Control strategy based on double coordinates for three-phase grid-connected inverters

The conventional indirect current control mode for three-phase grid-connected inverter is analyzed according to mathematical model of inverter. The d-axis component of inverter voltage is always equal to peak voltage of power grid if power factor (PF) is equal to 1 and equivalent line resistor is ignored. A novel indirect current control strategy, which uses closed-loop of d-axis component of grid current to adjust q-axis component of inverter voltage, is proposed according to this conclusion. The power factor is affected by R and accuracy of measured grid voltage. In order to improve the power factor, a control strategy for grid-connected inverter based on double d-q coordinates is proposed. The different variables are located in different coordinates. However, all variables are still satisfied parallelogram law and the inverter can run in unity power factor. The validity and advancement of the proposed control scheme are verified by the simulation results.