A Lyapunov-Based Nonlinear Power Control Algorithm for Grid-Connected VSCs

Abstract

For grid-connected voltage source converters (VSCs), it is commonly required that its power outputs can track the power references given by operators under various grid conditions. To achieve this objective, this article presents a Lyapunov-based nonlinear power control algorithm. The system dynamics is developed in the stationary frame, which facilitates the design of the control algorithm in the absence of phase-locked loops (PLLs) that may cause instability issues in ultra-weak grids. A virtual resistance is then introduced to allow fast power tracking performance and relax the requirement on accurate system parameters. Further, to simplify the control design, the quasi-stationary line (QSL) impedance model is applied, based on which a nonlinear control algorithm that only utilizes the output voltage and current information is developed. Afterward, the stability of the closed-loop system is analyzed via the Lyapunov theory. The theoretical results illustrate that the power regulation goal can be achieved and the VSC can maintain synchronization with the power grid. Finally, experimental results demonstrate the effectiveness of the proposed control algorithm under temporary grid faults and various short circuit ratios (SCRs).

Fault Recovery Analysis of Grid-Forming Inverters With Priority-Based Current Limiters

“…P OWER electronic inverters have been widely applied in power grids due to their efficient conversion and flexible control of electricity [1], [2]. Generally, inverters can be classified into two categories according to their control methods, i.e., grid-following (GFL) inverters and grid-forming (GFM) inverters [3], [4].…”

Impact of Circular Current Limiters on Transient Stability of Grid-Forming Converters

“…The stability analysis results are further verified on a prototype experimental setup, whose topology and parameters are discussed in [11]. In the experimental tests, the system and control parameters in Table I are used.…”

“…Figs. [10][11] give the experimental results with the increased voltage magnitude control gain 𝐾 𝑉 𝑃 = 3 p.u. Again, when the circular current limiter is transparent, transient stability is ensured under the grid voltage disturbance as shown in Fig.…”

“…For the inner control loops, a virtual admittance is applied to generate the converterside current reference [10]. To prevent the converter from over-current, a circular current limiter is utilized to restrict the current reference that is further achieved by a quasiproportional-resonant current controller [11]. 𝑖 𝑓 abc and 𝑖 abc are the converter-side and grid-side currents, respectively.…”

Equivalent Circuit Model of Grid-Forming Converters With Circular Current Limiter for Transient Stability Analysis

“…The detailed experimental setup can be found in [10] with the system and control parameters listed in Table I. The experimental results are delivered in Figs.…”