基于IGCT串联的三电平高压变频器直流环节研究

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

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。

With series connected IG-CTs 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 turu-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 tGCT （SSHX14H4502） 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.