Research On SVPWM Algorithm Of Three-level Inverter

Three-level inverter gradually replaces two-level inverter in life because of its advantages such as low electromagnetic interference and low harmonic content,which is suitable for the application of medium-high voltage and high-power applications.At the same time,three-level structure is relative to higher level.Its topology structure is simple,the control algorithm is easy to realize,and it is more suitable for the research of school and the practical application in life,so it is very necessary to study three-level.The traditional three-level SVPWM algorithm needs to judge the small sector and the large sector,and the neutral voltage is not easy to control.When the DC voltage changes,the output waveform is prone to distortion,and even degenerates to the two-level waveform.This unstable phenomenon is apt to cause the switch on or off at the same time.This paper studies the common three-level SVPWM modulation algorithms,such as four small sectors and six small sectors,and summarizes the development history of the three-level modulation.The main research contents are as follows:A new three-level SVPWM modulation algorithm,direct vector SVPWM modulation algorithm,is proposed,which divides the vector region into 12 sectors directly.By sampling the reference vector,the time-state ratio with modulation depth is directly generated.The PWM wave with modulation information can be generated by comparing the frequency with the sawtooth wave of the input signal.The step waveform is obvious,the harmonic content is small,and the DC side voltage is changing from low voltage to high voltage.The steps are still intact.A simplified algorithm of direct SVPWM algorithm is presented.The method is further simplified in form,but there is a problem that the step wave segmentation is not obvious.For this reason,two hypothetical reasons are given in this paper.For two hypothetical reasons,by adopting the mode of starting vector from negative short vector,the original 11-segment direct SVPWM algorithm is improved to 9-segment direct SVPWM algorithm.This improvement not only corrects the unobvious step waveproblem mentioned above,but also further simplifies the algorithm.Finally,it is proved that the direct SVPWM algorithm is a mature modulation algorithm.All the simulations are built in Matlab/Simulink environment.At the same time,the hardware circuit of three-level inverter based on DSP CPLD is designed and the software is written on CCSV6.0 platform.