Adaptive Positive-Negative Inertia-Emulation Control for Grid-Connected and Interlinking Converters

The contribution of virtual inertia through grid-connected converters is essential to tackle the stability issues that arise from the substitution of traditional synchronous generators by converter-interfaced systems. In the last decade, different adaptive virtual inertia controllers have been proposed, but the contribution of negative inertia to the transient response of grids has not been addressed yet. In this paper, an adaptive positive-negative inertia (A-PNIE) control is proposed, where the inertial contribution of the converter is optimised according to grid conditions. In addition, a Dual A-PNIE control is proposed for interlinking converters (IC), which adapts the bidirectional inertia support by switching from positive to negative inertia. A key advantage of the proposed controller is that it can be used for ac and dc grids interchangeably, using a per-unit representations of the frequency and voltage. The simulation results at a single-grid and two-grid scenario, and the experimental results on the single-grid scenario emulated at a Power-HIL testbench demonstrate the effectiveness and feasibility of the proposed controller, as well as the role of the negative inertia concept in accelerating the recovery of the frequency towards its nominal value after a power perturbation.