Stability analysis of matrix converter with constant power loads and LC input filter

In this paper, the stability of a matrix converter system, supplying a three-phase constant power load (CPL), is analyzed. The model of the whole system, with its input filter, power supply, and modulation strategy taking into account, is established by state average method and then linearized around the steady-state operation point. Furthermore, the CPL, which is introduced by either the feed-forward compensation of the modulation or the strictly feedback control, is linearly approximated as negative impedance. Subsequently, the stability of the small signal system is evaluated by investigating the poles of the transfer function, the eigenvalues of the Jacobian matrix and the characteristic loci of the return ratio matrix. These three distinct techniques congruously confirm that the negative impedance of the CPL is detrimental to the damp of the system filter and may be the root cause that leads the under-damped system to unstable. The analytical prediction, reinforced by the simulations, provides insight into the oscillation phenomenon at the input side, and serves as guidelines for designing the damped filter and close-loop control of the whole system.