Summary This paper presents a control method of a three‐phase power converter operating under grid imbalance and harmonics. The proposed control system uses virtual flux of the grid, and a voltage fundamental harmonic to calculate reference instantaneous power oscillations, in order to maintain sinusoidal converter current. Thus, there is no need for symmetrical sequence decomposition. The presented method ensures current asymmetry corresponding to or opposite to voltage asymmetry, depending on the operation mode. Application of a stationary frame power control provides that the system does not require a dq transformation, and thus no grid voltage phase angle determination is needed, as the power components are the same in every coordinates system. Moreover, the power limitation method allowing limitation of the phase current amplitude was applied.

The paper presents a new approach to positive and negative sequence current vector control of a grid connected three-phase three-wire power electronic converter operating under grid voltage imbalance conditions. The concept utilizes representation of unbalanced converter current in the new coordinates frame in which the current vector components are constant. The nonlinear trigonometric transformation of twodimensional current vector components from the stationary frame to the new frame is found on-line depending on the reference current asymmetry. The presented concept of new coordinates utilization allows implementation of proportionalintegral terms as current regulators without the use of resonant terms and without the use of the measured current symmetrical sequences decomposition. The paper presents the theoretical approach, simulation results, as well as laboratory tests results.

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