This paper proposes to optimally coordinate multiple Energy Storage System (ESS) based stabilizers and Power System Stabilizers (PSS) to increase damping in a multi-machine power system using an improved particle swarm optimization (IPSO). The IPSO has the strong and global searching ability and high efficiency by applying chaos initialization and simulated annealing (SA) algorithm in iteration. All eigenvalues, including both electromechanical and non-electromechanical modes, that meet the stability requirements in a wide range of operating conditions have been included in the objective function. In the 4-machine power system, the power system oscillations are effectively suppressed at different operating conditions by multiple ESS-based stabilizers and PSSs coordinated by IPSO, where the damping effect is better with the stabilizers designed by the IPSO than with the stabilizers tuned individually by the conventional compensation method. The results show the validity, robustness and superiority of the IPSO design.