Brake unit suppliers remind you that with the rapid development of power electronics technology, computer technology, and automatic control technology, electrical transmission technology is facing a new revolution. In the field of electrical transmission, variable frequency speed control systems have become mainstream due to their high efficiency and good performance. Benefiting from strategies such as energy conservation, emission reduction, and green environmental protection, as an important equipment for variable frequency speed regulation, the variable frequency drive industry has become one of the industries with enormous market potential in the coming years. Along with it comes the research and application of variable frequency drive functions. Below are some application tips for variable frequency drives.
1. Shielded wires should be used for signal and control lines to prevent interference. When the line is long, such as a distance jump of 100m, the wire cross-section should be enlarged. Signal and control lines should not be placed in the same cable trench or bridge as power lines to avoid mutual interference. It is better to place them in conduit for better suitability.
2. The transmission signal mainly uses current signals, as current signals are not easily attenuated or interfered with. In practical applications, the signal output by sensors is a voltage signal, which can be converted into a current signal through a converter.
3. The closed-loop control of frequency converters is generally positive, meaning that when the input signal is large, the output is also large. But there is also a reverse effect, that is, when the input signal is large, the output quantity decreases.
4. When using pressure signals in closed-loop control, do not use flow signals. This is because pressure signal sensors have low prices, easy installation, low workload, and convenient debugging. But if there are flow ratio requirements in the process and precision is required, a flow controller must be selected, and a suitable flow meter must be selected based on actual pressure, flow rate, temperature, medium, speed, etc.
5. The built-in PLC and PID functions of the frequency converter are suitable for systems with small and stable signal fluctuations. However, due to the built-in PLC and PID functions only adjusting the time constant during operation, it is difficult to obtain satisfactory transition process requirements, and debugging is time-consuming.
6. Signal converters are also frequently used in the peripheral circuits of frequency converters, typically consisting of Hall elements and electronic circuits. According to signal transformation and processing methods, it can be divided into various converters such as voltage to current, current to voltage, DC to AC, AC to DC, voltage to frequency, current to frequency, one in multiple out, multiple in one out, signal superposition, signal splitting, etc.
7. When using a frequency converter, it is often necessary to equip it with peripheral circuits, which can be done in the following ways:
(1) A logic functional circuit composed of self-made relays and other control components;
(2) Buy ready-made unit external circuits;
(3) Choose a simple programmable controller;
(4) When using different functions of the frequency converter, function cards can be selected;
(5) Select small and medium-sized programmable controllers.
8. Reducing the base frequency is the most effective way to increase the starting torque. The principle analysis is as follows.
Due to the significant increase in starting torque, some difficult to start equipment such as extruders, cleaning machines, spin dryers, mixers, coating machines, mixers, large fans, water pumps, Roots blowers, etc. can all be started smoothly. This is more effective than usually increasing the starting frequency for starting. By using this method and combining it with the measures of changing from heavy load to light load, the current protection can be increased to the maximum value, and almost all equipment can be started. Therefore, reducing the base frequency to increase the starting torque is the most effective and convenient method.
(1) When applying this condition, the base frequency does not necessarily have to decrease to 30Hz. It can be gradually decreased every 5Hz, as long as the frequency reached by the decrease can start the system.
(2) The lower limit of the base frequency should not be lower than 30Hz. From the perspective of torque, the lower the lower limit, the greater the torque. However, it should also be considered that the IGBT may be damaged when the voltage rises too quickly and the dynamic du/dt is too large. The actual use result is that this torque boosting measure can be safely and confidently used when the frequency drops from 50Hz to 30Hz.
(3) Some people are concerned that, for example, when the base frequency is lowered to 30Hz, the voltage has already reached 380V. Therefore, when normal operation may require reaching 50Hz, should the output voltage jump to 380V so that the motor cannot withstand it? The answer is that such a phenomenon will not occur.
(4) Some people are concerned that if the base frequency drops to 30Hz, the voltage has already reached 380V. Therefore, normal operation may require an output frequency of 50Hz to reach the rated frequency of 50Hz. The answer is that the output frequency can certainly reach 50Hz.