New Protection Principles Of Distribution Network And Micro Grid With Distributed Generation

In order to deal with the crisis of fossil energy,the deterioration of the environment and improve the operation security,stability and power supply reliability of the power system,clean energy power generation technology including wind power and photovoltaic power generation has been vigorously development in China,and becomes one of the key development strategies of electricity and energy.Distributed generations(DGs)have the characteristics of volatility and intermittent and the access of DGs will result in the complexity of the structure and operation mode of the power grid.These will change the fault characteristics of the power grid and bring challenge to the fault analysis and relay protection of the power grid.Since the DGs are always connected to the grid through the inverters,therefore,this paper mainly focuses on the fault analysis and relay protection of distributed power distribution network and micro grid with inverter interface distribution generators(IIDGs).1.Based on the establishment of PQ control,the IIDG fault equivalent model with the elimination of negative sequence current control and fault ride through control capability,the IIDG fault crossing control strategy with adaptive voltage support capability is proposed.The self-adaptive voltage support coefficient is used when the short-circuit current has not reached the maximum value and the IIDG outputs the maximum reactive current in a power grid fault to fully realize its voltage support ability under the premise of ensuring safety.The effectiveness and practicability of the proposed control strategies are verified based on RTDS simulation.2.Based on the iterative solution of equations,the fault analysis method of distribution network with PQ-controlled IIDGs is proposed,and the convergence of the iterative solution is proved by using fixed point theorem.A new principle of self-adaptive current protection for distribution network with PQ-controlled IIDGs is proposed.The MMS communication in IEC61850 is used to obtain the power reference value of IIDGs in the self-adaptive protection principle,and the phase currents of different types of metallic short circuits at the end of the protected line is calculated to realize the adaptive of protection setting.With a small economic cost,the self-adaptive current protection has a fixed protection range under different DG output conditions.The accuracy and rapidity of the proposed fault analysis method and the validity of the protection principle is verified by RTDS and the protection-monitoring device.3.According to the characteristics of small resistance grounding system,the fault analysis method and the new principle of self-adaptive zero-sequence current protection for smallresistance grounding system with PQ-controlled IIDGs are proposed.The technical route is similar to the above fault analysis method and the self-adaptive current protection.The accuracy and rapidity of the proposed fault analysis method and the validity of the protection principle are verified by RTDS and the protection-monitoring device.4.The fault equivalent model of V/f-controlled IIDG with different control objectives is established based on analysis of control characteristics of V/f-controlled IIDG,and the simulation results verify the correctness of the V/f-controlled IIDG fault equivalence model.Through the establishment of fault currents iterative solution equation group of micro grid with V/f-controlled IIDG and PQ-controlled IIDGs the fault analysis method and the self-adaptive current protection principle for micro grid with V/f-controlled IIDG and PQ-controlled IIDGs are proposed,and the convergence of the iterative solution is proved by using fixed point theorem.The accuracy and rapidity of the proposed fault analysis method and the validity of the protection principle are verified by RTDS and the protection-monitoring device.5.Two sets of protection-monitoring devices for distributed power distribution network and micro grid are developed in this paper.One of the protection-monitoring devices is based on DSP + ARM dual core processor,with A/D conversion module,close/trip module circuit and MMS substation layer communication,which can be used in traditional substation with IEC61850 substation layer communication.The other protection-monitoring device is based on 2DSP + 2ARM quad core processor,with two 1000 MHz and two 100 MHz Ethernet ports which support SV,GOOSE and MMS communication protocols,suitable for digital substation.Two sets of devices have the advantages of high reliability,strong computing ability,low cost and good flexibility,that can meet the new protection requirements of the distribution network and micro grid with DGs.