High Power Factor Rectifier Simulation Experiment Platform Based on MATLAB

1 Overview

Simple systems can be directly modeled, and the relationships between modules and the input-output relationships of modules can be analyzed. However, for relatively complex systems, Simulink contains multiple modules, which makes the relationships between modules very complex and not conducive to analysis. To this end, module groups with certain functions can be encapsulated, and users do not need to understand their internal structure, but only need to understand their functions and input parameters. Moreover, each module is portable. The main modules encapsulated in the simulation experiment platform include: a typical single-phase rectifier main circuit, a three-phase fully controlled bridge rectifier main circuit, a detection module (coordinate transformation), a pulse generation module, a control module, a measurement module, etc. The main circuit inductance value, switching frequency and other parameters of the three-phase reversible PWM rectifier are obtained through simulation, and the total harmonic distortion (THD) of the input current, the power factor of the power supply and the output DC voltage of the system are affected, thereby providing a reliable basis for determining the parameters of the main circuit in the actual design, which has practical significance for the design of the three-phase reversible PWM rectifier.

2. Establishment of module library

The simulation platform is established by creating a module library under the Simulink Library Browser. The new library is named kongde. Right-click to open the module library and add the modules you encapsulate to the library. After adding all the modules and saving, click kongcle under the Simulink Library Browser to display all the modules in the module library, as shown in Figure 1. During simulation, you only need to add each functional module from the module library to the model file, set the corresponding parameters, and connect each functional module according to the principle to observe the results.

3 Module Packaging

3.1 Rectifier main circuit

The main circuit of the built rectifier adopts a resistive inductive load. The main circuit of the three-phase voltage-type PWM rectifier is shown in Figure 2. For Simulink, based on the mathematical model of the rectifier, the model is built using a switch function differential equation group, and the simulation operation speed is relatively fast. Since the module library has detailed modeling of parameters such as IGBT buffer circuit parameters and switch delay, it is closer to the actual situation, as shown in Figure 3.

3.2 Control module

The control module used in the simulation is a current decoupling control algorithm based on the space voltage vector. The current decoupling control module is shown in FIG4 .

3.3 Power factor measurement module

Factor measurements include power factor, fundamental displacement factor, distortion factor, as well as active power, reactive power, apparent power, etc. For a three-phase system, if the three-phase voltage and current waveforms are symmetrical, the active power is the sum of the three-phase active power, and the reactive power is the sum of the three-phase reactive power, as shown in Figure 5. This module can measure the power factor of a three-phase system, as well as active, reactive, and apparent power.

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4 Simulation of three-phase VSR system based on simulation module

The whole system is a dual-loop control structure with two inner loops and one outer loop, which is composed of a voltage loop and two current loops. The voltage loop not only controls the DC output voltage, but also takes the output of the voltage loop regulator as the given active current id, and the given reactive current iq can be directly set to zero. In the current and voltage dual-loop system, the current loop as the inner loop directly determines the quality of the dynamic and static characteristics of the whole system. The simulation model of the whole system is shown in Figure 6. The system includes a main circuit module, a detection module, a current decoupling control module, an SVPWM module, and a measurement module. The main modules in the model are added from the Kongde module library, and the corresponding modules can be simulated by connecting them according to the functions. Set the system parameters, and the specific parameters are shown in Table 1.

After setting the parameters, the system can be simulated. The voltage and current waveforms on the AC side and the load waveform on the DC side when the load increases suddenly are shown in Figure 7; the three-phase current waveform on the AC side when the load increases suddenly is shown in Figure 8; the voltage and current waveforms on the AC side and the load waveform on the DC side when the load decreases suddenly are shown in Figure 9; the three-phase current waveform on the AC side when the load decreases suddenly is shown in Figure 10.

From the simulation results, it can be seen that the current decoupling control algorithm based on the space voltage vector makes the AC side current waveform of the three-phase VSR symmetrical and sinusoidal in steady state, the phase current and the phase voltage are in phase, and the DC side voltage is stable. When the load changes suddenly, the voltage fluctuates to a certain extent, but it quickly catches up with the given value within one cycle. It can be seen that the system has strong robustness. Through measurement, it can be seen that the power factor of the three-phase system is approximately 1, and the voltage and current of one phase are measured. The fundamental displacement factor and distortion factor are both approximately 1. In the transient process, the current has a fast following performance, and the system transient transition time is short. When the load changes suddenly, the sinusoidal current waveform can be maintained and the high power factor operation can be maintained. The current decoupling control based on the space voltage vector of the three-phase VSR makes the DC side voltage more stable, the ripple is smaller, and the power factor is higher. At the same time, the three-phase VSR can also operate in the unity power factor inverter state.

5 Conclusion

The established simulation platform can provide an opportunity to learn basic theories more deeply, rather than just book knowledge. In the simulation process, various problems will inevitably be encountered. By changing various parameters to analyze the waveform, the influence of the parameters on the entire simulation system can be analyzed. The simulation platform has certain limitations. It only encapsulates several common rectifiers. At the same time, some parameters are fixed, such as the PWM cycle (0.02 s). If the cycle is to be changed, the power cycle must also be changed. These need to be improved.