Standards & Knowledge / Resources and tools
Battery cell simulation in detail: virtual batteries for BMS testing
Battery cell simulation gives your BMS a virtual battery with controlled electrical inputs.
A battery management system acts on cell voltage, current, temperature, timing and communication. Virtual battery cells make those inputs, boundaries and faults safe, repeatable and automatable, from a single monitoring IC to a complete high-voltage BMS HiL.
- What for
- Engineers planning BMS tests with virtual battery cells.
- What it covers
- How cell voltage, current, temperature and faults are simulated – for configurations from 12 to 300 cells, 0.1 to 8 V per cell, up to 1,500 V.
- Not covered
- Tests whose requirement depends on real chemistry, such as capacity or ageing – those still need real cells or packs.
Start with the decision chain
The BMS evaluates the complete battery system
A battery pack contains cells, modules and several monitoring and control layers. Cell Management Controllers (CMCs), also called Cell Supervising Circuits (CSCs), monitor individual cell voltages and temperatures. The Battery Management Unit (BMU), within the Battery Management System (BMS), combines these measurements with pack current, voltage, isolation and contactor states to assess operating condition, support safe operation and determine permissible limits.
Test the complete chain by controlling the physical inputs, observing the distributed measurements, and verifying the resulting BMS decision.
Three simplified examples show how cell monitoring scales from one battery module to a multi-module BMS. The connections represent functional relationships, without specifying a physical bus topology or protocol.
Actual implementations and communication topologies may vary.
Follow the physical signals from the cells and sensors through the CMC to the BMU, and see the responsibilities at each level.
Virtual battery cells
How battery cell simulation supports repeatable BMS tests
Real cells are essential for battery characterization. For BMS boundary and fault tests, a virtual cell provides a defined electrical interface whose inputs can be repeated and automated. This supports controlled testing of scenarios that depend on cell state, ageing or temperature, including hazardous conditions that are difficult to reproduce with real cells.
Passive and active balancing
Reproduce the current path alongside the voltage setpoint.
Cell variation causes different charge levels within one series stack. The BMS uses balancing to bring those states closer together. A valid test challenges thresholds, current direction, amplitude, timing, completion criteria and the effect on neighbouring channels.
Schematic examples with equal-capacity cells; the illustrated SoC levels are not measured product performance. In a BMS test, correlate cell settings, balancing current and diagnostic response over time.
Integrated fault simulation
Introduce the failure at the same electrical boundary the BMS monitors.
Fault insertion near the individual cell channel preserves the configured voltage path and makes the fault attributable to one defined input.
Represent a broken sense lead, connector problem or material fatigue and verify detection, timing, latching and recovery.
Represent a faulty cell path or electronic defect while maintaining a controlled and repeatable laboratory condition.
Challenge cabling, assembly and plausibility diagnostics with a defined reversal at the selected channel.
Combine temperature-sensor opens or shorts with quiescent and leakage-current observation where the selected configuration supports it.
Development bench
Work with defined, released test states.
Compact and rack-based systems can bring cell simulation, fault insertion and control interfaces into the same test architecture. The exact faults, current paths and isolation concept remain configuration specific.
Review the current BCS platform
Precision and traceability
Verify the electrical output that implements the battery model.
Many cell chemistries have a comparatively flat voltage curve across part of the usable SoC range. In that region, a small voltage error can create a much larger uncertainty in the estimated state. Precision must therefore hold while the channel sources or sinks balancing current, across the configured stack and over the intended test duration.
Current product context. The public BMS Tester page describes scalable systems from 12 to 300 cells, 0.1 to 8 V per cell and system voltages up to 1,500 V. Current ranges and accuracy depend on the selected BCS variant. The released quotation and technical specification remain decisive.
Current measurement
Balancing is a time-domain event.
Quiescent current can expose unwanted consumption while the BMS should be inactive. Leakage current can reveal defective outputs or incorrect software control. During balancing, current integration can show how much charge moved over a defined interval.
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1
Set the cell state
Define the voltage, temperature and operating mode before the balancing command.
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2
Capture the current
Measure direction and magnitude with the range and resolution required by the DUT (device under test).
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3
Integrate over time
Optional coulomb measurement converts repeated samples into transferred charge.
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Verify the decision
Compare the BMS command, actual path, thresholds and final diagnostic state.
Thermal input and environment
Temperature is a control input, a plausibility signal and a safety boundary.
The BMS uses cell and pack temperatures to limit charge and discharge, coordinate cooling and recognize unsafe states. Isolated NTC and PTC emulation replaces the physical sensor with a programmable resistance path and enables sensor faults that would be difficult to reproduce safely with a real pack.
Move individual channels or groups through defined temperatures and gradients while observing limits and derating.
Verify sensor diagnostics, substitute values, timing, latching and recovery after a defined electrical fault.
Combine signal simulation with climate chambers and, where required, multiplexing for repeated tests across DUTs and temperatures.
Automation and battery models
Use static values for thresholds and closed-loop models for behaviour.
A BMS test strategy normally uses both. Deterministic static sequences expose accuracy, boundaries and fault reactions. Dynamic battery models change cell values with SoC, SoH, current, temperature and BMS actions so algorithms can be evaluated in a closed loop.
- Configure
Set cell count, limits, initial states, sensors, faults and DUT identification.
- Connect
Use the released CAN, Ethernet or EtherCAT interface and the required real-time environment.
- Execute
Run static sequences, parameter sweeps, dynamic models and fault campaigns.
- Preserve
Retain model, configuration, measurements, events and result with one test identity.
Design the BMS test bench
Specify the electrical boundary before selecting the rack.
A modular BMS HiL (hardware-in-the-loop) can start with a compact channel set and expand to a complete high-voltage stack.
Monitoring IC, AFE (analogue measurement front end), CMC, central BMS, complete pack controller or integrated vehicle function.
Channel count, voltage window, stack voltage, isolation concept and connector topology.
Passive or active behaviour, source and sink current, low-current measurement and optional coulomb integration.
NTC or PTC channels, pack current, isolation, open wire, short circuit, polarity and project-specific I/O.
Static sequences, closed-loop models, cycle time, CAN, Ethernet, EtherCAT, MATLAB/Simulink and reporting.
Development, validation, endurance, climate, production, EOL (end-of-line), maintenance, calibration and future expansion.
From electrical channel to safe DUT access
Control physical access as part of the fault-injection setup.
In a rack-based BMS HiL, the BMS and CMUs can be mounted on a threaded grid plate inside an interlocked side enclosure. Opening its door or an integrated DUT drawer interrupts the system enable chain, shuts down the complete setup and switches the BCS outputs to a de-energised state.
The safety chain in one view
- DUT mounted on a threaded grid plate
- Access door coupled to the BMS HiL interlock
- Door opening triggers system shutdown
- BCS outputs become de-energised
- Same principle available for integrated DUT drawers
Engineering boundary: The finished protection concept is defined by the delivered system, DUT, interfaces and project risk assessment.
Beyond the isolated BMS
Connect battery decisions to the application that depends on them.
In an electric vehicle, the BMS exchanges limits and state information with the vehicle controller, OBC (onboard charger) and EVCC (vehicle-side charging communication controller). An integrated test bench can combine virtual battery behaviour with EV charging simulation to verify how a cell-level condition propagates into charging communication and vehicle-level action.
Why this matters: detecting a critical cell is only half of the safety chain. If a cell overheats or is overcharged during charging, the stop has to travel from the BMS through the vehicle controller and EVCC – to the OBC in AC charging, to the charging station in DC charging – before the BMS can take countermeasures without further stressing the cells. About one in six EV fires starts during charging; in South Korea it was 17.2 % of 238 EV fires between 2016 and 2024 (National Fire Agency data).
Build the validation strategy from monitoring IC to complete battery application.
Integrated HiLCheck that a critical cell actually ends the charging session – through EVCC, OBC and the charging station.
Review the current modular BCS platform and released configuration envelope.
Add EV or EVSE (electric vehicle supply equipment, or charging station) communication simulation and synchronised charging data.
Source and product status
Use the guide for the method. Use the current release for the specification.
Based on comemso’s technical article on virtual battery cells. Check the current BCS specification, quotation and released documentation for product limits, options and interfaces.
Official article covering monitoring, balancing, virtual cells, faults, precision, thermal signals and automation.
Current public BCS system range, interfaces and configurable functions.
Automated adjustment and calibration route for applicable Battery Cell Simulator systems.
DocumentCurrent 2026 product overview. The quotation and released specification remain decisive for the selected system.
FAQ
Battery cell simulation, precisely bounded.
What is a virtual battery cell?
It is an electrically controlled channel that reproduces the voltage and relevant source or sink behaviour presented to one BMS cell input. Depending on the configured system, it can be combined with current measurement, temperature-sensor emulation and cell-level fault insertion.
Why not use real battery cells for every BMS test?
Real cells are required for electrochemical characterization, but many BMS boundary and fault scenarios are hazardous, slow, state dependent or difficult to reproduce. Virtual cells make those electrical inputs deterministic and automatable.
Can the same system test passive and active balancing?
Yes, when the selected BCS variant provides the required sink and source current ranges. For passive balancing, the simulated-cell channel sources current into the BMS bleed resistor. Active-balancing tests can require source and sink operation, depending on the energy-transfer path. The delivered current range is configuration specific.
Which cell faults can be simulated?
Published configurations can include open circuits, short circuits and polarity reversal. Sensor faults, isolation functions and additional I/O depend on the selected hardware and project scope.
Why is cell-voltage precision so important?
The voltage-to-SoC relationship can be comparatively flat across part of the usable range. A small voltage error can therefore obscure the BMS threshold or estimation behaviour being evaluated. Accuracy also has to remain valid under balancing current and across the complete configured stack.
What is coulomb measurement used for?
It integrates measured current over time to quantify the charge transferred during balancing. Assess that quantity alongside the instantaneous current measurements. Availability, timing and range depend on the selected BCS option.
Battery simulator, battery emulator or battery cell simulator?
The term battery simulator can describe different electrical boundaries. A battery emulator may reproduce the pack terminals as a controllable source or load; a battery cell simulator reproduces individual cell inputs to a BMS. Select the boundary from the device under test, not from the label alone. A charger or inverter power test needs a different arrangement from cell-monitoring validation.
For battery cell simulation, individual channels make cell imbalance and supported channel faults controllable. The configuration may also provide sensor stimulation and relevant interfaces. Define which inputs the BMS actually sees and which signals come from another part of the test bench. A virtual battery is the complete agreed test representation, not a claim that every physical battery characteristic is reproduced.
When specifying a battery simulator, state cell or pack level, electrical range, required current direction, sensor boundary and model connection. A battery emulator at pack level does not automatically provide every cell connection. Conversely, a cell-level setup does not automatically supply the power needed to test an HV load. These distinctions prevent a technically unsuitable selection.
BMS simulation with virtual batteries
BMS simulation couples controlled electrical inputs with the behaviour you want to investigate. Begin with a defined initial state: cell conditions, sensor values, BMS operating mode and communication status. A static virtual battery is useful for checking thresholds or a single fault. A battery model is useful when the next cell condition should depend on the measured BMS response.
In closed-loop BMS simulation, identify who owns time progression and which interface transfers model values. Record the model output separately from the actual electrical output and the BMS feedback. Latency, update rate and signal scaling belong in the test definition. A correct model value does not prove that the BMS received the intended signal at its connector.
Use battery cell simulation to repeat one scenario before and after a correction. Keep the model, starting values and enabled faults unchanged. State which battery properties the model represents and which are outside its scope. BMS simulation produces useful results when the relationship between input, physical measurement and BMS decision remains traceable.
Coulomb counting: the principle of current measurement
Coulomb counting estimates charge change by integrating current over time. The result depends on the chosen current direction, measurement offset, sampling interval and initial charge estimate. A persistent small offset accumulates into a charge error. Testing only a voltage threshold therefore does not show whether the BMS current measurement and integration behave as intended.
For battery cell simulation, define how the BMS receives pack-current information. It may come from a real sensor, a configured sensor emulator or another part of the bench. Identify that boundary explicitly. Apply repeatable charge and discharge sequences, include a zero-current interval and compare the reported change with the independently defined current-time reference.
Record timestamps, scaling, reset conditions and the expected accumulation window. Check how the BMS behaves when current changes sign or when a measurement becomes unavailable. The virtual battery and the pack-current signal must describe the same scenario. Cell stimulation alone does not establish a calibrated current reference; the corresponding measurement chain needs its own verification.
Battery cell simulation in the EMC chamber
An EMC test needs a defined electrical setup before exposure starts. Identify which components are inside the chamber, how the DUT connects to the simulated cells and sensors, and which communication paths cross the boundary. Battery cell simulation should reproduce the intended operating state without making an uncontrolled cable or external instrument part of the disturbance path.
Run a baseline without exposure and confirm channel values, communication and the expected BMS state. Repeat the sequence during the selected exposure and preserve the timing relationship between the event and the BMS response. Distinguish a DUT failure from a disrupted control connection or an invalid simulator output. A virtual battery does not eliminate setup-related faults.
The permitted environment and connection arrangement follow the selected equipment and test plan. Confirm suitable components and routing before placing hardware in the chamber. After exposure, repeat the baseline and inspect the recorded setup status. The goal is a reproducible BMS operating condition, not an unsupported promise that any simulator configuration is suitable for any EMC test.
Calibration and fine tuning of the simulated cell boundary
Calibration compares the actual electrical output with an appropriate traceable reference under defined conditions. It is distinct from adjusting the instrument and from demonstrating that the BMS algorithm is correct. For battery cell simulation, specify the channels, ranges, measurement points and relevant operating conditions. Include loading or balancing conditions when they matter to the application.
Check the measurement chain at the connection point relevant to the BMS. Leads, contact resistance, temperature and reference uncertainty can affect the result. Record the requested value, reference reading, observed deviation and applicable uncertainty. A virtual battery model may be mathematically exact while its physical output differs from the intended value.
SmartCal supports the calibration workflow for suitable Battery Cell Simulator configurations. Review its released scope and the associated reference arrangement before planning automatic channel checks. Repeat verification after an adjustment and keep the resulting record with the system version. Calibration of the cell outputs does not substitute for calibration of a separate pack-level battery simulator or current-sensor chain.
Integrated interface testing at the BMS test bench
A useful BMS test bench records stimulus and response together. Define which cell channels, sensor connections and communication interfaces are required. Specify signal units, channel mapping and the BMS messages used for assessment. Battery cell simulation supplies one part of this setup; the controller, model and data acquisition provide the rest.
Begin with a connection check and a normal operating state before injecting a fault. Capture the physical channel condition, BMS decision and relevant communication on a documented time base. When an interface stops responding, determine whether the BMS entered its expected state or whether the bench lost control. Preserve the setup status in the result.
For automatic testing, assign a stable case identifier and store configuration, firmware and expected criteria with each run. Define which event ends a test and how an invalid setup is classified. Reuse the same virtual battery conditions after a correction. Interface integration improves reproducibility only when control, measurement and assessment each have a clear responsibility.
Plan the BMS setup around the right cell simulator
BMS-controller test planning
Specify the BMS, emulated cell and sensor channels, controlled faults and required records.