Stability analysis and nonlinear current-limiting control design for DC micro-grids with CPLs

Abstract

In this study, a DC micro-grid consisting of multiple paralleled energy resources interfaced by both bidirectional AC/DC and DC/DC boost converters and loaded by a constant power load (CPL) is investigated. By considering the generic dq transformation of the AC/DC converters' dynamics and the accurate nonlinear model of the DC/DC converters, two novel control schemes are presented for each converter-interfaced unit to guarantee load voltage regulation, power sharing and closed-loop system stability. This novel framework incorporates the widely adopted droop control and using input-to-state stability theory, it is proven that each converter guarantees a desired current limitation without the need for cascaded control and saturation blocks. Sufficient conditions to ensure closed-loop system stability are analytically obtained and tested for different operation scenarios. The system stability is further analysed from a graphical perspective, providing valuable insights of the CPL's influence onto the system performance and stability. The proposed control performance and the theoretical analysis are first validated by simulating a three-phase AC/DC converter in parallel with a bidirectional DC/DC boost converter feeding a CPL in comparison with the cascaded PI control technique. Finally, experimental results are also provided to demonstrate the effectiveness of the proposed control approach on a real testbed.

Keywords

• cascade control
• nonlinear control systems
• voltage control
• ac-dc power convertors
• control system synthesis
• power distribution control
• electric current control
• closed loop systems
• power generation control
• distributed power generation
• dc-dc power convertors
• power system stability
• control design
• cpl
• dc microgrid architecture
• multiple paralleled energy resources
• constant power load
• nonlinear model
• control schemes
• converter-interfaced unit
• load voltage regulation
• power sharing
• closed-loop system stability
• novel control framework
• input-to-state stability theory
• converter unit
• current limitation
• cascaded control
• dc microgrid instability
• system performance
• control performance
• theoretical stability analysis
• traditional cascaded pi control technique
• control approach
• droop control expressions