Stabilising PID tuning for a class of fourth-order integrating nonminimum-phase systems

Fed-batch fermentation processes are commonly used in bioprocessing industry. A fed-batch fermentation process often exhibits integrating/unstable type of dynamics with multiple right-half plane zeros. A class of fourth-order integrating model can be used to adequately represent such a complex dynamics of the fed-batch fermentation process. In this paper, rigorous stability analysis of proportional-integral-derivative (PID) controller based on the Routh-Hurwitz criteria for the fourth-order integrating system is presented. A set of all stabilising PID controller parameter regions is established. Based on these stabilising regions, a general PID controller tuning procedure is proposed for the fourth-order integrating system with two right-half plane zeros. Numerical study shows that based on the proposed tuning procedure, a low-order PID controller can outperform a fifth-order optimal LQG controller in terms of servo and regulatory controls.     

A unified design for feedback-feedforward control system to improve regulatory control performance

The PID controller is widely used in industries because of its simplicity and robustness. A simple approach to improve regulatory control performance is to combine both feedback PID and feedforward controllers. The feedforward controller enables early compensation of a measured disturbance before it can seriously affect the process. The conventionally derived non-ideal feedforward controllers are not often used in practice. The reason is that an ideal feedforward controller based on direct inversion of process model is often not physically realizable. Several non-ideal feedforward control designs have been proposed where some of them involve rather intensive tuning procedure to obtain good disturbance rejection. In this paper, we present a new systematic method for designing a combined feedback-feedforward control system. The proposed design method is easy to use and applicable to stable, unstable and integrating deadtime processes where the ideal feedforward controller is physically not realizable.     

热处理对锐钛矿/金红石混晶TiO2质量分数及光催化性能的影响

采用溶胶凝胶法制备锐钛矿/金红石混合晶型TiO₂,通过晶体结构、表面形貌、元素组成以及光催化性能分析研究热处理对锐钛矿/金红石混晶TiO₂质量分数以及光催化性能的影响。实验结果表明:热处理温度升高以及保温时间延长都能促进锐钛矿向金红石转变,使金红石含量增加;混晶TiO₂的光催化性能高于单一的锐钛矿和金红石TiO₂;550 ℃保温3 h样品有最佳的光催化性能,其锐钛矿的质量分数为40%,金红石质量分数为60%,反应3 h后对罗丹明B的降解率达到84.1%。     

High-performance multi-scale control scheme for stable,integrating and unstable time-delay processes

This paper presents a new multi-scale control scheme which is applicable to both stable and integrating/unstable time-delay processes. The salient feature of the proposed scheme is to decompose a given plant into a sum of basic modes, where an individual sub-controller is specifically designed to control each of these modes. An overall multi-scale controller is then synthesized by combining all the sub-controllers in such a way to achieve good cooperation among the different plant modes as to achieve good nominal performance and performance robustness. Extensive numerical study shows that the proposed multi-scale control scheme provides substantial improvement in control performance/robustness over the classical Smith predictor and some of its well-established variants.     

Organochlorinated pesticide multiresidues in surface sediments from Beijing Guanting reservoir

For the analysis of organochlorine pesticides (OCPs) in sediments and water, a multiresidue analysis method based on gas chromatography with electron capture detection (GC/ECD) was developed. Solid-phase extraction (SPE) using Oasis HLB cartridges was also applied in sample extraction. Mean recoveries were satisfactory with 72-103% and 71-103% for water and sediment, respectively. Twenty-one OCPs were analyzed in water and surface sediment samples from Beijing Guanting reservoir. Total concentrations of 21 OCPs were 16.7-791 ng/l (mean 234 ng/l), 275-1,600 ng/l (mean 644 ng/l), 5250-33,400 ng/kg (mean 13,000 ng/kg) in surface water, pore water and sediment (dry weight), respectively. P, p'-DDE, delta-HCH, aldrin, gamma-HCH and beta-HCH are the most abundant compounds in water while p, p'-DDE, o, p'-DDT, beta-HCH, delta-HCH, p, p'-DDT and aldrin accounted for about 85% of total 21 OCPs in sediment in Beijing Guanting reservoir. Concentrations of OCPs were high both in water and sediment samples in Beijing Guanting reservoir for municipal water supply. The data provides information on the levels and sources of OCPs in Guanting reservoir. The study indicated that measures should be taken to decrease OCPs residues in order to improve the quality of municipal water supply in Beijing.