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The setting of several important parameters of the inverter

Aug 25, 2020

The setting of several important parameters of the inverter

01


V/f type selection


The choice of V/f type includes the highest frequency, basic frequency and torque type. The highest frequency is the highest frequency that the inverter-motor system can run. Since the highest frequency of the inverter itself may be higher, when the highest allowable frequency of the motor is lower than the highest frequency of the inverter, it should be set according to the requirements of the motor and its load. The basic frequency is the dividing line between the inverter's constant power control and constant torque control of the motor. It should be set according to the rated voltage of the motor; the torque type refers to whether the load is a constant torque load or a variable torque load. Choose one of the V/f type diagrams and load characteristics in the inverter manual. According to the actual situation and actual requirements of the motor, the highest frequency is set to 83.4Hz, and the basic frequency is set to 50Hz. Load type: constant torque load below 50Hz, constant power load at 50~83.4Hz.

02


How to adjust the starting torque


Adjusting the starting torque is to improve the low-speed performance of the inverter 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 complicated. In the low frequency range, the influence of resistance and leakage reactance cannot be ignored. If the V/f is kept constant, the magnetic flux will be reduced, thereby reducing The output torque of the motor. For this reason, the voltage should be properly compensated in the low frequency band to increase the torque. However, the influence of the leakage impedance is not only related to the frequency, but also related to the size of the motor current, so accurate compensation is very difficult. In recent years, some inverters capable of self-compensation have been developed abroad, but they require a large amount of calculation, and the hardware and software are relatively complicated. Therefore, the general inverters are manually set and compensated by users.


03


How to set acceleration and deceleration time


The frequency change rate of the inverter in the process of starting and braking is set by the user. If the motor moment of inertia J and the motor load change increase or decelerate according to the preset frequency change rate, the acceleration torque may be insufficient, which will cause the motor to stall, that is, the motor speed is not coordinated with the output frequency of the inverter, resulting in excessive Current or overvoltage. Therefore, it is necessary to reasonably set the acceleration and deceleration time according to the moment of inertia of the motor and the load, so that the frequency change rate of the inverter can be coordinated with the change rate of the motor speed. The way to check whether this setting is reasonable is to select the acceleration and deceleration time based on experience. If over-current occurs during starting, the acceleration time can be appropriately extended; if over-current occurs during braking, the deceleration time should be appropriately extended; on the other hand, the acceleration and deceleration time should not be set too long, otherwise it will affect production efficiency , Especially in the case of frequent starting and braking.


04


Frequency span


When a V/f-controlled inverter drives an asynchronous motor, the current and speed of the motor will oscillate in certain frequency ranges. In severe cases, the system cannot run, and even overcurrent protection occurs during acceleration, which prevents the motor from starting normally. It is more serious when the load is light or the amount of rotation is small. Ordinary inverters are equipped with a frequency jump function. Users can set the jump point and the width of the jump point on the V/f curve according to the frequency point at which the system oscillates. When the motor accelerates, these frequency bands can be automatically skipped to ensure the normal operation of the system.


05


Overload rate setting


This setting is used for inverter and motor overload protection. When the output current of the inverter is greater than the OL setting value determined by the overload rate setting value and the rated current of the motor, the inverter will perform overload protection (OL) with the inverse time characteristic, and the inverter will stop output when the overload protection is activated.


06


Input of motor parameters


Some of the parameter input items of the inverter are the input of basic parameters of the motor, such as the power of the motor, rated voltage, rated current, rated speed, number of poles, etc. The input of these parameters is very important and will directly affect the normal performance of some protection functions in the inverter. The actual parameters of the motor must be entered correctly to ensure the normal use of the inverter.