Sponsored by Pickering Interfaces.

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

Battery Administration Programs (BMS)

Electrical car (EV) battery packs – which may include from a number of dozen to greater than 1,000 cells – have to 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 techniques using them. Additionally, security measures/options have to 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 purposes, the packs and all car/platform elements 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 allows 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 have to be monitored on the battery pack’s inputs and outputs, and on the particular person cell stage. 
• Present move into and from the pack have to be monitored. 
• SoC and SoH needs to be monitored and made obtainable to techniques that draw energy from the pack and which cost it. 
• Thermal administration – for instance, lithium-ion cells carry out finest 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 situations, corresponding to over-charging and fault situations (like a person cell failing or wires breaking). It should additionally defend in opposition to human errors, corresponding to getting the polarity incorrect throughout a upkeep or restore activity. 

Verifying by check that the above necessities and others have been met is greater than only a improvement activity, nevertheless. Each manufacturing unit have to 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 crucial. Nevertheless, the usage of an precise battery pack presents challenges, together with: 

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

There may be additionally the problem of check repeatability and documenting check situations and outcomes. Take a look at 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 information may very well 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 equipped to the BMS in lieu of particular person cells could be monitored, so there are values in opposition to which the BMS’s observations could be in contrast. 

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

Excessive Voltage Switching

Pickering Interfaces’ PXI excessive voltage switching modules assist sizzling 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 could be sizzling 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 contains 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 ability provides on the module can due to this fact be used to emulate a stack of battery cells which, as talked about, the BMS have to be confirmed to observe on a person cell foundation. Additionally, every channel can sink as much as 300mA to emulate a battery beneath cost. Every channel supplies unbiased 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 optimistic or unfavourable temperature coefficient thermistors, for instance, the PT100 resistance temperature sensor (with a resistance of 100Ω at 0^oC), which is usually 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 could be simulated in the course of 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 could be operated over three voltage ranges to simulate the three commonest thermocouple varieties in use. 

Fault Insertion

Pickering’s vary of PXI fault insertion items (FIUs) – also referred to as fault injection switches – is designed particularly for safety-critical purposes the place the habits of a management system, corresponding 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 purposes requiring the simulation of varied faults in advanced designs that function a excessive variety of alerts/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 Take a look at System

A complete HIL check system for BMS verification could 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 may also be examined (to confirm that the BMS would acknowledge a producing defect, corresponding to an inverted cell within the pack). 
• Cost Emulation – programmable present supply. 
• COMMS – the power to ship instructions to and obtain information from the BMS (in automotive purposes, usually utilizing CAN bus). 
• Load Emulation – programmable resistive load to emulate battery stack loading.
• Temperature Sensor Simulation – supplies the BMS with inputs from RTDs or thermocouples.
• Isolation Resistance Simulator – verifies the BMS’s electrical isolation monitoring perform. 

Collectively, this check system can be utilized in a wide range of permutations to duplicate all the usual working situations 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 acceptable measures. 

Abstract

Simulation is the most secure approach 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 situations with reside cells. It is usually simple to duplicate open circuits and temperature extremes. 

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

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