Single-phase grid-connected converters are widely used in many applications, such as photovoltaics, fuel cells, active power filters, etc. An important topic for the development of their control schemes is ac signal detection, such as grid phase detection for grid-interfacing inverters, and harmonic detection for harmonic compensation devices. Since only one ac signal is available, the task is more difficult than in three-phase systems. Among the existing methods, the frequency-domain ones are known to have a one-cycle delay and heavier computational burden. Meanwhile, the time-domain methods often rely on phase-locked loop, quadrature signal generation and complex filtering techniques; the resulted multiple-looped system may suffer from slow transients and stability issues. This paper proposes a new detection method based on anti-conjugate harmonic decomposition and cascaded delayed signal cancellation. The method uses constant zero as the quadrature signal, and has a completely open-looped structure. The resulted detection system is very simple and robust. The fundamental and harmonic detection transients can be as short as 0.47 cycle, while zero steady-state error can be guaranteed in complicated harmonic scenarios, including all typical single-phase system harmonics. The performance of the proposed detection method is verified by experimental results.
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