链式动态电压恢复器的新型控制策略分析与设计

New Control Strategy Analysis of the Cascaded Dynamic Voltage Restorer

链式动态电压恢复器(DVR)作为一种有效的改善电压跌落问题的设备,近年来已经逐步应用于电力系统中,用以改善用户的电能质量。为此,将级联多电平技术与载波移相技术相结合,针对6kV配电系统设计了5MVA无耦合变压器的11电平链式DVR,通过将级联多电平逆变器等效线性化,在传统单闭环控制系统基础上,在电压外环控制的同时,引入了耦合电容器的电流反馈,设计了双闭环控制器。针对任意时刻的电路故障,对其电压跌落做了系统的电压补偿仿真分析。研究表明,链式结构的DVR大大提高了功率单元的开关频率,谐波失真小、电压变化率低,满足了DVR对高电压质量的要求,采用双闭环控制策略,通过调整相应的控制参数可以提高电力系统的阻尼和稳定性,减小补偿电压的稳态误差,提高了DVR的响应速度和电压震荡等性能指标,有较高的实用价值。

Cascaded dynamic voltage restorer（DVR） which is an effective setup in modifying the power quality problems caused by voltage sags has been applied in the power system.Thereby,the carrier phase-shifted modulation technology was used in the cascaded multilvevel inverter.A 5 MVA uncoupled transformer 11-level cascaded DVR was researched for the 6 kV power system.The double loop control strategy was designed which employed a slow outer voltage loop and a fast inner current loop.Voltage sag was simulated at a random time when multi-level DVR was under the control of any control strategy.Results show that the DVR based on voltage shifted pulse width modulation technology can greatly increase the inverter switching frequency and decrease the harmonic distortion and variation rate of voltage,and the system damping ratio and stability and error can be regulated by adjusting relevant parameters.The application of this technology can greatly enhance the performance indicators of DVR and has a high practical value.