The patented robust droop controller is equipped with an integrator to robustify the droop control against numerical errors, component mismatches, parameter drifts etc. so that it is able to regulate frequency and voltage at the same time. It has been mathematically proven that it structurally resembles conventional synchronous machines and enhanced phase-locked loops. Hence, it is another implementation of VSM. Moreover, it has been proven that it is universal for converters with different types of impedances and can be equipped with the self-synchronization capability without a phase-locked loop, which makes it a preferred technical route for SYNDEM. Technical details of this can be found from the SYNDEM Fundamentals section.
A synchronverter is a power converter with a controller that includes the mathematical model of a synchronous machine. Hence, it has the intrinsic synchronization mechanism of synchronous machines to achieve autonomous synchronization without the help of a phase-locked loop or the estimation of the grid frequency. It is ideal to explain the concept of VSM and SYNDEM but many other additional benefits can be obtained via controlling power electronic converters to behave as VSM. For example, the robust droop control strategy described above is universal for converters with any type of impedances but the synchronverter is designed for the case with an inductive impedance.