七电平电流源型换流器无源逆变试验与分析

普通晶闸管换流阀无关断电流的能力,需要借助电网电压完成换相,不适用于没有交流电网的无源逆变电路.为了将晶闸管换流阀应用于柔性交直流电网,以并联十二脉动晶闸管换流器为前级,以七电平直流电流分配单元为后级构成级联型电流源逆变器.七电平直流电流分配单元不仅实现了对直流母线电流的动态平均分配,而且形成了周期性的直流电流过零点,...

Test and analysis of passive inversion for seven-level current source converter

Common thyristor converter valve is unable to turn off currents by itself and commutates with the help of the grid voltage, so it is not suitable for the passive inverter circuit without AC grid. In order to apply the thyristor valve in flexible AC/DC grid, the cascaded current source inverter is constituted by using the parallel twelve-pulse thyristor converter as the front stage and the seven-level DC current distribution unit as the back stage. The seven-level DC current distribution unit not only realizes the dynamic average distribution of the DC bus current, but also forms the periodic DC current zero crossing section, which provides the zero current switching condition for the twelve-pulse thyristor converter, so as to realize the forced commutation of thyristor converter valve. The external characteristics of the thyristor converter valve which realizes forced commutation are equivalent to the fully controlled reverse voltage-blocking device, so the converter can realize passive inversion. Based on the detailed analysis of the circuit topology and modulation method, an experimental device of seven-level flexible DC converter with rated power of 0.5 MW is designed, which employs the three-phase resistance as the load to carry out the passive inversion experiment. The test results verify that, under the high current condition, the controlled shutoff of thyristor converter valve under the cooperation of multi-level DC current distribution unit is feasible and reliable.