A current detection circuit in the bidirectional current conversion process of urban subway rail transit

Abstract

The invention discloses a current detection circuit for a bidirectional current conversion process in urban subway rail transit, and relates to the field of current detection. The current detection circuit for a bidirectional current conversion process in urban subway rail transit comprises: a DC sampling control module, for detecting a DC voltage value of a train, and driving an AC sampling module to operate if the DC voltage value is greater than an upper threshold value or less than a lower threshold value; an AC sampling module, for detecting AC power in a power grid, and providing a working signal to a zero-crossing closing module and a zero-crossing disconnecting module when the AC power passes through a zero point. Compared with the prior art, the invention has the following beneficial effects: the invention controls the instant at which an AC / DC converter is turned on or off to be when the AC power passes through a zero point through the cooperation of the DC sampling control module, the AC sampling module, the zero-crossing closing module, and the zero-crossing disconnecting module, so that the instant current of the AC / DC converter being turned on or off is small, thereby increasing the service life of the bidirectional current conversion device.

Description

Technical Field

[0001] The present invention relates to the field of current detection, in particular to a current detection circuit in a bidirectional current conversion process of urban subway rail transit. Background Art

[0002] The bidirectional conversion process for urban subway rail transit is as follows: Traction state: When the train is determined to be in traction and the DC grid voltage is below the set value, the bidirectional converter immediately activates the traction voltage stabilization power supply function, converting AC power into DC traction power for train traction. Braking state: When the train is determined to be in braking and the DC grid voltage is above the set value, the bidirectional converter immediately activates the energy feedback function, feeding the braking energy back to the grid. During this process, the device uses high-power inverter feedback technology to quickly invert the DC energy generated by the train's regenerative braking and feed it back to the AC grid. This not only significantly improves energy utilization efficiency but also effectively reduces carbon emissions.

[0003] It should be noted that during the voltage conversion process, the current size based on the alternating current of the power grid changes. If the bidirectional converter is closed when the current is large, the instantaneous high current will be relatively large, which may easily damage the bidirectional converter and needs to be improved. Summary of the Invention

[0004] The object of the present invention is to provide a current detection circuit for a bidirectional current conversion process in urban subway rail transit, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A current detection circuit for a bidirectional current conversion process in urban subway rail transit, comprising:

[0007] The DC sampling control module is used to detect the DC voltage value of the train. If the DC voltage value is greater than the upper threshold or less than the lower threshold, the AC sampling module is driven to work;

[0008] The AC sampling module is used to detect the AC power of the power grid and provide working signals for the zero-crossing closing module and the zero-crossing disconnecting module when the AC power passes through zero.

[0009] The delay driving module is used to provide a trigger signal to the zero-crossing closing module after a delay after the AC sampling module starts working;

[0010] The zero-crossing closing module is used to receive a trigger signal and then a working signal to start working. After a delay in starting working, it controls the switch of the bidirectional converter to close. The delay time is one cycle time of the AC mains power.

[0011] The zero-crossing disconnection module is used to receive a working signal when the DC voltage value of the train is between the upper and lower thresholds. After a delay, it drives the DC sampling control module to delay the control of the bidirectional converter switch to disconnect. The delay time is one cycle time of the AC mains power.

[0012] The first output end of the DC sampling control module is connected to the input end of the AC sampling module, the second output end of the DC sampling control module is connected to the first input end of the zero-crossing disconnection module, the first output end of the AC sampling module is connected to the input end of the delay driving module, the second output end of the AC sampling module is connected to the second input end of the zero-crossing closing module and the second input end of the zero-crossing disconnection module, the output end of the delay driving module is connected to the first input end of the zero-crossing closing module, and the output end of the zero-crossing disconnection module is connected to the input end of the DC sampling control module.

[0013] As a further solution of the present invention: the DC sampling control module includes:

[0014] The DC sampling unit is used to sample the DC voltage value of the train, obtain the sampled voltage, and output it to the lower limit detection control unit and the upper limit detection control unit;

[0015] A lower limit detection control unit is used to compare the sampled voltage with the first reference voltage. When the sampled voltage is lower than the first reference voltage (corresponding to the lower limit threshold), the first switch, the second switch, and the third switch are closed to drive the AC sampling module to operate.

[0016] An upper limit detection control unit is used to compare the sampling voltage with the second reference voltage. When the sampling voltage is greater than the second reference voltage (corresponding to the upper limit threshold), the fourth switch, the fifth switch, and the sixth switch are closed to drive the AC sampling module to work;

[0017] The output end of the DC sampling unit is connected to the first input end of the lower limit detection control unit and the first input end of the upper limit detection control unit, the first output end of the lower limit detection control unit is connected to the input end of the AC sampling module (the first relay controls the second switch and the third switch), the second output end of the lower limit detection control unit is connected to the first input end (common point A1 and common point A2) of the zero-crossing disconnection module, the first output end of the upper limit detection control unit is connected to the input end of the AC sampling module (the fourth relay controls the fifth switch and the sixth switch), the second output end of the upper limit detection control unit is connected to the first input end (common point B1 and common point B2) of the zero-crossing disconnection module, and the output end of the zero-crossing disconnection module is connected to the second input end (common point A3) of the lower limit detection control unit and the second input end (common point B3) of the upper limit detection control unit.

[0018] As a further solution of the present invention: the DC sampling unit includes a seventh resistor and an eighth resistor, one end of the seventh resistor is connected to the DC voltage value of the train, the other end of the seventh resistor is connected to one end of the eighth resistor, the first input end of the lower limit detection control unit, and the first input end of the upper limit detection control unit, and the other end of the eighth resistor is grounded.

[0019] As a further embodiment of the present invention, the lower limit detection control unit includes a fifth amplifier, a sixth amplifier, a fourth MOS transistor, a fifth MOS transistor, and a first relay. The non-inverting terminal of the fifth amplifier is connected to the first reference voltage, the inverting terminal of the fifth amplifier is connected to the non-inverting terminal of the sixth amplifier and the output terminal of the DC sampling unit, the inverting terminal of the sixth amplifier is connected to the output terminal of the fifth amplifier and one end of a ninth resistor, the output terminal of the sixth amplifier is connected to a common point A1, the other end of the ninth resistor is connected to a control electrode of a second thyristor, the anode of the second thyristor is connected to the S electrode of the fourth MOS transistor, the D electrode of the fourth MOS transistor is connected to a power supply voltage and one end of a tenth resistor, the other end of the tenth resistor is connected to the G electrode of the fourth MOS transistor and the D electrode of the fifth MOS transistor, the S electrode of the fifth MOS transistor is grounded, the G electrode of the fifth MOS transistor is connected to a common point A3, the cathode of the second thyristor is connected to the common point A2 and one end of an eleventh resistor, the other end of the eleventh resistor is connected to the cathode of an eighth diode and one end of the first relay, the other end of the first relay is grounded, and the anode of the eighth diode is grounded.

[0020] As a further solution of the present invention: the AC sampling module includes an AC optocoupler and a second amplifier, the first end of the AC optocoupler is connected to the twenty-first resistor, the second end of the AC optocoupler is connected to the twenty-second resistor, the third end of the AC optocoupler is connected to one end of the twenty-third resistor and the non-inverting end of the second amplifier, the other end of the twenty-third resistor is connected to the power supply voltage, the fourth end of the AC optocoupler is grounded, the inverting end of the second amplifier is connected to the third reference voltage, the output end of the second amplifier is connected to the second input end of the zero-crossing closing module and the second input end of the zero-crossing disconnecting module, the other end of the twenty-first resistor is connected to one end of the second switch and one end of the fifth switch, the other end of the second switch is connected to the other end of the fifth switch and the live wire, the other end of the twenty-second resistor is connected to one end of the third switch, one end of the sixth switch, and the input end of the delay driving module, and the other end of the third switch is connected to the other end of the sixth switch and the neutral wire.

[0021] As a further solution of the present invention: the delay driving module includes a first diode, a first capacitor, a first resistor, a second diode, a second capacitor, and a third diode. The positive pole of the first diode is connected to the first output end of the AC sampling module, the negative pole of the first diode is connected to one end of the first capacitor and one end of the first resistor, the other end of the first capacitor is grounded, the other end of the first resistor is connected to the negative pole of the second diode, one end of the second capacitor, and the positive pole of the third diode, the positive pole of the second diode is grounded, the other end of the second capacitor is grounded, and the negative pole of the third diode is connected to the first input end of the zero-crossing closing module.

[0022] As a further solution of the present invention: the zero-crossing closing module includes a first MOS tube, a first thyristor, and a seventh relay. The D pole of the first MOS tube is connected to the power supply voltage, the G pole of the first MOS tube is connected to the output end of the delay driving module, the S pole of the first MOS tube is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to the positive pole of the first thyristor, the control pole of the first thyristor is connected to the second output end of the AC sampling module through the second resistor, the negative pole of the first thyristor is connected to one end of the first potentiometer, the other end of the first potentiometer is connected to one end of the third capacitor and the negative pole of the fourth diode, the other end of the third capacitor is grounded, the positive pole of the fourth diode is connected to one end of the third resistor, the other end of the third resistor is connected to one end of the seventh relay and the negative pole of the fifth diode, the other end of the seventh relay is grounded, and the positive pole of the fifth diode is grounded.

[0023] As a further solution of the present invention: the zero-crossing disconnection module includes two zero-crossing disconnection units, the zero-crossing disconnection unit includes a third AND gate, a second MOS tube, a fourth thyristor, the D pole of the second MOS tube is connected to the second output end of the AC sampling module, the G pole of the second MOS tube is connected to the output end of the third AND gate, the two input ends of the third AND gate are respectively connected to the common point A1 and the common point A2, the S pole of the second MOS tube is connected to the control pole of the fourth thyristor, the positive pole of the fourth thyristor is connected to the power supply voltage, the negative pole of the fourth thyristor is connected to one end of the second potentiometer through a fifth resistor, the other end of the second potentiometer is connected to the negative pole of the sixth diode and one end of the fourth capacitor, the other end of the fourth capacitor is grounded, and the positive pole of the sixth diode is connected to the common point A3.

[0024] Compared with the prior art, the beneficial effect of the present invention is that: the present invention controls the instant when the AC / DC converter is turned on or off to be when the AC power crosses the zero point through the cooperation of the DC sampling control module, the AC sampling module, the zero-crossing closing module and the zero-crossing disconnecting module, so that the instant current when the AC / DC converter is turned on or off is small, thereby increasing the service life of the bidirectional converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1The schematic diagram of a current detection circuit in the bidirectional current conversion process of urban subway rail transit.

[0026] Figure 2 This is the circuit diagram of the DC sampling control module.

[0027] Figure 3 This is the circuit diagram of the AC sampling module, delay drive module, zero-crossing closing module and zero-crossing disconnecting module.

[0028] Figure 4 Schematic diagram of a bidirectional converter. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] See also Figure 1 , a current detection circuit in a bidirectional current conversion process of urban subway rail transit, comprising:

[0031] The DC sampling control module 1 is used to detect the DC voltage value VDD of the train. If the DC voltage value is greater than the upper threshold or less than the lower threshold, the AC sampling module 2 is driven to work;

[0032] The AC sampling module 2 is used to detect the AC power of the power grid (live line L, neutral line N), and provides a working signal to the zero-crossing closing module 4 and the zero-crossing disconnecting module 5 when the AC power passes through zero.

[0033] The delay driving module 3 is used to provide a trigger signal to the zero-crossing closing module 4 after a delay after the AC sampling module 2 starts working;

[0034] The zero-crossing closing module 4 is used to receive a trigger signal and then receive a working signal to start working. After a delay in starting working, it controls the switch of the bidirectional converter to close. The delay time is one cycle time of the AC mains power.

[0035] The zero-crossing disconnection module 5 is used to receive a working signal when the DC voltage value VDD of the train is between the upper threshold and the lower threshold, and after a delay, it drives the DC sampling control module 1 to delay the control of the bidirectional converter switch to disconnect. The delay time is one cycle time of the AC mains power.

[0036] The first output end of the DC sampling control module 1 is connected to the input end of the AC sampling module 2, the second output end of the DC sampling control module 1 is connected to the first input end of the zero-crossing disconnection module 5, the first output end of the AC sampling module 2 is connected to the input end of the delay driving module 3, the second output end of the AC sampling module 2 is connected to the second input end of the zero-crossing closure module 4 and the second input end of the zero-crossing disconnection module 5, the output end of the delay driving module 3 is connected to the first input end of the zero-crossing closure module 4, and the output end of the zero-crossing disconnection module 5 is connected to the input end of the DC sampling control module 1.

[0037] In this example: See Figure 2 , the DC sampling control module 1 includes:

[0038] The DC sampling unit is used to sample the DC voltage value VDD of the train, obtain the sampled voltage, and output it to the lower limit detection control unit and the upper limit detection control unit;

[0039] The lower limit detection control unit is used to compare the sampled voltage with the first reference voltage VREF1. When the sampled voltage is lower than the first reference voltage VREF1 (corresponding to the lower limit threshold), the first switch S1, the second switch S2, and the third switch S3 are controlled to close, thereby driving the AC sampling module 2 to operate.

[0040] The upper limit detection control unit is used to compare the sampling voltage and the second reference voltage VREF2. When the sampling voltage is greater than the second reference voltage VREF2 (corresponding to the upper limit threshold), the fourth switch S4, the fifth switch S5, and the sixth switch S6 are controlled to be closed, thereby driving the AC sampling module 2 to work;

[0041] The output end of the DC sampling unit is connected to the first input end of the lower limit detection control unit and the first input end of the upper limit detection control unit. The first output end of the lower limit detection control unit is connected to the input end of the AC sampling module 2 (the first relay J1 controls the second switch S2 and the third switch S3). The second output end of the lower limit detection control unit is connected to the first input end (common point A1 and common point A2) of the zero-crossing disconnect module 5. The first output end of the upper limit detection control unit is connected to the input end of the AC sampling module 2 (the fourth relay controls the fifth switch S5 and the sixth switch S6). The second output end of the upper limit detection control unit is connected to the first input end (common point B1 and common point B2) of the zero-crossing disconnect module 5. The output end of the zero-crossing disconnect module 5 is connected to the second input end (common point A3) of the lower limit detection control unit and the second input end (common point B3) of the upper limit detection control unit.

[0042] In this example: See Figure 2The DC sampling unit includes a seventh resistor R7 and an eighth resistor R8. One end of the seventh resistor R7 is connected to the DC voltage value VDD of the train, and the other end of the seventh resistor R7 is connected to one end of the eighth resistor R8, the first input end of the lower limit detection control unit, and the first input end of the upper limit detection control unit. The other end of the eighth resistor R8 is grounded.

[0043] The DC voltage value VDD of the train is divided by the seventh resistor R7 and the eighth resistor R8. The voltage on the eighth resistor R8 is the sampling voltage, which is output to the lower limit detection control unit and the upper limit detection control unit.

[0044] In another embodiment, the seventh resistor R7 may be replaced with a potentiometer to facilitate adjustment of the proportion of the eighth resistor R8 in the DC voltage value VDD of the train.

[0045] In this example: See Figure 2 and Figure 4 The lower limit detection control unit includes a fifth amplifier U5, a sixth amplifier U6, a fourth MOS transistor V4, a fifth MOS transistor V5, and a first relay J1. The non-inverting terminal of the fifth amplifier U5 is connected to the first reference voltage VREF1, the inverting terminal of the fifth amplifier U5 is connected to the non-inverting terminal of the sixth amplifier U6 and the output terminal of the DC sampling unit, the inverting terminal of the sixth amplifier U6 is connected to the output terminal of the fifth amplifier U5 and one end of the ninth resistor R9, the output terminal of the sixth amplifier U6 is connected to the common point A1, the other end of the ninth resistor R9 is connected to the control electrode of the second thyristor Z2, and the positive electrode of the second thyristor Z2 is connected to the first resistor R9. The S electrode of the fourth MOS transistor V4 and the D electrode of the fourth MOS transistor V4 are connected to the power supply voltage VCC and one end of the tenth resistor R10. The other end of the tenth resistor R10 is connected to the G electrode of the fourth MOS transistor V4 and the D electrode of the fifth MOS transistor V5. The S electrode of the fifth MOS transistor V5 is grounded. The G electrode of the fifth MOS transistor V5 is connected to the common point A3. The cathode of the second thyristor Z2 is connected to the common point A2 and one end of the eleventh resistor R11. The other end of the eleventh resistor R11 is connected to the cathode of the eighth diode D8 and one end of the first relay J1. The other end of the first relay J1 is grounded. The anode of the eighth diode D8 is grounded.

[0046] When the train's DC voltage VDD is less than the lower threshold, the sampling voltage is too low, causing the first reference voltage VREF1 to be greater than the sampling voltage. The fifth amplifier U5 outputs a high level, driving the second thyristor Z2 to conduct. The power supply voltage VCC drives the first relay J1 through the fourth MOS tube V4, the second thyristor Z2, and the eleventh resistor R11 to operate, controlling the first switch S1, the second switch S2, and the third switch S3 to close. The AC sampling module 2 operates.

[0047] The structure of the upper limit detection control unit is similar to that of the lower limit detection control unit, such as Figure 2As shown, when the DC voltage value VDD of the train is greater than the upper threshold, the sampling voltage is too large, so that the second reference voltage VREF2 is less than the sampling voltage, and the seventh amplifier U7 outputs a high level, driving the third thyristor Z3 to turn on. The power supply voltage VCC drives the fourth relay J4 to work through the sixth MOS tube V6, the third thyristor Z3, and the thirteenth resistor R13, controlling the fourth switch S4, the fifth switch S5, and the sixth switch S6 to be closed; the AC sampling module 2 is working.

[0048] In another embodiment, the eleventh resistor R11 may be omitted. The eleventh resistor R11 is provided to avoid mismatch between the power supply voltage VCC and the voltage of the first relay J1 , thereby reducing circuit current and avoiding damage to components.

[0049] In this example: See Figure 3 The AC sampling module 2 includes an AC optocoupler U1 and a second amplifier U2. A first end of the AC optocoupler U1 is connected to a twenty-first resistor R21, a second end of the AC optocoupler U1 is connected to a twenty-second resistor R22, a third end of the AC optocoupler U1 is connected to one end of a twenty-third resistor R23 and a non-inverting end of the second amplifier U2, the other end of the twenty-third resistor R23 is connected to a power supply voltage VCC, a fourth end of the AC optocoupler U1 is grounded, an inverting end of the second amplifier U2 is connected to a third reference voltage VREF3, an output end of the second amplifier U2 is connected to a second input end of the zero-crossing closing module 4 and a second input end of the zero-crossing disconnecting module 5, the other end of the twenty-first resistor R21 is connected to one end of the second switch S2 and one end of the fifth switch S5, the other end of the second switch S2 is connected to the other end of the fifth switch S5 and the live wire L, the other end of the twenty-second resistor R22 is connected to one end of the third switch S3, one end of the sixth switch S6, and the input end of the delay driving module 3, and the other end of the third switch S3 is connected to the other end of the sixth switch S6 and the neutral wire N.

[0050] After the second switch S2 and the third switch S3 are closed (or the fifth switch S5 and the sixth switch S6 are closed), the voltage signals of the live wire L and the neutral wire N are input to the AC optocoupler U1. Two photosensitive diodes are provided inside the AC optocoupler U1, and the two photosensitive diodes are in opposite directions, so that when the input voltage is positive or negative, as long as the voltage is sufficient, there is always one photosensitive diode that lights up, so that the non-inverting end of the second amplifier U2 is low level. Only when the AC mains passes through zero point (or is close to zero point), it is not enough to turn on the photosensitive diode inside the AC optocoupler U1. At this time, the non-inverting end of the second amplifier U2 is high level, and the second amplifier U2 outputs a high level signal to indicate the zero crossing point.

[0051] In another embodiment, the second amplifier U2 can be replaced with a transistor, which also outputs a voltage signal to the zero-crossing closing module 4 and the zero-crossing disconnecting module 5 when receiving a high level.

[0052] In this example: See Figure 3 The delay driving module 3 includes a first diode D1, a first capacitor C1, a first resistor R1, a second diode D2, a second capacitor C2, and a third diode D3. The positive electrode of the first diode D1 is connected to the first output end of the AC sampling module 2, the negative electrode of the first diode D1 is connected to one end of the first capacitor C1 and one end of the first resistor R1, the other end of the first capacitor C1 is grounded, the other end of the first resistor R1 is connected to the negative electrode of the second diode D2, one end of the second capacitor C2, and the positive electrode of the third diode D3, the positive electrode of the second diode D2 is grounded, the other end of the second capacitor C2 is grounded, and the negative electrode of the third diode D3 is connected to the first input end of the zero-crossing closing module 4.

[0053] After the second switch S2 and the third switch S3 are closed (or the fifth switch S5 and the sixth switch S6 are closed), the voltage passes through the first diode D1 to charge the first capacitor C1. The voltage on the first capacitor C1 passes through the first resistor R1 and is clamped by the second diode D2 (Zener diode), providing a stable voltage for the zero-crossing closing module 4.

[0054] In another embodiment, the third diode D3 can be omitted. The third diode D3 is a light emitting diode and serves as an indicator.

[0055] In this example: See Figure 3 and Figure 4 The zero-crossing closing module 4 includes a first MOS transistor V1, a first thyristor Z1, and a seventh relay J7. The D electrode of the first MOS transistor V1 is connected to the power supply voltage VCC, the G electrode of the first MOS transistor V1 is connected to the output end of the delay driving module 3, the S electrode of the first MOS transistor V1 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is connected to the positive electrode of the first thyristor Z1, the control electrode of the first thyristor Z1 is connected to the second output end of the AC sampling module 2 through the second resistor R2, the negative electrode of the first thyristor Z1 is connected to one end of the first potentiometer RP1, the other end of the first potentiometer RP1 is connected to one end of the third capacitor C3 and the negative electrode of the fourth diode D4, the other end of the third capacitor C3 is grounded, the positive electrode of the fourth diode D4 is connected to one end of the third resistor R3, the other end of the third resistor R3 is connected to one end of the seventh relay J7 and the negative electrode of the fifth diode D5, the other end of the seventh relay J7 is grounded, and the positive electrode of the fifth diode D5 is grounded.

[0056] After the output voltage of the delay drive module 3 drives the first MOS tube V1 to turn on, when the AC power passes through zero, the second amplifier U2 outputs a high level, causing the first thyristor Z1 to turn on. The supply voltage VCC passes through the first MOS tube V1, the fourth resistor R4, the first thyristor Z1, the first potentiometer RP1, the third capacitor C3, the fourth diode D4, and the third resistor R3 to control the seventh relay J7 to operate, and control the seventh switch S7 and the eighth switch S8 to be closed. Previously, the first relay J1 (or the fourth relay) has operated to close the first switch S1 (or the fourth switch S4). The AC power is converted from the AC to DC circuit to generate a DC voltage, thereby increasing the DC voltage value VDD of the train (or the DC voltage value VDD of the train is converted from the DC to AC circuit to generate AC power, and the braking energy is fed back to the power grid); the bidirectional converter is a common technology and will not be described in detail here.

[0057] Because there is a delay in the relay controlling the switch to be closed or opened, a high level is output to the first thyristor Z1 when the AC mains voltage crosses zero. The time when the seventh relay J7 controls the seventh switch S7 and the eighth switch S8 to be closed is not the time when the AC mains voltage crosses zero. Therefore, the charging time of the third capacitor C3 is changed by adjusting the resistance value of the first potentiometer RP1. As a result, after the second amplifier U2 outputs a high level, the seventh switch S7 and the eighth switch S8 are closed after one AC mains voltage cycle (including the time it takes for the third capacitor C3 to charge and turn on the fourth diode D4, and the time it takes for the seventh relay J7 to control the switch).

[0058] In another embodiment, the supply voltage VCC may be converted from AC mains power, or may be obtained by converting the DC voltage value VDD of the train.

[0059] In this example: See Figure 2 、 Figure 3 and Figure 4 The zero-crossing disconnection module 5 includes two zero-crossing disconnection units, which include a third AND gate U3, a second MOS transistor V2, and a fourth thyristor Z4. The D pole of the second MOS transistor V2 is connected to the second output end of the AC sampling module 2, the G pole of the second MOS transistor V2 is connected to the output end of the third AND gate U3, and the two input ends of the third AND gate U3 are respectively connected to the common point A1 and the common point A2. The S pole of the second MOS transistor V2 is connected to the control pole of the fourth thyristor Z4, the positive pole of the fourth thyristor Z4 is connected to the power supply voltage VCC, the negative pole of the fourth thyristor Z4 is connected to one end of the second potentiometer RP2 through the fifth resistor R5, the other end of the second potentiometer RP2 is connected to the negative pole of the sixth diode D6 and one end of the fourth capacitor C4, the other end of the fourth capacitor C4 is grounded, and the positive pole of the sixth diode D6 is connected to the common point A3.

[0060] After the seventh relay J7 works, the DC voltage value VDD of the train gradually increases through the AC power supply to reach the lower limit threshold. At this time, the output of the fifth amplifier U5 changes from high level to low level, and the output terminal A1 of the sixth amplifier U6 changes from low level to high level. At the same time, based on the second thyristor Z2 being turned on, the common point A2 is also high level, so that the input terminals of the third AND gate U3 are all high level, the third AND gate U3 outputs high level, the second MOS tube V2 is turned on, and when the AC power passes through zero point, the second amplifier U2 outputs high level through the second MOS tube V2 to trigger the fourth thyristor Z4 to turn on, and the power supply is turned on. The voltage VCC passes through the fourth thyristor Z4, the fifth resistor R5, the second potentiometer RP2, the fourth capacitor C4, and the sixth diode D6, causing the common point A3 to become high. The fifth MOS transistor V5 is grounded, the fourth MOS transistor V4 is turned off, the first relay J1 stops working, the first switch S1, the second switch S2, and the third switch S3 are disconnected, and the bidirectional current converter stops working. Here, by adjusting the resistance value of the second potentiometer RP2, the time from the second amplifier U2 outputting a high level until the first switch S1 is disconnected is one AC mains cycle. The first switch S1 is disconnected when the AC mains next crosses zero.

[0061] Similarly, after the seventh relay J7 works, the DC voltage value VDD of the train is fed back to the AC power through discharge and gradually decreases to the upper limit threshold. The working principles at the common points B1, B2, and B3 are similar to those at the common points A1, A2, and A3, so that the second switch S2 is disconnected when the AC power passes through zero next time.

[0062] After the first switch S1 (or the second switch S2) is disconnected, the delayed driving module 3 has no voltage input. Based on the stored voltage of the first capacitor C1 and the second capacitor C2, the first MOS transistor V1 is disconnected after a delay. Similarly, based on the stored voltage of the third capacitor C3, the seventh relay J7 is disconnected after a delay. Therefore, after the first switch S1 (or the second switch S2) is disconnected, the seventh switch S7 and the eighth switch S8 are disconnected after a delay. The switches of the bidirectional converter device are disconnected twice, and the device returns to the initial state, waiting for the next operation of the bidirectional converter device.

[0063] In another embodiment, the third AND gate U3 can be replaced by two switch tubes connected in series.

[0064] The working principle of the present invention is as follows: the DC sampling control module 1 is used to detect the DC voltage value VDD of the train. If the DC voltage value is greater than the upper threshold or less than the lower threshold, the AC sampling module 2 is driven to work; the AC sampling module 2 is used to detect the AC power of the power grid, and when the AC power passes through zero, it provides a working signal to the zero-crossing closing module 4 and the zero-crossing disconnecting module 5; the delay driving module 3 is used to provide a trigger signal to the zero-crossing closing module 4 after a delay after the AC sampling module 2 works; the zero-crossing closing module 4 is used to receive the trigger signal, and then receive the working signal to start working, and control the bidirectional converter device switch to close after a delay after starting to work, and the delay time is one cycle time of the AC mains; the zero-crossing disconnecting module 5 is used to receive the working signal when the DC voltage value VDD of the train is between the upper threshold and the lower threshold, and drive the DC sampling control module 1 to control the bidirectional converter device switch to disconnect after a delay, and the delay time is one cycle time of the AC mains.

[0065] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive.

[0066] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A current detection circuit for bidirectional current conversion in urban subway rail transit, characterized in that: The current detection circuit in the bidirectional current conversion process of the urban subway rail transit includes: The DC sampling control module is used to detect the DC voltage value of the train. If the DC voltage value is greater than the upper threshold or less than the lower threshold, the AC sampling module is driven to work; The AC sampling module is used to detect the AC power of the power grid and provide working signals for the zero-crossing closing module and the zero-crossing disconnecting module when the AC power passes through zero. The delay driving module is used to provide a trigger signal to the zero-crossing closing module after a delay after the AC sampling module starts working; The zero-crossing closing module is used to receive a trigger signal and then a working signal to start working. After a delay in starting working, it controls the switch of the bidirectional converter to close. The delay time is one cycle time of the AC mains power. The zero-crossing disconnection module is used to receive a working signal when the DC voltage value of the train is between the upper and lower thresholds. After a delay, it drives the DC sampling control module to delay the control of the bidirectional converter switch to disconnect. The delay time is one cycle time of the AC mains power. The first output end of the DC sampling control module is connected to the input end of the AC sampling module, the second output end of the DC sampling control module is connected to the first input end of the zero-crossing disconnect module, the first output end of the AC sampling module is connected to the input end of the delay driving module, the second output end of the AC sampling module is connected to the second input end of the zero-crossing closing module and the second input end of the zero-crossing disconnect module, the output end of the delay driving module is connected to the first input end of the zero-crossing closing module, and the output end of the zero-crossing disconnect module is connected to the input end of the DC sampling control module; The DC sampling control module includes: The DC sampling unit is used to sample the DC voltage value of the train, obtain the sampled voltage, and output it to the lower limit detection control unit and the upper limit detection control unit; A lower limit detection control unit is used to compare the sampling voltage with the first reference voltage. When the sampling voltage is lower than the first reference voltage, the first switch, the second switch, and the third switch are controlled to close, thereby driving the AC sampling module to operate. An upper limit detection control unit is used to compare the sampling voltage with the second reference voltage. When the sampling voltage is greater than the second reference voltage, the fourth switch, the fifth switch, and the sixth switch are controlled to close, thereby driving the AC sampling module to operate. The output end of the DC sampling unit is connected to the first input end of the lower limit detection control unit and the first input end of the upper limit detection control unit, the first output end of the lower limit detection control unit is connected to the input end of the AC sampling module, the second output end of the lower limit detection control unit is connected to the first input end of the zero-crossing disconnection module, the first output end of the upper limit detection control unit is connected to the input end of the AC sampling module, the second output end of the upper limit detection control unit is connected to the first input end of the zero-crossing disconnection module, and the output end of the zero-crossing disconnection module is connected to the second input end of the lower limit detection control unit and the second input end of the upper limit detection control unit; The lower limit detection control unit includes a fifth amplifier, a sixth amplifier, a fourth MOS transistor, a fifth MOS transistor, and a first relay. The non-inverting end of the fifth amplifier is connected to the first reference voltage, the inverting end of the fifth amplifier is connected to the non-inverting end of the sixth amplifier and the output end of the DC sampling unit, the inverting end of the sixth amplifier is connected to the output end of the fifth amplifier and one end of the ninth resistor, the output end of the sixth amplifier is connected to a common point A1, the other end of the ninth resistor is connected to the control electrode of the second thyristor, the positive electrode of the second thyristor is connected to the S electrode of the fourth MOS transistor, the D electrode of the fourth MOS transistor is connected to the power supply voltage and one end of the tenth resistor, the other end of the tenth resistor is connected to the G electrode of the fourth MOS transistor and the D electrode of the fifth MOS transistor, the S electrode of the fifth MOS transistor is grounded, the G electrode of the fifth MOS transistor is connected to the common point A3, the negative electrode of the second thyristor is connected to the common point A2 and one end of the eleventh resistor, the other end of the eleventh resistor is connected to the negative electrode of the eighth diode and one end of the first relay, the other end of the first relay is grounded, and the positive electrode of the eighth diode is grounded; The AC sampling module includes an AC optocoupler and a second amplifier. The first end of the AC optocoupler is connected to the twenty-first resistor, the second end of the AC optocoupler is connected to the twenty-second resistor, the third end of the AC optocoupler is connected to one end of the twenty-third resistor and the non-inverting end of the second amplifier, the other end of the twenty-third resistor is connected to the power supply voltage, the fourth end of the AC optocoupler is grounded, the inverting end of the second amplifier is connected to the third reference voltage, the output end of the second amplifier is connected to the second input end of the zero-crossing closing module and the second input end of the zero-crossing disconnecting module, the other end of the twenty-first resistor is connected to one end of the second switch and one end of the fifth switch, the other end of the second switch is connected to the other end of the fifth switch and the live wire, the other end of the twenty-second resistor is connected to one end of the third switch, one end of the sixth switch, and the input end of the delay driving module, and the other end of the third switch is connected to the other end of the sixth switch and the neutral wire; The zero-crossing disconnection module includes two zero-crossing disconnection units, which include a third AND gate, a second MOS tube, a fourth thyristor, and the D pole of the second MOS tube is connected to the second output end of the AC sampling module, the G pole of the second MOS tube is connected to the output end of the third AND gate, the two input ends of the third AND gate are respectively connected to the common point A1 and the common point A2, the S pole of the second MOS tube is connected to the control pole of the fourth thyristor, the positive pole of the fourth thyristor is connected to the power supply voltage, the negative pole of the fourth thyristor is connected to one end of the second potentiometer through the fifth resistor, the other end of the second potentiometer is connected to the negative pole of the sixth diode and one end of the fourth capacitor, the other end of the fourth capacitor is grounded, and the positive pole of the sixth diode is connected to the common point A3.

2. The current detection circuit in the bidirectional current conversion process of urban subway rail transit according to claim 1 is characterized in that: The DC sampling unit includes a seventh resistor and an eighth resistor. One end of the seventh resistor is connected to the DC voltage value of the train, the other end of the seventh resistor is connected to one end of the eighth resistor, the first input end of the lower limit detection control unit, and the first input end of the upper limit detection control unit. The other end of the eighth resistor is grounded.

3. The current detection circuit in the bidirectional current conversion process of urban subway rail transit according to claim 1 is characterized in that: The delay driving module includes a first diode, a first capacitor, a first resistor, a second diode, a second capacitor, and a third diode. The positive pole of the first diode is connected to the first output end of the AC sampling module, the negative pole of the first diode is connected to one end of the first capacitor and one end of the first resistor, the other end of the first capacitor is grounded, the other end of the first resistor is connected to the negative pole of the second diode, one end of the second capacitor, and the positive pole of the third diode, the positive pole of the second diode is grounded, the other end of the second capacitor is grounded, and the negative pole of the third diode is connected to the first input end of the zero-crossing closing module.

4. The current detection circuit in the bidirectional current conversion process of urban subway rail transit according to claim 1, characterized in that: The zero-crossing closing module includes a first MOS tube, a first thyristor, and a seventh relay. The D pole of the first MOS tube is connected to the power supply voltage, the G pole of the first MOS tube is connected to the output end of the delay driving module, the S pole of the first MOS tube is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to the positive pole of the first thyristor, the control pole of the first thyristor is connected to the second output end of the AC sampling module through the second resistor, the negative pole of the first thyristor is connected to one end of the first potentiometer, the other end of the first potentiometer is connected to one end of the third capacitor and the negative pole of the fourth diode, the other end of the third capacitor is grounded, the positive pole of the fourth diode is connected to one end of the third resistor, the other end of the third resistor is connected to one end of the seventh relay and the negative pole of the fifth diode, the other end of the seventh relay is grounded, and the positive pole of the fifth diode is grounded.

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