Week 5 Battery characteristics using drive cycle

1. AIM

Simulate generic battery model charge-discharge using UDDS data.

2. THEORY

Drive Cycle

A driving cycle is a series of data points representing the speed of a vehicle versus time.

Driving cycles are produced by different countries and organizations to assess the performance of vehicles in various ways, as for instance fuel consumption, electric vehicle autonomy, and polluting emissions. Fuel consumption and emission tests are performed on chassis dynamometers. Tailpipe emissions are collected and measured to indicate the performance of the vehicle.

Another use for driving cycles is in vehicle simulations. More specifically, they are used in propulsion system simulations to predict the performance of internal combustion engines, transmissions, electric drive systems, batteries, fuel cell systems, and similar components.

Some driving cycles are derived theoretically, as it is preferred in the European Union, whereas others are direct measurements of a driving pattern deemed representative.

There are two types of driving cycles:

1. Transient driving cycles involve many changes, representing the constant speed changes typical of on-road driving.
2. Modal driving cycles involve protracted periods at constant speeds.

UDDS Drive Cycle

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.

It is also known as U.S. FTP-72 (Federal Test Procedure) cycle, LA-4 cycle, in Sweden as A10 or CVS (Constant Volume Sampler) cycle, and in Australia as the ADR 27 (Australian Design Rules) cycle.

Though it was originally created as a reference point for fossil-fueled vehicles, it is also used to give estimates on how many miles an electric vehicle will travel on a single charge.

Simulink Model

The blocks used in the above model

1. Signal Builder

• The Signal Editor block displays, creates, and edits interchangeable scenarios. You can also use the block to switch scenarios in and out of models.
• The Signal Editor block supports MAT-files that contain one or more scalar Simulink data objects.
• You can port Signal Builder block configurations to the Signal Editor block using the signal builder function.
• By using this block, we can give UDDS cycle current as input, for this we have to import the UDDS cycle into the signal builder block.

Importing the drive cycle excel file to the signal builder.

File --> Import --> Select the file --> Then select the data.

Once we import the excel file we can see the current profile in the signal builder as shown above.

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.

You can initialize the Controlled Current Source block with a specific AC or DC current. If you 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.

3. Battery

The Battery block implements a generic dynamic model that represents the most popular types of rechargeable batteries.

The battery parameters can be changed according to the requirements as shown above.

4. Bus selector

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

So we take the battery output as the input for the bus selector and we can give the separate outputs of SoC, Current and Voltage.

5. PowerGUI

The powergui block allows you to choose one of these methods to solve your 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

The powergui block also opens tools for steady-state and simulation results analysis and for advanced parameter design.

You need the powergui block to simulate any Simulink model containing Simscape™ Electrical™ Specialized Power Systems blocks. It stores the equivalent Simulink circuit that represents the state-space equations of the model.

6. Scope

The scope shows the output of the model.

3. OUTPUT

SoC (%)

• It is observed from above that the SoC of the battery was initially at 100% but at the end of the drive cycle it is at 95%.
• Every rise and fall in the plot corresponds to the charging and discharging of the battery.

Current (A)

• The plot shows the current profile for the given drive cycle.
• The positive current is during the acceleration of the vehicle which is when the battery is discharging.
• The negative current is during the braking of the vehicle which charges the battery.

Voltage (V)

• The plot shows the voltage profile.
• The voltage increases when the battery is being charged while braking.
• The voltage decreases due to discharge as there is a need for power while the acceleration of the vehicle.

4. LEARNING OUTCOME

We learn how to simulate generic battery model charge-discharge using UDDS data.