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The importance of distributed generation and renewable energies inclusion has led to obtain the maximum from power converters, in terms of total harmonic distortion (THD) reduction and power injection. The reachable operating point is associated with the inverter output voltage, which is limited by the input dc voltage. Some capabilities, such as reactive power injection, require a high-voltage margin. Furthermore, in modern applications, the combination with harmonic capabilities for THD reduction can increase the required voltage leading to extra harmonic pollution. In this paper, a distortion-free instantaneous multifrequency saturator (DFIMS) is proposed, which delivers the maximum power in a multifrequency environment, conditioned to the minimum current THD. This novel saturator instantaneously calculates a trajectory that avoids overmodulation at every time step. Simulation and experimental results state the benefits of proposed procedures. [ABSTRACT FROM AUTHOR]

LCL-filter-based grid-tie inverters require damping for the current-loop stability. There are only software modifications in active damping, whereas resistors are added in passive damping. Although passive damping incurs in additional losses, it is widely used because of its simplicity. This paper considers the active damping in medium-voltage parallel inverters for wind turbines. Due to cost reasons, only minimal software changes are allowed and no extra sensors can be used. The procedure must be robust against line-inductance variations in weak grids. Double-update mode is needed so the resonance frequency is under the Nyquist limit. The bandwidth reduction when using active damping is also required to be known beforehand. Moreover, the design procedure should be simple without requiring numerous trial-and-error iterations. In spite of the abundant literature, the options are limited under these circumstances. Filter-based solutions are appropriate and a new procedure for tuning the notch filter is proposed. However, this procedure requires that the resistance of the inductors is known and a novel filter-based solution is proposed that uses lag filters. The lag filters displace the phase angle at the resonance frequency so that the Nyquist stability criterion is fulfilled. Simulations and experiments with a 100-kVA prototype validate the analysis. [ABSTRACT FROM AUTHOR]

Current control is a common feature in power electronics voltage source converters connected to the grid. In this scenario frequency drifts can entail a big loss in performance of these controllers, significantly worsening the quality of the power delivered to the grid. This article focuses on the study and implementation of current control algorithms for DC-AC voltage source converters (VSCs) that are able of both reducing the harmonic contents of the grid current and maintaining the selectivity of the current control against frequency drifts, so that the stability of the system is preserved. Two types of current control techniques are investigated here, namely, resonant and repetitive controllers. A thorough study of alternative implementation structures is carried out whilst spelling out the frequency-adaptive algorithm in each case. Besides, basic guidelines for their software implementation are given and the computational load for each alternative is analyzed. [ABSTRACT FROM AUTHOR]

The presence of an unbalanced voltage at the point of common coupling (PCC) results in the appearance of a negative sequence current component that deteriorates the control performance. Static synchronous compensators (STATCOMs) are well-known to be a power application capable of carrying out the regulation of the PCC voltage in distribution lines that can suffer from grid disturbances. This article proposes a novel PCC voltage controller in synchronous reference frame to compensate an unbalanced PCC voltage by means of a STATCOM, allowing an independent control of both positive and negative voltage sequences. Several works have been proposed in this line but they were not able to compensate an unbalance in the PCC voltage. Furthermore, this controller includes aspects as antiwindup and droop control to improve the control system performance. [ABSTRACT FROM AUTHOR]

A novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage vector based on a generalization of the delayed signal cancellation method is proposed in this paper. The technique is implemented by sampling and storing the instantaneous αβ voltage vector. A mathematical transformation is then proposed through which the current and delayed voltage vectors are combined. It is shown that the proposed transformation has unity gain for the fundamental-frequency positive-sequence voltage vector, while its gain is equal to zero for some chosen components. Cascaded transformations can then be used for eliminating the fundamental-frequency negative-sequence vector, as well as chosen positive- and negative-sequence harmonic vector components and, thus, for accurately obtaining the fundamental-frequency positive-sequence voltage vector. The output of the last transformation block is input to a synchronous reference frame phase-locked loop for detecting frequency and position of the positive-sequence vector. A proposal for making the scheme frequency adaptive is also presented. The good performance of the proposed method is verified with simulations and experiments by using distorted and unbalanced signals, containing fundamental-frequency as well as positive- and negative-sequence harmonic components. The proposed method frequency adaptation capability is also verified. [ABSTRACT FROM AUTHOR]