Analytical Damping Contribution Assessment Method of Multiconverters System Based on Energy Network Model

Abstract

Multiconverters connected to grid can induce subsynchronous oscillation (SSO). This article proposed an analytical damping contribution assessment method that can explicitly reveal how (positively or negatively) and to which degree each converter in the multiconverters system changes the system stability level. First, the energy network model of the multiconverters system that satisfies energy conservation is proposed. On this basis, a theory proof is presented that the real part of eigenvalue of SSO mode in the multiconverters system is equal to the sum of coefficient in the aperiodic components of the derivative of dynamic energies injected by each converter and dissipation energy of network, which illustrates analytically how the SSO stability level is shaped. The dynamic energy showing a decreasing trend is good for the oscillation to disappear, and the faster the dynamic energy decreases, the faster the oscillation amplitude decreases. Thus, how and to which degree converter changes stability level can be revealed by the changing trend and rate of its dynamic energy, respectively. Moreover, the expression of dynamic energy is brief, which is, thus, readily for online use, and is universal for converters with different control strategies. Finally, hardware in loop tests verifies that, eliminate converters’ rapidly increasing dynamic energy, the unstable SSO converges rapidly, and eliminate converters’ slowly increasing dynamic energy, the unstable SSO converges but slowly, and eliminate converters’ decreasing dynamic energy, unstable SSO diverges more rapidly, which demonstrates that dynamic energy can precisely assess damping contribution of converter.