Reasearch On NPC Three Level Inverter Control Method For Temperature Equalization

Inverter plays an important role in new energy fields such as photovoltaic power generation and wind power generation.With the continuous development of new energy generation technology,the demand of high-power and multi-level inverter is increasing,and the control strategy is also a hot topic.In this paper,the problem of uneven heating of power devices in Neutral Point Clamped(NPC)three level inverter is studied,and a power device loss calculation model and temperature calculation model is established.A control strategy for temperature balance of power devices is proposed to achieve the temperature balance of power devices.The main contents of this paper are as follows:In this paper,the pulse width modulation method of the NPC three-level inverter is studied.The modulation process of sinusoidal pulse width modulation(PWM)and space vector pulse width modulation(SVPWM)method are analyzed,and a simplified SVPWM method is proposed based on this.The simplified method reducd the difficulty of computing the vector synthesis,and decreased the loss of switching devices.In order to explore the cooling principal of inverter,the loss models and temperature models of power devices are analyzed.Based on the simplified SVPWM method,the working mode of the NPC three level inverter is analyzed,and the loss calculation method of the power device is put forward in combination with the loss model of the power device.The internal physical structure of power devices is studied.Based on this,a temperature model for the steady state of power devices is proposed.Under different working conditions,the loss and junction temperature of various power devices are obtained through the loss model and temperature model.Aiming at the problem of unbalanced heating of power devices,the working principle of Active NPC(ANPC)three level inverter is analyzed.The calculation method of power device loss under the traditional control strategy is obtained.Based on this,an improved control strategy with the function of temperature balance is proposed and the maximum temperature of the power device is reduced.To some extent,the temperature balance control of power devices is realized.The experimental platform of the high power ANPC three level inverter is set up,and the algorithm flow and control procedures of the temperature balance control are designed.The temperature balance control experiment is carried out under different working conditions.The results show that the improved control strategy can reduce the maximum temperature of the power device,which is of great significance to the capacity improvement of the high power three level inverter.