Non-contact electric vehicle charging method analysis

The value of the resonant frequency changes as the distance between the power transmitting and receiving units changes. When the transmission distance changes, the transmission efficiency will also decrease as quickly as the electromagnetic induction. To this end, the resonant frequency can be adjusted by the control circuit so that the circuits of the two units resonate, that is, "resonate". Therefore, this magnetic resonance state is also called "magnetic resonance".

By changing the frequency of transmission and reception under the control loop, the power transmission distance can be increased to several meters, and the resistance of the two-unit circuit can be minimized to improve the transmission efficiency.

Of course, the transmission efficiency is also related to the diameter of the transmitting and receiving electrical units, and the larger the transmission area, the higher the transmission efficiency. The current transmission distance can reach about 400mm, and the transmission efficiency can reach 95%.

Third, the microwave mode

The power is transmitted using a 2.45 GHz radio wave generating device, and the transmitting device is basically the same as the "magnetron" used in the microwave oven. The transmitted microwave is also an alternating current wave, which can be received by the antenna in different directions, converted into a direct current by a rectifying circuit to charge the car battery, and can realize long-distance transmission from one point to multiple points.

Microwave mode can transmit long distances from one point to multiple points

In order to prevent microwave leakage during charging, the charging part is provided with a metal shielding device. In use, effective shielding between power transmission and reception prevents microwave leakage.

The main problem currently exists is that the efficiency of the magnetron when generating microwaves is too low, causing a lot of power to become thermal energy to be consumed in vain.

Application of non-contact charging device in Japan

In July 2009, Nissan and Showa Flight Company disclosed an electromagnetic induction type non-contact charging system with a transmission distance of about 100 mm and a transmission efficiency of 90%.

However, when there is a deviation in the parking position and a large error occurs between the transmitting and receiving disks, the power transmission efficiency is seriously affected. At present, the horizontal and vertical deviations of parking are being worked in the range of 200 to 300 mm, and it is also ensured that it has a transmission efficiency of more than 90%.

a) Charging working state, the upper part is the car part, the lower part is the transmitting part

b) Vehicle receiving device assembly

Electromagnetic induction type non-contact charging device developed by Showa Flight Machine Co., Ltd.

In addition, the above two companies have also studied the adverse effects of animals and metal fragments between transmission and reception. Because such foreign matter can cause eddy currents between the two, which causes heat generation and affects transmission efficiency.

Nagano Japan Wireless Co., Ltd. announced the development of a magnetic resonance-based charging system in August 2009. Compared with the electromagnetic induction method, the magnetic resonance method has the advantages of long transmission distance and low parking error requirement. It is possible to ensure 90% transmission efficiency over a transmission distance of 600 mm. However, the current transmission power is still relatively small (about 1 kW or so), and it is planned to enter the market from the scope of use of forklifts. With the maturity of technology and the increase of transmission power, it is expected to enter the field of electric vehicle charging.

The microwave non-contact charging system developed by Mitsubishi Heavy Industries Co., Ltd. uses a group of 48 silicon rectifier diodes as receiving antennas. Each silicon rectifier diode can generate 20V voltage and a certain DC power, which can raise the voltage to the required index for charging and A power output of 1 kW can be achieved. The advantage is that the cost is low, and the whole set of costs is about RMB 20,000. The disadvantage is that the transmission efficiency is low, and the current transmission efficiency is only 38%. In this regard, Mitsubishi Heavy Industries believes that: “Although it is not suitable for fast charging, as a nighttime valley charging, the electricity cost is only 10% to 20% of the traditional fuel cost. If the excessively large magnetron is used for domestic water heating, then comprehensive The efficiency can reach 70%. In addition, there is also a microwave leakage prevention device in terms of safety, which does not affect the electronic devices on the vehicle and the pacemakers on the surrounding personnel.

Once the non-contact charging method was introduced, it has received widespread attention from all over the world, and it is also worth learning and learning from domestic counterparts. Compared with the construction investment of charging station and charging pile, the cost is lower, and the operation and waiting time required for wiring are eliminated, and the absolute advantages such as flexible arrangement, convenient use, safety and reliability are provided.