Service life optimization method and equipment of ANPC inverter and storage medium

Abstract

The invention is suitable for the field of photovoltaic technology, and provides a life optimization method and equipment of an ANPC inverter and a storage medium, and the life optimization method of the ANPC inverter comprises the following steps: respectively calculating the power loss of each switch tube in a first modulation mode and the power loss of each switch tube in a second modulation mode; calculating a mixing proportion coefficient of the first modulation mode in a sine period according to the power loss of each switch tube; and controlling each switch tube to operate the first modulation mode and / or the second modulation mode in the sine period according to the mixing proportionality coefficient. According to the technical scheme, the service life of the inverter can be prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of electronic power technology, and in particular relates to a life optimization method, device and storage medium for an ANPC inverter. Background Art

[0002] In the field of electronic power, the reliability and life of the inverter are key indicators of its performance, and the uneven distribution of power switch losses is a key bottleneck that restricts the life of the inverter. The three-point active neutral point clamp (ANPC) topology is widely used in new energy power generation, electric vehicle drive and other fields due to its significant advantages such as low harmonic content, high conversion efficiency and high bus voltage utilization.

[0003] However, traditional ANPC inverters often adopt a single modulation strategy, and a single modulation strategy will lead to a particularly prominent problem of unbalanced loss distribution of power switch tubes. For example, under the PWMA modulation mode, the upper bridge arm switch tube T1 will suffer significant switching losses due to high-frequency switching action, causing the junction temperature to rise sharply; while under the PWMB modulation mode, the upper bridge arm switch tube T2 accumulates a large amount of conduction losses due to the long conduction state, which also causes the junction temperature to exceed the limit. This loss concentration phenomenon directly causes the life of the entire inverter to be restricted by the shortest life of a single power switch tube. Especially when operating under wide operating conditions, the limitations of a single modulation strategy are further magnified, resulting in a decrease in system reliability.

[0004] In the existing technology, some solutions balance the loss by means of fixed ratio mixed modulation or parallel IGBT, but fail to give full play to the bidirectional conduction characteristics of the switch tube, and lack a dynamic adaptive adjustment mechanism. Therefore, how to optimize the modulation strategy to achieve power switch tube loss balance, extend the service life of the ANPC inverter and improve the reliability of the ANPC inverter has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] An embodiment of the present invention provides a life optimization method for an ANPC inverter, aiming to optimize the service life of the inverter.

[0006] The embodiments of the present invention are implemented as follows. A method for optimizing the lifespan of an ANPC inverter, where the ANPC inverter includes: an upper bridge arm composed of a first switching tube and a second switching tube connected in series, a lower bridge arm composed of a third switching tube and a fourth switching tube connected in series, and a clamping bridge arm composed of a fifth switching tube and a sixth switching tube connected in series; the upper bridge arm and the lower bridge arm are connected in series between the positive and negative poles of the DC bus, the clamping bridge arm is connected between the middle nodes of the upper bridge arm and the lower bridge arm, the middle node of the clamping bridge arm is connected to the neutral point, and the common node of the upper bridge arm and the lower bridge arm is connected to the AC output terminal; wherein, the first switching tube to the sixth switching tube are all SiCMOSFETs; the method for optimizing the lifespan of the ANPC inverter includes the following steps: Calculate the power losses of each switching tube under the first modulation mode and the power losses of each switching tube under the second modulation mode respectively; Calculate the mixing ratio coefficient of the first modulation mode in the sine period according to the power losses of each switching tube; Control each switching tube to operate in the first modulation mode and / or the second modulation mode within the sine period according to the mixing ratio coefficient.

[0007] Furthermore, the step of calculating the power losses of each switching tube under the first modulation mode and the power losses of each switching tube under the second modulation mode respectively includes: Collect the operating condition parameters of the inverter under the first modulation mode and the second modulation mode respectively; Based on the conduction loss model and the switching loss model, calculate the conduction loss and switching loss of each switching tube respectively according to the operating condition parameters under the first modulation mode; Take the sum of the conduction loss and the switching loss of each switching tube as the power loss of each switching tube under the first modulation mode; Based on the conduction loss model and the switching loss model, calculate the conduction loss and switching loss of each switching tube respectively according to the operating condition parameters under the second modulation mode; Take the sum of the conduction loss and the switching loss of each switching tube as the power loss of each switching tube under the second modulation mode.

[0008] Furthermore, the step of calculating the mixing ratio coefficient of the first modulation mode in the sine period according to the power losses of each switching tube includes: Establish a loss balance equation with the goal of making the power losses of two switching tubes in the same bridge arm tend to be balanced; Substitute the power losses of the two switching devices in the same bridge arm into the loss equalization equation; where the loss equalization equation is a*x + c*(1 - x) = b*x + d*(1 - x); a is the power loss of one of the two switching devices in the same bridge arm under the first modulation mode, b is the power loss of the other switching device under the first modulation mode, c is the power loss of one of the switching devices under the second modulation mode, d is the power loss of the other switching device under the second modulation mode, and x is the mixing ratio coefficient of the first modulation mode in the sine period; Solve the loss equalization equation to obtain the mixing ratio coefficient of the first modulation mode in the sine period.

[0009] Further, the step of controlling each of the switching devices to operate in the first modulation mode and / or the second modulation mode in the sine period according to the mixing ratio coefficient includes: Judge the interval where the mixing ratio coefficient x is located; When x > 1, control each of the switching devices to operate in the first modulation mode in the full sine period; When x < 0, control each of the switching devices to operate in the second modulation mode in the full sine period; When 0 ≤ x ≤ 1, control each of the switching devices to alternately operate in the first modulation mode and the second modulation mode in the sine period according to the ratio of x:(1 - x).

[0010] Further, after the step of controlling each of the switching devices to operate in the first modulation mode and / or the second modulation mode in the sine period according to the mixing ratio coefficient, it further includes: Obtain the junction temperature of each switching device in real time; Calculate the junction temperature difference value of the two switching devices in the same bridge arm in each switching device respectively; Judge whether the junction temperature difference value is greater than a preset junction temperature threshold; When the junction temperature difference value is greater than the preset junction temperature threshold, adjust the mixing ratio coefficient.

[0011] Further, the step of obtaining the junction temperature of each switching device in real time includes: Collect the case temperature of each switching device in real time; Based on the Foster thermal model, obtain the junction temperature of each switching device according to the case temperature of each switching device.

[0012] Further, it is characterized in that, after the step of controlling each of the switching devices to operate in the first modulation mode and / or the second modulation mode in the sine period according to the mixing ratio coefficient, it further includes: Estimate the service life of each switching tube based on the rainflow counting method, the CIP08 model, and the Miner's rule; Predict the failure probability of each switching tube based on the Monte Carlo model; Optimize the mixing ratio coefficient according to the service life and the failure probability.

[0013] An embodiment of the present invention further provides a life optimization device for an ANPC inverter. The life optimization device for the ANPC inverter includes: a memory, a processor, and a life optimization program for the ANPC inverter stored on the memory and executable on the processor. When the life optimization program for the ANPC inverter is executed by the processor, the steps of the life optimization method for the ANPC inverter described in any one of the above are implemented.

[0014] An embodiment of the present invention further provides a storage medium. A life optimization program for the ANPC inverter is stored on the storage medium. When the life optimization program for the ANPC inverter is executed by a processor, the steps of the life optimization method for the ANPC inverter described in any one of the above are implemented.

[0015] Since the switching tubes of the ANPC inverter of the present invention all use SiC MOSFETs, which have the characteristics of bidirectional conduction, high voltage resistance, and low loss, it can support a more flexible hybrid modulation strategy, breaking through the limitation that the traditional ANPC inverter cannot achieve complex modulation methods due to the unidirectional conduction characteristics of the switching tubes, and expanding the modulation freedom; since the present invention dynamically adjusts the mixing ratio coefficient through the power losses of each switching tube in the first modulation mode and the second modulation mode respectively, it can balance the loss distribution of the two switching tubes in the same bridge arm in real time, avoid a single device becoming the life bottleneck of the inverter due to local overheating, and effectively extend the service life of the entire inverter. Description of the Drawings

[0016] Figure 1 is a schematic circuit structure diagram of the ANPC inverter of the present invention; Figure 2 is a schematic flowchart of an embodiment of the life optimization method for the ANPC inverter provided by an embodiment of the present invention; Figure 3 is a schematic flowchart of another embodiment of the life optimization method for the ANPC inverter provided by an embodiment of the present invention; Figure 4 is a schematic flowchart of still another embodiment of the life optimization method for the ANPC inverter provided by an embodiment of the present invention. Detailed Embodiments

[0017] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] Briefly describe the distinguishing features between the present invention and the prior art, and these distinguishing features constitute the inventive points of the present invention. In the NAPC inverter, the present invention uses a full SiC MOSFET topology and an adaptive hybrid modulation strategy to balance the losses of each switching tube, solving the core problems of uneven loss distribution and limited lifespan in traditional ANPC inverters, and significantly extending the service life of the inverter and improving the reliability of the inverter.

[0019] The present invention provides a method for optimizing the lifespan of an ANPC inverter. Refer to Figure 1 As shown, the ANPC inverter includes an upper arm composed of a series connection of a first switching tube T1 and a second switching tube T2, a lower arm composed of a series connection of a third switching tube T3 and a fourth switching tube T4, and a clamping arm composed of a series connection of a fifth switching tube T5 and a sixth switching tube T6; wherein, after the upper arm and the lower arm are connected in series, they are connected between the positive pole DC+ and the negative pole DC- of the DC bus, the clamping arm is connected between the middle node of the upper arm and the middle node of the lower arm, the middle node of the clamping arm is connected to the neutral point NP, and the common node of the upper arm and the lower arm is connected to the AC output terminal AC.

[0020] The common end of the first switching tube T1 and the second switching tube T2 is the middle node of the upper arm, the common end of the third switching tube T3 and the fourth switching tube T4 is the middle node of the lower arm, the common end of the fifth switching tube T5 and the sixth switching tube T6 is the middle node of the clamping arm, and the common end of the second switching tube T2 and the third switching tube T3 is the common node of the upper arm and the lower arm. And the first switching tube T1 and the second switching tube T2 are located on the same arm, the third switching tube T3 and the fourth switching tube T4 are located on the same arm, and the fifth switching tube T5 and the sixth switching tube T6 are located on the same arm; wherein, the first switching tube T1 and the fourth switching tube T4 are complementary switching pairs, the second switching tube T2 and the third switching tube T3 are complementary switching pairs, and the fifth switching tube T5 and the sixth switching tube T6 are complementary switching pairs. Complementary switching pairs have opposite states under normal circumstances, but sometimes they can be turned off simultaneously, for example, during the dead time. And the switching tubes T1, T2, T5 and the switching tubes T3, T4, T6 have symmetry, and during the operation of the inverter, the losses of the switching tubes T1, T2, T5 and the switching tubes T3, T4, T6 are the same.

[0021] In this embodiment, the first switch tube T1 to the sixth switch tube T6 are all SiC MOSFETs. The two-way conduction characteristic and low-loss characteristic of the SiC MOSFET are utilized in combination with the hybrid modulation strategy to optimize the service life of the ANPC inverter.

[0022] Embodiment 1 Referring to Figure 2 , based on the above topological structure of the ANPC inverter, the method for optimizing the life of the ANPC inverter provided by the present invention includes the following steps: Step S1, calculate the power loss of each switch tube under the first modulation method and the power loss of each switch tube under the second modulation method respectively; The first modulation method and the second modulation method are preset in the system. The first modulation method is the PWMA modulation method. Under the PWMA modulation method, the first switch tube T1 and the fourth switch tube T4 have high-frequency switching in the positive half cycle, and the second switch tube T2 and the third switch tube T3 operate with low loss. The second modulation method is the PWMB modulation method. Under the PWMB modulation method, the second switch tube T2 and the third switch tube T3 have high-frequency switching in the full cycle, and the first switch tube T1 and the fourth switch tube T4 operate with low loss. The power loss refers to the energy loss of the switch tube SiC MOSFET in the switching and conduction states. During the operation of the inverter, according to the operating condition parameters of the inverter, combined with the preset switching loss model and conduction loss model, the power loss of each switch tube under different modulation methods can be calculated; or the fitting of the PLECS software can be used to simulate the loss of the power device. In other embodiments, the first modulation method can also be set as the PWMB modulation method, and the second modulation method can be set as the PWMD modulation method. Among them, the PWMD modulation method focuses on dynamically allocating the conduction loss and the switching loss by controlling the conduction timing and state of the switch tube. Therefore, the loss rate of each switch tube can also be balanced through the hybrid modulation of PWMB and PWMD. For example, the losses of the first switch tube T1 and the second switch tube T2 can reach the optimal balance state.

[0023] In a specific embodiment, step S1 includes: Step S11, collect the operating condition parameters of the inverter under the first modulation method and the second modulation method respectively; Step S12, based on the conduction loss model and the switching loss model, calculate the conduction loss and the switching loss of each switch tube respectively according to the operating condition parameters under the first modulation method; Step S13, use the sum of the conduction loss and the switching loss of each switch tube as the power loss of each switch tube under the first modulation method; Step S14, based on the conduction loss model and the switching loss model, calculate the conduction loss and the switching loss of each switch tube respectively according to the operating condition parameters under the second modulation method; Step S15: Use the sum of the conduction loss and switching loss of each switching device as the power loss of each switching device in the second modulation mode.

[0024] In this embodiment, the operating conditions parameters of the inverter include but are not limited to the DC bus voltage Udc, modulation index m, output current I, switching frequency f sw , the switching device case temperature Tc, power factor cosφ, and drain-source supply voltage Vref. The DC bus voltage Udc and output current I can be collected in real time by a Hall sensor, and the switching frequency f can be obtained through the built-in timer of the controller sw , and the modulation index m is calculated according to the sine wave amplitude and triangular wave amplitude. The switching device case temperature Tc can be obtained through a temperature sensor such as a thermistor. The conduction loss model , where R ds is the on-resistance of the SiC MOSFET, θ is the phase angle, θ = 2*π*f, and Vo is the knee voltage of the SiC MOSFET. Usually, the knee voltage of the SiC MOSFET is 0. Therefore, the conduction loss model can be simplified to . The switching loss model ; where a sw , b sw and c sw are switching loss fitting coefficients, which can be obtained by fitting based on experimental data or parameters in the device data sheet.

[0025] The conduction loss refers to the energy loss generated when the switching device is in the on state and the current flows through the device. The switching loss refers to the instantaneous power loss caused by the overlap of voltage and current during the turn-on and turn-off processes of the switching device. In this embodiment, the operating conditions parameters of the inverter in the first modulation mode are collected, and the conduction loss and switching loss of each switching device in the first modulation mode are calculated respectively by combining the preset conduction loss model and switching loss model, and then the sum of the conduction loss and switching loss of each switching device is calculated. Use the sum of the conduction loss and switching loss of each switching device as the power loss of each switching device in the first modulation mode. Similarly, collect the operating conditions parameters of the inverter in the second modulation mode, and calculate the conduction loss and switching loss of each switching device in the second modulation mode respectively by combining the preset conduction loss model and switching loss model, and then calculate the sum of the conduction loss and switching loss of each switching device, and use the sum of the conduction loss and switching loss as the power loss of each switching device in the second modulation mode.

[0026] Step S2: Calculate the mixing ratio coefficient of the first modulation mode in the sine cycle according to the power loss of each of the switching devices; The sine period refers to the fundamental wave period of the alternating current output by the inverter; the mixing ratio coefficient represents the proportion of the operation duration of the first modulation method in the full sine period, which is represented by x in this embodiment. It can be understood that x represents the proportion of the operation duration of the first modulation method in the full sine period, and 1 - x represents the proportion of the operation duration of the second modulation method in the full sine period. The mixing ratio coefficient can be calculated based on a preset loss balancing equation according to the power losses of each switching tube, and then the hybrid modulation strategy within the full sine period can be determined according to the mixing ratio coefficient, so as to achieve the purpose of balancing the power losses of each switching tube, such as reducing the loss of the switching tube with the maximum stress.

[0027] In a specific embodiment, step S2 includes: Step S21, establish a loss balancing equation with the goal of making the power losses of two switching tubes in the same bridge arm tend to be balanced; Step S22, substitute the power losses of two switching tubes in the same bridge arm into the loss balancing equation; where the loss balancing equation is a * x + c * (1 - x) = b * x + d * (1 - x); a is the power loss of one of the two switching tubes in the same bridge arm under the first modulation method, b is the power loss of the other switching tube under the first modulation method, c is the power loss of one of the switching tubes under the second modulation method, d is the power loss of the other switching tube under the second modulation method, and x is the mixing ratio coefficient of the first modulation method in the sine period; Step S23, solve the loss balancing equation to obtain the mixing ratio coefficient of the first modulation method in the sine period.

[0028] In practical applications, under the PWMA modulation method, the first switching tube T1 has a high - frequency switching frequency and conduction loss in the positive half - cycle, resulting in the largest power loss and the highest junction temperature of the first switching tube T1 under the PWMA modulation method, which affects the service life of the entire inverter; similarly, under the PWMB modulation method, the second switching tube T2 has switching losses and conduction losses throughout the full sine period, resulting in the largest power loss and the highest junction temperature of the second switching tube T2 under the PWMB modulation method, which affects the service life of the entire inverter; while the fifth switching tube T5 has little loss under any modulation method. It can be understood that since the switching tubes T1, T2, T5 and the switching tubes T3, T4, T6 are symmetric, the above analysis also applies to the switching tubes T3, T4, T6.

[0029] To optimize the lifespan of the inverter, avoid the failure of a certain switching device due to long-term high losses, which may affect the service life of the inverter. Referring to the bucket principle, i.e., the short board effect, a loss balance equation is established with the goal of balancing the power losses of the two switching devices in the same bridge arm. Substitute the power losses of the two switching devices in the same bridge arm under different modulation methods into the loss balance equation to solve for the optimal mixing ratio coefficient. Among them, the loss balance equation is a*x + c*(1 - x) = b*x + d*(1 - x); a is the power loss of one of the two switching devices in the same bridge arm under the first modulation method, b is the power loss of the other switching device under the first modulation method, c is the power loss of one of the switching devices under the second modulation method, d is the power loss of the other switching device under the second modulation method, and x is the mixing ratio coefficient of the first modulation method in the sine period; taking the upper bridge arm as an example, a is the power loss of the second switching device T2 under the PWMA modulation method, b is the power loss of the first switching device T1 under the PWMA modulation method, c is the power loss of the second switching device T2 under the PWMB modulation method, and d is the power loss of the first switching device T1 under the PWMB modulation method. Taking the lower bridge arm as an example, a is the power loss of the third switching device T3 under the PWMA modulation method, b is the power loss of the fourth switching device T4 under the PWMA modulation method, c is the power loss of the third switching device T3 under the PWMB modulation method, and d is the power loss of the fourth switching device T4 under the PWMB modulation method.

[0030] By solving the loss balance equation, the expression of the mixing ratio coefficient is obtained. Substitute the power losses of the two switching devices in the same bridge arm under different modulation methods into the expression of the mixing ratio coefficient to calculate the mixing ratio coefficient. For example, substitute the power losses of the first switching device T1 and the second switching device T2 under different modulation methods into the expression to calculate the mixing ratio coefficient x; or, substitute the power losses of the third switching device T3 and the fourth switching device T4 under different modulation methods into the expression to calculate the mixing ratio coefficient x.

[0031] Step S3, control each of the switching devices to operate the first modulation method and / or the second modulation method within the sine period according to the mixing ratio coefficient.

[0032] According to the determined mixing ratio coefficient, dynamically allocate the operation duration of the two modulation methods within the sine period to achieve the loss balance of the switching devices in the same bridge arm, thereby extending the overall lifespan of the ANPC inverter.

[0033] Specifically, in one embodiment, step S3 includes: Step S31, determine the interval where the mixing ratio coefficient x is located; Step S32: When x > 1, control each of the switching tubes to operate in the first modulation mode within the full sine period; Step S33: When x < 0, control each of the switching tubes to operate in the second modulation mode within the full sine period; Step S34: When 0 ≤ x ≤ 1, control each of the switching tubes to alternately operate in the first modulation mode and the second modulation mode within the sine period according to the ratio of x:(1 - x).

[0034] After calculating the hybrid ratio coefficient x based on the power loss of the switching tubes, the modulation method required at the current moment is determined according to the interval where the hybrid ratio coefficient is located. Specifically: when x > 1, control each switching tube to operate in the first modulation method, that is, the PWMA modulation method, within the full sine period to achieve concentrated loss optimization and ensure stability. For example, reduce the loss of the second switching tube T2, extend the life of the second switching tube T2, and avoid introducing additional stress due to hybrid modulation. When x < 0, control each switching tube to operate in the second modulation method, that is, the PWMB modulation method, within the full sine period to optimize the loss distribution and improve the dynamic response ability of the system. For example, avoid the junction temperature of the first switching tube T1 being too high, optimize the loss distribution, and improve the dynamic response ability of the system. If 0 ≤ x ≤ 1, control each switching tube to alternately operate the first modulation method and the second modulation method within the sine period according to the running time ratio of x:(1 - x). For example, if x = 0.6, then within the entire sine period, the PWMA modulation method is used for 60% of the sine period, and the PWMB modulation method is used for 40% of the sine period. By mixing and operating the PWMA modulation method and the PWMB modulation method in proportion within the full sine period, the losses of the two switching tubes in the same bridge arm are dynamically balanced, and a single switching tube is prevented from becoming the short board of the life. The switching tubes of the ANPC inverter of the present invention adopt SiC MOSFETs, and utilize the high breakdown voltage characteristics and bidirectional conduction characteristics of SiC MOSFETs, combined with an adaptive hybrid modulation method to achieve the purpose of loss balance, life extension and reliability improvement of each switching tube. In other embodiments, PWMB and PWMD can also be used as the first modulation method and the second modulation method respectively. Further, based on the rainflow counting method, the CIP08 model (Coffin-Manson model) and Miner's rule, the fatigue life of the switching tube under the maximum stress can be systematically estimated in different modulation methods. Among them, the rainflow counting method is used to extract the stress cycle characteristics of the switching tube under actual working conditions and quantify its fatigue damage; the CIP08 model combines the junction temperature fluctuation of the switching tube and material characteristics to calculate the thermomechanical fatigue life; Miner's rule can linearly accumulate the damage theory to comprehensively accumulate the damage under multi-level stress and predict the final life of the switching tube. It can be known from the rainflow counting method, the CIP08 model and Miner's rule that the life distribution of the switching tube usually shows the characteristics of a lognormal distribution. After a large number of simulation calculations, the median life interval, such as 35 years, is used as the core life characterization of the switching tube. And the Monte Carlo model can be used to simulate the parameter dispersion and working condition fluctuation of the switching tube through random sampling, and statistically calculate the failure probability of the switching tube under different modulation methods.Based on the above verification results, it can be seen that a single modulation method such as PWMA has a system failure probability of approximately 2% within 15 - 20 years. While dynamically mixing the two modulation methods of PWMA and PWMB within the sine period, by equalizing the power losses and junction temperature distributions of the two switching tubes in the same bridge arm, the median life is extended to more than 50 years. And Monte Carlo analysis shows that the failure probability density curve under the hybrid modulation method is flatter, and the dispersion of the system failure time increases, further verifying its optimization of the overall life and reliability of the inverter. That is, through the dual verification of experiments and simulations, the reliability and effectiveness of the technical solution are ensured.

[0035] The switching tubes of the ANPC inverter of the present invention all adopt SiC MOSFETs, which have the characteristics of bidirectional conduction, high voltage resistance and low loss, and can support more flexible hybrid modulation strategies, breaking through the limitation that traditional ANPC inverters cannot achieve complex modulation methods due to the unidirectional conduction characteristics of the switching tubes, and expanding the modulation freedom. And the present invention can dynamically adjust the hybrid ratio coefficient through the power losses of each switching tube under the first modulation method and the second modulation method, and can evenly balance the loss distributions of the two switching tubes in the same bridge arm in real time, avoiding a single device from becoming the life bottleneck of the inverter due to local overheating, and effectively extending the service life of the entire inverter.

[0036] Embodiment 2 Refer to Figure 3 , in a specific embodiment, after step S3, it further includes: Step S4, obtaining the junction temperature of each switching tube in real time; The junction temperature refers to the temperature of the internal chip of each switching tube in the PN junction region, which is a core parameter for measuring the working state and reliability of the switching tube. The junction temperature of each switching tube can be calculated through a thermal model such as the Cauer thermal model or the Foster thermal model, or the junction temperature of each switching tube can be obtained in real time through a preset mapping relationship between the shell temperature and the junction temperature of the switching tube.

[0037] In a specific embodiment, step S4 includes Step S41, collecting the shell temperature of each switching tube in real time; Step S42, based on the Foster thermal model, obtaining the junction temperature of each switching tube according to the shell temperature of each switching tube.

[0038] Temperature sensors can be installed on the heat sink or chip attachment of each switching tube to collect the shell temperature of each switching tube in real time. The Foster thermal model is: , and , because, the thermal model can be simplified to , the is the thermal impedance of the Foster thermal model, T j is the junction temperature, Tc is the case temperature, P in is the input loss, R i is the thermal resistance, C i is the heat capacity, f i is the input frequency, and τ is the time constant. Substitute the collected case temperatures of each switching device into the Foster thermal model to solve for the junction temperature of each switching device.

[0039] Step S5, calculate the difference in junction temperature between the two switching devices located in the same bridge arm for each switching device; Step S6, determine whether the difference in junction temperature is greater than a preset junction temperature threshold; Step S7, when the difference in junction temperature is greater than the preset junction temperature threshold, adjust the mixing ratio coefficient.

[0040] Calculate the difference in junction temperature between the two switching devices in the same bridge arm respectively. For example, the difference in junction temperature between the first switching device T1 and the second switching device T2, or the difference in junction temperature between the third switching device T3 and the fourth switching device T4. Further, the temperature difference calculation period can be set according to the switching frequency. For example, it is updated every 1 ms. The preset junction temperature threshold can be determined according to the thermal fatigue characteristics of the SiC MOSFET (such as the curve of the influence of junction temperature fluctuation on the life) and the system reliability. For example, 10 °C is used as the junction temperature threshold. When the difference in junction temperature between the two switching devices in the same bridge arm is greater than the preset junction temperature threshold, adjust the mixing ratio coefficient x. Dynamically adjust the modulation strategy by adjusting the mixing ratio coefficient. For example, if the junction temperature of the first switching device T1 is significantly higher than that of the second switching device T2, then reduce the proportion of the running time of the PWMA modulation method and increase the proportion of the running time of the PWMB modulation method to reduce the junction temperature of the first switching device T1. In this embodiment, the mixing ratio coefficient x is dynamically adjusted according to the difference in junction temperature, and the modulation method is dynamically optimized through the real-time difference in junction temperature, solving the pain point of uneven loss distribution in traditional ANPC inverters and achieving double optimization of the inverter life and reliability.

[0041] Embodiment III Refer to Figure 4 , in a specific embodiment, after step S4, it further includes Step S8, estimate the service life of each switching device based on the rainflow counting method, the CIP08 model, and the Miner's rule; Step S9, predict the failure probability of each switching device based on the Monte Carlo model; Step S10, optimize the mixing ratio coefficient according to the service life and the failure probability.

[0042] Based on the rainflow counting method, the CIP08 model (Coffin-Manson model), and the Miner's rule, the fatigue life of the switching device under the maximum stress in the hybrid modulation mode can be systematically estimated in this embodiment. The Monte Carlo model is used to simulate the parameter dispersion and operating condition fluctuations of the power switching device through random sampling, and the failure probability of the switching device in the hybrid modulation mode is statistically analyzed. The hybrid ratio coefficient is optimized according to the fatigue life and failure probability of the switching device, that is, the hybrid ratio coefficient is optimized based on the quantitative data of the fatigue life and random failure risk of the switching device, so as to further ensure that the adjustment of the hybrid ratio coefficient can not only extend the service life of the inverter, but also suppress the failure risk.

[0043] The present invention also provides a device for optimizing the life of an ANPC inverter. The device for optimizing the life of an ANPC inverter includes: a memory, a processor, and an ANPC inverter life optimization program stored on the memory and executable on the processor. When the ANPC inverter life optimization program is executed by the processor, the steps of the ANPC inverter life optimization method described in any one of the above are implemented.

[0044] The present invention also provides a computer-readable storage medium. An ANPC inverter life optimization program is stored on the computer-readable storage medium. When the ANPC inverter life optimization program is executed by a processor, the steps of the ANPC inverter life optimization method described in any one of the above are implemented.

[0045] The above are only optional embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the description and drawings of the present invention under the inventive concept of the present invention, or any direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for optimizing the lifespan of an ANPC inverter, characterized in that, The ANPC inverter includes: an upper arm composed of a first switch tube and a second switch tube connected in series, a lower arm composed of a third switch tube and a fourth switch tube connected in series, and a clamping arm composed of a fifth switch tube and a sixth switch tube connected in series; the upper arm and the lower arm are connected in series between the positive and negative poles of the DC bus, the clamping arm is connected between the middle node of the upper arm and the middle node of the lower arm, the middle node of the clamping arm is connected to the neutral point, and the common node of the upper arm and the lower arm is connected to the AC output terminal; wherein, the first to sixth switch tubes are all SiC MOSFETs; the method for optimizing the lifespan of the ANPC inverter includes the following steps: Calculate the power losses of each switch tube under the first modulation mode and the power losses of each switch tube under the second modulation mode respectively; Calculate the mixing ratio coefficient of the first modulation mode in the sine period according to the power losses of each switch tube; Control each switch tube to operate in the first modulation mode and / or the second modulation mode within the sine period according to the mixing ratio coefficient.

2. The method for optimizing the lifespan of the ANPC inverter according to claim 1, characterized in that The step of calculating the power losses of each switch tube under the first modulation mode and the power losses of each switch tube under the second modulation mode respectively includes: Collect the operating condition parameters of the inverter under the first modulation mode and the second modulation mode respectively; Based on the conduction loss model and the switching loss model, calculate the conduction loss and switching loss of each switch tube respectively according to the operating condition parameters under the first modulation mode; Take the sum of the conduction loss and switching loss of each switch tube as the power loss of each switch tube under the first modulation mode; Based on the conduction loss model and the switching loss model, calculate the conduction loss and switching loss of each switch tube respectively according to the operating condition parameters under the second modulation mode; Take the sum of the conduction loss and switching loss of each switch tube as the power loss of each switch tube under the second modulation mode.

3. The lifespan optimization method of the ANPC inverter according to claim 1, characterized in that, The step of calculating the mixing ratio coefficient of the first modulation mode in the sine period according to the power losses of each switch tube includes: Establish a loss balance equation with the goal of making the power losses of two switch tubes in the same arm tend to be balanced; Substitute the power losses of two switch tubes in the same arm into the loss balance equation; wherein, the loss balance equation is a*x + c*(1 - x) = b*x + d*(1 - x); a is the power loss of one of the two switch tubes in the same arm under the first modulation mode, b is the power loss of the other switch tube under the first modulation mode, c is the power loss of one of the switch tubes under the second modulation mode, d is the power loss of the other switch tube under the second modulation mode, and x is the mixing ratio coefficient of the first modulation mode in the sine period; Solve the loss balance equation to obtain the mixing ratio coefficient of the first modulation mode in the sine period.

4. The method for optimizing the lifespan of the ANPC inverter according to claim 3, wherein, The step of controlling each switch tube to operate in the first modulation mode and / or the second modulation mode within the sine period according to the mixing ratio coefficient includes: Determine the interval in which the mixing ratio coefficient x lies; When x > 1, control each of the switching tubes to operate in the first modulation mode within the full sine period; When x < 0, control each of the switching tubes to operate in the second modulation mode within the full sine period; When 0 ≤ x ≤ 1, control each of the switching tubes to alternately operate in the first modulation mode and the second modulation mode within the sine period according to the ratio of x:(1 - x).

5. The method for optimizing the lifespan of the ANPC inverter according to claim 1, wherein, After the step of controlling each of the switching tubes to operate in the first modulation mode and / or the second modulation mode within the sine period according to the mixing ratio coefficient, the method further includes: Obtain the junction temperature of each switching tube in real time; Calculate the junction temperature difference between two switching tubes located in the same bridge arm in each switching tube respectively; Determine whether the junction temperature difference is greater than a preset junction temperature threshold; When the junction temperature difference is greater than the preset junction temperature threshold, adjust the mixing ratio coefficient.

6. The method for optimizing the lifespan of the ANPC inverter according to claim 5, characterized in that, The step of obtaining the junction temperature of each switching tube in real time includes: Collect the shell temperature of each switching tube in real time; Based on the Foster thermal model, obtain the junction temperature of each switching tube according to the shell temperature of each switching tube.

7. The method for optimizing the lifespan of the ANPC inverter according to any one of claims 1 to 6, characterized in that After the step of controlling each of the switching tubes to operate in the first modulation mode and / or the second modulation mode within the sine period according to the mixing ratio coefficient, the method further includes: Estimate the service life of each switching tube based on the rainflow counting method, the CIP08 model, and the Miner rule; Predict the failure probability of each switching tube based on the Monte Carlo model; Optimize the mixing ratio coefficient according to the service life and the failure probability.

8. A life optimization device for an ANPC inverter, characterized in that, The life optimization device of the ANPC inverter includes: a memory, a processor, and a life optimization program of the ANPC inverter stored on the memory and executable on the processor. When the life optimization program of the ANPC inverter is executed by the processor, the steps of the life optimization method of the ANPC inverter according to any one of claims 1 to 7 are implemented.

9. A storage medium, characterized in that, A life optimization program of the ANPC inverter is stored on the storage medium. When the life optimization program of the ANPC inverter is executed by the processor, the steps of the life optimization method of the ANPC inverter according to any one of claims 1 to 7 are implemented.

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