Battery Emulation Equipment Keysight E36731a

How Battery Emulation Makes Electric Cars and Medical Devices Safer

Though batteries are used in billions of consumer devices and industrial equipment, they're not simple devices. They heavily influence the convenience and reliability of devices and continue to present several unsolved challenges to engineers.

Understanding battery characteristics over the short and long term is a critical part of device testing. However, their complex behaviors make comprehensive testing a difficult and laborious activity.

Fortunately, battery emulation enables engineers to reliably simulate and reproduce their behaviors much faster than physically testing them. In this article, find out what battery emulation is all about.

What is battery emulation?

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Fig 1. Scope of battery emulation

Battery emulation involves using hardware and software to realistically reproduce the states and behaviors of real batteries for testing:

sourcing scenarios where batteries various power devices under test (DUTs), ranging from low-voltage consumer or internet-of-things (IoT) devices to high-voltage electric vehicle battery banks
sinking scenarios where the battery acts as a load LiFePO₄ to consume power from wall chargers, solar panels, or regenerative braking

What can battery emulators do?

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Fig 2. PathWave BenchVue battery emulation software

Battery emulators are a combination of programmable power supplies and electronic loads along with fine-grained programmability that enables them to accurately capture and emulate battery states and behaviors.

The Keysight E36731A is a good example of a capable battery emulator. It can either supply up to 200 watts (W) of power or sink 250 W of power. Its companion software, the PathWave BenchVue advanced battery test and emulation software, provides fine-grained control over these features. The software also enables the emulator to work as a battery profiler to accurately capture the behaviors of real batteries and create realistic battery models. Finally, the software enables the emulation of captured behaviors.

Battery emulation in the lab

In this section, we explore why emulation is so essential for testing any system that includes batteries.

What are the common problems of testing with real batteries?

Conducting tests using real batteries can be:

Time-consuming: Testing charging, discharging, and cycling using real batteries can take anywhere from hours for consumer batteries to days for electric vehicle battery packs.
Difficult to reliably reproduce results: Another problem is the reliable repeatability of the testing and results. For example, the battery parameters and charge levels must be identical when comparing test results, which is exceedingly difficult with real batteries.
Difficult for edge cases and abnormal scenarios: Setting up anomalous scenarios and edge cases with real batteries can get laborious.
Hazardous: Stress-testing batteries, especially lithium-polymer and lithium-ion batteries, can result in explosions, short circuits, electrical fires, and other dangers to life and property. Some battery systems, like high-voltage electric vehicle batteries, are inherently hazardous even without any stress testing.

Battery emulation alleviates these problems.

What are the advantages of using battery emulators over testing with actual batteries?

The benefits of using battery emulation over real batteries include:

Easier to set up: Setting up tests is easier and quicker with an all-in-one emulator compared to rigging two or more separate instruments to a real battery.
Faster testing: Battery charging and discharging behaviors can be replayed at higher speeds, unlike real batteries that only support real-time measurements.
Rigorous testing: Due to their virtual nature, emulators can test a wide range of edge cases and rare scenarios quickly and effectively.
Automated tests: Emulators enable the automation of battery run-down and cycle testing to accurately estimate battery run time and aging effects.
Repeatability: Battery profiles and the data captured during emulation enable teams, in different locations and over time, to reliably repeat the tests. This is useful for auditing, regulatory, and legal compliance too.
Safety: Emulators can be used for rigorous battery stress tests without any of the dangers of real batteries. They have built-in real-time monitoring and protection against overvoltage, overcurrent, and overheating conditions in case of runaway scenarios.
Safety and environmental standards compliance: Emulators can help ensure that devices can meet standards like the Underwriters Laboratories Certification and Waste Electrical and Electronic Equipment guidelines.

What are the differences between battery emulators and instruments like power supplies and power analyzers?

If we treat these instruments as different categories based on their unique features, then emulators stand out in two key aspects:

Operate as both sources and loads: For battery emulators, two-quadrant operation as sources and sinks is a necessity. In contrast, most power supplies and power analyzers only act as sources — though some vendors do offer two-quadrant models too.
Accompanied by specialized battery emulation software: Another key differentiator of emulators is their purpose-built software for convenient battery emulation. Programmable power supplies and analyzers can probably emulate batteries with some clever programming, but that's likely to be a clumsy hack rather than a reliable and repeatable testing workflow.

How do you simulate a battery load?

There are two approaches to setting up a battery load for an emulated battery in order to check the latter's behavior under different conditions:

Use a second emulator or any programmable load: Since emulators can act as sinks and their sinking behaviors are programmable, a second emulator can be used as a virtual load while the first emulator acts as a virtual battery.
Use real devices: Another option is to set up the actual devices that are powered by the real version of the emulated battery in production and customer installations. This is called the hardware-in-the-loop (HIL) approach and is preferred during system-level and customer acceptance testing.

How to use battery emulation

In this section, we look at the low-level concepts and understanding required for operating battery emulators.

What key charging and discharging behaviors must battery emulators simulate?

Battery emulators must support profiling and emulation of the following charging behaviors:

Constant current (CC) mode: The emulator, acting as a load, draws a steady current to simulate the initial 90% of a charging cycle.
Constant voltage (CV) mode: The emulator switches from CC mode as the battery reaches close to full capacity.

Similarly, emulators must support the profiling and emulation of the following essential discharging behaviors when acting as a power source:

constant voltage supply to a device
constant current supply to a device
constant resistance model
constant power mode

What are the key parameters that battery emulators simulate?

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Fig 3. Battery voltages and internal resistance

Battery emulators simulate and profile the following battery parameters:

State of charge (SOC): The SOC is the current charge level of a battery relative to its capacity. Its reading is typically reported as a percentage, indicating how much energy is currently stored in the battery in comparison to its total storage capacity. Accurately measuring the SOC is critical for managing battery performance and longevity.
Battery voltage: This is the voltage across the battery terminals when it's charging or discharging.
Open circuit voltage (OCV): This is the voltage across the battery terminals when it's not connected to any load and no current is flowing. OCV helps to estimate the SOC.
Internal resistance: This is the inherent resistance of a battery due to the materials and construction of its electrolyte, electrodes, and contacts.
Individual battery cell voltages: Emulators also act as battery cell simulators to recreate the phenomena related to individual cells in multi-cell configurations. These include cell balancing, voltage monitoring, temperature control, and failure isolation, among others.
Voltage slew rate: This is the speed at which the output voltage of the battery emulator can change in response to a command or load variation. It is typically measured in volts per second (V/s). A high voltage slew rate can mimic real-world rapid voltage fluctuations seen during acceleration of electric vehicles or switching on of high-power equipment.

Applications of battery emulation

Let’s look at how battery emulation is used in different applications and industries.

How do battery emulators aid in the validation and verification of electric vehicles?

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Fig 4. Electric vehicle battery ecosystem

Battery emulators are extensively used to test systems in the electric vehicle (EV) ecosystem by vehicle manufacturers, battery makers, charging station manufacturers, and others. Emulation assists in tasks like:

Emulating battery pack charging: Battery emulation enables the real-time simulation of battery pack charging from the grid or regenerative braking.
Ensuring interoperability between charging systems: Battery emulation enables the testing of interoperability between chargers, charging stations, and connectors. Onboard chargers must support the charging standards of different countries, some of which specify alternating current (AC) while others require direct current (DC).
Simulating battery discharge in a moving vehicle: Acting as a power source, battery emulation allows engineers to simulate the supply of battery power to the DC-AC powertrain inverter that runs the engine and to the low-voltage DC-DC converter that powers the traction motors.
Estimating and testing the state of charge: Battery emulation facilitates accurate calculation of a real battery's state of charge (SOC).
Reliably estimating battery life: Battery emulation enables the accurate estimation and reporting of the remaining battery life under realistic operating conditions.
Performing rigorous testing: Emulators enable rigorous stress testing of the charger, multi-cell battery packs, battery management system (BMS), and other systems under harsh environmental conditions, including extreme temperatures and vibrations, to ensure durability and safety. Battery profiling is used to measure the effects of temperature on battery performance, and emulation is used to replay those conditions for different tests.
Analyzing battery effects on other systems: Battery emulation enables engineers to study the effects of different SOCs, transient voltage dropouts, and power surges on other vehicle systems like the infotainment system, the controller area network, the lighting system, and the air conditioning.
Following safety standards: Safety is crucial in electric vehicles due to high-voltage onboard batteries and their incendiary hazards. An EV contains a mix of high-voltage and low-voltage systems, which is different from the generally low-voltage environments of regular vehicles. So emulation is crucial to ensure safety features and comply with standards like the National Fire Protection Association 79 standard.

How can battery emulation be integrated into the testing process for internet of things devices or wearables?

Battery life affects the cost and reliability of IoT-based infrastructure. It's also a key purchasing consideration for consumer IoT devices and wearables. For these reasons, IoT device manufacturers must correctly estimate battery life under typical operating conditions of their devices.

Battery emulators help to accurately estimate and extend the runtime of IoT devices as follows:

Create accurate battery profiles: Battery emulators can create accurate profiles by applying charging and discharging cycles. Profiling allows characterization of critical factors like the open-circuit voltage and the internal resistance, which are critical to real-world performance and IoT device run time.
Test various operating conditions: Battery emulation can test devices under various operating conditions, like constant power or constant resistance. In addition, the current drain, discharge current, usage patterns, and temperature affect battery performance.
Emulate charge states: Emulation of different charge states helps to gain insights, reduces the test time compared to real battery testing, and improves reliability in safety-critical applications.
Perform battery cycling: Battery capacity and performance decline over many cycles of charging and discharging. That is emulating battery cycling is critical to accurately determine capacity loss and battery life reduction.

How is battery emulation used with renewable energy systems?

Battery emulation helps in the development and optimization of renewable energy systems, enabling precise testing and validation of equipment like photovoltaic panels, battery management systems, and inverters under varying conditions.

It facilitates the simulation of environmental impacts on energy storage, ensuring systems maintain stable output, manage fluctuating loads, and handle variable renewable sources.

How is battery emulation used with medical devices?

Health care is a highly safety-critical environment for batteries. The industry relies heavily on high-quality long-term batteries to support portable medical devices like blood pressure monitors, hearing aids, pacemakers, and insulin pumps.

Battery emulation helps to test edge cases and extreme scenarios that can't be realistically tested on human subjects.

Optimize device runtimes through battery emulation

In this article, we explored different facets of battery simulation and understood its key role in improving the reliability and lifetime of any device or equipment that runs on batteries.

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