Abstract: A double winding electric machine assembly including a double winding electric machine having a first stator winding and a second stator winding; a first converter including a first modulator and a first power unit whose output is electrically connected to the first stator winding; a second converter including a second modulator and a second power unit whose output is electrically connected to the second stator winding. The assembly includes a current determining system adapted to determine at least one instantaneous phase current in the output of the first power unit; and a synchronizing system adapted to analyse ripple in the at least one instantaneous phase current, and to synchronize the first modulator with the second modulator by adjusting a phase shift between the first modulator and the second modulator until a minimum peak-to-peak current is obtained.

Abstract: A method is provided for balancing voltages of a DC link of a multi-level inverter, where the DC link is divided into two halves by a neutral point connection. The method includes injecting a periodic common-mode voltage injection signal to a common-mode voltage reference and a periodic power injection signal to a power reference of the inverter. The power injection signal has the same frequency as the common-mode voltage injection signal. A phase shift between the common-mode voltage injection signal and the power injection signal is constant. The amplitude of at least one of the common-mode voltage injection signal and the power injection signal is controlled on the basis of a difference between voltages over the two halves of the DC link. An apparatus is also provided for implementing the method.

Abstract: An exemplary device and method for estimating an active and/or reactive component of output power of a three-level inverter having a DC link divided into two halves by a neutral point. The device having control unit for determining a voltage ripple at the neutral point, determining a magnitude of a third harmonic component of the voltage ripple in a rotating coordinate system that rotates synchronously with an output voltage of the inverter, and calculating a component of an output current or power in the rotating coordinate system on the basis of the magnitude of the third harmonic component.

Abstract: A method is provided for balancing voltages of a DC link of a multi-level inverter, where the DC link is divided into two halves by a neutral point connection. The method includes injecting a periodic common-mode voltage injection signal to a common-mode voltage reference and a periodic power injection signal to a power reference of the inverter. The power injection signal has the same frequency as the common-mode voltage injection signal. A phase shift between the common-mode voltage injection signal and the power injection signal is constant. The amplitude of at least one of the common-mode voltage injection signal and the power injection signal is controlled on the basis of a difference between voltages over the two halves of the DC link. An apparatus is also provided for implementing the method.

Abstract: A method and an arrangement are provided for identifying parameters of an induction machine when the induction machine is connected to the output phases of a voltage source inverter and the induction machine is in standstill state. The method includes providing a DC magnetization current (idc—magn) to the induction machine with the inverter, controlling the power semiconductors of the inverter to an off-state, controlling all the output phases of the inverter to the same potential to provide a zero voltage vector, measuring the stator current (isd) during the zero voltage vector, and determining parameters of the induction machine from the stator current (isd) measured during the zero voltage vector.

Abstract: A method and an arrangement are disclosed for identifying one or more parameters of an induction machine when the induction machine is connected to the output phases of a voltage source inverter and the induction machine is in standstill state. The method can include a first phase for magnetizing the machine by providing a first DC magnetization current until the induction machine reaches steady state, the current reference of the inverter having a first value (idc—ref1). A first maximum value (imz—max) of the stator current (isd) is measured during a zero voltage vector. In a second phase, the machine is magnetized by providing a second DC magnetization current, the current reference having a second value (idc—ref2) which is higher than the first reference (idc—ref1). A second maximum value of (isdz—max) the stator current is measured during a zero voltage vector, and a parameter of the induction machine is estimated when the measured first and second maximum values are equal.

Abstract: A method is disclosed for estimating a rotation speed of an electric motor supplied by an inverter, by determining a time derivative of a stator current vector of the electric motor during a zero vector state of the inverter; and determining an estimate of the rotation speed of the electric motor on the basis of the determined time derivative of the stator current vector.

Abstract: A method and an arrangement are provided for identifying parameters of an induction machine when the induction machine is connected to the output phases of a voltage source inverter and the induction machine is in standstill state. The method includes providing a DC magnetization current (idc—magn) to the induction machine with the inverter, controlling the power semiconductors of the inverter to an off-state, controlling all the output phases of the inverter to the same potential to provide a zero voltage vector, measuring the stator current (isd) during the zero voltage vector, and determining parameters of the induction machine from the stator current (isd) measured during the zero voltage vector.

Abstract: A method and an arrangement are disclosed for identifying one or more parameters of an induction machine when the induction machine is connected to the output phases of a voltage source inverter and the induction machine is in standstill state. The method can include a first phase for magnetizing the machine by providing a first DC magnetization current until the induction machine reaches steady state, the current reference of the inverter having a first value (ide—ref1). A first maximum value (imz—max) of the stator current (isd) is measured during a zero voltage vector. In a second phase, the machine is magnetized by providing a second DC magnetization current, the current reference having a second value (idc—ref2) which is higher than the first reference (ide—ref1). A second maximum value of (isdz—max) the stator current is measured during a zero voltage vector, and a parameter of the induction machine is estimated when the measured first and second maximum values are equal.

Abstract: A method is disclosed for estimating a rotation speed of an electric motor supplied by an inverter, by determining a time derivative of a stator current vector of the electric motor during a zero vector state of the inverter; and determining an estimate of the rotation speed of the electric motor on the basis of the determined time derivative of the stator current vector.

Abstract: A method and arrangement for determining the effective time of a voltage pulse of phase voltage generated by a frequency converter provided with an intermediate voltage circuit, the voltage pulses of the phase voltage being generated from the upper and lower voltage levels (UDC, 0) of the intermediate voltage circuit, the voltage levels showing a difference in potential (UDC).

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 rotor time constant (?r) of an induction machine when the stator resistance (Rs) and rotor resistance (Rr) of the induction machine are known. The method comprises the steps of feeding a DC current to the stator of the induction machine, injecting a sine-wave current component into the stator of the induction machine, the current having an amplitude (isc) and an angular frequency (?c), measuring the voltage component (uscd) of the stator voltage of the induction machine in the same direction and with the same angular frequency as the injected current, and calculating the rotor time constant using equation ? r = 1 ? c ? u scd - R s ? i sc ( R s + R R ) ? i sc - u scd .

Abstract: A method for determining output currents of a three-phase frequency converter comprising a voltage intermediate circuit and three power switch pairs constituting an output of the frequency converter, wherein the power switches constituting a pair are coupled in series between a positive and a negative busbar of the voltage intermediate circuit so that a midpoint of each switch pair constitutes a phase output of the frequency converter.

Abstract: A method for estimating the rotor time constant (?r) of an induction machine when the stator resistance (Rs) and rotor resistance (Rr) of the induction machine are known. The method comprises the steps of feeding a DC current to the stator of the induction machine, injecting a sine-wave current component into the stator of the induction machine, the current having an amplitude (isc) and an angular frequency (?c), measuring the voltage component (uscd) of the stator voltage of the induction machine in the same direction and with the same angular frequency as the injected current, and calculating the rotor time constant using equation ? r = 1 ? c ? u scd - R s ? i sc ( R s + R R ) ? i sc - u scd .

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 and arrangement for determining the effective time of a voltage pulse of phase voltage generated by a frequency converter provided with an intermediate voltage circuit, the voltage pulses of the phase voltage being generated from the upper and lower voltage levels (UDC, 0) of the intermediate voltage circuit, the voltage levels showing a difference in potential (UDC).

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 output currents of a three-phase frequency converter comprising a voltage intermediate circuit and three power switch pairs constituting an output of the frequency converter, wherein the power switches constituting a pair are coupled in series between a positive and a negative busbar of the voltage intermediate circuit so that a midpoint of each switch pair constitutes a phase output of the frequency converter.

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.