Project 2 Thermal modeling of battery pack

Project 2 Thermal modeling of the battery pack

For a 10-cell series lithium-ion battery model, simulate the thermal effects and compare life cycle performance at various temperatures, and charge & discharge rates using MATLAB.

Answer:

Simulink Model of 10 Lithium-ion cells in series battery model:

• Lithium-ion battery pack with fault is modified into the above model.
• In this model 10 lithium-ion cells are connected in series.
• The fault in the model is removed.
• The cyclic charge-discharge current source is replaced by a controlled current source.
• The input to the current source is the signal builder block in which the values of current are given.
• The complete SOC of the battery pack is measured.
• This battery model is tested for various temperatures of the cells and the charge and discharge rates.
• The SOC of each cell is measured and how SOC change for different temperature is measured.

• A cell subsystem consists of a thermal model and lithium cell RC block which calculate the temperature and the thermal effect for cells and overall calculate for the battery pack.
• The blocks inside the subsystem are PS gain block which multiplies the input physical signal by a constant i.e. y = u*gain. Other blocks are voltage sensor and controlled voltage source
• The voltage sensor block represents an ideal voltage sensor that is a device that converts voltage measured between any electrical connections into a physical signal proportional to the voltage.
• The controlled voltage source represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V = Vs, where Vs is the numerical value presented at the physical signal port

• Thermal reference: This block represents a reference point in a thermal network where the temperature is equal to absolute zero.
• Controlled Heat Flow Rate Source: This block represents an ideal energy source in a thermal network that can maintain a controlled heat flow rate regardless of the temperature difference. The heat flow rate is set by the physical signal port S. A positive heat flow rate flows from port A to port B.
• Thermal mass: This block models internal energy storage in a thermal network. The rate of temperature increases in proportion to the heat flow rate into the material and is inversely proportional to the mass and specific heat of the material.
• Temperature sensor: This block measures the temperature in a thermal network. There is no heat flow through the sensor. The physical signal port T reports the temperature difference across the sensor. The measurement is positive when the temperature at port A is greater than the temperature at port B.

• This block basically consists of capacitance value C block which depends on o an external physical signal inputs SOC and T. It is assumed that the capacitance value is slowly varying with time, and hence the equation I = C*dv/dt holds.
• The resistance value (R) block depends on an external physical signal inputs SOC and T.
• Voltage value (EM) which implements the cell main branch voltage source and determines values for capacity (C) and state of charge (SOC). The defining equations depend on cell temperature T.

• In this case, the ambient temperature is 293.1K and the temperature of all the cells is 293.1 K.
• The input current for charging and discharging modes varies in the manner shown below.

• In the above figure, the positive waveform shows the charging of the battery, and the negative waveform shows the discharging of the battery.
• When the waveform is zero it shows the battery is at rest.

• The above graph shows the temperature of all the cells.
• As the temperature is the same for all the cells, so the graph is similar for all the cells.
• During the charging mode, the temperature is increased.
• During the rest period of the battery, the temperature is decreased.
• And during the discharging mode also the temperature of the cell increase.

• The above graph shows the SOC of each cell and it is the same for all the cells as their temperatures and the characteristics are the same.

• The above graph shows the SOC of the battery pack.
• It is seen that the SOC is increased during the charging of the battery and decreased during the discharging of the battery.
• The SOC is constant when the battery is at rest.

• In the above figure, the temperature of each cell starts increasing from the ambient temperature.
• The temperatures are increasing as per the current drawn from the battery.
• Cell number 10 has the highest temperature and cell number 1 has the lowest temperature of all the cells.
• The nature of all the cell temperatures is the same.

• The above graph shows the SOC of each cell when we zoom the graph.
• AS seen during the charging of the battery the SOC of cell 10 is higher.
• Cell 10 has a higher temperature and draws more current than other cells therefore it charges earlier as compared to other cells.
• Cell 1 has the lowest SOC of all the cells as it has the lowest temperature.

• The above graph shows the SOC of each cell when the battery is at rest.
• The SOC of cell 10 has higher SOC and cell 01 has the lowest SOC.

• During the discharging of the battery also the cell having the higher temperature discharges fast.
• And the cell with lower temperature discharges slowly.

• The above graph shows the entire SOC of the battery pack and it is nearly the same for both the cases of the same and different temperatures.
• There is a slight difference in the SOC of each sell therefore SOC of the battery pack is the same as in case 2.

• In case 1, the temperature of each cell is the same and the SOC of each cell is also the same.
• In case 2, as each cell has a different temperature, then the SOC is also different for each and has a slight difference.
• The cell with the higher temperature has the highest charging and discharging rate.
• And the cell with the lowest temperature has the lowest charging and the discharging rate.
• The cell with a higher temperature has the higher SOC and the cell with the lower temperature has the lowest SOC.