Research On Active And Passive Hybrid Three-Phase Power Balancing Technology

With the improvement of production and living standards,types of electricity load are increasing and electricity consumption rising year after year.In low voltage distribution system,three phase unbalance,harmonics and other power quality problems become increasingly outstanding,which affects the stable operation of low-voltage distribution system and the safety of electricity.Although the active power filter technology is powerful,it is expensive and not suitable for processing zero sequence current.The project is cooperated with Shandong Bangshi Electric Company,researching a hybrid three-phase power balancer with active filtering and passive filtering technology.Firstly,this paper introduces the harm and control measures of three phase unbalance,the definition of three phase unbalance in different countries and the definition of three phase unbalance degree in national standard.Then the paper introduces the development of three-phase power balance technology and power filter technology,and briefly analyzes the advantages and disadvantages of various power quality controlled technology.On this basis,this paper introduces the basic structure and principle of the hybrid three-phase power balance technology and shows the superiority of them in the three phase unbalance problem.Passive filter module of the hybrid three-phase power balance technology consists of two special reactor:Zero sequence blocker(ZSBT)and zigzag transformer(Zig-Zag transformer).Zig-Zag transformer is actually Zig-zag transformer with only a primary winding,which is designed on the basis of the traditional transformer design and its own characteristics.Three phase winding of ZSBT wound on the same iron core.Design of ZSBT is based on the traditional design method of the reactance and its structural features which main designed parameters are obtained,and then the 3D simulation model was established in ANSOFT,a modification of the main parameters.Finally the prototype of ZSBT was tested.Active filter module of the hybrid three-phase power balance technology includes current detection,the design of the main circuit,current tracking control and PWM control.There are many methods of current detection.This paper uses the instantaneous reactive power theory to detect the unbalanced current and harmonic current.The current detection model is established in Simulink.In this paper,the PWM control mode adopts the SVPWM with high DC voltage utilization rate,and the C language program is written in DSP to track the sinusoidal voltage vector.In this paper,the three level circuit which is more stable than the two level circuit is used as the main circuit.The method of PI+ repetitive control is used in current tracking,and the control flow chart is deduced.The control system of the hybrid three-phase power balance balancer is based on the DSP TMS320F28335 control system in the industrial core board.DSP as the core device,the detection circuit of three-phase voltage current and the DC side voltage,the power supply circuit,the zero crossing detection circuit,the output amplification conversion circuit and the communication circuit are designed.On the basis of the hardware design,this paper designs the corresponding control software according to the control requirements of the hybrid three-phase power balance balancer.Finally,simulation model of the hybrid three-phase power balance balancer was established in the Simulink according to the design,which is analyzed.The prototype is analyzed according to the existing experiment condition.