What Is Droop Control?

The so-called droop control is to select the frequency droop characteristic curve (Droop Character) similar to the traditional generator as the micro-source control method, that is, to obtain stable frequency and voltage through P/f droop control and Q/V droop control respectively. The control method separately controls the active power and reactive power of the micro-source output in the micro-grid, without the communication coordination between the gensets, realizes the goal of micro-source plug-and-play and peer-to-peer control, and ensures the unity of power balance and frequency in the micro-grid under the island, which has the characteristics of simplicity and reliability.

Using the frequency active droop characteristic (Droop Character), the unbalanced power of the system is dynamically allocated to each unit to ensure the uniformity of the frequency and voltage in the micro-grid system, which is simple and reliable. The droop control adopts voltage and current double loop control, and the current inner loop dynamic response speed is fast, which is used to improve the power quality of the inverter output. The voltage outer loop controller has a slow dynamic response speed, which can control the output voltage of the system and generate the reference signal  of the inner loop.

The voltage-current double closed-loop control used in droop control includes voltage outer loop control and current inner loop control. Firstly, the voltage and current of the load point are collected by the measurement module, and the output instantaneous active and reactive power of the micro power supply are calculated, and then the corresponding average power is obtained through the low-pass filter LPF.

The principle is that the inverter power source detects the output power of each power, and performs independent decoupling control on the active and reactive parts. The droop characteristic is used to obtain the reference value of the output frequency and the voltage amplitude, so as to reasonably distribute the active power and reactive power of the system.