Online Monitoring Technique of Power Condition for Inverter-Fed Motor Driven Hydraulic System

As a new type of global energy-saving transmission mode, frequency conversion hydraulic drive system has been widely used. Since hydraulic systems become more complex and transfer more power, operating accidents often occur unexpectedly. Therefore, online monitoring of the running state of the hydraulic system is significant during its long-term operation. The pressure, flow, and vibration signals obtained by traditional monitoring methods are nonstationary and susceptible to disturbance. In order to solve this problem, a method of monitoring power condition of the motor driven hydraulic system based on input voltage and current of the motor is proposed. The present study uses the amplitude and phase information of the voltage and current signals on the stator side of the AC motor to form a dynamic power circle graph and extracts feature information from the graph to monitor the power state and its dynamic change process of the hydraulic system. Results obtained from experiments conducted under different frequencies and loads indicate that the proposed method can realize the online monitoring successfully and effectively. Furthermore, the method has another advantage of monitoring the dynamic power change process of the hydraulic drive system and the power matching process between the motor and the system load condition in a visualized way.