The "2010 Shanghai World Expo" will make Shanghai, an international metropolis, the focus of world attention once again. The magnificent Expo complex and various exhibition halls with different styles will provide a stage for the people of the world to display. As the "nerve" of the World Expo Group's buildings, smart electrical products are as large as the construction of the venue's electrical system to as little as every micro switch, and they are everywhere controlling the body of this huge "giant", showing its extraordinary innovative ideas and top-notch advanced The level of technology also promotes the development and innovation of advanced technologies in the industry. At the same time, China's power industry is developing rapidly, and the installed power capacity continues to grow. Especially in 2009, China proposed to build a strong smart grid, and the matching low-voltage electrical products are in great demand, which brings huge development opportunities to the low-voltage electrical industry. Active filter and other purified power grid products will enter the period of full popularization, and are expected to become standard products in the construction of smart grids, making a significant contribution to China's development of a low-carbon economy.
The active power filter ACTSine series products developed and produced by Shanghai Lisi Electric Co., Ltd. have beaten many international and domestic well-known brands after many rounds of fierce competition, with perfect technical solutions, excellent product performance, good after-sales service and health The corporate image of the company won the power filtering projects such as the State Grid Pavilion and the China Petroleum Pavilion at the Shanghai World Expo in one fell swoop. The product successfully passed the inspection and certification of the Quality Inspection Center of the Ministry of Power Industry, which not only won the appreciation of experts from all sides, but also received high evaluation from other related user companies.
Causes of harmonics in LED display
LEDs require low-voltage DC drive, so LED display screens use a large number of switching power supplies to provide drive for the display module. In order to reduce the loss of low-voltage DC current in various transmission links, display screen power distribution generally uses a large number of low-power switching power supply modules and is configured as a distributed local low-voltage DC power supply mode. The low-power (less than 350W) switching power supply module itself generates a rich harmonic power supply. The impact of the harmonic current generated by one or several of these switching power supply modules on the power grid is minimal, even the user does not even notice it, but when the number of switching power supply increases, the impact of harmonic current on the power supply system must be considered into the whole design. This implementation method solves the problem of low-voltage transmission loss, but also brings about problems such as harmonic pollution and excessive neutral current. The reasons are:
The switching power supply is a typical harmonic source, its harmonic content is very high, and its waveform is an intermittent spike. Due to the small capacity of the switching power supply generally used (the typical case is the power supply of larval computers), it has not attracted enough attention. However, if a large number of switching power supplies work at the same time, the harmonics generated by them will not be negligible. If not dealt with, it may cause pollution to the power supply network and unpredictable harm to other equipment in the same network.
For a conventional three-phase approximately balanced load, the normal current of the neutral wire is generally less than 30% of the phase current. No matter how the display system configures the load distribution, due to changes in the display screen, it will eventually bring instantaneous three-phase imbalance. Value of the influence of harmonic current, where the neutral current can reach 280% of the phase current
Brief introduction of the project site
The Magic Box exhibition area of ​​the State Grid Pavilion of the Shanghai World Expo is the highlight of the State Grid Pavilion. The whole magic box area is composed of six large LED screens. The electrical load of the magic box area is 4000 switching power supplies of 200W each controlled by three electric control cabinets. The switching power supply is a typical harmonic source. It has electrical characteristics such as high current harmonic distortion rate, large harmonic content, wide harmonic spectrum, equipment for capacitive load and low power factor. When a large number of switching power supplies are used intensively, it will result in excessively high center line current, low power factor, and high current harmonic distortion rate, which affects the normal work of the entire magic box exhibition area.
Harmonic treatment plan:
Based on the characteristics of the site, an ACTSine-100F power active filter developed and produced by Shanghai Lisi Electric Co., Ltd. is installed in parallel next to the three-sided electrical control cabinet in the magic box area. The equipment parameters are as follows:
Parameter value description model ACTSine-100F
Dimensions 600X1800X1600 (Depth X Width X Height) Non-standard design cabinet rated voltage 400VAC / 50Hz ± 10% three-phase four-wire parallel compensation capacity 100kVA
Compensation harmonic order 2 ~ 50 times Response speed 200 us
Switching device operating frequency 10kHz
Working temperature -10 ~ + 45 ℃ Ambient temperature Rated current 150A Single-phase effective value ACTSine-100F power active filter produced by Shanghai Lisi Electric Co., Ltd. has: large compensation capacity, fast tracking speed, and can simultaneously compensate harmonic The characteristics of reactive power and phase-deficient work fully meet the requirements of on-site harmonic compensation.
Harmonic control effect analysis:
The LED large screen in the Magic Box area displays the publicity movie of the State Grid Pavilion. Its operating current changes very quickly. The active power filter has a significant harmonic compensation effect during the entire process of operation: the current harmonic distortion rate after compensation is from 80 % -95.7% reduced to 4.5% -8.4%, harmonic suppression rate reached more than 95%; the power factor after compensation increased from about 0.5 to more than 0.97; after compensation, the total neutral current of the three-sided electrical control cabinet was 12A Between 29A (150A to 350A before compensation).
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