Research On The Key Problems And Experimental For Three-level Inverter

The neutral point clamp three-level converter has been one of the research focus topics in the field of high-voltage and capacity electrical energy.Through different combinations of switches,multi-1evel ladder wave output voltage can effectively improve capacity and voltage pressure levels of inverters,reduce the output voltage harmonic and switching losses.But more switches and control demand cause complicated control method. So the space-vector PWM(SVPWM) is analyzed in three-level converters.The relevant theory of three-level converters,in turn the working principle of diode clamp-type three-level inverter,SVPWM modulation algorithm,the problems and their solutions approach about neutral point potential imbalance are presented firstly.Based on a simplified SPWM algorithrm for decomposition of reference voltage,an improved PWM modulation algorithm is presented. Balancing neutral point potential and common-mode voltage reducing methods are studied in the paper. Neutral point potential unbalance is an inherent problem in neutral point clamped three-level converters. A detailed analysis by vectors and neutral point current about the regularity and principle of the problem is presented. neutral point balancing methods based on mid-point potential balancing factor which used to SPWM simplify algorithm.In the method, the balance can be perfectly controlled by the balancing factor. Thesis.Common-mode voltage generated by voltage source PWM inverter and the essences of its adverse effects ale investigated,and common-mode voltage reducing methods are also presented.Otherwise, an idea about a vector generator is defined for implementing SVPWM of three-level converters. And then, two schemes of vector generation are compared for selection.Results prove the feasibility of the improved PWM modulation method.The improved method of carrier modulation which based on simple three-level SVPWM algorithm and the neutral point balancing methods and common-mode voltage reducing methods are all simulated by Matlab/Simulink.The control effects of neutral point potential and common-mode voltage reducing are very obvious.Through theoretical study and simulation a control system which has a DSP(TMS320LF2812) as the control center of the system has been constructed. The improved method of carrier modulation which based on simple three-level SVPWM algorithm and the neutral point balancing methods and common-mode voltage reducing methods are applied in the experiments. The experiment results show the feasibility and effectiveness of the global algorithm and the control strategy.