CN107957546B - Detection method and equipment for inverter grid-connected alternating-current relay - Google Patents
Detection method and equipment for inverter grid-connected alternating-current relay Download PDFInfo
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- CN107957546B CN107957546B CN201711138260.5A CN201711138260A CN107957546B CN 107957546 B CN107957546 B CN 107957546B CN 201711138260 A CN201711138260 A CN 201711138260A CN 107957546 B CN107957546 B CN 107957546B
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Abstract
The invention discloses a method for detecting an inverter grid-connected alternating current relay, wherein a first end of the alternating current relay is connected with an output end of an inverter, a second end of the alternating current relay is connected with an alternating current power grid, when the alternating current relay is detected, a first voltage difference between the first end and the second end of the alternating current relay is detected firstly, when the absolute value of the first voltage difference is judged to be smaller than a first threshold value, a point-to-ground voltage in a direct current bus at the input end of the inverter is changed, a second voltage difference between the first end and the second end of the alternating current relay is detected again, and if the absolute value of the second voltage difference is smaller than a second threshold value, the fact that the. The method prevents the phenomenon of false detection of the alternating-current relay due to the short circuit of a certain phase line to the ground or the inconsistent resistance of a three-phase power grid to the ground, and improves the accuracy of the detection of the adhesion fault of the alternating-current relay.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a method and equipment for detecting a grid-connected alternating-current relay of an inverter.
Background
In the technical field of photovoltaic grid connection, after direct current output by a solar panel is subjected to inversion processing by an inverter, alternating current capable of being merged into an alternating current power grid can be obtained, a relay is arranged between the alternating current power grid and the inverter, and when the relay is closed, the alternating current output by the inverter can be merged into the alternating current power grid.
In the prior art, when the relay is disconnected, the function of the relay is detected, specifically, a difference between a voltage on the ac power grid side and a voltage on the inverter side is calculated, and whether the relay is adhered or not is directly judged according to the difference.
However, a short circuit between a phase line and the ground or an impedance inconsistency between a three-phase power grid and the ground often occurs, at this time, the voltage between the phase line and the ground is zero or other low values, and if the function of the relay is detected at this time, the relay is erroneously detected to be stuck, so that a fault occurs.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a method and equipment for detecting an inverter grid-connected alternating-current relay, which can accurately detect whether the relay is adhered.
The invention provides the following technical scheme:
a detection method of an inverter grid-connected alternating current relay is characterized in that a first end of the alternating current relay is connected with an output end of an inverter, and a second end of the alternating current relay is connected with an alternating current power grid; the method comprises the following steps:
detecting a first voltage difference between a first end and a second end of the alternating current relay;
when the absolute value of the first voltage difference is judged to be smaller than a first threshold value, changing the voltage to ground of a midpoint of a direct-current bus at the input end of the inverter, and detecting a second voltage difference between a first end and a second end of the alternating-current relay;
and when the absolute value of the second voltage difference is judged to be smaller than a second threshold value, determining that the AC relay is adhered.
Optionally, the changing of the voltage to ground of the midpoint of the dc bus at the input end of the inverter specifically includes:
a first controllable switch and an additional resistor are connected in series between the positive input end of the inverter and the ground;
and changing the voltage to ground of the midpoint of the direct current bus at the input end of the inverter by controlling the switching state of the first controllable switch.
Optionally, the changing of the voltage to ground of the midpoint of the dc bus at the input end of the inverter specifically includes:
when the input of the inverter is connected to a PV assembly, connecting a controlled voltage source in series between the negative terminal of the PV assembly and ground; or, a controlled voltage source is connected in series between the positive terminal of the PV assembly and ground;
and changing the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter by controlling the controlled voltage source.
Optionally, the changing of the voltage to ground of the midpoint of the dc bus at the input end of the inverter specifically includes:
and a bus discharge circuit is connected between the positive bus or the negative bus and the midpoint of the direct current bus, and the voltage to ground of the midpoint of the direct current bus is changed by controlling the conducting state of the bus discharge circuit.
The invention also provides another detection method of the inverter grid-connected alternating current relay, wherein the first end of the alternating current relay is connected with the output end of the inverter, and the second end of the alternating current relay is connected with an alternating current power grid; the method comprises the following steps:
detecting a first voltage difference between a first end and a second end of the alternating current relay;
when the absolute value of the first voltage difference is judged to be smaller than a first threshold value, changing the output voltage of the inverter, and detecting a second voltage difference between a first end and a second end of the alternating current relay;
and when the absolute value of the second voltage difference is judged to be smaller than the second threshold value, determining that the AC relay is adhered.
Optionally, the changing the output voltage of the inverter specifically includes:
and changing the switching state of a switching tube in the inverter to change the output voltage of the inverter.
The invention also provides a detection device of the inverter grid-connected alternating current relay, wherein the first end of the alternating current relay is connected with the output end of the inverter, and the second end of the alternating current relay is connected with an alternating current power grid;
the detection apparatus includes: the device comprises a voltage detection circuit, a disturbance circuit and a controller;
the voltage detection circuit is used for detecting a first voltage difference between a first end and a second end of the alternating current relay;
the controller is used for controlling the disturbance circuit to change the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value;
the voltage detection circuit is used for detecting a second voltage difference between the first end and the second end of the alternating current relay;
and the controller is used for determining that the AC relay is adhered when the absolute value of the second voltage difference is judged to be smaller than a second threshold value.
Optionally, the disturbance circuit includes a first controllable switch and an additional resistor connected in series between the positive input terminal of the inverter and ground;
and the controller is used for controlling the switching state of the first controllable switch to change the voltage-to-ground voltage of the midpoint of the direct-current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value.
Optionally, when the input of the inverter is connected to a PV module, the perturbation circuit comprises a second controllable switch and a controlled voltage source connected in series between the negative terminal of the PV module and ground; or, the second controllable switch and controlled voltage source in series between the positive terminal of the PV assembly and ground;
and the controller is used for controlling the switching state of the second controllable switch to change the voltage-to-ground voltage of the midpoint of the direct-current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value.
Optionally, the disturbance circuit includes a bus discharge circuit connected between a positive bus and a midpoint of the direct current bus, or includes a bus discharge circuit connected between a negative bus and a midpoint of the direct current bus;
and the controller is used for controlling the conducting state of the bus discharging circuit to change the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter when judging that the absolute value of the first voltage difference is smaller than a first threshold value.
The invention also provides another detection device for the inverter grid-connected alternating current relay, wherein the first end of the alternating current relay is connected with the output end of the inverter, and the second end of the alternating current relay is connected with an alternating current power grid;
the detection apparatus includes: a voltage detection circuit and a controller;
the voltage detection circuit is used for detecting a first voltage difference between a first end and a second end of the alternating current relay;
the controller is used for changing the output voltage of the inverter when judging that the absolute value of the first voltage difference is smaller than a first threshold value;
the voltage detection circuit is used for detecting a second voltage difference between the first end and the second end of the alternating current relay;
and the controller is used for determining that the AC relay is adhered when the absolute value of the second voltage difference is judged to be smaller than a second threshold value.
Optionally, the controller is configured to change a switching state of a switching tube in the inverter to change the output voltage of the inverter when determining that the absolute value of the first voltage difference is smaller than a first threshold.
Compared with the prior art, the invention has at least the following advantages:
the application provides a detection method of an inverter grid-connected alternating current relay, which is used for disturbing the midpoint voltage of a direct current bus at the input end of an inverter in the detection process and accurately judging whether the alternating current relay is adhered or not. Specifically, the output of dc-to-ac relay is connected to ac relay's first end, ac relay's second end is connected ac power grid, when detecting ac relay, detect the first voltage difference of ac relay first end and second end earlier, when judging that the absolute value of this first voltage difference is less than first threshold value, change the direct current bus midpoint grounding voltage of inverter input, detect the second voltage difference of ac relay first end and second end once more, if the absolute value of this second voltage difference is less than the second threshold value, then can confirm that this ac relay takes place the adhesion trouble.
According to the method for detecting the inverter grid-connected alternating-current relay, when the alternating-current relay is detected, the midpoint voltage of the direct-current bus at the input end of the inverter is changed, and after the midpoint voltage of the direct-current bus is changed, whether the alternating-current relay is adhered or not is judged according to the difference value of the voltages at the two ends of the relay.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be 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 described in the present application, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a block diagram of a three-phase inverter topology for a typical ungrounded system of power supply neutral points;
fig. 2 is a flowchart of a method for detecting an inverter grid-connected ac relay according to the present invention;
FIG. 3 is a topology structure diagram of a three-phase inverter under a power supply neutral point ungrounded system provided by the invention;
FIG. 4 is a topology structure diagram of a three-phase inverter in another system with a non-grounded neutral point of a power supply provided by the invention;
FIG. 5 is a topology structure diagram of a three-phase inverter in a system with a non-grounded neutral point of a power supply according to another embodiment of the present invention;
fig. 6 is a flowchart of another method for detecting an inverter grid-connected ac relay according to the present invention;
fig. 7 is a structural diagram of a detection device of an inverter grid-connected ac relay according to the present invention;
fig. 8 is a structural diagram of another detection device for an inverter grid-connected ac relay according to the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, 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.
When the power grid is isolated from the ground, the situation that a certain phase live wire is short-circuited to the ground or the three-phase power grid is inconsistent to the ground resistance often occurs, at this time, the voltage of the phase live wire to the ground is zero or other low values, and if the relay function is detected by using the prior art, the relay is possibly mistakenly detected to be adhered.
The reason why the erroneous detection of the relay occurs in the above-described case is analyzed below with reference to fig. 1:
as shown in fig. 1, a typical topology of a three-phase inverter in a non-grounded system of a neutral point of a power supply is set to zero, a neutral point voltage of a bus is V (ne), voltages output by the three-phase inverter are V (Inv _ R), V (Inv _ S) and V (Inv _ T), and voltages of a three-phase ac power Grid are V (Grid _ R), V (Grid _ S) and V (Grid _ T).
In the case where the driving of the inverter is not on, the voltage output by the three-phase inverter satisfies formula (1):
V(Inv_R)＝V(Inv_S)＝V(Inv_T)＝V(NE)＝V_0 (1)
the relation of the phase-to-phase voltages of the relay at the three phases R, S, T respectively satisfies the formulas (2), (3) and (4):
V(Inv_R)-V(Grid_R)＝V(NE)-V(Grid_R) (2)
V(Inv_S)-V(Grid_S)＝V(NE)-V(Grid_S) (3)
V(Inv_T)-V(Grid_T)＝V(NE)-V(Grid_T) (4)
when the voltage of R to ground is small, even zero, V (Grid _ R) is 0. At this time, the interphase voltage relationship of the relay in the R phase satisfies formula (5):
V(Inv_R)-V(Grid_R)＝V(NE) (5)
v (ne) is the bus midpoint voltage to ground, and its magnitude depends on the dc positive and negative impedance to ground, i.e. PV + impedance to ground and PV-impedance to ground, and when PV + impedance to ground is equal to PV-impedance to ground, the bus midpoint potential to ground, i.e. v (ne) is 0. At this time, the interphase voltage relationship of the relay in the R phase satisfies formula (6):
V(Inv_R)-V(Grid_R)＝V(NE)＝0 (6)
if the relay is detected at the moment, the adhesion fault of the relay is detected by mistake.
In order to solve the problem that false detection can occur when the alternating current relay is detected, the application provides the detection method of the inverter grid-connected alternating current relay.
Specifically, the output of dc-to-ac relay is connected to ac relay's first end, ac relay's second end is connected ac power grid, when detecting ac relay, detect the first voltage difference of ac relay first end and second end earlier, when judging that the absolute value of this first voltage difference is less than first threshold value, change the direct current bus midpoint grounding voltage of inverter input, detect the second voltage difference of ac relay first end and second end once more, if the absolute value of this second voltage difference is less than the second threshold value, then can confirm that this ac relay takes place the adhesion trouble.
According to the method for detecting the inverter grid-connected alternating-current relay, when the alternating-current relay is detected, the midpoint voltage of the direct-current bus at the input end of the inverter is changed, and after the midpoint voltage of the direct-current bus is changed, whether the alternating-current relay is adhered or not is judged according to the difference value of the voltages at the two ends of the relay.
Method embodiment one
Referring to fig. 2, a flowchart of a method for detecting an inverter grid-connected ac relay according to this embodiment is provided.
The first end of the alternating current relay is connected with the output end of the inverter, the second end of the alternating current relay is connected with an alternating current power grid, and the method comprises the following steps:
step 201: a first voltage difference between a first end and a second end of the alternating current relay is detected.
The voltage measuring device is used for detecting the voltage of the alternating current relay on the output end side of the inverter and the voltage of the alternating current relay on the alternating current network side, namely the voltage measuring device is used for respectively detecting the voltages of the first end and the second end of the alternating current relay, and the voltage of the first end and the voltage of the second end are subjected to subtraction to obtain a first voltage difference.
Step 202: and when the absolute value of the first voltage difference is judged to be smaller than the first threshold value, changing the voltage to ground of the midpoint of the direct-current bus at the input end of the inverter, and detecting a second voltage difference between the first end and the second end of the alternating-current relay.
And judging the absolute value of the first voltage difference, judging whether the absolute value of the first voltage difference is smaller than a first threshold value, indicating that the AC relay is likely to have an adhesion fault when judging that the absolute value of the first voltage difference is smaller than the first threshold value, and changing the voltage-to-ground voltage of the midpoint of the DC bus at the input end of the inverter.
And after the point-to-ground voltage in the direct current bus of the input end of the inverter is changed, measuring the voltage of the first end and the voltage of the second end of the alternating current relay again, and subtracting the voltage of the first end from the voltage of the second end to obtain a second voltage difference.
The first threshold value is a small value and may be set according to actual conditions, and the method for determining the first threshold value is not limited herein.
Step 203: and when the absolute value of the second voltage difference is judged to be smaller than the second threshold value, determining that the AC relay is adhered.
And judging whether the absolute value of the second voltage difference is smaller than a second threshold value, and if the second voltage difference is smaller than the second threshold value, determining that the AC relay is adhered. If the absolute value of the second voltage difference is larger than or equal to the second threshold, the fact that the alternating current relay is not stuck is indicated, and the fact that the absolute value of the first voltage difference is smaller than the second threshold is caused by the fact that a certain phase line is short-circuited to the ground or the fact that three-phase power grids are inconsistent in impedance to the ground.
The second threshold value may be set according to actual conditions, may be equal to or different from the first threshold value, and the method for determining the second threshold value is not limited herein.
According to the method for detecting the inverter grid-connected alternating-current relay, when the alternating-current relay is detected, the midpoint voltage of the direct-current bus is changed, and after the midpoint voltage of the direct-current bus is changed, whether the alternating-current relay is adhered or not is judged according to the difference value of the voltages at two ends of the relay.
In practical application, the following two methods are generally adopted for changing the voltage to ground of the midpoint of the direct-current bus at the input end of the inverter: the first method is that the voltages of a positive bus and a negative bus to the ground are directly changed, so that the voltages of the positive bus and the negative bus to the ground are unbalanced, and further the voltages of a midpoint of a direct current bus to the ground are changed; in the second method, the voltages of the positive bus and the negative bus to the midpoint of the direct current bus are changed, and accordingly, the voltages of the midpoint of the direct current bus to the ground are changed.
The first method is described in detail below with reference to the accompanying drawings:
method embodiment two
As shown in fig. 3, the topology structure of the three-phase inverter in the system without grounding of the neutral point of the power supply is shown, and a first controllable switch S4 and an additional resistor R1 are added in the topology structure.
A first controllable switch S4 and an additional resistor R1 are connected in series between the positive input of the inverter 301 and ground.
The voltage to ground of the dc bus midpoint NE at the input of the inverter 301 is changed by controlling the switching state of the first controllable switch S4.
In the three-phase circuit, an ac relay is provided between the inverter output terminal and the ac grid input terminal, and is S1, S2, and S3, respectively.
Specifically, the difference between the voltage of the ac relay on the output end side of the inverter and the voltage of the ac relay on the ac power grid side is calculated, the first controllable switch S4 is controlled to be turned off, and at this time, the first voltage difference between the first end and the second end of the ac relay is calculated. When the absolute value of the first voltage difference is determined to be smaller than the first threshold, the first controllable switch S4 is closed, the positive input terminal of the inverter 301 is grounded via the additional resistor R1, and the voltage of the positive bus to the ground is changed accordingly. As the positive bus voltage to ground changes, the voltage at the dc bus midpoint NE at the inverter input to ground also changes.
And at the moment, the voltages of the first end and the second end of the alternating current relay are detected again, a second voltage difference between the first end and the second end is calculated, and if the second voltage difference is smaller than a second threshold value, the fact that the adhesion fault occurs in the alternating current relay is indicated.
It should be noted that, the voltage to ground of the negative bus, and thus the voltage to ground of the dc bus midpoint NE at the input end of the inverter, may also be changed by the above method. Specifically, a first controllable switch and an additional resistor are connected in series between the negative input end of the inverter and the ground, and when the first voltage difference is judged to be smaller than a first threshold value, the first controllable switch is closed, so that the negative bus is grounded through the additional resistor, namely, the voltage to ground of the negative bus is changed, and further, the voltage to ground of a neutral point NE in the direct current bus at the input end of the inverter is changed.
It should be noted that, in order to improve the ground insulation performance of the photovoltaic array and reduce the leakage current of the photovoltaic array to the ground, the resistance of the selected additional resistor is relatively large, and can generally reach several mega ohms.
In addition, the present embodiment also provides another method for changing the voltages of the positive and negative bus bars to the ground, as shown in fig. 4, which is a topology structure diagram of a three-phase inverter in a power supply neutral point ungrounded system to which the method is applied. A controlled voltage source is additionally arranged in the structure.
When the inverter 301 input is connected to the PV assembly, a controlled voltage source V1 is connected in series between the negative terminal of the PV assembly and ground; alternatively, a controlled voltage source V1 is connected in series between the positive terminal of the PV assembly and ground.
The voltage to ground of the dc bus midpoint NE at the input of the inverter 301 is changed by controlling the controlled voltage source V1.
Specifically, when the absolute value of the first voltage difference is determined to be smaller than the first threshold, the controlled voltage source V1 is controlled to close the branch where the controlled voltage source V1 is located, and the controlled voltage source V1 is controlled to change the voltage between the negative terminal of the PV module and the ground, or change the voltage between the positive terminal of the PV module and the ground. As the voltage between the negative or positive terminal of the PV and ground changes, the voltage at the dc bus midpoint NE to ground at the input of the inverter 301 changes.
After the neutral point NE of the direct current bus at the input end of the inverter is changed to the ground, the voltages of the first end and the second end of the alternating current relay are measured again, the difference value between the voltages of the first end and the second end is judged, namely whether the absolute value of the second voltage difference is smaller than a second threshold value or not is judged, and if the absolute value is smaller than the second threshold value, the adhesion fault of the alternating current relay can be determined.
It should be noted that, the controlled voltage source V1 can control its on and off according to the control signal of the controller, when the control signal controls the controlled voltage source V1 to be closed, the controlled voltage source V1 is connected to the circuit, and correspondingly, when the control signal controls the controlled voltage source V1 to be opened, the current of the controlled voltage source V1 is disconnected. In addition, the controlled voltage source V1 can change its own voltage value according to the control signal.
Of course, a controllable switch may be added to the branch where the controlled voltage source V1 is located, and the controlled voltage source V1 is controlled by the controllable switch to be connected to the branch or disconnected from the branch.
According to the method for detecting the grid-connected AC relay of the inverter, the voltage to ground of the midpoint of the DC bus at the input end of the inverter is changed by changing the voltage to ground of the positive bus and the negative bus, and whether the AC relay has the adhesion fault or not is judged according to the second voltage difference after the voltage to ground of the midpoint of the DC bus at the input end of the inverter.
The second method is described in detail below with reference to the accompanying drawings:
method embodiment three
Fig. 5 is a schematic diagram of a topology of a three-phase inverter in a system in which a neutral point of a power supply is not grounded, to which the second method is applied.
A bus discharge circuit is additionally arranged in the structure.
A bus discharge circuit is connected between the positive bus or the negative bus and the DC bus midpoint NE, and the voltage of the DC bus midpoint NE to the ground is changed by controlling the conduction state of the bus discharge circuit.
Specifically, the bus discharging circuit may be formed by connecting a controllable switch S5 and an additional resistor R2 in series. When the controllable switch S5 is opened, whether the absolute value of the first voltage difference between the first end and the second end of the alternating current relay is smaller than a first threshold value or not is judged, when the absolute value of the first voltage difference is smaller than the first threshold value, the controllable switch S5 on the bus discharging circuit is closed, the positive bus or the negative bus discharges through the bus discharging circuit, the voltage of the positive bus or the negative bus to the direct current bus midpoint NE of the input end of the inverter changes along with the discharging, and accordingly, the voltage of the direct current bus midpoint NE of the input end of the inverter changes.
And at the moment, the voltages of the first end and the second end of the alternating current relay are detected again, a second voltage difference between the first end and the second end is calculated, and if the second voltage difference is smaller than a second threshold value, the fact that the adhesion fault occurs in the alternating current relay is indicated.
The configuration of the bus discharge circuit may be other circuits capable of realizing a discharge function, and the configuration of the bus discharge circuit is not limited at all.
According to the method for detecting the grid-connected AC relay of the inverter, the voltage to ground of the midpoint of the DC bus at the input end of the inverter is changed by changing the voltage of the midpoint of the DC bus of the positive bus and the negative bus to the input end of the inverter, and whether the AC relay has the adhesion fault or not is judged according to the second voltage difference after the voltage to ground of the midpoint of the DC bus at the input end of the inverter.
Besides the method for determining whether the AC relay is adhered by changing the voltage to ground of the midpoint of the DC bus at the input end of the inverter, the application also provides another method for detecting the grid-connected AC relay of the inverter.
Method example four
As shown in fig. 6, a flowchart of another method for detecting an inverter grid-connected ac relay is provided in this embodiment. The first end of the alternating current relay is connected with the output end of the inverter, and the second end of the alternating current relay is connected with an alternating current power grid; the method comprises the following steps:
step 601: a first voltage difference between a first end and a second end of the alternating current relay is detected.
Step 602: and when the absolute value of the first voltage difference is judged to be smaller than the first threshold value, changing the output voltage of the inverter, and detecting a second voltage difference between the first end and the second end of the alternating current relay.
Step 603: and when the absolute value of the second voltage difference is judged to be smaller than the second threshold value, determining that the AC relay is adhered.
The method for obtaining the first voltage difference between the first terminal and the second terminal of the ac relay is the same as that of the above embodiment, and is not described herein again.
And when the absolute value of the first voltage difference is smaller than a first threshold value, changing the output voltage of the inverter, obtaining a second voltage difference between the first end and the second end of the alternating current relay again after changing the output voltage of the inverter, and if the second voltage difference is smaller than the second threshold value, changing the output voltage of the inverter, wherein the second voltage difference has no great influence on the second voltage difference, and further, the fact that the alternating current relay is adhered is explained.
The first threshold and the second threshold are both values close to zero, and both can be set according to actual conditions. The first threshold may be equal to the second threshold, or may be different from the second threshold, and may be set according to actual conditions.
Specifically, changing the output voltage of the inverter can be realized by changing the switching state of the switching tube. According to actual needs, the duty ratio of the driving pulse of the switching tube in the inverter is changed, and further, the output voltage of the inverter is changed.
Of course, the output voltage of the inverter may be changed by another method, and the method of changing the output voltage of the inverter is not limited herein.
In the method for detecting the grid-connected ac relay of the inverter provided in this embodiment, when the first voltage difference is smaller than the first threshold, the output voltage of the inverter is changed, and a second voltage difference after the output voltage of the inverter is changed is determined, and if the second voltage difference is smaller than the second threshold, it is determined that the ac relay is stuck. The method prevents the phenomenon of false detection of the alternating-current relay due to the short circuit of a certain phase line to the ground or the inconsistent resistance of a three-phase power grid to the ground, and improves the accuracy of adhesion fault detection.
Apparatus embodiment one
Referring to fig. 7, a structure diagram of a detection apparatus of an inverter grid-connected ac relay is provided in this embodiment.
The first end of the alternating current relay is connected with the output end of the inverter, and the second end of the alternating current relay is connected with an alternating current power grid.
The detection device provided by the embodiment comprises: a voltage detection circuit 701, a disturbance circuit 702, and a controller 703.
The voltage detection circuit 701 is configured to detect a first voltage difference between a first end and a second end of the ac relay.
And the controller 703 is configured to control the disturbance circuit 702 to change the voltage-to-ground voltage of the midpoint of the dc bus at the input end of the inverter when it is determined that the absolute value of the first voltage difference is smaller than a first threshold.
And the voltage detection circuit 701 is used for detecting a second voltage difference between the first end and the second end of the alternating current relay.
And the controller 703 is configured to determine that the ac relay is stuck when the absolute value of the second voltage difference is smaller than a second threshold value.
Optionally, the perturbation circuit 702 comprises a first controllable switch and an additional resistor in series between the positive input of the inverter and ground.
And the controller 703 is configured to control the switching state of the first controllable switch to change the voltage-to-ground voltage of the midpoint of the dc bus at the input end of the inverter when it is determined that the absolute value of the first voltage difference is smaller than a first threshold.
Optionally, when the input of the inverter is connected to a PV assembly, the perturbation circuit 702 comprises a second controllable switch and a controlled voltage source in series between the negative terminal of the PV assembly and ground; or, the second controllable switch and controlled voltage source in series between the positive terminal of the PV assembly and ground;
and the controller 703 is configured to control the switching state of the second controllable switch to change the voltage-to-ground voltage of the midpoint of the dc bus at the input end of the inverter when it is determined that the absolute value of the first voltage difference is smaller than a first threshold.
Optionally, the disturbance circuit 702 includes a bus discharge circuit connected between the positive bus and the midpoint of the dc bus, or includes a bus discharge circuit connected between the negative bus and the midpoint of the dc bus;
and the controller 703 is configured to control the on-state of the bus discharge circuit to change the voltage-to-ground voltage of the midpoint of the dc bus at the input end of the inverter when it is determined that the absolute value of the first voltage difference is smaller than a first threshold.
The detection device for the inverter grid-connected ac relay provided in this embodiment is a device corresponding to the above method embodiment, and specific reference is made to the description in the method embodiment, and details are not repeated here.
According to the detection equipment for the inverter grid-connected alternating current relay, when the alternating current relay is detected, the midpoint voltage of the direct current bus is changed, after the midpoint voltage of the direct current bus is changed, whether the alternating current relay is adhered or not is judged according to the difference value of the voltages at two ends of the relay, the phenomenon that the alternating current relay is falsely detected due to the fact that a certain line of fire is short-circuited to the ground or a three-phase power grid is inconsistent in resistance to the ground is avoided, and the accuracy of adhesion detection of the alternating current relay is improved.
Apparatus embodiment II
Referring to fig. 8, another detection apparatus for an inverter grid-connected ac relay provided in this embodiment is provided, where a first end of the ac relay is connected to an output end of an inverter, and a second end of the ac relay is connected to an ac grid.
The detection apparatus includes: a voltage detection circuit 801 and a controller 802.
The voltage detection circuit 801 is configured to detect a first voltage difference between the first terminal and the second terminal of the ac relay.
And a controller 802, configured to change the output voltage of the inverter when determining that the absolute value of the first voltage difference is smaller than a first threshold.
And the voltage detection circuit 801 is configured to detect a second voltage difference between the first end and the second end of the ac relay.
And the controller 802 is configured to determine that the ac relay is stuck when the absolute value of the second voltage difference is smaller than a second threshold value.
Optionally, the controller 802 is configured to change the switching state of the switching tube to change the output voltage of the inverter when determining that the absolute value of the first voltage difference is smaller than a first threshold.
The detection device for the inverter grid-connected ac relay provided in this embodiment is a device corresponding to the above method embodiment, and specific reference is made to the description in the method embodiment, and details are not repeated here.
In the detection apparatus for the inverter grid-connected ac relay provided in this embodiment, when the first voltage difference is smaller than the first threshold, the output voltage of the inverter is changed, and a second voltage difference after the output voltage of the inverter is changed is determined, and if the second voltage difference is smaller than the second threshold, it is determined that the ac relay is adhered. The device prevents the phenomenon of false detection of the alternating-current relay due to the fact that a certain phase line is short-circuited to the ground or the three-phase power grid is inconsistent to the ground resistance, and improves the accuracy of adhesion fault detection.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.
Claims (12)
1. The detection method of the inverter grid-connected alternating current relay is characterized in that a first end of the alternating current relay is connected with an output end of an inverter, and a second end of the alternating current relay is connected with an alternating current power grid; the method comprises the following steps:
detecting a first voltage difference between a first end and a second end of the alternating current relay;
when the absolute value of the first voltage difference is judged to be smaller than a first threshold value, changing the voltage to ground of a midpoint of a direct-current bus at the input end of the inverter, and detecting a second voltage difference between a first end and a second end of the alternating-current relay;
and when the absolute value of the second voltage difference is judged to be smaller than a second threshold value, determining that the AC relay is adhered.
2. The method for detecting the inverter grid-connected alternating-current relay according to claim 1, wherein the step of changing the voltage to ground of the midpoint of the direct-current bus at the input end of the inverter specifically comprises the steps of:
a first controllable switch and an additional resistor are connected in series between the positive input end of the inverter and the ground;
and changing the voltage to ground of the midpoint of the direct current bus at the input end of the inverter by controlling the switching state of the first controllable switch.
3. The method for detecting the inverter grid-connected alternating-current relay according to claim 1, wherein the step of changing the voltage to ground of the midpoint of the direct-current bus at the input end of the inverter specifically comprises the steps of:
when the input of the inverter is connected to a PV assembly, connecting a controlled voltage source in series between the negative terminal of the PV assembly and ground; or a controlled voltage source in series between the positive terminal of the PV assembly and ground;
and changing the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter by controlling the controlled voltage source.
4. The method for detecting the inverter grid-connected alternating-current relay according to claim 1, wherein the step of changing the voltage to ground of the midpoint of the direct-current bus at the input end of the inverter specifically comprises the steps of:
and a bus discharge circuit is connected between the positive bus or the negative bus and the midpoint of the direct current bus, and the voltage to ground of the midpoint of the direct current bus is changed by controlling the conducting state of the bus discharge circuit.
5. The detection method of the inverter grid-connected alternating current relay is characterized in that a first end of the alternating current relay is connected with an output end of an inverter, and a second end of the alternating current relay is connected with an alternating current power grid; the method comprises the following steps:
detecting a first voltage difference between a first end and a second end of the alternating current relay;
when the absolute value of the first voltage difference is judged to be smaller than a first threshold value, changing the output voltage of the inverter, and detecting a second voltage difference between a first end and a second end of the alternating current relay;
and when the absolute value of the second voltage difference is judged to be smaller than a second threshold value, determining that the AC relay is adhered.
6. The method for detecting the inverter grid-connected alternating-current relay according to claim 5, wherein the changing of the output voltage of the inverter specifically comprises:
and changing the switching state of a switching tube in the inverter to change the output voltage of the inverter.
7. The detection equipment of the inverter grid-connected alternating current relay is characterized in that a first end of the alternating current relay is connected with an output end of an inverter, and a second end of the alternating current relay is connected with an alternating current power grid;
the detection apparatus includes: the device comprises a voltage detection circuit, a disturbance circuit and a controller;
the voltage detection circuit is used for detecting a first voltage difference between a first end and a second end of the alternating current relay;
the controller is used for controlling the disturbance circuit to change the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value;
the voltage detection circuit is used for detecting a second voltage difference between the first end and the second end of the alternating current relay;
and the controller is used for determining that the AC relay is adhered when the absolute value of the second voltage difference is judged to be smaller than a second threshold value.
8. The inverter grid-connected ac relay detection apparatus according to claim 7, wherein the disturbance circuit includes a first controllable switch and an additional resistor connected in series between the positive input terminal of the inverter and ground;
and the controller is used for controlling the switching state of the first controllable switch to change the voltage-to-ground voltage of the midpoint of the direct-current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value.
9. The inverter grid-connected ac relay detection apparatus of claim 7, wherein when the input of the inverter is connected to a PV module, the perturbation circuit comprises a second controllable switch and a controlled voltage source connected in series between a negative terminal of the PV module and ground; or, the second controllable switch and controlled voltage source in series between the positive terminal of the PV assembly and ground;
and the controller is used for controlling the switching state of the second controllable switch to change the voltage-to-ground voltage of the midpoint of the direct-current bus at the input end of the inverter when the absolute value of the first voltage difference is judged to be smaller than a first threshold value.
10. The apparatus according to claim 7, wherein the disturbance circuit includes a bus discharge circuit connected between a positive bus and the dc bus midpoint, or includes a bus discharge circuit connected between a negative bus and the dc bus midpoint;
and the controller is used for controlling the conducting state of the bus discharging circuit to change the voltage-to-ground voltage of the midpoint of the direct current bus at the input end of the inverter when judging that the absolute value of the first voltage difference is smaller than a first threshold value.
11. The detection equipment of the inverter grid-connected alternating current relay is characterized in that a first end of the alternating current relay is connected with an output end of an inverter, and a second end of the alternating current relay is connected with an alternating current power grid;
the detection apparatus includes: a voltage detection circuit and a controller;
the voltage detection circuit is used for detecting a first voltage difference between a first end and a second end of the alternating current relay;
the controller is used for changing the output voltage of the inverter when judging that the absolute value of the first voltage difference is smaller than a first threshold value;
the voltage detection circuit is used for detecting a second voltage difference between the first end and the second end of the alternating current relay;
and the controller is used for determining that the AC relay is adhered when the absolute value of the second voltage difference is judged to be smaller than a second threshold value.
12. The apparatus according to claim 11, wherein the controller is configured to change the output voltage of the inverter by changing a switching state of a switching tube in the inverter when determining that the absolute value of the first voltage difference is smaller than a first threshold.
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| EP4033263A1 (en) * | 2021-01-21 | 2022-07-27 | Solar Power Network Technology (Zhejiang) Co., Ltd. | Method for testing the relay failure of a three-phase grid-connected inverter |
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| CN109103979B (en) * | 2018-10-24 | 2023-11-10 | 珠海格力电器股份有限公司 | Photovoltaic electric equipment, charging control method and device thereof, circuit and storage medium |
| CN109521361A (en) * | 2019-01-18 | 2019-03-26 | 上海熠动动力科技有限公司 | A kind of relay contact adhesion detection circuit and its detection device |
| CN110261689B (en) * | 2019-06-26 | 2021-04-20 | 爱士惟新能源技术(江苏)有限公司 | Relay detection method for photovoltaic inverter BUS voltage unbalance and live wire grounding |
| CN110703085B (en) * | 2019-11-11 | 2021-04-16 | 爱士惟新能源技术(扬中)有限公司 | Relay fault detection method for grid-connected inverter |
| CN111521928B (en) * | 2020-04-28 | 2023-03-31 | 阳光电源股份有限公司 | Grid-connected switch failure detection method and system of three-phase inverter |
| CN112858898B (en) * | 2021-01-07 | 2023-04-04 | 上海新时达电气股份有限公司 | Relay fault detection method |
| CN113049950B (en) * | 2021-03-05 | 2024-02-09 | 阳光电源股份有限公司 | Relay detection device and method and charging pile |
| WO2023039775A1 (en) * | 2021-09-16 | 2023-03-23 | 华为数字能源技术有限公司 | Photovoltaic system, relay detection method, and power source system |
| CN115184838B (en) * | 2022-09-08 | 2023-01-31 | 深圳市云天数字能源有限公司 | Relay short circuit failure detection method and device |
| CN115833166B (en) * | 2022-11-04 | 2024-03-22 | 上海正泰电源***有限公司 | Resonance protection design method for grid-connected inverter |
| CN116165529B (en) * | 2022-12-20 | 2023-09-15 | 上海百竹成航新能源有限责任公司 | Relay adhesion detection method, electronic equipment and energy storage inverter system |
| CN117214690B (en) * | 2023-11-08 | 2024-04-09 | 深圳市首航新能源股份有限公司 | Relay adhesion detection method, electronic equipment and energy storage system |
| CN117955047B (en) * | 2024-03-26 | 2024-05-31 | 锦浪科技股份有限公司 | Leakage current suppression method in relay self-test |
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