A detection system for broken neutral line of distributed photovoltaic access monitoring equipment

Abstract

The present invention discloses a detection system for a broken neutral line of distributed photovoltaic access monitoring equipment, including three built-in voltage detection modules, a loop control module and a signal acquisition control module. The built-in voltage detection module includes at least two resistors connected between each phase line and the neutral line, and the signal acquisition control module is connected between the resistors to output the detection voltage corresponding to each phase line; the loop control module includes: three phase lines are respectively connected to a load switching loop through a diode, a control switch in the load switching loop is connected to the signal acquisition control module, and is used to input a control instruction for controlling the switching end of the control switch, and a signal conversion module is also provided to output waveform data, which is connected to the signal acquisition control module. The present invention solves the problem of rapid and accurate detection of a broken neutral line, thereby improving the safety and operation and maintenance efficiency of photovoltaic power stations.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power system monitoring, and in particular to a detection system for a broken neutral line of distributed photovoltaic access monitoring equipment. Background Art

[0002] As an important part of renewable energy, the safety and reliability of distributed photovoltaic systems are directly related to the stable operation of the power grid and the user's electricity experience. In photovoltaic power stations, the neutral line is the key path for current return. Once a line break occurs, it will cause circuit imbalance, which will not only affect the efficiency of photovoltaic power generation, but also may cause equipment damage or even fire and other safety accidents. Therefore, the development of an efficient and accurate method for detecting broken neutral lines is of great significance to ensure the safe operation of photovoltaic power stations.

[0003] Most of the existing methods for detecting broken neutral wires rely on manual inspections and traditional electrical testing methods, which have problems such as long detection cycles, low efficiency, and easy missed detections. Alternatively, a neutral wire current transformer is added to detect whether there is current in the neutral wire to determine whether the neutral wire loop is normal. This method has limited application scenarios and is relatively costly: in a three-phase fully balanced system, a normally wired neutral wire loop will not have current flowing through it. With the rapid development of technologies such as the Internet of Things and big data, intelligent and automated monitoring equipment has gradually become the mainstream trend in photovoltaic power station management. However, how to use these technologies to achieve accurate detection of broken neutral wires remains an urgent problem to be solved. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] Based on the above problems, the present invention provides a detection system for a broken neutral line of a distributed photovoltaic access monitoring device, which solves the problem of rapid and accurate detection of a broken neutral line, thereby improving the safety and operation and maintenance efficiency of a photovoltaic power station.

[0006] (II) Technical solution

[0007] Based on the above technical problems, the present invention provides a detection system for a broken neutral line of a distributed photovoltaic access monitoring device, comprising three built-in voltage detection modules, a loop control module and a signal acquisition control module, wherein the built-in voltage detection module comprises at least two resistors connected between each phase line and the neutral line, and the signal acquisition control module is connected between the resistors to output the detection voltage corresponding to each phase line; the loop control module comprises: three phase lines are respectively connected to one end of a resistor R1 through a diode, the other end of the resistor R1 is connected to one end of a resistor R2 and a first switching end of a control switch, the other end of the resistor R2 is connected to a second switching end of the control switch, the output end of the control switch is connected to the neutral line, the control switch is connected to the signal acquisition control module, and is used to input a control instruction for controlling the switching end of the control switch, and a signal conversion module is further provided between the resistor R1 and the control switch, and between the resistor R2 and the control switch, the signal conversion module outputs waveform data and is connected to the signal acquisition control module; the signal acquisition control module sets a target setting value according to the magnitude of the detection voltage corresponding to each phase line, generates a duty cycle according to the waveform data, and when the duty cycle is continuously lower than the target setting value, it is determined that a broken neutral line fault occurs at the input end of the monitoring device.

[0008] Furthermore, the signal acquisition control module sets the target setting value according to the size of the detection voltage corresponding to each phase line, including: when the detection voltages corresponding to each phase line are all greater than 0.7Un, the target setting value of the duty cycle is 90%; when there is one item of the detection voltages corresponding to each phase line that is lower than 0.5Un, the target setting value of the duty cycle is 75%; when there are two voltages of the detection voltages corresponding to each phase line that are lower than 0.5Un, the target setting value of the duty cycle is 50%, and Un is the nominal voltage.

[0009] Furthermore, the resistor R2 is greater than the resistor R1.

[0010] Furthermore, the signal acquisition control module controls the switch to close at the second switching end, and calculates the first effective duty cycle data; then the signal acquisition control module controls the switch to close at the first switching end, and calculates the second effective duty cycle data, and compares the second effective duty cycle data with the first effective duty cycle data, and repeats the operation. If the first effective duty cycle data and the second effective duty cycle data in each round of operation are consistent, the subsequent control switches are all closed at the second switching end; otherwise, the subsequent control switches are all closed at the first switching end.

[0011] Furthermore, the signal conversion module between the resistor R2 and the control switch includes a resistor R3 and an optocoupler U1, the resistor R3 is connected in series between the resistor R2 and the control switch, the input end of the optocoupler U1 is connected in parallel at both ends of the resistor R3, and the output end is connected to the signal acquisition control module; the signal conversion module between the resistor R1 and the control switch includes a resistor R4 and an optocoupler U2, the resistor R4 is connected in series between the resistor R1 and the control switch, the input end of the optocoupler U2 is connected in parallel at both ends of the resistor R4, and the output end is connected to the signal acquisition control module.

[0012] Furthermore, the signal acquisition control module includes a microcontroller, the microcontroller is connected to a communication module, and the communication module is used to report to a concentrator or a master station.

[0013] Furthermore, the communication module reports the broken neutral line fault status code, occurrence time and geographical location information.

[0014] (III) Beneficial effects

[0015] The above technical solution of the present invention has the following advantages:

[0016] (1) The present invention sets different target setting values ​​of the duty cycle according to the different sizes of the detection voltage of each phase line output by the built-in voltage detection module, generates the current duty cycle according to the waveform data of each phase line output by the loop control module, and then realizes the rapid and accurate detection of the broken neutral line by making the current duty cycle continuously lower than the corresponding duty cycle target setting value, thereby improving the safety and operation and maintenance efficiency of the photovoltaic power station;

[0017] (2) The present invention switches different load circuits by controlling the switching of switches through the circuit control module, measures the corresponding duty cycle, and quickly eliminates the interference introduced by the capacitive load through intelligent regulation of the load circuit current, thereby further improving the detection accuracy of the broken neutral line. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0019] Figure 1 It is a schematic diagram of the overall structure of a system for detecting a broken neutral line of distributed photovoltaic access monitoring equipment according to an embodiment of the present invention;

[0020] Figure 2 This is an overall circuit diagram of a system for detecting a broken neutral line of distributed photovoltaic access monitoring equipment according to an embodiment of the present invention;

[0021] Figure 3 is a circuit diagram of a built-in voltage detection module according to an embodiment of the present invention;

[0022] Figure 4 is a circuit diagram of a loop control module according to an embodiment of the present invention;

[0023] Figure 5 4 is a circuit diagram of a signal acquisition control module according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] The embodiment of the present invention is a detection system for a broken neutral line of a distributed photovoltaic access monitoring device, such as Figure 1-2 As shown, it includes 3 built-in voltage detection modules, a loop control module and a signal acquisition control module. The built-in voltage detection module includes at least two resistors connected between each phase line and the neutral line, and the signal acquisition control module is connected between the resistors to output the detection voltage corresponding to each phase line; the loop control module includes: the three phase lines are respectively connected to one end of the resistor R1 through a diode, the other end of the resistor R1 is connected to one end of the resistor R2 and the first switching end of the control switch, the other end of R2 is connected to the second switching end of the control switch, the output end of the control switch is connected to the neutral line, the control switch is connected to the signal acquisition control module, and is used to input the control instruction of the switching end of the control switch, and a signal conversion module is also provided between the R1 and the control switch, and between the R2 and the control switch, and the signal conversion module outputs waveform data and is connected to the signal acquisition control module.

[0026] The built-in voltage detection module is used to detect the input three-phase grid voltage and output it to the signal acquisition control module for real-time monitoring of the grid voltage instantaneous quantity. Figure 3 As shown, one end of the series-connected resistors R11, R12, R13 and R14 is connected to each phase line A / B / C, one end of the resistor R15 is connected to the neutral line N, the other ends of the resistors R11, R12, R13 and R14 and the other end of the resistor R15 are connected to the microcontroller of the signal acquisition control module, and the output detection voltage VA / VB / VC is used for monitoring;

[0027] The loop control module is used to build a load loop between the phase lines, i.e., between A and N, B and N, and C and N, and output the signal to the signal acquisition control module after signal shaping to determine whether the path between each phase line A / B / C and the neutral line N is normal. Figure 4As shown, the phase lines A, B, and C are connected to one end of the resistor R1 through diodes D1, D2, and D3 respectively, the other end of R1 is connected to one end of the resistor R2 and the first switching end of the control switch, the other end of R2 is connected to the second switching end of the control switch, the input end of the control switch is connected to the neutral line N, and the control switch is connected to the control instruction output by the microcontroller of the signal acquisition control module, so as to control the control switch to switch between the two switching ends. A signal conversion module is also provided between R1 and the control switch and between R2 and the control switch. The signal conversion module outputs waveform data and is connected to the microcontroller of the signal acquisition control module. Therefore, the control switch can be switched to the first switching end according to the control instruction output by the microcontroller, and the current only passes through the load R1 if it is switched to the second switching end; the current passes through the load R1+R2; when passing through different loads, the waveform data is sent to the microcontroller through the signal conversion module for state judgment; the signal conversion module between R2 and the control switch includes a resistor R3 and an optocoupler U1, the resistor R3 is connected in series between the R2 and the control switch, the input end of the optocoupler U1 is connected in parallel to both ends of the resistor R3, one end of the output end is connected to the signal acquisition control module, and is connected to the power supply through the resistor R5, and the other end of the output end is connected to the ground wire; the signal conversion module between R1 and the control switch includes a resistor R4 and an optocoupler U2, the resistor R4 is connected in series between the R1 and the control switch, the input end of the optocoupler U2 is connected in parallel to both ends of the resistor R4, one end of the output end is connected to the signal acquisition control module, and is connected to the power supply through the resistor R5, and the other end of the output end is connected to the ground wire.

[0028] In particular, since the capacitive load of the power grid or other equipment (such as HPLC communication module) will introduce additional load paths and cause missed detection, the loop control module intelligently adjusts the load loop current according to the instructions of the signal acquisition control module to quickly eliminate the interference introduced by the capacitive load; the specific method is as follows: If other equipment in the power grid introduces capacitive loads, the loop control module needs a smaller load impedance or a larger load current to consume the loop composed of the capacitive load, and cause the duty cycle data to change; therefore, a 2-level load impedance R1 is added to the loop control module, R1+R2, where R2 is greater than R1, and the size of the 2-level load is distinguished as much as possible. In order to control the power consumption of the equipment, the signal acquisition control module controls the switch First, close the second switching end, use R1+R2 as the load, and calculate the first effective duty cycle data; then the signal acquisition control module controls the switch to close at the first switching end, use R1 as the load, close the first switching end, calculate the second effective duty cycle data, compare the second effective duty cycle data with the first effective duty cycle data, and repeat at least one round of operation. If the first effective duty cycle data and the second effective duty cycle data of each round of operation are consistent, then the subsequent control switch uses R1+R2 as the load, that is, the second switching end is closed and the first switching end is disconnected; if the duty cycle data of the two rounds are inconsistent, then R1 is used as the load in the subsequent operation, that is, the first switching end is closed and the second switching end is disconnected.

[0029] The signal acquisition control module is responsible for real-time acquisition of the grid voltage instantaneous signal from the built-in voltage detection module and the waveform data generated by the loop control module, such as Figure 5 As shown, the target setting value is set according to the magnitude of the detection voltage corresponding to each phase line, and the duty cycle is generated according to the waveform data. When the duty cycle is continuously lower than the target setting value, it is determined that a broken neutral line fault has occurred at the input end of the monitoring device. At the same time, the fault status information and geographical location information are reported to the main station system through the communication module for timely warning; this is because the duty cycle D is a linear function of the grid voltage, that is, D=K1*U A +K2*U B +K3*U C , coefficients K1, K2, K3 are respectively related to the corresponding voltage U A , U B , U CThe duty cycle is directly proportional to the voltage. Therefore, the higher the voltage, the larger the target duty cycle. For example, if the voltages of the three phases A, B, and C of the power grid are all greater than 0.7Un, the duty cycle needs to be greater than 90%, and the target setting value of the duty cycle is 90%; if any one of the three phases A, B, and C is lower than 0.5Un, the duty cycle needs to be greater than 75%, and the target setting value of the duty cycle is 75%; if two of the three phases A, B, and C have voltages lower than 0.5Un, the duty cycle needs to be greater than 50%, and the target setting value of the duty cycle is 50%; Un is the nominal voltage, indicating the rated voltage of the system; if it is continuously lower than the corresponding target setting value of the duty cycle, it is determined that a broken neutral line fault has occurred at the input end of the monitoring device.

[0030] The detection method of the above detection system includes:

[0031] The monitoring device has a built-in three-phase voltage detection circuit to detect the input voltage. The three phases are sampled separately and then output to the microcontroller for sampling, so as to monitor the instantaneous value of the three-phase voltage of the power grid in real time.

[0032] A load control detection circuit is built between the phase lines, i.e., between A and N, B and N, and C and N. The circuit outputs shaped waveform data to detect whether the path between each phase line A / B / C and the neutral line N is normal;

[0033] The microcontroller in the signal acquisition control module samples the waveform data given by the loop control module in real time, and intelligently adjusts the duty cycle judgment threshold value in combination with the instantaneous value of the three-phase voltage of the power grid. The more power supply phases, the higher the voltage, and the larger the duty cycle threshold. If the duty cycle is significantly lower than the threshold, it is recorded as a broken neutral line state; if the duty cycle is close to the threshold, the duty cycle is detected again after the loop load adjustment switch is turned on in each cycle. If the duty cycle is significantly lower than the threshold, it is recorded as a broken neutral line state to prevent misjudgment and missed judgment caused by interference.

[0034] The microcontroller synchronously records the time when the broken neutral line state occurs, and reports the broken neutral line fault state code, the time of occurrence and the geographical location information to the concentrator or the main station through the communication module.

[0035] In summary, the above-mentioned detection system for the broken neutral line of distributed photovoltaic access monitoring equipment has the following beneficial effects:

[0036] (1) The present invention sets different target setting values ​​of the duty cycle according to the different sizes of the detection voltage of each phase line output by the built-in voltage detection module, generates the current duty cycle according to the waveform data of each phase line output by the loop control module, and then realizes the rapid and accurate detection of the broken neutral line by making the current duty cycle continuously lower than the corresponding duty cycle target setting value, thereby improving the safety and operation and maintenance efficiency of the photovoltaic power station;

[0037] (2) The present invention switches different load circuits by controlling the switching of switches through the circuit control module, measures the corresponding duty cycle, and quickly eliminates the interference introduced by the capacitive load through intelligent regulation of the load circuit current, thereby further improving the detection accuracy of the broken neutral line.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations shall fall within the scope defined by the appended claims.

Claims

1. A detection system for a broken neutral line of a distributed photovoltaic access monitoring device, characterized in that: It includes three built-in voltage detection modules, a loop control module and a signal acquisition control module. The built-in voltage detection module includes at least two resistors connected between each phase line and the neutral line. The signal acquisition control module is connected between the resistors to output the detection voltage corresponding to each phase line; the loop control module includes: the three phase lines are respectively connected to one end of the resistor R1 through a diode, the other end of the resistor R1 is connected to one end of the resistor R2 and the first switching end of the control switch, the other end of the resistor R2 is connected to the second switching end of the control switch, the output end of the control switch is connected to the neutral line, the control switch is connected to the signal acquisition control module, and is used to input a control instruction for controlling the switching end of the control switch. A signal conversion module is also provided between the resistor R1 and the control switch, and between the resistor R2 and the control switch. The signal conversion module Output waveform data, connect to the signal acquisition control module; the signal acquisition control module sets the target setting value according to the size of the detection voltage corresponding to each phase line, generates the duty cycle according to the waveform data, and when the duty cycle is continuously lower than the target setting value, it is determined that a broken neutral line fault has occurred at the input end of the monitoring device; the signal acquisition control module sets the target setting value according to the size of the detection voltage corresponding to each phase line, including: when the detection voltages corresponding to each phase line are all greater than 0.7Un, the target setting value of the duty cycle is 90%; when there is one item of the detection voltages corresponding to each phase line that is lower than 0.5Un, the target setting value of the duty cycle is 75%; when there are two voltages of the detection voltages corresponding to each phase line that are lower than 0.5Un, the target setting value of the duty cycle is 50%, and Un is the nominal voltage; The signal acquisition control module controls the switch to close at the second switching end, and calculates the first effective duty cycle data; then the signal acquisition control module controls the switch to close at the first switching end, calculates the second effective duty cycle data, compares the second effective duty cycle data with the first effective duty cycle data, and repeats the operation. If the first effective duty cycle data and the second effective duty cycle data of each round of operation are consistent, the subsequent control switches are all closed at the second switching end; otherwise, the subsequent control switches are all closed at the first switching end.

2. The detection system for the broken neutral line of distributed photovoltaic access monitoring equipment according to claim 1 is characterized in that: The resistor R2 is greater than the resistor R1.

3. The system for detecting a broken neutral line of distributed photovoltaic access monitoring equipment according to claim 1, characterized in that: The signal conversion module between the resistor R2 and the control switch includes a resistor R3 and an optocoupler U1, wherein the resistor R3 is connected in series between the resistor R2 and the control switch, the input end of the optocoupler U1 is connected in parallel to both ends of the resistor R3, and the output end is connected to the signal acquisition control module; the signal conversion module between the resistor R1 and the control switch includes a resistor R4 and an optocoupler U2, wherein the resistor R4 is connected in series between the resistor R1 and the control switch, the input end of the optocoupler U2 is connected in parallel to both ends of the resistor R4, and the output end is connected to the signal acquisition control module.

4. The system for detecting a broken neutral line of distributed photovoltaic access monitoring equipment according to claim 1, characterized in that: The signal acquisition control module includes a microcontroller, the microcontroller is connected to a communication module, and the communication module is used to report to a concentrator or a master station.

5. The system for detecting a broken neutral line of distributed photovoltaic access monitoring equipment according to claim 4 is characterized in that: The communication module reports the broken neutral line fault status code, occurrence time and geographical location information.

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