Motor driving system health monitoring method and system based on discharge time

Abstract

The invention provides a motor driving system health monitoring method and system based on discharge time, and the method comprises the steps: employing the discharge characteristic of a DC bus capacitor after the motor driving system is turned off, and measuring the discharge time, namely, the time needed for reducing the DC bus voltage from a first fixed value to a second fixed value, as a health index, and evaluation of the overall health state of the system is realized. The method does not need extra hardware investment, only depends on the existing DC bus voltage information in the system, is simple in calculation process, does not need a complex algorithm, carries out monitoring after the system is stopped, and does not interfere with normal operation. Experimental verification shows that the method has high sensitivity to degradation of a direct current bus capacitor and a power semiconductor device, can effectively reflect the health state change of the system, and is suitable for health management and predictive maintenance of motor driving systems in the fields of electric automobiles, industrial driving, aerospace and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power electronic system state and health monitoring, and particularly relates to a motor drive system health monitoring method and system based on discharge time. BACKGROUND

[0002] Motor drive systems play a vital role in automotive, railway and aerospace applications, which require zero-failure operation to ensure personal and property safety. However, the DC bus capacitor and power semiconductor devices in the motor drive system will degrade due to long-term operation and environmental stress, which may cause unexpected failures. In order to improve the safety and availability of the system and reduce the maintenance cost, it is necessary to monitor the health status of these two key reliability components.

[0003] In the prior art, a large number of researches have been invested in implementing state and health monitoring at the component level. Based on the consensus on the physical degradation mechanism of the DC bus capacitor and the power semiconductor device, many health indicators have been proposed, such as the equivalent series resistance ESR and the capacitance value for monitoring the DC bus capacitor, and the switching time and the on-saturation voltage for monitoring the power semiconductor device, and various measurement or estimation methods for obtaining these health indicators have also been developed. These component-level monitoring schemes are effective in identifying the degradation of individual components, but their applicability needs to be further considered in practical applications. In field applications, according to the specific maintenance strategy, the entire motor drive system can be regarded as the minimum unit for maintenance and replacement, without the need to explicitly distinguish which component in the motor drive system has degraded. Therefore, it is necessary to evaluate the health of the motor drive system as a whole, so as to achieve more comprehensive health management.

[0004] Currently, there are some system-level health monitoring strategies proposed. The efficiency-based method takes the efficiency of the motor drive system as the health indicator to monitor the DC bus capacitor and power semiconductor devices in the motor drive system. When these two components degrade, their power losses will also increase, which in turn reduces the efficiency of the motor drive system. However, the system DC input current and AC output voltage required to calculate the efficiency are not existing information in the motor drive system, and additional sensors and high-performance measurement equipment need to be added. The harmonic-based method considers that the harmonics in the motor drive system controller output variables and system input voltage are sensitive to the degradation of power semiconductor modules and DC bus capacitors, and takes the harmonics as the health indicator. Although the harmonic-based method does not involve additional sensors, it needs to upgrade the hardware to improve the sampling rate and resolution to accurately capture the harmonic signal, and it also needs to use complex spectral analysis algorithms, which undoubtedly increases the monitoring cost and complexity. In addition, the efficiency-based and harmonic-based methods have a common problem, which is that their sensitivity to component degradation is relatively low, meaning that the changes in the health indicators caused by degradation are easily masked by noise and variable operating conditions, making it difficult to be accurately identified. Algorithm-based methods identify system degradation by injecting excitation signals into the system loop and then analyzing the system response through specific identification algorithms. These techniques have been widely used in control optimization. These algorithms can be based on pre-defined model structures or can not rely on specific models. Digital twinning, as an emerging technology, is also a powerful tool for health monitoring. Some studies establish a digital virtual model of the motor drive system and combine particle swarm optimization and genetic algorithm to extract health indicators. With the rapid development of artificial intelligence technology, data-driven health monitoring methods have also received widespread attention. These methods perform well in solving classification and regression problems and are particularly suitable for scenarios where system models are difficult to accurately construct. These algorithm-based monitoring solutions can use existing hardware sensors in motor drive systems without additional hardware investment. However, these methods usually require high-speed and high-precision data sampling, and the system modeling and artificial intelligence algorithm computation burden is quite heavy, increasing the complexity of implementation.

[0005] In summary, existing system-level health monitoring methods rely on hardware upgrades and complex algorithms in practical applications, and generally face the challenges of high cost and complex implementation. Both component-level and system-level health monitoring methods are performed in real-time during normal system operation, which can interfere with normal operation and cause reliability problems due to additional hardware and software requirements. SUMMARY

[0006] Invention purposes: The application provides a motor drive system health monitoring method and system based on discharge time, which aims to utilize the discharge characteristics of the DC bus capacitor after the system is turned off, and measure the time required for the DC bus voltage to drop from one preset fixed value to another preset fixed value, i.e. the discharge time, as a new health indicator, to realize health status evaluation without hardware incremental investment, without complex algorithm, and without disturbing the normal operation of the system.

[0007] Technical solutions: The application provides a motor drive system health monitoring method based on discharge time, comprising:

[0008] After the motor drive system stops running, a DC bus discharge operation mode is triggered;

[0009] The change process of the DC bus voltage is monitored, and the discharge time is recorded; the discharge time is the time required for the DC bus voltage to drop from a preset first fixed value V DC1 to a second fixed value V DC2 ; the first fixed value V DC1 is lower than the minimum initial DC bus voltage, and the second fixed value V DC2 is higher than the discharge termination safety voltage; both the first fixed value V DC1 and the second fixed value V DC2 are within the discharge steady state interval;

[0010] The discharge time data at different stages are collected, and probability density analysis, median filtering processing and unitization processing are performed to obtain a unitized discharge time median;

[0011] The unitized discharge time median is compared with a set end-of-life indicator to evaluate the health status of the system; if the unitized discharge time median is lower than the end-of-life indicator, the motor drive system needs to be maintained.

[0012] Further, the triggering of the DC bus discharge operation mode comprises:

[0013] After the normal operation of the motor drive system ends, the driving signal is stopped to be provided to the power semiconductor module, so that the motor drive current rapidly decreases;

[0014] When the electronic control unit confirms that the motor speed and the drive current have both dropped to zero, the motor drive system is isolated from the front-end power supply by disconnecting the circuit breaker;

[0015] The electronic control unit generates a set of discharge instructions in the rotating reference coordinate system, including q-axis current i q_ref and d-axis current i d_ref , to trigger the DC bus discharge operation mode.

[0016] Further, the calculation of the discharge time comprises:

[0017] In a switching cycle T s , the energy E module_Ts consumed by the whole power semiconductor module in the motor drive system is calculated, and the formula is:

[0018]

[0019] wherein S i represents the collective term of the power semiconductor device Q i and its corresponding freewheeling diode D i ;

[0020] i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, which is determined by the rotor electrical angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-state resistance of the power semiconductor device, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty ratio of the power semiconductor device, which is determined by the rotor electrical angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ;

[0021] E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, which is related to the DC bus voltage V dc , the rotor electrical angle θ e , the d-axis current i d_ref and the junction temperature T j,Si in the switching cycle;

[0022] In a switching cycle T s , the energy E motor_Ts consumed by the load motor in the motor drive system is calculated, and the formula is:

[0023]

[0024] wherein R wa (T load ), R wb (T load ), R wc (T load ) represent the equivalent resistance of the stator winding of the three-phase motor, and the resistance values vary with the temperature T cool of the cooling liquid;

[0025] Suppose that the interval from the voltage V DC1 to the voltage V DC2 of the DC bus voltage contains n switching periods, then the total energy consumed by the power semiconductor module and the load motor in the interval is approximately:

[0026]

[0027] According to the principle of energy conservation, the sum of the energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is:

[0028]

[0029] wherein C(Deg C ) represents the capacitance value of the DC bus capacitor, which decreases with the increase of the degradation degree of the DC bus capacitor;

[0030] The discharge time is calculated by the formula:

[0031]

[0032] Further, the discharge time data processing comprises:

[0033] The collected discharge time data is divided into a health data cluster and a current data cluster, the health data cluster represents the discharge time data when the motor drive system is in a healthy state, and the current data cluster represents the discharge time data when the motor drive system is not in a healthy state, and the health data cluster and the current data cluster are subjected to probability density analysis and median filtering processing to obtain a health discharge time median and a current discharge time median;

[0034] The health discharge time median is used to normalize the current discharge time median to obtain a normalized discharge time median.

[0035] The application further provides a motor drive system health monitoring system based on discharge time, comprising:

[0036] The switching discharge module is used to trigger the DC bus discharge operation mode after the motor drive system stops running;

[0037] a detection voltage module for monitoring the change process of the DC bus voltage, recording the discharge time; the discharge time is the time required for the DC bus voltage to drop from a preset first fixed value V DC1 to a second fixed value V DC2 ; DC1 the first fixed value V DC2 is lower than the minimum initial DC bus voltage, and the second fixed value V DC1 is higher than the discharge termination safety voltage; DC2 both of which are within the discharge steady state interval;

[0038] a data collection module for collecting discharge time data at different stages, performing probability density analysis, median filtering processing and normalization processing to obtain a normalized discharge time median;

[0039] a state evaluation module for comparing the normalized discharge time median with a set end-of-life indicator to evaluate the health state of the system, and if the normalized discharge time median is lower than the end-of-life indicator, the motor drive system needs maintenance.

[0040] Further, in the switching discharge module, the triggering of the DC bus discharge operation mode includes:

[0041] stopping providing driving signals to the power semiconductor module after the normal operation of the motor drive system ends, so that the motor drive current rapidly decreases;

[0042] when the electronic control unit confirms that the motor speed and the drive current have both dropped to zero, isolating the motor drive system from the front-end power supply by opening the circuit breaker;

[0043] the electronic control unit generates a set of discharge instructions in the rotating reference coordinate system, including q-axis current i q_ref and d-axis current i d_ref , triggering the DC bus discharge operation mode.

[0044] Further, in the detection voltage module, the calculation of the discharge time includes:

[0045] in a switching period T s during the discharge process, the energy E module_Ts consumed by the entire power semiconductor module in the motor drive system is calculated, and the formula is:

[0046]

[0047] wherein S i represents the collective term of the power semiconductor device Q i and its corresponding freewheeling diode D i ;

[0048] i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, determined by the motor rotor electrical angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-state resistance of the power semiconductor device, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty ratio of the power semiconductor device, determined by the rotor electrical angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ;

[0049] E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, related to the DC bus voltage V dc , the motor rotor electrical angle θ e , the d-axis current i d_ref and the junction temperature T j,Si in the switching period;

[0050] In a switching period T s in the discharging process, the energy E motor_Ts consumed by the load motor of the motor drive system is calculated, and the formula is:

[0051]

[0052] wherein R wa (T load ), R wb (T load ), R wc (T load ) respectively represent the equivalent resistances of the three-phase motor stator windings, which change with the cooling liquid temperature T cool ;

[0053] It is assumed that for the DC bus voltage from voltage VDC1 decreases to the voltage V DC2 If the interval containing n switching cycles, the total energy consumed by the power semiconductor module and the load motor in the interval is approximately:

[0054]

[0055] According to the principle of energy conservation, the total energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is:

[0056]

[0057] Wherein, C(Deg C ) represents the capacitance value of the DC bus capacitor, which will decrease with the increase of the degradation degree of the DC bus capacitor;

[0058] The discharge time is calculated, and the formula is:

[0059]

[0060] Further, in the data collection module, the discharge time data processing includes:

[0061] The collected discharge time data is divided into a health data cluster and a current data cluster, the health data cluster represents the discharge time data when the motor drive system is in a healthy state, the current data cluster represents the discharge time data when the motor drive system is not in a healthy state, and the health data cluster and the current data cluster are subjected to probability density analysis and median filtering processing to obtain a health discharge time median and a current discharge time median.

[0062] The health discharge time median is used for standardization processing of the current discharge time median to obtain a standard discharge time median.

[0063] The application also provides a computer device, including a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor executes the computer program to realize the steps of the above method.

[0064] The application also provides a computer readable storage medium, which stores a computer program, and the computer program is executed by the processor to realize the steps of the above method.

[0065] Beneficial effects: the application provides a motor drive system health monitoring method and system based on discharge time, which has the following significant effects compared with the prior art:

[0066] (1) Zero hardware incremental investment: This method only uses the measured DC bus voltage information in the motor drive system, without adding any additional sensors or measurement devices. In addition, this method has low performance requirements for DC bus voltage sampling, only requiring regular sampling synchronized with the system switching frequency, avoiding the cost of hardware upgrades. This efficient reuse of system resources significantly reduces the implementation cost of the health monitoring system.

[0067] (2) Easy to implement: This method uses discharge time as a health indicator, with a very simple calculation principle. It only needs to record the two time points when the DC bus voltage drops from the first fixed value to the second fixed value and subtract them. This simple time difference calculation does not require complex signal processing algorithms or spectrum analysis, and does not depend on high-performance computing resources. Any level of controller can easily complete the method, and the simplicity of the method significantly reduces the implementation threshold, making it particularly suitable for engineering applications.

[0068] (3) System-level monitoring: This method evaluates the health status of the motor drive system as a whole, without distinguishing which component is degraded, providing more comprehensive health information, which is highly consistent with the actual maintenance strategy.

[0069] (4) High sensitivity: Discharge time shows high sensitivity to both internal DC bus capacitance and power semiconductor module degradation. For only 2.7% of capacitor degradation, more than 2% of discharge time change can be generated, effectively reflecting the change in system health status. The existing system-level monitoring method based on efficiency reduces only about 0.11% (see paper M. V. H. Wang, and F. Blaabjerg, “End-of-life detection of power electronic converters by exploiting an application-level health precursor,” IEEE Open J. Power Electron., vol. 3, pp. 549-559, 2022.) when the system components reach the end-of-life state. This small change is easily masked by measurement noise. The sensitivity of the present invention is improved by nearly 20 times compared to this technology, greatly improving the reliability of monitoring.

[0070] (5) No operational interference: Unlike existing health monitoring methods, the present method is executed after the system is completely turned off, without any interference with the normal operation of the system, and without introducing new reliability issues, greatly reducing the safety risk. Especially for motor drive applications, this non-invasive monitoring avoids affecting the system's working state and control performance.

[0071] In summary, compared with the prior art system-level monitoring methods in the background art, the efficiency-based method in the prior art requires additional sensors, the harmonic-based method and the algorithm-based method both require additional hardware upgrades, while the method of the present application does not; the harmonic-based method and the algorithm-based method have high implementation complexity, while the method of the present application has low implementation complexity; the efficiency-based method, the harmonic-based method and the algorithm-based method are monitored in normal operation, which has high operation interference, while the method of the present application is monitored after the system is turned off, which has low operation interference; the efficiency-based method and the harmonic-based method have low degradation sensitivity, while the method of the present application has high degradation sensitivity. BRIEF DESCRIPTION OF DRAWINGS

[0072] Figure 1 A typical configuration diagram of a motor drive system, where C represents a DC bus capacitor, EM represents a load motor, ECU is an electronic control unit, Q1-Q6 and D1-D6 represent power devices and freewheeling diodes in a power semiconductor module, respectively.

[0073] Figure 2 A DC bus discharge simulation waveform of a motor drive system, which shows the variation curves of the DC bus voltage, the three-phase drive current and the three-phase upper switch duty cycle during the discharge process, and marks the definition intervals of the initial DC bus voltage, the discharge steady-state interval, the safety voltage and the discharge time.

[0074] Figure 3 A discharge time data processing flowchart, which shows the processing flow of the original discharge time data collected over time, including probability density analysis, median filtering and health state evaluation.

[0075] Figure 4 A motor drive system experimental platform for electric vehicles, where (a) shows the topology of the experimental platform, and (b) shows the hardware implementation of the experimental platform.

[0076] Figure 5 A DC bus discharge experimental waveform of a motor drive system.

[0077] Figure 6 Data distribution of discharge time of a DC bus capacitor at different degradation levels.

[0078] Figure 7 Data distribution of discharge time of an IGBT module at different degradation levels.

[0079] Figure 8 Data distribution of discharge time when the DC bus capacitor and the IGBT module both degrade at different degradation levels. DETAILED DESCRIPTION

[0080] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0081] Example 1

[0082] Please see Figures 1 to 3 As shown, the present invention provides a health monitoring method for a motor drive system based on discharge time, comprising:

[0083] Step 1, as follows Figure 1 As shown, after the motor drive system finishes normal operation, the drive signal to the power semiconductor module is stopped, causing the motor drive current to drop rapidly.

[0084] Step 2: Once the electronic control unit (ECU) confirms that the motor speed and drive current have both dropped to zero, it isolates the motor drive system from the front-end power supply by disconnecting the circuit breaker.

[0085] Step 3: The Electronic Control Unit (ECU) generates a set of discharge commands in the rotating reference coordinate system, including the q-axis current i. q_ref and d-axis current i d_ref This is used to trigger the DC bus discharge operation mode. Typically, to prevent torque generation, i q_ref Set to 0, i d_ref It can be set to any value below the system rating, but it must be ensured that the discharge time complies with relevant regulations. The EU standard requires ≤5 seconds, and the Chinese standard requires ≤3 seconds.

[0086] Step 4: Using the existing current control loop of the motor drive system, discharge the energy stored in the DC bus capacitor according to the discharge command i. q_ref i d_ref and the electric angle θ of the motor rotor e Released through power semiconductor devices and load motor windings.

[0087] Step 5: Monitor the DC bus voltage change process and record the voltage from the preset first fixed value V. DC1 Reduced to the second fixed value V DC2 The required time is defined as the discharge time, such as... Figure 2 As shown. The first fixed value V DC1 With the second fixed value V DC2 The determination of the first fixed value V needs to be reasonably set according to the voltage operating range of the specific application. DC1 The voltage should be lower than the minimum initial DC bus voltage Vinitial before system discharge, with a certain margin, to avoid the transient process at the beginning of discharge. The second fixed value VDC2 The safe voltage should be higher than the discharge termination voltage and have a sufficient margin to avoid the transient process at the end of the discharge, to ensure that the discharge time is only related to the system degradation state and stable operation conditions, and is not affected by the transient process at the discharge start and end stages, and to determine whether the discharge stage is in the discharge steady state interval according to the three-phase drive current.

[0088] The calculation of the discharge time specifically includes:

[0089] During the discharge process of the DC bus, the energy stored in the DC bus capacitor is mainly consumed by the power semiconductor devices and the load motor windings. The energy consumption of the power semiconductor devices includes conduction loss and switching loss. The rear-end motor mainly consumes the energy stored in the DC bus capacitor in the form of heat energy during the discharge process.

[0090] In one switching period T s during the discharge process, the energy E module_Ts consumed by the entire power semiconductor module in the motor drive system is calculated, and the formula is:

[0091]

[0092] Wherein, S i represents the collective term of the power semiconductor device Q i and its corresponding freewheeling diode D i ;

[0093] i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, which is determined by the motor rotor electric angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-resistance of the power semiconductor device in the on state, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) of the power semiconductor device and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty cycle of the power semiconductor device, which is determined by the rotor electric angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ;

[0094] E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, which is related to the DC bus voltage V dc , the motor rotor electrical angle θ e and the d-axis current i d_ref and the junction temperature T j,Si in a switching period;

[0095] In the discharging process of the motor drive system, the rotor electrical angle of the motor remains unchanged, resulting in zero back electromotive force. At this time, the stator winding of the load motor can be regarded as a three-phase RL load, and the energy consumed by the load motor in the discharging process can be calculated by the equivalent resistance.

[0096] In a switching period T s in the discharging process, the energy E motor_Ts consumed by the load motor of the motor drive system is calculated, and the formula is:

[0097]

[0098] Where R wa (T load ), R wb (T load ), R wc (T load ) represent the equivalent resistances of the three-phase motor stator windings, which vary with the cooling liquid temperature T cool ;

[0099] Assuming that the interval from the voltage V DC1 to the voltage V DC2 contains n switching periods, the total energy consumed by the power semiconductor module and the load motor in this interval is approximately:

[0100]

[0101] According to the principle of energy conservation, the sum of the energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is:

[0102]

[0103] Where C(Deg C ) represents the capacitance value of the DC bus capacitor, which decreases with the increase of the degradation degree of the DC bus capacitor;

[0104] The discharging time is calculated, and the formula is:

[0105]

[0106] For a given voltage interval V DC1 to V DC2 Because the degradation of the DC bus capacitor will cause its capacitance value C(Deg C ) to decrease, the numerator on the right side of the formula will decrease, so the discharge time will decrease with the degradation of the DC bus capacitor; because the degradation of the power semiconductor device will cause its equivalent on-resistance R cond,Si to increase, the denominator on the right side of the formula will increase, so the discharge time will also decrease with the degradation of the power semiconductor device; the discharge time can reflect the degradation of both the DC bus capacitor and the power semiconductor device.

[0107] Step 6, collect the discharge time data clusters at different stages, divide them into a healthy data cluster and a current data cluster, the healthy data cluster represents the discharge time data when the motor drive system is in a healthy state, and the current data cluster represents the discharge time data when the motor drive system is not in a healthy state, and establish a discharge time history database.

[0108] Step 7, as shown in Figure 3 , perform probability density analysis and median filtering processing on the collected healthy discharge time data cluster and current discharge time data cluster, reduce the influence of operating conditions and measurement noise, obtain a healthy discharge time median and a current discharge time median that can better represent the real health state of the motor drive system, take the healthy discharge time median of the motor drive system in a healthy state as a reference, and perform normalization processing on the current discharge time median using the healthy discharge time median to obtain a normalized discharge time median.

[0109] Step 8, compare the normalized discharge time median with a set end-of-life indicator EOL, evaluate the health state of the motor drive system, and decide whether maintenance is needed, if the normalized discharge median is lower than the end-of-life indicator, the motor drive system needs maintenance.

[0110] For the technical solutions of the above embodiment, the experimental process of applying the technical solutions to a specific motor drive test experiment and the technical effects of the technical solutions will be described in detail below. Figures 4 to 8

[0111] To verify the effectiveness of the method of the present application, an experimental test was performed on a full-power motor drive system for an electric vehicle, as shown in Figure 4 . The system configuration includes a custom vehicle film capacitor and an Infineon HybridPACK TM ​IGBT power module (model FS380R12A6T4B) is mounted on a liquid cooling baseplate. The load motor is an asynchronous motor for vehicle with a rated continuous power of 60 kW and a rated torque of 120 Nm. The cooling liquid circulates through the motor winding and the IGBT module to ensure good thermal management.

[0112] Figure 5 The experimental waveform of DC bus discharge is shown. In this embodiment, the operating parameters are set as follows: q-axis current reference i q_ref is 0, d-axis current reference i d_ref is 100 A, initial DC bus voltage Vinitial is 400 V, motor rotor electrical angle θ e is 3π / 5, cooling liquid temperature Tcool is 24℃. It can be seen from the figure that the discharge mode is activated at 0.01 s, and then the DC bus voltage gradually decreases. The three-phase drive current reaches a steady state at 0.02 s, and the device duty cycle is maintained at about 50% during steady-state operation. In this embodiment, the range of initial DC bus voltage Vinitial is set to 350 V to 500 V, so the discharge time is defined as the time required for the DC bus voltage to decrease from 330 V (V DC1 ) to 160 V (V DC2 ). As indicated by the markers in Figure 5 , the selection of these two voltage values ensures that they always fall within the discharge steady-state interval and are not affected by transient processes.

[0113] To verify the effectiveness of discharge time as a health monitoring indicator, experiments need to be conducted on DC bus capacitors and power module samples with different degradation levels. Therefore, this embodiment first conducts degradation simulation experiments. For the DC bus capacitor, by connecting additional capacitors with different capacitances in parallel on the DC bus, the capacitance of the parallel capacitor is changed to simulate the degradation level of the DC bus capacitor. For the IGBT module, because the bond wire cut will cause the equivalent resistance of the device to increase, the method of manually cutting the bond wires of IGBT Q3 and diode D1 is used to simulate the degradation level. The simulation results are shown in Table 2.

[0114] Table 2. Degradation level settings for DC bus capacitor and IGBT module

[0115]

[0116] From Table 2, for the DC bus capacitor, a parallel 38 μF film capacitor can be used to simulate the healthy state, i.e. degradation level 0; a parallel 20 μF film capacitor, which is equivalent to a 2.7% reduction in the capacitance value, simulates the degradation level 1; and no additional capacitor, which is equivalent to a 5.7% reduction in the capacitance value, simulates the degradation level 2. For the IGBT module, all the bonding wires are intact, simulating the degradation level 0; one bonding wire of the IGBT Q3 and the diode D1 is cut, simulating the degradation level 1; and two bonding wires of the IGBT Q3 and the diode D1 are cut, simulating the degradation level 2.

[0117] Then, the feasibility of the discharge time under various degradation combinations and actual operating conditions is comprehensively evaluated, and a comprehensive test scheme shown in Table 3 is designed to record the time required for the DC bus voltage to decrease from 330 V (V DC1 ) to 160 V (V DC2 ) under each test condition.

[0118] Discharge test conditions under different degradation levels

[0119]

[0120] The test scheme has 7 test conditions, A1, A2 and A3 are tests of the DC bus capacitor under different degradation levels, A1, A4 and A5 are tests of the IGBT module under different degradation levels, and A1, A6 and A7 are tests of the complex scenario of the degradation of the DC bus capacitor and the IGBT module. Each test condition is tested under multiple actual operating conditions, including 7 motor rotor electrical angles (ranging from 17π / 30 to 23π / 30), 3 cooling liquid temperatures (20°C, 25°C and 30°C), and 2 initial DC bus voltages (400 V and 500 V), a total of 42 different operating condition combinations, i.e. the same DC bus capacitor degradation level and IGBT module degradation level are operated under 42 different operating conditions and the time required for the DC bus voltage to decrease from 330 V (V DC1 ) to 160 V (V DC2 ) is recorded. This comprehensive test matrix design ensures the reliability and applicability of the experimental results, and can simulate various working scenarios that the motor drive system may encounter in actual applications.

[0121] To ensure the statistical validity and reliability of the experimental results, 100 random sampling analyses were performed on 42 groups of data under each test condition (A1 to A7) in this embodiment; in each random sampling, 50% of the data, i.e., 21 groups, were randomly selected from the 42 groups of data. Subsequently, median filtering was performed on the 21 groups of data to obtain the discharge time median value representing the true health status of the motor drive system, including the health discharge time median value and the current discharge time median value; after 100 random samplings and median filtering, 100 discharge time median values were finally obtained for each test condition. The discharge time median value distribution is shown in the box plot as follows: Figures 6 to 8 The dispersion of the discharge time at the same degradation level is mainly caused by the varying operating conditions.

[0122] When the capacitance value decreases by 5%, the film capacitor reaches the end-of-life (EoL) standard, and the motor drive system needs to be replaced.

[0123] Figure 6 The discharge time distribution under the condition of only DC bus capacitor degradation is shown, corresponding to test numbers A1, A2 and A3. A1 shows the discharge time median value distribution in the healthy state, i.e., at a degradation level of 0, A2 shows the discharge time median value distribution when the capacitance value decreases by 2.7%, i.e., at a degradation level of 1, and A3 shows the discharge time median value distribution when the capacitance value decreases by 5.7%, i.e., at a degradation level of 2. When the capacitance value decreases by 5%, the film capacitor reaches the end-of-life (EoL) standard, and the motor drive system needs to be replaced. As can be seen from Figure 6 With the increase of the degradation level of the DC bus capacitor, the discharge time is significantly shortened. When the capacitance value decreases by 2.7%, i.e., at a degradation level of 1, the discharge time median value is at least 2.1% lower than the discharge time median value in the healthy state; when the capacitance value decreases by 5.7%, i.e., at a degradation level of 2, the discharge time median value is at least 5.2% lower than the discharge time median value in the healthy state, indicating that the health monitoring method provided by the present application has high sensitivity and can meet the needs of actual monitoring.

[0124] Figure 7 The discharge time distribution under the condition of only IGBT module degradation is shown, corresponding to test numbers A1, A4 and A5. A1 shows the discharge time median value distribution in the healthy state, i.e., at a degradation level of 0, A4 shows the discharge time median value distribution at a degradation level of 1 for the IGBT module, and A5 shows the discharge time median value distribution at a degradation level of 2 for the IGBT module. As can be seen from Figure 7As can be seen, when the IGBT module is at degradation level 1, the median discharge time is reduced by at least 0.9% compared to the median discharge time in the healthy state. When the IGBT module is at degradation level 2, the median discharge time is reduced by at least 2.5% compared to the median discharge time in the healthy state. This indicates that the discharge time also has good sensitivity to the degradation of power semiconductor devices.

[0125] Figure 8 The discharge time distributions of both the DC bus capacitor and the IGBT module under simultaneous degradation are shown, corresponding to test numbers A1, A6, and A7. A1 shows the median discharge time distribution for the healthy state, i.e., degradation level 0. A6 shows the median discharge time distribution for both the DC bus capacitor and the IGBT module at degradation level 1. A7 shows the median discharge time distribution for both the DC bus capacitor and the IGBT module at degradation level 2. Figure 8 As can be seen, under this combined degradation condition, the median discharge time is significantly lower than the median discharge time in the healthy state. When the DC bus capacitor and IGBT module are both at degradation level 1, the median discharge time is at least 3.9% lower than the median discharge time in the healthy state. When the DC bus capacitor and IGBT module are both at degradation level 2, the median discharge time is at least 8.9% lower than the median discharge time in the healthy state. This indicates that the discharge time is more sensitive to the combined degradation of multiple components in the motor drive system. This characteristic is particularly important in practical applications because multiple components often degrade simultaneously in real-world systems.

[0126] from Figures 6 to 8 It can be seen that even under the worst-case scenario considering data randomness, i.e., using the lower adjacent value of A1 as the benchmark, the upper adjacent values ​​of A2 to A7 still show a significant decrease compared to this benchmark, effectively eliminating the influence of random factors and fully demonstrating the stability and reliability of the method of the present invention in practical application scenarios. Experiments show that this method can not only effectively detect the individual degradation of capacitors and IGBT modules, but also accurately identify their combined degradation state, providing highly sensitive technical support for the health status assessment of motor drive systems.

[0127] Example 2

[0128] Please see Figures 1 to 3 As shown in Embodiment 1, the present invention provides a health monitoring system for a motor drive system based on discharge time, comprising:

[0129] The speed reduction module is used to stop supplying drive signals to the power semiconductor module after the motor drive system has finished normal operation, causing the motor drive current to drop rapidly, such as... Figure 1 As shown.

[0130] Isolation module, to isolate the motor drive system from the front-end power supply by opening the circuit breaker after the electronic control unit ECU confirms that both the motor speed and the drive current have dropped to zero.

[0131] Discharge instruction module, to generate a set of discharge instructions on the rotating reference coordinate system by the electronic control unit ECU, including q-axis current i q_ref and d-axis current i d_ref for triggering the DC bus discharge operation mode. Usually to prevent torque generation, i q_ref is set to 0, i d_ref can be set to any value below the system rating, but it needs to ensure that the discharge time meets the relevant regulatory requirements, with the EU standard requiring ≤5 seconds and the Chinese standard requiring ≤3 seconds.

[0132] Release module, to release the energy stored in the DC bus capacitor according to the discharge instructions i q_ref , i d_ref and motor rotor electrical angle θ e through power semiconductor devices and load motor windings.

[0133] Monitoring calculation module, to monitor the DC bus voltage change process, record the time required for the voltage to drop from a pre-set first fixed value V DC1 to a second fixed value V DC2 , and define this time as the discharge time, as shown in Figure 2 . The determination of the first fixed value V DC1 and the second fixed value V DC2 needs to be reasonably set according to the voltage operating range of the specific application, the first fixed value V DC1 should be lower than the minimum initial DC bus voltage Vinitial before system discharge and have a certain margin to avoid the transient process at the beginning of discharge, the second fixed value V DC2 should be higher than the safety voltage at the end of discharge and have sufficient margin to avoid the transient process at the end of discharge, to ensure that the discharge time is only related to the system degradation state and stable operating conditions, and is not affected by the transient process at the start and end of discharge, and to determine whether the discharge phase is in the discharge steady state interval according to the three-phase drive current.

[0134] The calculation of the discharge time specifically includes:

[0135] During the DC bus discharge process, the energy stored in the DC bus capacitor is mainly consumed through power semiconductor devices and load motor windings. The energy consumption form of power semiconductor devices includes conduction loss and switching loss. The back-end motor mainly consumes the energy stored in the DC bus capacitor in the form of heat energy during the discharge process.

[0136] one switching period T in the discharging process s The energy E consumed by the whole power semiconductor module in the motor drive system is calculated module_Ts The formula is:

[0137]

[0138] Where S i represents the collective term of the power semiconductor device Q i and its corresponding freewheeling diode D i ; i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, which is determined by the rotor electrical angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-state resistance of the power semiconductor device, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty cycle of the power semiconductor device, which is determined by the rotor electrical angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ;

[0139] E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, which is related to the DC bus voltage V dc , the rotor electrical angle θ e and the d-axis current i d_ref in the switching period, and the junction temperature T j,Si ;

[0140] In the discharging process of the motor drive system, the rotor electrical angle of the motor remains unchanged, resulting in zero back electromotive force. At this time, the stator winding of the load motor can be regarded as a three-phase RL load, and the energy consumed by the load motor in the discharging process can be calculated by the equivalent resistance.

[0141] one switching period T in the discharging process s The energy E consumed by the load motor of the motor drive system is calculated motor_Ts , the formula is:

[0142]

[0143] wherein R wa (T load ), R wb (T load ), R wc (T load ) respectively represent the equivalent resistance of the three-phase motor stator winding, and the resistance values vary with the cooling liquid temperature T cool ;

[0144] Suppose that the interval from the voltage V DC1 to the voltage V DC2 contains n switching periods, then the total energy consumed by the power semiconductor module and the load motor in the interval is approximately:

[0145]

[0146] According to the principle of energy conservation, the sum of the energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is:

[0147]

[0148] wherein C(Deg C ) represents the capacitance value of the DC bus capacitor, which decreases with the increase of the degradation degree of the DC bus capacitor;

[0149] The discharging time is calculated, and the formula is:

[0150]

[0151] For a given voltage interval V DC1 to V DC2 , because the degradation of the DC bus capacitor will cause the capacitance value C(Deg C ) to decrease, thus reducing the numerator on the right side of the formula, so the discharging time will decrease with the degradation of the DC bus capacitor; because the degradation of the power semiconductor device will cause the equivalent on-resistance R cond,Si to increase, thus increasing the denominator on the right side of the formula, so the discharging time will also decrease with the degradation of the power semiconductor device; the discharging time can reflect the degradation of the DC bus capacitor and the power semiconductor device at the same time.

[0152] The data collection module is used for collecting discharge time data clusters in different stages, which are divided into a health data cluster and a current data cluster, the health data cluster represents discharge time data when the motor drive system is in a healthy state, and the current data cluster represents discharge time data when the motor drive system is not in a healthy state, and a discharge time history database is established.

[0153] The data processing module, as shown in Figure 3 , performs probability density analysis and median filtering processing on the collected health discharge time data cluster and current discharge time data cluster, reduces the influence of operating conditions and measurement noise, obtains health discharge time median and current discharge time median which can better represent the real health state of the motor drive system, takes the health discharge time median of the motor drive system in a healthy state as a reference, and performs normalization processing on the current discharge time median to obtain a normalized discharge time median.

[0154] The state evaluation module evaluates the health state of the motor drive system by comparing the normalized discharge time median with a set end-of-life indicator EOL, and decides whether maintenance is needed, if the normalized discharge time median is lower than the end-of-life indicator, the motor drive system needs maintenance.

[0155] Since the second embodiment is a modular product expression of the monitoring method in the first embodiment, the test experiment corresponding to the second embodiment is the same as the test experiment in the first embodiment (combined with Figures 4 to 8 ), and will not be described here.

[0156] The computer device described in the application comprises a memory, a processor and a computer program stored on the memory and executable on the processor, and the processor implements the steps of the above method when executing the computer program.

[0157] The computer readable storage medium described in the application has a computer program stored thereon, and the computer program is executed by the processor to implement the steps of the above method.

Claims

1. A discharge time based motor drive system health monitoring method, characterized by, The application relates to a method for evaluating the health state of a motor drive system, comprising the following steps: triggering a DC bus discharge operation mode after the motor drive system stops running; monitoring the DC bus voltage change process and recording the discharge time; said discharge time is the time required for the DC bus voltage to decrease from a first fixed value V DC1 to a second fixed value V DC2 ; said first fixed value V DC1 is lower than a minimum initial DC bus voltage, said second fixed value V DC2 is higher than a discharge termination safety voltage; said first fixed value V DC1 and said second fixed value V DC2 are both within a discharge steady state interval; collecting discharge time data at different stages, performing probability density analysis, median filtering processing and unitization processing to obtain a unitized discharge time median value; comparing the unitized discharge time median value with a set life termination index to evaluate the health state of the system, and if the unitized discharge time median value is lower than the life termination index, the motor drive system needs to be maintained.

2. The discharge time based motor drive system health monitoring method of claim 1, wherein, The method for triggering the DC bus discharge operation mode comprises the following steps: stopping the provision of driving signals to the power semiconductor module after normal operation of the motor drive system ends, so that the motor drive current rapidly decreases; when the electronic control unit confirms that the motor speed and the drive current have both decreased to zero, the motor drive system is isolated from the front-end power supply by disconnecting the circuit breaker; The electronic control unit generates a set of discharge commands in the rotating reference frame, including q-axis current i q_ref and d-axis current i d_ref , triggering the DC bus discharge operating mode.

3. The discharge time based motor drive system health monitoring method of claim 1, wherein, The calculation of the discharge time comprises the following steps: One switching cycle T in the discharging process s The energy E consumed by the entire power semiconductor module in the motor drive system is calculated module_Ts The formula is: where S i represents the sum of the power semiconductors Q i and their corresponding freewheeling diodes D i ; i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, determined by the motor rotor electrical angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-state resistance of the power semiconductor device, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty ratio of the power semiconductor device, determined by the rotor electrical angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ; E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, which is related to the DC bus voltage V dc , the motor rotor electrical angle θ e , the d-axis current i d_ref , and the junction temperature T j,Si ; One switching cycle T in the discharging process s The energy E consumed by the load motor of the motor drive system is calculated motor_Ts The formula is: wherein R wa (T load ), R wb (T load ), R wc (T load ) represent the equivalent resistance of the stator winding of the three-phase motor, which varies with the temperature T cool of the cooling liquid. Assume that for the interval of the direct current bus voltage from the voltage V DC1 down to the voltage V DC2 contains n switching periods, then the total energy consumed by the power semiconductor module and the load motor in the interval is approximately: according to the energy conservation principle, the total energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is: where C(Deg C ) represents the capacitance value of the DC bus capacitor, which decreases as the DC bus capacitor degradation increases; the discharge time is calculated, and the formula is:

4. The discharge time based motor drive system health monitoring method of claim 1, wherein, The discharge time data processing comprises the following steps: the collected discharge time data is divided into a health data cluster and a current data cluster, the health data cluster represents the discharge time data when the motor drive system is in a healthy state, the current data cluster represents the discharge time data when the motor drive system is not in a healthy state, and the health data cluster and the current data cluster are subjected to probability density analysis and median filtering processing to obtain a health discharge time median value and a current discharge time median value; the health discharge time median value is used to unitize the current discharge time median value to obtain a unitized discharge time median value.

5. A discharge time based motor drive system health monitoring system, characterized by, The application relates to a method for evaluating the health state of a motor drive system, comprising the following steps: a switching discharge module is used for triggering a DC bus discharge operation mode after the motor drive system stops running; The detection voltage module is used for monitoring the change process of the DC bus voltage, recording the discharge time; the discharge time is the time required for the DC bus voltage to drop from a preset first fixed value V DC1 to a second fixed value V DC2 ; the first fixed value V DC1 is lower than the minimum initial DC bus voltage, and the second fixed value V DC2 is higher than the discharge termination safety voltage; the first fixed value V DC1 and the second fixed value V DC2 are both within the discharge steady state interval. a data collection module is used for collecting discharge time data at different stages, performing probability density analysis, median filtering processing and unitization processing to obtain a unitized discharge time median value; a state evaluation module is used for comparing the unitized discharge time median value with a set life termination index to evaluate the health state of the system, and if the unitized discharge time median value is lower than the life termination index, the motor drive system needs to be maintained.

6. The discharge time based motor drive system health monitoring system of claim 5, wherein, In the switching discharge module, the method for triggering the DC bus discharge operation mode comprises the following steps: stopping the provision of driving signals to the power semiconductor module after normal operation of the motor drive system ends, so that the motor drive current rapidly decreases; when the electronic control unit confirms that the motor speed and the drive current have both decreased to zero, the motor drive system is isolated from the front-end power supply by disconnecting the circuit breaker; The electronic control unit generates a set of discharge commands in the rotating reference frame, including q-axis current i q_ref and d-axis current i d_ref , triggering the DC bus discharge operating mode.

7. The discharge time based motor drive system health monitoring system of claim 5, wherein, In the detection voltage module, the calculation of the discharge time comprises the following steps: One switching cycle T in the discharging process s The energy E consumed by the entire power semiconductor module in the motor drive system is calculated module_Ts The formula is: wherein S i represents a power semiconductor device Q i and its corresponding freewheeling diode D i in general; i cond,Si (θ e ,i d_ref ) represents the conduction current of the power semiconductor device, determined by the motor rotor electrical angle θ e and the d-axis current i d_ref ; R cond,Si (θ e ,i d_ref ,T j,Si ,Deg Si ) represents the equivalent on-state resistance of the power semiconductor device, which increases with the increase of the device degradation degree, and is also related to the conduction current i cond,Si (θ e ,i d_ref ) and the junction temperature T j,Si ; d Si (θ e ,V dc ,i d_ref ) represents the duty ratio of the power semiconductor device, determined by the rotor electrical angle θ e , the DC bus voltage V dc and the d-axis current i d_ref ; E switching,Si (V dc ,θ e ,i d_ref ,T j,Si ) represents the switching energy loss of the power semiconductor device, which is related to the DC bus voltage V dc , the motor rotor electric angle θ e , the d-axis current i d_ref , and the junction temperature T j,Si ​ One switching cycle T in the discharging process s The energy E consumed by the load motor of the motor drive system is calculated motor_Ts The formula is: wherein R wa (T load ), R wb (T load ), R wc (T load ) represent the equivalent resistance of the stator winding of the three-phase motor, which varies with the temperature T cool of the cooling liquid. Assume that the interval for the direct current bus voltage from the voltage V DC1 down to the voltage V DC2 contains n switching periods, then the total energy consumed by the power semiconductor module and the load motor in this interval is approximately: according to the energy conservation principle, the total energy consumed by the power semiconductor module and the load motor is equal to the energy released by the DC bus capacitor, and the formula is: where C(Deg C ) represents the capacitance value of the DC bus capacitor, which decreases as the DC bus capacitor degradation increases; the discharge time is calculated, and the formula is:

8. The discharge time based motor drive system health monitoring system of claim 5, wherein, In the data collection module, the discharge time data processing comprises the following steps: The collected discharge time data is divided into a health data cluster and a current data cluster, the health data cluster represents the discharge time data when the motor drive system is in a healthy state, and the current data cluster represents the discharge time data when the motor drive system is not in a healthy state, and the health data cluster and the current data cluster are subjected to probability density analysis and median filtering processing to obtain a health discharge time median and a current discharge time median; The health discharge time median is used to normalize the current discharge time median to obtain a normalized discharge time median.

9. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to implement the steps of the method of any one of claims 1 to 4.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method of any one of claims 1 to 4.

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