The blackout area is partitioned into small areas when large-area blackout occurs because of natural disasters in an urban distribution system. An emergency microgrid consisting of mobile emergency power sources is used to supply important loads in each area. The hierarchical control structure is utilized in the emergency microgrid. The primary control is the conventional linear droop control while the secondary control can achieve frequency and voltage restoration by feedback control based on local information. Without the central controller or communication system

the good dynamic characteristic of primary linear droop control is maintained. A low-pass filter is designed in the secondary control to decouple the dynamic characteristics of the primary control and secondary control into different time scales. In addition

the active loads are dispatched based on the apparent power of the sources.