Suppliers of frequency converter supporting equipment remind you that with the improvement of frequency conversion technology, the application of AC motors is becoming more and more widespread. Using frequency conversion speed regulation can improve the control accuracy, production efficiency, and product quality of production machinery, which is conducive to achieving automation of the production process. AC drive systems have excellent control performance and significant energy-saving effects in many production occasions.
Application of frequency converter
The electricity consumption of electric motors in our country accounts for 60% to 70% of the national electricity generation, and the annual electricity consumption of fans and water pumps accounts for 1/3 of the national electricity consumption. The main reason for this situation is that the traditional speed control method for fans, water pumps, and other equipment is to adjust the air and water supply by adjusting the opening of the inlet or outlet baffles and valves. The input power is large, and a large amount of energy is consumed in the interception process of the baffles and valves.
Due to the fact that most fans and water pumps are flat torque loads, the shaft power and speed have a cubic relationship. Therefore, when the speed of fans and water pumps decreases, the power consumption also greatly decreases. Therefore, there is great potential for energy conservation. The most effective energy-saving measure is to use a frequency converter to regulate the flow rate. The application of frequency converters has a power saving rate of 20% to 50%, and the benefits are significant.
Many machines require electric motors to be able to adjust speed due to process requirements. In the past, due to the difficulty in regulating the speed of AC electric motors and the high requirements for speed regulation performance, DC speed regulation was used. However, DC electric motors have complex structures, large volumes, and difficult maintenance in winter. Therefore, with the maturity of variable frequency speed regulation technology, AC speed regulation is gradually replacing DC speed regulation, often requiring quantitative and direct torque control to meet various process requirements.
By using a frequency converter to drive an electric motor, the starting current is small, allowing for soft starting and stepless speed regulation. This facilitates acceleration and deceleration control, enabling the motor to achieve high performance and significantly save energy. Therefore, frequency converters have been increasingly widely used in industrial production and daily life.
Existing problems and countermeasures
With the expansion of the application scope of frequency converters, there are more and more problems that occur during operation, mainly manifested as high-order harmonics, noise and vibration, load matching, heating and other issues. This article analyzes the above issues and proposes corresponding measures.
The main circuit form of a universal frequency converter generally consists of three parts: rectification, inversion, and filtering. The rectification part is a three-phase bridge uncontrolled rectifier, the middle filtering part uses a large capacitor as the filter, and the inverter part is an IGBT three term bridge inverter with PWM waveform input. The output voltage contains harmonics other than the fundamental wave, and lower order harmonics usually have a greater impact on the motor load, causing torque ripple; And higher harmonics increase the leakage current of the output cable of the frequency converter, resulting in insufficient output of the motor. Therefore, both high and low order harmonics output by the frequency converter must be suppressed. The following methods can be used to suppress harmonics.
1. Increase the power supply of the frequency converter
The internal impedance of the power supply device can usually act as a buffer for the reactive power of the DC filtering capacitor of the frequency converter. The larger the internal impedance, the lower the harmonic content. This internal impedance is the short-circuit impedance of the transformer. Therefore, when choosing a frequency converter power supply, it is best to choose a transformer with a high short-circuit impedance.
2. Install the reactor
Connect suitable reactors or install harmonic filters in series between the input and output terminals of the frequency converter. The filter is composed of LC type, which absorbs harmonics and increases the impedance of the power supply or load to achieve the purpose of suppression.
3. Multiple operations using transformers
The universal frequency converter is a six pulse rectifier, which generates large harmonics. If multi-phase operation of transformers is adopted, with a phase angle difference of 30 ° between each other, the combination of Y - △ and △ - △ transformers can form a 12 pulse effect, which can reduce low order harmonic currents and effectively suppress harmonics.
4. Set up dedicated harmonics
Set up a dedicated filter to detect the frequency converter and phase, and generate a current with the same amplitude and opposite phase as the harmonic current, which is passed to the frequency converter to effectively absorb the harmonic current.