"Electric vehicles (EVs) are getting more attractive for the sake of reducing air pollutions in urban areas. Wireless power transfer (WPT), a key enabling technology, affects the acceptance of EVs in the market. For high power WPT, inductive power transfer (IPT) has been researched for decades and successfully used in several EV systems. However, higher efficiency and higher power density IPT systems are still in demand. The unique feature of this IPT system is that the coupling coefficient of the primary side and secondary side windings is usually less than 0.1. Compensation networks are needed on both primary and secondary side to cancel the huge leakage inductances. Series resonant converter (SRC), with simply compensation networks, is widely adopted as a high efficiency topology for IPT system. Owing to the small coupling coefficient, the SRC acts like a band-pass filter, which only allows the resonant frequency component passing to the secondary side. The band-pass filter can be designed to match one harmonic frequency and only that frequency component carries the power. The passive components can shrink a lot if the resonant frequency is far higher than the switching frequency, and this leads to a more compact IPT system. A harmonic oriented IPT system is proposed. The design considerations of the proposed system and the comparison of different harmonic systems are presented in Chapter 2. Load regulation function is required for battery chargers. However, for the SRC, Small drift away from resonant frequency leads to huge drop on gain and huge increment on circulating current. Traditional frequency modulation control loses soft switching when doing load regulation, which is the main advantage of a resonant converter. A harmonic burst control is proposed to achieve soft switching at both turn-ons and turn-offs under all load conditions. It improves the system efficiency over 10% for light-load conditions. Chapter 3 illustrates this harmonic burst control in detail. IPT systems also includes a power factor correction (PFC) front end, which is usually a boost PFC converter, and an isolated DC-DC converter. In order to reduce the cost of two stage solution, a Z-source resonant converter is researched as a single stage solution that can perform PFC and load regulation at the same time. The mechanism of this Z-source resonant converter is presented in Chapter 4. And the high power factor control schemes are proposed for this Z-source resonant converter in Chapter 5."--Pages ii-iii.
Read
