CN117129910A - Open circuit detection method and system for photovoltaic inverter power device - Google Patents

Open circuit detection method and system for photovoltaic inverter power device Download PDF

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CN117129910A
CN117129910A CN202311408238.3A CN202311408238A CN117129910A CN 117129910 A CN117129910 A CN 117129910A CN 202311408238 A CN202311408238 A CN 202311408238A CN 117129910 A CN117129910 A CN 117129910A
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power device
photovoltaic
leakage current
boost
node
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CN117129910B (en
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许颇
王一鸣
魏剑雄
林万双
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Ginlong Technologies Co Ltd
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Ginlong Technologies Co Ltd
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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
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/54—Testing for continuity
    • 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
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention provides a method and a system for detecting an open circuit of a power device of a photovoltaic inverter, which relate to the technical field of inverters, and the method comprises the following steps: the TL-BOOST photovoltaic inverters in the photovoltaic power supply branches are controlled to be respectively and independently combined into a power grid, and the current leakage value of each photovoltaic power supply branch when the grid is connected is recorded; comparing the recorded multiple leakage current values to obtain a maximum leakage current value; analyzing the average value of a plurality of leakage current values to obtain a leakage level average value; obtaining a leakage threshold value according to the leakage average value and the floating coefficient; judging whether the maximum leakage current value is larger than a leakage threshold value or not; and when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open. Before the whole power supply system operates, the open circuit problem of the power device can be found in time, workers are reminded of maintenance, and the reliability and stability of the power supply system are guaranteed.

Description

Open circuit detection method and system for photovoltaic inverter power device
Technical Field
The invention relates to the technical field of inverters, in particular to a method and a system for detecting an open circuit of a power device of a photovoltaic inverter.
Background
The three-level direct current converter (TL-BOOST converter) is based on the deduction of the common BOOST converter and the half-bridge three-level direct current converter, the voltage of a switching tube is reduced by half compared with that of the common BOOST converter, the pressure of the switching tube is reduced, and the TL-BOOST conversion circuit is applied to the photovoltaic inverter, so that the reliability of a photovoltaic system is improved.
In the working process of a photovoltaic system, sometimes, one power device in the TL-BOOST conversion circuit may be open, at the moment, the TL-BOOST conversion circuit can still work, a photovoltaic inverter can also run in a grid-connected mode, the open-circuit problem of the power device is difficult to detect, but for the whole power supply system, the open-circuit power device can cause uneven bus voltage, the long-term running affects the reliability of the system, and more faults are easy to induce.
Disclosure of Invention
The problem to be solved by the invention is that the open circuit of the power device in the photovoltaic inverter is not easy to be perceived immediately, and the reliability of a power supply system can be reduced when the power device is continuously operated.
In order to solve the above problems, in one aspect, the present invention provides a method for detecting an open circuit of a power device of a photovoltaic inverter, including:
the TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches are controlled to be respectively and independently combined into a power grid, and the current leakage value of each photovoltaic power supply branch when grid connection is carried out is recorded, wherein the photovoltaic power supply branches are respectively and electrically connected with the power grid;
comparing the recorded multiple leakage current values to obtain a maximum leakage current value;
analyzing the average value of a plurality of leakage current values to obtain a leakage level average value;
obtaining a leakage threshold according to the leakage average value and the floating coefficient;
judging whether the maximum leakage current value is larger than the leakage threshold value or not;
and when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open.
Optionally, the TL-BOOST photovoltaic inverter includes a front stage TL-BOOST direct current BOOST circuit and a rear stage inverter circuit, an input end of the front stage TL-BOOST direct current BOOST circuit is used for being connected with the photovoltaic power generation system, an output end of the front stage TL-BOOST direct current BOOST circuit is connected with an input end of the rear stage inverter circuit, and an output end of the rear stage inverter circuit is used for being connected with a power grid.
Optionally, the front-stage TL-BOOST direct-current BOOST circuit includes a first inductor, a second inductor, a first power device, a second power device, a first capacitor, a second capacitor, a first diode, a second diode, a first load, and a second load;
one end of the first inductor is used for being connected with the positive electrode of the photovoltaic power generation system, one end of the second inductor is used for being connected with the negative electrode of the photovoltaic power generation system, the other end of the first inductor is respectively connected with the positive electrode of the first diode and one end of the first power device, and the negative electrode of the first diode is respectively connected with the positive electrode of the first capacitor and one end of the first load; the other end of the second inductor is respectively connected with the cathode of the second diode and one end of the second power device, and the anode of the second diode is respectively connected with the cathode of the second capacitor and one end of the first load; the other end of the first power device, the other end of the second power device, the negative electrode of the first capacitor, the positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected.
Optionally, when the first power device and the second power device are triodes, the other end of the first inductor is connected with the collector of the first power device, the other end of the second inductor is connected with the emitter of the second power device, and the emitter of the first power device, the collector of the second power device, the negative electrode of the first capacitor, the positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected;
or when the first power device and the second power device are MOS tubes, the other end of the first inductor is connected with the drain electrode of the first power device, the other end of the second inductor is connected with the source electrode of the second power device, and the source electrode of the first power device, the drain electrode of the second power device, the negative electrode of the first capacitor, the positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected.
Optionally, the controlling TL-BOOST photovoltaic inverters in the plurality of photovoltaic power supply branches to be individually incorporated into a power grid, and recording the leakage current value of each photovoltaic power supply branch when the photovoltaic power supply branches are connected includes:
a synchronous modulation strategy is adopted to control the synchronous switching-on of power devices in the front-stage TL-BOOST direct-current BOOST circuit;
and controlling the TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently integrated into a power grid.
Alternatively, the leakage current value is expressed as follows.
。
。
。
Wherein, node A, node B and node C are respectively positioned at the three-phase output end of the photovoltaic inverter, node N is positioned at the negative electrode of the second capacitor, nodepAt the other end of the first inductor, nodenAt the other end of the second inductor,the node is positioned at the positive electrode of the parasitic capacitor;/>for the leakage current value, +.>For the voltage between said node A and said node N, +.>For the voltage between said node B and said node N, +.>For the voltage between said node C and said node N, +.>For the nodepAnd the voltage between said nodes N, +.>For the nodenAnd the voltage between said nodes N, +.>And L is the resistance of the first inductor and the second inductor, ld is the resistance of the rectifying resistor of the three-phase output end of the photovoltaic inverter, s is s domain, and K1 and K2 are simplification coefficients.
Optionally, the voltage between the node p and the node NThe expression of (2) is as follows.
。
The voltage between the node N and the node NThe expression of (2) is as follows.
。
Wherein,for the voltage between the positive pole of the first capacitor and the negative pole of the second capacitor,/>For the output voltage of the photovoltaic power generation system, m represents the mth harmonic,/th harmonic>For the phase shift angle between the control PWM signals of two power devices in the front-stage TL-BOOST direct-current booster circuit, < >>For carrier angular frequency, < >>The harmonic amplitude is the m-th order switch.
Optionally, before comparing the recorded multiple leakage current values to obtain the maximum leakage current value, the open circuit detection method of the photovoltaic inverter power device further includes:
monitoring whether the post-stage inverter circuit in each TL-BOOST photovoltaic inverter operates normally or not;
and when the latter inverter circuit normally operates, comparing the recorded multiple leakage current values to obtain a maximum leakage current value.
Optionally, after the monitoring whether the post-stage inverter circuit in each TL-BOOST photovoltaic inverter operates normally, the photovoltaic inverter power device open circuit detection method further includes:
and when the rear-stage inverter circuit operates abnormally, generating an abnormal alarm signal.
In another aspect, the present invention further provides a system for detecting an open circuit of a power device of a photovoltaic inverter, including:
the grid-connected control module is used for controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently combined into a power grid, and recording a leakage current value of each photovoltaic power supply branch when grid connection is performed;
the current data analysis module is used for comparing the recorded multiple leakage current values to obtain a maximum leakage current value; the leakage current measuring device is also used for analyzing the average value of a plurality of leakage current values to obtain a leakage level average value; the leakage threshold value is also obtained according to the leakage average value and the floating coefficient;
the judging module is used for judging whether the maximum leakage current value is larger than the leakage threshold value or not; and the method is also used for judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open-circuited when the maximum leakage current value is larger than the leakage threshold value.
Compared with the prior art, the invention has the following beneficial effects:
according to the open circuit detection method and system for the photovoltaic inverter power device, disclosed by the invention, before a plurality of photovoltaic power supply branches are simultaneously integrated into a power grid, TL-BOOST photovoltaic inverters in the photovoltaic power supply branches are controlled to be respectively and independently integrated into the power grid, so that the leakage current value generated when each photovoltaic power supply branch is connected with the power grid can be collected, a plurality of leakage current values are collected in real time, the influence of switching subharmonic on an analysis result is reduced, the accuracy of the analysis result is improved, and the maximum leakage current value in the plurality of leakage current values and the average value of the plurality of leakage current values are screened out; because the influence of the open circuit of the power device on the leakage current value is obvious, a reasonable floating coefficient is added for the average value of the leakage level, the probability of misjudgment can be reduced, and the accuracy of an analysis result is improved; when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open, and before the whole power supply system operates, timely finding the open problem of the power device, reminding a worker to maintain, and guaranteeing the reliability and stability of the power supply system.
Drawings
FIG. 1 is a schematic diagram of a photovoltaic grid-tie circuit according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a pre-stage TL-BOOST DC BOOST circuit in accordance with an embodiment of the invention;
FIG. 3 is a schematic diagram showing an output state of a pre-stage TL-BOOST DC BOOST circuit according to an embodiment of the invention;
FIG. 4 is a schematic diagram showing a boosting state of a pre-stage TL-BOOST DC boosting circuit according to an embodiment of the invention;
FIG. 5 is a schematic diagram showing an open circuit state of a pre-stage TL-BOOST DC BOOST circuit in accordance with an embodiment of the invention;
fig. 6 is a schematic flow chart of a method for detecting an open circuit of a power device of a photovoltaic inverter according to an embodiment of the present invention;
FIG. 7 shows a simplified schematic diagram of a photovoltaic grid-tie circuit in an embodiment of the present invention;
fig. 8 shows a schematic structural diagram of a photovoltaic inverter power device open circuit detection system according to an embodiment of the present invention.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
It is noted that the terms "first," "second," and the like in the description and claims of the invention and in the foregoing figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein.
In the description of the present specification, the descriptions of the terms "embodiment," "one embodiment," and the like mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or embodiment is included in at least one embodiment or implementation of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same examples or implementations. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or implementations.
Fig. 1 shows a schematic diagram of a photovoltaic grid-connected circuit according to an embodiment of the present invention, in which fig. 1 shows a circuit diagram of grid connection of a photovoltaic power supply branch by way of example only, the photovoltaic grid-connected circuit includes a TL-BOOST photovoltaic inverter and a photovoltaic power generation system (PV), wherein the TL-BOOST photovoltaic inverter includes a front-stage TL-BOOST direct-current BOOST circuit and a rear-stage inverter circuit, an input end of the front-stage TL-BOOST direct-current BOOST circuit is connected to the photovoltaic power generation system, an output end of the front-stage TL-BOOST direct-current BOOST circuit is connected to an input end of the rear-stage inverter circuit, and an output end of the rear-stage inverter circuit is connected to a power grid.
Specifically, the front-stage TL-BOOST direct-current BOOST circuit is used for increasing direct-current voltage output by the photovoltaic power generation system, the rear-stage inverter circuit is used for converting direct-current voltage ratio output by the front-stage TL-BOOST direct-current BOOST circuit into alternating-current voltage, and the rear-stage inverter circuit is a three-level inverter circuit.
In one embodiment of the present invention, the pre-stage TL-BOOST DC BOOST circuit comprises a first inductor L1, a second inductor L2, a first power device Q1, a second power device Q2, and a first capacitorSecond capacitor->A first diode D1, a second diode D2, a first load R1 and a second load R2; one end of the first inductor L1 is used for being connected with the positive electrode of the photovoltaic power generation system, one end of the second inductor L2 is used for being connected with the negative electrode of the photovoltaic power generation system, the other end of the first inductor L1 is respectively connected with the positive electrode of the first diode D1 and one end of the first power device Q1, and the negative electrode of the first diode D1 is respectively connected with the first capacitor>Is connected with one end of the first load R1; the other end of the second inductor L2 is connected with the cathode of the second diode D2 and one end of the second power device Q2 respectively, the second inductor L2 is connected with the first inductor LThe anode of the two diodes D2 are respectively connected with the second capacitor +.>Is connected to one end of the second load R2; the other end of the first power device Q1, the other end of the second power device Q2 and the first capacitor +.>Is the negative pole of said second capacitor->The positive electrode of the first load R1, the other end of the second load R2 are all connected.
In one embodiment of the present invention, as shown in fig. 1, when the first power device Q1 and the second power device Q2 are MOS transistors, the other end of the first inductor L1 is connected to the drain of the first power device Q1, the other end of the second inductor L2 is connected to the source of the second power device Q2, the source of the first power device Q1, the drain of the second power device Q2, and the first capacitorIs the negative pole of said second capacitor->The positive electrode of the first load R1, the other end of the second load R2 are all connected.
In one embodiment of the present invention, as shown in fig. 2, when the first power device Q1 and the second power device Q2 are transistors, the other end of the first inductor L1 is connected to the collector of the first power device Q1, the other end of the second inductor L2 is connected to the emitter of the second power device Q2, the emitter of the first power device Q1, the collector of the second power device Q2, and the first capacitorIs the negative pole of said second capacitor->The positive electrode of the first load R1, the other end of the second load R2 are all connected.
Specifically, the principle of the front-stage TL-BOOST direct current BOOST circuit is that the power device is used for carrying out switch control on the circuit in an inductive energy storage mode and a capacitive energy storage mode, so that the input voltage is increased in the inductive energy storage process and then increased again in the capacitive energy storage process, and the voltage is increased. Specifically, as shown in fig. 3, when the first power device Q1 and the second power device Q2 are turned on synchronously, the current in the first inductor L1 and the second inductor L2 starts to increase, and the voltage across the inductor starts to increase at this time because the current change rate in the inductor is proportional to the voltage change rate, and the first capacitor at this timeAnd a second capacitance->The first load R1 and the second load R2 are supplied with power. As shown in fig. 4, when the first power device Q1 and the second power device Q2 are synchronously turned off, the current accumulated in the inductor starts to flow to the capacitor in the state of fig. 3, the current in the inductor decreases, and the voltage in the capacitor starts to increase, so that the output voltage further increases. Thus, the input voltage can be raised by continuously repeating the cycle.
As shown in fig. 5, it is assumed that the first power device Q1 is turned on and the second power device Q2 is open-circuited, the first capacitorAfter the internal current is released, the first resistor cannot be supplied with power later. And a second capacitor->When the first power device Q1 is switched on, the charge can still be obtained continuously, and when the first power device Q1 is switched off, only the second capacitor +.>The first load R1 and the second load R2 are powered, so that the output voltage becomes smaller, the photovoltaic power supply branch where the front-stage TL-BOOST direct-current BOOST circuit is located is smaller than other photovoltaic power supply branches, the problem of uneven output voltage is generated among a plurality of photovoltaic power supply branches, uneven bus voltage can be caused for the whole power supply system, and the stability and reliability of the power supply system are reduced.
Fig. 6 shows a flowchart of a method for detecting an open circuit of a power device of a photovoltaic inverter according to an embodiment of the present invention, where the method includes:
s1: and controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently combined into a power grid, and recording a current leakage value of each photovoltaic power supply branch when grid connection is performed, wherein the photovoltaic power supply branches are respectively and electrically connected with the power grid.
Fig. 7 is a simplified schematic diagram of a photovoltaic grid-connected circuit according to an embodiment of the present invention, where l1=l2=l, la=lb=lc=ld, and the effect of the low-frequency voltage source grid on the common-mode current is ignored, regardless of the parasitic capacitance of the power device to ground. Can be analyzed according to the node voltage methodThe expression of the leakage current is thus obtained as follows.
（1）。
For ease of analysis, the coefficients K1 and K2 are introduced, and the expression of the leakage current can be simplified as the following.
（2）。
（3）。
（4）。
Wherein, node A, node B and node C are respectively positioned at the three-phase output end of the photovoltaic inverter, and node N is positioned at the second capacitorIs a negative electrode, nodepIs positioned at the other end of the first inductor L1 and is connected with a nodenAt the other end of said second inductance L2, ">The node is positioned at the positive electrode of the parasitic capacitor; />For the leakage current value, +.>For the voltage between said node A and said node N, +.>For the voltage between said node B and said node N, +.>For the voltage between said node C and said node N, +.>For the nodepAnd the voltage between said nodes N, +.>For the nodenAnd the voltage between said nodes N, +.>For parasitic capacitance, L is the resistance of the first inductor L1 and the second inductor L2, ld is the resistance of the rectifying resistor at the three-phase output end of the photovoltaic inverter, s represents s domain, and K1 and K2 are simplification coefficients.
As can be seen from the above simplified expression, the leakage current value is not only subjected to the latter stageThe modulation strategy of the inverter circuit is influenced by the switching state of the front-stage TL-BOOST direct current BOOST circuit, the front half part of the simplified expression is mainly related to the modulation strategy of the inverter side, as long as the modulation strategy is stable, the leakage current value of the rear-stage inverter side is equivalent to a fixed value, and the value variation of the rear half part of the simplified expression is larger when the front-stage TL-BOOST direct current BOOST circuit is synchronous and phase-shifted in two modulation strategies, and then common mode analysis is carried out only on the front-stage TL-BOOST direct current BOOST circuitAnd->After fourier transformation, the voltage between the node p and the node N is +.>The expression of (2) is as follows.
（5）。
The voltage between the node N and the node NThe expression of (2) is as follows.
（6）。
Wherein,for the first capacitance->Is equal to the positive electrode of said second capacitor +.>Is provided, the voltage between the cathodes of (a),for the output voltage of the photovoltaic power generation system, m represents the mth harmonic,/th harmonic>For the phase shift angle between the control PWM signals of two power devices in the front-stage TL-BOOST direct-current booster circuit, < >>For carrier angular frequency, < >>The harmonic amplitude is the m-th order switch.
From the aboveAnd->The expression of (2) shows that the leakage current is influenced by the amplitude of the switching subharmonic, but the influence of the switching subharmonic on the leakage current is global, namely, each photovoltaic power supply branch is influenced by the amplitude of the switching subharmonic, and under the same operation environment, the TL-BOOST photovoltaic inverter in each photovoltaic power supply branch is independently integrated into a power grid, and the obtained leakage current value of each branch is influenced by the switching subharmonic. Thus->The balance among the photovoltaic power supply branches is not affected.
For a clearer understandingAnd->The influence of the variables in (a) on the leakage current value, taking the 1 st harmonic as an example, i.e. when m=1, the latter half of the leakage current reduction expression +.>And->The expression of the sum is as follows.
。
It can be clearly seen that the leakage current is mainly affected by the phase shift angle between the two power devices, and when the two power devices synchronously modulate (synchronously send waves to the two power devices and send control PWM signals with the same waveform),=0, and the leakage current value is theoretically 0 or the actual test is very small, so that the theoretical fluctuation range of the leakage current value can be calculated or predicted.
But when an open circuit occurs in one of the power devices in the front-stage TL-BOOST dc BOOST circuit,not equal to 0, the measured leakage current value increases significantly. Based on the above, the current leakage value generated when the TL-BOOST photovoltaic inverter in each photovoltaic power supply branch is independently integrated into the power grid is collected, monitored and analyzed.
S2: and comparing the recorded multiple leakage current values to obtain a maximum leakage current value.
Specifically, the maximum leakage current value is firstly screened out at a time, and when the photovoltaic power supply branch corresponding to the maximum leakage current value is analyzed, the open circuit condition does not appear, so that the photovoltaic power supply branch corresponding to the smaller leakage current value is left, and the open circuit problem of the power device does not occur. When the photovoltaic power supply branches corresponding to the maximum leakage current value at the moment are repaired, the other maximum leakage current value can be continuously monitored and analyzed in the rest photovoltaic power supply branches, and the analysis can be carried out for a plurality of times until it is determined that the power device open circuit problem does not occur in all the photovoltaic power supply branches. In addition, the recorded leakage current values can be subjected to difference between two pairs to obtain a plurality of absolute difference values; comparing a plurality of absolute differences to obtain a maximum absolute difference; and extracting two leakage current values corresponding to the maximum absolute difference value, and comparing the two leakage current values to obtain the maximum leakage current value.
S3: and analyzing the average value of the leakage current values to obtain a leakage level average value.
Specifically, as can be seen from the above, the leakage current value is affected by the switching subharmonic, but the effect of the switching subharmonic on the leakage current is global, each photovoltaic power supply branch is affected by the switching subharmonic, and under the same operating environment, the TL-BOOST photovoltaic inverter in each photovoltaic power supply branch is independently integrated into the power grid, and the obtained leakage current value of each branch is affected by the switching subharmonic. Therefore, when the open circuit fault monitoring is carried out each time, the leakage current value corresponding to each photovoltaic power supply branch is required to be collected in real time, and the leakage average value is calculated, so that on one hand, the average level of a plurality of leakage current values is calculated, and on the other hand, the influence of the leakage current value corresponding to the photovoltaic power supply branch with the open circuit fault of the power device on the average level is weakened.
S4: and obtaining a leakage threshold according to the leakage average value and the floating coefficient.
Specifically, the floating coefficient is generally set to 3-5, and the floating coefficient is additionally arranged, so that the compatibility of the leakage threshold is enlarged, and the occurrence of erroneous judgment is reduced.
S5: and judging whether the maximum leakage current value is larger than the leakage threshold value.
Specifically, when one power device is open,not equal to 0, the collected leakage current value becomes larger, and as +.>The leakage current value is larger, and the maximum leakage current value can be obviously monitored to be larger than the leakage threshold value.
S6: and when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open.
S7: and when the maximum leakage current value is smaller than or equal to the leakage threshold value, judging that the power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is normally turned on.
In the embodiment, before a plurality of photovoltaic power supply branches are simultaneously integrated into a power grid, TL-BOOST photovoltaic inverters in the plurality of photovoltaic power supply branches are controlled to be respectively and independently integrated into the power grid, so that leakage current values generated when each photovoltaic power supply branch is connected with the power grid can be collected, the plurality of leakage current values are collected in real time, the influence of switching subharmonics on analysis results is reduced, the accuracy of the analysis results is improved, and the maximum leakage current value in the plurality of leakage current values and the average value of the plurality of leakage current values are screened out; because the influence of the open circuit of the power device on the leakage current value is obvious, a reasonable floating coefficient is added for the average value of the leakage level, the probability of misjudgment can be reduced, and the accuracy of an analysis result is improved; when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open, and before the whole power supply system operates, timely finding the open problem of the power device, reminding a worker to maintain, and guaranteeing the reliability and stability of the power supply system.
In one embodiment of the present invention, the controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be individually incorporated into a power grid, and recording a leakage current value when each of the photovoltaic power supply branches is connected to the power grid includes:
a synchronous modulation strategy is adopted to control the synchronous switching-on of power devices in the front-stage TL-BOOST direct-current BOOST circuit;
and controlling the TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently integrated into a power grid.
In this embodiment, the adopted front-stage TL-BOOST dc BOOST circuit has symmetry, and when the synchronous modulation strategy is adopted to control the front-stage TL-BOOST dc BOOST circuitCan only ensure when the power device is usedThe power device does not adopt the phase-shifting asynchronization on as can be seen from the formula (6), and the phase-shifting asynchronization brings about larger +.>The value of the leakage current is obviously increased, the safety of workers is endangered, and in addition, the phase-shifting asynchronous switching on can also generate the problem of uneven output voltage of the photovoltaic power supply branch. Therefore, the synchronous modulation strategy is adopted to control the synchronous opening of the two power devices, thereby being beneficial to improving the stability of the photovoltaic power supply system.
In an embodiment of the present invention, before comparing the recorded plurality of leakage current values to obtain the maximum leakage current value, the open circuit detection method of the photovoltaic inverter power device further includes:
and monitoring whether the post-stage inverter circuit in each TL-BOOST photovoltaic inverter operates normally.
Specifically, as can be seen from the formula (2), the leakage current value is also affected by the modulation strategy of the post-stage inverter circuit, so that before the open-circuit fault of the power device of the pre-stage TL-BOOST direct-current BOOST circuit is monitored, whether the post-stage inverter circuit operates normally is required to be monitored, and the leakage current value change is eliminated as a result of the abnormality of the post-stage inverter circuit. The method comprises the steps of monitoring the voltage value of the input end of the back-stage inverter circuit, calculating a theoretical output voltage value through the input voltage value, collecting the output voltage value of the back-stage inverter circuit, judging whether the absolute difference value between the actually collected output voltage value and the theoretical output voltage value is in an allowable range, judging that the back-stage inverter circuit normally operates when the actually collected output voltage value and the theoretical output voltage value are not greatly different, and indicating that the back-stage inverter circuit abnormally operates when the absolute difference value between the actually collected output voltage value and the theoretical output voltage value exceeds the allowable range.
And when the latter inverter circuit normally operates, comparing the recorded multiple leakage current values to obtain a maximum leakage current value.
Specifically, the leakage current value brought by the post-stage inverter circuit which is normally operated is analyzed by the formula (1) and the formula (2) to be a fixed value, and the open-circuit fault analysis of the power device in the pre-stage TL-BOOST direct-current booster circuit is not influenced.
In one embodiment of the present invention, after the monitoring whether the post-stage inverter circuit in each TL-BOOST photovoltaic inverter operates normally, the method for detecting an open circuit of a power device of the photovoltaic inverter further includes:
when the latter inverter circuit operates abnormally, an abnormal alarm signal is generated so as to remind workers of maintenance in time. That is, the latter inverter circuit may be provided with a separate monitoring system for detecting whether the latter inverter circuit is operating normally.
In this embodiment, the existing fault detection scheme generally only needs to detect once, that is, only judges whether the final leakage current value exceeds the threshold value, and in this embodiment, the single-dimensional detection may have instability, so before the maximum leakage current value is obtained, whether the post-stage inverter circuit operates normally is detected by a separate detection system, which is different from the original detection system, but separately detects the pre-stage TL-BOOST dc circuit and the post-stage inverter circuit, thereby realizing multiple detection of circuit faults and achieving the purpose of improving the accuracy of circuit fault detection.
Fig. 8 shows a schematic structural diagram of an open circuit detection system for a power device of a photovoltaic inverter according to an embodiment of the present invention, where the open circuit detection system for a power device of a photovoltaic inverter includes:
the grid-connected control module 10 is used for controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently combined into a power grid, and recording a leakage current value of each photovoltaic power supply branch during grid connection;
a current data analysis module 20, configured to compare the recorded plurality of leakage current values to obtain a maximum leakage current value; the leakage current measuring device is also used for analyzing the average value of a plurality of leakage current values to obtain a leakage level average value; the leakage threshold value is also obtained according to the leakage average value and the floating coefficient;
a judging module 30, configured to judge whether the maximum leakage current value is greater than the leakage threshold; and the method is also used for judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open-circuited when the maximum leakage current value is larger than the leakage threshold value.
In this embodiment, the grid-connected control module 10 controls TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently integrated into a power grid, so that leakage current values generated when each photovoltaic power supply branch is connected to the grid can be collected, a plurality of leakage current values can be collected in real time, the influence of switching subharmonics on analysis results is reduced, the accuracy of the analysis results is improved, and the current data analysis module 20 screens out the largest leakage current value of the plurality of leakage current values and the average value of the plurality of leakage current values; because the influence of the open circuit of the power device on the leakage current value is obvious, a reasonable floating coefficient is added for the average value of the leakage level, the probability of misjudgment can be reduced, and the accuracy of an analysis result is improved; the judging module 30 judges whether the maximum leakage current value is greater than the leakage threshold value, and judges that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open circuit when the maximum leakage current value is greater than the leakage threshold value, so that the open circuit problem of the power device can be found in time before the whole power supply system operates, and the staff is reminded to maintain, thereby ensuring the reliability and stability of the power supply system.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims (10)

1. The open circuit detection method for the photovoltaic inverter power device is characterized by comprising the following steps of:
the TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches are controlled to be respectively and independently combined into a power grid, and the current leakage value of each photovoltaic power supply branch when grid connection is carried out is recorded, wherein the photovoltaic power supply branches are respectively and electrically connected with the power grid;
comparing the recorded multiple leakage current values to obtain a maximum leakage current value;
analyzing the average value of a plurality of leakage current values to obtain a leakage level average value;
obtaining a leakage threshold according to the leakage average value and the floating coefficient;
judging whether the maximum leakage current value is larger than the leakage threshold value or not;
and when the maximum leakage current value is larger than the leakage threshold value, judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open.
2. The method for detecting the open circuit of the power device of the photovoltaic inverter according to claim 1, wherein the TL-BOOST photovoltaic inverter comprises a front-stage TL-BOOST direct current BOOST circuit and a rear-stage inverter circuit, an input end of the front-stage TL-BOOST direct current BOOST circuit is used for being connected with a photovoltaic power generation system, an output end of the front-stage TL-BOOST direct current BOOST circuit is connected with an input end of the rear-stage inverter circuit, and an output end of the rear-stage inverter circuit is used for being connected with a power grid.
3. The method for detecting an open circuit of a photovoltaic inverter power device according to claim 2, wherein the pre-stage TL-BOOST direct current BOOST circuit comprises a first inductor, a second inductor, a first power device, a second power device, a first capacitor, a second capacitor, a first diode, a second diode, a first load, and a second load;
one end of the first inductor is used for being connected with the positive electrode of the photovoltaic power generation system, one end of the second inductor is used for being connected with the negative electrode of the photovoltaic power generation system, the other end of the first inductor is respectively connected with the positive electrode of the first diode and one end of the first power device, and the negative electrode of the first diode is respectively connected with the positive electrode of the first capacitor and one end of the first load; the other end of the second inductor is respectively connected with the cathode of the second diode and one end of the second power device, and the anode of the second diode is respectively connected with the cathode of the second capacitor and one end of the first load; the other end of the first power device, the other end of the second power device, the negative electrode of the first capacitor, the positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected.
4. The open circuit detection method of a photovoltaic inverter power device according to claim 3, wherein when the first power device and the second power device are transistors, the other end of the first inductor is connected to a collector of the first power device, the other end of the second inductor is connected to an emitter of the second power device, and the emitter of the first power device, the collector of the second power device, a negative electrode of the first capacitor, a positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected;
or when the first power device and the second power device are MOS tubes, the other end of the first inductor is connected with the drain electrode of the first power device, the other end of the second inductor is connected with the source electrode of the second power device, and the source electrode of the first power device, the drain electrode of the second power device, the negative electrode of the first capacitor, the positive electrode of the second capacitor, the other end of the first load and the other end of the second load are all connected.
5. The method for detecting an open circuit of a power device of a photovoltaic inverter according to claim 2, wherein the controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be individually incorporated into a power grid, and recording a leakage current value of each of the photovoltaic power supply branches when connected to the power grid comprises:
a synchronous modulation strategy is adopted to control the synchronous switching-on of power devices in the front-stage TL-BOOST direct-current BOOST circuit;
and controlling the TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently integrated into a power grid.
6. The open circuit detection method of a photovoltaic inverter power device according to claim 3, wherein the expression of the leakage current value is:
；
；
；
wherein, node A, node B and node C are respectively positioned at the three-phase output end of the photovoltaic inverter, node N is positioned at the negative electrode of the second capacitor, nodepAt the other end of the first inductor, nodenAt the other end of the second inductor,the node is positioned at the positive electrode of the parasitic capacitor; />For the leakage current value, +.>For the voltage between said node A and said node N, +.>For the voltage between said node B and said node N, +.>For the voltage between said node C and said node N, +.>For the nodepAnd the voltage between said nodes N, +.>For the nodenAnd the voltage between said nodes N, +.>And L is the resistance of the first inductor and the second inductor, ld is the resistance of the rectifying resistor of the three-phase output end of the photovoltaic inverter, s is s domain, and K1 and K2 are simplification coefficients.
7. The method for detecting an open circuit of a photovoltaic inverter power device according to claim 6, wherein a voltage between the node p and the node NThe method comprises the following steps:
；
the voltage between the node N and the node NThe method comprises the following steps:
；
wherein,for the voltage between the positive pole of the first capacitor and the negative pole of the second capacitor,/>For the output voltage of the photovoltaic power generation system, m represents the mth harmonic,/th harmonic>For the phase shift angle between the control PWM signals of two power devices in the front-stage TL-BOOST direct-current booster circuit, < >>For carrier angular frequency, < >>The harmonic amplitude is the m-th order switch.
8. The method for detecting an open circuit of a photovoltaic inverter power device according to claim 2, wherein the comparing the recorded plurality of leakage current values to obtain a maximum leakage current value further comprises:
monitoring whether the post-stage inverter circuit in each TL-BOOST photovoltaic inverter operates normally or not;
and when the latter inverter circuit normally operates, comparing the recorded multiple leakage current values to obtain a maximum leakage current value.
9. The method of claim 8, wherein after monitoring whether the post-inverter circuit in each TL-BOOST photovoltaic inverter is operating properly, further comprising:
and when the rear-stage inverter circuit operates abnormally, generating an abnormal alarm signal.
10. A photovoltaic inverter power device open circuit detection system, comprising:
the grid-connected control module (10) is used for controlling TL-BOOST photovoltaic inverters in a plurality of photovoltaic power supply branches to be respectively and independently combined into a power grid and recording a leakage current value of each photovoltaic power supply branch when grid connection is performed;
the current data analysis module (20) is used for comparing the recorded multiple leakage current values to obtain a maximum leakage current value; the leakage current measuring device is also used for analyzing the average value of a plurality of leakage current values to obtain a leakage level average value; the leakage threshold value is also obtained according to the leakage average value and the floating coefficient;
a judging module (30) for judging whether the maximum leakage current value is greater than the leakage threshold value; and the method is also used for judging that one power device in the TL-BOOST photovoltaic inverter corresponding to the maximum leakage current value is open-circuited when the maximum leakage current value is larger than the leakage threshold value.
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