CN113567748A - Converter direct current capacitance detection method, life prediction method and system - Google Patents
Converter direct current capacitance detection method, life prediction method and system Download PDFInfo
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Abstract
The invention discloses a converter direct current capacitance detection method, a life prediction method and a system, wherein the direct current capacitance detection method comprises the following steps: s1, injecting alternating current detection voltage with preset frequency and amplitude into a direct current bus of a tested converter; s2, detecting and acquiring input voltage and input current on a direct current bus of the converter, and detecting and acquiring phase current of an alternating current output end of the converter; calculating to obtain a first current of a direct current capacitor according to the input current and the phase current; s3, extracting a voltage component with the preset frequency from the input voltage, and extracting a current component with the preset frequency from the first current; and S4, calculating and determining the capacitance value of the direct current capacitor according to the voltage component and the current component. The device has the advantages of simple structure, low cost, convenient implementation, on-line detection and the like.
Description
Technical Field
The invention relates to the technical field of converters, in particular to a converter direct-current capacitor detection method, a converter direct-current capacitor service life prediction method and a converter direct-current capacitor service life prediction system.
Background
The development of power electronic technology enables electrical equipment containing direct-current bus support capacitors, such as uninterruptible power supplies, frequency converters, current transformers and the like, to be widely applied. The direct current bus support capacitor is used as a key energy storage element and mainly has the functions of buffering direct energy exchange between the power grid side and a load, stabilizing the bus voltage and inhibiting the direct current bus voltage from greatly fluctuating due to sudden change of the load.
The typical structure of a photovoltaic power generation system is shown in fig. 1, a photovoltaic power generation panel generates direct current, the direct current is converted into alternating current through a converter, and the alternating current is filtered and transformed and then output to a power grid for users to use. In a photovoltaic power generation system, a converter bears conversion work from direct current to alternating current, and is a core unit in the photovoltaic power generation system, and the stability of the photovoltaic power generation system is determined to a great extent by the stable state of the converter. In order to improve the working stability of the converter in the photovoltaic power generation system, the requirements on the aspects of fault diagnosis, health management and the like of the converter are higher and higher. The direct current support capacitor (capacitor C in fig. 1) is used as a key energy storage element in the converter and is also an element with a high fault rate in the converter, so that the running state and the residual life of the converter can be predicted, problems can be found in advance, and health maintenance prompt can be timely carried out, and the direct current support capacitor has very important significance.
In the prior art, in order to detect the service life of a capacitor, an off-line detection scheme is adopted, namely, the capacitor is periodically detached from a converter and then detected, however, a direct-current supporting capacitor is generally composed of a plurality of small-capacity capacitors in series-parallel connection to form a series-parallel capacitor assembly, the detachment is inconvenient, the operation can be carried out only by powering off and stopping the equipment, and a great deal of inconvenience is caused in practical application. In addition, some technologies collect the temperature and the voltage and the current of the capacitor, and then estimate the service life of the capacitor based on an Arrhenius empirical formula, or estimate the service life of the capacitor after capacitance value calculation based on a capacitance charge-discharge principle.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides a converter direct current capacitance detection method, a converter direct current capacitance service life prediction method and a converter direct current capacitance service life prediction system which are simple in structure, low in cost, convenient to implement and capable of conducting online detection.
In order to solve the technical problems, the technical scheme provided by the invention is as follows: a converter direct current capacitance detection method comprises the following steps:
s1, injecting alternating current detection voltage with preset frequency and amplitude into a direct current bus of a tested converter;
s2, detecting and acquiring input voltage and input current on a direct current bus of the converter, and detecting and acquiring phase current of an alternating current output end of the converter; calculating to obtain a first current of a direct current capacitor according to the input current and the phase current;
s3, extracting a voltage component with the preset frequency from the input voltage, and extracting a current component with the preset frequency from the first current;
and S4, calculating and determining the capacitance value of the direct current capacitor according to the voltage component and the current component.
Further, in step S1, the preset frequency is smaller than a disturbance frequency generated by the switching operation of the converter on the dc current and smaller than an ac-side voltage fundamental frequency of the converter.
Furthermore, the value range interval of the preset frequency is [0.1X, 0.5X ], and X is the fundamental frequency of the alternating-current side voltage of the converter.
Further, step S2 includes detecting and acquiring a switching tube state of each phase of the ac output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the phase outputs current; when the lower tube of the switching tube of the phase is conducted, the phase has no output current.
Further, the first current is determined by subtracting the phase current from the input current in step S2.
Further, step S3 specifically includes filtering the input voltage and the first current at a preset filtering frequency interval, taking the filtered input voltage as a voltage component, and taking the filtered input current as a current component.
A method for predicting the service life of a direct current capacitor of a converter comprises the steps of determining the capacitance value of the direct current capacitor according to the method for detecting the direct current capacitor of the converter, judging whether the ratio of a capacitance error value to the nominal capacitance value of the direct current capacitor is larger than a preset threshold value, if so, judging that the service life of the direct current capacitor is limited, and otherwise, judging that the direct current capacitor is effective; the capacitance error value is a difference between the capacitance value and a nominal capacitance value of the dc capacitor.
A converter direct current capacitance detection system comprises a detection voltage injection module, an input end electric energy detection module, an output end electric energy detection module and an analysis processing module; the voltage injection module, the input end electric energy detection module and the output end electric energy detection module are respectively connected with the analysis processing module;
the detection voltage injection module is connected with a direct current bus of the converter and used for injecting alternating current detection voltage with preset frequency and preset amplitude into the direct current bus;
the input end electric energy detection module is used for detecting and acquiring input voltage and input current on a direct current bus of the converter;
the output end electric energy detection module is used for detecting and acquiring phase current of the alternating current output end of the converter;
the analysis processing module is used for calculating to obtain a first current of a direct current capacitor according to the input current and the phase current, extracting a voltage component with the preset frequency from the input voltage, extracting a current component with the preset frequency from the first current, and calculating and determining a capacitance value of the direct current capacitor according to the voltage component and the current component.
Furthermore, the output end electric energy detection module also comprises a switching tube state detection submodule;
the switching tube state detection submodule is used for detecting and acquiring the state of a switching tube of each phase of the alternating current output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the output end electric energy detection module outputs the current of the phase; when the lower tube of the switching tube of the phase is conducted, the output end electric energy detection module outputs no current of the phase.
Further, the analysis processing module further includes a filtering submodule, where the filtering submodule is configured to filter the input voltage and the first current in a preset filtering frequency interval, and use the input voltage obtained after filtering as a voltage component and the input current obtained after filtering as a current component.
Compared with the prior art, the invention has the advantages that:
1. the invention can complete the detection of the direct current capacitor by utilizing the hardware equipment of the current transformer only by adding the detection voltage injection module for injecting the alternating current detection voltage to the current transformer, and has the advantages of simple structure, convenient implementation, low cost and the like.
2. According to the invention, in the process of detecting the direct-current capacitor, the direct-current capacitor can be detected in the running process without stopping and powering off the power generation system and the converter, namely, the detection process can be carried out on line, and the detection convenience is good.
3. According to the invention, the capacitance value of the direct current capacitor can be calculated by injecting the alternating current detection voltage into the direct current bus and extracting the component with the alternating current detection voltage frequency from the input voltage and the first current, and the detection speed is high, the efficiency is high, and the accuracy is good; meanwhile, the frequency of the injected alternating current detection voltage is low, the duration is short, the normal operation of the converter cannot be influenced, and the continuous, stable and reliable operation of the converter can be ensured.
Drawings
Fig. 1 is a schematic diagram of a typical structure of a photovoltaic power generation system in the prior art.
Fig. 2 is a schematic diagram of a detection process according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of a current situation according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a detection system according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
As shown in fig. 2, the method for detecting the dc capacitance of the current transformer of the present embodiment includes: s1, injecting alternating current detection voltage with preset frequency and amplitude into a direct current bus of a tested converter; s2, detecting and acquiring input voltage and input current on a direct current bus of the converter, and detecting and acquiring phase current of an alternating current output end of the converter; calculating to obtain a first current of a direct current capacitor according to the input current and the phase current; s3, extracting a voltage component with the preset frequency from the input voltage, and extracting a current component with the preset frequency from the first current; and S4, calculating and determining the capacitance value of the direct current capacitor according to the voltage component and the current component.
In this embodiment, in step S1, the preset frequency is preferably smaller than a disturbance frequency generated by the switching operation of the inverter on the dc current and smaller than an ac-side voltage fundamental wave frequency of the inverter. Further preferably, the range of the preset frequency is [0.1X, 0.5X ], where X is the fundamental frequency of the ac-side voltage of the converter.
In this embodiment, preferably, in step S2, the method further includes detecting and acquiring a switching tube state of each phase of the ac output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the phase outputs current; when the lower tube of the switching tube of the phase is conducted, the phase has no output current. The first current is determined by subtracting the phase current from the input current in step S2.
In this embodiment, preferably, the step S3 specifically includes filtering the input voltage and the first current in a preset filtering frequency interval, taking the filtered input voltage as a voltage component, and taking the filtered input current as a current component.
A method for predicting the service life of a direct current capacitor of a converter comprises the steps of determining the capacitance value of the direct current capacitor according to the method for detecting the direct current capacitor of the converter, judging whether the ratio of a capacitance error value to the nominal capacitance value of the direct current capacitor is larger than a preset threshold value, if so, judging that the service life of the direct current capacitor is limited, and otherwise, judging that the direct current capacitor is effective; the capacitance error value is a difference between the capacitance value and a nominal capacitance value of the dc capacitor.
A converter direct current capacitance detection system is shown in figure 4 and comprises a detection voltage injection module, an input end electric energy detection module, an output end electric energy detection module and an analysis processing module; the voltage injection module, the input end electric energy detection module and the output end electric energy detection module are respectively connected with the analysis processing module; the detection voltage injection module is connected with a direct current bus of the converter and used for injecting alternating current detection voltage with preset frequency and preset amplitude into the direct current bus; the input end electric energy detection module is used for detecting and acquiring input voltage and input current on a direct current bus of the converter; the output end electric energy detection module is used for detecting and acquiring phase current of the alternating current output end of the converter; the analysis processing module is used for calculating to obtain a first current of a direct current capacitor according to the input current and the phase current, extracting a voltage component with the preset frequency from the input voltage, extracting a current component with the preset frequency from the first current, and calculating and determining a capacitance value of the direct current capacitor according to the voltage component and the current component.
In this embodiment, preferably, the output end electric energy detection module further includes a switching tube state detection submodule; the switching tube state detection submodule is used for detecting and acquiring the state of a switching tube of each phase of the alternating current output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the output end electric energy detection module outputs the current of the phase; when the lower tube of the switching tube of the phase is conducted, the output end electric energy detection module outputs no current of the phase.
In this embodiment, preferably, the analysis processing module further includes a filtering submodule, where the filtering submodule is configured to filter the input voltage and the first current in a preset filtering frequency interval, and use the input voltage obtained after filtering as a voltage component and the input current obtained after filtering as a current component.
In this embodiment, a specific detection process is taken as an example to describe the operation process of the method and the system, and as shown in fig. 3, a photovoltaic power station converts generated direct current electric energy into three-phase alternating current through a converter and outputs the three-phase alternating current to a power grid, and the converter converts the direct current into power frequency alternating current with a frequency of 50 Hz. The converter converts direct current into alternating current by on-off control of the switch tube, and the disturbance frequency generated by the action of the switch tube is mainly distributed above 100Hz, therefore, in the embodiment, the frequency of the alternating current detection voltage injected into the direct current bus of the converter is 20Hz, the voltage is 20V, and the preferable frequency range is [5Hz, 25Hz ]]Preferably, the voltage range is [0.02Y, 0.05Y ]]And Y is the converter dc bus voltage, and the converter dc bus operating voltage in this embodiment is about 600V, so as to ensure that the voltage component and the current component required for calculating the capacitance value of the dc capacitor C can be conveniently detected, and the normal operation of the converter is not affected. The injected ac detection voltage can be expressed as: vinfF × sin (2 × pi × H × t), H being a predetermined frequency and F being a predetermined amplitude, a party according to the present embodiment, i.e., Vinf＝20×sin(2×π×20×t)。
In this embodiment, the voltage between the positive and negative electrodes of the dc bus can be detected by the voltage sensor to be VdcThe current value of the positive level of the direct current bus can be detected to be I through the current sensorin. Meanwhile, the current sensors arranged on the output ends of the current transformer can detect the output currents I of the three phases of the current transformer A, B, Ca、Ib、IcThen, the output current of the converter is Ia+Ib+IcThen, the first current on the DC capacitor C can be calculated as Icap＝Iin-(Ia+Ib+Ic). In this embodiment, considering the influence of the switching state of the switching tube on the output current, it is preferable to further obtain the state of the switching tube, and in the same two switching tubes, when the upper tube is conducted, the phase is considered to have current output, and when the lower tube is conducted, the phase is considered to have no current output, that is, the output current isAnd 0, the upper pipe is a switch pipe connected with the positive pole of the direct current bus, and the lower pipe is a switch pipe connected with the negative pole of the direct current bus. In the present embodiment, a state parameter S of the switch tube is definedx＝a,b,cIs provided with
a, b, and C represent phases of the output, the first current on the dc capacitor C can be obtained as: i iscap＝Iin-(Ia×Sa+Ib×Sb+Ic×Sc)。
In the present embodiment, the input voltage V is obtaineddcAnd a first current IcapThen, the filter frequency interval is preset [15Hz, 25Hz ]]Filtering to obtain voltage component required for calculating capacitance value and current component required for calculating capacitance value, and passing through
The capacitance of the dc capacitor can be calculated, where I is the current component, V is the voltage component, and f is the frequency of the injected ac detection voltage. In this embodiment, f is 20.
In the embodiment, the predetermined filtering frequency interval is determined according to a predetermined frequency of the ac detection voltage, preferably [ f- λ, f + λ ], preferably λ is smaller than 10, and f + λ is smaller than a disturbance frequency generated by the switching tube.
The foregoing is considered as illustrative of the preferred embodiments of the invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.
Claims (10)
1. A method for detecting a direct current capacitor of a converter is characterized by comprising the following steps:
s1, injecting alternating current detection voltage with preset frequency and amplitude into a direct current bus of a tested converter;
s2, detecting and acquiring input voltage and input current on a direct current bus of the converter, and detecting and acquiring phase current of an alternating current output end of the converter; calculating to obtain a first current of a direct current capacitor according to the input current and the phase current;
s3, extracting a voltage component with the preset frequency from the input voltage, and extracting a current component with the preset frequency from the first current;
and S4, calculating and determining the capacitance value of the direct current capacitor according to the voltage component and the current component.
2. The converter direct current capacitance detection method according to claim 1, characterized in that: in step S1, the preset frequency is smaller than a disturbance frequency generated by a switching operation of the converter on the dc current and smaller than an ac-side voltage fundamental frequency of the converter.
3. The converter direct current capacitance detection method according to claim 1, characterized in that: the value range interval of the preset frequency is [0.1X, 0.5X ], and X is the fundamental frequency of the alternating-current side voltage of the converter.
4. The converter direct current capacitance detection method according to claim 2, characterized in that: step S2, detecting and acquiring the state of a switch tube of each phase of the alternating current output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the phase outputs current; when the lower tube of the switching tube of the phase is conducted, the phase has no output current.
5. The converter direct current capacitance detection method according to claim 4, characterized in that: the first current is determined by subtracting the phase current from the input current in step S2.
6. The converter direct current capacitance detection method according to claim 4, characterized in that: step S3 specifically includes filtering the input voltage and the first current at a preset filtering frequency interval, taking the filtered input voltage as a voltage component, and taking the filtered input current as a current component.
7. A method for predicting the service life of a direct current capacitor of a converter is characterized by comprising the following steps: the converter direct current capacitance detection method according to any one of claims 1 to 6, determining a capacitance value of a direct current capacitor, determining whether a ratio of a capacitance error value to a nominal capacitance value of the direct current capacitor is greater than a preset threshold, if so, determining that the direct current capacitor has reached a lifetime limit, otherwise, determining that the direct current capacitor is valid; the capacitance error value is a difference between the capacitance value and a nominal capacitance value of the dc capacitor.
8. A converter direct current capacitance detection system which characterized in that: the device comprises a detection voltage injection module, an input end electric energy detection module, an output end electric energy detection module and an analysis processing module; the voltage injection module, the input end electric energy detection module and the output end electric energy detection module are respectively connected with the analysis processing module;
the detection voltage injection module is connected with a direct current bus of the converter and used for injecting alternating current detection voltage with preset frequency and preset amplitude into the direct current bus;
the input end electric energy detection module is used for detecting and acquiring input voltage and input current on a direct current bus of the converter;
the output end electric energy detection module is used for detecting and acquiring phase current of the alternating current output end of the converter;
the analysis processing module is used for calculating to obtain a first current of a direct current capacitor according to the input current and the phase current, extracting a voltage component with the preset frequency from the input voltage, extracting a current component with the preset frequency from the first current, and calculating and determining a capacitance value of the direct current capacitor according to the voltage component and the current component.
9. The converter dc capacitance detection system of claim 8, wherein: the output end electric energy detection module also comprises a switching tube state detection submodule;
the switching tube state detection submodule is used for detecting and acquiring the state of a switching tube of each phase of the alternating current output end of the converter; when the upper tube of the switching tube of the phase is in a conducting state, the output end electric energy detection module outputs the current of the phase; when the lower tube of the switching tube of the phase is conducted, the output end electric energy detection module outputs no current of the phase.
10. The converter dc capacitance detection system of claim 9, wherein: the analysis processing module further comprises a filtering submodule, wherein the filtering submodule is used for filtering the input voltage and the first current in a preset filtering frequency interval, the input voltage obtained after filtering is used as a voltage component, and the input current obtained after filtering is used as a current component.
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