Direct current insulation monitoring circuit and method

Abstract

The embodiment of the invention discloses a direct-current insulation monitoring circuit and method. The direct-current insulation monitoring circuit comprises a to-be-monitored high-voltage direct-current system, a positive bridge sampling resistor, a bridge circuit, a negative bridge sampling resistor, a sampling resistor and an injection voltage source. Wherein the positive electrode of the to-be-monitored high-voltage direct-current system is connected with one end of the positive bridge sampling resistor, and the other end of the positive bridge sampling resistor is connected with the negative electrode of the to-be-monitored high-voltage direct-current system sequentially through the bridge midpoint of the bridge circuit and the negative bridge sampling resistor. The bridge midpoint of the bridge circuit is also grounded through a sampling resistor and an injection voltage source. The negative bridge sampling resistor comprises a first negative bridge resistor and at least one negative bridge resistor assembly connected in parallel with the first negative bridge resistor. The positive bridge sampling resistor comprises a first positive bridge resistor and at least one positive bridge resistor assembly connected with the first positive bridge resistor in parallel. According to the embodiment of the invention, the ground insulation resistance can be accurately calculated, and then direct current insulation monitoring can be accurately carried out.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a DC insulation monitoring circuit and method. Background Art

[0002] The operating status of the DC side of power equipment such as electric vehicles and charging piles, photovoltaic power generation equipment, and battery energy storage equipment will directly affect the safety and reliability of the power system. If an insulation accident occurs on the DC side of these power equipment, it will cause the relay protection device to malfunction, causing power supply failure or even equipment damage. In order to prevent such accidents, a DC insulation monitoring circuit is usually required to monitor the insulation resistance of the DC system to ground, and then determine whether a DC grounding fault occurs in the DC system through the insulation resistance to ground.

[0003] In the related art, the DC insulation monitoring circuit can be used to monitor the insulation resistance to ground by using the injection method of DC insulation monitoring. In practical applications, in order to increase the monitoring accuracy, a high-voltage injection method can be used. However, high-voltage injection will reduce system safety, and will cause the voltage of the battery pack on the DC side to be unbalanced, thereby affecting the battery life. In addition, the injection method of DC insulation monitoring can also use a low-voltage injection method. However, the low-voltage injection method will reduce the monitoring accuracy due to the limitation of the resolution of the AD sampling device. Summary of the invention

[0004] The embodiments of the present specification provide a DC insulation monitoring circuit and method for performing DC insulation monitoring on a high-voltage DC system to be monitored.

[0005] To solve the above technical problems, the embodiments of this specification are implemented as follows:

[0006] A DC insulation monitoring circuit provided in an embodiment of the present specification includes: a high-voltage DC system to be monitored, a positive bridge sampling resistor, a bridge circuit, a negative bridge sampling resistor, a sampling resistor, and an injection voltage source;

[0007] The positive electrode of the high-voltage DC system to be monitored is connected to one end of the positive bridge sampling resistor, and the other end of the positive bridge sampling resistor is connected to the negative electrode of the high-voltage DC system to be monitored through the bridge midpoint of the bridge circuit and the negative bridge sampling resistor in sequence; the bridge midpoint of the bridge circuit is also grounded through the sampling resistor and the injection voltage source;

[0008] The negative bridge sampling resistor includes a first negative bridge resistor and at least one negative bridge resistor component connected in parallel with the first negative bridge resistor; any of the negative bridge resistor components includes a second negative bridge resistor and a first high-voltage switch connected to the second negative bridge resistor;

[0009] The positive bridge sampling resistor includes a first positive bridge resistor and at least one positive bridge resistor component connected in parallel with the first positive bridge resistor; any positive bridge resistor component includes a second positive bridge resistor and a second high-voltage switch connected to the second positive bridge resistor.

[0010] Optionally, resistance values ​​of the first negative bridge resistor, each of the second negative bridge resistors, the first positive bridge resistor, and each of the second positive bridge resistors are equal.

[0011] Optionally, the number of the negative bridge resistance components is equal to the number of the positive bridge resistance components.

[0012] Optionally, the bridge midpoint of the bridge circuit is grounded through the sampling resistor and the injection voltage source, specifically including:

[0013] The bridge midpoint of the bridge circuit is connected to one end of the sampling resistor, the other end of the sampling resistor is connected to the positive electrode of the injection voltage source, and the negative electrode of the injection voltage source is grounded;

[0014] or,

[0015] The bridge midpoint of the bridge circuit is connected to the positive electrode of the injection voltage source, the negative electrode of the injection voltage source is connected to one end of the sampling resistor, and the other end of the sampling resistor is grounded.

[0016] Optionally, the DC insulation monitoring circuit further includes an operational amplifier circuit and a boost circuit;

[0017] The operational amplifier circuit is connected in parallel to both ends of the sampling resistor; the operational amplifier circuit is used to amplify the voltage of the sampling resistor to obtain an amplified voltage;

[0018] The boosting circuit is connected to the operational amplifier circuit; the boosting circuit is used to boost the amplified voltage to facilitate AD sampling.

[0019] A DC insulation monitoring method provided in an embodiment of the present specification is used in a DC insulation monitoring circuit, and the method includes:

[0020] Controlling the injection voltage source to output 0V, sampling the first voltage of the negative bridge sampling resistor and the second voltage of the positive bridge sampling resistor; if the difference between the first voltage and the second voltage is not within a preset difference range, controlling the on / off state of at least part of the first high-voltage switch and / or the on / off state of at least part of the second high-voltage switch, so that the difference is within the preset difference range;

[0021] Controlling the output voltage of the injection voltage source to be a first output voltage, and sampling a first sampling voltage on the sampling resistor;

[0022] Controlling the output voltage of the injection voltage source to be a second output voltage, sampling a second sampling voltage on the sampling resistor; the second output voltage has a different voltage value from the first output voltage;

[0023] Calculating the insulation resistance of the DC insulation monitoring circuit to ground according to the first sampling voltage and the second sampling voltage;

[0024] Direct current insulation monitoring is performed based on the insulation resistance to ground.

[0025] Optionally, the high-voltage switches of the DC insulation monitoring circuit are all in a disconnected state; if the difference between the first voltage and the second voltage is not within a preset difference range, controlling the on / off state of at least part of the first high-voltage switches and / or the on / off state of at least part of the second high-voltage switches so that the difference is within the preset difference range, specifically includes:

[0026] If the difference between the first voltage and the second voltage is not within a preset difference range, and the first voltage is greater than the second voltage, closing a preset number of first high-voltage switches to make the difference within the preset difference range;

[0027] If the difference between the first voltage and the second voltage is not within a preset difference range, and the second voltage is greater than the first voltage, a preset number of second high-voltage switches are closed to make the difference within the preset difference range.

[0028] Optionally, the resistance values ​​of the first negative bridge resistor, each second negative bridge resistor, the first positive bridge resistor and each second positive bridge resistor in the DC insulation monitoring circuit are equal;

[0029] The method further comprises:

[0030] The preset number is calculated according to the ratio of the first voltage to the second voltage; the preset number is less than or equal to the number of negative bridge resistance components in the DC insulation monitoring circuit, or the preset number is less than or equal to the number of positive bridge resistance components in the DC insulation monitoring circuit;

[0031] in, D represents the preset number, and D is an integer, v 1 represents the first voltage, v 2 represents the second voltage, c represents the accuracy coefficient, and c is greater than or equal to 1.

[0032] Optionally, if the difference between the first voltage and the second voltage is within the preset difference range, the step of controlling the output voltage of the injection voltage source to be the first output voltage and sampling the first sampling voltage on the sampling resistor is executed.

[0033] Optionally, performing DC insulation monitoring according to the insulation resistance to ground specifically includes:

[0034] Determine whether the insulation resistance to ground is less than or equal to a preset resistance threshold, and obtain a determination result;

[0035] If the judgment result indicates that the insulation resistance to ground is less than or equal to the preset resistance threshold, it is determined that a fault occurs in the high-voltage DC system to be monitored in the DC insulation monitoring circuit.

[0036] An embodiment of this specification can achieve the following beneficial effects:

[0037] The embodiments of the present specification can control the opening and closing states of the high-voltage switches in the negative bridge resistance component or the positive bridge resistance component by setting a negative bridge sampling resistor including a first negative bridge resistance and at least one negative bridge resistance component connected in parallel with the first negative bridge resistance, and a positive bridge sampling resistor including a first positive bridge resistance and at least one positive bridge resistance component connected in parallel with the first positive bridge resistance, so that the difference between the first voltage of the negative bridge sampling resistor and the second voltage of the positive bridge sampling resistor is within a preset difference range, thereby avoiding the limitation of the resolution of the AD sampling device, and thus being able to accurately calculate the insulation resistance to ground and accurately perform DC insulation monitoring.

[0038] In addition, the embodiments of this specification can use low-voltage injection to perform DC insulation monitoring, which can improve system safety compared to high-voltage injection methods, while avoiding voltage imbalance of the battery pack on the DC side that affects battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a structural diagram of a DC insulation monitoring circuit in the related art;

[0041] Figure 2 A structural diagram of a DC insulation monitoring circuit provided in an embodiment of this specification;

[0042] Figure 3 It is a schematic diagram of a DC insulation monitoring circuit in the related art;

[0043] Figure 4 A method corresponding to the embodiment of this specification is provided Figure 3 Structural diagram of two equivalent circuits;

[0044] Figure 5 A method corresponding to the embodiment of this specification is provided Figure 3 A structural diagram of the folding circuit of the first equivalent circuit in FIG.

[0045] Figure 6 A circuit structure diagram when the sampling resistor is ignored provided in an embodiment of this specification;

[0046] Figure 7 A flow chart of a DC insulation monitoring method provided in an embodiment of this specification. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of one or more embodiments of this specification clearer, the technical solutions of one or more embodiments of this specification will be clearly and completely described below in combination with the specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of one or more embodiments of this specification.

[0048] Figure 1 FIG. 1 is a structural diagram of a DC insulation monitoring circuit in the related art. Figure 1 As shown, the high voltage DC system to be monitored v dc The positive electrode and the positive bridge sampling resistor R P One end is connected to the positive bridge sampling resistor R P The other end passes through the bridge midpoint M and negative bridge sampling resistor R of the bridge circuit in turn. N Connect the high voltage DC system to be monitored dc The bridge midpoint M of the bridge circuit also passes through the sampling resistor R e And the injected voltage source v g Ground.

[0049] In the injection method of DC insulation monitoring in the related art, the process of low voltage injection includes two stages. In the first stage, the injection voltage source v is controlled. g Output a certain voltage v g1 , get the sampling resistance R e The sampled voltage v e1 ; In the second stage, control the injection voltage source v g Output another voltage v g2 , get the sampling resistance R e The sampled voltage v e2 Then calculate the insulation resistance to ground R using the following formula: fm.

[0050]

[0051] Among them, the sampling resistor R e , positive bridge sampling resistor R P , negative bridge sampling resistor R N is a known value, v g1 and v g2 To control the injection voltage source v g The given value of the output, v e1 and v e2 is the measured value. It can be seen that in the above formula, v e1 and v e2 Is the influence of insulation resistance to ground R fm The key.

[0052] In practical applications, due to the low-pressure injection method, v g1 and v g2 will be much smaller than the high voltage DC system v to be monitored dc The voltage of the high voltage DC system to be monitored is dc The influence of voltage, v e2 With v e1 will be very small, and due to the resolution limitation of the AD sampling device, the AD sampling device will not be able to accurately sample v e1 With v e2 , so the insulation resistance to ground R cannot be calculated accurately fm , affecting the accuracy of DC insulation monitoring.

[0053] The technical solutions provided by the embodiments of this specification are described in detail below in conjunction with the accompanying drawings.

[0054] In order to solve the defects in the prior art, this solution provides the following embodiments.

[0055] Figure 2 A structural diagram of a DC insulation monitoring circuit provided in an embodiment of this specification, such as Figure 2 As shown, the DC insulation monitoring circuit of the embodiment of this specification includes a high voltage DC system v to be monitored dc , positive bridge sampling resistor R P , bridge circuit, negative bridge sampling resistor R N , sampling resistor R e And the injected voltage source v g The positive pole v of the high voltage DC system to be monitored dc With the positive bridge sampling resistor R P One end is connected to the positive bridge sampling resistor R P The other end passes through the bridge midpoint M and negative bridge sampling resistor R of the bridge circuit in turn. NConnect the high voltage DC system to be monitored dc The bridge midpoint M of the bridge circuit also passes through the sampling resistor R e And the injected voltage source v g Ground.

[0056] Among them, the negative bridge sampling resistor R N Including the first negative bridge resistor R 1 and the first negative bridge resistor R 1 At least one negative bridge resistor component is connected in parallel. Any negative bridge resistor component includes a second negative bridge resistor and a first high-voltage switch connected to the second negative bridge resistor.

[0057] In the embodiments of the present specification, one negative bridge resistor component may be included, or multiple negative bridge components may be included. For example, multiple negative bridge components may be included, such as m negative bridge components, where m is a positive integer greater than or equal to 2. Specifically, the first negative bridge component may include a second negative bridge resistor R 1_1 and the first high voltage switch Q 1_1 The second negative bridge component may include a second negative bridge resistor R 1_2 and the first high voltage switch Q 1_2 , the mth negative bridge component may include a second negative bridge resistor R 1_m and the first high voltage switch Q 1_m etc.

[0058] Positive bridge sampling resistor R P Including the first positive bridge resistor R 2 and the first positive bridge resistor R 2 At least one positive bridge resistor component is connected in parallel. Any positive bridge resistor component includes a second positive bridge resistor and a second high-voltage switch connected to the second positive bridge resistor.

[0059] In the embodiment of the present specification, one positive bridge resistor component may be included, or multiple positive bridge components may be included. For example, multiple positive bridge components may be included, such as n positive bridge components, where n is a positive integer greater than or equal to 2. Specifically, the first positive bridge component may include a second positive bridge resistor R 2_1 and the second high voltage switch Q 2_1 The second positive bridge component may include a second positive bridge resistor R 2_2 and the second high voltage switch Q 2_2 , the nth positive bridge component may include a second positive bridge resistor R 2_n and the second high voltage switch Q 2_n etc.

[0060] In the embodiment of this specification, m may be equal to n. Optionally, m may not be equal to n.

[0061] In the embodiment of this specification, the negative bridge sampling resistor R N The first voltage v 1 With the positive bridge sampling resistor R P The second voltage v 2 The difference between them is within the preset difference range, such as zero or close to zero. e The voltage v e The range of change becomes smaller, the voltage v e After the variation range is mapped to the sampling range of the AD sampling device, the sampling resistance R can be accurately obtained based on the AD sampling device. e The sampled voltage v e1 With v e2 , and then accurately calculate the insulation resistance R to ground fm , so as to accurately monitor the DC insulation. The following is a detailed description of the solution of the embodiment of this specification in conjunction with the accompanying drawings.

[0062] Figure 3 FIG. 1 is a schematic diagram of a DC insulation monitoring circuit in the related art. Figure 3 As shown, the insulation resistance to ground R fm It can be understood as the insulation resistance R fP The insulation resistance to ground R fN The parallel value of the sampling resistor R e The sampling current is i e ,in

[0063] Figure 4 A method corresponding to the embodiment of this specification is provided Figure 3 The structural diagram of the two equivalent circuits. Figure 3 The high voltage DC system to be monitored in dc Equivalent to a short circuit, we can get Figure 4 The first equivalent circuit in Figure 3 The injected voltage source v g Equivalent to a short circuit, we can get Figure 4 The second equivalent circuit in .

[0064] Figure 5 A method corresponding to the embodiment of this specification is provided Figure 3 The structural diagram of the folding circuit of the first equivalent circuit in FIG. Figure 5 As shown, due to Therefore, the current of the first equivalent circuit can be obtained

[0065] In addition, according to Figure 4The second equivalent circuit in can be obtained Then we can get the current of the second equivalent circuit

[0066] Furthermore, the current of the first equivalent circuit is added to the current of the second equivalent circuit to sample the current.

[0067] After simplifying the above sampling current, we can get in

[0068]

[0069] Then we can get:

[0070]

[0071] In the injection method of DC insulation monitoring in the related art, the process of low voltage injection includes two stages. In the first stage, the injection voltage source v is controlled. g Output a certain voltage v g1 , get the sampling resistance R e The sampled voltage v e1 ; In the second stage, control the injection voltage source v g Output another voltage v g2 , get the sampling resistance R e The sampled voltage v e2 . The following formula can be obtained:

[0072]

[0073] Through the above formula (2) and Subtracting the insulation resistance to ground, we can get R fm :

[0074]

[0075] According to formula (1), v e Contains g Components and v o component, due to the low pressure injection method, v g will be much smaller than the high voltage DC system v to be monitored dc The voltage, and v dc It will also affect v o , so the component v g The range of variation is much smaller than that of component v o The range of change makes v e The range of variation is large.

[0076] In the embodiment of this specification, before the first stage and the second stage in the related technology are performed, the negative bridge sampling resistor R N The first voltage v 1 With the positive bridge sampling resistor R P The second voltage v 2 The difference between is within the preset difference range, such as zero or close to zero. Then increase the component v g v e The effect of reducing the voltage v e range of change.

[0077] Specifically, we can Convert to

[0078]

[0079] Since the first voltage v 1 With the second voltage v 2 The difference between them is within the preset difference range, such as zero or close to zero, etc., and in actual applications, the sampling resistor R e is very small, the sampling resistor R can be ignored e , the sampling resistor R e Assuming it is a short circuit, we can get Figure 6 The circuit structure diagram is shown.

[0080] like Figure 6 As shown, if the first voltage v 1 With the second voltage v 2 The difference between them is within the preset difference range. Assuming that the difference is 0, then v 1 =v 2 , then R fP R N =R fN R P , v o The value of is 0. Therefore, the first voltage v is reduced 1 With the second voltage v 2 The difference between them can reduce the component v o , thereby increasing the component v g v e The effect of reducing the voltage v e range of change.

[0081] Furthermore, assuming that v dc The maximum value of v dcm , v g1 v gm , v g2 -v gm , then in vg1 =v gm , R fP =∞、R fN =0, R fm =0, R N =R, we can get v e The maximum value, at v g2 =-v gm , R fP =0, R fN =∞、R fm =0, R P =R, When v e The minimum value of (for ease of calculation, take n = m). e The range of changes is as follows:

[0082]

[0083] In practical applications, gm will be much smaller than v dcm It can be seen that the larger the m value, the larger the v e The smaller the range of change. e The range of change corresponds to the full range of the AD sampling device, and the sampling accuracy of the AD sampling device will be higher. Thus, the insulation resistance to ground R can be calculated more accurately. fm , accurately perform DC insulation monitoring.

[0084] The following v e The relationship between the variation range and the sampling accuracy of the AD sampling device is explained in detail.

[0085] In the related art, the sampling range of the AD sampling device is (0, 5V), the resolution is 4096, and the minimum scale of the AD sampling device is 5 / 4096, which is about 0.0012V. Assume that after amplification by the operational amplifier circuit and boosting by the boosting circuit, v e The range of change is (0, 5000V), then the AD sampling device samples v within this range. e When v e When it is 0V, the AD sampling device will sample 0V, v e When it is 1000V, the AD sampling device will sample 1V, v e When it is 3000V, the AD sampling device will sample 3V, v e When it is 1000V, the AD sampling device will sample 5V.

[0086] In practical applications, v e The value of is very small, such as v eIt can be 0.2V, which requires an AD sampling device to sample 0.0002V, but the minimum scale of the AD sampling device is 0.0012V, so it is impossible to sample 0.0002V.

[0087] Assuming v e The range of change becomes smaller, such as after being amplified by the operational amplifier circuit and raised by the boost circuit, v e The range of change is (0, 5V). If at this time v e The AD sampling device can sample 0.2V based on the minimum scale of 0.0012V.

[0088] In the embodiment of this specification, the negative bridge sampling resistor R N The first voltage v 1 With the positive bridge sampling resistor R P The second voltage v 2 The difference between the e The range of change can be improved to improve the sampling accuracy of the AD sampling equipment, thereby accurately monitoring the DC insulation.

[0089] Optionally, in order to facilitate the calculation of the number of openings or closings of the high-voltage switch and thus facilitate DC insulation monitoring, the resistance values ​​of the first positive bridge resistor, each second positive bridge resistor, the first negative bridge resistor and each second negative bridge resistor in the DC insulation monitoring circuit in the embodiment of this specification are equal.

[0090] In practical applications, there are two ways to connect the midpoint of the bridge circuit to ground through a sampling resistor and an injection voltage source. Optionally, the midpoint of the bridge circuit to ground through the sampling resistor and the injection voltage source may specifically include:

[0091] The bridge midpoint of the bridge circuit is connected to one end of the sampling resistor, the other end of the sampling resistor is connected to the positive electrode of the injection voltage source, and the negative electrode of the injection voltage source is grounded.

[0092] or,

[0093] The bridge midpoint of the bridge circuit is connected to the positive electrode of the injection voltage source, the negative electrode of the injection voltage source is connected to one end of the sampling resistor, and the other end of the sampling resistor is grounded.

[0094] In the embodiments of this specification, the DC insulation monitoring circuit may further include an operational amplifier circuit and a boost circuit.

[0095] Wherein, the operational amplifier circuit is connected in parallel to both ends of the sampling resistor; the operational amplifier circuit is used to amplify the voltage of the sampling resistor to obtain an amplified voltage.

[0096] The boosting circuit is connected to the operational amplifier circuit; the boosting circuit is used to boost the amplified voltage to facilitate AD sampling.

[0097] Based on the same idea, the embodiments of this specification also provide a DC insulation monitoring method corresponding to the above DC insulation monitoring circuit.

[0098] Figure 7 The following is a flow chart of a DC insulation monitoring method provided in an embodiment of this specification. Figure 7 As shown, the method may include the following steps.

[0099] Step 702: Control the injection voltage source output voltage to 0V, sample the first voltage of the negative bridge sampling resistor and the second voltage of the positive bridge sampling resistor. If the difference between the first voltage and the second voltage is not within the preset difference range, control the on / off state of at least part of the first high-voltage switch and / or the on / off state of at least part of the second high-voltage switch so that the difference is within the preset difference range.

[0100] In the embodiment of the present specification, by controlling the output voltage of the injection voltage source to 0V, controlling the on / off state of at least part of the first high-voltage switch and / or the on / off state of at least part of the second high-voltage switch, the first voltage of the sampled negative bridge sampling resistor and the second voltage of the positive bridge sampling resistor can be within a preset range. For example, the preset range can be (0±k), where k is a preset threshold value and k is a positive number. Increase the influence of the voltage output by the injection voltage source on the sampled voltage of the sampling resistor, and reduce the variation range of the sampled voltage of the sampling resistor. Improve the monitoring accuracy of the sampled voltage of the sampling resistor, and then accurately obtain the insulation resistance to ground, and accurately perform DC insulation monitoring.

[0101] Specifically, the high-voltage switches of the DC insulation monitoring circuit are all in the disconnected state; if the difference between the first voltage and the second voltage is not within the preset difference range, controlling the on-off state of at least part of the first high-voltage switches and / or the on-off state of at least part of the second high-voltage switches so that the difference is within the preset difference range, may specifically include:

[0102] If the difference between the first voltage and the second voltage is not within a preset difference range, and the first voltage is greater than the second voltage, a preset number of first high-voltage switches are closed to make the difference within the preset difference range.

[0103] If the difference between the first voltage and the second voltage is not within a preset difference range, and the second voltage is greater than the first voltage, a preset number of second high-voltage switches are closed to make the difference within the preset difference range.

[0104] Optionally, if the difference between the first voltage and the second voltage is within the preset difference range, the step of controlling the output voltage of the injection voltage source to be the first output voltage and sampling the first sampling voltage on the sampling resistor is executed.

[0105] As a specific implementation, in order to facilitate the calculation of the number of openings or closings of the high-voltage switch, and thus facilitate DC insulation monitoring, the resistance values ​​of the first positive bridge resistor, each second positive bridge resistor, the first negative bridge resistor, and each second negative bridge resistor in the DC insulation monitoring circuit in the embodiment of this specification are equal.

[0106] The DC insulation monitoring method may further include:

[0107] The preset number is calculated based on the ratio of the first voltage to the second voltage; the preset number is less than or equal to the number of negative bridge resistance components in the DC insulation monitoring circuit, or the preset number is less than or equal to the number of positive bridge resistance components in the DC insulation monitoring circuit.

[0108] in, D represents the preset number, and D is an integer, v 1 represents the first voltage, v 2 represents the second voltage, c represents the accuracy coefficient, and c is greater than or equal to 1.

[0109] Step 704: Control the output voltage of the injection voltage source to be a first output voltage, and sample a first sampling voltage on the sampling resistor.

[0110] Step 706: Control the output voltage of the injection voltage source to be a second output voltage, and sample the second sampled voltage on the sampling resistor; the second output voltage has a different voltage value from the first output voltage.

[0111] Step 708: Calculating the insulation resistance of the DC insulation monitoring circuit to ground according to the first sampling voltage and the second sampling voltage;

[0112] Step 710: Perform DC insulation monitoring according to the insulation resistance to ground.

[0113] In the embodiment of this specification, the DC insulation monitoring according to the insulation resistance to ground may specifically include:

[0114] It is determined whether the insulation resistance to ground is less than or equal to a preset resistance threshold value to obtain a determination result.

[0115] If the judgment result indicates that the insulation resistance to ground is less than or equal to the preset resistance threshold, it is determined that a fault occurs in the high-voltage DC system to be monitored in the DC insulation monitoring circuit.

[0116] The detection process of the embodiment of this specification can be understood as three stages. Specifically, stage 0: controlling the output voltage of the injection voltage source to be 0V.

[0117] If the first voltage v of the negative bridge sampling resistor 1 The second voltage v is greater than the positive bridge sampling resistor 2 , we can calculate And rounded to the nearest integer, assuming And round it up to D 12 , then D can be closed 12 The first high-voltage switch (if D 12 is greater than m, then D 12 Take it as m). At this time, the negative bridge sampling resistor R N The value of R / (D 12 +1), where R is the resistance value of the first positive bridge resistor, each second positive bridge resistor, the first negative bridge resistor, and each second negative bridge resistor. When all the second high-voltage switches are disconnected, the positive bridge sampling resistor R P The value of is R.

[0118] If the second voltage v of the negative positive bridge sampling resistor 2 The first voltage v greater than the bridge sampling resistor 1 , we can calculate And rounded to the nearest integer, assuming And round it up to D 21 , then D can be closed 21 A second high voltage switch (if D 21 If D is greater than n, 21 Taken as n). At this time, the positive bridge sampling resistor R P The value of R / (D 21 +1). When all the first high-voltage switches are disconnected, the negative bridge sampling resistor R N The value of is R.

[0119] The first stage: Control the output voltage of the injected voltage source to be the first output voltage v g1 , sampling the first sampling voltage v on the sampling resistor e1 .

[0120] The second stage: Control the output voltage of the injected voltage source to be the second output voltage v g2 , sampling the second sampling voltage v on the sampling resistor e2 .

[0121] Then, based on the first sampling voltage v e1 and the second sampling voltage v e2 , using formula (3) to calculate the insulation resistance to ground R fm, the insulation resistance to ground R fm Compared with the preset resistance threshold, if the insulation resistance to ground R fm If the insulation resistance R fm If the resistance is greater than the preset resistance threshold, it can be determined that there is no ground fault in the DC system.

[0122] In order to further illustrate the solution of the embodiments of this specification, the embodiments of this specification also provide a specific application example.

[0123] For example, the high voltage DC system to be monitored dc The maximum value v dcm The first voltage v in the 0th stage is obtained by sampling. 1 is 200V, the second voltage v 2 is 600V, then v dc is 800V. At this time, the second voltage v 2 Greater than the first voltage v 1 , calculate D 21 If it is 2, the two second high-voltage switches are closed. Positive bridge sampling resistor R P The value of is R / 3, which is 1MΩ, and the negative bridge sampling resistance R N The value of R is 3MΩ.

[0124] The first stage controls the injection voltage source output voltage v g1 The second stage controls the injection voltage source output voltage v g2 is -5V. According to formula (4), we can get v e The range of the AD sampling device is (0, 5V), and the operational amplifier circuit is used to measure v e Amplified 2.5 times, and raised to 2.5V through the boost circuit, and then sampled by the AD sampling device, the sampled v e1 is 0.273V, v e2 is 0.26V.

[0125] According to formula (3), the insulation resistance to ground R can be calculated fm The value is about 1.5MΩ.

[0126] Then, 1.5 MΩ is compared with a preset resistance threshold to monitor the high voltage DC system to be monitored.

[0127] The embodiments of this specification can be used for insulation monitoring of DC systems on the DC side of electric vehicles and charging piles, photovoltaic power generation equipment, battery energy storage equipment, etc. According to the scheme of the embodiments of this specification, the AD sampling device can accurately obtain the sampling voltage on the sampling resistor, accurately calculate the insulation resistance to ground, and then accurately monitor the DC insulation of the above DC system.

[0128] It should be understood that the order of some steps in the methods described in one or more embodiments of this specification can be interchanged according to actual needs, or some steps can be omitted or deleted.

[0129] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0130] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the embodiments of this specification are not limited by the order of the actions described, because according to the embodiments of this specification, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the embodiments of this specification.

[0131] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0132] The preferred embodiments of this specification disclosed above are only used to help explain this specification. The optional embodiments do not describe all the details in detail, nor do they limit the invention to only the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the embodiments of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the embodiments of this specification, so that technicians in the relevant technical field can well understand and use this specification. This specification is only limited by the claims and their full scope and equivalents.

Claims

1. A DC insulation monitoring circuit, characterized in that: include: A high voltage DC system to be monitored, a positive bridge sampling resistor, a bridge circuit, a negative bridge sampling resistor, a sampling resistor, and an injection voltage source; The positive electrode of the high-voltage DC system to be monitored is connected to one end of the positive bridge sampling resistor, and the other end of the positive bridge sampling resistor is connected to the negative electrode of the high-voltage DC system to be monitored through the bridge midpoint of the bridge circuit and the negative bridge sampling resistor in sequence; the bridge midpoint of the bridge circuit is also grounded through the sampling resistor and the injection voltage source; The negative bridge sampling resistor includes a first negative bridge resistor and at least one negative bridge resistor component connected in parallel with the first negative bridge resistor; any of the negative bridge resistor components includes a second negative bridge resistor and a first high-voltage switch connected to the second negative bridge resistor; The positive bridge sampling resistor comprises a first positive bridge resistor and at least one positive bridge resistor component connected in parallel with the first positive bridge resistor; Any of the positive bridge resistor components includes a second positive bridge resistor and a second high-voltage switch connected to the second positive bridge resistor.

2. The DC insulation monitoring circuit according to claim 1, characterized in that: The resistance values ​​of the first negative bridge resistor, each of the second negative bridge resistors, the first positive bridge resistor, and each of the second positive bridge resistors are equal.

3. The DC insulation monitoring circuit according to claim 1, characterized in that: The number of the negative bridge resistance components is equal to the number of the positive bridge resistance components.

4. The method according to claim 1, characterized in that: The bridge midpoint of the bridge circuit is grounded through the sampling resistor and the injection voltage source, specifically comprising: The bridge midpoint of the bridge circuit is connected to one end of the sampling resistor, the other end of the sampling resistor is connected to the positive electrode of the injection voltage source, and the negative electrode of the injection voltage source is grounded; or, The bridge midpoint of the bridge circuit is connected to the positive electrode of the injection voltage source, the negative electrode of the injection voltage source is connected to one end of the sampling resistor, and the other end of the sampling resistor is grounded.

5. The DC insulation monitoring circuit according to claim 1, characterized in that: The DC insulation monitoring circuit also includes an operational amplifier circuit and a boost circuit; The operational amplifier circuit is connected in parallel to both ends of the sampling resistor; the operational amplifier circuit is used to amplify the voltage of the sampling resistor to obtain an amplified voltage; The boosting circuit is connected to the operational amplifier circuit; the boosting circuit is used to boost the amplified voltage to facilitate AD sampling.

6. A DC insulation monitoring method, characterized in that: For use in a DC insulation monitoring circuit, the method comprises: Controlling the injection voltage source to output 0V, sampling the first voltage of the negative bridge sampling resistor and the second voltage of the positive bridge sampling resistor; if the difference between the first voltage and the second voltage is not within a preset difference range, controlling the on / off state of at least part of the first high-voltage switch and / or the on / off state of at least part of the second high-voltage switch, so that the difference is within the preset difference range; Controlling the output voltage of the injection voltage source to be a first output voltage, and sampling a first sampling voltage on the sampling resistor; Controlling the output voltage of the injection voltage source to be a second output voltage, sampling a second sampling voltage on the sampling resistor; the second output voltage has a different voltage value from the first output voltage; Calculating the insulation resistance of the DC insulation monitoring circuit to ground according to the first sampling voltage and the second sampling voltage; Direct current insulation monitoring is performed based on the insulation resistance to ground.

7. The method according to claim 6, characterized in that The high-voltage switches of the DC insulation monitoring circuit are all in the disconnected state; if the difference between the first voltage and the second voltage is not within the preset difference range, the on-off state of at least part of the first high-voltage switches and / or the on-off state of at least part of the second high-voltage switches are controlled so that the difference is within the preset difference range, specifically including: If the difference between the first voltage and the second voltage is not within a preset difference range, and the first voltage is greater than the second voltage, closing a preset number of first high-voltage switches to make the difference within the preset difference range; If the difference between the first voltage and the second voltage is not within a preset difference range, and the second voltage is greater than the first voltage, a preset number of second high-voltage switches are closed to make the difference within the preset difference range.

8. The method according to claim 7, characterized in that The resistance values ​​of the first negative bridge resistor, each second negative bridge resistor, the first positive bridge resistor and each second positive bridge resistor in the DC insulation monitoring circuit are equal; The method further comprises: The preset number is calculated according to the ratio of the first voltage to the second voltage; the preset number is less than or equal to the number of negative bridge resistance components in the DC insulation monitoring circuit, or the preset number is less than or equal to the number of positive bridge resistance components in the DC insulation monitoring circuit; in, D represents the preset number, and D is an integer, v1 represents the first voltage, v2 represents the second voltage, c represents the accuracy coefficient, and c is greater than or equal to 1.

9. The method according to claim 6, characterized in that If the difference between the first voltage and the second voltage is within the preset difference range, the step of controlling the injection voltage source output voltage to be the first output voltage and sampling the first sampling voltage on the sampling resistor is performed.

10. The method according to claim 6, characterized in that Performing DC insulation monitoring according to the insulation resistance to ground specifically includes: Determine whether the insulation resistance to ground is less than or equal to a preset resistance threshold, and obtain a determination result; If the judgment result indicates that the insulation resistance to ground is less than or equal to the preset resistance threshold, it is determined that a fault occurs in the high-voltage DC system to be monitored in the DC insulation monitoring circuit.

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