Study On High Efficiency Reactive Power And Harmonic Dynamic Control Method And Its Application

Electrical energy plays an important role in the economic development and people's lives. With widely used of the non-linear load in the grid, the supply current and voltage become distortion which causes harmonic pollution and energy losses. Meanwhile, voltage fluctuation and voltage flicker caused by the impulsive load and reactive power variation have greatly disturbed the industrial production and people's lives. It also increases the line loss of the grid. The line loss rate of distribution grid is about 6.72% in our country. It can save more than 74 billion kWh per year, if the line loss rate reaches about 4.7% of the Western developed countries.Aiming at the key problem of power quality control technology in distribution grid, and based on the financial support of The National Natural Science Foundation of China (Project No.60774043) and The National High Technology Research and Development of China (863 Program) (Project No.2008AA05Z211), the connotation of the high-effiency power quality control is firstly explained in detail in this paper. Novel theories and methods of high-effieccy reactive power compensation and harmonic elimination in distribution grid have been studied in a deep-going way. Two novel comprehensive power quality controller, named High-efficiency Var and Harmonic hybrid Controller (HVHC) and High-efficiency Hybrid Var Controller (HHVC), were proposed to improve the power quality and decrease power losses. The working mechanism, mathematical model, control method, optimal operation and the critical technical problems in application of comprehensive power quality controller are described in detail in this paper. The emphasis and achievement of the paper mainly manifests in the following aspects:(1) High-efficiency Var and Harmonic hybrid Controller (HVHC) is proposed to realize harmonic currents dynamical suppression and reactive power dynamical compensation at the same time in high voltage distribution grid. The shortcomings of HAPF and SVC are avoided in this system. Based on the analysis of its working principle, the electric model is established. The compensation characteristics of harmonic and reactive power are also given in this paper. Furthermore, suppressing coupling crosstalk hybrid control strategy is proposed to eliminate the infection between SVC and IHAPF. Simulation and experiment results show that, HVHC can realize the harmonic currents dynamical suppression and reactive power dynamical compensation at same time. It can also realize the unbalance compensation, voltage support, damping oscillation, etc which can reduce the harmonic losses and reactive power loss greatly.(2) This paper mainly focuses on the DC voltage stability of HVHC under interference. Based on the analysis of HVHC's DC voltage problem, optimizing the parameters of HVHC's injection circuit, improving the main circuit of HVHC's active part and composite control strategy are proposed to improve system reliability.(3) This paper proposes a High-efficiency Hybrid Var Controller to realize the low-cost, high-capacity continuous adjustment of reactive power. It can also eliminate harmonic currents and flicker, which has significantly improved the power quality and power utilization of low-voltage distribution grid. Based on the topology and electrical model of HHVC, the stability and operation mechanism are described in detail in the control strategy of detecting the load's harmonic current. HHVC expert cooperative hybrid control method is proposed in this paper to maintain the economic and stable operation of system.(4) Based on the establishment of node admittance matrix in harmonic domain, harmonic power flow calculation method of distribution grid is described in this paper. Heuristic Perturbation Frequency domain Analysis method is proposed to arrange the compensation device and simplify the iteration calculation of power flow. Sensitivity analysis is used to get the reasonable installation location. Combining the advantage of Benders decomposition method in solving mixed integer problems and Lagrange multiplier method in getting the optimal solution of continuous variable, a method is used to obtain the optimal solution in the alternative solutions. At last, harmonic suppression and reactive power optimization planning are described in detail in this paper. Simulation results verify the validity of the proposed method in this paper.(5) Based on the project of harmonic suppression and var compensation in a 35kV distribution grid in copper material factory, several critical technical problems in the application of power electronic hybrid system HVHC and HHVC are described in detail in this paper. The power quality technical scheme of this factory is designed. And the application results verify the validity of the proposed method in this paper.Based on the proposed theory and design method, this paper makes a deep research on several critical technical problems in the application of power electronic hybrid system HVHC and HHVC to meet the industrial need on harmonic suppression and var compensation in large industrial enterprise. The overall design scheme of HVHC and HHVC is described in detail in this paper. The compensation system of HVHC and HHVC has been developed. The application result shows that the compensation system has good performance and the power quality of this enterprise has improved greatly.Accroding to the research of distribution grid power quality control and the electric energy saving of enterprise, power electronic hybrid system HVHC and HHVC are proposed in this paper. Besides, harmonic suppression and reactive power optimization planning are also described in detail. HVHC and HHVC overcome the shortcomings of single power electronics in compensation performance, realizing the dynamic compensation of harmonic and reactive power, voltage support and flicker suppression in the high and low voltage side of distribution grid. The research on HVHC and HHVC is very practical for the other researches of power electronic hybrid system. The overall program design ideas and some engineering experience can be extended to the design and application of other power electronic systems. It also provides a useful practical reference for the development of power electronic hybrid system.