AC Voltage Sensorless Method With Bumpless Start for Current-Controlled Converters Connected to Microgrids

Abstract

This paper presents a novel grid synchronization method with bumpless start which requires minimal computational load and can selectively track the positive sequence of the grid voltage in an unbalanced and distorted three-phase weak grid. Only twelve floating-point operations (flops) are required to obtain the in-phase and quadrature components that define a synchronous frame which tracks the positive sequence of the grid voltage. Contrarily to a phase-locked loop (PLL), the presented scheme does not require to measure any ac voltages. Therefore, this sensorless method is particularly suitable in weak-grid conditions in which the voltage at the point of common coupling (PCC) is different from the grid voltage and may contain significant noise. The error in the estimated phase depends on the accuracy of the plant model. If the grid-impedance is assumed to be zero and the LCL filter parameters are known, both the proposal and a PLL-based scheme result in the same steady-state error. Experimental results show the advantages of the proposal compared to a moving average filter (MAF)-based PLL.