PTAB

IPR2022-00015

SolarEdge Technologies Ltd v. Koolbridge Solar Inc

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petition

1. Case Identification

2. Patent Overview

  • Title: Transformerless DC to AC Converter
  • Brief Description: The ’710 patent discloses a DC to AC power inverter that converts a DC input into a sinusoidal AC output without a transformer. The system uses a plurality of series-connected, controlled switches (e.g., H-bridges), each associated with a DC power source, which are selectively controlled by ternary-valued signals (+1, -1, or 0) to sum their respective voltages and approximate a desired AC waveform.

3. Grounds for Unpatentability

Ground A: Anticipation by Bowles - Claims 1, 7, and 8 are anticipated under 35 U.S.C. §102 by Bowles.

  • Prior Art Relied Upon: Bowles (Patent 5,757,633).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Bowles discloses every element of independent claim 1. Bowles teaches a multistep DC to AC inverter comprising a plurality of series-connected secondary inverters (controlled switches/H-bridges) that each receive a DC voltage. The outputs of these inverters are directly connected in series to produce a summed voltage that approximates a sinusoidal AC waveform. Petitioner asserted that Bowles’s output is transformerless and that grounding one of its output terminals (as shown in its Fig. 3) creates the claimed hot and neutral terminals. Bowles’s control circuit generates ternary-valued signals (+V, -V, 0V) to control the switches, meeting the limitations for claims 1, 7, and 8.

Ground B: Obviousness over Bowles and Lipo - Claims 2, 4, 5, and 12 are obvious over Bowles in view of Lipo.

  • Prior Art Relied Upon: Bowles (Patent 5,757,633) and Lipo (Patent 6,005,788).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that while Bowles teaches the fundamental inverter architecture, it describes using a common DC voltage for its H-bridges. Claims 2 and 5 require at least some of the DC voltages to be different, specifically differing by a factor of 3. Lipo was cited to teach the advantages of using different DC source voltages for series-connected H-bridge inverters, including geometric progressions with a factor of three. Lipo explains this technique achieves a substantially higher number of distinct output voltage levels, improving sine wave smoothness without increasing the number of inverters.
    • Motivation to Combine: A POSITA would combine Lipo's teaching of using geometrically progressing DC voltages with Bowles’s inverter to improve the spectral performance and increase the resolution of the output waveform, a well-known objective in inverter design.
    • Expectation of Success: The combination represented the application of a known technique (using varied DC voltages) to a known inverter topology (Bowles) to achieve the predictable result of a smoother, higher-resolution AC output.

Ground F: Obviousness over Bowles and Iwata - Claims 10-11 are obvious over Bowles in view of Iwata.

  • Prior Art Relied Upon: Bowles (Patent 5,757,633) and Iwata (Application # 2008/0192519).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner argued that claims 10 and 11 require the highest-voltage DC source to be a battery and the lower-voltage DC sources to be derived from it via bi-directional DC-DC conversion circuitry. While Bowles does not teach this, Iwata discloses an inverter for an uninterruptible power supply (UPS), which inherently uses a battery as a DC source. Iwata further teaches using a bi-directional DC-DC converter to derive multiple lower DC voltages from the primary (highest) DC source at predetermined ratios (e.g., 1:3:9), which corresponds to the claimed power and voltage relationships.
    • Motivation to Combine: A POSITA would have been motivated to modify the power supply of Bowles’s inverter with the battery and DC-DC converter configuration taught by Iwata. This modification would allow the inverter to function as a reliable UPS, a known and desirable application for such converters.
    • Expectation of Success: This combination involved the straightforward substitution of one known DC power supply architecture (Iwata's battery and DC-DC converter) for another (Bowles's rectified sources) to achieve the predictable result of an uninterruptible power source.

  • Additional Grounds: Petitioner asserted numerous other obviousness challenges. These grounds relied on the core combination of Bowles and other references to teach remaining dependent claim features, including using a battery and DC-DC converter (Iwata, Tracy); implementing specific ternary control signal logic (Mori ’265); adding memory for precomputed switching signals (Flanagan); adding common-mode and low-pass output filters (Koyama, Ahmed); and including a start-up in-rush current limiting circuit (Phadke).

4. Key Claim Construction Positions

  • Petitioner contended that all claim terms should be given their plain and ordinary meaning. However, Petitioner preemptively addressed two terms that could potentially be construed as means-plus-function limitations under 35 U.S.C. §112.
  • “a switch selection signal generator operative to” (claims 7-9): Petitioner argued this is not a means-plus-function term. If the Board were to find otherwise, Petitioner identified the corresponding structure in the ’710 patent as controller 200, which includes a microcontroller or microprocessor.
  • “bi-directional DC-DC conversion circuitry operative to” (claims 10-11): Similarly, Petitioner argued this is not a means-plus-function term. If construed as such, Petitioner identified the corresponding structure as transformer windings with specific turn ratios and center taps as disclosed in the specification.

5. Relief Requested

  • Petitioner requests the institution of an inter partes review and the cancellation of claims 1-17 of Patent 10,784,710 as unpatentable.