Droop Control

What Is Droop Control?

Droop control is a technique for controlling synchronous generators and inverter-based resources in electric grids. It allows multiple generation units to be connected in parallel, sharing loads in proportion to their power rating. In droop control, frequency and voltage “droop” values are assigned to each generation unit in the grid. These droop values represent how much the frequency and voltage are allowed to deviate from their nominal values to account for changes in power demands.

The most common type of droop control is conventional droop control. In conventional droop control, frequency and voltage vary linearly with respect to active and reactive power, respectively. For instance, assigning a 1% frequency droop to a converter means that its frequency deviates 0.01 per unit (pu) in response to a 1.0 pu change in active power. Reverse droop control is an alternative technique that can be useful in low-voltage microgrids.

Two graphs of frequency and voltage droop curves. On the left, a frequency droop of four percent is used, meaning that varying the active power demand from zero to its full nominal value, or one per unit, results in a frequency value of 0.96 per unit. On the right, a voltage droop of two percent is used, meaning that varying the reactive power demand from zero to one per unit results in a voltage value of 0.98 per unit.

Example frequency and voltage conventional droop curves.

Simulink®, Simulink Control Design™, and Simscape Electrical™ accelerate droop control design by enabling you to:

A microgrid plant model constructed using Simscape Electrical blocks. The microgrid is driven by two inverters that are controlled by droop controllers.

Droop-controlled microgrid implemented in Simscape Electrical.

Software Reference

See also: Simulink for electrification, grid-tied inverter, design power conversion controls faster with Simulink