SolarEdge Technologies Ltd v. Koolbridge Solar Inc

1. Case Identification

• Case #: IPR2022-00011
• Patent #: 8,937,822
• Filed: October 11, 2021
• Petitioner(s): SolarEdge Technologies Ltd.
• Patent Owner(s): Koolbridge Solar, Inc.
• Challenged Claims: 14-19

2. Patent Overview

• Title: Solar Energy Conversion and Utilization System
• Brief Description: The ’822 patent describes a method for detecting ground leaks in the DC wiring of a solar energy installation. The system uses a DC to AC converter (inverter) that inherently generates a common-mode AC voltage, which in the event of a ground fault, creates an unusual common-mode current that is detected by a current transformer.

3. Grounds for Unpatentability

Ground 1: Obviousness over Fujimoto and Boniface - Claims 14, 15, 18, and 19 are obvious over Fujimoto in view of Boniface.

• Prior Art Relied Upon: Fujimoto (Japanese Patent Application Publication No. JP 11-122819) and Boniface (Application # 2009/0207543).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Fujimoto taught a solar power generation system with a DC power supply, an inverter, and a ground leak detector that meets most limitations of independent claim 14. Fujimoto’s detector used a current transformer to sense a "common current" (i.e., common-mode current) having an AC component at twice the inverter's output frequency. However, Fujimoto did not explicitly disclose routing the DC conductors "in parallel with an array grounding conductor." Boniface was asserted to cure this deficiency by teaching a photovoltaic system where positive, negative, and equipment ground conductors are routed together in parallel within a conduit.
  • Motivation to Combine: A POSITA would combine Fujimoto with Boniface to implement standard, well-known safety features. Routing a grounding conductor in parallel with power conductors as taught by Boniface was a known technique to prevent shock hazards and improve safety in solar installations.
  • Expectation of Success: Petitioner asserted a high expectation of success, as the combination involved applying a standard, required safety and wiring practice (from Boniface) to a conventional solar power system (Fujimoto).

Ground 2: Obviousness over Fujimoto and NEC Handbook - Claims 14-16, 18, and 19 are obvious over Fujimoto in view of the NEC Handbook.

• Prior Art Relied Upon: Fujimoto (Japanese Patent Application Publication No. JP 11-122819) and the U.S. National Electrical Code Handbook, 2008 Edition (NEC Handbook).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground presented a similar argument to Ground 1 for claim 14, substituting the NEC Handbook for Boniface. The NEC Handbook, a standard for electrical installations in the U.S., was argued to teach routing PV array circuit conductors together with an equipment grounding conductor in the same raceway or cable. For dependent claim 16, which adds a storage battery, Petitioner argued the NEC Handbook (e.g., Exhibit 690.4) explicitly illustrates a solar system with a battery bank charged by a PV array and a ground fault detector positioned to protect the DC conductors leading to and from the battery.
  • Motivation to Combine: A POSITA would combine Fujimoto with the NEC Handbook to comply with established safety standards and improve system utility. For claim 16, the motivation was to add a desirable backup power source (the battery), a known system enhancement, and implement it according to the safety configurations shown in the NEC Handbook.
  • Expectation of Success: The combination would have been a predictable implementation of industry-standard safety requirements and known system enhancements on a conventional solar inverter design.

Ground 3: Obviousness over Fujimoto, Boniface/NEC Handbook, and Iwata - Claim 17 is obvious over Fujimoto in view of Boniface or the NEC Handbook, and further in view of Iwata.

• Prior Art Relied Upon: Fujimoto, Boniface or the NEC Handbook, and Iwata (Application # 2008/0192519).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground addressed claim 17, which requires the common-mode AC probe signal to correspond to "the changing value of a selected digit within a multi-digit number sequence representing said AC output waveform." Petitioner argued the base combination of Fujimoto and Boniface/NEC Handbook established the foundational solar energy installation. Iwata was introduced to teach the specific waveform generation method. Iwata disclosed a multilevel inverter using series-connected H-bridges, where the AC output is synthesized based on a multi-digit ternary number sequence. The switching of each H-bridge, corresponding to a digit in this sequence, was known to generate a common-mode voltage at its input that directly corresponds to the changing value of that specific digit.
  • Motivation to Combine: A POSITA would combine the teachings by replacing Fujimoto's inverter with Iwata's more advanced multilevel inverter. The motivation was to achieve the known benefits of multilevel inverters, such as improved conversion efficiency, reduced power loss, and reduced output filtering requirements, which were desirable improvements for any solar power system.
  • Expectation of Success: Petitioner contended success was highly likely, as it involved substituting one known type of inverter for an improved, known type of inverter to gain predictable advantages.

4. Key Claim Construction Positions

• Petitioner argued that two terms in claim 14 should be construed as means-plus-function limitations under 35 U.S.C. § 112, ¶ 6.
  • "DC to AC converter": Petitioner asserted the recited function is creating an AC output and a common-mode AC probe signal. The corresponding structure in the ’822 patent was identified as various inverter circuits, including those with pluralities of H-bridge switches.
  • "detector": Petitioner asserted the function is detecting an unusual current with the common-mode waveform and providing an indication of a ground leak. The corresponding structure was identified as a current transformer, such as toroid 800 with toroidal winding 801 shown in the patent.

5. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under §314(a) based on Fintiv factors would be inappropriate. The Patent Owner had previously asserted the ’822 patent against the Petitioner in district court. However, after being notified of Petitioner's intent to file IPRs, the Patent Owner voluntarily dismissed the lawsuit without prejudice. Petitioner contended that because there was no co-pending litigation, the Fintiv factors strongly weighed against denial of institution.

6. Relief Requested

• Petitioner requested institution of an inter partes review and cancellation of claims 14-19 of the ’822 patent as unpatentable under 35 U.S.C. §103.