Research on The Requirement of Using Industrial UPS in Rail Transit Industry (2)

The voltage waveform of power grid is seriously distorted, which is the most serious problem in the rail transit industry. We know that the hardware circuit of three-phase PWM rectifier mainly includes detection circuit, phase-locked loop circuit, over-current protection circuit, optocoupler isolation circuit and drive circuit. The driving circuit, when working, takes the sine wave of the input power grid voltage as the modulation wave. The detection circuit and the phase-locked loop circuit are all related to the sinusoidal waveform of the grid voltage. In order to realize the unit power factor control of three-phase, the phase-locked loop circuit needs to find the reference value which is synchronized with the input voltage waveform, so as to obtain the frequency and phase of the grid voltage.

Here we need to talk about the input characteristics of UPS, generally including the expression of input voltage range: ± 20% and input frequency range: 50Hz ± 10%. Therefore, most of us think that when the input voltage and frequency range are exceeded, the ups itself will be judged as power failure, and the inverter will work. This is true in normal conditions, but in some abnormal transient distortions, even if you widen the input voltage and frequency range, it will not solve the problem. Because, when we judge the input voltage and frequency out of range, we usually use the average method, that is to say, it has several reference points in a unit time to be determined after acquisition. For example, we will not judge the zero crossing in the 50Hz sine wave as power failure. So, there's a transient time problem. If the input voltage waveform of UPS is seriously distorted, the rectifier of ups will fail due to the high distortion rate of the tracking sine waveform, the disorder of IGBT driving pulse, the insufficient power of the driver or the wrong selection, which will burn down the IGBT components of the rectifier. These problems, which are the immunity requirements of industrial UPS, have been well solved, and have been widely used in power plants, power stations, metallurgy, steel and other industries where the voltage waveform is seriously distorted.

In conclusion, the rail transit industry should use industrial ups. Industrial UPS has three elements in terms of dominance: 1. High level immunity; 2. Optional high-level IP protection; 3. Electrical isolation of power frequency transformer. In terms of application environment, commercial grade UPS is usually used in IDC room, which has strict requirements on temperature, humidity, dust and corrosive gas, and cannot be used in severe occasions, while industrial grade UPS is usually used in high temperature, high humidity, multi dust or salt fog occasions; in terms of reliability, the design life of commercial grade UPS is usually about 5 years, while industrial grade UPS is selected by industrial grade or even military The life span of products can reach or even exceed 20 years by using level devices, increasing redundancy, strengthening process design and improving safety configuration. In addition, in terms of electrical environment, load characteristics, mechanical strength, electrical isolation, input and output protection, communication interface, bypass requirements, accessory selection, IP protection level and sheet metal requirements, the market requirements for industrial grade ups are far higher than those for commercial grade ups.

About AVIC-Tech

AVIC-Tech (Xiamen)Electric Power Technology Co.,Ltd is a high-tech enterprise specializing in R&D, manufacture, sales and service of high-end power supply. Our flagship products are industrial UPS (1kVA-800kVA), dynamic voltage restorer (10kVA-2000kVA), and lithium battery system, which are widely used in nuclear power, electric power, petroleum and petrochemical, rail transportation, industrial manufacturing and other fields.

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