How are grid-tied inverters controlled for renewable energy applications?

Grid-tied inverters must: synchronize with grid voltage (PLL for angle/frequency extraction), control current injection (typically dq-frame PI controllers or PR controllers), meet grid codes (reactive power support, fault ride-through, anti-islanding), and maximize power extraction (MPPT for PV, optimal speed for wind). Control hierarchy includes: MPPT/turbine control sets power reference, DC link voltage control determines current magnitude, current control ensures sinusoidal injection. Advanced functions include: grid-forming capability, virtual synchronous generator, harmonic compensation, and black-start support.