Model reduction by the low-frequency approximation balancing method for unstable systems

The unstable system model reduction technique is investigated by the low-frequency approximation balancing method. The reduced models retain the DC gain of the original model which offer a good approximation at low frequencies. Various relevant properties of the reduced model are available. In particular, the reduced models ensure the minimality and the number of the unstable poles as the original model. An upper bound for model reduction error is also provided in the frequency domain.