The dq (Park) Transformation for Inverter Control
The dq transformation for inverter control: Clarke and Park, why AC becomes DC, active and reactive current, and a worked example with the matrices.
Inside a Grid-Following Inverter: The Control Loops
Grid-following inverter control: the cascaded PLL, current and outer loops, dq decoupling, IMC tuning, and why fault current is limited. With worked math.
Inside a Grid-Forming Inverter: Droop, VSM and Power Synchronization
Grid-forming control: droop, virtual synchronous machine and power synchronization, the shared voltage/current cascade, with worked droop and inertia math.
SRF-PLL Design: Synchronizing an Inverter to the Grid
SRF-PLL design for grid synchronization: the structure, second-order Kp and Ki tuning, the bandwidth trade-off, weak-grid limits, and DSOGI variants.
PLL Synchronization Instability in Weak Grids
PLL instability in weak grids explained: what a phase-locked loop does, why grid-following inverters go unstable at low SCR, and how to fix it.
