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Samuli Heikkilä

Mikko Vertanen

Mikko Norrkniivilä

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.

Double winding electric machine assembly

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.

Method and apparatus for balancing voltages of multi-level inverter DC link

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 (i) 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 (i) during the zero voltage vector, and determining parameters of the induction machine from the stator current (i) measured during the zero voltage vector.

Induction motor parameter identification

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 (i). A first maximum value (i) of the stator current (i) 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 (i) which is higher than the first reference (i). A second maximum value of (i) 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.

Estimation of parameters of an induction machine

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.

Method and apparatus for estimating a rotation speed of an electric motor

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 (U) of the intermediate voltage circuit, the voltage levels showing a difference in potential (U). The method includes generating a first reference voltage (U) and a second reference voltage (U); scaling the phase output voltage by the scaling coefficient (k); comparing the low-pass filtered phase output voltage with the first reference voltage (); detecting a time instant (t) when the low-pass filtered phase output voltage exceeds the first reference voltage (U); comparing the low-pass filtered phase output voltage with the second reference voltage (U); detecting a time instant (t) when the low-pass filtered phase output voltage is lower than the second reference voltage (U); and calculating the effective time of the voltage pulse on the basis of the time between the first and the second time instants and a constant term.

Measuring average of phase voltage of a frequency converter based on an idealized waveform

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 (&#x3c8;) 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.

Method for estimating the sum of stator and rotor resistances

A method for estimating the rotor time constant (&#x3c4;) of an induction machine when the stator resistance (R) and rotor resistance (R) 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 (i) and an angular frequency (&#x3c9;), measuring the voltage component (u) 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 

Method for estimating the rotor time constant of an induction machine

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.

Method for coupling inverter to alternating voltage

Direct torque control inverter arrangement

Method for determining a stator flux estimate for an asynchronous machine

Method for determining the short-circuit inductance of an asynchronous

The invention relates to a method for determining the stator flux of an asynchronous machine when a stator current (i.sub.2) and stator voltage (u.sub.s) of the asynchronous machine are measured and a short-circuit inductance (.sigma.L.sub.s), stator inductance (L.sub.s) and rotor time constant (.tau..sub.r) of the machine are assumed to be known, wherein the product of the stator current (i.sub.s) and a stator resistance estimate (R.sub.se) is determined, the obtained product is subtracted from the stator voltage (u.sub.s), and the obtained voltage difference is integrated with respect to time to obtain a first stator flux estimate (.psi..sub.se). In the invention, the method further comprises the steps of determining a second stator flux estimate (.psi..sub.se,id) on the basis of the stator voltage (u.sub.s), the stator current (i.sub.s), the short-circuit inductance (.sigma.L.sub.s), the stator inductance (L.sub.s), the rotor time constant (.tau..sub.r) and the stator resistance estimate (R.sub.se); determining a stator flux correction term (.DELTA..psi..sub.se) as a difference between the first stator flux estimate (.psi..sub.se) and the second stator flux estimate (.psi..sub.se,id), and summing the stator flux correction term (.DELTA..psi..sub.se) weighted by a constant coefficient (w) with said voltage difference.

Method for determining the stator flux of an asynchronous machine

The invention relates to a method of preventing the stalling of an asynchronous machine controlled by a controller (6) affecting the slip and having a response time less than a rotor time constant (.tau..sub.r) of the machine. To minimize the safety margin between the allowable maximum torque and the stalling torque, the method comprises the steps of measuring rotational vectors (i.sub.s, u.sub.s) for the stator current and stator voltage of the machine; determining, on the basis of the measured rotational vectors (i.sub.s, u.sub.s) of the stator current and stator voltage and a short-circuit inductance (.sigma.L.sub.s) of the machine, two vectors one of which (.phi..sub.s) is parallel to the direction of the stator flux (.psi..sub.s) and the other (.phi..sub.r) to the rotor flux (.psi..sub.r); determining an angle (.gamma.) between said vectors parallel to the stator and rotor fluxes or a value (.mu.) proportional to it; and preventing the controller from performing operations tending to increase the torque of the asynchronous machine when said angle (.gamma.) or the value (.mu.) proportional to it corresponds to a predetermined angle between the stator and rotor flux vectors.

Growing community of inventors

Helsinki, Finland

Samuli Heikkilä