An apparatus comprising: means for performing angular position error estimation, sequentially for each of one or more torque operating points of a synchronous motor, by operating the synchronous motor according to a pre-defined pulsating torque signal using a sensorless vector control method with high-frequency voltage injection, wherein a peak amplitude of the pre-defined pulsating torque signal corresponds to a torque operating point of the synchronous motor and the pre-defined pulsating torque signal has a zero mean, measuring , based on a high-frequency component of an output stator current signal received from the synchronous motor , at least a first value of an estimated angular position of a rotor of the synchronous motor, θ 1 est , at a first time instance corresponding to an end point of the pre-defined pulsating torque signal, a second value of the estimated angular position, θ 2 est , at a second time instance occurring a pre-defined time, Δ t , after the first time instance and a second value of an estimated angular speed, ω r 2 est , at the second time instance, estimating an error, Δ θ , in the first value of the estimated angular position as Δθ = θ 1 est − θ 2 est + ω r 2 est Δt and storing at least the error in the estimated angular position to a lookup table in a database; and means for operating , following the angular position error estimation, the synchronous motor at the one or more torque operating points using the sensorless vector control method with high-frequency voltage injection, wherein any error in the angular position of the synchronous motor is corrected, in the operating at the one or more torque operating points, according to the lookup table. means for performing angular position error estimation, sequentially for each of one or more torque operating points of a synchronous motor, by operating the synchronous motor according to a pre-defined pulsating torque signal using a sensorless vector control method with high-frequency voltage injection, wherein a peak amplitude of the pre-defined pulsating torque signal corresponds to a torque operating point of the synchronous motor and the pre-defined pulsating torque signal has a zero mean, measuring , based on a high-frequency component of an output stator current signal received from the synchronous motor , at least a first value of an estimated angular position of a rotor of the synchronous motor, θ 1 est , at a first time instance corresponding to an end point of the pre-defined pulsating torque signal, a second value of the estimated angular position, θ 2 est , at a second time instance occurring a pre-defined time, Δ t , after the first time instance and a second value of an estimated angular speed, ω r 2 est , at the second time instance, estimating an error, Δ θ , in the first value of the estimated angular position as Δθ = θ 1 est − θ 2 est + ω r 2 est Δt and storing at least the error in the estimated angular position to a lookup table in a database; and means for operating , following the angular position error estimation, the synchronous motor at the one or more torque operating points using the sensorless vector control method with high-frequency voltage injection, wherein any error in the angular position of the synchronous motor is corrected, in the operating at the one or more torque operating points, according to the lookup table. <EOS>