Single-phase grid-synchronization algorithms for converter interfaced distributed generation systems
ABSTRACT This paper briefly reviews the synchronization techniques for single-phase converter-interfaced distributed generation (DG) systems. These techniques are compared in terms of their capability in tracking frequency variations, and the phase angle of the grid signal in the presence of low order harmonic. The techniques introduced in this paper are applicable for a wide range of equipment like converter-interfaced distributed generation (DG) units, e.g. wind, photovoltaic, and fuel cells, and are also applicable for active power filters and uninterrupted power supplies.
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ABSTRACT: It is well known that network analyzers perform reliable estimations of the Total Harmonic Distortion (THD). A distorted signal is actually decomposed in real time into its harmonic components using the Fourier transform. The implemented algorithm requires a 200ms observation window in order to meet both the necessary accuracy and standard requirements. Though the adopted observation time is compatible with the dynamic behavior of large generators, it is however not acceptable for small distributed generators (DG). Moreover, DGs are usually intermittent energy sources connected to a distribution network through inverters with time constants of dozens of microseconds. For this reason, smart grids with a massive presence of distributed renewable generation have to be monitored by fast algorithms in order to guarantee high levels of power quality. Actually, a remarkable distortion of the voltage waveform, which may also be due to a malfunctioning inverter, can cause for instance an incorrect behavior of digital protection systems. Herein a fast algorithm for the estimation of voltage harmonics is introduced, which, contrarily to algorithms currently adopted for the discrete Fourier transform, can be implemented also in non-updated, low performing microprocessors. The proposed method uses a second order generalized integrator that refers to the SOGI-based Frequency Locked Loop (SOGI-FLL). A number of simulations were performed in order to validate the method, and the results showed that the time response of the algorithm is less than 20 ms, which means the method can be profitably used to improve smart grid power quality.01/2011;
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ABSTRACT: This paper mainly studies the PLL algorithms for TCSC, expecting the PLLs to achieve the following performances: rapidly and accurately tracking line current phase and frequency, effectively suppressing sub-harmonics and harmonics, robustness to the disturbances and other types of pollutions. The paper first describes the concept of PLL. Then on the basis of the comparison among several kinds of single-phase PLLs, it presents that the PLL based SOGI-FLL is a more appropriate synchronization scheme for TCSC.Power and Energy Engineering Conference (APPEEC), 2012 Asia-Pacific; 01/2012
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ABSTRACT: The scope of this work is to find the best approach to control advanced inverters used to connect electric vehicles to the grid. Phase-locked Loop (PLL) is a grid voltage phase detection that makes use of an orthogonal voltage to lock the grid phase. This method is suitable for both single and three phase systems, although in single-phase, because they have less information, more advanced systems are required. The easiest way to obtain the orthogonal voltage system is using a transport delay block to introduce a phase shift of 90 degrees with respect to the fundamental frequency of the grid voltage. This method is known as Synchronous Reference Frame PLL (SRF-PLL). The use of inverse Park transformation is also possible. To lower the complexity and increasing the filtering of the output signals, methods using adaptive filters are a good alternative. For this approach, the use of a second order generalized integrator (SOGI) or Adaptive Notch filter combined with PLL, Enhanced PLL (EPLL) and Quadrature PLL (QPLL), leads to satisfactory results.Energetics (IYCE), Proceedings of the 2011 3rd International Youth Conference on; 01/2011