An HVDC converter transforms high-voltage alternating current (AC) to high-voltage direct current (HVDC) or vice versa. HVDC is a high-voltage direct current (HVDC) power system that is used as an alternative to alternating current (AC) for transporting electrical energy over large distances or between alternating current power systems of various frequencies. The conversion process in an HVDC transmitter uses thyristors which can be controlled to turn on and off very quickly, thus allowing the passage of DC across the transmission line while avoiding any significant voltage ripple.
Line commutated converters (LCCs) are a type of semiconductor device that can switch currents on the order of hundreds of amperes at voltages below 100 volts. They have found widespread use in transmission lines for the transmission of electricity from a power station to an industrial site, or from a group of power stations to a single location. Because LCCs can be turned off instantly, there is no need for continuous current flow through them, which reduces energy loss due to resistance heating.
Commutation means controlling something in order to achieve a specific result. In this case, the outcome is disconnecting each LCC in sequence so that they all have time to turn off before the next group of LCCs is switched on.
Almost all HVDC converters are bidirectional by design; they may convert from AC to DC (rectification) or from DC to AC (inversion). A full HVDC system always contains at least one converter that acts as a rectifier (converting alternating current to direct current) and at least one that acts as an inverter (converting DC to AC). The conversion process in both cases is based on magnetic coupling, usually using iron cores and semiconductor components. Semiconductors can also be used for rectification but this technique is now mostly restricted to low voltage applications where silicon diodes are still able to handle the load.
Bidirectionality is important for HVDC because it allows the use of single-phase AC power distribution networks. On the other hand, it limits the application of HVDC technology to situations where there is no load switching involved. If the load varies significantly with time, then unidirectional converters would be needed instead. Some types of loads, such as induction motors, cannot be powered from either direction without some form of reverse power flow preventing devices being required in addition to the converter itself.
The main advantage of HVDC over conventional dc transmission is its ability to transmit power over long distances for a given cable size. This is due to the fact that high voltages can be transmitted economically using small cables compared with aysmmetrical ac systems where large conductors are necessary to carry the same amount of current.
A voltage converter is an electric power converter that alters the voltage of a power source. Voltage converters can be used to change the voltage of a battery or electrical generator for use with equipment designed for a different voltage. They can also be used as an accessory device for vehicles using 12 volts as their main power source.
The most common voltage converters are step-down and step-up converters. A step-down converter takes input voltage at one level and produces a lower output voltage. An example would be a car's electrical system which provides 12 volts when the engine is turned on but needs to run other accessories such as lights and refrigerators at less than 12 volts. A step-up converter does just the opposite - it increases the voltage of a low-power source like a battery to a higher value needed by heavy equipment like motors. The simplest type of voltage converter is a transformer - a device that contains multiple coils of wire wrapped around a core material such as iron or plastic. When current is passed through one coil, the magnetic field created by that coil links up with the magnetic field from another coil to produce a single combined field. This new combined field then induces a current in another coil connected in parallel with the first.