Research Of 400Hz Medium Frequency Aviation Ground Supply Based On T-type Three Level Inverter

Ground Power Unit(GPU)is the second generation medium frequency power supply based on inverter technology.It requires good electrical performance,large capacity and lightweight in aviation applications.Because of the high fundamental frequency,there are some problems in the design of medium frequency power supply,such as low quality of output waveform and poor dynamic stability,and the control strategy is more complex.This paper introduces the research status,latest product specifications and development trend of 400 Hz aviation power supply at home and abroad,and puts forward the application of T-type three-level structure in the circuit structure design of aviation ground power supply.The superiority of the design is verified by control strategy analysis and simulation calculation.Firstly,aiming at the technical standard of aeronautical ground power supply,a 400 Hz medium frequency power supply circuit using T-type three-level inversion technology is designed,and the device parameters of key modules such as rectifier,DC-side filter energy storage,inverters and output filter are calculated and selected respectively.On this basis,the typical structure of three-level inverters is compared,The working principle of T-type three-level circuit is expounded emphatically,the mathematical model of T-type three-level inverters is established,and the mutual conversion relations of T-type three-level inverters in abc,?? and dq are analyzed.In the control strategy research of inverters,The three-phase AC output is stabilized by PI double-loop control.the unbalance of DC bus neutral point voltage is analyzed,According to the different effect of basic voltage vector on capacitor charging and discharging based on the principle of SVPWM,By different means of directly controlling the reference voltage vector and introducing control factor to regulate the action time of small vector,the adjustment and optimization were carried out.Aiming at the unbalanced load characteristics of medium frequency power supply,an improved control method based on PI double-loop control is proposed.The single-phase input signal is converted into three-phase control signal by symmetrical component method,and the optimal control of output is realized.In the model predictive control strategy for TNPC inverters,a cost function based on the relationship between the output current and the predicted current difference and the current fluctuation coefficient is established,and a control strategy aiming at the minimum solution of the cost function is established.Finally,the simulation system of 400 Hz medium frequency power supply circuit based on T-type three-level inverters is established through the relevant modules of MATLAB.The calculation models of PI double-loop control,improved PI double-loop control and model predictive control strategy are designed respectively.The results show that the medium frequency power supply with T-type three-level inverter has higher output power in different three-level structure models.Among the different control strategies,the total harmonic distortion rate of the output of the system is the lowest under PI double-loop control strategy,and the waveform stability can be achieved under the condition of 400 Hz AC three-phase output.Moreover,the neutral-point voltage imbalance problem is effectively improved by controlling the small vector of voltage vector SVPWM modulation.