Impedance-Based Modelling of Hybrid AC/DC Grids With Synchronous Generator for Interaction Study and Dynamic Improvement

Abstract

Hybrid AC/DC grids are increasingly been seen as the most important network structure for future transmission infrastructures. An emerging challenge to such grids is the constant interaction between various components in the system. Interactions could occur in many intricate forms including between and within the AC and DC subnetworks. However, considering the complexities involved, methods for detection that are intuitive, compact, and relatively straightforward to apply are lacking. In this paper, device-level closed-loop impedance models of subsystems in a hybrid AC/DC grid are extended compactly to subnetwork equivalents in the form of matrices. Then, interaction analysis between a voltage source converter (VSC) interconnected on both sides, and a synchronous generator with excitation control is carried out as a case study to highlight potentially detrimental interactions. The analysis is carried out in the frequency domain and validated with a nonlinear time domain simulations in MATLAB/SIMULINK.

A Review on the Driving Forces, Challenges, and Applications of AC/DC Hybrid Smart Microgrids

“…• District/Distribution level: The suitability of AC/DC hybrid smart microgrids can be expanded from a single building application to a district-level application, as presented in Figure 5 [32][33][34]. As in buildings, so in distribution grids, the penetration of DC-based RES and storage renders the AC/DC hybrid configuration • Public installations: A beneficiary of AC/DC hybrid grids could be various public installations.…”

Stability improvement of MMC‐based hybrid AC/DC grids through the application of a decentralized optimal controller

“…The figure shows that the 𝜔 m1 and 𝛿 4 waveforms, which are oscillating at the frequency related to the mode 𝜆 1,2 , settle in a much shorter time under the decentralized optimal controller. Figure 15 is given to show the 𝜔 m1 waveform under the same fault at a higher fictitious clearing time of 5 s. It is evident from the figure that the decentralized optimal controller can significantly reduce the FIGURE 11 Decentralized optimal controller performance after applying a 20% step increase to MMC1 reference AC-side active power at t = 10 s: (yellow) with decentralized optimal controller only, (blue) with MMC1 droop only, (red) with both decentralized optimal controller and MMC1 droop FIGURE 12 Decentralized optimal controller performance after applying a 20% step increase to MMC1 reference zero-sequence energy sum at t = 10 s: (yellow) with decentralized optimal controller only, (blue) with MMC1 droop only, (red) with both decentralized optimal controller and MMC1 droop FIGURE 13 Decentralized optimal controller performance under the worst-case perturbation scenario, x 0,worst , applied at t = 10 s FIGURE 14 Decentralized optimal controller performance under the three-phase short circuit fault at bus B2 applied at t = 10 s and cleared after 500 ms: (yellow) with decentralized optimal controller only, (blue) with PSS1 only, (red) with both decentralized optimal controller and and (green) without both decentralized optimal controller and PSS1 𝜔 m1 fluctuations after the fault and improve the grid stability compared with the PSS1.…”

“…A number of recent studies have addressed the control and stability challenges in multiterminal hybrid AC/DC grids [5,12]. The potential detrimental dynamic interactions between the AC and DC subnetworks are assessed through the impedance-based modelling of the hybrid AC/DC grids in [13]. The AC grid here is represented through a simplified model of the synchronous generator with an automatic voltage regulator (AVR)/exciter, and the considered converter topology is the conventional 2level voltage source converter (VSC).…”