Research Of The Voltage Balancing Of Series Connected IGBTs In High-voltage Switch Of Auxiliary Heating System

In order to achieve nuclear fusion,it is necessary to heat the plasma to hundreds of millions of degrees.As the conventional ohmic heating can not achieve such high temperature,the auxiliary heating is needed.In the auxiliary heating system,high voltage power supply is usually equipped to accelerate particle or driven-RF source,the power supply voltage reaches tens to hundreds of volts.Ignition failure may occur in auxiliary heating system.At this point,there is a strict limit on the energy released by the high voltage power supply to the load equipment,otherwise it will lead to the damage of the equipment.Therefore,the auxiliary heating system needs quick-action protection measures.The crowbar protection system has the problems of safety and long cycle of action.The PSM power self turn off measures has the problems of control complex and poor reliability.Therefore,it is necessary to develop an auxiliary heating system protection device with faster action and simple control method.The fast high-voltage DC switch based on series connected IGBTs is suitable for auxiliary heating system protection device for it has the advantages of fast switching speed(nanosecond level),easy realization of precise control and no arc generation during operation.Due to the high voltage circumstance the auxiliary heating system requires,as a result,the investigation of the voltage balance of series connected IGBTs has important practical significance when a single IGBT can not meet the requirements.Due to the individual differences of switching devices together with the difference of driving signal generated by driving circuit and the influence of distribution,parameters of main circuit,the voltage sharring of each series connected IGBT were significantly different by asynchrono?s action.Voltage imbalancing of series connected IGBTs may directly affect the stable operation of the circuit and severe cases will result in serious damage to circuit equipment.Therefore,it is necessary to add an additional series technology to improve the problem of unequal voltage distribution in series connected IGBTs.Based on the extensive investigation of IGBT series voltage equalization technology,the idea of active driving voltage phase control technology is suitable for the high voltage switch formed by series connected IGBTs of auxiliary heating system.IGBT series voltage balancing problem is the inconsistent of the action of series connected IGBT,which lead to voltage imbalance.According to the cause of IGBT series voltage equalization problem,this paper analyzes the characteristics of IGBT.The mechanism and influence degree of IGBT series voltage equalization of the grid parameters of series connected IGBTs,which includes grid resistance,grid voltage and grid drive signal delay,are analyzed and calculated in detail,together with IGBT self-parameters,distributed capacitance and stray inductance in the circuit.The simulation experiment is carried out by using the OrCad/pspice software.Its results show that the dynamic performance of IGBT is mainly affected by the grid parameters,while the distributed capacitance and stray inductance in the circuit have some influence on the dynamic voltage balancing of IGBT,and the static performance of IGBT is mainly affected by the IGBT self-parameters.This conclusion lays the theoretical foundation for the research of voltage balancing technology of series connected IGBTs.In this paper,a novel active grid trigger time compensation technology is proposed for the dynamic voltage balancing problem of IGBT in series.The principle of active grid trigger time compensation technology is to add a corresponding delay to each IGBT drive signal so that the IGBT can switch on or off at the same time.Compared with the traditional active driving voltage phase control technology,the active grid trigger time compensation technology has the advantages of high precision,simple control and so on.The simulation results of the control strategy of active grid trigger time compensation technology are carried out by ModelSim software.The simulation results show that the proposed technique can effectively adjust the action time of the IGBTs in order to make the synchronization.To solve the problem of static voltage balancing in IGBT,this paper proposes a scheme by static compressive resistance parallelled IGBT.In this paper,a 1200V/6.7A test circuit of 3 series connected IGBTs has been built,together with the corresponding grid drive circuit,the control circuit and the signal detection circuit.In addition,in order to optimize the distributed capacitance in the circuit,IGBT vertical layout structure is used.The experimental circuit test results show that the active grid trigger time compensation technology can limit the action time error of the IGBTs within 20ns,so as to realize good dynamic voltage balancing.Static compressive resistance can make all the IGBT's static voltage equal.IGBT vertical layout structure can reduce the voltage difference by 37%between the IGBTs.On the basis of the above research results,a 10kV/150A high voltage switch prototype formed by series connected IGBTs is designed and manufactured.In order to eliminate the influence of stray inductance in the circuit,this paper designs a laminated busbar to replace the traditional wire.Experimental results show that the 10kV/150A high voltage switch prototype can be switch on or off within one microsecond,while the IGBT's action time error is less than 20ns which lead to a good voltage equalizing effect.At the same time,the laminated busbar that is proposed in this paper can reduce the overvoltage of IGBT by 55.8%,which provides an effective supplement for solving the problem of voltage equalization of series connected IGBTs.