A leakage current relay protection circuit

Abstract

The present invention relates to the technical field of leakage current protection, and particularly relates to a leakage current relay protection circuit, which includes a leakage current detection circuit, a rectification circuit, a voltage comparison circuit, and a relay control circuit. The leakage current detection circuit is used to convert the leakage current into a voltage signal. The rectification circuit is used to rectify the voltage signal and output a detection voltage. The voltage comparison circuit compares the detection voltage with a preset voltage and outputs a comparison result to the relay control circuit and the controller. The relay control circuit controls the operation of the relay according to the comparison result and the control signal sent by the controller. The leakage current relay protection circuit provided by the present invention can meet the relay operation time limit requirements when the leakage current is any value, timely disconnect the charging line, and ensure personal and equipment safety.

Description

Technical Field

[0001] The present invention relates to the technical field of leakage current protection, and particularly relates to a leakage current relay protection circuit. Background Art

[0002] When an electric vehicle power supply device charges an in-vehicle charging device, if a leakage current occurs, it will pose a threat to the safety of personnel and equipment, and the relay needs to act promptly to disconnect the charging line. The national standard stipulates that the relay needs to act when the leakage current is greater than 30 mA. Figure 1 Shows the relationship between the relay action time limit and the magnitude of the leakage current. The greater the leakage current, the smaller the relay action time limit, and when the instantaneous value of the leakage current is greater than 300 mA, the relay needs to act immediately to disconnect. The existing leakage current protection schemes in the prior art cannot fully meet the relay action time limit requirements. Summary of the Invention

[0003] In order to solve the technical problem that the existing leakage current protection schemes in the prior art cannot fully meet the relay action time limit requirements, the present invention provides a leakage current relay protection circuit, which can meet the relay action time limit requirements at any value of the leakage current and promptly disconnect the charging line.

[0004] The technical solution adopted by the present invention:

[0005] A leakage current relay protection circuit, comprising:

[0006] A leakage current detection circuit, configured to convert the leakage current into a voltage signal;

[0007] A rectification circuit, configured to rectify the voltage signal and output a detection voltage;

[0008] A voltage comparison circuit, configured to compare the detection voltage with a preset voltage and output a comparison result to a relay control circuit and a controller;

[0009] A relay control circuit, configured to control the relay to act according to the comparison result and a control signal issued by the controller.

[0010] Further, the leakage current detection circuit includes a current transformer connection circuit, the current transformer connection circuit includes a zero-sequence current transformer T1 and a resistor R1, the primary side of the zero-sequence current transformer T1 detects the leakage current, the secondary side of the zero-sequence current transformer T1 is connected with the resistor R1, one end of the resistor R1 is grounded, and the other end of the resistor R1 outputs the voltage signal.

[0011] Further, the leakage current detection circuit further includes a proportional amplification circuit. The input end of the current transformer connection circuit detects the leakage current. The output end of the current transformer connection circuit is connected to the input end of the proportional amplification circuit, and the output end of the proportional amplification circuit outputs the voltage signal.

[0012] Further, the proportional amplification circuit includes an operational amplifier U1. The other end of the resistor R1 is connected to the non-inverting input end of the operational amplifier U1 through the resistor R4. The inverting input end of the operational amplifier U1 is grounded through the resistor R2. A resistor R3 is connected between the inverting input end and the output end of the operational amplifier U1, and the output end of the operational amplifier U1 outputs the voltage signal.

[0013] Further, the rectification circuit includes an operational amplifier U2, an operational amplifier U3 and a peripheral circuit. The operational amplifier U2 and the operational amplifier U3, combined with the peripheral circuit, form a precision full-wave rectification circuit to rectify the voltage signal and output a detection voltage.

[0014] Further, the voltage comparison circuit includes a voltage comparator U4. The non-inverting input end of the voltage comparator U4 inputs the detection voltage. The inverting input end of the voltage comparator U4 inputs the preset voltage. The output end of the voltage comparator U4 outputs a comparison result to the relay control circuit.

[0015] Further, the relay control circuit includes a first switching element and a second switching element. The first pin and the third pin of the first switching element are connected in series in the main relay circuit. The second pin of the first switching element inputs the control signal. The second pin of the first switching element is connected to the first pin of the second switching element. The third pin of the second switching element is grounded. The second pin of the second switching element inputs the comparison result.

[0016] Further, the leakage current relay protection circuit further includes a voltage conditioning circuit. The input end of the voltage conditioning circuit is connected to the output end of the leakage current detection circuit. The output end of the voltage conditioning circuit is connected to a controller for RMS calculation. The controller outputs a control signal to the relay control circuit according to the calculation result to control the operation of the relay.

[0017] Further, the voltage conditioning circuit includes a voltage conversion circuit and a voltage follower circuit. The voltage conversion circuit is used to convert the voltage signal into a unipolar voltage. The voltage follower circuit is used for signal isolation. The input end of the voltage follower circuit is connected to the output end of the voltage conversion circuit. The output end of the voltage follower circuit is connected to the controller.

[0018] Further, the voltage conversion circuit includes a resistor R16 and a resistor R17. The first end of the resistor R16 is connected to the output end of the leakage current detection circuit. The second end of the resistor R16 is connected to the first end of the resistor R17. The second end of the resistor R17 is connected to the power supply VCC. The second end of the resistor R16 is connected to the input end of the voltage follower circuit.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] (1) The leakage current detection circuit and the rectification circuit of the present invention output detection voltages of different magnitudes corresponding to different magnitudes of leakage current. When the detection voltage is less than the preset voltage, the voltage comparison circuit outputs a low level, and the relay control circuit controls the relay to remain connected and not act; when the detection voltage exceeds the preset voltage, the voltage comparison circuit outputs a high level, and the relay control circuit controls the relay to act immediately and disconnect the charging circuit. By setting the preset voltage, the present invention can meet the relay action time limit requirements for any magnitude of leakage current and eliminate potential safety hazards.

[0021] (2) The leakage current relay protection circuit of the present invention further includes a voltage conditioning circuit. A voltage signal is input to the input end of the voltage conditioning circuit. The output end of the voltage conditioning circuit is connected to a controller for RMS calculation. The controller controls the relay to act according to the calculation result. When the leakage current is less than 30 mA, the relay works normally; when the leakage current is relatively large, the relay control circuit controls the relay to act according to the comparison result of the voltage comparator and the control signal of the controller and immediately disconnects the charging circuit; when the leakage current is at an intermediate value, the controller performs RMS calculation and then outputs a control signal according to the calculation result to control the relay to act. In this way, under any magnitude of leakage current, the action time limit requirements can be met, the circuit can be disconnected in time, and the relay acts accurately and is not prone to misoperation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a curve graph showing the relationship between the relay action time limit and the magnitude of the leakage current;

[0024] Figure 2 It is a schematic diagram of the leakage current relay protection circuit of the present invention;

[0025] Figure 3Circuit structure diagram of the current transformer connection circuit of the present invention;

[0026] Figure 4 Circuit structure diagram of the proportional amplification circuit of the present invention;

[0027] Figure 5 Circuit structure diagram of the rectification circuit of the present invention;

[0028] Figure 6 Waveform diagram of the detected voltage of the present invention;

[0029] Figure 7 Circuit structure diagram of the voltage comparison circuit of the present invention;

[0030] Figure 8 Waveform diagram of the comparison result of the present invention;

[0031] Figure 9 Circuit structure diagram of the relay control circuit of the present invention;

[0032] Figure 10 Circuit structure diagram of the voltage conditioning circuit of the present invention. Detailed implementation manners

[0033] The object of the present invention is to provide a leakage current relay protection circuit, which can disconnect the relay when the effective value of the leakage current exceeds 30 mA, and can immediately disconnect the relay when the leakage current is large, and can meet the action time limit requirements of the relay under any leakage current magnitude. The implementation manners of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Embodiment 1:

[0035] As Figure 2 shown, the leakage current relay protection circuit of this embodiment includes a leakage current detection circuit, a rectification circuit, a voltage comparison circuit and a relay control circuit. Among them, the leakage current detection circuit is used to detect the magnitude of the leakage current and convert the leakage current into a voltage signal. The rectification circuit is used to rectify the voltage signal and output a detected voltage. The voltage comparison circuit compares the detected voltage with a preset voltage and outputs a comparison result to the relay control circuit. The relay control circuit controls the action of the relay according to the comparison result.

[0036] In this way, the leakage current detection circuit and the rectification circuit of this embodiment output different magnitudes of detected voltages corresponding to different magnitudes of leakage currents. When the detected voltage is less than the preset voltage, the voltage comparison circuit outputs a low level, and the relay control circuit controls the relay to remain connected and not act; when the detected voltage exceeds the preset voltage, the voltage comparison circuit will output a high level, and the relay control circuit controls the relay to act immediately and disconnect the charging line.

[0037] It can be seen from this that only by selecting a preset current according to the operating time limit requirement of the relay, where the preset current corresponds to a preset voltage, and setting the preset voltage to the detection voltage when the leakage current is equal to the preset current, the relay can act immediately when the leakage current exceeds the preset current. For example, if the preset current is selected as 30 mA, then when the leakage current is greater than 30 mA, the detection voltage is greater than the preset voltage, and at this time the relay will act. In this embodiment, by setting the value of the preset voltage, it can be ensured that the operating time limit requirement of the relay is satisfied when the leakage current is any value, and the charging circuit can be disconnected in time.

[0038] Further, the leakage current detection circuit of this embodiment includes a current transformer connection circuit and a proportional amplification circuit. The input end of the current transformer connection circuit detects the leakage current, the output end of the current transformer connection circuit is connected to the input end of the proportional amplification circuit, and the output end of the proportional amplification circuit outputs a voltage signal linearly proportional to the leakage current. Specifically, as Figure 3 - 4 shown, the current transformer connection circuit includes a zero-sequence current transformer T1 and a resistor R1. The primary side of the zero-sequence current transformer T1 detects the leakage current. The zero-sequence current transformer T1 can be, but is not limited to, a through-core current transformer. The wire serving as the leakage current carrier can pass through the middle of the zero-sequence current transformer T1, so that the wire forms the primary side coil of the zero-sequence current transformer T1. The secondary side of the zero-sequence current transformer T1 is connected with a resistor R1. One end of the resistor R1 is grounded, and the other end of the resistor R1 outputs the secondary side voltage V1, and the other end of the resistor R1 is connected to the input end of the proportional amplification circuit. The output end of the proportional amplification circuit outputs the voltage signal V2. Further, as Figure 4 shown, the proportional amplification circuit of this embodiment includes an operational amplifier U1. The other end of the resistor R1 is connected to the non-inverting input end of the operational amplifier U1 through a resistor R4. The inverting input end of the operational amplifier U1 is grounded through a resistor R2. A resistor R3 is connected between the inverting input end and the output end of the operational amplifier U1. The output end of the operational amplifier U1 outputs the voltage signal V2.

[0039] See Figure 3 and Figure 4 , assuming that the secondary side current of the zero-sequence current transformer is I, then V1 = R1×I, and the amplification ratio of the proportional amplification circuit is then

[0040] Further, since the leakage current is an AC signal, the voltage signal V2 output by the leakage current detection circuit is also an AC signal. In this embodiment, a rectification circuit is used to convert the voltage signal V2 into a unidirectional pulsating detection voltage. Specifically, as Figure 5As shown, the rectifier circuit of this embodiment includes operational amplifiers U2 and U3 and a peripheral circuit. The operational amplifiers U2 and U3, in combination with the peripheral circuit, form a precision full-wave rectifier circuit to rectify and output the voltage signal V2. Figure 6 The detected voltage V3 with a period of 10 ms as shown is used to compare with a preset voltage.

[0041] Further, as Figure 7 - 8 shown, the voltage comparison circuit of this embodiment compares the detected voltage V3 with the preset voltage and outputs the comparison result to the relay control circuit. Specifically, the voltage comparison circuit of this embodiment includes a voltage comparator U4. The non-inverting input terminal of the voltage comparator U4 inputs the detected voltage V3, the inverting input terminal of the voltage comparator U4 inputs the preset voltage V4, and the output terminal of the voltage comparator U4 outputs Figure 8 the comparison result V5 as shown to the relay control circuit. Further, a pull-up resistor R11 is also provided at the output terminal of the voltage comparator U4. Since the comparator has an open-collector output, a high level is output through the pull-up resistor R11.

[0042] Further, as Figure 9 shown, the relay control circuit of this embodiment includes a first switching element and a second switching element. The first and third pins of the first switching element are connected in series in the main relay circuit. The second pin of the first switching element is connected to the first pin of the second switching element. The third pin of the second switching element is grounded, and the second pin of the second switching element inputs the above comparison result. Specifically, the first switching element is a triode Q1, and the second switching element is a triode Q2. The first pins of both are the collectors, the second pins are the bases, and the third pins are the emitters. The collector of the triode Q1 is connected to one end of the relay K1, the other end of the relay K1 is connected to the power supply VCC, the emitter of the triode Q1 is grounded, and the base of the triode Q1 is connected to the switch S2A via the resistor R12. Further, the base of the triode Q1 is connected to the collector of the triode Q2 via the resistor R15. The emitter of the triode Q2 is grounded. The base of the triode Q2 is connected to the first end of the resistor R13. The second end of the resistor R13 is connected to the switch S1A, and the second end of the resistor R13 is grounded via the resistor R14.

[0043] It should be noted that here S2A represents the control signal output by the controller. In the initial state, the initial control signal output by the controller is at a high level, which is equivalent to the switch S2A being closed and conducting; S1A represents the comparison result output by the above voltage comparison circuit. When the comparison result is at a high level, it is equivalent to the switch S1A being closed and conducting. When the comparison result is at a low level, it is equivalent to the switch S1A being open. This is only for illustration here. In the actual circuit, the port for the controller to output the control signal can be connected to point M at the front end of resistor R12, and the output end of the voltage comparison circuit can be connected to point N at the front end of resistor R13.

[0044] In the initial state, the controller outputs an initial control signal at a high level (equivalent to the switch S2A being closed) according to the charging requirement, and at this time, the triode Q1 conducts. When the leakage current is less than the preset current, the detected voltage is less than the preset voltage, and the comparison result V5 is at a low level (equivalent to the switch S1A being open), at this time, the triode Q2 is turned off, the triode Q1 remains conducting, the working contact of the relay K1 is attracted, the main circuit of the relay conducts, the charging circuit works, and it is in the normal working state at this time; when the leakage current is greater than the preset current, the comparison result V5 is a square wave with a certain duty cycle. When the comparison result V5 is at a high level (equivalent to the switch S1A being closed), the triode Q2 conducts, pulling down the base voltage of the triode Q1, causing the triode Q1 to turn off, and the working contact of the relay K1 immediately disconnects and stops working, and the charging circuit is disconnected. Further, the comparison result of this embodiment is simultaneously output to the controller, and the controller outputs a control signal to control the relay action according to the comparison result. Specifically, when the controller detects that the comparison result is at a high level or rises from a low level to a high level, the output control signal is always at a low level (equivalent to the switch S2A always being open). At this time, even if the comparison result changes from a high level to a low level, the relay K1 will not conduct again. By the controller processing the comparison result of the voltage comparison circuit, it is possible to prevent the relay K1 from frequently conducting and disconnecting.

[0045] Since it takes a certain amount of time, about several hundred microseconds, for the controller to process the comparison result, in this embodiment, the triode Q2 is set and the comparison result is output to the base of the triode Q2, so that the relay K1 can be immediately disconnected, and the disconnection is more rapid and timely.

[0046] Preferably, the preset current can be set to 30 mA. When the leakage current is less than 30 mA, the main circuit of the relay conducts. When the leakage current is greater than 30 mA, the main circuit of the relay immediately disconnects. At this time, the action time of the relay is only about 15 ms of its own action time, and by Figure 1It can be known that when the leakage current is greater than 300 mA, its operating time limit is 20 ms. Therefore, it can meet the operating time limit requirements of the relay for any leakage current. It should be noted that the 30 mA here is generally the effective value, and the corresponding preset voltage should also be the effective value. However, the detection voltage in this embodiment is the instantaneous value. Therefore, the preset voltage needs to be set to the peak value corresponding to the effective value. For example, in a sine wave, it can be set to times of the effective value.

[0047] In summary, the leakage current relay protection circuit of this embodiment can meet the operating time limit requirements of the relay for any value of the leakage current, timely disconnect the charging line, and ensure the safety of personnel and equipment.

[0048] Embodiment 2:

[0049] As Figure 10 shown, the difference between the leakage current relay protection circuit of this embodiment and that of Embodiment 1 is that the leakage current relay protection circuit of this embodiment further includes a voltage conditioning circuit. The input end of the voltage conditioning circuit inputs the above voltage signal V2, and the output end of the voltage conditioning circuit is connected to the controller as an AD input for RMS calculation. The controller outputs a control signal according to the RMS calculation result to control the operation of the relay, that is, output to Figure 9 the M point in. Further, the voltage conditioning circuit includes a voltage conversion circuit, a voltage follower circuit, a filtering circuit, and a clamping circuit. The input end of the voltage follower circuit is connected to the output end of the voltage conversion circuit, and the output end of the voltage follower circuit is connected to the controller through the filtering circuit and the clamping circuit. The controller outputs a control signal according to the RMS calculation result to control the operation of the relay.

[0050] Specifically, the voltage conversion circuit includes a resistor R16 and a resistor R17. The first end of the resistor R16 is connected to the output end of the proportional amplification circuit, the second end of the resistor R16 is connected to the first end of the resistor R17, the second end of the resistor R17 is connected to the power supply VCC, and the second end of the resistor R16 is connected to the input end of the voltage follower circuit. The voltage follower circuit includes a voltage follower U5. The output end of the voltage follower U5 is connected to the filtering circuit. The filtering circuit is composed of a resistor R18 and a capacitor C2. The first end of the resistor R18 is connected to the output end of the voltage follower U5, the second end of the resistor R18 is grounded through the capacitor C2, and the second end of the resistor R18 is connected to the clamping circuit. The clamping circuit includes a diode D3 and a diode D4. The cathode of the diode D3 is connected to the power supply VCC, the anode of the diode D3 is connected to the cathode of the diode D4, the anode of the diode D4 is grounded, and the cathode of the diode D4 is connected to the controller as an AD input.

[0051] Among them, the voltage conversion circuit is used to convert the voltage signal V2 into a unipolar voltage V2' of 0 - 3.3V. The voltage follower circuit has the characteristics of high input impedance and low output impedance, making it present a high impedance state to the previous-stage circuit and a low impedance state to the next-stage circuit, so as to isolate the front and rear-stage circuits, eliminate the mutual influence between them, facilitate impedance matching, and reduce the sampling error. The filtering circuit is used for filtering, and the clamping circuit is used to ensure that the voltage input to the AD remains within 0 - 3.3V to prevent the AD input voltage from exceeding the limit. This AD input voltage is input into the controller for RMS calculation. When the calculated effective value is greater than 30mA, the controller outputs a control signal with a low level, which is equivalent to Figure 9 the switch S2A in Figure 9 is disconnected, and the relay K1 is disconnected.

[0052] After setting the voltage conditioning circuit, the above preset current can be set to other values, such as 200mA. In this way, when the leakage current is 0 - 30mA, the detected voltage is less than the preset voltage, the comparison result is low level, and the RMS calculation shows that the leakage current is less than 30mA. The controller outputs a control signal with a high level. At this time, the working contact of the relay K1 closes and works normally; when the leakage current is 30 - 200mA, the detected voltage is less than the preset voltage, the comparison result is low level, but the controller calculates through RMS that the effective value of the leakage current exceeds 30mA, and outputs a control signal with a low level. The working contact of the relay K1 disconnects. At this time, the disconnection time is the time of 20ms for RMS calculation plus the action time of 15ms of the relay itself, about 35ms. And from Figure 1 it can be seen that when the leakage current is less than 200mA, the action time limit requirement of the relay is less than 38ms, which can meet the requirement at this time. Therefore, it is preferred to set the preset current to 200mA; when the leakage current is greater than 200mA, the detected voltage is greater than the preset voltage, the comparison result is high level, and the working contact of the relay K1 immediately disconnects. At this time, the disconnection time is the action time of the relay itself, only 15ms. And when the leakage current is greater than 300mA, the action time limit of the relay is 20ms, which can also meet the action time limit requirement at this time. It can be seen that the leakage current relay protection circuit of this embodiment can also meet the action time limit requirements of the relay for any leakage current magnitude, and the controller is used to calculate the effective value within 30 - 200mA, making the action of the relay more accurate.

[0053] If the preset current is directly set to 30 mA, although the operating time limit requirement of the relay can be met, since the 30 mA preset current is the effective value, when setting the preset voltage, it is necessary to convert the corresponding alternating current with an effective value of 30 mA into the peak value corresponding to the effective value. Generally, the waveform of the leakage current will be interfered by other modules in the circuit and there is a certain fluctuation. Therefore, there is a certain deviation between the preset voltage after conversion and the actual value. If the preset voltage is set too low, it is prone to misoperation. If the preset voltage is set too high, the operating requirement when the specified leakage current is 30 mA cannot be achieved. In this embodiment, when the leakage current exceeds 30 mA, the accurate effective value can be obtained through RMS calculation, making the relay operate accurately. Although there is also a certain error in the converted preset voltage value when the preset current is set to 200 mA, at this time, the preset voltage can be set too low, without misoperation and can meet the operating time limit requirement.

[0054] If only the scheme of calculating the effective value by RMS and disconnecting the relay when it is greater than 30 mA is adopted, the operating time limit requirement of the relay cannot be fully met, because in order to obtain the accurate effective value, it is necessary to sample for one cycle when sampling the AD input voltage, that is Since the relay itself has a working time of about 15 ms, it takes about 35 ms for it to completely disconnect. When the leakage current is small, the operating time limit is long. At this time, the operating time of the relay can meet the operating time limit requirement. However, when the leakage current is large, such as when the leakage current reaches 300 mA, the operating time limit of the relay should be less than 20 ms. Obviously, the operating time of the relay is too long at this time and it cannot be disconnected in time, failing to meet the requirement of protecting the circuit and there is a potential safety hazard.

[0055] It can be seen that for the leakage current relay protection circuit of this embodiment, when the leakage current is 30 - 200 mA, the scheme of controlling the relay operation according to the RMS calculation result of the controller is adopted, and when the leakage current is greater than 200 mA, the scheme of controlling the relay operation according to the comparison result of the voltage comparator is adopted, which can meet the relay operating time limit requirement for any leakage current magnitude, and the relay operates accurately and is not prone to misoperation. Of course, the interval value of 200 mA here can be set to other values according to the actual situation, such as setting according to relays with different self-operating times or according to different relay operating time limit requirement curves to meet the operating time limit requirement.

[0056] Embodiment 3:

[0057] Such as Figure 3 , in this embodiment, the zero-sequence current transformer in the leakage current detection circuit is of the model HCT2018-LF, its turns ratio is 1000 / 1, that is, 1 A / 1 mA, and the secondary side voltage is V1 = R1 × I. Taking R1 = 200 Ω, then V1 = 200 × I.

[0058] For example Figure 4 , take R3 = 900 Ω, R2 = 100 Ω, and the balance resistor R4 = R2 / / R3 = 90 Ω. Then the amplification factor of this proportional amplification circuit is 1 + R3 / R2 = 10, and the voltage signal V2 = 10×V1.

[0059] For example Figure 10 , in the voltage conversion circuit, both the resistor R16 and the resistor R17 are taken as 1 kΩ, then V2’ = 0.5V2 + 1.65. The translated voltage signal V2’ is isolated through a voltage follower circuit, and then after passing through an RC filter circuit, the clamping circuit makes the AD input voltage not exceed 3.3V. This AD input voltage is input to the controller for RMS calculation. The RMS calculation is the root mean square calculation, and the calculation result is actually the effective value, which is the square root of the average value of the squares of a set of data. The RMS calculation is divided into three parts. The first part is a multiplier that squares the input voltage Ub to obtain the voltage Ua = Ub 2 ; the second part is an integrator that averages the voltages Ua obtained from the above calculations to obtain the voltage The third part is a square root circuit that takes the square root of the above voltage Uc to obtain the effective value Here, Ua, Ub, and Uc are all for illustration. When it is calculated that the effective value of the leakage current is greater than 30 mA, the controller outputs a control signal to control the triode Q1 to turn off, and the relay K1 stops attracting, and the charging circuit is disconnected.

[0060] For example Figure 1 , when the leakage current is 200 mA, the action time limit of the relay is about 38 ms, and the time when the relay is completely disconnected is about 35 ms, which meets the requirements. That is, when the leakage current is less than 200 mA, the action time of the relay is 35 ms, meeting the action time limit requirement of 38 ms. When the leakage current is greater than 200 mA, the action time of the relay is 15 ms, meeting the action time limit requirement of 20 ms. Therefore, in this embodiment, it is preferably to take 200 mA as the preset current, and when the leakage current is greater than 200 mA, the relay directly acts and immediately disconnects the charging circuit.

[0061] Further, assuming the preset current is 200 mA, the secondary-side voltage V1 output by the zero-sequence current transformer T1 is V1 = 200×I = 200×0.2 / 1000 = 0.04 V. After passing through the proportional amplification circuit, the voltage signal V2 = 10×V1 = 0.4 V is obtained. The detected voltage V3 = 0.4 V, and this detected voltage is the effective value, and its corresponding peak value is greater than 0.4 V. In theory, the preset voltage can be set to be the same as this peak value. Preferably, in this embodiment, the preset voltage is set to be on the low side. For example, the preset voltage V4 can be directly set to 0.4 V. This means that when the leakage current is below 200 mA and close to 200 mA, the relay will operate to disconnect the circuit, which can fully meet the time limit requirements.

[0062] In other embodiments, zero-sequence current transformers of other models can be selected. For example, a zero-sequence current transformer with a turns ratio of 100 / 1, then its output voltage is 0.4 V, and this output voltage can be directly used as the voltage signal, and the proportional amplification circuit can be omitted.

[0063] In the present invention, unless otherwise clearly defined and limited, terms such as "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0064] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0065] The above embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary engineering and technical personnel in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A leakage current relay protection circuit, characterized in that, Comprising: A leakage current detection circuit for converting the leakage current into a voltage signal; A rectification circuit for rectifying the voltage signal and outputting a detection voltage; A voltage comparison circuit for comparing the detection voltage with a preset voltage and outputting a comparison result to a relay control circuit and a controller; A relay control circuit for controlling the operation of a relay according to the comparison result and a control signal issued by the controller; The leakage current relay protection circuit further includes a voltage conditioning circuit. The input end of the voltage conditioning circuit is connected to the output end of the leakage current detection circuit, and the output end of the voltage conditioning circuit is connected to the controller for RMS calculation. The controller outputs a control signal to the relay control circuit according to the calculation result to control the operation of the relay; The voltage conditioning circuit includes a voltage conversion circuit and a voltage follower circuit. The voltage conversion circuit is used for converting the voltage signal into a unipolar voltage, and the voltage follower circuit is used for signal isolation. The input end of the voltage follower circuit is connected to the output end of the voltage conversion circuit, and the output end of the voltage follower circuit is connected to the controller.

2. The leakage current relay protection circuit according to claim 1, characterized in that, The leakage current detection circuit includes a current transformer connection circuit. The current transformer connection circuit includes a zero-sequence current transformer T1 and a resistor R1. The primary side of the zero-sequence current transformer T1 detects the leakage current, the secondary side of the zero-sequence current transformer T1 is connected with the resistor R1, one end of the resistor R1 is grounded, and the other end of the resistor R1 outputs the voltage signal.

3. The leakage current relay protection circuit according to claim 2, wherein The leakage current detection circuit further includes a proportional amplification circuit. The input end of the current transformer connection circuit detects the leakage current, the output end of the current transformer connection circuit is connected to the input end of the proportional amplification circuit, and the output end of the proportional amplification circuit outputs the voltage signal.

4. The leakage current relay protection circuit according to claim 3, wherein The proportional amplification circuit includes an operational amplifier U1. The other end of the resistor R1 is connected to the non-inverting input end of the operational amplifier U1 through a resistor R4. The inverting input end of the operational amplifier U1 is grounded through a resistor R2. A resistor R3 is connected between the inverting input end and the output end of the operational amplifier U1. The output end of the operational amplifier U1 outputs the voltage signal.

5. The leakage current relay protection circuit according to claim 1, wherein The rectification circuit includes an operational amplifier U2, an operational amplifier U3 and a peripheral circuit. The operational amplifier U2 and the operational amplifier U3 together with the peripheral circuit form a precision full-wave rectification circuit for rectifying the voltage signal and outputting a detection voltage.

6. The leakage current relay protection circuit according to claim 1, characterized in that, The voltage comparison circuit includes a voltage comparator U4. The non-inverting input end of the voltage comparator U4 inputs the detection voltage, the inverting input end of the voltage comparator U4 inputs the preset voltage, and the output end of the voltage comparator U4 outputs a comparison result to the relay control circuit and the controller.

7. The leakage current relay protection circuit according to claim 1, characterized in that, The relay control circuit includes a first switching element and a second switching element. The first terminal and the third terminal of the first switching element are connected in series in the main circuit of the relay. The control signal is input to the second terminal of the first switching element. The second terminal of the first switching element is connected to the first terminal of the second switching element. The third terminal of the second switching element is grounded. The comparison result is input to the second terminal of the second switching element.

8. The leakage current relay protection circuit according to claim 1, characterized in that, The voltage conversion circuit includes a resistor R16 and a resistor R17. The first end of the resistor R16 is connected to the output terminal of the leakage current detection circuit. The second end of the resistor R16 is connected to the first end of the resistor R17. The second end of the resistor R17 is connected to the power supply VCC. The second end of the resistor R16 is connected to the input terminal of the voltage follower circuit.

Images