This work presents a Voltage Source Converter (VSC) controller that operates simultaneously as GFL and GFM. The GFL part functions as a GFL in a conventional wind generator (WG), and the GFM part can ensure grid support. This solution does not require additional hardware and is named the Hybrid Control Converter (HCC). The HCC was applied to the grid-side converter of a Type IV WTG, which was modelled in PSCAD. This approach aims to have a WTG that, in steady-state conditions, operates as a GFL converter guaranteeing MPPT, if its active power reference is the MPPT power, and during a disturbance in the grid, operates seamlessly as GFM, providing frequency and voltage support, like a synchronous generator. Simulation results are presented to show the latest advances of using HCC, such as: (i) black start capability, supplying power to a load or not; (ii) operation continuously isolated from the grid, allowing 100% wind generation, provided there is enough wind; (iii) ability to operate with or without a PLL algorithm, which could be an advantage for the cases highlighted in the literature in which instability problems in the converter control system are attributed to the PLL.
Watanabe et al. (Sun,) studied this question.