WO2024060688A1

WO2024060688A1 - Monitoring method for micro-cracks of transformer

Info

Publication number: WO2024060688A1
Application number: PCT/CN2023/098798
Authority: WO
Inventors: 袁文琦; 李富国; 卢进; 赵鹏; 袁文
Original assignee: 联合汽车电子有限公司
Priority date: 2022-09-20
Filing date: 2023-06-07
Publication date: 2024-03-28
Also published as: CN115639269A

Abstract

A monitoring method for micro-cracks of a transformer. The method comprises: providing a device to be monitored, wherein a circuit assembly is arranged inside said device, and the circuit assembly comprises at least one transformer which has been subjected to a pouring sealant treatment; providing a crack-free device, and placing the crack-free device in a monitoring environment, so as to monitor the characteristics of the crack-free device and to obtain a first curve graph related to the characteristics, wherein the characteristics change due to the influence of the magnetic induction flux of the transformer; placing said device in the monitoring environment, and applying a voltage to test the characteristics of said device, so as to obtain at least one group of test data concerning the characteristics of said device; obtaining a second curve graph according to the at least one group of test data; comparing the first curve graph with the second curve graph; and obtaining a micro-crack determination result of said device. By means of the monitoring method, whether micro-cracks appear on a transformer inside a charging machine after the charging machine is pre-aged for a period of time can be identified without disassembling a prototype to take out the transformer.

Description

A method for monitoring microcracks in transformers

Technical field

The invention relates to the field of transformer defect monitoring, and in particular to a method for monitoring microcracks in transformers.

Background technique

As countries have more and more requirements for environmental protection, new energy vehicles are developing more and more rapidly in the automotive industry; in new energy vehicles, on-board chargers are becoming more and more important, and their technical requirements are also increasing. More and more strict. In new energy vehicles, the input of the on-board charger comes from the power grid. The AC input of the power grid often needs to be added through a rectifier circuit and a power factor correction circuit to reduce harmonics, and then sent to the subsequent DCDC (direct current) circuit. Through the DCDC circuit Charge the high-voltage battery in the car. The downstream DCDC circuit in the on-board charger usually uses a higher-efficiency LLC resonant converter. As shown in Figure 2, the driving waveform of the switching tube in the LLC (resonant circuit) resonant converter does not consider the dead zone. The duty cycle is 50%. It adjusts the output of the circuit topology by changing the frequency of the switching tube driving waveform, that is, PFM (Pulse Frequency Modulation) modulation. Compared with the PWM (Pulse Width Modulation) modulation topology, the LLC resonant converter has higher conversion efficiency. This advantage is more obvious in the case of low power output, and the characteristics of the LLC resonant circuit can ensure that all switches in its circuit Soft turn-on of the tube and soft turn-off of the diode.

The core magnetic component in the LLC resonant converter is the transformer. As the power density of on-board chargers becomes higher and higher, the frequency design of the transformer becomes higher and higher, and the thermal problems caused by high frequency become more and more serious. Therefore, the LLC transformer in the car charger needs to be heat dissipated through potting glue; the magnetic core of the LLC transformer is selected from ferrite materials suitable for frequency and temperature. The thermal expansion of the ferrite core due to the effect of potting glue It is very easy to crack due to the influence of cold shrinkage and temperature difference, causing sudden changes in magnetic induction, affecting the working status of the charger, directly reporting a fault and being unable to work normally, causing the car to be unable to charge normally. In order to solve the problem of magnetic core cracking, the industry has made many considerations on the research on potting glue and magnetic core structural strength, so as to solve the problem of magnetic core cracking; however, the problem of magnetic core micro-cracks is, first of all, because It is difficult to find the potting glue package. Secondly, the influence of micro-cracks on the magnetic induction is still within the error range of the magnetic induction. Therefore, it is difficult for micro-cracks to be reflected in the operating status of the whole machine in the early stage. However, after a long time, whether Will it have an impact on the charging life of the entire vehicle? Microcracks are a hidden risk. Even if the risk is low, it is necessary to identify it to facilitate the location of problems after failure.

Therefore, there is a need for a monitoring method for microcracks in potted transformers, which can identify whether microcracks appear in the internal transformer of the charger after a period of pre-aging without dismantling the prototype and taking out the transformer.

Contents of the invention

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for monitoring microcracks in a transformer to solve some problems in the prior art. For example, it is difficult to detect microcracks in the magnetic core caused by encapsulation with potting glue; If the influence of micro-cracks on the magnetic induction is within the error range of the magnetic induction, it will be difficult for the micro-cracks to be reflected in the operating status of the whole machine in the early stages, leading to potential risks.

In order to achieve the above objectives and other related objectives, the present invention provides a method for monitoring microcracks in a transformer, including:

Step 1. Provide equipment to be monitored, which is provided with circuit components inside, and the circuit components include at least one transformer that has been treated with potting glue; provide equipment without cracks, and place the equipment without cracks under monitoring environment to monitor the characteristics of the crack-free equipment and obtain a first curve graph related to the characteristics, wherein the characteristics change due to the influence of the magnetic induction of the transformer;

Step 2: Place the equipment to be monitored in the monitoring environment, and apply voltage to test the characteristics of the equipment to be monitored, and obtain at least one set of test data about the characteristics of the equipment to be monitored;

Step 3: Obtain a second curve graph based on at least one set of test data;

Step 4: Compare the first curve graph with the second curve graph;

Step 5: Obtain the microcrack judgment result of the equipment to be monitored.

Preferably, the circuit component is an LLC resonant converter.

Preferably, the device to be monitored and the crack-free device both include a plurality of switch tubes, and the switch tubes are used to drive the magnitude of the waveform frequency to adjust the output of the transformer.

Preferably, the circuit formed by the circuit component includes at least one of a boost circuit or a buck circuit. Preferably, the transformer in step one is a single-phase transformer or a multi-phase transformer.

Preferably, the water temperature in the monitoring environment is greater than 55 degrees Celsius, and the ambient temperature is greater than 85 degrees Celsius.

Preferably, the characteristic is the frequency of the switching tube.

Preferably, said characteristic is a ripple value of the current of said circuit component.

Preferably, the method of obtaining the second curve in step three includes: taking the time used to test the characteristics of the equipment to be monitored as the abscissa, and taking the characteristics as the ordinate to obtain at least one initial curve. , wherein each of the initial curves respectively corresponds to different phases of the transformer; and then each of the initial curves is filtered to obtain the second curve.

Preferably, the monitoring method further includes: after obtaining the microcrack judgment result of the transformer, if the judgment indicates that the transformer has cracks, repeat steps 2 to 4 N times to obtain each set of test data. The judgment result, where N is greater than or equal to two.

As mentioned above, the method for monitoring microcracks in transformers of the present invention has the following beneficial effects:

The monitoring method of the present invention can identify whether micro-cracks appear in the internal transformer of the charger after a period of pre-aging without dismantling the prototype and taking out the transformer, and can well distinguish micro-cracks on the prototype after the aging experiment. Marking and tracking can also reduce problems such as accidental probability, secondary damage, inoperability and a large number of scraps caused by disassembling prototypes.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic flow diagram of a method according to an embodiment of the present invention;

Figure 2 is a schematic diagram of an LLC resonant converter in the prior art;

Figure 3 is a schematic diagram of the relationship between the magnetic inductance of the transformer and the operating switching frequency of the circuit according to the embodiment of the present invention;

Figure 4 is a schematic diagram of the switching frequency and test time of the transformer according to the embodiment of the present invention. Wherein, the transformer has no microcracks;

Figure 5 is a schematic diagram of Figure 4 after filtering;

Figure 6 is a schematic diagram of switching frequency and test time of a transformer according to an embodiment of the present invention, wherein one phase of the transformer has microcracks;

Figure 7 is a schematic diagram of Figure 6 after filtering;

Figure 8 is a schematic diagram of switching frequency and test time of a transformer according to an embodiment of the present invention, wherein two phases of the transformer have microcracks;

Figure 9 is a schematic diagram of Figure 8 after filtering;

Figure 10 is a schematic diagram of the switching frequency and test time of the transformer according to an embodiment of the present invention, wherein the transformer has undergone multiple micro-crack experiments and the schematic diagram has been filtered.

Detailed ways

The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

Embodiment 1

Please refer to Figure 1. The present invention provides a method for monitoring microcracks in a transformer, which includes the following steps:

Step 1: Provide a device to be monitored. The device includes a circuit component disposed inside the device. The circuit component includes at least one transformer that has been processed by potting glue. The transformer treated with potting glue may be, for example, a transformer wrapped with potting glue. Since the transformer is wrapped with potting glue, it is difficult to detect micro-cracks in the magnetic core. That is to say, the impact of micro-cracks on the magnetic induction is still within the error range of the magnetic induction. Therefore, it is difficult to detect micro-cracks in the initial operation state of the whole machine. reflected. In order to determine whether a microcrack failure occurs in the transformer without dismantling the prototype, the inventor found that the characteristics affected by the magnetic induction can be monitored. This characteristic can be the switching tube frequency and current that change due to changes in the magnetic induction. and other parameters. It should be noted that the specific shape of the inductor core of the transformer is not limited and may be an EE-shaped core, a U-shaped core or other special-shaped cores known to those skilled in the art.

Step one further includes: providing a crack-free device, placing it in a monitoring environment to monitor its characteristics and obtaining a first curve graph, wherein the characteristics change due to the influence of the magnetic induction of the transformer. The monitoring time here should be able to reflect changes in magnetic induction, so the monitoring time is preferably greater than 30 minutes.

Generally speaking, the above-mentioned equipment to be monitored and the equipment without cracks should be understood as two equipments of the same type. Except for the difference in crack conditions, other structures between the two are the same.

In a possible implementation, the circuit component in step one is an LLC resonant converter, which includes at least one transformer processed by potting glue and is located in the device to be monitored.

In a possible implementation, the transformer in step one is a single-phase transformer or a multi-phase transformer.

In a possible implementation, the monitoring environment in step one is a water temperature greater than 55 degrees Celsius and an ambient temperature greater than 85 degrees Celsius. The monitoring environment here simulates the working environment of the circuit component inside the car under normal circumstances. The simulated temperature value here varies according to different actual conditions and is not specifically limited here.

In a possible implementation, please refer to FIG. 2 , the duty cycle of the switch tube driving waveform is 50% without considering the dead zone. The output of the circuit component topology is adjusted by changing the magnitude of the switch tube driving waveform frequency. The voltage gain in the entire circuit component directly affects the output voltage, and a key quantity in the voltage gain is the primary magnetizing inductance of the transformer, so the magnetic inductance of the transformer affects the output voltage, which in turn affects the switching frequency in the loop. The device in step one (e.g., the device to be monitored and/or the crack-free device) includes a plurality of switch tubes, which are used to drive the magnitude of the waveform frequency to adjust the output of the transformer.

In a possible implementation, please refer to Figure 3. In a car charger, micro-cracks in the magnetic core in the transformer will affect the air gap. The air gap has an inverse relationship with the magnetic induction. Once micro-cracks in the magnetic core occur, , the air gap between the magnetic cores becomes larger, the magnetic induction will become smaller, and the frequency will become larger; during the aging process of product off-line testing, frequency monitoring can effectively and accurately reflect whether micro-cracks appear in the transformer, that is, the steps The first characteristic is the frequency of the switching tube. By monitoring the frequency change of the switching tube, the change of its magnetic induction can be reflected, and then whether there are micro-cracks.

Step 2: Place the equipment to be monitored in the monitoring environment, and then apply voltage for testing to obtain Test data for at least one set of features. The number of sets of test data here is determined by the number of phases of the transformer. If the transformer is a single-phase transformer, there will be one set of test data corresponding to that phase. If the transformer is a multi-phase transformer, there will be multiple sets of test data corresponding to different phases. ; Specifically, take a two-phase (divided into phase A and phase B below) staggered and parallel LLC converter as an example. After its production and assembly, it is subjected to high water temperature (such as 65℃) and high ambient temperature (such as 85℃) high voltage output for the first time. (such as 470V) aging full load test, which simulates the working environment inside the car.

Step 3: Obtain a second curve graph based on at least one set of test data.

In a possible implementation, the method of obtaining the second curve in step 3 includes: taking the test time as the abscissa and taking the characteristics as the ordinate to obtain at least one initial curve, where each initial curve corresponds to the transformer's Out of phase; each initial curve is then filtered to obtain the second curve.

Step 4: Compare the first curve with the second curve.

The LLC resonant converter adjusts the output of the circuit topology by changing the operating frequency of the circuit. When operating in a stable operating condition, the switching frequency in the circuit is relatively stable and will fluctuate slightly. At the same time, the frequency under this operating condition The value can be monitored through the MCU control software and extracted in real time at intervals (such as 1min). All frequency data running for a period of time (such as 2h) after the first full load startup is extracted, and the frequencies are drawn in chronological order. The relationship between the curve and time is shown in Figure 4. After the real frequency value is extracted, it is the curve state before filtering in Figure 4. There will be slight fluctuations. The fluctuation is due to the certain ripple in the output voltage that needs to be controlled in real-time adjustment and sampling intervals. It is a normal phenomenon. After filtering, the theoretical curve state after filtering is shown in Figure 5. The filtered curve can be better used to analyze the principle and determine whether there are microcracks. Phase A and Phase B in Figure 5 are just An illustration of a case. In practice, there are phase A curves and phase B curves that are close to overlapping, and phase A is below phase B. The determination of microcracks in a certain transformer is only related to the changing trend of the frequency curve of that phase, and other There is no direct relationship with the changing trend of the phase frequency curve. Figure 5 represents the frequency curve of the transformer without microcracks. The principle of the frequency change trend in this state is: when the transformer starts to operate at full load, it will generate heat after generating losses, and the temperature will rise. The initial operating temperature After increasing, due to the inherent characteristics of the ferrite core material, the electromagnetic inductance of the transformer It will rise slightly. According to the working characteristics of LLC resonant converter, after the magnetic induction increases slightly, the frequency will decrease slightly. After running for a period of time and the temperature reaches a certain value, the magnetic induction will basically remain stable, and the overall frequency trend will be stable. , with a slight fluctuation. The judgment method in this state is: the frequency initially drops slightly or almost does not drop, and the subsequent frequency curve reaches a stable state with slight fluctuations. The first curve graph as the reference group can be obtained, which is the case where the transformer has no microcracks.

Figure 6 represents the frequency curve of a transformer with micro-cracks in one phase (such as A-phase transformer). After filtering, the frequency curve shown in Figure 7 can be obtained. The principle of frequency change trend in this state is: when full load operation is started After the transformer starts working, it will generate heat after generating losses, and the temperature will rise. After the temperature rises in the initial stage of operation, the electromagnetic induction of the transformer will rise slightly due to the inherent characteristics of the ferrite core material. According to LLC resonance conversion The working characteristics of the transformer: after the magnetic induction increases slightly, the frequency will decrease slightly. After running for a period of time and the temperature reaches a certain value, if micro-cracks appear in a certain phase core due to thermal stress or other reasons, the overall air gap of the transformer will After becoming larger, the magnetic induction will suddenly become smaller. According to the working characteristics of the LLC resonant converter, the frequency will suddenly rise (an obvious step jitter will appear). However, because the micro-cracks are very slight, in a stable temperature environment, the air gap If it remains stable, the magnetic induction can continue to stabilize, that is, the operating frequency is still stable at another value, with a slight fluctuation, and the overall state is stable, then the charger can still work normally and smoothly without any malfunction. The judgment method in this state is: the frequency curve in the early stage of operation is similar to the early stage of Figure 4. After stabilization, the frequency of a certain phase will suddenly have an obvious step upward jitter in the middle of operation, and the subsequent frequency curve will have slight fluctuations. steady state.

Figure 8 represents the frequency curve of two phases of the transformer (such as phase A and phase B transformer) with microcracks. After filtering, the frequency curve shown in Figure 9 can be obtained. The principle of the frequency change trend in this state is: when the full-load operation is started, the transformer begins to work, and it will generate heat after loss, and the temperature will rise. After the temperature rises in the initial operation, due to the inherent characteristics of the ferrite core material, the electromagnetic inductance of the transformer will rise slightly. According to the working characteristics of the LLC resonant converter, after the magnetic inductance rises slightly, the frequency will drop slightly. After running for a period of time, when the temperature reaches a certain value, if a phase core suddenly has hidden cracks or slight cracks due to thermal stress or other reasons, the other phase also has microcracks at another time. After the overall air gap of the transformer becomes larger, the magnetic inductance will suddenly decrease. According to the LLC resonant converter, the frequency will drop slightly after the magnetic inductance rises slightly. After running for a period of time, when the temperature reaches a certain value, if a phase core suddenly has hidden cracks or slight cracks due to thermal stress or other reasons, the other phase also has microcracks at another time. After the overall air gap of the transformer becomes larger, the magnetic inductance will suddenly decrease. The working characteristics of the vibration converter are that the frequency will suddenly rise (there will be an obvious step jitter), but because the crack is very slight, under a stable temperature environment, the air gap remains stable, and the magnetic induction can continue to stabilize, that is, the working frequency is still stable at another value, with a slight fluctuation, and the overall state is stable, then the charger can still work normally and smoothly without any faults. The judgment method under this state is: the frequency curve in the early stage of operation is similar to the early stage of Figure 4. After stabilization, the frequency of the two phases will suddenly have an obvious step upward jitter in the middle of operation, and the subsequent frequency curve is a stable state with slight fluctuations, but the frequency jitter of the two phases is not necessarily synchronized in time, and the amplitude of the step increase is not necessarily equal.

Step 5: Obtain the microcrack judgment results of the equipment to be monitored.

If the second curve obtained from the equipment to be monitored matches the frequency curve of the first curve and no step occurs, it means that no crack occurs;

If the frequency curve of the second curve obtained from the equipment to be monitored does not match the frequency curve of the first curve, and a step occurs as shown in Figure 7 or Figure 9, it means that a crack has occurred.

In a possible implementation, if the A-phase frequency has micro-cracks in its magnetic core, the temperature will rise in the early stage of secondary aging, the air gap will become larger, and the magnetic induction will become smaller. According to the working characteristics of the LLC resonant converter , the frequency will increase, but because the micro-cracks are very slight, in a stable temperature environment, the air gap remains stable, and the magnetic induction can continue to stabilize, that is, the operating frequency is still stable at another value, with a slight fluctuation, and the overall state is stable , the charger can still work normally and smoothly without any malfunction. Therefore, the monitoring method also includes: after obtaining the microcrack judgment result of the transformer, if the judgment result is that there is a crack, repeat steps 2 to 4 N times, where N is greater than or equal to two, and then obtain the judgment results of each set of test data, The frequency curve after the subsequent aging experiment is obtained as shown in Figure 10.

Embodiment 2

In another possible implementation, the circuit formed by the circuit components in step one includes at least one of a boost circuit or a buck circuit, and whether there are microcracks can be monitored by monitoring changes in its current value.

In a possible implementation, in a boost circuit or a buck circuit, the power inductor Micro-cracks in the magnetic core will affect the air gap. The air gap and the magnetic inductance are inversely proportional. Once micro-cracks in the magnetic core appear, the air gap between the magnetic cores will become larger, the magnetic inductance will become smaller, and the current ripple of the inductor will will become larger; during the aging process of product off-line testing, monitoring the current ripple value can effectively and accurately reflect whether micro-cracks appear in the inductor. The characteristic in step one is the ripple value of the inductor current. By monitoring the current ripple The change of the wave can reflect the change of its magnetic induction, and then reflect the presence of micro-cracks.

In summary, the monitoring method of the present invention can identify whether micro-cracks appear in the internal transformer of the charger after a period of pre-aging without dismantling the prototype and taking out the transformer, and can effectively monitor the charger after the aging experiment. Prototypes are marked and tracked for micro-crack identification, which can also reduce problems such as accidental probability, secondary damage, inoperability and a large number of scraps caused by dismantling prototypes. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. The drawings only show the components related to the present invention and do not follow the actual implementation of the component numbers, shapes and components. In actual implementation of dimension drawing, the type, quantity and proportion of each component can be changed at will, and the component layout may also be more complex.

The above embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims

A method for monitoring microcracks in transformers, which is characterized by at least including:

Step 1. Provide equipment to be monitored, which is provided with circuit components inside, and the circuit components include at least one transformer that has been treated with potting glue; provide equipment without cracks, and place the equipment without cracks under monitoring environment to monitor the characteristics of the crack-free equipment and obtain a first curve graph related to the characteristics, wherein the characteristics change due to the influence of the magnetic induction of the transformer;

Step 2: Place the equipment to be monitored in the monitoring environment, and apply voltage to test the characteristics of the equipment to be monitored, and obtain at least one set of test data about the characteristics of the equipment to be monitored;

Step 3: Obtain a second curve graph based on at least one set of test data;

Step 4: Compare the first curve graph with the second curve graph;

Step 5: Obtain the microcrack judgment results of the equipment to be monitored.
The method for monitoring microcracks in a transformer according to claim 1, wherein the circuit component is an LLC resonant converter.
The method for monitoring microcracks in a transformer according to claim 2, characterized in that: both the equipment to be monitored and the crack-free equipment include a plurality of switching tubes, and the switching tubes are used to drive the frequency of the waveform to adjust the frequency of the transformer. transformer output.
The method for monitoring microcracks in a transformer according to claim 1, wherein the circuit formed by the circuit component includes at least one of a boost circuit or a buck circuit.
The method for monitoring microcracks in a transformer according to claim 1, wherein the transformer is a single-phase transformer or a multi-phase transformer.
The method for monitoring microcracks in transformers according to claim 1, characterized in that: the water temperature in the monitoring environment is greater than 55 degrees Celsius, and the ambient temperature is greater than 85 degrees Celsius.
The method for monitoring microcracks in a transformer according to claim 3, wherein the characteristic is the frequency of the switching tube.
The transformer microcrack monitoring method according to claim 4 is characterized in that: the characteristic is the ripple value of the current of the circuit component.
The transformer microcrack monitoring method according to claim 1 is characterized in that: the method for obtaining the second curve graph in the step three comprises: taking the time used for testing the characteristic of the monitored equipment as the horizontal coordinate and taking the characteristic as the vertical coordinate to obtain at least one initial curve, wherein each of the initial curves corresponds to a different phase of the transformer; and then filtering each of the initial curves to obtain the second curve graph.
The method for monitoring microcracks in a transformer according to claim 1, characterized in that: the monitoring method further includes: after obtaining the microcrack judgment result of the transformer, if the judgment result indicates that the transformer has a crack, then Repeat steps 2 to 4 N times to obtain the judgment results of each set of test data, where N is greater than or equal to two.