As much wind power is integrated into the power grid through power electronic equipment, the use of wind power is increased rapidly. Wind power system makes the power grid lack inertia and damping, thereby reducing power grid stability; in severe cases, it may even be disconnected. virtual synchronous generator (VSG) has been put forward to enhance the anti-disturbance performance of power grid. However, conventional VSG adopts an outer power loop and inner-current loop control. The inner-current loop control needs a pulse width modulation (PWM) module and proportion integration (PI) parameter settings. In order to reduce the parameter settings and simplify control structures, in this study, model predictive control (MPC) is used instead of inner-current loop control. At the same time—for the overall stability and control flexibility of the back-to-back system—we further propose to use outer-voltage loop control (OVLC) and MPC to stabilize direct current (DC) voltage on the machine-side and to employ model predictive virtual synchronous controls to provide inertia and damping for the power grid. The proposed control method was simulated in Matlab/Simulink (MathWorks, Massachusetts, MA, 2016) and verified by experimental results.

Flow and heat transfer characteristics of slot jets impingement to a cylindrical convex surface are numerically investigated. Suitable turbulence models have been determined through comparison with the experimental data. Flow structures are described and impingement heat transfer characteristics are discussed. The effects of Re, H/B and D/B on single-slot jets impingement heat transfer are analyzed and heat transfer characteristics of multiple-slot jets are investigated. The results show that: Gas flows along the convex surface and boundary layer separation occurs in both single and multiple-slot jets impingement. A maximum stagnation Nu appears at H/B=8 and the local Nu decreases with increasing H/B in the region far away from the stagnation. The Nu in the stagnation region decreases with increasing D/B but the Nu is nearly the same in the region far away from the stagnation. Pressure gradient is an important factor on heat transfer enhancement. Correlations of the Nu m for single-slot, double-slot and quadric-slot jets impinging on a convex surface are obtained. It indicates the effects of Re and D/B on Nu m could become more important in less slot jets impingement.

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