Abstract
Dual pump distribution hydraulic system is an due to its economical and efficient characteristics widely used in plant hydraulic drive system. It has the characteristics of simple structure, lightweight, high efficiency, easy maintenance, low repair cost and easy control, but it has its own limitations, the hydraulic system main load performance is not good, the uniformity of the speed response of two pumps is low. This paper first introduces the structure of the dual pump distribution hydraulic system, and then analyzes the control characteristics of the system, followed by the application of fuzzy control method and cascade control method.
1 Introduction
The dual pump distribution hydraulic system is widely used in plant hydraulic drive system. It has the characteristics of simple structure, low cost, high efficiency and easy control. Compared with the traditional single pump hydraulic system, the dual pump distribution hydraulic system has the advantages of high output efficiency and low fuel consumption. The main load performance of the system is not good, the uniformity of the two pump speed response is low, the staleness of the control process is large, the rapid shock absorption capacity of the system is poor, and the stability of the system is poor. In order to solve these problems, this paper plans to use fuzzy control and cascade control methods to control the dual pump distribution hydraulic system.
2 Hydraulic system structure
The dual-pump distribution hydraulic system is made up of two independent hydraulic pumps and a hydraulic distributor. The hydraulic distributor controls the flow of oil by means of a control signal, and the hydraulic distributor is connected with two hydraulic pumps by hydraulic pipelines and hydraulic control valves. When one of the hydraulic pumps starts to work, the hydraulic distributor will supply oil to the working pump, and at the same time, the other pump will be blocked, and when the working pump fails, the oil supply of the other pump will be selected:
Figure 1. Dual-pump distribution hydraulic system
3 Characteristics of Control System
The dual pump distribution hydraulic system has the characteristics of fast response, high purity, low ripple and low dead zone. It also has the ability to preserve its control parameters when the load changes, thus ensuring the correct operation of the system.
The dual pump distribution hydraulic system can control the output flow and speed of the pumps to a large extent. Generally speaking, the system has the characteristics of strong overload capability, good low-speed response and smoothness, and small impact on environment. In addition, the system also has the ability to anticipate and compensate for the changing load of the system, thus ensuring smooth and continuous changing output flow and speed.
4 Fuzzy Control Method
The fuzzy control method is a kind of soft computing technology which can be used as a control strategy to solve the control problems which are difficult to determine the control rules by analytic methods or hard control methods. It is not necessary to obtain the precise mathematical model of the controlled objects and systems, and fuzzy rules and linguistic variables can be used to describe the operating characteristics of the controlled object.
In order to improve the control precision of the dual pump distribution hydraulic system, fuzzy control method is used. That is, to realize the two pumps working in the same speed by fuzzy control, the rule base is built, the input parameters are set, the controller is designed and then the simulation experiment is conducted.
The input parameters include the working pressure of the two pumps, the mechanical power of the two pumps, the working power of the two pumps, the flow rate of the two pumps and the working speed of the two pumps. The operator can set the speed they want, and then design the fuzzy rules according to the speed they want. The output parameters include the speed of the two pumps.
5 Cascade Control Method
The cascade control method is a kind of control method with the auxiliary variable in the outer loop controlling the output of the inner loop. The advantage of Cascade control is that the system has fast response, large overload capacity and good stability.The cascade control system consists of a primary controller and a secondary controller which are connected in series.
The purpose of this scheme is to achieve a greater control accuracy than the fuzzy control method. The input parameters include the mechanical power of the two pumps, the actual speed of the two pumps, the flow rate of the two pumps and the desired speed of the two pumps. The output parameters are the speed of the two pumps. The two controllers are designed to adjust the speed of the two pumps, so that the two pumps can work in the same speed.
6 Simulation
The MATLAB/Simulink simulation environment is used to set up the dual pump distribution hydraulic system, and the simulation results are compared with different control methods. The results show that the cascade control method has a better control performance than the fuzzy control method, and the speed error is greatly reduced.
7 Conclusion
The dual pump distribution hydraulic system is a very common drive system, and its control precision is one of the important factors affecting the system performance. In order to improve the control accuracy of the dual pump distribution hydraulic system, fuzzy control and cascade control methods are used to control. The simulation results show that the cascade control system has better control performance than the fuzzy control system, and the speed control accuracy is better.
