Overcurrent protection method and system for vehicle-mounted inverter

Abstract

The present invention discloses an overcurrent protection method and system for a vehicle-mounted inverter, relating to the field of inverter technology. The method comprises: step 1: within a single pulse width modulation cycle, performing multiple rapid sampling of the output current of the shunt resistor of the vehicle-mounted inverter to obtain a phase current estimate that is closer to the true instantaneous phase current; step 2: constructing a transient overcurrent risk index based on the phase current estimate, combined with the motor phase inductance, DC bus voltage, and the motor's electrical time constant; step 3: using the nominal rated current as a reference, adaptively adjusting the trip threshold according to the transient overcurrent risk index; and step 4: activating soft shutdown logic to perform overcurrent protection on the vehicle-mounted inverter based on the transient overcurrent risk index and the phase current estimate. The present invention significantly improves the accuracy and sensitivity of overcurrent protection, achieving intelligent quantitative risk assessment and dynamic adaptation of protection boundaries.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to an overcurrent protection method and system for a vehicle-mounted inverter. Background Art

[0002] Electric vehicles, the predominant form of new energy vehicle, typically have a core powertrain consisting of a battery, a motor controller (onboard inverter), and a drive motor. As the critical link between the battery's DC power and the drive motor's AC power, the inverter's performance, reliability, and safety are directly impacting the vehicle's overall power, economy, comfort, and operational safety. With the rapid advancement of electric vehicle technology, demands on the inverter's power density, efficiency, dynamic response, and reliability over wide temperature ranges, in complex electromagnetic environments, and under severe vibration are increasing. In particular, the pursuit of longer driving range and faster acceleration performance places increasing electrical and thermal stresses on the inverter and its internal power semiconductors (such as IGBTs and SiC MOSFETs).

[0003] Among the various potential failure modes in automotive inverters, overcurrent is a frequent and highly destructive fault type. Overcurrent can be caused by a variety of factors, including interphase or phase short circuits in the motor windings, inverter arm breakdown leading to a direct current between the upper and lower transistors, control system command errors, drive signal interference, motor stall, or sudden load changes. Once an overcurrent occurs, power semiconductor devices may experience currents several times their rated value in an extremely short period of time (microseconds or even nanoseconds), resulting in a sharp increase in instantaneous power consumption. Failure to quickly and effectively shut down or suppress the overcurrent before device damage occurs can lead to device performance degradation and shortened lifespan at best, or even catastrophic consequences such as device explosion, inverter damage, or even vehicle fire. Therefore, designing a fast, reliable, accurate, and intelligent overcurrent protection system is a top priority in automotive inverter design. Summary of the Invention

[0004] The purpose of the present invention is to provide an overcurrent protection method and system for an on-board inverter, which significantly improves the accuracy and sensitivity of overcurrent protection, realizes intelligent quantitative assessment of risks and dynamic adaptation of protection boundaries, and ensures the safety and low impact of the shutdown process through a hierarchical and flexible soft shutdown strategy, thereby comprehensively improving the reliability, performance and safety margin of the on-board inverter under complex working conditions.

[0005] To solve the above technical problems, the present invention provides an overcurrent protection method for a vehicle-mounted inverter, the method comprising:

[0006] Step 1: Within a single pulse width modulation cycle, the output current of the vehicle inverter's shunt resistor is sampled multiple times quickly. The instantaneous junction temperature of the vehicle inverter's power components and the charging and discharging behavior of the DC bus energy storage capacitor are taken into account. After temperature proportional correction and harmonic ripple compensation, a phase current estimate that is closer to the actual instantaneous phase current is obtained.

[0007] Step 2: Construct a transient overcurrent risk index based on the estimated phase currents, combined with the motor phase inductance, DC bus voltage, and the motor's electrical time constant.

[0008] Step 3: Using the nominal rated current as a benchmark, adaptively adjust the trip threshold according to the instantaneous overcurrent risk index;

[0009] Step 4: Based on the instantaneous overcurrent risk index and the estimated phase current, the soft shutdown logic is activated to protect the on-board inverter from overcurrent.

[0010] Furthermore, in step 4, the process of starting the soft shutdown logic to perform overcurrent protection on the on-board inverter includes: the controller first calculates the differential magnetic energy stored in the DC side stray inductance of the on-board inverter, and simultaneously evaluates the additional energy value generated by the integration of the motor back electromotive force and the instantaneous overcurrent risk index. If the additional energy value exceeds the design limit, the gate level is immediately exponentially weakened, and a zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the on-board inverter; otherwise, the on-board inverter is allowed to maintain the existing modulation, and normal drive is automatically restored after the output current of the shunt resistor of the on-board inverter and the instantaneous junction temperature of the power device of the on-board inverter fall back to the safe zone.

[0011] Furthermore, the phase current estimation value for:

[0012] ;

[0013] in, The number of times the output current of the shunt resistor of the vehicle inverter is quickly sampled within a single pulse width modulation cycle; is the sampling integer subscript index; For the The output current of the shunt resistor of the vehicle inverter obtained by sampling, in A; is the upper safety limit temperature, in K; is the reference temperature, which is equal to room temperature and is in K; is the instantaneous junction temperature of the power device of the vehicle inverter, in K; is the DC bus voltage, in V; is the nominal bus voltage; is the DC bus energy storage capacitor, in F; is the electrical time constant of the motor; is the oversampling period; for Time the output current of the on-board inverter's shunt resistor.

[0014] Furthermore, the electrical time constant of the motor It is the time required for the stator winding current to reach 63% of the steady-state value when the voltage excitation suddenly changes.

[0015] Furthermore, the instantaneous overcurrent risk index for:

[0016] ;

[0017] in, is the motor phase inductance, unit is H.

[0018] Furthermore, the trip threshold for:

[0019] ;

[0020] in, is the nominal rated current; The power module case temperature refers to the temperature of the power semiconductor module housing or substrate inside the vehicle inverter; The switching frequency is the number of times the inverter power switching device is turned on and off per second, and is also the carrier or pulse width modulation carrier frequency.

[0021] Furthermore, in step 4, when the instantaneous overcurrent risk index is greater than 1 and the estimated phase current exceeds the trip threshold, the soft shutdown logic is activated to perform overcurrent protection on the on-board inverter.

[0022] Furthermore, in step 4, when and When the instantaneous differential energy storage is calculated, the soft shutdown logic is activated to protect the vehicle inverter from overcurrent:

[0023] ;

[0024] in, Indicates that only positive values ​​are taken; is the DC side stray inductance; is the peak value of the motor back electromotive force; if Exceeding design limits , the exponential weakening of the gate level is immediately executed, and the zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the vehicle inverter; if , the on-board inverter maintains the existing modulation, waits for the output current of the on-board inverter's shunt resistor and the instant junction temperature of the on-board inverter's power device to fall back to the safe zone, and then automatically resumes normal driving.

[0025] Furthermore, in step 4, the switching frequency The following constraints are met: .

[0026] An overcurrent protection system for an on-board inverter comprises: a phase current estimation section for rapidly sampling the output current of the on-board inverter's shunt resistor multiple times within a single pulse width modulation cycle, taking into account the instantaneous junction temperature of the on-board inverter's power devices and the charging and discharging behavior of the DC bus energy storage capacitor, and obtaining a phase current estimate that is closer to the true instantaneous phase current after temperature proportional correction and harmonic pulsation compensation; an instantaneous overcurrent risk index calculation section for constructing an instantaneous overcurrent risk index based on the phase current estimate, combined with the motor phase inductance, the DC bus voltage, and the motor's electrical time constant; a trip threshold adjustment section for adaptively adjusting the trip threshold based on the instantaneous overcurrent risk index using the nominal rated current as a reference; and an overcurrent protection section for initiating soft shutdown logic to provide overcurrent protection for the on-board inverter based on the instantaneous overcurrent risk index and the phase current estimate.

[0027] The present invention provides an overcurrent protection method and system for an on-board inverter, which has the following beneficial effects: This method performs multiple rapid current samplings within a switching cycle and innovatively takes into account the instantaneous thermal state inside the power device and the dynamic charging and discharging behavior of the DC bus energy storage capacitor. After fine temperature proportional correction and harmonic pulsation compensation, it can obtain an equivalent instantaneous phase current estimate that is much closer to physical reality than the traditional measurement average value or simple peak value. This deep and precise perception of current stress significantly improves the sensitivity and accuracy of identifying potential overcurrent risks and avoids protection failure caused by underestimation of actual stress. Secondly, this method abandons the simple fixed threshold judgment logic and introduces the concept of an instantaneous overcurrent risk index. This index does not view the current magnitude in isolation, but intelligently integrates the accurately estimated current, the inductance and electrical time constant that reflect the motor energy storage and dynamic response characteristics, the current supply voltage level of the system, and, most critically, the thermal-magnetic coupling physical effect where the increase in device temperature may accelerate current runaway. This multi-dimensional, quantitative risk assessment enables the protection system to understand the true level of danger under different operating conditions, providing a more reliable basis for subsequent decision-making. Furthermore, this method achieves truly adaptive adjustment of the protection margin. The trip current threshold is no longer a fixed value. Instead, it is dynamically generated based on multiple factors, including the rated current and a real-time calculated overcurrent risk index, the stability of the DC bus voltage, the power module case temperature (which reflects overall heat dissipation), and the inverter's own switching frequency. This means that the inverter can fully realize its performance potential when heat dissipation is good, voltage is stable, and risks are low. However, in the event of high temperatures, voltage fluctuations, or when higher risks are identified, the protection margin is automatically tightened, achieving a dynamic optimal balance between safety and performance output. Finally, this method provides a more sophisticated and secure protection execution mechanism. When intervention is confirmed, it first assesses the severity of the event by calculating an energy index that accounts for the differential energy storage of stray inductance and the accumulated voltage-driven risk. Based on the comparison of this energy index with the preset safety limit, a decision is made whether to execute a strong but gentle soft shutdown or allow the system to attempt self-recovery under continuous monitoring. Robust soft shutdown utilizes advanced technologies such as exponential gate voltage reduction and zero-vector injection to effectively suppress overcurrent while minimizing damaging voltage spikes and mechanical shock. This hierarchical response strategy, based on energy assessment, significantly improves the targeted and safe nature of protection actions, reduces unnecessary downtime, and enhances system robustness and user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of a method flow of an overcurrent protection method for a vehicle-mounted inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1: Reference Figure 1 , an overcurrent protection method for a vehicle-mounted inverter, the method comprising:

[0032] Step 1: Within a single pulse width modulation cycle, the output current of the vehicle inverter's shunt resistor is sampled multiple times quickly. The instantaneous junction temperature of the vehicle inverter's power components and the charging and discharging behavior of the DC bus energy storage capacitor are taken into account. After temperature proportional correction and harmonic ripple compensation, a phase current estimate that is closer to the actual instantaneous phase current is obtained.

[0033] Step 2: Construct a transient overcurrent risk index based on the estimated phase currents, combined with the motor phase inductance, DC bus voltage, and the motor's electrical time constant.

[0034] Step 3: Using the nominal rated current as a benchmark, adaptively adjust the trip threshold according to the instantaneous overcurrent risk index;

[0035] Step 4: Based on the instantaneous overcurrent risk index and the estimated phase current, the soft shutdown logic is activated to protect the on-board inverter from overcurrent.

[0036] An on-board inverter overcurrent protection method is a key technical link to ensure the safe and reliable operation of electric vehicle power systems. With the continuous improvement of vehicle performance requirements, the increase in power density, and the increasingly complex operating conditions, traditional protection strategies based on fixed thresholds or simple current average values ​​can no longer meet the protection requirements under harsh conditions such as high temperature, high voltage, high-speed switching, and drastic dynamic load changes. These traditional methods are often too conservative, resulting in limited driving performance or slow response, and cannot effectively prevent power devices from being damaged by transient overstress. Therefore, it is particularly important to develop an advanced overcurrent protection method that can accurately sense, intelligently evaluate, dynamically adapt, and flexibly control. The following will detail a method for on-board inverter overcurrent protection consisting of four interrelated steps. This method aims to achieve accurate, fast, and adaptive protection functions by more deeply integrating physical models and real-time operating conditions.

[0037] The first step of the method is to obtain an estimate of the instantaneous phase current that is as close as possible to the actual conditions experienced by the power device. . In automotive inverters, current is usually measured through shunt resistors placed on the DC bus or phase output path. However, directly using a single sampling value or a simple average value within a pulse width modulation (PWM) cycle cannot fully reflect the actual current stress. First, PWM control itself will cause the phase current to contain high-frequency ripple, and its peak value may far exceed the average value, causing a transient impact on power devices (such as IGBT or SiCMOSFET). Secondly, the resistance of the shunt resistor will change with temperature, introducing measurement errors. More importantly, the operating state of the power device itself, especially its junction temperature , which has a decisive influence on the overcurrent tolerance. The junction temperature increase will not only increase the on-resistance of the device Increase, resulting in greater conduction loss and further temperature rise, forming positive feedback, and directly approaching the safe operating area boundary of the device, reducing its ability to withstand overcurrent shock. In addition, the large-capacity energy storage capacitor on the DC bus side It plays the role of energy buffer in the system, and its charging and discharging behavior is closely related to the dynamic changes of phase current. For example, during the rapid rise or fall of current, the capacitor will absorb or release energy, causing the bus voltage to These fluctuations, transmitted through the inverter, affect the actual phase current waveform and measurement interpretation. Simply ignoring these factors and relying solely on the average current value to determine overcurrent is clearly inaccurate and unsafe.

[0038] Therefore, in step 1, the current signal output by the shunt resistor needs to be Do this multiple times, for example This oversampling technology can capture more details of the current in a switching cycle, including peak information and high-frequency ripple components, laying the foundation for subsequent accurate estimation. After that, it is not a simple averaging, but two key corrections are required. The first is temperature ratio correction. This requires real-time acquisition or estimation of the junction temperature of the power device. The junction temperature can be measured directly by an embedded temperature sensor, or more commonly by building an accurate thermal model of the device based on its power dissipation (conduction loss and switching loss, which can be derived from current, voltage, switching frequency, etc.). etc.) and the thermal resistance of the heat dissipation path to estimate online. Then, it can be compared with a reference temperature (For example ) and the maximum junction temperature allowed by the device (For example ) to form a correction factor. This factor reflects the current junction temperature relative to its allowable range. As the current increases, this factor increases, which is used to moderately amplify the measured value of the current or its equivalent risk. This correction reflects that at high temperatures, even if the absolute value of the current is the same, the actual thermal stress on the device is greater, and the protection system needs to be more sensitive. The second item is harmonic ripple compensation, which is intended to take into account the DC bus energy storage capacitor. The impact of the charge and discharge behavior of the current on the current measurement, especially the rapid change of current The system dynamic response caused by fast In the system stray inductance (such as DC bus stray inductance or phase line stray inductance) produces a voltage spike, causing Rapid charge and discharge to stabilize bus voltage This dynamic process may make the current waveform measured on the shunt resistor not fully represent the current output from the inverter bridge arm to the motor end, or in other words, this rapid pulsation itself poses a threat to system stability. The compensation term will be based on the estimated , real-time bus voltage and busbar capacitance The value of the temperature correction is used to calculate an additional value, which is added to the average current after temperature correction. This additional value represents the additional equivalent current stress caused by the interaction between the dynamic change of current and the bus capacitance. Combining the above oversampling, temperature proportional correction and harmonic ripple compensation, we can finally get a phase current estimate. , which can better reflect the real instantaneous electrical and thermal comprehensive stress that power devices are subjected to under current complex working conditions than simple measurement average values.

[0039] Get accurate instantaneous phase current estimates After that, the second step of the method is to construct an instantaneous overcurrent risk index Setting a fixed overcurrent threshold is simple, but it cannot adapt to changing operating conditions. For example, at a lower bus voltage or at higher junction temperatures Under these conditions, even with the same current value, the risk of failure may be higher. Therefore, a dynamic indicator is needed that can comprehensively assess the degree of overcurrent danger in the current state. The index is designed for this purpose. Its calculation basis mainly includes: the estimated phase current value obtained in step 1 , the single-phase inductance of the motor , real-time DC bus voltage , and the electrical time constant of the motor .in, Represents the current stress level. It reflects the energy storage capacity of the motor phase winding. Proportional to the magnetic field energy stored in the inductor, this energy needs to be safely dissipated when the fault is cleared, so It is an important factor in measuring potential risks. It represents the benchmark of the system's driving capability. A higher bus voltage usually means that the system has a stronger ability to control current changes or withstand certain disturbances. Appearing in the denominator, it means that the higher the voltage, the lower the relative risk. Usually defined as (Among them Phase resistance), which characterizes how quickly the motor current responds to a voltage step. This means that the current changes relatively slowly, giving the control system more time to react. Therefore, it is also placed in the denominator, indicating that the larger the time constant, the lower the risk. Combining these factors can form a basic risk assessment item, such as a form similar to However, a key improvement lies in further introducing the impact of temperature on risk, especially the thermal-magnetic coupling effect. High temperature not only affects its own characteristics, but also affects the performance of the motor. For example, the permanent magnet may be partially demagnetized at high temperature, resulting in weakened magnetic flux, which in turn causes the motor back electromotive force to At the same speed, the voltage is reduced. According to the motor voltage balance equation ,when When the voltage difference between the resistor and the inductor increases, the current Accelerated rise, more likely to cause overcurrent. In order to reflect this additional risk caused by high temperature, it is necessary to introduce a The gain factor should be near When the In this form, the cubic term This makes the factor extremely sensitive to temperature changes in the high temperature area. Combining current size, energy storage, system voltage, dynamic response characteristics and key thermal-magnetic coupling effects, a quantitative assessment of the degree of overcurrent hazard under the current operating state is given. is designed to be a dimensionless or normalized value, e.g. when , it means that the system determines that the current risk has reached a level that requires vigilance or intervention.

[0040] Next, the third step of the method is to calculate the instantaneous overcurrent risk index based on the second step , adaptively adjust the trip threshold Conventional protection methods typically use a fixed trip threshold, such as the rated current. This fixed threshold cannot fully utilize the actual load capacity of the inverter under different operating conditions. For example, when the temperature is low and the bus voltage is stable, the inverter may be able to withstand a peak current higher than the fixed threshold for a short period of time without protective action; on the contrary, when the temperature is high, the voltage fluctuates, or a higher risk has been identified ( When the current is large, the protection may need to be triggered in advance even if the current has not yet reached the fixed high threshold. The core idea of ​​adaptive tripping threshold is to make the protection limit "dynamic". In this step, the nominal rated current of the motor is first set to As the baseline threshold. Then, use The index adjusts this benchmark. The way it is adjusted needs to reflect the design strategy: one possibility is that when When increasing, increase appropriately , because the system has recognized the risk and It has been quantified, and the next step (step 4) will be based on and The combination of determines the precise control action, thus allowing Short-lived Dynamically adjusted, slightly higher In this strategy, the threshold adjustment may be as follows ,in It is a random Increased functions, such as those containing The factor makes the threshold grow with the logarithm of risk, reflecting the focus on high-risk situations without over-magnifying the threshold. Another possibility is that when When increasing, decrease , adopt a more conservative strategy. The choice of which strategy depends on the overall protection philosophy and the confidence in the subsequent soft shutdown capability. , you can also consider other factors to fine-tune For example, the DC bus voltage If Relative to its nominal value Too much deviation (e.g. If the power supply system is unstable or abnormal, the threshold should be adjusted conservatively. , which reflects the overall heat dissipation condition. Higher This means that the heat dissipation margin is reduced and should be reduced accordingly. , for example by multiplying by a factor that decreases as the value increases, such as In addition, the switching frequency may also be taken into account, although its impact is relatively small, but high frequency may mean higher switching losses or more complex dynamic behavior, which can affect Make minor adjustments, such as adding a Related items, such as Through comprehensive consideration and possible stability, and Other factors, the benchmark Dynamic adjustment is performed to finally obtain an adaptive tripping threshold that changes in real time and is highly matched to the current working conditions. .

[0041] The last step of the method, the fourth step, is to perform specific overcurrent protection actions, especially to start the soft shutdown logic. This step is triggered based on the results of the previous steps: it requires two conditions to be met at the same time, namely the instantaneous overcurrent risk index High risk has been shown (e.g. ), and the instantaneous phase current estimate The adaptive trip threshold calculated in step 3 is indeed exceeded (Right now ). This dual-condition judgment mechanism ensures that the protection action is based on a comprehensive assessment of the risk and the confirmation of the actual current overlimit, avoiding the false triggering of protection due to a temporary increase in the risk index (possibly caused by temperature fluctuations) or a momentary glitch in the current (not posing a continuous risk). Once the triggering conditions are met, the protection action needs to be initiated. Unlike the traditional direct hard shutdown (immediately cutting off all gate drive signals), on-board inverters generally tend to adopt a soft shutdown strategy. Although hard shutdown is fast, it will cause the current path to be suddenly interrupted. The energy stored in the motor inductance and the system stray inductance has nowhere to be released, which will generate very high voltage spikes at both ends of the power device (collector-emitter or drain-source) ( ), this voltage spike may exceed the rated voltage of the device, causing it to break down and damage. At the same time, the sudden interruption of current will also cause mechanical shock to the motor and transmission system. The purpose of soft shutdown is to ensure that the current is effectively suppressed while controlling the voltage overshoot and current change rate during the shutdown process within a safe range. The specific soft shutdown logic can be designed according to the severity of the situation. For example, Beyond degree, or A possible implementation is to calculate an indicator related to the severity of overcurrent (similar to the above Energy concepts, including The difference, stray inductance , driving voltage and risk score If the indicator exceeds a certain limit value , a faster soft shutdown is performed, such as reducing the gate voltage at an exponential rate and injecting a zero vector (shorting the motor terminals through a specific combination of switch tubes to provide a low-impedance freewheeling path for the current). If the indicator is within the limit, a more gentle soft shutdown may be used, or simply temporarily suppressing the PWM output and relying on the control loop to recover on its own. The key to soft shutdown technology lies in the fine control of the gate drive signal. By slowly reducing the gate voltage or shutting down different switch tubes in stages, the current drop time is extended, thereby reducing , suppressing voltage spikes. Zero vector injection provides an effective current attenuation channel. and and The soft shutdown logic triggered by the comparison result and possibly adjusted according to the severity can effectively protect the inverter from overcurrent damage while minimizing the side effects of the shutdown process, thereby improving the overall robustness and safety of the system.

[0042] Consider a real-world example: an electric vehicle equipped with a permanent magnet synchronous motor (PMSM) is operating in a hot summer (ambient temperature ) Climb a long slope with full load. The nominal DC bus voltage of its onboard inverter is , motor rated phase current The inverter uses SiCMOSFET power module with a maximum allowable junction temperature of , reference temperature . Motor phase inductance , electrical time constant . DC bus capacitor In the initial state, due to the continuous high power output, the junction temperature of the power device estimated by the thermal model is Reached , real-time bus voltage At this moment, the driver suddenly steps deeply on the accelerator pedal, requesting more torque.

[0043] In step 1, the control system is operated in one PWM cycle (e.g. switching frequency , the period is ) The shunt resistor current of one phase is measured. times oversampling to obtain a series of sample values. After processing (such as filtering and possible estimated), and found that the average current is about , but considering The temperature proportional correction and the current ripple compensation caused by the fast torque request (adding an equivalent 5A) are finally obtained. .

[0044] In step 2, use , , , as well as To calculate the instantaneous overcurrent risk index . Assume basic risk item The calculated result is 0.7. Thermal-magnetic coupling correction factor . Then finally .at this time , the risks are still controllable.

[0045] In step three, according to To adjust the trip threshold. Assume that the adjustment logic is , and considering the shell temperature (set up ) correction factor .but .

[0046] Now, assume that during the next few PWM cycles, the current continues to rise due to changes in road conditions or control system response. rise to , bus voltage Stable . Step 1 is recalculated to obtain Step 2: Recalculate :The basic risk item is now about . Temperature correction factor . .at this time The risk level increases. Step 3 Recalculate ,use (if It also increased accordingly ,but The factor becomes : The threshold is slightly raised because increased, but remained significantly below the no-adaptation threshold at high temperatures.

[0047] In step 4, make a judgment: and . Both conditions are met at the same time. The system triggers the soft shutdown logic. The controller responds according to the preset strategy (possibly also evaluating Beyond The degree and The turn-off rate is determined by the value of ) and then starts to be executed: for example, gradually reducing the gate drive voltage of SiCMOSFET , so that it smoothly transitions from the fully on state to the off state. At the same time, the PWM modulator may be instructed to output the zero vector state, providing a controlled attenuation path for the motor current. This process is completed within tens to hundreds of microseconds, causing the phase current to Safely fall back to zero or near zero, while ensuring that voltage overshoots on the device are suppressed to a safe range (for example, less than 80% of its rated voltage). After the protection action is completed, the system may enter a short cooling or waiting state before attempting to resume normal operation. If the overcurrent condition persists, the protection will be triggered again.

[0048] Furthermore, in step 4, the process of starting the soft shutdown logic to perform overcurrent protection on the on-board inverter includes: the controller first calculates the differential magnetic energy stored in the DC side stray inductance of the on-board inverter, and simultaneously evaluates the additional energy value generated by the integration of the motor back electromotive force and the instantaneous overcurrent risk index. If the additional energy value exceeds the design limit, the gate level is immediately exponentially weakened, and a zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the on-board inverter; otherwise, the on-board inverter is allowed to maintain the existing modulation, and normal drive is automatically restored after the output current of the shunt resistor of the on-board inverter and the instantaneous junction temperature of the power device of the on-board inverter fall back to the safe zone.

[0049] The core of the soft shutdown logic lies in a decision-making mechanism based on energy evaluation. After detecting the trigger condition, the controller does not immediately perform a unified shutdown action, but first performs a quick "severity assessment". This assessment involves calculating a comprehensive energy index to quantify the potential impact energy or energy that needs to be safely managed under the current overcurrent state. According to the description, this energy assessment mainly includes two aspects. The first aspect is to calculate the "differential magnetic energy" stored in the stray inductance on the DC side of the on-board inverter. There is inevitably a certain amount of parasitic inductance on the DC bus path, namely stray inductance. Although its value is usually small (nanohenry level), it is very useful when the current changes rapidly (high ), the magnetic energy stored on it becomes significant, and when the current is forced to shut off, this energy needs to be released, which may produce dangerous voltage spikes The protection logic focuses on the energy contributed by the current that exceeds the threshold, that is, the "differential" energy. Relative to The excess amount, that is , and only in This value is meaningful only when Indicates that This part of energy can be roughly expressed as It represents the additional magnetic energy stored in the DC side stray inductance due to current exceeding the limit, which needs to be handled with special care during the shutdown process. In more sophisticated designs, the current junction temperature may also be considered. , for example, by a Factors of change (such as ) to adjust the weight of this energy item to reflect the reduced ability of the device to handle this part of energy or the increased risk at high temperature.

[0050] The second aspect is to evaluate the so-called "added energy value", which is related to the motor back EMF and transient overcurrent risk index During the operation of the motor, there is a dynamic balance between the phase voltage, phase current and back electromotive force. When overcurrent occurs, the phase inductance is applied The effective voltage difference on the inverter (roughly the inverter output voltage minus the back EMF The voltage difference and the resistance voltage drop) are the reasons for the change in driving current. The product of this voltage difference and the current represents the power input to the inductor. At the same time, the transient overcurrent risk index Describes the degree of danger of the state. In a short time window (e.g. an oversampling period or one PWM cycle) , can be seen as a cumulative measure of risk during this period. correlation) and risk accumulation measures Combined with the above, a second energy-related indicator can be constructed. This indicator reflects the energy or power accumulation generated by the voltage driver and injected into the overcurrent state at the current risk level. For example, its form may be similar to Similarly, it represents the intensity of energy injected into the system towards the runaway trend during this period.

[0051] The controller adds up the energy values ​​(or properly weighted and calibrated indicators) calculated from the above two aspects to obtain a total "added energy value", which is called .this It is a quantitative assessment of the severity of the current overcurrent event, which combines the current exceeding the threshold, stray inductance energy storage, system drive voltage, motor status (through ) and the ongoing level of risk (via ). Calculate The decision logic then becomes clear: compare it to a pre-defined design limit Make a comparison. This represents the maximum additional energy surge that the inverter and its protection system can safely absorb or handle through soft shutdown. This limit depends on factors such as the robustness of the power devices, heat dissipation capabilities, busbar capacitance, and shutdown circuit design.

[0052] If the evaluation result is , which indicates that the severity of the current overcurrent event has exceeded the system's ability to handle it gently, and the potential destructive energy is high, so decisive and strong intervention measures must be taken immediately. At this time, the controller will execute an emergency soft shutdown procedure. This includes two key actions: "exponential weakening of the gate level" and "periodic injection of zero vectors." Exponential weakening of the gate level means that the controller will reduce the gate drive voltage of the power device (such as SiCMOSFET or IGBT) according to the law of an exponential function. or Compared with linear decline, exponential decline can reduce the driving voltage faster in the initial stage, but then the rate slows down, which helps to control the current change rate more smoothly throughout the shutdown process. and voltage change rate , thereby suppressing voltage spikes, but its overall shutdown speed is still faster than the shutdown under ordinary modulation. At the same time, the controller instructs the PWM generator to "periodically inject zero vectors." Zero vector refers to a switching state of the inverter, which makes the voltage output to the three phases of the motor zero (relative to the bus midpoint or negative pole), which is equivalent to short-circuiting the motor winding through the upper bridge arm or the lower bridge arm. This provides a low-impedance freewheeling path for the current stored in the inductor, allowing it to decay quickly and in a controlled manner. The so-called "periodic injection" refers to the continuous application of zero vectors for several switching cycles, or alternating with other vectors as needed to achieve the best current suppression effect. The common goal of these two actions is to "inject the output current of the shunt resistor of the on-board inverter (i.e. , whose estimated value is )’s rising slope is forcibly flattened, or even turned into a rapid decline, thereby quickly curbing the development of the overcurrent state and controlling the current within a safe range.

[0053] On the other hand, if the calculated additional energy value , the controller determines that the current overcurrent situation is not critical, but is just a transient event with low energy impact, or the normal control loop of the system has the ability to correct itself. In this case, the controller will choose to "allow the on-board inverter to maintain the existing modulation." This means that it will not immediately force a change in gate drive or PWM mode, but let the inverter continue to work according to the current instructions (such as instructions from the upper torque controller). The logic behind this is that minor, low-energy overcurrent events may be allowable transient behaviors, or the closed-loop control of the system (such as the current loop) can pull the current back to the desired value within the next control cycle. Forced shutdown may be unnecessary in this case and may even affect the smoothness of driving. However, this is not a laissez-faire approach. The system will continue to monitor the status, especially the output current of the shunt resistor. (or its estimated value ) and the instantaneous junction temperature of the power device Only when both of these key indicators fall back to the preset safety zone, the system will confirm that the risk has been eliminated and "automatically resume normal driving" (actually confirming that normal driving has not been interrupted or has been restored under control). If the current or temperature fails to fall back in the subsequent cycle, or continues to deteriorate, then in the next round of protection logic evaluation, may grow and eventually exceed , thereby triggering the aforementioned emergency soft shutdown procedure.

[0054] For example, before and Based on the case, the controller calculates . Assume that the DC side stray inductance , the current back EMF peak , bus voltage , junction temperature , , . Oversampling period . Calculate the differential magnetic energy term (considering temperature correction): ; Calculate the additional energy term (simplified form, assume that Related): Set the integral term The additional energy term is proportional to Through calibration or design, let this contribution be converted to Overall . Preset design limits .Compare: Decision: Since the calculated additional energy exceeds the limit, the controller determines that the situation is serious and immediately performs an emergency soft shutdown: it starts the gate voltage exponential decrease program and sends a command to the PWM module to start periodic injection of zero vectors, with the goal of quickly reducing the phase current from Pull it down.

[0055] Furthermore, the phase current is estimated as:

[0056] ;

[0057] in, The number of times the output current of the shunt resistor of the vehicle inverter is quickly sampled within a single pulse width modulation cycle; is the sampling integer subscript index; For the The output current of the shunt resistor of the vehicle inverter obtained by sampling, in A; is the upper safety limit temperature, in K; is the reference temperature, which is equal to room temperature and is in K; is the instantaneous junction temperature of the power device of the vehicle inverter, in K; is the DC bus voltage, in V; is the nominal bus voltage; is the DC bus energy storage capacitor, in F; is the electrical time constant of the motor; is the oversampling period; for Time the output current of the on-board inverter's shunt resistor.

[0058] The first part is This term is a weighted correction to the base current measurement. First, It embodies the idea of ​​high-resolution sampling. In one pulse width modulation (PWM) cycle, the output current of the shunt resistor is conduct Sub-fast sampling ( From 1 to ), and then taking the arithmetic mean. Compared to sampling only once or several times at specific moments in the PWM cycle, this oversampling method can better capture the dynamic changes in current within a switching cycle, reduce single-point sampling errors caused by switching ripple and noise, and obtain a more stable baseline current value. Representative The instantaneous current reading is obtained by sampling. However, averaging alone is not enough because the tolerance of the power device is closely related to its own temperature. Therefore, a temperature correction factor is introduced. Here It is the instantaneous junction temperature of a power device (such as an IGBT or SiC MOSFET), which is a direct indicator of the thermal stress of the device. is a reference temperature, usually taken as room temperature (e.g. or ),and is the maximum junction temperature specified in the device data sheet for safe operation (e.g. or ). Difference represents the current temperature rise, and represents the total temperature rise allowed. Therefore, the fraction It is a standardized temperature rise ratio, and its value is between 0 and 1 (theoretically it may exceed 1, indicating overheating). When , the fraction is 0 and the correction factor is 1, which means that the current value is not adjusted at the reference temperature. As the temperature rises, the fraction increases, making the overall correction factor greater than 1. This means that the formula multiplies the average sampled current by a coefficient that increases as the junction temperature rises. The physical meaning of this is that even if the measured current value is the same, at a higher junction temperature, the device is closer to the boundary of thermal failure and its potential risk is greater. Therefore, by amplifying the current value in this way, the obtained The first part is not just the physical quantity of current, but also coupled with thermal stress information, making the protection system more sensitive to current at high temperature. This correction is crucial and is usually calculated online using a device thermal model combined with measured power consumption and heat dissipation conditions.

[0059] The second part is This item aims to compensate and quantify the additional system pressure caused by the dynamic change of current and the characteristics of DC bus capacitance. The core is to consider the current change rate , which reflects the dynamic intensity of the current. is the time interval between two oversamplings, that is .So Approximately equal to the current change between two samples The numerator of this term contains , which is the square of the current change, which means that faster current changes are given higher weight. The denominator is ,in is the real-time DC bus voltage, The main function of the DC bus capacitor is to stabilize the bus voltage, absorb the fluctuations from the power grid and the high-frequency current pulsation caused by the inverter switching operation, and provide or absorb energy when the load power changes rapidly. When rapid changes occur, Rapid charge and discharge to maintain Stable. If the current change rate Very large, or bus voltage Low (small system margin), or bus capacitance If the numerator is smaller (buffering capacity is weak), the system is more likely to generate excessive voltage ripple or instability due to this dynamic current impact. Therefore, the value calculated by this item can be understood as a "dynamic pressure index": the more drastic the current change (larger the numerator) or the weaker the bus voltage / capacitor support capacity (smaller the denominator), the larger the index value. Add this index to In the calculation, a compensation related to the system dynamic stability margin is added to the estimated current. It attempts to quantify the additional burden on the system caused by high-frequency harmonic pulsations or fast load transients. This burden may not be fully reflected in the average current or simple peak current, but it also poses a threat to system safety. This item takes into account the impact of the DC bus charging and discharging behavior, making More comprehensive.

[0060] Furthermore, the electrical time constant of the motor It is the time required for the stator winding current to reach 63% of the steady-state value when the voltage excitation suddenly changes.

[0061] Furthermore, the instantaneous overcurrent risk index for: ;

[0062] in, is the motor phase inductance, unit is H.

[0063] Furthermore, the trip threshold for:

[0064] ;

[0065] in, is the nominal rated current; The power module case temperature refers to the temperature of the power semiconductor module housing or substrate inside the vehicle inverter; The switching frequency is the number of times the inverter power switching device is turned on and off per second, and is also the carrier or pulse width modulation carrier frequency.

[0066] According to the description, It is the time required for the stator winding current to reach its final steady-state value when the voltage excitation suddenly changes. This definition is directly related to the step response characteristics of a first-order linear system (such as an RL circuit). and inductance A circuit composed of series, applying a voltage step After that, the current The response is , where the time constant .then , .therefore, Directly reflects the motor stator winding (whose main electrical characteristics can be approximated as resistance and inductance The inherent electrical dynamic response speed of the series connection). A larger This means that the motor current responds slowly to voltage changes, and vice versa. In the context of overcurrent protection, The intrinsic time scale for the development of current runaway is characterized, as well as the possible reaction time window of the control system.

[0067] Next, analyze the instantaneous overcurrent risk index The calculation formula is: This formula aims to go beyond simple current amplitude comparison and provide a comprehensive quantitative indicator of the degree of danger of overcurrent events in the current operating state. It consists of two parts multiplied together. The first part is , can be regarded as a basic risk assessment item. Among them, It is the instantaneous phase current estimate obtained in the first step after compensation for temperature and dynamic effects, and is a direct reflection of the current electrical stress. is the single-phase inductance of the motor. The magnetic field energy stored in the phase inductance It is directly proportional to the potential energy level in the system that needs to be safely handled in the event of a failure. The higher the energy, the greater the potential risk. Is the real-time DC bus voltage. A higher bus voltage usually means that the power system is more "robust" and can better maintain stability and provide the voltage margin required for control, so it appears in the denominator, indicating a higher It will relatively reduce the risk index. is the motor electrical time constant defined previously. The larger This means that the current changes relatively slowly, giving the control system more time to detect abnormalities and respond. It also appears in the denominator, which means that slower dynamic response corresponds to lower instantaneous risk. This basic term provides a preliminary risk assessment by comparing the energy / stress factors related to the square of the current and the inductance, normalized to the system voltage level and dynamic response time scale.

[0068] The second part of the formula is , which is a key thermal-magnetic coupling correction factor. is the instantaneous junction temperature of the power device obtained or estimated from the first step, is the maximum safe junction temperature allowed by the device. Represents how close the current junction temperature is to the limit value. Perform a cubic operation on it. Make this item near When , it grows very rapidly and shows a very high nonlinearity. For example, when When ;when When ; and when When , it reaches 1. Add 1 and then take the square root The correction factor is always greater than or equal to 1 and is amplified sharply in high temperature areas. Its physical significance is to simulate the adverse effects of high temperature on motor performance, especially the possible thermal-magnetic coupling effect. High temperature may cause the permanent magnet flux to weaken or the magnetic saturation characteristics of the silicon steel sheet to change, thereby reducing the back electromotive force of the motor. According to the motor voltage equation, the lower Under the same supply voltage, the voltage difference applied to the winding impedance will increase, thereby accelerating the current rise rate, making overcurrent more likely to occur or develop faster. This correction factor significantly improves the The value is taken into account in the assessment of the potential risk of thermally affecting the magnetic field and accelerating electrical runaway. The value combines electrical stress, system status, dynamic characteristics and key thermal effects to provide a better A more comprehensive risk indicator. When a certain threshold (for example, 1) is exceeded, the system considers that the system has entered a high-risk state.

[0069] Next, analyze the adaptive trip threshold The calculation formula is: The goal of this formula is to abandon the fixed overcurrent threshold and dynamically set a protection boundary based on the real-time working conditions. , so that the protection is neither too conservative nor too aggressive. The main part of the formula is based on the rated current Make adjustments. is the nominal operating current of the motor or inverter and is the basis for setting the threshold. The first adjustment factor is This section will calculate the risk index The threshold is adjusted by combining the stability of the DC bus voltage. Risk Index . Natural logarithm function (in ) is a monotonically increasing function, but the growth rate increases with This means that when When it increases (risk increases), this item will make the value in the square brackets greater than 1, thereby increasing the basic threshold This seems to indicate that the system is identifying higher risks. When the current is higher, a slightly higher instantaneous current peak is allowed. . The risk assessment itself has been included, and the subsequent soft shutdown (step 4) will be based on and The specific situation can be finely controlled, so in some high However, under controlled conditions, the instantaneous peak limit can be slightly relaxed to maintain operation. Taking into account the deviation of the DC voltage from its nominal value When the real-time voltage and When the gap is large (whether it is too high or too low), the absolute value item Increase, making the denominator greater than 1, thus weakening This reflects a conservative strategy: when the power supply voltage is unstable, even if It is not advisable to increase the tripping threshold significantly, but should be closer to the benchmark .

[0070] The second adjustment factor is This item introduces the power module shell temperature impact. Refers to the temperature of the power semiconductor module housing or substrate, and is an important indicator for measuring the overall heat dissipation and heat accumulation of the module. When the denominator increases Increase, score Reduce (because ). After taking the square root, this factor is less than 1 and As a multiplier, it directly reduces the threshold value calculated above. This achieves thermal de-rating based on actual heat dissipation conditions: the hotter the module ( The higher the value), the smaller the heat dissipation margin is, and the upper limit of the current allowed to pass is should be lower to ensure the junction temperature No more than Here (Maximum Junction Temperature) and (case temperature) together to construct a derating ratio related to the actual thermal state. . is the switching frequency of the inverter. This term adds a small positive offset to the threshold that increases with the switching frequency. For example, if the frequency increases from 10kHz to 160kHz (16 times), this term only increases by 2 times ( ). A higher switching frequency may correspond to faster control loop response, so slightly higher transient noise or peaks can be tolerated; or it is used to compensate for the average thermal effect of increased switching losses at high frequencies (although the main thermal effect is already and It may also be related to the specific behavior of the measured signal or filtering characteristics at high frequencies. Regardless of the specific cause, it represents a weak, positive compensation for the effects of the switching frequency.

[0071] Assume that the vehicle is accelerating uphill, and the state is updated as follows: Instantaneous phase current estimation value , junction temperature , DC bus voltage The motor parameters are: phase inductance , electrical time constant . Inverter parameters: Maximum junction temperature , rated current , nominal bus voltage , current shell temperature , switching frequency .

[0072] Calculating the instantaneous overcurrent risk index :Basic risk item= .

[0073] Thermal-magnetic coupling correction factor = . (Calculated using degrees Celsius: Here, the temperature value K is more rigorous, and the results are not much different, so we continue to use 1.379). If the value is greater than 1, it indicates that the system is in a high-risk state.

[0074] Calculating adaptive trip thresholds : Risk adaptive term The voltage deviation factor in the risk adaptive term = . First adjustment factor = Thermal Derating Factor = . (Calculated using degrees Celsius: Continuing with the K temperature value, the result is 0.743). Switching frequency compensation term = Switching frequency compensation term = . .

[0075] In this example, the calculated , which is much greater than 1, confirms a high-risk state. The calculated adaptive trip threshold This threshold is much higher than the rated current , mainly because the risk index The higher the first adjustment factor, the greater the value of the first adjustment factor. This results in a derating of about 26% (factor 0.743), but the final threshold is still high. This shows that the protection strategy may allow a short-term high peak current (up to 100%) when a high risk is detected. ), relying on the energy assessment and soft shutdown in step 4 to accurately manage the risk, rather than just relying on lowering the threshold to avoid triggering. In the next step, the and .because ,even though , the forced shutdown logic in step 4 will not be triggered at this time. This shows the characteristics of this method: high risk ( ) is a necessary condition, but the current exceeds the dynamically adjusted threshold ( ) is the sufficient condition for triggering protection action. And this threshold itself already contains considerations of risks and various working conditions.

[0076] Furthermore, in step 4, when the instantaneous overcurrent risk index is greater than 1 and the estimated phase current exceeds the trip threshold, the soft shutdown logic is activated to perform overcurrent protection on the on-board inverter.

[0077] Furthermore, in step 4, when and By calculating the instantaneous differential energy storage Start the soft shutdown logic to protect the vehicle inverter from overcurrent:

[0078] .

[0079] in, Indicates that only positive values ​​are taken; is the DC side stray inductance; is the peak value of the motor back electromotive force; if Exceeding design limits , the exponential weakening of the gate level is immediately executed, and the zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the vehicle inverter; if , the on-board inverter maintains the existing modulation, waits for the output current of the on-board inverter's shunt resistor and the instant junction temperature of the on-board inverter's power device to fall back to the safe zone, and then automatically resumes normal driving.

[0080] Furthermore, in step 4, the switching frequency The following constraints are met: .

[0081] The protection action is initiated based on dual criteria, which requires two conditions to be met at the same time: instantaneous overcurrent risk index Greater than 1, and corrected instantaneous phase current estimate The dynamically calculated trip threshold is exceeded That is, when and This dual-condition mechanism reflects the prudence of the strategy: it not only requires that the current exceeds the dynamic upper limit ( ), and also requires the system to assess that the current state itself has a high inherent risk ( Only when both conditions are met at the same time, subsequent intervention measures are initiated, avoiding false protection caused by instantaneous fluctuations of a single indicator. Once the trigger condition is met, the system does not immediately perform a fixed shutdown action, but enters a decision-making process based on energy evaluation. The controller calculates a quantity called "instantaneous differential energy storage" ,this It is designed to quantify the severity of a current overcurrent event or the amount of energy contained within it that needs to be managed safely. The formula consists of two main components.

[0082] Item 1 The concern is the stray inductance stored in the DC side energy in the current, but with particular emphasis on the portion of the current that exceeds the threshold Contributed by. The symbol indicates that only positive values ​​are taken, that is, only Indeed greater than This item will only contribute when Although it is a parasitic parameter, its energy storage cannot be ignored when the current changes rapidly. If this energy is not handled properly, it will be one of the main reasons for the voltage spike. Therefore, calculating this "differential" magnetic energy is a dimension to evaluate the severity of the impact. At the same time, this item also includes a The associated exponential decay factor This factor increases with From the reference temperature Increase to near the maximum allowable temperature And gradually decrease from 1 to close to or smaller (set is the temperature reference in the denominator). This shows that at high temperatures, this term contributes to the total The contribution will be weakened. At high temperatures, the system's heat dissipation capacity decreases and it is more sensitive to any energy shock. Therefore, even if the calculated magnetic energy value is not large, the overall risk assessment (through ) also needs to be adjusted accordingly; or it reflects the change in the ability of the device or system to cope with this energy release at high temperature. In any case, it couples the thermal state of the device into the energy assessment.

[0083] Item 2 Energy injection or risk accumulation can be evaluated from another perspective. Voltage difference Approximately represents the inductance applied to the motor phase The effective voltage that drives the current change (ignoring the resistance voltage drop, etc.). is the peak value of the motor's back electromotive force, which resists the effect of the power supply voltage. The square of this voltage difference reflects the strength of the driving source. Related to the inductive energy storage. More importantly, the product term , which is in an oversampling period In such a short time, the instantaneous overcurrent risk index If during this period If the value is continuously high, the integral value will be large, indicating a rapid accumulation of risk. Therefore, this whole term can be understood as the product of the energy injection rate driven by the driving voltage difference and the degree of risk accumulation in the system in a short period of time. It quantifies the momentum of the overcurrent condition under the action of the voltage source and the accompanying risk accumulation. When the driving voltage difference is large, the motor inductance is small, and the risk index is continuously high, this term will Make significant contributions.

[0084] The calculated total The value is then compared to a preset "design limit" Make a comparison. It is a threshold determined based on the inverter hardware capabilities (such as the avalanche energy tolerance of the power device, the bus capacitor's ability to suppress voltage fluctuations, the design of the soft shutdown circuit, etc.), representing the maximum instantaneous energy impact that the system can safely handle. The comparison result determines the next specific protection action: If Exceeding design limits ( ), indicating a severe overcurrent event, the energy impact exceeding the system's normal soft shutdown capability, necessitating immediate and robust protective measures. At this point, the controller executes an emergency soft shutdown procedure, including exponential reduction of the gate voltage and periodic injection of zero vectors. Exponential reduction of the gate drive voltage aims to achieve a controlled yet sufficiently rapid shutdown of the power devices, balancing the need for shutdown speed with the need to suppress voltage spikes. Simultaneously, periodic injection of zero vectors (as previously described, by short-circuiting the motor terminals through a specific switch combination) provides a path for rapid current decay. These two actions work together to flatten the output current slope of the on-board inverter's shunt resistor, effectively preventing further current increase and causing it to decrease in a controlled manner, thereby returning the system to a safe state.

[0085] like Does not exceed design limits ( ), it means that although the current overcurrent situation has triggered the protection condition, its energy impact assessment result is still within the controllable range of the system, which may be just a short disturbance or a slight overlimit. In this case, the controller will adopt a more moderate strategy: "The on-board inverter maintains the existing modulation." This means that it will not force shutdown or change the PWM mode immediately, but allow the inverter to continue to operate for a short period of time according to the current control instructions. The system hopes that its own closed-loop control system (such as a fast current loop) can adjust the current back to the normal range by itself. However, this is not a complete release of protection, and the system will continue to monitor the current ( or ) and junction temperature Only when these two key indicators are confirmed to have fallen back to the safe zone, the protection status will be truly lifted and "normal driving will be automatically restored" (or normal driving will be confirmed to have never been interrupted). If the status fails to recover on its own or continues to deteriorate, it will be re-evaluated in the next protection cycle. It is likely to grow and exceed , which will eventually trigger the above-mentioned emergency soft shutdown.

[0086] In addition, this protection method also controls the switching frequency of the inverter A constraint is proposed: .here is the electrical time constant of the motor. The physical significance of this constraint is to ensure that the switching action (control behavior) of the inverter is fast enough relative to the inherent electrical response of the motor. The electrical dynamic characteristics of the motor are determined by its time constant Decision, its countdown It can be regarded as the characteristic frequency of the motor electrical system. The switching frequency constraint requires This is similar to the sampling theorem in control theory, which requires that the sampling frequency (here the switching frequency, which determines the update rate of the control action) must be much higher than the bandwidth of the controlled object (given by Only when this condition is met can the inverter accurately and quickly control the motor current through PWM, effectively tracking commands and rapidly changing the current state when needed (such as when executing protection actions). If the switching frequency is too low, the inverter's ability to control current will be reduced, and it may not be able to respond to rapid current changes or effectively execute the sophisticated protection logic described above, especially those steps that require microsecond-level evaluation and reaction. Therefore, this constraint is one of the fundamental conditions for the effective implementation of the entire advanced overcurrent protection method.

[0087] An overcurrent protection system for an on-board inverter comprises: a phase current estimation section for rapidly sampling the output current of the on-board inverter's shunt resistor multiple times within a single pulse width modulation cycle, taking into account the instantaneous junction temperature of the on-board inverter's power devices and the charging and discharging behavior of the DC bus energy storage capacitor, and obtaining a phase current estimate that is closer to the true instantaneous phase current after temperature proportional correction and harmonic pulsation compensation; an instantaneous overcurrent risk index calculation section for constructing an instantaneous overcurrent risk index based on the phase current estimate, combined with the motor phase inductance, the DC bus voltage, and the motor's electrical time constant; a trip threshold adjustment section for adaptively adjusting the trip threshold based on the instantaneous overcurrent risk index using the nominal rated current as a reference; and an overcurrent protection section for initiating soft shutdown logic to provide overcurrent protection for the on-board inverter based on the instantaneous overcurrent risk index and the phase current estimate.

[0088] The present invention has been described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the method and core ideas of the present invention. It should be noted that, for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for overcurrent protection of a vehicle-mounted inverter, characterized in that: The method comprises: Step 1: Within a single pulse width modulation cycle, the output current of the vehicle inverter's shunt resistor is sampled multiple times quickly. The instantaneous junction temperature of the vehicle inverter's power components and the charging and discharging behavior of the DC bus energy storage capacitor are taken into account. After temperature proportional correction and harmonic ripple compensation, a phase current estimate that is closer to the actual instantaneous phase current is obtained. Step 2: Based on the estimated phase current, combined with the motor phase inductance, DC bus voltage and the motor electrical time constant τ e , construct the instantaneous overcurrent risk index; Step 3: Using the nominal rated current as a benchmark, adaptively adjust the trip threshold according to the instantaneous overcurrent risk index; Step 4: Based on the instantaneous overcurrent risk index and the estimated phase current, the soft shutdown logic is activated to protect the on-board inverter from overcurrent.

2. The overcurrent protection method for a vehicle-mounted inverter according to claim 1, wherein: In step 4, the process of starting the soft shutdown logic to protect the on-board inverter from overcurrent includes: the controller first calculates the differential magnetic energy stored in the DC side stray inductance of the on-board inverter, and simultaneously evaluates the additional energy value generated by the integration of the motor back electromotive force and the instantaneous overcurrent risk index. If the additional energy value exceeds the design limit, the gate level is immediately exponentially weakened, and a zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the on-board inverter; otherwise, the on-board inverter is allowed to maintain the existing modulation, and normal drive is automatically restored after the output current of the shunt resistor of the on-board inverter and the instantaneous junction temperature of the power device of the on-board inverter fall back to the safe zone.

3. The overcurrent protection method for a vehicle-mounted inverter according to claim 2, wherein: Phase current estimated value I est for: Wherein, N is the number of times the output current of the shunt resistor of the vehicle inverter is quickly sampled in a single pulse width modulation cycle; k is the sampling integer subscript index; I sh (k) is the output current of the shunt resistor of the vehicle inverter obtained by the kth sampling, in A; T max is the upper safety limit temperature, in K; T ref is the reference temperature, which is equal to room temperature and is in K; T j is the instantaneous junction temperature of the power device of the vehicle inverter, in K; U dc is the DC bus voltage, in V; C dc is the DC bus energy storage capacitor, in F; Δt is the oversampling period; I sh (t) is the output current of the shunt resistor of the vehicle inverter at time t.

4. The overcurrent protection method for a vehicle-mounted inverter according to claim 3, wherein: The electrical time constant τ of the motor e It is the time required for the stator winding current to reach 63% of the steady-state value when the voltage excitation suddenly changes.

5. The overcurrent protection method for a vehicle-mounted inverter according to claim 4, wherein: The instantaneous overcurrent risk index OCR is: Among them, L ph is the motor phase inductance, in H; τ e is the electrical time constant of the motor.

6. The overcurrent protection method for a vehicle-mounted inverter according to claim 5, wherein: Tripping threshold I trip for: Among them, I nom is the nominal rated current; T c is the power module shell temperature, which refers to the temperature of the power semiconductor module shell or substrate inside the vehicle inverter; f sw is the switching frequency, which is the number of times the inverter power switch device is turned on and off per second, and is also the carrier or pulse width modulation carrier frequency; U nom is the nominal bus voltage.

7. The overcurrent protection method for a vehicle-mounted inverter according to claim 6, wherein: In step 4, when the instantaneous overcurrent risk index is greater than 1 and the estimated phase current exceeds the trip threshold, the soft shutdown logic is activated to perform overcurrent protection on the on-board inverter.

8. The overcurrent protection method for a vehicle-mounted inverter according to claim 7, wherein: In step 4, when OCR>1 and I est >I trip When the instantaneous differential energy storage ΔE is calculated, the soft shutdown logic is activated to protect the vehicle inverter from overcurrent: in,[·] + Indicates that only positive values ​​are taken; L d is the DC side stray inductance; E back is the peak value of the motor back electromotive force; if ΔE exceeds the design limit E lim , the exponential weakening of the gate level is immediately executed, and the zero vector is periodically injected to forcibly flatten the rising slope of the output current of the shunt resistor of the vehicle inverter; if ΔE <E lim , the on-board inverter maintains the existing modulation, waits for the output current of the on-board inverter's shunt resistor and the instant junction temperature of the on-board inverter's power device to fall back to the safe zone, and then automatically resumes normal driving.

9. The overcurrent protection method for a vehicle-mounted inverter according to claim 8, wherein: In step 4, the switching frequency f sw The following constraints are met:

10. An overcurrent protection system for a vehicle-mounted inverter for implementing the method according to any one of claims 1 to 9, characterized in that: The system includes: a phase current estimation part, which is used to quickly sample the output current of the shunt resistor of the on-board inverter multiple times within a single pulse width modulation cycle, and consider the instantaneous junction temperature of the power device of the on-board inverter and the charging and discharging behavior of the DC bus energy storage capacitor. After temperature proportion correction and harmonic pulsation compensation, a phase current estimation value that is closer to the actual instantaneous phase current is obtained; an instantaneous overcurrent risk index calculation part, which is used to construct an instantaneous overcurrent risk index based on the phase current estimation value, combined with the motor phase inductance, DC bus voltage and the electrical time constant of the motor; a trip threshold adjustment part, which is used to use the nominal rated current as a reference and adaptively adjust the trip threshold according to the instantaneous overcurrent risk index; and an overcurrent protection part, which is used to start the soft shutdown logic to perform overcurrent protection on the on-board inverter based on the instantaneous overcurrent risk index and the phase current estimation value.

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