Control method for a grid following voltage source converter without phase locked loop

Abstract

A control method for a grid following voltage source converter (VSC) that does not require a phased locked loop (PLL) allows the VSC to operate stably with an AC system with any strength. The voltage reference for converter valves of a controller of the VSC is produced by a proportional controller and the input to the proportional controller is the difference between the reference and the actual converter instantaneous current values. The instantaneous reference converter current waveform for each phase is generated by adding a scaled version of the voltage waveform of the same phase and a 90 degrees phase shifted waveform of the same. The instantaneous reference current waveform for each phase is multiplied by a gain K_I which is adjusted automatically based on the sum of the differences between the absolute values (or magnitudes) of the actual converter instantaneous phase currents and the reference converter instantaneous phase currents.