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Type selection of mechanical system of governor

what types of mechanical hydraulic system of Governor? How to select the governor mechanical system

the mechanical hydraulic system of governor can be divided into electro-hydraulic converter, proportional servo valve, digital valve and motor according to different electro-hydraulic conversion modes. Among them, the motor is also divided into stepping motor and servo motor. When the microcomputer governor of hydraulic turbine is a typical digital hydraulic position servo system due to the needs of coherent operation, the digital hydraulic position servo system is mainly divided into two categories according to the interface control mode of electro-hydraulic conversion link: indirect digital control and direct digital control

indirect digital control refers to the digital control of the electro-hydraulic servo system through the d/a conversion link and the analog interface. The proportional servo valve uses 4 ~ 20mA linear current as the driving signal, and the microcomputer regulator must be controlled through the d/a conversion link and the analog interface. Therefore, the proportional servo valve governor is a typical digital hydraulic position servo system with indirect control mode. The traditional plastic recycling granulator reprocesses the waste plastics in daily life to generate the plastic raw material servo valves required by the enterprise, which also belong to this kind of servo system

with the extensive application of computer technology in fluid control system, digitalization has become an inevitable trend. In contrast to the indirect digital control method, the direct digital control method is called direct digital control, in which the control quantity is directly connected with the electro-hydraulic servo system through the digital switch signal instead of through the d/a interface. At present, there are mainly two ways to realize it:

one is to use the digital actuator stepper motor plus an appropriate rotation linear motion conversion mechanism to drive the valve core to realize direct digital control. Because this kind of digital control element generally works in a step-by-step manner, it is often called a step-by-step digital valve or a discrete proportional valve. Through reasonable design, this kind of valve has the advantages of high repetition accuracy and no hysteresis

the other is the control of high-speed on-off valve (pulse width or pulse modulation). By controlling the on-off time ratio of the switching element, the average value of the flow in a certain period of time can be obtained, and then the control of the next level actuator can be realized. In the fluid power system, the control signal of this control mode is switching value, so it is direct digital control. The control method has the advantages of non blocking, strong anti pollution ability and simple structure

the system composed of indirect control mode realizes digital control through d/a interface. This method has the following disadvantages: (1) due to the existence of analog circuit in the controller, it is easy to produce temperature drift and zero drift, which not only makes the system vulnerable to temperature changes; At the same time, it is difficult for the controller to completely compensate the nonlinear factors of the servo valve, such as dead time, hysteresis, etc. (2) The proportional electromagnet and torque motor used to drive the proportional valve and servo valve have inherent magnetic leakage, resulting in 2%-8% hysteresis in the external control characteristics of the valve. Closed loop control methods such as valve core position detection and feedback can basically eliminate the hysteresis of the proportional valve, but the cost of the valve is greatly increased, the structure is complex, and the reliability is reduced. (3) Due to the structural characteristics, the magnetic circuit of proportional electromagnet can only be composed of integral magnetic materials. Under the action of high-frequency signals, the temperature rise caused by iron loss is more serious. Therefore, the direct digital control mode is obviously superior to the indirect digital control mode

compared with the on-off valve, the stepping digital valve as a direct digital control mode has the advantages of high repetition accuracy and no hysteresis loop. However, the stepping digital valve converts the input signal into the corresponding number of steps (pulses) through the stepping motion of the valve core, so there is a quantization error. By increasing the number of working steps of the valve, the quantization error can be reduced, but the response speed of the valve is greatly reduced. At the same time, the step-by-step governor must retain the guide valve and the main configuration, resulting in a more complex structure of the step-by-step governor and a large number of machined parts. It will not continue to expand its business in China in the future, with good general interchangeability

in comparison, the interface between the high-speed on-off valve and the control system is simpler, and the direct digital control system can be formed without intermediate links, so the application prospect is very broad. Applying the high-speed on-off valve to the microcomputer governor of water turbine can realize the digitalization of the whole system and constitute a full digital governor

however, because the flow is not only limited to solving people's travel problems, pressure pulsation and other factors, the application range of digital valve in large-scale governor is limited to a certain extent. At present, it can only be applied to operating power not greater than 17000kg Regulation control of non dual commissioning unit of M

to sum up, digital valve is suitable for small and medium-sized governors, and stepper motor is suitable for large-scale governors (but pay attention to the control mode - refer to the comparison description of motor governors later). (end)

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