal is received: In the case of two lower bridge arm switching elements to be turned on, if current flows into the at least one phase bridge arm from the AC output terminal of the at least one phase bridge arm, then delayed turn-on control of the outer switching element is implemented; if current flows out of the at least one phase bridge arm from the AC output terminal, then delayed turn-on control of the outer switching element is not implemented. In the case of two upper bridge arm switching elements to be turned on, if the current flows out of the at least one phase bridge arm from the AC output terminal, then the delayed turn-on control of the outer switching element is implemented; if the current flows into the at least one phase bridge arm from the AC output terminal, then the delayed turn-on control of the outer switching element is not implemented.

7. The method according to any one of claims 1 to 6, wherein, Upon receiving an active short-circuit protection exit signal, the two upper bridge arm switching elements that have been turned on in each phase of the NPC-type three-level inverter are controlled to be completely turned off, or the two lower bridge arm switching elements that have been turned on in each phase are controlled to be completely turned off. For at least one phase, in at least some cases, the inner switching element of the two upper bridge arm switching elements to be turned off or the inner switching element of the two lower bridge arm switching elements to be turned off is delayed compared to the outer switching element.

8. The method according to any one of claims 1 to 7, wherein, The active short-circuit protection trigger signal includes: An overcurrent fault signal indicates that the current at the AC output terminal of at least one phase arm of the NPC-type three-level inverter deviates from the preset operating range. A voltage fault signal indicates that the deviation between the drive signal to be applied to the switching element of the NPC type three-level inverter and the preset voltage exceeds a threshold.

9. The method according to any one of claims 1 to 8, wherein, When the NPC-type three-level inverter is controlled to enter the active short-circuit protection mode, each phase arm is controlled synchronously. If delayed conduction control is implemented on the outer switching elements of at least two phase arms, the delayed conduction time of the outer switching element in at least one phase arm is the same as the delayed conduction time of the outer switching element in at least another phase arm.

10. A control device for an NPC-type three-level inverter, wherein, The control device includes: The microcontroller unit is configured to generate switching signals that control the switching elements of the NPC-type three-level inverter to perform switching operations by executing software programs. An active short-circuit protection circuit, implemented as a hardware logic circuit, is configured to directly relay the switching signal output by the microcontroller unit to the NPC-type three-level inverter or the drive circuit of the NPC-type three-level inverter when no active short-circuit protection trigger signal is received; and to control the NPC-type three-level inverter to enter the active short-circuit protection mode according to the method of any one of claims 1 to 9 when an active short-circuit protection trigger signal is received.

11. A computer program product having program code units configured to cause the computer to perform the method according to any one of claims 1 to 9 when the computer program product is run on a computer or stored on a computer-readable storage medium.

Images