Insulation fault detection circuit, method and ungrounded system

Abstract

The present invention discloses an insulation fault detection circuit, method and ungrounded system. The ungrounded system is provided with a first connection end and a second connection end for connecting a main line, and the main line is used to connect a plurality of branches. The insulation fault detection circuit includes: at least one equipotential terminal, and a first current providing circuit for coupling between the first connection end and the equipotential terminal, or / and a second current providing circuit for coupling between the second connection end and the equipotential terminal. The first and second current providing circuits are respectively used to provide current Is1 to the insulation resistors Rni and Rpi coupled on both sides of at least one of the branches, and the insulation resistors Rna and Rpa coupled on both sides of the main line. The voltage of at least one branch on the loop where each insulation resistor is located can be used to indicate an insulation change or insulation fault of the insulation resistor. The present invention realizes insulation detection of an ungrounded system, and the current provided can be configured, which has high safety.

Description

Technical Field

[0001] The present invention belongs to the field of insulation detection of circuit systems, and in particular relates to an insulation fault detection circuit, method and ungrounded system. Background Art

[0002] Insulation detection and leakage protection are widely used in grounding systems, where the grounding system includes ordinary 220V single-phase AC systems or three-phase four-wire three-phase systems.

[0003] Figure 1 A grounding system is shown, which is provided with a ground terminal G, and a live terminal L and a neutral terminal N as outputs connected to the main circuit. L , I N is the main circuit current, where: several branches are drawn from the main circuit to connect and drive various loads, I L1 , I N1 The main circuit is equipped with a leakage current protection switch (LB0), while the branches are equipped with leakage current protection switches (LB1 and LB2). In a grounding system, both the main circuit and the branches are coupled to the ground terminal (G). When leakage currents (Iag and Ibg) flow to the ground terminal on the corresponding lines, the leakage current protection switches (LB0 and LB2) are turned off.

[0004] CN114430159A discloses a DC microgrid system with independent branch leakage detection and protection. Each branch is equipped with a leakage protector (which has the same function as the leakage protection switch). The leakage protector includes: a leakage current detection element, a tripping device, and an arc extinguishing device.

[0005] Alternatively, insulation resistance can be measured to determine whether an insulation fault exists in the system. For example, CN105356848A discloses an insulation impedance detection device for a multi-channel MPPT input photovoltaic inverter, and CN211905521U discloses an insulation impedance detection circuit and its application device. These devices calculate the insulation resistance using a combination of an external resistor and a relay. However, these technical solutions lack the ability to indicate the specific fault point. When the branch circuit is large, the inability to quickly determine the fault point affects system stability and maintenance efficiency.

[0006] Figure 2 This diagram illustrates an ungrounded system. Due to the lack of a ground terminal and the absence of a ground loop, leakage protection through leakage current detection is objectively impossible. Both the live terminal (L) and the neutral terminal (N) are suspended relative to the ground. The insulation resistances Rp and Rn between the live terminal (L) and the ground terminal are extremely high, both exceeding the Ω level. When insulation damage occurs, the insulation resistances Rp and Rn drop significantly, forming a leakage loop and generating leakage current.

[0007] In an ungrounded system, when a single-ended insulation fault occurs in the live or neutral wire, no leakage current will be generated, so leakage protection cannot be achieved by detecting leakage. Summary of the Invention

[0008] On the one hand, in order to realize insulation fault detection in an ungrounded system, the present invention provides an insulation fault detection circuit for being configured in the ungrounded system. By detecting insulation faults, protective measures can be taken before leakage actually occurs to realize leakage protection.

[0009] The insulation fault detection circuit is used in an ungrounded system, wherein the ungrounded system is provided with a first connection terminal and a second connection terminal for connecting to a main circuit, and the main circuit is used to connect to a plurality of branch circuits.

[0010] The insulation fault detection circuit comprises:

[0011] At least one equipotential terminal, and

[0012] a first current supply circuit coupled between the first connection terminal and the equipotential terminal, or / and a second current supply circuit coupled between the second connection terminal and the equipotential terminal.

[0013] The first current providing circuit is used to provide current Is1 to the insulation resistor Rni coupled between one side of at least one of the branches and the equipotential terminal, or / and the insulation resistor Rna coupled between one side of the main line and the equipotential terminal.

[0014] The first current supply circuit may form a loop with the insulation resistor Rni or the insulation resistor Rna for the current Is1 to flow, or simultaneously form a shunt loop of the insulation resistor Rni and the insulation resistor Rna.

[0015] The second current providing circuit is used to provide current Is2 to the insulation resistance Rpi coupled between the other side of at least one of the branches and the equipotential end, or / and the insulation resistance Rpa coupled between the other side of the main line and the equipotential end.

[0016] The second current supply circuit may form a loop with the insulation resistor Rpi or the insulation resistor Rpa for the current Is1 to flow, or simultaneously form a shunted loop of the insulation resistor Rpi and the insulation resistor Rpa.

[0017] When the current Is1 / current Is2 in the loop is agreed upon, the voltage distribution in these loops also changes when the resistance value of each insulation resistor changes. The voltage of each branch on the loop where each insulation resistor is located can be used to indicate the insulation resistance, and then used to notify maintenance personnel or to determine insulation faults.

[0018] The branch for indicating the insulation resistance includes but is not limited to the voltage across the insulation resistance itself and the voltage across the first / second current supply circuit.

[0019] Compared with the prior art, the present invention provides current to the insulation resistor on at least one side of the main line or each branch line. Under the condition of a given current, based on the change of voltage distribution with the insulation resistance, the change of the insulation resistance value is indicated and detected, thereby realizing the judgment of insulation fault. The present invention realizes insulation detection of ungrounded systems. Secondly, the current provided to the insulation resistor can be configured according to the configuration of the system and the actual operation requirements. Unlike the actual leakage caused by, for example, electric shock to personnel, its size can be configured to be far lower than the actual leakage range, thus having better safety. In addition, the present invention can be used to complete detection and judgment before the actual leakage, effectively protecting the safety of personnel, and maintenance personnel can also eliminate safety hazards in a timely manner to improve operation and maintenance efficiency.

[0020] To facilitate configuration of the provided current Is1 / Is2 and simplify the circuit structure for providing current, the ungrounded system, as a high-voltage system, can optionally comprise two coupled mirror subcircuits, one for injecting current and the other for providing a current determined by the injected current to the corresponding insulation resistor. Thus, one mirror subcircuit is coupled to the low-voltage system, and the other is coupled to the high-voltage system.

[0021] Optionally, the first current providing circuit includes a first current injection circuit, an input end of which is used to connect to a power supply VCC1.

[0022] Optionally, the second current providing circuit includes a second current injection circuit, an input end of which is used to connect to a power supply VCC2.

[0023] When the first and second current supply circuits are provided at the same time, the power supply VCC1 and the power supply VCC2 are isolated from each other.

[0024] Optionally, the first current injection circuit includes a filter circuit that receives a PWM signal and outputs a DC current. Optionally, the second current injection circuit includes a filter circuit that receives a PWM signal and outputs a DC current. The output current can be modulated by the PWM signal.

[0025] Optionally, the first current supply circuit is provided with a first switch control circuit coupled thereto, for inputting a switch control signal to the first current supply circuit to drive the first current supply circuit to supply current or not.

[0026] Optionally, the second current supply circuit is provided with a second switch control circuit coupled thereto, for inputting a switch control signal to the second current supply circuit to drive the second current supply circuit to supply current.

[0027] Optionally, when the first and second current supply circuits are provided at the same time, the first current supply circuit and the second current supply circuit supply current alternately.

[0028] Optionally, the insulation fault detection circuit also includes a first voltage reading circuit, whose input end is connected in parallel between the first connection end and the equipotential end of the ungrounded system, and whose output end outputs the voltage between the first connection end and the equipotential end, which is used to indicate the insulation resistance Rni and / or the insulation resistance Rna.

[0029] Optionally, the insulation fault detection circuit also includes a second voltage reading circuit, whose input end is connected in parallel between the second connection end and the equipotential end of the ungrounded system, and whose output end outputs the voltage between the second connection end and the equipotential end, which is used to indicate the insulation resistance Rpi and / or the insulation resistance Rpa.

[0030] On the other hand, in order to implement insulation fault detection in an ungrounded system, the present invention provides an ungrounded system, comprising:

[0031] The insulation fault detection circuit,

[0032] Used to set up the leakage protection switch LB0 on ​​the main line,

[0033] Used to set up leakage protection switches LBi on several of the branches one by one.

[0034] Optionally, the current Is1 / current Is2 may also be used to attempt to trigger a leakage protection switch on a corresponding line to perform a protection action.

[0035] Optionally, the ungrounded system further includes a control module, which includes:

[0036] Several PWM signal output interfaces, used to control the magnitude of the current Is1 and / or the current Is2;

[0037] Several level signal output interfaces, used to control whether to provide the current Is1 and / or the current Is2;

[0038] A plurality of voltage signal input interfaces are used to receive a voltage signal indicating at least one of the insulation resistance Rni, the insulation resistance Rna, the insulation resistance Rpi, and the insulation resistance Rpa.

[0039] On the other hand, in order to realize insulation fault detection of an ungrounded system, the present invention provides an insulation fault detection method, which is applied to the insulation fault detection circuit, or applied to the ungrounded system.

[0040] The insulation fault detection method comprises:

[0041] In one cycle, the time T1 during which the first / second current supply circuit supplies current is defined as a detection window, and the time T2 during which the first / second current supply circuit does not supply current is defined as a detection interval;

[0042] Define the operating time Ta of the leakage protector, where T1≥Ta;

[0043] A current Id1 driving the first current supply circuit is defined, where, within at least one of the detection windows in one or more cycles, the current Id1 is a constant value, or varies discretely, continuously, or incrementally from a minimum value Ismin to a maximum value Ismax; a voltage indicating at least one of the insulation resistors Rni and / or Rna on a loop where the insulation resistors Rni and / or Rna are located is obtained when the first current supply circuit supplies current to the insulation resistors Rni and / or Rna; or / and,

[0044] Define the current Id2 that drives the second current providing circuit, and within at least one of the detection windows in one or more cycles, the current Id2 is a constant value, or changes discretely or continuously or from small to large within the range of the minimum value Ismin to the maximum value Ismax; obtain the voltage on the loop where the insulation resistor Rpi and / or the insulation resistor Rpa are located when the second current providing circuit provides current to the insulation resistor Rpi and / or the insulation resistor Rpa, which can indicate at least one of the two.

[0045] By using a configurable or variable drive current to modulate / attempt to modulate the current provided to each insulation resistor, the current introduced into the working power grid of the ungrounded system can be set within a lower range, or a smaller current can be set within a portion of the detection window or a portion of the time within the detection window, further reducing the impact on the ungrounded system.

[0046] Optionally, a minimum operating current Ip of the leakage protector is defined, and the maximum value Ismax of the current Id1 or the current Id2 satisfies: Ismax≥Ip, where:

[0047] When the current Id1 or the current Id2 reaches or exceeds Ip, an attempt is made to trigger the leakage protection switch on the corresponding route to perform a protection action.

[0048] As mentioned above, when the leakage protection switch on a line is actuated, the branch where the insulation fault occurs can also be located accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the existing AC grounding system.

[0050] Figure 2 Schematic diagram of an existing ungrounded system.

[0051] Figure 3 Schematic diagram of an ungrounded system and its insulation fault detection circuit in an embodiment.

[0052] Figure 4 FIG. 4 is a schematic block diagram of an insulation fault detection circuit according to an embodiment.

[0053] Figure 5 A schematic block diagram of a first current providing circuit according to an embodiment.

[0054] Figure 6 FIG. 4 is a specific circuit diagram of an insulation fault detection circuit according to an embodiment of the present invention.

[0055] Figure 7 FIG. 1 is a timing reference diagram of the working state of the first / second current providing circuit in one embodiment.

[0056] Figure 8 FIG. 4 is a schematic block diagram of a current injection circuit in one embodiment.

[0057] Figure 9 FIG. 1 is a timing reference diagram of the first / second current providing circuit operating status in another embodiment.

[0058] Figure 10 FIG. 1 is a timing reference diagram of the first / second current providing circuit operating status in another embodiment.

[0059] Figure 11 Schematic diagram of the relationship between the current Is provided to the detection loop by the first current providing circuit and the output current Isi of the current injection circuit when the insulation resistance is in a normal state.

[0060] Figure 12 Schematic diagram of the relationship between the current Is provided to the detection loop by the first current providing circuit and the output current Isi of the current injection circuit in the insulation resistance fault state.

[0061] Figure 13 FIG. 1 is a schematic block diagram of a first current providing circuit including a first switch control circuit in one embodiment.

[0062] Figure 14 FIG. 4 is a schematic block diagram of an insulation fault detection circuit according to another embodiment.

[0063] Figure 15 This is a schematic block diagram of a second current providing circuit according to an embodiment.

[0064] Figure 16 FIG. 1 is a schematic block diagram of a second current providing circuit provided with a second switch control circuit in one embodiment.

[0065] Description of the figure number:

[0066] 100. Ungrounded system, 200. Trunk line, 300. Branch line, 400. Load.

[0067] 500. First current supply circuit, 510. First mirror sub-circuit, 520. Second mirror sub-circuit, 530. First current injection circuit, 531. Filter circuit, 540. First switch control circuit, 541. First photocoupler, 542. Second photocoupler, 550. First voltage follower, 560. First differential amplifier circuit.

[0068] 600. Second current supply circuit, 610. Third mirror sub-circuit, 620. Fourth mirror sub-circuit, 630. Second current injection circuit, 640. Second switch control circuit, 641. Third photocoupler, 642. Fourth photocoupler, 650. Second voltage follower, 660. Second differential amplifier circuit.

[0069] 700. Equipotential terminal, 800. Control module. DETAILED DESCRIPTION

[0070] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0071] In the present invention, the connection in the circuit can be understood as connection through a wire, or as electrical connection; the coupling in the circuit can be understood as direct connection through a wire, or indirect connection through a wire through electrical components including but not limited to resistors, capacitors, etc. or connection points.

[0072] like Figure 3 As shown, an ungrounded system 100 includes a first connection terminal L and a second connection terminal N, a main circuit 200 connected to the first connection terminal L and the second connection terminal N, and a plurality of branches 300. The number N of branches 300 satisfies N ≥ 1. In actual use, the number of branches 300 in a power grid system is relatively large. As an example, two branches 300 are shown in the figure. Each branch 300 is connected to a corresponding load 400. In the figure, the load 400 connected to one branch 300 is load 1, and the load 400 connected to the other branch is load 2.

[0073] In general circuits, the first connection terminal L and the second connection terminal N correspond to the positive and negative poles. When used in a civil power grid, the first connection terminal L and the second connection terminal N correspond to the live and neutral wire terminals to connect the live and neutral wires.

[0074] refer to Figure 4 As shown, in this embodiment, the insulation fault detection circuit mainly includes an equipotential terminal 700 and a first current providing circuit 500. The first current providing circuit 500 is coupled between the positive electrode of the ungrounded system 100 and the equipotential terminal 700. Figure 3 As shown, one end of the first current supply circuit 500 is connected to the positive electrode of the ungrounded system 100 , and the other end is connected to the equipotential terminal 700 .

[0075] An insulation resistor Rni is coupled between the side of any branch 300 of the ungrounded system 100 connected to the negative electrode and the equipotential terminal 700 .

[0076] When the first current providing circuit 500 provides current, a closed loop is formed along the positive electrode, the first current providing circuit 500, the equipotential terminal 700, the insulation resistor Rni, and the negative electrode in sequence.

[0077] If there is no insulation fault on the side of the branch 300 connected to the negative electrode, then in the aforementioned closed loop, ignoring the voltage drop of the line itself, the voltage drop between the positive electrode of the ungrounded system 100 and the equipotential terminal 700 is close to 0V. That is, when the closed loop is formed, the potential of the equipotential terminal 700 is the same as the potential of the positive electrode of the ungrounded system 100.

[0078] If an insulation fault occurs on the side of insulation resistor Rni, its resistance decreases, causing a change in the voltage divider on the circuit. Given a given current Is1 provided by first current supply circuit 500 and a given output voltage of ungrounded system 100, the change in voltage divider indicates an insulation change.

[0079] In other embodiments, an insulation resistor Rna is coupled between the side of the trunk line 200 of the ungrounded system 100 connected to the negative electrode and the equipotential terminal 700. When the first current supply circuit 500 supplies current, another closed loop is formed sequentially along the positive electrode, the first current supply circuit 500, the equipotential terminal 700, the insulation resistor Rna, and the negative electrode.

[0080] If an insulation fault occurs on the side of insulation resistor Rna, its resistance decreases, causing a change in the voltage divider within the loop. Given a given current Is1 provided by first current supply circuit 500 and a given output voltage of ungrounded system 100, the change in voltage divider indicates an insulation change.

[0081] refer to Figure 5 As shown, in other embodiments, the first current providing circuit 500 is a mirror current source circuit, which includes a first mirror sub-circuit 510 and a second mirror sub-circuit 520 coupled thereto, wherein: one end of the second mirror sub-circuit 520 is connected to the positive electrode of the ungrounded system 100, and the other end of the second mirror sub-circuit 520 is connected to the equipotential terminal 700.

[0082] The insulation fault detection circuit is further provided with a first current injection circuit 530 connected to the first current providing circuit 500 .

[0083] One end of the first mirror sub-circuit 510 is connected to the first current injection circuit 530 , and the other end of the first mirror sub-circuit 510 is connected to the equipotential terminal 700 .

[0084] Optionally, the current Iom1 flowing through the end of the second mirror sub-circuit 520 connected to the positive electrode of the ungrounded system 100 to the equipotential terminal 700 is equal to the current Iim1 flowing through the end of the first mirror sub-circuit 510 connected to the first current injection circuit 530 to the equipotential terminal 700. The current Iom1 is the current Is1 provided to the detection loop by the first current providing circuit 500.

[0085] The current Iim1 is determined by the output current of the first current injection circuit 530 .

[0086] Combine Figure 6 As shown, in this embodiment, the first mirror sub-circuit 510 is formed by a transistor Q1, and the second mirror sub-circuit 520 is formed by a transistor Q2. The bases of the transistors Q1 and Q2 are connected, and their emitters are connected to the equipotential terminal 700. The base of the transistor Q1 is connected to its collector. The collector of the transistor Q1 is connected to the first current injection circuit 530, and the collector of the transistor Q2 is connected to the positive electrode of the ungrounded system 100.

[0087] In other embodiments, the mirror current source circuit may also be formed by a MOS transistor, or may be further modified.

[0088] In the above embodiment, the first current injection circuit 530 is used to inject a certain current into the first mirror sub-circuit 510 and set the magnitude of the current passing through the closed loop through the mirror current source circuit.

[0089] The first current supply circuit 500 may supply current intermittently. When the first current supply circuit 500 does not supply current, the closed circuit is converted into an open circuit.

[0090] The following includes embodiments of a detection method applied to the insulation fault detection circuit.

[0091] refer to Figure 7 As shown, the first current supply circuit 500 supplies current at a certain period, which includes a time length T1 and a time length T2. The time length T1 can be defined as a detection window, during which the first current supply circuit 500 supplies current to form a closed loop; the time length T2 can be defined as a detection interval, during which the first current supply circuit 500 does not supply current and is in an open circuit state.

[0092] In some other embodiments, the output current of the first current injection circuit 530 is configured to be modulatable.

[0093] refer to Figure 8 As shown, in this embodiment, the first current injection circuit 530 includes a filter circuit 531 that receives a PWM signal and outputs a DC current. The voltage output by the filter circuit 531 is proportional to the duty cycle of the PWM signal. The PWM signal is adjusted to modulate the voltage output by the filter circuit 531, thereby modulating the output current.

[0094] Combine Figure 6 As shown, optionally, the filter circuit 531 is an RC filter circuit mainly composed of a resistor R3 and a capacitor C1.

[0095] The PWM signal may be provided by a PWM1 interface of a control module 800 .

[0096] The insulation resistor Rni has a larger value than the resistance of the circuit within its loop. The voltage across it approximates the voltage between the positive and negative electrodes of the ungrounded system 100. The voltage Vp0 between the positive electrode and the equipotential terminal 700 approaches 0V, while the voltage Vn0 between the negative electrode and the equipotential terminal 700 approaches the voltage between the positive and negative electrodes of the ungrounded system 100. Therefore, Rni can be calculated as Vn0 / Is1.

[0097] When insulation resistor Rni experiences a fault, its resistance decreases. Given a given current Is1, voltage Vn0 decreases. Conversely, voltage Vp0 between the positive electrode of ungrounded system 100 and the equipotential terminal 700 increases. Thus, voltage Vp0 can qualitatively indicate changes in insulation resistance Rni. Clearly, within the same circuit, changes in voltage distribution caused by changes in insulation resistance Rni occur in any branch of the circuit. Therefore, changes in voltage in any branch can also qualitatively indicate changes in insulation resistance Rni.

[0098] refer to Figure 9 and Figure 10As shown, in other embodiments, the current output by the first current injection circuit 530 is variable within a detection window or between different detection windows, wherein a minimum output current Ismin and a maximum output current Ismax are configured, and the output current can vary discretely or continuously within the range of the minimum output current Ismin to the maximum output current Ismax.

[0099] Within the variable range of current Is1, current Is1 can be modulated by the current output by the first current injection circuit 530. The relationship between the insulation resistance Rni and the voltage Vp0 is not affected, and the voltage Vp0 can also qualitatively indicate the change in insulation resistance Rni.

[0100] Back to Figure 3 As shown, in this embodiment, two branch circuits 300 are equipped with leakage protectors LB1 and LB2, respectively. Optionally, the main circuit 200 is equipped with a leakage protection switch LB0. Leakage protectors are existing products that detect leakage current in the circuit and initiate circuit breaker protection when the leakage current reaches a certain level. The operating time Ta of a leakage protector is its primary operating parameter and is typically around 0.1s.

[0101] The detection window and the action time satisfy: T1≥Ta. Optionally, in some embodiments, the detection window is 0.15-0.2s.

[0102] In order to reduce the time of introducing leakage current, the detection interval can be set to be longer. Optionally, in some embodiments, the detection interval and the detection window meet: T2≥10T1. In some embodiments, the detection interval is 2 to 5 seconds.

[0103] Alternatively, as Figure 9As shown, along the time axis, within time T1, the current output by the first current injection circuit 530 can increase from the minimum output current Ismin to the maximum output current Ismax. In this case, T1 can be set to be longer, and multiple sub-periods T11, T12, etc. can be divided within T1. Taking the example of the division into two sub-periods shown in the figure, where both T11 and T12 are not less than the action time Ta, at least two leakage levels, Ismin and (Ismax + Ismin) / 2, can be detected within time T1. The above division is not exclusive and can also be considered as detection at leakage levels between Ismin and (Ismax + Ismin) / 2. Assuming that T12 is exactly equal to the action time Ta, a current above the (Ismax + Ismin) / 2 level does not last for the action time Ta and can be considered as ineffective detection. In other embodiments, time T1 can be configured to include more sub-periods. This configuration can be achieved by adjusting the length of the detection window and the maximum and minimum current values, thereby changing the slope of the current line.

[0104] Alternatively, as Figure 10 As shown, different levels of the output current are configured in different detection windows T1. For example, a large cycle consisting of three adjacent detection windows T1 is used, and the current in the first detection window T1 is Ismin, the current in the second detection window T1 is between Ismin and Ismax, and the current in the third detection window T1 is Ismax.

[0105] In other embodiments, it is also possible to combine Figure 9 、 Figure 10 The two current configurations shown, or further variations.

[0106] As configured above, a smaller current can be configured during at least a portion of the detection time, thereby reducing the current level artificially introduced into the system.

[0107] In some embodiments, the maximum output current Ismax is not lower than the minimum protection current Ip of the leakage current protector.

[0108] refer to Figure 11As shown, under normal conditions, due to the large resistance of the insulation resistor, the current that can be allowed to pass is limited. When the current Isi output by the first current injection circuit 530 increases to a certain level, the leakage current on the insulation resistor cannot increase accordingly, but is limited to Ilim. When Isi increases to the maximum output current Ismax, the actual leakage current generated is still limited to Ilim, so the leakage protector will not be triggered. When there are multiple branch insulation resistors in the system, or when there are main insulation resistors and branch insulation resistors at the same time, taking the example of a fault in one of the insulation resistors, the current will preferentially pass through the path where the insulation resistor with lower impedance is located; while the current flowing through other fault-free insulation resistors is smaller. When the resistance of the insulation resistor is very large, the branches where these insulation resistors are located can be regarded as open circuits.

[0109] refer to Figure 12 As shown, in a fault state, the insulation resistance decreases, allowing the current to flow through to increase. When the current Isi output by the first current injection circuit 530 increases and exceeds the minimum protection current Ip, the current Is provided to the detection circuit by the first current supply circuit increases with the increase in current Isi, thereby triggering the leakage protector.

[0110] The above also applies to configuring different levels of the output current in different detection windows T1.

[0111] The minimum protection current of the leakage current protector is one of its main working parameters, which is usually above 10 mA. Optionally, the maximum output current Ismax is at least 20 mA.

[0112] The minimum output current Ismin can be determined based on the insulation resistance value of interest and the system voltage. For example, for a 1000V system, if the insulation resistance value is below 1Mohm, then Ismin = 1000V / 1Mohm = 1mA.

[0113] refer to Figure 13 As shown, the first current providing circuit 500 is further provided with a first switch control circuit 540 coupled thereto, for inputting a switch signal to the first current providing circuit 500 to control whether the first current providing circuit 500 provides current.

[0114] Combine Figure 6As shown, the control module 800 is provided with an interface Test1 for outputting a switching signal, which is coupled to the input end of the first photocoupler 541 through a resistor R5. The output end of the first photocoupler 541 is coupled between the base of the transistor Q1 and the transistor Q2 and the ground end. When the interface Test1 outputs a high level, the base potential of the transistor Q1 and the transistor Q2 is pulled down, and then it is in a cut-off state. At this time, the first current providing circuit 500 does not provide current. When the interface Test1 outputs a low level, the base of the transistor Q1 and the transistor Q2 is not grounded and can maintain a high potential, and then it is in a conducting state. At this time, the first current providing circuit 500 provides current. Among them, the first photocoupler 541 can also play an isolation role.

[0115] Combine Figure 6 As shown, the first current supply circuit 500 further includes a second photocoupler 542. The second photocoupler 542 is coupled between the interface PWM1 of the control module 800 and the RC filter circuit. The resistor R3 in the RC filter circuit is coupled to the power source VCC1 via the resistor R2.

[0116] A first voltage follower 550 is coupled between one end of the resistor R3 and the capacitor C1 connected to the collector of the transistor Q1 .

[0117] refer to Figure 14 As shown, in this embodiment, the insulation fault detection circuit includes a second current providing circuit 600 , wherein the second current providing circuit 600 is coupled between the negative electrode of the ungrounded system 100 and the equipotential terminal 700 .

[0118] Combine Figure 3 As shown, an insulation resistor Rpi is coupled between the side of any branch 300 of the ungrounded system 100 connected to the positive electrode and the equipotential terminal 700 .

[0119] When the second current providing circuit 600 provides current, a closed loop is formed along the positive electrode, the insulation resistor Rpi, the equipotential terminal 700, the second current providing circuit 600, and the negative electrode in sequence.

[0120] The principle and method of fault detection of the insulation resistor Rpi are the same as those of the insulation resistor Rni. Based on the adaptive adjustment of the circuit connection polarity, the above-mentioned embodiment of fault detection of the insulation resistor Rni can be directly referred to.

[0121] The distribution of voltages of the branches in the closed loop where the insulation resistor Rpi is located changes when the resistance value of the insulation resistor Rpi changes. Therefore, such a change in voltage distribution can also be used to indicate a change in the insulation resistor Rpi.

[0122] In other embodiments, an insulation resistor Rpa is coupled between the side of the trunk line 200 of the ungrounded system 100 connected to the positive electrode and the equipotential terminal 700. When the second current supply circuit 600 supplies current, a closed loop is formed sequentially along the positive electrode, the insulation resistor Rpa, the equipotential terminal 700, the second current supply circuit 600, and the negative electrode. The distribution of voltage across the branches of the closed loop containing the insulation resistor Rpa changes when the resistance value of the insulation resistor Rpa changes. Therefore, this change in voltage distribution can also be used to indicate changes in the insulation resistor Rpa.

[0123] refer to Figure 15 As shown, the second current providing circuit 600 is a mirror current source circuit, which includes a third mirror sub-circuit 610 and a fourth mirror sub-circuit 620 coupled thereto, wherein: one end of the fourth mirror sub-circuit 620 is connected to the negative electrode of the ungrounded system 100, and the other end of the fourth mirror sub-circuit 620 is connected to the equipotential terminal 700.

[0124] The insulation fault detection circuit is further provided with a second current injection circuit 630 connected to the second current providing circuit 600 .

[0125] One end of the third mirror sub-circuit 610 is connected to the second current injection circuit 630 , and the other end of the third mirror sub-circuit 610 is connected to the equipotential terminal 700 .

[0126] Optionally, the current Iom2 flowing through the end of the fourth mirror sub-circuit 620 connected to the equipotential terminal 700 and the negative electrode of the ungrounded system 100 is equal to the current Iim2 flowing through the end of the third mirror sub-circuit 620 connected to the second current injection circuit 630 and the negative electrode of the ungrounded system 100. The current Iom2 is the current Is2 provided to the detection loop by the second current providing circuit 600.

[0127] The current Iim2 is determined by the output current of the second current injection circuit 630 .

[0128] refer to Figure 6 As shown, in this embodiment, the third mirror sub-circuit 610 is formed by a transistor Q3, and the fourth mirror sub-circuit 620 is formed by a transistor Q4. The bases of the transistors Q3 and Q4 are connected, and their emitters are connected to the negative terminal of the ungrounded system 100. The base of the transistor Q3 is connected to its collector. The collector of the transistor Q3 is connected to the second current injection circuit 630, and the collector of the transistor Q4 is connected to the equipotential terminal 700.

[0129] refer to Figure 7As shown, similar to the first current providing circuit 500, in this embodiment, the second current providing circuit 600 provides current in a certain period, including a detection window of time length T1 and a detection interval of time length T2.

[0130] In some other embodiments, the output current of the second current injection circuit 630 is configured to be modulatable.

[0131] Similar to the first current injection circuit 530 , in this embodiment, the second current injection circuit 630 includes a filter circuit that receives a PWM signal and outputs a DC current, and the output current is modulated by PWM.

[0132] Combine Figure 6 As shown, optionally, the filtering circuit of the second current injection circuit 630 is an RC filtering circuit mainly composed of a resistor R8 and a capacitor C2, wherein the PWM signal can be provided by a PWM2 interface of a control module 800.

[0133] The modulation of the output current of the second current injection circuit 630 and the current Is2 that the second current providing circuit 600 can provide, as well as the corresponding detection interval, detection window and other parameters can all refer to the configuration of the first current injection circuit 530 and the first current providing circuit 500 in the above embodiment.

[0134] refer to Figure 16 As shown, similar to the first current providing circuit 500, the second current providing circuit 600 is further provided with a second switch control circuit 640 coupled thereto, for inputting a switch signal to the second current providing circuit 600 to control whether the second current providing circuit 600 provides current Is2.

[0135] Combine Figure 6 As shown, optionally, in this embodiment, the control module 800 is provided with an interface Test2 for outputting a switching signal, which is coupled to the input end of the third photocoupler 641 via a resistor R10. The output end of the third photocoupler 641 is coupled between the collector, base, and emitter of the transistor Q3. When the interface Test2 outputs a high level, the base potential of the transistors Q3 and Q4 is pulled down, thereby being in a cut-off state. At this time, the second current supply circuit 600 does not provide current. When the interface Test2 outputs a low level, the base potential of the transistors Q3 and Q4 is not pulled down, and can maintain a high potential, thereby being in a conducting state. At this time, the second current supply circuit 600 provides current. The third photocoupler 641 can also serve as an isolation function.

[0136] Optionally, in this embodiment, the second current supply circuit 600 further includes a fourth photocoupler 642. The fourth photocoupler 642 is coupled between the interface PWM2 of the control module 800 and the RC filter circuit. The resistor R8 in the RC filter circuit is coupled to the power supply VCC2 via the resistor R7.

[0137] In this embodiment, a second voltage follower 650 is coupled between one end where the resistor R8 and the capacitor C2 are connected and the collector of the transistor Q3 .

[0138] Optionally, the equipotential terminal 700 is grounded.

[0139] The power supply VCC1 is connected to the equipotential terminal 700, and a loop through which the current Iim1 passes is formed along the power supply VCC1, resistors R2 and R3, the first voltage follower 550, the resistor R4, the transistor Q1, and the equipotential terminal 700. The equipotential terminal 700 and the power supply VCC1 may be connected to a common ground.

[0140] The power supply VCC2 is connected to the negative electrode of the ungrounded system 100, and a loop through which the current Iim2 passes is formed along the power supply VCC2, the resistor R7, the resistor R8, the second voltage follower 560, the resistor R9, the transistor Q3 and the negative electrode of the ungrounded system 100.

[0141] The power supply VCC1 and the power supply VCC2 are isolated from each other.

[0142] Optionally, the first current supply circuit 500 is further provided with a first differential amplifier circuit 560 connected thereto. The input end of the first differential amplifier circuit 560 is connected in parallel between the collector and emitter of the transistor Q2 to collect the voltage between the positive electrode of the ungrounded system 100 and the equipotential terminal 700.

[0143] Optionally, the second current providing circuit 600 is further provided with a second differential amplifier circuit 660 connected thereto. The input end of the second differential amplifier circuit 660 is connected in parallel between the collector and emitter of the transistor Q4 to collect the voltage between the negative electrode of the ungrounded system 100 and the equipotential terminal 700.

[0144] The output ends of the first differential amplifier circuit 560 and the second differential amplifier circuit 660 can be connected to the control module 800, and the voltage signals collected by the two circuits can be transmitted to the control module 800. The control module 800 can determine an insulation fault based on the voltage signal, or further calculate and process the voltage signal to obtain the insulation resistance indicated by the voltage signal, and notify maintenance personnel.

[0145] The control module 800 may be a single chip microcomputer system, a PLC or other controller.

[0146] The above embodiments can be further combined to obtain other embodiments.

[0147] In some embodiments, when the first current supply circuit 500 supplies current to the insulation resistors Rni and Rna, it is not necessary to distinguish between the two, and the two can be judged as a whole. In a circuit system with a large number of branches, the primary focus is on locating insulation faults in the branches. Since the main circuit is relatively unique, this does not affect the rapid location of branch faults. When the second current supply circuit 600 supplies current to the insulation resistors Rpi and Rpa, the situation is the same as above, so it will not be further described.

[0148] In some embodiments, the insulation fault detection circuit is provided with a first current providing circuit 500 and a second current providing circuit 600, wherein the first current providing circuit 500 is used to provide current to the insulation resistance on the negative side of the main circuit 200 and the branch circuit 300 to detect the insulation fault on the negative side; the second current providing circuit 600 is used to provide current to the insulation resistance on the positive side of the main circuit 200 and the branch circuit 300 to detect the insulation fault on the positive side.

[0149] The first current providing circuit 500 and the second current providing circuit 600 provide current alternately. Figure 4 During the T1 time, the first current providing circuit 500 provides current, and the second current providing circuit 600 does not; during the T2 time, the first current providing circuit 500 does not provide current, and a time length T1' within the T2 time is selected, and the second current providing circuit 600 provides current within the said time length T1'.

[0150] The embodiments of the present invention are only used to illustrate the present invention and do not limit the scope of the claims. Other substantially equivalent alternatives that can be thought of by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. An insulation fault detection circuit for an ungrounded system, wherein: The ungrounded system is provided with a first connection terminal and a second connection terminal for connecting a main circuit, wherein the main circuit is used to connect a plurality of branch circuits; wherein the insulation fault detection circuit comprises: At least one equipotential terminal, and a first current supply circuit coupled between the first connection terminal and the equipotential terminal, or / and a second current supply circuit coupled between the second connection terminal and the equipotential terminal; wherein: The first current providing circuit is used to provide a current Is1 to an insulation resistor Rni coupled between one side of at least one branch and the equipotential terminal, or / and an insulation resistor Rna coupled between one side of the main line and the equipotential terminal; The second current providing circuit is used to provide current Is2 to the insulation resistance Rpi coupled between the other side of at least one of the branches and the equipotential terminal, or / and the insulation resistance Rpa coupled between the other side of the main line and the equipotential terminal; wherein: The voltage of at least one branch of the circuit where each insulation resistor is located can be used to indicate insulation change or insulation fault of the insulation resistor; The first current providing circuit includes: a first mirror sub-circuit and a second mirror sub-circuit coupled thereto, wherein: one end of the first mirror sub-circuit is used to receive the injected current Iim1, one end of the second mirror sub-circuit is used to connect to the first connection end of the ungrounded system, and the other ends of the first mirror sub-circuit and the second mirror sub-circuit are connected to the equipotential terminal, wherein the current Is1 flows through the second mirror sub-circuit and is determined by the current Iim1; or / and, The second current supply circuit includes a third mirror sub-circuit and a fourth mirror sub-circuit coupled thereto, wherein: one end of the third mirror sub-circuit is used to receive the injected current Iim2, one end of the fourth mirror sub-circuit is connected to the equipotential terminal, the other end of the third mirror sub-circuit and one end of the fourth mirror sub-circuit are used to connect to the second connection terminal of the ungrounded system, wherein the current Is2 flows through the fourth mirror sub-circuit and is determined by the current Iim2; The first current providing circuit includes a first current injection circuit, an input end of which is used to connect to the power supply VCC1, and an output end of which is coupled to the first mirror sub-circuit to inject current into the first mirror sub-circuit; or / and, The second current providing circuit includes a second current injection circuit, whose input end is used to connect to the power supply VCC2, and whose output end is coupled to the third mirror sub-circuit to inject current into the third mirror sub-circuit; wherein: The power supply VCC1 and the power supply VCC2 are isolated from each other; The first current injection circuit includes a filter circuit that receives a PWM signal and outputs a direct current, or / and the second current injection circuit includes a filter circuit that receives a PWM signal and outputs a direct current.

2. The insulation fault detection circuit according to claim 1, wherein: The first mirror sub-circuit includes a transistor Q1, and the second mirror sub-circuit includes a transistor Q2, wherein the base of the transistor Q1 is connected to the base of the transistor Q2; or / and, The third mirror sub-circuit includes a transistor Q3, and the fourth mirror sub-circuit includes a transistor Q4, wherein the base of the transistor Q3 is connected to the base of the transistor Q4.

3. The insulation fault detection circuit according to claim 1, wherein: The filter circuit of the first current injection circuit or the second current injection circuit is an RC filter circuit.

4. The insulation fault detection circuit according to claim 1, wherein: The first current injection circuit includes a photocoupler, an input end of which is used to receive a PWM signal, and an output end of which is coupled between a ground end and an input end of the filter circuit of the first current injection circuit; or / and, The second current injection circuit includes a photocoupler, an input end of which is used to receive a PWM signal, and an output end of which is coupled between the second connection end of the ungrounded system and an input end of the filter circuit of the second current injection circuit.

5. The insulation fault detection circuit according to claim 1, wherein: The first current injection circuit includes a voltage follower, an input end of which is connected to the filter circuit of the first current injection circuit, and an output end of which is coupled to the first mirror sub-circuit; or / and, The second current injection circuit includes a voltage follower, an input end of which is connected to the filter circuit of the second current injection circuit, and an output end of which is coupled to the third mirror sub-circuit.

6. The insulation fault detection circuit according to claim 1, wherein: The first current supply circuit is provided with a first switch control circuit coupled thereto, for inputting a switch control signal to the first current supply circuit to drive the first current supply circuit to determine whether to supply current; or / and, The second current supply circuit is provided with a second switch control circuit coupled thereto, for inputting a switch control signal to the second current supply circuit to drive the second current supply circuit to determine whether to supply current.

7. The insulation fault detection circuit according to claim 6, characterized in that: The first switch control circuit includes a photocoupler, whose input end is used to receive a level signal, and whose input end is coupled to the first current providing circuit; or / and, The second current providing circuit includes a photocoupler, an input end of which is used to receive a level signal and is coupled to the second current providing circuit.

8. The insulation fault detection circuit according to claim 6, wherein: The first current supply circuit and the second current supply circuit alternately supply current.

9. The insulation fault detection circuit according to any one of claims 1 to 8, characterized in that: The invention also includes a first voltage reading circuit, whose input terminal is connected in parallel between the first connection terminal and the equipotential terminal of the ungrounded system, and whose output terminal outputs the voltage between the first connection terminal and the equipotential terminal, and the voltage is used to indicate the insulation resistance Rni and / or the insulation resistance Rna; or / and, It also includes a second voltage reading circuit, whose input end is connected in parallel between the second connection end and the equipotential end of the ungrounded system, and whose output end outputs the voltage between the second connection end and the equipotential end, which is used to indicate the insulation resistance Rpi and / or the insulation resistance Rpa.

10. The insulation fault detection circuit according to any one of claims 1 to 8, characterized in that: The equipotential terminal is a ground terminal.

11. An ungrounded system, characterized in that: include: The insulation fault detection circuit according to any one of claims 1 to 10, Used to set up a leakage protection switch LB0 on ​​the main line, Used to set up leakage protection switches LBi on several of the branches one by one.

12. The ungrounded system according to claim 11, wherein: Also included is a control module comprising: Several PWM signal output interfaces, used to control the magnitude of the current Is1 and / or the current Is2; Several level signal output interfaces, used to control whether to provide the current Is1 and / or the current Is2; A plurality of voltage signal input interfaces are used to receive a voltage signal indicating at least one of the insulation resistance Rni, the insulation resistance Rna, the insulation resistance Rpi, and the insulation resistance Rpa.

13. A method for detecting insulation faults, characterized in that: Applied to the insulation fault detection circuit according to any one of claims 1 to 10, or applied to the ungrounded system according to claim 11 or 12, the insulation fault detection method includes: In one cycle, the time T1 during which the first / second current supply circuit supplies current is defined as a detection window, and the time T2 during which the first / second current supply circuit does not supply current is defined as a detection interval; Define the operating time Ta of the leakage protector, where T1≥Ta; A current Id1 driving the first current supply circuit is defined, where, within at least one of the detection windows in one or more cycles, the current Id1 is a constant value, or varies discretely, continuously, or incrementally from a minimum value Ismin to a maximum value Ismax; a voltage indicating at least one of the insulation resistors Rni and / or Rna on a loop where the insulation resistors Rni and / or Rna are located is obtained when the first current supply circuit supplies current to the insulation resistors Rni and / or Rna; or / and, Define the current Id2 that drives the second current providing circuit, and within at least one of the detection windows in one or more cycles, the current Id2 is a constant value, or changes discretely or continuously or from small to large within the range of the minimum value Ismin to the maximum value Ismax; obtain the voltage on the loop where the insulation resistor Rpi and / or the insulation resistor Rpa are located when the second current providing circuit provides current to the insulation resistor Rpi and / or the insulation resistor Rpa, which can indicate at least one of the two.

14. The insulation fault detection method according to claim 13, characterized in that: The minimum operating current Ip of the leakage protector is defined, and the maximum value Ismax of the current Id1 or the current Id2 satisfies: Ismax ≥ Ip, where: When the current Id1 or the current Id2 reaches or exceeds Ip, an attempt is made to trigger the leakage protection switch on the corresponding route to perform a protection action.

15. The insulation fault detection method according to claim 13, characterized in that: The detection window and the detection interval satisfy: T2≥10T1.

16. The insulation fault detection method according to claim 13, characterized in that: The detection window is 0.15 to 0.2 s, and the detection interval is 2 to 5 s.

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