Simulation of photovoltaic power inverter circuit

Abstract

This paper introduces solar power generation and switch circuit technology on the basis of relevant research at home and abroad.The switching circuit technology includes battery charging and discharging, three-phase full-bridge inverter circuit technology, and the simulation of photovoltaic power inverter circuit is carried out by combining the two technologies.

In this paper, based on the characteristics of solar cells, the use of photovoltaic cell engineering mathematical model of the output characteristic of photovoltaic power supply, drawing for photovoltaic cells in certain conditions and only a maximum power point, so by the Boost circuit and disturbance observation method for maximum power point tracking (MPPT) simulation, and realizes the maximum utilization of solar energy.
A bidirectional Buck/Boost circuit is designed to store excess energy.

In this experiment, matlab software was used for simulation, and the test results showed that the designed circuit could realize the charge and discharge control of the battery and generate better sine waves.

Keywords: Photovoltaic power generation;Maximum power tracking;Battery charge and discharge;Inverter control technology

Introduction

China’s solar power generation technology began to develop in the 1960s, initially used for space technology, with the reduction of cost and technology maturity, this technology gradually into civilian.Compared with the international, China’s photovoltaic technology is still a big shortage.After the reform and opening up, China introduced a number of solar power production lines, so that China’s solar industry for the first time has been greatly developed.After 2000, influenced by the launch of international projects and government projects and the international environment, China’s photovoltaic industry has been developed for the second time.In short, China’s photovoltaic industry has maintained steady development in recent decades, playing an important role in people’s production and life.In addition, China is located in the northern hemisphere, with a large land area and sufficient sunshine. Therefore, China is extremely rich in solar energy resources and has a great potential for the development and utilization of solar energy.

In recent years, power supply technology has developed rapidly and has been applied in many fields, such as aviation, telecommunications, office, etc.The development of power technology is mainly high-frequency inverter.The electronic switch of the first generation switching power supply is mainly silicon controlled, the second generation power transistor, and the third generation is mainly field controlled device.With the development of electric energy conversion technology, it is no longer an optional spare device, but an indispensable and important part in the electric power system.In particular, the combination with photovoltaic power generation will have great development potential in the central and western regions of China, because the population density here is small, living scattered, and solar energy resources are sufficient, which is very suitable for the development of solar energy technology [1].

This paper carries on the simulation research of the photovoltaic power inverter circuit, which is composed of the photovoltaic power supply, the energy storage circuit, the inverter circuit and the filter circuit.The research work of this paper mainly includes:

1. Research on maximum power point tracking technology of photovoltaic system.Since photovoltaic cells have and only have one maximum power point under certain working conditions, maximum power tracking is needed to maximize the use of solar energy.
2. Energy storage technology.Energy storage system USES voltage and current double closed loop control, dc bus voltage as the outer ring, which can adjust the PI and the results as the reference value of the storage battery charging and discharging current, current inner PI after regulation as the duty ratio, and by the outer loop PI regulating work results to determine the battery in charging or discharging state.
3. Inverter technology.The voltage - type three - phase full - bridge inverter is used to invert the input dc voltage into ac voltage.
4. Filtering technology.LC filter circuit is used to filter the output voltage to make the output voltage meet the requirements.

Outline

As shown in the figure1,we modeled and analyzed the characteristics of photovoltaic cells.The relationship between the output current $I_L$IL​ and the input voltage can be obtained.

Fig.1. Photovoltaic cell equivalent circuit

And by infering, we can get the i-u equation for the photovoltaic cell$I=I_{\mathrm{st}}\left\{1-C_{1}\left[\exp \left(\frac{U}{C_{2} U_{\infty}}\right)-1\right]\right\}\tag{1}$I=Ist​{1−C1​[exp(C2​U∞​U​)−1]}(1)

and $C_{1}=\left(1-\frac{I_{\mathrm{m}}}{I_{\infty}}\right) \exp \left(-\frac{U_{m}}{C_{2} U_{\infty}}\right)\tag{2}$C1​=(1−I∞​Im​​)exp(−C2​U∞​Um​​)(2)

$C_{2}=\left(\frac{U_{m}}{U_{\alpha}}-1\right) /\left(1-\frac{\mathrm{I}_{\mathrm{m}}}{I_{\mathrm{sc}}}\right)\tag{3}$C2​=(Uα​Um​​−1)/(1−Isc​Im​​)(3)

Based on the engineering mathematical model derived above, the simulation model of photovoltaic cells can be built as shown in figure 2.

Fig.2. Photovoltaic cell simulation diagram

Write the program and put in the parameters to get the output characteristic curve of the photovoltaic cell under different light intensity and temperature, as shown in figure 3, 4, 5, and 6.

Fig.3. $I-U$I−U characteristic curves of photovoltaic cells at different temperatures at 1000W/m²

Fig.4. $P-U$P−U characteristic curves of photovoltaic cells at different temperatures at 1000W/m²

Fig.5. $P-U$P−U characteristic curve of photovoltaic cells under different illumination at 25℃

Fig.6. $I-U$I−U characteristic curve of photovoltaic cells under different illumination at 25℃

I also designed a maximum power point tracking circuit for photovoltaic power supply for better use of solar energy, as shown in figure 7.

Fig.7. BOOST circuit simulation diagram for MPPT

Since the current generated by the photovoltaic power supply is direct current, it needs to be converted to ac. Therefore, I designed an inverter circuit as shown in the figure 8.

Fig.8. Voltage - type three - phase full - bridge inverter

In addition, in order not to waste electricity,And considering the lack of sunlight,As shown in the figure 9, I designed an energy storage circuit to store and release dc power.

Fig.9. Energy storage circuit simulation circuit diagram

After the above analysis, the complete circuit diagram is shown in the figure 10.

Fig.10. Simulation diagram of photovoltaic power inverter circuit

Conclusion

The main tasks accomplished in this paper are:

1. Research on maximum power point tracking technology (MPPT) of photovoltaic system. The disturbance control method is used to control the maximum power tracking of photovoltaic cells, and the maximum power tracking control model is established to verify the feasibility of the system.
2. Battery charge and discharge technology. The topology and parameters of the battery charging circuit with feedback control are designed to control the charging voltage and charging current of the battery.
3. Inverse technology. The three - phase full - bridge voltage inverter is adopted.
4. Limited by experimental conditions, the whole system needs to be further improved. The first is the maximum power tracking system, which needs further debugging to realize the application of the results of simulation debugging and finally realize the combination of the maximum power tracking system and uninterruptible power supply.

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