Abstract: When the grid voltage is unbalanced，the negative sequence current will seriously affect the quality

of the output power of the grid-connected inverter. The detection speed of the grid information is one of the main

factors of negative sequence current compensation. Therefore，a control strategy without phase-locked loop（PLL）based on virtual vector was proposed. Firstly，the difference between the control strategy with and without PLL was analyzed. Secondly，the reordering elimination algorithm was adopted to eliminate the second harmonic component generated under the imbalance of the power grid. Finally，the double-loop control was used to directly control the negative sequence current in a fixed frequency rotating frame. The experiment results show that the control strategy without PLL not only suppresses the negative sequence current，but also omits the previous PLL tracking process of the grid voltage，which is better in response time.

      Key words: unbalanced voltage；without phase-locked loop（PLL）；negative sequence current；grid-connected inverter