Research On Voltage And Harmonic Control Of Low Voltage Distribution Network Based On The Power Quality Controller With Compound Control

In order to meet the development needs of new energy and energy Internet in the process of achieving the goal of peak carbon dioxide emissions and carbon neutralization,all kinds of distributed or renewable energy are connected to the power grid,and small hydropower stations are connected to the low-voltage distribution network,resulting the fact that the power electronic degree of the power system is developed more,which will inevitably cause the end user voltage of the low-voltage distribution network to be more and more limited,and the nonlinear power electronic load would also bring harmonic pollution.Therefore,it is of great significance to do some research on the voltage and harmonic problems in lowvoltage distribution network.In this paper,aiming at the problem of voltage fluctuation and harmonic pollution in low-voltage distribution network,a power quality controller was proposed,which showed the characteristics of controllable voltage source to compensate voltage and high harmonic impedance to isolate harmonics.Based on the basic theory of magnetic flux compensation(MFC),the harmonic suppression principle of the power quality controller was analyzed.By detecting the harmonic currents from the main circuit,the output voltage of voltage source inverter(VSI)at the secondary side of transformer was controlled,so that the harmonic component at the primary side of transformer presented high impedance to isolate harmonics.At the same time,the principle and application characteristics of four kinds of voltage deviation compensation strategies were analyzed.The pre transient voltage compensation strategy could be applied to the voltage compensation scheme in this paper.In this paper,an improved phase-locked loop(PLL)was studied for fast and accurate signal synchronization under the condition of signal amplitude or phase jump,harmonic and three-phase imbalance.An enhanced moving average filter(EMAF)was proposed to analyze its application advantages in high frequency noise suppression,harmonic amplitude decay rate,sampling frequency sensitivity,response time and data storage.EMAF was applied to the improved SPLL proposed in this paper,which has open-loop and larger bandwidth design,and was applied to the harmonic and signal deviation detection method based on phase discrimination principle.In order to realize the signal tracking without static error,a control system based on the equivalent resonant controller was proposed,and the parameters of this controller before and after correction,the control system and the stability of the control system were analyzed.The equivalent resonant controller was realized by using the feedback and feedforward link,which could show high gain to odd or 6h ± 1 harmonic to play the role of no static difference tracking.To solve the problem that the delay link cannot be divided by sampling time and signal frequency offset in digital control,an adaptive equivalent resonant controller with variable fractional delay frequency was proposed,based on FIR-LPF and Farrow filter.The parameters of each link of the control system were selected in detail,and the whole control system has good stability.Finally,the function of power quality controller was simulated and verified in Matlab/Simulink software,and the hardware experimental platform of this scheme has also been built.The results of harmonic isolation and voltage compensation experiment respectively verified that the power quality control proposed in this paper could effectively isolate harmonic from the voltage and current harmonic source nonlinear load,and could compensate the voltage deviation quickly when the voltage of power grid rises or decreases,which shows its application value in the low-voltage distribution network.