CN110470967B

CN110470967B - Pulse power alternating-current aging test platform and test method

Info

Publication number: CN110470967B
Application number: CN201910778881.2A
Authority: CN
Inventors: 孙兆龙; 袁志方; 刘小虎
Original assignee: Naval University of Engineering PLA
Current assignee: Naval University of Engineering PLA
Priority date: 2019-08-22
Filing date: 2019-08-22
Publication date: 2021-10-26
Anticipated expiration: 2039-08-22
Also published as: CN110470967A

Abstract

The invention discloses a pulse power alternating-current aging test platform and a test method, which are used for testing the aging condition of an IGBT module under the condition of pulse power and evaluating the service life of the IGBT module, wherein the test platform comprises the following units: the main circuit unit is used for simulating a complete aging period; the measurement circuit unit is used for measuring the saturation voltage drop and the junction-crust thermal resistance of the IGBT module; the protection circuit unit is used for correspondingly protecting the test platform; the information processing unit is used for controlling and processing various information in the test process; and the upper computer is used for receiving various information sent by the information processing unit and displaying and controlling the information. The invention realizes the aging test of the IGBT module under the condition of pulse power, completes the measurement of saturation voltage drop and crusting thermal resistance of the IGBT module, and can provide powerful support for evaluating the service life of the IGBT module.

Description

Pulse power alternating-current aging test platform and test method

Technical Field

The invention belongs to the technical field of electrical equipment, relates to an IGBT module, and particularly relates to a pulse power alternating current aging test platform and a test method.

Background

An igbt (insulated Gate Bipolar transistor), which is called an insulated Gate Bipolar transistor, is a product of a combination of a MOSFET and a GTR (power transistor). Its three poles are collector (C), emitter (E) and gate (G), respectively.

The IGBT has the characteristics that: the breakdown voltage can reach 1200V, and the maximum saturation current of the collector exceeds 1500A. The capacity of the frequency converter using the IGBT as the inverter reaches more than 250kVA, and the working frequency can reach 20 kHz.

As one of the important high-power main flow devices of power electronics, the IGBT has been widely used in the fields of household appliances, transportation, power engineering, renewable energy, smart grid, and the like. In industrial applications such as traffic control, power conversion, industrial motors, uninterruptible power supplies, wind and solar installations, and frequency converters for automatic control. In consumer electronics, IGBTs are used in household appliances, cameras, and mobile phones.

The actual aging process of the device can be reflected better by the AC aging, but under the AC aging, the device works in a high-frequency switching state, and the online extraction of the aging characteristic quantity is still a difficult problem in the world. In the prior art, effective measurement and evaluation on the alternating current aging of the IGBT cannot be realized, and a platform and a method for performing an alternating current aging test on the IGBT are lacked.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a pulse power alternating-current aging test platform and a test method, which realize the aging test of the IGBT module under the condition of pulse power, complete the measurement of saturation voltage drop and crusting thermal resistance of the IGBT module and can provide powerful support for evaluating the service life of the IGBT module.

Therefore, the invention adopts the following technical scheme:

a pulse power alternating-current aging test platform is used for testing the aging condition of an IGBT module under the condition of pulse power and evaluating the service life of the IGBT module, and comprises the following units:

the main circuit unit comprises a full-bridge inverter main circuit and an IGBT module driving circuit; the main circuit works in a pulse power mode and is used for simulating a complete aging period;

the measurement circuit unit comprises an IGBT module saturation voltage drop measurement circuit and an IGBT module junction-to-shell thermal resistance measurement circuit and is used for measuring the saturation voltage drop and the junction-to-shell thermal resistance of the IGBT module;

the protection circuit unit is used for correspondingly protecting the test platform, and the test platform is protected based on the direct current bus short-circuit current;

the information processing unit is used for controlling and processing various information in the test process;

and the upper computer is used for receiving various information sent by the information processing unit and displaying and controlling the information.

Preferably, the main circuit unit adopts an H-bridge inverter structure, two IGBT modules packaged by IGBT are added at a bus capacitor and a bus, the upper pipe of the IGBT module is a bus capacitor switch, and the lower pipe of the IGBT module is a bus switch; when the upper tube is opened, allowing the bus capacitor to discharge, otherwise, not discharging the bus capacitor; when the lower tube is switched on, the direct current power supply or the bus capacitor is allowed to provide electric energy for the main circuit, otherwise, the connection between the power supply side and the main circuit is blocked through the diode.

Preferably, the IGBT module saturation voltage drop measurement circuit adopts a measurement circuit capable of isolating a dc bus high voltage, and the pairWhen the IGBT is switched off, the high voltage of the collector is blocked by the diode, so that the rear-stage operational amplifier and the AD chip are protected; the measurement of junction-to-shell thermal resistance of the IGBT module is defined according to thermal resistance

When the device reaches a thermal steady state, the temperature of the temperature and the temperature of the shell are adopted for calculation, wherein T_jTo junction temperature, T_cIs shell temperature, P_HFor heating power, R_{th_JC}And the junction thermal resistance of the IGBT module.

Preferably, the protection circuit unit comprises a system level protection and an IGBT module level protection; the system level protection is used for preventing bus capacitor damage, IGBT overvoltage breakdown or insulation breakdown caused by system overvoltage operation; reasonably configuring an overvoltage protection threshold of a direct-current side direct-current power supply to perform overvoltage protection on the whole system, and when the overvoltage phenomenon occurs to the system, locking the output voltage of the power supply to be the protection threshold, so that the whole system is protected from being damaged; the IGBT module level protection mainly considers overcurrent protection, and two realization modes are mainly adopted: firstly, bus current is monitored, and when short-circuit current is found, the IGBT is turned off in a soft/hard mode; and the other method is to monitor the saturation voltage drop of the IGBT, when the full-bridge circuit is subjected to a direct short circuit, the current of the IGBT is rapidly increased, the voltage drop at two ends of the CE is increased, and the IGBT exits from the saturation region and enters a linear region.

Preferably, the IGBT drive board overcurrent protection parameters are configured by changing the resistance of the relevant IGBT drive board.

Preferably, one half-bridge packaged IGBT module is reversely connected into the bus; when the upper tube and the lower tube are both turned off, the anti-parallel diode in the upper tube ensures that the capacitor does not discharge; an anti-parallel diode in the lower tube blocks the input of the power supply; the aging and measurement integrated automatic control system is used for realizing aging and measurement integration and automation.

Preferably, the information processing unit adopts DSP/SCI and SPI to carry out field digital control and transmits information to an upper computer through RS 232/485.

Preferably, the upper computer mainly comprises the following parts:

the administrator logs in the system: the system is used for logging in by an administrator, and the administrator can enter the system only when the user name and the password are both correct;

setting power supply parameters: the device is used for setting parameters of the direct current power supply, including voltage and current in an aging stage and voltage and current in a measuring stage;

platform control and monitoring: the upper computer controls the start and stop of the platform; displaying the working stage of the platform in real time, wherein the working stage comprises an aging stage or a measuring stage; displaying the working state of the platform in real time, wherein the working state comprises the alarm of normal work or abnormal work of the platform; the aging process of the IGBT module is displayed in real time and comprises module aging times, junction temperature shell temperature waveforms in the aging process and aging characteristic quantities;

and (3) historical data query: the storage of the aging characteristic quantity of the IGBT module is realized, the upper computer queries a change curve graph of the corresponding aging characteristic quantity by selecting query conditions, and the query conditions comprise aging times and the aging characteristic quantity;

platform initialization: for emptying all aging data of the last aging module before starting to age a new module.

An alternating current aging test method of the pulse power alternating current aging test platform is characterized in that a pulse power inverter platform is used as a research object, and an alternating current aging method is used for designing the aging test platform based on an H-bridge inverter topological structure; the method comprises the following steps:

the main circuit structure: a full-bridge topology structure is selected to reduce the purchase cost of a special power supply, and under the full-bridge topology structure, in order to achieve the same output current, the bus voltage and the load voltage are both half of the original voltage, and the capacity is also half of the original capacity; under a full-bridge topology structure, an alternating-current aging test platform is used for simulating actual working conditions, is slightly different from a common inverter in a control strategy and is mainly reflected on output voltage amplitude and output frequency change;

selecting aging characteristic quantity: the stress applied to the IGBT is mainly large junction temperature fluctuation and high average junction temperature caused by the temperature rise effect of low-frequency current, and the large junction temperature fluctuation and the high average junction temperature mainly affect a bonding wire and a solder layer of the IGBT; the saturated pressure drop and the crusting thermal resistance reflect the health states of the two materials, and the two parameters are set as characteristic quantities to be measured;

designing an alternating current aging test platform: designing a small IGBT aging test platform for a laboratory environment, wherein during design, the working condition of the aging platform is close to the real condition as much as possible; whether the service life of the IGBT is greatly different or not is considered under two different working conditions.

Preferably, the two different working conditions comprise a nine-level single-phase inverter circuit and a two-level single-phase inverter circuit, the nine-level circuit has four IGBTs simultaneously bearing the bus voltage, and the two-level circuit has only one IGBT bearing the bus voltage; after the whole nine-level and two-level inverter circuits are built, carrying out electric analysis on the IGBT, namely carrying out loss analysis on the IGBT in operation; after the IGBT thermal network model is established, the IGBT junction temperature waveform is obtained after circulation is carried out for 18 times at a nine-level and a two-level respectively, and a basis is provided for subsequent life evaluation.

Compared with the prior art, the invention has the beneficial effects that:

(1) the IGBT alternating current aging test platform for the laboratory is designed, and is simple and easy to use, strong in operability and highly automatic.

(2) An inverter of a single-phase H-bridge topology is designed and is configured with corresponding protection; and the topological structure of the H bridge is optimized, and the automation of measurement and aging is realized.

(3) The control strategy and the heat dissipation condition are provided, and the electrothermal stress of the IGBT of the inverter under a certain special working condition can be well simulated.

(4) And reasonably selecting the IGBT saturation voltage drop and the IGBT module crusting thermal resistance as aging characteristic quantities for evaluating the state of the IGBT, and realizing accurate measurement of the two characteristic quantities.

(5) An upper computer system matched with the test platform is designed, and monitoring of the running condition of the platform and reading, writing and displaying of aging data are achieved.

Drawings

Fig. 1 is a functional structure block diagram of a pulse power ac aging test platform provided by the present invention.

Fig. 2 is a schematic diagram of an overall working cycle of a pulse power ac aging test platform provided by the present invention.

Fig. 3 is a diode clamped three-level H-bridge topology.

Fig. 4 is a main circuit topology structure diagram of a pulse power ac aging test platform provided by the present invention.

Fig. 5 is a circuit diagram of a nine-level single-phase inverter circuit.

Fig. 6 is a circuit diagram of a two-level single-phase inverter circuit.

Fig. 7 is a circuit diagram of an IGBT module saturation drop measurement circuit.

Fig. 8 is a timing sequence of the heating current and the measured current and the junction temperature of the corresponding phase.

Fig. 9 is an equivalent thermal circuit diagram of the IGBT module and heat sink in a thermal steady state.

Fig. 10 is an IGBT overcurrent protection timing diagram.

Fig. 11 is a main function design flowchart of the upper computer.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings and specific embodiments, which are provided for illustration only and are not to be construed as limiting the invention.

Examples

A pulse power AC aging test platform is shown in FIG. 1 and mainly comprises the following parts:

a main circuit: full-bridge inverter main circuit and IGBT module drive circuit. Considering that the load is close to a purely inductive load, it is considered to incorporate an array of buffer capacitors at the dc voltage input side to provide reactive power.

A measurement circuit: the IGBT module saturation voltage drop measuring circuit and the IGBT module junction-to-shell thermal resistance measuring circuit are included;

a protection circuit: an IGBT overcurrent detection circuit, a soft turn-off circuit after fault and a system overvoltage protection configuration;

the signal conditioning circuit: the IGBT module shell temperature extraction circuit and the saturation voltage drop and thermal resistance information processing circuit are arranged on the IGBT module shell;

an embedded system for field digital control, coordination and information processing with DSP as core;

an upper computer: and (3) a host computer program developed by MATLAB or LabView.

The measurement scheme of the saturation voltage drop and the crusting thermal resistance of the IGBT module is as follows:

saturated pressure drop measurement protocol: by adopting the measuring circuit capable of isolating the high voltage of the direct current bus, when the corresponding IGBT is turned off, the high voltage of the collector is blocked by the diode, and chips such as a rear-stage operational amplifier and an AD (analog-digital) are protected.

Encrustation steady state thermal resistance measurement scheme: considering the actual operation mode of the test platform, the measurement scheme of the crusting thermal resistance is defined according to the thermal resistance

And when the device reaches a thermal steady state, the temperature of the device is set and the temperature of the shell is calculated.

The overall working state of the test platform is shown in fig. 2, and the main circuit will work in a pulse power mode (intermittent operation mode): the main circuit will be at 0-t₁Is inverted at t₁-t₂Intermittent cooling, 0-t₁-t₂For one cycle, n × 18 cycles is one complete aging period.

The pulse power inverter platform is used as a research object, and an alternating current aging method is used for designing an aging test platform based on an H-bridge inverter topological structure. The alternating current aging test of the IGBT belongs to power cycle aging, and the temperature of each layer of the device can be cyclically fluctuated by the IGBT module in a certain period. In general alternating current aging, an IGBT module is in a switching state from 5kHz to 20kHz, and the junction temperature and the shell temperature of the IGBT module are increased due to the switching loss and the conduction loss of a device. In ac aging, the heating current flowing through the device is an ac load current, and the power supply is changed from a constant current heating source to a constant voltage source (for a voltage source inverter), so the ac aging also takes into account the aging effect of the high voltage of the bus on the device.

Considering that the poor current sharing generates unnecessary interference on the aging result of the module, a strategy of redundant parallel connection of a plurality of IGBT modules is not used, and the simplification has no influence on the aging research of the device level. In addition, the basic module of the cascade multilevel topology is a diode-clamped three-level circuit, and the electrothermal stress of each group of modules is similar. In consideration of more real reflection working conditions, the aging platform can be built by using a diode-clamped three-level circuit. However, this presents inevitable problems:

as shown in fig. 3, to reach a peak value of i_{ac_peak}The dc bus voltage is calculated to be U for an output current of 80A_dclink844V, the maximum value of the peak value of the variable-voltage variable-frequency output voltage is U_{o_peakmax}628V. Research has found that the output voltage of the single DC power supply is generally 450V or less, and the procurement cost of the series-parallel connection of the power supplies is too high. Under the condition that the platform is not derated, three-level topology alternating current aging cannot be selected.

In order to control the budget of expenditure, a full-bridge topology is selected to reduce the purchase cost of a special power supply. As shown in fig. 4, the main circuit adopts an H-bridge topology structure, and to achieve the same output current, the bus voltage and the load voltage are both half of the original voltage, which are respectively U_dclink＝422V，U_acpeakmax314V, also half the original capacity, about 12.5 kVA. Under the structure of a full-bridge topology, an alternating-current aging platform is used for simulating actual working conditions, and is slightly different from a common inverter in a control strategy, wherein the main difference is reflected in output voltage amplitude and output frequency change.

In addition, the AC aging can reflect the real aging process of the device. However, under alternating current aging, the device works in a high-frequency switching state, and online extraction of aging characteristic quantities is still a difficult problem worldwide. For a special inverter working condition with intermittent work, offline characteristic quantity measurement can be carried out to avoid the problem that the traditional alternating current aging characteristic quantity is difficult to extract, and finally, a scheme for selecting and using alternating current aging is determined.

The aging failure of the IGBT device can be understood from the perspective of material science as the inevitable result caused by performance degradation in the long-term operation process, and is the basis for realizing reliability degradation evaluation of the IGBT device or analyzing the operation risk of the IGBT device from the perspective of failure physics. Since the degradation of the IGBT performance is mainly caused by a change in the physical structure and is difficult to observe visually, the state monitoring of the IGBT is generally performed indirectly by measuring the electrical and thermal characteristics of the IGBT. Some of the characteristics are static parameters of the IGBT, mainly including saturation voltage drop, junction thermal resistance, threshold voltage, etc. of the IGBT, and some are dynamic parameters of the IGBT, such as on-off time, miller platform voltage, etc. The characteristics respectively and obviously change along with the degradation of the physical structure of each part of the IGBT, and the changes can reflect the health state of the IGBT.

Researches on large junction temperature fluctuation and high average junction temperature caused by the fact that the stress borne by the IGBT of the platform and the actual platform is mainly the temperature rise effect of low-frequency current show that the large junction temperature fluctuation and the high average junction temperature mainly affect a bonding wire and a solder layer of the IGBT. The health states of the two materials can be well reflected by the saturated pressure drop and the crusting thermal resistance, so that the platform sets the two parameters as characteristic quantities to be measured.

The basic circuit topology structure of the test platform is shown in fig. 4, and is an H-bridge inverter structure. On the basis, the platform main circuit is added with an IGBT module packaged by two IGBTs at a bus capacitor and a bus. The upper tube is called a bus capacitor switch, and the lower tube is called a bus switch. When the upper tube is switched on, the bus capacitor is allowed to discharge, otherwise, the bus capacitor is not discharged, but the capacitor is still allowed to be charged by the direct-current power supply due to the existence of the anti-parallel diode; when the lower tube is switched on, the direct current power supply or the bus capacitor is allowed to provide electric energy for the main circuit, otherwise, the connection between the power supply side and the main circuit is blocked through the diode.

A small-sized IGBT aging test platform for a laboratory environment is designed, during design, the working condition of the aging test platform is close to the real condition as much as possible, but due to the factors of capacity reduction, different load properties, difference in topology and modulation methods and the like, the working characteristics of the AC aging test platform cannot be completely consistent with the actual condition. In order to make the conclusion of the aging test platform more meaningful, whether the service life of the IGBT is greatly different under two different working conditions should be considered.

Fatigue refers to the development of localized, permanent structural changes in a material that undergoes a perturbation stress at a point or points and, after sufficient cyclic perturbation effects, forms cracks or breaks completely. The rupture of a material structure means the end of its fatigue process, and the time or number of cyclic perturbations experienced in this process is called the "life" of the structure.

Fatigue damage (fatigue failure) refers to the occurrence and long-term accumulation of damage to a structure or component that results in cracking of the structural material and propagation of the crack until complete failure. The repeatedly changing load that causes fatigue failure to occur is called the fatigue load. The magnitude and direction of the load acting on a structure typically varies over time and is generally described in terms of a stress or strain cycle, with the primary loading and unloading of the stress or strain on the member due to the load being referred to as a stress cycle.

For an IGBT module, "load" is understood to mean the junction temperature of the device, and "stress" is the material deformation stress caused by the load.

In order to compare the stress of the nine-level and two-level circuits, a nine-level and two-level full-bridge inverter circuit is built in the PLECS, and the topological structures are respectively shown in FIG. 5 and FIG. 6. Nine-level circuit parameter of U_dcmax＝1688V，U_acmax＝1256V，I_acmax＝80A，f_max＝85Hz，S_max12.5 kVA; since four IGBTs of the nine-level are bearing the bus voltage at the same time, and only one IGBT of the two-level is bearing the bus voltage, the voltage stress which can be borne by the nine-level is four times that of the two-level. Thus, the two-level circuit parameter is U_dcmax＝1688/4＝422V，U_acmax＝1256/4＝314V，I_acmax＝80A，f_max＝85Hz，S_max＝12.5kVA。

An electric heating model of a nine-level inverter circuit and a two-level inverter circuit is built in the PLECS, the working condition is that the operation is carried out for 2.8s, the stop is carried out for 0.7s, the circulation is carried out for 36 times, and the starting temperature of the IGBT is 40 ℃.

After the whole nine-level and two-level inverter circuits are built, the IGBT is subjected to electrical analysis, namely, the IGBT is subjected to loss analysis in the running process. At nine levels, the lower tube IGBT (i.e., IGBT6) of the upper right arm experiences the greatest loss by analysis. At two levels, the upper tube IGBT (i.e., IGBT1) of the left leg loses the most by analysis. The three-level and two-level loss waveforms are similar, both the low frequency band has a large integral value (i.e., energy) over time and a large effect on junction temperature, the nine level is 148W, the two level is 154W, and the difference between the highest loss values is about 15W. The IGBT loss difference between the nine-level topology and the two-level topology is not large.

After the IGBT thermal network model is established, under a nine-level and a two-level respectively, the IGBT junction temperature waveform is obtained after circulation is carried out for 18 times. The highest junction temperature of the nine-level IGBT6 is 101 ℃, the highest junction temperature of the two-level IGBT1 is 104 ℃, and a basis is provided for subsequent life evaluation. It is ensured that the junction temperature of the IGBT after cycle 18 does not exceed 120 ℃.

And simulating a cascade nine-level H bridge and a full-bridge topology of the alternating current aging test platform in the PLECS to obtain the junction temperature change condition of the IGBT tube in the PLECS. The temperature cycles were counted separately in MATLAB using a rain flow counting method.

The theory of linear cumulative damage considers that fatigue damage under various stress levels is carried out independently, damage can be accumulated linearly, and when the accumulated fatigue damage reaches a certain value, the structure is subjected to fatigue damage. For the IGBT module, the Miner theory considers that fatigue damage amount is respectively and independently calculated for each junction temperature fluctuation and average junction temperature stress cycle of a random load spectrum and linearly accumulated, and when the damage amount accumulation is larger than 1, fatigue damage occurs to a device.

Calculating the fatigue damage amount based on an LESIT analytical model of the IGBT service life, and defining the fatigue damage amount of any certain load as D_i

Wherein N is_iCounting the number of cycles of a certain load, N_fFor the failure cycle number under the load, the invention particularly refers to the failure cycle number calculated by an LESIT life analytical model (formula 2).

The damage is counted in MATLAB by using a rain flow counting method, all the damages are linearly accumulated, and the service life of the IGMT can be obtained after reciprocal calculation, wherein the comparison result of the service lives of the alternating current aging test platform and the IGBT of the nine-level inverter provided by the invention is shown in Table 1.

TABLE 1 AC aging test platform and nine-level inverter IGBT life prediction

IGBT service life of AC aging test platform	Nine-level inverter IGBT lifetime
		17122 times of circulation	18421 cycles

The difference between the service lives of the two inverters is not large, which shows that even if the two inverters have different parameters, the alternating current aging test platform provided by the invention can still better simulate the actual working condition, and can provide a certain reference for the service life of the nine-level inverter.

As shown in fig. 7, the IGBT saturation voltage drop measurement circuit employs a measurement circuit capable of isolating the high voltage of the dc bus, and when the corresponding IGBT is turned off, the high voltage of the collector is blocked by the reverse diode, so as to protect the chips such as the post-stage operational amplifier and the AD.

The operating principle of the IGBT device saturation voltage drop measuring device of one bridge arm is as follows:

(a) when the IGBT is turned off, the high-voltage-withstanding fast-recovery diode is cut off in a reverse direction, and a voltage protection Vce acquisition circuit on the side of the direct-current bus is isolated;

(b) when the IGBT is conducted, the operational amplifier output voltage is as follows:

sampling by adopting a 14-bit high-precision bipolar AD chip AD7367, and then reading by using a DSP (digital signal processor)And (5) measuring the saturation voltage drop of the IGBT.

Considering that the IGBT saturation voltage drop is not only related to the aging state but also to the junction temperature, it is necessary to keep the junction temperature the same each time when measuring the saturation voltage drop. According to the measurement sequence, the voltage drop between CEs is continuously measured while the device is heating, the heating current is intermittently interrupted and a small current is injected to measure the junction temperature. Thus, the pressure drop between CEs measured continuously includes two, one is the aging characteristic saturated pressure drop V_ce(sat)One is a small current drop for extracting junction temperature information. When the junction temperature reaches a set value (the test platform is 60 ℃), the saturation voltage drop measured last time is taken as the aging characteristic quantity measured this time. Heating was then continued to measure the crusting resistance.

The measurement accuracy of the IGBT saturated voltage drop mainly depends on the ADC accuracy and the wiring condition of a PCB of the measurement device, and the expected measurement error of the IGBT saturated voltage drop is less than +/-10 percent (taking oscilloscope reading as reference) after debugging.

The IGBT module junction thermal resistance measurement is followed by the saturation voltage drop measurement. The measurement scheme of junction-to-case thermal resistance of the IGBT module comprises the following steps: firstly, the IGBT module and the heat sink are heated according to the control strategy of fig. 8, the temperature of the module and the shell temperature are continuously measured in the process similar to the measurement of the saturation pressure drop, and the historical shell temperature standard difference is calculated according to the formula 3.

When the standard deviation is less than K_TCcritThe system is considered to enter a thermal steady state. The IGBT module, heat sink and environment after entering thermal steady state form a thermal network as shown in fig. 9. Collection of this time V_ceAnd a heating current I_hCalculating the heating power P_H＝V_ce×I_HCalculating the junction-to-case thermal resistance R of the IGBT module according to the thermal resistance definition formula 4_{th_JC}. Wherein the junction temperature T_jTemperature T of the shell_cAll are measured by a measuring circuit.

The measurement precision of the junction-case thermal resistance of the IGBT module depends on the design of a measurement circuit, and also mainly depends on the aspects of the smearing condition of heat-conducting silicone grease, the selection of a case temperature acquisition reference point, the accurate calculation of heating power and the like. The expected theoretical measurement error of the crusting thermal resistance will not be higher than ± 10%.

In order to ensure the safe and reliable operation of the test platform and ensure that the phenomenon of transient failure does not occur in the aging process of the IGBT, the reasonable protection function is configured and mainly divided into the following two levels.

And (4) system level protection. The system level protection mainly aims to prevent the problems of bus capacitor damage, IGBT overvoltage breakdown or insulation breakdown and the like caused by system overvoltage operation. Considering that the system energy source is a direct current side direct current power supply and a bus capacitor connected in parallel with the direct current side direct current power supply, the OVP (over voltage protection) threshold value of the direct current side direct current power supply is reasonably configured to perform over voltage protection on the whole system, and when the overvoltage phenomenon occurs to the system, the output voltage of the power supply is locked as the protection threshold value, so that the whole system is protected from being damaged.

And (4) IGBT module level protection. The transient failure of the IGBT module is generally caused by the junction temperature exceeding the safe operating range due to excessive current, so overcurrent protection is mainly considered for the protection of the IGBT module level. The problem that its main solution is the straight-through short circuit condition of contravariant bridge arm, mainly has two realization methods:

(1) bus current (capacitor back side) is monitored and the IGBT is turned off soft/hard when a short circuit current is found. There are various ways to detect the bus current: current Hall, Rogowski coil, sampling resistor, etc. However, in the actual use process, it is found that after the system is integrally designed, the current hall cannot be installed in the laminated busbar due to the large volume of the current hall, and the method of externally connecting the sampling resistor cannot be realized due to the integral design of the system; although the rogowski coil can be fixed in the busbar, the rogowski coil is not selected because the current detection accuracy is problematic and the reliability of the platform is ensured. Protection cannot be performed by monitoring the bus current.

(2) Monitoring IGBT saturation voltage drop. When the full-bridge circuit is in a direct short circuit, the current of the IGBT is rapidly increased, the voltage drop at two ends of the CE is increased, the IGBT exits from the saturation region and enters the linear region, and therefore overcurrent protection for monitoring the saturation voltage drop is also called IGBT desaturation protection. The test platform uses a drive of a falling wood source model TX-Da962D, an IGBT tube voltage drop protection threshold value is configured to be 8.5V through hardware, when the IGBT tube voltage drop is detected to be more than 8.5V, the IGBT of the whole platform is turned off hard, and the system cannot be restarted again (namely, T is set through software)_rstInfinity), to avoid false triggering of protection due to interference, the protection action will set the dead zone time t by hardware_blind3 mus. In addition, the alarm signal is transmitted to the DSP and the upper computer, the DSP performs subsequent processing (such as the actions of turning off the main switch, stopping the output of the power supply and the like) and the upper computer performs alarm. The timing diagram is shown in fig. 10. The specific parameter configuration method can refer to the Larix GmbH TX-Da962D product manual.

The main functional design flow of the upper computer is shown in fig. 11. All equipment and devices in the platform are subjected to field digital control by the DSP/SCI and the SPI, information is transmitted to a PC upper computer through RS232/485, and upper computer software is developed by adopting MATLAB/GUI. The host computer mainly realizes the following functions: (1) the administrator logs in the system; (2) setting power supply parameters; (3) platform control and aging process monitoring; (4) storing and checking aging characteristic quantity; (5) and (5) initializing a platform.

(1) Administrator login system

In order to ensure that platform information is not leaked, an administrator login interface is designed, and the system can be accessed only when a user name and a password are correct.

(2) Power supply parameter setting

The upper computer is communicated with the lower computer DSP through a serial port and sends power supply parameters to be set to the DSP; the DSP is communicated with the power supply through a serial port, and the received power supply parameters are sent to the power supply to realize power supply parameter setting.

(3) Platform control and aging process monitoring

The upper computer sends platform start and stop commands through the serial port, and the DSP correspondingly controls the platform to start and stop according to the received commands. In the operation process of the platform, the DSP sends the collected junction temperature and shell temperature data to an upper computer, and the upper computer displays junction temperature and shell temperature waveforms in real time; in addition, if the platform has a fault alarm, the DSP immediately controls the platform to stop, alarm information is sent to the upper computer, and the upper computer displays corresponding alarm information (over-temperature alarm or over-current alarm).

Counting the aging times of the IGBT module through a variable count, finishing one-time aging, adding 1 to the count value and displaying the count value on an interface; in addition, the count value is written into an Excel file in real time for storage, so that the aging times of the module can be correctly displayed when the platform is started next time.

The operation stage of the platform is indicated through a variable stage _ flag, the upper computer sends a platform aging command, the stage _ flag is 1, and the platform is indicated to be in an aging stage; and the upper computer sends a platform measurement command, and the stage _ flag is 2, so that the platform is indicated to be in a measurement stage. When the platform is shut down, the value of stage _ flag is stored in Excel to instruct the platform to enter the aging phase or the measurement phase the next time the platform is started. And when the measurement stage is finished, the DSP sends the measured aging characteristic quantity to the upper computer, and the upper computer displays and stores the corresponding aging characteristic quantity.

(4) Aging feature quantity storage and viewing

And storing the received aging characteristic quantity in an Excel file, inputting the aging times and the inquired object on an upper computer interface, correspondingly calling data in the Excel file, and displaying the data in a graph form. In addition, if data needs to be manually processed, the upper computer is provided with a data storage function, and the whole Excel file (containing all aging characteristic quantity data) can be stored to any specified path.

(5) Platform initialization

When the aging of one module is finished and before a new module is aged, all the aging data of the previous module needs to be emptied, and all the aging data of the previous module can be emptied by clicking a 'platform initialization' button.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and scope of the present invention are intended to be covered thereby.

Claims

1. The utility model provides a pulse power exchanges ageing tests platform for the ageing condition of IGBT module tests under the pulse power condition to evaluate the life-span of IGBT module, its characterized in that: the method comprises the following units:

the protection circuit unit is used for correspondingly protecting the test platform, and the test platform is protected based on the short-circuit current of the direct-current bus;

the upper computer is used for receiving various information sent by the information processing unit and displaying and controlling the information;

the main circuit unit adopts an H-bridge inverter structure, two IGBT modules packaged by IGBT are added at a bus capacitor and a bus, the upper pipe of the main circuit unit is a bus capacitor switch, and the lower pipe of the main circuit unit is a bus switch; when the upper tube is opened, allowing the bus capacitor to discharge, otherwise, not discharging the bus capacitor; when the lower tube is switched on, allowing the direct current power supply or the bus capacitor to provide electric energy for the main circuit, otherwise, blocking the connection between the power supply side and the main circuit through the diode;

the protection circuit unit comprises system level protection and IGBT module level protection; the system level protection is used for preventing bus capacitor damage, IGBT overvoltage breakdown or insulation breakdown caused by system overvoltage operation; reasonably configuring an overvoltage protection threshold of a direct-current side direct-current power supply to perform overvoltage protection on the whole system, and when the overvoltage phenomenon occurs to the system, locking the output voltage of the power supply to be the protection threshold, so that the whole system is protected from being damaged; the IGBT module level protection considers overcurrent protection, and has two realization modes: firstly, bus current is monitored, and when short-circuit current is found, the IGBT is turned off in a soft/hard mode; monitoring the saturation voltage drop of the IGBT, wherein when the full-bridge circuit is subjected to a direct short circuit, the current of the IGBT is rapidly increased, the voltage drop at two ends of the CE is increased, and the IGBT exits from the saturation region and enters a linear region;

configuring overcurrent protection parameters of the IGBT drive board by changing the resistance of the relevant IGBT drive board;

the IGBT module saturation voltage drop measuring circuit adopts a measuring circuit capable of isolating high voltage of a direct current bus, and when the corresponding IGBT is turned off, the high voltage of a collector is blocked by a diode, so that a rear-stage operational amplifier and an AD chip are protected; the measurement of junction-to-shell thermal resistance of the IGBT module is defined according to thermal resistance

When the device reaches a thermal steady state, the temperature and the shell temperature are adopted for calculation, wherein T_jTo junction temperature, T_cIs shell temperature, P_HFor heating power, R_{th_JC}And the junction thermal resistance of the IGBT module.

2. The pulsed power ac aging test platform of claim 1, wherein: reversely connecting an IGBT module packaged by a half bridge into a bus; when the upper tube and the lower tube are both turned off, the anti-parallel diode in the upper tube ensures that the capacitor does not discharge; an anti-parallel diode in the lower tube blocks the input of the power supply; the aging and measurement integrated device is used for realizing aging and measurement integration and automation.

3. The pulsed power ac aging test platform of claim 1, wherein: the information processing unit adopts SCI or SPI to carry out field digital control and transmits information to an upper computer through RS232 or RS 485.

4. The pulsed power ac aging test platform of claim 1, wherein: the upper computer mainly comprises the following parts:

5. An AC aging test method of the pulse power AC aging test platform according to any one of claims 1 to 4, characterized in that: designing an aging test platform by using an alternating current aging method based on an H-bridge inversion topological structure by taking a pulse power inverter platform as a research object; the method comprises the following steps:

the main circuit structure: a full-bridge topology structure is selected to reduce the purchase cost of a special power supply, and under the full-bridge topology structure, in order to achieve the same output current, the bus voltage and the load voltage are both half of the original voltage, and the capacity is also half of the original capacity; under the full-bridge topology structure, an alternating current aging test platform simulates the actual working condition;

6. An AC aging test method according to claim 5, wherein: the two different working conditions comprise a nine-level single-phase inverter circuit and a two-level single-phase inverter circuit, wherein the nine-level circuit has four IGBTs simultaneously bearing the bus voltage, and the two-level circuit has only one IGBT bearing the bus voltage; after the whole nine-level and two-level inverter circuits are built, carrying out electric analysis on the IGBT, namely carrying out loss analysis on the IGBT in operation; after the IGBT thermal network model is established, the IGBT junction temperature waveform is obtained after circulation is carried out for 18 times at a nine-level and a two-level respectively, and a basis is provided for subsequent life evaluation.