PTAB

IPR2022-00008

SolarEdge Technologies Ltd v. Koolbridge Solar Inc

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Solar Energy Conversion and Utilization System
  • Brief Description: The ’822 patent discloses systems for converting direct current (DC) electrical power to alternating current (AC) electrical power. The primary embodiment at issue involves a single-phase inverter that uses a plurality of series-connected H-bridge switches, each fed by a separate floating DC voltage source, to generate a stepped AC output waveform approximating a sinusoid.

3. Grounds for Unpatentability

Ground 1: Obviousness over Mori and Tolbert - Claims 1-3, 8-10, and 12 are obvious over Mori in view of Tolbert.

  • Prior Art Relied Upon: Mori (Japanese Patent Publication No. 2006-238630A) and Tolbert (a 1999 IEEE article).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Mori discloses a nearly identical DC-AC inverter to that claimed in the ’822 patent. Mori’s inverter uses multiple H-bridges connected in series, each receiving a floating DC voltage, to generate a stepped AC output waveform. Petitioner asserted that Mori’s inverter, due to its identical structure and switch timing, necessarily generates the claimed AC output waveform at a first frequency and a corresponding common-mode voltage waveform on its DC input terminals at a second frequency, as required by independent claims 1 and 8. Tolbert was cited as teaching the specific H-bridge control states (positive, negative, and pass-through) used to generate the waveforms.
    • Motivation to Combine: A person of ordinary skill in the art (POSITA) would combine Mori's inverter architecture with Tolbert's explicit teaching of H-bridge control sequences. The motivation would be to achieve the precise voltage outputs disclosed in Mori using a known control scheme. Tolbert further taught that its sequence beneficially equalizes stress across all switching devices, providing an independent reason for its adoption.
    • Expectation of Success: A POSITA would have a high expectation of success, as the combination involved applying a known control method (Tolbert) to a known inverter topology (Mori) to achieve the predictable result of a specific output waveform and its inherent common-mode characteristics.

Ground 2: Obviousness over Mori/Tolbert and De - Claims 6 and 20 are obvious over the combination of Mori and Tolbert in view of De.

  • Prior Art Relied Upon: Mori, Tolbert, and De (Application # 2007/0278988).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground builds on the Mori/Tolbert combination for the base inverter. Dependent claim 6 adds a common-mode filter connected between the DC source and the inverter’s DC input terminals. Petitioner argued De explicitly discloses such a common-mode filter (including an inductor and capacitor) used in an identical context—between a rectifier DC source and an inverter—to solve the known problem of common-mode noise generated by inverter switching. De’s filter was configured to prevent high-frequency components from being exported to the DC source and to minimize voltage overshoot, meeting all limitations of claim 6.
    • Motivation to Combine: A POSITA would recognize that the Mori/Tolbert inverter would generate the same type of high-frequency common-mode noise as the inverter in De. Therefore, a POSITA would be motivated to incorporate De’s well-known filter solution into the Mori/Tolbert system to improve electromagnetic compatibility and reduce hazards, which are known benefits of such filters.
    • Expectation of Success: The combination was presented as the application of a known solution (De's filter) to a known problem (inverter-generated noise) in a similar system, with a high expectation of achieving the predictable result of noise suppression.

Ground 3: Obviousness over Mori/Tolbert and Fujimoto - Claims 4 and 11 are obvious over the combination of Mori and Tolbert in view of Fujimoto.

  • Prior Art Relied Upon: Mori, Tolbert, and Fujimoto (Japanese Patent Application Publication No. JP 11-122819).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground adds Fujimoto to the Mori/Tolbert combination to teach the "AC ground leak detector" recited in claim 4. Petitioner asserted that Fujimoto discloses a DC ground fault detector, including a current transformer, inserted into the positive and negative DC conductors between a DC power supply and an inverter. This detector is designed to identify an imbalance current caused by leakage to ground, which corresponds to the claimed detector structure and function.
    • Motivation to Combine: A POSITA would be motivated to add Fujimoto’s ground fault detection circuit to the Mori/Tolbert inverter to improve safety. Detecting leakage impedance is a critical safety function that prevents hazards such as fire and component damage and is often required to comply with government safety standards like the National Electric Code.
    • Expectation of Success: A POSITA would have reasonably expected success in combining the references, as it involved adding a standard safety circuit (Fujimoto) to a power conversion system (Mori/Tolbert) to gain a known safety benefit.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combinations with Bond (Patent 6,112,158) to teach a three-phase grid-interactive configuration (Claim 7) and with Iwata (Application # 2008/0192519) and Nishimura (Application # 2009/0086520) to teach a bidirectional DC-to-DC converter (Claims 5 and 13).

4. Key Claim Construction Positions

  • Petitioner argued that several claim terms should be construed as means-plus-function limitations under 35 U.S.C. § 112, para. 6.
  • “DC to AC converter” (Claim 1): Petitioner proposed this term performs the function of causing specific AC output and common-mode voltage waveforms. The corresponding structure was identified as the inverter circuits depicted in the ’822 patent, particularly the configuration of multiple series-connected H-bridges.
  • “A switch[ing] controller” (Claims 2, 5): Petitioner argued this term performs the function of controlling electronic switches according to specific timing or ternary logic. The corresponding structure was identified as a microcontroller with memory or a crystal oscillator with a ROM containing precomputed waveforms.
  • “bidirectional DC-to-DC converter” (Claims 5, 13): Petitioner contended this term performs the function of converting an input voltage to floating supplies with voltages related by successive powers of three. The corresponding structure was identified as one or more transformers with center-tapped windings.

5. Arguments Regarding Discretionary Denial

  • Petitioner argued against discretionary denial, noting that the prior art references relied upon in the petition were not cited or considered during the original prosecution of the ’822 patent.
  • Petitioner also noted that a related district court case, Koolbridge Solar, Inc. v. SolarEdge Technologies, Inc., was voluntarily dismissed without prejudice by the Patent Owner after the Patent Owner was notified of Petitioner's intent to file these IPRs.

6. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 1-13 and 20 of Patent 8,937,822 as unpatentable.