When a patent concerns how electricity moves around a network rather than how a single device works, it tends to land in Cooperative Patent Classification (CPC) class H02J. This is the class for the grid as a system: the arrangements that supply power, distribute it across a network, balance it between sources, and store it for later. For anyone tracking the patents behind grid interconnection, distributed generation, and energy storage management, H02J is the primary classification handle, and its title sets the scope precisely.

The USPTO's CPC scheme states the class heading verbatim, and the three clauses of the title map cleanly onto three different kinds of invention — the network, the supply-and-distribution circuitry, and storage.

"ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY"— CPC class title, H02J, source

Below the class heading, the subgroup structure separates the kind of network and the way power is fed into it. The subgroup H02J 3/00 carries the title "Circuit arrangements for AC mains or AC distribution networks" — the alternating-current grid most people mean when they say "the grid." Deeper inside that branch, H02J 3/38 is titled "Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel." That second subgroup is the one to know, because it is the formal classification home for the act of connecting a new source — a solar array, a wind turbine, a battery — to a grid that other sources are already feeding. Renewable integration, in the patent office's filing cabinet, is largely an H02J 3/38 question.

How the class frames a grid-integration filing

The classification line on a real record shows the class doing this work. Take the published application US20250330022A1, "Grid-Forming Inverter and Grid-Forming Inverter System for Distributed Power Sources Based on Intermittent Renewable Energy Sources and Control Method Thereof," published October 23, 2025 and assigned to the Korea Institute of Energy Research. Its CPC line includes H02J 3/1835, H02J 3/38, and the indexing symbol H02J 2300/26. Reading those symbols: the H02J 3/38 placement says the disclosure concerns feeding a network from a source in parallel with others — the grid-integration act; the H02J 3/1835 branch concerns the regulation of voltage or reactive power in the network; and the 2300 indexing symbol annotates the renewable-source context. The abstract describes "a power stage to convert electric power according to on/off controls of switching devices and to output the converted electric power to a grid," with a control circuit that calculates a frequency command — the device — but its H02J symbols are about what that device does to the network.

This is the line a grid-IP reader has to hold. A patent can describe a physical converter and still be classified in H02J because what it claims is a network function. The same record may also carry symbols from H02M (the power-conversion class) for the converter hardware itself. The two classes answer different questions: H02M asks what the box does to a waveform, H02J asks what the box does to the grid. When both appear on one record, the filing sits at the boundary between a device and the network it serves — which, for grid-integration and interconnection technology, is exactly where the interesting inventions live.

The subgroup structure also lets a reader separate the several distinct grid problems that all get loosely called "grid tech." The H02J 3/00 branch for AC distribution networks subdivides into voltage and reactive-power regulation (the 3/16 and 3/18 ranges), frequency control, islanding and protection, and the parallel-source feeding of 3/38. A separate top-level branch, H02J 7/00, covers charging and depleting batteries — the storage-device side rather than the network side — and H02J 9/00 covers standby and emergency supply. So when an assignee's H02J filings concentrate in 3/38, the signal is renewable interconnection; when they concentrate in 7/00, the signal is storage and charging control. The class is granular enough that the distribution of subgroups within H02J is itself a description of what kind of grid problem an assignee is working on, which is more information than the class label alone conveys.

Reading H02J without overreading it

Two limits keep an H02J-based landscape grounded. First, classification marks disclosure, not deployment. A cluster of H02J 3/38 filings from an assignee shows where that assignee is describing grid-integration inventions; it does not establish that any described system is connected to a live grid, or that the issued claims cover the full breadth the symbol suggests. The published application above is a pre-grant document — the description of an invention whose claims have not yet been fixed by examination. Second, H02J is heavily populated with indexing symbols in the 2203, 2207, and 2300 ranges that annotate context (smart-grid communication, monitoring, source type) rather than name the core invention. A landscape that counts those indexing symbols as if they were invention symbols will overstate activity. Read the terminal subgroups — the 3/00 branch for AC distribution, the 3/38 branch for parallel sources, the 9/00 branch for standby and emergency supply — as the substance, and treat the high-number indexing symbols as the annotations they are. Done that way, H02J is the cleanest available map of who is filing on the grid as a system, and where the renewable-integration filings are concentrating.