The Research Of The Impedance Measurement Method Of New-energy Grid-Connected Inverter And Equipment Development

With the strategic adjustment of China's energy structure and the in-depth advancement of energy transformation,the new-energy power generation industry has developed rapidly.New-energy generation grid-connected inverters are connected to the grid on a large scale,and the power system is increasingly characterized by power electronics.The interaction between inverters and the grid is becoming more and more intense,threatening the stability of power system.The impedance analysis method can be used to establish the impedance model of the grid-connected inverter of new energy,reveal the unstable factors of the grid-connected inverter of new energy,and provide theoretical basis and scientific support for improving the stability of the grid-connected system of new energy.The impedance model is the basis of the impedance analysis method.The impedance model of the new energy power generation equipment,that is,the grid-connected inverter is generally obtained by small-signal modeling.However,the different control characteristics of the actual application of the new-energy power generation equipment.bringing great difficulties to modeling and analysis.The highpower wide-band impedance measurement equipment can accurately describe the impedance model of the new-energy power generation equipment,and solve the modeling problem of the black box of the internal control system of the grid-connected inverter.To this end,this paper proposes a new energy power generation equipment impedance measurement scheme;studies the influence of impedance measurement equipment control method on impedance measurement and system stability;develops 380V/100 kVA broadband impedance measurement equipment,measuring frequency range from 10 Hz to 1000 Hz.The main research contents and innovations of this paper are as follows:1.The impedance modeling of the photovoltaic grid-connected inverter in the dq coordinate system is carried out.In the modeling process,the influence of the phaselocked loop on the impedance model is studied and the influence of the current loop control parameters on the impedance model is analyzed.The stability analysis method of grid-connected system based on generalized Nyquist stability criterion is studied.The influence of phase-locked loop parameters and grid impedance on system stability is studied.2.The basic method of impedance measurement is analyzed.A broadband impedance measurement equipment topology is proposed.The voltage disturbance injection device adopts a multi-power module cascade structure,and each power module is composed of a three-phase uncontrollable rectifier module and a singlephase H-bridge inverter module.The control method and SPWM modulation strategy of the voltage disturbance injection device are analyzed.The effects of open-closed control method of impedance measurement equipment on impedance measurement and grid-connected system stability under different short-circuit ratios are studied.The switching control method of the impedance measuring equipment is analyzed.The correctness of the impedance measurement method and topology proposed in this paper is verified by building a simulation model.3.A 380V/100 kVA wide-band impedance measurement equipment was developed and a low-voltage impedance measurement platform was built.The DC side capacitor design,power device selection,drive circuit design,filter design and hardware and software design of the control system of the power unit of the research equipment are described in detail.The software based on LabVIEW upper computer impedance calculation unit is designed.The effectiveness of the proposed impedance measurement method and equipment is verified by experiments.