| With the development of the photovoltaic industry,its safety and reliability should be paid more and more attention.The inverter need the low-voltage ride through(LVRT)ability to resist the grid failure,in this period,the accuracy of Phase-locked loop and the stability of control loop are very important.This article took the actual project as background,in order to solve the shortcomings of traditional three-phase phase-locked loop in terms of accuracy and stability,came up with an improved algorithm,based on the Active Neutral-point-clamped(ANPC)inverter and the LVRT experiences,to verify the theoretical reliability.This paper introduced the ANPC topology,analyzed its commutation path and PWM control method.A control method was proposed to solve the midpoint potential imbalance in the three-level inverter and the effectiveness of the algorithm was verified by simulation.The structural and application of SRF-PLL and DSOGI-PLL were studied.Aiming at the problem that the DSOGI-PLL phase-locked loop commonly used in engineering fluctuates frequently when the frequency of the grid fluctuates,an improved method was proposed.The output characteristics of the phase-locked loops were compared.Based on the mathematical model of the inverter,the grid-connected control strategy of the PV inverter was discussed.According to the technical requirements of LVRT,a pass strategy based on reactive power support was proposed.The control logic in the process of crossing was introduced in detail.Finally,the theoretical analysis was verified by simulation.A 1MW experimental platform of grid-connected inverter was built.The prototype of the main parameters of the device and the part of hardware circuit and software flow chart were introduced.The input and output characteristics and low-voltage traversing ability were tested under different working conditions.The experimental results were analyzed and the validity of the proposed theory was verified. |
PDF Full Text Request