基于IGCT的中心点钳位型三电平高压变频器直流环节研究

将IGCT串联技术应用于中性点箝位型三电平高压大功率变频器，研究了变频器直流环节（包括限流电感、箝位电容及限流电阻）对变频器安全运行的影响。通过分析三电平结构的开关暂态过程，建立了变频器暂态开关数学模型，并设计了直流环节部分的限流电抗。在综合考虑三电平的开关过程、直流限流电感的大小及IGCT过压能力的基础上，研究了直流箝位电容对变频器逆变侧持续性直流电压的影响，并推导了直流箝位电容及限流电阻的设计要求。基于PDPWM调制方式，分析了限流电阻对死区时间、最小脉宽及开关频率对开通及关断di/dt的影响，并基于IGCT5SHX14H4502文中设计了6kV、2.5MW二极管箝位型三电平中压变频器直流环节，并通过了6kV高压试验的检验，仿真结果验证了所选参数的有效性。

Discussion on the DC-link of 6kV NPC Three-level Medium Voltage Drives Based on IGCTs' Series Connection

With series connected IGCTs used in neutral point clamped (NPC) three-level medium voltage drives (MVDs), the contribution of the DC-Link (including DC-Link choke, DC-Link resistor and clamped capacitor) to the MVDs safe operation is discussed in this paper. Through the analysis on the turn-on and turn-off transience of NPC three-level MVDs, the corresponding mathematical models are developed, based on which the DC-Link choke value is deduced. With the DC-Link choke, switching transient state and device's over-voltage capability taken into accounts, the relationship among the clamped capacitor, DC-Link resistor and inverter's permanent DC voltage is studied. Accordingly, the design rule of the clamped capacitor and DC-Link resistor is described. For suppressing the high turn-on and turn-off di/dt, the dead time, Min pulse width and the switching frequency are analyzed with the phase disposition pulse width modulation (PDPWM) applied. Furthermore, with the IGCT (5SHX14H4502) used, the DC-Link part of 6kV, 2500kW MVDs is designed. The simulation results confirm its efficiency and the MVDs with the proposed DC-Link passed 6kV tests.