Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 8842454

This analysis identifies combinations of prior art references that would render the independent claims of US Patent 8842454 obvious to a person having ordinary skill in the art (PHOSITA) as of the priority date (2010-11-29). The motivation to combine these references stems from the common goals in the field of photovoltaic (PV) power conversion: maximizing efficiency, ensuring stable grid connection, and optimizing performance under variable environmental conditions, such as partial shading.

Claims under analysis

The key features of the independent claims (Claim 1 - Apparatus, Claim 10 - Method, Claim 17 - Computer-Readable Medium) of US8842454 involve:

• A plurality of inverters converting DC power from respective DC sources (e.g., PV cells) to AC power for an AC load.
• A hierarchical control system comprising:
  • A primary (master) controller generating a primary control signal based on the total AC current and total AC voltage delivered to the AC load by the plurality of inverters.
  • A plurality of secondary (local) controllers, each receiving the primary control signal and producing a respective secondary control signal based on it.
  • Each secondary control signal controlling a corresponding inverter to provide its portion of the AC power.

Combination of Prior Art References

The combination of the following prior art references would render claims 1, 10, and 17 obvious:

1. US20110026282A1 to Chapman et al. (published 2011-02-03, filed 2009-07-31)
2. US5745356A to Exide Electronics Corporation (published 1998-04-28, filed 1996-06-25)

Analysis of Obviousness for Independent Claim 1 (Apparatus)

Claim 1: An apparatus to deliver alternating current (AC) power, the apparatus comprising: a plurality of inverters configured to receive direct current (DC) power from a respective DC power source and respectively provide AC power to an AC load; a primary controller configured to generate a primary control signal based on total AC current and total AC voltage being delivered to the AC load by the plurality of inverters; and a plurality of secondary controllers configured to each receive the primary control signal and produce a respective secondary control signal based on the primary control signal, wherein the respective secondary control signal for each of the plurality of secondary controllers controls a corresponding one of the plurality of inverters to provide the respective AC power.

1. "a plurality of inverters configured to receive direct current (DC) power from a respective DC power source and respectively provide AC power to an AC load;"

   • US20110026282A1 discloses an apparatus for converting DC to AC, including a "plurality of inverter sub-modules" (106 in FIG. 1) electrically coupled to receive DC power from PV cells (102) and provide an AC output to an AC load. This directly teaches a plurality of inverters receiving DC power from respective DC power sources (PV cells) and providing AC power to an AC load.

2. "a primary controller configured to generate a primary control signal based on total AC current and total AC voltage being delivered to the AC load by the plurality of inverters;"

   • US20110026282A1 discloses a "master controller" (108 in FIG. 1) configured to provide a "control signal" (110) to each of the inverter sub-modules. While the abstract of US20110026282A1 does not explicitly state that this master control signal is based on total AC current and total AC voltage, the purpose of the master controller, as described in US20110026282A1 (and implicitly for any master controller in a grid-tied multi-inverter system), is for "locally controlling energy balance within each of the plurality of inverter sub-modules." For a system providing AC power to an AC load (such as a utility grid), maintaining system-level energy balance and ensuring proper grid synchronization necessarily involves monitoring the aggregate AC output (total AC current and voltage).
   • US5745356A teaches "independent load sharing of AC power systems connected in parallel." Such systems inherently require a control mechanism that monitors the total AC current and/or voltage of the combined output to effectively manage load sharing among multiple AC sources. This demonstrates that it was well-known in the art to base control signals for multi-source AC systems on aggregate AC load parameters.

3. "a plurality of secondary controllers configured to each receive the primary control signal and produce a respective secondary control signal based on the primary control signal,"

   • US20110026282A1 explicitly teaches that "Each of the inverter sub-modules 106 may include a local controller (see FIG. 2)." Furthermore, "The inverter module 104 may include a master controller 108 to provide one or more control signals 110 to each of the inverter sub-modules 106. Each of the inverter sub-modules 106 may use the control signals 110 to locally control the energy balance within each inverter sub-module 106." This directly describes a plurality of secondary (local) controllers receiving a primary (master) control signal and using it to generate local control actions (i.e., respective secondary control signals).

4. "wherein the respective secondary control signal for each of the plurality of secondary controllers controls a corresponding one of the plurality of inverters to provide the respective AC power."

   • This is the functional outcome of the local control described in US20110026282A1. The local controllers use the master control signal (110) to "locally control the energy balance" of their respective inverter sub-modules (106), which directly impacts the AC power provided by that inverter.

Motivation to Combine:
A PHOSITA in the field of power electronics for PV applications, seeking to improve the efficiency and stability of multi-inverter PV systems, particularly under varying environmental conditions like shading (as acknowledged in the background of US8842454), would have been motivated to combine the teachings of US20110026282A1 with the common knowledge and practices exemplified by US5745356A.

US20110026282A1 provides the core hierarchical control architecture with a master controller coordinating local inverter modules to manage energy balance. To optimize the overall system performance and ensure stable and compliant power delivery to an AC load (e.g., a utility grid), a PHOSITA would readily recognize the necessity of making the "master controller" (primary controller) responsive to the aggregate AC load conditions. References like US5745356A show that monitoring total AC current and voltage for system-level control, such as load sharing, was a well-established practice in modular AC power systems. It would be a straightforward engineering decision to feed the total AC current and voltage measurements to the master controller of US20110026282A1 to generate a more effective primary control signal, thereby ensuring the overall system meets grid requirements while local controllers optimize individual inverter performance. This combination addresses the problem of maximizing efficiency and reliability in distributed PV systems connected to an AC grid.

Analysis of Obviousness for Independent Claim 10 (Method)

Claim 10: A method of controlling alternating current (AC) power delivered to an AC load, the method comprising: producing the AC power with an array of inverters based on an amount of received respective DC power; generating a first control signal in response to the AC power; generating a plurality of second control signals in response to the first control signal; and controlling respective output AC power of each inverter of the array of inverters based on a corresponding one of the second control signals, wherein the AC power is a combination of the respective output AC power of each inverter of the array of inverters.

The method steps directly parallel the components of Claim 1.

1. "producing the AC power with an array of inverters based on an amount of received respective DC power;" Taught by the inverter sub-modules (106) receiving DC from PV cells (102) and providing AC output in US20110026282A1.
2. "generating a first control signal in response to the AC power;" This corresponds to the primary control signal based on total AC current and voltage. As discussed for Claim 1, a master controller performing system-level energy balance in a grid-tied context (as in US20110026282A1) would inherently generate its primary control signal in response to the total AC power, using feedback from total AC current and voltage (as commonly known in the art, e.g., US5745356A).
3. "generating a plurality of second control signals in response to the first control signal;" Taught by the local controllers in US20110026282A1 receiving the master control signal (110) and using it for local control actions.
4. "controlling respective output AC power of each inverter of the array of inverters based on a corresponding one of the second control signals, wherein the AC power is a combination of the respective output AC power of each inverter of the array of inverters." This is the outcome of the local control in US20110026282A1, where local controllers regulate the energy balance and output of their respective inverters.

Motivation to Combine: The motivation for the method claim is identical to that for the apparatus claim. A PHOSITA would seek to implement a method for distributed PV power generation that combines system-level control based on aggregate AC output (for grid stability and power quality) with localized control (for individual inverter optimization and fault tolerance), using a hierarchical signaling approach as taught.

Analysis of Obviousness for Independent Claim 17 (Computer-Readable Medium)

Claim 17: A computer-readable medium comprising a plurality of instructions executable by a processor, the computer-readable medium comprising: instructions to direct an array of inverters to generate AC power based on an amount of received respective DC power; instructions to generate a first control signal in response to the AC power; instructions to generate a plurality of second control signals in response to the first control signal; and instructions to control respective output AC power of each inverter of the array of inverters based on a corresponding one of the second control signals, wherein the AC power is a combination of the respective output AC power of each inverter of the array of inverters.

Claim 17 describes a computer-readable medium for implementing the method of Claim 10. Given that power electronics control systems are commonly implemented using processors and computer-readable media (as explicitly noted in US8842454's own disclosure for its master and local controllers, which can be digital and include processors and memory devices), it would be obvious for a PHOSITA to implement the obvious method of Claim 10 using a computer-readable medium. Therefore, if the method of Claim 10 is obvious, the computer-readable medium of Claim 17 is also obvious.