Control system configured for, and a method for, emulating a virtual synchronous machine of a grid-forming voltage source converter

A control system configured for grid forming control using a voltage source converter (VSC) connected to a grid at a point-of-common-coupling (PCC), the control system comprising:

• an alternate current (AC) controller configured to calculate a converter voltage reference (Vc,ref) for the VSC based at least on a reference current (Ig,ref);
• an active-power controller configured to calculate a phase-angle (θEMF) of an electromotive force (EMF) voltage vector (VEMF) of the VSC based on at least an active power reference (Pg,ref);
• and
• a voltage controller configured to calculate a voltage amplitude (VEMF) of the EMF voltage vector (VEMF) based on at least a grid voltage (Vg) at the PCC and a grid voltage reference (Vg,ref);
• wherein the EMF voltage vector (VEMF), comprising the phase-angle (θEMF) and the voltage amplitude (VEMF), minus the grid voltage (Vg) are multiplied by a virtual admittance to calculate the reference current (Ig,ref),
• said control system further comprising:
• a current limiter configured to prevent operation of the VSC above a maximum allowed current threshold (llim);
• an active power reference limiter configured to limit the active power reference (Pg,ref) input to the active-power controller based at least on the maximum allowed current threshold (llim);
• and
• a voltage limiter configured to limit the voltage amplitude (VEMF) output from the voltage controller based at least on the maximum allowed current threshold (llim);
• wherein the limitation of the active power reference (Pg,ref) and the limitation of the voltage amplitude (VEMF) prevent the reference current (Ig,ref) from exceeding the maximum allowed current threshold (Ilim);
• wherein the active power reference (Pg,ref) is a sum of an active power setpoint (Pset,ref) and an inertial active power reference (PH);
• and
• wherein the control system further comprises an inertial phase-locked loop (IPLL) unit configured to calculate the inertial active power reference (PH) based on the grid voltage (Vg) at the PCC and the converter voltage reference (Vc,ref).