Power storage apparatus and power system stabilization system

A power system stabilization system, comprising:

• a power storage apparatus;
• and
• a power conversion device connected between a power system and the power storage apparatus,
• the power storage apparatus comprising:
• a positive electrode terminal connected to a high-potential-side DC terminal of the power conversion device;
• a negative electrode terminal connected to a low-potential-side DC terminal of the power conversion device;
• a storage bank including a plurality of power storage elements connected to each other;
• and
• a plurality of first cells, wherein
• the storage bank and the plurality of first cells are connected in series between the positive electrode terminal and the negative electrode terminal,
• each of the plurality of first cells includes:
• a pair of input/output nodes;
• a bridge circuit including at least two semiconductor switching elements;
• and
• a power storage element connected to the pair of input/output nodes via the bridge circuit,
• a storage capacity of the power storage element of each of the plurality of first cells is smaller than a storage capacity of the storage bank, and
• storage capacities of the plurality of first cells are different from each other.