Improved Droop Control With Segmented Virtual Impedance Based on ADRC

When the parallel converters are used for capacity expansion, the deviation between their line impedances leads to active/reactive power coupling, which affects both performance and effect of droop control and causes the circulation that makes the power loss of the system increased. For this reason, based on active disturbance rejection control (abbr. ADRC) an improved droop control strategy with segmented virtual impedance was proposed. In the proposed control strategy the deviation between positive and negative sequence voltage and rated voltage as well as the deviation between realtime power and rated reactive power were taken as the basis, and the piecewise functions of virtual impedances were designed respectively to constitute the improved droop control strategy based on the voltage deviation and reactive power deviation to trace and monitor the voltage and reactive power to realize the realtime updating of the coefficient of droop control to satisfy the demand on the control of different operating conditions. Meanwhile, in the droop control the positive and negative sequence decomposition was utilized to prevent the harmonics affecting the control accuracy, reduce the circulation and decrease the loss. To prevent the voltage sag due to the connection of virtual impedance, a secondary voltage compensation strategy based on ADRC was proposed, and by means of tracking DC bus reference voltage and the rated voltage the compensation value of secondary voltage was updated in realtime. Finally, selecting two-parallel system and four-parallel converter system were taken as research objects, the simulation on Matlab/Simulink platform was conducted. Simulation results show that the proposed improved droop control strategy plays an obvious role in improving circulation and compensating the voltage sag, thus, it possesses a better engineering applicability.