The invention relates to a method for determining the temperature (ϑstator) of the
stator winding of a vectorially controlled
electric motor by superimposing a
periodic excitation signal (f(t)) with an excitation frequency (fA) on a manipulated variable (id). Meanwhile, from motor signals (x(t)), comprising at least a first and second
voltage component (ud, uq), a first and second current component (id, iq) and an
angular frequency (ωel), a set (Tx) of
signal characteristics ({x0, x1,sin, x1,cos}) is determined, comprising the DC component (x0), the component of the magnitude of the fundamental amplitude (x1,sin) at the excitation frequency (fA) in phase with the
excitation signal (f(t)) and the component of the magnitude of the fundamental amplitude (x1,cos) at the excitation frequency (fA) 90°
out of phase with the
excitation signal (f(t)) in the respective motor
signal (x(t)).From a
system of equations, a set of motor parameters (Rs, Ld, Lq, Ψpm) is calculated using the signal characteristics ({x0, x1,sin, x1,cos}), which includes the electrical
stator resistance (RS). The
stator winding temperature (ϑStator) is then calculated from a temperature model (ϑStator(Rs)) that relates the stator winding temperature (ϑStator) to the stator resistance (Rs), or estimated using a function approximator (6) that uses at least the set of motor parameters (RS, Ld, Lq, Ψpm) and the sets (Tx) of signal characteristics ({x0, x1,sin, x1,cos}).