Split phase, also known as phase separation, refers to the split phase of single-phase direct current into multi-phase alternating current. Taking the power grid structure in North America and Japan as an example, the common split-phase power grid has the demand of split-phase 120v (combined phase 240v) with split-phase unbalanced load. Specifically, a split-phase grid system is composed of two live wires and a neutral wire in a three-phase power grid system. In general, a split-phase system has a first live wire l1, a second live wire l2, and a neutral wire n. The voltage of the first live wire l1 to the second live wire l2 is 202v or 240v (indicated by 240v).
In the application of the inverter to the split-phase power grid, the inverter needs to convert the direct current into the multi-phase alternating current of the split-phase power grid. For example, the photovoltaic inverter converts the direct current generated by the photovoltaic panel into alternating current and merges it into the public power grid; the solar-storage hybrid inverter combines the photovoltaic panel and the energy storage battery (lithium battery, lead-acid battery) into the grid or feeds energy to the load; the AC-coupled inverter combines the direct current of the battery (lithium battery, lead-acid battery) into the grid or feeds the load. However, an inverter can only output the voltage of one grid structure, such as single-phase grid 230v, three-phase grid 230/230/230 structure, cannot simultaneously output 120v/240v grid, and cannot meet the output requirements of split-phase grid. 4) In order to meet the needs of the split-phase power grid, a common method is to connect a power frequency isolation transformer or an autotransformer to the off-grid output port of the inverter for phase separation. In this way, the inverter only outputs a voltage level of 240v in the off-grid operation mode, and the power frequency isolation transformer or autotransformer separates the output voltage, so that two voltages of 120v and 240v can be obtained. However, in this common method, due to the use of power frequency isolation transformers or autotransformers, the volume of the inverter itself increases, and the overall weight of the equipment is heavy. In addition, the energy consumption of the additional transformer itself reduces the overall efficiency of the system accordingly. Another way to achieve phase separation is to use the method of connecting an electronic phase splitter to replace a power frequency isolation transformer or an autotransformer. However, the connection of an electronic phase splitter is a loop composed of switching tubes, inductors, capacitors and other energy storage devices. In order to achieve phase separation, it can be regarded as adding a first-level power conversion circuit to the original system. Due to the addition of more components, additional energy loss is naturally generated during the conversion process, and the equipment cost is further increased, making the system configuration process more cumbersome.
To sum up, it can be seen that in the existing split-phase technology, if the transformer is used for single-split-phase power grid conversion, it will bring disadvantages such as low conversion efficiency, high cost, and difficulty in controlling the volume and weight of the equipment within the normal range of household appliances; and if the electronic phase splitter is used for single-split-phase power grid conversion, it will also add a first-level topology at the back end of the original inverter topology, adding first-level components and capacitors. Realize the plan. Therefore, the improvement of the split-phase topology circuit based on the inverter can effectively avoid the shortcomings of the above-mentioned split-phase technology. For example, the application number is “cn202010206115.1” and the title of the application is “A Bidirectional Conversion Structure and Output Control Method Applicable to Split-Phase Power Grid”, which proposes a bidirectional conversion structure that meets the needs of split-phase power grids for inverters and avoids the shortcomings of traditional split-phase technology.