船舶电力推进永磁同步电机矢量控制系统仿真研究

在船舶电力推进系统的MATLAB/SIMULINK仿真模型为基础,重新提出六相永磁同步电机的矢量控制相关方案,通过对六相永磁同步电机和船舶负载系统的仿真来验证模型,最终表明六相永磁同步电机的矢量控制方案,满足船舶电力推进系统的动态性能要求。     

船舶电力推进技术概况

本文主要介绍了船舶电力推进的特点和结构，在电力推进系统中常用的推进器，以及船舶电力推进的关键技术。阐述了船舶电力推进是今后船舶动力的发展方向，以及应该解决的技术难点。     

船舶机械电力推进系统的探讨

随着海上石油开采的不断发展，船舶也向着多功能化的方向发展，因此对船舶总体设计重要部分之一的电力系统也有了更高的要求。由于电力推进船舶具有良好的性能和明显的节能效果，因此对电力推进系统的研究具有重要的意义。     

电力推进船舶电能质量探讨

船舶电力推进技术的兴起是现代电力电子技术进步的必然结果。随着电力电子器件的改进、现代控制理论和谐波抑制等技术的发展及推进电机控制技术的不断完善,必将进一步降低电力推进船舶的初投资,为电力推进技术开拓更广阔的市场。     

船舶推进装置气囊隔振系统对中可控性问题研究

本文对船舶推进装置气囊隔振系统对中可控性问题进行了系统研究。通过建立控制响应计算模型、多目标对中控制模型,提出了对中可控性分析方法,使得控制系统能够根据不同工作情况自主调整控制系统工作参数,以保持良好的对中控制收敛性能,并通过实验验证了该方法的可行性。该方法已应用于某型船舶推进装置气囊隔振系统,成功实现了气囊柔性支撑状态下的推进装置高效隔振。     

潜艇电力推进装置的动态模型辨识

将系统辩识的方法应用到潜艇电力推进系统的动态特性的分析中，辩识算法采用递推增广矩阵法(RELS)，并采用变遗忘因子，以改善系统的跟踪性能，研究对象为一模拟电力推进机组，在实验数据的基础上建立了该系统励磁控制下的动态模型。     

有机朗肯循环发电系统中换热过程模拟与系统经济性分析

有机朗肯循环发电系统中的能量主要损失在换热设备中。换热设备性能对其发电效率有着直接的影响。为提高有机朗肯循环发电系统的经济性,以最小电力生产成本为目标函数,建立经济性模型,并以实际搭建的有机朗肯循环发电系统对模型进行优化,对安装预热器和过热器的经济性进行分析。研究结果表明:电力生产成本主要受热源介质流量、冷却水流量、系统发电功率、蒸发器节点温差及蒸发温度的影响;在有机朗肯循环发电系统中,尤其是在中大型发电系统中,预热器的安装是经济可靠的;过热器的安装对电力生产成本的增加值较小,而其可提高系统的稳定性、延长系统的使用寿命。     

换热通道对固体蓄热电加热装置温度分布均匀性的影响

针对固体蓄热电加热装置在运行中电加热丝时常烧断的问题，依托于4 MW蓄热装置，提出保持蓄热体组质量和换热面积不变，改变换热通道数目的方案，分别对原装置模型和改变换热通道数目后的装置模型进行数值模拟，对比分析蓄热体温度和换热通道内壁温度。结果表明：当换热通道数目为8条时，蓄热体组垂直于换热通道方向的蓄热体和换热通道内壁温差明显减小，有效改善温度分布不均匀的问题。     

船舶推进轴系变结构控制

以船舶主推进轴系为研究对象,在变结构控制理论和设计方法的基础上,对主推进轴系的变结构控制方法进行研究。考虑到推进轴系在螺旋桨处的位移响应最大,在螺旋桨部位设置主动控制作动器,对推进轴系进行振动控制,并以主推进系统的弹性体动力学模型为基础,建立系统的变结构控制方法。采用单位向量控制形式的最终滑动模态控制器,并采用二次型最优控制理论设计最终滑动模态的切换函数。最后以一个带有六个弹性支撑的推进轴为例进行仿真计算。实例分析指出:变结构控制对于推进轴系的振动控制具有显著的效果。     

强化换热管实验台测控系统的研制

研制换热器用强化换热管实验台的测控系统。针对管内蒸发实验,构建热水循环系统、乙二醇循环系统和制冷剂循环系统,设计系统中流体温度、压力、流量的采集方案和控制方案,采用Delphi编程工具编制测控系统软件,实现对实验台的控制、数据采集和数据处理。     

Improving the performance of CUSUM charts

The control chart is an important statistical technique that is used to monitor the quality of a process. Shewhart control charts are used to detect larger disturbances in the process parameters, whereas CUSUM and EWMA charts are meant for smaller and moderate changes. Runs rules schemes are generally used to enhance the performance of Shewhart control charts. In this study, we propose two runs rules schemes for the CUSUM charts. The performance of these two schemes is compared with the usual CUSUM, the weighted CUSUM, the fast initial response CUSUM and the usual EWMA schemes. The comparisons revealed that the proposed schemes perform better for small and moderate shifts, whereas they reasonably maintain their efficiency for large shifts as well. Copyright © 2010 John Wiley & Sons, Ltd.     

Two CUSUM schemes for simultaneous monitoring of parameters of a shifted exponential time to events

Two‐parameter (shifted) exponential distribution is widely applied in many areas such as reliability modeling and analysis where time to failure is protected by a guaranty period that induces an origin parameter in the exponential model. Despite a large volume of works on inferential aspects of two‐parameter exponential distribution, only few studies are done from the perspective of process monitoring. In the modern production process, where items come with a warranty, we often encounter shifted‐exponential time between events from consumers' perspective, and therefore, in this paper, we propose two CUSUM schemes for joint monitoring of the origin and scale parameters based on the Maximum Likelihood estimators. We study the in‐control behavior of the proposed procedures via Markov chain approach as well as applying Monte Carlo. We provide detailed implementation strategies of the two schemes along with the follow‐up procedures to identify the source of shifts when an out‐of‐control signal is obtained. We examine the performance properties of CUSUM schemes and find that the two proposed schemes offer performance advantages over the Shewhart‐type schemes especially for monitoring small to moderate shifts. Further, we provide some guidance for choosing the appropriate schemes and study the effect of reference parameter k of the CUSUM schemes. We also investigate the optimal design of reference values both in known and unknown shift cases. Finally, two examples are given to illustrate the implementation of the proposed approach.     

Enhancing the performance of EWMA charts

Control charts are extensively used in processes and are very helpful in determining the special cause variations so that a timely action may be taken to eliminate them. One of the charting procedures is the Shewhart‐type control charts, which are used mainly to detect large shifts. Two alternatives to the Shewhart‐type control charts are the cumulative (CUSUM) control charts and the exponentially weighted moving average (EWMA) control charts that are specially designed to detect small and moderately sustained changes in quality. Enhancing the ability of design structures of control charts is always desirable and one may do it in different ways. In this article, we propose two runs rules schemes to be applied on EWMA control charts and evaluate their performance in terms of the Average Run Length (ARL). Comparisons of the proposed schemes are made with some existing representative CUSUM and EWMA‐type counterparts used for small and moderate shifts, including the classical EWMA, the classical CUSUM, the fast initial response CUSUM and EWMA, the weighted CUSUM, the double CUSUM, the distribution‐free CUSUM and the runs rules schemes‐based CUSUM. The findings of the study reveal that the proposed schemes are able to perform better than all the other schemes under investigation. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical analysis of three-time-level finite difference schemes for unsteady diffusion–convection problems

For the linear diffusion–convection model problem, this paper develops the numerical analysis of two classes of three-time-level second order finite difference schemes: weighed schemes similar to two-step schemes for differential equations and LF schemes based on the classical conservative approximation of the wave equation. As in our paper devoted to two-level schemes, Fourier Analysis is an essential tool which yields several key properties (stability, dissipation, numerical diffusion and dispersion). It also permits the analysis of parasitic solutions characteristic of three-level schemes and their control in terms of the starting scheme. The analysis is completed by giving results on the accuracy, positivity and parabolicity of the numerical schemes. The main conclusions are the expected superiority of these schemes over two-level schemes when the diffusion phenomenon is not negligible (cell Reynolds number less than 1) and the very limited possibilities of obtaining satisfactory numerical results (even with upstream differencing) when convection is strongly predominating.     

CUSUM Schemes for Monitoring Prespecified Changes in Linear Profiles

Because of the characteristics of a system or process, several prespecified changes may happen in some statistical process control applications. Thus, one possible and challenging problem in profile monitoring is detecting changes away from the ‘normal’ profile toward one of several prespecified ‘bad’ profiles. In this article, to monitor the prespecified changes in linear profiles, two two‐sided cumulative sum (CUSUM) schemes are proposed based on Student's t‐statistic, which use two separate statistics and a single statistic, respectively. Simulation results show that the CUSUM scheme with a single statistic uniformly outperforms that with two separate statistics. Besides, both CUSUM schemes perform better than alternative methods in detecting small shifts in prespecified changes, and become comparable on detecting moderate or large shifts when the number of observations in each profile is large. To overcome the weakness in the proposed CUSUM methods, two modified CUSUM schemes are developed using z‐statistic and studied when the in‐control parameters are estimated. Simulation results indicate that the modified CUSUM chart with a single charting statistic slightly outperforms that with two separate statistics in terms of the average run length and its standard deviation. Finally, illustrative examples indicate that the CUSUM schemes are effective. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of Model Accuracy on Residual Control Charts

Residual control charts are acknowledged to be effective tools for statistical process control of multistage processes. In these monitoring procedures, the models on the stage‐wise correlation should be first derived before the control charts are implemented. Therefore, the monitoring performance is inevitably affected by the model fitting scheme. Most of the previous works are under the assumption that the derived models represent the process behavior perfectly. Far less is known about the effects of the model inaccuracy on the monitoring performance. To investigate the effects of the underlying models on the monitoring performance, residual control charts based on two different modeling schemes are compared in this paper. The results indicate that the charting performance is correlated with the model fitting schemes. That is, a more accurate model will significantly increase the detection power and decrease the false alarm rate as well. Copyright © 2015 John Wiley & Sons, Ltd.     

Adaptive optimal tuning of a general class of stable LTI systems with restricted inputs

The problem addressed is one of model reference adaptive control (MRAC) of asymptotically stable plants of unknown order with zeros located anywhere in thes-plane except at the origin. The reference model is also asymptotically stable and lacking zero(s) ats = 0. The control law is to be specified only in terms of the inputs to and outputs of the plant and the reference model. For inputs from a class of functions that approach a non-zero constant, the problem is formulated in an optimal control framework. By successive refinements of the sub-optimal laws proposed here, two schemes are finally designed. These schemes are characterized by boundedness, convergence and optimality. Simplicity and total time-domain implementation are the additional striking features. Simulations to demonstrate the efficacy of the control schemes are presented. This paper is dedicated to Dr R M Umesh.     

Design and comparison of some Shewhart‐type schemes for simultaneous monitoring of Weibull parameters

Weibull distribution is one of the most important probability models used in modeling time between events, system reliability, and particle sizes, among others. Therefore, efficiently and consequently monitoring certain changes in Weibull process is considered as an important research topic. Various statistical process monitoring schemes have been developed for monitoring different process parameters, including some for Weibull parameters. Most of these schemes are, however, designed to monitor and control a single process parameter, although there are two important model parameters for Weibull distribution. Recently, several researchers studied various schemes for jointly monitoring the mean and variance of a normally distributed process using a single plotting statistic. Nevertheless, there is still dearth of researches in joint monitoring of non‐normal process parameters. In this context, we develop some control schemes for simultaneously monitoring the scale and shape parameters of processes that follow the Weibull distribution. Implementation procedures are developed, and performance properties of various proposed schemes are investigated. We also offer an illustrative example along with a summary and recommendations.     

Adaptive Exponentially Weighted Moving Average Schemes Using a Kalrnan Filter

Two adaptive exponentially weighted moving average control schemes are proposed. The weighting coefficient is updated using a Kalman filter algorithm. The two test statistics incorporate an integral error term. Simulated average run lengths indicate the proposed schemes are sensitive to small process shifts, but do tend to ring false alarms when there is no process change. For medium and large process changes and trends their performance is comparable to that, of Lucas's combined Shewhart-CUSUM control scheme. Some application of the proposed schemes to correlated data indicate robust performance. Conclusions are drawn that the Kalman filter used to model a process together with a detection mechanism applied to the residuals closely resembles the work done in control theory.     

Enhancing the Performance of Exponentially Weighted Moving Average Charts: Discussion

Abbas et al. (Abbas N, Riaz M, Does RJMM. Enhancing the performance of EWMA charts. Quality and Reliability Engineering International 2011; 27(6):821–833) proposed the use of signaling schemes with exponentially weighted moving average charts (named as 2/2 and modified ? 2/3 schemes) for their improved design structures. A two‐sided control structure of these schemes is given in the paper. The computational results in some of the tables of that paper for modified ? 2/3 are mistakenly given for the one‐sided control structure. The corrected two‐sided results are provided here. It is noticed that the superiority of the proposed scheme over the classical exponentially weighted moving average chart remains but is less pronounced. Copyright © 2014 John Wiley & Sons, Ltd.