Reserch On The Influence Analysis Of Overlap Time Of Current Source Converter And Restraining Method

The Current Source Converter(CSC)is widely used in uninterruptible power supply,reactive power compensation,and new energy and renewable energy grid-connected power generation due to its bidirectional energy flow,high power factor and low harmonic content.The CSC is different from the Voltage Source Converter(VSC)in that it allows the upper and lower arms to short-through,but it is necessary to add a overlap-time to ensure continuous current on the DC side.The overlap-time in one switching cycle has little effect on the grid.However,with the cumulative effect of multiple overlap-time,a large number of harmonics will be injected into the grid,causing severe distortion of the grid current and voltage,thus suppressing the overlap-time impact on the current is an extremely important measure to improve power quality.This paper conducts the following studies for the overlap-time effect.Firstly,in this paper,the space vector modulation strategy of three-phase CSC is analyzed,and the influence of the overlap-time on the AC side current is analyzed.Based on the principle of overlap-time setting and the diode clamping,a novel space vector modulation method for suppressing the overlap-time effect by effective switching method is proposed.This method insteads of setting the overlap-time,reduces the distortion of the current on the AC side and reduces the switching loss.Then,the paper also introduces the space vector modulation strategy of five-phase CSC,and analyzes the influence of the overlap-time on the AC side current.In this paper,the actual dwell time of the space current vector in the overlap-time is analyzed,and the overlap-time effect compensation strategy based on time compensation is proposed.In addition,the three-phase CSC proposed method based on the effective switching method is extended to the five-phase CSC.The simulation results show that the two suppression strategies can prevent a large number of harmonics injecting to the current,effectively improve the current waveform and prolong the service life of the equipment.Finally,the main circuit of three-phase CSC system is built.Based on TMS320F28335 DSP and Xilinx SC6SLX9-2TQG144 C FPGA digital control hardware is designed.The overlap-time effect suppression strategy based on invalid switching method and time compensation method is experimentally verified.The experimental results verify the correctness and feasibility of the theoretical scheme.