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A Novel Per Unit (P.U.) Integer Format Applied to the Control of a Grid-Tied Solar PV Inverter

In advanced power electronic applications such as a grid-tied solar photovoltaic (PV) inverter, control algorithms demand high-level computational support, typically provided by an expensive 32-bit digital-signal-processor (DSP) or microcontroller. In cost-sensitive markets, this may prove to be a significant component of the overall cost of the system. Using a low-cost 16-bit microcontroller is, therefore, highly desirable. However, it poses certain challenges such as fewer bits for the mathematical and logical operations, computations in the fixed-point environment, and lower speeds. In this article, a novel per-unit integer system is proposed towards using a low-cost microcontroller for complex computations, which overcomes the above limitations while maintaining the core functionality in a fixed-point environment. An improved hybrid phase locked loop implementation scheme, that uses the p.u. integer system has also been presented, which significantly reduces the execution time for grid-synchronization. To demonstrate the performance of the proposed concepts, control of a grid-tied PV inverter has been implemented on a low-cost fixed-point microcontroller (dsPIC33FJ16GS402) as well as on an advanced DSP microcontroller (TMS320F28069). Timing analysis and experimental results for a 1 kW grid-tied PV system confirm that the performance of the system using a low-cost microcontroller is comparable to that of the advanced microcontroller.