PTAB

IPR2022-00012

SolarEdge Technologies Ltd v. Koolbridge Solar Inc

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Key Events
Petition

1. Case Identification

2. Patent Overview

  • Title: Solar Energy Conversion and Utilization System
  • Brief Description: The ’822 patent describes a solar energy system that uses a DC-to-AC inverter to convert power from photovoltaic panels. The system includes a ground leak detector that identifies faults in the DC wiring by sensing an "unusual" common-mode AC current generated by the inverter's normal operation.

3. Grounds for Unpatentability

Ground 1: Claims 14, 15, 16, 18, and 19 are obvious over Mirafzal in view of Ivan and the NEC Handbook.

  • Prior Art Relied Upon: Mirafzal (Application # 2008/0080106), Ivan (Patent 7,649,360), and the NEC Handbook (National Electrical Code Handbook, Eleventh Edition, 2008).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that the combination of these references teaches every element of the challenged claims. Mirafzal disclosed a power conversion system with an inverter and a ground fault detector that senses common-mode current imbalances between positive and negative DC conductors. While Mirafzal did not specify a solar array, the NEC Handbook taught using photovoltaic arrays as a standard DC power source for such inverters, including necessary ground-fault protection. The NEC Handbook also taught routing positive, negative, and grounding conductors in parallel within the same raceway for safety, fulfilling a key limitation of claim 14. Ivan taught that the switching of an inverter inherently creates a common-mode AC voltage on its DC input bus at a characteristic frequency related to the inverter’s fundamental operating frequency, and that this voltage is in-phase on both the positive and negative conductors.
    • Motivation to Combine: A person of ordinary skill in the art (POSITA) would combine Mirafzal and the NEC Handbook to create a standard, safe solar energy installation, as the NEC Handbook provided industry-standard guidance for just such systems. A POSITA would then incorporate Ivan's teachings to improve Mirafzal’s ground fault detection. Since Mirafzal already detected common-mode current, Ivan’s method of correlating the frequency of the common-mode signal to the inverter’s operating frequency provided a known technique to improve detection reliability by confirming the fault's source.
    • Expectation of Success: Combining these known elements would have been predictable. A POSITA would expect that a standard solar array and wiring from the NEC Handbook would work with Mirafzal's inverter, and that applying Ivan's frequency analysis to Mirafzal's detected common-mode current would successfully improve the system's diagnostic capability.

Ground 2: Claim 17 is obvious over Mirafzal, Ivan, and the NEC Handbook, further in view of Mori.

  • Prior Art Relied Upon: Mirafzal (Application # 2008/0080106), Ivan (Patent 7,649,360), the NEC Handbook, and Mori (Japanese Patent Publication No. 2006-238630).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground adds Mori to address the limitation of 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 the AC output waveform. Mori disclosed a multi-level inverter using a series of H-bridges, each powered by a different DC voltage (e.g., in a 1:3:9 ratio). The state of these H-bridges (e.g., +V, 0, -V) can be represented as a multi-digit ternary number that changes over time to approximate a sine wave AC output. Petitioner argued it was well-known that the switching of each H-bridge creates a corresponding common-mode voltage at its input. Therefore, the common-mode signal at the input of any given H-bridge in Mori directly corresponds to the changing state of its associated "digit" in the multi-digit sequence.
    • Motivation to Combine: A POSITA would have been motivated to replace the inverter in the system of Ground 1 with Mori's more advanced multi-level inverter. Mori explicitly taught that its design achieves a "highly accurate output voltage waveform" using inexpensive control circuitry. This presented a clear advantage over simpler inverter designs.
    • Expectation of Success: The proposed modification was an exercise of routine skill. It involved substituting one known type of inverter for another to gain a predictable improvement in performance. The ground fault detection system from the primary combination would still function as intended, as Mori's inverter also generates a detectable common-mode signal based on its switching, which Ivan taught could be analyzed for fault detection.

4. Key Claim Construction Positions

  • "DC to AC converter" (Claim 14): Petitioner argued this term should be construed under 35 U.S.C. § 112, ¶ 6 (pre-AIA) as a means-plus-function term.
    • Function: "[having] an AC output having an output waveform with an output repetition frequency [and] creating a common mode AC probe signal waveform [] at a characteristic repetition frequency that is in phase on both said DC positive and negative input conductors."
    • Structure: The corresponding structures disclosed in the ’822 patent were identified as various inverter circuits, including a plurality of H-bridge switches with series-connected outputs.
  • "detector" (Claim 14): Petitioner argued this term should also be construed as a means-plus-function term.
    • Function: "detect[ing] an unusual current with said common mode waveform at said characteristic repetition frequency and upon detection of said unusual current providing an indication of the presence of an unwanted ground leak."
    • Structure: The corresponding structure was identified as a current transformer, such as the toroid 800 with toroidal winding 801 shown in the patent's figures.

5. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 14-19 of the ’822 patent as unpatentable.