Virtual Synchronous Compensator with Virtual Braking Resistor for Stable DC-link Voltage Control

The Virtual Synchronous Machine (VSM) algorithm represents a well-established control method for interfacing renewable energy sources with the grid. However, VSM suffers from transient stability issues, particularly when operating as a Virtual Synchronous Generator (VSG). Furthermore, maintaining control stability can be more challenging when the DC-link voltage control is implemented. Indeed, the DC-link voltage is controlled by regulating the power exchanged with the grid. However, the injected power can be limited by the applied current saturation strategy, potentially leading to DC-link overvoltage. Therefore, this article proposes implementing a Virtual Synchronous Compensator (VSC) algorithm to regulate the DC-link voltage. The VSC structure ensures the control remains stable even under current-saturation conditions. Furthermore, the Virtual Braking Resistor (VBR) concept is introduced to keep DC-link operation within the permitted voltage range without requiring communication between the DC/DC and DC/AC converters. The proposed control solution has been experimentally validated using a 30 kVA converter setup and a grid emulator, meeting both AC and DC test requirements.