A method of estimating at least one leakage inductance of a 3n-phase electrical machine having at least two 3-phase windings, the method comprising: performing a first machine investigation scheme comprising: ordering a machine drive stage to control one of the 3-phase windings, obtaining from said one of the 3-phase windings a first set of measured currents (ia,1, ib,1, ic,1) of three phases of the electrical machine, and processing the first set of measured currents to obtain primary characteristics of an electrical quantity of the electrical machine, characterized by performing a second machine investigation scheme comprising: ordering the machine drive stage to control all the 3-phase windings using a vector space decomposition control model, where the controlling involves only controlling a first fundamental subspace of the VSD control model, obtaining a second set of measured currents (ia,1, ib,1, ic,1, ia,2, ib,2, ic,2) from all 3-phase windings, and processing the second set of measured currents to obtain a leakage inductance estimate and secondary characteristics of the electrical quantity of the electrical machine, for which leakage inductance estimate the primary and secondary characteristics match. performing a first machine investigation scheme comprising: ordering a machine drive stage to control one of the 3-phase windings, obtaining from said one of the 3-phase windings a first set of measured currents (ia,1, ib,1, ic,1) of three phases of the electrical machine, and processing the first set of measured currents to obtain primary characteristics of an electrical quantity of the electrical machine, characterized by ordering a machine drive stage to control one of the 3-phase windings, obtaining from said one of the 3-phase windings a first set of measured currents (ia,1, ib,1, ic,1) of three phases of the electrical machine, and processing the first set of measured currents to obtain primary characteristics of an electrical quantity of the electrical machine, characterized by performing a second machine investigation scheme comprising: ordering the machine drive stage to control all the 3-phase windings using a vector space decomposition control model, where the controlling involves only controlling a first fundamental subspace of the VSD control model, obtaining a second set of measured currents (ia,1, ib,1, ic,1, ia,2, ib,2, ic,2) from all 3-phase windings, and processing the second set of measured currents to obtain a leakage inductance estimate and secondary characteristics of the electrical quantity of the electrical machine, for which leakage inductance estimate the primary and secondary characteristics match. ordering the machine drive stage to control all the 3-phase windings using a vector space decomposition control model, where the controlling involves only controlling a first fundamental subspace of the VSD control model, obtaining a second set of measured currents (ia,1, ib,1, ic,1, ia,2, ib,2, ic,2) from all 3-phase windings, and processing the second set of measured currents to obtain a leakage inductance estimate and secondary characteristics of the electrical quantity of the electrical machine, for which leakage inductance estimate the primary and secondary characteristics match.