Implementation of Inner-Loop Current Decoupling Control for Grid Integration

Stable operation of single-phase grid-connected inverters requires solving two key challenges: decoupling control of inner-loop currents and control strategies for power outer-loops. Below are the core techniques and implementation approaches:

Grid Synchronization with Frequency and Phase Locking Grid-connected inverters must maintain synchronization with grid voltage, typically achieved through Phase-Locked Loop (PLL) technology for phase and frequency tracking. Code implementation often involves discrete PLL algorithms using trigonometric calculations and proportional-integral controllers to ensure inverter output voltage matches grid frequency/phase, minimizing inrush currents and harmonics during grid connection.

Inner-Loop Current Decoupling Control Inner-loop current control typically employs d-q axis decoupling strategy, converting AC quantities to DC components for independent control. Through feedforward compensation and feedback regulation, this approach eliminates coupling effects between d-axis (active) and q-axis (reactive) currents. Algorithm implementation involves Park/Clarke transformations and PI controllers with decoupling terms for fast dynamic response and high-precision tracking.

Power Outer-Loop Control Design The outer-loop generates reference signals for the inner current loop based on power targets (active/reactive). By adjusting the d-axis component of the inner current loop to control active power, and the q-axis component to regulate reactive power or power factor, the inverter output meets grid requirements. Implementation typically uses power calculation blocks and reference generators with saturation limits.

System Stability and Anti-Interference Capability Robust control or adaptive strategies enhance system resilience against grid voltage fluctuations and load variations. Controller parameter optimization balances dynamic performance and steady-state accuracy, often implemented through gain scheduling or online tuning algorithms.

Through these methods, single-phase grid-connected inverters achieve efficient, stable power transmission while meeting grid synchronization and power quality requirements.