Abstract: This paper proposes a design and MATLAB simulation method for a fuzzy PID control of a switching power supply. Simulation results show that the fuzzy control PID has a fast dynamic response, small overshoot, and small output voltage fluctuations caused by load changes. Keywords: switching power supply; PID control; fuzzy control 1 Introduction A switching power supply is a DC regulated power supply controlled by switching. It is widely used in various electronic devices due to its small size, high efficiency, and lightweight characteristics. The control section of a switching power supply is mostly designed and operates based on analog signals, resulting in poor anti-interference capabilities and signal distortion. Due to the rapid development of computer technology, the control and processing of digital signals have shown more and more advantages: it is easy for computers to process and control, avoids the distortion of analog signal transmission, reduces the interference of stray signals, and is convenient for software debugging. Digital PID control has emerged. It has made the switching power supply develop towards digitalization, intelligence and multi-functionality. This has undoubtedly improved the performance and reliability of the switching power supply. However, since the switching power supply itself is a nonlinear object, it is quite difficult to establish its accurate model. Approximate processing is often used. Moreover, the power supply system and load changes are uncertain. Therefore, it is often difficult to make the parameters of the PID regulator change accordingly when using the above analog or digital PID control methods, and the control effect is not ideal. The recently developed Fuzzy control is a kind of human-like intelligent control method. It does not rely on the mathematical model of the controlled object and is easy to use human experience knowledge to implement control. This is very suitable for some complex and variable or structurally uncertain systems that are difficult to describe with an accurate mathematical model. It has strong robustness [1], especially for complex objects that cannot be determined. This paper proposes the design and simulation of fuzzy control of switching power supply based on this idea. 2. Circuit Structure and Control Strategy 2.1 Main Circuit Structure The main circuit topology is shown in Figure 1. A 220V single-phase AC power supply is rectified by a full-wave uncontrolled rectifier to obtain approximately 300V DC voltage. This DC voltage is then converted to the required high-frequency pulsating voltage via a half-bridge high-frequency converter composed of IGBTs, and finally rectified to obtain the required DC voltage. Since the power supply's power is not large (output 45V, 10A), the main circuit adopts an IGBT half-bridge topology to prevent magnetization and save costs. The main frequency is selected as 20kHz to ensure the IGBTs operate at their optimal state. In the figure, L1 and C1 are used to suppress differential-mode noise, while L2, C2, and C3 are used to suppress common-mode noise. Calculations for each parameter are omitted. [align=center] Figure 1 Main Circuit Schematic[/align] 2.2 PID Control Circuit Design The main circuit and PWM generation circuit of the switching power supply are modeled in the MATLAB environment, as shown in Figure 3. For simulation convenience, some filtering, protection, and absorption circuits are omitted in the figure. Figure 2 is the simulation schematic of the PWM subsystem. Due to the nonlinearity of switching power supplies, significant approximations are made when abstracting their models. Based on the above model, the transfer function of the PID controller is designed using the traditional design method. As can be seen in the following analysis, the control performance of this controller is not ideal when the power supply voltage or load changes abruptly. [align=center] Figure 2 PWM Subsystem Figure 3 Conventional PID Control Model of Switching Power Supply[/align] 2.3 Design of Fuzzy Controller The structure of the fuzzy controller is shown in Figure 4. In the figure, Ug is the given voltage, Ur is the feedback voltage, e and ec are the deviation and the rate of change of the deviation, and E and EC are the fuzzified deviation and the rate of change of the deviation. The output U of the fuzzy controller is defuzzified into u, and then controlled by the PWM circuit to control the main circuit of the switching power supply. [align=center] Figure 4 Model of Switching Power Supply[/align] The input and output linguistic variables both take 7 linguistic values, namely: PB, MB, PS, ZE, NS, NM, NP. The membership functions used to describe the fuzzy subsets on the domain of each linguistic variable are shown in Figure 5. The fuzzy control table obtained based on experience is as follows: [align=center] Figure 5 Membership functions of input and output variables[/align] Fuzzy inference rule table Based on the above design, the fuzzy control circuit of the switching power supply based on MATLAB is shown in Figure 6. 3 Experimental Results Based on the experiments on PID controller and fuzzy controller, the two control algorithms were compared. [align=center] Figure 6 Fuzzy control circuit model of switching power supply[/align] 3.1 Comparison of dynamic characteristics during startup The first half of Figure 7 (t: 0-0.15) is a comparison of the output characteristics of the fuzzy controller of the PID controller during startup. This curve was measured when the load was 8.5A and the output voltage setpoint was 38V. It can be seen from the figure that the overshoot of fuzzy control is much smaller than that of PI control. Fuzzy control can prevent large overvoltages in the system during startup, which is very beneficial for the normal operation of the equipment. [align=center] Figure 7 Startup characteristics and dynamic characteristics of operating point change[/align] 3.2 Comparison of dynamic characteristics when parameters change Since the voltage required by the load of the switching power supply is adjustable, that is, the operating point is variable. The latter half of Figure 7 (t: 0.15–0.3) shows the dynamic characteristics of the PID controller and the fuzzy controller when the operating point changes (voltage: 38V→28V, current: 8.5A→6.4A). The figure shows that when the operating point changes, the fuzzy control process is faster and less oscillating than the PID control process. 4. Conclusion Fuzzy control is a type of nonlinear control whose control rules are based on human experience. It exhibits good robustness and overshoot suppression capabilities for controlling nonlinear objects such as switching power supplies. Introducing fuzzy control strategies into switching power supplies will open up new possibilities for their development. The innovation of this paper is the proposal of a design and MATLAB simulation method for fuzzy control PID in switching power supplies. References [1] Ding Fang, Li Yanfang, Fei Yulong. Application of intelligent PID algorithm in liquid level control system. 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