Function of frequency converter

Frequency converter refers to the power converter that changes the frequency (excluding zero frequency) related to electric energy. According to the definition, the function of frequency converter is to change frequency. What changes will be brought about by changing frequency, and what functions can be improved?

1、 The function of frequency converter frequency conversion energy saving

The most obvious application of frequency conversion energy saving is in the fan water pump industry. Because the power consumption of the fan pump is directly proportional to the cube of the speed, when the external air / water consumption is not high, the energy saving effect is obvious if the speed is reduced by using frequency conversion. The energy-saving principle of other industries is roughly the same, which is achieved by lowering the motor speed when full speed operation is not required.

2、 The function of frequency converter soft start

When the motor is directly started at power frequency, it will produce 7 to 8 times of the rated current of the motor. This current value will greatly increase the electrical stress of the motor winding and generate heat, thus reducing the life of the motor, and at the same time, it will cause great impact on the power grid. The variable frequency speed regulation can be started at zero speed and zero voltage (torque can be increased appropriately). Once the relationship between frequency and voltage is established, the inverter can drive the load to work according to V / f or vector control mode. The use of variable frequency speed regulation can fully reduce the starting current, improve the bearing capacity of winding, reduce the impact of starting current on the motor and power grid, and prolong the service life of the motor. At the same time, it will not cause the problem of excessive peak valley difference, which will cause the fault trip or abnormal operation of voltage sensitive equipment in the power supply network.

3、 The function of frequency converter -- simplification of control system

Variable frequency speed regulation can start at zero speed and accelerate uniformly according to the needs of users, and its acceleration curve can also be selected (linear acceleration, S-shaped acceleration or automatic acceleration). The running speed can be adjusted at any time according to the needs, and can be changed rapidly according to the process. The speed can be changed by remote control PLC or other controllers.

4、 The function of frequency converter -- reducing mechanical wear and loss

When starting by power frequency, the motor or the connected mechanical shaft or gear will produce severe vibration. This vibration will further aggravate the mechanical wear and loss and reduce the life of mechanical components and motors. In the variable frequency speed regulation, the stop mode can be controlled, and there are different stop modes to choose (deceleration parking, free parking, deceleration parking + DC braking), which can reduce the impact on mechanical parts and motors, so as to make the whole system more reliable, increase the service life and improve the stability of the system.

5、 Function of frequency converter -- adjustable torque limit

Through the frequency control, the corresponding torque limit can be set to protect the machine from damage, thus ensuring the continuity of the process and the reliability of the product. The current frequency conversion technology makes not only the torque limit adjustable, but also the torque control accuracy can reach about 3% - 5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, but can not set the precise torque value to act as in the frequency conversion control.

With the development of science, the use of frequency converter will be more and more widely, and the role of frequency converter will be further increased. No matter on industrial equipment or household appliances, frequency converter will play a greater role as an electric energy converter.

The main circuit of frequency converter can be roughly divided into two categories: voltage type is to convert DC voltage source into AC converter, DC circuit filter is capacitor. The current mode is a frequency converter which transforms the DC of current source into AC. the filter of DC loop is inductance. It consists of three parts: a "rectifier" which transforms the power supply from power frequency to DC power, and a "smoothing circuit" which absorbs the voltage fluctuation generated by the converter and inverter

Classification of frequency converter

Classification by transformation link

(1) AC-DC-AC frequency converter, is the first power frequency AC through the rectifier into DC, and then the DC into the frequency and voltage adjustable AC, also known as indirect inverter, is currently widely used in general inverter.

(2) It can be divided into AC-AC converter, that is, power frequency AC is directly transformed into AC with adjustable frequency and voltage, also known as direct frequency converter.