Search

In this article, a new discrete-time control strategy for three-phase three-wire shunt active power filters (APFs) is presented, based on a mathematical model in the stationary reference frame. It involves a feedback-linearization-type approach to control the filter currents, whereby the voltage control loop is decoupled from the current control. The voltage control loop is for controlling the dc-side voltage of the pulsewidth modulation (PWM) converter, and employs a proportional–integral (PI) controller to generate the reference amplitude for the compensated grid currents. An important feature of the proposed control strategy is the compensation of the one-sampling-period delay caused by microcontroller computation using a finite impulse response (FIR) predictor. This predictor is designed to accomplish one-step-ahead prediction of the control variable, which is the PWM converter's switching function space vector. Furthermore, the FIR predictor is optimized so that the low-order harmonics in the control variable are predicted with minimal error. The proposed control strategy is analyzed to obtain the steady-state filter current error and ranges for the PI controller gains for stability. Simulation and experimental results are presented to show the effectiveness of the proposed shunt APF. [ABSTRACT FROM AUTHOR]

In this paper, a new robust adaptive beamforming algorithm is proposed with increased attenuation of interference signals. This is achieved by reconstructing the interference-plus-noise covariance matrix using the Capon spatial power estimator. In the latter the total sample covariance matrix is replaced by its square, which is shown to enhance the interference rejection capability of the minimum variance distortionless response beamformer. Also, a new method for estimating the desired signal's steering vector is introduced based on reconstructing the desired signal's covariance matrix and employing the discrete Fourier transform of the correlation sequence. The effectiveness of the proposed method is demonstrated by numerical results. [ABSTRACT FROM AUTHOR]

In this paper, a new Lyapunov-based model predictive controller is proposed for a 7-level packed U-cell (PUC7) grid-connected inverter. A cost function of the proposed model predictive controller is designed from the system stability point of view, inspired by the Lyapunov control theory. The proposed controller eliminates the need for gains that are associated with cost function coefficients, as seen in classical model predictive control based controllers. Therefore, the control design problem is significantly simplified. In addition, the average switching frequency is also reduced, as shown in both simulation and experimental results, leading to a reduction in switching losses. Simulation and experimental tests, on a PUC7 lab prototype, demonstrate the excellent performance of the proposed control system, in terms of high disturbance rejection, robustness to parameter mismatches, and fast dynamic response. Such features qualify the proposed control strategy as a good candidate for grid-tied applications. [ABSTRACT FROM AUTHOR]

In this paper, a model-based current control strategy with virtual time constant is proposed for three-phase grid-connected LCL-filtered voltage source inverters. The proposed control strategy is based on controlling the inverter currents in the rotating dq frame by using current-oriented proportional-integral (PI) controllers rather than voltage-oriented PI. The PI controllers determine the inverter current references in the d- and q-axes by regulating the grid current. It is shown that the proposed strategy decouples the inverter current from other variables provided that the inverter-side inductance and its resistance values used in the control variable match the actual values in the system. In addition, the virtual time constant is introduced in the control variables to offer flexibility for adjusting the inverter current dynamics as desired. Moreover, the integral gain of PI controller has the ability to keep the LCL-resonance peak below 0 dB. Unlike the existing methods, the proposed strategy does not require a dedicated active damping. Computer simulations and experimental studies show that the proposed control strategy exhibits a good performance in achieving fast dynamic response and sinusoidal grid current with low THD under balanced, unbalanced, and distorted grid conditions. [ABSTRACT FROM AUTHOR]

In this paper, a new robust adaptive beamforming technique based on a modification of the robust Capon beamforming approach is introduced. It is shown that this technique leads to an approximate eigenspace projection-based array steering vector estimation. The steering vector is estimated as an approximation for the orthogonal projection of the presumed steering vector of the desired signal onto the signal-plus-interference subspace. Also, it is demonstrated that the optimal diagonal loading factor corresponds to the minimum of the estimated beamformer output power. Furthermore, the formulation of the proposed method provides the possibility of estimating the direction-of-arrival of the desired signal. This estimation is then used to update the presumed steering vector. An important virtue of the proposed method is its better or comparable performance with less computational complexity than the recent existing methods. [ABSTRACT FROM AUTHOR]

The recently proposed Recursive Inverse (RI) algorithm has shown a significant performance improvement compared to that of the Recursive Least Squares (RLS) algorithm, in various noise environments. However, both algorithms fail to converge in certain impulsive noise environments, especially if the Signal-to-Noise Ratio (SNR) is low. In this paper, a Robust RI algorithm is proposed. Analytical results show that robustness against impulsive noise is achieved by choosing the weights on the basis of the L norms of the autocorrelation matrix and the cross-correlation vector. Simulation results confirm that the proposed algorithm provides an improved performance, with a reduction in computational complexity, compared to those of the RLS and the Robust RLS in white and correlated impulsive noise. [ABSTRACT FROM AUTHOR]

Abstract: A nonlinear dynamical model of a memoryless nonlinear gradient IIR adaptive notch filter for estimating the frequency of a noisy sinusoid is derived. The model is verified through simulations, where simulated responses of the estimated frequency are compared with the responses obtained from the model with good agreement. Convergence properties of the filter are studied using the model, and maximum step sizes and initial frequency ranges for convergence are determined. The performance of the adaptive filter in tracking a time-varying signal frequency is also examined. [Copyright &y& Elsevier]

A new approach to the sliding-mode control of single-phase uninterruptible-power-supply inverters is introduced in continuous time. A three-level hysteresis sliding function is used to directly control the inverter switches, with the result that a transistor is switched during a half-cycle while it remains either on or off during the other cycle. An expression is derived for the predicted switching frequency. The performance of the proposed control method has been tested through computer simulations and experiments under different loads (a resistive load and a diode bridge rectifier load). Simulation and experimental results verify the correct operation of the proposed control strategy. In addition, the switching frequency prediction is seen to be quite accurate. [ABSTRACT FROM AUTHOR]

Several methods for dc voltage control of single-phase pulse width modulation ac/dc voltage-source converters are known. They differ in their performance and the complexity of the hardware and software they use. One of the basic requirements of the control method is a nearly sinusoidal input current with unity power factor. However, global stability of the converter is not guaranteed by the methods proposed so far. This paper describes a new control method based on Lyapunov's direct method. It is shown that the converter can be stabilized globally to handle large signal disturbances. The closed-loop system not only ensures stability, but also exhibits excellent transient response for abrupt changes in the load. More importantly, the proposed control method can keep the advantages and remove the disadvantages of the existing methods. Computer simulations and experiments are presented to show the effectiveness and applicability of the proposed control method for the converter. [ABSTRACT FROM AUTHOR]

Presents a novel current-control-based control strategy, obtained in stationary frame, for a three-phase pulsewidth-modulated ac/dc voltage-source converter. System modeling; Characteristic equation of the system; Use of the error voltage by a proportional plus integral controller to generate a command signal for the input line current amplitude.

Presents a study in which a control law for three-phase pulsewidth modulation (PWM) alternating current/direct current (ac/dc) voltage-source converters is described based on Lyapunov's stability theory. Stabilization of the converter; Information on the optimal ac/dc converter; What are the main objectives in the control of the PWM ac/dc converters; In-depth look at the proposed control strategies; Advantages and disadvantages of these control strategies.

This article proposes a Lyapunov-based model predictive control (MPC) design for a dual output multilevel rectifier. The investigated topology, a seven-level packed U-cell (PUC7) converter, is selected based on its high reliability, compactness, and low cost. The proposed controller has the following advantages over the conventional MPC controllers: First, no gain tuning is required; second, easy implementation; and third, reduced number of sensors (the load currents are estimated using the mathematical model of the PUC7 rectifier). Simulation and experimental results are provided to show the high dynamic performance and effectiveness of the Lyapunov-based MPC controller in tracking the output voltage references under grid change and parameters mismatch conditions. [ABSTRACT FROM AUTHOR]

In this article, a multi-input multi-output sliding mode control methodology with constant switching frequency for single-phase quasi-Z-source inverters (qZSI) is proposed. The mathematical model of the entire system is derived in state-space form. The proposed sliding mode control is capable of controlling both dc and ac sides of the system concurrently. Unlike the existing methods, the proposed control does not require proportional-integral controller in the dc-side. Furthermore, it offers several advantages, such as simple implementation, reduced gain requirement, robustness against system parameters, and zero steady-state error in the load voltage. The fixed switching frequency is attained by altering the sliding manifold behavior inside a boundary layer. The power balance equation is used to generate the dc-side inductor current reference. The feasibility of the proposed control method is investigated experimentally when qZSI feeds linear and nonlinear loads. [ABSTRACT FROM AUTHOR]

This paper proposes an effective sliding mode controller (SMC) for a grid-connected 7-level packed U-cell (PUC7) inverter. The aim is to design a simple controller that deals effectively with the complex control problem of the PUC7 inverter (multiobjective control problem). The selection of the control actions is achieved according to the system state error at every sampling time, regardless of the previous values, which makes the control technique model-independent. The control algorithm evaluates online two cost functions (one for each state error), which are derived on the basis of sliding mode theory, and it selects the optimal control input in order to satisfy the reaching conditions of the two cost functions. Compared with the existing solutions, the proposed SMC technique ensures lower average switching frequency by tuning the hysteresis bandwidth of the capacitor-voltage error. The fast implementation, needless of gains tuning, and simple design procedure are the main features of the proposed algorithm. Simulation and experimental results are presented to prove the effectiveness of the proposed technique in controlling the PUC7 inverter with high dynamic performance and robustness against disturbances and parameters mismatch. [ABSTRACT FROM AUTHOR]

This paper presents a sliding-mode control (SMC) strategy for single-phase grid-connected \mboxLCL-filtered voltage source inverters (VSIs) with double-band hysteresis scheme. The proposed SMC is simpler than the existing SMC methods devised for grid-connected VSIs since its sliding-surface function requires the sensing of capacitor voltage and grid current only. In addition, a double-band hysteresis scheme which ensures the switching of a transistor in the VSI during a half cycle while it remains either on or off in the other half cycle of the fundamental period is used to mitigate the switching frequency. Furthermore, the analytical expressions for the instantaneous and average switching frequencies are derived. The theoretical considerations and analytical results are verified through computer simulations and experimental results obtained from a 3.3-kW system. Simulation and experimental results show that the proposed SMC strategy exhibits an excellent performance in achieving the required control objectives such as fast dynamic response, robustness, sinusoidal grid current with low total harmonic distortion, and simplicity in a practical implementation. [ABSTRACT FROM PUBLISHER]

• Design a robust adaptive beamforming method for uniform linear arrays based on a virtual sensor. • A novel approach to reconstruct the IPNC matrix using a low-complexity spatial sampling process (LCSSP). • The power spectrum sampling is realized by a proposed projection matrix orthogonal to the signal subspace that retains the interference-plus-noise in a higher dimension. • A new robust adaptive beamforming algorithm is developed. The performance of robust adaptive beamforming (RAB) based on interference-plus-noise covariance (IPNC) matrix reconstruction can be degraded seriously in the presence of random mismatches (look direction and array geometry), particularly when the input signal-to-noise ratio (SNR) is high. In this work, we present a RAB technique to address covariance matrix reconstruction problems. The proposed RAB technique involves IPNC matrix reconstruction using a low-complexity spatial sampling process (LCSSP) and employs a virtual received array vector. In particular, the power spectrum sampling is realized by a proposed projection matrix in a higher dimension. The essence of the proposed technique is to avoid reconstruction of the IPNC matrix by integrating over the angular sector of the interference-plus-noise region. Simulation results are presented to verify the effectiveness of the proposed RAB approach. [ABSTRACT FROM AUTHOR]