High-voltage direct current (HVDC)

Making the energy transition happen

Strengthening the transmission system with grid solutions and HVDC systems. High-voltage direct current (HVDC) transmission systems are becoming more and more important in the global energy landscape which is characterized by increased digitalization, accelerated decarbonization and the unprecedented uptake of distributed energy resources (DER), inverter based resources (IBR) and distributed power generation in general.

HVDC PLUS® technology is a most efficient solution to transmit large amounts of power across long distances, facilitate the integration of renewable power resources and provide enhanced control features to stabilize the grid together with our leading portfolio of FACTS & storage solutions.

HVDC PLUS® addresses many of today's challenges to make the energy transition happen on a global scale. Its adoption not only signifies an important step towards achieving sustainability goals but also delivers tangible benefits ranging from operational efficiencies for TSOs to environmental conservation efforts benefiting society at large. As we continue to transition and seek ways to make our electrical transmission grids smarter and more resilient, embracing technologies like HVDC PLUS® will be key to energize society and create a more sustainable future for all.

Symmetric Monopole

The HVDC PLUS® symmetric monopole configuration is a foundational design configuration in high-voltage direct current (HVDC) systems, characterized by its superior simplicity and reliability.

In this setup, the HVDC converter is connected with fully insulated DC conductors, operating at equal but opposite DC voltages to ground and offers the following main advantages:

This arrangement effectively reduces earth return currents, minimizing environmental impacts associated with ground currents.
As the transformers are not exposed to DC voltage stresses the sym. monopole configuration enables the use of standard AC power transformers.
No excessive infeed of fault currents from the AC grid at DC pole-ground faults.
Siemens Energy successfully scaled the sym. monopole configuration over the last decades. Pioneering HVDC PLUS® using MMC technology Siemens Energy is the world record holder for the highest max. DC voltage in sym. monopole configurations.

Bipole

The bipole configurations represent a logical evolution and up-scaling in HVDC PLUS® technology which provides greater capacity and flexibility compared to symmetric monopole configurations.

There are three main types:

Bipole with Metallic Return (DMR): Utilizes a metallic path as return conductor, offering cost benefits by not requiring full insulation on the return path.
Bipole with Electrode: Uses earth or sea electrodes for returning current in case of (asym.) monopole operation due to maintenance or fault conditions.
Rigid Bipole: Consists of two conductors with opposite polarities and no metallic return or earth electrode return paths under normal operating conditions.
The bipole configuration incorporates associated DC switchgear which allows for increased system redundancy allowing for continued operation even if one pole fails. Higher power transmission capabilities are facilitated accordingly. Rigid bipole configuration enables optimized CAPEX for long distance cable transmission systems.

Point-to-Point HVDC

Point-to-point HVDC transmission involves two converter stations connecting two grid connection points directly using an DC transmission line in between.

This set-up is ideal for long-distance energy transmission between two specific locations using DC cable or DC OHL systems.

It's widely used for cross-border interconnections and connecting remote renewable energy sources to major consumption centers. Siemens Energy is the most experienced trusted partner to make cutting-edge and most reliable point-to-point HVDC transmission schemes a reality.

Back-to-Back

A back-to-back HVDC PLUS® system consists of two converter stations located in close proximity, usually within the same building, converting AC power from one network frequency directly into another network frequency via HVDC without any actual DC transmission line involved.

This setup is utilized primarily for connecting asynchronous electrical grids efficiently while also providing advanced control capabilities for active & reactive power as well as AC voltage control.

Multiterminal HVDC

Multiterminal HVDC PLUS® systems build upon point-to-point concepts by incorporating more than two converter stations in a single integrated HVDC system with multiple converter stations and multiple DC transmission lines.

This enables more flexible and more complex power transmission opportunities such as collecting power from multiple generation sites (e.g., offshore wind farms, remote renewable energy sources) and distributing it across various load centers efficiently through strategic routing decisions made possible by advanced control systems inherent within specific and custom tailor-made multiterminal HVDC designs.

These set-ups enable increased flexibility in integrating multiple renewable sources into a single integrated HVDC system enhancing grid efficiency and footprint. It allows for dynamic rerouting of energy based on generation and/or demand fluctuations ensuring optimal utilization of power resources available across regions.

A key component which facilitates these advanced capabilities of multiterminal HVDC systems is the converter technology used – specifically, half-bridge and full-bridge converters. Each offers unique advantages and characteristics suited to different operational / performance requirements.

Siemens Energy vast experience from 15 successfully executed point-to-point HVDC systems showcases the reliability and capability of Siemens Energy as a most reliable and most trusted partner in the industry making complex multiterminal HVDC systems a reality.

Siemens Energy leverages decades of HVDC expertise & modular multilevel converter technology to its fullest capabilities, applying half-bridge as well as full-bridge converters. If required parallel converters can be used for increased power transmission capabilities and provide superior redundancy and unmatched flexibility.

The Modular Multilevel Converter (MMC) technology was first introduced to the market by Siemens Energy in 2007. It was successfully commissioned and put into commercial operation in 2010 with the pivotal pilot project Transbay Cable (San Francisco, USA).

Eventhough several other HVDC converter concepts were tested and trialed in the late 1990s/early 2000s all alternative HVDC converter concepts were abandoned & vanished from the HVDC market landscape.

Today MMC technology is the well-proven & established industry standard for VSC-based HVDC systems worldwide. Siemens Energy is the #1 market leader and trailblazer of MMC-based HVDC systems.

Benefit from our project experience and proven technology

With over 50 years of experience, Siemens Energy is a globally renowned technology partner for HVDC systems and a most trusted partner in the industry to make even the most complex HVDC projects a reality.

Up to his date, Siemens Energy is counting more than 70 projects among its HVDC references, in over 25 countries around the globe. This is a testament to cutting-edge HVDC technology provided worldwide making Siemens Energy a preferred global partner of choice for HVDC projects.

43 HVDC Classic® projects are designed to operate with line-commutated converters (LCC / Thyristor technology). This showcases highest quality standards and most reliable performance. Siemens Energy covers the whole HVDC lifecyle and is in close contact with our customers worldwide to provide tailor-made services and support clients regarding upgrade and refurbishment packages.

On top of that, 34 HVDC PLUS® projects are based on voltage-sourced converters (VSC / IGBT technology) using modular multilevel converters (MMC). This is a testament to Siemens Energy’s role as a pioneer and trail blazer for HVDC VSC technology. Besides several other converter concepts had been introduced and tested in the market in the late 1990s/early 2000’s, it is now a fact: MMC technology has become and is the proven and unrivalled industry standard for HVDC systems. Siemens Energy introduced MMC-based HVDC PLUS® technology 2007 and continuously innovates converter technology and fully power electronic based HVDC transmission systems.