2-Dimensional Control of HVDC
Authors
Svean, Magnus ; Thoen, Astrid
Term
4. term
Education
Publication year
2018
Submitted on
2018-06-01
Pages
119
Abstract
This thesis tackles a practical issue in upper-level control of VSC-based HVDC systems: transient disturbances caused by switching between control modes in the conventional 1-dimensional (1-D) current vector control. The objective is to develop and assess a 2-dimensional (2-D) upper-level control structure that couples DC voltage and active power in the d-axis and AC voltage and reactive power in the q-axis, thereby avoiding explicit mode switching and enabling seamless transitions. The proposed 2-D controller reduces four control loops to two, each implemented with a tuned PI regulator. Performance is first evaluated in controlled single-converter test cases (step response, droop control, and limit enforcement) and benchmarked against the 1-D controller, then validated in a point-to-point (PtP) HVDC link and a 3-terminal multi-terminal HVDC system, including tests of seamless mode changes and fault conditions. Results indicate the 2-D controller achieves seamless switching with negligible oscillations in the tested PtP and 3-terminal setups; in some cases it responds more slowly than the 1-D controller but exhibits fewer transients and, with the proposed tuning, maintains limits during faults. The work thus highlights a control approach that delivers smoother transitions with a clear speed–smoothness trade-off.
Dette speciale adresserer et praktisk problem i overordnet styring af VSC-baserede HVDC-systemer: transiente udsving ved skift mellem kontroltilstande i den konventionelle 1-dimensionelle (1-D) strømvektorstyring. Formålet er at udvikle og vurdere en 2-dimensionel (2-D) overordnet styringsstruktur, der kobler spænding og aktiv effekt i d-aksen samt AC-spænding og reaktiv effekt i q-aksen, så eksplicit skift mellem tilstande undgås og overgange bliver sømløse. Den foreslåede 2-D styring reducerer fire kontrolsløjfer til to, hver baseret på en PI-regulator med afstemte forstærkninger. Ydelsen vurderes først i kontrollerede testcases for én konverter (trinrespons, droop-styring og håndtering af grænser) og sammenlignes med 1-D styringen. Herefter valideres styringen i både en punkt-til-punkt (PtP) HVDC-forbindelse og et 3-terminalt multi-terminal HVDC-system, inklusive tests af sømløs tilstandsskift og fejlscenarier. Resultaterne viser, at 2-D styringen opnår sømløst skift med ubetydelige oscillationer i de testede PtP- og 3-terminal-opsætninger; den har i nogle tilfælde en langsommere respons end 1-D, men udviser færre transienter og holder de satte grænser under fejl med de foreslåede indstillinger. Specialet peger dermed på en styringsløsning, der byder på mere glatte overgange mod en mindre, men tydelig, hastigheds–glathed–afvejning.
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