One-Dimensional Space Vector Modulation Technology Of Multilevel Inverter

Multi-level inverters have many advantages,such as large number of levels,low switching frequency,good output waveform quality,low du/dt and low electromagnetic interference.They have more and more important applications in the field of new energy,high voltage and high power.But with the increase of the inverter's output level,and topology is becoming more complex,traditional sinusoidal pulse width modulation(SPWM)and space vector pulse width modulation(SVPWM)have disadvantages of poor generality,complex calculation and large common-mode voltage.This paper proposes a sawtooth carrier implementation method based on one-demensional space vector,the specific work is as follows:(1)Aiming at the problem of poor generality and complex computation of traditional modulation strategies,the output states of the bridge arm are simulated as one-dimensional voltage vectors,and the vector action time is obtained by simple judgment and calculation.According to the vector action time,a pulse is divided into several pulses,then decompose the modulated wave,which is compared with the sawtooth carrier to output the pulse.By simple calculation,it has three controllable degrees of freedom:redundant vector selection,pulse width and pulse position,so it has a strong universality.(2)In order to balance the clamping capacitor voltage for the Seven-level inverters with switched capacitors,there are two methods based on one-dimensional space vector modulation:pulse width proportional distribution and pulse number proportional distribution.The results show that the pulse width distribution is slightly better than the pulse number distribution in terms of switching loss,and the pulse number distribution is obviously better than the pulse width distribution in terms of output harmonic performance.Simulation and experiment prove the correctness and feasibility of this method.(3)After deducing the common-mode and differential-mode equivalent circuits of LCL filters whose filter capacitors are connected back to the DC-side neutral-point,according to the filter requirements,filtering parameters for decoupling common-mode and differential-mode loops is given by using common mode inductance.The design method is applied to the evaluation of single-phase and three-phase modulation methods.Simulation and experiment prove the correctness and feasibility of this method.(4)For different occasions of single-phase inverters,the combination characteristics of different levels bridge arms are compared in terms of level number,common mode voltage,harmonic performance and filtering parameters.The results show that the maximum common-mode voltage jump of 27 combinations is Udc,which is suitable for situations without common-mode voltage requirements,it uses the least devices and can output up to 13 levels.The harmonic performance of differential-mode voltage is in the middle of the three.When carrier phase shifting,the maximum common-mode voltage jump of 77 combinations is±1/12Udc.It is suitable for the occasion of small parasitic capacitance,it can output up to 13 levels,and the harmonic performance of differential-mode voltage is the best of the three.When there is no carrier phase shift,the common-mode voltage jump of 77 combinations is 0.It is suitable for occasions with large parasitic capacitance.It can output up to 7 levels,and the harmonic performance of differential mode voltage is the worst.Simulation and experiment prove the correctness and feasibility of this method.(5)Aiming at the application of one-dimensional space vector modulation in three-phase inverters,it is concluded that the common-mode voltage amplitude can be divided into three cases(0?E/3?2E/3)after analyzing the relationship between the relative position of three-phase's PWM wave.Three cases are realized by using one-dimensional space vector modulation,they are compared in terms of harmonic performance of differential mode voltage,amplitude of common mode voltage and filtering parameters.The modulation strategy in which the common mode voltage is 0,it can be used in situations where large parasitic capacitance and common-mode leakage current are difficult to suppress.There are many overlapping areas of the line voltage,its harmonic performance is the worst,and its switching frequency is the highest.The modulation strategy in which the common mode voltage is E/3,it can be used in situations where the parasitic capacitance is small.The overlapping phenomenon of line voltage is mainly concentrated in the area where phase voltage polarity is opposite,and the harmonic performance is in the middle.The modulation strategy in which the common mode voltage is 2E/3,it can be used in situations where there is no common-mode voltage requirement or the parasitic capacitance is small.It eliminates the overlapping phenomenon of line voltage by using positive and negative half-period carrier phase shifting method.It has the best harmonic performance.Simulation and experiment prove the correctness and feasibility of this method.(6)For the problem of the neutral point potential on the DC side unbalance of the topology used in this paper,it could be controlled by zero sequence injection.Simulation and experiment prove the correctness and feasibility of this method.