The role of frequency converter in motor control

For Electric Motor products, when they are produced strictly according to the design parameters and process parameters, the speed difference of motors of the same specification is very small, generally not more than two revolutions. For the motor of a single-machine driving device, there is no overly stringent requirement for the motor speed, but for equipment or equipment systems driven by multiple motors, the control of the motor speed is very important.

In traditional transmission systems, to ensure a certain speed relationship between multiple actuators, including ensuring speed synchronization or a certain speed ratio, mechanical transmission rigid connection devices are often used. However, if the mechanical transmission device between multiple actuators is large and the distance between the actuators is far, it is necessary to consider using an independent control non-rigid connection transmission control method.

As the frequency converter technology matures and its application scope expands, it can be controlled by programmable controllers to meet the different requirements of speed control flexibility, accuracy and reliability in the transmission system. In actual production, the application of PLC and frequency converter for speed control can also better achieve the expected synchronization or given speed ratio control requirements.

The energy-saving effect of the frequency converter is mainly reflected in the application of fans and water pumps. After the fan and pump loads adopt frequency conversion speed regulation, the power saving rate is 20%~60%. This is because the actual power consumption of the fan and pump loads is basically proportional to the cube of the speed. When the average flow required by the user is small, the fan and pump adopt frequency conversion speed regulation to reduce their speed, and the energy-saving effect is very obvious. Traditional fans and pumps use baffles and valves to adjust the flow, the motor speed remains basically unchanged, and the power consumption does not change much. According to statistics, the power consumption of fan and pump motors accounts for 31% of the national power consumption and 50% of industrial power consumption. It is of great significance to use frequency conversion speed regulation devices on such loads. At present, the more successful applications are constant pressure water supply, various fans, central air conditioners and hydraulic pumps.

Direct motor starting will not only cause serious impact on the power grid, but also place too high a demand on the power grid capacity. The large current and vibration generated during starting will cause great damage to the baffles and valves, and are extremely detrimental to the service life of equipment and pipelines. After using the inverter, the inverter's soft start function will make the starting current change from zero, and the maximum value will not exceed the rated current, reducing the impact on the power grid and the demand for power supply capacity, extending the service life of equipment and valves, and also saving equipment maintenance costs.

Since the inverter has a built-in 32-bit or 16-bit microprocessor, has a variety of arithmetic logic operations and intelligent control functions, the output frequency accuracy is 0.1%~0.01%, and is equipped with perfect detection and protection links, it is widely used in automation systems. For example: winding, stretching, metering, wire guide in the chemical fiber industry; flat glass annealing furnace, glass kiln stirring, edge drawing machine, bottle making machine in the glass industry; automatic feeding and batching system of arc furnace and intelligent control of elevators. Application of inverters in improving process level and product quality in CNC machine tool control, automobile production line, papermaking and elevators.

Frequency converters can also be widely used in various mechanical equipment control fields such as transmission, lifting, extrusion and machine tools. It can improve the process level and product quality, reduce the impact and noise of equipment, and extend the service life of equipment. After adopting frequency conversion speed control, the mechanical system is simplified, the operation and control are more convenient, and some can even change the original process specifications, thereby improving the function of the entire equipment. For example, the temperature in the setting machine used in textile and many industries is adjusted by changing the amount of hot air sent in. The circulating fan is usually used to transport hot air. Since the fan speed is constant, the amount of hot air sent in can only be adjusted by the damper. If the damper fails to adjust or adjusts improperly, it will cause the setting machine to lose control, thereby affecting the quality of the finished product. The circulating fan starts at high speed, and the wear between the transmission belt and the bearing is very severe, making the transmission belt a consumable. After adopting frequency conversion speed control, temperature regulation can be achieved by the frequency converter automatically adjusting the speed of the fan, solving the problem of product quality. In addition, the frequency converter can easily realize the fan starting at low frequency and low speed and reduce the wear between the transmission belt and the bearing. It can also extend the service life of the equipment and save energy by 40%.