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This paper proposes a constrained modulated-model predictive control (M 2 PC) scheme for an LC-filtered voltage source converter (VSC). To tackle the coupling effects of the state variables in a second-order LC filter, a dual-objective cost function (CF) is used to explicitly track both capacitor voltage and inductor current references, which can achieve an improved voltage quality. To handle the state and control input constraints of VSCs, a constrained M 2 PC scheme is proposed with an 'online post-correction' constraint-handling technique. First, the unconstrained optimal voltage vector (OVV) is derived. It is generated by seeking the minimum analytical solution of the CF offline, simplifying the online implementation. Then, an 'online postcorrection' strategy is employed by reconsidering the constraints to correct the precalculated OVV online, which guarantees the future states within the allowed range. Finally, the corrected OVV is synthesized by the space vector modulation (SVM), resulting in a fixed switching frequency and low harmonics. Compared with the typical constrained MPC, the presented scheme has the advantages of improved steady-state performance, flexible constraint-handling ability and lower computational cost. Additionally, design procedures for weighting factor (WF) selection in the CF are given. Comparative experiments are investigated to verify the presented control strategy.
Conventional primary control employs outerloop droop and inner-loop cascaded linear control to realize local voltage regulation and power-sharing of an islanded ac microgrid. However, it has a complex structure, limited dynamic response and a rapid rate of change of frequency when disturbances occur. This paper resolves these issues by proposing a model predictive control based virtual synchronous generator (VSG-MPC). An improved finite-set MPC is first proposed for the inner loop, achieving simplified control structure, faster dynamic response, enhanced bandwidth and stability, as well as improved current limitation. In the outer control loop, a simplified VSG without a phase-locked loop is employed to realize active powersharing and inertia emulation. The merits above are verified by a description function of MPC and the frequency-domain response of the overall VSG. Simulation and experimental results verify the feasibility of the proposed method.
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