To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spo...To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spool position,the proposed approach adopted the pressure drop across the valve metering orifice to accomplish the dead⁃zone compensation.The first step was to test and get the_(max)imum output flow,Q_(max),at a preset reference pressure drop,such asΔP_(0).The next step was to construct the target compensation flow curve,which is a line through(0,0)and(ΔP_(0),Q_(max)).Then a compensation law was designed to approach the target curve.However,the research results show that the above strategy caused over⁃compensation once the actual pressure drop deviated fromΔP_(0).Thus a correction coefficient,β,was presented to correct the initial compensation law as the pressure drop deviated fromΔP_(0).For example,the test results indicate that the corrected compensation approach could reduce the dead⁃zone from 53.9%to 3.5%at a pressure drop of 1 MPa;as the pressure drop was increased to 5 MPa,the dead⁃zone was reduced from 51.7%to 3.5%.Therefore,the following conclusions can be drawn:the proposed compensation approach is feasible,which can effectively reduce the dead⁃zone and improve the output flow static performance of the proportional flow valve without spool displacement feedback.展开更多
The natural frequency of the electrohydraulic system in mobile machinery is always very low,which brings difficulties to the controller design.To improve the tracking performance of the hydraulic system,mathematical m...The natural frequency of the electrohydraulic system in mobile machinery is always very low,which brings difficulties to the controller design.To improve the tracking performance of the hydraulic system,mathematical modeling of the electrohydraulic lifting system and the rubber hose was accomplished according to an electrohydraulic lifting test rig built in the laboratory.Then,valve compensation strategy,including spool opening compensation (SOC) and dead zone compensation (DZC),was designed based on the flow-pressure characteristic of a closed-centered proportional valve.Comparative experiments on point-to-point trajectory tracking between a proportional controller with the proposed compensations and a traditional PI controller were conducted.Experiment results show that the maximal absolute values of the tracking error are reduced from 0.039 m to 0.019 m for the slow point-to-point motion trajectory and from 0.085 m to 0.054 m for the fast point-to-point motion trajectory with the proposed compensations.Moreover,tracking error of the proposed controller was analyzed and corresponding suggestions to reduce the tracking error were put forward.展开更多
Since the dead zone phenomenon occurs in electro-hydraulic servo system, the output of the system corresponding to a sinusoidal input contains higher harmonic besides the fundamental input, which causes harmonic disto...Since the dead zone phenomenon occurs in electro-hydraulic servo system, the output of the system corresponding to a sinusoidal input contains higher harmonic besides the fundamental input, which causes harmonic distortion of the output signal. The method for harmonic cancellation based on adaptive filter is proposed. The task is accomplished by generating reference signals with frequency that should be eliminated from the output. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone, and the total harmonic distortion （THD） is greatly reduced. The weights of filter are adjusted on-line according to the control error by using least-mean-square （LMS） algorithm. Simulation results performed with a hydraulic system demonstrate the efficiency and validity of the proposed adaptive feed-forward compensator （AFC） control scheme展开更多
Ecological compensation or eco-compensation has been implemented mainly through institutional arrangement in China. In the farming-pastoral transitional zone of Inner Mongolia, eco-compensation has been implemented in...Ecological compensation or eco-compensation has been implemented mainly through institutional arrangement in China. In the farming-pastoral transitional zone of Inner Mongolia, eco-compensation has been implemented in two modes, one for land use abandonment and the other for productionstructure adjustment. Based on a detailed field survey, this study performs a comparative analysis of the willingness of households to accept economic compensation and consequently evaluates the effects of the two eco-compensation modes. The mode of eco-compensation for land use abandonment lacks a mechanism for generating employment opportunities and so is unsustainable. In contrast, ecocompensation for production-structure adjustment makes the pastoral and farming scales of households decrease significantly and most importantly helps to generate more job opportunities. Although this mode faces households with more market risk, it provides an effective means for resolving conflicts between ecosystems restoration and regional socio-economic development.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.51775362 and 51805350)the Natural Science Foundation of Shanxi Province(Grant No.201801D221226).
文摘To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spool position,the proposed approach adopted the pressure drop across the valve metering orifice to accomplish the dead⁃zone compensation.The first step was to test and get the_(max)imum output flow,Q_(max),at a preset reference pressure drop,such asΔP_(0).The next step was to construct the target compensation flow curve,which is a line through(0,0)and(ΔP_(0),Q_(max)).Then a compensation law was designed to approach the target curve.However,the research results show that the above strategy caused over⁃compensation once the actual pressure drop deviated fromΔP_(0).Thus a correction coefficient,β,was presented to correct the initial compensation law as the pressure drop deviated fromΔP_(0).For example,the test results indicate that the corrected compensation approach could reduce the dead⁃zone from 53.9%to 3.5%at a pressure drop of 1 MPa;as the pressure drop was increased to 5 MPa,the dead⁃zone was reduced from 51.7%to 3.5%.Therefore,the following conclusions can be drawn:the proposed compensation approach is feasible,which can effectively reduce the dead⁃zone and improve the output flow static performance of the proportional flow valve without spool displacement feedback.
基金Project(2006CB705400)supported by the National Basic Research Program of China
文摘The natural frequency of the electrohydraulic system in mobile machinery is always very low,which brings difficulties to the controller design.To improve the tracking performance of the hydraulic system,mathematical modeling of the electrohydraulic lifting system and the rubber hose was accomplished according to an electrohydraulic lifting test rig built in the laboratory.Then,valve compensation strategy,including spool opening compensation (SOC) and dead zone compensation (DZC),was designed based on the flow-pressure characteristic of a closed-centered proportional valve.Comparative experiments on point-to-point trajectory tracking between a proportional controller with the proposed compensations and a traditional PI controller were conducted.Experiment results show that the maximal absolute values of the tracking error are reduced from 0.039 m to 0.019 m for the slow point-to-point motion trajectory and from 0.085 m to 0.054 m for the fast point-to-point motion trajectory with the proposed compensations.Moreover,tracking error of the proposed controller was analyzed and corresponding suggestions to reduce the tracking error were put forward.
文摘Since the dead zone phenomenon occurs in electro-hydraulic servo system, the output of the system corresponding to a sinusoidal input contains higher harmonic besides the fundamental input, which causes harmonic distortion of the output signal. The method for harmonic cancellation based on adaptive filter is proposed. The task is accomplished by generating reference signals with frequency that should be eliminated from the output. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone, and the total harmonic distortion （THD） is greatly reduced. The weights of filter are adjusted on-line according to the control error by using least-mean-square （LMS） algorithm. Simulation results performed with a hydraulic system demonstrate the efficiency and validity of the proposed adaptive feed-forward compensator （AFC） control scheme
基金National Natural Science Foundation of China (40788001)Key Research Project Supported by MOST (2006BAC08B06)
文摘Ecological compensation or eco-compensation has been implemented mainly through institutional arrangement in China. In the farming-pastoral transitional zone of Inner Mongolia, eco-compensation has been implemented in two modes, one for land use abandonment and the other for productionstructure adjustment. Based on a detailed field survey, this study performs a comparative analysis of the willingness of households to accept economic compensation and consequently evaluates the effects of the two eco-compensation modes. The mode of eco-compensation for land use abandonment lacks a mechanism for generating employment opportunities and so is unsustainable. In contrast, ecocompensation for production-structure adjustment makes the pastoral and farming scales of households decrease significantly and most importantly helps to generate more job opportunities. Although this mode faces households with more market risk, it provides an effective means for resolving conflicts between ecosystems restoration and regional socio-economic development.
文摘在国家积极实施低碳减排政策的背景下,推动长江经济带建设资源节约型、低碳集约型区域对我国早日实现碳中和目标具有重要借鉴意义。论文以引导地区推动绿色低碳发展为目标,基于四阶段DEA(data envelopment analysis)模型测算出碳排放效率,构建碳排放量修正模型,然后在采用ESV(ecosystem service valuation)代表各地区的生态本底构建碳汇量修正模型的基础上,综合考虑了长江经济带不同地区在人口数量、土地面积、科技水平、生态环境状况、经济发展水平等先天禀赋方面的差异性,改进原始碳补偿测算模型,计算得出长江经济带各省市的碳补偿金额,并引入空间自相关分析模型,探究各省市间碳补偿金额的空间相关性。结果表明:1)引入修正系数前后计算所得的碳补偿金额差异明显;2)修正后长江经济带碳补偿金额平均值明显增加;3)长江经济带临近省市之间的碳补偿额度具有紧密的联系且相互影响;4)长江经济带碳补偿支付地区主要分布在长三角,接受地区主要分布在中上游。对此提出政府应构建地区碳排放生态系统服务功能测评机制、碳补偿区域项目综合绩效评估和反馈机制,完善碳补偿横向转移支付制度,加强制度管控,扩大绿化范围,加快产业转型升级和人才培养。
