DMC leveraged our established Battery Management System (BMS) Testing Platform to deliver an automated Battery Simulator System to a NASA research group. NASA needed this system to facilitate development of highly specialized battery devices. These battery systems were designed to provide mobile power for advanced electromechanical systems such as Robonaut 2, a dexterous humanoid robot created to perform a wide range of tasks to assist astronauts on the International Space Station
The Battery Simulator System delivered by DMC provides the ability to test BMS devices using a Hardware In the Loop (HIL) testing approach. This HIL testing is performed before those devices are fully incorporated into the large battery packs they are designed to monitor and manage. The system provides software-controlled simulated signals for all input sensors connected to the BMS, and provides the ability measure relevant outputs and responses from the BMS. This makes it possible to perform fully automated testing and validation of BMS functionality across any realistic range of input conditions the device may encounter in field operation.
Table of Contents
- System Introduction
- System Details
- Overview of Hardware System
- System Enclosure
- Battery Stack Simulation
- Cell Voltage / Current Measurement Module (Optional)
- Battery Stack Simulator Connections
- Temperature Sensor Simulation Module
- PXI Chassis to Controller Interface
- Software Driver Libraries for System Control
- Safety / Interlock Functions
- National Instruments / LabVIEW Experience
- Test and Measurement Experience
- Related Past and Current Projects
System Introduction
The Battery Simulator System leverages the DMC Battery Testing Platform hardware and software. DMC’s modular Battery Testing Platform incorporates open software and hardware technologies, along with flexible and reliable subsystem components and instruments, which are completely customized to the end user’s specifications.
The Battery Testing Platform is built around high-quality off-the-shelf hardware assembled from a variety of vendors, including Pickering Interfaces, National Instruments (NI), Lambda, and Agilent, among others. Selection of individual instruments in the DMC system is based completely on required performance, not allegiance to a single hardware vendor.
The system is capable of simulating a stack of 108 battery cells in series and 50x 4-bit temperature sensors. The system was delivered with source code libraries for low-level driver functions that provide full control over the available functionalities of the Battery Simulator system. This software code is based on pre-existing software modules, which were assembled and customized to accommodate the customer’s specific test system and test application. No higher-level test execution control application was developed by DMC, as the customer wished to develop their primary test control application themselves.
System Details
- BMS: Battery Management System – An electronic system for managing a rechargeable battery by continuously monitoring the battery state, calculating and reporting data on the battery, performing safety functions in fault conditions, performing cell balancing functions, etc.
- NI: National Instruments, Inc.
- PXI: Programmable eXtensions for Instrumentation – hardware platform for test and measurement IO.
- DMM: Digital Multi-Meter – An electronic measurement device, commonly capable of acquiring high-resolution voltage, current, resistance, or capacitance measurements, as either single-point measurements or waveform captures.
- DUT: Device Under Test – Client’s BMS device to be tested.
Overview of Hardware System
A high-level functional diagram of the DMC Battery Simulator system is shown below.
System Enclosure
The Battery Simulator System is built upon the Media Director Lectern V2, a portable (wheeled) rack-mount enclosure desk, as shown below:
This mobile desk provides 32U of total rack-mount space in two separate columns for mounting primary system components, including 6U of rack-mount space in the upper portion of the lectern just beneath the desk surface.
Controller and Accessories
The primary controller for the Battery Simulator system is a rack mount PC. This PC serves as the primary controller for the test system and runs a LabVIEW test application developed by customer engineers.
A listing of the performance specifications of this PC is provided below:
- Processor(s): Intel® i7 – 2600 (LGA1155) Quad Core Processor 3.4GHz/8MB Cache
- 2U Riser Card PCIe – x16, x4, x1
- Memory – DDR3: 16 GB DDR3-1333/PC3-10600
- Hard Drive: 2TB SATA III 7200RPM
- Optical Drive: Plextor® PX-890SA 24x DVD±R/W
- Video Card: PCI-EXPRESS RADEON HD6450 1GB/PCIe 2.0 (Dual Monitor)
- Operating System: Microsoft® Windows® 7 Professional 64-bit OE
The system includes dual DellTM UltraSharpTM U2410 monitors that are mounted above the desk surface of the enclosure via a dual flat panel mounting arm.
The system includes the Logitech Wireless Keyboard/Mouse MK710 peripheral devices for user operation of the PC.
Battery Stack Simulation
The Battery Stack Simulation sub-system consists of Pickering PXI 41-752, 6-cell battery simulator cards placed inside a PXI chassis, providing independent cell voltage simulated outputs. The Battery Simulator System includes 18 PXI Cell Simulator cards, enabling simulation of a battery stack of 108 cells.
The cell simulator current outputs and voltage sense lines from each card connect to a custom-built circuit board which configures the independent simulated cells into a full simulated battery stack; it also handles battery stack management and safety functions. Past this custom circuit board, the cell supply/sense lines route to a single high-density DUT connection on the front panel of the test stand.
The Pickering cell simulator cards offer no direct means of reading back their output current or voltage. As a result, the cards themselves provide no direct capability for voltage supply line leakage current measurement, or for actual cell voltage measurements.
Since these measurements are useful for the characterization and calibration of a BMS device, DMC’s Battery Simulator System provides the capability to acquire independent cell voltage and current output measurements using a high-resolution Cell Current/Voltage Measurement Module. This module consists of an active high-density relay switch matrix that enables measurement of the current flow on any cell line or of the voltage differential between any two cell lines in the battery stack. This high-resolution cell current/voltage measurement module is described in more detail later in this document.
DMC considers the Pickering 41-752 battery simulator card to be an excellent tool for simulating a battery input to a BMS for the following reasons:
- The 750V isolation barrier allows the outputs to be stacked in series without inducing un-intentional ground faults or loops and without voiding the manufacturer’s warranty.
- The cards are capable of both sourcing and sinking current, just like an actual chemical cell. Accurate testing of BMS cell balancing operations requires this current-sinking function.
The 750V isolation barrier of the Pickering 41-752 card allows it to be used to emulate an entire low power battery stack representative of those used for vehicle propulsion.
The Pickering PXI 41-752 is a PXI based, 6-channel battery simulator module. Each channel of the module is capable of supplying up to 7V and 300mA to the load. Each channel is fully isolated from ground and from each other, allowing the channels to be connected in series to simulate batteries arranged in a stacked architecture. The 750V isolation barrier permits the 41-752 to be used to emulate a low power battery stack representative of those used for vehicle propulsion.
Each battery simulator provides independent power and sense connections, allowing the battery simulator to sense a remote load and correct for wiring voltage losses. The battery simulator is designed to be fast-responding to dynamic loads, minimizing the need for local decoupling capacitors at the load.
A signal line on the user connector allows the user to shut down all battery simulator channels with a single connection. Multiple module control lines are linked together to provide an easy way of inhibiting voltage generation (E-Stop) when using many series-connected modules that provide high output voltages
Cell Voltage / Current Measurement Module (Optional)
The Cell Voltage/Current Measurement Module provides independent (DMM based) high-resolution measurement of the voltage between any two cells in the simulated battery stack or of the current on any given cell voltage supply line. These measurements are useful for the characterization (cell balancing functions, power consumption, leakage currents, etc.) or calibration of a BMS device. This module also enables automated calibration of the Battery Stack Simulator device itself.
To deliver this extensive range of measurements in a cost-effective manner, the module utilizes a single high accuracy digital multimeter in conjunction with an active high-density switching matrix to connect this meter to any desired set of measurement points. The Battery Simulation system contains a NI PXI-4071 Digital Multi-Meter (DMM) installed in one of the PXI chassis. This 7 ½ digit DMM delivers the following measurement capabilities:
- Voltage measurements from ±10 nV to 1000 VDC
- 8 DC current ranges with sensitivity down to 1 pA
- ±500 VDC/Vrms common-mode isolation
- Resistance measurements from 10 µΩ to 5 GΩ
- 1.8 MS/s isolated, 1000 V waveform acquisition
The Cell Voltage/Current Measurement Module uses a single DMM, and thus it is only possible to acquire one particular measurement at a given time (i.e. the specific probe point that the current relay multiplexer state is connecting the DMM to measure). It is very straightforward, however, to set up functions in the test control software in order to scan through all cell voltage or current measurement points by simply reconfiguring the relay state between each measurement acquired by the DMM.
The switching matrix in this module also makes it possible to simulate a broken connection between a simulated cell and the BMS or to simulate a shorted connection between two adjacent cells; these can be useful fault insertion mechanisms in BMS testing regiments. Similarly, the Voltage/Current Measurement Module also provides the ability to perform complete and total disconnection of the cell simulator from the BMS device under test.
The Cell Voltage/Current Measurement Module fundamentally consists of multiple removable/swappable relay multiplexing cards that are seated in a 4U (7”) high Vector card cabinet. It is designed to be located either directly above or directly below a PXI chassis containing cell simulator modules (as shown in the image below). Each relay card connects directly to a cell simulator card and handles the measurement multiplexing for those 6 simulated cells. This design makes it easy to scale the multiplexer module when adding or removing cell simulator cards to increase/decrease the size of the simulated cell stack.
Battery Stack Simulator Connections
Each simulated cell has one supply and one sense line that needs to be routed independently to the Device Under Test (to allow the cell simulator modules to accurately compensate for voltage drop in harness/wiring). Therefore, the complete set of simulated cell connections consists of 108 cell voltage supply lines and 108 cell voltage sense lines. The Battery Simulator System provides two parallel connections to the simulated cells.
Battery Stack Connection 1 is used to interface with the Device Under Test through a pair of connectors that are panel mounted in the system enclosure panel. There are separate connectors (with identical pin-out mappings for consistency) for the simulated cell voltage stack sense and supply lines, as shown below.
Battery Stack Connection 1 utilizes 2x 160 position connectors as depicted below:
Battery Stack Connection 2 provides an auxiliary parallel connection to all simulated cell supply and sense lines for external monitoring, measurement, and diagnostic purposes. This parallel connection has an available standard screw terminal connection for each cell voltage supply and sense line, as depicted below. These breakout terminal connections are mounted facing out the front of the primary system enclosure so as to make them externally accessible.
Temperature Sensor Simulation Module
The Temperature Sensor Simulation module supports simulation of 50x 4-bit resistive temperature. To enable future flexibility, the module provides the ability to alternatively simulate 25x 8-bit with some minor reconfiguration of built-in jumper points. The figures below illustrate the simulation of either one 8-bit or two 4-bit resistor chains and how the module supports switching from 4-bit to 8-bit simulation through the installation of jumpers. An N-bit simulated temperature sensor essentially consists of N fixed resistors that can be inserted or removed from the simulated temperature sensor circuit using a relay switching matrix. The resistor values that are placed in line with the simulated temperature sensor circuit add with one another (since they are in a series configuration) to produce the desired resistance to simulate a particular temperature reading.
For a 4-bit simulated sensor, there are a total of 2^4 = 16 discrete resistance values (including a short circuit) that can be applied by each simulated sensor. For an 8-bit simulated sensor, there are a total of 2^8 = 256 resistance values that can be generated. The actual resistor values used in the module (which thus affect the total range and the set of overall resistance values that can be generated) are fully configurable and are determined by the requirements of the test application.
The temperature sensor simulation system utilizes a modular motherboard and daughter card architecture. The actual physical resistors that comprise the simulated temperature sensors are all installed on swappable daughter cards that plug into the module’s motherboard. The motherboard handles the “infrastructure” of aggregating independent resistors into simulated temperature sensors, integrating relays to control the simulated temperature circuits, etc. By swapping in and out sets of daughter cards containing different resistor values, different types of temperature sensors or different temperature ranges can be simulated to accommodate varying testing requirements or DUT models.
The relays that are responsible for configuring the desired output state of the simulated temperature sensors are contained on and controlled by two high-density PXI relay cards. Control of the Temperature Sensor Simulation module is accomplished through a set of LabVIEW driver VI’s provided along with the system.
The simulated temperature sensor module drivers include algorithms to automatically calculate the optimal combination of resistors that should be inserted into a given simulated temperature sensor circuit in order to achieve the closest possible resistance to the commanded value. Thus, the interface for controlling the temperature sensor module is simple and abstracts away the lower-level hardware operations. It is simply necessary to specify the desired resistance (corresponding to the temperature reading you want to simulate) to apply to a particular temperature sensor number.
Each simulated thermistor requires two connection lines, and thus for a total of 50 simulated thermistors the system has 100 total connections from the Temperature Sensor Simulation Module to the DUT. The Temperature Sensor Simulation Module has a 104 position connector mounted in the front panel of its enclosure, as depicted in the image below.
PX Chassis to Controller Interface
The Battery Simulator System includes two full 18 slot NI PXI-1045 chasses to house Cell Simulator PXI cards as well as supporting instrumentation and device control cards.
This MXI Express interface provides a software-transparent link between the controller PC and the PXI chasses that house system instrumentation and card modules. This linkage allows the Battery Simulator hardware to effectively be available as native or directly connected instrumentation on the controller computer.
Software Driver Libraries for System Control
The Battery Simulator System includes LabVIEW driver libraries (with full unlocked source code) that provide full control over the available functionalities of the Battery Simulator system. No higher-level test execution control application was developed by DMC for this particular system, as the customer wished to develop a primary test control application internally.
DMC has provided the following control drivers (with accompanying documentation) for use on the controller PC:
- DMC custom LabVIEW drivers for full simulated battery stack control and management
- DMC custom LabVIEW drivers for control of Cell Voltage/Current Measurement Module
- DMC custom LabVIEW drivers for control/management of simulated temperature sensors
- DMC custom LabVIEW Digital Multi-Meter Drivers for higher-level DMM functions (waveform capture and analysis, etc.)
- VISA (Virtual Instrument Software Architecture) driver set for direct control of individual Cell Simulator modules and Pickering relay cards
- Direct IO driver set for direct control of individual Cell Simulator modules and Pickering relay cards
Safety / Interlock Functions
Since the Battery Simulator system is capable of generating high voltages (as required for battery stack simulation), it contains both hardware and software-based safety features to disable all voltage output during a safety event.
- Large Red ESTOP button in the middle of the top desk surface of Battery Simulator System enclosure
- External / Remote Interlock connector on the right-side panel of the enclosure
- Software-based disable command to open PC controlled relay that is in series with safety interlock loop
Activating any of these safety features will immediately turn off all voltage outputs from the Battery Stack Simulator.
Company Overview And Qualifications
DMC is a well-known and established controls engineering & consulting firm focused on the industrial automation market. We develop and implement solutions for a wide range of industries using a variety of technologies. DMC has successfully delivered solutions for hundreds of companies including 3M, Abbott Laboratories, Argonne National Labs, Bosch, BRP, Caterpillar, Chrysler, Fermilab, Ford, John Deere, UL, Wrigley, and Yaskawa. Every solution we develop is based on a solid understanding of engineering principles with the primary objective of helping our client increase profitability and productivity using world-class solutions.
DMC is a certified member of the Control Systems Integrators Association (CSIA). DMC passed a rigorous third-party audit of 200 criteria that span all aspects of business performance in the areas of:
- General Management
- Human Resources Management
- Marketing and Business Development
- Financial Management
- Project Management
- System Development Lifecycle
- Quality Assurance Management
National Instruments / LabVIEW Experience
DMC has been a National Instruments (NI) Alliance member for over 10 years with one of the largest teams of Certified LabVIEW developers in the country, including several National Instruments’ Certified LabVIEW Architects (highest level of certification available), and multiple NI Certified LabVIEW Developers.
Test and Measurement Experience
Our Test and Measurement Automation Services help clients automate laboratory testing using the latest technologies. We have years of experience delivering world-class solutions to leaders in research, development, production, quality, and certification testing. Our flexible and collaborative approach has shown to deliver efficient, accurate, and robust test systems, as well as the tools to leverage test data for effective results analysis.
DMC has employed LabVIEW in many industries, including product development, test and measurement engineering, R&D, and high-tech manufacturing. We have developed LabVIEW solutions for hundreds of projects at dozens of customers, including:
- Argonne National Laboratories
- Fermi National Accelerator Laboratory (Fermilab)
- Bombardier Recreational Products Bosch
- Underwriters Laboratories
- LG
- Bosch
DMC applies a disciplined and systematic approach to LabVIEW software design. Engineers at DMC employ software conventions and architectures so that code is structured and well-organized. One example of these structures is a LabVIEW state machine that builds a system based on states, events, and actions
DMC has a vast, reliable code library that has been tested and can be used to significantly reduce the development time and risk. Leverage the work we've already done to reduce start-up time now and downtime later. We've also developed LabVIEW tools for additional features such as HTML and PDF reporting, TDMS file storage, external data viewers, and SQL databases.
Related Past and Current Projects
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