Wireless charging for electric vehicles is an emerging technology, and one that humanity has long dreamed of. It allows us to completely revolutionize the way electric vehicles are charged. With it, your car can be fully charged automatically without any cables or outlets.
introduce
This is a very convenient process; wireless charging systems are based on the principle of electromagnetic induction. Charging circuits, typically located under the floor, are connected to the power grid. If a vehicle designed for this type of charging is positioned above the circuit, a magnetic field is created, inducing a current in the car's electrical system to charge its battery. With this, cables are eliminated, making the process simpler and safer.
The risks of overheating and battery damage are also minimized. However, this power transfer method is not ideally efficient unless the coils are very close and properly aligned. Magnetic resonance can be implemented to improve efficiency when the distance between the source and receiver is greater and the alignment is less than ideal. Most wireless systems today are intelligent enough to detect the battery's state and automatically stop charging when it is not needed. Furthermore, maintenance is minimized due to the absence of easily worn mechanical parts. Technology is making wireless charging systems increasingly efficient, even at a high cost. However, not all electric vehicles are compatible with this charging system, and the power used in the circuit is even lower than that of cable-based charging systems.
Charging can be performed in a stationary mode, where the vehicle is stationary on the charging rack or while in motion. In a second mode, the charging circuit is located on the road or near traffic lights, using special asphalt that can sense current. In the future, there may be dedicated lanes specifically for charging electric vehicles during normal traffic.
Wireless charging details
Wireless car charging is a popular method that eliminates the need for physical contact between the car and the power source. This method utilizes electromagnetic induction and magnetic resonance to induce current through a magnetic field. The distance between the car and the charging system is crucial; typically, a distance of just a few centimeters is sufficient to significantly reduce the amount of energy transferred.
Therefore, vehicle parking must be extremely precise, and the two coils (Tx and Rx) must be placed within a very short distance. Energy is transferred by inducing an electric current through the generation of a magnetic field. In practice, there are two coils, one located beneath the vehicle and the other in a special container on the ground. If the two coils are very close to each other, a current is induced from the first coil to the second, allowing the car battery to be charged just like a conventional cable connection system. Wireless charging systems are conceptually very simple but deserve widespread attention because they are poised to become a future method for restoring energy from batteries and supercapacitors.
The system typically consists of two parts: a transmitter and a receiver (see the overall diagram in Figure 1). The transmitter converts the input voltage into magnetic flux, and the receiver converts the magnetic flux into a DC output voltage. To induce a current between the first and second inductors, an AC signal is required; its shape is irrelevant, but a sinusoidal signal is most effective. Transferring energy without a physical electrical connection requires the presence of switching circuitry, typically at a high frequency. Therefore, wireless charging systems usually emit electromagnetic fields nearby.
When two circuits are close enough, an identification process is established between them. The transmitter sends a signal from its coil, which is received by the receiving coil, thus allowing a magnetic field to pass through both coils, even though they are not physically connected. A small amount of energy is lost in this process, which is perfectly normal. The receiving coil collects the magnetic field and generates alternating current (AC), which is then rectified by a power supply and sent to the battery to be charged, this time as direct current (DC). To increase the magnetic field, the current in the transmitting circuit or the size of the coils can be increased, or the distance between them can be reduced.
Wireless charging is a highly valuable technology, and its value is enhanced when combined with lithium batteries. While current technology is less efficient and slower than traditional charging, companies are making significant progress every day. To maximize the energy transferred, the coil size must be very large, inevitably resulting in unnecessary bulk. Therefore, optimal alignment between the two inductors is crucial to maximize current transfer. State-of-the-art systems offer visual and audible monitoring, alerting users to the alignment process. Furthermore, wireless charging is brand-independent, allowing devices from different brands to charge without issues. Additionally, due to the absence of direct physical contact, all electrical and electronic components are waterproof and sealed, eliminating contact oxidation problems.
Basic working principle of circuit
The left side constitutes the transmitter, and the right side constitutes the receiver. The transmitter generates an AC voltage, which is boosted by a power device and passed through a transmission inductor. Nearby is a receiving inductor that carries the same transmitted signal but with minimal loss. The signal, after rectification and leveling, can be used for battery charging. This inductor solution essentially represents a virtual transformer because it has the same characteristics as a traditional transformer, but typically does not increase or decrease voltage; it only transmits energy wirelessly.
The principle applied is the mutual inductance between two inductors placed very close to each other. The frequency of the alternating current signal is typically quite high to generate the electromagnetic field required for signal transmission. Understandably, the transmitter needs an oscillator with its frequency and voltage properly calibrated.
It is worth noting the circuit's response to different coupling coefficients. Typically, the car is not precisely at the optimal charging point, so the signal received by the receiver is not at its maximum. As mentioned earlier, even small changes in the vehicle's position relative to the charging pad can significantly alter the charging voltage level. The graph in Figure 3 shows the rectified voltage level of the receiver, involving the coupling coefficients of the two coils, which change depending on the vehicle's position relative to the receiver. A small amount of ripple is intentionally added to the graph to emphasize that the current originates from alternating current and is then rectified.
It requires a lot of power.
Wireless charging for electric vehicles requires high-power operation. For example, there are electric bus charging stations with a power of approximately 200 kW that can charge a journey of hundreds of kilometers in minutes. This research aims to develop new technologies aimed at enabling the circulation of zero-emission vehicles. Wireless charging trials have been very successful for some time, as it eliminates the need for cables and requires no physical contact between the charging infrastructure and the vehicle (Figure 4). When a vehicle is positioned above the charging pad, the transmitter detects its presence and begins to induce a current using a magnetic field.
The receiving plate begins capturing induced current and uses electrical energy to charge the battery. The driver simply places the car on the charging plate, and the charging process begins automatically. Depending on the system used, the power involved can be very high, ranging from tens to hundreds of kilowatts. An important factor to consider is that wireless charging is not currently a complete replacement for traditional wired charging of electric vehicles, but rather a supplementary method for shorter, more frequent charging during journeys. For larger-scale charging, vehicles can be charged using home wall-mounted charging boxes or electric charging stations. According to recent research, wireless power transfer programs can currently automatically inductively charge electric vehicles very efficiently, reaching up to approximately 93%.
in conclusion
Significant progress has been made in the field of wireless charging for vehicles, and wireless charging will see wider application on roads in the coming years. As mentioned earlier, the most crucial factor is the correct positioning of the TX and RX terminals to effectively capture the required energy. The battery charger can then operate autonomously in terms of management, control, and automation. A major benefit of short charging times is extended battery life, as shorter charging cycles protect the battery and extend its average lifespan.
