Topology And Control Strategy Of Cascaded Uhv Ac Withstand Voltage Test Power Supply

Under the general situation of rapid global economic development,the power industry,as a basic industry to protect people's livelihood,maintain national security and people's happy life,is facing unprecedented problems such as energy depletion and air pollution.Power resources in the new era should be targeted for cleanliness.Renewable energy.China's national conditions are the energy center of most renewable renewable energy sources that are far away from the load center.Therefore,accelerating the development of UHV power grids,accelerating the adjustment of energy structure,and implementing cross-regional power transmission projects are the established strategies for China's power grid development.The construction of UHV power grids is inseparable from UHV electrical equipment.In order to ensure the safety of power grids,equipment and personnel,these equipments must undergo various UHV AC tests before they are put into operation in the grid system.According to China's national conditions,due to the lack of high-voltage AC withstand voltage test power supply in the previous research of UHV transmission engineering,many technical studies related to UHV transmission and the withstand voltage test of UHV equipment have to be carried out abroad.Therefore,in view of the shortcomings of the traditional UHV AC withstand voltage test power supply structure,this paper focuses on the power supply mechanism,topology and control method of cascaded UHV AC frequency modulation resonance test based on power electronic system.First of all,for the traditional FM resonant high-voltage test power supply due to the topology of the single-stage converter,the total output voltage distortion rate is too large,the test power input voltage level is low(380/220V),which easily leads to insufficient grid voltage support capability,filtering A series of defects such as high volume and high cost of the device and too large a ratio of intermediate transformers are required.This paper proposes a cascaded multi-level frequency modulation resonant UHV test power supply topology,referred to as cascaded UHV test power supply.This optimized topology replaces the carrier phase-shifted back-to-back cascading multilevel converter with a conventional single-stage AC/AC converter to form a high-power FM signal source and raises the input voltage level to 10 kV.The topology of the cascaded UHV test power supply is divided into the rectification part and the inverter part from the signal conversion angle,and its working mechanism and mathematical model are explained in detail.The cascading multilevel converter of therectification part uses the switching function description method to establish its mathematical model.The inverter part is divided into three parts: cascade H bridge,LC filter and series resonance.The mathematical model is established by transfer function method.Secondly,the control strategy of the topology structure of the frequency-modulated resonant UHV test power supply based on cascaded multilevel is studied.The rectification part mainly composed of cascaded multilevel rectifier adopts the classical double closed loop control strategy of current inner loop voltage outer loop,and on this basis,the DC side voltage balance control strategy based on active voltage vector superposition and the grid voltage are added.Feedforward link;the inverter part consisting of cascaded multilevel inverter,LC filter,step-up transformer,and series resonant circuit.In order to achieve accurate voltage adjustment,voltage RMS and instantaneous value and resonance are adopted.Multi-loop control strategy for resistance current feedback.Finally,based on the aforementioned topology and control method,the stability analysis of the inverter part of the cascaded UHV test power supply is carried out;taking the cascaded five-level converter as an example,the cascaded UHV on the PSIM platform The test power supply is used for system simulation.The simulation results verify that the method successfully reduces the total output voltage distortion rate of the high-power FM voltage source and reduces the variation ratio of the intermediate excitation step-up transformer.Therefore,the filter device is simplified and required.The volume and weight of the transformer are greatly reduced,the cost of the overall device is greatly reduced,and the overall efficiency of the system is improved.