Why Choose a Frequency Inverter?

A frequency inverter (Variable-frequency Drive, VFD) is a power control device that uses frequency conversion technology and microelectronics technology to control AC motors by changing the motor's operating power supply frequency. The frequency inverter mainly comprises rectification (AC to DC), filtering, inverter (DC to AC), braking unit, drive unit, detection unit and micro-processing unit. The inverter adjusts the voltage and frequency of the output power supply by switching off the internal IGBT, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation.

Why choose a frequency inverter?

Some people say that I can just use the motor directly, why should I choose the frequency converter? If the power of your motor is very small for household use and there is no need for speed regulation or constant voltage automation, you can directly start the electrical use. If there are no effects such as voltage conversion and frequency conversion, then the inverter must be used, not only to help you protect the motor and prolong the service life of the motor, but also to effectively protect the motor and on-site electricity safety, and protect other surrounding electrical equipment and factory circuits. So what function does the frequency converter have, and when must the frequency converter be used?

Why choose a frequency inverter?

Energy saving of frequency conversion speed regulation

  • After adopting frequency conversion speed regulation, the energy-saving effect of fans and pump loads is the most obvious, and the power saving rate can reach 20% to 60%. This is because the power consumption of fans and pumps is proportional to the cube of the speed. When the user When the required average flow rate is small, the speed of the fan and water pump is low, and its energy-saving effect is also very considerable. However, when the traditional baffle and French door are used for flow adjustment, the power consumption does not change much. Since there are many such loads, accounting for about 20% to 30% of the total capacity of the AC motor, their energy saving is of great significance.
  • For some constant torque loads running at low speed, such as conveyor belts, frequency control can also save energy. In addition, the original speed regulation method consumes a lot of energy, the original speed regulation method is relatively complicated, and the efficiency is low. After adopting frequency conversion speed regulation, the energy saving effect is also obvious.

Advantages of frequency conversion speed regulation in motor operation

  1. It is easy to realize the positive and negative rotation of the motor with frequency conversion speed regulation. It is only necessary to change the switching sequence of the inverter tube inside the frequency converter to achieve output commutation, and there is no problem of burning the motor due to improper commutation.
  2. Most of the frequency conversion speed regulation systems start from low speed and low frequency. The acceleration and deceleration time can be set arbitrarily, so the acceleration and deceleration time is relatively gentle, the starting current is small, and it can start and stop at a higher frequency.
  3. When the frequency conversion speed regulation system is braking, the frequency converter can use its own braking circuit to consume the energy of the mechanical load on the braking resistor, and also feed it back to the power grid. However, special accessories are needed to feed back to the grid, and the investment is relatively high. big. In addition, the frequency converter also has a DC braking function. When braking is required, the frequency converter applies a DC voltage to the motor for braking, so there is no need to add a braking control circuit.
  4. The DC motor can be replaced by a frequency converter, and an induction motor is used at this time. Like DC motors, no brushes, slip-rings, etc. are required, and maintainability and environmental resistance are excellent.
  5. One inverter can run in parallel to control several engines
  6. The inverter can be soft-started and soft-closed, and the acceleration/deceleration time of the engine can be adjusted arbitrarily.
  7. Reduce the starting current. Through the soft start and soft close of the frequency converter, the starting current can be reduced to 1.5~2 times of the rated current when the motor starts. Generally, when starting straight-in, a starting current 6 times the rated current flows, so that loads are imposed on the frequent operation and stop of the motor.
  8. The rebound braking of the inverter is convenient for electric braking.

Applications aimed at improving process level and product quality

In addition to the application of frequency conversion speed regulation in fan and pump loads, it can also be widely used in various mechanical equipment control fields such as transmission, winding, lifting, extrusion, and machine tools. It can improve its production yield, prolong the normal working cycle and service life of the equipment, simplify the operation and control system, and some can even change the original process specifications, thereby improving the control level of the entire equipment.

How to choose the configuration of the inverter?

When selecting the inverter configuration, it is necessary to fully grasp the load characteristics, but it is also difficult to do.

  1. Confirm the load characteristics such as load type, speed and nature;
  2. Confirm whether it is continuous operation, long-term operation, short-term operation and other operating characteristics;
  3. Confirm the maximum consumption output value and rated output value;
  4. Confirm the maximum number of revolutions and the rated number of revolutions;
  5. Confirm the speed control range;
  6. Confirm load changes, current, voltage, frequency, temperature changes, etc.;
  7. Confirm the required control precision;
  8. Confirm the braking method;
  9. Confirm the input power configuration, that is, select the capacity based on factors such as speed-torque characteristics, overload capacity, time rating, starting torque, rated output value, operation mode, control mode, number of revolutions, efficiency-power, etc.

However, it is not easy to select the inverter configuration using the above method, so ordinary users can choose the inverter according to the motor configuration. Select the configuration voltage (220V, 380V, 440V) and select the inverter capacity according to the engine capacity (kW). Generally, products with low starting torque and load, such as fans and water pumps, use motors and inverters with a capacity of 1:1; for elevators, cranes, etc. that require more torque and large loads, the selected capacity is one higher than that of the motor to the second-stage inverter.

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