Research On Circulation Problems For Paralleled Three-Phase Voltage-Source Converters Based On CAN BUS

As today’s world energy crisis is becoming increasingly serious, new energy, distributed generation, smart grid and energy Internet has been rapid development. Renewable energy power generation accounted for more and more proportion of the whole power system generating capacity, large capacity and modular power electronic devices are becoming one of the important directions in the development of power electronic technologies. It is especially important on the research work to ensure the stability of the inverter parallel operation systems. But for the parallel operating systems, it is easy to produce the circulating current problem, which could cause power quality of the system distortion, drops system working efficiency, decreases the lifespan of the equipments and other hazards.This dissertation is supported by the National High Technology Research and Development 863 Program of China "Key technology research and development of micro grid with distributed generation" (serial number: 2011AA05A107). This dissertation firstly summarized the research results of the existing theory and application of parallel control of inverter, then analyzed the effect of interleaved carrier on the parallel system power quality, based of these related suppression strategies based on the CAN (Controller Area Network) bus on paralleled three-phase voltage-source converters is mainly discussed for the problems of high frequency circulation current and harmonic in these systems. The main contents are as follows:In this dissertation, the switching cycle average model of the VSC converter module in the abc static coordinate system and the dq synchronous rotating coordinate system is firstly established, then analyzed the two-phase dq synchronous coordinate system PI linear current control strategy, presenting a method of parameter design based on the transfer function of the discrete domain (Z domain). In the end, the steady-state performance, dynamic performance and anti disturbance performance of the designed parameters are simulated and analyzed.Based on double Fourier analysis, the spectrum model of SPWM converter module output voltage and current is established. Through the established spectrum model, the effection of inter-module carrier interleaved on common-mode voltage, parallel current and circulating current of the VSC module parallel system is studied. Then the carrier interleaved scaling factor is presented, studying the effects of carrier irregular asymmetric interleaved on the specific harmonics and the total harmonics, revealing the essence that carrier interleaved can eliminate grid-connected current harmonics, while increase the equivalent switching frequency, points out the advantages of carrier irregular asymmetric interleavied in respect of he specific harmonics and the total harmonics. Finally, analyzied the impact of VSC module circulating current becsuse of carrier interleaved, which provided the necessary basis for the design of VSC module parallel system.A control strategy is proposed combined with carrier synchronization technology based on CAN bus and coupled inductors for the problem of high frequency circulating current in paralleled VSC modules. Then applying power electronic network control to the carrier synchronization control of VSC module parallel system on the basis of centralized control and distributed control. Moreover, based on CAN bus clock reference achieving high accuracy carrier synchronization between parallel VSC modules. Finally, two different kinds of high frequency coupling reactor is designed to suppress the high frequency circulation caused by dead zone nonlinear factors and inevitable carrier synchronization error in actual system.In the end of this dissertation, part experiments is done based on the prototypes of two independent lOkVA parallel VSC operation modules to verified that control strategies.