Chattering-Free Robust Adaptive Sliding Mode Speed Control for Switched Reluctance Motor

This study describes an adaptive sliding mode control (ASMC) for the control of switched reluctance motor (SRM). The main objective is to minimize torque ripples with controller effort smoothness while the system is under perturbation by structured uncertainties, unknown parameters, and external disturbances. The control algorithm employs an adaptive approach to remove the need for prior knowledge within the bound of perturbations. This is suitable for tackling the chattering problem in the sliding motion of ASMC. In order to achieve control effort smoothness and more effective elimination of chattering, the algorithm then incorporates proper modifications in order to build a chattering-free robust adaptive sliding mode control (RASMC) using Lyapunov stability theory. A final advantage of the algorithm is that system stability and error convergence are guaranteed. The effectiveness of the proposed controller in improving robustness and minimizing ripples is demonstrated by numerical simulation. Experimental validation is used to demonstrate the efficiency of the proposed scheme. The results indicate that RASMC provides a superior performance with respect to speed tracking and disturbance rejection over the conventional sliding mode control (CASMC) in the face of uncertainties in model and dynamic loads

Stabilization of DC–DC buck converter with unknown constant power load via passivity-based control plus proportion-integration

Abstract It is known that constant power load (CPL) may cause a negative impedance, which seriously affects the stability of power system. In this paper, a new control algorithm for DC–DC buck converter feeding unknown CPL is proposed. First, under the assumption of known extracted power load, the standard passivity–based control (PBC) is presented to reshape the system energy and compensate for the negative impedance and a proportion‐integration (PI) action around passive output is added to improve disturbance rejection performance, which forms the PBC plus PI (PBC+PI). Then, a parameter estimation algorithm is developed, based on immersion and invariance (I&I) technique, in order to online estimate the extracted power load. In the next step, the online estimation scheme is adopted to construct an adaptive strategy. Finally, the stability analysis of the cascaded system containing a closed‐loop control system and observer error dynamics is conducted. Simulation and experimental results are demonstrated to validate the performance of the proposed controller

Passivity-based Control of Switched Reluctance-based Wind System Supplying Constant Power Load

This paper presents a passivity-based control (PBC) scheme for the switched reluctance generator (SRG) in small-scale wind energy conversion systems for dc microgrid applications. The main objective is to stabilize the output voltage in case the system supplies constant power loads (CPLs) and operates with maximum power point tracking (MPPT). Stability improvement and dc-link ripple reduction in the presence of CPLs is achieved using system-level modeling of SRG-based dc microgrid through the Euler-Lagrange system (ELS) from the viewpoint of the machine physical structure. Compared with other control methods, the proposed MPPT method based on passivity-based speed controller employs the back electromotive force (EMF) in the generation process as a position-dependent voltage source to overcome the major challenge of SRG complicated uncertain dynamic model. To deal with the time-varying inductance and back EMF of SRG, an adaptation mechanism is incorporated in the proposed adaptive PBC and the control design is constructed by using the Lyapunov theorem where the closed-loop stability is ensured. The effectiveness of the proposed method in avoiding instability effects of SRG and CPL with voltage ripple reduction and precise wind turbine speed tracking is investigated with simulation results and validated with experimental by using a four-phase, 8/6 SRG drive system

The Prevalence of Hepatitis B Virus Surface Antigen (HBsAg) Variations and Correlation with the Clinical and Serologic Pictures in Chronic Carriers from Khorasan Province, North-East of Iran

This study was designed to determine the correlation of hepatitis B virus surface Ag (HBsAg) variations with the clinical/serological pictures among chronic HBsAg positive patients. The surface gene (S-gene) was amplified and directly sequenced in twenty-five patients. Eight samples (group I) contained at least one mutation at the amino acid level. Five showed alanine aminotransferase (ALT) levels above the normal range of which only one sample was anti-HBe positive. Group II (17 samples) did not contain any mutation, 4 were anti-HBe positive and 9 had increased ALT levels. In both groups, from a total of 18 mutations, 5 (27.5%) and 13 (72.5%) occurred in anti-HBe and HBeAg positive groups respectively. The small number of amino acid mutations might belong to either the initial phase of chronicity in our patients; or that even in anti-HBe positive phase in Iranian genotype D-infected patients, a somehow tolerant pattern due to the host genetic factors may be responsible

Risk of gastric non-cardia cancer associated with serum ghrelin presented as either quintiles or continuous variable before and after adjustment for serum PG I/II ratio, <i>H.pylori</i> status and smoking.

<p>Risk of gastric non-cardia cancer associated with serum ghrelin presented as either quintiles or continuous variable before and after adjustment for serum PG I/II ratio, <i>H.pylori</i> status and smoking.</p

Risk of esophageal squamous cell carcinoma associated with serum ghrelin presented as either quintiles or continuous variable before and after adjustment for serum PG I/II ratio, <i>H.pylori</i> status and smoking.

<p>Risk of esophageal squamous cell carcinoma associated with serum ghrelin presented as either quintiles or continuous variable before and after adjustment for serum PG I/II ratio, <i>H.pylori</i> status and smoking.</p

Frequency of studied risk factors in cases and their matched controls for gastric and esophageal cancers by anatomical and histological classification.

<p>Frequency of studied risk factors in cases and their matched controls for gastric and esophageal cancers by anatomical and histological classification.</p