Grid- Connected Inverter Sensorless Damping Control And New Repetitive Control

With the reduction of traditional fossil energy such as oil, coal and natural gas, as well as the rapid growth of energy demand, the development of new energy sources has received extensive attention, among which wind power generation and photovoltaic power generation are rapidly developed due to their less pollution characteristics. And distributed generation emerge as the times require, the grid-connected inverter is a bridge between power plant and power grid, so grid-connected inverter plays a critical role in distributed generation.The quality and stability of grid current has a direct impact on the entire power grid, so the quality of grid-connected current must meet the strict nerwork requirements. As the selection of the current controller has a great influence on the quality of the output current, the selection and design of the current controller has always been a hot research issue. Among them, repetitive control has been widely used in grid-connected inverter because of its excellent harmonic suppression ability. This paper mainly focus on two aspects: the grid-connected inverter sensor-less damping control and the new repetitive control.In order to solve the resonance problem of LCL inverter, domestic and foreign scholars have put forward a lot of solutions, such as active damping, split capacitor, etc. Among most of these methods, an extra capacitance current sensor is needed, which will increase cost and reduce the reliability of the system. This leads to the generation of non-capacitance current sensor control method, which includes lead compensation estimation method, the lead compensation observer method and digital notch filter method. The lead compensation estimation method is proposed based on the capacitance current estimation method, and the delay of the estimation method is compensated, which improves the performance of the active damping. Compared with the traditional observer, the lead compensation observer has its own characteristic of having no delay, so it can be applied to the active damping. Notch filter method is a control method for the damping,which provides trapped waves at the resonant frequency.But the discretization of the continuous notch filter brings resonance point offset, of which the compensation will make controller design complex. But digital notch filter has advantages of simple design, accurate trap points and no need of discretization. Finally, simulation and experiment are carried out. The results of simulation and experiment show the correctness of the theoretical analysis.The basic concept, basic structure, typical application, the parameter design of the repetitive control and internal model principle are studied. The pole distribution of repetitive control is studied, and the poles were merged or classified. The digital resonant controller is obtained by combining, which is an improvement to the current resonant controller and quasi-resonant controller. Hybrid repetitive control is obtained through the classfication. The control parameter of the different RC can be set separately, so parameter design of the hybrid repetitive control system is more flexible than the traditional repetitive control system. The relationship between repetitive control and multi-resonance control is studied. Based on the analysis of the current repetitive control problems, a new repetitive control with low-pass function is proposed.