Simulation Research on Switching Power Supply System Based on PWM Control

0 Introduction

Through 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 to improve the simulation speed. Matlab is an advanced mathematical analysis software, and Simulink is a software package running in the Matlab environment 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 with Simulink to simulate power electronic systems more conveniently. With the development of power supply technology, PWM-controlled switching power supplies have been widely studied and applied, such as communication power supplies, locomotive power supplies, etc. Here, a 220 V high-frequency switching power supply is taken as the research object and a model is established. The power supply adopts pulse width modulation control to achieve multiple index requirements such as weight reduction, volume reduction, and accuracy improvement. It is very representative in the system model research of switching power supplies. The main circuit adopts a DC-HFAC-DC-LFAC structure, and a discrete, nonlinear model is established using Matlab. The system is simulated in open and closed loops, and the simulation results are compared and analyzed.

1 Circuit Schematic

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: DC boost circuit simulation parameter settings: operating frequency ∫ = 20 kHz; transformer ratio k = 13; output filter L = 8 μH, c = 300/μF. Full-bridge inverter circuit simulation parameter settings: operating frequency f = 25 kHz, output filter L = 80 mH, c = 100 μF. The corresponding simulation parameters are set here for simulation debugging.

2.1 Modeling of the input circuit

The power module and resistor and capacitor module of the power system toolbox can be used to easily build a simulation model of the input loop. The input adopts a two-stage LC DC input filter technology, which limits the transient resonance peak while ensuring the steady-state filtering effect. It has the advantages of no power consumption, high attenuation, and controllable resonance peak.

2.2 DC-DC loop modeling

As shown in Figure 1, the rectifier diode in the output circuit cannot flow through the reverse current. This is also a nonlinear link, and a nonlinear mathematical model is established.

2.2.1 Modeling of DC-DC main circuit

According to Figure 1, the current in the filter inductor is:

In the formula: Ui is the output voltage of uncontrolled rectification; UF is the load voltage; UL is the inductor voltage; the load voltage is:

In the formula: UC is the capacitor voltage; IL is the inductor current; Ic is the capacitor current; LF is the load current.

2.2.2 Modeling of PI Regulator

The simulation model of proportional integral regulator (PI) is shown in Figure 5.

The output waveform of the PI regulator is shown in Figure 6.

2.2.3 Modeling of PWM Controller

The simulation uses the integral relationship to generate a triangular wave. The Sources in Simulink have a pulse generator (PulseGenerator), 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 the inverter circuit

The inverter circuit simulation model (Inverter) is shown in Figure 9.

2.3.1 Modeling of PI Regulator

The proportional-integral regulator simulation model (P11) is shown in FIG10 , and its output waveform is shown in FIG11 .

2.3.2 SPWM Modeling

The sinusoidal width modulation model simulation module (SPwM) is shown in FIG12 .

2.4 Modeling of the Output Circuit

The output and display module simulation model (output) is shown in Figure 13.

3 Simulation Results

A simulation model of the Sireulink system is established. The simulation time is set to 0.3 s, and the variable step size odel5 algorithm is selected. When the input voltage is 48 V and the load is rated load, the output waveform can be obtained by starting the simulation. 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.

From the spectrum analysis, it can be seen that when the loop is open, the total harmonic coefficient (THD) is 3.02%, and the third harmonic content is relatively large. When the loop is closed, the total harmonic coefficient (THD) is 0.07%, and the harmonic content is very small. From the voltage waveform, it can be seen that when the loop is open, the voltage output waveform reaches stability in the third cycle, while when the loop is closed, it reaches stability in the second cycle, so the speed at which the voltage reaches a stable value in the closed loop is faster than in the open loop.

4 Conclusion

The model can not only be used to examine the transient change process of the main state inside the system, but also to analyze and design the control loop. This has practical significance and research value for improving the performance of the control system. The switching power supply system is modeled by mathematical methods, and the simulation time is selected as 0.3 s. It only takes about 40 s to complete the simulation, which not only avoids the extremely slow simulation speed of other tools, but also improves the reliability of the simulation. Sireulink is a powerful dynamic simulation tool for control system simulation with complete functions, easy system control, and simple model construction.