An Improved Spread-Spectrum Technique for Reduction of Electromagnetic Emissions of Wireless Power Transfer Systems

Abstract

The application of conventional spread spectrum techniques for conducted electromagnetic emission (EME) reduction in inductive-resonant wireless power transfer (WPT) systems may not reduce conducted EME enough due to specific frequency characteristics of the resonant systems and it can lead to some “adverse effects”, mainly in terms of decreased efficiency. Therefore, in this paper, an improved spread spectrum approach, multi-switching frequency and multi-duty cycle (MFMD) technique, is proposed. The proposed approach can give a considerably better conducted EME reduction along with a better efficiency than the conventional spread spectrum techniques based on a multi-switching frequency scheme. In the proposed approach, the inductive-resonant WPT system can operate at multiple switching frequencies (e.g., three different frequencies) and for a part of a control signal with a specific switching frequency, there is a specific duty cycle. The technique can be implemented in a simple way using an inexpensive 8-bit microcontroller. The effect of the MFMD scheme on the conducted EME and efficiency of the WPT system is studied in detail. The WPT system conducted EME and the efficiency are studied experimentally with a designed laboratory prototype. The performance characteristics of the WPT system with the MFMD scheme are compared to those with the multi-switching frequency scheme and without the spread spectrum. The WPT system with the proposed spread spectrum technique has a better performance than that with the conventional spread spectrum technique.

Thorough Study of Multi-Switching-Frequency-Based Spread-Spectrum Technique for Suppression of Conducted Emissions from Wireless Battery Chargers

“…The switching frequencies fk change from low to high, and d1 = d2 = dk in both classical cases. In order to improve the conducted emission reduction in open-loop WPT systems, the modified multi-switching-frequency technique (also known as multi-switching-frequency-multi-duty-cycle technique) was proposed in [15]. In the modified technique, the k-th duty cycle values are not equal (d1 ≠ d2 ≠ d3), but N1 = N2 = N3, τ1 ≠ τ2 ≠ τk, and the frequency order is from low to high.…”

“…In the modified technique, the k-th duty cycle values are not equal (d1 ≠ d2 ≠ d3), but N1 = N2 = N3, τ1 ≠ τ2 ≠ τk, and the frequency order is from low to high. Despite the fact that the modified technique [15] showed better performance in the open-loop WPT systems, its implementation in closed-loop WPT systems used for wireless battery charging would be more challenging, because the output voltage or current of the wireless battery charger can be changed through a variation of the average duty cycle of the inverter. As a result, the technique will require more computational and memory resources from a microcontroller that would prevent the use of relatively inexpensive microcontrollers with transceivers in the wireless battery chargers with closed-loop control.…”

“…In the classical multi-switching-frequency techniques, N 1 = N 2 = N k , but τ 1 = τ 2 = τ k [15] or τ 1 = τ 2 = τ k and N k depends on τ k [12]. The switching frequencies f k change from low to high, and d 1 = d 2 = d k in both classical cases.…”

“…In order to reduce size and cost of the passive filters or even eliminate them, an interesting and useful approach called the spread spectrum was adapted from communication engineering and applied to conventional switch-mode power converters last decade [10]. Recently, the approach was also applied to inductive-resonant wireless battery chargers for reducing conducted and radiated emissions [11][12][13][14][15][16]. Spreading the spectrum of the conducted emissions of the wireless chargers can be achieved by different approaches, such as switching frequency modulation [5,13,16], simultaneous switching frequency and duty cycle modulation (also known as the hybrid modulation) [11], multi-switching frequency technique [12] or even multi-frequency-multi-duty-cycle approach [15].…”

“…Recently, the approach was also applied to inductive-resonant wireless battery chargers for reducing conducted and radiated emissions [11][12][13][14][15][16]. Spreading the spectrum of the conducted emissions of the wireless chargers can be achieved by different approaches, such as switching frequency modulation [5,13,16], simultaneous switching frequency and duty cycle modulation (also known as the hybrid modulation) [11], multi-switching frequency technique [12] or even multi-frequency-multi-duty-cycle approach [15]. In contrast with the passive or active filters, the spread spectrum approach does not increase the size, weight or cost of inductive-resonant WPT systems because it can be implemented by using, for instance, a microcontroller with a suitable code.…”