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This paper examines the accuracy of the zero-order hold (ZOH) model of the digital pulsewidth modulator (DPWM). The influence of the computational delay on the precision of this equivalent DPWM model is discussed in detail. A compensation method is proposed to compensate the deviation of this DPWM model for accurately calculating the stability region with different computational delay and duty-cycle...
The high number of cells employed in a Modular Multilevel Converter represents a challenge for the control hardware. Some authors have proposed the use of digital communications to simplify the assemblage and maintenance in such converters, but the latency they add has undesirable consequences for the closed-loop performance. In this paper, we propose a model-based compensation of the latency that...
Medium/High power converters usually employ low switching frequency to reduce power loss, resulting in large system delay in their control system. The multi-sampling technique is an effective method to reduce the system delay while this will make the system a Linear Periodic Time Varying (LPTV) system. Modeling this kind of system by using LTI modeling method, such as Laplace transform, Z-transform,...
The resonance problems may arise among multi-connected LCL-filtered inverters and make the system instable. The recently proposed GSPWM can reduce the filter order without reducing other performance in large-scale application, which has potential to avoid the resonance. But GSPWM will introduce specific phase delay to PWM sequences and it may influence the response character in different grid conditions...
This paper develops a distributed cooperative control scheme for DC microgrids with time-varying coupling delays in noisy environments. The proposed distributed cooperative control, consisting of distributed primary control and secondary control, will regulate the voltage of microgrids to the desired values and through a sparse communication network with asymmetric communication delays and noise disturbances...
This paper proposes a frequency adaptive discrete Fourier transform (DFT) based repetitive control (RC) scheme for DC/AC converter. DFT-based RC is an improved RC scheme aiming to eliminate waveform distortion on selected harmonics without influencing the overall system stability. However, the traditional DFT-based RC is insufficient to accommodate frequency fluctuation as fractional delay period...
Chatter vibration highly limits the accuracy and the material removal rate of numerical control (NC) machining operations. In this paper, an adaptive spindle speed selection method, based on an analysis using the semi-discretization method, is proposed to avoid and minimize chatter vibration in high-precision NC machining. Moreover, the proposed method is robust to modeling uncertainty and changing...
Unknown delayed systems are present in many domains and control this kind of systems remains a difficult problem. Indeed, we can find theses systems in physics, chemistry, aeronautics, etc. The main problem is that the delay is unknown, and so the model is not exactly well-known. By the way, the use of model-free control (MFC) remains a suitable solution to tackle this problem. This paper deals with...
Grid-connected converters have been widely used in distributed generations. However, the resonance brought by converters in weak grid has been a great threat to system stability. Impedance-based method provides a powerful tool for stability analysis. Active damping is also widely applied to improve system stability. This paper derives the impedance model of grid-connected converter system and analyzes...
DC (Direct Current) microgrid has gained more attention caused by the development of distributed generations and DC loads. The control objectives for DC microgrid are voltage regulation and current sharing. In order to achieve these objectives, consensus based control methods with communication have been extensively studied recently. It is a common strategy to modify the voltage set point of local...
In this paper, we investigate the sampled-data control problem for polynomial sampled-data fuzzy system with time-varying delay. Based on sampled-data technique, a fuzzy controller is designed to guarantee the stability of closed-loop polynomial fuzzy system. By examining the stabilization problem, the Lyapunov-Krasovskii functional (LKF) is adopted and a delay-dependent stabilization condition is...
This paper overviews the literature pertaining to the stability analysis of systems with delay-dependent coefficients, which can arise from various scientific and engineering applications. Research on Stability analysis for systems with a single delay is first reviewed, followed by a discussion of some techniques also applicable to the multiple-delay case. We attempt to provide the main ideas of various...
Transparency and stability issues have been a major concern for haptic tele-operation. Researchers in this area have already shown that a minimum refresh rate of 1 kHz is required to achieve smoothness for human perception in force-feedback experiments. This rate requires the highest priority for real-time applications to achieve transparent haptic tele-presence. As a result, this rate leads to a...
This paper investigates the problem of network-based fault-tolerant controller design for networked control systems (NCSs) in the presence of random delays and data packet dropouts. A novel actuator fault model which is more general and practical than the conventional actuator fault models is developed. Considering this new fault model, the NCSs are firstly modeled as a Markovian jump system (MJS)...
In our physical settings, most of the problems encountered are nonlinear in nature whose solutions can better be captured in fractional space. In this paper, a semi-analytical method is proposed for the approximate-analytical solutions of certain system of time-fractional differential equations (TFDDEs) prompted by proportional delays. The proposed semi-analytical technique is built on the basis of...
This paper investigates the fuzzy H∞ filter design issue for nonlinear systems with time-varying delay. In order to obtain less conservative fuzzy H∞ filter design method, a novel integral inequality is employed to replace the conventional Lebniz-Newton formula to analyze the stability conditions of the filtering error system. Besides, the information of the membership functions is introduced in the...
This paper designs a boundary controller for a reaction-advection-diffusion equation on the cylindrical surface with input delay. We introduce a transport partial differential equation (PDE) to remove the input delay by transforming the time delay into a spatial travelling. Then the system with time delay turns to a cascade system composed of two PDEs without delay. For the cascade system, we design...
Under the weaker assumption on the drift and diffusion terms, this paper proposes a new parameter-dependent state-feedback controller design scheme for a class of stochastic time delay systems. On the basis of stochastic time delay system stability theory, by tactfully choosing a suitable Lyapunov-Krasovskii functional (LKF), the proposed controller can ensure that the closed-loop system is globally...
This paper investigates the receding horizon state estimation for the linear discrete-time system with multi-channel observation delays. The receding horizon estimation is designed by the reorganized observation technique and the linear unbiased estimation method. A batch form and an recursive form for receding horizon estimation are developed based on the reorganized measurements. The estimation...
This paper investigates the mean-square stabilizability of a networked discrete-time linear feedback system with multi-step random delay induced by a communication channel. It is assumed that the probability mass function (PMF) of the random delay is known. According to this model, an averaged channel transfer function and the spectral density of the channel uncertainty caused by the delay are obtained...
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