In this study, an inland reservoir water quality parameters’ inversion model was developed using a back propagation (BP) neural network to conduct reservoir eutrophication evaluation, according to ...multi-temporal remote sensing images and field observations. The inversion model based on the BP neural network (the BP inversion model) was applied to a large inland reservoir in Jiangmen city, South China, according to the field observations of five water quality parameters, namely, Chlorophyl-a (Chl-a), Secchi Depth (SD), total phosphorus (TP), total nitrogen (TN), and Permanganate of Chemical Oxygen Demand (CODMn), and twelve periods of Landsat8 satellite remote sensing images. The reservoir eutrophication was evaluated. The accuracy of the BP inversion model for each water parameter was compared with that of the linear inversion model, and the BP inversion models of two parameters (i.e., Chl-a and CODMn) with larger fluctuation range were superior to the two multiple linear inversion models due to the ability of improving the generalization of the BP neural network. The Dashahe Reservoir was basically in the state of mesotrophication and light eutrophication. The area of light eutrophication accounted for larger proportions in spring and autumn, and the reservoir inflow was the main source of nutrient salts.
To improve the suppression ability of uncertain disturbance of the sliding mode control driving system of the surface-mounted permanent magnet synchronous motor (SPMSM) and to reduce the chattering ...of the control output, a robust sliding mode control strategy with an improved power reaching law (IPRL) is proposed in this paper. Compared with the traditional fast power reaching law (FPRL), the IPRL incorporates the sum of the power terms of the system state variables into the conventional power terms, and uses hyperbolic tangent saturation function to replace the piecewise function, which can effectively suppress the sliding mode chattering and improve the convergence speed of the system state to the sliding mode surface. Furthermore, the robust sliding mode speed controller and sliding mode current controller of the SPMSM are designed separately with the IPRL, and detailed simulation verification is carried out to reveal the effectiveness of the IPRL. Simulation and experimental results show that compared with the FPRL, the proposed IPRL can reduce the inherent chattering phenomenon in sliding mode control, and the IPRL-based speed and current control strategy can effectively improve the dynamic performance and robustness of the system.
Permanent magnet synchronous motor (PMSM) possesses the advantages of low power loss, high power density and high torque density and, hence, has achieved broad applications in both industrial drives ...and home appliances. With the increasing demands for high power density, the PMSM often operates at high speed and high frequency, leading to high power loss and temperature rise. Consequently, proper consideration of power loss, including the core loss, has attracted much attention for the modelling, designing, controlling and optimizing of PMSMs. However, the widely used equivalent circuit model, capable of providing good analysis results with fast calculation, often ignores the core loss, which may lead to unsatisfactory motor performance. This paper aims to investigate the development of equivalent circuit models, with predictable core loss for PMSMs, and proposes novel equivalent circuit models, which improve the core loss prediction accuracy in the load conditions. Some thoughts about the further improvement of the models are proposed and discussed.
Thanks to the merits of superior dynamic response capability and current tracking performance, the deadbeat predictive current control (DPCC) has become a research hotspot for the permanent magnet ...synchronous motor (PMSM) drive system. However, DPCC is a model parameter sensitive control method. If there is a motor parameter mismatch, the performance of the DPCC drive system in terms of expected voltage vector, current harmonics, and torque ripple would be influenced. In this paper, firstly, a novel power sliding mode reaching law is proposed, which shortens the convergence time of the system state no matter what the initial state is. Then, an improved non-homogeneous disturbance observer (NHDO) with the proposed power sliding mode reaching law is established, which guarantees d-q axis current errors converge to zero when the PMSM drive system suffers uncertain disturbances, such as motor parameter mismatch. Finally, an improved DPCC using the novel stator current and disturbance observer, which includes the proposed power sliding mode reaching law and NHDO, is established. Hence the accuracy of the predicted current increases significantly, and voltage vectors can be immediately compensated once disturbances occur. Both simulation and platform experiments verify that the improved DPCC can maintain the current tracking performance with lower current ripples than the traditional DPCC when the major motor parameters mismatch. The proposed novel stator current and disturbance observer may also enhance the PMSM's drive performance under other control strategies.
Abstract
Since 2011, China has implemented its most stringent water management system to effectively protect water resources and guarantee socioeconomic development. More basin-scale water division ...schemes have been developed to act as references for basin-scale water resources management. Water dispatching during dry periods is an effective way to guarantee the water supply for the river basin, and is also an important component of basin-scale water resources management. Given this, the present study proposes a framework for the water dispatching of river basins during dry periods under the most stringent water management system in China. This framework mainly consists of the analysis and forecasting of rainfall and inflow, the dispatching requirements for the main water users, major reservoirs, and sections, as well as safeguard measures. The Jian River Basin in South China is presented as a case study. The total discharge of the Gaozhou Reservoir in 2017 was 25 million m3 more than the target discharge specified in the water dispatching scheme, and the total water storage utilization ratio during the dispatch period was 4.7% higher than the target utilization ratio. These factors demonstrate the effectiveness and applicability of the proposed framework.
Enhancing water use efficiency (WUE) is essential for the sustainable and green development of water utilization. The conventional Super Slack-Based Measure (CSSBM) model is commonly employed to ...measure WUE, however, it is prone to underestimating WUE due its exaggeration of the slack variable. Recognizing the need to deal with problems involving the slack variable without limitation, we propose an improved Super-SBM (ISSBM) model that assigns an upper bound to the slack variables. In addition, the general deprivation index (GDI) of water resource exploitation is then introduced as the output indicator representing the social equality, resulting in a comprehensive set of output indicators related to the economy, society, and ecological environment. The ISSBM and CSSBM models were applied to determine the WUE in Guangdong province, China from 2009 to 2018, and the results indicate that the WUE calculated via CSSBM exhibited relatively extreme performance (i.e., the high and low values were greater than 2 and less than 0.1, respectively), while the ISSBM-estimated WUE showed relatively stable performance (i.e., the majority of the city’s WUE was located in the range between 0.5 and 1). The WUE determined from the output indicators involving GDI thus demonstrated stronger discriminating power compared to that without GDI. Furthermore, the spatial pattern of WUE in Guangdong province presents an essentially radial distribution, with high WUE located in Pearl River Delta and low WUE located North, East, and West of Guangdong. These results verify that the proposed ISSBM model can obtain a relatively appropriate WUE and could potentially be applied to other regions.
Equivalent circuit model (ECM) of the permanent magnet (PM) synchronous motor (PMSM) lays the foundation of the motor analysis, design, optimization, and control. However, the most widely used ECM of ...the PMSM ignores the core loss, which accounts for a considerable part of the electromagnetic loss and may exceed the copper loss in the medium and high-speed ranges. Previous researches of ECMs with predictable core loss are hard to satisfy the prediction precision over a broad range of speed and current. Therefore, a generalized per-phase ECM of the PMSM with predictable core loss is proposed. The proposed ECM topology and parameter identification method can effectively enhance the prediction accuracy of both the no-load and load core loss, and each component of the core loss in terms of the hysteresis, eddy current, and anomalous loss can be analyzed separately. Apart from the core loss, the proposed ECM has better precision in predicting the motor's output performance, such as mechanical characteristics, compared with traditional ECMs. The merits of the proposed ECM have been experimentally validated on the prototype of a PM transverse flux synchronous motor. This proposed ECM can be promotionally employed in other control strategies, such as model predictive control, to improve the PMSM performance.
There are numerous anomalies in the financial markets, which is difficult to be explained by the traditional efficient market theory. Overconfidence theory, motivated by the psychological evidence, ...increasingly becomes popular for better understanding the stock markets. This study aims to comprehensively and thoroughly review the relevant literature which looks at the economic consequences of investor overconfidence, and analyze how the overconfidence theory consequently raises some financial markets anomalies.
•Paddy field failed to achieve quantitative balance and dry land was the main farmland compensated by woodland and grassland.•Landscape fragmentation and heterogeneity of farmland have been ...intensified.•Integrated institution involved RCBF could be established and farmers engaged in compensatory farmland should be encouraged.•Concrete technical specifications should be developed for land exploitation, reclamation and consolidation.•Problems and causes of farmland’s spatial distribution and landscape pattern changes under RCBF were quantitatively verify.
This study analyzed the amount, heterogeneity, and pattern of farmland subject to the requisition–compensation balance of farmland (RCBF) policy from 2011 to 2015 in China’s economic development frontier area of Guangdong Province. The study used vector data for land-use and land-cover change and farmland quality from the Department of Land Resources of Guangdong Province and socio-economic statistical data from the statistical yearbook. To determine practical and potential problems during the implementation of RCBF, we calculated the differences between the area of compensatory farmland and requisitioned farmland according to different farmland types and quality grades at both the provincial and sub-regional scale. A series of pattern metrics reflecting land fragmentation and aggregation were identified at the class and landscape levels. The results revealed the presence of “superior occupation and inferior compensation” and “paddy field occupation and dry land compensation.” The landscape pattern experienced different degrees of influence after farmland requisition and compensation. The tendency was for a large area of woodland and grassland adjacent to each other to be exploited, leading to a series of ecological and environmental problems. Due to considerations of economic benefit and cost, much of the compensatory farmland provided following land exploitation has been inefficient, unreasonable, and unstable. Although some complementary policies have been proposed, such as “linking the increase in urban construction land with a decrease in rural construction land,” primary problems of RCBF are still difficult to be solved. We suggest that specific technical specifications for land exploitation, land reclamation, and land consolidation should be formed based on regional characteristics. Local government should improve the existing relevant support policies and continue to strengthen land reclamation and land consolidation in the future, with full consideration of the need for ecological environmental protection and improvement of the farmland landscape.
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