US 8279642

US Patent 8279642, titled "Apparatus for converting direct current to alternating current using an active filter to reduce double-frequency ripple power of bus waveform," was filed on September 21, 2009, and issued on October 2, 2012.

Inventors:
Patrick L. Chapman, Brian T. Kuhn, Robert S. Balog, Jonathan W. Kimball, Philip T. Krein, and Alexander Gray.

Assignee:
The original assignee was Solarbridge Technologies Inc. The current assignees are GRIDSCALE SOLUTIONS, LLC, and Enphase Energy Inc.

Abstract:
The patent describes an inverter designed to convert an input direct current (DC) waveform from a DC source into an output alternating current (AC) waveform for delivery to an AC grid. This inverter comprises an input converter, an output converter, and an active filter, all electrically connected to a power bus (which can be either DC or AC). The input converter transforms the initial DC waveform into a bus waveform. The output converter then converts this bus waveform into the final AC output at the grid frequency. A key feature is the active filter, which is configured to reduce undesirable double-frequency ripple power on the bus waveform by actively supplying and absorbing power from the power bus.

Independent Claims Overview:

• Claim 1: Describes an inverter that converts DC to AC for an AC grid. It features an input converter with a transformer to process the DC input into a bus waveform, an output converter to change the bus waveform into the AC output, and an active filter. The active filter is connected to the power bus, works to reduce double-frequency ripple power by adding and removing power to keep the bus voltage steady, and includes a switching circuit connected to an energy storage device.

• Claim 15: Describes an apparatus comprising a solar panel (with a solar cell generating DC) and an inverter. The inverter takes the solar panel's DC and converts it to AC. This inverter contains an input converter (connected to the solar cell and a DC bus), an output converter (connected to the DC bus to create the AC output), and an active filter (connected to the DC bus) that reduces double-frequency ripple power by interacting with the DC bus.

• Claim 23: Describes a power inverter with a DC bus, an input converter, an output converter, and an active filter, all linked to the DC bus. The input converter includes a transformer, a first inverter circuit (converting input DC to AC for the transformer's primary winding), and a rectifier circuit (connected to the transformer's secondary winding and the DC bus) that produces a DC waveform on the bus. The output converter converts this DC bus waveform to the AC output. The active filter reduces double-frequency ripple power on the DC bus by dynamically supplying and absorbing power.

• Claim 32: Similar to Claim 1, this claim specifies an inverter with an input converter (including a transformer), an output converter, and an active filter. The active filter is specifically connected to a tertiary winding of the transformer and functions to reduce double-frequency ripple power on the power bus by exchanging power to track a desired bus voltage. The active filter includes a switching circuit coupled to an energy storage device.

• Claim 37: Similar to Claim 15, this apparatus includes a solar panel and an inverter. However, in this claim, the input converter transforms the DC from the solar cell into an AC waveform for an AC power bus. The output converter then uses a frequency converter circuit to change this AC bus waveform into the final output AC waveform. The active filter is coupled to the AC bus and functions to reduce double-frequency ripple power.

• Claim 41: Similar to Claim 23, this power inverter has an AC bus. The input converter is designed to convert the input DC to a first AC waveform (the bus waveform) on this AC bus. It includes a transformer with a primary winding (connected to a first inverter circuit for DC-to-AC conversion) and a secondary winding (connected to the AC bus). The output converter converts the AC bus waveform to the final output AC. The active filter is coupled to the AC bus to reduce double-frequency ripple power.

USPTO and CAFC 2026 Dockets Search:
A search for US Patent 8279642 on the USPTO database, as reflected by Google Patents, confirms the provided patent details including publication, assignment history, and legal status. The patent is currently active and is set to expire on October 20, 2030.

Regarding the U.S. Court of Appeals for the Federal Circuit (CAFC) 2026 dockets, a search for US8279642 did not yield any specific active cases or litigation records involving this patent number directly in the publicly available scheduled cases or general case information for 2026. This does not definitively mean there is no litigation, but rather that no easily searchable public records for 2026 dockets pertaining to this specific patent number were found through the conducted search.