【作者】 胡东明；

【导师】 杨华勇； 徐兵；

【作者基本信息】 浙江大学 ， 机械电子工程， 2009， 博士

【摘要】 液压系统的节能研究是流体传动领域的重要课题之一,变转速容积调速的液压系统由于其功率自适应的特点而具有较好的节能效果,其中,闭式油路的变转速容积调速液压系统具有结构简单和节能效果显著的优点,适合应用在势能可回收且速度持续变化的大惯量液压提升机械中,如液压电梯、液压抽油机等。然而,在节能化的同时仍然要保证系统的运行性能及控制特性,在闭式油路的变转速容积调速液压系统的应用研究中,发现其存在着开环控制精度不高和启动始终有滞后的问题,而这也是大惯量的变转速容积调速液压系统的共性问题和难点,因此,需要从以下两个方面开展研究:第一,分析开环控制策略和传统的闭环控制策略在该类惯量变转速容积调速液压系统的速度控制中存在的局限性,提出有效的速度控制策略;第二,分析影响该类系统的启动性能的因素,提出智能控制策略以实现良好的启动。除上述两方面外,基于液压提升机械节能技术发展的要求,探索变转速容积调速以外的新型节能方法.论文以闭式油路变转速液压电梯为研究对象,研究该类系统除节能特性以外的运行性能及控制特性。为提高系统的速度运行精度,对系统的稳定性进行分析,由于该系统是一个高阶零型系统且具有低频的特性,其存在着闭环控制下稳态误差大和采用积分校正有较大滞后的问题;为此,提出了基于比例微分控制的前馈-反馈控制策略来克服上述问题。针对变转速容积调速液压系统的启动控制问题,重点分析了系统运动部件中的非线性摩擦力对启动性能的影响,通过试验建立了系统非线性摩擦力的模型,并提出了基于专家控制器和模型预测控制策略的启动控制方法,变工况下启动性能的试验结果表明,基于智能预测的启动控制方法能使系统在不同负载工况下获得非常好的启动性能。论文还针对闭式油路变转速液压电梯的轿厢振动特性进行分析,建立了系统垂直方向上8自由度的动力学模型,在此基础上对电梯系统进行试验模态分析,结果表明所建立的动态模型是准确的。另外,试验模态分析结果还表明,轿厢的主频率在100-150Hz的范围内,系统在运行过程中应避免该频率段的激励而导致的共振。基于液压提升机械节能技术发展的要求,论文中还从理论上探讨了一种变配重节能方法,提出变液压配重和机械配重变速度的两种方案,详细分析了变液压配重的方案在液压电梯系统中的应用,将其与已有变转速液压电梯系统进行了对比分析,结果表明变配重系统具有更优的节能效果。通过以上研究,大惯量闭式油路的变转速容积调速液压系统的速度闭环控制不好和启动不佳的本质原因得以阐述,且论文中提及的一些研究方法和结论适用于其它变转速容积调速的液压系统。论文主要结构如下:第一章,介绍了变转速容积调速的液压系统,并由此引出其典型应用——变转速液压电梯;综述了变转速液压电梯的研究和发展历程,分析了目前变转速液压电梯中依然存在的问题,指出目前变转速容积调速液压系统的发展需要和变转速液压电梯依然存在的市场需求,在此基础上提出课题的研究内容。第二章,分析了闭式油路变转速液压电梯系统的稳定性,提出适合该系统的速度控制策略。建立了系统中关键环节的数学模型和传递函数,结合经典控制理论对系统的稳定性进行分析,结果表明闭式油路变转速液压电梯系统是低频、低阻尼的高阶零型系统,其存在着闭环控制下有稳态误差和采用积分校正带来较大滞后的问题;针对该问题,提出基于比例微分控制的前馈-反馈控制策略,并通过仿真和试验验证了该方法的有效性。第三章,研究了以变转速液压电梯为代表的大惯量变转速容积调速液压系统的启动控制方法。指出了由于系统的大惯量和时滞特性,采用压力预平衡方法和速度比较启动法都存在着问题;重点分析了非线性摩擦力对系统启动性能的影响,指出非线性摩擦力的影响程度并通过试验建立了系统中摩擦力的模型,依据该模型针对性的提出了基于专家控制器和预测控制原理的智能预测启动方法;在变工况下对系统的启动性能进行了试验研究,结果表明基于智能预测的启动方法能使系统获得良好的启动性能。第四章,从闭式油路变转速液压电梯轿厢的振动特性入手,分析电梯系统的动态特性和系统中存在的激振源对轿厢振动的影响。通过对电梯轿厢的原始振动加速度信号和液压系统的负载压力信号进行频谱分析来寻找系统中的激振源;建立液压电梯垂直方向上的8自由度集中质量动力学模型并进行计算模态分析,依据该模型对系统进行了计算模态分析,并通过试验模态分析验证了所建立的动态模型的准确性;另外,分析结果还表明,电梯轿厢主频率在100-150Hz的范围内,系统在运行过程中应避免该频率段的激励。第五章,基于液压提升机械节能技术发展的要求,阐述了变配重的节能方法。提出了变液压配重和机械配重变速度的两种方案,重点对变液压配重的方案在液压电梯系统中的应用进行了论述,讨论了其中主要元件的设计计算与选型;采用Amesim仿真软件对采用变液压配重的液压电梯系统的能耗特性进行了仿真,将其和已有的三种变转速液压电梯系统进行了对比分析;讨论了变配重的节能技术目前在系统效率、配重预存储能量、动态特性三个方面存在的问题,给出了相应的对策.第六章,对本论文所作的研究工作进行总结,给出主要的研究结论,指出课题的创新点,并对未来的研究工作进行展望。更多还原

【Abstract】 Energy-saving is one of the most important research areas of hydraulic systems.The variable-speed control is applied in the hydrostatic system for its high efficiency.The variable-speed control system is developed for large inertia hydraulic lift equipment,such as hydraulic elevators,hydraulic pumping units.In addition to the discussion of energy-saving, the system performance should be investigated also.In the velocity performance research of the system,there were two problems existed:the open-loop control method had the limitations in achieving high precision control of velocity and the hysteresis occurred in the startup of the system.Therefore,this research focused on developing the appropriate velocity control algorithm and speed startup method for the system.Besides these two aspects,the new energy-saving idea need be discussed because of the requirement of developing higher efficiency approach for hydraulic lift equipment.In this thesis,the behavior of the variable-speed controlled hydrostatic system was investigated on a hydraulic elevator test rig.To achieve high precision control of the velocity,the stability of the system was analyzed.Because the hydraulic elevator is a type 0 system with the feature of low frequency,the steady-state error of velocity still existed by unity-feedback control without compensation,and the velocity lag occurred with the integral compensation.A compound algorithm of PD & feedforward-feedback control was proposed to deal with the steady-state error.In order to overcome the hysteresis in the speed startup control of hydraulic elevator,the relationship between the startup performance and the nonlinear friction in the system was investigated.The speed startup method,based on expert control and model predictive strategy was developed,and was validated by the experiments under different working conditions.In addition,the vibration characteristics of the hydraulic elevator were analyzed.The dynamic model with 8 degree-of-freedom was established for describing the vertical dynamics of the hydraulic elevator system.The results of theoretical and experimental modal analysis on the system showed the validity of the dynamic model.And the results indicated that the frequency coverage of the main response of the system were within 100~150 Hz.Therefore,to avoid the resonance vibrations of the cabin in hydraulic elevator,the vibration source with frequencies range of 100~150 Hz should be isolated.Based on the requirement of higher efficiency in hydraulic lift equipment,an innovative idea of variable counterweight was developed.Compared with other variable-speed controlled hydraulic systems,the efficiency of the variable counterweight system was higher.In general,the results from this research can be applied to not only the variable-speed controlled hydraulic elevator,but also other variable-speed controlled hydrostatic systems.The thesis is outlined as follows.In chapter 1,the variable-speed controlled hydrostatic system and its typical application in hydraulic elevator are introduced.The development of the hydraulic elevator is expatiated and its existed problems are analyzed.The necessity of research on variable-speed control hydrostatic system and the markets requirement of hydraulic elevator are pointed out.Consequently,the contents and difficulties of the research are proposed.In chapter 2,the velocity behavior of the variable-speed controlled hydraulic elevator by feedback control is analyzed.The mathematic models of the system and the transfer function are established.Frequency-domain analyses show that it is a type 0 system with the feature of low frequency and poor damping.The steady-state error still exists in the system by the unity-feedback control without compensation.And the velocity lag occurs if the approach of integral compensation is adopted to eliminate the steady-state error.The compound algorithm of PD & feedforward-feedback control is proposed,which satisfies the requirement of the system against steady-state error and nonlinearities.In chapter 3,the method of speed startup control for the system is discussed.The speed startup behavior of the system by pressure pre-balanced control and speed feedback control is poor because of its friction and large inertia.The influence of nonlinear friction on the speed startup behavior of the system is analyzed,and the friction model is established through experiments.The speed startup method is developed based on the expert control and model predictive strategy,and experiments are conducted under different working conditions,namely variable loads and variable friction.The results show that the speed startup behavior of the improved system is excellent.In chapter 4,the cabin vibration characteristics of the variable-speed controlled hydrostatic hydraulic elevator are discussed.The 8 degree-of-freedom dynamic model of vertical direction for the system is established and the modal analyses are conducted.The experiments of modal analyses for the system are also carried out,which show that the dynamic model is correct and the frequency coverage of the main response of the system are within 100-150 Hz.And so,if the frequencies of outside vibration source are within 100-150 Hz,it must be avoided.In chapter 5,an innovative energy-saving idea of variable counterweight is proposed, and two different kinds of principles of the idea are introduced,namely variable hydraulic-counterweight and mechanical-counterweight with variable speed.The hydraulic elevator system applying the variable hydraulic-counterweight is discussed in detail,and the characteristic of energy consumption of the system is studied based on AMEsim simulation. The features of the system are discussed,which mainly involve efficiency,storage energy in counterweight and dynamic response,and the development of the variable counterweight technology is prospected.In chapter 6,all the research contents are summarized,and some new views are put forward in the future.更多还原