1. What is acceleration time? What factors should be considered when setting the parameter acceleration time?
Acceleration time is the time required for the operating frequency of the inverter to rise from 0Hz to the basic frequency (50Hz). This provision also applies to cases where the acceleration termination frequency is an arbitrary value. For example, in multiband speed operation, if the operating frequency of a certain speed grade is set to 30Hz and the acceleration time is set to 30 seconds, the actual acceleration time (the time to accelerate to 30Hz) of this speed grade is (30Hz/50Hz) × 30 seconds = 18 seconds, and it is not to be construed that 30 seconds are required to accelerate to 30Hz.
Setting the acceleration time should be considered as follows: the acceleration process takes time, too long acceleration time will reduce the efficiency of the work, especially the frequent starting and stopping of the equipment, but the acceleration time is too short will make the starting current becomes large, therefore, should be in the starting current and productivity to seek a balance between the starting current and under the premise of the starting current allows, try to shorten the acceleration time. In addition, the acceleration time should be longer when the inertia of the load equipment is larger, and the acceleration time can be shortened when the inertia of the load equipment is smaller.
2. What is deceleration time? What factors should be considered when setting the parameter of deceleration time?
Deceleration time is the time required to reduce the working frequency of inverter from the basic frequency (50Hz) to 0Hz. This specification also applies when deceleration starts at any frequency value. For example, in multiband speed operation, if the operating frequency for a certain time period is 40Hz and the deceleration time is set to 45 seconds, the actual deceleration time (the time to decelerate to 0Hz) at the end of the operation of this rotational speed band will be (40Hz/50Hz) × 45 seconds = 36 seconds, not 45 seconds.
The principle of setting the deceleration time is similar to setting the acceleration time, but also consider the following issues: if the deceleration time is set too short, it will make the frequency converter DC link voltage rises, the formation of the pump voltage, which need to take appropriate technical measures to absorb this regenerative energy, so that the equipment complexity, and investment will increase. The reason is: the deceleration time is set too short, will make the rotating magnetic field speed down too fast, and the motor rotor due to the role of load inertia, can not be quickly down, resulting in the motor rotor speed is higher than the rotating magnetic field speed, motor is in the state of generating power, so the frequency converter DC link voltage rises. Therefore, the setting of deceleration time should seek a balance between production efficiency, pumping voltage and equipment investment.
3. What is S-shaped acceleration mode? How to set the relevant parameters?
The so-called S-shaped acceleration, is relative to the linear acceleration shown in Figure 1 (a), S-shaped acceleration is in the beginning and end of the acceleration process, so that the frequency converter's output frequency rise rate becomes slower, as shown in Figure 1 (b) in the curve ts section.
S-shape acceleration method is suitable for the acceleration response is more sensitive to the place, such as glass bottle conveyor belt, passenger elevator, etc.; and inertia of the drag system.
The method of setting S-shaped acceleration mode: find the relevant parameters from the instruction manual of the frequency converter, and set the selection can be made. Table 1 is an example of S-shaped acceleration and deceleration mode parameters of several kinds of inverters.
4. What kind of situation needs to set the starting frequency?
When the motor starts, it usually accelerates from 0Hz, while some cases need to accelerate directly from a certain frequency, and then the frequency of the inverter is the starting frequency. Need to set the starting frequency of the situation:
(1) in a number of pumps at the same time in the water supply system, due to the pipeline there has been a certain amount of water pressure, after the start of the pump if the pump from 0Hz start, it will be difficult to rotate up, so the motor needs to start directly from a certain frequency.
(2) The static friction of some loads is large, and it is difficult to start from 0Hz. Setting the starting frequency can produce a certain starting impulse at the starting moment, so that the system can rotate smoothly.
(3) There is a certain friction between the stator and rotor when the conical motor starts, setting the starting frequency can quickly establish enough magnetic flux during starting to keep a certain air gap between the rotor and stator.