Control system capable of realizing automatic switching of double frequency converters

Abstract

The invention relates to the technical field of frequency converters for petrochemical enterprises, in particular to a control system capable of realizing automatic switching of double frequency converters. A motor of the control system is connected with a standby frequency converter, the standby frequency converter is connected with commercial power, and the standby frequency converter has no power frequency bypass; the in-use frequency converter and the standby frequency converter are respectively in communication connection with the PLC, and the PLC comprises a fault judgment module and a secondary starting module. Two sets of frequency converter control loops are adopted to control one motor, when one frequency converter goes wrong, the system is automatically switched to the standby frequency converter under the action of the PLC, the standby frequency converter continues to control the motor to operate, and stable operation of the motor is ensured.

Description

Technical Field:

[0001] The present invention relates to the technical field of frequency converters for petrochemical enterprises, and particularly relates to a control system capable of realizing automatic switching of dual frequency converters. Background Art:

[0002] As a driving device, a frequency converter can adjust the voltage and frequency of the output power supply, provide the required power supply voltage according to actual needs, and ensure the continuous and stable operation of the load. In petrochemical enterprises, for 0.4 kV motors with a capacity of 200 kW and above, direct starting results in a relatively large starting current and a large bus voltage drop, which has a certain impact on the stable operation of other electrical equipment on the same bus. Therefore, motors with a capacity of 200 kW and above are started by frequency converters, and no industrial frequency circuit is set up. Since the motor only has a frequency converter circuit, once the frequency converter fails, the motor needs to be stopped and waited for the fault to be eliminated before it can be started, and the fault handling time is long, which has a greater impact on production. In some boiler power supply circuits, there is only one motor for the induced draft fan, and it can only be started by a frequency converter. When the main frequency converter fails, the probability of the boiler going out of fire or even negative pressure increases sharply.

[0003] Currently, the commonly adopted solution to solve the above problems is to install a frequency converter cabinet of the same specification without an industrial frequency circuit near the frequency converter cabinet. When the in-use frequency converter fails, the cable is manually migrated to the standby frequency converter cabinet, and the construction time is about 2 hours, which also has a certain impact on the production device. Summary of the Invention:

[0004] The technical problem to be solved by the present invention is to provide a control system capable of realizing automatic switching of dual frequency converters. The system realizes the control of a motor by using two sets of frequency converter control circuits. When one of the frequency converters has a problem, the system automatically switches to the standby frequency converter under the action of the PLC, and the standby frequency converter continues to control the operation of the motor to ensure the stable operation of the motor.

[0005] The technical solution adopted by the present invention is: a control system capable of realizing automatic switching of dual frequency converters, including a motor, the motor is connected to the in-use frequency converter, the in-use frequency converter is connected to the commercial power, and the in-use frequency converter has no industrial frequency bypass; the motor is connected to the standby frequency converter, the standby frequency converter is connected to the commercial power, and the standby frequency converter has no industrial frequency bypass; the in-use frequency converter and the standby frequency converter are respectively communicatively connected to the PLC controller, and the PLC controller includes a fault judgment module and a secondary start module;

[0006] The fault judgment module can judge the fault situation of the in-use frequency converter, send a start command to the standby frequency converter when an internal fault of the in-use frequency converter occurs, and send a lock automatic switching command to the standby frequency converter when an external fault of the in-use frequency converter occurs;

[0007] After the standby frequency converter receives a start command and fails to start, the secondary start module outputs a frequency converter fault reset signal to the standby frequency converter. After the standby frequency converter is successfully reset, a start signal is output to the standby frequency converter again to perform a secondary start of the standby frequency converter.

[0008] Further, the external faults of the frequency converter include overload fault, phase-to-phase short circuit fault, and single-phase ground fault.

[0009] Further, after the standby frequency converter starts, it tracks the operating frequency of the original in-use frequency converter and continuously drives the motor to operate.

[0010] Further, the PLC controller is connected to an independent power supply, and this independent power supply is not controlled by the power supplies of the in-use frequency converter and the standby frequency converter.

[0011] The beneficial effects of the present invention are as follows:

[0012] (1) When a fault occurs in the frequency converter, it can be automatically switched to a fault-free frequency converter and automatically started.

[0013] (2) The present invention greatly shortens the switching time after the frequency converter fails and reduces the impact on the device. Description of the drawings:

[0014] The following further describes the present invention in detail in conjunction with the drawings and specific embodiments.

[0015] Figure 1 It is the main wiring diagram of the present invention.

[0016] Figure 2 It is the secondary wiring diagram of the in-use frequency converter BP-A.

[0017] Figure 3 It is the secondary wiring diagram of the standby frequency converter BP-B.

[0018] Figure 4 It is the wiring diagram of the PLC controller.

[0019] Figure 5 It is the operation flowchart of the present invention. Specific embodiments:

[0020] Such as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4As shown in the figure, a control system capable of realizing automatic switching of dual inverters includes a motor. The motor is connected to the in-use inverter BP-A. The in-use inverter BP-A is connected to the commercial power, and the in-use inverter BP-A has no industrial frequency bypass; the motor is connected to the standby inverter BP-B. The standby inverter BP-B is connected to the commercial power, and the standby inverter BP-B has no industrial frequency bypass; the in-use inverter BP-A and the standby inverter BP-B are respectively connected to the PLC controller for communication. The PLC controller includes a fault judgment module and a secondary start module;

[0021] The fault judgment module can judge the fault situation of the in-use inverter BP-A. When an internal fault occurs in the in-use inverter BP-A, a start instruction is sent to the standby inverter BP-B. When an external fault occurs in the in-use inverter BP-A, a lockout automatic switching instruction is sent to the standby inverter BP-B;

[0022] After the standby inverter BP-B receives the start instruction and fails to start, the secondary start module outputs an inverter fault reset signal to the standby inverter BP-B. After the standby inverter BP-B is successfully reset, a start signal is output to the standby inverter BP-B again to perform secondary start of the standby inverter BP-B.

[0023] The external faults of the inverter include overload fault, phase-to-phase short circuit fault, and single-phase ground fault.

[0024] After the standby inverter BP-B is started, it tracks the operating frequency of the original in-use inverter BP-A and continuously drives the motor to operate.

[0025] The PLC controller is connected to an independent power supply, and this independent power supply is not controlled by the power supplies of the in-use inverter BP-A and the standby inverter BP-B.

[0026] The in-use inverter BP-A and the standby inverter BP-B can be used as each other's standby. According to the actual situation, each inverter operates for one maintenance cycle, which is carried out through a manual selection switch in the inverter cabinet. The conversion switch has three gears: BP-A is in use and BP-B is on standby; BP-B is in use and BP-A is on standby; both BP-A and BP-B are out of service. The control power supplies of the two inverters are completely independent. During the maintenance of one inverter, it does not affect the operation of the other inverter.

[0027] Since the motor being dragged has no standby motor or cannot be started at power frequency, when the in-use frequency converter BP-A fails without a short-circuit fault, the standby frequency converter BP-B should be made to operate quickly and reliably as much as possible. Due to reasons such as a long standby time, slow system recovery, and the reverse impact of the motor on the standby frequency converter BP-B during startup, the first startup of the standby frequency converter BP-B may fail. The present invention has a secondary startup function for the standby frequency converter BP-B. When the in-use frequency converter BP-A fails, the standby frequency converter BP-B starts. After the startup fails, the PLC controller automatically sends a reset command to the standby frequency converter BP-B, and then sends a startup command again, which can greatly increase the probability of successful startup of the standby frequency converter BP-B.

[0028] The present invention can quickly judge the frequency converter fault, the location of the fault point, and confirm whether to switch. It greatly shortens the switching time after the frequency converter fails and reduces the impact on the device. If the PLC controller judges that the fault point is located at the load cable or the motor end, it issues an alarm command, which can guide the fault handling personnel to quickly cut off the fault and reduce the fault handling time.

[0029] As Figure 5 shown, the flow of using the present invention is as follows:

[0030] I. Start the motor

[0031] (1) Switch the "Frequency Conversion / Exit" switch of the BP-A and BP-B frequency converter cabinets to the "Exit" position; energize in sequence and switch the frequency converter selection switch to the "BP-A Input" position;

[0032] Operation: Switch the "Frequency Conversion / Exit" switch of the BP-A frequency converter cabinet to the "Frequency Conversion" position;

[0033] Check: 1KM1 is closed, the frequency conversion status indicator light of the BP-A frequency converter cabinet is on, and the fault light is not on;

[0034] Operation: Switch the "Frequency Conversion / Exit" switch of the BP-B frequency converter cabinet to the "Frequency Conversion" position;

[0035] Check: 2KM2 is closed, the frequency conversion status indicator light of the BP-B frequency converter cabinet is on, and the fault light is not on;

[0036] Operation: Press the start button of the on-site operation column to start the motor;

[0037] Check: KA4 is closed momentarily and then de-energized, 1KA3 and 1KA2 are closed, the frequency conversion operation indicator light 1-01 of the PLC controller is on, the numerical values on the panel of the BP-A frequency converter are normal, the motor is running, and the ammeter indicates the correct current.

[0038] II. Frequency converter speed regulation

[0039] Operation: Adjust the 4-20mA input signal of the frequency converter from the instrument side; (For speed regulation, a one-in-two-out form is selected, and the in-use frequency converter and the standby frequency converter receive the frequency modulation signal synchronously.)

[0040] Check: Whether the "AI2" of the two frequency converters is the same, and the changes of "inverter output current", "inverter output power", and "motor voltage" shown on the panel of the BP-A frequency converter are correct.

[0041] III. Stop the motor

[0042] Operation: Press the on-site operation stop button to stop the motor;

[0043] Check: The motor stops running, KA6 loses power and then gets powered on after the stop button is pressed, 1KA3 and 1KA2 lose power simultaneously, the frequency conversion operation indicator light goes out, and 1-01 of the PLC goes out. The "inverter output current", "inverter output power", and "motor voltage" on the panel of the BP-A frequency converter are zero, and the current of the ammeter is zero. When necessary, stop the machine through the DCS interlock signal, and the phenomenon is the same as when stopping the motor with the operation column button.

[0044] IV. Maintenance of the motor and cable

[0045] Confirm that the motor has stopped running and the frequency converter has no output;

[0046] Switch the BP-B frequency converter cabinet to the "frequency conversion / exit" position, and the changeover switch to the "exit" position; switch the BP-A frequency converter cabinet to the "frequency conversion / exit" position, and the changeover switch to the "exit" position; switch the frequency converter selection switch to the "all exits" position;

[0047] Disconnect the power switches of the BP-A and BP-B frequency converter cabinets;

[0048] Disconnect Figure 4 the main power supply of the PLC controller in the middle.

[0049] After obtaining the consent of the production workshop, start the maintenance of the motor and cable.

[0050] V. Automatic switching treatment measures for the frequency converter

[0051] Fault phenomenon: (1) BP-A is the in-use frequency converter. Due to frequency converter failure, it automatically switches to BP-B frequency conversion, and the fault indicator light of the BP-A frequency converter lights up;

[0052] (2) A fault message is generated on the panel of the BP-A frequency converter, I-01 of the PLC goes out, I-00 lights up, and at the same time I-03 lights up;

[0053] (3) The BP-B frequency converter is running and the motor has not stopped running.

[0054] Operation steps:

[0055] Switch the frequency converter selection switch to the "BP-B input" position;

[0056] Switch the "Frequency Conversion / Exit" switch of the BP-A frequency converter cabinet to the "Exit" position;

[0057] Disconnect the power switch of the BP-A frequency converter cabinet;

[0058] Handle the faulty frequency converter, noting that the lower end of the 1KM1 contactor is energized;

[0059] The handling is completed;

[0060] Close the power switch of the BP-A frequency converter cabinet;

[0061] Switch the "Frequency Conversion / Exit" switch of the BP-A frequency converter cabinet to the "Frequency Conversion" position;

[0062] If it is necessary to switch back to the operation of the BP-A frequency converter, switch the frequency converter cabinet selection switch to the "BP-A input" position, press the stop button on the operation column, switch the "Frequency Conversion / Exit" switch of the BP-B frequency converter cabinet to the "Exit" position, or directly switch the "Frequency Conversion / Exit" switch of the BP-B frequency converter cabinet to the "Exit" position, press the start button on the on-site operation column, and switch the "Frequency Conversion / Exit" switch of the BP-B frequency converter cabinet to the "Frequency Conversion" position.

[0063] Note: To switch back to the operation of the BP-A, the motor needs to be stopped.

[0064] VI. Handling measures for the motor shutdown with the locking indicator light on

[0065] When the motor shuts down and the locking light is on, it can be preliminarily judged that there is an external fault with the frequency converter;

[0066] For example: motor grounding, motor phase-to-phase short circuit, cable grounding, cable phase-to-phase short circuit, etc.;

[0067] Switch the "Frequency Conversion / Exit" switches of the BP-A and BP-B frequency converter cabinets to the "Exit" position; disconnect the power supplies of the BP-A and BP-B frequency converter cabinets;

[0068] Open the motor junction box, separate the cable from the motor, and use a megohmmeter to measure the insulation resistance of the motor and the cable respectively to determine the fault location; if necessary, use a bridge to measure the DC resistance of the motor;

[0069] Handle the fault, and reconnect the motor and the cable after the megohmmeter measurement is normal;

[0070] Restore power supply to the BP-A and BP-B frequency converter cabinets;

[0071] Switch the selection switch of the BP-A frequency converter cabinet to the "Frequency Conversion" position; switch the selection switch of the BP-B frequency converter cabinet to the "Frequency Conversion" position;

[0072] Start the BP-A frequency converter cabinet, the locking light goes out, and the motor runs.

[0073] It can be understood that the above specific description of the present invention is only for explaining the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effect; as long as it meets the usage requirements, it is within the protection scope of the present invention.

Claims

1. A control system capable of realizing automatic switching of dual inverters, including a motor, the motor is connected to the in-use inverter, the in-use inverter is connected to the commercial power supply, and the in-use inverter has no industrial frequency bypass; characterized in that: The motor is connected to a standby frequency converter, and the standby frequency converter is connected to the commercial power supply. The standby frequency converter has no industrial frequency bypass; the in-use frequency converter and the standby frequency converter are respectively communicatively connected to a PLC controller, and the PLC controller includes a fault judgment module and a secondary start module; The fault judgment module can judge the fault condition of the in-use frequency converter, send a start command to the standby frequency converter when an internal fault of the in-use frequency converter occurs, and send a locking automatic switching command to the standby frequency converter when an external fault of the in-use frequency converter occurs; After the standby frequency converter receives the start command and fails to start, the secondary start module outputs a frequency converter fault reset signal to the standby frequency converter. After the standby frequency converter is successfully reset, the secondary start module outputs a start signal to the standby frequency converter again to perform secondary start of the standby frequency converter.

2. The control system capable of realizing automatic switching of dual inverters according to claim 1, characterized in that: The external faults of the frequency converter include overload fault, phase-to-phase short circuit fault, and single-phase ground fault.

3. The control system capable of realizing automatic switching of dual inverters according to claim 1, characterized in that: After the standby frequency converter is started, it tracks the operating frequency of the original in-use frequency converter and continuously drives the motor to run.

4. The control system capable of realizing automatic switching of dual inverters according to claim 1, characterized in that: The PLC controller is connected to an independent power supply, and this independent power supply is not controlled by the power supplies of the in-use frequency converter and the standby frequency converter.

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