A Graphic Monitoring Method For Electric Power Of VVVF Hydraulic System

The mechanical electrical and hydraulic system is a multi-domain coupling system integrating the characteristics of machinery,electricity,liquid,and control.Which has the advantages of wide range of speed regulation,good dynamic and static behavior,easy to control and strong adaptability to various complex working conditions.It has been widely used in many fields such as engineering construction,material processing,national defense equipment,aerospace and so on.However,due to the complex structure of hydraulic system and the energy conversion between multi-energy domains involved in the operation process,its operation status information and fault information are difficult to obtain and easy to be disturbed,which bring difficulties to the condition monitoring and fault diagnosis of hydraulic system.Therefore,finding a parameter signal with few interference sources and abundant system operation information,and revealing its relationship with the operation status of hydraulic system and equipment failure,which is the key to realize the condition monitoring and early fault prediction of hydraulic system.The electrical signals input by the motor can be obtained by Hall sensors,which has the advantages of convenient acquisition,high signal-noise ratio and good anti-interference performance.Therefore,this paper takes the variable voltage and variable frequency(VVVF)hydraulic system as the research object,and proposes a graphic monitoring method that fuses the information of variable-frequency electric parameters.This method could make full use of the electrical parameter information of amplitude,frequency,phase information and phase sequence information to monitor the running state of VVVF hydraulic system,and reveal the relationship between the features of Lissajous figure and system running state.This method provides a new idea and a new method for condition monitoring and fault diagnosis of VVVF hydraulic system.(1)Research on the control principle of frequency converter and the principle of Lissajous figure fusion.Firstly,for the frequency conversion motor,the waveform of the output voltage and current of the frequency converter changes with the frequency when the speed is adjusted below the fundamental frequency.Then,using the characteristics of stator phase voltage and phase current frequency,rigorous theoretical analysis establishes the function between the electric power of the variable-frequency motor(VFM)and the features of the plotted dynamic figures including area of diagram,area of bounding rectangle,tilt angle,etc.Then,the power circle diagram is drawn by this relationship,which is convenient for observing the power matching of the system.The above research provides a theoretical basis for the graphic on-line monitoring method of electric power of VVVF hydraulic system.(2)Experiments demonstrate the effectiveness of the graphical on-line monitoring method of electric power.Based on the theory and technology research platform of mechanical-electrical-hydraulic integration,this paper designs and simulates the test environment of variable speed and variable load conditions.Firstly,slope acceleration,speed sinusoidal change and load experiments are designed,and collect three-phase voltage and current signals synchronously by three-phase electric parameter acquisition device.Then the obtained electrical signals are fused into Lissajous figure and power circle after processing,and calculate the three electric power values and the tilt angles of active and reactive Lissajous figure.Finally,analyze the variation of Lissajous figure and its characteristic with motor speed and load under different working conditions.The experiment verifies the feasibility and validity of the graphical on-line monitoring method of electric power of the state of hydraulic system.(3)Development of graphical on-line monitoring method of electric power for VVVF hydraulic system.Based on the theory of Lissajous figure fusion and the relationship between Lissajous figure characteristic parameters and electrical parameters,a graphical on-line monitoring system of electric power is developed by using LabVIEW and MATLAB software mixed programming method.This system realizes the functions of collecting and displaying three-phase voltage and current,drawing Lissajous figures and power circle diagram,calculating Lissajous figure characteristic quantity and preserving original data.The validity and accuracy of the system have been verified by corresponding experiments.