A repetitive control method for reducing the output current thd of a high-power photovoltaic grid-connected inverter

Abstract

The invention discloses a three-phase high-power photovoltaic grid-connected inverter and a repetitive control method for reducing output current THD thereof, belonging to the technical field of powerelectronics and control thereof. According to the scheme of the invention, after performing DQ conversion on the output grid-connected current, a PI control and improved repetitive control parallel composite control mode is adopted, the weights of adjacent two units in discrete tables 1 and 2 are respectively calculated according to the number of beats to be advanced by using a linear interpolation theory, the values of the adjacent two units are respectively multiplied by the own weights and then summed, and the obtained sum is multiplied by a constant less than 1 and then is subjected to low-pass filtering to serve as an output value of a repetitive controller, and thus the arbitrary phase compensation in the full cycle range of a power grid can be realized, the grid-connected current waveform can be effectively improved, the THD of the current waveform can be reduced, and meanwhile, the scheme of the invention also plays a good role in reducing the volume and cost of LCL-type filters.

Description

technical field [0001] The invention relates to the technical field of power electronics and its control, more specifically, to a repetitive control method for reducing the output current THD of a high-power photovoltaic grid-connected inverter. Background technique [0002] At present, in the three-phase high-power photovoltaic grid-connected inverters, most of them adopt the three-phase full-bridge topology, and in order to improve the utilization rate of the DC side voltage, the SVPWM modulation algorithm is used. Among all the indicators of high-power photovoltaic grid-connected inverters, the device efficiency and the total harmonic distortion (THD) of the grid-connected current waveform are the two most important assessment indicators. Low device efficiency means high input-output ratio, and large THD means high harmonic content in the waveform, which will have an adverse effect on the safe and stable operation of the power grid. However, these two indicators are cont...

AI Technical Summary

Problems solved by technology

However, due to the low switching frequency of the high-power photovoltaic grid inverter, the PWM control period is relatively long, and each beat (that is, each PWM period) means a large electrical angle, while the conventional repetitive control technology uses Phase compensation is carried out by an integer number of beats in advance. Therefore, any phase compensation within the full cycle of the power grid cannot be realized, which makes it difficult for conventional repetitive control technology to achieve accurate control effects in the control process of grid-connected current of high-power photovoltaic inverters.

Images