Inverter's bad influence and solution

Inverter's bad influence and solution:

1. Bad effects of the inverter: When the inverter is working, harmonic currents and radio frequency noise currents are emitted to the power grid. These will cause distortion of the voltage, electromagnetic interference to electronic devices on the same power grid, and electromagnetic interference caused by the inverter. Problems, people often can not determine the cause of the problem, so it can not take the correct countermeasures, people familiar with strong power, often think that the cause of interference is the harmonic currents, and people who are familiar with the weaknesses, often think that cause interference The reason is radio frequency current. It should be known that the countermeasures for these two problems are different, which also leads to people's failure to solve the problem. When there are: phenomena such as abnormal PLC operation, wrong meter readings, and increased control system errors, they are often RF currents. As a result, the phenomena caused by harmonic currents mainly include: 1 Reactive power compensation capacitors cannot be switched or burned; 2 Cables, transformers are overheated, Switchboards are tripped, Transformer noise is increased; 3 Motor temperature rise on the same power grid increases, Noise Larger; the inverter not only has a bad influence on the grid side, but also affects the load side. There will also be adverse effects, mainly in the damage to the motor, the inverter damage to the motor mainly in the following aspects: 1 motor heat is serious, noise increases, leading to shorten the life of the motor; 2 stator winding insulation damage to the motor, The occurrence of this phenomenon is indefinite, ranging from a few weeks to a few months. 3 The bearing of the motor is damaged. The occurrence of this phenomenon is indefinite, ranging from a few weeks to a long time. The root cause of these failure phenomena is Inverter output PWM pulse voltage waveform, the steeper the rising edge of the pulse voltage, the higher the frequency, the more serious damage to the motor; modern inverter pursuit of smaller, more efficient, to achieve this purpose is to increase the PWM voltage waveform The steepness, however, has led to the above-mentioned problems becoming more and more serious;

2. The root cause of bad influence of the inverter: The reason why the inverter will cause a lot of electromagnetic compatibility and power quality problems is determined by the working principle of the inverter; the inverter is mainly composed of two parts: rectifier and inverter, rectifier Harmonic currents are generated during operation. This has been discussed in the first sub-chapter. The inverter controls the DC voltage and generates pulse width modulation waves. The voltage waveform is the fundamental cause of electromagnetic interference and damage to the motor; the harmonics of the inverter The current emission is related to the brand of the frequency converter, mainly due to the different filter circuits used in different brands of frequency converters. This includes whether or not DC reactors or AC reactors and filter capacitors are embedded; The degree of damage to the motor is related to the brand and power of the inverter, the voltage of the inverter, and the power of the motor.

3. How to eliminate the adverse effects of the inverter: Input processing: • Install a harmonic filter at the input; • Install the output of the RF filter at the input: • Install a sine wave filter at the output; • At the output Install RF filters; • Install peak voltage absorbers on the motor side; install suitable filters at the input and output of the inverter is an effective way to solve various problems brought by the inverter; Aerospace Green Series Green Products In order to solve the problem of electromagnetic compatibility of the inverter, it is possible to install the HTHF harmonic filter at the input end of the inverter, which not only can effectively reduce the emission of harmonic currents, but also control the emission of radio frequency interference if the radio frequency is used. The interference control further requires that an EMFI RF interference filter be installed. At the output of the inverter, installing a SWF filter can effectively solve the problem of motor damage. If you want to strengthen the protection of the motor bearings, you can install an EMFO filter. This method works best, but the cost is higher. If you only want to protect the stator winding of the motor, you can use the following Lower cost options; the SVA peak voltage converter absorber provide low-cost protection scheme for the motor, this method occasions cable length between the inverter and the motor applies to less than 300 m;

4. Not all filters can be matched with the inverter: The inverter harmonic filter should meet: 1. Filter effect determination: To promise the harmonic current emission degree after the inverter installs the filter, for example: THID <8% 2. Do not absorb upstream harmonic currents: The drive system will be installed anywhere on the power grid, and the filter cannot be overloaded because there are other harmonic sources upstream. 3. Do not adversely affect the system: When used in any power grid, Can't resonate with the grid system or produce other adverse effects; 4. Do not send excessive capacitive reactive power: The main problem of the inverter is the harmonic current, not the low cosφ, the filter emits too much capacitive reactive power, It will damage the grid, especially for diesel generators. To control the harmonic current emission of the inverter, the most cost-effective method is passive filter. However, it should be noted that general passive filters cannot be used for harmonic control of inverters. The general passive harmonic filter adopts LC trap circuit, which is connected in parallel on the line and provides a low-impedance path for harmonic current. The filtering of this principle mainly exists in the following aspects: Problems: 1. The filtering effect is uncertain: The actual effect of the filter is greatly related to the impedance of the grid, so it cannot be guaranteed that the frequency converter is equipped with a filter to meet the requirements of specific harmonic limits; 2. Absorb upstream harmonic current: not only absorption The harmonic current generated by the inverter also absorbs harmonic currents from the upstream, which can easily cause overload or even damage to the filter. 3. Excessive capacitive reactive power is issued: This is a good thing for the traditional industrial power grid because it can be While filtering, the reactive power is compensated. However, the inverter itself does not require capacitive reactive power, and the filter issues excessive capacitive and reactive power, which can make the drive system a capacitive load and adversely affect the power grid. 4. Possible resonance with the system: The filter may have resonance with the system's capacitance or inductance, causing the system to become unstable. In severe cases, it may even damage the system.