A method for operating an electric machine comprises ascertaining an electric stator current of the electric machine, calculating a magnetic flux which is generated based on the ascertained electric stator current, and controlling a torque generated by means of the electric machine, as a function of the calculated magnetic flux.

A closed-loop system may include a plant (an elctric machine requiring control) and a fractional-order proportional-resonant controller. The fractional-order proportional-resonant controller may have an order greater than zero and less than or equal to one. The order for the fractional-order proportional-resonant controller may be selected to yield a target amplitude and target slope for frequency response. The frequency response may be such that a steady-state error associated with a speed of the electric machine is inversely proportional to the target amplitude and less than a predetermined threshold. The order of the controller may be 0.9.

A method for field-oriented control of a frequency converter for a three-phase motor includes the setting of a new position of the rotary field in the electric motor being performed by voltage pulses for the stator coils. An amplitude and the angle of the rotary field vector are specified by the duration of the voltage pulses for the respective coils and by their temporal offset. The duration and the offset of voltage pulses for the stator coils are the result of the calculation of manipulated variables in a digitally controlled process in a coordinate system fixed in respect of the rotor, depending on the prevailing angular rotation (theta) and the prevailing speed of rotation (omega) as well as on the prevailing current values, a predetermined torque and a predetermined speed of rotation.

A method for field-oriented control of a frequency converter for a three-phase motor includes the setting of a new position of the rotary field in the electric motor being performed by voltage pulses for the stator coils. An amplitude and the angle of the rotary field vector are specified by the duration of the voltage pulses for the respective coils and by their temporal offset. The duration and the offset of voltage pulses for the stator coils are the result of the calculation of manipulated variables in a digitally controlled process in a coordinate system fixed in respect of the rotor, depending on the prevailing angular rotation (theta) and the prevailing speed of rotation (omega) as well as on the prevailing current values, a predetermined torque and a predetermined speed of rotation.

An apparatus includes a switch module that selectively turns on a switch to connect an input power conductor connected to a voltage source to a motor in a sequence. The switch for each phase is turned on for a portion of a cycle of a fundamental frequency of the voltage source. A source phase module determines a phase of the AC voltage source, a back-EMF phase module determines a phase of a back-EMF of the motor, and a torque module determines when a phase difference between the phase of the AC voltage source and the phase of the back-EMF is within a phase range indicative of a positive motor torque. A pulse module enables the switches in response to the phase difference having a phase within the phase range and disables the switches in response to the phase difference having a phase not in the phase range.

A variable magnetization machine controller has a current command module, a magnetization module and a reducing current module. The current command module computes a vector current command in a dq axis based on a torque command. The magnetization module applies a magnetization control pulse to a d-axis current of the vector current command. Thus, the reducing current module applies a reducing current to a q-axis current of the vector current command based on the torque command and one of an estimated torque of the variable magnetization machine and a measured torque of the variable magnetization machine.

A variable magnetization machine controller has a current command module, a magnetization module and a reducing current module. The current command module computes a vector current command in a dq axis based on a torque command. The magnetization module applies a magnetization control pulse to a d-axis current of the vector current command. Thus, the reducing current module applies a reducing current to a q-axis current of the vector current command based on the torque command and one of an estimated torque of the variable magnetization machine and a measured torque of the variable magnetization machine.

A method for field-oriented control of a frequency converter for a three-phase motor includes the setting of a new position of the rotary field in the electric motor being performed by voltage pulses for the stator coils. An amplitude and the angle of the rotary field vector are specified by the duration of the voltage pulses for the respective coils and by their temporal offset. The duration and the offset of voltage pulses for the stator coils are the result of the calculation of manipulated variables in a digitally controlled process in a coordinate system fixed in respect of the rotor, depending on the prevailing angular rotation (theta) and the prevailing speed of rotation (omega) as well as on the prevailing current values, a predetermined torque and a predetermined speed of rotation.

A method for field-oriented control of a frequency converter for a three-phase motor includes the setting of a new position of the rotary field in the electric motor being performed by voltage pulses for the stator coils. An amplitude and the angle of the rotary field vector are specified by the duration of the voltage pulses for the respective coils and by their temporal offset. The duration and the offset of voltage pulses for the stator coils are the result of the calculation of manipulated variables in a digitally controlled process in a coordinate system fixed in respect of the rotor, depending on the prevailing angular rotation (theta) and the prevailing speed of rotation (omega) as well as on the prevailing current values, a predetermined torque and a predetermined speed of rotation.

One aspect of the invention relates to a control device (2) for starting up a synchronous electric motor (1) up to a predetermined threshold speed, comprising: a current regulator (4) that delivers a voltage setpoint (V #dq) in accordance with a regulation current setpoint (l #dq), a computing unit (5) for computing a current feedback. (Idq) in accordance with measurements of the phase currents (lu, Iv, Iw), an estimator (6) for estimating an angular position of the rotor (elec), in accordance with a difference between a reference stator flux vector (q) that depends on the feedback currents (Iq) and an adaptive stator flux vector (qv) that depends on the voltage setpoint (V.sup.#dq), on the feedback currents (Iq, Id), and on an estimated electrical speed (elec), a setpoint current modifier (7) that computes, when the estimated electrical speed (elec) is lower than the predetermined threshold speed, a regulator setpoint DC current (l.sup.#d) having a non-zero value.