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Methods and systems for controlling an electric motor are provided. An electric motor controller is configured to be coupled to an electric motor. The controller includes a rectifier, an inverter coupled to the rectifier, and a control unit coupled to the inverter. The rectifier is configured to rec

Methods and systems for controlling an electric motor are provided. An electric motor controller is configured to be coupled to an electric motor. The controller includes a rectifier, an inverter coupled to the rectifier, and a control unit coupled to the inverter. The rectifier is configured to rectify an alternating current (AC) input voltage to produce a pulsed direct current (DC) voltage that drops to approximately zero during each cycle when the AC input voltage transits zero. Energy is stored on a load coupled to the motor when AC input voltage is available. The inverter is configured to receive the DC voltage and to provide a conditioned output voltage to the motor. The control unit is configured to manage energy transfer between the motor and the load such that the motor generates positive torque when the DC voltage supplied to the inverter has approximately 100% voltage ripple.

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1. An electric motor controller configured to be coupled to an electric motor, said motor controller comprising: a rectifier configured to rectify a nominal alternating current (AC) input voltage from a power supply to produce a pulsed direct current (DC) voltage that drops to a value of approximate

1. An electric motor controller configured to be coupled to an electric motor, said motor controller comprising: a rectifier configured to rectify a nominal alternating current (AC) input voltage from a power supply to produce a pulsed direct current (DC) voltage that drops to a value of approximately zero during each cycle of the AC input voltage when the AC input voltage transits a value of zero;an inverter coupled to an output of said rectifier, said inverter configured to receive the pulsed DC voltage that drops to the value of approximately zero during each cycle and to provide a conditioned output voltage to the electric motor;a DC link defined between said rectifier and said inverter, wherein said DC link includes a capacitor having a capacitance between 0.1 mircofarad (μF) and 10 μF; anda control unit coupled to said inverter and configured to: receive a measurement of current being provided to the electric motor;receive a measurement of voltage output by said rectifier;determine, based on the measured voltage output by said rectifier, whether the AC input voltage is increasing or decreasing relative to the value of zero; andwhen the AC input voltage is decreasing towards the value of zero, inject a negative value of a flux linkage component of current into control signals transmitted to said inverter to maintain a corresponding torque component of the current at a positive value such that the electric motor continues to generate torque as the nominal AC input voltage transits the value of zero and no input voltage is momentarily provided to the electric motor. 2. The motor controller in accordance with claim 1, wherein said control unit is further configured to maintain torque of the electric motor above a predefined torque threshold when the AC input voltage transits a value of zero. 3. The motor controller in accordance with claim 1, wherein said control unit is further configured to increase a rotational speed of the electric motor when input voltage is available, wherein the increased rotational speed generates energy that is stored on the load as inertia. 4. The motor controller in accordance with claim 3, wherein the inertia limits speed variations of the electric motor to enable continuing torque production when input voltage is unavailable. 5. The motor controller in accordance with claim 1, wherein said control unit is further configured to maintain positive torque of the electric motor when the AC input voltage transits a value of zero by using energy stored in the motor windings. 6. The motor controller in accordance with claim 1, wherein to control current to the electric motor, said control unit is configured to induce a flux linkage component of current to maintain a torque component of the current above zero. 7. The motor controller in accordance with claim 6, wherein said control unit is further configured to induce the flux linkage component of current while reducing stator winding losses in the electric motor. 8. The motor controller in accordance with claim 6, wherein said control unit is further configured to induce the flux linkage component of current while reducing torque ripple in the electric motor. 9. The motor controller in accordance with claim 6, wherein said control unit is further configured to induce the flux linkage component of current while manipulating torque harmonics to reduce audible noise in the electric motor. 10. The motor controller in accordance with claim 1, further comprising a DC link positioned between said rectifier and said inverter. 11. The motor controller in accordance with claim 10, further comprising a voltage clamping device coupled across said DC link, said voltage clamping device configured to protect said controller against an over-voltage condition. 12. The motor controller in accordance with claim 1, further comprising a capacitor coupled across said DC link, said capacitor configured to mitigate switching frequency harmonics. 13. A method of controlling an electric motor using a motor controller, the electric motor configured to be coupled to a power supply and to a load, said method comprising: rectifying, by a rectifier, a nominal alternating current (AC) input voltage received from the power supply to produce a pulsed direct current (DC) voltage, wherein the DC voltage drops to a value of approximately zero during each half cycle of the AC input voltage when the AC input voltage transits a value of zero;receiving, by an inverter coupled to an output of the rectifier, the DC voltage that drops to the value of approximately zero during each cycle to provide a conditioned output voltage to operate the electric motor;receiving, by a control unit coupled to the inverter, a measurement of current provided to the electric motor;receiving, by the control unit, a measurement of voltage output by the rectifier at a DC link defined between the rectifier and the inverter, wherein the DC link includes a capacitor having a capacitance between 0.1 mircofarad (μF) and 10 μF;determining, by the control unit, whether the AC input voltage is increasing or decreasing relative to the value of zero; andwhen the AC input voltage is decreasing towards the value of zero, injecting, by the control unit, a negative value of a flux linkage component of current into control signals transmitted to the inverter to maintain a corresponding torque component of the current at a positive value such that the electric motor continues to generate torque as the nominal AC input voltage transits the value of zero and no input voltage is momentarily provided to the electric motor. 14. The method in accordance with claim 13, further comprising: increasing, by the control unit, a rotational speed of the electric motor when input voltage is available; andstoring energy generated by the increased rotational speed on the load as inertia. 15. The method in accordance with claim 13, wherein controlling the energy transfer comprises controlling current flowing to the electric motor to produce positive torque when input voltage is one of approaching zero and equal to zero. 16. A system comprising: an electric motor; anda motor controller coupled to said electric motor, said motor controller comprising:a rectifier configured to rectify a nominal alternating current (AC) input voltage from a power supply to produce a pulsed direct current (DC) voltage that drops to a value of approximately zero during each cycle of the AC input voltage when the AC input voltage transits a value of zero;an inverter coupled to an output of said rectifier, said inverter configured to receive the pulsed DC voltage and to provide a conditioned output voltage to said electric motor;a DC link defined between said rectifier and said inverter, wherein said DC link includes a capacitor having a capacitance between 0.1 mircofarad (μF) and 10 μF; anda control unit coupled to said inverter, said control unit configured to: receive a measurement of current being provided to said electric motor;receive a measurement of voltage output by said rectifier;determine, based on the measured voltage output by said rectifier, whether the AC input voltage is increasing or decreasing relative to the value of zero; andwhen the AC input voltage is decreasing towards the value of zero, inject a negative value of a flux linkage component of current into control signals transmitted to said inverter to maintain a corresponding torque component of the current at a positive value such that the electric motor continues to generate torque as the nominal AC input voltage transits the value of zero on the reference x-axis and no input voltage is momentarily provided to the electric motor. 17. The system in accordance with claim 16, wherein said control unit is further configured to increase a rotational speed of said electric motor when input voltage is available, wherein the increased rotational speed generates energy that is stored on the load as inertia.