A method for fault diagnosis of power devices in three-level bidirectional DC converters

Abstract

A method for diagnosing power device faults in a three-level bidirectional DC converter relates to the field of state monitoring and fault diagnosis of three-level bidirectional DC converters. To address the drawbacks of existing three-level bidirectional DC converters, such as converter failures due to short-circuit faults in power switching tubes, a lack of fault detection, and an inability to accurately locate the fault point, the present invention collects operating status information of the three-level bidirectional DC converter; determines characteristic values that can characterize the operating status of the three-level bidirectional DC converter; processes and determines the fault characteristic information of the three-level bidirectional DC converter; and performs fault diagnosis on the three-level bidirectional DC converter. The present invention is primarily used for monitoring, diagnosing, and providing early warning of power device short-circuit problems commonly encountered in mid-point clamped three-level DC converters commonly used in energy storage power stations, ship propulsion systems, and new energy power generation systems.

Description

Technical Field

[0001] The present invention relates to the field of three-level bidirectional DC converter state monitoring and fault diagnosis, and in particular to a three-level bidirectional DC converter power device fault diagnosis method based on frequency analysis. Background Art

[0002] In recent years, the energy storage industry has developed rapidly. As the power level of energy storage systems continues to increase, DC converters with higher bus voltage levels and larger voltage differences on both sides are needed to meet their high voltage and high current characteristics. Therefore, multi-level technology, especially hybrid three-level technology, has become an effective means to build DC converters. It achieves multi-level output by modifying the main circuit topology, reducing the voltage stress of power devices and avoiding the series connection of power devices, which is conducive to the realization of systems with larger output capacity and higher voltage levels.

[0003] However, with the advancement of multi-level technology, the number of switches has also increased, leading to an increased probability of failure in hybrid three-level converters. Statistics show that the majority of these failures are caused by power switches (i.e., IGBTs), ultimately manifesting as short-circuit failures.

[0004] A short-circuit failure in the power switch tube of a multi-level converter is a fatal blow to the converter and may even affect the harmonic level and vibration and noise performance of the energy storage system. Energy storage systems are increasingly tending to be unmanned or with few personnel on duty, which places higher demands on the prevention and handling of such failures.

[0005] Therefore, there is a need for a three-level bidirectional DC converter power device fault diagnosis method that can detect the hybrid three-level converter's open circuit fault, provide early warning, and accurately locate the fault. Summary of the Invention

[0006] In order to address the defects of existing three-level bidirectional DC converters, such as converter failure caused by short-circuit faults in power switching tubes, lack of fault detection, and inability to accurately locate the fault point, the present invention provides a three-level bidirectional DC converter power device fault diagnosis method that can detect short-circuit faults in hybrid three-level converters, provide early warnings, and accurately locate the fault.

[0007] A method for diagnosing a fault in a power device of a three-level bidirectional DC converter according to the present invention comprises the following steps:

[0008] Step 1: collecting operating status information of a three-level bidirectional DC converter;

[0009] Step 2: determining a characteristic value that can characterize the operating state of the three-level bidirectional DC converter;

[0010] Step 3: Process and determine the fault characteristic information of the three-level bidirectional DC converter; perform fault diagnosis on the three-level bidirectional DC converter;

[0011] In S3, the processing and determining of the fault characteristic information of the converter specifically includes the following steps:

[0012] Step 31: Analyze the voltage frequency domain parameter changes of the three-level bidirectional DC converter to obtain the center frequency change value. as follows:

[0013] , y=ab, cd, ef, gh;

[0014] in, is the center frequency of the voltage waveform obtained by the x-th sampling, y=ab represents the distance between the midpoints of the leading bridge arm and the lagging bridge arm on the high-voltage side, y=cd represents the distance between the leading bridge arm and the lagging bridge arm on the high-voltage side, y=ef represents the distance between the midpoints of the leading bridge arm and the lagging bridge arm on the low-voltage side, and gh represents the distance between the leading bridge arm and the lagging bridge arm on the low-voltage side;

[0015] Step 32: Determine the specific location of the open circuit fault of the three-level bidirectional DC converter by comparing and analyzing the characteristic values of the three-level bidirectional DC converter.

[0016] Further: In S1, the operating status information includes the voltage between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the high-voltage side , the voltage across the high-voltage side leading bridge arm and lagging bridge arm , the voltage between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the low-voltage side and the voltage across the leading bridge arm and the lagging bridge arm on the low-voltage side .

[0017] Furthermore, in S2, determining the characteristic value that can characterize the operating state of the three-level bidirectional DC converter specifically includes the following steps:

[0018] Step 21: Before the three-level bidirectional DC converter is put into operation, the voltage and current waveforms of the three-level bidirectional DC converter under rated working conditions are tested according to its working conditions, and are recorded as , as the initial value of the operating state of the three-level bidirectional DC converter;

[0019] Step 22: Perform fast Fourier decomposition on the initial voltage waveform to obtain frequency domain distribution curves of the initial voltage test waveform in different frequency bands, as follows:

[0020] ;

[0021] The frequency band distribution diagram of the initial voltage waveform is analyzed to determine the center frequency where the frequency distribution is most concentrated, which are recorded as 、 、 、 , and use it as the voltage component characteristic value.

[0022] Furthermore, in S3, the processing and determining of the fault characteristic information of the three-level bidirectional DC converter is to periodically sample and determine the operating status of the three-level bidirectional DC converter that has been put into operation, analyze the data collected by the monitoring voltage probe every x time, and repeat the above-mentioned processing to obtain the fault characteristic value of the three-level bidirectional DC converter obtained by the x-th sampling process.

[0023] Furthermore, the fault characteristic value of the three-level bidirectional DC converter includes the center frequency related to the voltage frequency domain parameter, which includes the center frequency of the voltage waveform between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the high-voltage side obtained by the x-th sampling. The center frequency of the voltage waveform at both ends of the high-voltage side leading bridge arm and lagging bridge arm is obtained by the xth sampling The center frequency of the voltage waveform between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the low voltage side is obtained by the xth sampling The center frequency of the voltage waveform at both ends of the leading bridge arm and the lagging bridge arm on the low-voltage side is obtained by sampling for the xth time .

[0024] Furthermore, in S32, when the electric energy is transmitted from the left side to the right side, the specific steps of comparing and analyzing the characteristic values of the three-level bidirectional DC converter are as follows:

[0025] when >0.1, <0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left;

[0026] when <0.1, >0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the second bridge arm on the left;

[0027] when <0.1, <0.1, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the right;

[0028] when <0.1, <0.1, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the right.

[0029] Furthermore: the first bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The second bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The first bridge arm on the right side includes a switch tube and switch tube The second bridge arm on the right side includes a switch tube and switch tube .

[0030] Furthermore, in S32, when the electric energy is being transmitted from the right side to the left side, the judgment basis for the converter circuit breaker fault will be partially changed. The adjusted judgment basis is as follows:

[0031] when >0.5, <0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right leading bridge arm;

[0032] when <0.5, >0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right lagging bridge arm;

[0033] when <0.5, <0.5, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left;

[0034] when <0.5, <0.5, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the left.

[0035] Furthermore: the first bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The second bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The right leading bridge arm includes a switch tube and switch tube The second bridge arm on the right side includes a switch tube and switch tube .

[0036] The beneficial effects of the present invention are:

[0037] The frequency analysis-based fault diagnosis method for power devices in three-level bidirectional DC converters described in the present invention can determine the operating status and fault location of multi-level DC converters commonly used in energy storage systems. It also uses frequency analysis to enable real-time monitoring of the status of the converter's switches, more accurately and quickly identifying midpoint voltage imbalance issues.

[0038] The frequency analysis-based fault diagnosis method for power devices of a three-level bidirectional DC converter according to the present invention can quickly identify and diagnose the early stage of a short-circuit fault in a power switch tube by combining continuous online monitoring with intelligent diagnosis, and can also provide an early warning of the occurrence of the fault.

[0039] The frequency analysis-based three-level bidirectional DC converter power device fault diagnosis method described in this invention can monitor, diagnose, and provide early warning for power device short circuit problems commonly encountered in midpoint-clamped three-level DC converters, commonly used in energy storage power plants, ship propulsion systems, and renewable energy power generation systems. This effectively reduces the probability of problems such as converter arm short circuits and continuous power device damage caused by the continued development and spread of short circuit faults. Furthermore, by combining continuous online monitoring with intelligent diagnosis, this method rapidly diagnoses and locates device short circuit faults at their initial stages, preventing the spread and aggravation of the faults. This helps improve the safe operation of multilevel DC converters in facilities such as energy storage power plants, ship propulsion systems, and renewable energy power generation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of the implementation of a method for diagnosing power device faults in a three-level bidirectional DC converter based on frequency analysis;

[0041] Figure 2 The figure shows the driving waveform and midpoint voltage waveform of the three-level bidirectional DC converter during actual operation. DETAILED DESCRIPTION

[0042] The following are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the scope of protection of the present invention. The embodiments described below are only used to explain the present invention and cannot be interpreted as limiting the present invention. The scope of protection of the present invention should be based on the scope of protection of the claims. The embodiments of the present invention are described in detail below. In order to facilitate the description of the present invention and simplify the description, the technical terms used in the description of the present invention should be interpreted broadly, including but not limited to conventional replacement schemes not mentioned in this application, and also including direct implementation and indirect implementation.

[0043] Example 1

[0044] Combine Figure 1 and Figure 2 This embodiment describes a method for diagnosing power device faults in a three-level bidirectional DC converter based on frequency analysis, to achieve real-time monitoring of the status of switching tubes in the three-level bidirectional DC converter. The method includes the following steps (power flows from left to right):

[0045] Step 1: Collecting operating status information of a three-level bidirectional DC converter;

[0046] Connect monitoring voltage probes a, b, c, d, e, f, g, and h at key positions of the three-level bidirectional DC converter, and measure the voltage Vab between the midpoint of the high-voltage side leading bridge arm and the midpoint of the lagging bridge arm, the voltage Vcd at both ends of the high-voltage side leading bridge arm and the lagging bridge arm, the voltage Vef between the midpoint of the low-voltage side leading bridge arm and the midpoint of the lagging bridge arm, and the voltage Vgh at both ends of the low-voltage side leading bridge arm and the lagging bridge arm, respectively. Record the voltage waveforms within N cycles and record them as 、 、 、 ,in:

[0047] ;

[0048] Where t is the time of the sampled voltage waveform, is the time domain value, is the operating frequency of the three-level bidirectional DC converter, is the single working cycle time of the power device of the three-level bidirectional DC converter;

[0049] Step 2: determining a characteristic value that can characterize the operating state of the three-level bidirectional DC converter;

[0050] Step 21: Before the three-level bidirectional DC converter is put into operation, the voltage and current waveforms at various positions of the three-level bidirectional DC converter under rated working conditions are tested according to its working conditions, and are recorded as 、 、 、 , as the initial value of the operating state of the three-level bidirectional DC converter;

[0051] Step 22: Perform fast Fourier decomposition on the initial voltage waveform to obtain frequency domain distribution curves of the initial voltage test waveform in different frequency bands, as follows:

[0052] ;

[0053] The frequency band distribution diagram of the initial voltage waveform is analyzed to determine the center frequency where the frequency distribution is most concentrated, which are recorded as 、 、 、 , and use it as the voltage component characteristic value;

[0054] Step 3: Processing and judging fault characteristic information of the three-level bidirectional DC converter;

[0055] For the three-level bidirectional DC converter that has been put into operation, its operating status is periodically sampled and judged. The collected data of the monitoring voltage probe, monitoring current sensor, etc. are analyzed every X time. X can be set as needed. The above process is repeated to obtain the fault characteristic value of the three-level bidirectional DC converter obtained by the x-th sampling process: including the voltage frequency domain parameter related 、 、 、 wait;

[0056] Step 31: Analyze the change of the voltage frequency domain parameters of the three-level bidirectional DC converter to obtain the center frequency change value Δfy as follows:

[0057] , y=ab, cd, ef, gh;

[0058] Step 32: Determine the specific location of the open circuit fault in the three-level bidirectional DC converter by comparing and analyzing the characteristic values of the three-level bidirectional DC converter:

[0059] when >0.1, <0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left (S1, S2, S3, S4);

[0060] when <0.1, >0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the second bridge arm on the left (S5, S6, S7, S8);

[0061] when <0.1, <0.1, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the right (Q1, Q2);

[0062] when <0.1, <0.1, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the right (Q3, Q4).

[0063] In addition, the present invention can also achieve the following functions:

[0064] When power is transmitted from the right side to the left side, the judgment basis for a three-level bidirectional DC converter circuit breaker fault will be partially changed. The adjusted judgment basis is as follows:

[0065] when >0.5, <0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right leading bridge arm (Q1, Q4);

[0066] when <0.5, >0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right lagging bridge arm (Q2, Q3);

[0067] when <0.5, <0.5, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left (S1, S2, S3, S4);

[0068] when <0.5, <0.5, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the left (S5, S6, S7, S8).

Claims

1. A method for diagnosing a fault in a power device of a three-level bidirectional DC converter, characterized in that: The steps include: Step 1: Collect the operating status information of the three-level bidirectional DC converter; the operating status information includes the voltage between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the high-voltage side , the voltage across the high-voltage side leading bridge arm and lagging bridge arm , the voltage between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the low-voltage side and the voltage across the leading bridge arm and the lagging bridge arm on the low-voltage side ; Step 2: Determine a fault characteristic value that can characterize the operating state information of the three-level bidirectional DC converter by performing fast Fourier decomposition on an initial value that can characterize the operating state information of the three-level bidirectional DC converter; Step 3: Process and determine the fault characteristic value of the three-level bidirectional DC converter; perform fault diagnosis on the three-level bidirectional DC converter; the fault characteristic value of the three-level bidirectional DC converter includes a voltage frequency domain parameter fy, where y=ab, cd, ef, gh; In S3, the processing and determining of the fault characteristic value of the three-level bidirectional DC converter specifically includes the following steps: Step 31: Analyze the voltage frequency domain parameter changes of the three-level bidirectional DC converter to obtain the center frequency change value. as follows: ,y=ab、cd、ef、gh! in, is the center frequency of the voltage waveform obtained by the x-th sampling, y=ab represents the distance between the midpoints of the leading bridge arm and the lagging bridge arm on the high-voltage side, y=cd represents the distance between the leading bridge arm and the lagging bridge arm on the high-voltage side, y=ef represents the distance between the midpoints of the leading bridge arm and the lagging bridge arm on the low-voltage side, and gh represents the distance between the leading bridge arm and the lagging bridge arm on the low-voltage side; Step 32: Determine the specific location of the open circuit fault of the three-level bidirectional DC converter by comparing and analyzing the fault characteristic values of the three-level bidirectional DC converter.

2. A three-level bidirectional DC converter power device fault diagnosis method according to claim 1, characterized in that: In S2, determining the fault characteristic value that can characterize the operating state of the three-level bidirectional DC converter specifically includes the following steps: Step 21: Before the three-level bidirectional DC converter is put into operation, the voltage and current waveforms of the three-level bidirectional DC converter under rated working conditions are tested according to its working conditions, and are recorded as , as the initial value of the operating state of the three-level bidirectional DC converter; Step 22: Perform fast Fourier decomposition on the initial voltage waveform to obtain frequency domain distribution curves of the initial voltage test waveform in different frequency bands, as follows: ； The frequency band distribution diagram of the initial voltage waveform is analyzed to determine the center frequency where the frequency distribution is most concentrated, which are recorded as 、 、 、 , and use it as the fault characteristic value of the voltage component.

3. A three-level bidirectional DC converter power device fault diagnosis method according to claim 1, characterized in that: In S3, the processing and determination of the fault characteristic value of the three-level bidirectional DC converter is performed by periodically sampling and determining the operating state of the three-level bidirectional DC converter in operation, analyzing the collected voltage data every x time interval, and repeating the aforementioned process to obtain the fault characteristic value of the three-level bidirectional DC converter obtained by the x-th sampling process.

4. A three-level bidirectional DC converter power device fault diagnosis method according to claim 3, characterized in that: The fault characteristic value of the three-level bidirectional DC converter includes the center frequency related to the voltage frequency domain parameter, and includes the center frequency of the voltage waveform between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the high-voltage side obtained by the x-th sampling. The center frequency of the voltage waveform at both ends of the high-voltage side leading bridge arm and lagging bridge arm is obtained by the xth sampling The center frequency of the voltage waveform between the midpoint of the leading bridge arm and the midpoint of the lagging bridge arm on the low voltage side is obtained by the xth sampling The center frequency of the voltage waveform at both ends of the leading bridge arm and the lagging bridge arm on the low-voltage side is obtained by sampling for the xth time .

5. The method for diagnosing a fault in a three-level bidirectional DC converter power device according to claim 1, wherein: In S32, when the electric energy is being transmitted from the left side to the right side, the specific steps of comparing and analyzing the fault characteristic values of the three-level bidirectional DC converter are as follows: when >0.1, <0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left; when <0.1, >0.1, and <0.1, <0.1, the circuit breaker fault only occurs in the second bridge arm on the left; when <0.1, <0.1, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the right; when <0.1, <0.1, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the right.

6. A three-level bidirectional DC converter power device fault diagnosis method according to claim 5, characterized in that: The left first bridge arm includes a switch tube , switch tube , switch tube and switch tube The second bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The first bridge arm on the right side includes a switch tube and switch tube The second bridge arm on the right side includes a switch tube and switch tube .

7. A three-level bidirectional DC converter power device fault diagnosis method according to claim 6, characterized in that: In S32, when the electric energy is being transmitted from the right side to the left side, the judgment basis for the converter circuit breaker fault will be partially changed. The adjusted judgment basis is as follows: when >0.5, <0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right leading bridge arm; when <0.5, >0.5, and <0.1, <0.1, the circuit breaker fault only occurs in the right lagging bridge arm; when <0.5, <0.5, and >0.1, <0.1, the circuit breaker fault only occurs in the first bridge arm on the left; when <0.5, <0.5, and <0.1, >0.1, the circuit breaker fault only occurs in the second bridge arm on the left.

8. A three-level bidirectional DC converter power device fault diagnosis method according to claim 7, characterized in that: The left first bridge arm includes a switch tube , switch tube , switch tube and switch tube The second bridge arm on the left side includes a switch tube , switch tube , switch tube and switch tube The right leading bridge arm includes a switch tube and switch tube The second bridge arm on the right side includes a switch tube and switch tube .

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