Negative Sequence Impedance Emulation: A New Perspective and Control

The decoupling control of negative sequence active and reactive components becomes crucial for voltage source converters to prevent the misoperation of protection elements and achieve desirable control performances. However, conventional current controls with an additional negative sequence phase-locked loop (PLL) can cause transient instability and extra computing burden. To address these issues, this letter introduces a new perspective of negative sequence impedance emulation, which converts the control object from an absolute phase angle-defined negative sequence current to a relative phase angle-defined negative sequence impedance. Due to the inherent nature of emulated resistance and inductance/capacitance, the active and reactive components can be decoupled automatically, eliminating the need for the negative sequence PLL. Meanwhile, a dual control is proposed to ensure an accurate emulation of the negative sequence impedance facing diverse control needs. Finally, the effectiveness of the above analysis and controls is verified through control-hardware-in-the-loop test results.