HIL test automation for modular multilevel converters: how Siemens Energy streamlined control validation

The company

Siemens Energy – Grid Solutions, a business unit of Siemens AG, is a global leader in delivering advanced FACTS (Flexible AC Transmission Systems) and HVDC (High-Voltage Direct Current) systems. These technologies are critical for integrating renewable energy into power grids and ensuring stability, flexibility, and efficiency in global power transmission.

Focused on innovation, Siemens Energy is at the forefront of developing and validating Modular Multilevel Converters (MMC), enabling the reliable transfer of high-voltage power across long distances and international borders.

The challenges

With FACTS and HVDC systems playing a pivotal role in modern grid infrastructure, control software quality is essential. Siemens Energy needed to:

• Test converter control software with high reliability and consistency across diverse global transmission projects
• Automate HIL testing of MMC control systems to speed up development and reduce human error
• Integrate HIL simulation into their GitLab CI/CD pipeline to enable continuous testing
• Simulate complex electrical models with time steps under 1 microsecond, without deep FPGA knowledge
• Maintain flexibility to support multiple hardware configurations and project-specific parameters

Ensuring real-time validation of control firmware and detecting performance issues early were key goals in their strategy.

The OPAL-RT solution

Siemens Energy partnered with OPAL-RT to develop an automated HIL test bench for MMC control validation, using:

• OPAL-RT’s FPGA-based eHS Power Electronics Toolbox, enabling sub-microsecond execution of Simscape Specialized Power Systems models without complex FPGA development
• RT-LAB and its Python API to automate model generation, testing sequences, and data analysis
• A flexible simulation workflow running directly from MATLAB/Simulink, preserving Siemens Energy’s native toolchain
• Seamless integration into a GitLab CI/CD pipeline, enabling test execution with every code commit or merge request

The results

• Rapid deployment of a fully automated HIL test bench integrated with Siemens Energy’s CI/CD pipeline
• A test system capable of continuously validating new software releases, catching regressions, and maintaining control system performance under real-world scenarios.
• Immediate feedback to developers upon each control software update, improving development speed and software stability
• Simplified integration using Linux OS and compatibility with Docker, paving the way for scalable testing environments
• Reliable cross-core execution time monitoring, helping to identify and address firmware inefficiencies early
• Enhanced validation of MMC control systems across project-specific variants and hardware configurations

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