Research Of Control Strategy For Swing Drive System In Hybrid Excavator

Hydraulic excavators are typical construction machines with wide usage,high fuel consumption and bad emissions.The research on hydraulic excavator energy saving has important implications for the current energy shortage and environmental degradation.The rotator and working mechanisms of hydraulic excavator feature high inertia,frequent moving and high repeatability during working,releasing a large amount of energy especially in the starting-braking process.Achieving effective collection and recycling of the energy mentioned above can reduce the energy consumption of hydraulic excavators and become a new way of energy saving.Research the energy recovery and utilization of the swing drive system for hybrid excavators is important helpful for in current.Targeted at the energy saving of swing drives system of excavators,an energy conservation plan based on the swing drives system of excavators is proposed in this paper,and aiming at the control problems existing in the kinetic energy recovering of rotator,strategies which can balance well between effective energy conservation and operating performance are sought.Swing drive system includes several parts: Start/generator and PWM converter,swing motor and PWM converter,bi-directional DC/DC converter.Also the researches on energy management control strategy are carried targeted at effective energy recycling,which provide complete solving ideas for the control problems of energy conservation system.This paper studies key control technologies of the swing drive system.such as the control of permanent magnet synchronous motor in generating operation;the drive operation control technology of SPMSM based on rotor position sensorless,the control technology of two-phase Interleaved DC/DC converters;the coordinated control strategy of the swing drive system for hybrid excavator.The paper seeks to provide valuable technical reference for engineering applications of energy recovering system on excavators.Each part is illustrated as follows.The first chapter discusses the importance of energy recovery technology for excavators energy saving research.Analyzes the development process of hybrid excavator technologies.And a reviewed research on the control technology of permanent magnet synchronous motor and the energy storage system made from theoretical technologies and systems development,then the background factors are analyzed and an overview of the research work of this thesis is finished.In the second chapter,a new design program of the swing drive system for hybrid excavator based on super capacitors is proposed in this paper.It introduced compositions and working principle of the program,potential energy of kinetic energy of swing platform are analyzed quantitatively;then a experiment platform for a 20-ton hydraulic excavator is established and a excavators’ energy recovering solution based on engine-pump-generator integrated unit is proposed after analyzing the characteristics of recyclable energy.In the third chapter,On the basis of analyzing the mathematical model and vector control principle of PMSM,the system model of Improved current model predictive control technology control of the PMSM based on in generating operation,which provides a theoretical basis for carrying out experiment.At the same time,the drive and control system of PMSM based on is designed.The system design includes hardware circuit design and software program module design.then analyzed the reason and compensating scheme of Phase error Produced by Model predicted current control(MPCC)with mathematical method.The experiments results indieate that MPCC has the advantages of controllable power fator,simple arithmetic and system structure,fixeds switching frequeney,better dynamic response,easy to digitization etc.The estimation accuracy of the rotor position estimation is very important for achieving the whole speed-range operation of sensorless surface-mount permanent magnet synchronous motor(SPMSM).A hybrid position observer with the position error information fusion that combines the pulsating high-frequency signal injection and the method based on SMO(Sliding Mode Observer)is proposed for vector control system.For low speed operation,the position error signal is obtained by the magnitude of the induced high-frequency current.While at higher speed,the error information is achieved from an EMF based sliding-mode observer.Then both the normalized position error signals are combined directly with a weighting function.A software phase-locked loop is adopted to obtain the hybrid rotor position information.Both the stability and the parameter design of the hybrid observer are analyzed.The experimental results demonstrate the feasibility of the proposed estimation strategy by a SPMSM sensorless vector controlled drive.The experimental results show that the system performance meets the design requirements.Different operation modes in corresponding with diverse conditions of the hybrid excavator are analyzed firstly.In order to enhance the current capacity and power density,interleaving parallel technology is introduced.Working principles and parameters of the interleaved bidirectional DC/DC converter are expounded.In this paper,dynamic models of this bidirectional DC/DC converter under different operation modes are derived.Then design of the hardware circuit and realization of the control arithmetic are described detailedly in the following thesis.Controllers corresponding to different working modes are also devised to improve the performance of this system.The coordinated control method is proposed.The four processes of the super capacitor pre-charge and the starting,uniform,braking of rotary motor are analyzed in detail,and the factors which affect the stability of the dc bus voltage have been found out.In order to make the system operate safely and reliably,appropriate control schemes for generator PWM converter,rotary motor PWM converter,bi-directional DC/DC converter and discharge resistor have been adopted in corresponding modes.