battery-management-systems-ev-phevConsumers continue to care about their environmental footprint, which has kept the clean energy trend on an upward trajectory. As clean energy continues to gain popularity, more and more electric vehicles of all kinds –quadcopters, bikes, cars and even cargo trucks – are gradually acquiring a presence in niches currently dominated by fossil fuel technologies.

Market forecasts for electric and plug-in hybrid vehicles (EV & PHEV) point toward a promisingly high annual growth rateThanks to the notoriety of car brands like Tesla, EVs and PHEVs are an exciting part of the automobile industry's future. According to research by Grand View Research, Inc., the global electric vehicle market is estimated to reach almost $46 billion by 2025. Much of this growth is thanks to incentive programs, like tax rebates and subsidies.

Most recently France, a major car producing country, announced that they’re forcing the extinction of fossil fuel driven vehicles by promising they’ll aim to ban the sale of gasoline and diesel cars by 2040; and they’re not alone.

Norway, one of the world’s biggest oil producers, has been waving high taxes imposed on car sales for electric cars. Furthermore, paying toll road fees have been waived, letting them cruise in bus lanes and even providing free charging stations: all of these aimed at the goal to abandon fossil fuel vehicles by 2025.

India has also been pursuing a change to EVs by targeting to fill up the streets with electric cars by 2030. The UK has also announced they will ban the sale of new gasoline and diesel cars starting in 2040, and at least 10 other countries are following their lead.

With more energy demanding devices hitting the market every day, new advances in power electronics are successfully breaking the paradigm of an overwhelming fossil fuel driven world. However, the toughest challenge rests on the shoulders of electrical engineers and designers: developing a reliable, efficient and adaptable battery management system.

This article will delve into some of the power electronic components of battery management systems (BMS) that are key to delivering a reliable and robust solution to power conversion.

Battery Management Systems are Key in EV & PHEV Vehicles

The battery management system can be thought of as the “brains” of a battery pack, primarily responsible for protecting the battery cells from operating out of safe conditions. Today’s leading electrical energy storage technology for electric vehicles are batteries with lithium ion cells. Portability, high energy density, low self-discharge and memory effect has placed this technology as the ideal solution for EV & PHEV. However they face two critical design issues.

Two design issues of battery management systems: 

  • Overcharging produces overheating
  • Discharging them below a certain threshold can reduce their capacity permanently; that threshold is, typically, around 5 percent of their total capacity.

battery-management-systems-flowchartBatteries are a small explosive charge that needs to be carefully managed to be safe and reliable for its users. Since batteries work through chemical reactions, they operate in a “gray zone” of being under or over charged, where heat plays a fundamental role; as it’s known that when heat increases conductors tend to increase their resistance while conversely, insulators decrease theirs.

Think of electricity as water, it can be still and unharmful when contained, but upon finding an opening, it will flow recklessly through the path that offers the fewest obstacles.

Using the same water analogy, think of battery cells as water reservoirs that feed a city’s water supply network. The gates regulate water flow in and out of each reservoir to keep its level high enough to maintain minimum water pressure but not too high that it will burst a pipe and drain all the water reservoirs.

To regulate energy flow a Battery Management System usually has two MOSFETS per battery cell that serve as gates to charge or discharge them according to the state of charge, voltage and temperature conditions of the cell. The BMS generates the pulses that turn on and off those MOSFETS. However, high isolation transformers, such as our PH9185.XXXNL series, protect the control circuit from the batteries power.

3 Ways Battery Managment Systems Power EV & PHEV Vehicles

1. Voltage

Battery management systems are responsible for measuring the voltage of each battery cell because over or under voltage conditions can also lead to thermal runaways that might cause a battery failure. Since keeping the voltage uniform along the battery cells is critical, this system applies an “equalizing charge” that favors the compromised battery cell. To accomplish this, power electronic components, such as the Pulse Electronics PA4334 series inductor, can act as sensors to help identify a drop or increase in cell voltage, thus allowing the system to determine if a cell is over or under driven.

2. Temperature

Battery management systems are also in charge of measuring temperature along the battery packs. If an overheating condition is detected, the control system might stop regenerative charging or reduce the power draw from a pack to return individual cell temperatures to a safe range of operation.

3. State of Charge (SoC)

Another important energy management function of a BMS is to determine the state of charge (SoC) to ensure all cells are discharged equally and safeguard them from going below the threshold that permanently reduces their total capacity. For that, a BMS performs a task known as “Coulomb counting,” which determines the amount of electric power that is left in each battery cell and communicates it to the controls through a low EMI susceptible interface, such as our HM1188NL, which through a stackable architecture can support hundreds of cells.

Lithium ion cells store energy by steadily moving lithium from the cathode to the anode in exchange to an opposite electron flow through the electrolyte. Their ideal charging algorithm is through a constant current and then constant voltage phase, for which a BMS uses high current inductors, such as our PA434xNL series, to limit the rate of change in current flow and eliminate ripple on the charging current.

A Good Battery Management System is Worth The Effort

Overall, a BMS ensures the electrical energy storage system will perform safely and efficiently. It seems like the toughest challenge for the EV & PHEV industry is to demonstrate that the future of electric vehicles is not going to be like the past.

Vehicles have always been complicated, and even some drivers don’t really understand how their fossil fuel vehicle works. For many people, understanding the benefits of EVs & PHEVs without experiencing it can be slightly bewildering. It’s up to electrical engineers and designers to properly integrate robust Battery Management Systems that rely on innovative power magnetic components that effectively assess and control the performance and health of each battery cell to offer safer and more durable electrical energy storage systems.


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Topics: Switch Mode Transformers, Current Sensing Magnetics