What is the impact of power grid quality on inverter life?

by:V&T Technologies     2019-11-09
Inverter is a high-tech product, mainly composed of power electronic devices and microelectronics devices. Three-phase AC power grid to connect to frequency converter of input. The input of the inverter is a rectifier circuit, and the output is a frequency conversion circuit. Therefore, the voltage and current on the input and output sides contain abundant harmonics, which will lead to distortion of the waveform of the power grid; At the same time, whether the grid voltage is symmetrical, balanced, the size of the transformer capacity, and whether the nonlinear equipment is connected to the distribution bus will also affect the normal operation of the inverter. The current inverter has a DSP chip or a computer chip to realize control, and the control of the main circuit of the inverter driving the inverter. Due to the small voltage and current computer chip, at high operating speed, it is vulnerable to some external electrical interference. Therefore, in order to realize the power supply, it can drive safe and reliable operation, and measures must be taken to suppress mutual interference between the two. The rectifier circuit and inverter circuit of the inverter are composed of nonlinear devices. The circuit structure causes distortion of grid voltage and current waveforms. The three-phase AC voltages ur, us and ut change AC into DC through the three-phase bridge rectifier circuit. After filtering by electrolytic capacitor, the DC voltage basically remains unchanged. The diode used in the rectifier circuit is a nonlinear device. The rectified output voltage is charged for the filter capacitor. The charging current waveform depends on the difference between the rectifier voltage and the capacitor voltage. When the frequency converter is in different frequencies and different current working states, the input current waveform is also different. Figure 10- 6 shows the input current waveform when the load of the cage asynchronous motor driven by 55kW inverter is 10Hz, 20Hz and 50Hz. It can be seen that as the frequency and current of the motor increase, the input current changes from intermittent to continuous, and the waveform distortion of the current becomes smaller and smaller. Many harmonic current components will be obtained by mathematical Fourier series decomposition of these waveforms. The experiment also proves that when the inverter is running, the commutation of the rectifier diode will cause a certain gap source voltage waveform and protrusion. To sum up, when the frequency converter is running, the voltage and current waveforms of the power grid will be distorted. In order to comprehensively judge the impact of this distortion on the system, the comprehensive voltage distortion rate d can be calculated by the following formula. What is the impact of power grid quality on the life of the inverter in the workshop, the drive will be available on different loads, and the impact of different loads on the inverter itself is different. Under impact loads such as welding machines, electric arc furnaces and rolling mills, voltage flashes often occur. At this time, the harmonics generated by the inverter have very serious pollution to the quality of the power grid, and also have considerable harm to the equipment itself. If it is light, it cannot work continuously and normally, and if it is heavy, it will damage the input circuit of the equipment. This will seriously affect the service life of the product. 1, in the case of impact load, such as electric welding machine, electric arc furnace, steel mill, etc. It is recommended that users add reactive static compensation devices to improve the power factor and quality of the grid. 2. Concentration rectifier recommended by inverter concentration workshop, common bus of DC power supply. 12 pulse rectifier mode is recommended. Small harmonics and energy efficiency are especially suitable for the advantages of frequent starting, braking and motor running under the condition of motor running and power running. 3. A passive LC filter is installed on the input side of the converter to reduce the input harmonics, improve the power factor, have high reliability and good effect. 4. The input side of the inverter is installed on the source PFC device, which has the best effect but high cost. The way through these words can help the drive completely prolong its service life.
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