“…In comparison to passivity theory, which can deal with systems of relative degree zero and one [19], an advantage of NI systems theory is that it can deal with systems of relative degree zero, one and two [20], [21]. Since it was introduced, NI systems theory has attracted attention among control theorists (see e.g., [22]- [28]) and has found its application in many fields including nanopositioning control [29]- [33], the control of lightly damped structures [9], [34], [35], and the control of electrical power systems [36], [37], etc.…”