Kajal Pokharel1*, Masoud Ataei1*, Jan L Diaz2, Vikas Dhiman1, Hepeng Li1, Fabio Andrade Rengifo2, Reinaldo Tonkoski3
1University of Maine | 2University of Puerto Rico, Mayagüez | 3Technical University of Munich
*These authors contributed equally · IEEE PES General Meeting (PESGM), 2026, Accepted · Paper No: 26PESGM1495
Conventional current controllers for grid-following inverters, such as PI and LQR, can overshoot during voltage sags and transients, pushing inverter currents past their safe operating limits. This work embeds current-safety guarantees directly into the control law by combining a Control Lyapunov Function (CLF), built from the LQR Riccati solution, with two Control Barrier Functions (CBFs) that enforce the IEEE 1547 d- and q-axis current limits.
The CLF and CBF constraints are unified into a single quadratic program (QP) solved every switching cycle: the CLF term drives the current toward its reference, while the CBF constraints act as hard safety walls that are never violated, using a super-linear class-𝕂 function for smooth control away from the limit and aggressive correction near it.
In MATLAB/Simulink simulations of a 100 kVA grid-connected inverter under a 0.6 pu voltage sag, the CLF-CBF-QP controller kept the peak current at 219.5 A, within the 224.5 A safe limit, while PI and LQR controllers overshot to 237.8 A and 240.8 A respectively. The proposed controller also achieved the lowest total harmonic distortion (3.46% vs. 4.72% for PI and 5.63% for LQR), with QP solve times (271.5 μs) comparable to the PI and LQR baselines.
Three-phase grid-following inverter with LCL filter; the CLF-CBF-QP controller computes safe voltage commands (v1d, v1q) every switching cycle.
| Controller | Peak Current | THD | Safe (≤ 224.5 A)? |
|---|---|---|---|
| PI | 237.8 A | 4.72% | ✗ |
| LQR | 240.8 A | 5.63% | ✗ |
| CLF-CBF-QP | 219.5 A | 3.46% | ✓ |
d-axis current tracking. PI overshoots and recovers slowly. LQR recovers fast but breaches the limit. CLF-CBF-QP: fast recovery, limit never crossed.
This work is supported by the National Science Foundation (NSF) under OIA-2316399, OIA-2218063, and OIA-2316401.
@inproceedings{pokharel2026safe,
title={Safe Control of Grid-Following Inverters using Control Lyapunov and Barrier Functions with Stability Guarantees},
author={Pokharel, Kajal and Ataei, Masoud and Diaz, Jan L and Andrade Rengifo, Fabio and Tonkoski, Reinaldo and Dhiman, Vikas and Li, Hepeng},
booktitle={2026 IEEE PES General Meeting (PESGM)},
year={2026},
organization={IEEE}
}