Helber E. P. de Souza

A Generalized Delayed Signal Cancellation Method for Detecting Fundamental-Frequency Positive-Sequence Three-Phase Signals

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.

A method for extracting the fundamental frequency positive-sequence voltage vector based on simple mathematical transformations

In this paper a novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage is proposed. The method is based on four simple mathematical transformations, two of them in the stationary reference frame, which are able to eliminate odd harmonics from the original signals. The other two transformations are implemented in a synchronously rotating reference frame in order to eliminate even harmonics. 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 voltage vector. The proposed algorithm was verified through simulations and experiments by applying distorted and unbalanced signals, containing positive and negative-sequence components. The results are in agreement with those theoretically predicted and indicate that the proposed scheme has a great potential for using in grid connected converters synchronization algorithms.

Variable-Structure Generalized Delayed Signal Cancellation PLL to Improve Convergence Time

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.

A space-vector discrete Fourier transform for detecting harmonic sequence components of three-phase signals

In this paper, a discrete-time algorithm for separately detecting the positive- and negative-sequence harmonic space-vector components of a three-phase signal is presented. The discrete Fourier transform is applied to the three-phase signals represented by the Clarkes aß vector. The proposed transform outputs the instantaneous values of the fundamental frequency and harmonic component vectors of the input three-phase signals. A recursive algorithm for low-effort online implementation is also presented. The detection performance for variable frequency and inter-harmonic input signals is discussed. The proposed method performance is verified through experiments.

Frequency adaptive phase-sequence separation method based on a generalized delayed signal cancelation method

A new frequency adaptive method for detecting the Fundamental Frequency Positive Sequence (FFPS) voltage vector is proposed in this paper. The analytical developments demonstrate that the proposed method allows obtaining the FFPS αβ voltage vector canceling the effects of fundamental-frequency negative-sequence components, as well as the influences of all harmonic voltage vectors up to 24th order and also dc offsets. A high bandwidth output synchronous reference frame phase locked loop (SRF-PLL) is then used for obtaining the amplitude and position of the fundamental frequency vector. A scheme for making the proposed method adaptive to input frequency variations is also presented. The proposed method performance is verified through simulations and experiments.

FPGA implementation of a sequence separation algorithm based on a generalized delayed signal cancelation method

A system-on-chip fundamental-frequency positive-sequence detector based on FPGA technology is proposed in this paper. The method is implemented by using the instantaneous alphabeta voltage vector and also this vector delayed in time. A mathematical transformation is then implemented through which the original and delayed voltage vectors are combined. Cascaded transformations are then 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 (SRF-PLL) for detecting frequency and position of the positive-sequence vector. A discrete fixed-point FPGA-based design of the method described is proposed. The approach is implemented and tested with a Spartan 3E (XC3S500) FPGA.

The SVFT-Based Control

In this paper, a controller based on the space vector Fourier transform (SVFT) is proposed. The vector controller is implemented in the stationary αβ 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.

Low effort digital filters for fast sequence components separation of unbalanced and distorted three-phase signals

In this paper, two methods for determining 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 cancelation such as computational burden and response time for different possible implementations, frequency adaptation schemes, stability of recursive implementation and rounding error effects are discussed. Simulations and experiments are presented in order to verify the performances and illustrate the theoretical conclusions.

A GDSC-Based Technique to Distinguish Transformer Magnetizing From Fault Currents

This paper presents a novel technique to distinguish a transformer magnetization inrush current from a fault current. The proposed scheme is based on the behavior of fundamental and second-harmonic positive- and negative-sequence components. These four components are computed by using generalized delayed signal cancelation (GDSC). After a transient analysis for the GDSC filters, related to the behavior of those four components detection, some features were proposed. These features depict the trajectory change of the most relevant components in the

Frequency adaptivity improvement in GDSC-PLL

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