Abstract
This paper presents a novel method for current control for a modular multilevel converter (MMC). The proposed current control methodology is based on a modified sliding mode control (SMC) with proportional and integral (PI) sliding surface which allows fast transient responses and improves the robustness of the MMC control performance. As the proposed method is derived via Lyapunov direct method, the closed-loop stability is ensured and results in globally asymptotically stable. Furthermore, the reaching time is also guaranteed by the proposed method, leading to fast transient responses. The proposed method is validated by comparing with some existing methods, which are proportional integral controller and conventional SMC, via offline and hardware-in-loop (HIL) simulations where a 10 MW, medium-voltage MMC system is tested. According to these results, the proposed method is able to provide fast transient responses, zero overshoot, and robustness to the weak grid and short-circuit conditions.
Highlights
Renewable energy (RE) technologies offer the promise of clean, abundant energy gathered from self-renewing resources such as the sun and wind [1]
To derive the model of the modular multilevel converter (MMC), one may follow the analysis presented in [11,27], and the single-phase equivalent circuit, as shown in Figure 2 is considered
Three cases will be studied, and they are active and reactive currents tracking, currents regulation under short-circuit conditions, and investigation on the interaction between the output current and circulating current control to show the superior performances of the proposed method
Summary
Renewable energy (RE) technologies offer the promise of clean, abundant energy gathered from self-renewing resources such as the sun and wind [1]. To extract the RE, power converters are used as interface from renewable sources to the grid or load. A voltage source converter (VSC) is the main interconnection device for distributed generators (DGs) and energy storage systems. According to their topologies, VSCs are categorized into two-level VSCs [3], cascaded multilevel converters [4], diodeclamped VSCs [5], flying capacitor converters [4], and MMCs [6]. For gridconnected PV systems [12], modular multilevel inverters are the preferred solution to connect large-scale PV plants [13] to the medium-voltage (MV) grid because the costly and bulky transformer can be removed
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