Abstract: To represent a switching power supply system as a mathematical model or a nonlinear control model, a discrete, nonlinear simulation model must be established using Matlab. This model is then used to simulate a 220V high-frequency switching power supply. Simulation experiments analyze the inverter's operating process and dynamic characteristics, including its output voltage, spectrum analysis, and total harmonic distortion (THD). Analysis of the output voltage waveform shows that the system exhibits relatively low output harmonic content and good steady-state performance.
Keywords: switching power supply; Matlab; sine wave inverter; pulse width modulation
0 Introduction
By using mathematical methods, the low-power switching power supply system is represented as a mathematical model and a nonlinear control model, and a simulation model of the entire switching power supply system is established, which improves the simulation speed. Matlab is an advanced mathematical analysis software, and Simulink is a software package that runs in the Matlab environment and is used for modeling, simulating and analyzing dynamic systems. It supports continuous, discrete and mixed linear and nonlinear systems. The Power System Toolbox was introduced in Matlab 5.2. This toolbox can be used in conjunction with Simulink to more conveniently simulate power electronic systems. With the development of power supply technology, PWM-controlled switching power supplies have been widely studied and applied, such as communication power supplies and locomotive power supplies. Here, a 220V high-frequency switching power supply is taken as the research object and a model is established. This power supply adopts pulse width modulation control mode and realizes multiple index requirements such as weight reduction, volume reduction and accuracy improvement. It is highly representative in the system model research of switching power supplies. The main circuit adopts a DC-HFAC-DC-LFAC structure [1] , and a discrete and nonlinear model is established using Matlab. The system is simulated in open loop and closed loop respectively, and the simulation results are compared and analyzed.
1. Circuit schematic diagram
The circuit principle is shown in Figure 1.
2. Simulation Circuit
The simulation models of each submodule in Figure 2 are shown in Figures 3 to 10. The simulation parameters of the system are as follows: DC boost circuit simulation parameters: operating frequency f = 20 kHz; transformer turns ratio k = 13; output filter L = 8μH, C = 300μF. Full-bridge inverter circuit simulation parameters: operating frequency f = 25kHz, output filter L = 80mH, C = 100μF. The corresponding simulation parameters are set here for simulation debugging.
2.1 Modeling of the input loop
The power supply module and resistor-capacitor module of the power system toolbox can be used to easily build a simulation model of the input circuit. The input adopts a two-stage LC DC input filtering technology [2] , which limits the transient resonance peak while ensuring the steady-state filtering effect. It has the advantages of no power consumption, attenuation, and highly controllable resonance peak.
2.2 Modeling of DC-DC Loops
As shown in Figure 1, the rectifier diode in the output circuit cannot carry reverse current, which is also a nonlinear element. Therefore, a nonlinear mathematical model is established.
2.2.1 Modeling of DC-DC Main Circuit
As shown in Figure 1, the current in the filter inductor is:
In the formula: U <sub>i </sub> is the output voltage of the uncontrolled rectifier; U<sub> F </sub> is the load voltage; U<sub> L </sub> is the inductor voltage; the load voltage is:
In the formula: U <sub>C </sub> is the capacitor voltage; I<sub> L </sub> is the inductor current; I <sub>C </sub> is the capacitor current; IF is the load current.
2.2.2 Modeling of PI Regulator
The simulation model of the proportional-integral controller (PI) is shown in Figure 5.
The output waveform of the PI controller is shown in Figure 6.
2.2.3 Modeling of the PWM Controller
The simulation uses integral relationships to generate triangular waves. Simulink's Sources have a Pulse Generator, which generates a signal with a frequency of 20 kHz, an amplitude of 4 × 10⁴ , and a duty cycle of 50%.
2.3 Modeling of Inverter Circuit
The inverter circuit simulation model (Inverter) is shown in Figure 9.
2.3.1 Modeling of PI Regulator
The proportional-integral controller (PII) simulation model is shown in Figure 10, and its output waveform is shown in Figure 11.
2.3.2 Modeling of SPWM
The sinusoidal width modulation (SPWM) model simulation module is shown in Figure 12.
2.4 Modeling of the output loop
The simulation model of the output and display module (ourput) is shown in Figure 13.
3 Simulation Results
A Simulink system simulation model was established. The simulation time was set to 0.3s, and the Odel5 algorithm with variable step size was selected. With an input voltage of 48V and a rated load, the simulation was started to obtain its output waveform. The output voltage waveform and THD spectrum are shown in Figures 14 and 15.
3.1 Open-loop simulation
The open-loop simulation is shown in Figure 14.
3.2 Closed-loop simulation
The closed-loop simulation is shown in Figure 15. Spectrum analysis shows that in the open-loop configuration, the total harmonic distortion (THD) is 3.02%, with a relatively high third harmonic content. In the closed-loop configuration, the THD is 0.07%, with very low harmonic content. The voltage waveform shows that the voltage output waveform stabilizes in the third cycle in the open-loop configuration, while it stabilizes in the second cycle in the closed-loop configuration. Therefore, the voltage reaches a stable value faster in the closed-loop configuration than in the open-loop configuration.
4 Conclusion
This model can be used not only to examine the transient changes of the main states within a system, but also to analyze and design control loops. This has practical significance and research value for improving the performance of control systems. Using mathematical methods to model the switching power supply system, with a simulation time of 0.3 seconds, the simulation can be completed in approximately 40 seconds, avoiding the extremely slow simulation speed of other tools and improving simulation reliability. Simulink is a powerful dynamic simulation tool for control systems, offering comprehensive functions, easy system control implementation, and simple model construction.
References:
[1] Lin Weixun. Modern Power Electronic Circuits [M]. Hangzhou: Zhejiang University Press, 2002.
[2] Chen Daolian. DC-AC Inverter Technology and Its Applications [M]. Beijing: Machinery Industry Press, 2005.
[3] Xie Shaojun, Han Jun, Zhang Yong, et al. Research on high-power inverter technology with low input voltage [J]. Journal of Nanjing University of Aeronautics and Astronautics, 2004(4): 231-234.
[4] Li Qiang, Tong Xide. Development of vehicle-mounted single-phase sinusoidal pulse width modulation IGBT inverter [J]. Power Electronics Technology, 1997(1): 23-26.
[5] Lu Zhiguo. Computer simulation technology for power supply [M]. Beijing: Science Press, 2001.
For details, please click: Simulation Study of Switching Power Supply System Based on PWM Control
