At present, the self-consumption electrode vacuum arc furnace electrode lift control system generally adopts pure analog device control mode. It has been proved that the control mode of the pure analog device brings a series of problems such as high failure rate, large maintenance amount and high production cost. In order to solve these problems, a new control method must be adopted. Considering PLC's complete functions, flexible application, convenient operation, stable and reliable, it is the development direction of modern control system equipment, and has been successfully applied to various industrial occasions such as metallurgy, petrochemical, machinery, etc. Therefore, PLC is selected and PLC and designed. An electrode lift control system consisting of an analog governor.
This paper introduces the design process of the self-consumption electrode vacuum arc furnace electrode lifting PLC control system from two aspects of hardware configuration and software programming, and analyzes the field operation results. The analysis shows that the system fully meets the production requirements and has reached the expected level. Effect.
2 hardware configuration hardware configuration and system control principle as shown.
It is a modular small and medium-sized PLC that can be expanded freely and is very flexible. The system S7-300PLC consists of power supply module PS307, central processing unit CPU314, analog input module SM331, analog output module SM332, digital input module SM321, digital output module SM322 and so on.
Operation panel operation panel OP27 as the man-machine interface The ProTool configuration software is used to customize the display and operation method of the OP27 to achieve the best results of the process. The OP27 is connected to the S7-300PLC via an MPI cable to form an MPI network.
The governor governor 514C is used to control the speed of the DC motor and can operate in four quadrants. It adopts the current speed double loop negative feedback control mode, the inner loop is the current loop, the current loop feedback signal is obtained by the 514C internal circuit self-test; the outer loop is the speed loop, the speed loop feedback signal is taken from the armature voltage, and it mainly controls the DC motor The speed so that it tracks the given value.
3 system software design S7-300PLC programming language STEP7 manages the written program and the data required for the program to run in the form of file blocks.
The sequence of operations prepares environment variables and parameters.
The organization block OB1 organization block OB1 is the main program loop ±, and its block diagram is as shown. When the organization block OB1 is executed, FC1, FB1, etc. function blocks for different functions are called. In addition, the organization block OB1 also calls the interrupt block OB35 periodically. The scale conversion block FC1 scale conversion block FC1 is responsible for the manual set value, arc The four digital quantities of the voltage set value, the arc voltage value, and the speed signal value are respectively converted into engineering quantities corresponding to the actual size.
Filter block FB1 filter block FB1 is responsible for filtering the data from the field.
The OB1 block diagram is called once by the organization block OB1, and the control block FB2 is called when the OB35 is executed. 6) Control block FB2 The control block FB2 mainly implements manual and automatic control functions.
The system described in this paper is applied to the smelting of titanium, which requires arc stabilization (ie, the arc voltage and arc current are kept stable). At the initial stage of smelting, the arc is manually adjusted until the arc is stabilized and transferred to the automatic control mode. To ensure that the smelting arc is always in a steady state, manual to automatic must be switched without disturbance. Because the PID adjustment principle is simple, the adaptability is good, the robustness is strong, and the control effect can fully meet the requirements of smelting titanium. Therefore, the system adopts PID adjustment. The introduction of differentiation is to reduce the overshoot and suppress the controlled amount of vibration, thereby improving the stability of the system.
Let Kc be the proportional coefficient, Ts be the sampling period, Ti be the integration time, Td is the derivative time, and e(k) is the deviation signal. Then the HD controller outputs: It is easy to cause system stability considering the deviation e(k) is large. As the decline, the integral separation algorithm is adopted. When Ie(k)l>M, the control amount of the current time can be obtained by knowing the output of the previous time and calculating the increment.
Set the control amount received by the governor to ut, the manual given amount is us, then in order to realize the manual to automatic bumpless switching when manual, in the manual mode, always calculate a tracking compensation amount: timing interrupt block OB35 timing interrupt block When OB35 moves, the version corresponds to 1u(t)s°re. When it is put into the automatic mode, the nki.net is used to realize the bumpless switching from manual to automatic.
3.2 Operation panel OP27 configuration Main screen The main screen of the electrode lift control system is set up, the AC/DC motor's running status display, arc voltage display, arc voltage set value display, manual setpoint display, DC motor speed display And an alarm display. In addition, the current time and date display is also set on the main screen.
System operation status screen The system operation status screen sets the PLC status display, the melting mode display, the electrode lift control mode display, and the electrode pneumatic status display.
The PID adjustment screen PID adjustment screen is used to adjust the parameters of the PID controller online.
After the alarm source query screen alarm appears, you can enter the alarm source query screen to query the alarm cause.
4 Operation results measured data According to the production process requirements, when the arc voltage is set to 30V, the measured data is shown in Table 1. Performance index 1 arc voltage: *1V; 2 arc running curve from the measured data to draw the system running curve, as shown .
Results Analysis and analysis of the measured data and the operating curve, we can see that the system overshoot is small, the smelting arc is stable, and fully meets the technical requirements.
Table 1 measured data serial number arc voltage / arc current / A running curve 5 Conclusion This system has been put into operation in Shenyang Sujiatun Titanium Plant for nearly 6 months, the operating conditions are good, to achieve the expected display and control functions, smelting The titanium products meet the requirements of the design process.
Practice has proved that the electrode lifting control adopts PLC control system based on PID control law, which is easy to operate, small in maintenance, stable and reliable in operation, and has certain promotion value.
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