Controlled output variance based diagnosis tree for feedforward/feedback control systems

A diagnosis tree based on the controlled output variance is proposed to assess a feedforward/feedback control performance. It is used for diagnosing and removing its fault causes. Based on the controlled output, the current output variance of the feedback/feedforward system is contributed by the feedback-only effect and the combination of feedback with feedforward effects, respectively. The feedback loop variance can be further expressed as the sum of the feedback invariant (FBI) term and the feedback-dependent (FBD) term. The feedforward loop variance can also be decomposed into the feedback/feedforward invariant (FBI/FFI) term, the feedback-invariant/feedforward-dependent (FBI/FFD) term and the feedback/feedforward-dependent (FBD/FFD) term. These effect variations are systematically conducted by a sequence of the statistic hypothesis testing procedures and the isolation strategy to compare the current control performance and the achievable benchmark operating one. Without the traditional complex physical model and/or any external input to change the current operating process, the diagnosis tree with hierarchical structure is constructed. The capability of the proposal is illustrated through two simulation cases with multiple faults.