Abstract: Traditional virtual synchronous generator（VSG）is a primary frequency regulation technique. After

load power changes，the frequency of microgrid cannot return to the rated level，influencing the safety of the microgrid in a severe condition. In order to avoid steady-state errors under large load fluctuations，a secondary frequency regulation technique based on VSG was proposed for microgrid. First，the frequency error calculated in the outer control loop was used to automatically generate the feedforward power by the use of a PI controller，which is used to compensate the output mechanical power of the frequency-active power（f —P）droop controller. The sum of the two parts of power was treated as the input of the mechanical equation of the synchronous generator. Then，referring to the mechanism and applications of the secondary frequency regulation techniques used in power systems，a concept of frequency error threshold was defined. Only when the load power disturbances are large enough to cause a large frequency error，the secondary frequency regulation algorithms are executed. In this case，the steady-state errors will be avoided without influencing the system dynamics in the low load disturbance situations. Both simulation and experiment were carried out to verify the effectiveness of the proposed secondary frequency regulation method.

      Key words: microgrid；virtual synchronous generator（VSG）；secondary frequency regulation；feedforward

power