Dynapower Reduces Power Converter Development Time With the NI GPIC

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"The key to this design was the ability for our power engineers to directly program their product without a software engineer in the middle. This new platform and method of development changed our development time from 72 weeks to 24 weeks….These tools take design to the next level. We can have a 90 percent confidence factor in a first design and minimize hardware iterations during the prototype stage."

- Kyle Clark, Dynapower Company, LLC

The Challenge:
Requiring a unique power conversion and inverter system topology to fully realize the benefits of advanced carbon batteries for grid storage.

The Solution:
Using the new NI Single-Board RIO General Purpose Inverter Controller (GPIC) to provide real and reactive power to the grid to help stabilize the utility with high penetrations of varying generation sources, such as wind and solar, or to compensate for volatile loads.

Author(s):
Kyle Clark - Dynapower Company, LLC

Recently, Dynapower developed a line of power converters specifically for grid-tied energy storage based on the NI LabVIEW reconfigurable I/O (RIO) architecture and NI Single-Board RIO GPIC. The LabVIEW power electronics design platform and FPGA-based NI GPIC helped us reduce development time on power converter designs from 72 weeks to 24 weeks and got us to market with an advanced, high-quality product in one-third the time that was required before we had the NI GPIC and LabVIEW toolchain.

Design Overview

For the last 50 years, Dynapower Company, LLC has produced high-voltage, high-current power converters for industrial, mining, and high-energy physics applications. We are a leader in efficiently addressing the most complicated challenges in power conversion, and we serve customers such as the Los Alamos and Oak Ridge national laboratories.

Recently, Axion Power International approached us with an advanced carbon battery product to use in our line of power converters. Advanced carbon batteries for grid-tied energy storage have many benefits, including fast charge and discharge rates, long cycle life, and deep-cycle discharge capability. However, they require a unique power conversion and inverter system topology to fully realize the benefits.

Upon evaluation of the most advanced digital control technologies, we chose the new NI GPIC to develop an advanced multistring DC-to-DC converter application for the Axion Power International carbon-battery grid storage systems. The NI GPIC is based on the LabVIEW RIO architecture and provides a specific I/O set to meet the cost and performance requirements of commercial, high-volume digital energy systems.

This system provides real and reactive power to the grid to help stabilize the utility with high penetrations of varying generation sources, such as wind and solar, or to compensate for volatile loads. Several strings of carbon batteries are connected where there is a DC/DC converter connected to each string. The common DC link is connected to the inverter, which is coupled directly to the grid. The processing power of the NI GPIC FPGA helps a single controller manage multiple parallel converters.

Figure 1. Dynapower DC-to-DC Converter Topology With Strings

System Components         

The system components include:

-A 50 kW DC/DC Converter Power Block
The design challenge we were given was difficult to meet. Axion Power came to us with requirements for controllable current distribution and careful balance between the parallel converters in both utility interactive operation and in a microgrid mode. A high-speed response was required to seamlessly transfer between the two modes.

Figure 2. Dynapower 50 kW Modular DC-to-DC Converter Topology and Advanced FPGA-Based Power Electronics Controller

-NI LabVIEW RIO Architecture 
An NI RIO FPGA-based architecture, which integrates a processor, an FPGA, and inverter I/O that are all programmed using LabVIEW system design software, can handle this readily due to hardware parallelism and high-speed communication between converters. The controller manages the Inner Current Loop and Outer System Loop in addition to the charge and discharge of batteries in certain modes.

Figure 3. LabVIEW RIO Architecture

-An FPGA-Based Power Electronics Controller
We were able to cost-effectively address this challenge using modern FPGA-based control systems. We chose the new NI GPIC because the FPGA platform gave us 40 times more performance per dollar than the traditional digital signal processors we used in the past. The LabVIEW toolchain and development platforms reduced our development cost and risk significantly, compared to a full custom controller design. Low-level text-based programming and full custom design became a liability, and, more importantly, that previous division produced a roadblock between power engineers and programmers.

Figure 4. NI Single-Board RIO GPIC

Impact of a Graphical System Design Approach on Development Cost and Time

The key to this design was the ability for our power engineers to directly program their product without a software engineer in the middle. This new platform and method of development changed our development time from 72 weeks to 24 weeks. With the NI Single-Board RIO GPIC, we could develop our advanced LabVIEW FPGA power electronics control algorithms using desktop co-simulation with NI Multisim, then develop a custom mating board interface using NI Ultiboard, and deploy our commercial grid-tied power conversion system using the NI GPIC. These tools take design to the next level resulting in a typical development time savings of 114 person-months per design by helping us complete our development in less than half the time with a team that was 2.4X smaller. We can have a 90 percent confidence factor in a first design and minimize hardware iterations during the prototype stage.

Figure 5. NI GPIC Development Methodology 

Figure 6. The Dynapower development cycle features a traditional embedded design process involving a conventional DSP board and text-based control programming based on high-level simulation models.

Figure 7. The Dynapower development cycle uses the new NI GPIC hardware and graphical system design process, which helped Dynapower achieve a 3X reduction in development time.

Future Applications

The next steps for our grid-tied converters include embedded power analysis; autonomous operation; remote communication and control; data aggregation; and a multiport, multilevel AC-to-DC converter to integrate a solar battery charger all through a common DC link. The flexibility offered by the NI platform will help us take on a lot of new business. We are happy to base future designs on a high-level language that is more readily understandable and accessible to the experts in power conversion.

Author Information:
Kyle Clark
Dynapower Company, LLC
kclark@dynapower.com

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