Project-1: Modelling an electric Car with Li-ion battery
COMPONENTS:
Major component used are as below:
- Wheel/tier
- Vehicle body
- Battery system
- Transmission Sytem
- Power Converter
- Motor Controller
Main Simulation:
The below image shows the simulink design of complete EV. By using the above mention block the design is made.The Drive cycle block is used to give input to the vehicle & accleration / deceration inputs are given.
Now let us look in details each block used in Simulation and their paramaters:
VEHICLE BODY:
Represents a two-axle vehicle body in longitudinal motion. The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. The vehicle can have the same or a different number of wheels on each axle. Optionally include pitch and suspension dynamics or additional variable mass and inertia. The vehicle does not move vertically relative to the ground.
Connection H is the mechanical translational conserving port associated with the horizontal motion of the vehicle body. The resulting traction motion developed by tires should be connected to this port. Connections V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively. Wheel forces are considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively. If variable mass is modeled, the physical signal input ports CG and M are exposed. CG accepts a two- element vector representing the x and y distance offsets from vehicle CG to additional load mass CG. M represents the additional mass. If both variable mass and pitch dynamics are included, the physical signal port J accepts the inertia of the additional mass about its own CG.
The parameters selected are as below:
TIRE:
Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road Interaction (Magic Formula) and Simscape Foundation Library Wheel and Axle blocks. Optionally, the effects of tire inertia, stiffness, and damping can be included.
Connection A is the mechanical rotational conserving port for the wheel axle. Connection H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Connection N is a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports the tire slip. Optionally expose physical signal port M by setting Parameterize by to Physical signal Magic Formula coefficients. Physical signal port M accepts a four element vector corresponding to the B, C, D, and E Magic Formula coefficients.
The parameters selected are as below:
SIMPLE GEAR:
Represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in this block. You can optionally include gear meshing and viscous bearing losses.
Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by right-clicking on the block and selecting Simscape block choices to switch between variants.
VEHICLE BODY SUBSYSTEM:
By using all above blocks a susbsytem is created. All the component are connected to their respective terminal and whole system is created as a subsytem of EV which is as below.
STATE OF CHARGE:
The below system shows the calcultion of SOC:
The blocks used are:
- Integrator:Continuous-time integration of the input signal.
- Gain:Element-wise gain (y = K.*u) or matrix gain (y = K*u or y = u*K).
- Add:
Add or subtract inputs. Specify one of the following:
- a) character vector containing + or - for each input port, | for spacer between ports (e.g. ++|-|++)
- b) scalar, >= 1, specifies the number of input ports to be summed.
When there is only one input port, add or subtract elements over all dimensions or one specified dimension
- Constant: To take refrence as battery 100% charge
140Ah And 3600 sec.
Futher this block output is connected to the scope and the SOC is observed.
MOTOR CONTROLLER SUBSYSTEM:
The major blocks used in the subsystem are as below:
- DC motor
- Controlled PWM Voltage.
- H-Bridge
Now let us look at each block in details:
DC MOTOR:
This block represents the electrical and torque characteristics of a DC motor.
The block assumes that no electromagnetic energy is lost, and hence the back-emf and torque constants have the same numerical value when in SI units. Motor parameters can either be specified directly, or derived from no-load speed and stall torque. If no information is available on armature inductance, this parameter can be set to some small non-zero value.
When a positive current flows from the electrical + to - ports, a positive torque acts from the mechanical C to R ports. Motor torque direction can be changed by altering the sign of the back-emf or torque constants.
The parameters are kept as below:
The motors used in EV are huge hence 50KW is selected with Rated speed of 5000 rpm.
The DC motor is connected to Mechanical Ref:
This block represents a mechanical rotational reference point, that is, a frame or a ground. Use it to connect mechanical rotational ports that are rigidly affixed to the frame (ground).
H-BRIDGE:
This block represents an H-bridge motor drive. The block can be driven by the Controlled PWM Voltage block in PWM or Averaged mode. In PWM mode, the motor is powered if the PWM port voltage is above the Enable threshold voltage. In Averaged mode, the PWM port voltage divided by the PWM signal amplitude parameter defines the ratio of the on-time to the PWM period. Using this ratio and assumptions about the load, the block applies an average voltage to the load that achieves the correct average load current. The Simulation mode parameter value must be the same for the Controlled PWM Voltage and H-Bridge blocks.
If the REV port voltage is greater than the Reverse threshold voltage, then the output voltage polarity is reversed. If the BRK port voltage is greater than the Braking threshold voltage, then the output terminals are short circuited via one bridge arm in series with the parallel combination of a second bridge arm and a freewheeling diode. Voltages at ports PWM, REV and BRK are defined relative to the REF port.
If exposing the power supply connections, the block only supports PWM mode.
The Simulation mode is kept averaged for faster simulation & the regenerative braking is enabled.
CONTROLLED PWM VOLTAGE:
This block creates a Pulse-Width Modulated (PWM) voltage across the PWM and REF ports. The output voltage is zero when the pulse is low, and is equal to the Output voltage amplitude parameter when high. Duty cycle is set by the input value. Right-click the block and select Simscape->Block choices to switch between electrical +ref/-ref ports and PS input u to specify the input value.At time zero, the pulse is initialized as high unless the duty cycle is set to zero or the Pulse delay time is greater than zero.The Simulation mode can be set to PWM or Averaged. In PWM mode, the output is a PWM signal. In Averaged mode, the output is constant with value equal to the averaged PWM signal.
CONTROLLED VOLTAGE SOURCE:
The block 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.
CURRENT CALCULATION:
BATTERY :
This block models a battery. If you select Infinite for the Battery charge capacity parameter, the block models the battery as a series internal resistance and a constant voltage source. If you select Finite for the Battery charge capacity parameter, the block models the battery as a series internal resistance plus a charge-dependent voltage source defined by:
V = Vnom*SOC/(1-beta*(1-SOC))
where SOC is the state of charge and Vnom is the nominal voltage. Coefficient beta is calculated to satisfy a user-defined data point [AH1,V1].
CURRENT SENSOR:
The block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current.
Connections + and - are conserving electrical ports through which the sensor is inserted into the circuit. Connection I is a physical signal port that outputs current value.
DRIVER:
A parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on reference and feedback velocities.
Use the external actions to input signals that can disable, hold, or override the closed-loop commands determined by the block. The block uses this priority for the input commands: disable, hold, override.
DRIVE CYCLE BLOCK:
Generates a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed. You can import drive cycles from:
- Predefined sources
- Workspace variables, including arrays and time series objects
- mat, xls, xlsx, or txt files
Use the fault tracking parameters to identify drive cycle faults within specified speed and time tolerances.
RESULTS:
PID PARAMETER ARE KEPT TO DEFAULTS WE GOT BELOW RESULTS:
From these results, we can see that the vehicle only begins its acceleration at t = 3.4 seconds as opposed to the commanded t = 8 seconds from the drive cycle. At t = 4 seconds, the vehicle speed has increased to 0.2 m/s whereas the commanded speed from the drive cycle is 5 m/s at the same time period. By t = 5 seconds, the vehicle is meant to start its After t = 5 seconds, the vehicle's acceleration appears to be linear and the vehicle speed reaches its peak value of 3.1 m/s at t=9 seconds. Immediately after, the vehicle begins deceleration and the vehicle speed drops to 3 m/s at t = 10 seconds.
THE PID VALUES ARE AS BELOW:
Ki=650
Kp=150
Kd=0
From these results, we can see that the vehicle only begins its acceleration at t = 3.4 seconds as opposed to the commanded t = 3 seconds from the drive cycle. At t = 4 seconds, the vehicle speed has increased to 0.2 m/s whereas the commanded speed from the drive cycle is 5 m/s at the same time period. By t = 5 seconds, the vehicle is meant to start its deceleration back to rest, but the vehicle is still in its acceleration phase as the speed increases to 0.8 m/s at the same time period. After t = 5 seconds, the vehicle's acceleration appears to be linear and the vehicle speed reaches its peak value of 5.5 m/s at t=20 seconds. Immediately after, the vehicle begins deceleration and the vehicle speed drops to 5 m/s at t = 25 seconds.
THE PID VALUES ARE AS BELOW:
Ki= 100
Kp=850
Kd=0
From these results, we can see that the vehicle only begins its acceleration at t = 3.4 seconds and then it is rising expotentinaly.
hence this type of values are not suitable.
CONCLUSION: