Publish Time: 2022-08-10 Origin: Site
There are many setting parameters for variable frequency drives, and each
Learn common function parameters of AC frequency inverters, so that users can set parameters correctly, quickly diagnose and modify parameter setting faults.
1. V/F Type
The selection of V/F type includes the highest frequency, basic frequency and torque type.
The highest frequency is the highest frequency at which the VFD-motor system can operate. Since the maximum frequency of the frequency drive itself may be higher, when the maximum frequency allowed by the motor is lower than the maximum frequency of the inverter, it should be set according to the requirements of the motor and its load.
The basic frequency is the boundary between constant power control and constant torque control of the motor by the inverter, and 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, and the user selects it according to the V/F type diagram in the instruction manual of the inverter and the characteristics of the load. The power, current, voltage, speed, and maximum power parameters of the motor can be directly obtained from the motor nameplate.
2. Selection of Motor Control Mode
Commonly used control methods in AC drives include V/F coordinated control, slip frequency control, vector control (VC), direct torque control (DTC), etc. These control methods have their own characteristics and objects of use, and are mainly selected according to the performance of the equipment used and the process requirements.
a. V/F control
It is suitable for occasions where the load requirements are not high, or a frequency inverter drives multiple motors, such as fans and pumps.
b. Speed Sensorless Vector Control (SVC)
Refers to open-loop vector control, usually suitable for high-performance control occasions, a frequency drive can only drive one motor. Such as machine tools, centrifuges, wire drawing machines, injection molding machines and other loads.
3. The starting method of the VFD
Generally, the adjustable frequency drive is set as panel startup at the factory, and the user can choose the panel, external terminals, communication methods, etc. according to the actual situation.
4. Given signal selection
There are many ways to give the frequency of the AC frequency drive, such as panel setting, external setting, external voltage or current setting, communication method setting, etc. One or a collection of several methods. When set correctly, the frequency drive can basically work normally. If you want to get better control effect, you can only modify the relevant parameters according to the actual situation.
1. Starting torque adjustment
The purpose of adjusting the starting torque is to improve the low-speed performance when the inverter starts, so that the torque output by the motor can meet the requirements of production start-up.
In the variable frequency speed regulation system of asynchronous motor, the control of torque is more complicated. Since the influence of resistance and leakage reactance cannot be ignored at low frequency, if V/f is still kept constant, the magnetic flux will decrease, which will lead to the decrease of motor output torque. Therefore, the voltage should be properly compensated to increase the torque. , the compensation amount is usually set to 1% to 5%.
2. Torque limit
The torque limit function can realize automatic acceleration and deceleration control, which is mainly divided into driving torque limit and braking torque limit.
The drive torque function provides a strong starting torque. During steady-state operation, the motor torque is limited to the maximum set value by controlling the motor slip. When the load torque suddenly increases, even when the acceleration time is set too short , it will not cause the inverter to trip. It is appropriate to set the driving torque to 80% to 100%.
The smaller the braking torque setting value, the greater the braking force, which is suitable for the occasion of rapid acceleration and deceleration. The braking torque is set to 0%, so that the motor can decelerate to a stop without using a braking resistor during deceleration without tripping. But for some loads, if the braking torque is set to 0%, there will be short-term idling during deceleration, causing the inverter to start repeatedly, and in severe cases, the inverter will trip.
3. Selection of acceleration and deceleration mode
Also called acceleration and deceleration curve selection. Generally, there are three kinds of linear, non-linear and S curves for variable frequency drives, and most of them usually choose linear curve. When setting, the corresponding curve can be selected according to the load torque characteristics.
Non-linear curves are suitable for variable torque loads, such as fans.
S-curve is suitable for constant torque load, and its acceleration and deceleration change is relatively slow.
4. Carrier frequency setting
By adjusting the carrier frequency, the motor noise can be reduced, the resonance point of the mechanical system can be avoided, the leakage current of the line to the ground and the interference generated by the inverter can be reduced.
When the carrier frequency is low, the higher harmonic components of the output current increase, the loss of the motor increases, and the temperature rise of the motor increases.
When the carrier frequency is high, the motor loss decreases and the motor temperature rise decreases, but the inverter loss increases, the inverter temperature rise increases, and the interference increases.
When the vfd is running, the user can adjust the carrier frequency (ie, adjust the PWM switching frequency) within a certain range to reduce noise or interference.
1. Acceleration and deceleration time
The acceleration time is the time it takes for the output frequency to rise from 0 to the maximum frequency, and the deceleration time is the time it takes for the output frequency to drop from the maximum frequency to 0. Usually, the acceleration and deceleration time is determined by the rise and fall of the frequency setting signal. When the motor accelerates, the rate of increase of the frequency setting must be limited to prevent overcurrent, and when the motor is decelerated, the rate of decrease must be limited to prevent overvoltage.
Acceleration time setting requirements:
Limit the acceleration current below the overcurrent capacity of the ac drive, so as not to cause the inverter to trip due to overcurrent stall.
The main point of deceleration time setting is to prevent the voltage of the smoothing circuit from being too large, and to prevent the regenerative overvoltage from stalling and tripping the vfd.
The acceleration and deceleration time can be calculated according to the load, but in debugging, a longer acceleration and deceleration time is often set according to the load and experience, and the overcurrent and overvoltage alarms are observed by starting and stopping the motor. Then gradually shorten the setting time of acceleration and deceleration. Based on the principle that no alarm occurs during operation, repeat the operation several times to determine the best acceleration and deceleration time.
2. Frequency Limit
That is, the upper and lower limits of the output frequency of the vfd. Frequency limit is a protection function to prevent misoperation or failure of external frequency setting signal source, which causes the output frequency to be too high or too low to prevent damage to the equipment. You can set it according to the actual situation in the application.
This function can also be used as a speed limiter. For some belt conveyors, since there are not too many materials to be conveyed, in order to reduce the wear of machinery and belts, a adjustable frequency drive can be used to drive, and the upper limit frequency of the VFD is set to a certain frequency value. This allows the belt conveyor to run at a fixed, lower operating speed.
3. Electronic thermal overload protection
This function is set to protect the motor from overheating. It is the CPU in the variable frequency drive that calculates the temperature rise of the motor according to the operating current value and frequency, so as to perform overheating protection.
This function is only applicable to the "one-to-one" occasion, and in the case of "one-to-many", a thermal relay should be installed on each motor.
Electronic thermal protection setting value (%)=[rated current of motor (A)/rated output current of VFD (A)]×100%.
4. Frequency jump setting
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 will not be able to run, and even overcurrent protection occurs during acceleration, making the motor unable to start normally, which is more serious when the motor is lightly loaded or has a small amount of rotation.
Therefore, ordinary frequency inverters are equipped with frequency jumping function, the user can set the jumping point and jumping point width on the v/f curve according to the frequency point where the system oscillates. When the motor accelerates, these frequency segments can be automatically skipped to ensure the normal operation of the system.