iSTFT n (k) = iSTFT n (k-1) + C(tgt - u(k))

iSTFT n (k) = Individual cylinder STFT

u(k): Estimated individual cylinder λ deviation?

tgt: Target (No deviation = zero)

C: Control gain (negative value)

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*individual cylinder λ deviation: u(k)

= Individual cylinderλ - averageλ during 720°CA

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Estimated individual cylinder λ deviation "u(k)" is calculated by model (as described below).