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In present state of art, compressor blades can work efficiently between the span of 20%–80%, while nearly 30% of the total loss comes from endwall region. Previous studies have shown that Blended Blade and End Wall (BBEW) which is a control technique can reduce the corner separation effectively. To further reduce the loss, enhance diffusion capability and restrain the secondary flow in the endwall region, in addition of a kind of non-axisymmetric endwall, Full-BBEW technique is put forward. Firstly, the geometric method of the Full-BBEW technique is presented on a NACA65 cascade with the unchanged axial passage area. Moreover, under the category of Full-BBEW technique, according to the different geometry characteristic, BBEW (blended blade and endwall) model, IOEW (inclining-only hub) model and Full-BBEW model are presented. Then in order to find the most effective design, numerical investigation and optimization based on the Kriging surrogate model are employed on the models. Compared with the prototype, the total pressure loss coefficient decreases by 7%–9% in optimized Full-BBEW cases and the aerodynamic blockage coefficient decreases about 23%–36%. Through analysis, the blended blade geometry creates a radial pressure gradient at the end section and push the low-energy fluid up to the mainstream. As the result, the loss decreases significantly between 5%–25% span range. Meanwhile, the intersection of boundary layer weakens because of the expanded dihedral angle. On the other hand, the inclining-only hub geometry reduces the circumferential pressure gradient and restrains the crossflow in corner. Overall, though the loss in mainstream increases slightly, Full-BBEW technique can reduce the boundary layer intersection and the crossing flow in corner so that the diffusion capability further increases and the aerodynamic performance in the endwall region improves effectively.

Two kinds of three-phase cascaded quasi-Z-source AC/AC converter topologies are proposed in this paper, which overcome the shortcomings of traditional three-phase chopper controlled AC/AC voltage regulator and three-phase voltage type quasi-Z-source AC/AC converter. Analyze its circuit structure and working principle, The relationship between duty ratio and output voltage, as well as capacitance voltage stress, is derived using Kirchhoff's law and the volt-second balance principle. MATLAB/Simulink is used to simulate the two topologies, Pulse width modulation (PWM) is used to control the duty ratio. Finally, the simulation results verify the correctness and feasibility of the theoretical analysis.

Through an in-depth analysis of the working principle and working process of the Y-source inverter, an abnormal working state of the Y-source inverter is found, which causes a large drop to the dc-link voltage of the inverter bridge when it operates in the active vector state. The article elaborates the circuit conditions of the abnormal state, and analyzes the relationship between the falling voltage amplitude and the shoot-through duty ratio. The relationship between other parameters in the circuit and the minimum free-wheeling inductance is discussed. The advantages and disadvantages of the two feasible methods are analyzed, and it is found that only changing the primary side inductance to be greater than the minimum freewheeling theoretical value that can fundamentally solve the discontinuity problem. Finally, the feasibility of the technical measures to avoid the abnormal state is verified by experiments.