Dispatchable Current Source Virtual Oscillator Control Achieving Global Stability
Kehao Zhuang, Linbin Huang, Huanhai Xin, Xiuqiang He, Verena Häberle, Florian Dörfler
TL;DR
This paper addresses instability of grid-following (GFL) converters in weak-grid conditions by extending dispatchable virtual oscillator control (dVOC) to a dispatchable current source form (dCVOC) using GFM–GFL duality. The proposed method couples reactive-power–driven frequency with active-power–driven current magnitude, yielding dynamics $\dot{\theta}_i=\omega_0+k_p\left(q_\varphi-q^{ref}\right)+k_{\rm plli}\int i\left(q_\varphi-q^{ref}_\varphi\right)dt$ and $\dfrac{\dot{i}}{i}=k_p\left(p_\varphi-p^{ref}_\varphi\right)$ with $p_\varphi+jq_\varphi= e^{j(\pi/2-\varphi)}\dfrac{p+jq}{i^2}$. The work proves the existence of a unique equilibrium and global asymptotic stability under mild conditions (e.g., invertibility of $e^{J\varphi_g}Z_g-\mathbf{S}_{ref}$ and $0<\epsilon<\epsilon_s$, $\epsilon=k_{plli}/k_p^2$), and shows stability under current saturation and LVRT grid-code requirements. EMT simulations validate robust performance across grid strengths, with dCVOC maintaining equilibrium and providing reactive support during LVRT, unlike conventional GFL control. The results offer a robust, grid-source-agnostic approach for integrating large-scale power-electronic devices while complying with grid-code constraints.
Abstract
This work introduces a novel dispatchable current source virtual oscillator control (dCVOC) scheme for grid-following (GFL) converters, which exhibits duality with dispatchable virtual oscillator control (dVOC) in two ways: a) the current frequency is generated through reactive power control, similar to a PLL ; b) the current magnitude reference is generated through active power control. We formally prove that our proposed control always admits a steady-state equilibrium and ensures global stability under reasonable conditions on grid and converter parameters, even when considering LVRT and current saturation constraints. Our approach avoids low-voltage transients and weak grid instability, which is not the case for conventional GFL control. The effectiveness of our proposed control is verified through high-fidelity electromagnetic transient simulations.