China's largest wired network is the transmission and distribution network. If you can use 220V low-voltage power lines that extend in all directions, spread all over urban and rural areas, and reach thousands of households, it is undoubtedly the most competitive solution to the "last 300 meters / 100 meters". At the same time, it will undoubtedly provide a powerful technical weapon to effectively break the local monopoly of the resident network and bring equal opportunities for multiple operators.
Although the provision of broadband communication services on power lines has just emerged, it is gradually showing its strong vitality from the perspective of application models, investment return analysis, and operating experience in Europe and North America. Here, do some simple analysis on the application model, operation model and return on investment of this technology.
1. Overview of Power Line Communication Technology
In recent years, with the rapid development of Internet technology and integrated services built on broadband technology, how to make full use of the high-priced IP backbone network to provide a wide range of services for netizens, especially voice services, has become an important consideration for operators. problem. Obviously, the traditional dial-up access method can no longer meet the needs of the majority of netizens. The broadband access market is rapidly developing and maturing. Broadband integrated wiring, ADSL and other access methods are gradually replacing the original dial-up network.
What kind of more economical and fast communication method is used to connect user terminals to the nearest broadband network equipment has become a difficult problem for service providers for a long time, and it is also one of the bottlenecks in popularizing broadband Internet access. The question of "last mile / last 300 meters / last 100 meters".
The largest wired network in China is the transmission and distribution network. If you can use 220V low-voltage power lines that extend in all directions, spread all over urban and rural areas, and reach hundreds of thousands of households to transmit high-speed data, it is undoubtedly the most competitive solution to the "last 300 meters / 100 meters". To this end, high-speed power line communication (PLC: Power Line CommunicaTIon) came into being.
Power line communication technology is abbreviated as PLC, which is a communication method that uses power line to transmit data and voice signals. Power line communication is not a new technology. It has a development history of several decades. On the medium and high voltage transmission grid (above 35kV), the power carrier communication machine uses a lower frequency to transmit remote data or voice at a lower rate. This is the application of power line communication technology. One of the main forms. In the field of low voltage (220V), PLC technology is first used for load control, remote meter reading and home automation. The transmission rate is generally 1200bps or lower, which is called low-speed PLC. In recent years, the high-speed PLC is a power line communication technology developed at home and abroad that utilizes low-voltage power line transmission rates above 1 Mbps.
Beijing Justel CommunicaTIon Equipment Co. Ltd is a high-tech company that provides advanced technology and equipment. It has in-depth research on high-speed PLC technology and soft switching technology. Operators ’needs are deeply understood. To enable operators, especially those who currently do not have access resources, to achieve high-speed access for a large number of users with broadband access needs, and at the same time have the ability to provide broadband voice services, Jiezhixun high-speed PLC technology and Softswitch technology is organically combined to launch Jiezhixun PLCISS (PLC-based Integrated Services Systems) system-an integrated business system based on power line communication. The system can provide users with data communication bandwidth up to 14Mbps, and can simultaneously transmit data, voice and video services.
Jiezhixun PLCISS system can be divided into three subsystems in function: PLCISS broadband access subsystem, PLCISS softswitch core subsystem and PLCISS value-added service subsystem. The whole system architecture follows the next-generation network (NGN) layered and fully open system architecture in design, which has the advantages of convenience, flexibility, clear layers, high standardization, and easy expansion.
2. Main technical performance of power line communication equipment
1. Technical principle of high-speed power line communication equipment
The communication bandwidth of high-speed power line communication equipment on the market is usually 2M, 14M, 45M and other standards according to the protocol used and the core chip. Based on a comprehensive comparison of carrying capacity, investment economy and maturity, 14M products should be said to be the mainstream of development and the most widely used products.
High-speed power line communication refers to high-speed signal transmission on low-voltage power lines. The main technologies involved are: signal modulation and demodulation technology, media access control technology, and link layer QoS guarantee mechanism. Take the PLCISS series products of Beijing Jiezhixun Communication Equipment Co., Ltd. as an example to introduce its main technology.
Compared with the dedicated communication line, there are many additional interference factors for data transmission on the power line, such as the opening and closing of various household appliances, especially the switching and use of equipment such as inverter air conditioners, energy-saving lamps with adjustable brightness, vacuum cleaners Often, large interference signals are injected into the power supply line, resulting in a very low signal-to-noise ratio when the signal is transmitted on the power supply line, and the signal is difficult to extract. In response to the above problems, high-speed power line access equipment is usually designed with special considerations, and a lot of experiments have been carried out on the products. Solving the interference problem mainly depends on choosing the appropriate modulation technology. Traditional modulation technologies such as ASK, PSK, or FSK are not suitable for such a communication environment. Jiezhixun high-speed PLC products use orthogonal frequency division multiplexing (OFDM) technology. OFDM loads digital information on multiple carriers (up to 84). Multiple carriers are used simultaneously. Each carrier transmits a low-speed message, and the information is combined and recovered at the receiving end. For example, the bandwidth required when sending data is B, and N carriers are used at the same time, then the actual rate of each carrier is 1 / N * B. In this way, the carrier with the best communication quality can be selected and used from multiple carriers according to the actual environment. In the presence of noise, although a certain carrier may be affected and cannot communicate normally, there are still other carriers available and communication will not be interrupted. At the same time, the forward error correction technology is used to enhance the reliability of each carrier.
In the Jiezhixun high-speed power line communication products, the MAC protocol used is a variant of CSMA / CA. Similar to 802.11, the virtual carrier detection technology is used to effectively reduce conflicts.
Jiezhixun high-speed power line communication products fully consider the characteristics of power line communication and adopt the "large packet segmentation, multiple delivery" method to effectively avoid the problem that a large number of long packets occupy the channel for a long time and affect service quality. Among them, high-priority packets can be preferentially forwarded, and small packets of the same level are superior to the mechanism of long packet forwarding first. The adoption of these mechanisms provides technical guarantee for providing real-time services such as voice and video in the high-speed power line communication environment.
A single-phase VFD, also known as a variable frequency drive, is a specialized electronic device used for precise control and regulation of single-phase motors. Unlike three-phase motors that are commonly used in industrial applications, single-phase motors are predominantly found in residential and small-scale applications.
The primary function of a single-phase VFD is to control the frequency and voltage supplied to the single-phase motor, thereby enabling accurate regulation of motor speed. By adjusting the frequency and voltage output, the VFD allows for smooth and precise control over the motor's rotational speed. This feature is particularly useful in applications where speed control is required, such as in residential HVAC systems, small-scale machinery, and household appliances.
Energy efficiency is a significant advantage offered by single-phase VFDs. By adjusting the motor speed to match the load requirements, the VFD reduces energy wastage and improves overall energy efficiency. When the motor operates at a lower speed during periods of low demand, energy consumption is significantly reduced, resulting in energy savings and lower operating costs.
Motor protection is another important aspect addressed by single-phase VFDs. They incorporate various protective features, including overload protection, short circuit detection, and thermal protection, which help safeguard the motor against damage due to excessive current, voltage fluctuations, or overheating. This ensures reliable motor operation, prolongs the motor's lifespan, and reduces the risk of unexpected failures.
Harmonic filtering is also a critical consideration in single-phase VFD applications. When single-phase VFDs operate, they can introduce harmonics into the power supply, which may cause issues such as voltage distortions and interference with other electrical equipment. To mitigate these problems, single-phase VFDs often incorporate harmonic filtering techniques to suppress harmonics and ensure a clean and stable power supply, maintaining power quality and preventing damage to connected equipment.
Control algorithms play a significant role in single-phase VFD operation. These algorithms allow for precise control and adjustment of motor speed, ensuring smooth acceleration, deceleration, and accurate speed regulation. Advanced control algorithms enable efficient motor operation and enhance overall system performance.
In summary, single-phase VFDs provide precise control and regulation of single-phase motors in residential and small-scale applications. With their energy efficiency, motor protection features, harmonic filtering capabilities, and advanced control algorithms, single-phase VFDs enhance motor performance, reduce energy consumption, and ensure reliable operation in various residential and small-scale applications.
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