A reduced surface electric field in an AlGaN/GaN high electron mobility transistor （HEMT） is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas （2-DEG） channel as an electr...A reduced surface electric field in an AlGaN/GaN high electron mobility transistor （HEMT） is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas （2-DEG） channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional sourceconnected field plates and double field plates, the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, Lm, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with VGS = -5 V, Lm 1.5 m, a peak Mg doping concentration of 8×10^17 cm-3 and a drift region length of 10 m, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.展开更多
The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electrom...The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.展开更多
With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,a...With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.展开更多
大规模安全约束机组组合(security constrained unit commitment,SCUC)问题的混合整数线性规划(mixed integer linear programming,MILP)模型因其高维、非凸的特点导致求解困难,尤其在考虑故障态安全约束后模型规模骤增,MILP算法常遇到...大规模安全约束机组组合(security constrained unit commitment,SCUC)问题的混合整数线性规划(mixed integer linear programming,MILP)模型因其高维、非凸的特点导致求解困难,尤其在考虑故障态安全约束后模型规模骤增,MILP算法常遇到收敛间隙下降瓶颈问题。为满足现货市场出清对SCUC问题求解时间的要求,提出了基于热启动的快速求解方法,从待求模型的一个可行解出发,根据节点边际电价和机组收益分析进行整数变量固定,同时削减无约束力的安全约束,以缩减模型规模,加快收敛进程。仿真结果表明:所提方法能够大幅缩减SCUC模型规模,尤其对于考虑故障态安全约束的大规模SCUC问题,能有效克服收敛间隙下降瓶颈问题,求解效率提高特别显著。展开更多
文摘A reduced surface electric field in an AlGaN/GaN high electron mobility transistor （HEMT） is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas （2-DEG） channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional sourceconnected field plates and double field plates, the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, Lm, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with VGS = -5 V, Lm 1.5 m, a peak Mg doping concentration of 8×10^17 cm-3 and a drift region length of 10 m, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.
基金This work was supported in part by the National Key Research and Development Program of China under Grant 2017YFB0902904,in part by the Natural Science Foundation of Hubei Province under Grant 2016CFB448,and in part by the Shenzhen City Science and Technology Innovation Plan under Grant JCYJ20170306170937861,and in part by Wuhan City Science and Technology Program under Grant 2016070204020165.
文摘The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.
基金supported by the National Natural Science Foundation of China under Grant 61863023.
文摘With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.
文摘大规模安全约束机组组合(security constrained unit commitment,SCUC)问题的混合整数线性规划(mixed integer linear programming,MILP)模型因其高维、非凸的特点导致求解困难,尤其在考虑故障态安全约束后模型规模骤增,MILP算法常遇到收敛间隙下降瓶颈问题。为满足现货市场出清对SCUC问题求解时间的要求,提出了基于热启动的快速求解方法,从待求模型的一个可行解出发,根据节点边际电价和机组收益分析进行整数变量固定,同时削减无约束力的安全约束,以缩减模型规模,加快收敛进程。仿真结果表明:所提方法能够大幅缩减SCUC模型规模,尤其对于考虑故障态安全约束的大规模SCUC问题,能有效克服收敛间隙下降瓶颈问题,求解效率提高特别显著。
