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Battery Cell Simulation in Detail

Test the battery management system (BMS) with a virtual battery you can control.

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.

Understand the test method View the Battery Cell Simulator (BCS)
comemso application engineer working on a rack-based Battery Cell Simulator in the laboratory.
Cell-level controlSet every simulated voltage and sensor state independently
Source and sinkChallenge passive and active balancing under controlled current
Faults by designIntroduce opens, shorts, polarity and sensor faults repeatably
HiL readyConnect models, automation and evidence through open interfaces

Start with the decision chain

The BMS sees the Battery as a System, not a Single Value

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.

BMS Architecture & Scalability

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.

Single CMC & Battery module

CMC 1 is inside the dashed BMS electronics boundary and connects to Module 1 below, outside that boundary.
One Cell Management Controller (CMC) monitors the cells of one battery module.

BMS with two Battery modules

A central BMU connects to CMC 1 and CMC 2 inside the BMS electronics boundary. Their assigned battery modules are below and outside the boundary.
A central Battery Management Unit (BMU) communicates with two CMCs. Each CMC monitors its assigned battery module.

Scalable Multi-Module BMS

A central BMU connects to four CMCs inside the BMS electronics boundary. Each CMC connects to its own battery module, Module 1 to Module 4, outside the boundary.
The BMU and multiple CMCs form a scalable BMS architecture. Each CMC monitors one battery module.

Actual implementations and communication topologies may vary.

Signal Flow & Functional Responsibilities

Follow the physical signals from the cells and sensors through the CMC to the BMU, and see the responsibilities at each level.

Cell & Sensor Level

Cell voltage and temperature sensing in the light-blue cell interface feed the CMC. Connection diagnostics at the CMC identify wiring faults.
Cell voltages and temperature-sensor signals form the physical inputs to the cell-monitoring electronics. Connection diagnostics help identify wiring faults.

CMC & Cell Monitoring Level

The module sends cell signals to the CMC. The CMC measures and digitizes, diagnoses, supports balancing and reports. It exchanges data with the BMU.
The CMC measures and digitizes cell signals, supports diagnostics and balancing, and reports module data to the BMU.

BMU & System Level

The BMU exchanges cell data with the CMC and communicates with the vehicle or application. A separate input brings pack current, voltage, isolation status and contactor states. BMU tasks are SoC and SoH estimation, plausibility checks, protection coordination, operating limits and communication.
The BMU combines cell and module data with pack-level information such as current, voltage, isolation status and contactor states to assess the battery’s operating condition, coordinate protection and determine permissible operating limits.

Virtual battery cells

Replace chemical uncertainty with controlled electrical behaviour.

Real cells are essential for battery characterization. They are a poor source for many BMS boundary and fault tests because their state, ageing and temperature drift. Hazardous conditions are difficult to reproduce, and automation is constrained. A virtual cell establishes a deterministic interface to the BMS.

Test control software, a Battery Cell Simulator and virtual cell signals connected to the BMS under test.
The software defines the cell state. BCS hardware reproduces it electrically at the real BMS interface. View full-size virtual battery cell diagram
Controlled output Independent cell voltage
Bidirectional behaviour Source and sink current
Thermal input Isolated NTC / PTC emulation
Negative testing Repeatable electrical faults
Method boundary. A virtual battery verifies what the BMS measures and decides. It does not replace electrochemical cell characterization, ageing tests or abuse tests on real cells and packs.

Passive and active balancing

The test system must reproduce the current path, not only 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.

Passive Cell Balancing

1. Initial state
Four illustrative equal-capacity cells start at 50%, 50%, 50% and 80% SoC. The excess charge in the fourth cell is red.
Four cells start unbalanced: three have the same state of charge and one has a higher SoC.
2. Balancing process
The fourth cell discharges through a resistor connected across it. Arrows show the discharge path and red waves mark heat. The three lower cells remain at 50%; the fourth is illustrated at 65% during balancing.
The higher-charge cell discharges through a balancing resistor. Excess energy is dissipated as heat.
3. Balanced state
After passive balancing, all four illustrative cells are at 50% SoC. Excess energy from the initially higher cell has been dissipated as heat.
All four cells reach an aligned SoC level. Energy has been removed from the higher-charge cell.

Active Cell Balancing

1. Initial state
Four illustrative equal-capacity cells start at 50%, 50%, 50% and 80% SoC, matching the passive-balancing starting point. The excess in the fourth cell is red.
The same initial imbalance: one cell has a higher SoC than the other three.
2. Balancing process
A red arrow carries energy from the fourth cell into an active balancing circuit. Three blue arrows transfer energy into the lower cells. An illustrative intermediate state shows 54%, 54%, 54% and 64% SoC, including conceptual losses.
The balancing circuit transfers energy from the higher-charge cell to the lower-charge cells.
3. Balanced state
All four cells finish at an illustrative 56% SoC. A simplified idealised lossless reference is 57.5%, the arithmetic mean of the four starting percentages. The lower illustrated result represents transfer losses, not measured performance.
The four cells reach an aligned SoC level. Energy transfer includes losses.

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.

01
Open-circuit fault in a cell sense connection to the cell monitoring unit.

Open circuit

Represent a broken sense lead, connector problem or material fatigue and verify detection, timing, latching and recovery.

02
Short-circuit fault in the cell connections to the cell monitoring unit.

Short circuit

Represent a faulty cell path or electronic defect while maintaining a controlled and repeatable laboratory condition.

03
Reversed cell-polarity connection to the cell monitoring unit.

Polarity reversal

Challenge cabling, assembly and plausibility diagnostics with a defined reversal at the selected channel.

04
Schematic of an open temperature-sensor connection, a shorted sensor path and a separate leakage-current path with current observation at the cell monitoring unit.

Sensor and leakage faults

Combine temperature-sensor opens or shorts with quiescent and leakage-current observation where the selected configuration supports it.

Development bench

Move from manual fault hunting to approved 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
Close-up of an engineer connecting a rack-based Battery Cell Simulator beside a laptop.

Precision and traceability

A battery model is only as credible as the electrical output that implements it.

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.

Voltage Accuracy at the BMS input
Current Source, sink and low-current resolution
Timing Dynamic response without unintended overshoot
Lifecycle Calibration, adjustment and retained evidence

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.

Illustrative open-circuit voltage curve against state of charge, with the relatively flat mid-range highlighted.
Illustrative method diagram. The exact voltage-to-SoC relationship depends on chemistry, temperature, ageing and operating history. View full-size cell voltage soc curve diagram

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.

Current samples integrated across successive measurement intervals for coulomb measurement.
Optional coulomb measurement integrates 500 samples taken over each 50 ms measurement interval; availability depends on the selected BCS option. View full-size coulomb current measurement diagram
  1. 1
    Set the cell state

    Define the voltage, temperature and operating mode before the balancing command.

  2. 2
    Capture the current

    Measure direction and magnitude with the range and resolution required by the DUT (device under test).

  3. 3
    Integrate over time

    Optional coulomb measurement converts repeated samples into transferred charge.

  4. 4
    Verify the decision

    Compare the BMS command, actual path, thresholds and final diagnostic state.

Version boundary. Sampling rate, integration interval, current range and available measurement channels are defined by the selected module generation, option and software release.

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.

Normal range

Temperature profiles

Move individual channels or groups through defined temperatures and gradients while observing limits and derating.

Fault range

Open and short

Verify sensor diagnostics, substitute values, timing, latching and recovery after a defined electrical fault.

Environment

Climate and EOL

Combine signal simulation with climate chambers and, where required, multiplexing for repeated tests across DUTs and temperatures.

Rack-based comemso Battery Cell Simulator installed in an EMC chamber.
Original laboratory photograph: a Battery Cell Simulator in an EMC chamber.

Automation and battery models

Static values prove thresholds. Closed-loop models prove 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.

BCS connected to comframe and customer software environments through CAN, Ethernet and EtherCAT.
Official integration overview. Availability and responsibility for third-party software remain project-specific. View full-size bcs software integration diagram
  1. Configure

    Set cell count, limits, initial states, sensors, faults and DUT identification.

  2. Connect

    Use the released CAN, Ethernet or EtherCAT interface and the required real-time environment.

  3. Execute

    Run static sequences, parameter sweeps, dynamic models and fault campaigns.

  4. 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.

Original BMS test-bench diagram with switchbox, temperature-sensor simulation, cell simulation, fault simulation and isolation-resistor emulation.
Example BMS test-bench architecture. Required modules, electrical limits and supported faults depend on the selected configuration. View full-size bms testbench architecture diagram
1

DUT scope

Monitoring IC, AFE (analogue measurement front end), CMC, central BMS, complete pack controller or integrated vehicle function.

2

Cell architecture

Channel count, voltage window, stack voltage, isolation concept and connector topology.

3

Balancing depth

Passive or active behaviour, source and sink current, low-current measurement and optional coulomb integration.

4

Sensors and faults

NTC or PTC channels, pack current, isolation, open wire, short circuit, polarity and project-specific I/O.

5

Dynamics and automation

Static sequences, closed-loop models, cycle time, CAN, Ethernet, EtherCAT, MATLAB/Simulink and reporting.

6

Lifecycle

Development, validation, endurance, climate, production, EOL (end-of-line), maintenance, calibration and future expansion.

From electrical channel to safe DUT access

Fault injection remains controlled only when the physical access path is controlled too.

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.

Configuration illustration of the open interlocked side enclosure next to a BCS Flex system
Configuration illustration: the product render explains the physical principle; exact DUT interfaces and safety scope are project-specific.

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.

Illustration of an integrated BCS and EVCA test system with charging emulation, cell simulation, EVCC, BMS, measurement and control
Illustrative integrated BCS and EVCA setup: charging emulation, cell simulation and correlated measurement and control. Open the full-size BCS and EVCC integration illustration
Application
BMS Testing

Build the validation strategy from monitoring IC to complete battery application.

 Integrated HiL
EVCC + BMS

Verify the handoff between battery limits, OBC control and charging communication.

 Product
Battery Cell Simulator

Review the current modular BCS platform and released configuration envelope.
Charging platform
EVCA

Add EV or EVSE (electric vehicle supply equipment, or charging station) communication simulation and synchronised charging evidence.

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.

Technical source
Battery Cell Simulation in Detail

Official article covering monitoring, balancing, virtual cells, faults, precision, thermal signals and automation.

Current product context
comemso BMS Tester

Current public BCS system range, interfaces and configurable functions.

 Lifecycle
BCS SmartCal

Automated adjustment and calibration route for applicable Battery Cell Simulator systems.

 Document
BCS brochure

Current 2026 product overview. The quotation and released specification remain decisive for the selected system.

Free BMS testing whitepaper

Planning BMS temperature tests?

Explore the practical questions behind cold starts, heat exposure, climate-chamber wiring and reliable cell and sensor simulation.

Illustration of an engineer planning BMS thermal validation with cell simulation and a climate chamber
Explore the BMS testing whitepaper

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 so balancing charge transfer can be evaluated as a quantity, not only as an instantaneous current value. Availability, timing and range depend on the selected BCS option.

BMS-controller test planning

Replace real cells with a safe, controllable test boundary.

Specify the BMS, emulated cell and sensor channels, controlled faults and required evidence.

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