The Research Of Suppressing Circulating Current In The Parallel Three-phase Converter System

Since the three-phase voltage source PWM converter having a two-way flow of energy, power factor control, network side current sinusoidal, low harmonic content, it is possible to realize the power of "green change", etc., so that the three-phase voltage source PWM converteris becoming a key power conversion equipment.Converter device which constructed by power electronics building block(PEBB) has the advantage of having facilitate reconstruction, high reliability, and low cost. Meanwhile dispersed PEBB can implement distributed control and hierarchical control of power conversion device. The research for parallel technology of power electronic modular conversion device is very meaningful. The object in this paper is a three-phase voltage source PWM converter parallel system that has common DC and AC bus.Firstly, in d-q rotating coordinate system, a mathematical model of the parallel three-phase voltage source converter has established. And through analysis of SVPWM algorithm got parallel equivalent circuit model running parallel converter. Thereby on the basis of parallel modules to ensure the consistency of the driving signal, zero-sequence voltage offset correction link was added to suppress circulation between the converter modules. This paper presents a reconstruction based on PWM wave distributed from the master control program.Secondly, master-slave distributed control scheme was researched based on PWM wave reconstruction. Traditional double-loop PI control algorithm is applied to master-slave distributed control scheme of PWM wave reconstruction. And the stability of the system was studied. In order to ensure consistency of drive signal in parallel module, serial optical fiber communication technology of parallel modules was researched on the master-slave distributed control scheme. High-speed fiber-optic star topology scheme was achieved by HDLC protocol. Meanwhile, in order to improve the dynamic response of the system and reduce the load disturbance, the load current feed feedback control strategy was introduced and the Second Order Rhomberg state observer was designed to estimating the load current.Then, for dynamic and robust inadequate of a traditional double-loop PI algorithm, the model predictive control(MPC) was researched on the master-slave distributed control scheme. On the basis of ensuring suppression circulation, dynamic performance and harmonic content was improved. By analyzing the MPC algorithm principle, the converter mathematical model suitable for MPC algorithm has been established. The solving problems of MPC algorithm was transformed into quadratic programming problem, then the optimal amount of control was obtained.Finally, a parallel simulation and experimental platform of integrated modules for converter was set up. With DSP and FPGA dual-processor, completing control algorithm and serial fiber optic communications and other functions. The experiment of converter parallel system was completed to verify the effectiveness and feasibility of the proposed control scheme and control strategy.