  Switching control strategies that unite a potentially high-performance but
uncertified controller and a stabilizing albeit conservative controller are
shown to be able to balance safety with efficiency, but have been less studied
under partial observation of state. To address this gap, we propose a switching
control strategy for partially observed linear-Gaussian systems with provable
performance guarantees. We show that the proposed switching strategy is both
safe and efficient, in the sense that: (1) the linear-quadratic cost of the
system is always bounded even if the original uncertified controller is
destabilizing; (2) in the case when the uncertified controller is stabilizing,
the performance loss induced by the conservativeness of switching converges
super-exponentially to zero. The effectiveness of the switching strategy is
also demonstrated via numerical simulation on the Tennessee Eastman Process.
