Grid forming Converter with MVDC input and LVAC output: Analysis and Control Hardware-in-the-Loop Validation

This research investigates the modeling and control hardware-in-the-loop (HIL) implementation of a voltage source converter (VSC) with a medium voltage DC (MVDC) input and low voltage AC (LVAC) output in grid-forming mode. The system employs a step-down transformer between the L and C components of the converter output filter, enhancing cost-effectiveness and safety. However, this configuration presents challenges in modeling and control design due to the separation of feedback signals for the control system: the inverter current, used as the inner loop feedback signal, is measured on the primary side, while the capacitor voltage, used as the outer loop feedback signal, is measured on the secondary side. This paper addresses these challenges and presents a control strategy tailored for this configuration. The study utilizes a three-level converter with a Dyn11 transformer configuration. The validation process involves control hardware-in-the-loop (HIL) testing, using a Texas Instruments DSP F28379D for control implementation, MATLAB/Simulink for code generation, and Typhoon HIL for real-time simulation. The primary contribution is the development of a control strategy that effectively handles dual-sided feedback from the transformer, maintaining stable operation in grid-forming mode. This approach ensures low Total Harmonic Distortion (THD) and excellent dynamic response, enhancing the converter output voltage stability, and power quality.