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Repetitive controllers represent an attractive solution for systems having periodic reference or disturbance signals with high harmonic content. In order to obtain some performance improvements for three-phase plants, as grid-connected converters, complex repetitive controllers were proposed later in literature. In this article, the advantages of complex repetitive control systems over the real ones are analyzed. In addition, sufficient conditions for the input–output stability of complex repetitive control systems and modified complex repetitive control systems are obtained from the small gain theorem. These stability conditions are then used to derive the stability domains for complex repetitive control systems. Further, a relative stability analysis based on the sensitivity function is introduced. An experimental application based on an active power filter is used to exemplify the effectiveness of the proposed stability analysis. [ABSTRACT FROM AUTHOR]

The fast detection of magnitude, frequency, and phase angle of the fundamental-frequency component is very useful in many three-phase power system applications. Most techniques to accomplish this task are based on different versions of three-phase phase-locked loop (PLL) schemes. Some variables of three-phase systems may experience phase angle jumps after some disturbances. In this paper, a method for the fast detection of phase angle jump occurrence, estimation of the phase angle jump, and its use for improving the performance of the generalized delayed signal cancelation (GDSC) PLL is proposed. The proposed method is based on the detailed evaluation of the GDSC filter transient behavior after a phase jump. Results considering typical three-phase grid disturbances are used to evaluate the proposed scheme, in comparison with other usual PLL techniques. The use of the proposed phase jump angle estimator allowed a reduction in the GDSC-PLL convergence time of about 50%. [ABSTRACT FROM AUTHOR]

In this paper, a generic complex repetitive controller ($nk + m$ RC, $k\in \mathbb {Z}$), based on the inverse transfer function of the generalized delayed signal cancelation transformation is proposed. The presented complex controller can be designed for regulating different positive- and negative-sequence harmonic components through a space-vector error signal, with improved response time as compared to traditional repetitive controllers. An evaluation of the proposed control scheme stability, based on phase margin, Nyquist diagram, and sensitivity function is presented. The effects of the controller parameters on the system's stability and also on its dynamic response are shown and allow the definition of some control design guidelines. Experimental results are presented to validate the theoretical assumptions through applying the proposed controller for regulating the currents in a three-phase active power filter. [ABSTRACT FROM AUTHOR]

Integration of distributed generation (DG) such as photovoltaics (PV) represents a challenge for the traditional operation of distribution power systems. As the installed power of DGs grows, grid codes are being modified to involve DGs in the provision of ancillary services. This includes the ability to ride-through large disturbances. In this paper, the behavior of a single-stage PV system under unbalanced voltage conditions is studied, and a fault ride-through control scheme is proposed which is able to support the grid through the injection of reactive power. Furthermore, adjustable power quality is enabled as a tradeoff between power ripple and current harmonics. The control scheme makes use of a current controller based on the space vector Fourier transform concept. No rotational transformation is required, and zero steady-state error is ensured when tracking distorted current references. The controller was tested in detailed PSCAD/EMTDC computer simulations, and implemented in a real grid-connected PV system to demonstrate its performance under unbalanced voltage conditions. [ABSTRACT FROM PUBLISHER]

This paper shows a scheme for improving the detection performance of the fundamental-frequency positive-sequence (FFPS) space vector through the generalized delayed signal cancellation phase-locked loop (GDSC-PLL). We implemented a variable-structure scheme in order to reduce the convergence time by changing the traditional datapath whenever even harmonics are not present in the input signal. If this condition is not true, the performances of the variable-structure GDSC-PLL and the traditional GDSC-PLL for detecting the FFPS space vector will be similar. Therefore, the variable-structure GDSC-PLL does not require a previous knowledge about the harmonic components of the three-phase signal. Furthermore, we improved the frequency-adaptive scheme. The performances of the original and proposed schemes were compared through transient test cases based on IEC 61000 and typical electrical events. The new approach led to a reduction of up to 62% in the convergence time. [ABSTRACT FROM PUBLISHER]

In this paper, a controller based on the space vector Fourier transform (SVFT) is proposed. The vector controller is implemented in the stationary \alpha\beta reference frame and can be designed to track unbalanced and distorted three-phase reference signals containing specific positive-sequence, negative-sequence, and harmonic components. In order to evaluate the proposed controller closed-loop response, three-phase unbalanced and distorted reference currents are imposed in a grid-connected voltage source converter. The ability of the controller to follow the references with zero steady-state error is proved through frequency response plots and stability analysis. Experimental results are obtained to confirm the properties of the proposed scheme. [ABSTRACT FROM PUBLISHER]

Fundamental-frequency and harmonic positive- and negative-sequence components detection is an important task for implementing power converters for renewable energy systems, uninterruptible power supplies, active power filters, dynamic voltage restorers, and also for power systems protection relays. Detection techniques of this kind are generally implemented in digital signal processor (DSP) with the execution time limited by the sampling period. The computational effort of the control algorithm can considerably increase the execution time, due to the sequential nature of processing in DSP. A promising technique for sequence components separation of three-phase signals is the so called the generalized delayed signal cancelation—phase locked loop (GDSC-PLL). Field programmable gate array's (FPGA's) capacity of exploring the parallelism of operations present in the GDSC-PLL is demonstrated in this paper through the mapping of this technique directly in hardware, allowing for a much shorter execution time than in DSP. The proposed architecture is presented, and the efficient detection of the fundamental-frequency positive-sequence with FPGA is demonstrated, with the obtained results compared with a traditional DSP implementation. In particular, the advantages and possibilities of the use of FPGA are demonstrated in comparison with the DSP. For this comparison, a metric for evaluating the capacity of complexity increase in application algorithms is proposed. [ABSTRACT FROM PUBLISHER]

In this paper, two methods for determining the fundamental frequency and harmonic positive- and negative-sequence components of three-phase signals are investigated. Many aspects of the space-vector discrete Fourier transform and generalized delayed signal cancellation (GDSC) such as response time for different possible implementations, frequency adaptation schemes, stability of recursive implementation, and rounding error effects are discussed. A new design procedure for GDSC transformations is presented. New indices for characterizing three-phase unbalanced and distorted signals are proposed. Simulations and experiments are included in order to verify the performances and illustrate the theoretical conclusions. [ABSTRACT FROM PUBLISHER]