The focus of this chapter is the electromagnetic interference (EMI) and the electromagnetic compatibility (EMC) that the wireless power transfer (WPT) systems reveal as problems. The wireless power transfer (WPT) was introduced by Nikola Tesla more than one hundred years ago, and only recently it attracted the attention of specialists, due to the improved technical means. The WPT technology now has many applications, especially for charging of various electronic devices (i.e., mobile phones, laptops, implants, and home appliances), informatics, and electronics equipment. The high-power equipment and installations (e.g., intelligent machining systems, robots, forklift trucks, and electric cars) are also getting wireless. Moreover, much attention has been focused on the electric transportation system for improving the safe and convenient charging of electric vehicle (EV) batteries.
Top1. Introduction
The focus of this chapter is the electromagnetic interference (EMI) and the electromagnetic compatibility (EMC) that the Wireless Power Transfer (WPT) systems reveal as problems. The wireless power transfer was introduced by Nikola Tesla more than one hundred years ago, and one decade ago was attracted the attention of specialists, due to the improved technical means. The WPT technology has now many applications, especially for charging of various electronic devices, i.e., mobile phones, laptops, implants and home appliances, informatics and electronics equipment (Lu, Wang, Niyato, Kim, & Han, 2016). The high-power equipment and installations, e.g. intelligent machining systems, robots, forklift trucks and electric cars are also getting wireless. Moreover, much attention has been focused on the electric transportation system for improving the safe and convenient charging of the electric vehicles (EV) batteries (Boys, Covic, & Green, 2002; Li, & Mi, 2015; Imura, Okabe, & Hori, 2009; Baikova, Valtchev, Melicio, & Pires, 2016a).
Fundamentally, there are two different methods of WPT, defined by physical phenomena of the electromagnetic fields (EMF) propagation: near field and far field. The near field methods are based on capacitive coupling, inductive coupling and magnetic resonance and are used for wireless power transmission over relatively short distances, usually much shorter than 1 m, exceptionally reaching up to a few meters. The far field methods allow greater distances power transfer and usually involve electromagnetic (EM) energy in a form of radiation, including microwave, lasers and radio wave transmissions (Brown, 1984).
Today the inductive coupling is considered a functional and mature technology between the near field methods. The advantages of inductive coupling are the simple design, convenient operation, high efficiency in close distance (typically less than a coil diameter) and high safety (Lu et al., 2016). Despite the above advantages, there are drawbacks, namely a limited transmission range, a low yield and a requirement for accurate alignment between the transmitter and receiver coils (Boys et al., 2002; Ahn et al., 2011). The applications based on capacitive coupling are applicable in the smart card equipment or in small robots (Kline, Izyumin, Boser, & Sanders, 2011), but they are limited by the low transmitted power and the short distance. Among the existent near field methods, the best result was achieved by the group of Massachusetts Institute of Technology that uses magnetic resonance enabling longer distance efficient WPT transmission (Imura et al., 2009, Kurs et al., 2007).
The magnetic resonance technique is recognized to be the most suitable for wireless EV battery charging (Li et al., 2015; Imura et al., 2009; Sample, Meyer, & Smith, 2009) since it has more positional freedom and does not need an accurate parking position of the vehicle as in the case of generic, non-resonant inductive coupling. With the progress of magnetic resonance technology, the transmitted power and the distance between the source and the load is expected to increase. The performance of these magnetic resonance systems requires a bi-directional exchange of information between the transmitter and the receiver, i.e., the required power, the operation frequency, the vehicle identification, the payment information. The EMF, through which the energy is transferred between the transmitter coil and the receiver coil, is a high-frequency field and induces EMI into the other devices. The transmitted power for wireless EV charging is in the order from several to tens kW. So, the high-intensity EMF can have an adverse impact on other electrical and electronic equipment and on the communication channel between the transmitter and receiver. Moreover, the EMF produced by the WPT system may induce high voltages and currents in the human body (Christ et al., 2013). The stray EMF emitted by WPT systems it's far to be uniform and could exceed the reference levels set defined by international guidelines (Pinto, Lopresto, & Genovese, 2017).