Insulation monitoring device and method based on injection method

Abstract

The invention discloses an injection method insulation monitoring device and method, and the device comprises a logic processing and control module, a signal injection module, a signal collection module, a signal filtering module, and a direct current isolation module. The signal injection module generates positive and negative alternating direct current signals, and injects the positive and negative alternating direct current signals into a protection ground wire of an ungrounded power distribution system. The signal acquisition module acquires a bus response voltage signal; the signal filtering module filters interference of alternating current power frequency in the response voltage signal and high-frequency interference in a direct current system; the direct current isolation module filters a system direct current voltage component from the response voltage signal under the synchronous time sequence control of the logic processing and control module; the logic processing and control module calculates insulation parameters of the system according to the processed response voltage signals and judges the insulation state according to a preset threshold value. Compared with the prior art, through positive and negative alternating direct current signal injection and integration of the signal filtering module and the direct current isolation module, general insulation monitoring in an alternating current and direct current ungrounded system is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ungrounded power distribution system, in particular to an injection method insulation monitoring device and method. BACKGROUND

[0002] With the rapid development of industry, ungrounded systems are increasingly widely used in the field of power distribution. In recent years, the new energy industry has developed rapidly, and the scale of photovoltaic power generation, energy storage systems and other fields continues to expand. In these systems, if two or more phase lines have reduced insulation or grounding faults, it will cause electric leakage or even serious short circuit faults. Therefore, effective monitoring of the insulation condition of such power distribution systems is a key link to ensure safe operation, and the importance of insulation monitoring technology is increasingly prominent.

[0003] In the current insulation monitoring related technology, the conventional scheme is divided into two categories, one is the passive bridge method, and the other is the active injection method. The bridge method is generally used in direct current systems with small leakage capacitance such as charging piles, and its advantages are simple circuit, low cost and easy to implement. The disadvantage is that it is not suitable for systems with large capacitance, and because it is a passive scheme, it cannot be used in offline systems. The injection method solves the problem that the bridge method cannot be used in offline systems and can also be used in alternating current ungrounded systems. However, in the multi-frequency injection scheme, improper selection of the injection frequency can cause large errors, and the pure direct current injection method cannot be used in direct current systems.

[0004] Therefore, how to realize reliable monitoring of the insulation condition of AC / DC ungrounded power distribution systems is a technical problem to be solved. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide an injection method insulation monitoring device and method.

[0006] The purpose of the present application can be achieved by the following technical solutions: According to a first aspect of the present application, an injection method insulation monitoring device is provided, which is applied to an ungrounded power distribution system, and the device comprises a logic processing and control module, a signal injection module, a signal acquisition module, a signal filtering module and a direct current isolation module. The signal injection module is configured to generate a positive and negative alternating direct current signal and inject it into the protective ground line of the ungrounded power distribution system. The signal acquisition module is configured to acquire a response voltage signal on the bus of the ungrounded power distribution system. The signal filtering module is configured to filter out the interference of alternating working frequency in the response voltage signal. The direct current isolation module includes a capacitor and a switch, and the system direct current voltage component is eliminated from the response voltage signal through cooperation of the capacitor and the switch. The logic processing and control module is configured to control the signal injection module to generate the positive-negative alternating direct current signal, calculate the insulation parameter of the ungrounded power distribution system based on the processed response voltage signal, and determine the insulation state according to a preset threshold value.

[0007] As a preferred technical solution, the signal filtering module and the direct current isolation module are connected in series after the signal acquisition module. When the ungrounded power distribution system is a direct current system, the response voltage signal is input to the direct current isolation module after high-frequency interference is filtered out by the signal filtering module. When the ungrounded power distribution system is an alternating current system, the direct current isolation module is bypassed.

[0008] As a preferred technical solution, the direct current isolation module includes a capacitor and a switch, and the switch controls the charging and discharging state of the capacitor to make the outgoing line end of the capacitor respond only to the change amount of the positive-negative alternating direct current signal.

[0009] As a preferred technical solution, the signal acquisition module includes two sampling circuits, and each sampling circuit is connected to one direct current isolation module; the on-off state of the switch in each direct current isolation module is synchronized with the signal injection direction of the signal injection module, and the on-off logic of the two switches is complementary to each other.

[0010] As a preferred technical solution, the frequency of the positive-negative alternating direct current signal is lower than the power frequency of the measured alternating current system.

[0011] As a preferred technical solution, the logic processing and control module determines the charging completion time of the system distribution capacitor according to the change curve of the processed response voltage signal by using a voltage smoothness algorithm, and calculates the insulation resistance based on the steady-state signal value after charging is completed.

[0012] As a preferred technical solution, the voltage smoothness algorithm includes: obtaining three time points t1, t2, t3 and corresponding voltage values u1, u2, u3 at equal time intervals on the voltage decay curve after signal injection, and calculating the voltage difference and When the ratio of the voltage difference satisfies the relationship , it is determined that the response voltage signal reaches a steady state, where e is a natural constant.

[0013] As a preferred technical solution, the device further includes an alarm module configured to send an alarm signal when the logic processing and control module determines that the insulation is abnormal.

[0014] As a preferred technical solution, the insulation parameters include system voltage, system overall ground insulation resistance, positive busbar ground insulation resistance, negative busbar ground insulation resistance and system distributed capacitance.

[0015] According to a second aspect of the present application, an insulation monitoring method is provided, the method comprising: The control signal injection module generates and injects a forward DC signal and a reverse DC signal into the protective ground wire of the ungrounded power distribution system in an alternating manner; At each time of injecting a signal, the signal acquisition module acquires a response voltage signal on the system busbar; The signal filtering module filters the response voltage signal to suppress AC power frequency interference; The DC isolation module filters out the system DC voltage component from the response voltage signal in a timing sequence synchronized with the signal injection; The insulation parameters of the ungrounded power distribution system are calculated based on the processed response voltage signal; The calculated insulation parameters are compared with preset threshold values, and the insulation state of the ungrounded power distribution system is determined according to the comparison result.

[0016] As a preferred technical solution, before calculating the insulation parameters, the method further comprises the step of executing a voltage stabilization algorithm to determine whether the system response has reached a steady state, the voltage stabilization algorithm comprising: calculating the ratio of voltage difference values at consecutive equal time intervals based on the acquired voltage signal, and determining that the response voltage signal has entered a steady state when the ratio of voltage difference values is equal to the natural constant e.

[0017] Compared with the prior art, the present application has the following advantages: 1. The present application uses positive and negative alternating DC signal injection, integrates a signal filtering module and a DC isolation module controlled in a timing sequence synchronized with the signal injection, effectively filters out the power frequency interference of the AC system and the background voltage of the DC system, and realizes universal insulation monitoring of AC ungrounded systems and DC systems.

[0018] 2. The present application can accurately determine the charging completion time of the system distributed capacitance through the voltage stabilization algorithm, effectively overcoming the influence of the distributed capacitance on the measurement accuracy, so that the device can achieve high-precision measurement in systems with different sizes of distributed capacitance.

[0019] 3. The present application can calculate the system voltage, system overall insulation resistance, busbar ground insulation resistance and system distributed capacitance and other parameters in real time, providing data support for realizing comprehensive evaluation of system insulation state, accurate fault positioning and preventive maintenance.

[0020] 4、The application integrates complex signal processing and calculation logic inside the device, reduces the dependence on external systems, and facilitates engineering deployment and popularization in photovoltaic, energy storage, rail transit and other industrial scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural block diagram of the device of the application; Figure 2 is a simplified circuit diagram of the device of the application connected to the power distribution system; Figure 3 is a diagram of the DC isolation module of the application, wherein Figure 3 (a) the sampling branch corresponding to L1 / positive bus, Figure 3 (b) the sampling branch corresponding to L2 / negative bus; Figure 4 is a circuit diagram of the application ignoring system distribution capacitance, only considering the signal source; Figure 5 is a voltage change relationship diagram of the signal source applied to the sampling resistor when there is a large distribution capacitance in the system of the application; Figure 6 is a circuit diagram of the device and system connection when the signal source fully charges the distribution capacitance; DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should be within the protection scope of the application.

[0023] Embodiment 1: This embodiment provides an injection method insulation monitoring device, the module composition of which is as shown in Figure 1 including: logic processing and control module, signal injection module, signal acquisition module, signal filtering module, DC isolation module, signal amplification module, alarm module, communication module, human-computer interaction module and power supply module, each module cooperates to realize insulation monitoring of AC and DC ungrounded power distribution systems.

[0024] The simplified circuit topology diagram of the device connected to the ungrounded power distribution system is as shown in Figure 2As shown in the figure, wherein Un is the voltage source of AC or DC system, Re1 and Ce1 are the equivalent insulation resistance and distributed capacitance of L1 / positive bus to protective earth PE, Re2 and Ce2 are the equivalent insulation resistance and distributed capacitance of L2 / negative bus to PE, Us is the signal source generated by the signal injection module of the device, and two sampling resistors Rs and a voltage dividing resistor Rd constitute the sampling circuit of the signal acquisition module.

[0025] The logic processing and control module is the core of the system, responsible for coordinating the entire monitoring process. It first controls the signal injection module to generate a forward DC signal and inject it into the PE end of the system. The injection signal flows through PE, system equivalent insulation resistors Re1 and Re2, and system distributed capacitances Ce1 and Ce2, to reach system buses L1 / L+ and L2 / L-.

[0026] The signal acquisition module synchronously acquires the voltages U1 and U2 at sampling points 1 and 2. Both voltages are the superposition of system voltage Un and injection signal voltage Us, i.e. U1 = Un1 + Uss and U2 = Un2 + Uss, where Un1 and Un2 are the voltages applied by the power source Un of the distribution system on the two sampling resistors. Since the insulation resistors Re1 and Re2 of the two buses of the system to PE are not necessarily equal, Un1 and Un2 are not necessarily equal according to the voltage division after parallel connection of resistors. However, for the signal source Us, the two sampling resistors Rs and the voltage dividing resistor Rd are in parallel, and the voltage of the signal source Us on the two sampling resistors Rs is equal, both being Uss. According to this circuit, the magnitude of the system voltage Un can be calculated in real time: , The acquired signals then enter the signal filtering module. In AC systems, this module mainly filters out power frequency and harmonic interference; in DC systems, it is used to suppress high-frequency noise. The filtered signals are sent to the DC isolation module.

[0027] The simplified circuit of the DC isolation module is shown in Figure 3 , which functions to eliminate the superimposed interference of the inherent DC voltage Un of the system on the injection signal, ensuring that the pure injection signal is extracted for insulation resistance calculation. This module contains two sub-circuits with the same structure, corresponding to the L1 / positive bus sampling circuit and the L2 / negative bus sampling circuit of the distribution system, respectively. One of the two sub-circuits integrates capacitor C1 and switch K1, and the other integrates capacitor C2 and switch K2. The on-off timing of the two switches K1 and K2 is controlled by the logic processing and control module, ensuring strict synchronization with the injection of positive and negative alternating DC signals and maintaining complementary logic relationship at all times. The specific working process is as follows: Step 1: When the signal is not injected The first road (corresponding to L1 / positive bus sampling circuit): the potential of U1 point at the left end of capacitor C1 is system response value Un1, K1 is grounded, the potential of Uc1 is 0, and the capacitor starts to charge to voltage difference Un1; The second road (corresponding to L2 / negative bus sampling circuit): the potential of U2 point at the left end of capacitor C2 is system response value-Un2, K2 is grounded, the potential of Uc2 is 0, and the capacitor starts to charge to voltage difference-Un2.

[0028] Step 2: signal source positive injection The first road: the potential of U1 point at the left end of capacitor C1 is Un1 of the previous state plus signal source response value Uss, that is, U1=Un1+Uss, since the voltage difference in the capacitor cannot be suddenly changed, and K1 is disconnected, the voltage difference of the capacitor should maintain the previous state, that is, Un1, and the potential of Uc1 point synchronously increases Uss with U1 point, that is, Uc1=Uss; The second road: the potential of U2 point at the left end of capacitor C2 is-Un2 of the previous state plus signal source response value Uss, that is, U2=-Un2+Uss, K2 is grounded, the potential of Uc2 is 0, and the voltage difference of the capacitor is discharged from-Un2 of the previous state to-Un2+Uss.

[0029] Step 3: signal source reverse injection The first road: the potential of U1 point at the left end of capacitor C1 is system response value Un1 plus reverse signal source response-Uss, that is, U1=Un1-Uss, K1 is grounded, the potential of Uc1 is 0, and the voltage difference of the capacitor is discharged from Un1 of the previous state to Un1-Uss; The second road: the potential of U2 point at the left end of capacitor C2 is-Un2+Uss of the previous state, which becomes-Un2-Uss, that is, it is reduced by 2Uss, K2 is disconnected, the potential of Uc2 is lowered from 0 of the previous state, synchronously with the decrease of 2Uss of U2, that is, Uc2=-2Uss, and the voltage difference of the capacitor remains unchanged.

[0030] Step 4: signal source positive injection The first road: the potential of U1 point at the left end of capacitor C1 is Un1-Uss of the previous state, which becomes Un1+Uss, since the voltage difference in the capacitor cannot be suddenly changed, and K1 is disconnected, the voltage difference of the capacitor should maintain the previous state, that is, Un1-Uss, and the potential of Uc1 point synchronously increases 2Uss with U1 point, that is, Uc1=2Uss; The second road: the potential of U2 point at the left end of capacitor C2 is-Un2-Uss of the previous state, which becomes-Un2+Uss, K2 is grounded, the potential of Uc2 point is 0, and the voltage difference of the capacitor remains unchanged.

[0031] The steps 3 and 4 are repeated, and after the two-way logic complement, the positive and negative 2 times signal source response voltage Uss can be obtained at the output end of the capacitors C1 and C2. After that, the signal is linearly amplified through the signal amplification module to adapt to the sampling input range of the internal ADC of the logic processing and control module, so as to ensure the measurement accuracy.

[0032] For the scenario where the system distributed capacitance cannot be ignored, the logic processing and control module performs a voltage smoothing algorithm based on the voltage change curve on the sampling resistor Rs after the injection signal, as shown in the formula: Figure 5 Where Umax is the voltage applied to Rs when the distributed capacitances Ce1 and Ce2 are short-circuited at the moment of signal injection, and Umin is the voltage applied to Rs when the distributed capacitances are fully charged by the signal source Us, is the product of the insulation resistance and the internal resistance of the instrument in parallel with the distributed capacitance.

[0033] Taking u1, u2, and u3 corresponding to t1, t2, and t3 on the curve, where Δt = t2-t1 = t3-t2, we have: Taking the voltage differences Δu1 and Δu2 of the two segments t1 to t2 and t2 to t3: Dividing Δu1 by Δu2 gives the ratio of the two differences: When t2 - t1 = , p = e, and according to this relationship, the time when the signal source Us fully charges the distributed capacitances Re1 and Re2 can be accurately and timely found, and the accurate Us = Umin can be obtained, so that the overall insulation resistance of the system can be calculated, and then the overall distributed capacitance Ce of the system can be calculated according to the injection time and the insulation resistance.

[0034] After obtaining the steady-state detection signal, the logic processing and control module calculates according to the circuit model. First, ignore the distributed capacitance, and consider the system power Un as short-circuited. The circuit can be simplified as Figure 4 At this time, the overall insulation resistance Re of the system can be obtained by the following formula: Where​​​​​​​​​ .

[0035] When the system distribution capacitance is large and has reached the charging steady state, a model containing the distribution capacitance is used, and the circuit is equivalent to as shown in Figure 6 , , , Considering the joint action of the system voltage Un and the signal source Us, according to the superposition theorem and Kirchhoff's law, the insulation resistance of each bus to PE can be solved by simultaneously solving equations: , , , , Wherein, the voltage of the system power Un between the system L1 / positive bus h and L2 / negative bus and PE is: , , The final solution is: , , At the same time, the overall distribution capacitance Ce of the system can also be estimated according to the time τ of reaching the steady state of the injected signal and the calculated Re.

[0036] The insulation parameters Re, Re1, Re2, Ce, Un calculated will exceed the preset threshold, the alarm module will drive the audible and visual alarm and perform digital output, the communication module can upload data to the remote monitoring center, the man-machine interaction module is used for on-site display and parameter setting, and the power supply module provides stable and isolated working power for all the above modules.

[0037] The device alternately injects positive and negative direct current signals, in an alternating current system, the signal filtering module is used to suppress power frequency interference, and in a direct current system, the direct current isolation module synchronized with the injection is used to eliminate the system direct current voltage component, so that the pure response voltage signal is extracted to calculate the insulation parameter, and universal and high-precision insulation monitoring is realized.

[0038] Embodiment 2: The embodiment provides an insulation monitoring method based on the device in embodiment one, and the method specifically comprises the following steps: ​Step S1: the device is powered on, the logic processing and control module initializes each peripheral interface, and the user can set the alarm threshold, working mode and other parameters through the man-machine interaction module; Step S2: the logic processing and control module controls the signal injection module, starts a complete monitoring cycle, generates a forward direct current signal and injects it into the system PE end; Step S3: during the signal injection, the signal acquisition module synchronously acquires the response voltage signals U1 and U2 on the system bus; For an AC ungrounded system, the response voltage signal is inhibited by the signal filtering module to suppress the interference of the AC system frequency, and the injected signal component is extracted; For a DC ungrounded system, the response voltage signal is mainly processed through the DC isolation module. According to the timing synchronized with the signal injection, the module dynamically separates the pure injected signal component generated by the injected signal from the superimposed signal through the cooperation of switches and capacitors; Step S5: the separated injected signal component is linearly amplified by the signal amplification module, and then converted into a digital quantity by the ADC module of the logic processing and control module; Step S6: the logic processing and control module executes the voltage stability algorithm, analyzes the acquired digital signal sequence, judges whether the signal enters the steady state by calculating the voltage difference ratio of continuous equal time intervals, continuously acquires and judges if it is not in the steady state, and records the current steady state signal value Umin if it is in the steady state; Step S7: based on the captured forward injected steady state signal value, the logic processing and control module calculates the overall insulation resistance Re of the system according to the pre-stored circuit model and algorithm; Step S8: after the calculation of the forward signal is completed, the logic processing and control module controls the signal injection module to generate a reverse direct current signal, and repeats steps S3 to S7 to obtain the steady state signal under reverse injection and perform calculation; Step S9: the signals obtained by the forward and reverse injections are integrated to calculate more accurate system overall insulation resistance Re, positive bus-to-ground insulation resistance Re1, negative bus-to-ground insulation resistance Re2 and system distributed capacitance Ce and other parameters, and the final calculation result is compared with the preset alarm threshold; Step S10: according to the judgment result, the corresponding operation is performed: the display is updated through the man-machine interaction module, the data is uploaded through the communication module, and if an insulation fault occurs, the alarm module is immediately driven to issue an alarm; Step S11: after completing a forward and reverse injection cycle, the device can enter hibernation to wait for the next monitoring cycle, or continuously perform alternating injection and calculation to realize real-time or quasi-real-time monitoring.

[0039] The method of the present application eliminates the power frequency interference by alternating injection of positive and negative direct current signals, adopts filtering technology for AC system to eliminate the power frequency interference, adopts synchronous DC isolation technology for DC system to eliminate the system DC voltage component, and then determines the signal steady state through voltage smoothing algorithm, finally calculates the system insulation parameters, and realizes the general and high-reliable insulation state monitoring scheme.

[0040] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements shall be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An injection method insulation monitoring device for use in an ungrounded electrical distribution system, characterized in that The device comprises a logic processing and control module, a signal injection module, a signal acquisition module, a signal filtering module and a DC isolation module. The signal injection module is configured to generate positive and negative alternating DC signals and inject the signals into the protective ground wire of the ungrounded power distribution system. The signal acquisition module is configured to acquire a response voltage signal on the bus of the ungrounded power distribution system. The signal filtering module is configured to filter out AC power frequency interference in the response voltage signal. The DC isolation module comprises a capacitor and a switch, and the system DC voltage component is eliminated from the response voltage signal through the cooperation of the capacitor and the switch. The logic processing and control module is configured to control the signal injection module to generate the positive and negative alternating DC signals, calculate the insulation parameters of the ungrounded power distribution system based on the processed response voltage signal, and determine the insulation state according to a preset threshold.

2. The apparatus of claim 1, wherein, The signal filtering module and the DC isolation module are connected in series after the signal acquisition module. When the ungrounded power distribution system is a DC system, the response voltage signal is input into the DC isolation module after being filtered by the signal filtering module to remove high-frequency interference. When the ungrounded power distribution system is an AC system, the DC isolation module is bypassed.

3. An implantation monitoring apparatus according to claim 1, wherein The switch of the DC isolation module controls the charging and discharging state of the capacitor, so that the output terminal of the capacitor only responds to the change amount of the positive and negative alternating DC signals.

4. An implantation monitoring apparatus according to claim 3, wherein The signal acquisition module comprises two sampling circuits, each of which is connected to a DC isolation module; the on-off state of the switch in each DC isolation module is synchronized with the signal injection direction of the signal injection module, and the on-off logic of the two switches is complementary to each other.

5. The implantation monitoring apparatus of claim 1, wherein The logic processing and control module determines the charging completion time of the system distribution capacitor according to the change curve of the processed response voltage signal by using a voltage smoothing algorithm, and calculates the insulation resistance based on the steady-state signal value after charging is completed.

6. An implant monitoring device according to claim 5, wherein The voltage stabilization algorithm comprises: obtaining three time points t1, t2, t3 and corresponding voltage values u1, u2, u3 of equal time intervals on a voltage decay curve after signal injection, and calculating voltage difference values of adjacent time periods With When the ratio of the voltage difference values satisfies the relationship , the response voltage signal reaches a steady state, wherein e is a natural constant.

7. The implantation monitoring apparatus of claim 1, wherein The device further comprises an alarm module that sends an alarm signal when the logic processing and control module determines that the insulation is abnormal.

8. The implantation monitoring apparatus of claim 1, wherein The insulation parameters include system voltage, overall insulation resistance to ground, positive bus insulation resistance to ground, negative bus insulation resistance to ground and system distribution capacitor.

9. A method of insulation monitoring based on the device of any of claims 1-8, characterized by, The method comprises: controlling the signal injection module to generate and inject positive and negative DC signals into the protective ground wire of the ungrounded power distribution system in an alternating manner; acquiring a response voltage signal on the bus of the system through the signal acquisition module at each time of injecting the signal; filtering the response voltage signal through the signal filtering module to suppress AC power frequency interference; filtering out the system DC voltage component from the response voltage signal through the DC isolation module in a timing sequence synchronized with the signal injection; calculating the insulation parameters of the ungrounded power distribution system based on the processed response voltage signal; comparing the calculated insulation parameters with a preset threshold, and determining the insulation state of the ungrounded power distribution system according to the comparison result.

10. The insulation monitoring method according to claim 9, characterized by Before calculating the insulation parameter, a step of performing a voltage stabilization algorithm to determine whether the system response reaches a steady state is further included, the voltage stabilization algorithm comprising: calculating a ratio of voltage difference values of consecutive equal time intervals according to the collected voltage signal, and determining that the response voltage signal enters a steady state when the ratio of the voltage difference values is equal to a natural constant e.

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