Medium and low voltage frequency converter parameter setting

01

V/f type selection

The selection of v/f type includes the highest frequency, basic frequency and torque type. The maximum frequency is the highest frequency that the frequency converter motor system can operate. Because the maximum frequency of the frequency converter itself may be higher, when the maximum frequency allowed by the motor is lower than the maximum frequency of the frequency converter, it should be set according to the requirements of the motor and its load; The basic frequency is the dividing line between constant power control and constant torque control of the motor by the frequency converter, which should be set according to the rated voltage of the motor; Torque type refers to whether the load is constant torque load or variable torque load. The user selects one type according to the v/f type diagram and load characteristics in the operation manual of the frequency converter. According to the actual situation and requirements of the motor, the maximum frequency is set to 83.4hz and the basic frequency is set to 50Hz. Load type: constant torque load is below 50Hz, and constant power load is 50 ~ 83.4hz.

02

How to adjust the starting torque

The purpose of adjusting the starting torque is to improve the low-speed performance of the frequency converter when starting, so that the torque output by the motor can meet the production starting requirements. In the variable frequency speed regulation system of asynchronous motor, the torque control is more complex. In the low frequency band, the influence of resistance and leakage reactance can not be ignored. If v/f is still kept constant, the magnetic flux will be reduced, thereby reducing the output torque of the motor. Therefore, the voltage should be properly compensated in the low frequency band to improve the torque. However, the influence of leakage impedance is not only related to frequency, but also to the size of motor current, so it is very difficult to accurately compensate. In recent years, foreign countries have developed some frequency converters that can compensate by themselves, but the amount of calculation required is large, and the hardware and software are complex. Therefore, generally, the frequency converters are manually set and compensated by users.

03

How to set acceleration and deceleration time

The frequency change rate of the frequency converter in the process of starting and braking is set by the user. If the motor inertia J and the motor load change according to the preset frequency change rate, the acceleration torque may be insufficient, resulting in motor stall, that is, the motor speed is inconsistent with the output frequency of the frequency converter, resulting in overcurrent or overvoltage. Therefore, it is necessary to reasonably set the acceleration and deceleration time according to the motor inertia and load, so that the frequency change rate of the frequency converter can be coordinated with the motor speed change rate. The method to check whether this setting is reasonable is to select the acceleration and deceleration time according to experience. If overcurrent occurs during startup, the acceleration time can be extended appropriately; If overcurrent occurs during braking, the deceleration time shall be extended appropriately; On the other hand, the acceleration and deceleration time should not be set too long, otherwise the production efficiency will be affected, especially in the case of frequent starting and braking.

04

Frequency jump

When the inverter controlled by v/f drives the asynchronous motor, the current and speed of the motor will oscillate in some frequency bands. In serious cases, the system cannot run, and even overcurrent protection occurs during the acceleration process, which makes the motor unable to start normally. It is more serious when the motor is under light load or the rotation is small. Ordinary frequency converters are equipped with frequency jump function. Users can set the jump point and jump point width on the v/f curve according to the frequency point where the system oscillates. When the motor accelerates, it can automatically skip these frequency bands to ensure the normal operation of the system.

05

Overload rate setting

This setting is used for overload protection of frequency converter and motor. When the output current of the frequency converter is greater than the ol set value determined by the overload rate and the rated current of the motor, the frequency converter will carry out overload protection (OL) with inverse time limit characteristics, and the frequency converter will stop output when the overload protection acts.

06

Input of motor parameters

Some of the parameter input items of the frequency converter are the input of the basic parameters of the motor, such as the power, rated voltage, rated current, rated speed, number of poles, etc. The input of these parameters is very important, which will directly affect the normal play of some protection functions in the frequency converter. We must input them correctly according to the actual parameters of the motor to ensure the normal use of the frequency converter.