| Modular Multilevel Converter(MMC)based on the switchable switching device IGBT has a high voltage level and a large operating current.Some accidental processes during the operation of the converter valve and the rapid switching of sub-modules will cause some transient electromagnetic disturbances,Such transient signals are coupled to the IGBT drive circuit in the form of conduction and radiation disturbances through parasitic parameters in the sub-module circuit.When the absolute value of the sub-module driving port voltage exceeds 20V,the IGBT gate will be broken down.In addition,the positive and negative spikes introduced by the drive port may also cause the IGBT to be turned on or turned off by mistake,causing the IGBT to work abnormally.In severe cases,it will damage the primary equipment and threaten the safe operation of the system which will seriously affect the reliability of the flexible straightening project.Therefore,it is necessary to deeply study the electromagnetic disturbance problem of the drive port of the flexible DC converter valve from the aspects of electromagnetic disturbance type,coupling path and influence mechanism.First of all,this thesis analyzes the generation mechanism of the conduction disturbance voltage at the drive port of the MMC submodule and the change rule of the gate voltage of the down tube IGBT drive port during the switching flow of the submodule.It provides a theoretical basis for the simulation analysis of the conduction electromagnetic disturbance of the sub-module drive port under different operating conditions of the flexible DC converter valve.An electromagnetic transient model of the sub-module power loop including the IGBT mechanism model and the anti-parallel diode macro model is established,and the stray parameters in the sub-module power loop are extracted using the boundary element method and the flux linkage method.Finally,a double-pulse experiment platform was built,and the double-pulse experiment was used to verify the accuracy of the sub-module power loop transient model.Secondly,this thesis uses the finite element method to establish a power frequency and a pulse magnetic field calculation model in the vicinity of the MMC sub-module,analyzes the transfer process of the internal current of the sub-module during normal operation of the 500kV flexible DC converter valve,and determines the current excitation paths in different stages in the magnetic field calculation.Based on the double-pulse test platform,the measured and calculated values of the magnetic field above the driving board and near the central control board when the devices in the MMC sub-module are switched on and off are compared,and the accuracy of the sub-module space magnetic field calculation model is verified.Finally,this thesis uses the sub-module drive port conduction electromagnetic disturbance simulation model to simulate and analyze the change of the gate voltage of the IGBT drive port during the commutation process of the sub-module switching on or off under the converter valve works in different operating conditions.The change rule of the gate voltage with the driving resistance and power-drive loop coupled inductance is given,and the electromagnetic disturbance characteristic of the sub-module driving port is analyzed.The sub-module space magnetic field calculation model is used to calculate and analyze the power frequency AC current component in the sub-module under different operating conditions and the pulse current generated by the transient commutation process to the radiated electromagnetic disturbance level of the drive port,and the general law is obtained.The conducted disturbance of the sub-module drive port cannot be ignored,and the radiated disturbance has a small impact on the drive port and can be ignored. |
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