Electric Vehicle Battery Management

Future deadlines for reducing or eliminating new diesel and petrol vehicle sales are already in place and the only alternative currently available is the Electric Vehicle. Although the majority of Electric-only models are purchased as a second car, the major car manufacturers – Audi, Mercedes, Volvo etc – have begun to introduce vehicles with a more practical range which will see the take-up of EVs as the primary household vehicle increase considerably.

Much of the range advancements are due to developments in battery technology where the size and weight no longer determine power output. In electric and hybrid vehicles, power is derived from a multi-cell power pack based, in most cases, on Lithium Ion or Nickel-Metal Hydride technology.

Power Packs Need to be Monitored and Managed

These power packs need to be monitored and managed to provide the vehicle’s central management system with a continuous flow of status information relating to the battery pack’s condition across a variety of parameters. For this, EVs and hybrids require a battery management system to provide this information to the vehicle’s central control system.

Determining the State of Charge (SoC)

EV power packs are rechargeable which increases the complexity of the battery management system. For example, EV drivers need to see a “fuel” gauge to tell them how much further the vehicle can travel before recharging. Unlike measuring the position of a float in a conventional fuel tank, determining the state of charge (SoC) of a battery pack is not an easy task. Traditional Lead Acid batteries give a fair indication of SoC just by measuring the voltage on their terminals. However, since EV power packs give a fairly constant voltage output throughout the majority of their charge cycle, other techniques have to be used to measure the current flow over time to gauge how much energy has gone into the power pack or how much has been taken out.

The Importance of State of Health (SoH)

In addition to state of charge calculations it is also important to determine state of health (SoH). For example, any battery management system needs to ensure that the power packs do not overheat or do not get overcharged – situations that can have serious consequences for this type of battery technology where the fire hazard is very much a possibility. A correctly designed battery management system will not only monitor and communicate the status of the power pack, but also provide the optimum charging conditions and could even extend the life of each cell. Many OEMs require each individual cell of the battery pack to be constantly monitored to give an accurate picture of the pack’s lifetime history. However, in the cost-conscious automotive sector, this is not always the case so the battery management system will monitor cell groups rather than each cell.

The Case For Using An ASIC

A Single Chip Solution

Much of a BMS can be included in a tiny single chip device. Sensing and measurement, on-board processing, software as well as different wireless communications standards. An ASIC offers customers a high degree of flexibility when it comes to selecting how the device will communicate. We can incorporate all of the leading communications protocols including 2.4GHz proprietary, Bluetooth Low Energy (BLE), Power Line Communications (PLC) and, if the applications suits, Near Field Communication (NFC).
As well as the ability to incorporate all the functionality required, there are many other reasons to commission an ASIC designed specifically for this type of application. These include size, performance, cost and reliability and an assurance against product obsolescence. An ASIC solution will reduce a user’s inventory and bill of materials (BOM) while protecting the originator’s Intellectual Property (IP). The wrongful use of IP is a major threat to all technology companies and ASICs provide a solution where reverse engineering of the device is difficult if not impossible to achieve.

Customers will also choose the ASIC route to guarantee component supply for the lifetime of their product with no gaps in availability. This is in sharp contrast to a solution built using standard components whose manufacturers readily consign them to the obsolescence bin once the part no longer make financial sense to the supplier or is superseded.

Leaders in the Automotive Sector

Already totally committed to providing highly advanced electronic sensors and systems to the automotive sector, Swindon is able to ensure that stringent functional safety criteria (ISO 26262) are incorporated at chip level in line with the safety case as supplied by our customer. Devices and sensors designed and produced by Swindon Silicon Systems along with parent company Sensata Technologies, can be found in Tyre Pressure Monitoring Systems (TPMS), where the company supplies around 50% of the global demand. Swindon’s single chip devices can also be found in battery management, automatic braking systems (ABS), haptics, position and proximity sensing and touch screen displays, to name but a few.

As we have said, the global market for Electric Vehicles will soon begin to grow significantly as the choice of make and model increases along with the usable range and a more widespread EV charging infrastructure. Since EV batteries comprise many cells, each of which need to be monitored for current, voltage and temperature it can mean large numbers of ICs in a battery pack.

The Battery Management System is vital to the vehicle’s well -being and performance. Due to the stringent performance requirements with cost, size and weight restrictions inherited at the design phase, the ability to include all of the required functionality into a small single footprint, coupled with high quality and low cost solutions that ICs provide, it is the perfect application for a mixed signal ASIC.