Continuous power regulation in wireless power transfer system with a new magnetic field superposition transmitter
Graphical abstract
Introduction
WPT refers to the technology that uses electromagnetic fields or electromagnetic waves to transfer energy. It frees the transmission of energy from the tangible medium, and effectively makes up for the defects of line friction, aging leakage, and contact spark in the traditional charging mode. It is a safe and convenient mode to transfer energy. With the increasing development of WPT, wireless power transmission system is being applied to charge electric vehicles [1], [2], [3], [4], [5], [6], [7], implantable medical devices [8], [9], [10], [11], [12], [13], intelligent greenhouse [14], smart robots [15], smart sensors [16], [17] and so on. In this way, how to adjust the power of transmission effectively in the concrete circuit is significant.
For small and medium power appliances, wireless power transmission is desirable [18]. It can eliminate the use of cables. On the other hand, it also reduces the risk of electric shock hazards. Because of this, many scholars have carried out research on that. For example, the quartz clock is used as a receiver to supply power of the wireless sensor. But this technology is only applicable to the wireless intelligent sensors with low power consumption. It cannot be applied to small and medium power appliances such as fans and lights [19]. Jeong S ’s team used flexible printed circuit board coils as transmitter and receiver to design a smart watch with wireless power supply. However, as the system is a DC-DC energy conversion device, it is also not suitable for AC loads which are more general in the life [20].
In summary, there are three main ways to regulate power in WPT: buck amplitude modulation method, frequency modulation method, and phase-shifting method. Buck amplitude modulation method refers to change the output voltage of the inverter by DC-DC circuit, thus to regulate the output power of the wireless energy transfer system. This method works in the soft switching state and reduce switching loss by separating the power regulating link from the inverter. However, due to the addition of power regulation link, the system cost is increased. Frequency modulation method [21] means that the output power of the inverter is controlled by adjusting the switching frequency of the inverter, thereby to regulate the output power of the system. Compared with the Buck amplitude modulation method, this method does not need the power regulation link. Nevertheless, because the switching frequency of the inverter could deviate the actual frequency from the resonant frequency, the power transmission efficiency will be reduced. The phase shifting method refers to take the superimposed waveform as the drive plus of the inverter. It changes the phase of the driving pulse to control the output voltage of the inverter, so that to control the load power of the basic coils. The phase-shifting method is simple, and the transfer efficiency is high.
The new system proposed in this paper which is divided a large coil in a conventional transmitter into two small transmitting coils, while the total coil volume is constant. The phase difference of the current in the two transmitting coils is controlled. Based on the superposition principle of magnetic field, different power is provided to the receiver to meet the requirements of different loads. This system can adjust the output power smoothly and continuously, and has the advantages such as clear thinking, simple structure, and convenient operation. It also provides a new idea for wireless energy transmission technology in power regulation.
This paper consists of 5 parts. The first part is instruction. It introduces the latest WPT applications and compares three kinds of power regulations in WPT. Then, it proposes the continuous wireless power transfer regulation system which is equipped with a new magnetic field superposition transmitter. The second part analyzes the principle of power regulation and shows the schematic diagram of the system. In the third part, the mathematical relation and magnetic field are simulated by software. The fourth part builds an experimental platform to verify the designed power regulation system. The fifth part summarizes the results of simulation, experiment and draws a conclusion. It also analyzes the existing limitations of the system and looks forward to the next work.
Section snippets
Power regulation principle
The continuous power regulation WPT system has a new type transmitter to regulate the power. A large coil in a conventional transmitter is divided into two small transmitting coils, while the total coil volume is constant. The transmission power of WPT is regulated by the superposition of the magnetic field produced by the two coils. The superposition of the magnetic field is regulated by the phase difference of the current between the two coils. The current in a coil is fixed which is called
Mathcad simulation
Import the principle formulas of the system into Mathcad software for simplification.
The input frequency of the basic transmitter coil and the phase-shifting transmitter coil is 30 kHz. The amplitude is 1 A. The phase difference ranges from 0° to 180°. When phase difference equals 0°, the input current in the basic transmitting coil and phase-shifting transmitting coil are in the same phase. At this moment, the amplitude of induced voltage and the transmission power of WPT is maximal. As the
Experimental verification
To verify the continuous power regulation WPT system can continuously regulate the transmission power by adjusting the superposition of the magnetic field, an experimental device is set up which is shown in Fig. 5. The experimental device is divided into three parts: the phase-shifting power generation device, the new magnetic field superposition transceiver, and the load circuit. The phase-shifting generator uses the classical inverter principle to generate alternating current with phase
Conclusion
In this work, both theoretical derivation and simulation verification can conclude that the proposed new transmitter can regulate the transmission power in a certain range by adjusting the phase difference between the two transmitter coils. In addition, the experimental results also show the cosine relationship between the phase difference of the input currents and the transmission power. When the phase difference is 0°, the transmission power reaches the maximum value. With the increase of
Declaration of Competing Interest
None.
Jin Xu received his PhD degrees in electrical engineering from South East University, Nanjing, China, in 2007. Research interests include motor control, Wireless Power Transfer, High-frequency switching mode power supply, Control of Buck-Boost DC-DC Converter, soft-switching inverter, highe fficiency power electronics conversions for high power, and energy applications
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Jin Xu received his PhD degrees in electrical engineering from South East University, Nanjing, China, in 2007. Research interests include motor control, Wireless Power Transfer, High-frequency switching mode power supply, Control of Buck-Boost DC-DC Converter, soft-switching inverter, highe fficiency power electronics conversions for high power, and energy applications
Qiyu Tian was born in Zaozhuang, China, in 1999. She will receive the B.S. degree in agricultural electrical engineering from Nanjing Agricultural University, Nanjing, China, in 2021. Now she has obtained the offer of direct doctoral study in Zhejiang University, Hangzhou, China. Her current research interests include wireless power transfer and digital control techniques.
This paper is for regular issues of CAEE. Reviews processed and recommended for publication to the Editor-in-Chief by Associate Editor Dr. H. Vahdat-Nejad.