Transient Cable Overvoltage Calculation and Filter Design: Application to Onshore Converter Station for Hydrokinetic Energy Harvesting

The facilitation of maintenance of hydrokinetic energy conversion systems is supported by minimizing the exposure of components located underwater. The described onshore converter station´s design was motivated by this thought. The station includes the functions of power-electronic ac-dc-ac conversion and connection to the electric grid, thus leaving only turbine, variable-frequency ac generator, and connecting ac cable exposed underwater. A challenge in this configuration are potential electromagnetic traveling waves on the ac cable. They can be triggered through power-electronic pulses and cause significant overvoltages at the generator side. A key contribution is the modification of existing mathematical equations resulting in a novel methodology for expressing the overvoltages as a function of the traveling time and steepness of the pulses. This serves as the basis for an overvoltage reduction method involving the targeted selection of parameters of a suitable filter. It is applicable to distributed tidal energy and instream river conversion and electric drive systems involving long ac cables. The resulting overall design is validated through electromagnetic transients simulation. The results substantiate the proposed methodology of analysis and design.