Week 7 State of charge estimation

AIM:- State of charge estimation:-

OBJECTIVE:-

Simulate the 3 test cases from harness dashboard and write a detailed report on the results

What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ? 

INTRODUCTION:-

The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC 

Coulomb counting method is done to estimate the , which is estimated from the discharging current, , and previously estimated SOC values.

Rising crude oil prices and worldwide awareness of environmental issues have resulted in increased development of energy storage systems.

The battery is one of the most attractive energy storage systems because of its high efficiency and low pollution.

There are several kinds of batteries currently being used in industry: lead-acid battery, Ni-MH battery, Ni-Cd battery, and Li-ion battery.

SOC estimation is a fundamental challenge for battery use.

The SOC of a battery, which is used to describe its remaining capacity, is a very important parameter for a control strategy.

As the SOC is an important parameter, which reflects the battery performance, so accurate estimation of the SOC can not only protect battery, prevent overdischarge, and improve the battery life but also allow the application to make rational control strategies to save energy.

The Specifications of BMS Are highly accurate with each block given their specific function and all the blocks are inter-related with each other for better performance.

The entire model has a large number of component level and system level analysis.

A 6 cell Module is selceted as our Battery Pack for the system with each cell having 4V as their Standard cell Voltage.

The battery management system (BMS) ECU designs that enable highly accurate monitoring of and control over the high-voltage battery stack.

state_machine; SOC_estimation; balancing_logic block. 

Driving Charateristics: tells us the response to the different driving conditions.

Charging : Response to the EV while Charging.

Balancing : Response to the fault options.

The SOC-Estimation is also a key important block in the BMS_ECU, which helps to tell the estimate of the battey charging condition; wheather cells are charging properly or not etc.

The Balancing_Logic is repsonible for the management of the battery pack while charging so that there is occurance of weak cell into the system. introducing weak cell in the pack compromises with the SOC and SOH.

The Test Sequence Varient has in build 3 models.

It has 3 stages of driving condition

Driving

Charging & Balancing 

Standby

 The indicators are green. So there is no errors and we check the plot for this model and it is represented below.

RESULT: :-

The input cycle can be seen in the 5th graph in which vehicle initially undergoes driving, then charging till SOC 90% and then later in standby state.

During Charging The Battery pack voltage is increased upto 4V.

The cell temperature increases during driving and charging cycle.

The SOC drops to less than 50% after the driving cycle and then later put into charging untill SOC Reaches 90%. 

The Current supplied to the EV during driving phase can be seen in the current graph.

Sequence Varient 2

   2. It has 2 Phases for the battery pack

when this input is provided to the BMS model, the Scope result and the dashboard refelects the following result:

The Result shows that there is a fault condition in the vehicle. The dashboard on the model dipicts the same with a red colour indication. 

After 10,000 sec when the driving cycle is over, during charging and balancing phase the fault condition occurs.

RESULT:-

During the initial phase i.e. the driving mode,the volatge at start of driving was around 4V, after which the voltage steadly drops and reaches around 3.5 V at 10,000 sec.

At the same time, the BMS_ Stage is changed to fault condition. The SOC has also dropped down to 0% after the driving mode.

The fault that occured in the system is the due to HIGH TEMERATURE. The dashboard on the model dipicts the same with a red colour indication.

This fault might have occured due to improper using of battery pack to drive the EV or due to over useage of the battery pack for 10,000 sec which is more than 2.5 hr of continuous use.  

This condition has only one phase and that is charging. So we can simulate this condition and can analyse the plot for charging phase.

Soc reached 100% in charging and remained in stand by mode. Cell temperature also decrased when stsndby mode was acheived.

Every value reached its ideal value and remained constant.

So we can conclude that, if there is no faulty condition, the system work perfectly with ideal conditions in standby mode.

OBJECTIVE:-2

What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ? 

It is a method used for estimating the state of charge (SOC) of a battery.

The coulomb counting method is expedient for state-of-charge (SOC) estimation of lithium-ion batteries with high charging and discharging efficiencies.

The charging and discharging characteristics are investigated and reveal that the coulomb counting method is convenient and accurate for estimating the SOC of lithium-ion batteries.

The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC.

Coulomb counting method is done to estimate the soc (t), which is estimated from the discharging current, I(t) , and previously estimated SOC values, SOC(t-1). SOC is calculated by the following equation:

But there are several factors that affect the accuracy of Coulomb counting method including temperature, battery history, discharge current, and cycle life.

To improve the Coulomb counting method, a new technique called modified Coulomb counting method is proposed.

The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation.

The corrected current is the function of discharging current.

There is a quadratic relationship between the corrected current and discharging current of battery.

By practice of experimental data, corrected current is calculated by the following form:

The experimental results show that the accuracy of the modified Coulomb counting method is superior to the conventional Coulomb counting method.

Now select the BMS ECU unit and the representation is given below.

Select the SOC estimation sub sytem from the model and it is given below.

This system does the estimation by coulomb counting equation mentioned above.

Temperature and current from the battery is given as inputs.

Current signal is given to a gain block and temperature is given to capacity since it varies according to temperature.

These inputs are given for integration where current will be integrated with respect to time.

This outout is given to another block where it is divided by capacity. This result in soc estimation.

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