Vector inverter parameter setting

Vector inverter parameter setting steps

Because the functions of various types of inverters are different, and the names of the same function parameters are also inconsistent, for the convenience of description, this article takes the basic parameter name of a certain inverter as an example. Since the basic parameters are common to almost all types of inverters, you can learn by analogy.

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 fall from the maximum frequency to 0. The acceleration and deceleration time are usually determined by the rise and fall of the frequency setting signal. When the motor is accelerating, the frequency setting rise rate must be limited to prevent overcurrent, and when decelerating, the frequency falling rate must be limited to prevent overvoltage.

The acceleration time setting requirement is: limit the acceleration current to below the inverter overcurrent capacity, so as not to cause the inverter to trip due to overcurrent loss; the deceleration time setting key point is: prevent the smoothing circuit voltage from being too large, so as not to cause the inverter to trip due to regeneration overvoltage loss. The acceleration and deceleration time can be calculated according to the load, but in debugging, it is often adopted to set a longer acceleration and deceleration time according to the load and experience, and observe whether there is overcurrent and overvoltage alarm by starting and stopping the motor; then gradually shorten the acceleration and deceleration setting time, with the principle of no alarm during operation, repeat the operation several times, and then determine the good acceleration and deceleration time.

2. Torque improvement

Also called torque compensation, it is a method of increasing the low frequency range f/V to compensate for the torque reduction at low speed caused by the resistance of the motor stator winding. When set to automatic, the voltage during acceleration can be automatically increased to compensate for the starting torque, so that the motor can accelerate smoothly. If manual compensation is used, the best curve can be selected through experiments based on the load characteristics, especially the starting characteristics of the load. For variable torque loads, if the selection is inappropriate, the output voltage at low speed will be too high, which will waste electric energy, and even the current will be large when the motor starts with load, but the speed will not increase.

3. Electronic thermal overload protection

This function is set to protect the motor from overheating. The CPU in the inverter calculates the temperature rise of the motor according to the operating current value and frequency, thereby performing overheat protection. This function is only applicable to "one-to-one" occasions, while in "one-to-many" situations, thermal relays should be installed on each motor.

Electronic thermal protection setting value (%) = [rated motor current (A) / inverter rated output current (A)] × 100%.

4. Frequency Limitation

That is, the upper and lower limits of the inverter output frequency. Frequency limit 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, so as to prevent damage to the equipment. It can be set according to the actual situation in the application. This function can also be used for speed limit. For example, some belt conveyors can be driven by inverters to reduce the wear of the machinery and belts because the conveying materials are not too much, and the upper limit frequency of the inverter can be set to a certain frequency value, so that the belt conveyor can run at a fixed and lower working speed.

5. Bias frequency

Some are also called deviation frequency or frequency deviation setting. Its purpose is that when the frequency is set by an external analog signal (voltage or current), this function can be used to adjust the output frequency when the frequency setting signal is low, as shown in Figure 1. When the frequency setting signal of some inverters is 0%, the deviation value can be applied in the range of 0 to fmax. Some inverters (such as Meidensha and Sanken) can also set the bias polarity. For example, when the frequency setting signal is 0% during debugging, the inverter output frequency is not 0Hz, but xHz. At this time, setting the bias frequency to negative xHz can make the inverter output frequency 0Hz.

6. Frequency setting signal gain

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

7. Torque Limitation

It can be divided into two types: driving torque limit and braking torque limit. It is based on the output voltage and current value of the inverter, and the CPU performs torque calculation, which can significantly improve the impact load recovery characteristics during acceleration, deceleration and constant speed operation. The torque limit function can realize automatic acceleration and deceleration control. Assuming that the acceleration and deceleration time is less than the load inertia time, it can also ensure that the motor automatically accelerates and decelerates according to the torque setting value.

The drive torque function provides a strong starting torque. In steady-state operation, the torque function will control the motor slip and limit the motor torque to a large set value. When the load torque suddenly increases, even when the acceleration time is set too short, it will not cause the inverter to trip. When the acceleration time is set too short, the motor torque will not exceed the set value. A large drive torque is beneficial to starting, and it is more appropriate to set it to 80-100%.

The smaller the braking torque setting value, the greater the braking force, which is suitable for rapid acceleration and deceleration. If the braking torque setting value is set too large, an overvoltage alarm will occur. If the braking torque is set to 0%, the total amount of regeneration added to the main capacitor can be close to 0, so that the motor can be decelerated to a stop without tripping when decelerating without using a braking resistor. However, on some loads, if the braking torque is set to 0%, a short idling phenomenon will occur during deceleration, causing the inverter to start repeatedly, the current to fluctuate greatly, and in severe cases, the inverter will trip, which should be paid attention to.

8. Acceleration and deceleration mode selection

It is also called the selection of acceleration and deceleration curves. Generally, frequency converters have three types of curves: linear, nonlinear and S. Usually, linear curves are selected; nonlinear curves are suitable for variable torque loads, such as fans; S curves are suitable for constant torque loads, and their acceleration and deceleration changes are relatively slow. When setting, you can select the corresponding curve according to the load torque characteristics, but there are exceptions. When debugging a frequency converter for a boiler induced draft fan, I first selected a nonlinear curve for the acceleration and deceleration curve. The frequency converter tripped as soon as it started. Adjusting and changing many parameters had no effect. After changing to the S curve, it became normal. The reason is: before starting, the induced draft fan rotates automatically due to the flow of flue gas, and reverses to become a negative load. In this way, the S curve is selected, which makes the frequency rise slower at the beginning, thereby avoiding the occurrence of frequency converter tripping. Of course, this is the method used for frequency converters without starting DC braking function.

Vector inverter application

Under the premise of not causing any negative impact on the normal use of the escalator, the concept of vector variable frequency speed regulation is introduced. That is, the frequency converter runs at the original speed (50Hz) when there are people on the escalator according to the signal generated by the sensor; when there are no people, the escalator slows down to a low speed or stops running.

The system requires the inverter to start and run smoothly, have good acceleration performance, large starting torque, and strong overload capacity. At the same time, it should be able to automatically switch to industrial frequency operation when the inverter speed control system fails to ensure the normal implementation of the escalator's conveying function.

For passenger escalators, the peak usage period is usually in the afternoon and evening, and the usage rate is low during other periods, which provides considerable energy saving space. Based on the above transformation principles, considering the investment cost and automation level, the following variable frequency traction scheme is proposed:

The SAJ-8000G inverter is used to drive the elevator host. The inverter adopts multi-speed control mode and sets two operating frequencies: main frequency (low speed) and multi-speed frequency 1 (high speed);

An infrared sensor switch is installed at the head and tail of the elevator. When passengers pass through the elevator, the infrared sensor switch is triggered and sends a switch signal to the inverter;