A drive system comprising: a motor including a rotor, the motor configured to receive a measured three-phase alternating current; a controller configured to generate a voltage for the motor at a stationary reference frame, the generated voltage having a frequency and the measured three-phase alternating current being based on the voltage; a direct current, DC, bus capacitor, wherein the energy used for detection by the controller is provided by a discharging of the DC bus capacitor, wherein the drive system is configured to receive a high voltage DC source that is selectably coupled to the motor , wherein the high voltage DC source is disconnected from the motor during a discharging of the DC bus capacitor; a filter configured to filter selected frequency components from the measured three-phase alternating current to obtain position information of the rotor in a stationary frame, wherein the filter comprises a matched filter configured to filter noise from each phase of the measured three-phase alternating current and apply a transformation to the filtered phases of the measured three-phase alternating current to obtain a stationary-frame, direct-axis current and a stationary-frame, quadrature current, wherein the filter further comprises a stationary frame reference filter configured to output a negative sequence signal of the stationary-frame, direct-axis current and stationary-frame, quadrature current as the position information of the rotor in the stationary frame; and a nonlinear observer configured to estimate, while the DC bus capacitor discharges, a rotor position of the motor in the stationary reference frame based on the position information, wherein the controller is further configured to control the motor based at least in part on the estimated rotor position. a motor including a rotor, the motor configured to receive a measured three-phase alternating current; a controller configured to generate a voltage for the motor at a stationary reference frame, the generated voltage having a frequency and the measured three-phase alternating current being based on the voltage; a direct current, DC, bus capacitor, wherein the energy used for detection by the controller is provided by a discharging of the DC bus capacitor, wherein the drive system is configured to receive a high voltage DC source that is selectably coupled to the motor , wherein the high voltage DC source is disconnected from the motor during a discharging of the DC bus capacitor; a filter configured to filter selected frequency components from the measured three-phase alternating current to obtain position information of the rotor in a stationary frame, wherein the filter comprises a matched filter configured to filter noise from each phase of the measured three-phase alternating current and apply a transformation to the filtered phases of the measured three-phase alternating current to obtain a stationary-frame, direct-axis current and a stationary-frame, quadrature current, wherein the filter further comprises a stationary frame reference filter configured to output a negative sequence signal of the stationary-frame, direct-axis current and stationary-frame, quadrature current as the position information of the rotor in the stationary frame; and a nonlinear observer configured to estimate, while the DC bus capacitor discharges, a rotor position of the motor in the stationary reference frame based on the position information, wherein the controller is further configured to control the motor based at least in part on the estimated rotor position. <EOS>