Abstract: This paper introduces the design method of DC speed control system based on engineering design method, and uses Matlab/Simulink for modeling and simulation research. Finally, the simulation output of the control system is shown. Keywords: regulator , SimuLink, speed loop 1 Introduction DC motors have advantages such as good speed regulation performance, large starting torque, and easy smooth speed regulation over a wide range. Their speed control system has always occupied an extremely important position in industrial control. With the development of power technology, especially after the advent of high-power power electronic devices, DC motor drives will gradually be replaced by AC motor drives. However, in medium and small power applications, permanent magnet DC motors are often used, which only require control of the armature circuit and are relatively simple. Especially in high-precision position servo control systems, and in places where speed regulation performance is required or large torque is required, DC motors are still widely used [2]. The most typical speed regulation system in DC speed regulation control system is the speed and current double closed speed regulation system. The design of DC speed regulation system needs to complete the processes of open-loop speed regulation, single closed-loop speed regulation, and double closed-loop speed regulation. It requires observation of a lot of performance, and with a lot of calculation parameters, it is often difficult to achieve the desired result. For example, if the SimuLink utility tool in Matlab is used to assist in the design process, since it can build the dynamic model of the controlled system and observe the waveforms of each point intuitively and quickly, the performance improvement of the speed regulation system can be completed by repeatedly modifying its dynamic model, without having to repeatedly disassemble and debug the physical model [4]. The dynamic modeling and simulation tool SimuLink in Matlab has the advantages of convenient module configuration and intuitive performance analysis, which can shorten the product design and development process and also provide a virtual experimental platform for teaching. 2. Schematic diagram of dual closed-loop DC speed control system: Based on the dynamic mathematical model of single closed-loop speed control system, considering the structure of dual closed-loop control, the dynamic structure diagram of current and speed dual closed-loop DC speed control system can be drawn, as shown in Figure 1. [align=center] Figure 1 Current and speed dual closed-loop DC speed control system[/align] 3. Engineering design method of regulator There are many design methods for the correction link, and they are very flexible. The classic dynamic correction method for designing regulators must simultaneously solve the contradictory static and dynamic performance requirements of stability, accuracy, speed, and anti-interference. Designers need to have a solid theoretical foundation, rich practical experience, and skilled design techniques. This is often difficult for beginners to master and is not very convenient in engineering applications. Therefore, a simpler and more practical engineering design method has been developed. (1) Design of current regulator: In actual systems, there are often some inertial links with small time constants. Their reciprocals are all in the high-frequency range of logarithmic frequency characteristics. Approximating them will not significantly affect the dynamic performance of the system. Therefore, when the system has multiple small inertial links, under certain conditions, they can be approximated as a small inertial link, whose time constant is equal to the sum of the small time constants of the original system [6]. After the processing of the small inertial link, and ignoring the influence of back electromotive force on the current loop, and assuming ideal no-load, the simplified structure of the current loop is shown in Figure 2. [align=center] Figure 2 Simplified structure of current loop (inner loop) [/align] In order to limit the excessive overcurrent, an anti-saturation current regulator is used in the current loop. Since the current detection signal often contains AC components, a low-pass filter is required. Its filter time constant is selected as needed. The filter can suppress the AC components in the feedback signal, but it also brings delay to the feedback signal. In order to balance this delay, an inertial link with the same time constant is added to the given signal channel, which is called the given filter link. Its significance is to let the given signal and the feedback signal go through the same delay so that the two can be properly matched. In the figure, Since the important function of the current loop is to keep the armature current from not exceeding the allowable value during dynamic processes, it is desirable to minimize the overshoot and at the same time require good anti-disturbance performance. Therefore, the current loop is generally designed according to the typical type I system. The D in the anti-saturation current regulator (PID) is taken as zero, and the current loop of the double closed-loop speed control system is established as shown in Figure 3. The SIMULINK system structure diagram is shown in Figure 3.2 Design of electric drive control system. Since the controlled object of the current loop is a dual-inertia type, to correct it into a typical Type I system, a PI regulator should be used, and its transfer function is: (3.1) Where: —— proportional coefficient of the current regulator —— lead time constant of the current regulator The undetermined parameters of the current regulator include and, in order to make the zero point of the regulator cancel the time constant pole of the controlled object, let = Then the closed-loop transfer function of the current loop is (3.2) Where: After the order reduction processing, it is approximately: (3.3) In general, the desired overshoot is, and the damping ratio can be taken from Table 1, Table 1 Relationship between dynamic following performance index and parameters of typical Type I system Therefore (3.4) (2) Design of speed regulator: In order to simplify the system, after the current loop is built, it must be module encapsulated and named "controlled object", and then its speed outer loop is built. In order to limit the speed and avoid the negative rotation phenomenon, an anti-saturation regulator (PID) is also used in the speed loop. The speed feedback voltage obtained from the tachogenerator contains commutation ripple from the motor, therefore it also needs filtering. The filtering time constant is denoted as , similar to the current loop. A given filtering element with a time constant of is also added to the speed setting channel. After effectively moving the filtering element into the loop, and merging the two small inertial elements with time constants and into an approximation of a single inertial element with a time constant of , the speed loop is simplified as shown in the figure. The speed loop generally uses a typical Type II system. This is primarily based on the requirement of zero steady-state error, and secondly, from a dynamic performance perspective, it has good disturbance rejection capabilities. The speed regulator should also be a PI regulator, and its transfer function is: (3.5) Where, Kn is the proportional coefficient of the speed regulator and τn is the lead time constant of the speed regulator. Thus, the open-loop transfer function of the speed system is (3.6) Where, the open-loop gain of the speed loop is the parameter of the speed regulator, which includes Kn and τn. According to the parameter selection method of typical type II system, the proportional coefficient h of the speed regulator should be determined by the requirements of the system for dynamic performance. Generally, h=5 is selected. 4. Simulation Example of a Dual-Closed-Loop DC Speed ​​Control System: A thyristor-powered dual-closed-loop DC speed control system uses a three-phase bridge circuit as the rectifier. Basic data is as follows: DC motor: 220V, 136A, 1460r/min, Cε = 0.132V/r/min, allowable overload factor λ = 1.5; Thyristor amplification factor: Ks = 40; total armature circuit resistance R = 0.5Ω; armature circuit inductance: L = 0.015H. Design requirements: Steady-state performance: no steady-state error; Dynamic performance: current overshoot, speed overshoot output waveform when starting from no-load to rated speed. [align=center] Figure 3: Simulation curve of speed output of the dual-closed-loop DC speed control system. 5. Conclusion: By modeling the current and speed dual-closed-loop DC speed control system using Simulink and obtaining the simulation curve of the control system, it is shown that the engineering design method is feasible and simple. References: 1. Han Lu, DC Motor Dual Closed-Loop Speed ​​Control System and Its Simulation with SIMULINK, Marine Engineering 2/2003 2. Shu Huailin, DC Motor PID Neural Network Dual Closed-Loop Control System, Motor Control 11/2005 3. Jiao Hongwei, Application of Thyristor in DC Motor Stepless Speed ​​Regulation, Science and Technology Information • Industrial Technology 1/2006 4. Xu Yuehua, Wang Renhuang, Application of Matlab in DC Speed ​​Control Design, Microcomputer Information 8/2003 5. Chen Boshi, Automatic Control System, Machinery Industry Press, 1981.7 6. Li Xianyun, Automatic Control System, Higher Education Press, 2003.2 7. Huang Jian, Automatic Control Principles and Applications, Higher Education Press, 2000.4