Study Of Control For High-Power Grid-connected Inverter Based On Multi-sampling

With the continuous development of photovoltaic, wind power and other new energy generation systems, high-power grid-connected inverter has been widely used. However, for the high-power grid-connected inverter, on one hand, the low switch frequency is used in order to reduce the loss of system, thus the large control delays are introduced in the digital control process, which limits the bandwidth and the stability margin of the system. On the other hand, LCL filter is widely used due to its better filtering effect, however, the resonance problem of LCL filter is easy to cause the system instability. In this paper, to deal with influence of the control delays and the LCL filter resonance on the system, the control strategy based on multi-sampling for high-power grid-connected inverter is studied.This paper establishes the mathematical model of the three-phase LCL filter grid-connected inverter, which is the foundation for the later analysis. The multi-sampling pulse width modulation (PWM) principle is introduced. Compared with conventional sampling PWM, the control delays and the mechanism of abnormal waveform in the implementing process for the multi-sampling PWM are analyzed, and the solution is put forward.Based on the existing literatures about active damping (AD) method to damp the LCL filter resonance, choosing the capacitor voltage feedback, this paper analyzes the conventional sampling AD control performance and studies the multi-sampling AD to improve the system control performance.Aiming at the problem that the AD method usually requires additional sensors and complex control algorithm, the influence of delay on the control stability of LCL grid-connected inverter is analyzed and the control without additional damping (CWAD) based on multi-sampling is studied. Through the inverter-side current feedback based on multi-sampling, the system can be stable in single-current-loop control and obtain the high bandwidth and stability margin.At last, through the Matlab/Simulink simulation analysis and experimental verification, it is proved that the theory analysis is correct and the control strategy is effective.