Charged EVs | BMS purposeful verification: the safety-first strategy

Sponsored by Pickering Interfaces.

Herein, we talk about the objectives of BMS verification and clarify how simulation with hardware-in-the-loop offers a wealth of knowledge, saves time and is safer than working with precise reside cells. We additionally clarify how a BMS HIL check system will be created utilizing PXI simulation modules from Pickering Interfaces. 

Battery Administration Methods (BMS)

Electrical automobile (EV) battery packs – which may comprise from a number of dozen to greater than 1,000 cells – should be managed for optimum efficiency when it comes to releasing and accepting energy. The packs should even be monitored to report SoC and SoH (state-of-charge and -health, respectively) to the methods using them. Additionally, security measures/options should be current to isolate the packs (or modules/banks of cells) in case of a fault. These roles are all carried out by the BMS. 

Security

Security is an important consideration wherever battery packs are used. In automotive functions, the packs and all automobile/platform parts that electrically connect with them (together with the BMS) are thought-about hazardous gadgets and should adjust to ISO 26262. 

BMS Design & Verification

Most firms undertake a TDD (test-driven improvement) technique when designing a BMS. This permits them to not solely optimize the battery pack’s dimension (each bodily and power capability), but in addition confirm the performance of the BMS all through the product improvement lifecycle. 

Typical top-level purposeful necessities for a BMS embrace: 

• Voltages should be monitored on the battery pack’s inputs and outputs, and on the particular person cell degree. 
• Present move into and from the pack should be monitored. 
• SoC and SoH needs to be monitored and made obtainable to methods that draw energy from the pack and which cost it. 
• Thermal administration – for instance, lithium-ion cells carry out greatest between 10 and 45^oC, so the BMS should management the heating or cooling of the pack accordingly. 
• The BMS should defend in opposition to in-use circumstances, similar to over-charging and fault circumstances (like a person cell failing or wires breaking). It should additionally defend in opposition to human errors, similar to getting the polarity fallacious throughout a upkeep or restore activity. 

Verifying by means of check that the above necessities and others have been met is greater than only a improvement activity, nevertheless. Each manufacturing unit should be functionally verified as a part of its high quality assurance. 

Simulation with {Hardware}-in-the-Loop

BMS improvement with HIL (hardware-in-the-loop) is important. Nevertheless, the usage of an precise battery pack presents challenges, together with: 

• Performing over-voltage checks is harmful – with the chance of fireside or explosion. 
• It’s not simple to alter the voltages of particular person cells, that means it’s tough to confirm that the BMS’s cell balancing operate works. 
• The place the monitoring of particular person cell voltages is anxious, it’s solely attainable to test what the BMS thinks it’s seeing. However what are the actual cell voltages? 
• How can the BMS’s temperature monitoring operate be checked with out subjecting the pack to harmful temperature extremes? 

There’s additionally the problem of check repeatability and documenting check circumstances and outcomes. Check set-up and the reporting of outcomes are each open to human error. This implies the accuracy (and by extension, validity) of the BMS verification knowledge could possibly be referred to as into query. 

The answer to those points is simulation. It removes the necessity to work with reside cells, making it safer. The voltages provided to the BMS in lieu of particular person cells will be monitored, so there are values in opposition to which the BMS’s observations will be in contrast. 

Simulation can be extremely repeatable, as fault circumstances, similar to damaged wires and overheating cells, are far simpler to simulate than they’re to duplicate with reside cells. The recording of check circumstances (stimuli utilized) and outcomes are simple. 

Excessive Voltage Switching

Pickering Interfaces’ PXI excessive voltage switching modules help scorching switching of 0.25A at as much as 7.5kV (DC and AC peak) and chilly switching as much as 9kV (DC and AC peak). Additionally, 5A will be scorching switched at as much as 1kV. 

Battery Cell Simulation

Pickering’s PXI/PXIe multi-channel battery simulator module (Determine 1) was created with BMS design and verification in thoughts. The module includes energy provide channels (two, 4 or six per slot) able to supplying as much as 7V and 300mA remoted from each other and from floor. The facility provides on the module can subsequently be used to emulate a stack of battery cells which, as talked about, the BMS should be confirmed to observe on a person cell foundation. Additionally, every channel can sink as much as 300mA to emulate a battery below cost. Every channel offers impartial energy and sense connections, permitting the simulator to sense a distant load and proper for wiring losses. 

RTD & Thermocouple Simulation

RTD (resistance temperature detector) simulators can emulate the habits of constructive or unfavorable temperature coefficient thermistors, for instance, the PT100 resistance temperature sensor (with a resistance of 100Ω at 0^oC), which is often employed in battery packs. 

Pickering has PXI simulator modules (with 4, 8, 12, 16, 20 and 24 channels) that may simulate the resistance vary 40 to 900Ω, which equates to a temperature of -150 to 850^oC, to a decision of lower than 10mΩ. 

Thermocouples are additionally employed in battery packs, significantly throughout product improvement, due to their excessive accuracy. These too will be simulated throughout the improvement and verification of the BMS forward of its connection to (or integration inside) an precise battery pack. 

Pickering has a spread of PXI millivolt thermocouple simulator modules that present 8, 16, 24 or 32 channels of extremely correct low-voltage sources. Every channel will be operated over three voltage ranges to simulate the three commonest thermocouple sorts in use. 

Fault Insertion

Pickering’s vary of PXI fault insertion models (FIUs) – also called fault injection switches – is designed particularly for safety-critical functions the place the habits of a management system, similar to a BMS, must be totally evaluated. 

For instance, the 40-592 FIBO (fault insertion break-out) is a large-scale, high-density switching matrix. It’s one in every of a spread of modules designed for functions requiring the simulation of assorted faults in advanced designs that characteristic a excessive variety of indicators/connections – a battery pack being a primary instance. Typical faults that may be simulated are open circuits and brief circuits to both one other sign/part or to floor (see Determine 2). 

BMS HIL Check System

A complete HIL check system for BMS verification will be created utilizing PXI/PXIe-based modules (see Determine 3 and Video): 

• Battery Cell Simulator – simulates every cell’s voltage and present output and has particular person present sinks to emulate cell charging. 
• Fault Insertion Switching – simulates short- and open-circuits on every battery cell output, in addition to wiring faults between cells and the BMS. Polarity reversal will also be examined (to confirm that the BMS would acknowledge a producing defect, similar to an inverted cell within the pack). 
• Cost Emulation – programmable present supply. 
• COMMS – the power to ship instructions to and obtain knowledge from the BMS (in automotive functions, sometimes utilizing CAN bus). 
• Load Emulation – programmable resistive load to emulate battery stack loading.
• Temperature Sensor Simulation – offers the BMS with inputs from RTDs or thermocouples.
• Isolation Resistance Simulator – verifies the BMS’s electrical isolation monitoring operate. 

Collectively, this check system can be utilized in quite a lot of permutations to duplicate all the usual working circumstances the BMS and battery mixture are designed to deal with, and to confirm that the BMS performs all its capabilities, together with cell balancing, voltage and present monitoring, cell balancing, temperature monitoring, reporting faults and taking applicable measures. 

Abstract

Simulation is the most secure option to confirm {that a} BMS’s options carry out as supposed – as a result of it doesn’t contain creating over-voltage or short-circuit circumstances with reside cells. It is usually simple to duplicate open circuits and temperature extremes. 

A complete HIL check surroundings will be created utilizing COTS PXI-based simulators, emulators and fault insertion switches, the place the favored and industry-standard PXI platform offers modularity, flexibility, and scalability. 

Importantly, for traceability and certification functions, simulation offers extra significant knowledge that’s simple to seize and document.