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This paper proposes an analytical target cascading (ATC) based distributed optimal voltage control (DOVC) scheme for the voltage-source-converter high-voltage-directcurrent (VSC-HVDC) connected large-scale wind farm cluster (WFC). The aims are to minimize the voltage fluctuations of the point of connection (POC), collector buses, and wind turbine (WT) terminal buses inside the WFC while regulating the bus voltages close to the rated voltage and smooth the reactive power outputs of the WTs. With the DOVC scheme, the large-scale strongly coupled sensitivity-based voltage optimization problem is decomposed and solved in the WFC voltage-sourceconverter (WFCVSC) controller and sub-wind farm controllers in parallel. The DOVC scheme considers the N − 1 principle to improve the reliability, and distributes computation burden to several controllers to achieve better scalability of the WFC. The optimization subproblems are solved with local constraints and local measurements while guaranteeing the optimality of the primal optimization problem. A WFC with 5 wind farms and each wind farm consisting of 20 WTs is used to validate the proposed DOVC scheme. Index Terms-analytical target cascading (ATC), distributed, voltage control, wind farm cluster (WFC).

The permanent magnet synchronous motor (PMSM) has become a core component of electromechanical energy conversion in the modern industrial field. In order to expand the application of the PMSM in the field of high power traction, a robust predictive torque control (R-PTC) strategy for the Nsegment three-phase PMSM (N*3-phase PMSM) is proposed in this paper. Firstly, the output characteristics of the N*3-phase PMSM are illustrated with the finite element analysis method, and the mathematical model is established. Then, the six-segment three-phase PMSM predictive control system driven by six parallel inverters is designed to generate the required torque. Further, the influence of the parameter mismatch on the predicted torque and stator flux is taken into consideration based on the conventional predictive torque control (PTC). Finally, a novel R-PTC method with the proportional controller is developed for the N*3-phase PMSM, which can effectively improve accuracy and robustness of predictive control performance under parameters mismatch. Simulation and experimental results verify that, compared with the conventional PTC, the proposed R-PTC method can make the predicted stator flux and torque value accurately track its reference values while achieving lower stator flux and torque ripple.

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