Control circuit for causing and solving dcs interference in frequency converter applications

Abstract

The utility model discloses a kind of control circuit that causes DCS interference in frequency converter application and solves, including pump motor, further including frequency converter and electric reactor, electric reactor includes input electric reactor and output electric reactor, the power input end of pump motor is connected to the power output end of frequency converter by output electric reactor, the power input end of frequency converter is connected to commercial power by input electric reactor and master switch.This control circuit that causes DCS interference in frequency converter application and solves of the utility model, pump motor power cord is connected in configuration with frequency converter and DCS system, by installing frequency converter reaches the purpose of accurate control overflow pump machine, and, input electric reactor and output electric reactor are connected in configuration before and after frequency converter, by series connection and access with its capacity matched electric reactor, the harmonic generated by frequency converter can be effectively absorbed.

Description

Technical Field

[0001] This utility model relates to the field of frequency conversion control technology, and in particular to a control circuit that causes DCS interference in frequency converter applications and how to solve it. Background Technology

[0002] As a widely used power control device in industrial production, the importance of frequency converters cannot be ignored. Their working principle is based on converting industrial frequency power energy to power energy of the required frequency through the switching on and off of electronic devices, thus constituting a power energy control device. This device can perform soft starting and variable frequency speed regulation for squirrel-cage AC asynchronous motors and permanent magnet synchronous motors of different voltage levels, significantly improving the accuracy of equipment operation control, enhancing the power factor, and providing overcurrent, over(under)voltage, and overload protection functions for electrical equipment. In various factories, frequency converters are widely used due to their ability to achieve smooth speed regulation, a wide speed adjustment range, low equipment starting current, and diverse protection functions.

[0003] In the automated control production process of sedimentation, the configured slurry overflow pump (such as the Pc305E slurry overflow pump) meets the selection requirements of motor and variable frequency speed control drive. By adding a frequency converter to improve the design, the pump can be controlled efficiently and accurately, meeting the process adjustment needs under different working conditions. Utility Model Content

[0004] The purpose of this invention is to address the above-mentioned problems by providing a control circuit that causes DCS interference in frequency converter applications and solves the problem. Specifically, it is used for slurry overflow pumps and is a frequency converter control circuit for slurry overflow pumps, which can perform frequency conversion control and prevent harmonic interference from frequency conversion control.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0006] The control circuit that causes DCS interference and is used to resolve it in frequency converter applications includes a pump motor, a frequency converter, and a reactor. The reactor includes an input reactor and an output reactor. The power input terminal of the pump motor is connected to the power output terminal of the frequency converter through the output reactor. The power input terminal of the frequency converter is connected to the mains power through the input reactor and the main switch.

[0007] The main switch is a load switch QM, and the pump motor is a three-phase motor. The U1, V1 and W1 terminals of the pump motor are connected to the U, V and W pins of the frequency converter, respectively. The L1, L2 and L3 pins of the frequency converter are connected to the L1, L2 and L3 phases of the three-phase power supply, respectively.

[0008] The frequency converter control system is equipped with a DCS system, which is connected to the frequency converter. The speed setpoint and speed feedback pins of the frequency converter are connected to the DCS system.

[0009] As mentioned above, the frequency converter and DCS system are connected to the pump power line. By adding the frequency converter, the overflow pump can be accurately controlled. In addition, input reactors and output reactors are connected before and after the frequency converter. By connecting reactors with matching capacity in series, the harmonics generated by the frequency converter can be effectively absorbed.

[0010] Based on the aforementioned scheme, in an improved scheme, the frequency converter control system further includes a field control unit. The field control unit includes a control switch SA, a first relay, a second relay, and a third relay. The coils of the first, second, and third relays are connected in parallel across the power supply terminals of the control unit. The two sets of contacts of the control switch SA are respectively connected to the control circuits of the second and third relay coils. The first contact of the first relay is connected to the power supply pin of the DCS system, the first contact of the second relay is connected to the remote pin of the DCS system, and the first contact of the third relay is connected to the operating pin of the frequency converter. Thus, field and remote control are achieved through the coordination of relays.

[0011] Based on the aforementioned solution, in an improved version, the field control unit of the frequency converter control system further includes a switch SB1, which is connected between the coil of the third relay and the control switch SA. Thus, by configuring the push-button switch SB1 to disconnect the switch in an emergency, emergency switch control can be achieved.

[0012] Based on the aforementioned scheme, in an improved scheme, the field control unit of the frequency converter control system further includes switch SB2. Switch SB2 is connected in parallel with the second contact of the third relay and then connected between the coil of the third relay and the control switch SA. By configuring push-button switch SB2 in conjunction with the third relay and its second contact (normally open contact), SA, SB1, and SB2 are connected during startup, energizing the coil of the third relay and causing its second contact to engage. Afterwards, SB2 is disconnected, and the coil of the third relay and its second contact remain conductive. This achieves self-locking control after startup, and since SB must be connected for the next startup, it effectively prevents accidental startup after the control circuit is disconnected.

[0013] By adopting the above technical solution, this utility model has the following beneficial effects:

[0014] This invention relates to a control circuit that addresses DCS interference in frequency converter applications. The frequency converter and DCS system are connected to the pump power line. By adding the frequency converter, the overflow pump can be accurately controlled. Furthermore, input and output reactors are connected before and after the frequency converter. By connecting reactors with matching capacities in series, the harmonics generated by the frequency converter can be effectively absorbed. Attached Figure Description

[0015] Figure 1 This is the circuit diagram of this utility model. Detailed Implementation

[0016] Example

[0017] As mentioned above, this application improves the frequency conversion control of the overflow pump, including basic and improved solutions. For example, one improved solution is equipped with both on-site and remote control solutions, another improved solution is equipped with an emergency switch SB1 solution, and yet another improved solution is equipped with a self-locking circuit. Please refer to the above description for application examples and feature combinations. They will not be described in detail here. The following will use preferred examples of all feature combinations as examples for explanation.

[0018] This embodiment describes the control circuit that causes DCS interference and addresses it in the application of the frequency converter, aiming to achieve precise control of the process flow. Taking a Pc305E slurry overflow pump with a power of 55kW as an example, an AB 1336 model frequency converter with a rated power of 90kW is used for motor speed control. The power cable from the frequency converter to the motor in the field is YJ-VV-0.6 / 1KV 3*50+1*25, with a length of 300 meters, fully meeting the selection requirements for the motor and frequency converter speed drive. In terms of control, a remote DCS control method is adopted to ensure convenient operation and system stability. Digital signals are used for communication of start, stop, operation, and fault signals, while analog signals are responsible for communication of speed adjustment, speed, and current feedback. This ensures that the pump's operating status is accurately and in real-time fed back to the operator, thereby achieving efficient and precise pump control and meeting the process adjustment needs under different operating conditions.

[0019] The main circuit of frequency converters generally adopts a standard "AC-DC-AC" structure. The input terminal connects to a 380V, 50Hz power supply conforming to national standards. The AC power is converted to DC power through a three-phase thyristor rectifier bridge at the front end of the frequency converter. Subsequently, after filtering by a capacitor bank, the DC power is inverted by the high-power IGBT switching elements at the output of the frequency converter into AC power suitable for production needs, thereby achieving precise speed control of the motor under different operating conditions. During use, it was also found that the harmonic currents and electromagnetic interference generated during the start-up and operation of the frequency converter can cause communication errors in the DCS system modules.

[0020] To gain a deeper understanding of the types of interference generated by frequency converters, it is necessary to analyze the generation mechanism of harmonics in detail. The generation of harmonics is mainly related to the nonlinear load characteristics of the frequency converter. During the rectification process of the frequency converter, the nonlinear characteristics of the three-phase thyristor rectifier bridge cause distortion of the input current waveform, thereby generating harmonics.

[0021] On the one hand, on the input side of the frequency converter, the rectifier circuit converts alternating current into direct current. During this process, the input alternating current waveform actually presents an irregular rectangular wave shape. This irregular waveform can be decomposed using Fourier series mathematical methods to obtain an ideal fundamental frequency and multiple harmonic components of different frequencies. In actual industrial production, the orders of these harmonic components usually follow a specific pattern, namely, they are in the form of 6n±1. The presence of these higher harmonics can interfere with the power supply system on the input side of the frequency converter, affecting its normal operation and power quality.

[0022] On the other hand, in the inverter output circuit of the frequency converter, the AC current waveform at the output terminal is a pulse wave modulated by a pulse width modulation (PWM) carrier signal. The PWM carrier frequency of high-power inverter switching power components like IGBTs can reach up to 15kHz. Simultaneously, the output AC current can be decomposed into the fundamental and harmonic components of a sine wave, and these harmonics can also interfere with the inverter's output circuit and other lines on the cable tray. Furthermore, in the inverter output stage of the frequency converter, the rapid switching action of the IGBT switching elements generates a high-frequency PWM carrier signal. When these high-frequency signals propagate through cables and equipment, they generate electromagnetic interference to the surrounding environment through radiation and conduction. This interference not only affects the normal operation of the frequency converter itself but may also affect other connected equipment, such as sensors and controllers, leading to data transmission errors or equipment malfunctions.

[0023] High-order harmonics or electromagnetic interference can cause malfunctions in lines, cable trays, and other electrical and electronic equipment on the same power supply, leading to data fluctuations and statistical errors in electrical or metering instruments, or even malfunctions, thus affecting production efficiency. Electromagnetic interference can also affect the input and output signals of frequency converters, as well as low-voltage signals such as detection and control signals from nearby equipment. In severe cases, it can prevent the control system from receiving actual measured detection signals or cause control system malfunctions. Typically, because large power grids have harmonic compensation and mitigation measures, the impact of harmonics generated by frequency converters and other equipment on the total load of the grid is relatively small. This often leads to harmonic impact and mitigation issues not being given much attention by most electricity users. However, for smaller systems, the harmonic interference generated during the use of frequency converters cannot be ignored.

[0024] Therefore, to address the interference problem generated by frequency converters, filters and reactors are installed on both the input and output sides of the converter to reduce the generation and propagation of harmonics; cables and equipment are rationally laid out to reduce electromagnetic interference; and the use of frequency converters is considered during the design phase, selecting appropriate frequency converter models and configurations to ensure compatibility with the entire production system. Through these measures, the interference generated by frequency converters can be effectively controlled and reduced, ensuring the stability and safety of the production process. These measures mainly include shielding and isolation technologies, as follows.

[0025] (1) Shielding. In practical applications, to effectively prevent the leakage of electromagnetic radiation generated by the frequency converter, the frequency converter is installed inside a metal distribution cabinet. The main output power line is shielded with steel pipes, while the signal cable is a shielded cable with a metal shielding layer to further enhance the protection effect. In addition, the main power circuit and control system circuit of the frequency converter are completely separated, maintaining a safe distance of at least 20cm between them, and ensuring that they are not placed in the same cable tray, thereby avoiding potential interference. For electrical equipment lines that are particularly sensitive to interference around the output lines, appropriate shielding measures are also taken to ensure that these devices can operate normally without being affected. The grounding of the cable shielding layer and the equipment shielding cover must be effective and reliable, which is a key step to ensure that the electrical shielding effect is fully realized. In this case, the Pc305E slurry overflow pump that caused the interference, these frequency converter devices are all installed in their own independent metal frame distribution cabinets.

[0026] (2) Isolation. The application of reactors is not limited to the input and output terminals of frequency converters. In fact, they can also be installed in the DC link of the frequency converter to further reduce harmonic generation. By connecting a reactor of matching capacity in series between the power input terminal and the output load terminal of the frequency converter, harmonics generated by the frequency converter equipment can be effectively absorbed. This not only helps increase the impedance of the power supply or load, but its main function is to suppress harmonics generated by the equipment, thereby reducing the interference of electromagnetic radiation carried during power transmission to the environment. Furthermore, in the same power grid system, using isolation transformers at the power supply terminal of other electrical equipment can effectively block harmonic currents on the line, further reducing harmonic interference to the power grid.

[0027] (3) Other. ① Proper and reliable shielding and grounding can effectively suppress external interference in the electrical system and reduce the interference of the electrical equipment itself to the outside world. ② Shortening the length of electrical cables can also reduce equipment interference to some extent, but this is often not feasible due to actual site conditions. ③ Power cables and signal cables should be laid in cable trays of different levels to avoid crossing between cables. If this is unavoidable, a perpendicular crossing method must be adopted, and parallel cable laying should never be used. The shielding layer of the signal cable should not be connected to the grounding terminal of the motor or frequency converter, but should be connected to the common terminal of the control line. However, this is often difficult to implement in practice. ④ Install EMI power filters, but cost factors need to be considered at this time.

[0028] See Figure 1 As described above, the power input terminal of the pump motor is connected to the power output terminal of the frequency converter via an output reactor. The power input terminal of the frequency converter is connected to the mains power via an input reactor and a main switch. The DCS system is configured and connected to the frequency converter. The speed setting pins (AI2- and AI2+) and speed feedback pins (AO1- and AO1+) of the frequency converter are connected to the DCS system. The coils of the first relay KA1, the second relay KA2, and the third relay KA3 are connected in parallel to the power supply terminals L11 and N of the control unit. The two sets of contacts of the control switch SA are respectively connected to the control circuits of the second and third relay coils. The first contact of the first relay is connected to the power supply pin of the DCS system, the first contact of the second relay is connected to the remote pin of the DCS system, and the first contact of the third relay is connected to the operating pin of the frequency converter. Switch SB1 is connected between the coil of the third relay and the control switch SA. Switch SB2 is connected in parallel with the second contact of the third relay and then connected between the coil of the third relay and the control switch SA. Etc. The frequency converter and DCS system are existing technologies and will not be described in detail here. This application applies them to a 55kW slurry overflow pump to form an improved solution. The frequency converter and DCS system are configured and connected to the pump power line. By adding the frequency converter, the overflow pump can be accurately controlled. Moreover, by configuring input and output reactors before and after the frequency converter, and by adding reactors with a capacity matching the frequency converter's capacity in series at the input and output terminals of the frequency converter, the interference problem of the DCS system is successfully solved, preventing harmonics generated during the operation of the frequency converter from interfering with the normal operation of other equipment.

[0029] It should be noted that the examples of the above embodiments can preferably be combined with one or more of each other according to actual needs, and the accompanying drawings of multiple examples adopt a set of combined technical features, which will not be described in detail here.

[0030] The above description is a detailed explanation and illustration of the preferred embodiments of the present utility model. However, these descriptions are not intended to limit the scope of protection claimed by the present utility model. All equivalent changes or modifications made under the technical teachings of the present utility model shall fall within the patent protection scope covered by the present utility model.

Claims

1. A control circuit for causing DCS interference in frequency converter applications and for resolving it, comprising a pump motor, characterized in that: It also includes a frequency converter and a reactor. The reactor includes an input reactor and an output reactor. The power input terminal of the pump motor is connected to the power output terminal of the frequency converter through the output reactor. The power input terminal of the frequency converter is connected to the mains power through the input reactor and the main switch.

2. The control circuit for causing and resolving DCS interference in frequency converter applications according to claim 1, characterized in that: It also includes a field control unit and a DCS system. The DCS system is configured to be connected to the frequency converter. The field control unit includes a control switch SA, a first relay, a second relay, and a third relay. The coils of the first relay, the second relay, and the third relay are connected in parallel to the power supply terminals of the control unit. The two sets of contacts of the control switch SA are respectively connected to the control circuits of the coils of the second relay and the third relay. The first contact of the first relay is connected to the power supply pin of the DCS system. The first contact of the second relay is connected to the remote pin of the DCS system. The first contact of the third relay is connected to the operating pin of the frequency converter.

3. The control circuit for causing DCS interference and resolving it in the application of frequency converters according to claim 2, characterized in that: The field control unit also includes a switch SB1, which is connected between the coil of the third relay and the control switch SA.

4. The control circuit for causing and resolving DCS interference in frequency converter applications according to claim 2, characterized in that: The field control unit also includes a switch SB2, which is connected in parallel with the second contact of the third relay and then connected between the coil of the third relay and the control switch SA.

5. The control circuit for causing and resolving DCS interference in frequency converter applications according to claim 1, characterized in that: The main switch is a load switch QM, and the pump motor is a three-phase motor. The U1, V1 and W1 terminals of the pump motor are connected to the U, V and W pins of the frequency converter, respectively. The L1, L2 and L3 pins of the frequency converter are connected to the L1, L2 and L3 phases of the three-phase power supply, respectively.

6. The control circuit for causing DCS interference and resolving it in the application of frequency converters according to claim 1, characterized in that: The speed setting pin and speed feedback pin of the frequency converter are connected to the DCS system.

Images