Research on The Requirement of Using Industrial UPS in Rail Transit Industry (1)

AbstractThis paper analyzes the application status of ups in the rail transit industry, and points out that, especially in the subway system, when the locomotive enters and exits the station, a large amount of harmonic current is injected into the power grid due to the operation of high-power non-linear electrical equipment, resulting in the distortion of the power grid voltage waveform. When serious distortion occurs, the voltage will appear positive and negative half wave asymmetry, three-phase voltage asymmetry, and frequency will also change. This is the reason for the high failure rate of ups in the subway system. In order to ensure the safe and reliable operation of rail transit industry, it is proposed to select industrial ups and improve its adaptability and reliability.

Key words: there are high-power nonlinear loads on the power grid, the voltage waveform of the power grid is distorted, the positive and negative half waves of the voltage will be asymmetric, the three-phase voltage will be asymmetric, and the frequency will change, etc. Select industrial ups.


At present, in the rail transit industry, especially in the subway system, the UPS power supply system is responsible for the power supply of the communication system and monitoring system of the control center, station, depot, etc. and the power supply of the information management system in the data room of the control center and depot. Because UPS power supply mainly supplies power to communication system, integrated monitoring system and information management system, a large number of people use commercial UPS, resulting in high failure rate of UPS, safe and reliable operation of rail transit industry, bringing a great potential safety hazard. The reason is that the lack of understanding of the electrical environment of rail transit industry only considers the input green requirements of ups and the output overload capacity. That is, input power factor ≥ 0.95, input current harmonic < 5%, no pollution to the power grid. Overload capacity 125%: 10 minutes, 150%: 1 minute. It seems that there are requirements on both sides of the grid and load. However, the industrial characteristics of rail transit industry are not considered, that is, the adaptability and reliability of UPS itself in the electrical environment of rail transit industry. It can also be said that the robustness of UPS system is insufficient (robustness is the robustness of the system).


Let's learn about the working electrical environment of ups in the rail transit industry. Take a subway as an example.


When the locomotive enters and exits the station, a large amount of harmonic current is injected into the power grid due to the operation of high-power non-linear electrical equipment, resulting in the distortion of the power grid voltage waveform. According to our observation, when serious distortion occurs, the positive and negative half waves of the voltage will be asymmetric, the three-phase voltage will be asymmetric, and the frequency will also change.


As we know, in the control strategy of commercial UPS three-phase PWM rectifier, it is generally assumed that the voltage imbalance degree of three-phase power grid is not more than 2% and 4% in a short time, that is, the allowable value of normal voltage imbalance degree of public connection point in power system. In this way, once the actual When the power grid voltage imbalance is too large, the characteristic harmonics of 6, 12, 18 and 2, 4, 8, 10 will be generated in the DC side current of the three-phase PWM rectifier, while the DC current harmonics will cause the DC voltage harmonics of the three-phase PWM rectifier, and the DC voltage harmonics will affect the AC current waveform of the three-phase PWM rectifier through PWM The current waveform contains odd harmonics. Among them, the second harmonic of DC voltage and the third harmonic of AC current produced by it seriously affect the operation performance of three-phase PWM rectifier due to the low frequency and high amplitude, and even burn out the rectifier.


In order to ensure the reliability of industrial UPS in the severe working electrical environment, the general control strategy of three-phase PWM rectifier assumes that the voltage imbalance degree of three-phase power grid is up to 40%. For example, the instantaneous power control strategy of SVPWM and power frequency three-phase IGBT rectifier technology, that is, full bridge rectifier plus active filter, are also called hybrid rectifier technology. The hybrid rectifier technology can operate without phase when the load is less than 70%.




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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