Abstract: A dynamic power balance equation and an electrical parameters information fusion method are presented to study on state recognition and power control technique of the hydraulic system driven by alternating current(AC) motor. To analyse the electrical, mechanical, hydraulical energy conversion and coupling process, the power balance equation of the hydraulic system is established using electromechanical dynamics. Based on the analysis result of equation, the single-phase and three-phase lissajous graph are drawn dynamically by means of the multi-source information such as phase,amplitude and phase sequence provided by the three-phase currents and voltages. The functional relations between the graphics features and dynamic powers of the AC motor are put forward, and then the functional relations are transferred into the power circle function for graphical analysis of the dynamic power. The results of the prototype experiments and on-site tests show that the typical running conditions such as loading, unloading, impact, overflow, energy-storage and so on, can be recognized by the calculations of the graphics features. A state recognition technique via information fusion is built finally. The research leads to the conclusion that the closed area of planar lissajous graph shows the real power of AC motor, which indicates the changing of load and lossed power, and the out-rectangle area represents the apparent power, the power circle can on-line monitor the matching process of the motor power with the typical running conditions, the swing angle of the graph provides some characteristic information relevant to the motor running status. In additional, three-phase lissajous graph is used not only to identify the running condition, but to classify the fault of the motor and hydraulic system.

Key words: Hydraulic system, Information fusion, Power matching, State recognition