The first governor used in diesel engines was the mechanical governor. The mechanical governor senses the change of the engine speed by the change of the centrifugal force of the flying block, and adjusts the oil supply amount of the fuel injection pump through the mechanical mechanism, thereby adjusting the rotational speed. Because of its simple structure, safe and reliable maintenance and low cost, the mechanical governor is widely used in small and medium power diesel engines. There are obvious disadvantages of the mechanical governor: First, from the control point of view, it is equivalent to a proportional controller, there is an adjustment static difference; when the load changes, the balance point between the governing spring force and the centrifugal force of the flying block also follows Change, the steady speed is not equal to the original speed. Second, there is mechanical transmission friction in the governor. During operation, the centrifugal force of the flying block generates an adjustment lag due to the need to overcome the frictional force. When this hysteresis is large, the rotational speed of the diesel engine will fluctuate greatly.
In the subsequent hydraulic governor, the centrifugal force of the flying block is only used to control the sliding valve. Due to the action of the hydraulic servo, the working piston has a large thrust and a compact structure. The hydraulic governor is sensitive, stable and reliable, and has a large working force. It is widely used in large and medium-sized diesel engines.
With the further improvement of diesel engine speed control accuracy requirements, an electronic governor has emerged, which uses a rotational speed sensor instead of a centrifugal flying block as a quick-sensing component, and an electromagnetic actuator acts on the oil quantity adjusting mechanism. The structure is simpler and the adjustment precision is more high. Table 1 shows a comparison of the performance parameters of the three governors.
Table 1 Mechanical. Hydraulic. Electronic governor performance comparison can refer to governor type mechanical hydraulic electronic speed fluctuation rate% instantaneous adjustment rate% stability time (S) accuracy level 1 diesel power generation system control target 1.1 power generation diesel engine control fund project : The diesel engine of power generation project funded by the Youth Research Fund of Inner Mongolia University of Technology, the main feature is the high precision of the speed control, and the precise control of the speed. The core problem lies in the governor. Both the mechanical governor and the hydraulic governor are difficult to meet the requirements for accuracy; the electromechanical hybrid governor solution is simple and easy to implement, and is a new method with low cost.
The electrical condition only needs to control the speed, and it can completely achieve the target by controlling the oil quantity without having to control the injection timing.
1.2 Power supply system quality control The power supply quality of the power supply system is measured by the following: constant voltage level, constant sine wave, three-phase power balance, reliability level, etc. We mainly consider the control of diesel engines and generators from the first two.
For synchronous generators, the supply frequency is /=np/60, where / is the terminal voltage frequency n is the generator speed, and p is the pole number of the pole. It can be seen that to ensure a constant power supply frequency, the speed of the diesel engine must be accurately adjusted. Generally, the power supply frequency requirement is 5 vomit. If the magnetic pole pair is taken as 1, the corresponding diesel engine speed fluctuation range is 300 vomiting 12 (rpm).
2 control scheme design 2.1 diesel engine speed control electromechanical hybrid governor, on the original two-pole mechanical governor, remove the connection between the throttle and the governor, install the actuator at the speed control handle.
In the control strategy, the feedforward and feedback control method is adopted: the diesel engine load is changed by detecting the effective power of the generator, and the control MAP map is pre-stored in the single-chip microcomputer to check the control oil quantity value; at the same time, the speed sensor will detect The diesel engine speed signal is sent to the electronic control unit, and the electronic control unit obtains the control oil quantity value according to the pre-programmed algorithm. When the two are added, the command is issued, and the actuator controls the oil pump adjustment mechanism position to give the oil supply quantity, thereby adjusting the diesel engine. Rotating speed. The mechanism diagram is as shown.
2.1.3 Feedforward and feedback control strategy Bit 馇 DM conversion -|gig. People's Communications Press, 1990. Gao Guoquan. Diesel engine speed control system for power stations. People's Communications Publishing House, 1983. Qin Zenghuang. Electrical Engineering. Higher Education Press, 1990. He Liquan, Qiu Guoyue. Power system reactive power and active power control. Chongqing University Press, 1995. Zhou Degui, Gong Beining. Synchronous generator operation technology and practice. China Electric Power Press, 1996. Gang Hanbing, Qi Qiuqun. Principle and application of MOTOROLA 8-bit enhanced MCU M68HC11. Beijing Institute of Technology Press, 1993. Fan Jun, Chen Zhong, Tu Guangyu. Synchronous generator semiconductor excitation principle and application. Water Resources and Electric Power Press, 1991. Zhou Shuangxi, Li Dan. Synchronous generator digital excitation regulator. China Electric Power Press, 1998. 11.1 Speed ​​measurement Using the Hall speed sensor mounted on the flywheel housing, the number of teeth of the turned flywheel is detected, and the square wave pulse signal with the same number of teeth is emitted, and the time taken to count the number of teeth is obtained. . The time is measured by the 16-bit free-running counter in the single-chip microcomputer. The clock frequency is 2MHz, and the timing error is up to one clock cycle of 0. 0005ms. This error is negligible compared to the diesel engine revolution time of 20ms.
For the six-cylinder diesel engine, the measurement is performed three times per revolution, so that each cylinder is fired, and the oil quantity obtained by the updated speed is provided to ensure that the diesel engine reacts to the fluctuation of the rotation speed in a very short time. The measured position starts from 0 teeth, 1/3 total teeth, and 2/3 total teeth. Each time the total number of teeth of the flywheel is measured, the flywheel just rotates for one week, which reduces the measurement error caused by the process error of the tooth and increases the speed. The accuracy of the measurement.
2.1.2 Actuator control To accurately control the oil supply of the oil pump, the speed fluctuation range is controlled within 014%, and the accuracy of the sensor D/A conversion and the actuator and the sensitivity of the electromagnet are required to be sufficiently high. The actuator uses a linear electromagnet. According to our experience, the electromagnet has a control accuracy of at least 0.01 mm, and its total stroke can reach 25.4 mm. The 12-bit or higher 16-bit D/A conversion is used. The control flow chart is as shown.
In addition, in order to enable the linear electromagnet to follow the control signal from the unit, the PID position is applied to the linear electromagnet.
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