Advanced Battery Management System for Electric Vehicles

The huge energy requirement of the automobile industry cannot be met by the non-renewable petroleum in the long term. With the rapid development of global economy, the problems of energy shortage and environmental pollution are becoming increasing prominent. The transformation of the automobile industry, which currently accounts for a large proportion of the global petroleum consumption and pollutive emissions, is an inevitable trend.

Power battery is widely used in energy storage system. The batteries performances affect the performances and market recognition of new energy vehicles. The requirements on batteries include safety, energy density, power density, efficiency, maintenance level, management, cost, ambient condition and environmentally friendly issue.

The main differences between traditional fuel vehicles and electric vehicles are that electric vehicles are powered by batteries. Power batteries are the indispensable parts of electric vehicles. Battery Management System (BMS) is the core technique for battery packs. BMS is designed to improve safety, reliability of batteries, increase discharge rate, extend lifetime and prolong mileagues. BMS is a significant connection of battery pack, whole vehicle system and motor. BMS optimize the power and mileague for electric vehicle since single cell has limited capacity and voltage. Battery packs are composed of battery cells in series or in parallel. BMS monitors battery modules and manages batteries according to battery parameters such as current, voltage, internal resistance and capacity. BMS conducts calculation, gives order, executes and gives warning. For battery modules of low performances, BMS is important. Therefore, BMS is studied by researchers around the world. Although single cells have different form factors and performances, they have similar functions.

Lithium ion batteries (LIBs) have become the favorite choice as the power sources for electric vehicles (EVs) due to the advantages such as long service life, high energy and power density and environmental friendliness, etc. The operating conditions of the LIBs in EVs vary with the environment, and the BMS is key to ensuring system safety, longevity and high efficiency.

Battery state of charge (SOC) is the ratio between the battery’s remaining charge and the total charge capacity. The SOC is not directly measurable. It can be calculated under a fixed discharge rate according to the ‘Battery Test Procedure for Electric Vehicle’ by the Advanced Battery Consortium of America.

The battery energy and power capacities will decrease with ageing. The ageing indicator, state of health (SOH), is of great significance to the battery safety, the EV’s performance and the user’s driving experience. Once the SOH drops below a threshold value, the battery needs to retired from EV to prevent safety hazards.

State of power (SOP) is an important parameter for EVs, especially hybrid EVs, for safety control and regenerative braking. SOP represents the battery’s peak power capacity within a time window. The accurate SOP estimation is important for optimizing the power management of the vehicle while ensuring battery safety during acceleration, regenerative braking and climbing.

SOC is usually used to predict the remaining energy of the battery. However, the battery’s remaining energy depends on the load current profile, which is not considered by the SOC indicator. Further, the high energy loss due to the battery’s internal heat generation at high current cannot be captured by the SOC indicator.

For battery pack in charge and discharge, the available capacity is limited by the cell with the least capacity. Due to the heterogeneities between cells in pack, the charge throughput of individual cells is different. Thus, cells in the pack are degraded differently. For battery pack of 18,650 cells in parallel, the difference of their available capacity can reach 3%. This difference accumulates with time and accelerates degradation of the battery pack.

The energy storage system of power battery is one of the significant aspects of electric vehicles. It determines the travel range and lifetime of electric vehicles. Lithium-ion battery is the ideal power battery due to its high energy density and long cycle lifetime, and has been studied comprehensively.

Temperature has a significant effect on capacity, impedance, maximum charge/discharge rate and degradation of lithium-ion battery. The thermal gradients will accelerate the inhomogeneity within the battery and are detrimental to battery performances. Generally, the effects of temperature on electrical vehicles are: (1) discharge performance is exasperated in low temperature (2) degradation is accelerated in high temperature (3) inhomogeneity can be increased and (4) safety reliability is reduced. Figure 11.1 schematically shows temperature relations with the above 4 aspects.

With the extensive application of electrical devices, electronic equipment and programmable electronic devices in the field of automobile control, safety-related problems have become more and more prominent, brake failure, engine or gearbox control software failure and other automobile recalls frequently occur, not only to automobile enterprises caused huge economic losses, but also to people’s lives and property security has brought serious threats.

With the in-depth integration of automobile manufacturing technology and new-generation technologies such as information and communication technology, the automobile industry is accelerating its development in the direction of electrification, intelligence, networking and sharing. In-vehicle electronic systems have become more and more complex, and have gradually equipped with networked communication functions, including communication with other vehicles, infrastructure, and access to the internet.

As the most important energy storage system of electric vehicle, all kinds of available batteries, such as lead acid battery, nickel metal hydride battery and lithium-ion battery, have been used in electric vehicles. Among them, Li-ion battery has many advantages such as high energy density, long cycle life, low self-discharge rate, good safety performance and environmental friendliness, at present, it has become the most widely used type of power battery in electric vehicle, which can be divided into lithium iron phosphate, lithium manganese oxide, lithium nickel oxide, ternary (nickel–cobalt–manganese mixture or nickel–cobalt–aluminum mixture) according to the cathode material system The anode materials used are mainly graphite, carbon materials and lithium titanate; according to the shape, there are three kinds of cylindrical, prismatic and pouch cells, but the pouch cells presents the fast rising tendency (Xiong et al. in Renew Sustain Energy Rev 131, 2020).

Digital twin is a technology which integrates multi-physics, multi-scale, multi-subject attributes, has the characteristics of real-time synchronization, faithful mapping and high fidelity, and can realize the interaction and fusion between the physical world and the information world. With the concept of digital twin shop put forward, the potential application of digital twin in intelligent manufacturing has obtained more and more attention. Digital twin is to create a corresponding “virtual world” in cyberspace by digitizing all elements of the physical world, such as people, objects and events, the result is that the physical world in the physical dimension and the virtual world in the information dimension coexist and blend with each other.

An intelligent battery management system is a crucial enabler for energy storage systems with high power output, increased safety and long lifetimes. With recent developments in cloud computing and the proliferation of big data, machine learning approaches have begun to deliver invaluable insights, which drives adaptive control of battery management systems (BMS) with improved performance.