CN109375099A - A kind of fault detection method of photovoltaic inverter grid-connected relay - Google Patents
A kind of fault detection method of photovoltaic inverter grid-connected relay Download PDFInfo
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- CN109375099A CN109375099A CN201811219717.XA CN201811219717A CN109375099A CN 109375099 A CN109375099 A CN 109375099A CN 201811219717 A CN201811219717 A CN 201811219717A CN 109375099 A CN109375099 A CN 109375099A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention discloses a kind of fault detection method of photovoltaic inverter grid-connected relay, the fault detection method includes: sample circuit detection, for judging line voltage sample circuit with the presence or absence of abnormal；Impedance earth detection, the case where for judging whether there is firewire impedance earth；If it exists the case where firewire impedance earth, then the Relay detection under the conditions of impedance earth is carried out, for the Relay abnormality detection under the conditions of firewire impedance earth；If it does not exist the case where firewire impedance earth, then the Relay detection under the conditions of non-impedance earth is carried out, for the Relay abnormality detection under the conditions of non-firewire impedance earth；The detection of Relay contact impedance, for detecting Relay, whether contact impedance is excessive.The present invention can distinguish grid-connected inverters relay failure and cause the abnormal conditions of simultaneously network relay fault misdescription, it is ensured that quick positioning failure reason simultaneously ensures machine reliable grid connection.
Description
Technical field
The present invention relates to photovoltaic DC-to-AC converter and network relay field, and in particular to a kind of photovoltaic inverter grid-connected relay
Fault detection method.
Background technique
It is higher and higher to the reliable and stable service requirement of photovoltaic generating system with the continuous development of photovoltaic industry.Safety
To guarantee that photovoltaic DC-to-AC converter in the reliable suspension of fault moment energy, generally requires photovoltaic DC-to-AC converter to have two groups of concatenated grid-connected relays
Device, can needing to detect two group relays before grid-connected inverters reliably can disconnect and be attracted.Currently, conventional detection side
Method judges only by detection network voltage and inverter voltage and whether network relay is normal, and this method has very big blind
Area.As sample circuit exception, the failures such as firewire impedance earth easily cause and the wrong report of network relay failure.This is greatly improved
The difficulty of relay fault detection, increases maintenance cost, simultaneously because wrong report causes the shutdown of inverter to also reduce is
The generated energy of system causes the benefit of client impaired.
Summary of the invention
In order to solve the problems, such as the wrong report of grid-connected inverters relay, mesh of the invention is to provide a kind of photovoltaic inverter grid-connected
The fault detection method of relay, can distinguish grid-connected inverters relay failure with cause and network relay fault misdescription it is different
Reason condition, it is ensured that quick positioning failure reason simultaneously ensures machine reliable grid connection.
In order to achieve the above objectives, the technical solution adopted by the present invention are as follows:
A kind of fault detection method of photovoltaic inverter grid-connected relay, described and network relay (are referred to as herein
Relay) include three-phase the main Relay being connected with inverter side and the secondary Relay being connected with grid side or load-side, the institute of every phase
It states main Relay and the secondary Relay is mutually concatenated, the fault detection method includes:
Sample circuit detection, for judging line voltage sample circuit with the presence or absence of abnormal；
Impedance earth detection, the case where for judging whether there is firewire impedance earth；If it exists the case where firewire impedance earth,
The Relay detection under the conditions of impedance earth is then carried out, for the Relay abnormality detection under the conditions of firewire impedance earth；If not depositing
The firewire impedance earth the case where, then the Relay detection under the conditions of non-impedance earth is carried out, non-firewire impedance earth condition is used for
Under Relay abnormality detection；
The detection of Relay contact impedance, for detecting Relay, whether contact impedance is excessive.
Wherein, if sampled point road detection judges that line voltage sample circuit is without exception, the impedance earth is carried out
Detection；If the Relay of the Relay abnormality detection of the firewire impedance earth condition or the non-firewire impedance earth condition is abnormal
Relay exception is not detected in detection, then carries out the Relay contact impedance detection.
Further, the sample circuit detection includes the following steps:
It calculates three-phase voltage and samples Ua_sample, Ub_sample, Uc_sampleThe sum of Uzero_avgVirtual value Uzero_rms；
Judge to meet U with the presence or absence of m (m < n) is secondary in n grid cyclezero_rms > Uzero_set, otherwise report sample circuit hardware
Abnormal failure is to carry out the impedance earth detection.
Further, the impedance earth detection includes the following steps:
Calculate three-phase inversion voltage effective value Uinv_a, Uinv_b, Uinv_c, three-phase inversion voltage is ranked up to obtain Uinv_max,
Uinv_mid, Uinv_min；
Judge Uinv_midWhether U is metmin_set < Uinv_mid < Umax_set, meet under the conditions of then carrying out the impedance earth
Relay detection, is unsatisfactory for, and performs the next step suddenly, wherein Umin_set、Umax_setRespectively indicate minimum inverter voltage setting value (e.g.,
For 0.3*Ugrid), maximum inverter voltage setting value (e.g., be 0.7*Ugrid)；
Calculate the end three-phase relay voltage Urelay_a, Urelay_b, Urelay_c；
Judge at least end two-phase Relay voltage Urelay_x < k1*Ugrid, it is to report Relay failure, otherwise performs the next step rapid
Wherein Urelay_xSelected from Urelay_a, Urelay_b, Urelay_c, k1It (e.g., is 0.3) U for proportionality coefficientgridFor network voltage；
Judgement only has the end a phase Relay voltage Urelay_x < k1*Ugrid, and three-phase inversion voltage Uinv_x < k2*Ugrid, it is then
The Relay detection under the conditions of otherwise carrying out the non-impedance earth suddenly is performed the next step, wherein Uinv_xSelected from Uinv_a, Uinv_b,
Uinv_c, k2It is proportionality coefficient (e.g., for 0.7)；
Failure phase voltage grid sampling is subtracted by three-phase inversion sampled voltage and obtains new three-phase inversion sampled voltage, by new inverse
Inverter voltage virtual value U is calculated in Variable sampling voltageinv_a, Uinv_b, Uinv_c, under the conditions of the progress non-impedance earth
Relay detection, wherein Ugrid_yTo meet U in previous steprelay_x < k1*UgridThat phase network voltage.
Further, the Relay detection under the conditions of the non-impedance earth includes the following steps:
Judge Urelay_x<c1*Ugrid, it is to report Relay failure, otherwise carries out next step, wherein c1(e.g., it is for proportionality coefficient
0.3)；
According to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges Uinv_x>c2*Ugrid, it is to report Relay failure,
Otherwise next step is carried out, wherein c2It is proportionality coefficient (e.g., for 0.7)；
It is closed secondary Relay, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out next step；
It is closed main Relay, carries out next step；
PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out the Relay contact impedance detection.
Further, the Relay detection under the conditions of the impedance earth includes the following steps:
Judge absolute difference > U two-by-two of three-phase inversion voltage effective valuemin, report Relay failure；Judge that three-phase inversion voltage has
Absolute difference < U two-by-two of valid valueminAnd the minus number of instantaneous value product of two-phase inverter voltage in grid cycle >
Count reports Relay failure, otherwise carries out next step, and wherein Count is setting count value (e.g., being 20 times)；
According to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges the difference two-by-two of three-phase inversion voltage effective value
Absolute value > Umin, report Relay failure；Judge absolute difference < U two-by-two of three-phase inversion voltage effective valueminAnd grid cycle
Minus number > the Count of the instantaneous value product of interior two-phase inverter voltage, reports Relay failure, otherwise carries out next step；
It is closed secondary Relay, judges absolute difference > U two-by-two of Relay voltage effective valuemin, report Relay failure；Judge inversion
Absolute difference > U two-by-two of voltage effective valueminAnd the instantaneous value product of two-phase inverter voltage is minus in grid cycle
Number > Count reports Relay failure, otherwise carries out next step；
It is closed main Relay, carries out next step；
PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out the Relay contact impedance detection.
Further, the Relay contact impedance detection includes the following steps:
Machine is grid-connected, judges Urelay_x > k3*Ugrid, it is to report Relay failure, wherein k3It is proportionality coefficient (e.g., for 0.2).
In one embodiment, specifically comprise the following steps:
S1, three-phase voltage sampling U is calculateda_sample, Ub_sample, Uc_sampleThe sum of Uzero_avgVirtual value Uzero_rms；
S2, judge to meet U with the presence or absence of m (m < n) is secondary in n grid cyclezero_rms > Uzero_set, otherwise report sample circuit hard
Part abnormal failure is to carry out following step S3(to carry out the impedance earth detection)；
S3, three-phase inversion voltage effective value U is calculatedinv_a, Uinv_b, Uinv_c, three-phase inversion voltage is ranked up to obtain
Uinv_max, Uinv_mid, Uinv_min；
S4, judge Uinv_midWhether U is metmin_set < Uinv_mid < Umax_set, meet and then carry out following step 9b(progress institute
State the Relay detection under the conditions of impedance earth), it is unsatisfactory for, executes following step S5, wherein Umin_set、Umax_setIt respectively indicates
Minimum inverter voltage setting value (0.3*Ugrid), maximum inverter voltage setting value (0.7*Ugrid)；
S5, the end three-phase relay voltage U is calculatedrelay_a, Urelay_b, Urelay_c；
S6, the judgement at least end two-phase Relay voltage Urelay_x < k1*Ugrid, it is to report Relay failure, otherwise executes following
Step S7, wherein Urelay_xSelected from Urelay_a, Urelay_b, Urelay_c, k1For proportionality coefficient (0.3), UgridFor network voltage；
S7, judgement only have the end a phase Relay voltage Urelay_x < k1*Ugrid, and three-phase inversion voltage Uinv_x < k2*Ugrid, it is
Following step S8 is then executed, following step 9a is otherwise executed, carries out the Relay detection of the non-impedance earth condition, wherein
Uinv_xSelected from Uinv_a, Uinv_b, Uinv_c, k2For proportionality coefficient (0.7)；
S8, failure phase voltage grid sampling is subtracted by three-phase inversion sampled voltage obtain new three-phase inversion sampled voltage, by new
Inversion sampled voltage inverter voltage virtual value U is calculatedinv_a, Uinv_b, Uinv_c, execute following step 9a, wherein Ugrid_y
To meet U in previous steprelay_x < k1*UgridThat phase network voltage；
S9a, judge Urelay_x<c1*Ugrid, it is to report Relay failure, otherwise executes following step 10a, wherein c1For ratio system
Number (0.3)；
S10a, according to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges Uinv_x>c2*Ugrid, it is to report Relay
Otherwise failure executes following step 11a, wherein c2For proportionality coefficient (0.7)；
S11a, closure secondary Relay, judge Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 12a；
S12a, the main Relay of closure, execute following step 13a；
S13a, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 14；
S9b, the absolute difference > U two-by-two for judging three-phase inversion voltage effective valuemin, report Relay failure；Judge three-phase inversion electricity
It is pressed with absolute difference < U two-by-two of valid valueminAnd minus time of the instantaneous value product of two-phase inverter voltage in grid cycle
Number > Count reports Relay failure, otherwise executes following step 10b, and wherein Count is setting count value (20 times)；
S10b, according to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges three-phase inversion voltage effective value two-by-two
Absolute difference > Umin, report Relay failure；Judge absolute difference < U two-by-two of three-phase inversion voltage effective valueminAnd power grid
Minus number > the Count of the instantaneous value product of two-phase inverter voltage, reports Relay failure, otherwise executes following step in period
11b；
S11b, closure secondary Relay, judge absolute difference > U two-by-two of Relay voltage effective valuemin, report Relay failure；Judgement
Absolute difference > U two-by-two of inverter voltage virtual valueminAnd the instantaneous value product of two-phase inverter voltage is less than in grid cycle
Zero number > Count, reports Relay failure, otherwise executes following step 12b；
S12b, the main Relay of closure, execute following step 13b；
S13b, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 14；
S14, machine are grid-connected, judge Urelay_x > k3*Ugrid, it is to report Relay failure, wherein k3For proportionality coefficient (0.2).
The present invention uses above scheme, has the advantages that compared with prior art
The wrong report of relay test failure caused by sample circuit abnormal, firewire ground connection and impedance earth can be effectively distinguished,
And quickly positioning failure reason and corresponding measure can be taken rapidly, both reduce because wrong report leads to generated energy caused by machine down
Loss, and quickly can position and solve the problems, such as to reduce maintenance cost and better services client.
Detailed description of the invention
It, below will be to attached drawing needed in embodiment description in order to illustrate more clearly of technical solution of the present invention
It is briefly described, it should be apparent that, drawings in the following description are only some embodiments of the invention, general for this field
For logical technical staff, without creative efforts, it is also possible to obtain other drawings based on these drawings.
Fig. 1 is the hardware system schematic diagram using fault detection method of the invention；
Fig. 2 is a kind of flow chart of fault detection method according to the present invention.
Specific embodiment
The preferred embodiments of the present invention will be described in detail with reference to the accompanying drawing, so that advantages and features of the invention energy
It is easier to be understood by the person skilled in the art.It should be noted that the explanation for these embodiments is used to help
Understand the present invention, but and does not constitute a limitation of the invention.In addition, involved in the various embodiments of the present invention described below
And to technical characteristic can be combined with each other as long as they do not conflict with each other.
Fig. 1 has used a kind of hardware system of photovoltaic DC-to-AC converter, and fault detection method provided by the invention is for detecting this
The relay of hardware system whether there is failure and failure cause.Shown in referring to Fig.1, described and network relay includes the master of three-phase
Relay and secondary Relay, wherein each main Relay is mutually electrically connected with inverter side (Inverter) respectively, each secondary Relay respectively with power grid
Side (Grid) or load-side are mutually electrically connected, and the main Relay of every phase and the secondary Relay are mutually concatenated.The pair of every phase
Inverter voltage sample circuit, network voltage are respectively arranged between the outlet side of Relay, the main Relay and the secondary Relay
Sample circuit.
The fault detection method of photovoltaic inverter grid-connected relay of the invention, comprising: sample circuit detection；Impedance earth
Detection；Relay detection under the conditions of impedance earth；Relay detection under the conditions of non-impedance earth；The detection of Relay contact impedance.
Sample circuit detection is for judging line voltage sample circuit with the presence or absence of abnormal；Impedance earth is detected for judging whether there is
The case where firewire impedance earth；Relay detection is examined extremely for Relay under the conditions of firewire impedance earth under the conditions of impedance earth
It surveys；Relay detects logic for the Relay abnormality detection under the conditions of non-firewire impedance earth under the conditions of non-impedance earth；Relay
Contact impedance detection is for detecting Relay with the presence or absence of contact impedance problems of too.
Referring to flow chart shown in Fig. 2, the fault detection method of photovoltaic inverter grid-connected relay of the invention is specifically wrapped
Include following steps:
A, sample circuit detects:
S1, three-phase voltage sampling U is calculateda_sample, Ub_sample, Uc_sample(pass through inverter line voltage sample circuit respectively
Sampled value by dsp chip ADC module processing after obtain) the sum of Uzero_avgVirtual value Uzero_rms；
S2, judge to meet U with the presence or absence of m (m < n) is secondary in n grid cyclezero_rms > Uzero_set, otherwise report sample circuit hard
Part abnormal failure is to enter step S3.
B, impedance earth detects:
S3, three-phase inversion voltage effective value U is calculatedinv_a,Uinv_b,Uinv_c, U is ranked up to three-phase inversion voltageinv_max,
Uinv_mid, Uinv_min；
S4, judge Uinv_midWhether U is metmin_set < Uinv_mid < Umax_set, satisfaction then enter step S9b, be unsatisfactory for then into
Enter step S5；
S5, the end three-phase relay voltage effective value U is calculatedrelay_a, Urelay_b, Urelay_c；
S6, the disconnected at least end two-phase Relay voltage Urelay_x < k1*Ugrid, it is to report Relay failure, otherwise enters step S7；
S7, judgement only have the end phase Relay voltage (being assumed to be an a phase) Urelay_a < k1*Ugrid, and three-phase inversion voltage
Uinv_x < k2*Ugrid, it is to carry out step S8, otherwise improve step S9a；
S8, subtracted by three-phase inversion sampled voltage failure phase voltage grid sampling obtain newly three-phase inversion sampled voltage (e.g., walk
Assume to meet U in rapid S7relay_a < k1*UgridA phase be failure phase), inversion is calculated by new inversion sampled voltage
Voltage effective value Uinv_a, Uinv_b, Uinv_c, enter step S9a.
C, the Relay detection under non-impedance conditions:
S9a, judge Urelay_x<c1*UgridRelay failure is then reported, S10a is otherwise entered step；
S10a, PWM generation open-loop voltage is opened according to network voltage Ugrid instruction, judge Uinv_x>c2*UgridThen report Relay event
Barrier, otherwise enters step S11a；
S11a, closure secondary Relay, judge Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise enters step S12a；
S12a, the main Relay of closure, enter step S13a；
S13a, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise enters step S14.
D, the Relay detection under impedance conditions:
S9b, judge three-phase inversion voltage effective value absolute difference > U two-by-twomin, report Relay failure；Judge three-phase inversion voltage
Virtual value absolute difference < U two-by-twominAnd the minus number > Count of two-phase instantaneous value product in grid cycle, report
Relay failure, otherwise improve step S10b；
S10b, PWM generation open-loop voltage is opened according to network voltage Ugrid instruction, judge that three-phase inversion voltage effective value is poor two-by-two
It is worth absolute value > Umin, it is to report Relay failure；Judge three-phase inversion voltage effective value absolute difference < U two-by-twominAnd power grid
Minus number > the Count of two-phase instantaneous value product in period, is to report Relay failure, and otherwise improve step S11b；
S11b, closure secondary Relay, judge Relay voltage effective value absolute difference > U two-by-twomin, report Relay failure；Judge inverse
Time variant voltage virtual value absolute difference > U two-by-twominAnd the minus number > Count of two-phase instantaneous value product in grid cycle
, it is to report Relay failure, otherwise enters step S12b；
S12b, the main Relay of closure, enter step S13b；
S13b, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise enters step S14.
E, Relay contact impedance detects:
S14: machine is grid-connected, judges Urelay_x > k3*Ugrid, it is to report Relay failure.
The above embodiments merely illustrate the technical concept and features of the present invention, is a kind of preferred embodiment, and purpose exists
It cans understand the content of the present invention and implement it accordingly in person skilled in the art, protection of the invention can not be limited with this
Range.Equivalent transformation or modification made by all Spirit Essences according to the present invention, should all cover protection scope of the present invention it
It is interior.
Claims (8)
1. a kind of fault detection method of photovoltaic inverter grid-connected relay, described and network relay include three-phase and inverter side
The connected main Relay and secondary Relay being connected with grid side or load-side, the main Relay of every phase and the secondary Relay phase
Mutually concatenation, which is characterized in that the fault detection method includes:
Sample circuit detection, for judging line voltage sample circuit with the presence or absence of abnormal；
Impedance earth detection, the case where for judging whether there is firewire impedance earth；If it exists the case where firewire impedance earth,
The Relay detection under the conditions of impedance earth is then carried out, for the Relay abnormality detection under the conditions of firewire impedance earth；If not depositing
The firewire impedance earth the case where, then the Relay detection under the conditions of non-impedance earth is carried out, non-firewire impedance earth condition is used for
Under Relay abnormality detection；
The detection of Relay contact impedance, for detecting Relay, whether contact impedance is excessive.
2. fault detection method according to claim 1, which is characterized in that if sampled point road detection judges power grid electricity
It presses sample circuit without exception, then carries out the impedance earth detection；If the Relay abnormality detection of the firewire impedance earth condition
Or Relay exception is not detected in the Relay abnormality detection of the non-firewire impedance earth condition, then carries out the Relay contact
Impedance detection.
3. fault detection method according to claim 1, which is characterized in that the sample circuit detection includes following step
It is rapid:
It calculates three-phase voltage and samples Ua_sample, Ub_sample, Uc_sampleThe sum of Uzero_avgVirtual value Uzero_rms；
Judge to meet U with the presence or absence of m (m < n) is secondary in n grid cyclezero_rms > Uzero_set, otherwise report sample circuit hardware different
Normal failure is to carry out the impedance earth detection.
4. fault detection method according to claim 1, which is characterized in that the impedance earth detection includes following step
It is rapid:
Calculate three-phase inversion voltage effective value Uinv_a, Uinv_b, Uinv_c, three-phase inversion voltage is ranked up to obtain Uinv_max,
Uinv_mid, Uinv_min；
Judge Uinv_midWhether U is metmin_set < Uinv_mid < Umax_set, meet under the conditions of then carrying out the impedance earth
Relay detection, is unsatisfactory for, and performs the next step suddenly, wherein Umin_set、Umax_setRespectively indicate minimum inverter voltage setting value, most
Big inverter voltage setting value；
Calculate the end three-phase relay voltage Urelay_a, Urelay_b, Urelay_c；
Judge at least end two-phase Relay voltage Urelay_x < k1*Ugrid, it is to report Relay failure, otherwise performs the next step rapid
Wherein Urelay_xSelected from Urelay_a, Urelay_b, Urelay_c, k1For proportionality coefficient, UgridFor network voltage；
Judgement only has the end a phase Relay voltage Urelay_x < k1*Ugrid, and three-phase inversion voltage Uinv_x > k2*Ugrid, it is to hold
Otherwise row next step carries out the Relay detection under the conditions of the non-impedance earth, wherein Uinv_xSelected from Uinv_a, Uinv_b,
Uinv_c, k2For proportionality coefficient；
Failure phase voltage grid sampling is subtracted by three-phase inversion sampled voltage and obtains new three-phase inversion sampled voltage, by new inverse
Inverter voltage virtual value U is calculated in Variable sampling voltageinv_a, Uinv_b, Uinv_c, under the conditions of carrying out the non-impedance earth
Relay detection.
5. fault detection method according to claim 1, which is characterized in that the Relay under the conditions of the non-impedance earth
Detection includes the following steps:
Judge Urelay_x<c1*Ugrid, it is to report Relay failure, otherwise carries out next step, wherein c1For proportionality coefficient；
According to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges Uinv_x>c2*Ugrid, it is to report Relay failure,
Otherwise next step is carried out, wherein c2For proportionality coefficient；
It is closed secondary Relay, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out next step；
It is closed main Relay, carries out next step；
PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out the Relay contact impedance detection.
6. fault detection method according to claim 1, which is characterized in that the Relay inspection under the conditions of the impedance earth
Survey includes the following steps:
Judge absolute difference > U two-by-two of three-phase inversion voltage effective valuemin, report Relay failure；Judge that three-phase inversion voltage has
Absolute difference < U two-by-two of valid valueminAnd the minus number of instantaneous value product of two-phase inverter voltage in grid cycle >
Count reports Relay failure, otherwise carries out next step, and wherein Count is setting count value；
According to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges that the difference two-by-two of three-phase inversion voltage effective value is exhausted
To value > Umin, report Relay failure；Judge absolute difference < U two-by-two of three-phase inversion voltage effective valueminAnd in grid cycle
Minus number > the Count of the instantaneous value product of two-phase inverter voltage, reports Relay failure, otherwise carries out next step；
It is closed secondary Relay, judges absolute difference > U two-by-two of Relay voltage effective valuemin, report Relay failure；Judge inversion
Absolute difference > U two-by-two of voltage effective valueminAnd the instantaneous value product of two-phase inverter voltage is minus in grid cycle
Number > Count reports Relay failure, otherwise carries out next step；
It is closed main Relay, carries out next step；
PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise carries out the Relay contact impedance detection.
7. fault detection method according to claim 1, which is characterized in that the Relay contact impedance detection includes such as
Lower step:
Machine is grid-connected, judges Urelay_x > k3*Ugrid, it is to report Relay failure, wherein k3For proportionality coefficient.
8. fault detection method according to claim 1 or 2, which is characterized in that specifically comprise the following steps:
S1, three-phase voltage sampling U is calculateda_sample, Ub_sample, Uc_sampleThe sum of Uzero_avgVirtual value Uzero_rms；
S2, judge to meet U with the presence or absence of m (m < n) is secondary in n grid cyclezero_rms > Uzero_set, otherwise report sample circuit hard
Part abnormal failure is to carry out following step S3；
S3, three-phase inversion voltage effective value U is calculatedinv_a, Uinv_b, Uinv_c, three-phase inversion voltage is ranked up to obtain Uinv_max,
Uinv_mid, Uinv_min；
S4, judge Uinv_midWhether U is metmin_set < Uinv_mid < Umax_set, meet and then carry out following step 9b, be unsatisfactory for then
Following step S5 is executed, wherein Umin_set、Umax_setRespectively indicate minimum inverter voltage setting value, maximum inverter voltage setting value；
S5, the end three-phase relay voltage U is calculatedrelay_a, Urelay_b, Urelay_c；
S6, the judgement at least end two-phase Relay voltage Urelay_x < k1*Ugrid, it is to report Relay failure, otherwise executes following
Step S7, wherein Urelay_xSelected from Urelay_a, Urelay_b, Urelay_c, k1For proportionality coefficient, UgridFor network voltage；
S7, judgement only have the end a phase Relay voltage Urelay_x < k1*Ugrid, and three-phase inversion voltage Uinv_x >k2*Ugrid, it is then
Following step S8 is executed, otherwise executes following step 9a, wherein Uinv_xSelected from Uinv_a, Uinv_b, Uinv_c, k2For proportionality coefficient；
S8, failure phase voltage grid sampling is subtracted by three-phase inversion sampled voltage obtain new three-phase inversion sampled voltage, by new
Inversion sampled voltage inverter voltage virtual value U is calculatedinv_a, Uinv_b, Uinv_c, execute following step 9a, wherein Ugrid_y
To meet U in step S7relay_x < k1*UgridThat phase network voltage；
S9a, judge Urelay_x<c1*Ugrid, it is to report Relay failure, otherwise executes following step 10a, wherein c1For ratio system
Number；
S10a, according to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges Uinv_x>c2*Ugrid, it is to report Relay
Otherwise failure executes following step 11a, wherein c2For proportionality coefficient；
S11a, closure secondary Relay, judge Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 12a；
S12a, the main Relay of closure, execute following step 13a；
S13a, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 14；
S9b, the absolute difference > U two-by-two for judging three-phase inversion voltage effective valuemin, report Relay failure；Judge three-phase inversion electricity
It is pressed with absolute difference < U two-by-two of valid valueminAnd minus time of the instantaneous value product of two-phase inverter voltage in grid cycle
Number > Count reports Relay failure, otherwise executes following step 10b, and wherein Count is setting count value；
S10b, according to network voltage UgridInstruction opens PWM and generates open-loop voltage, judges three-phase inversion voltage effective value two-by-two
Absolute difference > Umin, report Relay failure；Judge absolute difference < U two-by-two of three-phase inversion voltage effective valueminAnd power grid
Minus number > the Count of the instantaneous value product of two-phase inverter voltage, reports Relay failure, otherwise executes following step in period
11b；
S11b, closure secondary Relay, judge absolute difference > U two-by-two of Relay voltage effective valuemin, report Relay failure；Judgement
Absolute difference > U two-by-two of inverter voltage virtual valueminAnd the instantaneous value product of two-phase inverter voltage is less than in grid cycle
Zero number > Count, reports Relay failure, otherwise executes following step 12b；
S12b, the main Relay of closure, execute following step 13b；
S13b, PWM is closed, judges Uinv_x < c2*Ugrid, it is to report Relay failure, otherwise executes following step 14；
S14, machine are grid-connected, judge Urelay_x > k3*Ugrid, it is to report Relay failure, wherein k3For proportionality coefficient.
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