The application layer software architecture in a battery management system (BMS) is responsible to supervise and control the batteries in a multicell battery energy storage system. includes high and low voltage administration, charging management, state approximation, balance jurisdiction, and fault management, etc.
High and low voltage management
Due to the restricted operating windows of lithium-ion batteries regarding temperature, voltage, and current and the dangerous situations that can arise if the parameters contravene the windows operating. Hence, a battery management system (BMS) is responsible to supervise and control the batteries in a multicell battery energy storage system.
Generally, when the power is on in the application layer software, the VCU will wake up the (BMS) Battery Management System through the 12V of the CAN signal. Once the battery management system (BMS) completes the self-check and enters the standby mode, further, the VCU sends the high-voltage command, and the BMS commands the closed relay to complete the high-voltage. When the power is off, the VCU sets off a high-voltage command and then disconnects and wakes up at 12V. It awakens when the gun plugs itself in the power-off state.
- Charging management
(1) Slow charge
Slow charging in application layer software is safer and puts less stress on the battery which can make it last longer. Slow charging utilizes an AC charging station (or 220V power supply) to convert AC to DC to charge the battery through an onboard charger. The charging station enumerations are generally 16A, 32A, and 64A, and they charge through a household power supply. The BMS awakens by CC or CP signal, but ensure that it can sleep normally after charging.
(2) Fast charge
The battery charging system is built-in application layer software to recharge the high voltage battery from the AC grid. The system in cars is the onboard charging unit. By increasing the battery capacity and the energy efficiency of the electric components, battery pack voltage tends to become standardized at approx. Usually, 80% of the power can be charged in 45 minutes. Wake up by the auxiliary power A+ signal of the charging pile, the fast charging process in the national standard is more complicated, and there are two versions of 2011 and 2015 at the same time, and the different understanding of the technical details of the charging pile manufacturer’s unclear technical details of the national standard process also causes the vehicle charging adaptability.
(1) State Of Power
SOP (State Of Power) mainly obtains the available charge and discharge power of the current battery through the temperature and SOC lookup table. The VCU determines how the current vehicle utilizes according to the transmitted power value. The only power source available in the EV is the battery itself. So a BMS should be designed to be powered by the same battery which it is supposed to protect and maintain. This might sound simple but it does increase the difficulty of the design of the BMS. When an EV is left uncharged for weeks or months the BMS and other circuitry tend to drain the battery by themselves and eventually require to be cranked or charged before the next use. Of course, this will have a certain impact on the driving experience of the whole vehicle.
(2) State of Health
SOH (state of health) mainly characterizes the current state of health of the battery, which is a value between 0-100%. The SOH measurement tells us about the age and expected life cycle of the battery based on its usage history. When using the capacity, the actual capacity of the current battery is gauged through the battery operating process data, and the ratio of the rated capacity to the rated capacity is the SOH. The BMS should also calculate SOH and keep track of it. Accurate SOH will improve the estimation accuracy of other modules when the battery decays.
(3) State Of Charge
SOC (State Of Charge) belongs to the BMS core control algorithm. Further, it characterizes the current remaining capacity state, mainly through the ampere-hour integration method and EKF (Extended Kalman Filter) algorithm, combined with correction strategies (such as open-circuit voltage correction, full charge correction, charging End correction, capacity correction under different temperatures, and SOH, etc.). It tells us the battery capacity of the pack in percentage. The most commonly used method is the coulomb counting method.
(4) State Of Energy
Generally, electric vehicles can be classified according to the power source as follows: solely hybrid electric vehicles (HEVs), battery-powered electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), photovoltaic electric vehicles (PEVs), and fuel cell vehicles (FCVs). SOE (State Of Energy) algorithm manufacturers use a simpler algorithm but mainly used to estimate the remaining cruising range.
(1) Fault diagnosis
Fault diagnosis is an intermedial task of Battery Management Systems (BMS) of electric vehicle batteries. The effective implementation of fault diagnosis in the BMS can prevent catastrophic consequences like the thermal runaway of battery cells. According to the different performance of the battery, it divides into different fault levels. Moreover, in different fault levels, the BMS and VCU will take different treatment measures, warning, limiting power.
(2) Balance control
The equalization function is to eliminate the inconsistency of the battery cells generated during battery use. The cells with the worst performance during charging and discharging first reach the cut-off condition,
A balance control method comprises the following steps:
(1) When the balance control method initiates, the battery pack carries itself out before equilibrium at BMS.
(2) When BMS unlatching carries out equilibrium to the battery pack. It measures respectively balanced rear each battery cell transient voltage value U2 that opens;
(3) measure respectively the real-time measuring voltage value U3 of each battery cell in balancing procedure;
(4) Firstly, measure U1, the U2, and the U3 that is obtained, respectively. Then each battery cell real-time voltage revises itself, obtains each battery cell real-time voltage U4;
(5) According to the real-time voltage U4 of each battery cell, the balance control method judges whether to finish the equalization operation.
The present embodiment is more excellent execution mode of the present invention. A good battery management system will greatly promote the development of new energy vehicles.
To sum up, companies like Renesas, Texas Instruments, etc. possess their series of BMS IC’s and Tool kits. Moreover, they could do the hardware pulling for all of us. With every new EV in the market, the BMS evolves to get much smarter and easy to use.
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