A portable external device for a mechanical circulation support system comprising: a power source configured to power an implantable pump; digital memory storing an algorithm for controlling an electric motor configured to drive the implantable pump; and control electronics configured to control the electric motor employing the algorithm, wherein the algorithm comprises instructions for causing the control electronics to: control the electric motor according to a field-oriented control algorithm stored within the digital memory; while controlling the electric motor according to the FOC algorithm, estimate a back electromotive force of the electric motor; determine a rotational position of a rotor of the electric motor based on the estimated back EMF of the electric motor; determine a pulse width modulated voltage signal to send from the power source to the electric motor to drive the implantable pump based on the rotational position of the rotor of the electric motor; determine an error of the estimated back EMF; compare the error of the estimated back EMF to a threshold; and control the electric motor employing a trapezoidal control algorithm stored on the digital memory if the error of the estimated back EMF is greater than the threshold. a power source configured to power an implantable pump; digital memory storing an algorithm for controlling an electric motor configured to drive the implantable pump; and control electronics configured to control the electric motor employing the algorithm, wherein the algorithm comprises instructions for causing the control electronics to: control the electric motor according to a field-oriented control algorithm stored within the digital memory; while controlling the electric motor according to the FOC algorithm, estimate a back electromotive force of the electric motor; determine a rotational position of a rotor of the electric motor based on the estimated back EMF of the electric motor; determine a pulse width modulated voltage signal to send from the power source to the electric motor to drive the implantable pump based on the rotational position of the rotor of the electric motor; determine an error of the estimated back EMF; compare the error of the estimated back EMF to a threshold; and control the electric motor employing a trapezoidal control algorithm stored on the digital memory if the error of the estimated back EMF is greater than the threshold. control the electric motor according to a field-oriented control algorithm stored within the digital memory; while controlling the electric motor according to the FOC algorithm, estimate a back electromotive force of the electric motor; determine a rotational position of a rotor of the electric motor based on the estimated back EMF of the electric motor; determine a pulse width modulated voltage signal to send from the power source to the electric motor to drive the implantable pump based on the rotational position of the rotor of the electric motor; determine an error of the estimated back EMF; compare the error of the estimated back EMF to a threshold; and control the electric motor employing a trapezoidal control algorithm stored on the digital memory if the error of the estimated back EMF is greater than the threshold.