PTAB

IPR2022-00014

SolarEdge Technologies Ltd v. Koolbridge Solar Inc

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Transformerless DC To AC Converter
  • Brief Description: The ’710 patent describes a transformerless DC to AC inverter. The inverter uses a plurality of series-connected H-bridge switches, each receiving a distinct DC voltage, to generate a summed output voltage that approximates a desired AC sinusoidal waveform through ternary (+1, -1, 0) control of the switches.

3. Grounds for Unpatentability

Ground 1: Obviousness over Suzuki - Claims 1-5, 7-8, and 12 are obvious over Suzuki.

  • Prior Art Relied Upon: Suzuki (Japanese Patent Application Publication No. 2004-7941).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Suzuki disclosed the core architecture of the ’710 patent: a DC to AC power converter comprising multiple single-phase inverters (i.e., controlled switches) connected in series. Each inverter in Suzuki received a distinct DC voltage and was controlled by a ternary-valued signal to output the positive DC voltage, the negative (inverted) DC voltage, or zero voltage. Petitioner contended that the outputs of these inverters were directly connected in series to produce a summed voltage approximating a sine wave, rendering the output "transformerless." For claim 1’s "hot and neutral output terminals" limitation, Petitioner argued a POSITA would find it obvious to connect Suzuki’s two-wire output to a standard residential AC grid by connecting one terminal to a hot wire and the other to a neutral wire, as this is one of only two standard connection options.
    • Motivation to Combine (for §103 grounds): This ground relies on a single reference. The motivation was to apply the known teachings of Suzuki for their intended purpose. For the hot/neutral connection, the motivation was to connect the inverter to a standard residential electrical grid in compliance with known electrical codes (e.g., NEC 2008).
    • Expectation of Success: A POSITA would have had a high expectation of success in connecting Suzuki’s inverter to a standard grid, as it was a common and well-understood task for electrical engineers.

Ground 2: Obviousness over Suzuki in view of Tolbert - Claim 6 is obvious over Suzuki in view of Tolbert.

  • Prior Art Relied Upon: Suzuki (Japanese Patent Application Publication No. 2004-7941) and Tolbert (an IEEE journal article from 1999).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that while Suzuki taught the use of ternary-valued signals to control H-bridge switches, it did not explicitly disclose generating these signals from pairs of binary bits as required by claim 6. Tolbert allegedly supplied this missing element by teaching a common H-bridge control scheme where two binary bits (Gaip and Gain) create four possible states. Petitioner argued that Tolbert explicitly taught that two of these four combinations (e.g., Gaip=0, Gain=0 and Gaip=1, Gain=1) place the H-bridge into a zero-voltage output state, directly mapping to the claim limitation.
    • Motivation to Combine: A POSITA would combine Tolbert’s efficient two-bit control scheme with Suzuki’s inverter design. The motivation was to use a known, efficient encoding method that also allows for equalizing stress on switching devices by using all transistors for equal amounts of time.
    • Expectation of Success: This modification was argued to be within the skill of a POSITA, who would be familiar with H-bridge control logic and could readily implement Tolbert’s two-bit signal generation to control Suzuki’s switches with a reasonable expectation of predictable results.

Ground 3: Obviousness over Suzuki in view of Ball - Claims 10-11 are obvious over Suzuki in view of Ball.

  • Prior Art Relied Upon: Suzuki (Japanese Patent Application Publication No. 2004-7941) and Ball (Patent 5,029,064).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner argued that Suzuki did not teach using a battery as the highest-voltage DC power source or deriving lower voltages via a bidirectional DC-DC converter. Ball allegedly disclosed a universal bidirectional power converter capable of being powered by a battery. This converter could transfer power between multiple fixed DC voltage ports, with the voltage ratios determined by transformer turn ratios. Petitioner asserted that Ball’s converter structure was equivalent to the bidirectional DC-DC conversion circuitry claimed in the ’710 patent.
    • Motivation to Combine: A POSITA would combine Ball's battery and bidirectional converter with Suzuki's inverter to create a more versatile system, such as an uninterruptible power supply (UPS). Ball’s converter was capable of providing the multiple, floating DC voltages required by Suzuki’s design.
    • Expectation of Success: A POSITA would have a reasonable expectation of success, as Ball provided detailed schematics and operational descriptions, and connecting its DC voltage ports to Suzuki’s H-bridge inputs was a matter of basic engineering.

  • Additional Grounds: Petitioner asserted numerous other obviousness challenges. These included combining Suzuki with Nishimura for standard household voltage features; with Mori ’630 for an explicit switch signal generator; with Kumar for using memory to store precomputed switching patterns; with De or Koyama for adding a common-mode filter; with Ahmed for adding damping circuits to filters; and with Kang for adding an in-rush current limiting circuit.

4. Key Claim Construction Positions

  • Petitioner identified two terms that could be construed as means-plus-function elements under 35 U.S.C. § 112.
  • “a switch selection signal generator operative to” (claims 7-9): Petitioner argued that if this is a means-plus-function term, the function is producing ternary-valued selection signals, and the corresponding structure in the ’710 patent is a microcontroller or microprocessor-based controller (e.g., controller 200).
  • “bi-directional DC-DC conversion circuitry operative to” (claims 10-11): Petitioner argued that if this is a means-plus-function term, the function is deriving lower voltage or power values from a battery, and the corresponding structure is transformer windings with specific turn ratios and center taps.

5. Relief Requested

  • Petitioner requests the institution of an inter partes review and the cancellation of claims 1-17 of the ’710 patent as unpatentable.