Inverter should be installed in the control cabinet, control cabinet design should pay attention to the following issues:
1. Heat dissipation
The heating of frequency converter is caused by internal loss.The main circuit is the main part of the losses in the inverter, accounting for about 98%, and the control circuit accounts for 2%.In order to ensure the normal and reliable operation of the inverter, it is necessary to heat the converter.
The inner fan of the converter can take away the heat from the box of the converter. If the fan cannot work normally, the converter should be stopped immediately.High-power frequency converters also need to add fans on the control cabinet, the air duct of the control cabinet should be reasonably designed, all the air inlet should be set dustproof net, ventilation unobstructed, to avoid the formation of eddy current in the cabinet, in a fixed position to form dust accumulation;According to the ventilation volume of the inverter manual to choose the matching fan, fan installation should pay attention to the shock problem.
2. Electromagnetic interference problem.
Due to rectification and frequency conversion, a lot of interference electromagnetic waves are generated around the inverter. These high frequency electromagnetic waves have certain interference to nearby instruments and instruments, and will generate high order harmonics, which will enter the whole power supply network through the power supply loop and affect other instruments.If the power of inverter accounts for more than 25% of the whole system, it is necessary to consider the anti-interference measures of the control power.
When there is high-frequency shock load in the system, such as welding machine and electroplating power supply, the inverter itself will be protected due to interference, so the power quality of the whole system should be considered.
3. Protection issues need to pay attention to the following points
Waterproof and dew proof: if the inverter is placed on the site, it is necessary to pay attention to the pipe flange or other leakage points on the inverter cabinet, and there should be no splashing water near the inverter. In short, the protection level of the field cabinet should be above IP43.WeChat ID technology into training worthy of your attention!
Dustproof: all air intents shall be equipped with dustproof net to block entry of flocculent sundries. The dustproof net shall be designed as detachable to facilitate cleaning and maintenance.The grid of dustproof net is decided according to the specific situation of the spot, the union place of dustproof net all round and control cabinet should deal with closely.
Anti-corrosive gas: this situation is more common in the chemical industry. At this time, the frequency conversion cabinet can be placed in the control room.
4. Inverter wiring specification
Signal line and power line must be separated from each other: when using analog signal to remotely control the inverter, in order to reduce interference from the inverter and other equipment, please separate the signal line that controls the inverter from the strong current loop (main loop and auxiliary control loop).The distance should be over 30cm.This wiring specification should be maintained even in the control cabinet.The maximum control loop between the signal and the converter shall not exceed 50m.
Signal line and power line must be placed in different metal pipelines or metal hoses: if the signal line connecting PLC and inverter is not placed in the metal pipeline, it will be easily disturbed by inverter and external equipment;At the same time, because the inverter has no built-in reactor, the input and output power lines of the inverter will produce extremely strong interference with the external part. Therefore, the metal tube or metal hose where the signal line is placed should be extended to the control terminal of the inverter to ensure the complete separation of the signal line and the power line.
1) analog quantity control signal line shall use double stranded shielded wire with the wire specification of 0.75mm2.When wiring must pay attention to, the cable stripping should be as short as possible (5-7mm), at the same time after the stripping of the shielding layer should be wrapped with insulation tape, in order to prevent the shield wire and other equipment contact introduce interference.
2) in order to improve the simplicity and reliability of wiring, it is recommended to use the wire bar terminal on the signal line.
5. Operation of inverter and setting of relevant parameters
There are many setting parameters of the frequency converter, and each parameter has a certain selection range. In use, it is often encountered that the frequency converter cannot work normally due to the improper setting of some parameters.
Control mode: speed control, torque control, PID control or other methods.After the control mode is adopted, static or dynamic identification is generally required according to the control accuracy.
Minimum operating frequency: namely, the minimum running speed of the motor. When the motor runs at a low speed, its heat dissipation performance is very poor.And at low speeds, the current in the cable increases, causing the cable to heat up.WeChat ID technology into training worthy of your attention!
Operating frequency: the maximum frequency of general frequency converter is 60Hz, and some even reach 400hz. The high frequency will make the motor run at high speed.
Carrier frequency: the higher the carrier frequency is set, the larger the high-order harmonic component will be, which is closely related to cable length, motor heating, cable heating, frequency converter heating and other factors.
Motor parameters: the inverter sets the motor power, current, voltage, speed and maximum frequency in the parameters, which can be directly obtained from the motor nameplate.
Frequency hopping: resonance phenomenon may occur at a certain frequency, especially when the whole device is relatively high;When controlling the compressor, avoid the surge point of the compressor.