The Research Of Three-level NPC Inverter

For the NPC inverter(Neutral-point-clamped, NPC inverter), due to its own special topology caused by its many and natural disadvantages are mainly: the DC bus voltage will shift, resulting in the same bridge arm switch tube compression is not balanced, on the quality of output waveform and its power devices caused some serious influence. Second, after the power is common mode voltage is zero sequence voltage, common mode voltage exists seriously affect the motor service life, resulting in ambient electromagnetic interference, get an electric shock accidents caused some harm.In view of the above three level NPC inverter own shortcomings, this paper puts forward two effective control method, first, through the study of space vector modulation method(space vector pulse-width modulation, SVPWM), the traditional modulation method is improved and presents a feedback capacitor voltage offset size in real time to calculate the redundant small vector type N and P type modulation time and using the logarithmic method, not only is the mid point capacitor voltage balance and reduces the maximum switching frequency; second, starting from this control strategy based on the carrier modulation, a double modulation wave modulation strategy to solve the problem of neutral point voltage DC offset, is actually to adjust bus current by adjusting the switch state of "O", this strategy is compared with the traditional carrier modulation method, load power factor can be To adjust the whole process. Based on this the above two control strategies for modeling and Simulation in Matlab/simulink environment, the simulation results show that the above two methods in theory is feasible and effective, in order to make the above two kinds of control method is verified further in practical engineering, in this paper, a small power 2KW three level NPC prototype designed by DSP2812 IC control program for the actual test, before actually electric process to analyze the effect of dead time on the output voltage and current waveform, proposes a specific solution to achieve the compensation of dead time, make the experimental results more close to the theoretical simulation, then experimental results show that the control strategy based on whether the carrier or method of space vector control based on the control of in kind are correct and effective.Aiming at the common problems of common mode voltage, this paper analyzes the specific reasons for the three-level NPC inverter common mode voltage generated in the common mode voltage is caused by some particular vector, through the Matlab / Simulink for simulation theory. Simulation results show that the proposed theoretical assumptions are correct, finally puts forward some actual inhibition of the effective method to solve the problem of common mode voltage.