Robust Control Delay Compensation Method for Grid Connected Inverter Based on Improved Newton Interpolation

This paper investigates the control problem for a class of teleoperation systems with communication delays. The network-induced delays are usually inevitable in teleoperation systems, and may be time varying and unpredictable. Since the conventional Smith predictor is only useful for fixed delays, a novel delay compensation and controller design method is proposed in this paper. The proposed method combines a disturbance rejection controller and a communication disturbance observer (CDOB). Simulations are provided to show the effectiveness and superiority of the proposed delay compensation and controller design method.

Time delay significantly degrades the control performances of semi‐active magneto rheological damper. However, the robust control approaches combined with the Taylor series are difficult to perform time delay compensation because it has strict application conditions. In this study, two Taylor series compound robust control schemes are presented to address the robust control and time delay compensation problems for the semi‐active magneto rheological damper with time delay. The formulation of a quarter vehicle model with a magneto rheological damper is described by a hyperbolic tangent model. Given the mechanical characteristics, an experimental test was conducted to fit the hyperbolic tangent model parameters. As a prototype, the Taylor series‐H2/H∞ control approach is proposed through establishing a first‐order Taylor series‐delay equation in augmented state equation and using the H2/H∞ norms to constrain the predictive control force. Moreover, the Taylor series‐H2/H2 controller is proposed to reduce the conservatism and suppress the predictive control force amplification. Simulation results corroborate the efficacy of both control strategies. Specifically, compared with the Taylor series‐H2/H∞ control, the Taylor series‐H2/H2 control can obtain a better control effect for time delay compensation.

Real-time hybrid simulation (RTHS) plays an important role in obtaining the structural responses under dynamic loads. However, the nonlinearities in physical testing system often induce time-delay, which is detrimental to RTHS. To deal with this issue, a Kalman filter based adaptive delay compensation (KF-ADC) method had been proposed based on the discrete system model, whose parameters is estimated by Kalman filter (KF) algorithm. The delay compensation method was validated through a Benchmark problem in RTHS. This study intends to further investigate the performance of KF-ADC dealing with nonlinear physical substructures (PS). Virtual RTHSs are carried out on PS with bilinear and Bouc-wen restoring force characteristics, respectively. The results of virtual RTHSs reveal that the KF-ADC has an excellent tracking performance for nonlinear physical substructure and is beneficial for improving the accuracy and stability of RTHS.KeywordsReal-time hybrid simulationAdaptive delay compensationKalman filter

Among different factors that threaten the stability of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered inverters in grid-tied mode, the variation of grid impedance and computational delay in digital systems are the most important ones. Often, a control system based on either the inverter- or grid-side current and a combination of impedance estimation and delay compensation methods are used to deal with these challenges. Such control systems are quite effective; however, they often involve a quite high implementation complexity. Especially, computational and pulsewidth modulation delay causes a critical frequency, which may deteriorate the stability conditions in grids with varying grid impedance. To deal with this challenge, a robust approach based on a weighted average current control method is proposed in this article. The suggested control system employs the point of common coupling voltage as a control variable, which increases the system stability in weak grids. Thus, the control system does not need any delay compensation or grid impedance estimation methods, which in turn simplifies the control system. The effectiveness of the proposed method is examined using the experimental results in different case studies.

Traditional phase generated carrier (PGC) schemes require that the carrier phase delay be kept zero and the phase modulation depth be maintained at a certain value; otherwise, serious nonlinear errors will be introduced into the phase demodulation of a sinusoidal phase modulation interferometer. Proposed herein is a robust carrier phase delay extraction method for nonlinear errors compensation of PGC demodulation that mitigates the effect of the interference phase shift. The carrier phase delay is directly extracted by adopting the first-, second-, and fourth-order in-phase and quadrature harmonic components generated by quadrature multi-harmonics frequency down conversion. Further, with the extracted phase delay, real-time compensations for the phase delay and phase demodulation depth are realized simultaneously in PGC demodulation. Theoretical analysis and derivation of the proposed method are given in detail. Simulation and displacement measurement experiments with different phase delays and phase modulation depths are performed to verify the effectiveness of the proposed method. The experimental results demonstrate that the proposed method is able to precisely extract the phase delay and efficiently eliminate the effects of the phase delay and modulation depth instability.

Robust time delay estimation with unknown cyclic frequency in co-channel interference and impulsive noise

The robust synchronization control scheme for flexible resources considering the stochastic and delay response process

For the LCL‐type grid‐connected inverter, when the capacitor voltage feedforward is applied, the delay in the digital control system could change the phase characteristics of capacitor voltage feedback and affect the stability of the system. To solve the problem, a delay compensation method based on lead compensator is proposed in this paper, which can reduce the impacts of control delay on the capacitor voltage full feedforward control system. In this study, a lead compensator is introduced into the feedforward channel to compensate the phase lag, and the compensation function is designed to compensate for the phase margin but not change the system amplitude gain. The proposed strategy can keep the phase margin of the system above 25° when the grid impedance changes from 0 to 2.6 mH (0.1 p.u.), which enhances the robustness of the grid‐connected inverter under weak condition. The grid current distortion caused by grid background harmonics is greatly reduced and is kept within 4%. Moreover, the proposed strategy has fast dynamics while ensuring the system stability. Finally, the simulation and experimental results are presented to verify the effectiveness and robustness of the proposed control strategy.

This paper focuses on the model predictive current control of power converters with the aim of indicating the influence of some system parameters used in predictive control on the load current and load voltage. A model predictive current control algorithm is proposed, specifically directed at the utilization of power obtained from renewable energy systems (RESs). In this study the renewable energy systems model is used to investigate system performance when power is supplied to a resistive-inductive load (RL-load). A finite set-model predictive current control (FS-MPCC) method is developed to control the output current of three-phase, voltage source inverter (VSI). The approximation methods for the derivatives of the model differential equations and delay compensation of model predictive control (MPC) system for power converters are assessed. Simulation results of a two-level, three-phase VSI using FS-MPCC are carried out to show the effects of different approximation methods on the load current and voltage regulation as well as on the predictive current control operation with and without delay compensation for different sampling times. It has been noticed that the ripple in the load currents is considerable when the delay compensation is not accounted for and the delay compensation method that reduces the ripple and operation is similar to the ideal case. It is confirmed that for larger sampling times the delay is noticeable, but when the sampling time is smaller it is not visible.

This paper focuses on the problem of $H_{\infty}$ output tracking control for networked control systems (NeSs) with network-induced long time delays. First, by combining the controlled plant and the reference model, the augmented closed-loop system is established. On the basis of the robust control method and time delay nominal point technique, the exponential uncertainty terms in the sampled system model caused by network-induced long time delays are transformed into sums of nominal terms and norm-bounded uncertainties. Then, by employing the Lyapunov-Krasovskii method, linear matrix inequalities (LMls) technique and discrete Jensen inequality, sufficient conditions for the existence of the $H_{\infty}$ state feedback controller are derived, which guarantee that the augmented closed-loop system is stable and satisfies the prescribed $H_{\infty}$ tracking performance. Finally, the effectiveness of the proposed method is verified by a numerical example.

In this paper, an improved direct finite-control-set model predictive control with delay compensation and simplified computational approach is proposed for active front-end rectifiers. Specifically, an active voltage vector which only requires one exploration is directly selected and applied to avoid the exhaustive exploration for testing all feasible voltage vectors during one switching period. Meanwhile, a delay compensation method is presented. The control delay caused by the calculation effort can be compensated. The performance of the proposed method can be improved. Simulation results are presented to demonstrate the efficacy of the proposed method.

A robust time delay estimation method for ultrasonic echo signals and elastography

Based on zero-order statistics (ZOS), two robust adaptive approaches for time delay estimation (TDE) are introduced in the presence of impulsive noise, referred to as ZOSTDE and NZOSTDE. Through a logarithmic transform, the impulsive signals without finite variance become the logarithmic-order signals. In this case, all of the moments are finite. The ZOSTDE and NZOSTDE algorithm consider this property and the concept of geometric power, then the FIR filter models the two received signals added impulsive noises and its coefficients can be adaptive obtained under least mean square (LMS) error criterion in the logarithmic domain. Accordingly, the estimation of time delay between the two sources is the time index of the maximum in the coefficients. They overcome several shortcomings of algorithms using fractional lower-order moment. Simulation studies show they are robust for very impulsive environments.

Many available signals in the real world are usually weak with impulse noises and/or outliers, and we also need to have higher estimation precision in applications. Our focus of attention is pretty much on integrating robustness and accuracy under lower signal to noise ratio (SNR) with impulse noises. Although traditional fractional adaptive time delay estimation (TDE) methods have higher precision, the results of estimation are unreasonable when the signals contain some impulse noises. While, most proposed robust algorithms later can work well mainly with high SNR. In this paper, considering the practical problem in equipment fault acoustic localization based on TDE methods, an improved robust fractional adaptive time delay estimation method is addressed facing lower SNR conditions. First, the impulse noises are modeled as Alpha stable distribution, and the integer part of TDE is getting by using covariate correlation approach. Then, the integer estimation value is used as initial parameter value of time delay. Covariant sequence is the input of time delay estimator. Next, fractional TDE value is adaptive obtained by iteration under minimum average <i>p</i> norm criterion. Covariant sequence weakens irrelevant noises, meanwhile preserves time delay information between original sequences. Computer simulations and comparative experiments show that improved method has better estimation results. This method is robust and higher precision, and especially under impulse environment and low SNR conditions.

The influence of the active front steering system on the driver’s intention and the trade-off between the robustness and the performance of the active front steering controller have not been adequately addressed by current research studies. A new robust control method based on the normalized left coprime factorization model including uncertainty and perturbations is introduced, and the robustness of this method against high speeds and variations in the cornering stiffness without changing the intention of the driver is guaranteed by the design of the feedforward controller and the feedback controller. A single-step method is adopted to solve the feedforward robust controller and the feedback robust controller. The resulting controllers obtained by the proposed robust control method have a simple structure and do not require online optimization. Furthermore, simulations of the double-lane-change manoeuvre and of braking on a split- μ road are conducted to compare the performance and the stability of the new robust control method with those of the proportional–integral–derivative controller and the standard H∞ controller. Simulation results show that, in comparison with the other two control methods, the established new robust control method can enhance the vehicle stability and handling, and the tracking rapidity is improved by the introduction of feedforward control so that the active steering intervention does not affect the driver’s intention, regardless of the external interferences or emergency evasive manoeuvres.