Research On Topology Structure And Control Strategy Of SVG Type DC Ice-melting Device

Line icing will cause conductor galloping,power failure tripping,insulator ice flashover,and other phenomena.In serious cases,it will cause conductor fracture,tower collapse,and pose a huge threat to the stable operation of the power system.With the increasing frequency of ice disasters in recent years,the DC ice melting device has become an indispensable part of power grid deicing technology due to its excellent ice melting performance.The full-bridge DC ice melting device with reactive power compensation function(hereinafter referred to as SVG(static var generator)DC ice melting device)has attracted the attention of people in the industry due to its ability to provide controllable DC voltage,low output harmonic content,and reactive power compensation during the non-ice melting period.In view of the disadvantages of the existing SVG type DC ice melting device,such as complex control structure,large calculation,and large device area,this paper proposes an instantaneous current split-phase control strategy suitable for SVG type DC ice melting device.In this strategy,the upper and lower bridge arms of the SVG DC ice melting device are used as two independent SVGs for phase separation control.The control amount does not need dq transformation to reduce the operation amount of the control system,and the structure is simple and clear.The ice melting device outputs controllable and adjustable DC voltage in the way of SVG neutral point voltage offset.During the nonice melting period,it can be used as two independent SVGs to compensate for the reactive power of the power system,effectively improving the utilization rate of the device and the flexibility of the hardware configuration.Firstly,the paper introduces the working principle of SVG DC ice melting device under the ice melting mode and reactive power compensation mode,then analyzes the mathematical model and power relationship of the ice melting device,summarizes the general design principles of DC ice melting device parameters,and gives the detailed parameter design process of SVG DC ice melting device based on this principle.Secondly,through the detailed study of the principle of submodule capacitance-voltage fluctuation,the control method of submodule capacitance-voltage balance suitable for split-phase layered control is proposed.Then,according to the mathematical model of the SVG DC ice melting device,the control strategy of ice melting mode and pre-ice melting experiment is formulated,and the simulation is carried out.Finally,the simulation model of the SVG DC ice melting device is built-in MATLAB/SIMULINNK platform,and the composition of each simulation module is described in detail.Set the simulation parameters and carry out the simulation experiments under the ice melting mode and reactive power compensation mode.The simulation results show that the DC voltage of SVG type DC ice melting device with split-phase instantaneous current control can be continuously adjusted in a wide range and can be applied to different icing lines;the proposed capacitor voltage balance control strategy can effectively reduce the capacitance-voltage fluctuation of submodules;when the device operates in the dual SVG state,it can not only realize the three-phase reactive compensation function but also realize the split-phase reactive Power compensation,to a certain extent,can reduce the impact of three-phase imbalance on the power system and improve the stability of the system operation.