(C- Wireless Charging Electric Car) 2018TI Cup Wireless Charging Car

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(C- Wireless Charging Electric Car) 2018TI Cup Wireless Charging Car [Copy link]

I'll just make a fool of myself here~ Due to my limited level and resources at hand, and my poor preparation, I only completed the requirements of the topic and realized the charging and self-starting functions of the wireless car. This work is to design and make an electric car that can be charged wirelessly. After the charging device senses the car, it will automatically charge the car for one minute. After the charging is completed, the car will move forward horizontally and straight until the energy is exhausted. This device uses high-frequency electromagnetic induction to generate 137KHz high-frequency electromagnetic, and uses a coil with a certain turns ratio as a receiver to charge the supercapacitor. After charging is completed, the circuit short circuit caused by the conduction of the thyristor is used to connect the car motor to the circuit, and the supercapacitor discharges to drive the car motor, so that the car moves.

The following is the original report:

Wireless Charging Electric Car (Topic C)

Abstract: Wireless charging technology has been deeply studied and applied in the field of electronics. Although it has not been widely popularized, it has achieved good results in the field of consumer electronics. This work is to design and make an electric car that can be charged wirelessly. After the charging device senses the car, it will automatically charge the car for one minute. After the charging is completed, the car will move forward horizontally and straight until the energy is exhausted. This device uses high-frequency electromagnetic induction to generate 137KHz high-frequency electromagnetic, and uses a coil with a certain turns ratio as a receiver to charge the supercapacitor. After charging is completed, the circuit short-circuit caused by the conduction of the thyristor is used to connect the car motor to the circuit, and the supercapacitor discharges to drive the car motor, thereby making the car move.

Keywords: Copper coil charging supercapacitor

Overall design plan

(I) Design requirements

The requirement of this question is to design and make a wireless charging electric car, including a set of wireless charging devices. The mechanical part of the electric car can be modified from a finished four-wheel toy car. The overall size shall not exceed 30cm, and the height and weight are not limited.

1.1 Basic requirements

(1) Make a wireless charging device with a transmitter coil placed on the road surface. The transmitter is powered by a DC regulated power supply with automatic switching of constant current and constant voltage modes. The supply voltage is 5V and the supply current is not more than 1A. The wireless charging receiver is installed on the chassis of the car. Each charging time is limited to 1 minute.

(2) Make a wireless charging electric vehicle. The electric vehicle uses a supercapacitor (farad capacitor) of appropriate capacity to store energy and supplies power to the electric vehicle through DC-DC conversion. Batteries and other energy storage power supply devices shall not be used on the vehicle.

(3) After charging for 1 minute, when the electric vehicle detects that the wireless charging transmitter stops charging, it will immediately start automatically and drive forward in a straight horizontal direction until the energy is exhausted, and the driving distance shall not be less than 1m.

1.2 Playing part

After charging for 1 minute, the electric vehicle will climb the slope in a straight line along the inclined wood board road surface. The road surface length is no more than 1m, and the slope inclination angle θ is self-determined. Comprehensive multi-factor design makes the electric vehicle climb to the maximum height h=lsinθ after each 1 minute of charging. l is the distance the car travels in a straight line.

(II) Design ideas

2.1 Design ideas:

This question requires us to make a wireless charging device and an electric car. Analyzing the question, we know that the biggest difficulty in the question lies in the design and production of the wireless charging device. After consulting the information and a series of discussions, we decided to use a copper coil with a certain turns ratio to connect to the power supply to generate a magnetic field. Through the principle of electromagnetic induction, the induced electromotive force generated by the change of the magnetic field is used to charge the supercapacitor and store electrical energy, so that the car can move forward horizontally with the electrical energy stored in the supercapacitor.

2.2 Design flow chart:

(III) Scheme demonstration and comparison

(1) Selection of small car

Solution 1: Use an assembled electric car,

The electric car purchased online has a 3V/1A motor and a power of 3W. After assembly, the car is 4.6cm high, 21.9cm long, 18cm wide and weighs 1800g. The tires are heavy and made of rubber, which has greater friction. After power is turned on, it can move along the slope, but the slope speed is relatively slow due to the weight of the car body;

Solution 2: Use a four-wheel drive electric car

The four-wheel drive electric car toy bought in the toy store outside has a motor of 3V/0.89A and a power of 2.67W. The car is 4.5cm high, 16.7cm long, 10.5cm wide and weighs 600g. The tires are lightweight and made of plastic, but can be covered with rubber. The friction is average. After power is turned on, it can move along the slope at a fast speed.

Solution 3: Use a homemade car

The car body is built with a relatively hard circuit board, and the tires are the tires of solution 1. The car is 7.1mm high, 17.5cm long, and 11.6cm wide. The car is light in weight and has greater tire friction. When moving up the slope, it is easier than the first solution.

(2) Choice of supercapacitor

According to the requirements of the question: a 5V, 1A power supply is required.

The power utilization rate is about 60%, then I'=0.6I, from the formula U=Q/C, we get: Q=I'*t=0.6A*60s=36C, at this time the capacitor C=36/5=7F; assuming that after the car moves, the load consumes 1V voltage, U'=5-1=4V, and consumes Q'=U'*(I-I')=1.6C, at this time ΔU=1.6/7=0.22V, that is, the car will consume 0.22V voltage after moving, and the remaining U''=4-0.22=3.78V. The car movement voltage is generally between 3~6V, which meets the voltage required for the car movement.

From the above calculation formula, we can get: the specification of the supercapacitor must reach 7F. You can buy two 5.5V/4F supercapacitors on Taobao.

(3) Disconnecting wireless charging

Solution 1: Use microcontroller to cut off power:

The microcontroller is easy to operate, and the program to control the time period is not difficult. When the microcontroller determines that the time is up, the car will move forward, so that the charging of the car can be stopped. The car uses the energy stored in the supercapacitor to move forward until the energy is exhausted. However, the microcontroller also needs power to operate, which consumes the energy of the supercapacitor, which makes the car's available energy insufficient and the forward distance reduced; and the energy provided by the supercapacitor cannot make the microcontroller operate normally.

Scheme 2: Using thyristors

Use the conduction characteristics of thyristors to control. When the voltage stored in the supercapacitor reaches the conduction voltage of the thyristor, the thyristor opens, causing a short circuit in the circuit, thereby connecting the motor to the circuit, starting the motor, and moving the car forward.

(4) Decision of the scheme

We initially planned to adopt the first solution. This car is more convenient to use, but the speed of this car on flat ground can only reach 0.1m/s. The car is heavy and the tire friction is also large. If you want to drive the car, you need to drive four motors. Each motor is 3V/1A. Four motors require 4*3*1=12W of power, otherwise it will not be able to drive, and the power supply can only provide 5*1*60=300J of electricity. The power of the motor required is large, and it is difficult to achieve the motion conditions in a short time. It is difficult to meet the requirements of the question;

The second solution does not require us to make it. The motor consumes low power and is light in weight. It only needs to provide a small amount of electricity. However, due to insufficient preparation, it was impossible to buy a suitable four-wheel drive electric car within the specified time, so we had to give up this solution.

For the third solution, we need to make the car body by ourselves. The tires are the tires of the two assembled cars in the first solution as the rear wheels, and the rear wheels provide the kinetic energy of the whole car body. In this way, the power of the motor required is 1/2 of that of the first solution, and the weight of the car body is lighter than that of the first solution, and the energy consumption of the inclined plane movement is also less.

After analyzing the topic and discussing with the team members, we finally selected the car of solution three and two 5.5V/4F supercapacitors. The single-chip microcomputer has a good control effect, but it needs another circuit board to connect to the car, which increases the weight of the car and the power consumption of the car will increase. The thyristor only needs to change the circuit, but the time control is not very strong. After comprehensive consideration, we choose thyristor to control the charging time.

(IV) Unit Circuit Design

4.1 Rectifier Circuit Design

After DC inverter, the transmitter is powered. The transmitter emits high-frequency electromagnetic waves. After receiving the signal, the wireless coil converts it into a DC power supply, providing power to the supercapacitor charge and discharge switching circuit. After rectification, the supercapacitor is charged, so that the supercapacitor stores electrical energy. After charging, the motor uses the electrical energy stored in the supercapacitor to drive the car forward.

4.2 Supercapacitor charge and discharge switching circuit

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In the process of the transmitter outputting high-frequency electromagnetic to charge the supercapacitor, due to the internal resistance of the power supply, the voltage at both ends of the power supply slowly increases. At this time, ￡1=R4*C2=0.01, ￡2=R2//R3*C2=0.005, ￡1<￡2, the thyristor U2 does not reach the trigger pulse, that is, U2 cannot be turned on, and the motor cannot rotate; after the charging is completed, the charging of C2 in the circuit cannot be stopped immediately, C2 will continue to charge, and the stored energy of C2 will be higher than C3, which will eventually lead to ￡1>￡2, reaching the thyristor triggering condition, at which time the thyristor will be turned on, the motor is connected, and the motor starts.

[font=微软雅黑,4.3 MCU Timing Circuit

4.3 MCU Timing Circuit

When the microcontroller scan button is pressed, the timing is 1 minute, and it detects whether the timing is over. When the timing is over, the relay is turned off.

(V) System Test

Because of the word limit, I can only share it here!

Mr_Dai

I have learned it. The OP can continue to describe it in the next article.