A T-type three-level inverter aging state online monitoring method

Abstract

The application discloses a kind of T type three-level inverter aging state online monitoring method, belong to power electronics technical field, comprising the following steps: S1, construct the inverter mathematical model based on switching state;S2, carry out the synchronous acquisition of multiple physical quantity data;S3, calculate on-resistance by active voltage vector method;S4, measure on-resistance in real time by in-situ monitoring method;S5, carry out the weighted fusion of on-resistance multi-source data.The application adopts the above-mentioned T type three-level inverter aging state online monitoring method, integrates the respective advantages of active voltage vector monitoring and in-situ monitoring two methods, by fusing multiple physical quantity measurement information and operating state data, constructs aging feature extraction model with fault-tolerant check mechanism, can break through the precision bottleneck of traditional single data source monitoring method, real-time, accurately monitor the change of power device on-resistance, assess its aging state, provide basis for system maintenance.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an online monitoring method for the aging state of a T-type three-level inverter. Background Art

[0002] In existing technologies, the T-type three-level inverter, a typical example of a multilevel converter, is widely used in renewable energy power generation systems, high-power motor drives, and electric vehicle powertrains due to its high efficiency, low harmonic output, and excellent voltage stress characteristics. However, the power semiconductor devices (IGBTs, MOSFETs, etc.), core components of the inverter, can age and fail over time due to thermomechanical stress and electromigration effects, leading to drift in key parameters such as on-resistance. This aging significantly increases the conduction losses of these devices, and the resulting abnormally high junction temperature reduces system reliability.

[0003] Currently, there are three main approaches to power device aging monitoring: First, offline monitoring based on sensor networks uses external current / voltage / temperature sensors to acquire parameters. While this approach offers high measurement accuracy, it requires hardware modifications to the original circuit, increasing system complexity and economic costs. Second, lifetime prediction methods based on reliability models estimate remaining lifetime by establishing a physical failure model. However, due to the complexity of device degradation mechanisms and the time-varying nature of operating conditions, these methods suffer from the inherent flaw of insufficient model generalization. Third, direct monitoring methods based on electrical and thermal characteristic parameters assess the device's state by online extraction of characteristic quantities such as on-resistance and threshold voltage. Research results show that under the effects of power cycling and thermal cycling, the on-resistance of power devices can exhibit significant drift of 3% to 20%. This variation is much greater than the on-voltage drop and exhibits a strong linear correlation with the degree of aging, making it the optimal characteristic parameter for characterizing device degradation.

[0004] However, existing monitoring methods still face significant technical bottlenecks: monitoring schemes based on single-sensor data are susceptible to interference from operating conditions such as load fluctuations and temperature changes, resulting in increased errors in feature extraction; methods based on parameter identification require accurate device models, and model parameter mismatch is difficult to avoid in practical applications; and data-driven methods can circumvent modeling difficulties, but they require massive fault sample support and are costly to implement. These issues severely restrict the application of online monitoring technology, especially in application scenarios such as offshore wind power generation and aircraft motor drives, where operating conditions are complex and reliability requirements are stringent. Accuracy, reliability, and engineering applicability are several important indicators for evaluating system aging status monitoring methods.

[0005] Therefore, there is an urgent need for a solution that can integrate multi-source measurement data to improve the accuracy of aging status monitoring for T-type three-level inverters and enhance the fault tolerance of online monitoring technology. This invention addresses this need and discloses a method for online aging status monitoring of T-type three-level inverters based on multi-source data fusion. Summary of the Invention

[0006] The purpose of the present invention is to provide an online monitoring method for the aging status of a T-type three-level inverter, which can break through the accuracy bottleneck of the traditional single data source monitoring method, monitor the on-resistance changes of power devices in real time and accurately, evaluate their aging status, and provide a basis for system maintenance.

[0007] To achieve the above object, the present invention provides a method for online monitoring of the aging status of a T-type three-level inverter, comprising the following steps:

[0008] S1. Construct a mathematical model of the inverter based on the switching state;

[0009] S2. Synchronous acquisition of multiple physical quantity data;

[0010] S3. Calculate the on-resistance by the active voltage vector method;

[0011] S4, measuring the on-resistance in real time by in-situ monitoring method;

[0012] S5. Perform weighted fusion of multi-source on-resistance data.

[0013] Preferably, in S1, according to the topological structure characteristics of the T-type three-level inverter, an accurate mapping relationship between the switching state and the output voltage is established; the three-phase bridge arm switching function is defined as ， , whose value range is {1, 0, -1}, corresponding to: , then the upper bridge arm of this phase is turned on and outputs P level, + V dc / 2; if , then the bridge arm at the midpoint of the phase is turned on and the output is O level, 0; if , then the lower bridge arm of this phase is turned on and outputs N level, - V dc / 2;

[0014] The mathematical expression of the output voltage on the three-phase AC side is obtained as follows:

[0015] ;

[0016] in, V dc is the DC bus voltage, is the three-phase AC side output voltage;

[0017] The synthetic space vector expression of the output voltage of the T-type three-level inverter is:

[0018] ;

[0019] Where, is the synthetic space vector of the output voltage of the T-type three-level inverter. The specific value of the synthetic space vector is related to the three-phase bridge arm switching function. S a 、 S b 、 S c There are 27 combinations related to .

[0020] Preferably, the synthetic space vector presents a regular hexagonal structure in space, including 19 basic voltage vectors, namely: 6 large vectors, whose amplitude is , each large vector uniquely corresponds to one switching state; 6 medium vectors, whose amplitude is , each middle vector uniquely corresponds to one switching state; 6 small vectors, whose amplitude is , each small vector corresponds to 2 redundant switching states; 1 zero vector, its amplitude is 0, each zero vector corresponds to 3 switching states; the switching state is represented by the combination of bridge arm output levels P, O, and N.

[0021] Preferably, in S2, the following measurement data are obtained in real time through the voltage / current sensor network of the T-type three-level inverter: DC bus voltage V dc , three-phase load current and , load line voltage V ab 、 V bc After being processed by the isolation conditioning circuit, all signals are synchronously input into the controller at the same sampling rate to construct a time-aligned multi-dimensional data matrix.

[0022] Preferably, in S3, based on the transformation relationship between the three-phase stationary coordinate system and the two-phase rotating coordinate system, a two-phase rotating coordinate coefficient mathematical calculation model of the T-type three-level inverter power device is constructed:

[0023] Clarke transformation is used to convert the measured load line voltage into α - β The voltage vector in the coordinate system, the Clarke transformation formula is:

[0024] ;

[0025] in, V ab 、V bc They are the load side ab phase line voltage and bc phase line voltage respectively; V α 、 V β They are α - β Load line voltage in the coordinate system α axis, β Axis component;

[0026] In different switch states, V α 、 V β The value of is different, further introducing To represent vector Under the influence α - β Load voltage in the coordinate system α axis, β Axis components, where ; Vector and switch status ( , S b , S c ) have a one-to-one correspondence.

[0027] Preferably, define and are the on-state voltages of the power devices of phase a, phase b, and phase c, respectively. and is the number of the three-phase switch device that is turned on corresponding to the vector state, ; 23 represents the switching device T x2 and T x3 ; 、 V ob and V oc Respectively represent the load voltages of phase a, phase b, and phase c including on-resistance; and They represent the load voltages of phases a, b, and c, excluding on-resistance, as follows:

[0028] ;

[0029] Use Clarke transformation to transform the abc coordinate system and Convert to α - β In the coordinate system, we get and :

[0030] ;

[0031] The power device conduction voltage and Substituting it into the product of on-resistance and load current, we get:

[0032] ;

[0033] in, and Represents the on-resistance of the switching devices of phase a, phase b and phase c respectively. or When the value is 1 or 4, it represents the on-resistance of a single switch 1 or 4. When the value is 23, it represents the on-resistance of the two switches 2 and 3 in series. All represent load current, the subscript Indicates the voltage vector number of the load current measured by the sensor at the current moment. The letter part indicates the current current flowing through the power device. Phase load current, ;

[0034] Infer the circuit connection mode under each switching state and obtain the corresponding mathematical expression between the voltage vector, on-resistance and load current;

[0035] Combine the mathematical expressions of different switch states to solve the on-resistance of the power device and get and The values ​​are:

[0036] ;

[0037] The subscript part and All are vector state numbers. .

[0038] Preferably, in S4, a measurement circuit is added near the power device for monitoring, and the measurement circuit consists of two parts: a clamping circuit and a parameter acquisition circuit; the clamping circuit includes: Schottky diodes D1 and D2, a voltage regulator diode DZ2, a current limiting resistor R, a capacitor C and a DC voltage source; the parameter acquisition circuit includes: differential operational amplifiers OP1 and OP2;

[0039] The on-state current is indirectly obtained by connecting a precision sampling resistor in series with the power device. The on-state voltage drop is divided by the on-state current to obtain the on-state resistance of the power device to be measured.

[0040] Preferably, in S5, the on-resistance values ​​obtained by the active voltage vector method and the in-situ monitoring method are respectively recorded asR 1. R 2. The calculation formula is as follows:

[0041] ;

[0042] in, σ 1 and σ 2 are random errors of the resistance values ​​obtained. R 1 and R 2 are independent of each other, R 0 is the actual value of the resistor, assuming R Estimated value of 0 With the obtained value R 1 and R 2 is linearly related, and yes R The unbiased estimate of , then:

[0043] ;

[0044] in, is the weight coefficient of the values ​​obtained by the two methods:

[0045] ;

[0046] In the process of calculating with experimental data, it is assumed that the initial errors of each method are consistent, that is, the weight coefficient = =0.5; in actual operation, the R The values ​​are checked with the periodic test data and the weight coefficients of each method are revised;

[0047] Applying the data from the active voltage vector method and the in-situ monitoring method, the weighted fusion resistance value is:

[0048] ;

[0049] Where, and It is the mean square error calculated through prior knowledge or experimental data of the active voltage vector method and in-situ monitoring method.

[0050] Preferably, to prevent a sensor failure from causing the final resistance value R F Untrustworthy, the judgment formula is:

[0051] ;

[0052] in, R 0 is the rated on-resistance of the power device under test, is the actual allowable error;

[0053] Only when the criterion formula is established can the final resistance value be calculated using the weighted fusion of multi-source data R F Otherwise, when When the active voltage vector method is used to determine the resistance value R 1 is not credible, take ,Right now ;when When the resistance value obtained by the in-situ monitoring method is determined R 2 is not credible, take ,Right now ;in, R Fp It is the average on-resistance value calculated from the first n data windows. The initial value is R 0;

[0054] When the resistance value meets When the power device fails, it is judged that the power device fails and an alarm is issued, otherwise wait for the calculation of the next cycle.

[0055] Therefore, the beneficial effects of the above-mentioned online monitoring method for the aging state of a T-type three-level inverter adopted by the present invention are as follows:

[0056] (1) The present invention integrates system operating status data (load current, DC bus voltage, load voltage, switch status, etc.) with in-situ monitoring data of power device on-resistance to construct a high-precision aging feature extraction method with a redundant verification mechanism. This method effectively overcomes the defect that traditional single sensor data is easily disturbed by operating condition fluctuations, and improves the credibility and robustness of the monitoring results of the method.

[0057] (2) The present invention utilizes the inverter body sensors (load current sensor, DC bus voltage sensor, load voltage sensor) and the power device in-situ monitoring circuit as multi-source data input, eliminating the need for additional dedicated monitoring hardware and reducing hardware modification costs compared to traditional external sensor solutions.

[0058] (3) The present invention can update aging parameters online through multi-source data fusion, achieve early warning of the remaining life of the device, and support predictive maintenance.

[0059] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Schematic diagram of the online monitoring and control system for the aging state of a T-type three-level inverter in the present invention;

[0061] Figure 2is a synthetic space vector distribution diagram of the output voltage of the T-type three-level inverter in the present invention;

[0062] Figure 3 Schematic diagram of on-resistance monitoring based on active voltage vector method in the present invention;

[0063] Figure 4 Schematic diagram of the inverter and load connection state under the action of voltage vector V1(POO) in the present invention;

[0064] Figure 5 This is a wiring diagram of the in-situ monitoring method of the present invention;

[0065] Figure 6 Schematic diagram of the in-situ monitoring and measurement circuit in the present invention;

[0066] Figure 7 Schematic diagram of the weighted fusion algorithm for on-resistance multi-source data in the present invention;

[0067] Figure 8 The figure is a flow chart of the online monitoring method for the aging status of a T-type three-level inverter in the present invention.

[0068] Reference numerals

[0069] 1. DC voltage source; 2. T-type three-level inverter circuit; 3. Load; 4. Controller; 5. Aging status online monitoring module. DETAILED DESCRIPTION

[0070] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0071] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0072] Example 1

[0073] like Figure 1As shown, the present invention provides an online monitoring and control system for the aging status of a T-type three-level inverter. The system includes a DC voltage source 1, a T-type three-level inverter circuit 2, a load 3, a controller 4, and an online aging status monitoring module 5. The controller 4 is connected to the T-type three-level inverter circuit 2. It collects analog signals such as load current, DC bus voltage, and load voltage signals. After calculation, the controller 4 sends switching state instructions to the T-type three-level inverter circuit 2 using space vector pulse width modulation (SVPWM). The online aging status monitoring module 5 is connected to the T-type three-level inverter circuit 2 to read in-situ monitoring measurement data. The controller 4 is connected to the online aging status monitoring module 5 to read system operating status data (load current, DC bus voltage, load voltage, and switch status). Finally, the online aging status monitoring module 5 integrates multi-source data to provide highly accurate monitoring results.

[0074] The present invention also provides a method for online monitoring of the aging state of a T-type three-level inverter, comprising the following steps:

[0075] S1. Construct a mathematical model of the inverter based on the switching state.

[0076] According to the topological characteristics of the T-type three-level inverter, an accurate mapping relationship between the switching state and the output voltage is established. The three-phase bridge arm switching function is defined as , whose value range is {1, 0, -1}, corresponding to: , then the upper bridge arm of this phase is turned on and the output is P level (+ V dc / 2); if , then the bridge arm at the midpoint of the phase is turned on and the output is 0 level (0); if , then the lower bridge arm of this phase is turned on and outputs N level (- V dc / 2).

[0077] The mathematical expression of the output voltage on the three-phase AC side is obtained as follows:

[0078] (1);

[0079] in, V dc is the DC bus voltage, is the three-phase AC side output voltage.

[0080] The synthetic space vector expression of the output voltage of the T-type three-level inverter is:

[0081] (2);

[0082] Where, is the synthetic space vector of the output voltage of the T-type three-level inverter. The specific value of the synthetic space vector is related to the three-phase bridge arm switching function. S a 、 S b 、 S c The switching state of the T-type three-level inverter is actually a combination of switching functions (Sa, Sb, Sc), which has 27 possibilities, so there are 27 synthetic space vectors.

[0083] According to formula (2), we can generate Figure 2 The synthetic space vector distribution diagram of the output voltage of the T-type three-level inverter is shown in the figure. The synthetic space vector presents a regular hexagonal structure in space and contains 19 basic voltage vectors, namely: 6 large vectors with amplitudes of , each vector uniquely corresponds to one switching state; the 6 middle vectors have an amplitude of , each vector uniquely corresponds to one switching state; 6 small vectors, whose amplitude is , each vector corresponds to 2 redundant switching states; 1 zero vector, whose amplitude is 0, corresponds to 3 switching states. Therefore, the switching state is determined by the bridge arm output level P (+ V dc / 2)、O(0)、N(- V dc / 2) Combinatorial representation.

[0084] During the operation of the T-type three-level inverter, the controller selects the voltage vector to be output at the current moment according to the SVPWM principle to determine whether the power devices are turned on or off. It also converts the selected voltage vector into the corresponding switch state and submits it to the aging status online monitoring module 5 for on-resistance calculation. S2: Synchronous acquisition of multiple physical quantity data.

[0085] S2. Perform synchronous collection of multiple physical quantity data.

[0086] The following measurement data are obtained in real time through the voltage / current sensor network of the T-type three-level inverter: (1) DC bus voltage V dc ; (2) Three-phase load current 、 and ; (3) Load line voltage V ab 、 V bc .

[0087] After being processed by the isolation conditioning circuit, all signals are synchronously input into the controller at the same sampling rate to construct a time-aligned multi-dimensional data matrix.

[0088] S3. Calculate the on-resistance using the active voltage vector method.

[0089] like Figure 3 As shown, the aging status online monitoring module 5 reads the system operation status data (load current, DC bus voltage, load voltage, switch status) transmitted by the controller, combines different switch states with the corresponding current paths, and solves the real-time monitoring value of the on-resistance of the power device through the constraint relationship of Kirchhoff's voltage equation.

[0090] Based on the transformation relationship between the three-phase stationary coordinate system and the two-phase rotating coordinate system, a two-phase rotating coordinate coefficient mathematical calculation model of the T-type three-level inverter power device is constructed.

[0091] In this embodiment, Clarke transformation is used to convert the measured load line voltage into α - β The voltage vector in the coordinate system, the Clarke transformation formula is:

[0092] (3);

[0093] in, V ab 、 V bc They are the load side ab phase line voltage and bc phase line voltage respectively; V α 、 V β They are α - β Load line voltage in the coordinate system α axis, β Axis component. Here the load line voltage V ab 、 V bc Contains the on-resistance information of the power device, converted to α - β In the coordinate system V α 、 V β Naturally, it also includes the on-resistance information of the power device.

[0094] In different switch states, V α 、 V β The value of is different, so we further introduce 、 To represent vector The load voltage in the α-β coordinate system under the action of α axis,β Axis components, where .

[0095] Vector V i and switch status ( , S b , S c ) have a one-to-one correspondence, as follows: V 1 (1, 0, 0), V 2 (1, 0, -1), V 3 (1, -1, -1), V 4 (1, -1, 0), V 5 (1, -1, 1), V 6 (1, 0, 1), V 7 (1, 1, 1), V 8 (1, 1, 0), V 9 (1, 1, -1), V 10 (0, 1, -1), V 11 (0, 1, 0), V 12 (0, 1, 1), V 13 (0, 0, 1), V 14 (0, 0, 0), V 15 (0, 0, -1), V 16 (0, -1, -1), V 17 (0, -1, 0), V 18 (0, -1, 1), V 19 (-1, -1, 1), V 20 (-1, -1, 0), V 21 (-1, -1, -1), V 22 (-1, 0, -1), V 23 (-1, 0, 0), V 24 (-1, 0, 1), V 25 (-1, 1, 1), V 26 (-1, 1, 0), V27 (-1, 1, -1).

[0096] Basic Principles of Active Voltage Vectoring: Definition and are the on-state voltages of the power devices of phase a, phase b, and phase c, respectively. and is the number of the three-phase switch device that is turned on corresponding to the vector state, ; 23 represents the switching device T x2 and T x3 ; 、 V ob and V oc Respectively represent the load voltage of phase a, phase b and phase c including the on-resistance; and They represent the load voltages of phases a, b, and c, excluding on-resistance, as follows:

[0097] (4);

[0098] Use Clarke transformation to transform the abc coordinate system and Convert to α - β In the coordinate system, we get and :

[0099] (5);

[0100] The power device conduction voltage and Substituting it into the product of on-resistance and load current, we get:

[0101] (6);

[0102] in, and Represents the on-resistance of the switching devices of phase a, phase b and phase c respectively. or When the value is 1 or 4, it represents the on-resistance of a single switch 1 or 4. When the value is 23, it represents the on-resistance of the two switches 2 and 3 in series. All represent load current, the subscript Indicates the voltage vector number of the load current measured by the sensor at the current moment. The letter part indicates the current current flowing through the power device. Phase load current, .

[0103] Infer the circuit connection mode under each switching state and obtain the corresponding mathematical expression between the voltage vector, on-resistance and load current;

[0104] Combine the mathematical expressions of different switch states to solve the on-resistance of the power device and get and The values ​​are:

[0105] (7);

[0106] The subscript part and All are vector state numbers. .

[0107] like Figure 4 As shown, the switch state V Take 1 (1, 0, 0) as an example, V TA1 、 V TB2 、 V TB3 、 V TC2 and V TC3 They are power devices T A1 、T B2 、T B3 、T C2 and T C3 The on-state voltage; 、 V ob and V oc Respectively represent the load voltage of phase a, phase b and phase c including the on-resistance; V 1a 、 V 1b and V 1c They represent the load voltages of phases a, b, and c, excluding on-resistance, as follows:

[0108] (8);

[0109] Use Clarke transformation to transform the abc coordinate system V 1a 、 V 1b and V 1c Converted to the α-β coordinate system, we get V 1α and V 1β :

[0110] (9);

[0111] The power device conduction voltage V TA1 、 V TB2 、 V TB3 、 V TC2 and V TC3 Substituting it into the product of on-resistance and load current, we get:

[0112] (10);

[0113] in, R TA1 、 R TB23 and R TC23 Respectively represent T A1 Single tube, T B2 With T B3 Double tubes in series and T C2 With T C3 The on-resistance of two transistors in series. The subscript number indicates the load current. The subscript number indicates the voltage vector number of the load current measured by the sensor at the current moment. The letter indicates the current current flowing through the power device. Phase load current, .For example, Indicates V The a-phase load current measured under the action of vector 1 only flows through the power device T A1 .

[0114] The left side of equation (10) V 1α 、 V 1β By load line voltage V ab 、 V bc The DC bus voltage on the right is converted into V dc , and the load current and All the sensor data are collected synchronously, so the equation group (10) is also about the on-resistance R TA1 、 R TB23 and R TC23 A system of three linear equations.

[0115] According to the above method, the circuit connection mode in other switching states can be obtained in the same way, and the mathematical expressions between the corresponding voltage vector, on-resistance and load current can be obtained. By combining the mathematical expressions of multiple switching states, the on-resistance of the power device can be solved. For example, by analyzing the voltage vector V 1 and V 23 The circuit wiring can be obtained R TB23 and R TC23 The values ​​are:

[0116] (11);

[0117] in, and V 23β They are V 23 The load current and load line voltage of phase b and phase c under the action of vector β Axis component.

[0118] The on-resistances of the remaining power devices are calculated in the same way as above.

[0119] S4. Measure the on-resistance in real time through the in-situ monitoring method.

[0120] The wiring diagram of the in-situ monitoring method is as follows Figure 5 As shown in the figure, it is necessary to add a measurement circuit near the power device (take IGBT as an example) for monitoring.

[0121] The specific structure of the measurement circuit is as follows: Figure 6 As shown in Figure 1, the circuit consists of a clamping circuit and a parameter acquisition circuit. The clamping circuit includes Schottky diodes D1 and D2, a Zener diode DZ2, a current-limiting resistor R, a capacitor C, and a DC voltage source (+5V). The parameter acquisition circuit includes differential operational amplifiers OP1 and OP2.

[0122] The clamping circuit is responsible for clamping the high voltage when the IGBT is turned off; when the IGBT is turned on, only a low voltage is passed, that is, the conduction voltage drop V onThe Schottky diode D1 is connected to the collector of the IGBT, allowing current to flow only from the measurement circuit to the collector of the IGBT. The emitter of the IGBT is used as a reference: when the IGBT is turned off, the potential of its collector is higher than that of the emitter. At this time, the Schottky diode D1 is reverse biased and disconnects the collector from the measurement circuit; when the IGBT is turned on, the IGBT has a small potential difference between the collector and emitter. This potential difference causes the Schottky diode D1 to be forward biased, and the circuit completes the closed loop through the IGBT. The voltage at node 1 is the IGBT conduction voltage drop V on and the forward voltage drop of Schottky diode D1 V D Subtract the Schottky diode forward voltage drop from the absolute value of the voltage at node 1. V D Is the conduction voltage drop of the power device V on .

[0123] Generally, the forward voltage drop of a Schottky diode depends on the current flowing through it and the current junction temperature. Theoretically, if the current junction temperature is known, the forward voltage drop of a Schottky diode can be estimated; however, accurate and reliable junction temperature estimation is difficult in practical circuits. To overcome this problem, another Schottky diode, D3, with identical parameters, is connected in series after Schottky diode D1. Its position is close to D1, ensuring that they operate at similar junction temperatures. When the IGBT is on, the same current flows through D1 and D2, ensuring that D1 and D2 have the same forward voltage drop.

[0124] In the parameter acquisition circuit, the differential operational amplifier OP1 measures the forward voltage drop across the Schottky diode D3. The output voltage of OP1 is V D , which is also the voltage at node 2. The differential operational amplifier OP2 measures the voltage difference between node 1 and node 2. Based on the above analysis, the output voltage of OP2 (i.e. the voltage at node 3) is the conduction voltage drop of the power device under test. V on .

[0125] The on-state current can be indirectly obtained by connecting a precision sampling resistor in series with the emitter of the IGBT. The on-state voltage drop is divided by the on-state current to obtain the on-state resistance of the power device under test.

[0126] S5. Perform weighted fusion of multi-source on-resistance data.

[0127] The schematic diagram of the weighted data fusion algorithm is as follows Figure 7 As shown, the core idea is to minimize the total mean square error based on the measurement data obtained by each sensor. Find the corresponding optimal weighting factor Make the fused estimate Reach the best.

[0128] In this embodiment, the active voltage vector method and the in-situ monitoring method are respectively recorded as method 1 and method 2. The on-resistance values ​​obtained by method 1 and method 2 are respectively recorded as R 1. R 2. The calculation formula is as follows:

[0129] (12);

[0130] in, σ 1 and σ 2 are random errors of the resistance values ​​obtained. R 1 and R 2 are independent of each other, R 0 is the actual value of the resistor, assuming R Estimated value of 0 With the obtained value R 1 and R 2 is linearly related, and yes R The unbiased estimate of , then:

[0131] (13);

[0132] in, is the weight coefficient of the values ​​obtained by the two methods:

[0133] (14);

[0134] In the process of calculating with experimental data, it is assumed that the initial errors of each method are consistent, that is, the weight coefficient In actual operation, the R The values ​​are checked against the periodic test data and the weight coefficients of each method are revised.

[0135] The weighted data fusion method is applied to the online monitoring of on-resistance. The process of the designed inverter aging status online monitoring method is as follows: Figure 8 Applying the data from Method 1 and Method 2, the weighted fusion resistance value is:

[0136] (15);

[0137] Where, and It is the mean square error calculated by prior knowledge or experimental data of active voltage vector method and in-situ monitoring method. and are the weight coefficients of method 1 and method 2 respectively.

[0138] To prevent a sensor failure from causing the final resistance value R F Untrustworthy, the judgment formula is:

[0139] (16);

[0140] in, R 0 is the rated on-resistance of the power device under test (can be found in the data sheet), is the actual allowable error.

[0141] Only when equation (16) holds true can the final resistance value be calculated using weighted fusion of multi-source data. R F Otherwise, when hour( R Fp It is the average on-resistance value calculated from the first n data windows. The initial value is R 0), determine the resistance value obtained by method 1 R 1 is not credible, take ,Right now ;when When the resistance value obtained by method 2 is determined R 2 is not credible, take ,Right now .

[0142] When the resistance value meets When the power device fails, it is judged that the power device fails and an alarm is issued, otherwise wait for the calculation of the next cycle.

[0143] Therefore, the present invention adopts the above-mentioned online monitoring method for the aging status of a T-type three-level inverter, which can break through the accuracy bottleneck of the traditional single data source monitoring method, monitor the on-resistance changes of power devices in real time and accurately, evaluate their aging status, and provide a basis for system maintenance.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for online monitoring of the aging status of a T-type three-level inverter, characterized in that: The following steps are involved: S1. Construct a mathematical model of the inverter based on the switching state; S2. Synchronous acquisition of multiple physical quantity data; S3. Calculate the on-resistance by the active voltage vector method; In S3, based on the transformation relationship between the three-phase stationary coordinate system and the two-phase rotating coordinate system, a two-phase rotating coordinate coefficient mathematical calculation model of the T-type three-level inverter power device is constructed: The measured load line voltage is converted into a voltage vector in the α-β coordinate system using the Clarke transformation. The Clarke transformation formula is: ； in, They are the load side ab phase line voltage and bc phase line voltage respectively; are the α-axis and β-axis components of the load line voltage in the α-β coordinate system; Introduction To represent vector Under the influence Load voltage in the coordinate system axis, Axis components, where ; Vector and switch status ( , , ) have a one-to-one correspondence; definition and are the on-state voltages of the power devices of phase a, phase b, and phase c, respectively. , and is the number of the three-phase switch device that is turned on corresponding to the vector state, , , ; 23 represents the switching device T x2 and T x3 ; and Respectively represent the load voltage of phase a, phase b and phase c including the on-resistance; 、 and They represent the load voltages of phases a, b, and c, excluding on-resistance, as follows: ； Use Clarke transformation to transform the abc coordinate system and Convert to In the coordinate system, we get and : ； The power device conduction voltage and Replace it with the product of on-resistance and load current, and we get: ； in, and Represents the on-resistance of the switching devices of phase a, phase b and phase c respectively. or When the value is 1 or 4, it represents the on-resistance of a single switch 1 or 4. When the value is 23, it represents the on-resistance of the two switches 2 and 3 in series. All represent load current, the subscript Indicates the voltage vector number of the load current measured by the sensor at the current moment. The letter part indicates the current current flowing through the power device. Phase load current, ; Infer the circuit connection mode under each switching state and obtain the corresponding mathematical expression between the voltage vector, on-resistance and load current; Combine the mathematical expressions of different switch states to solve the on-resistance of the power device and get and The values ​​are: ； The subscript part and All are vector state numbers. ; S4, measuring the on-resistance in real time by in-situ monitoring method; In S4, a measurement circuit is added near the power device for monitoring. The measurement circuit consists of two parts: a clamping circuit and a parameter acquisition circuit. The clamping circuit includes Schottky diodes D1 and D2, a voltage-stabilizing diode DZ2, a current-limiting resistor R, a capacitor C, and a DC voltage source. The parameter acquisition circuit includes differential operational amplifiers OP1 and OP2. The on-state current is indirectly obtained by connecting a precision sampling resistor in series with the power device. The on-state voltage drop is divided by the on-state current to obtain the on-state resistance of the power device under test. S5. Perform weighted fusion of multi-source on-resistance data.

2. The method for online monitoring of aging status of a T-type three-level inverter according to claim 1, characterized in that: In S1, according to the topological characteristics of the T-type three-level inverter, an accurate mapping relationship between the switching state and the output voltage is established; the three-phase bridge arm switching function is defined as ， , whose value range is {1, 0, -1}, corresponding to: , then the upper bridge arm of this phase is turned on and outputs P level. ;like , then the bridge arm at the midpoint of the phase is turned on and the output is O level, 0; like , then the lower bridge arm of this phase is turned on and outputs N level. ; The mathematical expression of the three-phase AC side output voltage is obtained as follows: ； in, is the DC bus voltage, is the three-phase AC side output voltage; The synthetic space vector expression of the output voltage of the T-type three-level inverter is: ； Where, is the synthetic space vector of the output voltage of the T-type three-level inverter. The specific value of the synthetic space vector is related to the three-phase bridge arm switching function. There are 27 combinations related to this.

3. The method for online monitoring of aging status of a T-type three-level inverter according to claim 2, characterized in that: The synthetic space vector presents a regular hexagonal structure in space, which contains 19 basic voltage vectors, namely: 6 large vectors, whose amplitude is , each large vector uniquely corresponds to one switching state; 6 mean vectors, whose magnitude is , each middle vector uniquely corresponds to one switching state; 6 small vectors, whose amplitude is , each small vector corresponds to two redundant switch states; 1 zero vector, whose amplitude is 0, each zero vector corresponds to 3 switching states; The switching state is represented by the combination of bridge arm output levels P, O, and N.

4. The method for online monitoring of aging status of a T-type three-level inverter according to claim 2, characterized in that: In S2, the following measurement data are obtained in real time through the voltage / current sensor network of the T-type three-level inverter: DC bus voltage , three-phase load current and , load line voltage After being processed by the isolation conditioning circuit, all signals are synchronously input into the controller at the same sampling rate to construct a time-aligned multi-dimensional data matrix.

5. The method for online monitoring of aging status of a T-type three-level inverter according to claim 1, characterized in that: In S5, the on-resistance values ​​obtained by the active voltage vector method and the in-situ monitoring method are respectively recorded as R 1. R 2. The calculation formula is as follows: ； in, and are the random errors of the resistance values ​​obtained. and Independent of each other, is the actual value of the resistor, assuming Estimated value of With the obtained value and is a linear relationship, and yes The unbiased estimate of , then: ； in, is the weight coefficient of the values ​​obtained by the two methods: ； In the process of calculating with experimental data, it is assumed that the initial errors of each method are consistent, that is, the weight coefficient ; In actual operation, the R The values ​​are checked with the periodic test data and the weight coefficients of each method are revised; Applying the data from the active voltage vector method and the in-situ monitoring method, the weighted fusion resistance value is: ； Where, and It is the mean square error calculated through prior knowledge or experimental data of the active voltage vector method and in-situ monitoring method.

6. The method for online monitoring of aging status of a T-type three-level inverter according to claim 5, characterized in that: To prevent a sensor failure from causing the final resistance value R F Untrustworthy, the judgment formula is: ； in, is the rated on-resistance of the power device under test, is the actual allowable error; Only when the criterion formula is established can the final resistance value be calculated using the weighted fusion of multi-source data Otherwise, when When the active voltage vector method is used to determine the resistance value Unreliable, take ,Right now ;when When the resistance value obtained by the in-situ monitoring method is determined Unreliable, take ,Right now ;in, It is the average on-resistance value calculated from the first n data windows. The initial value is ; When the resistance value meets When the power device fails, it is judged that the power device fails and an alarm is issued, otherwise wait for the calculation of the next cycle.

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