  The sliding mode observer is a useful method for estimating the system state
and the unknown disturbance. However, the traditional single-layer observer
might still suffer from high pulse when the output measurement is mixed with
noise. To improve the estimation quality, a new cascade sliding mode observer
containing multiple discontinuous functions is proposed in this letter. The
proposed observer consists of two layers: the first layer is a traditional
sliding mode observer, and the second layer is a cascade observer. The
measurement noise issue is considered in the source system model. An
alternative method how to design the observer gains of the two layers, together
with how to examine the effectiveness of the compensator based closed-loop
system, are offered. A numerical example is provided to demonstrate the
effectiveness of the proposed method. The observation structure proposed in
this letter not only smooths the estimated state but also reduces the control
consumption.
