To achieve accurate and stable online identification of inductance parameters for permanent magnet synchronous motors (PMSMs), an online inductance observation method based on virtual voltage vector excitation and current differential response is proposed. Firstly, by introducing the concept of a virtual voltage vector–oriented coordinate system, it is analytically derived and proven that the d- and q-axis inductances of a PMSM can be observed independently of the angular position in the conventional d-q synchronous reference frame. The implementation procedure for extracting virtual voltage vectors and current differential information is discussed in detail, enabling non-intrusive inductance identification without any signal injection. The effectiveness and accuracy of the proposed method are validated by comparison with offline test procedures in IEEE standards.