In this paper, the determination of submarine cable burial depth and risk assessment method are studied. The main objective of the method is to optimize the burial depth of submarine cable in terms of specifying an economically feasible buried depth which ensures a satisfactory level of protection and by acceptable risk. The risk factors influencing the burial depth of submarine cables were analyzed. The primary risk to which submarine cables are exposed is anchoring, while the environmental factor and the cable itself have relatively smaller impact and cannot be mitigated by burial. Then the calculation method of probability and depth of penetration of anchor deployment near a submarine cable were studied. The method can reduce the protection cost while providing the cable with better protection and to guide the specification of the burial depth of submarine power cables. Compared with traditional methods which relying on operational experience, the probabilistic analysis determines the burial depth based on the water depth and seabed conditions of different sections as well as the vessel traffic of the cable route which is an accurate and quantitative approach.

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Aiming at the problem of harmonic pollution in the control system of large-scale steel rolling equipment in metallurgical plant, the mechanism of harmonic generation in AC-AC frequency conversion and AC-DC-AC variable-frequency speed regulation system is analyzed, and a double PWM back-to-back AC speed regulation system is proposed. This system can not only realize the regeneration energy of frequency converter, but also reduce the harmonic wave, and greatly improve the power factor of the system. Finally, through MATLAB simulation, the harmonic of AC-AC frequency conversion and AC-DC-AC variable-frequency speed regulation system is analyzed, and compared with PWM back-to-back AC speed regulation system, the superiority, effectiveness and feasibility of PWM back-to-back AC speed regulation system design for large-scale AC drive device control are proved.