A special insulation detection system for photovoltaic power station transformation

Abstract

The present invention provides a dedicated insulation detection system for photovoltaic power station retrofits, including an auxiliary detection system for connecting between a positive busbar and a negative busbar. The auxiliary detection system includes an R1 positive sampling resistor and an R2 negative sampling resistor, connected in series between the positive and negative busbars. A ground connection is provided between the R1 positive sampling resistor and the R2 negative sampling resistor, each of which is set to no less than 19 times the resistance of the sampling resistors in the original detection system. An auxiliary detection point is provided between the R1 positive sampling resistor and the R2 negative sampling resistor. The auxiliary detection point is connected to an auxiliary host and is used to obtain the current flowing between the R1 positive sampling resistor and the R2 negative sampling resistor to detect whether a ground fault has occurred. The present invention can retrofit existing insulation detection devices, improving their overall detection accuracy while also avoiding false alarms caused by conflicts between new and old detections.

Description

Technical Field

[0001] The present invention relates to the technical field of DC power supply insulation detection, and in particular to a special insulation detection system for photovoltaic power station reconstruction. Background Art

[0002] A photovoltaic power station is a photovoltaic power generation system connected to the power grid and supplying electricity to the grid. It can be categorized as either grid-connected with or without batteries. The entire power supply network involves a DC system, which carries a high probability of failures such as ground faults, AC-to-DC crosstalk, and DC-to-DC crosstalk. Once a failure occurs, it can cause significant losses. Therefore, insulation testing of the DC power supply is particularly important.

[0003] A DC power supply system includes a power supply module, which provides a DC circuit. The DC power supply is then connected in parallel to several loads. DC power supply systems are typically equipped with an insulation detection system to detect ground faults in the system. However, there is an upper limit on the number of branches that each insulation test can monitor. With the construction of substations and the expansion of DC power supply systems, the original insulation detection system is no longer sufficient to detect all branch loads. Installing a new insulation detection system requires completely dismantling the original system, resulting in a significant waste of existing resources and a significant cost in time and manpower. Directly connecting a new insulation detection device would introduce a new balancing bridge, leading to conflicts and false alarms between the old and new detections. Summary of the Invention

[0004] In view of this, the problem to be solved by the present invention is to provide a special insulation detection system for photovoltaic power station transformation, which can modify the old insulation detection device to increase the grounding fault detection of the expanded and newly added load branches, and can also avoid the false alarm caused by the conflict between the new and old detections.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A dedicated insulation detection system for photovoltaic power station reconstruction includes an auxiliary detection system for connecting between a positive busbar and a negative busbar. The auxiliary detection system includes an R1 positive sampling resistor and an R2 negative sampling resistor, which are sequentially connected in series between the positive busbar and the negative busbar. A ground connection is provided between the R1 positive sampling resistor and the R2 negative sampling resistor. Both the R1 positive sampling resistor and the R2 negative sampling resistor are megohm-level resistors. An auxiliary detection point is provided between the R1 positive sampling resistor and the R2 negative sampling resistor. The auxiliary detection point communicates data with an auxiliary host and is used to collect a circulating current value to detect whether a ground fault occurs.

[0007] Furthermore, an original detection system is provided between the positive busbar and the negative busbar, and the original detection system includes an original host. The auxiliary host reserves an input point of characteristic parameters of the original host through a human-machine interface for completing coordinated joint detection.

[0008] Furthermore, the auxiliary host calculates the ground voltages V+ and V- of the positive and negative electrodes according to the circulating current value, and then calculates the ground resistance R3;

[0009] The calculation formula for the positive electrode R3 grounding resistance is: V+ / V-=(R1 / / Rx1 / / R3) / (R2 / / Rx2); the calculation formula for the negative electrode R3 grounding resistance is: V+ / V-=(R1 / / Rx1) / (R2 / / Rx2 / / R3), Rx1 is the positive electrode sampling resistor of the original detection system, and Rx2 is the negative electrode sampling resistor of the original detection system.

[0010] Furthermore, the auxiliary detection system performs zero drift correction on the current sensor, and the correction method is as follows: obtaining the ground voltage of the positive and negative poles of the auxiliary detection system and the actual sampling value of the L current sensor, and checking whether the ground voltage of the positive and negative poles is the same. If not, a ground fault alarm is issued;

[0011] Yes, check whether the collected value of the L current sensor exceeds the set threshold. If not, perform zero drift correction. If yes, obtain the leakage current values ​​of the positive and negative poles of all branches and determine whether the algebraic sum of the positive leakage current values ​​is equal to the algebraic sum of the negative leakage current values. If yes, a potential balanced grounding fault prompt is issued (valid when the leakage current value is not zero) without correction.

[0012] Furthermore, the correction process is: obtaining the current sampling value X of the current L current sensor 实际 And defined as the correction value X 矫正 , define the output value of L current sensor as X=X 实际 -X 矫正 .

[0013] Furthermore, the set threshold value of the L current sensor is 100K, and the R3 grounding resistance of the single branch is obtained, and the calculation formula is: R3 = (V+ or V-) / I, where I is the grounding current collected by the L current sensor;

[0014] Determine the grounding resistance value of R3 and whether it is less than 100K. If it is, a balanced grounding alarm is triggered and the L current sensor does not perform zero drift correction.

[0015] Furthermore, the positive electrode sampling resistor R1 and the negative electrode sampling resistor R2 are both 990K.

[0016] Furthermore, the current sensor communicates data with the auxiliary host through a communication interface, and a data processing module for signal conversion and digital processing is integrated and installed.

[0017] The advantages and positive effects of the present invention are:

[0018] By adding an auxiliary detection system between the positive bus and the negative bus, the auxiliary detection system consists of two megohm-level R1 positive sampling resistors and R2 negative sampling resistors, which are used to put the positive bus and the negative bus in an open-circuit state, so that the connection of the R1 positive sampling resistor and the R2 negative sampling resistor does not affect the normal operation of the original detection system. When the DC power supply system is expanded, the auxiliary detection system can be connected between the positive bus and the negative bus to realize the transformation of the old insulation detection device and realize the ground fault detection of the newly added load branch. At the same time, the R1 positive sampling resistor and the R2 negative sampling resistor are large-value resistors, which can convert small current signals into voltage signals, effectively improving their detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 This is an overall system diagram of a dedicated insulation detection system for photovoltaic power station reconstruction according to the present invention;

[0021] Figure 2 This is a circuit diagram of a positive grounding fault in a dedicated insulation detection system for photovoltaic power station reconstruction according to the present invention;

[0022] Figure 3 The present invention discloses a circuit diagram of a negative pole grounding fault in a dedicated insulation detection system for photovoltaic power station reconstruction. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a central component. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] The present invention provides a special insulation detection system for photovoltaic power station transformation, such as Figure 1 As shown, the system includes a power module for providing DC power. The power module is connected in series to a number of load modules via a positive busbar and a negative busbar, respectively, to supply power to the load modules. A primary detection system is connected in series between the positive and negative busbars to detect ground faults.

[0027] When a new power module is expanded (by adding solar panels), more load branches will be added to the output end of the power module. The original detection system includes several L current sensors installed on the load branches and an original host for obtaining data collected by the L current sensors. Since the internal data processing system of the original host can only process a set number of L current sensor data, the original detection system cannot detect faults in the newly added load branches.

[0028] The original detection system includes several L current sensors installed on the load branches to detect whether the input and output currents are the same. If they are, the load has not experienced a ground fault; if they are different, the load has experienced a ground fault. Each load is fitted with an L current sensor on the outside of the positive and negative transmission wires. The original detection system obtains the data collected by the L current sensor, calculates the load's R3 grounding resistance based on the data, and locates the load with the ground fault.

[0029] like Figure 2 and Figure 3 As shown, a load resistor R4 is connected between the positive bus and the negative bus (taking one load as an example), and the power module is used to supply power to the R4 load resistor. The original detection system includes an original balancing bridge, which includes a series connection of an RX1 resistor and an RX2 resistor. The input end of the RX1 resistor is connected to the positive bus, and the output end of the RX2 resistor is connected to the negative bus. The RX1 resistor and the RX2 resistor are grounded so that the voltage between the RX1 resistor and the RX2 resistor is 0V.

[0030] The original balancing bridge also includes resistors RX3 and RX4. The RX3 resistor is connected in parallel with the RX1 resistor, and the RX4 resistor is connected in parallel with the RX2 resistor. A switch K1 is connected in series with the RX3 resistor to control whether the RX3 resistor is connected in parallel with the RX1 resistor. A switch K2 is connected in series with the RX4 resistor to control whether the RX4 resistor is connected in parallel with the RX2 resistor. A primary detection point is set between the RX1 and RX2 resistors. This primary detection point is connected to the original host to collect the current value between the RX1 and RX2 resistors when the RX3 and RX4 resistors are alternately connected to the circuit. The voltage to ground of the positive and negative busbars (the voltage applied to the RX1 and RX2 resistors) is calculated to detect whether a ground fault has occurred in the positive and negative poles.

[0031] An auxiliary detection system is added between the positive busbar and the negative busbar to detect whether a ground fault occurs between the positive busbar and the negative busbar, and to detect faults in the newly added load branch. The auxiliary detection system includes a large-resistance positive sampling resistor R1 and a negative sampling resistor R2. Preferably, the positive sampling resistor R1 and the negative sampling resistor R2 are both megohm-level resistors, so that the positive busbar and the negative busbar are in a disconnected state, which does not affect the normal operation of the original detection system, effectively preventing the connection of the auxiliary detection system from affecting the normal operation of the original detection system and causing false alarms.

[0032] The resistance of the positive sampling resistor R1 and the negative sampling resistor R2 is much larger than the resistance of the resistor in the original detection system (when the voltage between the positive and negative poles is 220V, the maximum resistance of the conventional balanced bridge sampling resistor does not exceed 30K, and the maximum resistance of the switching bridge does not exceed 120K), so that the current flowing through the positive sampling resistor R1 and the negative sampling resistor R2 is very small (approaching zero), making the positive bus and the negative bus equivalent to a disconnected state.

[0033] Theoretically, the larger the positive sampling resistor R1 and the negative sampling resistor R2 are, the less impact on the old balancing bridge can be achieved, making it equivalent to achieving a design without a balancing bridge. However, the larger the resistance of the positive sampling resistor R1 and the negative sampling resistor R2 is, the higher the detection accuracy requirement of the auxiliary host is, and the greater the production difficulty and the probability of error. Preferably, the resistance of the positive sampling resistor R1 and the negative sampling resistor R2 is 990K (this value is obtained through experiments).

[0034] The positive sampling resistor R1 and the negative sampling resistor R2 are connected in series, and the input end of the positive sampling resistor R1 is connected to the positive bus, and the output end of the negative sampling resistor R2 is connected to the negative bus. The positive sampling resistor R1 and the negative sampling resistor R2 are grounded so that the voltage between the positive sampling resistor R1 and the negative sampling resistor R2 is 0V (or the same). An auxiliary detection point is provided between the positive sampling resistor R1 and the negative sampling resistor R2. The auxiliary detection point is connected to the auxiliary host to obtain the current flowing between the positive sampling resistor R1 and the negative sampling resistor R2 (the resistance values ​​of the positive sampling resistor R1 and the negative sampling resistor R2 are known) and calculate the voltage of the positive bus or the negative bus to ground to determine whether a ground fault has occurred.

[0035] For example, if the voltage between the positive and negative busbars is 220V, and the auxiliary detection system detects a positive voltage to ground of 40V and a negative voltage to ground of 180V, this indicates a positive ground fault (if both voltages are 110V, there is no ground fault), and the R3 ground resistance of the positive busbar needs to be calculated. The auxiliary host reserves input points for the original host's characteristic parameters through the human-machine interface for coordinated joint detection. The auxiliary host also obtains the values ​​of the Rx1 and Rx2 resistors of the balancing bridge in the original detection system (the Rx1 and Rx2 values ​​can be manually entered into the auxiliary host) to calculate the R3 ground resistance.

[0036] The calculation method is: 40 / 180 = (R1 / / Rx1 / / R3) / (R2 / / Rx2). Given the values ​​of the positive sampling resistor R1, the negative sampling resistor R2, the resistors Rx1, and Rx2, the grounding resistance R3 can be directly calculated. Because the positive sampling resistor R1 and the negative sampling resistor R2 form a large-value balancing bridge, their sensitivity and accuracy are far superior to the original detection system, effectively improving the accuracy of ground fault detection.

[0037] In order to determine which newly added load branch has a ground fault and obtain the corresponding ground resistance value, an L current sensor is installed at the output end of the R4 load resistor. The L current sensor and the auxiliary detection system communicate with each other. Since the L current sensor is extremely susceptible to the magnetic field in space, the auxiliary detection system can be used to perform zero drift correction on the L current sensor.

[0038] Since the resistance of the positive sampling resistor R1 and the negative sampling resistor R2 is large, a small change in current will cause the calculated positive and negative voltages to fluctuate greatly (extremely high sensitivity), and the resistance of the resistor is less affected by external factors. To ensure the accuracy of the L current sensor, a correction can be performed once a day. The correction can be manually controlled or started at a scheduled time every day.

[0039] Preferably, the L current sensor may be a fluxgate sensor. When the input and output currents of the R4 load resistor are the same, the collected value of the L current sensor is 0 (less than a set threshold value). When the input and output currents of the R4 load resistor are different (part of the current is grounded), the collected value of the L current sensor is not 0 (exceeds the set threshold value).

[0040] When the R4 load resistor fails and is grounded, the following will occur: Figure 2 or Figure 3 The R3 ground resistor shown, Figure 2 For positive ground fault, Figure 3 It is a negative ground fault.

[0041] For example, the L current sensor's specifications are: input 10mA / output 5V / 65535 engineering quantities. When the value collected by the L current sensor is 65535 engineering quantities, the output voltage is 5V and the current flowing through the L current sensor is 10mA. If a ground fault occurs, the collected engineering quantity X exceeds the threshold and requires correction.

[0042] When the system has a balanced self-consistent grounding, that is, short circuit faults occur in both the positive and negative poles, but the algebraic sum of each resistance is zero, the auxiliary detection system detects that the positive pole-to-ground voltage and the negative pole-to-ground voltage are both 110V, and the auxiliary detection system cannot detect the grounding fault.

[0043] To correct the L current sensor: Obtain the actual sampled value of the L current sensor, which represents the current value collected by the sensor. Measure the ground voltages of the positive and negative electrodes (typically, zero-drift correction is performed on the L current sensor when the voltages are equal). If the actual sampled value of the L current sensor exceeds the set threshold (a large ground current in a single branch indicates a ground fault), the L current sensor has no zero-drift and no correction is required.

[0044] To further determine whether a balanced grounding fault occurs, continue to obtain the leakage current values ​​of the positive and negative poles of all branches (the collected values ​​of the L current sensor), and judge whether the algebraic sum of the positive leakage current values ​​is equal to the algebraic sum of the negative leakage current values. If so, a potential balanced grounding fault prompt is reported (valid when the leakage current value is not zero), and the L current sensor does not perform drift correction.

[0045] Alternatively, a ground fault can be determined by obtaining the R3 grounding resistance of a single branch and resetting the threshold. The calculation formula for obtaining the R3 grounding resistance of the single branch is: R3 = (V+ or V-) / I, where I is the value collected by the L current sensor. The threshold is set to 100K. The R3 grounding resistance is determined to be less than 100K. If so, a balanced ground fault alarm is triggered, and no drift correction is performed on the L current sensor.

[0046] The voltage between the positive and negative electrodes is equal to the ground (half the voltage between the positive and negative electrodes) and the actual sampling value is less than the set threshold, indicating that the L current sensor has a zero drift. The current actual sampling value is obtained and defined as the correction value X. 矫正 , complete the correction of the L current sensor.

[0047] The correction process is: Get the current engineering value X of the current L current sensor 实际 And defined as the correction value X 矫正 , define the output value of L current sensor as X=X 实际 -X 矫正 .

[0048] When the auxiliary detection system is used normally, the output value of the L current sensor is X = X 实际 -X 矫正 The output value X is used to calculate the ground current I: I = X / 65535*0.01A. The auxiliary detection system obtains the positive and negative voltages relative to ground. By connecting the R3 grounding resistor in parallel with the sampling resistor for the corresponding pole (with the same voltage across both ends), the resistance of the R3 grounding resistor can be calculated. The calculation formula is: R3 = (40V or 180V) / I.

[0049] The L current sensor communicates data with the auxiliary detection system. The L current sensor is equipped with a leakage current comprehensive processing circuit for signal transmission, digital quantity modulation and communication. Preferably, a data processing module is integrated in the L current sensor. The data processing module is used to perform signal conversion and digital processing on the collected data, so that the L current sensor can be directly connected to the auxiliary host through the communication interface.

[0050] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A special insulation detection system for photovoltaic power station transformation, characterized in that: The auxiliary detection system includes an auxiliary detection system for connecting between the positive bus and the negative bus. The auxiliary detection system includes an R1 positive sampling resistor and an R2 negative sampling resistor connected in series between the positive bus and the negative bus. A ground connection is set between the R1 positive sampling resistor and the R2 negative sampling resistor. The R1 positive sampling resistor and the R2 negative sampling resistor are both megohm-level resistors. An auxiliary detection point is set between the R1 positive sampling resistor and the R2 negative sampling resistor. The auxiliary detection point communicates data with the auxiliary host and is used to collect the circulating current value to detect whether a ground fault occurs.

2. A photovoltaic power station transformation dedicated insulation detection system according to claim 1, characterized in that: An original detection system is provided between the positive busbar and the negative busbar. The original detection system includes an original host. The auxiliary host reserves an input point of characteristic parameters of the original host through a human-machine interface for completing coordinated joint detection.

3. A photovoltaic power station transformation dedicated insulation detection system according to claim 2, characterized in that: The auxiliary host calculates the ground voltages V+ and V- of the positive and negative electrodes according to the current value of the flowing electricity, and then calculates the ground resistance R3; The calculation formula for the positive electrode R3 grounding resistance is: V+ / V-=(R1 / / Rx1 / / R3) / (R2 / / Rx2); the calculation formula for the negative electrode R3 grounding resistance is: V+ / V-=(R1 / / Rx1) / (R2 / / Rx2 / / R3), Rx1 is the positive electrode sampling resistor of the original detection system, and Rx2 is the negative electrode sampling resistor of the original detection system.

4. A photovoltaic power station transformation dedicated insulation detection system according to claim 1, characterized in that: The auxiliary detection system performs zero drift correction on the current sensor. The correction method is as follows: obtaining the ground voltage of the positive and negative poles of the auxiliary detection system and the actual sampling value of the L current sensor, and checking whether the ground voltage of the positive and negative poles is the same. If not, a ground fault alarm is triggered. If yes, check whether the collected value of L current sensor exceeds the set threshold; if no, perform zero drift correction; Yes, obtain the leakage current values ​​of the positive and negative poles of all branches, and determine whether the algebraic sum of the positive leakage current values ​​is equal to the algebraic sum of the negative leakage current values. Yes, a potential balanced grounding fault prompt is issued (valid when the leakage current value is not zero), and no correction is performed.

5. A photovoltaic power station transformation dedicated insulation detection system according to claim 4, characterized in that: The correction process is: Get the current engineering value X of the current L current sensor 实际 And defined as the correction value X 矫正 , define the output value of L current sensor as X=X 实际 -X 矫正 .

6. A photovoltaic power station transformation dedicated insulation detection system according to claim 4, characterized in that: The set threshold value of the L current sensor is 100K, and the R3 grounding resistance of a single branch is obtained. The calculation formula is: R3 = (V+ or V-) / I, where I is the grounding current collected by the L current sensor; the R3 grounding resistance value is judged and whether it is less than 100K. If so, a balanced grounding alarm is triggered, and the L current sensor does not perform drift correction.

7. The insulation detection system for photovoltaic power station reconstruction according to claim 1 is characterized in that: The positive electrode sampling resistor R1 and the negative electrode sampling resistor R2 are both 990K.

8. The insulation detection system for photovoltaic power station reconstruction according to claim 6 is characterized in that: The current sensor communicates data with the auxiliary host through a communication interface, and a data processing module for signal conversion and digital processing is integrated in the current sensor.

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