T-Type Three-Level Inverter Phase Current Reconstruction And Neutral-point Voltage Balance Control Method Research

Three-level inverter is widely used in new energy power conversion,high voltage motor drive and other fields,which have strict requirements on the accuracy of current acquisition,system reliability,cost and volume of the drive control system.Therefore,it is very important to improve the accuracy and reliability of current reconstruction while reducing the system cost and volume.Aiming at the problems such as large reconstruction error,low accuracy and unbalance of neutral-point voltage in the traditional SVPWM neutral current sampling phase current reconstruction strategy of T-type three-level inverter,the following research is carried out in this paper.The principle of phase current reconstruction strategy for neutral current sampling is analyzed and the unobserved regions is accurately divided by defining the minimum sampling time.In order to eliminate the unobserved regions,the observable voltage vector that does not meet the minimum sampling time is extended,and then the extended vector is compensated based on the principle of synthetic zero vector.A composite space vector pulse width modulation(CSVPWM)strategy is put forward,which realizes the accurate collection of the observable voltage vector current and ensures that the reference voltage vector satisfies the volt-second balance principle.Simulation and experiment verify that CSVPWM can complete phase current reconstruction under various working conditions,the maximum reconstruction error is less than 5.5%,and the phase current THD is controlled within 3.21%.By analyzing the zero-point drift of the neutral current sensor,the error enlargement effect mechanism of the zero-point drift reconstruction of the sampling phase current of the neutral current is revealed.Based on CSVPWM,the error suppression phase current reconstruction strategy is designed.The drift quantity is detected in the observable region according to the current information collected by two small vectors.The zero-point drift detection method of dynamic current double sampling is proposed to realize the self-detection and real-time correction of the zero-point drift of reconstructed current.Experimental results show that the reconstruction current error is less than 2.64% after error suppression is enabled.Aiming at the unbalance of neutral-point voltage in T-type three-level inverter,the causes and characteristics of neutral-point voltage deviation are studied.On the basis of analyzing the influence of basic voltage vector on neutral-point voltage,a compound control algorithm based on PI control and hysteresis control is proposed by dynamically adjusting the action time of N-type small vector and P-type small vector.The simulation results show that the voltage difference between two capacitors can be reduced to within ±1%.