Abstract: A method for stabilizing a DC link voltage of an electrical converter, the method including: determining a DC link voltage signal for the DC link voltage of the electrical converter; determining a fluctuation signal of the DC link voltage by applying a high pass filter to the DC link voltage signal; determining a torque offset by multiplying the fluctuation signal with a gain value; and modifying a reference torque with the torque offset for controlling the electrical converter. The gain value is adjusted by: determining a DC link voltage ripple from the DC link voltage signal; and comparing the DC link voltage ripple with a threshold and, when the DC link voltage ripple is higher than the threshold, increasing the gain value.

Abstract: A method for stabilizing a DC link voltage of an electrical converter, the method including: determining a DC link voltage signal for the DC link voltage of the electrical converter; determining a fluctuation signal of the DC link voltage by applying a high pass filter to the DC link voltage signal; determining a torque offset by multiplying the fluctuation signal with a gain value; and modifying a reference torque with the torque offset for controlling the electrical converter. The gain value is adjusted by: determining a DC link voltage ripple from the DC link voltage signal; and comparing the DC link voltage ripple with a threshold and, when the DC link voltage ripple is higher than the threshold, increasing the gain value.

Abstract: A method and device are disclosed for synchronizing an inverter with an alternating voltage source. The method includes measuring a current generated by the alternating voltage source and flowing through diodes of the inverter, determining a phase angle and angular velocity relating to the alternating voltage source from the measured current for enabling synchronization between the inverter and the alternating voltage source, and starting modulation of the inverter according to the obtained phase angle and angular velocity.

Abstract: A method for controlling an electric drive, having an inverter, an electric motor and control means configured in a first operating state of the electric drive to control the electric drive to run in a constant operating point, determine and store a value of an output voltage of the inverter or a value of a flux reference of the inverter, and a value of a switching frequency of the inverter with which a determined input power of the electric drive is lowest. The controller is configured in a second operating state of the electric drive to control the electric drive to use the stored values to run in the operating point.

Abstract: A method for controlling an electric drive, having an inverter, an electric motor and control means configured in a first operating state of the electric drive to control the electric drive to run in a constant operating point, determine and store a value of an output voltage of the inverter or a value of a flux reference of the inverter, and a value of a switching frequency of the inverter with which a determined input power of the electric drive is lowest. The controller is configured in a second operating state of the electric drive to control the electric drive to use the stored values to run in the operating point.

Abstract: A method and device are disclosed for synchronizing an inverter with an alternating voltage source. The method includes measuring a current generated by the alternating voltage source and flowing through diodes of the inverter, determining a phase angle and angular velocity relating to the alternating voltage source from the measured current for enabling synchronization between the inverter and the alternating voltage source, and starting modulation of the inverter according to the obtained phase angle and angular velocity.

Abstract: A method for estimating the sum of the stator and rotor resistances of an induction machine using a frequency converter when the frequency converter is connected to the induction machine. The method comprises the steps of controlling the stator current of the induction machine with the frequency converter such that the rotor flux (?R) changes substantially linearly while the stator current is substantially constant, determining the magnitude of stator voltage and stator current while the rotor flux is changing substantially linearly, and calculating the sum of the stator and rotor resistances from the determined magnitudes of stator voltage and stator current.

Abstract: A method for estimating the sum of the stator and rotor resistances of an induction machine using a frequency converter when the frequency converter is connected to the induction machine. The method comprises the steps of controlling the stator current of the induction machine with the frequency converter such that the rotor flux (?R) changes substantially linearly while the stator current is substantially constant, determining the magnitude of stator voltage and stator current while the rotor flux is changing substantially linearly, and calculating the sum of the stator and rotor resistances from the determined magnitudes of stator voltage and stator current.

Abstract: A method for determining the rotor flux vector of an electrical machine, the method comprising the steps of controlling the electrical machine with an inverter, forming an equation for the reactive power (Qinv) at the output of the inverter, forming an equation for the consumed reactive power ({circumflex over (Q)}mot) in the electrical machine, forming a reactive power balance equation (Qerr) between the reactive power (Qinv) at the output of the inverter and the reactive power ({circumflex over (Q)}mot) consumed in the electrical machine, determining the stator resistance ({circumflex over (R)}s) of the electrical machine from the balance equation (Qerr), determining the stator flux estimate ({circumflex over (?)}s) using the determined stator resistance ({circumflex over (R)}s) and the balance equation (Qerr), and determining the rotor flux estimate ({circumflex over (?)}R) using the determined stator flux estimate ({circumflex over (?)}s).

Abstract: A method for coupling an inverter to an alternating voltage source, the inverter comprising a current controller, which controls phase currents and implements reference current. The method comprises steps of giving zero current as the reference current for the current controller, determining phase voltages of the inverter, determining frequency of the alternating voltage source from the determined phase voltages, and synchronizing and coupling the inverter to the determined frequency of the alternating voltage source.

Abstract: A method for determining the rotor flux vector of an electrical machine, the method comprising the steps of controlling the electrical machine with an inverter, forming an equation for the reactive power (Qinv) at the output of the inverter, forming an equation for the consumed reactive power ({circumflex over (Q)}mot) in the electrical machine, forming a reactive power balance equation (Qerr) between the reactive power (Qinv) at the output of the inverter and the reactive power ({circumflex over (Q)}mot) consumed in the electrical machine, determining the stator resistance ({circumflex over (R)}s) of the electrical machine from the balance equation (Qerr), determining the stator flux estimate ({circumflex over (?)}s) using the determined stator resistance ({circumflex over (R)}s) and the balance equation (Qerr), and determining the rotor flux estimate ({circumflex over (?)}R) using the determined stator flux estimate ({circumflex over (?)}s).

Abstract: The invention relates to a method for compensating for a voltage unbalance in an electrical network, which is fed by using an apparatus based on controlling a flux linkage vector or a voltage vector. Concerning the apparatus based on controlling the flux linkage vector, the method comprises the steps of determining a flux linkage reference vector comprising a positive sequence component and a negative sequence component, and controlling the feeding apparatus of the network in such a manner that the flux linkage vector thereof follows the reference vector with predetermined precision. The negative sequence component of the flux linkage reference vector is arranged to compensate for the amplitude and phase unbalance of the voltage in the electrical network to be fed.

Abstract: The invention relates to a method for compensating for a voltage unbalance in an electrical network, which is fed by using an apparatus based on controlling a flux linkage vector or a voltage vector. Concerning the apparatus based on controlling the flux linkage vector, the method comprises the steps of determining a flux linkage reference vector comprising a positive sequence component and a negative sequence component, and controlling the feeding apparatus of the network in such a manner that the flux linkage vector thereof follows the reference vector with predetermined precision. The negative sequence component of the flux linkage reference vector is arranged to compensate for the amplitude and phase unbalance of the voltage in the electrical network to be fed.

Abstract: A method for coupling an inverter to an alternating voltage source, the inverter comprising a current controller, which controls phase currents and implements reference current. The method comprises steps of giving zero current as the reference current for the current controller, determining phase voltages of the inverter, determining frequency of the alternating voltage source from the determined phase voltages, and synchronizing and coupling the inverter to the determined frequency of the alternating voltage source.