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How does high-voltage direct current transmit electricity across thousands of kilometers? Do you know the technological secrets behind it?
As global electricity demand continues to rise, high-voltage direct current (HVDC) technology has gradually become an important option for solving large-scale power transmission needs compared to traditional high-voltage alternating current (AC) transmission methods. HVDC systems are particularly suitable for transmitting power over long distances and for interoperability between AC power systems of different frequencies. So, how are these technologies achieved?
Advantages of HVDC Technology
HVDC technology has many significant advantages over traditional AC power transmission. First, HVDC transmission has lower transmission losses. This enables electricity suppliers to efficiently deliver power from distant locations, such as hydroelectric plants or wind farms, to urban areas where demand is high. In addition, HVDC systems are more stable and flexible than AC systems, and can more easily integrate electricity from renewable energy sources.
High-voltage direct current technology can span thousands of kilometers, which not only improves the efficiency of power transmission, but also is an important cornerstone of the future of smart grids.
Working Principle of High Voltage DC Converter
HVDC converters are the core components of HVDC systems and are responsible for converting high-voltage AC to high-voltage DC, or vice versa. These converters are usually bidirectional, meaning they are capable of converting both AC to DC and DC to AC. A complete HVDC system requires at least one converter for DC rectification and at least one converter for DC inversion.
When electricity needs to be transmitted from one place to another, a converter makes it possible to transmit electricity over long distances by rectifying the AC voltage into DC and then converting the current back into AC through an inverter. In this process, the conversion of current is dynamic and can be adjusted according to the needs of the power grid.
Technological evolution of various types of HVDC converters
HVDC converters have evolved several times as technology has advanced. Early converters used rotating converter designs, but starting in the 1940s, electronic static converters gradually replaced these traditional technologies. There are two main types of HVDC converters today: line-commutated converters (LCCs) and voltage-source converters (VSCs).
Line Commutated Converter (LCC)
LCC converters are the most widely used HVDC converters, which rely on the voltage of the AC system to drive the switching process. Their operating principle is based on the use of control elements on the DC side to achieve the conversion, these elements such as thyristors function at high voltage currents.
A line-commutated converter is actually considered as a current source converter, and the direction of current flow remains unchanged. This means that the direction of power flow can be changed simply by adjusting the polarity of the DC voltage.
Voltage Source Converter (VSC)
Voltage source converters (VSCs) have been widely used since 1997. Such converters differ from LCCs because they can control the switching on and off. Using insulated gate bipolar transistors (IGBTs), VSCs can provide greater flexibility based on network demand and are no longer dependent on synchronous machines on the AC system, which allows them to connect to a grid consisting of passive loads.
With the growth of renewable energy, the demand for VSCs is increasing rapidly. By expanding into multi-port HVDC systems, they are able to connect multiple power supply systems, thereby facilitating a more balanced energy distribution.
Looking forward to future HVDC technology
As the global demand for renewable energy and long-distance power transmission increases, the application of HVDC systems will become more common. Countries are actively investing in HVDC infrastructure to support a more sustainable energy system in the future. Whether it is offshore wind power or cross-border electricity trading, HVDC technology is undoubtedly an important cornerstone of future power transmission.
The development of HVDC technology is not only a trend in the power industry, but also a necessary step towards a green grid.
However, as technology continues to advance, have we witnessed the ultimate possibilities of high voltage direct current, or is there still more unexplored potential waiting for us to tap?
