Grid frequency tracking control strategy without PLL for three-phase inverter

SVPWM is widely applied in the control of the three-phase inverter. The phase angle of the grid takes part in the coordinate transformation and PLL is necessary. However, the non-ideal grid may affect the accuracy of the phase angle. To eliminate the influence of the non-ideal grid, the PLL technology should be improved and it may complicate the control strategy. This paper proposes a novel grid frequency tracking control strategy without PLL for three-phase inverter. The angle which takes part in the coordinate transformation is directly generated by the controller. The grid frequency tracking method can ensure that the changing rate of the generated angle is the same as that of the grid phase angle. But the phases of them may be different. The feasibility of the control strategy and the necessity of the frequency tracking are analyzed in detail. An 18 kVA DSP-based three-phase inverter has been established and tested. Simulation and experimental results verify the theoretical analysis.