Ryokan of Murata Manufacturing Co., Ltd. has developed a resonant-mode wireless power supply system using switching technology. The characteristic of this mode is that the overall power efficiency of the system is high, which has a great influence on the transmission efficiency between the resonant components of the coil and the like for the wireless power supply system. Let the system developers introduce the principle of the DC resonance method. We developed the Wireless Power Transfer (WPT) called "DC Resonance Mode" (Figure 1). Compared with the WPT system that used the magnetic resonance method in the past, it is characterized by a simpler system structure, and the overall power efficiency of the system including the power source is high. Moreover, even if the transmission distance changes, or when the power transmission object becomes a large load such as a large change, the power transmission efficiency is not greatly reduced, which is one of the characteristics. Figure 1: DC power supply and power supply coil form a "resonance field" This demonstration of the "DC resonance mode" wireless power supply system demonstration. From the DC power source - the solar cell, the DC voltage is converted into a rectangular wave by a power supply module having a switching circuit, and a near-field "resonance field" of the electromagnetic field is generated by the power supply coil. Compared with the various methods of the original WPT, the DC resonance mode is expected to achieve the following characteristics (Fig. 2). First of all, compared with the magnetic resonance method, the overall power efficiency of the system can be improved, and the system configuration becomes very simple. Secondly, compared with the electromagnetic induction method, the positional freedom of the power receiving device is high, and the weight of the power receiving device is provided. Also become lighter. Compared with the electric field coupling method, it is more advantageous to extend the transmission distance. Compared with the radio wave method, the transmission power is 1 to 4). Figure 2: DC resonance mode is simple in structure and can achieve high power efficiency This figure shows the requirements (a) required for the WPT system, and several topics of the WPT implementation and the advantages of the DC resonance method (b). The drive method of the resonator is different The following is a detailed description of the main differences between the DC resonance method and the original magnetic resonance method. The following points are common. (1) DC resonance mode The near field of the electromagnetic field - "resonance field" is directly formed by the DC power source and the LC resonator. (2) As a result of (1), the system configuration is simple, and the size and weight can be reduced. (3) As a result of (1), the conversion efficiency of converting power source power into a resonance field is high. (1) The DC power supply is used because most of the power that we can use is DC power, so the availability is high. Even AC100V commercial AC power supplies such as 50Hz and 60Hz supplied from outlets in the home are mostly rectified and filtered by AC-DC converters in AC adapters or home appliances, and then used as DC power supplies. Needless to say, dry batteries and rechargeable batteries are also DC power supplies. Moreover, as described in (2), the circuit configuration of the system can be greatly simplified by using a direct current. At present, the power supply device of the commonly used magnetic resonance type WPT system is composed of a commercial AC power source, a power supply device for insulation, an oscillation amplification device that outputs a high-frequency current, an integration device, and a power supply device (Fig. 3). The power receiving device is composed of a power receiving device, a rectifying and smoothing circuit, and a DC-DC converter for integrating with a load. If the load is a rechargeable battery or the like, a charge and discharge circuit or the like is also required. Figure 3: Existing WPT system with large losses This figure shows the composition and power efficiency of a typical WPT system. Since the power is transmitted from the power source to the load via several functional circuits, the overall efficiency of the system becomes very low. Such a large number of power conversion devices are fatal to improve power utilization efficiency. For example, if the transmission efficiency of the power receiving device is 80% and the power efficiency of the five power transmission devices is also 80%, the power efficiency of the entire power supply system is calculated to be about 26% according to (0.8)6=0.262. Even if the efficiency of each device is 85%, the overall power efficiency is only about 38% based on (0.85)6=0.377. The overall system is very inefficient 4). The DC resonant system is very simple to construct and can be connected directly to the DC voltage supply and switching circuit (Figure 4). Thereby, the power transmission loss becomes very small, and as described in (3), the conversion efficiency of converting the power source electric power into the resonance field energy is higher than that of the original mode. Moreover, since the conversion efficiency from the power source power to the resonance field is high, it is also easy to be used for new wireless power transmission using a large number of resonance devices (Fig. 1). Figure 4: The difference from the original method is the way of power transmission. The DC resonance mode WPT(a) is different from the original magnetic resonance method WPT(b). The difference lies in the driving method of the power supply and the resonator.
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February 05, 2020