Relay protection instrument interface circuit and signal driving method thereof

Abstract

The invention provides a relay protection instrument interface circuit and a signal driving method thereof, and relates to the technical field of relay protection, the relay protection instrument interface circuit comprises a surge protection circuit used for receiving an external digital quantity input signal, a first filter circuit, an anti-reverse circuit, an optocoupler isolation circuit and a Schmidt level conversion circuit used for outputting a Schmidt trigger signal; the surge protection circuit is connected with the input end of the first filter circuit, the output end of the first filter circuit is connected with the input end of the anti-reverse circuit, the output end of the anti-reverse circuit is connected with the input end of the optical coupler isolation circuit, and the output end of the optical coupler isolation circuit is connected with the Schmidt level conversion circuit. According to the invention, false triggering actions and transient interference signals are effectively avoided, the signal driving capability is improved, the reliability of relay protection is ensured, and an important guarantee is provided for a direct current transmission line.

Description

Technical Field

[0001] The invention relates to the technical field of relay protection, and in particular to an interface circuit of a relay protection instrument and a signal driving method thereof. Background Art

[0002] In the power system, DC transmission lines are widely used due to their long-distance transmission, high efficiency and low loss. As the length of DC transmission lines increases, their failure rate also increases accordingly, which poses a severe challenge to the safety and stability of DC transmission systems. Therefore, studying the interface circuit of the relay protection instrument of the DC transmission line is of great significance to ensure system safety and rapid fault recovery.

[0003] At present, the DC transmission line protection scheme and device in the station distribution protection operation of rail transit substations and distribution stations rely largely on foreign technology, and the DC line protection in engineering applications has shortcomings such as incomplete theory and poor reliability. Line faults are responded to by the DC control system, resulting in DC locking and forced shutdown accidents. The prior art discloses a digital quantity input interface device and method for PLC, and a programmable controller including the digital quantity input interface device. The digital quantity input interface device comprises: an input current limiting resistor, connected to the output end of an external sensor to receive an input signal; a sampling resistor connected in series with the input current limiting resistor; an optical coupler, wherein the first and second input ends of the optical coupler are respectively connected in parallel with the two ends of the sampling resistor; a pull-up resistor, wherein one end of the pull-up resistor is connected to the first output end of the optical coupler, and the other end of the pull-up resistor is connected to a power supply, wherein the other output end of the optical coupler is connected to a digital ground; and a photoelectric switch, wherein one output end of the photoelectric switch is connected together with one end of the sampling resistor to the second output end of the optical coupler, and the other output end of the photoelectric switch is connected to the input common end of a PLC, wherein the input end of the photoelectric switch receives an input enable signal, and under the control of the input enable signal, the photoelectric switch is turned on and off accordingly, but this method does not utilize the flipping characteristics of the Schmidt inverter, cannot realize the difference between the thresholds of the forward trigger signal and the reverse trigger signal to adapt to different trigger signal characteristics, and is prone to false triggering actions, and does not adopt an isolated hardware integration circuit design, which is prone to transient interference signals, affecting the signal driving capability, resulting in poor reliability of relay protection. Summary of the invention

[0004] In order to solve the problem that the above-mentioned prior art is prone to false triggering and transient interference signals, and has weak signal driving capability, resulting in poor reliability of relay protection, the present invention proposes a relay protection instrument interface circuit and a signal driving method thereof, which effectively avoids the generation of false triggering and transient interference signals, improves the signal driving capability, ensures the reliability of relay protection, and provides important protection for DC transmission lines.

[0005] In order to achieve the above technical effects, the technical solution of the present invention is as follows:

[0006] A relay protection instrument interface circuit includes a surge protection circuit for receiving an external digital quantity input signal, a first filter circuit, an anti-reverse circuit, an optical coupling isolation circuit, and a Schmitt level conversion circuit for outputting a Schmitt trigger signal;

[0007] The surge protection circuit is connected to the input end of the first filter circuit, the output end of the first filter circuit is connected to the input end of the anti-reverse circuit, the output end of the anti-reverse circuit is connected to the input end of the optocoupler isolation circuit, and the output end of the optocoupler isolation circuit is connected to the Schmitt level conversion circuit.

[0008] Preferably, the surge protection circuit is a surge protection resistor R5, one end of the surge protection resistor R5 is respectively connected to an input end of an external digital input signal and a first input end of the first filter circuit, and the other end of the surge protection resistor R5 is respectively connected to another input end of the external digital input signal and a second input end of the first filter circuit.

[0009] Preferably, the first filtering circuit includes a first filtering resistor R1, a second filtering resistor R2, a third filtering resistor R3, a fourth filtering resistor R4 and a first filtering capacitor C1, one end of the surge protection resistor R5 is connected to one end of the first filtering resistor R1, the other end of the first filtering resistor R1 is connected to the input end of the second filtering resistor R2, the output end of the second filtering resistor R2 is respectively connected to the first input end of the anti-reverse circuit and one end of the first filtering capacitor C1, the other end of the first filtering capacitor C1 is respectively connected to the second input end of the anti-reverse circuit and one end of the fourth filtering resistor R4, the other end of the fourth filtering resistor R4 is connected to one end of the third filtering resistor R3, and the other end of the third filtering resistor R3 is connected to the other end of the surge protection resistor R5.

[0010] Preferably, the anti-reverse circuit includes a first diode D1, an anti-reverse resistor R6 and a second diode D2, one end of the first filter capacitor C1 is respectively connected to the positive end of the first diode D1 and one end of the anti-reverse resistor R6, the negative end of the first diode D1 is connected to the first input end of the optocoupler isolation circuit, the other end of the anti-reverse resistor R6 is respectively connected to the second input end of the optocoupler isolation circuit and the negative end of the second diode D2, and the positive end of the second diode D2 is respectively connected to one end of the fourth filter resistor R4.

[0011] Preferably, the optocoupler isolation circuit includes a primary circuit and a secondary circuit, the first input end of the primary circuit is connected to the positive end of the first diode D1, the second input end of the primary circuit is connected to the negative end of the second diode D2, and the collector and emitter of the secondary circuit are respectively connected to the Schmitt level conversion circuit.

[0012] Preferably, the primary circuit is a light emitting diode U1A, and the secondary circuit is a phototransistor U2A.

[0013] Preferably, the Schmitt level conversion circuit includes a second filtering circuit, a Schmitt inverter and a power supply VCC, the power supply VCC is connected to the collector of the secondary circuit, the emitter of the secondary circuit is connected to the input end of the second filtering circuit, the output end of the second filtering circuit is connected to the negative end of the Schmitt inverter, and the positive end of the Schmitt inverter is connected to the external microcontroller.

[0014] Preferably, the second filtering circuit includes a fifth filtering resistor R7 and a second filtering capacitor C2, one end of the fifth filtering resistor R7 is connected to one end of the second filtering capacitor C2 and then grounded together, and the other end of the fifth filtering resistor R7 is respectively connected to the emitter of the secondary circuit, the other end of the second filtering capacitor C2 and the positive terminal of the Schmidt inverter.

[0015] The present invention also proposes a signal driving method using the relay protection instrument interface circuit as described above, comprising the following steps:

[0016] S1. The surge protection circuit receives an external digital input signal, performs surge protection on the external digital input signal, and outputs a surge protection digital signal;

[0017] S2. The first filtering circuit receives the surge protection signal, filters the surge protection signal, and outputs a filtered digital signal;

[0018] S3. The anti-reverse circuit receives the filtered signal, conducts unidirectional conduction on the filtered signal, and outputs an anti-reverse digital signal;

[0019] S4. The optical coupling isolation circuit receives the anti-reverse digital signal, performs photoelectric conversion on the anti-reverse digital signal, and outputs a digital conversion signal;

[0020] S5. The Schmitt level conversion circuit receives the digital conversion signal, performs Schmitt triggering on the digital conversion signal, and outputs a Schmitt triggering signal.

[0021] Preferably, performing Schmitt triggering on the digital conversion signal comprises:

[0022] S51. Setting the rising edge detection voltage and the falling edge detection voltage of the Schmitt level conversion circuit;

[0023] S52. When the voltage of the digital conversion signal rises, determine whether the rising voltage exceeds the rising edge detection voltage. If so, the output high-level Schmitt trigger signal is valid; if not, the output high-level Schmitt trigger signal is invalid;

[0024] S53. When the voltage of the digital conversion signal drops, determine whether the dropped voltage exceeds the falling edge detection voltage. If so, the output low-level Schmitt trigger signal is valid; if not, the output low-level Schmitt trigger signal is invalid.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] The present invention proposes a relay protection instrument interface circuit and a signal driving method thereof. Firstly, a hardware circuit design of an interface is formed by a surge protection circuit, a first filtering circuit, an anti-reverse circuit, an optical coupling isolation circuit and a Schmidt level conversion circuit to realize different settings of the positive and reverse trigger thresholds of an external digital quantity input signal, so that the relay protection instrument interface circuit achieves the effect of Schmidt triggering, and effectively avoids the generation of false triggering actions; secondly, the external digital quantity input signal is subjected to surge protection by a front-end surge protection circuit, filtered and attenuated by a first filtering circuit, and then unidirectionally conducted by an anti-reverse circuit, and then optically isolated by an optical coupling isolation circuit, and shaped by a Schmidt level conversion circuit. The circuit completes the acquisition of external digital input signals, thereby outputting Schmitt trigger signals, in order to avoid transient interference signals generated by the relay protection interface circuit under complex electromagnetic environments; further, by setting up a Schmitt level conversion circuit, the voltage input range is effectively expanded, the signal driving capability is improved, and the reliability of relay protection is ensured; in addition, based on the high reliability characteristics of the relay protection interface circuit, it is applied to the urban rail transit traction power supply system. Scientific relay protection configuration is conducive to reducing the fault phenomenon of circuit breakage or circuit breaker in the power supply line, ensuring the reliability of the operation of the line power equipment, and significantly improving the safety of the entire rail transit system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A circuit structure block diagram showing a relay protection device interface circuit proposed in an embodiment of the present invention;

[0028] Figure 2 A block diagram showing the working principle of a relay protection device interface circuit proposed in an embodiment of the present invention;

[0029] Figure 3 A Bode diagram showing a cut-off frequency of an input of an interface circuit of a relay protection device proposed in an embodiment of the present invention;

[0030] Figure 4 A flowchart showing a signal driving method for a relay protection device interface circuit according to an embodiment of the present invention;

[0031] Figure 5 A schematic diagram of a Schmitt trigger proposed in an embodiment of the present invention is shown;

[0032] 1. Surge protection circuit; 2. First filter circuit; 3. Anti-reverse circuit; 4. Optocoupler isolation circuit; 41. Primary circuit; 42. Secondary circuit; 5. Schmitt level conversion circuit; 51. Second filter circuit; 52. Schmitt inverter. DETAILED DESCRIPTION

[0033] The accompanying drawings are only used for illustrative purposes and are not to be construed as limiting the present invention;

[0034] It is understandable to those skilled in the art that some well-known contents may be omitted in the drawings;

[0035] To facilitate the understanding of the following embodiments, first, the technical terms of this embodiment are explained:

[0036] Relay protection: Relay protection is an indispensable device in the power system. It can automatically determine the fault and automatically turn on the protection mode so that the normal operation of the power system is not affected. There are many types of relay protection devices, and contact relays are the most widely used in the operation protection of equipment such as generators. In the research of relay protection, no matter what technology it is combined with, the function of the relay protection itself must be guaranteed so that it can play an emergency rescue role when the power system fails. It needs to implement protection technology in a timely and sensitive manner according to the type of fault, so that the faulty equipment can be removed and the power system can be safe and reliable.

[0037] Rail transit: Rail transit-related carriages need to run on fixed tracks. They have a large transportation volume and high speed, which effectively alleviates the pressure of ground transportation. These advantages make the subway operation mode more and more widely used. Rail transit vehicles mainly rely on track power supply and contact network power supply to obtain operating power. The two power supply methods can be operated separately or mixed together to provide electricity for rail transit.

[0038] Analysis of rail transit power supply system protection: The protection of rail transit power supply system must meet the requirements of safety, stability and reliability, and protect the power supply process. Technically, we first start from the protection of the power supply system lines, and monitor and control the distribution system in real time. Secondly, we select the operating characteristics of the distribution system. During the operation of the power supply system, we collect system operation information, and filter out abnormal information through analysis and judgment. In a series of information processing processes, the relay protection device needs to extract the signal characteristics of the power supply system, and then determine the setting values ​​of each protection.

[0039] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0040] Example 1

[0041] like Figure 1As shown, this embodiment proposes a relay protection instrument interface circuit, including a surge protection circuit 1 for receiving an external digital input signal, a first filter circuit 2, an anti-reverse circuit 3, an optical coupling isolation circuit 4 and a Schmitt level conversion circuit 5 for outputting a Schmitt trigger signal;

[0042] The surge protection circuit 1 is connected to the input end of the first filter circuit 2, the output end of the first filter circuit 2 is connected to the input end of the anti-reverse circuit 3, the output end of the anti-reverse circuit 3 is connected to the input end of the optocoupler isolation circuit 4, and the output end of the optocoupler isolation circuit 4 is connected to the Schmidt level conversion circuit 5.

[0043] See also Figure 2 , the working principle of the relay protection instrument interface circuit is as follows:

[0044] First, the surge protection circuit 1 receives an external digital input signal, performs surge protection on the external digital input signal, and outputs a surge protection digital signal; then the first filtering circuit 2 receives the surge protection signal, filters the surge protection signal, and outputs a filtered digital signal; then the anti-reverse circuit 3 receives the filtered signal, unidirectionally conducts the filtered signal, and outputs an anti-reverse digital signal; further, the optical coupling isolation circuit receives the anti-reverse digital signal, performs photoelectric conversion on the anti-reverse digital signal, and outputs a digital conversion signal; finally, the Schmitt level conversion circuit 5 receives the digital conversion signal, performs Schmitt triggering on the digital conversion signal, and outputs a Schmitt triggering signal.

[0045] In this embodiment, firstly, the hardware circuit design of the interface composed of a surge protection circuit, a first filtering circuit, an anti-reverse circuit, an optocoupler isolation circuit and a Schmidt level conversion circuit is used to realize different settings of the positive and reverse trigger thresholds of the external digital input signal, so that the interface circuit of the relay protection instrument can achieve the effect of Schmidt triggering, and effectively avoid the generation of false triggering actions; secondly, the external digital input signal is subjected to surge protection by the front-end surge protection circuit, filtered and attenuated by the first filtering circuit, and then unidirectionally conducted by the anti-reverse circuit, and then optocoupled by the optocoupler isolation circuit. After shaping, the external digital input signal is completed through the Schmidt level conversion circuit. The input signal is collected to output a Schmitt trigger signal, the purpose is to avoid the transient interference signal generated by the relay protection interface circuit under complex electromagnetic environment; further, by setting up a Schmitt level conversion circuit, the voltage input range is effectively expanded, the signal driving ability is improved, and the reliability of relay protection is guaranteed; in addition, based on the high reliability characteristics of the relay protection interface circuit, it is applied to the urban rail transit traction power supply system. Scientific relay protection configuration is conducive to reducing the fault phenomenon of circuit breakage or circuit breaker in the power supply line, ensuring the reliability of the line power equipment operation, and significantly improving the safety of the entire rail transit system operation.

[0046] Example 2

[0047] The surge protection circuit 1 is a surge protection resistor R5, one end of the surge protection resistor R5 is respectively connected to an input end of an external digital input signal and a first input end of the first filter circuit 2, and the other end of the surge protection resistor R5 is respectively connected to another input end of the external digital input signal and a second input end of the first filter circuit 2.

[0048] The first filter circuit 2 includes a first filter resistor R1, a second filter resistor R2, a third filter resistor R3, a fourth filter resistor R4 and a first filter capacitor C1, one end of the surge protection resistor R5 is connected to one end of the first filter resistor R1, the other end of the first filter resistor R1 is connected to the input end of the second filter resistor R2, the output end of the second filter resistor R2 is respectively connected to the first input end of the anti-reverse circuit 3 and one end of the first filter capacitor C1, the other end of the first filter capacitor C1 is respectively connected to the second input end of the anti-reverse circuit 3 and one end of the fourth filter resistor R4, the other end of the fourth filter resistor R4 is connected to one end of the third filter resistor R3, and the other end of the third filter resistor R3 is connected to the other end of the surge protection resistor R5.

[0049] The anti-reverse circuit 3 includes a first diode D1, an anti-reverse resistor R6 and a second diode D2, one end of the first filter capacitor C1 is respectively connected to the positive end of the first diode D1 and one end of the anti-reverse resistor R6, the negative end of the first diode D1 is connected to the first input end of the optocoupler isolation circuit 4, the other end of the anti-reverse resistor R6 is respectively connected to the second input end of the optocoupler isolation circuit 4 and the negative end of the second diode D2, and the positive end of the second diode D2 is respectively connected to one end of the fourth filter resistor R4.

[0050] The optocoupler isolation circuit 4 includes a primary circuit 41 and a secondary circuit 42, wherein a first input terminal of the primary circuit 41 is connected to the positive terminal of the first diode D1, a second input terminal of the primary circuit 41 is connected to the negative terminal of the second diode D2, and a collector and an emitter of the secondary circuit 42 are respectively connected to the Schmitt level conversion circuit 5.

[0051] The primary circuit 41 is a light emitting diode U1A, and the secondary circuit 42 is a phototransistor U2A.

[0052] The Schmitt level conversion circuit 5 includes a second filtering circuit 51, a Schmitt inverter 52 and a power supply VCC, wherein the power supply VCC is connected to the collector of the secondary circuit 42, the emitter of the secondary circuit 42 is connected to the input end of the second filtering circuit 51, the output end of the second filtering circuit 51 is connected to the negative terminal of the Schmitt inverter 52, and the positive terminal of the Schmitt inverter 52 is connected to the external microcontroller.

[0053] The second filtering circuit 51 includes a fifth filtering resistor R7 and a second filtering capacitor C2. One end of the fifth filtering resistor R7 is connected to one end of the second filtering capacitor C2 and then grounded. The other end of the fifth filtering resistor R7 is respectively connected to the emitter of the secondary circuit 42, the other end of the second filtering capacitor C2 and the positive terminal of the Schmidt inverter 52.

[0054] Example 3

[0055] This embodiment further verifies the effect of the relay protection device interface circuit proposed in the above embodiment.

[0056] The first is the realization of the Schmitt trigger effect; in this embodiment, the surge protection circuit 1, the first filter circuit 2, the anti-reverse circuit 3, the optocoupler isolation circuit 4 and the Schmitt level conversion circuit 5 together constitute the relay protection instrument interface circuit, the external digital input signal is input through one input terminal XDin1_P of the external digital input signal, and the negative electrode is input through another input terminal XDin1_N of the external digital input signal, the surge protection resistor R5 is used for surge protection, the first filter circuit 2 includes a first filter resistor R1, a second filter resistor R2, a third filter resistor R3, a fourth filter resistor R4 and a first filter capacitor C1, forming a first-order RC filter, and the complete A low-pass filtering effect is achieved to remove high-frequency noise, making the output signal more stable. The cut-off frequency f of the first filtering circuit 2 is 1 / (2πRC) = 3.6KHz. Based on the unidirectional conduction characteristics of the first diode D1 and the second diode D2, and the high reverse impedance of the anti-reverse resistor R6, the reverse voltage and current can be prevented from damaging the optical coupling isolation circuit 4, which directionally constitutes the sampling circuit of the digital signal of the relay protection interface circuit; the rear-end Schmidt level conversion circuit adds a Schmidt inverter. According to the characteristics of the Schmidt inverter, the flipping level of the relay protection interface circuit can be controlled, and the signal driving capability can be improved at the same time, without the need to add an additional BUFFER drive.

[0057] The specific working principle is as follows: the forward voltage drop of the optocoupler isolation circuit 4 is about 1.2V, and the forward voltage drop of the diode in the anti-reverse circuit 3 is about 0.7V. Assuming that the voltage of the external digital input signal is Vin, the total current passing through the optocoupler isolation circuit 4 is: Ic = [Vin-(1.2+0.7)] / (R1+R2+R3+R4), the optocoupler current transfer ratio (IC / IF) of the optocoupler isolation circuit 4 is CTR. When the optocoupler isolation circuit 4 is effectively turned on, the input voltage through the Schmidt inverter is V = R7*Ic / CTR.

[0058] The primary circuit 41 and the secondary circuit 42 in the optocoupler isolation circuit 4 form an isolation optocoupler. In this embodiment, the isolation optocoupler uses PS2501, whose isolation voltage is 5000Vrms, exceeding the 3750Vrms requirement in GB / T 42148. The typical switching speed is 5us. The current transfer ratio (IC / IF) is typically 1:3. The DC relay protection device GB / T 42148 requires a DI resolution of 1ms. The sampling rate of a relay protection device interface circuit proposed in this embodiment is less than 100us, which can fully meet the requirements of isolation sampling and response speed of digital input circuits.

[0059] The model of the Schmitt inverter selected in this embodiment is SN74LVC14. The high level of the Schmitt trigger of SN74LVC14 is 0.7×VCC (the power supply VCC of the Schmitt inverter is 5V); the low level is 0.3×VCC. The input threshold level of SN74LVC14 is set by adjusting the value of the fifth filter resistor R7. Thus, the rising flip level of the digital input signal is about 15VDC, and the falling flip level of the digital input signal is about 12VDC.

[0060] It is also necessary to specially state that in the process of Schmitt triggering the digital conversion signal, the Schmitt triggering process includes: first setting the rising edge detection voltage and the falling edge detection voltage of the Schmitt level conversion circuit 5; then when the voltage of the digital conversion signal rises, it is judged whether the rising voltage exceeds the rising edge detection voltage, if so, the output of the high-level Schmitt trigger signal is valid; if not, the output of the high-level Schmitt trigger signal is invalid; then when the voltage of the digital conversion signal drops, it is judged whether the falling voltage exceeds the falling edge detection voltage, if so, the output of the low-level Schmitt trigger signal is valid; if not, the output of the low-level Schmitt trigger signal is invalid. In the digital quantity input signal of the interface circuit of the relay protection instrument, the rated high-level signal is 24VDC and the rated low-level signal is 0VDC. This embodiment is designed by circuit to meet the rising edge detection voltage of 15VDC and the falling edge detection voltage of 12VDC. That is, in the process of the input signal voltage rising, when the voltage stably exceeds 15VDC and is maintained, the high-level input signal is valid. During the voltage drop of the input signal, when the voltage is stable and less than 12VDC and remains less than 12VDC, the low-level input signal is valid. The second is a wide voltage range, high-sensitivity integration circuit; the optocoupler isolation circuit 4 uses the PS2501 diode terminal, and the typical operating current of the PS2501 diode terminal is I F =10mA as shown in Table 1;

[0061] Table 1 Interface rated drive range

[0062]

[0063] The maximum current is I F =80mA as shown in Table 2.

[0064] Table 2 Interface maximum drive current table

[0065]

[0066] When the level of the digital input signal rises, the typical value level corresponding to it is 15VDC. After passing through the RC network, the current value flowing through the PS2501 diode loop is about 0.7mA. After being amplified by the secondary circuit, the current is about 2.1mA. A voltage of about 4.2VDC is obtained on the sampling resistor R7=2K. Subtracting the voltage drop of the secondary circuit 0.7VDC is about 3.5VDC. The high level of SN74LVC14 flipping = 0.7×VCC = 3.5V, so it can be effectively flipped. The maximum current value of the PS2501 diode loop can be 80mA, that is, about: 0.08A×4×4.7K≈1500VDC. That is, the circuit theory is that the instantaneous pulse can reach 1KV.

[0067] The third is high impedance input and good electromagnetic compatibility. After the external digital signal is input, it can effectively resist the transient overvoltage shock from the power grid or external environment through the front-end surge protection, ensuring the safe and stable operation of the subsequent circuit. Then it is attenuated by the RC network. The function of this RC network is to smooth the signal and reduce the interference of high-frequency noise, while ensuring that the amplitude of the signal is suitable for the processing range of the subsequent circuit. Then the diode is directional to form a digital sampling circuit, which not only realizes the unidirectional transmission of the signal, but also further enhances the anti-interference ability of the circuit, forming the basis of the digital sampling circuit. After optical coupling isolation and shaping, the digital input acquisition is completed for stable reading by the core digital signal processor DSP of the relay protection instrument interface circuit.

[0068] In the simulated electromagnetic field environment of the capacitor compatibility test, it can achieve stable and error-free triggering. Therefore, the interface circuit design of the relay protection instrument proposed in this embodiment also adopts an isolated hardware integration circuit design, which has good electromagnetic compatibility and is not easily interfered by external transient signals; in addition, the rated rising jump trigger high level range of the circuit design is 15-24VDC, and the falling jump low level range is 0-12VDC; the signal drive current is 10mA, the circuit can work in the sampling level range of 0-36VDC, and the drive current is 5mA.

[0069] Since the front-end RC network cutoff frequency is about 3.6KHz, it has a large attenuation for pulses or surges greater than 3K. That is, it has little impact on the circuit board during fast transients or surges, and can meet the fast transient or surge test requirements; see Table 3, Table 4 and Figure 3 The cut-off frequency of the input of the relay protection interface circuit is approximately 3602 Hz.

[0070] Table 3 Communication port fast transient resistance requirements

[0071]

[0072] Table 4 Communication port surge protection requirements

[0073]

[0074] In this embodiment, the relay protection based on the relay protection instrument interface circuit has the characteristics of high reliability and is applied to the urban rail transit traction power supply system. Scientific relay protection configuration is conducive to reducing the fault phenomenon of circuit breakage or circuit breaker in the power supply line, ensuring the reliability of the operation of the line power equipment, and significantly improving the safety of the operation of the entire rail transit system.

[0075] Example 3

[0076] See also Figure 4 This embodiment proposes a signal driving method using the relay protection device interface circuit as described in the above embodiment, comprising the following steps:

[0077] S1. The surge protection circuit 1 receives an external digital input signal, performs surge protection on the external digital input signal, and outputs a surge protection digital signal;

[0078] S2. The first filtering circuit 2 receives the surge protection signal, filters the surge protection signal, and outputs a filtered digital signal;

[0079] S3. The anti-reverse circuit 3 receives the filtered signal, conducts unidirectional conduction on the filtered signal, and outputs an anti-reverse digital signal;

[0080] S4. The optical coupler isolation circuit 4 receives the anti-reverse digital signal, performs photoelectric conversion on the anti-reverse digital signal, and outputs a digital conversion signal;

[0081] S5. The Schmitt level conversion circuit 5 receives the digital conversion signal, performs Schmitt triggering on the digital conversion signal, and outputs a Schmitt triggering signal.

[0082] In S5, see Figure 5 , performing Schmitt triggering on the digital conversion signal comprises:

[0083] S51. Set the rising edge detection voltage and falling edge detection voltage of the Schmitt level conversion circuit 5;

[0084] S52. When the voltage of the digital conversion signal rises, determine whether the rising voltage exceeds the rising edge detection voltage. If so, the output high-level Schmitt trigger signal is valid; if not, the output high-level Schmitt trigger signal is invalid;

[0085] S53. When the voltage of the digital conversion signal drops, determine whether the dropped voltage exceeds the falling edge detection voltage. If so, the output low-level Schmitt trigger signal is valid; if not, the output low-level Schmitt trigger signal is invalid.

[0086] In this embodiment, firstly, the hardware circuit design of the interface composed of a surge protection circuit, a first filtering circuit, an anti-reverse circuit, an optocoupler isolation circuit and a Schmidt level conversion circuit is used to realize different settings of the positive and reverse trigger thresholds of the external digital input signal, so that the interface circuit of the relay protection instrument can achieve the effect of Schmidt triggering, and effectively avoid the generation of false triggering actions; secondly, the external digital input signal is subjected to surge protection by the front-end surge protection circuit, filtered and attenuated by the first filtering circuit, and then unidirectionally conducted by the anti-reverse circuit, and then optocoupled by the optocoupler isolation circuit. After shaping, the external digital input signal is completed through the Schmidt level conversion circuit. The input signal is collected to output a Schmitt trigger signal, the purpose is to avoid the transient interference signal generated by the relay protection interface circuit under complex electromagnetic environment; further, by setting up a Schmitt level conversion circuit, the voltage input range is effectively expanded, the signal driving ability is improved, and the reliability of relay protection is guaranteed; in addition, based on the high reliability characteristics of the relay protection interface circuit, it is applied to the urban rail transit traction power supply system. Scientific relay protection configuration is conducive to reducing the fault phenomenon of circuit breakage or circuit breaker in the power supply line, ensuring the reliability of the line power equipment operation, and significantly improving the safety of the entire rail transit system operation.

[0087] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A relay protection device interface circuit, characterized in that: It comprises a surge protection circuit (1) for receiving an external digital quantity input signal, a first filtering circuit (2), an anti-reverse circuit (3), an optical coupling isolation circuit (4), and a Schmitt level conversion circuit (5) for outputting a Schmitt trigger signal; The surge protection circuit (1) is respectively connected to the input end of the first filter circuit (2), the output end of the first filter circuit (2) is connected to the input end of the anti-reverse circuit (3), the output end of the anti-reverse circuit (3) is connected to the input end of the optocoupler isolation circuit (4), and the output end of the optocoupler isolation circuit (4) is connected to the Schmidt level conversion circuit (5).

2. The relay protection device interface circuit according to claim 1, characterized in that: The surge protection circuit (1) is a surge protection resistor R5, one end of the surge protection resistor R5 is respectively connected to an input end of an external digital input signal and a first input end of a first filter circuit (2), and the other end of the surge protection resistor R5 is respectively connected to another input end of the external digital input signal and a second input end of the first filter circuit (2).

3. The relay protection device interface circuit according to claim 2, characterized in that: The first filter circuit (2) comprises a first filter resistor R1, a second filter resistor R2, a third filter resistor R3, a fourth filter resistor R4 and a first filter capacitor C1; one end of the surge protection resistor R5 is connected to one end of the first filter resistor R1; the other end of the first filter resistor R1 is connected to the input end of the second filter resistor R2; the output end of the second filter resistor R2 is respectively connected to the first input end of the anti-reverse circuit (3) and one end of the first filter capacitor C1; the other end of the first filter capacitor C1 is respectively connected to the second input end of the anti-reverse circuit (3) and one end of the fourth filter resistor R4; the other end of the fourth filter resistor R4 is connected to one end of the third filter resistor R3; and the other end of the third filter resistor R3 is connected to the other end of the surge protection resistor R5.

4. The relay protection device interface circuit according to claim 3, characterized in that: The anti-reverse circuit (3) comprises a first diode D1, an anti-reverse resistor R6 and a second diode D2; one end of the first filter capacitor C1 is respectively connected to the positive terminal of the first diode D1 and one end of the anti-reverse resistor R6; the negative terminal of the first diode D1 is connected to the first input terminal of the optocoupler isolation circuit (4); the other end of the anti-reverse resistor R6 is respectively connected to the second input terminal of the optocoupler isolation circuit (4) and the negative terminal of the second diode D2; and the positive terminal of the second diode D2 is respectively connected to one end of the fourth filter resistor R4.

5. The relay protection device interface circuit according to claim 4, characterized in that: The optical coupling isolation circuit (4) comprises a primary circuit (41) and a secondary circuit (42), wherein a first input end of the primary circuit (41) is connected to the positive terminal of the first diode D1, a second input end of the primary circuit (41) is connected to the negative terminal of the second diode D2, and a collector and an emitter of the secondary circuit (42) are respectively connected to the Schmitt level conversion circuit (5).

6. The relay protection device interface circuit according to claim 5, characterized in that: The primary circuit (41) is a light emitting diode U1A, and the secondary circuit (42) is a phototransistor U2A.

7. The relay protection device interface circuit according to claim 5, characterized in that: The Schmitt level conversion circuit (5) comprises a second filter circuit (51), a Schmitt inverter (52) and a power supply VCC, wherein the power supply VCC is connected to the collector of the secondary circuit (42), the emitter of the secondary circuit (42) is connected to the input end of the second filter circuit (51), the output end of the second filter circuit (51) is connected to the negative terminal of the Schmitt inverter (52), and the positive terminal of the Schmitt inverter (52) is connected to an external microcontroller.

8. The relay protection device interface circuit according to claim 7, characterized in that: The second filter circuit (51) comprises a fifth filter resistor R7 and a second filter capacitor C2, one end of the fifth filter resistor R7 is connected to one end of the second filter capacitor C2 and then grounded, and the other end of the fifth filter resistor R7 is respectively connected to the emitter of the secondary circuit (42), the other end of the second filter capacitor C2 and the positive terminal of the Schmidt inverter (52).

9. A signal driving method using the relay protection device interface circuit according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. The surge protection circuit (1) receives an external digital input signal, performs surge protection on the external digital input signal, and outputs a surge protection digital signal; S2. The first filtering circuit (2) receives the surge protection signal, filters the surge protection signal, and outputs a filtered digital signal; S3. The anti-reverse circuit (3) receives the filtered signal, conducts unidirectional conduction on the filtered signal, and outputs an anti-reverse digital signal; S4. The optical coupling isolation circuit (4) receives the anti-reverse digital signal, performs photoelectric conversion on the anti-reverse digital signal, and outputs a digital conversion signal; S5. The Schmitt level conversion circuit (5) receives the digital conversion signal, performs Schmitt triggering on the digital conversion signal, and outputs a Schmitt triggering signal.

10. The signal driving method according to claim 9, characterized in that: The performing Schmitt triggering on the digital conversion signal comprises: S51. Setting the rising edge detection voltage and the falling edge detection voltage of the Schmitt level conversion circuit (5); S52. When the voltage of the digital conversion signal rises, determine whether the rising voltage exceeds the rising edge detection voltage. If so, the output high-level Schmitt trigger signal is valid; if not, the output high-level Schmitt trigger signal is invalid; S53. When the voltage of the digital conversion signal drops, determine whether the dropped voltage exceeds the falling edge detection voltage. If so, the output low-level Schmitt trigger signal is valid; if not, the output low-level Schmitt trigger signal is invalid.

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