I am confused with SMO module in DMC MATH. Why is there es(n) in the equation of sliding mode observer? According to your description in the document, by filtering z, we can obtain back emf. But If there is es(n) in the equation of sliding mode observer,the value of es(n) should be estimate back emf and the average of z will be zero when the observer reach stable. In this case, the result obtained by filtering z should be zero, right?