A device adapted to determine a rotor position in a polyphase electric motor having stator coils (26, 27, 28) comprising a first phase, a second phase and a third phase, comprising: a) a power control unit adapted to apply a first voltage on the first phase, and a second voltage on the second phase: (i) the first voltage and the second voltage both alternating between a first part (311, 321) of an alternating period (T31, T32) and a second part (312, 322) of the alternating period (T31, T32); (ii) the voltages, with respect to a zero level, in the first part and the second part of the alternating period (T31, T32) having opposite polarity, and the first voltage and the second voltage having opposite polarity; and (iii) a voltage time area of the first part of the first voltage is the same as a voltage time area of the second part of the first voltage and a voltage time area of the first part of the second voltage is the same as a voltage time area of the second part of the second voltage; b) the power control unit being adapted to ensure that the third phase is left as a floating phase during application of the first voltage on the first phase and the second voltage on the second phase, whereby a third voltage on the third phase is a function of the rotor position; the device characterised by comprising: c) a sample unit adapted to sample the third voltage on the third phase, the sample unit adapted to acquire a first sample at a first instant in the first part and a second sample at a second instant in the second part, and adapted to determine a difference value between the first sample and the second sample representing a mutual inductance between the stator coils due to the rotor position, wherein the sample unit is configured to: take the first sample at the first instant in the first part (311, 321) of the alternating period (T31, T32), halfway between subsequent zero crossings of the third voltage, and take the second sample at the second instant in the second part (312, 322) of the alternating period (T31, T32), halfway between further subsequent zero crossings of the third voltage; and d) a determination unit adapted to determine the rotor angle based on the difference value. a) a power control unit adapted to apply a first voltage on the first phase, and a second voltage on the second phase: (i) the first voltage and the second voltage both alternating between a first part (311, 321) of an alternating period (T31, T32) and a second part (312, 322) of the alternating period (T31, T32); (ii) the voltages, with respect to a zero level, in the first part and the second part of the alternating period (T31, T32) having opposite polarity, and the first voltage and the second voltage having opposite polarity; and (iii) a voltage time area of the first part of the first voltage is the same as a voltage time area of the second part of the first voltage and a voltage time area of the first part of the second voltage is the same as a voltage time area of the second part of the second voltage; (i) the first voltage and the second voltage both alternating between a first part (311, 321) of an alternating period (T31, T32) and a second part (312, 322) of the alternating period (T31, T32); (ii) the voltages, with respect to a zero level, in the first part and the second part of the alternating period (T31, T32) having opposite polarity, and the first voltage and the second voltage having opposite polarity; and (iii) a voltage time area of the first part of the first voltage is the same as a voltage time area of the second part of the first voltage and a voltage time area of the first part of the second voltage is the same as a voltage time area of the second part of the second voltage; b) the power control unit being adapted to ensure that the third phase is left as a floating phase during application of the first voltage on the first phase and the second voltage on the second phase, whereby a third voltage on the third phase is a function of the rotor position; c) a sample unit adapted to sample the third voltage on the third phase, the sample unit adapted to acquire a first sample at a first instant in the first part and a second sample at a second instant in the second part, and adapted to determine a difference value between the first sample and the second sample representing a mutual inductance between the stator coils due to the rotor position, wherein the sample unit is configured to: take the first sample at the first instant in the first part (311, 321) of the alternating period (T31, T32), halfway between subsequent zero crossings of the third voltage, and take the second sample at the second instant in the second part (312, 322) of the alternating period (T31, T32), halfway between further subsequent zero crossings of the third voltage; and take the first sample at the first instant in the first part (311, 321) of the alternating period (T31, T32), halfway between subsequent zero crossings of the third voltage, and take the second sample at the second instant in the second part (312, 322) of the alternating period (T31, T32), halfway between further subsequent zero crossings of the third voltage; and d) a determination unit adapted to determine the rotor angle based on the difference value.