Flexible Topological Converter and Its Digital Control Device Applied to Photovoltaic Micro-inverter

Abstract

The invention discloses a flexible topology converter applied to a photovoltaic micro-inverter. The converter is applied to the DC / DC link of the first stage in the micro-inverter. When the power is high, the micro-inverter works in a full-bridge mode. When the power is low, it works in the forward mode. The design parameters of the transformer are the same in both cases, and it can convert efficiently under high power and low power, realizing the high weighted efficiency of the micro-inverter.

Description

technical field [0001] The invention relates to a flexible topology converter applied to a photovoltaic micro-inverter and a digital control device thereof, belonging to the technical field of power electronic converters and their control. Background technique [0002] Micro-inverter is an important research direction of photovoltaic power generation. Compared with string power supply and centralized power supply, micro-inverter can ensure that photovoltaic cells work at the maximum power point, modular design, hot-swappable, and redundant. A series of advantages such as good performance, high reliability and convenient installation have attracted wide attention from all walks of life. [0003] The improvement of power conversion efficiency has always been an important research direction of photovoltaic micro-inverters. For this reason, researchers have proposed a variety of non-isolated micro-inverters and isolated micro-inverters. Due to the low output voltage of a single...

AI Technical Summary

Problems solved by technology

Since the output voltage of a single photovoltaic cell is low (25V-50V), to achieve grid connection, a two-stage circuit structure can be used, and then inverter is performed after boosting. It is difficult for the commonly used Boost converter to efficiently achieve a high boost ratio, so A high boost ratio converter with a specific structure is required. This type of converter generally uses the turn ratio of the coupled inductor to achieve a boost ratio of more than 10 times, but the high boost ratio converter also requires more diodes and passive components. However, micro-inverters that use high-frequency transformers to achieve electrical isolation can complete the inversion function with fewer power conversion stages. At present, flyback micro-inverters are more researched in isolated micro-inverters. In addition, forward, push-pull, full-bridge and Zeta micro-inverters have also been researched. The circuit structure of isolated full-bridge and Zeta micro-inverters is more complicated, which is not conducive to the improvement of circuit efficiency under low power conditions. Flyback and forward The circuit structure of the micro-inverter is relatively simple, but the secondary circuit diode of the forward micro-inverter commutates at the peak current, which causes parasitic oscillation and reverse recovery loss of the diode, and it is difficult to improve the efficiency; the flyback micro-inverter The power of the inverter is limited by the energy storage transformer. As the power of a single photovoltaic cell increases, so in recent years, the flyback micro-inverter is interleaved, but the reverse inverter must be added in the rear stage, which increases the complexity of the micro-inverter. sex

[0004] At present, weighted efficiency is commonly used to measure new energy power generation systems, such as European efficiency and CEC efficiency. As the interleaved flyback scheme of the mainstream topology of micro-inverters, researchers have proposed various schemes to improve its efficiency. The main ideas of these schemes are According to the grid-connected power and the power frequency phase of the grid, it is decided whether all or part of the circuits are put into power conversion to reduce the total loss of the circuit at low output power. These schemes have achieved high weighted efficiency; With the improvement of conversion efficiency, the output power of photovoltaic cells with the same area is also increasing. At present, a single photovoltaic cell has reached 350W, and it is expected to continue to increase in the future. Due to the limitation of the processing power of a single flyback converter, the interleaved flyback parallel connection The number of units will increase with the increase of power, which will greatly increase the complexity of the circuit; for this reason, it is necessary to subvert the existing micro-inverter and propose a solution to achieve high-efficiency conversion under high power and low power

Images