Protection function of frequency drive

VFD is a control device that uses frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's operating power supply. Vfd inverter is mainly composed of rectification (AC to DC), filter, inverter (DC to AC), braking unit, drive unit, detection unit, micro-processing unit, etc. VFD provides the power supply voltage it needs by turning off the internal IGBT, and then achieves the purpose of energy saving and speed regulation. In addition, VFD has many protection functions, such as over-current, over-voltage, overload protection and so on. The following is a brief analysis of the protection function of frequency drive.

The main reasons for the overcurrent are: encountering an impact load, short circuit on the output side of the VFD, and overcurrent caused by speed up and down. The main measures for frequency drive to prevent overcurrent: the user can set a current limit according to the rated current of the motor and the specific load conditions. When the operating current exceeds this limit, the vsd drive will automatically reduce its operating frequency. When the operating current decreases to the value Below, the working frequency will be restored gradually. When the current exceeds the current limit in the process of speed up and down, the VFD will suspend the speed up or down, and when the belt current drops below the limit, it will continue to speed up or down.

Overload protection and maintenance: In the VFD, the current can be measured conveniently and accurately, and the inverse time protection characteristic can be realized through precise calculation, which greatly improves the protection and reliability of the vsd drive.

Voltage protection is divided into over-voltage protection and under-voltage protection. The main causes of over-voltage are: over-voltage of power supply, regenerative over-voltage caused by feedback energy not being released in time during deceleration. In SPWM modulation mode, the circuit is based on a series of pulses way of working. Due to the existence of winding inductance and line inductance in the circuit, during the rise and fall of each pulse, a large pulse voltage may be generated at the peak. This pulse voltage will be superimposed on the DC voltage to form a destructive pulse voltage.

Protective measures: prevent power supply overvoltage, prevent tripping function during regenerative braking, and protect against pulse overvoltage. Causes of undervoltage: Power supply. The power supply voltage is too low, the power supply phase loss circuit and other reasons will lead to the occurrence of undervoltage. Undervoltage protection: One of the consequences of undervoltage is the torque drop of the motor, and the new series of frequency drive have various compensation functions to enable the motor to run continuously. Another consequence of undervoltage is when the current of the motor increases, and the frequency drive has a perfect overload protection function and checks the components in time.