Dec 14, 2020
New type of bidirectional grid-connected inverter to solve the problems of traditional H-bridge inverter
Researchers Wang Yifeng, Cui Yulu, Ma Xiaoyong, Meng Zhun, and Ji Ruilin from the School of Electrical Automation and Information Engineering of Tianjin University, the Economic and Technical Research Institute of State Grid Tianjin Electric Power Company, and State Grid Tianjin Customer Service Center, in the 21st issue of 2019 "Journal" wrote an article, proposed a staggered parallel two-way grid-connected inverter. Experimental results show that the inverter efficiency is higher than 98% in the range of 20% to full load.
With the increasing problems of environmental pollution and resource shortage, related researches in the field of distributed power generation have received extensive attention. Among them, the interface circuit is an important part of the distributed power generation system and the hub of energy conversion between various parts of the system. In order to popularize distributed power generation systems on a large scale, achieve a high proportion of distributed power generation and grid connection, and alleviate the problems caused by the energy crisis to society, the interface circuit of distributed power generation generally requires small size, high efficiency, strong reliability and bidirectional energy. Flow characteristics. Therefore, the research on the interface circuit topology for the above characteristics has become a hot spot.
At present, the traditional interface circuit topology is mainly based on the bridge circuit, which realizes the energy flow between the power grid and the renewable energy power generation system by controlling the switch tube of the bridge arm. The bridge circuit has been widely used due to its high reliability and simple control strategy. However, the bridge circuit has the problem of straight-through of the bridge arms. It is necessary to design the dead time and inevitably introduce low-order harmonics, which will cause waveform distortion, increase the size and cost of the filter, and cannot achieve the high efficiency and high efficiency of the converter. Power density.
In order to solve the above problems, some scholars propose to use two sets of the same Buck circuit structure to form an inverter. The inverter has the advantages of simple Buck circuit structure, easy control and no bridge arms. Some scholars propose to use two sets of the same Boost circuit structure to form a rectifier, and use the interleaved parallel technology to successfully reduce the output current ripple and switch tube current stress. At the same time, reduce the size of the filter and increase the power density. Some scholars have proposed that two sets of the same Buck-Boost circuit are used to form an inverter, which realizes the boost/buck conversion of the converter, avoids the bridge arm through problem, increases the switching frequency, and reduces the size of the filter.
However, the above three types of converters are all researched on the basis of unidirectional conversion, and the two-way flow of energy has not been realized, and the selection of filter parameters has not been analyzed and discussed in detail.
In terms of interface circuit filters, some scholars use LC filters on the basis of rectifier circuits to filter out grid-side current harmonics and reduce waveform distortion; some scholars use LCL third-order filters on the basis of inverters. Under the same filtering conditions, compared to the LC filter, the LCL filter has a better filtering effect and has a smaller requirement for inductance, which is beneficial to reduce the size of the filter and increase the power density.
However, the above-mentioned documents only design filters based on unidirectional conversion, and it is difficult to directly apply them to the circuit topology of bidirectional converters. In the two-way circuit topology, the design of the filter needs to meet the performance requirements of the rectification and inverter circuit modes at the same time, which is restricted by multiple conditions, which makes the design of the filter more complicated. Therefore, the research on the filter in the two-way topology needs to be perfected.
Therefore, researchers from the School of Electrical Automation and Information Engineering of Tianjin University, State Grid Tianjin Electric Power Company Economic and Technical Research Institute, and State Grid Tianjin Customer Service Center, based on the dual Buck circuit topology, introduced the interleaved parallel technology and adopted 4 identical Buck circuits. , Derived a new type of interleaved parallel double Buck full-bridge bidirectional converter. The new converter has the advantages of small output current ripple, low current stress of the switch tube and bidirectional energy flow.
In addition, the design of the new converter filter comprehensively considers the performance requirements of the rectification and inverter circuit modes, and takes into account the performance, cost and power density of the filter. And on this basis, the loss of the converter is theoretically analyzed and calculated, and the loss distribution in the two modes is obtained. Finally, the theoretical analysis is verified based on a 5kW experimental prototype.
The researcher carried out the filter parameter design, realized the minimum inductance and the good filtering effect. The power density of the prototype is about 22W/in3, which has a high power density, and the output current THD is 3.37% at full load, and the harmonics above the 20th order are almost filtered out.
The loss analysis shows that the proportion of switching tube losses in rectification mode is lower than that in inverter mode, and the proportion of inductance loss in inverter mode is lower than that in rectification mode. Because switching tube losses account for a relatively small proportion, the conversion efficiency in inverter mode is relatively rectifier Mode is higher.
In inverter mode, the maximum efficiency is 98.80% when the input power is 2.6kW, and the efficiency is 98.09% when full load; in rectifier mode, the maximum efficiency is 98.61% when the input power is 2.7kW, and the efficiency is 98.01% when full load. High-efficiency two-way power conversion in the load range.