A three-state switching dc insulation impedance on-line detection circuit and method

Abstract

A kind of tri-state switch switching DC insulation impedance online detection circuit and method, belong to DC power insulation monitoring technical field.The present application includes DC bus power supply, first measured insulation resistance, second measured insulation resistance, first controlled switch, second controlled switch, first voltage divider, second voltage divider, sampling resistance and voltage sampling unit, first measured insulation resistance is connected in parallel between the positive pole of DC bus power supply and equipment protection ground terminal, second measured insulation resistance is connected in parallel between the negative pole of DC bus power supply and equipment protection ground terminal, first controlled switch and first voltage divider are connected in series between the positive pole of DC bus power supply and voltage sampling unit, second controlled switch and second voltage divider are connected in series between the negative pole of DC bus power supply and voltage sampling unit in turn, sampling resistance is connected in series between voltage sampling unit and equipment protection ground terminal.The present application can eliminate the blind area of traditional bridge symmetry leakage, simple structure, low in cost and strong compatibility.

Description

Technical Field

[0001] This invention relates to the field of DC power insulation monitoring technology, and in particular to a three-state switch-type DC insulation impedance online detection circuit and method. Background Technology

[0002] In a DC power supply system, both the positive and negative terminals of the power supply have equivalent insulation resistance to the metal casing (ground) of the equipment. Insulation aging, moisture, and damage can lead to a decrease in insulation resistance, causing safety hazards such as leakage, equipment breakdown, electric shock, and excessive EMC interference.

[0003] Insulation testing methods mainly include the traditional unbalanced bridge method, the AC signal injection method, and the use of dedicated insulation testing chips. Among these, the AC signal injection method requires an oscillator, coupling capacitors, and filtering circuits, resulting in complex circuitry, high cost, and significant ripple interference, which can easily affect the EMC performance of the power supply system and is unsuitable for low-noise switching power supplies. Dedicated insulation testing chips have high procurement costs, require numerous peripheral components, and have poor compatibility, making them unsuitable for widespread use in small and medium power supply equipment. Therefore, both of these testing methods suffer from high costs and poor compatibility.

[0004] Therefore, the traditional unbalanced bridge method is currently the most mainstream insulation testing method due to its superior cost and compatibility. However, it only uses two voltage-dividing resistors and can only detect insulation offset; when the insulation resistance of the positive and negative poles to ground deteriorates simultaneously, the detection voltage does not change, resulting in a serious detection blind zone and making it impossible to identify symmetrical leakage faults. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and provide a three-state switch-type DC insulation impedance online detection circuit and method, which can eliminate the leakage dead zone of the traditional bridge symmetrical circuit, has a simple structure, low cost and strong compatibility.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A three-state switch-type online DC insulation impedance detection circuit includes a DC bus power supply, a first insulation resistance to be measured, a second insulation resistance to be measured, a first controlled switch, a second controlled switch, a first voltage divider resistor, a second voltage divider resistor, a sampling resistor, and a voltage sampling unit. The first insulation resistance to be measured is connected in parallel between the positive terminal of the DC bus power supply and the protective grounding terminal of the equipment. The second insulation resistance to be measured is connected in parallel between the negative terminal of the DC bus power supply and the protective grounding terminal of the equipment. The first controlled switch and the first voltage divider resistor are connected in series in sequence between the positive terminal of the DC bus power supply and the voltage sampling unit. The second controlled switch and the second voltage divider resistor are connected in series in sequence between the negative terminal of the DC bus power supply and the voltage sampling unit. The sampling resistor is connected in series between the voltage sampling unit and the protective grounding terminal of the equipment.

[0008] Preferably, the first voltage divider resistor and the second voltage divider resistor are high-precision surface mount resistors with the same resistance value.

[0009] Preferably, the first and second controlled switches are low-leakage-current optocoupler relays.

[0010] This specification also provides a three-state switch-type online DC insulation resistance detection method, applied to the three-state switch-type online DC insulation resistance detection circuit described above. The method includes the following steps:

[0011] The first controlled switch is closed and the second controlled switch is opened. The first sampled voltage is obtained through the voltage sampling unit, and the first solution equation is established.

[0012] The first controlled switch is opened and the second controlled switch is closed. The second sampled voltage is obtained through the voltage sampling unit, and the second solution equation is established.

[0013] The first and second controlled switches are closed simultaneously, and the third sampled voltage is obtained through the voltage sampling unit to establish a verification equation.

[0014] The resistance values ​​of the first and second insulation resistances to be measured are solved based on the first and second solution equations, and the solution results are verified based on the verification equation.

[0015] Preferably, the first solution equation is:

[0016]

[0017]

[0018] in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the first voltage divider resistor. This is the first sampling voltage.

[0019] Preferably, the second solution equation is:

[0020]

[0021]

[0022] in, This is the DC bus power supply voltage. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the second voltage divider resistor. This is the second sampling voltage.

[0023] Preferably, the verification equation is:

[0024] Normal state:

[0025] Positive grounding:

[0026] Negative grounding:

[0027] in, This is the third sampling voltage. This is the DC bus power supply voltage. For the equipment protection grounding voltage, The value of the sampling resistor. This is the first voltage divider resistor.

[0028] As a preferred option, when When the first and second insulation resistances to be measured are determined, the results are as follows:

[0029]

[0030]

[0031] in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. It is a voltage divider resistor.

[0032] The advantages of this invention are:

[0033] 1. Completely eliminates symmetrical leakage blind spots: Traditional bridge circuits cannot detect this. , Synchronous descent fault: This invention rigorously solves for the two insulation resistances using a system of equations, eliminating any detection blind spots;

[0034] 2. Pure passive resistor network, no AC injection: No need for oscillation circuit, coupling transformer, no additional electromagnetic interference, excellent EMC performance, and compatible with high-precision power supplies;

[0035] 3. Extremely simple topology and extremely low cost: Only two switches and three resistors are required, eliminating the need for a dedicated insulation detection chip and reducing BOM costs by more than 70%;

[0036] 4. Online non-stop testing: The insulation status can be inspected in real time for a long period of time without disconnecting the bus power supply;

[0037] 5. The analytical algorithm is stable and reliable: it requires no empirical fitting or approximation simplification, has a rigorous mathematical model, and is highly adaptable to temperature drift and resistance deviation. Attached Figure Description

[0038] Figure 1 A schematic diagram of a three-state switch-type DC insulation resistance online detection circuit provided in the embodiments of this specification;

[0039] Figure 2 This is a flowchart of a three-state switch-type DC insulation impedance online detection method provided in the embodiments of this specification. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown, this embodiment provides a three-state switch-type DC insulation resistance online detection circuit, including a DC bus power supply U and a first insulation resistance to be measured. Second insulation resistance to be tested First controlled switch S1, second controlled switch S2, first voltage divider resistor Second voltage divider resistor Sampling resistor And voltage sampling unit, first insulation resistance to be measured The second insulation resistance to be tested is connected in parallel between the positive terminal of the DC bus power supply U and the equipment protective grounding terminal. The first controlled switch S1 and the first voltage divider resistor are connected in parallel between the negative terminal of the DC bus power supply U and the equipment protective grounding terminal. The second controlled switch S2 and the second voltage divider resistor are connected in series between the positive terminal of the DC bus power supply U and the voltage sampling unit. The sampling resistor is connected in series between the negative terminal of the DC bus power supply U and the voltage sampling unit. It is connected in series between the voltage sampling unit and the equipment protective grounding terminal, which is typically the metal casing of the equipment and is grounded. In the diagram, the equipment protective grounding terminal represents the first insulation resistance to be measured. Second insulation resistance to be tested The intermediate node, denoted as Vo; the voltage sampling unit collects the voltage at the first voltage divider resistor. Second voltage divider resistor The voltage at the intermediate node is represented as V.

[0042] Among them, the first voltage divider resistor Second voltage divider resistor High-precision surface-mount resistors of the same resistance value are used to form a symmetrical voltage divider detection network. The first controlled switch S1 and the second controlled switch S2 employ low-leakage-current optocoupler relays, with a leakage current of less than 100nA, preventing the weak high-voltage insulation current from being overwhelmed by the switch leakage current. This circuit is suitable for online DC insulation monitoring scenarios in switching power supplies, energy storage battery systems, photovoltaic DC buses, and high-voltage power distribution equipment for electric vehicles, exhibiting strong compatibility.

[0043] Based on the above circuit, such as Figure 2 As shown, this specification also provides a three-state switch-type online detection method for DC insulation resistance, including the following steps:

[0044] Step 102: Close the first controlled switch S1 and open the second controlled switch S2. Obtain the first sampled voltage through the voltage sampling unit and establish the first solution equation:

[0045]

[0046]

[0047] in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the first voltage divider resistor. This is the first sampling voltage.

[0048] Step 104: Open the first controlled switch S1 and close the second controlled switch S2. Obtain the second sampled voltage through the voltage sampling unit and establish the second solution equation:

[0049]

[0050]

[0051] in, This is the DC bus power supply voltage. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the second voltage divider resistor. This is the second sampling voltage.

[0052] Step 106: Simultaneously close the first controlled switch S1 and the second controlled switch S2, obtain the third sampled voltage through the voltage sampling unit, and establish the verification equation:

[0053] Normal state:

[0054] Positive grounding:

[0055] Negative grounding:

[0056] in, This is the third sampling voltage. This is the DC bus power supply voltage. For the equipment protection grounding voltage, The value of the sampling resistor. This is the first voltage divider resistor.

[0057] It should be noted that the execution order of steps 102-106 above can be adjusted arbitrarily without affecting the result.

[0058] Step 108: Solve for the resistance values ​​of the first and second insulation resistances based on the first and second solution equations, and verify the solution results based on the verification equation. Specifically, when When the first and second insulation resistances to be measured are determined, the results are as follows:

[0059]

[0060]

[0061] in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. It is a voltage divider resistor.

[0062] Verification of the solution results:

[0063] Circuit state: The first controlled switch S1 and the second controlled switch S2 are closed simultaneously.

[0064] Two fault states are defined:

[0065] Positive grounding: That is, the positive busbar is directly connected to the ground;

[0066] Negative grounding: That is, the negative busbar is directly connected to the ground.

[0067] 1. When the positive terminal is grounded, Positive bus potential It was pulled directly to ground potential. Then the sampled voltage Substitute , Conclusion: When the positive terminal is grounded, the sampling voltage... .

[0068] II. When the negative terminal is grounded The intermediate node Vo is directly pulled to ground potential. Then the sampled voltage Substitute , .

[0069] Therefore, closing both switches simultaneously is equivalent to connecting both sampling branches, obtaining a set of joint sampling values, which can be compared with the calculation results of a single closed circuit: if the values ​​match, it indicates that the sampling circuit, switch, operational amplifier / acquisition channel are normal; if the values ​​deviate significantly, it indicates that there is a problem with the sampling branch being disconnected, the switch being stuck, or the acquisition channel being damaged.

[0070] The following provides a set of test parameter examples: DC bus voltage =400V; Voltage divider resistor = =1MΩ; sampling resistor =500kΩ; the switch uses a low-leakage optocoupler relay; the ADC sampling accuracy is 12bit; the insulation resistance simulation range is 200kΩ~10MΩ.

[0071] Simulation example:

[0072] set up =2MΩ =3MΩ;

[0073] Three sampled voltages: =29.706V, =-44.74V, =-9.63V;

[0074] Substitute into the formula to calculate: =2MΩ, =3MΩ; measurement error <3%, meeting the accuracy requirements for industrial insulation testing.

[0075] In summary, this embodiment can achieve the following:

[0076] 1. Identifying single-pole grounding faults:

[0077] Under normal insulation conditions, and They are all very large;

[0078] If the positive terminal is severely grounded: then When S1 and S2 are closed simultaneously, Vo is clamped, resulting in a characteristic voltage.

[0079] If the negative terminal is severely grounded: then This also produces a distinct voltage characteristic.

[0080] Therefore, by combining the single-circuit closed / double-circuit closed states, we can distinguish between: positive grounding, negative grounding, and both grounding simultaneously.

[0081] 2. Improve calculation accuracy under low insulation resistance: When and When the resistance is very small, for example, when the insulation deteriorates and the alarm threshold is approaching, the signal-to-noise ratio of a single sampling channel decreases. This can be mitigated by simultaneously accessing two channels and using two sets of redundant equations to correct errors and prevent false alarms.

[0082] 3. Switch logic diagnosis (hardware fault identification): By forcibly closing S1 and S2 simultaneously, it is used to detect: sticking of switching transistors (relays / analog switches), for example, they should be open but are always conducting; and failure of control I / O ports.

[0083] This embodiment employs two controlled switches and three precision resistors to construct a purely passive detection topology. By controlling the two switches to sequentially execute three operating states—single-pass, switching, and double-closed—three sets of sampling node voltages to ground are collected. Based on Kirchhoff's current law, three sets of node equations are established, and the true insulation resistance of the DC bus positive and negative terminals to ground is obtained analytically. This invention requires no AC signal injection, has no high-frequency interference, and features an extremely simple circuit structure. The symmetrical resistors simplify the calculation to obtain straightforward engineering formulas, resulting in low computational load and easy implementation with a microcontroller. Simultaneously, the third set of voltages is retained for data verification, significantly improving anti-interference capability and measurement stability. This invention completely eliminates the symmetrical leakage blind zone of traditional insulation detection, resulting in low measurement error, low cost, and suitability for long-term online insulation monitoring of high-voltage DC power supplies, energy storage systems, photovoltaic systems, electric vehicles, and other equipment. It has extremely high industrial application value.

[0084] The above are merely preferred embodiments of the present invention, and are implementations based on the overall concept of the present invention. Furthermore, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A three-state switch-type DC insulation resistance online detection circuit, characterized in that, The device includes a DC bus power supply, a first insulation resistance to be tested, a second insulation resistance to be tested, a first controlled switch, a second controlled switch, a first voltage divider resistor, a second voltage divider resistor, a sampling resistor, and a voltage sampling unit. The first insulation resistance to be tested is connected in parallel between the positive terminal of the DC bus power supply and the protective grounding terminal of the equipment. The second insulation resistance to be tested is connected in parallel between the negative terminal of the DC bus power supply and the protective grounding terminal of the equipment. The first controlled switch and the first voltage divider resistor are connected in series in sequence between the positive terminal of the DC bus power supply and the voltage sampling unit. The second controlled switch and the second voltage divider resistor are connected in series in sequence between the negative terminal of the DC bus power supply and the voltage sampling unit. The sampling resistor is connected in series between the voltage sampling unit and the protective grounding terminal of the equipment.

2. The three-state switch-type DC insulation resistance online detection circuit according to claim 1, characterized in that, The first voltage divider resistor and the second voltage divider resistor are high-precision surface mount resistors with the same resistance value.

3. The three-state switch-type DC insulation resistance online detection circuit according to claim 1, characterized in that, The first and second controlled switches are low-leakage-current optocoupler relays.

4. A method for online detection of DC insulation resistance using a three-state switch, applied to the online detection circuit for DC insulation resistance using a three-state switch as described in claim 1, characterized in that, The method includes the following steps: The first controlled switch is closed and the second controlled switch is opened. The first sampled voltage is obtained through the voltage sampling unit, and the first solution equation is established. The first controlled switch is opened and the second controlled switch is closed. The second sampled voltage is obtained through the voltage sampling unit, and the second solution equation is established. The first and second controlled switches are closed simultaneously, and the third sampled voltage is obtained through the voltage sampling unit to establish a verification equation. The resistance values ​​of the first and second insulation resistances to be measured are solved based on the first and second solution equations, and the solution results are verified based on the verification equation.

5. The method for online detection of DC insulation impedance using a three-state switch as described in claim 4, characterized in that, The first solution equation is: ； ； in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the first voltage divider resistor. This is the first sampling voltage.

6. The method for online detection of DC insulation impedance using a three-state switch as described in claim 4, characterized in that, The second solution equation is: ； ； in, This is the DC bus power supply voltage. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. This is the second voltage divider resistor. This is the second sampling voltage.

7. The method for online detection of DC insulation resistance using a three-state switch as described in claim 4, characterized in that, The verification equation is as follows: Normal state: ; Positive grounding: ; Negative grounding: ; in, This is the third sampling voltage. This is the DC bus power supply voltage. For the equipment protection grounding voltage, The value of the sampling resistor. This is the first voltage divider resistor.

8. The method for online detection of DC insulation resistance using a three-state switch as described in claim 4, characterized in that, when When the first and second insulation resistances to be measured are determined, the results are as follows: ； ； in, This is the DC bus power supply voltage. The first voltage at the equipment's protective grounding terminal. This is the second voltage at the equipment's protective grounding terminal. The resistance value of the first resistor to be measured. The resistance value of the second resistor to be measured. The value of the sampling resistor. It is a voltage divider resistor.

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