To keep phase balance and improve output voltage quality, a novel multiple-loop control system in 400-Hz inverter power supply based on unipolar sinusoidal pulse width modulation (SPWM) is proposed. The causes of phase imbalance in a threephase combined inverter power system are analyzed, and a new multiple-loop control strategy based on phase control is presented to eliminate it. For reducing the total harmonic distortion (THD) of high-power inverter output, unipolar SPWM is added with this new control strategy. The designs of drive circuit and snubber circuit are discussed to eliminate dead time effects and voltage oscillation. The stability of the control system is analyzed and the power system and the control strategies are realized with digital signal processing. Contrastive simulation results indicate the advantages and the correctness of this novel controller for inverter. A three-phase combined inverter system based on a multiple-loop control strategy is constructed, and experimental results show that the inverter system can make a phase difference between each phase less than 2 • , and the THD of output voltage can be controlled within 2%.Index Terms-Medium frequency, multiple-loop control, phase feedback, three-phase combined inverter, unipolar SPWM.

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Ladle slag carry-over detection technology (SCDT) is of important practical significance to steel continuous casting production (CCP), which can effectively improve the casting blank quality, increase molten steel yield ratio, and protract the service life of tundish. The current SCDT realization methods and their application circumstance were summarized, and their main problems during the course of factual production were pointed out. The difficult technical points of detection principle, digital signal processing for vibration style SCDT development were described. To aim at the problems of vibration style SCDT, such as low recognition stability and long applied adjustment time, its key technologies including water model experimental platform establishment, two-phase sink vortex entrapment mechanism, forced vibration response of shroud nozzle and steel stream shock vibration signal processing optimization were analyzed deeply, and the corresponding research route and advices were given. ladle slag carry-over, sink vortex, slag entrapment, shock vibration Citation: Tan D P, Ji S M, Li P Y, et al. Development of vibration style ladle slag detection methods and the key technologies.

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Aiming at the problem of difficult contact finishing for mini structural surface in course of mould manufacturing, a new no-tool precision machining method based on soft abrasive flow machining (SAFM) was proposed. It allocated restrained component near surface machined, constituted restrained abrasive flow passage, and made the surface become a segment of passage wall. It could control turbulence abrasive flow in restrained passage, realize micro cutting for passage wall, and utilize the irregular motion of abrasive flow to eliminate the mono-directional marks on machined surfaces, and the precision could reach the specular level. A two-phase dynamic model of abrasive flow oriented to SAFM combined with discrete phase model (DPM) was established, the law of two-phase flow motion and the related physical parameters was obtained by corresponding numerical simulation method, and the mechanism of precision machining in SAFM was discussed. Simulation results show that the abrasive flow machining process mainly appears as translation of ablating location with the influence by granular pressure, and as the variation of machining efficiency with the influence by near-wall particle velocity. Thus via control of the inlet velocity and its corresponding machining time, it is supposed to work out the machining process according to the machining requirements by using the Preston equation to seek the relationship among velocity, pressure and material removing rate. By tracking near-wall particles, it can be confirmed that the movement of near-wall abrasive particles is similar to stream-wise vortices. The cutting traces on workpiece surfaces assume disorderly arrangement, so the feasibility of the SAFM method can be reaffirmed. structural flow passage, ultra-precision machining, softness abrasive flow, discrete phase model Citation:Ji S M, Xiao F Q, Tan D P. Analytical method for softness abrasive flow field based on discrete phase model.

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