CN111521928A - Grid-connected switch failure detection method and system of three-phase inverter - Google Patents

Grid-connected switch failure detection method and system of three-phase inverter Download PDF

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Publication number
CN111521928A
CN111521928A CN202010353032.5A CN202010353032A CN111521928A CN 111521928 A CN111521928 A CN 111521928A CN 202010353032 A CN202010353032 A CN 202010353032A CN 111521928 A CN111521928 A CN 111521928A
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phase
grid
switch
phase inverter
connected switch
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CN111521928B (en
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李克成
张凤岗
李本强
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Sungrow Power Supply Co Ltd
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Sungrow Power Supply 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
    • G01R31/327—Testing of circuit interrupters, switches or circuit-breakers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
    • G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
    • G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
    • G01R19/16547—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies voltage or current in AC supplies
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Inverter Devices (AREA)

Abstract

The application discloses a grid-connected switch failure detection method and system for a three-phase inverter, so that whether a grid-connected switch contact is adhered or not is identified before the inverter is connected to a grid. Three filter capacitors in the inverter are connected in a star shape and led back to the midpoint of the bus; a voltage divider is connected between the negative pole of the bus and the ground; the grid-connected switch is formed by connecting two three-phase switches S1 and S2 in series. The method comprises the following steps: closing S2 when the inverter is stopped and S1 and S2 are both disconnected, and judging whether a preset condition is met, wherein the preset condition is that the deviation between any two phase line voltage waveforms corresponding to two ends of the grid-connected switch exceeds an error allowable range; if the three-phase switch is in the non-contact state, switching the switching states of the two three-phase switches, clamping the three filter capacitor voltages to a second preset value when the preset condition is met, switching the switching states of the two three-phase switches when the effective value of the alternating voltage of the voltage divider is not larger than a third preset value, and judging that the grid-connected switch is not in contact adhesion if the effective value of the alternating voltage of the voltage divider is not larger than the third preset value.

Description

Grid-connected switch failure detection method and system of three-phase inverter
Technical Field
The invention relates to the technical field of power electronics, in particular to a grid-connected switch failure detection method and system of a three-phase inverter.
Background
The grid-connected operation of the three-phase inverter means that the three-phase inverter converts direct current output by a direct current power supply (such as a photovoltaic array) into alternating current meeting the requirements of a power grid and sends the alternating current to the power grid. The three-phase inverter is connected to the grid via a grid-tie switch, which is usually composed of two three-phase switches connected in series according to the safety requirements, see three-phase switch S1 and three-phase switch S2 in fig. 1.
Once the contacts of the grid-connected switch are adhered, the connection between the three-phase inverter and the power grid cannot be timely disconnected when the three-phase inverter or the power grid fails to operate, and the situation is more severe. Therefore, before the three-phase inverter starts grid-connected operation, it is necessary to accurately recognize whether the grid-connected switch has a contact sticking condition.
Disclosure of Invention
In view of this, the present invention provides a method and a system for detecting a failure of a grid-connected switch of a three-phase inverter, so as to accurately identify whether a contact is attached to the grid-connected switch before the three-phase inverter starts grid-connected operation.
A grid-connected switch failure detection method of a three-phase inverter is disclosed, wherein three output filter capacitors in the three-phase inverter are connected in a star shape, and the central point of the star connection is connected back to the midpoint of a bus; a voltage divider is connected between the negative pole of the bus of the three-phase inverter and the ground; the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series;
the grid-connected switch failure detection method of the three-phase inverter comprises the following steps:
controlling the three-phase switch S2 to suck in and judging whether a preset condition is met or not in an initial state that the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both disconnected; the preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range;
if so, switching the switching states of the two three-phase switches, and judging whether the preset conditions are met again;
if the preset conditions are met during the second judgment, the voltages of the three star-connected output filter capacitors are clamped to a second preset value which is the same in frequency and phase with the power grid, and then whether the effective value of the alternating voltage on the voltage divider is larger than a third preset value is judged;
and if the effective value of the alternating voltage on the voltage divider is not greater than the third preset value, judging the condition that the grid-connected switch is not in contact adhesion.
Optionally, the clamping the voltage of the three star-connected output filter capacitors to a second preset value includes: and controlling the three-phase inverter to send waves to clamp the voltages of the three star-connected output filter capacitors to a second preset value which is the same in frequency and phase with the power grid.
Optionally, a transformer is connected between the three-phase inverter and the power grid;
the transformer secondary side winding adopts a star connection method, and the central point of the star connection method is not grounded, or the transformer secondary side winding adopts the star connection method, and the central point of the star connection method is grounded, or the transformer secondary side winding adopts a delta connection method; the secondary side winding of the transformer refers to a winding on the side of the transformer close to the three-phase inverter.
Optionally, before determining whether the effective value of the alternating voltage on the voltage divider is greater than a third preset value, the method further includes: and switching the switching states of the two three-phase switches again.
Optionally, when the switching states of the two three-phase switches are switched each time, the switching sequence of the three-phase switch S1 and the three-phase switch S2 is set, so that the situation that the two three-phase switches are attracted at the same time is avoided.
Optionally, the preset condition refers to that an effective value of a difference between instantaneous values of the line voltages AB and BC at the two ends of the grid-connected switch, an effective value of a difference between instantaneous values of the line voltages BC at the two ends of the grid-connected switch, and an effective value of a difference between instantaneous values of the line voltages CA at the two ends of the grid-connected switch are all greater than a first preset value.
Optionally, the method for detecting failure of the grid-connected switch of the three-phase inverter further includes:
clamping the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid;
then attracting a three-phase switch S1 and a three-phase switch S2;
and judging whether the preset conditions are met or not, and if not, judging the condition that the grid-connected switch is normally broken due to no contact burnout.
Optionally, the clamping the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid includes: and controlling the three-phase inverter to send waves to clamp the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid.
A grid-connected switch failure detection system of a three-phase inverter is characterized in that three output filter capacitors in the three-phase inverter are connected in a star shape, and the central point of the star connection is connected back to the midpoint of a bus; a voltage divider is connected between the negative pole of the bus of the three-phase inverter and the ground; the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series;
the grid-connected switch failure detection system of the three-phase inverter comprises a first detection unit and a second detection unit;
the first detection unit is used for controlling the three-phase switch S2 to attract and judge whether a preset condition is met or not in an initial state that the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both disconnected, if yes, switching the switching states of the two three-phase switches and judging whether the preset condition is met again; if the preset condition is met during the second judgment, triggering the second detection unit; the preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range;
the second detection unit is used for clamping the voltages of the three star-connected output filter capacitors to a second preset value which is the same in frequency and phase with the power grid, and then judging whether the effective value of the alternating voltage on the voltage divider is larger than a third preset value; if the voltage is not greater than the third preset value, switching the switching states of the two three-phase switches again, and judging whether the effective value of the alternating voltage on the voltage divider is greater than the third preset value again; and if the judgment result is not greater than the third preset value again, judging the condition that the grid-connected switch is not adhered to the contact.
Optionally, the grid-connected switch failure detection system of the three-phase inverter further includes a third detection unit, configured to clamp voltages of the three output filter capacitors to the same frequency and same amplitude as those of the power grid, and then pull in the three-phase switch S1 and the three-phase switch S2, to determine whether the preset condition is met, and if not, determine that the grid-connected switch is normally off due to no contact being burned.
According to the technical scheme, before the three-phase inverter is started, under the conditions that one three-phase switch is attracted and the other three-phase switch is disconnected, whether any two-phase or three-phase contact is adhered to the three-phase switch in the disconnected state or not is judged according to the difference value between the line voltages of any two phases corresponding to the two ends of the grid-connected switch, and then the judgment on the other three-phase switch is completed in the same way. If any two-phase or three-phase contact adhesion does not exist in the two three-phase switches, the three output filter capacitor voltages are clamped to a second preset value, under the condition that one three-phase switch is attracted and the other three-phase switch is disconnected, whether any one-phase contact adhesion exists in the three-phase switch in the disconnected state is judged according to the effective value of the alternating current voltage on the voltage divider connected between the negative pole of the bus and the ground, then the judgment of the other three-phase switch is finished in the same mode, and finally the detection of whether the contact adhesion exists in the whole grid-connected switch is finished.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a DC power grid-connected power generation system disclosed in the prior art;
fig. 2 is a schematic structural diagram of a dc power grid-connected power generation system disclosed in the embodiment of the present invention;
fig. 3 is a flowchart of a method for detecting failure of a grid-connected switch of a three-phase inverter according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a transformer having a secondary winding with a wye connection and a center point of the wye connection not grounded in the system of FIG. 2;
FIG. 5 is a schematic diagram of a transformer secondary winding in the system of FIG. 2 with delta connections;
fig. 6 is a flowchart of a grid-connected switch failure detection method for a three-phase inverter according to another embodiment of the present invention;
fig. 7 is a schematic structural diagram of a grid-connected switch failure detection system of a three-phase inverter according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention discloses a grid-connected switch failure detection method of a three-phase inverter, which is applied to a direct-current power supply grid-connected power generation system shown in figure 2.
The direct-current power supply grid-connected power generation system converts direct current output by a direct-current power supply (such as a photovoltaic array) into alternating current meeting the requirements of a power grid by using a three-phase inverter and sends the alternating current to the power grid. The three-phase inverter is connected with a power grid through a grid-connected switch, and the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series. The three-phase inverter comprises an inversion unit and an output filter circuit; the topology structure of the output filter circuit may be an LC type, an LCL type, or an LLCL type, and is not limited, and fig. 2 only uses the LC type topology structure as an example; the output filter circuit comprises three star-connected output filter capacitors which are respectively a capacitor Cf1 connected on an A phase line, a capacitor Cf2 connected on a B phase line and a capacitor Cf3 connected on a C phase line, and a center point O2 of the star connection is connected back to a bus midpoint O1. A voltage divider CY is further connected between the negative electrode of the bus of the three-phase inverter and the ground, and the voltage divider CY may be, for example, a voltage divider in a capacitive form, a resistive form, or a resistance-capacitance form, but is not limited to this, and fig. 2 only uses the voltage divider in the capacitive form as an example.
As shown in fig. 3, the method for detecting the grid-connected switch failure of the three-phase inverter includes:
step S01: in an initial state where the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both off, the three-phase switch S2 is controlled to be pulled in, and the process proceeds to step S02.
Step S02: and judging whether the preset conditions are met, if not, entering the step S09, and if so, entering the step S03. The preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range.
Specifically, the three line voltages at the head end of the grid-connected switch refer to three line voltages U at the left end of the three-phase switch S1AB、UBCAnd UCAThe three line voltages at the tail end of the grid-connected switch refer to three line voltages U 'at the right end of the three-phase switch S2'AB、U'BCAnd U'CA. The deviation between the AB line voltage waveforms at the two ends of the grid-connected switch is UABWaveform and U'ABThe deviation between the waveforms is U, and the deviation between the BC line voltage waveforms at the two ends of the grid-connected switch is UBCWaveform and U'BCThe deviation between the waveforms is U, and the deviation between the waveforms of the CA line voltages at the two ends of the grid-connected switch is UCAWaveform and U'CADeviation between waveforms.
Considering that there may be floating voltage at the head end of the grid-connected switch, and there may be error in the above determination by using the difference between the two line voltage effective values when determining the deviation between the two line voltage waveforms, the embodiment of the present invention recommends to use the effective value of the difference between the two line voltage instantaneous values for determination, at this time, the pre-determined value is used for determinationThe setting condition refers to an effective value (recorded as delta U) of the difference of instantaneous values of the voltages of the AB lines at two ends of the grid-connected switchAB) And the effective value (marked as delta U) of the difference between the instantaneous values of the voltages BC at the two ends of the grid-connected switchBC) And the effective value (recorded as delta U) of the difference between the instantaneous values of the line voltages CA at the two ends of the grid-connected switchCA) Are all larger than the first preset value.
When the three-phase switch is adhered to the contact, three conditions exist:
1. any phase contact is adhered (namely a single-phase switch on the phase is normally on), and the other two phases of contacts are normal;
2. any two-phase contact is adhered (namely, the single-phase switches on the two phases are always on), and the other phase contact is normal;
3. three-phase contacts are bonded (i.e., single-phase switches on the three phases are always on).
When the three-phase inverter is stopped, the three-phase switch S2 is closed, and the three-phase switch S1 is opened, the following operations are performed:
if the three-phase switch S1 goes to condition 1, Δ UAB、ΔUBCAnd Δ UCAAre all larger than zero, the former is a sufficiently unnecessary condition for the latter, since the latter is also likely to occur in the case where the three-phase switch S1 is normal or the three-phase switch S2 contacts are burned out and are normally off;
if the three-phase switch S1 occurs in case 2, described above, Δ UAB、ΔUBCOr Delta UCAThe value of (A) is zero, the former being a prerequisite for the latter; specifically, the method comprises the following steps: if the A, B two-phase contacts of the three-phase switch S1 are adhered, then Δ UABIs zero; if the B, C two-phase contacts of the three-phase switch S1 are adhered, then Δ UBCIs zero; if the A, C two-phase contacts of the three-phase switch S1 are adhered, then Δ UCAIs zero;
Δ U if the three-phase contacts of the three-phase switch S1 are stuckAB、ΔUBC、ΔUCAAre all zero, the former being an essential condition for the latter.
Based on this, in the case where the three-phase inverter is stopped, the three-phase switch S2 is pulled in, and the three-phase switch S1 is turned off: if Δ U is foundAB、ΔUBCAnd Δ UCAAt least one of them is zero, three-phase opening can be confirmedCase 2 or case 3 above exists with respect to S1; if Δ U is foundAB、ΔUBCAnd Δ UCAIf both of them are greater than zero, it indicates that the three-phase switch S1 may or may not exist in the above case 1, and it needs to be confirmed through the following steps S07 to S08.
In the above determination process, zero is used as a threshold, and in order to avoid erroneous determination in actual engineering application, a sufficient margin should be left in the threshold, so that in the embodiment of the present invention, a value slightly larger than zero, that is, a first preset value is used as the threshold in actual engineering application.
Step S03: the switching states of the three-phase switch S1 and the three-phase switch S2 are switched, and the process advances to step S04.
Step S04: and judging whether the preset conditions are met, if not, entering the step S09, and if so, entering the step S05.
Specifically, after detecting whether the above-mentioned case 2 or case 3 exists in the three-phase switch S1 (see steps S01 to S02) in a state where the three-phase inverter is stopped, the three-phase switch S2 is pulled in, and the three-phase switch S1 is turned off, the embodiment of the present invention switches the switching states of the three-phase switch S2 and the three-phase switch S1, and detects whether the above-mentioned case 2 or case 3 exists in the three-phase switch S2 in the same manner (see steps S03 to S04). The principle of steps S03-S04 is the same as steps S01-S02, and is not described here.
When switching the three-phase switch S2 and the three-phase switch S1, the embodiment of the present invention recommends the sequence of turning off the three-phase switch S2 and then turning on the three-phase switch S1, because: if the three-phase switch S1 is firstly closed and then the three-phase switch S2 is opened, after the three-phase switch S1 is closed and before the three-phase switch S2 is not opened, the three-phase switch S1 and the three-phase switch S2 are closed at the same time, and at this time, devices on a three-phase line may be damaged due to large current impact from a power grid.
Step S05: and clamping the voltage of the three star-connected output filter capacitors to a second preset value which is the same in frequency and phase with the power grid, wherein the amplitude of the second preset value is larger than zero.
Specifically, in the embodiment of the present invention, the voltage of the three star-connected output filter capacitors is clamped to the second preset value in the state that the three-phase switch S1 is closed and the three-phase switch S2 is opened. The specific implementation mode can be that the three-phase inverter is started and controlled to emit waves to clamp the voltages of the three star-connected output filter capacitors to a second preset value; the voltage of the output filter capacitors connected in three star-shaped ways can be clamped to a second preset value through an external charging circuit. In comparison, the former does not need an external charging circuit, which can save cost and is a more preferable implementation mode.
Since it is previously confirmed through steps S01 to S04 that neither of the three-phase switch S1 and the three-phase switch S2 is under the above-mentioned conditions 2 and 3 before the operation proceeds to step S05, after the three-phase inverter is started in a state where the three-phase switch S1 is closed and the three-phase switch S2 is opened, a short-circuit is not formed between any two phases, thereby ensuring safe starting operation of the three-phase inverter.
The second preset value is in the same frequency and phase with the power grid voltage, and the amplitude of the second preset value is not suitable to exceed the amplitude of the power grid voltage because devices in the system are basically configured according to the power grid voltage grade. The amplitude of the second preset value is not suitable for being too high or too low, the too high requirement on the withstand voltage of the capacitor C2 and the voltage divider CY is high, and the too low requirement on the withstand voltage can generate a detection error when the voltage detection precision is not high.
Step S06: and judging whether the effective value of the alternating voltage on the voltage divider CY is greater than a third preset value, if so, entering step S09, and if not, entering step S07.
Specifically, under the conditions that the three-phase switch S1 is closed, the three-phase switch S2 is disconnected, and the voltage of the three star-connected output filter capacitors is clamped to a second preset value:
if the three-phase switch S2 has the condition 1, assuming that the a-phase contact is adhered, an ac current is sent from the a-phase of the power grid, and finally flows into the ground through the a-phase switch of the three-phase switch S2, the a-phase switch of the three-phase switch S1, the capacitor Cf1, the capacitor C2 and the voltage divider CY in sequence, as shown by an ac current loop shown by a dotted arrow in fig. 2, an ac voltage is generated on the voltage divider CY; and due to the capacitance CThe voltage f1 is clamped to a second preset value, so that the sum of the AC voltage on the capacitor C2 and the voltage divider CY is equal to the phase voltage U at the tail end of the grid-connected switchASubtracting a second preset value, the capacitor C2 and the voltage divider CY distribute the sum of the ac voltages according to the magnitude of the impedance value; the same can be obtained when the phase B or phase C contacts are adhered;
if the three-phase switch S2 does not have the condition 1, the point-to-ground voltage of O2 is zero because the three output filter capacitors are balanced, and no ac voltage is generated on the voltage divider CY.
In summary, when the three-phase switch S1 is closed, the three-phase switch S2 is opened, and the voltages of the three star-connected output filter capacitors are clamped to the second preset value, it can be determined that the three-phase switch S2 has the condition 1 as soon as the voltage divider CY is found to have an ac voltage exceeding a certain value (i.e., the third preset value).
A transformer is usually connected between the three-phase inverter and the grid, and the secondary winding of the transformer (the winding on the side close to the three-phase inverter) may be star-connected with the center point of the star-connected being not grounded (as shown in fig. 4), may be star-connected with the center point of the star-connected being grounded, or may be delta-connected (as shown in fig. 5).
In the case that the secondary winding of the transformer is star-connected and the center point of the star-connection is not grounded, or the secondary winding of the transformer is delta-connected, if the three-phase switch S1 is closed and the three-phase switch S2 is opened without intervening the voltages of the three star-connected output filter capacitors, then when a load (see resistors R1 to R3 shown in fig. 4 and 5) with three phases asymmetrical and a neutral point grounded is connected to the secondary winding of the transformer, the phase voltage of the path with low impedance is relatively low. If the phase voltage is low to the extent of approximately zero, when the above-mentioned case 1 occurs in the three-phase switch S2, assuming that the a-phase contact is stuck, although the ac current loop shown in fig. 2 still exists, the ac voltage distributed to the capacitor Cf1 is approximately zero, which is very close to the result of detecting the ac voltage on the capacitor Cf1 when the three-phase switch S2 is normal, and therefore, it is no longer possible to accurately determine whether the above-mentioned case 1 occurs in the three-phase switch S2 based on the magnitude of the ac voltage on the capacitor Cf 1. In the embodiment of the invention, the voltage of the three star-connected output filter capacitors is clamped to the second preset value, so that the alternating voltage on the capacitor Cf1 is not reduced to a degree of approximately zero when the three-phase switch S2 has the condition 1, and whether the three-phase switch S2 has the condition 1 can be accurately judged according to the size of the alternating voltage on the capacitor Cf 1.
The magnitude of the ac voltage at the voltage divider CY is an effective value of the ac voltage at the voltage divider CY. In addition, the voltage divider CY is always superimposed with the dc voltage applied to the negative electrode of the dc power supply, and since the effective value and the average value of the dc voltage are equal and the effective value and the average value of the ac voltage are unequal, it can be determined whether the difference between the effective value and the average value of the voltage divider CY exceeds a fourth preset value to determine whether the effective value of the ac voltage on the voltage divider CY is greater than a third preset value, and if the difference between the effective value and the average value of the voltage divider CY exceeds the fourth preset value, it indicates that the three-phase switch S2 has the above condition 1.
Step S07: the switching states of the three-phase switch S1 and the three-phase switch S2 are switched back, and then the process proceeds to step S08.
Specifically, similarly to the above step S04, in step S07, it is recommended to turn off the three-phase switch S1 and then pull in the three-phase switch S2.
Step S08: and judging whether the effective value of the alternating voltage on the voltage divider CY is greater than the third preset value, if so, entering step S09, and if not, entering step S10.
Specifically, after the condition 1 does not exist in the three-phase switch S2 is detected in the switching state where the three-phase switch S2 is turned off and the three-phase switch S1 is turned on (see steps S05 to S06), the switching states of the three-phase switch S2 and the three-phase switch S1 are switched, and the condition 1 does not exist in the three-phase switch S1 (see steps S05, S07 to S08) in the same manner.
Step S09: and reporting the fault and finishing the detection.
Step S10: and judging that the three-phase switches S1 and S2 are not adhered to each other, and finishing the detection.
As can be seen from the above description, in the embodiment of the present invention, before the three-phase inverter is started, when one three-phase switch is closed and the other three-phase switch is opened, whether any two-phase or three-phase contact is adhered to the three-phase switch in the open state is determined according to the difference between the voltages of any two-phase lines corresponding to the two ends of the grid-connected switch, and then the determination on the other three-phase switch is completed in the same manner. If the two three-phase switches are not adhered to any two-phase or three-phase contact, the voltage of the three output filter capacitors is clamped to a second preset value, under the condition that one three-phase switch is attracted and the other three-phase switch is disconnected, whether any one-phase contact is adhered to the three-phase switch in the disconnected state is judged according to the effective value of the alternating current voltage on the voltage divider CY, then the judgment on the other three-phase switch is finished in the same mode, and finally the detection on whether the contact is adhered to the whole grid-connected switch is finished.
It should be noted that the above embodiment is performed in the order of detecting whether the three-phase switch S2 has the case 1 and then detecting whether the three-phase switch S1 has the case 1, but the detection order is actually changeable, and the above embodiment is merely an example.
Grid-tie switch failure includes a condition that the three-phase switch S1 and/or the three-phase switch S2 contacts are burnt out and are normally broken, in addition to a condition that the three-phase switch S1 and/or the three-phase switch S2 contacts are stuck. The three-phase switch contact is burned out and normally broken, which may be that any one phase contact is burned out to cause the single-phase switch on the phase to be normally broken, or any two-phase contact is burned out to cause the single-phase switch on the two phases to be normally broken, or may be that the three-phase contact is burned out to cause the single-phase switch on the three phases to be normally broken.
In order to simultaneously detect the condition that the three-phase switch S1 and/or the three-phase switch S2 contacts are burned out and are normally open, the embodiment of the present invention further discloses a grid-connected switch failure detection method for a three-phase inverter, where before or after any one of the steps S01 to S10 is executed (for example, after the step S10 is executed, as shown in fig. 6), the method further includes:
step S11: and clamping the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid. The specific implementation of the clamping is described in the foregoing, and is not described in detail here.
Step S12: attracting a three-phase switch S1 and a three-phase switch S2;
step S13: judging whether the preset conditions are met, if not, indicating that the three-phase switches S1 and S2 are normal, and entering the step S14; if yes, it is determined that the three-phase switch S1 or S2 is normally open due to the contact burnout, and the process proceeds to step S09.
Step S14: and judging the condition that the grid-connected switch is normally broken due to no contact burning, and finishing the detection.
It should be noted that, when the three output filter capacitor voltages are clamped to the same frequency and amplitude as the power grid by controlling the three-phase inverter to generate waves, it is recommended that the steps S11 to S14 are set to be executed after the step S10 is executed, because in this case, after the step S14 is executed, the three-phase inverter is directly and seamlessly switched to the grid-connected operation state, and the three-phase inverter starts grid-connected power generation to meet the power demand of the user.
Corresponding to the embodiment of the method, the embodiment of the invention also discloses a grid-connected switch failure detection system of the three-phase inverter, wherein three output filter capacitors in the three-phase inverter are connected in a star shape, and the central points of the star connection are connected back to the midpoint of the bus; a voltage divider is connected between the negative pole of the bus of the three-phase inverter and the ground; the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series;
the grid-connected switch failure detection system of the three-phase inverter, as shown in fig. 7, includes a first detection unit 100 and a second detection unit 200;
the first detection unit 100 is configured to, in an initial state where the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both off, control the three-phase switch S2 to be attracted, determine whether a preset condition is met, if not, report a fault, if yes, switch the switching states of the two three-phase switches, determine whether the preset condition is met again, and if not, report a fault; if the preset condition is met during the second judgment, triggering the second detection unit 200; the preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range;
the second detection unit 200 is configured to clamp the voltages of the three star-connected output filter capacitors to a second preset value that is the same in frequency and phase as the power grid, and then determine whether an effective value of the alternating voltage on the voltage divider is greater than a third preset value, and if the effective value of the alternating voltage is greater than the third preset value, report a fault; if the voltage is not greater than the third preset value, switching the switching states of the two three-phase switches again, judging whether the effective value of the alternating voltage on the voltage divider is greater than the third preset value again, and if the effective value of the alternating voltage on the voltage divider is greater than the third preset value again, reporting a fault; and if the judgment result is not greater than the third preset value again, judging the condition that the grid-connected switch is not adhered to the contact.
Optionally, still referring to fig. 7, the system for detecting failure of a grid-connected switch of a three-phase inverter further includes a third detecting unit 300, configured to clamp voltages of three output filter capacitors to the same frequency and same amplitude as those of a power grid, then pull in a three-phase switch S1 and a three-phase switch S2, determine whether the preset condition is met, and if not, determine that the grid-connected switch is normally off due to no contact being burned; if yes, reporting a fault.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
Each embodiment of the present invention is described based on a case that the three-phase inverter sequentially accesses the power grid through the three-phase switch S1 and the three-phase switch S2, but in practice, each embodiment of the present invention is also applicable to a case that the three-phase inverter sequentially accesses the power grid through the three-phase switch S2 and the three-phase switch S1, and the principle is the same, and therefore, the description is omitted here.
In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, the use of the verb "comprise a" to define an element does not exclude the presence of another, identical element in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the embodiments. Thus, the present embodiments are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A grid-connected switch failure detection method of a three-phase inverter is characterized in that three output filter capacitors in the three-phase inverter are connected in a star shape, and the central points of the star connection are connected back to the middle point of a bus; a voltage divider is connected between the negative pole of the bus of the three-phase inverter and the ground; the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series;
the grid-connected switch failure detection method of the three-phase inverter comprises the following steps:
controlling the three-phase switch S2 to suck in and judging whether a preset condition is met or not in an initial state that the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both disconnected; the preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range;
if so, switching the switching states of the two three-phase switches, and judging whether the preset conditions are met again;
if the preset conditions are met during the second judgment, the voltages of the three star-connected output filter capacitors are clamped to a second preset value which is the same in frequency and phase with the power grid, and then whether the effective value of the alternating voltage on the voltage divider is larger than a third preset value is judged;
and if the effective value of the alternating voltage on the voltage divider is not greater than the third preset value, judging the condition that the grid-connected switch is not in contact adhesion.
2. The grid-connected switch failure detection method of the three-phase inverter according to claim 1, wherein the clamping of the voltages of the three star-connected output filter capacitors to a second preset value comprises: and controlling the three-phase inverter to send waves to clamp the voltages of the three star-connected output filter capacitors to a second preset value which is the same in frequency and phase with the power grid.
3. The grid-connected switch failure detection method of the three-phase inverter according to claim 1, wherein a transformer is connected between the three-phase inverter and a power grid;
the transformer secondary side winding adopts a star connection method, and the central point of the star connection method is not grounded, or the transformer secondary side winding adopts the star connection method, and the central point of the star connection method is grounded, or the transformer secondary side winding adopts a delta connection method; the secondary side winding of the transformer refers to a winding on the side of the transformer close to the three-phase inverter.
4. The method for detecting the grid-connected switch failure of the three-phase inverter according to claim 1, wherein before determining whether the effective value of the ac voltage on the voltage divider is greater than a third preset value, the method further comprises: and switching the switching states of the two three-phase switches again.
5. The grid-connected switch failure detection method of the three-phase inverter according to claim 1 or 4, wherein the switching sequence of the three-phase switch S1 and the three-phase switch S2 is set every time the switching states of the two three-phase switches are switched, so as to avoid the situation that the two three-phase switches are simultaneously pulled.
6. The method for detecting the failure of the grid-connected switch of the three-phase inverter according to claim 1, wherein the preset conditions are that an effective value of a difference between instantaneous values of AB line voltages at two ends of the grid-connected switch, an effective value of a difference between instantaneous values of BC line voltages at two ends of the grid-connected switch, and an effective value of a difference between instantaneous values of CA line voltages at two ends of the grid-connected switch are all larger than a first preset value.
7. The grid-connected switch failure detection method of a three-phase inverter according to claim 1, further comprising:
clamping the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid;
then attracting a three-phase switch S1 and a three-phase switch S2;
and judging whether the preset conditions are met or not, and if not, judging the condition that the grid-connected switch is normally broken due to no contact burnout.
8. The method according to claim 7, wherein the step of clamping the voltages of the three output filter capacitors to the same frequency and amplitude as the grid voltage comprises: and controlling the three-phase inverter to send waves to clamp the voltages of the three output filter capacitors to the same frequency and amplitude as the power grid.
9. A grid-connected switch failure detection system of a three-phase inverter is characterized in that three output filter capacitors in the three-phase inverter are connected in a star shape, and the central points of the star connection are connected back to the middle point of a bus; a voltage divider is connected between the negative pole of the bus of the three-phase inverter and the ground; the grid-connected switch is formed by connecting a three-phase switch S1 and a three-phase switch S2 in series;
the grid-connected switch failure detection system of the three-phase inverter comprises a first detection unit and a second detection unit;
the first detection unit is used for controlling the three-phase switch S2 to attract and judge whether a preset condition is met or not in an initial state that the three-phase inverter is stopped and the three-phase switch S1 and the three-phase switch S2 are both disconnected, if yes, switching the switching states of the two three-phase switches and judging whether the preset condition is met again; if the preset condition is met during the second judgment, triggering the second detection unit; the preset conditions refer to that the deviation between AB line voltage waveforms at two ends of the grid-connected switch, the deviation between BC line voltage waveforms at two ends of the grid-connected switch and the deviation between CA line voltage waveforms at two ends of the grid-connected switch exceed an error allowable range;
the second detection unit is used for clamping the voltages of the three star-connected output filter capacitors to a second preset value which is the same in frequency and phase with the power grid, and then judging whether the effective value of the alternating voltage on the voltage divider is larger than a third preset value; if the voltage is not greater than the third preset value, switching the switching states of the two three-phase switches again, and judging whether the effective value of the alternating voltage on the voltage divider is greater than the third preset value again; and if the judgment result is not greater than the third preset value again, judging the condition that the grid-connected switch is not adhered to the contact.
10. The system for detecting the failure of the grid-connected switch of the three-phase inverter according to claim 9, further comprising a third detection unit, configured to clamp voltages of the three output filter capacitors to have the same frequency and the same amplitude as a power grid, pull in the three-phase switch S1 and the three-phase switch S2, determine whether the preset condition is met, and if not, determine that the grid-connected switch is normally off due to no contact being burned.
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