CN111722073B - MMC sub-module capacitor ESR value online monitoring method and device - Google Patents

MMC sub-module capacitor ESR value online monitoring method and device Download PDF

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CN111722073B
CN111722073B CN202010484929.1A CN202010484929A CN111722073B CN 111722073 B CN111722073 B CN 111722073B CN 202010484929 A CN202010484929 A CN 202010484929A CN 111722073 B CN111722073 B CN 111722073B
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马柯
辛熙锴
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Shanghai Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/26—Testing of individual semiconductor devices
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/26—Testing of individual semiconductor devices
    • G01R31/27—Testing of devices without physical removal from the circuit of which they form part, e.g. compensating for effects surrounding elements

Abstract

The invention provides an MMC submodule capacitor ESR value online monitoring method and device, comprising the following steps: sampling and conditioning the capacitance voltage of the MMC sub-module and the bridge arm current flowing into the MMC sub-module; carry out voltage jump to the MMC submodule piece capacitor voltage after above-mentioned sampling, conditioning and detect, include: detecting positive jump and negative jump; and recording the following characteristic values based on the detection result of voltage jump of the capacitance voltage of the MMC sub-module, and calculating the ESR value of the capacitor by detecting the capacitance voltage value of the MMC sub-module at the sampling moment before and after positive and negative jump of the capacitance voltage and the corresponding bridge arm current value. The method and the device provided by the invention can realize real-time online monitoring of the ESR value of the capacitor of the MMC sub-module, and the implementation process is simple to operate, economic and efficient.

Description

MMC sub-module capacitor ESR value online monitoring method and device
Technical Field
The invention relates to the technical field of state monitoring, in particular to an online monitoring method and device for a Modular Multilevel Converter (MMC) submodule capacitor Equivalent Series Resistance (ESR) value.
Background
The Equivalent Series Resistance (ESR) of the capacitor is an important parameter for representing the health state of the capacitor, and the existing research shows that the capacitor can be determined to be invalid when the ESR value of the capacitor is increased to 2-3 times of the initial value. By monitoring the ESR value of the capacitor, the health state evaluation and failure judgment of the capacitor can be realized, theoretical support is provided for predictive maintenance of the capacitor, and the method has important significance for improving the reliability of a capacitor device and the system reliability.
The existing capacitor ESR value state monitoring technology is divided into off-line monitoring and on-line monitoring. The off-line monitoring has universality and is suitable for the ESR value of the capacitor in any circuit structure, but the off-line detection requires that the system is in a shutdown state, and the capacitor needs to be separated from the system to avoid the interference of other components on the measurement; the online monitoring is provided by combining a circuit topological structure and an operation principle, so that the monitoring of the ESR value of the capacitor can be completed in the normal operation process of the system, but the existing online monitoring technology of the ESR value of the capacitor is mainly provided for DC/DC converters such as BUCK and BOOST circuits and direct-current end capacitors in single-phase/three-phase rectification and inversion circuits, and the technologies cannot be used in the ESR monitoring of the sub-module capacitor of the MMC system due to the difference of the circuit structure and the operation principle; the ESR value monitoring technology for the capacitor of the MMC sub-module is relatively short. The monitoring technology of the capacitor ESR value of the MMC sub-module comprises the following steps: 1) the ESR value of the capacitor is obtained through the ratio of the loss power of the capacitor to the square of the effective value of the current flowing through the capacitor, the method is based on an ideal situation for calculating the loss power of the capacitor, the loss power of a power semiconductor is ignored, and therefore a large error can be introduced; 2) the method comprises the steps of extracting high-frequency (such as switching frequency) components in capacitor voltage and capacitor current by using a high-pass filter, calculating the ratio of effective values of the high-frequency components to the effective values to obtain an ESR value, wherein the capacitor current can be directly measured from a capacitor branch circuit by using a current sensor, but the coupling problem between the current sensor and a capacitor exists, the capacitor current can also be indirectly obtained by bridge arm current flowing into a submodule and the switching state of the submodule, but the error of the measured value of the capacitor current is large, and the error of the measured value of the capacitor ESR value can be increased by using both the capacitor current obtaining methods.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an MMC sub-module capacitor ESR value online monitoring method and device, which can realize online monitoring of the ESR value of the sub-module capacitor.
According to a first aspect of the present invention, an online monitoring method for capacitance ESR values in an MMC submodule is provided, which includes:
sampling and conditioning the capacitance voltage of the MMC sub-module and the bridge arm current flowing into the MMC sub-module;
carry out voltage jump to the MMC submodule piece capacitor voltage after above-mentioned sampling, conditioning and detect, include: detecting positive jump and monitoring negative jump;
the following characteristic values are recorded based on the voltage jump detection result of the MMC submodule capacitor voltage:
MMC submodule capacitor voltage positive jump previous sampling moment capacitor voltage value uc1,r；
MMC submodule capacitor voltage value u at positive jump moment of capacitor voltagec2,r；
Bridge arm current value i at positive jump moment of capacitance and voltage of MMC sub-modulec,r；
Capacitance voltage value u of MMC sub-module at previous sampling moment of capacitance voltage negative jumpc1,f；
MMC submodule capacitor voltage value u at negative jump moment of capacitor voltagec2,f；
Bridge arm current value i at previous sampling moment of MMC sub-module negative jumpc,f；
According to the characteristic values, the ESR value of the capacitor of the MMC sub-module is calculated in real time, the real-time monitoring result of the ESR value is obtained, and the calculation formula of the ESR value is as follows:
Figure BDA0002518720160000021
optionally, before sampling and conditioning the MMC sub-module capacitor voltage and the MMC sub-module input current, the method further includes: and carrying out high-pass filtering on the capacitance voltage of the MMC sub-module.
Optionally, the real-time monitoring result of the ESR value is filtered by using a filtering algorithm, which is a moving average filtering, a least mean square error (LMS) or a Recursive Least Squares (RLS) wave algorithm.
According to a second aspect of the present invention, an online capacitance and ESR monitoring apparatus for an MMC submodule comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor is configured to execute the online capacitance and ESR monitoring method for the MMC submodule when executing the program.
Compared with the prior art, the embodiment of the invention has at least one of the following beneficial effects:
according to the method and the device for monitoring the ESR value of the capacitor of the MMC sub-module, the monitoring process is carried out when the MMC system normally operates, the operation state of the system cannot be changed or stopped, and the method and the device are a real-time online state monitoring method and a real-time online state monitoring device.
According to the method and the device for monitoring the capacitor ESR value of the MMC sub-module, provided by the invention, the capacitor ESR value estimated at the positive jump position and the capacitor ESR value estimated at the negative jump position are averaged by utilizing the positive jump and the negative jump existing in the capacitor voltage, so that the monitoring error of the capacitor ESR value is reduced, and the result is more accurate and stable.
The method and the device for monitoring the ESR value of the capacitor of the submodule of the MMC, provided by the invention, have no limit on the modulation strategy adopted by an MMC system, including a recent level approximation (NLC), a Carrier Phase Shift (CPS) or a carrier layer stack (PD) modulation strategy.
The method and the device for monitoring the ESR value of the capacitor of the submodule of the MMC, provided by the invention, have lower requirements on the sampling frequency, such as 20kHz, do not need to use a data acquisition card with high sampling frequency, and have lower cost.
Drawings
FIG. 1 is a flow chart of an ESR monitoring of a capacitor of a submodule of an MMC in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a single-phase MMC structure in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a sub-module structure of an MMC in an embodiment of the present invention;
fig. 4 is a schematic diagram of a capacitance-voltage positive transition time and a previous sampling time thereof, a negative transition time and a previous sampling time thereof of the MMC submodule in an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Fig. 2 is a schematic diagram of a single-phase MMC structure in an embodiment of the invention. Referring to fig. 2, the existing MMC single-phase structure includes an MMC upper and lower bridge arms, an ac side output inductor, an ac side output resistor, an ac power supply, and a dc power supply, where each bridge arm is composed of n submodules.
Fig. 3 is a schematic view of a sub-module structure of the MMC in an embodiment of the invention. The sub-module structure is a half-bridge structure, and the bus capacitor adopts an equivalent model of series combination of an ideal capacitor and an ideal resistor.
The embodiment will be described in detail below using the MMC structures shown in fig. 2 and 3.
Fig. 1 is a flow chart of ESR monitoring of a sub-module capacitor of an MMC in an embodiment of the present invention. Referring to fig. 1, in this embodiment, the online monitoring method for capacitance ESR values of MMC sub-modules may include the following steps:
s1, carrying out high-pass filtering on the capacitance voltage of the MMC sub-module;
s2, sampling and conditioning the capacitor voltage of the MMC sub-module subjected to the high-pass filtering of the S1 and the bridge arm current flowing into the MMC sub-module;
s3, voltage jump detection is carried out on the sampled and conditioned capacitor voltage of the MMC sub-module, and the voltage jump detection comprises the following steps: detecting positive jump and negative jump; the following characteristic values are recorded based on the voltage jump detection result of the MMC submodule capacitor voltage: MMC submodule capacitor voltage positive jump previous sampling moment capacitor voltage value uc1,r(ii) a MMC submodule capacitor voltage value u at positive jump moment of capacitor voltagec2,r(ii) a Bridge arm current value i at positive jump moment of capacitance and voltage of MMC sub-modulec,r(ii) a Capacitance voltage value u of MMC sub-module at previous sampling moment of capacitance voltage negative jumpc1,f(ii) a MMC submodule capacitor voltage value u at negative jump moment of capacitor voltagec2,f(ii) a Bridge arm current value i at previous sampling moment of MMC sub-module negative jumpc,f(ii) a According to the characteristic values, the ESR value of the capacitor of the MMC sub-module is calculated in real time, the real-time monitoring result of the ESR value is obtained, and the calculation formula of the ESR value is as follows:
Figure BDA0002518720160000041
in the above embodiments of the present invention, the conditioning means performing operations such as scaling and offset adjustment on analog signals from the voltage sensor and the current sensor so as to be suitable for the input of the analog-to-digital converter (ADC).
In one embodiment, the MMC submodule capacitance voltage positive jump detection includes: with a sampling period of TsamSampling capacitor voltage of MMC sub-module at sampling time nTsamSampled value of the capacitor voltage of uc[n]The sampling instant (n-1) T preceding the sampling instant TsamSampled value of the capacitor voltage of uc[n-1]The threshold value of the change of the capacitance voltage is set as Uth,rIf u isc[n]-uc[n-1]＞Uth,rMMC submodule capacitor voltage generatorGenerating positive jump.
In one embodiment, the MMC sub-module capacitance voltage negative transition detection includes: with a sampling period of TsamSampling capacitor voltage of MMC submodule at mT sampling timesamSampled value of the capacitor voltage of uc[m](ii) a Sampling time mTsamPrevious sampling instant (m-1) TsamSampled value of the capacitor voltage of uc[m-1]The threshold value of the change of the capacitance voltage is set as Uth,fIf u isc[m]-uc[m-1]＜Uth,fAnd the MMC sub-module capacitor voltage generates negative jump.
In the embodiment of the invention, the ESR value monitoring process is carried out when the MMC system normally runs, the running state of the system cannot be changed or stopped, and the method is a real-time online state monitoring method. Meanwhile, by utilizing positive jump and negative jump existing in the capacitor voltage, the ESR value of the capacitor estimated at the positive jump position and the ESR value estimated at the negative jump position are averaged, so that the monitoring error of the ESR value of the capacitor is reduced, and the result is more accurate and stable. The above embodiments can be applied to an on-line monitoring method for capacitance ESR of a submodule of an MMC under a recent level approximation (NLC), Carrier Phase Shift (CPS) or carrier stacking (PD) modulation strategy.
FIG. 4 is a schematic diagram of a positive transition time and a previous sampling time of a capacitor voltage of a submodule of an MMC in an embodiment of the present invention, a negative transition time and a previous sampling time of the capacitor voltage of the submodule of the MMC; wherein (n-1) Tsam、nTsam、(m-1)Tsam、mTsamRespectively corresponding to the positive jump moment and the previous sampling moment of the capacitance voltage of the MMC sub-module, and the negative jump moment and the previous sampling moment of the capacitance voltage of the MMC sub-module.
In the embodiment of the invention, the capacitor voltage and the bridge arm current are sampled at a fixed sampling frequency, and when positive jump on the capacitor voltage is detected, a capacitor voltage sampling value and a bridge arm current sampling value at the sampling moment are recorded, namely u isc1,rAnd ic,r(ii) a The sampling value of the capacitor voltage at the sampling moment before the sampling moment is uc2,r(ii) a Similarly, when a negative jump on the capacitor voltage is detected, the sampled value of the capacitor voltage at the sampling moment is recorded, i.e. uc1,f(ii) a And the samplingThe capacitance voltage sampling value and the bridge arm current sampling value at the previous sampling moment are uc2,fAnd ic,f。
The above embodiment is a preferred embodiment of the present invention, and in other embodiments, the MMC submodule capacitor voltage may not need to perform high-pass filtering, and the purpose of the present invention can also be achieved, which is only a difference in precision.
In one embodiment, the high-pass filtering of the capacitance voltage of the MMC submodule can be realized by an analog filter. The high-pass filtering can remove the direct current bias in the capacitor voltage, because the capacitor voltage contains a direct current voltage component and an alternating current fluctuation component, and the alternating current fluctuation amplitude is generally 5 percent of the former, the original voltage is directly sampled, the sampled voltage signal range is too wide, and the precision is not high. The measuring range of the voltage sensor can be reduced by filtering out the direct-current component in the voltage through high-pass filtering, so that the measuring precision is improved.
In one embodiment, after the capacitance voltage of the MMC sub-module is subjected to high-pass filtering, an analog sampling chip is used for sampling.
In one embodiment, the bandwidth of the filtering, sampling and conditioning process of the capacitance voltage of the MMC sub-module should satisfy: the switch frequency component in the capacitor voltage is not filtered, or the positive and negative jump of the capacitor voltage is completely reserved.
The embodiment of the invention can be used for online monitoring of the ESR value of the direct-current side capacitor of the MMC sub-module or the total ESR value of the capacitor bank, and the monitoring process is carried out when the MMC system normally runs, so that the running state of the system cannot be changed or stopped. Further, when the real-time online monitoring result of the ESR value of the capacitor of the MMC sub-module is within a preset range of the ESR value of the capacitor, determining that the capacitor is in a normal state, otherwise, determining that the capacitor is invalid, and maintaining and replacing the sub-module capacitor; the preset range of the capacitor ESR value is determined according to the parameters given by a capacitor manual.
In a preferred embodiment, after the real-time detection result of the ESR value is obtained, the real-time detection result of the ESR value is subjected to data processing by using a filtering algorithm, so that the smoothness and stability of the detection result of the ESR value can be improved, and the interference of random noise in the detection result can be eliminated. Wherein the filtering algorithm includes, but is not limited to, a moving average filtering, a least mean square error (LMS), a Recursive Least Squares (RLS), and the like.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (10)

1. The MMC submodule capacitor ESR value online monitoring method is characterized by comprising the following steps:
sampling and conditioning the capacitance voltage of the MMC sub-module and the bridge arm current flowing into the MMC sub-module;
carry out voltage jump to the MMC submodule piece capacitor voltage after above-mentioned sampling, conditioning and detect, include: detecting positive jump and negative jump;
the following characteristic values are recorded based on the voltage jump detection result of the MMC submodule capacitor voltage:
MMC submodule capacitor voltage positive jump previous sampling moment capacitor voltage value uc1,r；
MMC submodule capacitor voltage value u at positive jump moment of capacitor voltagec2,r；
Bridge arm current value i at positive jump moment of capacitance and voltage of MMC sub-modulec,r；
Capacitance voltage value u of MMC sub-module at previous sampling moment of capacitance voltage negative jumpc1,f；
MMC submodule capacitor voltage value u at negative jump moment of capacitor voltagec2,f；
Bridge arm current value i at previous sampling moment of MMC sub-module negative jumpc,f；
According to the characteristic values, the ESR value of the capacitor of the MMC sub-module is calculated in real time, the real-time monitoring result of the ESR value is obtained, and the calculation formula of the ESR value is as follows:
Figure FDA0002995994700000011
2. the MMC sub-module capacitor ESR value online monitoring method of claim 1, further comprising before sampling and conditioning the MMC sub-module capacitor voltage and the MMC sub-module input current:
and carrying out high-pass filtering on the capacitance voltage of the MMC sub-module.
3. The MMC sub-module capacitor ESR value online monitoring method of claim 2, wherein the MMC sub-module capacitor voltage is high-pass filtered by an analog filter.
4. The MMC sub-module capacitor ESR value online monitoring method of claim 2, wherein: and after the capacitance voltage of the MMC sub-module is subjected to high-pass filtering, sampling is carried out by utilizing an analog sampling chip.
5. The MMC sub-module capacitor ESR value online monitoring method of claim 2, wherein: the bandwidth of the filtering, sampling and conditioning process of the MMC sub-module capacitor voltage is required to meet the following requirements:
the switching frequency components in the capacitor voltage are not filtered out, or,
the positive and negative jumps of the capacitor voltage are completely preserved.
6. The MMC sub-module capacitor ESR value online monitoring method of claim 1, wherein the MMC sub-module capacitor voltage positive jump detection comprises:
with a sampling period of TsamSampling capacitor voltage of MMC sub-module at sampling time nTsamSampled value of the capacitor voltage of uc[n]The sampling instant (n-1) T preceding the sampling instant TsamSampled value of the capacitor voltage of uc[n-1]The threshold value of the change of the capacitance voltage is set as Uth,rIf u isc[n]-uc[n-1]＞Uth,rAnd the capacitance voltage of the MMC sub-module generates positive jump.
7. The MMC sub-module capacitor ESR value online monitoring method of claim 1, wherein the MMC sub-module capacitor voltage negative jump detection comprises:
with a sampling period of TsamSampling capacitor voltage of MMC submodule at mT sampling timesamSampled value of the capacitor voltage of uc[m](ii) a Sampling time mTsamPrevious sampling instant (m-1) TsamSampled value of the capacitor voltage of uc[m-1]The threshold value of the change of the capacitance voltage is set as Uth,fIf u isc[m]-uc[m-1]＜Uth,fAnd the MMC sub-module capacitor voltage generates negative jump.
8. The MMC sub-module capacitor ESR value online monitoring method of any of claims 1-7, wherein the real-time monitoring result of the ESR value is filtered by a filtering algorithm.
9. The MMC sub-module capacitor ESR value online monitoring method of claim 8, wherein the filtering algorithm is a moving average filtering, a least mean square error (LMS) or a Recursive Least Squares (RLS) filtering algorithm.
10. An online capacitance ESR monitoring apparatus for MMC submodule, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor is operable to execute the program to perform the method of any of claims 1 to 9.
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