Velocity-tracking Control of the Variable-speed Controlled Hydraulic System: Using Compound Algorithm of PD & Feedforward-feedback Control

The variable-speed controlled hydraulic system is applied in the large inertia hydraulic lift equipments for its high efficiency, such as hydraulic elevators, hydraulic pumping units. And it is a typical time-varying system. In addition to the energy-saving, the velocity performance is another research focus. This paper discussed about the velocity tracking control of the system, in which the compound algorithm of PD & feed forward-feedback control was proposed. The simplified working principle of this kind of pump/inverter-controlled system was first introduced. The mathematic models of the system and the transfer function were established based on the hydraulic elevator system. The frequency-domain analysis of the system showed that it is a type 0 system with the feature of low frequency and poor damping. The steady-state error of velocity is still existed by unity-feedback control without compensation, and the velocity lag occurs with the integral compensation. Simulation and experiments also show this. Then, the compound algorithm of PD & feed forward feedback control was proposed, which satisfied the requirement of the system against steady-state error and nonlinearities. And the experiment results show the stability and validity.