Method for coupling inverter to alternating voltage

1. 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, comprising the steps:

giving zero current as the reference current for the current controller,

controlling the phase currents of the inverter output to zero;

determining-phase voltages of the inverter while the current is controlled to zero,

determining frequency of the alternating voltage source from the determined phase voltages,

synchronizing and coupling the inverter to the determined frequency of the alternating voltage source,

calculating, based on the determined phase voltages, a flux estimate,

correcting the calculated flux estimate to be origin centered to provide a flux,

determining phase angle and amplitude of the flux,

determining rate ofchange of the flux phase angle, including the flux frequency, and

synchronizing and coupling the inverter to the alternating voltage source in accordance with properties of the flux.

2. A method according to claim 1 , wherein the correction of the flux estimate comprises the steps of:

adapting the flux estimate to a circle equation, and

solving an initial flux value from the circle equation after the adaptation.

3. A method according to claim 1 , wherein the correction of the flux estimate comprises the step of:

low-pass filtering the phase voltages during calculation of the flux estimate, the estimate then converging onto the origin centered flux.

4. A method according to claim 1 , wherein the flux amplitude is known, and the correction of the flux estimate comprises the steps of:

correcting the flux estimate according to known flux amplitude in a direction of the flux, and

correcting the flux estimate according to a dot product of the flux and stator voltage in the direction of the flux tangent.