Extraordinary and exact simulation in MATLAB software for a solar electric vehicle

The electrical components and the electrical circuit design are the most important parts of the solar vehicle.The solar panels form the first part of the electrical design of the system. They are to be mounted on top of the solar vehicle where the sunlight is largely concentrated on. The solar panels are connected directly to the solar charge controller which is manufactured according to the required specifications. The solar charge controller uses its first two ports for intake of power from the solar panel which is stored in the batteries. The charge produced by the batteries to run the motor is controlled by the solar charge controller. The motor controller is connected to the solar charge controller. While the solar charge controller regulates the power with which the motor runs, the motor controls the working of the BLDC motor. The motor controller is also provided with auxiliary connections such as speed control of the motor, forward and reverse switch, Lights and horn. The connection between every two components is protected by using fuses or MCBs. Although it is not mandatory to use LED detection for every connection, it is highly recommended to use both fuses and LEDs between batteries and solar charge controller and also between BLDC motor and motor controller. The wiring of all electric components should be done properly to ensure safety and for the ease of controlling them. The copper wires are suggested for the wiring as they have one of the highest electrical conductivity rates amongst metals and have high negative coefficient of temperature, hence copper is more preferable than aluminium as our wiring material. In India wire selection is done using standard wire gauge (SWG) system. Since our max current flowing in the circuit is 40 A (considering starting current of the motor) selection of 25 area of section of the copper wire is recommended

circuit design

electrical simulation in MATLAB software

 The solar panels are designed in the Simulink with a capacity of 500W. The capacity of the solar panels can be increased or decreased by addition or subtraction of the solar panel subsystems in the control system. A constant input of 1000 and a ramp input of slope 6 are given as input to every solar panel module in the subsystem. The outputs of these subsystems are voltage (Vpv) of photo voltaic cell and power (Ppv) of photo voltaic cell. All the outputs of the single photo voltaic cell are summed up to form the desired quantity. Photo voltaic cells are constant with respect to voltage so the I-V characteristics and P-V characteristics of the photo voltaic cells are considered as the proof of proper functioning of the photo voltaic module in the sub system. Photo voltaic cell is a practical source. As every practical source has a drop due to the shunt resistance, the photo voltaic cells has a drop in both current and voltage. The results can be seen clearly considering the I-V characteristics and the P-V characteristics. The current has a drop due to the shunt resistance and the voltage has a drop due to the series resistance. These forms the I-V curve (Y axis = current and X axis = voltage) of the photo voltaic cells. Similarly once the voltage and current are known in the system, the power can be determined as the product of voltage and current through which P-V curves (Y axis = power and X axis = voltage) are obtained.

subsystem of photo voltaic module

p-v characteristics

i-v characteristics

As physical quantities like sunlight, temperature, radiation etc. cannot be shown in MATLAB software, the photo voltaic cells also cannot be shown. Only if these curves are obtained, the sub system can be used as a photo voltaic cell in Simulink (MATLAB). Different curves are obtained for different positions of sun but it is essential for us to maintain at a point where maximum power can be derived. This is achieved from the maximum power point tracking (MPPT). There are many algorithms to implement the maximum power point tracking method. The algorithm used in this report is the perturb and observation method. This is the best control strategy for the MPPT technique. To know more about the perturb and observation method refer to the material mentioned in the references. Taking the voltage and current values from the photo voltaic cell, a MPPT with desired quality can be ordered. At the same time there is no requirement of any other converter as the load itself is dc (BLDC motor). If an ac motor is used, additional converter such as an inverter should be used to drive the motor. The power from the photo voltaic cells is not sufficient to run the motor so a dc to dc converter is to be used. It is also called as boost chopper or step up chopper. It is preferable to use a bidirectional chopper as we require to both step up as well as step down. A bidirectional dc to dc chopper is used to charge the batteries. This acts as a step down chopper when charging the batteries and as a step up chopper when the batteries are discharging. If the maximum power point tracking method is used to switch on/off the chopper, we shall always be at maximum power point. In the chopper it is essential to use a MOSFET switch as this chopper works on low voltage and high frequency applications. The MOSFET switch is to be commanded on when to switch on/off as only on this command the circuit decides on voltage requirement. Finally, to control all these we require a closed loop controller. To control the dc motor, actual speed of the motor is considered. Then the reference speed is given as an external input as the speed change due to acceleration is a physical quantity which cannot be expressed in the MATLAB software. From the comparison of these two speeds a duty cycle is obtained. Another duty cycle is taken from the MPPT. The average of these two duty cycles is used to switch on/off the dc to dc converter. Any change in speed is controlled through the chopper.  The comparison of both the actual speed as well as the reference speed is done and the error is fed to a PI controller. The PI controller corrects the duty cycle. Then the carrier voltage of the control system and the reference voltage (constant of 400 in this report) are compared and the resultant is fed to the chopper. Usually only a MPPT controller or a motor controller are used in one program in which individual duty cycles are considered but in this report both MPPT controller and motor controller are being used in a single program so the average of both the duty cycles must be fed into the chopper.

The MATLAB simulation of the entire scenario explained above can be obtained by a request through comments in which your mail id can be furnished so that it can be mailed directly to the individual.