Simulation of Dual-Loop Control System for Grid-Connected Inverters Using LCL Filters

In grid-connected inverter systems, LCL filters are widely adopted due to their excellent harmonic suppression capability. However, LCL filters introduce additional resonant points that can easily lead to system instability, requiring well-designed control strategies to ensure stable operation.

The system discussed in this paper employs a dual-loop control structure consisting of an inductor current outer loop and a capacitor current inner loop. The outer loop regulates the inverter-side inductor current to ensure it tracks the grid voltage reference, typically implemented using PI controllers with anti-windup compensation. The inner loop rapidly suppresses dynamic variations in capacitor current, enhancing system disturbance rejection and damping characteristics through active damping techniques or proportional-resonant controllers. This hierarchical control strategy effectively mitigates resonance issues caused by LCL filters while improving dynamic response performance.

In practical simulations, proper design of inner and outer loop controller parameters enables high-precision tracking of grid currents along with effective suppression of grid harmonic disturbances. Key simulation implementations include Clarke/Park transformations for reference frame conversions, space vector PWM generation for switching signals, and FFT analysis for harmonic assessment. Typical simulation results showcase grid current waveforms, harmonic analysis spectra, and dynamic response curves of the closed-loop system, validating the effectiveness of the control strategy through performance metrics like total harmonic distortion (THD) and settling time.

This dual-loop control scheme finds applications in distributed generation systems, microgrids, and renewable energy grid integration scenarios, demonstrating significant engineering practicality through its robustness against parameter variations and grid impedance changes.