EXPERT LABVIEW CONSULTING SERVICES
Controlling Zinc-flow Batteries and Switch-Mode
Power Regulation for Megawatt-scale Energy Storage
By François Normandin, Javier Ruiz, Tomi Maila, Jim Kring, and Ryan Talbot
Grid-scale energy storage is becoming increasingly important for enabling
renewable energy production, energy demand management, and microgrid applications. These large energy storage devices can be used across
the power delivery system (shown in Figure 1) to provide backup power
and act like shock absorbers for the grid. They are capable of handling
large spikes in energy supply and demand, for example: renewable supply
spikes when the sun is out or the wind is blowing, and consumer demand
spikes from large loads like air conditioning or heaters.
THE CHALLENGE
Creating a system to control the
electrochemical process of an industrial
zinc-flow battery and to regulate and
synchronize the DC power of multiple
zinc-flow batteries connected in series for
delivery onto the AC power grid.
THE SOLUTION
Using LabVIEW and multiple CompactRIO
controllers to develop a real-time
distributed system to control multiple zinc
flow-batteries and LabVIEW FPGA for
high-speed control and regulation of their
DC power to and from the AC power grid.
NI PRODUCTS USED
NI CompactRIO
LabVIEW FPGA
NI Linux Real-Time
LabVIEW
LabVIEW Real-Time
LabVIEW FPGA Compile Cloud Service
Figure 1: EnergyPod™ storage devices used across the delivery system.
Primus Power has developed an innovative large capacity zinc-flow
battery and power regulation system that is cost effective and safe to
operate. This system consists of multiple 30kW (72kWh) zinc-flow
batteries called EnergyCells contained within a larger 420kW EnergyPod™.
The EnergyPod™ provides centralized regulation of the batteries’ DC
power, inversion of the DC power to and from the AC power grid, and
thermal management. Multiple EnergyPods can be composed into an
EnergyFarm system for nearly unlimited storage capacity.
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The system had the following requirements:
• Real-time control and monitoring of the electrochemical processes
of each zinc-flow battery
• Real-time control of battery power distribution and inversion to allow
charging/discharging from/to the power grid
• Deterministic high-speed fault monitoring and protection to ensure
system performance and reliability
• High-speed communication to support real-time control across
multiple embedded controllers
• Flexible communication via multiple industrial protocols to support
third-party energy management systems
• Modular and expandable system architecture to support multiple
possible deployment scenarios
• Professional-grade human machine interfaces (HMI) to allow
operator control and monitoring of the high-level system, low-level
subsystems, and individual components
Primus Power had developed lab prototype systems using LabVIEW for
test and validation. When it came time to develop commercial systems for
shipment to customers, Primus Power partnered with JKI, a Silver NI
Alliance Partner specializing in commercial-quality LabVIEW development
and helping high-tech companies get their innovative products to market
with speed and impact.
Solution Details
Initially, a traditional PLC control system was considered for the
commercial systems. However, it quickly became clear that using NI
CompactRIO, powered by NI Linux Real-Time and LabVIEW FPGA, would
not only address the technical and performance requirements, but would
also reduce development time; this would enable us to get the product to
market much faster and generate considerable business value.
Each EnergyCell is controlled by an independent cRIO-9068 responsible
for managing the zinc-flow battery’s electrochemical process, state of
charge, and overall health by controlling and monitoring a variety of pumps,
valves, and sensors using NI 9375 and NI 9265 modules. Two NI 9205
modules are used to acquire 39 RSE voltage measurements for performing
real-time prediction of battery health and characterization of
electrochemical behaviors.
The EnergyCells are connected in series inside the EnergyPod to form a
high-power DC current loop called the “powertrain”. Each EnergyCell can
charge or discharge its zinc-flow battery by accepting or providing power
from or to the powertrain’s DC current loop. This is achieved with the
cRIO-9068’s FPGA plus NI 9474, NI 9401, and NI 9423 modules by
switching MOSFETs at high frequency to provide closed-loop current and
voltage regulation.
Figure 2: An Individual EnergyCell
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The EnergyPod™ has a cRIO-9068 controller that it uses
to manage the powertrain DC current loop in order to
accept or provide power to or from the AC grid, as
requested by the EnergyFarm. The EnergyPod™
cRIO-9068’s FPGA acts as a switch-mode power
regulator that modulates IGBTs to achieve closed-loop
current and voltage control for the overall powertrain,
while individually modulating power and or bypassing
EnergyCells. Using high-speed NI 9401, NI 9423, and NI
9474 C Series modules, the powertrain system
synchronizes each EnergyCell to a common triggering
signal and distributes ON and OFF times with
microsecond accuracy. Additionally, the system is able
to detect and react to potentially catastrophic faults
within microseconds.
Figure 3: An EnergyPod containing 14 EnergyCells
The EnergyPod™ also uses its cRIO-9068 to run a
complex thermal management system (controlling pumps
and valves, and monitoring temperatures), to communicate with groundfault protection devices via Modbus, and to manage the fire suppression
and ventilation systems.
The EnergyFarm has a cRIO-9068 that controls and monitors multiple
EnergyPods, communicates with an external energy management system
(EMS) via OPC or DNP3, and controls inverters and other devices via
Modbus. When the EnergyFarm cRIO receives a request from the EMS to
accept/provide power from/to the grid, it determines the necessary steps
and commands all the EnergyPods to accept/provide the necessary power.
JKI designed and developed a modular and
distributed control software architecture that
allows for networked communication and
high scalability. Built upon the NI Actor
Framework for LabVIEW, the architecture
seamlessly runs on both embedded and PC
targets and can accommodate various
system configurations ranging from just a
couple of cRIOs to more than a hundred.
Switching between subsystem
implementations allows for fast prototyping
and rapid changes in requirements. Loosely
coupled distributed system components
make it possible to reuse elements in both
the lab and manufacturing environments. JKI
also developed commercial-grade human
machine interfaces (HMI) using LabVIEW to
provide intuitive operator control of the entire
system and individual components.
Figure 4: The control system consists of 15 cRIOs per EnergyPod™,
plus 1 cRIO for the EnergyFarm.
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Project Conclusions
As with most high-tech product development efforts, we had an
aggressive project schedule and demanding requirements that continued
to evolve over the course of the project. NI CompactRIO, powered by NI
Linux Real-Time and LabVIEW FPGA, provided a fantastic platform for our
system, because of its performance, affordability, and ruggedness in
extreme environments where our EnergyFarm systems are deployed. We
saved thousands of dollars in custom board design and validation.
CompactRIOs were found to provide better performance and flexibility
than traditional PLCs and allowed for the reuse of existing LabVIEW code
originally written for testing and validation. Moreover, the NI Linux RealTime OS opens the door to augment the functionality of the system with
the ecosystem that Linux provides.
Using LabVIEW at all stages of the development cycle (from research to
proof-of-concept to product test and deployment) minimized the time to
market and facilitated code reusability. Moreover, LabVIEW allowed for
one programming language to be uniformly used all the way from low-level
FPGA control to high-level business logic and user interfaces.
Communication with external systems via OPC, Modbus, and DNP3 was
easily accomplished thanks to the extensive library of drivers for LabVIEW.
LabVIEW FPGA was used for running the complex high-speed control
algorithms and fault handling logic required for Primus Power’s powertrain
architecture. The LabVIEW FPGA-based solution allowed for extremely
short development iteration cycles, making it possible to go from prototype
to a shipping product in a fraction of the time compared to traditional FPGA
development. This accelerated development enabled Primus Power to
showcase its powertrain as part of an Advanced Microgrid Demonstration
at the National Renewable Energy Laboratory (NREL) in Golden, Colorado in
fall 2014, where the system was capable of islanded (off-grid) operation
using stored and high-penetration renewable energy.
Silver
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JKI is a National Instruments
Certified Silver Alliance Partner.
By all measures, using NI CompactRIO, NI Linux Real-Time, and LabVIEW
FPGA significantly reduced development time, enabling our team to get
the product to market much faster than alternative approaches and make
a significant impact in the energy storage market.
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