A Sensorless Grid Voltage Estimation Scheme for Initial Synchronisation of Single-phase Renewable-based Distributed Generators

Numerous research studies have explored voltage-sensorless strategies to minimise detrimental transient inrush currents during the initial synchronisation of distributed generators (DGs). Most of these approaches require that the DG’s voltage source inverter (VSI) briefly operates in rectification mode, demanding a DC-link energy storage unit to absorb the surplus power until synchronisation is achieved. This paper introduces a new voltage-sensorless scheme for the initial synchronisation of single-phase VSIs that achieves initial synchronisation while delivering power to the grid. In the proposed scheme, the VSI is modulated such that the filter inductor cyclically charges from the DC-link and discharges into the grid, while its current magnitude is primarily defined by the grid voltage. The resulting sampled inverter current is then used to estimate the grid voltage magnitude, phase and frequency. The proposed scheme enables the voltage-sensorless initial synchronisation of renewable-based DGs without requiring a DC-link energy storage unit. Key analytical design equations and results from switched simulations in Altair PSIM are presented to validate the proposed approach.