The customer was developing a new grid-scale flow battery and was looking for a low cost, custom, stack health monitor. The available commercial products contained features and functions that were not required as well as other aspects that would have added unnecessary cost into the product.
Achieving the desired accuracy while also staying within the production cost constraints proved to be the biggest challenge in implementing this unique cell data acquisition system.
AppliedLogix specified and developed the portion of this system that monitors the stack health of the flow battery, known as the Stack Health Monitor (SHM).
The SHM provides continuous real-time monitoring of the flow battery cell voltages, full stack voltage, and error conditions. The SHM aggregates the measured data and reports the statistics to the system controller.
- Low cost – 90% reduction in UMC versus the commercially available alternative
- Accuracy – high measurement accuracy by design and self-calibration
- Reliability – operational life of 20 years
The system samples the cell voltages that comprise the stack and communicates the critical parameters to the system controller.
The SHM provides continuous real-time monitoring of the flow battery cell voltages, full stack voltage, and conditions. The SHM aggregates the measured data and reports the statistics to the high-level system controller.
AppliedLogix gathered and documented the customer’s input and design requirements, assembled its multi-functional team, and then proceeded to execute the project. The key deliverables included:
- Product feasibility assessment
- System architecture specification
- Subsystem design – including all circuit simulations and noise floor analysis
- Quick-turn prototype fabrication and assembly
- Custom enclosure design and fabrication
- Delivered full SHM assemblies to the customer for integration
The software was developed in C, under the CMake build system, with unit testing in Ceedling, targeting ARM Cortex M3 and Cortex M7 microcontrollers. AppliedLogix developed all of the key functions for voltage measurement, self-calibration, CAN communication, interlock logic for fault-based shutdown, open cell connection (wire-break) detection, Modbus-over-TCP control system interface, on-board data logging, an embedded serial console for configuration, testing, and debug output, and a TFTP bootloader for firmware updates via Ethernet.
On the hardware side, a distributed system was designed and developed. The hardware is deployed multiple times in a system – allowing flexibility in system size. Critical design aspects included: precision analog measurement, digital sampling, self-calibration, signal filtering, and high voltage isolation.
The SHM gathers and assembles the cell data, automatically identifies the number and position of the input modules, provides safety status, supports the high voltage isolation requirements, and hosts system power as a Power over Ethernet (POE) client.