Research On Variable Frequency Motor Pump Control Strategies

Hydraulic power transmission has many good characteristics, such as smooth transmission, easy speed regulation and big capacity per unit volume, and is widely used in many fields. But there are some disadvantages, for instance, its energy utilization and its systems efficiency are both low. So, energy saving is always the important research area. Energy saving researches were based on hydraulic system in the past and tried best to low the wastage of itself. These researches had some noticeable effects in a way, but it did not considerate the efficiency characteristic of motor. When system does not work under rated load, motor works under high speed and its efficiency is low. It restrict the enhancement of power efficiency of the total system.Variable frequency hydraulic drive is a novel technology in energy saving transmission area. On the base of consulting many related records, domestic and overseas, this dissertation research a novel variable frequency hydraulic motor pump and researching effective control strategy of permanent magnet synchronism motor pump is the most important point.At the beginning,this dissertation introduces generally the development, state and tendency of variable frequency hydraulic technology and variable frequency motor speed regulation technology. And, this dissertation analyses detailedly the structural characteristics of permanent magnet synchronism motor pump and establishes its mathematic model.Then, in order to control effectively permanent magnet synchronism motor pump, fuzzy sliding-mode direct torque control strategy and adaptive sliding-mode vector control strategy of permanent magnet synchronism motor pump are proposed. As hydraulic pump is installed in the rotor of motor pump, the inertia of motor pump changes along with the changing of the oil's character, volume and energy in hydraulic pump and becomes the important factor that impact the stability of control system. To conquer the impacts of dynamic parameters and uncertain factors , enhance the robustness of control system, a strategy of sliding mode variable structure control is used in the design of speed controller based on introducing the theory of sliding mode variable structure control and the theory of stability in detail. This speed controller is used in direct torque control and vector control. In order to reduce instability and extend application, model reference adaptive observer is used to replace speed sensor in vector control. For enhancing stability of system, fuzzy speed controller is designed to replace PI controller.At last, the simulation model of permanent magnet synchronism motor pump is built based on the matlab/simulink. Under the strategies of direct torque control and vector control, the simulations are performed well. Results show that the control strategies are feasible and effective.