Droop Control with Voltage Restoration Compensation for DC Microgrids

In DC microgrids, droop control is a common distributed control strategy used to achieve proportional power sharing without centralized control. However, conventional droop control introduces voltage deviations that compromise system stability and power quality. Implementing a voltage restoration compensation mechanism thus becomes critical for control optimization.

Basic Droop Control Principle Droop control emulates the active power-frequency characteristics of synchronous generators by implementing voltage-current (V-I) droop curves in DC microgrids. Each distributed generator (DG) adjusts its output voltage based on local current measurements to enable proportional load power sharing. The core algorithm typically involves: V_output = V_ref - k_droop * I_output, where k_droop represents the droop coefficient. However, simple droop control causes bus voltage fluctuations under varying loads, potentially exceeding allowable voltage tolerance bands.

Necessity of Voltage Restoration Compensation Islanded microgrids lack main grid voltage support, making voltage sag issues more pronounced. Voltage restoration compensation introduces correction terms to gradually eliminate steady-state errors, restoring the system to nominal voltage levels while maintaining power sharing accuracy. Common implementation approaches include: Secondary Voltage Regulation: Integrating voltage error terms in the control loop through PI controllers, mathematically expressed as V_comp = K_p * ΔV + K_i * ∫ΔV dt, where ΔV represents voltage deviation. Virtual Impedance Adjustment: Dynamically modifying droop coefficients using adaptive algorithms to balance power distribution and voltage recovery objectives.

Compensation Strategy Implementation A frequently adopted solution superimposes voltage compensation signals on droop control outputs. This compensation signal, generated by detecting bus voltage deviations, undergoes low-pass filtering (e.g., first-order filter with cutoff frequency f_c) to gradually adjust reference voltages without affecting dynamic response. Code implementation often includes: voltage_error = V_nominal - V_measured; filtered_error = lowpass_filter(voltage_error); V_ref_compensated = V_ref_droop + K_comp * filtered_error. Alternative hierarchical control architectures add secondary control layers above primary droop control, employing centralized or distributed coordination for voltage restoration through communication-assisted algorithms.

Advantages and Challenges Advantages: Maintains voltage stability and improves power supply quality; Supports plug-and-play compatibility ideal for distributed energy resource expansion. Challenges: Requires careful compensation parameter tuning to prevent conflicts with existing control loops; Demands circulating current mitigation strategies during multi-source coordination, often implemented through current balancing algorithms or virtual impedance optimization.

This technology provides more robust solutions for islanded microgrids, particularly suitable for high renewable energy penetration scenarios. Future developments may integrate artificial intelligence techniques to optimize dynamic response through machine learning-based adaptive control algorithms.