A parallel conversion control method with a closed-loop selection of backup protection

Abstract

The present invention relates to parallel conversion control, and particularly to a parallel conversion control method with loop closing selection and backup protection removal. The parallel conversion control method with loop closing selection and backup protection removal can detect the loop closing current value in real time and execute a preset control logic according to the detection result. When the parallel conditions are met, the parallel conversion program is executed. If the loop closing current exceeds the limit, the executing switch is tripped; if the loop closing current is lower than the threshold value, the conversion is successfully completed. The loop closing current detection device uses a hardware circuit to implement the detection and judgment of the logic and outputs an action signal according to the comparison result of the current. In the parallel conversion control logic, on the one hand, as a signal receiving device, it receives the output signal from the controller, cooperates with the controller to execute the operation, improves the detection process, and enhances the market competitiveness; on the other hand, as an independent detection and execution mechanism, it adds a detection function without increasing the parallel conversion time, making the program run more efficiently and improving the reliability of the parallel conversion.

Description

Technical Field

[0001] The present invention relates to parallel conversion control, and particularly to a parallel conversion control method with loop closing selection and backup protection. Background Art

[0002] In order to meet the requirements of power supply reliability and ensure that electrical equipment will not be affected during short-term power outages of the power supply, parallel conversion measures for uninterrupted power supply are generally adopted at present. Operating practice shows that if a large loop closing current appears instantaneously when two power sources are connected in parallel and looped, when this loop closing current lasts for a long time, it may cause equipment damage, protection malfunction, and a decline in power supply reliability. Therefore, it is very necessary to add backup protection measures for loop closing selection during the parallel conversion process.

[0003] The existing parallel conversion technical routes for loop closing selection are roughly divided into two types. One technical measure is based on the existing parallel conversion logic. The incoming currents of the two incoming lines and the current flowing through the bus-tie switch are respectively collected, and the sampled current values at the three places are confirmed and compared through a default algorithm, and judged by the program. Once the calculated current exceeds the set threshold, the last executed circuit breaker is defaultly tripped. Different from the loop closing selection of any switch when the loop closing current is too large during the parallel conversion process mainly described in the present invention, the former parallel conversion method for loop closing selection has problems such as long detection time and relatively high requirements for hardware, and there is no logic for arbitrarily selecting and tripping, and the success rate of loop closing selection is relatively low.

[0004] Another technical measure is to only detect the loop closing current flowing through the bus-tie execution switch during the parallel conversion process, and use the magnitude of the loop closing current as the only criterion for judgment to execute the loop closing selection logic, and turn off each execution switch in order from high to low according to the selection and tripping priority. Although the latter is similar to the present invention in the position of loop closing current detection, there are significant differences in the control logic during the execution of parallel conversion. The application of the latter has preconditions, that is, the phase checking must be carried out between Bus Section 1 and Bus Section 2, and the capacities of the two transformers are basically the same, and the wiring groups of the transformers are the same before it can be implemented. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies existing in the prior art and provide a parallel conversion control method with loop closing and backup protection selection. The parallel conversion of the present invention has a wider application. The execution of the parallel conversion will first detect the synchronism of the two power supplies. If the parallel conditions are met, the parallel conversion process can be executed. During the parallel conversion process, the control logic of loop closing and backup protection selection is executed. When a problem occurs in the parallel conversion failure, it can effectively ensure the smooth completion of the parallel conversion, select the preset execution circuit breaker, and cut off the loop closing current, which not only ensures the continuous and efficient parallel switching of the program but also improves the reliability of the parallel conversion. The loop closing current detection device uses a hardware circuit to realize the detection and judgment of the logic, and outputs an action signal according to the comparison result of the current, and cooperates with the controller to complete the parallel conversion control logic, without occupying the detection time of the program logic judgment. Compared with the existing measures of loop closing and backup protection selection in parallel conversion technology, it has a wider application, a higher success rate, and is more reliable technically.

[0006] The present invention is realized through the following technical solutions: A parallel conversion control method with loop closing and backup protection selection, as Figure 1 shown, includes:

[0007] The power supply S1 of the first transformer, the power supply S2 of the second transformer, the air circuit breaker QF1 at the outlet of the first transformer, the air circuit breaker QF2 at the outlet of the second transformer, the bus coupler circuit breaker QF3, the three-phase current transformer TAabc installed at the lower port of the bus coupler circuit breaker, and the controller (the loop closing current detection device is built into the controller); The controller collects the power supply information of S1 through the QF1 adapter, controls the closing and opening coils of the QF1 circuit breaker through the QF1 adapter, and collects the closing and opening states and fault tripping signals of QF1; The controller collects the power supply information of S2 through the QF2 adapter, controls the closing and opening coils of the QF2 circuit breaker through the QF2 adapter, and collects the closing and opening states and fault tripping signals of QF2; The controller controls the closing and opening coils of the QF3 circuit breaker through the QF3 adapter and collects the closing and opening states and fault tripping signals of QF3; The loop closing current detection device in the controller collects the loop closing current flowing through QF3 during the parallel conversion process through TAabc, and realizes the loop closing and backup protection selection of the parallel conversion through the loop closing current detection device.

[0008] The loop closing current protection and selection function is usually realized by a loop closing current detection device (hereinafter referred to as "device"), and the device is integrated in the control loop of the controller. The control logic of the parallel conversion with synchronization detection is completed by the single-chip microcomputer of the controller, and the control logic of the loop closing and backup protection selection is completed by the hardware circuit connection, without occupying the program of the single-chip microcomputer for logical judgment. The threshold value of the loop closing current is preset in the device, and the delay time is set on the device by a DIP switch.

[0009] When parallel conversion is to be carried out, the controller continuously detects the synchronization of the two power supplies for 12S. When the two power supplies meet the parallel conditions, the controller drives the adapter to perform the parallel conversion of the three circuit breakers. The device participates in the switching process of the circuit breakers throughout as a backup protection measure for parallel conversion and collects the opening and closing states and closed-loop current of the circuit breakers. The device does not affect the normal parallel conversion control logic of the controller program and does not occupy the judgment time of the program. The control logic of synchronous parallel conversion and the control logic of closed-loop selection are coordinated with each other and independent. During the execution process, the control logic of synchronous parallel conversion is the main one, and the control logic of closed-loop selection is the auxiliary one. The interlock circuit is executed, that is, when the controller successfully performs parallel connection, a reset signal will be sent, and the device does not execute the selection logic; when the device detects that the current exceeds the limit and the controller does not send a reset command within the delay time, the device will execute the selection logic, and the preselected circuit breaker will execute the breaking of the closed-loop current.

[0010] The implementation of the closing loop selection control logic requires the addition of a manual selection switch on the control cabinet panel. The manual selection switch can determine whether the closing loop current detection device performs the closing loop selection function, or determine which circuit breaker performs the closing loop selection function. The manual selection switch should have 4 gears, namely: 0 does not perform the closing loop selection function; 1 closes the loop and selects QF1; 2 closes the loop and selects QF2; 3 closes the loop and selects QF3. Before the manual parallel conversion, the operator needs to select which circuit breaker to perform the closing loop selection function through the selection switch. When the device is in the "0" position of the selection switch, any triggering condition will fail; when the selection switch is in the "1, 2, 3" position, the device will be activated and enter the standby state, and the status of the three switches will be collected in real time (but the selection logic will not be executed). Then, the operator performs the parallel operation through the "Parallel" button and the "Manual" button of the controller. The controller will determine whether the S1 and S2 power supplies meet the parallel conditions. If the parallel conditions are met, the controller drives QF1, QF2, and QF3 to perform parallel conversion in the form of "first close and then open". When the three switches are in the closed position at the same time, the device starts to monitor the closed-loop current flowing through the bus tie switch. If the closed-loop current in the bus tie circuit is greater than the preset current value, and the current detected after delay is still greater than the preset current value (when the three switches are in the "111" state, the device will delay detection of the current exceeding the value twice and confirm the execution of the selection logic), the device will issue two commands at the same time: 1 is to trip the selected incoming line switch or bus tie switch to disconnect the closed-loop current; 2 is to cut off the signal loop output by the controller to prevent the selected switch and the controller from executing their respective tripping commands at the same time. When the controller detects that the switch does not execute its control logic (when the command issued by the controller is inconsistent with the switch state), the controller will issue an alarm signal. If the device completes the closed-loop selection logic, and the selected switch is consistent with the switch disconnected by the controller (that is, the command issued by the controller is consistent with the final state of the switch), the controller defaults to parallel success and does not alarm. If the closing current is within the limit, the device will not issue a selection command. When the controller executes the parallel conversion logic, the controller should send a reset command to the device, and the device will re-detect the closing current until the three switches are not in the fully closed state. The device will no longer start and enter the standby state. When the selection switch is turned to the "0" position, the device is not allowed to start. When any circuit breaker fails, the system will be in a fault state. In this case, the controller will prohibit any parallel closing operation, and the device will remain in the standby state.

[0011] The beneficial effects of the present invention are as follows: The parallel conversion control method for closing-loop selection to eliminate the backup protection can detect the closing-loop current value in real time and execute the preset control logic according to the detection result. Under the condition of meeting the parallel conditions (such as voltage difference ≤ 20V, frequency difference ≤ 0.2Hz, phase angle difference ≤ 5°), the parallel conversion program is executed. If the closing-loop current exceeds the limit, the executing switch is tripped; if the closing-loop current is lower than the threshold value, the single-chip microcomputer sequentially completes the switching of the switches according to the logic program, and the executing circuit breaker is tripped, without the need for the device to trip the executing circuit breaker again. The closing-loop current detection device uses a hardware circuit to realize the detection and judgment of the logic and outputs an action signal according to the comparison result of the current. In the parallel conversion control logic, on the one hand, as a signal receiving device, it receives the output signal from the controller, cooperates with the controller to execute the operation, improves the detection process, and enhances the market competitiveness; on the other hand, as an independent detection and execution mechanism, it adds a detection function without increasing the parallel conversion time, making the program operation more efficient and improving the reliability of the parallel conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 FIG. shows a schematic diagram of a parallel conversion control system with closing-loop selection to eliminate the backup protection according to an embodiment of the present invention.

[0013] Figure 2 FIG. shows a schematic diagram of the principle of parallel conversion control with closing-loop selection to eliminate the backup protection for the high-voltage part according to an embodiment of the present invention.

[0014] Figure 3 FIG. shows a schematic diagram of the principle of parallel conversion control with closing-loop selection to eliminate the backup protection for the low-voltage part according to an embodiment of the present invention.

[0015] Figure 4 FIG. shows a flowchart of the 101→110 parallel conversion according to Embodiment 1 of the present invention.

[0016] Figure 5 FIG. shows a flowchart of the 101→011 parallel conversion according to Embodiment 2 of the present invention.

[0017] Figure 6 FIG. shows a flowchart of the 110→101 parallel conversion according to Embodiment 3 of the present invention.

[0018] Figure 7 FIG. shows a flowchart of the 011→101 parallel conversion according to Embodiment 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and the best embodiments.

[0020] As Figure 2 and 3As shown in the figure, the controller is used to select the automatic and local control modes by the selector switch SA1. In the automatic mode, the controller can judge the synchronization of the two power supplies according to the detection of the normal power supply QF1 and the standby power supply QF2, and output the closing and opening signals by the single-chip microcomputer of the controller. In the local mode, the adapter can perform the opening and closing operations of the circuit breaker manually according to the SB1 button and the SB2 button.

[0021] The energy storage coil of QF1 is connected to the 380V control power supply through the CH contact of QF1 to realize the automatic energy storage of the energy storage coil M of QF1. The CH contact will automatically close or open according to the energy storage situation of the energy storage coil M. Similarly, the energy storage coil of QF2 is connected to the 380V control power supply through the CH contact of QF2 to realize the automatic energy storage of the energy storage coil M of Q2. Similarly, the energy storage coil of QF3 is connected to the 380V control power supply through the CH contact of QF3 to realize the automatic energy storage of the energy storage coil M of QF3.

[0022] The closing circuits of QF1, QF2, and QF3 under normal conditions are as follows: The controller drives KA1 to close through the single-chip microcomputer. KA1 drives the 1KA1 coil of the adapter to get energized through the control signal line. The 1KA1 contact closes and passes through the normally closed contact OF2 of QF2 or the normally closed contact OF2 of QF3, and is connected in series with the normally closed contact of PF ready to close of QF1 to apply an instantaneous 380V voltage to the XF coil of QF1 to realize the closing operation of QF1. Similarly, the controller drives KA3 to close through the single-chip microcomputer. KA3 drives the 2KA1 coil of the adapter to get energized through the control signal line. The 2KA1 contact closes and passes through the normally closed contact OF2 of QF1 or the normally closed contact OF3 of QF3, and is connected in series with the normally closed contact of PF ready to close of QF2 to apply an instantaneous 380V voltage to the XF coil of QF2 to realize the closing operation of QF2. Similarly, the controller drives KA5 to close through the single-chip microcomputer. KA5 drives the 3KA1 coil of the adapter to get energized through the control signal line. The 3KA1 contact closes and passes through the normally closed contact OF3 of QF1 or the normally closed contact OF3 of QF2, and is connected in series with the normally closed contact of PF ready to close of QF3 to apply an instantaneous 380V voltage to the XF coil of QF3 to realize the closing operation of QF3.

[0023] The opening circuits of QF1, QF2, and QF3 under normal conditions are as follows: The controller drives KA2 to close through a single-chip microcomputer. KA2 drives the 1KA2 coil of the adapter to be energized through a control signal line. The 1KA2 contact closes through the normally closed contact of KB2, and a momentary 380V voltage is applied to the MX coil of QF1 to achieve the opening action of QF1. Similarly, the controller drives KA4 to close through a single-chip microcomputer. KA4 drives the 2KA2 coil of the adapter to be energized through a control signal line. The 2KA2 contact closes through the normally closed contact of KB2, and a momentary 380V voltage is applied to the MX coil of QF2 to achieve the opening action of QF2. Similarly, the controller drives KA6 to close through a single-chip microcomputer. KA6 drives the 3KA2 coil of the adapter to be energized through a control signal line. The 3KA2 contact closes through the normally closed contact of KB2, and a momentary 380V voltage is applied to the MX coil of QF3 to achieve the opening action of QF3.

[0024] The following conditions shall be met for the parallel conversion under the closed-loop selection of the backup protection:

[0025] 1. The phase sequences and phases of the two power supplies must be the same.

[0026] 2. The frequency difference between the two power supplies meets the requirements. When the frequency cannot be adjusted, the frequency deviation shall not be greater than 0.3Hz; when paralleling, the frequencies of the two systems must be within the range of 50 ± 0.2Hz.

[0027] 3. The voltage difference between the two power supplies meets the requirements. When the voltage cannot be adjusted, the maximum voltage difference shall not exceed 20V.

[0028] 4. The closed-loop current meets the requirements of the system setting value. The closed-loop current ≤ 400A, and the delay time for the device to detect that the closed-loop current exceeds the preset value ≤ 200ms.

[0029] Test Items Test Power Supply Set Range Recommended Value Voltage Difference Three Phases of S1 & S2 0-20V 20V Phase Angle Difference Three Phases of S1 & S2 0-5° 5° Frequency Difference Three Phases of S1 & S2 0.1 - 0.2 Hz 0.1 Hz Closing Loop Current TAabc Three - Phase Current 400 A / 0~200 ms 400 A / 100 ms

[0030] When the two power supplies meet the parallel conversion conditions, the controller drives KA7 to close through the single-chip microcomputer to output a parallel unlocking signal. KA7 drives the coils of 1KA4, 2KA4, and 3KA4 of the adapter to be energized simultaneously for 200 ms through the control signal line. The closing of the 1KA4 contact causes the interlocking signal of the normally closed contact OF2 of QF2 or the normally closed contact OF2 of QF3 to be temporarily invalid. Therefore, the controller can execute the parallel conversion logic of checking synchronization through the single-chip microcomputer, drive the contacts of KA1, KA2, KA3, KA4, KA5, and KA6 to close and open, perform the operation of briefly closing QF1, QF2, and QF3 simultaneously and tripping according to the established program, and achieve normal parallel conversion operation; similarly, when 2KA4 closes, the interlocking signal of the normally closed contact OF2 of QF1 or the normally closed contact OF3 of QF3 is invalid. Therefore, the controller can execute the parallel conversion logic of checking synchronization through the single-chip microcomputer, drive the contacts of KA1, KA2, KA3, KA4, KA5, and KA6 to close and open, perform the operation of briefly closing QF1, QF2, and QF3 simultaneously and tripping according to the established program, and achieve normal parallel conversion operation; similarly, when 3KA4 closes, the interlocking signal of the normally closed contact OF3 of QF2 or the normally closed contact OF3 of QF2 is invalid. Therefore, the controller can execute the parallel conversion logic of checking synchronization through the single-chip microcomputer, drive the contacts of KA1, KA2, KA3, KA4, KA5, and KA6 to close and open, perform the operation of briefly closing QF1, QF2, and QF3 simultaneously and tripping according to the established program, and achieve normal parallel conversion operation. After the normal parallel conversion logic ends, KA7 resumes its normally open contact, 1KA4, 2KA4, and 3KA4 resume their normally open contacts, the interlocking signals of QF1, QF2, and QF3 are restored, and the normal parallel conversion ends.

[0031] The execution of the backup protection for loop closing selection is selected by the operator through the SA2 switch. When SA2 is in the "no loop closing selection" position (at position 0), the KB1 coil is energized and attracted, and the device does not start. When SA2 is not in the "no loop closing selection" position (not at position 0), the device will start and enter the standby state when the KB1 coil loses power. After the device starts, it collects the status information of QF1, QF2, and QF3 in real time through the controller. When QF1, QF2, and QF3 are all in the closing position at the same time, the device starts to detect the loop closing current flowing through the bus coupler switch. If the loop closing current in the bus coupler circuit is greater than the preset current value, after a time delay, when the detected current is still greater than the preset current value, the device will drive KA11, KA21, and KA31 to close instantaneously for 100 ms at the same time, drive the KB2 coil to be energized, and cut off the tripping signal circuit output by the controller to prevent the selected switch and the controller from executing their respective tripping commands simultaneously; at the same time, the device will drive KA11 to close for 100 ms and drive the 1KA5 coil to be energized. At this time, if the loop closing selection manual switch SA2 is in the "device outputs to select QF1", a voltage of 380 V will be instantaneously applied to the MX coil of QF1 to achieve the tripping action of QF1 and complete the selection logic; if the loop closing selection manual switch SA2 is not in the "device outputs to select QF1" position, QF1 will not act. Similarly, the device will drive KA21 to close for 100 ms and drive the 2KA5 coil to be energized. At this time, if the loop closing selection manual switch SA2 is in the "device outputs to select QF2", a voltage of 380 V will be instantaneously applied to the MX coil of QF2 to achieve the tripping action of QF2 and complete the selection logic; if the loop closing selection manual switch SA2 is not in the "device outputs to select QF2" position, QF2 will not act. Similarly, the device will drive KA31 to close for 100 ms and drive the 3KA5 coil to be energized. At this time, if the loop closing selection manual switch SA2 is in the "device outputs to select QF3" position, a voltage of 380 V will be instantaneously applied to the MX coil of QF3 to achieve the tripping action of QF3 and complete the selection logic; if the loop closing selection manual switch SA2 is not in the "device outputs to select QF3" position, QF3 will not act.

[0032] When the controller detects that the switch fails to execute its control logic (when the command issued by the controller is inconsistent with the switch state), the controller issues an alarm signal. If the device completes the loop closing and dropout logic and the dropped switch is the same as the switch disconnected by the controller (i.e., the command issued by the controller is consistent with the final realized state of the switch), the controller defaults that the parallel connection is successful and does not alarm. If the loop closing current does not exceed the limit and the device does not issue a dropout command, when the controller executes the parallel conversion logic, the controller should send a reset command to the device, and the device will re-detect the loop closing current until the three switches ≠ "111", then the device will no longer start and enter the standby state. When the selection switch is turned to the "0" position, the device is not allowed to start. When any one of the circuit breakers fails, the system will be in a fault state, and in this case, the controller will prohibit any parallel connection and loop closing operation.

[0033] Embodiment 1: The parallel conversion from S2 to S1 (i.e., 101 → 110), and the process is as Figure 5 shown.

[0034] Parallel Conversion Transformer 1# QF1 Bus - Tie Switch QF3 Transformer 2# QF2 Step 1 1 0 1 Step 2 1 1 1 Step 3 1 1 0

[0035] Note: 1 - Closing; 0 - Opening

[0036] 1) When the selection switch is turned to the positions of "1, 2, 3", the device remains open and allows the device to operate; when the selection switch is turned to the "0" position, the device remains closed and does not perform any dropout function.

[0037] 2) When the device receives the position signal of the selection switch "3", it enters the standby state, real-time collects the states of the three switches, and based on the current comparison result, drops out the QF3 switch. The closing states of the three switches are the only enabling ports of the device. When the switches = 111, the device starts; when the switches ≠ 111, the device does not start.

[0038] 3) When QF3 = 1, that is, when the three switches = 111, the device starts and detects the bus tie current.

[0039] 4) When the bus tie current is greater than 400A, after a 100ms delay, when the loop closing current is still greater than 400A, the device trips QF3, and at the same time breaks the QF2 trip signal of the controller (for a duration of 200ms) to prevent QF2 from tripping. The controller operates according to the normal logic. When it detects that QF3 = 0 and QF2 = 1, that is, when the three switches ≠ 110, it alarms.

[0040] 5) When the current is less than 400A, the device remains in the startup state but does not send any action signals. The controller operates according to the normal logic. When the controller sends a disconnection command for QF2, it must simultaneously send a reset command to the device, and the device re-detects the closed-loop current (i.e., the current is less than 400A, and the reset does not affect the logical judgment of the device). When switches QF1 = 1, QF3 = 1, and QF2 = 0, the parallel connection ends. Since the switches ≠ 111, the device does not start and enters the standby state, and no longer detects the closed-loop current.

[0041] 6) When the current is greater than 400A, within the 100ms delay, when the controller sends a disconnection command for QF2, it must simultaneously send a reset command to the device. The device will delay for another 100ms to wait for QF2 to disconnect. When the device detects that the switches ≠ 111, the device enters the standby state and no longer detects the closed-loop current, that is, it does not send any action signals, and the switches are normally paralleled and ended according to the logic of the controller; when the device detects that the closed-loop current is still greater than 400A and the three switches = 111 after the second 100ms delay, the device trips QF3 and simultaneously cuts off the QF2 trip signal of the controller (duration 200ms) to prevent QF2 from tripping. The controller will alarm.

[0042] 7) When the current is greater than 400A and the closed-loop current is still greater than 400A after a 100ms delay, when the device sends a selection trip command and receives a reset command sent by the controller (when the controller sends a disconnection command for QF2), the device will not execute it and continues to drive QF3 to trip, and simultaneously cuts off the communication signal of the controller (duration 200ms) to prevent QF2 from tripping. The controller operates according to the normal logic. When it detects that QF3 = 0 and QF2 = 1, that is, when the three switches ≠ 110, it alarms.

[0043] Embodiment 2: Conversion from S1 to S2 in parallel connection (i.e., 101 → 011), the process is as Figure 5 shown.

[0044]

[0045]

[0046] 1) When the selection switch is turned to the "3" position, the device enters the standby state, continuously acquires the states of the three switches, and selects to trip the QF3 switch based on the current comparison result. When the switches = 111, the device starts; when the switches ≠ 111, the device does not start.

[0047] 2) When QF3 = 1, that is, when the three switches = 111, the device starts and detects the bus tie current.

[0048] 3) When the bus-tie current is greater than 400A, a 100ms delay is applied. When the closed-loop current is still greater than 400A, the device trips QF3, and at the same time, the controller disconnects the QF1 trip signal (duration 200ms) to prevent QF1 from tripping. The controller operates according to the normal logic and alarms when it detects that QF3 = 0 and QF1 = 1, that is, when the three switches are not equal to 011.

[0049] 4) When the current is less than 400A, the device remains in the startup state but does not send any action signals. The controller operates according to the normal logic. When the controller sends a QF1 opening command, it must simultaneously send a reset command to the device, and the device re-detects the closed-loop current (i.e., when the current is less than 400A, the reset does not affect the device's logical judgment). When the switches QF1 = 0, QF3 = 1, and QF2 = 1, the parallel connection ends. Since the switches are not equal to 111, the device does not start and enters the standby state, and no longer detects the closed-loop current.

[0050] 5) When the current is greater than 400A, within the 100ms delay, when the controller sends a QF1 opening command, it must simultaneously send a reset command to the device. The device will delay for another 100ms waiting for QF1 to open in place. When the device detects that the switches are not equal to 111, the device enters the standby state and no longer detects the closed-loop current, that is, it does not send any action signals, and the switches are normally connected in parallel according to the controller's logic and end. When the device detects that the closed-loop current is still greater than 400A and the three switches are equal to 111 after the second 100ms delay, the device trips QF3, and at the same time, the controller disconnects the QF1 trip signal (duration 200ms) to prevent QF1 from tripping. The controller will alarm.

[0051] 6) When the current is greater than 400A, after a 100ms delay, when the closed-loop current is still greater than 400A and the device sends a selection trip command and receives a reset command sent by the controller (when the controller sends a QF1 opening command), the device will not execute it, continues to drive QF3 to trip, and at the same time, the controller disconnects the QF1 trip signal (duration 200ms) to prevent QF1 from tripping. The controller operates according to the normal logic and alarms when it detects that QF3 = 0 and QF1 = 1, that is, when the three switches are not equal to 011.

[0052] Example 3: Conversion from single power supply of S1 to separate power supply of S1 and S2 in parallel (i.e., 110 → 101), the process is as Figure 6 shown.

[0053] Parallel Conversion Transformer 1# QF1 Bus - Tie Switch QF3 Transformer 2# QF2 Step 1 1 1 0 Step 2 1 1 1 Step 3 1 0 1

[0054] 1) When the selection switch is turned to the "3" position, the device enters the standby state, continuously acquires the states of the three switches, and selects and trips the QF3 switch based on the current comparison result. When the switches are equal to 111, the device starts; when the switches are not equal to 111, the device does not start.

[0055] 2) When QF2 = 1, that is, when the three switches = 111, the device starts and detects the bus-tie current.

[0056] 3) When the bus-tie current is greater than 400A, a 100ms delay is applied. When the closed-loop current is still greater than 400A, the device trips QF3 and simultaneously breaks the QF3 trip signal of the controller (duration 200ms). The controller operates according to the normal logic. When it detects that QF3 = 0 and QF2 = 1, that is, when the three switches = 101, the controller defaults that the parallel connection is successful and does not alarm.

[0057] 4) When the current is less than 400A, the device remains in the startup state but does not send any action signals. The controller operates according to the normal logic. When the controller sends a QF3 opening command, it must simultaneously send a reset command to the device, and the device re-detects the closed-loop current (that is, when the current is less than 400A, the reset does not affect the logical judgment of the device). When the switches QF1 = 1, QF3 = 0, and QF2 = 1, the parallel connection ends. Since the switches ≠ 111, the device does not start and enters the standby state, and no longer detects the closed-loop current.

[0058] 5) When the current is greater than 400A, within the 100ms delay, when the controller sends a QF3 opening command, it must simultaneously send a reset command to the device. The device will delay for another 100ms waiting for QF3 to open in place. When the device detects that the switches ≠ 111, the device enters the standby state and no longer detects the closed-loop current, that is, it does not send any action signals, and the switches are paralleled normally according to the logic of the controller and end; when the device detects that the closed-loop current is still greater than 400A and the three switches = 111 after the second 100ms delay, the device trips QF3 and simultaneously breaks the QF3 trip signal of the controller (duration 200ms). The controller operates according to the normal logic. When it detects that QF3 = 0 and QF2 = 1, that is, when the three switches = 101, the controller defaults that the parallel connection is successful and does not alarm.

[0059] 6) When the current is greater than 400A, after a 100ms delay, when the closed-loop current is still greater than 400A and the device sends a selection trip command and receives the reset command sent by the controller (when the controller sends a QF3 opening command), the device will not execute it and continues to drive QF3 to trip, and simultaneously breaks the QF3 trip signal of the controller (duration 200ms). The controller operates according to the normal logic. When it detects that QF3 = 0 and QF2 = 1, that is, when the three switches = 101, the controller defaults that the parallel connection is successful and does not alarm.

[0060] Example 4: Conversion from separate power supply of S2 to separate power supply and parallel connection of S1 and S2 (that is, 011 → 101), the process is as Figure 7 shown.

[0061] Parallel Conversion Transformer 1# QF1 Bus - Tie Switch QF3 Transformer 2# QF2 Step 1 0 1 1 Step 2 1 1 1 Step 3 1 0 1

[0062] 1) When the selection switch is turned to the position of "2", the device enters the standby state, collects the states of the three switches in real time, and selects to trip the QF2 switch according to the current comparison result. When the switch = 111, the device starts; when the switch ≠ 111, the device does not start.

[0063] 2) When QF1 = 1, that is, when the three switches = 111, the device starts and detects the bus-tie current.

[0064] 3) When the bus-tie current is greater than 400A, a 100ms delay is applied. When the closed-loop current is still greater than 400A, the device trips QF2, and at the same time, the tripping signal of the controller QF3 is cut off (duration 200ms) to prevent QF3 from tripping. The controller operates according to the normal logic. When it detects that QF1 = 1, QF3 = 1, and QF2 = 0, that is, when the three switches ≠ 101, an alarm is issued.

[0065] 4) When the current is less than 400A, the device remains in the starting state but does not issue any action signals. The controller operates according to the normal logic. When the controller sends a QF3 opening command, it must send a reset command to the device at the same time, and the device re-detects the closed-loop current (that is, when the current is less than 400A, the reset does not affect the logical judgment of the device). When the switch QF1 = 1, QF3 = 0, and QF2 = 1, the parallel connection ends. Since the switch ≠ 111, the device does not start, enters the standby state, and no longer detects the closed-loop current.

[0066] 5) When the current is greater than 400A, within the 100ms delay, when the controller sends a QF3 opening command, it must send a reset command to the device at the same time. The device will delay for another 100ms to wait for QF3 to trip in place. When the device detects that the switch ≠ 111, the device enters the standby state, no longer detects the closed-loop current, that is, does not issue any action signals, and the switch is normally paralleled according to the logic of the controller; when the device detects that the closed-loop current is still greater than 400A and the three switches = 111 after the second 100ms delay, the device trips QF2, and at the same time, the tripping signal of the controller QF3 is cut off (duration 200ms) to prevent QF3 from tripping. The controller will issue an alarm.

[0067] 6) When the current is greater than 400A, after a 100ms delay, when the closed-loop current is still greater than 400A and the device sends a selection trip command and receives the reset command sent by the controller (when the controller sends a QF3 opening command), the device will not execute it, continues to drive QF2 to trip, and at the same time, the tripping signal of the controller QF3 is cut off (duration 200ms) to prevent QF3 from tripping. The controller operates according to the normal logic. When it detects that QF1 = 1, QF3 = 1, and QF2 = 0, that is, when the three switches ≠ 101, an alarm is issued.

[0068] The beneficial effects of the present invention are as follows: The parallel conversion control method for selecting and removing the backup protection during loop closing can detect the loop closing current value in real time and execute the preset control logic according to the detection result. When the parallel conditions (such as voltage difference ≤ 20V, frequency difference ≤ 0.2Hz, phase angle difference ≤ 5°) are met, the parallel conversion program is executed. If the loop closing current exceeds the limit, the executing switch is tripped; if the loop closing current is lower than the threshold value, the single-chip microcomputer completes the switching of the switches in sequence according to the logic program, and the executing circuit breaker is tripped, without the device having to trip the executing circuit breaker again. The loop closing current detection device uses a hardware circuit to implement the detection and judgment of the logic and outputs an action signal according to the comparison result of the current. In the parallel conversion control logic, on the one hand, as a signal receiving device, it receives the output signal from the controller, cooperates with the controller to execute the operation, improves the detection process, and enhances the market competitiveness; on the other hand, as an independent detection and execution mechanism, it adds a detection function without increasing the parallel conversion time, making the program run more efficiently and improving the reliability of the parallel conversion.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A parallel conversion control method with loop closing selection and backup protection, characterized in that, it includes the following steps: Before parallel conversion, adjust the backup protection gear. First, adjust the gear of the manual selection switch. When the manual selection switch is in the "0" gear, the loop closing current detection device does not start; when the manual selection switch is in the "1, 2, 3" gears, the loop closing current detection device starts, and the controller real-time collects the states of three switches QF1, QF2, and QF3. The "1" gear corresponds to QF1, the "2" gear corresponds to QF2, and the "3" gear corresponds to QF3; The controller drives the three switches QF1, QF2, and QF3 to close simultaneously, and the loop closing current detection device starts and monitors the loop closing current flowing through the bus-tie switch; The loop closing current detection device uses a hardware circuit to realize the detection and judgment of logic, and outputs an action signal according to the comparison result of the current, and cooperates with the controller to complete the parallel conversion control logic without occupying the program of the single-chip microcomputer of the controller for logical judgment. A preset current value is set in the loop closing current detection device. If the loop closing current exceeds the preset current value, the loop closing current detection device is in a standby state; If the loop closing current is greater than the preset current value, and the loop closing current detected after the delay is still greater than the preset current value, the loop closing current detection device disconnects the corresponding switch according to the gear and cuts off the trip signal circuit output by the controller; If the controller detects that the states of QF1, QF2, and QF3 do not execute its trip command, the controller issues an alarm signal; if the loop closing current detection device completes the loop closing selection and rejection logic and the states of QF1, QF2, and QF3 are consistent with the commands output by the controller, the controller defaults that the parallel connection is successful and does not alarm; If QF1, QF2, and QF3 are not in the simultaneous closing state, the controller makes the loop closing current detection device no longer start.

2. A parallel conversion control method with loop closing selection and backup protection according to claim 1, characterized in that, After the controller receives the signal to start parallel conversion, it judges whether the S1 and S2 power supplies meet the parallel conversion conditions. If they meet the parallel conversion conditions, the controller drives QF1, QF2, and QF3 to close simultaneously and starts the loop closing current detection device.

3. A parallel conversion control method with loop closing selection and backup protection according to claim 2, characterized in that, After the controller receives the signal to start parallel conversion, the controller continuously detects whether the S1 and S2 power supplies meet the parallel conversion conditions within 12S: (1) The phase sequence and phase of the two power supplies must be the same; (2) When the frequency cannot be adjusted, the frequency deviation between the two power supplies is not greater than 0.3Hz, and the frequencies of the two systems must be within the range of 50 ± 0.2Hz during paralleling; (3) When the voltage cannot be adjusted, the voltage difference between the two power supplies is not greater than 20V; (4) The loop closing current ≤ 400A, and the delay time for the loop closing current detection device to detect that the loop closing current exceeds the preset value ≤ 200ms.

4. A parallel conversion control method with loop closing selection and backup protection according to claim 1, characterized in that, When any one of QF1, QF2, and QF3 fails, the system will be in a fault state, the controller prohibits the closing-loop operation, and the closing-loop current detection device remains in the standby state.

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