Abstract
Tight voltage regulation and high efficiency are fundamental objectives of wireless power transfer systems (WPTSs) as power supplies. Although the well-established impedance matching control attempts to achieve high efficiency, the associated extra dc–dc converters or hard switching of converters in WPTSs reduce the overall system efficiency, particularly for high-power applications. In this article, under zero voltage switching (ZVS) conditions, the minimum power loss point is derived and proved in detail with different ZVS angles. Moreover, a joint control with variable ZVS angles (JC-VZA) is proposed to ensure ZVS of all switches and achieve the required output, simultaneously. This control scheme is implemented by use of controllers in both sides of WPTSs, which adjust their respective ZVS angles for dynamic efficiency optimization. Under ZVS conditions, the proposed JC-VZA features an optimal amount of reactive power that achieves the minimum total power loss by significantly reducing the switching loss. As a result, the experimental results obtained from our WPTS prototype verify its superiority. With a coupling coefficient $k$ of 0.2 or 0.15, the maximum efficiency reaches 96.8% or 95.0% under the power rating of 288 W (rated load) as well as 92.4% or 88.7% in the case of light load (9% of 288 W).
Highlights
W IRELESS power transfer (WPT) is an emerging means of power delivery in many applications, such as biomedical implants [1]–[3], consumer electronics [4]–[6], underwater loads [7]–[9], and electric vehicles (EVs) [10]–[13], where physical contact is inconvenient or impossible
When the turn-on resistance of a power switch is represented as Rdson, the total power loss of the WPT systems (WPTSs) can be reckoned as Pres, which can be obtained by
If Kcv is smaller than R2/2R1, φ∗ZAp needs to be set to 0◦ and φ∗ZAs should be changed to make the operating point of the WPTS move along the trajectory OA and search for the minimum power loss point
Summary
W IRELESS power transfer (WPT) is an emerging means of power delivery in many applications, such as biomedical implants [1]–[3], consumer electronics [4]–[6], underwater loads [7]–[9], and electric vehicles (EVs) [10]–[13], where physical contact is inconvenient or impossible. In EV applications, the ever-changing charging voltage and equivalent resistance of battery packs can greatly reduce the transfer efficiency of WPTSs during charging processes [14] To overcome this shortcoming, the concept of impedance matching control is introduced. To get rid of dc–dc converters while ensuring impedance matching, one option lies in the better utilization of an inverter and an active rectifier (AR) [16]–[19] It can be achieved by adjusting their phase shift angles, known as dual phase shift control (DPSC). Similar to TPS in DAB, an optimal TPS control strategy is proposed in the WPTSs [22] It features to adjust the phase shift angle between the ac square waveforms of the inverter and the AR to achieve ZVS. When the input dc voltage is unequal to the output dc voltage, the phase-shift soft-switching control strategy cannot always achieve the maximum transfer efficiency.
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