Siemens Energy is advancing High-Voltage Direct Current (HVDC) transmission through its proprietary HVDC PLUS® platform, a Voltage Source Converter (VSC)-based solution built on Modular Multilevel Converter (MMC) technology. This platform is designed to enable efficient long-distance bulk power transmission, while addressing the growing complexity of modern grids driven by decarbonization, distributed energy resources, and electrification.
HVDC PLUS® systems operate by converting AC power into DC at the sending station, transmitting it over long distances, and reconverting it back to AC at the receiving end. This approach significantly improves transmission efficiency compared to conventional AC systems, particularly for long-distance overhead lines, submarine cables, and underground transmission, where AC systems are limited by reactive power and capacitive effects.
A defining feature of HVDC PLUS® is its reliance on MMC-based converter technology, which Siemens Energy introduced commercially in 2007 and which has since become the industry standard for VSC-HVDC systems. The MMC architecture uses cascaded submodules to generate high-quality voltage waveforms, enabling reduced harmonic distortion, improved efficiency, and scalable system design for high-voltage applications.
HVDC PLUS® provides fully controllable active and reactive power flow in both directions, allowing grid operators to precisely regulate power transfer and stabilize AC networks. The system also enables accurate AC voltage control, making it suitable for weak grids and systems with low short-circuit capacity. Additionally, it supports standalone STATCOM operation, meaning it can provide reactive power compensation even without an active DC link.
The platform is engineered with advanced grid-support capabilities, including:
- Fault ride-through performance with reactive current injection
- Black-start capability for grid restoration
- Firewall functionality against cascading blackouts and system disturbances
- Operation even at very low or zero short-circuit ratios
HVDC PLUS® systems are available in multiple configurations to suit different transmission requirements. The symmetric monopole configuration uses two conductors with equal and opposite voltages, minimizing earth return currents and enabling the use of standard AC transformers. For higher capacity and redundancy, bipole configurations provide dual-pole operation with dedicated return paths, allowing continued operation even during partial system faults.
For more advanced grid architectures, Siemens Energy supports multi-terminal HVDC PLUS® systems, where multiple converter stations are interconnected within a single DC network. This enables dynamic routing of power between several generations and load points, making it particularly effective for integrating remote renewable energy sources such as offshore wind and large-scale solar plants into centralized grids.
HVDC PLUS® also supports back-to-back configurations, where AC systems with different frequencies are directly interconnected without the need for long-distance DC transmission lines. This capability is critical for linking asynchronous grids and enabling cross-border energy exchange.
HVDC transmission includes converter stations, transformers, DC transmission lines or cables, filters, reactive power compensation equipment, and digital control and protection systems. These components are tightly integrated to ensure reliable operation, high availability, and precise power flow management.
HVDC PLUS® is a key technology for modern power systems, offering:
- Efficient long-distance power transmission
- Seamless integration of renewable energy
- High controllability and grid stability support
- Flexible configurations for complex transmission networks
These capabilities make HVDC PLUS® a foundational solution for building resilient, efficient, and decarbonized energy systems.
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About Siemens Energy
Siemens Energy is a global energy technology company specializing in power generation, transmission, and grid infrastructure solutions. With more than 50 years of experience in HVDC systems and nearly 60 projects deployed across over 25 countries, the company is a leading provider of advanced transmission technologies, including HVDC PLUS®, transformers, and digital grid solutions that support the global transition toward sustainable energy systems.
