Understand and Be Able to Debug the Following Ten VFD Parameters

Considering the large number of inverter function parameters, there are usually dozens or even hundreds of parameters for users to choose. In actual operation, there is no need to set and debug every parameter, most of them only need to use the factory settings. However, some parameters are closely related to actual use, and some are related to each other, so they should be set and debugged according to the actual situation.

1. Acceleration and deceleration time

The acceleration time is the time required for the output frequency to rise from 0 to the maximum frequency, and the deceleration time is the time required for the output frequency to decrease from the maximum frequency to 0. Usually, the acceleration and deceleration times are determined by the rise and fall of the frequency setting signal. When the motor is accelerating, the rate of increase set by the frequency should be limited to prevent overcurrent, and when decelerating, the rate of decrease should be limited to prevent overvoltage.

Acceleration time setting requirements: limit the acceleration current below the overcurrent capacity of the inverter to avoid tripping of the inverter due to overspeed; the key point of deceleration time setting is to prevent the voltage of the smoothing circuit from being too high, so as to avoid regenerative overvoltage stall and the inverter. The acceleration and deceleration time can be calculated according to the load, but in debugging, it is often used to set a longer acceleration and deceleration time according to the load and experience, and observe whether there is an over-current or over-voltage alarm by starting and stopping the motor; then, the setting of acceleration and deceleration Time gradually shortened. Based on the principle of no alarm during operation, the best acceleration and deceleration time can be determined by repeating several operations.

2. Torque increase

Also known as torque compensation, it is a method of increasing f/V in the low frequency range to compensate for the torque reduction caused by the motor stator winding resistance at low speeds. When set to auto, the voltage during acceleration can be automatically boosted to compensate for the starting torque, so that the motor can accelerate smoothly. If manual compensation is used, according to the load characteristics, especially the start-up characteristics of the load, a better curve can be selected through experiments. For variable torque loads, if the selection is improper, the output voltage will be too high at low speed, wasting electric energy, and even the current will be too high when the motor starts with load, but the speed will not increase.

3. Electronic thermal overload protection

This function is set to prevent the motor from overheating. That is, the CPU in inverter calculates the temperature rise of the motor according to the operating current value and frequency, so as to protect the motor from overheating. This function is only applicable to the occasion of “one driving one”, while in the case of “one driving many”, the thermal relay should be installed on each motor.

Electronic protection setting (%) = [motor rated current (A) / inverter rated output current (A) > & times; 100%.

4. Frequency limitation

That is, the upper and lower limits of the output frequency of the inverter. Frequency limitation is a protection function to prevent the output frequency from being too high or too low due to misoperation or failure of the external frequency setting signal source, thereby preventing equipment damage. It can be set according to the actual situation in the application. This feature can also be used as a speed limit. For some belt conveyors, since there are not many materials to be transported, in order to reduce the wear of the machine and the belt, the inverter drive can be used, and the upper frequency of the inverter can be set to a certain frequency value, so that the belt conveyor can be fixed at a fixed frequency. low operating speed.

5. Bias frequency

Some are also called deviation frequency or frequency deviation setting. Its purpose is to use this function to adjust the output frequency when the frequency is set by an external analog signal (voltage or current), as shown in Figure 1. For some inverters, when the frequency setting signal is 0%, the deviation value can be in the range of 0 ~ fmax, and some inverters (such as Mingdiansha, Sanken) can also set the bias polarity. For example, when the frequency setting signal is 0% during debugging, the output frequency of the inverter is xHz instead of 0Hz, then setting the offset frequency to negative xHz can make the output frequency of the inverter 0Hz.

6. Frequency setting signal gain

This function is only valid when the frequency is set by an external analog signal. It is used to make up for the inconsistency between the external setting signal voltage and the internal voltage (+10v) of the inverter; at the same time, it is convenient to select the analog setting signal voltage. When set, when the analog input signal is at its maximum value (such as 10v, 5v, or 20mA), the frequency percentage of the output f/V graph is calculated and set as a parameter. If the external setting signal is 0 ~ 5V, if the output frequency of the inverter is 0 ~ 50Hz, the gain signal can be set to 200%.

7. Torque limit

It can be divided into driving torque limit and braking torque limit. According to the output voltage and current value of the frequency converter, the torque is calculated by the CPU, which can significantly improve the recovery characteristics of the impact load during acceleration, deceleration and constant speed operation. Torque limit function can realize automatic acceleration and deceleration control. Assuming that the acceleration and deceleration time is less than the load inertia time, the motor can automatically accelerate and decelerate according to the torque setting value.

The drive torque function provides strong starting torque. In steady state operation, the torque function will control the slip of the motor and limit the motor torque to a maximum set value. When the load torque increases suddenly, even if the acceleration time is set too short, it will not cause the inverter to malfunction. When the acceleration time is set too short, the motor torque will not exceed the maximum set value. A large driving torque is conducive to starting, and it is better to set it at 80 ~ 100%.

The smaller the setting value of the braking torque, the greater the braking force, which is suitable for rapid acceleration and rapid deceleration. For example, if the braking torque setting value is too high, there will be an overvoltage alarm. If the braking torque is set to 0%, the total amount of regeneration added to the main capacitor can be close to 0, so when the motor is decelerating, it can decelerate to stall without tripping without using a braking resistor. However, on some loads, if the braking torque is set to 0%, there will be a short idling phenomenon during deceleration, which will cause the inverter to start repeatedly and the current fluctuates greatly. In severe cases, the inverter will trip, so attention should be paid.

8.Acceleration and deceleration mode selection

Also known as acceleration and deceleration profile selection. General Inverter has three types of curves: linear, nonlinear, and S, most of which are linear curves; nonlinear curves are suitable for variable torque loads, such as fans. The s-curve is suitable for constant torque loads, whose acceleration and deceleration changes slowly. When setting, the corresponding curve can be selected according to the load torque characteristics, but there are exceptions. When debugging the frequency converter of a boiler induced draft fan, the author first selects a nonlinear curve for acceleration and deceleration curves, and then trips when the frequency converter is started together. Adjusting and changing many parameters has no effect, and then it is normal to change to S-curve. The reason is: before starting, the induced draft fan rotates by itself due to the flow of flue gas, and turns into a negative load. In this way, the S curve is selected, so that the frequency rises slowly at the initial stage of starting, thus avoiding the occurrence of the frequency converter. Of course, this is the method adopted by the frequency converter, it does not start the DC braking function.

9. Torque vector control

The theoretical basis of vector control is that asynchronous motors and DC motors have the same torque generation mechanism. The vector control method is to divide the stator current into the specified magnetic field current and torque current, and control them separately, and output the synthesized stator current to the motor at the same time. Therefore, the same control performance as that of a DC motor can be obtained in principle. Through the torque vector control function, the motor can output the maximum torque under various working conditions, especially in the low-speed operation area.

At present, almost all frequency converters adopt non-feedback vector control. Because the frequency converter can compensate the slip according to the magnitude and phase of the load current, the motor has very hard mechanical characteristics, which can meet the requirements of most occasions. There is no need to install a speed feedback circuit outside the inverter. This function can be set according to the actual situation by selecting one of valid and invalid.

The related function is slip compensation control, which can increase the slip frequency corresponding to the load current and compensate the speed deviation caused by load fluctuation. This function is mainly used for positioning control.

10. Energy saving control

Fans and water pumps are torque-reduced loads, that is, as the speed decreases, the load torque decreases proportionally to the square of the speed, and the frequency converter with energy-saving control function adopts a special V/f mode design, which can improve the performance of the motor and frequency converter. It can automatically reduce the output voltage of the inverter according to the load current to achieve the purpose of energy saving, and can be set to be valid or not according to the specific situation.

It should be noted that the nine and ten parameters are very advanced, but some users cannot enable these two parameters at all when the equipment is refitted, that is to say, the frequency converter is frequent after enabling, and everything is normal after disabling.

The reasons are as follows:
(1) The original motor parameters are too different from the motor parameters required by the inverter.
(2) Insufficient understanding of the functions of the set parameters, such as the energy-saving control function can only be used in the V/f control mode, but not in the vector control mode.
(3) The vector control mode is enabled, but the manual setting and automatic reading of the motor parameters are not performed, or the reading method is improper.