Research On Application Of Apf In Governing Three-phase Unbalanc Of Low Voltage Distribution Network

With the development of the social economy,a large number of high-power single-phase household appliances have been applied,resulting in the quantity of single-phase loads surged.This exacerbates the severity of the three-phase unbalanced problem which casued by the unequal distribution of single loads and its nonuniform work time.Because the three-phase unbalance will affect the the low voltage network's reliable and economy operation,we must take effective measures to govern it.This paper researched on application of APF in governing three-phase unbalanc of low voltage distribution network,the main research contents include APF's key technology,control strategy and designing.By analyzing the APF's system structure,compensation principle and basic function,the feasibility of applying it to govern the three-phase unbalanced problem of low voltage distribution network is proved theoretically.Because the problems of current distortion and lower power factor also exist in three-phase unbalanced low power distribution network,the working requirement of governing the unbalanced cureent component,harmonic current component and reactive power component integrated.Then,the command current detection algorithm is one of the key research works.In order to make full use of FBD algorithm's simple structure and ip-iq algorithm's flexibility,which can be superimposed by the the DC side voltage's equalization control instructions,the FBD algorithm and ip-iq algorithm are used in combination.The PLL is also needed by the composite command current detection algorithm.In this paper,to avoid the influence of the voltage distortion on the phase-locked precision,the fundamental normal component of the three-phase unbalanced voltage is extracted as the input signal of the traditional PLL,which based on dq coordinate transformation.The ability of APF's output compensation current to tracking on the command current affect the compensation accuracy directly.In this paper,PI control and repetitive control are used in parallel,which take full advantage of PI control's dynamic performance and repeated control's steady-state accuracy.Since the LCL filter has inherent resonant frequency,it is necessary to lake effective measures to suppress the output compensation current's resonance.In view of the passive damping control strategy would increase the system loss,the active damping control strategy of constructing virtual resistance is limited by the sampling delay and the high frequency component,this paper uses an active damping control strategy based on low-pass filter,which superimposes the current of capacitor branch through the low-pass filter to the command current.After simulating the feasibility and effectiveness of the above algorithms and control strategies,it is applied to the APF prototype.The running result shows that the APF is effective in reducing the degree of three-phase unbalance of low voltage distribution network,it can also reduce the total current distortion rate and improve the system power factor.