Single-Phase Grid Voltage Attributes Tracking for the Control of Grid Power Converters

Grid interfacing power converters are indispensable for renewable energy conversion schemes. Fast and precise detection of grid signal parameters is essential for effective operation and control of these converters. For such applications, synchronous reference frame phase-locked loop (SRF PLL) involving two orthogonal signals is widely deployed. For singlephase system, this requires another signal orthogonal to the input. In this paper, single-phase SRF PLL with fixed sampling period sliding discrete Fourier transform (SDFT) filter as orthogonal signal generator is proposed. Additionally, this filter is capable of rejecting dc offset and harmonics present in the grid voltage. With this arrangement, loop filter of PLL need not be equipped with filtering capability. Therefore, PLL could be designed with larger bandwidth which will result in better transient performance. However, SDFT output will be erroneous with asynchronous sampling, under grid frequency drift.With suitable study, relation between those errors and deviation of frequency from nominal value is established. Using this relation, error compensation at any grid frequency can be achieved. To validate the proposed method, various grid abnormalities are emulated with the aid of programmable power source and dSPACE realtime controller board. The effectiveness of the proposed scheme is demonstrated through experimental investigations.
by Chandrasekaran Subramanian and Ragavan Kanagaraj