Week 5 Battery characteristics using drive cycle

AIM:- To simulate generic battery model charge-discharge using UDDS driving cycle data.

Driving Cycle:- 

             A driving cycle commonly represents a set of vehicle speed points versus time. Driving cycles are produced by different countries and organizations to assess fuel consumption and pollutants emissions of a vehicle in a normalized way, so that different vehicle can be compared.

Purpose of the Driving cycle:-

• To assess the performance of a vehicle (fuel economy, emission tests in IC engine)
• To analyze battery state and energy consumption in electric vehicles.
• To simulate vehicle model prior to the actual development           

             In commercial vehicles area, the driving cycle is not performed on a vehicle dynamometer but on an engine dynamometer and is evaluated through a set of engine torque and speed points instead of vehicle speed points. 

            Though it is meant for an IC engine, the Drive Cycle can be used to simulate Electric Vehicles (EV) also. In this project, we are simulating the battery model and for that, we are converting the speed profile of the drive cycle to the current profile.

            There are two kinds of driving cycles,

1) the modal cycles as the European standard NEDC, or Japanese 10-15 Mode and

2) the transient cycles as the UDDS or Artemis cycle.

            The main difference is that modal cycles are a compilation of straight acceleration and constant speed periods and are not representative of a real driver behavior, whereas transient cycles involve many speed variations, typical of on-road driving conditions.

Driving Cycle Used in Project:-  UDDS

             UDDS stands for Urban Dynamometer Driving Schedule and refers to the United States Environmental Protection Agency mandated dynamometer test on fuel economy that represents city driving conditions which are used for light-duty vehicle testing.

             Below is the UDDS Cycle.

SIMULINK Model:-

Description of Blocks used:-

1) Signal Builder:

             The Signal Builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a model. You can quickly switch the signal groups into and out of a model to facilitate testing. In the Signal Builder window, create signals and define the output waveforms.To open the window, double-click the block.

            Here a signal builder block is used to create the drive cycle data of the UDDS cycle. The limitation of the signal builder is that it accepts data in the form of only the current profile. So, the speed v/s time data from the drive cycle is converted to its corresponding current profile with respect to time.

To Add The drive cycle-

• To open the window, double-click the block.
• Go to File > Import from file.
• Browse the file to import from the directory.
• From the drop-down menu in “placement for selected data” click on “Appended selected signals to all group”.
• Confirm selection > Apply > Ok
• Set the time limit of 1369 sec
• Connect the signal builder output port to (s) input port of controlled current source for input current signal.

Drive Cycle in Current Profile:-

             Above current Vs time plot is obtained for the input signal. Here converted current profile is taken from speed which in mph.

2) Controlled Current Source:

              The Controlled Current Source block converts the Simulink input signal into an equivalent current source. The generated current is driven by the input signal of the block. The positive current direction is as shown by the arrow in the block icon.

             We can initialize the Controlled Current Source block with a specific AC or DC current. If we want to start the simulation in steady-state, the block input must be connected to a signal starting as a sinusoidal or DC waveform corresponding to the initial values. 

             Connect the +ve terminal of the current source to the -ve terminal of the battery and the -ve terminal of the current source to the +ve terminal of the battery.

3) Battery:

              The Battery block implements a generic dynamic model that represents the most popular types of rechargeable batteries. We can extract the SOC, voltage, and current from the battery.

Parameters-

              Here I have used the default battery setup of a battery of 7.2 V and 5.2 Ah rating.

Battery Parameters-

Discharge Parameters-

Discharge Curve-

4)BUS Selector:-

              The Bus Selector block outputs the signals you select from the input bus. The block can output the selected elements separately or in a new virtual bus.

              Here output %SOC, Current(A), and Voltage(V) are drawn to view in the scope.

5) Powergui:-

              The powergui block allows us to choose one of these methods to solve the circuit:

1)Continuous, which uses a variable-step solver from Simulink
2)Discretization of the electrical system for a solution at fixed time steps
3)Continuous or discrete phasor solution

6) Scope:-

              The scope is used to check the output results in a graphical format.

OUTPUT RESULT:- 

               The below result is for UDDS Driving Cycle with a 7.2V and 5.4 Ah rating battery.

              The first graph shows the converted current profile path for the UDDS Drive Cycle.  

              In the second graph, we can observe the voltage drop over a period of time. From the Voltage graph, we can see that the voltage becomes low whenever the current requirement is high and increases when there is a decrease in the requirement of current.

              Here the simulation ran for 1369 secs for 1 cycle of UDDS drive cycle for which the SOC is around 95.7%. So we can say that around 4.3% of the charge is used for 1369 sec for 7.2V and 5.4 Ah rating battery. In the discharge curve i.e SOC curve, we can observe the up-down graph which indicates that the battery is charging whenever the current requirement is down/low.

              So in that way, we can observe the charge-discharge characteristics from the SOC curve.

UDDS Drive Cycle Current profile:-

 https://drive.google.com/file/d/1ZcL5xokvEi60CBhUwsItgAFHlGLDTH4y/view?usp=sharing 

REFERENCE:- 

https://skill-lync.freshdesk.com/support/solutions/articles/43000571390-how-to-model-generic-battery-model-using-udds-drive-cycle