Input Voltage Feedforward Control Technique for DC/DC Converters to Avoid Instability in DC Grids

DC grids are becoming more popular due to the penetration of renewables and storage systems that work at dc. In dc grids, most of the loads are connected through dc/dc converters, when their power does not change they behave as constant power loads (CPLs). It is known that CPLs have a small-signal negative resistance which can produce instabilities in dc grids. Methods to mitigate instabilities include damping (or lossy) elements in the input port of the dc/dc converters, and parallel converters to mitigate potential oscillations. In this article, a new feedforward technique from the input port is included in the control signal to modify the load-end dc/dc converter input admittance. Thus, CPL behavior is only canceled in the potential unstable frequency range with a small impact on the input-to-output voltage rejection. This article explains in a comprehensive way, how to cancel the negative impedance using a simple feedforward technique. The proposal mitigates oscillations in the dc grid without increasing the complexity of the system or adding dissipative elements. Simulations in complex dc grids with several devices validate the results. Finally, experimental results in a 2000-W test bench verify the proposal.

Automated summary

This article discusses the use of a new feedforward technique at the input port to modify the input admittance of the load-end dc/dc converter in order to cancel the negative impedance caused by CPLs, mitigating oscillations in dc grids without increasing complexity or adding dissipative elements. Experimental results in a 2000-W test bench validate the proposal, showing that the feedforward technique effectively cancels CPL behavior in the potentially unstable frequency range with minimal impact on voltage rejection from input to output.