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.
- SourceAvailable from: Francesco Muzi
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- "Where r Z is the resonant frequency. Due to the above feature, the system is known in literature as second order generalized integrator (SOGI) , . In filter construction, special attention must be paid to a discretization of the integral operator. "
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.
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ABSTRACT: In grid-connected application of distributed generation sets, accurate estimation of the phase of the grid voltage is a fundamental task for developing reliable control algorithms, especially in single-phase systems. Many algorithms have been proposed for estimation of the phase of the voltage grid based on Phased-Locked Loop (PLL) techniques. In this paper, in order to evaluate the performance in terms of noise rejection and dynamic response of most used PLL algorithms, a comparison accomplished through simulations and experimental results is presented in different operating conditions and voltage disturbance. The analysis conducted in the paper is synthesized in a table useful to choose the appropriate PLL structure at the design stage.Power Electronics Electrical Drives Automation and Motion (SPEEDAM), 2010 International Symposium on; 07/2010
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ABSTRACT: Converters for power grid interface are required to operate under abnormal operating conditions such as unbalanced and non-sinusoidal grid voltage waveforms and hence, the multilevel types of converters offer a good solution to achieve high power and high voltage and that modular control consisting of cascaded structures seems the most appropriate solution towards decentralising the control per individual phases as well. This paper investigates the use of the proposed hybrid repetitiveresonant control in a control scheme for a single phase converter designed to interface with power grids of highly distorted voltage waveforms. The proposed hybrid repetitive-resonant control is employed into two places of the control system to act in one place as a harmonics filter and in the second place as a current controller to provide respectively:- i) high performance extraction of clean and reliable phase angle information and magnitude of the fundamental grid voltage component and ii) control of grid current and the mitigation of harmonics. Grid voltage control is also considered. The Repetitive Controller RPC is known to reject all the harmonics content but with slow dynamics,  while the Resonant Controller RSC is faster but rejects only a single frequency component, . Hence, a hybrid RPC/RSC control approach is proposed where the RSC network is tuned at a number of selected low order frequencies and operated in parallel with a full range RPC. The hybrid RPC/RSC control approach is applied to compensate the grid current harmonics and to eliminate the harmonics distortion of the estimated phase angle and magnitude of the fundamental grid voltage component. Detailed modelling and simulation of the proposed control scheme are carried out using PSIM and the results show excellent performance.