  This paper presents the modal truncation and singular value decomposition
(SVD) technique as two main algorithms for dynamic model reduction of the power
system. The significance and accuracy of the proposed methods are investigated
with their detailed formulation derived for a constrained linear system. The
full linearized model of the original nonlinear system is determined and used
as the input of the dynamic reduction technique. Therefore, the variables of a
synchronous machine in a multi-machine system is studied and replaced with a
much simpler dynamic model. This equivalent dynamic model should behave
similarly to what is observed from the system under study. The capability of
each technique in keeping dominant oscillation modes after dynamic reduction is
utilized as the comparison criteria. The reduction techniques are simulated
over the dynamic 39-bus New England test system for validation.
