Benefits of High-Voltage Direct Current Transmission Systems

High-voltage direct current (HVDC) technology offers several advantages compared to alternating current transmission systems. For example, it allows more efficient bulk power transfer over long distances. However, cost is an important variable in the equation. Once installed, HVDC transmission systems are an integral part of the electrical power system, improving stability, reliability, and transmission capacity.

Typical utility-scale power plants generate alternating current (AC) electricity, and most electrical loads run on AC power. Thus, the majority of transmission lines carrying power around the world are of the AC type. However, there are instances when high-voltage direct current (HVDC) transmission systems offer significant benefits.

“One big advantage to HVDC is the efficiency of power transmission over long distances,” George Culbertson, vice president of power delivery markets for HDR, told POWER. “If the transmission line route is longer than about 300 miles, DC is a better option because AC lines have more line losses than DC for bulk power transfer.”

Converting from AC to DC

The challenge, however, is that to transmit via HVDC, two converter stations are needed. First, the AC power must be converted to DC to begin the transmission process, and then when it gets to the desired tie-in destination, the DC power must be converted back to AC to be utilized on the grid.

Conversion technology is well-established. Electrical pioneers were working on the building blocks for HVDC-links back in the late 1800s. Conventional HVDC converter technology is based on the use of line-commutated or phase-commutated converters. In 1954, ASEA, the predecessor of ABB, used this classic technology utilizing mercury arc valves to construct the world’s first commercial HVDC link between Västervik, on the east coast of Sweden, and Ygne, on the island of Gotland in the Baltic Sea. The original Gotland link could transfer 20 MW over a 98-kilometer (km)-long submarine cable with a voltage of 100 kV. The service was re-engineered in 1970, increasing capacity to 30 MW at a voltage of 150 kV through the addition of a thyristor valve bridge.

ASEA continued to push boundaries, developing new HVDC systems during the decades that followed. In 1997, ABB commissioned the world’s first HVDC demonstration project using voltage source converters (VSCs). VSC technology uses gate turn-off switching devices, such as insulated-gate bipolar transistors (IGBTs), to perform the conversion. An IGBTs high switching frequency capability allows more-precise VSC control and less-complex circuit configuration through the use of pulse width modulation techniques. ABB named its new VSC-based product HVDC Light.

VSC technology was further improved when Siemens introduced a modular multilevel converter (MMC). The Trans Bay Cable project, which runs between San Francisco and Pittsburg, California, was completed in 2010, using Siemens’ HVDC Plus system. MMC technology offers excellent harmonic performance and reduced power losses compared to previous VSCs. All HVDC manufacturers are applying MMC technology in VSCs today.

Products and reference designs of High-Voltage Direct Current Transmission

High-voltage direct current (HVDC) or ultra-high voltage (UHV) power transmission systems help reduce power losses and cost when energy is transported over long distances. We provide analog, digital, interface and protection products and reference designs for HVDC transmission systems.

As shown in the figure below, High-voltage direct current (HVDC) power transmission consists of 7 parts, each part is Gate driver module (xN)、Valve based electronic DC switch yard、Power supply、Isolated voltage / current sensing、Communication module、IO modules (AC/DC switch yard)、Control and protection

Gate driver module (xN)

Output power transistor and driversOutput power transistor and drivers. Gate driver module (xN) includes Arm-based processors、C2000 real-time microcontrollers、Isolated gate drivers、Precision ADCs、Ethernet PHYs, the corresponding products are AM6412、TMS320F28377D、ISO5852S、ADS8675、DP83848I

Valve based electronic DC switch yard

Wired signal interface to external devices or internal boardsWired signal interface to external devices or internal boards.  Valve based electronic DC switch yard includes Ethernet PHYs、Arm-based processors, the corresponding products are DP83867E、AM6412

Power supply

DC/DC Power Supply including power stage, incl. LDO. Power supply includes Multi-channel ICs (PMICs)、Supervisor & reset ICs、Buck converters (integrated switch)、eFuses & hot swap controllers、Linear & low-dropout (LDO) regulators, the corresponding products are LP873220、TPS3897、LM76003、TPS2662、LM2937

Communication module

On-board sensors and health monitoring. Communication module includes Arm-based processors、RS-485 & RS-422 transceivers、Ethernet PHYs、ESD protection diodes, the corresponding products are AM6412、SN65LBC184、DP83867E、TPD4E05U06

IO modules (AC/DC switch yard)

Isolated 115/230V AC/DC Power Supply including power stage. IO modules (AC/DC switch yard) includes General-purpose op amps, the corresponding products are TLV9062、TLV9001、OPA2990

Control and protection

Current and voltage control and protection. Control and protection includes Arm-based processors、Digital temperature sensors、Temperature switches、Analog temperature sensors、Precision ADCs、Precision op amps (Vos<1mV)、Isolated ADCs