Enhanced Control of Three-Phase Grid-Connected Renewables with Fault Ride-Through Capability under Voltage Sags

The uninterruptible operation of grid-connected renewables under the occurrence of grid voltage sags is addressed in this work. This is achieved due to the incorporation of an enhanced control algorithm of a renewable source. The low-voltage ride-through algorithm was developed in accordance to the voltage profile introduced by IEC 61400-21 regarding grid voltage sags. To guarantee continuous operation of the renewable agent during voltage sags, not only instantaneous reactive power but also instantaneous active power under moderate voltage sags was injected to the utility grid fulfilling grid code requirements. A dual second-order generalized integrator frequency-locked loop synchronization algorithm was used to estimate the system's frequency, together with the positive and the negative sequences of the three-phase utility grid voltages when unbalanced sags occurred. The current control was made in a stationary reference frame by using proportional-resonant regulators, and a DC voltage source was used to emulate the primary energy from any type of renewable system. The validation of the proposed control algorithm was conducted for a three-phase grid-connected renewable system with an apparent power of 500 kVA. The results from several experimental tests demonstrated the proper behavior of the enhanced algorithm.