Dual‐objective control strategy for maximum power and efficiency point tracking in wirelessly powered biomedical implanted devices

Abstract

Wireless charging is widely considered as a safe and reliable way for powering biomedical implants, as it avoids problems like surgical infection. Wireless power transfer (WPT) systems are desired to work efficiently against variations in coil–coil distance or output load. On the other hand, to maintain the maximum overall efficiency of the WPT system, the high frequency (HF) power amplifier, used to feed WPT system, must operate at optimal zero‐voltage switching (ZVS) condition. In this paper, an automated dual‐objective control strategy adaptive to variations in coil–coil distance or output load is proposed which ensures both targets of tracking maximum power point and operating at optimal ZVS condition by adjusting operating frequency and duty‐cycle of switching voltage of HF power amplifier, respectively; that is while there have been few studies which have addressed both the two targets. To evaluate the effectiveness of the proposed strategy, a PCB prototype, operating at 800 kHz, is fabricated. Experimental results, demonstrating the proposed strategy increases transferred power from 23 mW to about 45 mW, are in good agreement with theoretical predictions. Additionally, while implanting the receiver coil in a real biological tissue, experiments show only 2% of degradation in power transfer efficiency as well as no frequency shift.

Metal‐rim‐connected inductive coupler for smartwatch applications

“…Consequently, the efficiency of power transmission will be reduced in long transfer distances due to weakly‐coupled coils, and in short transfer distances, as a result of frequency splitting phenomenon [18]. To make the system robust against variations in distance and load transfer, closed‐loop control strategies are necessary and presented in literature for some applications such as biomedical implanted devices [19]. Proposing a closed‐loop control scheme for smartwatch applications will be one of our research directions in future research.…”

Real-Time Frequency Adaptive Tracking Control of the WPT System Based on Apparent Power Detection

“…To ensure that the WPT system operates at the resonant frequency point, there are three main control methods: coil topology optimization [8][9][10], dynamic compensation tuning [11][12][13], and frequency tracking. Compared to the other two methods, frequency tracking control is widely used in systems due to its easy implementation and fast response [14][15][16][17][18][19][20][21]. In [14], power allocation strategies are achieved targeted by adjusting the resonant frequency of the transmitting end to achieve stable output power that accurately counteracts load imbalance.…”

“…Additionally, a method to track the secondary resonance frequency to improve system performance is designed. A dual objective control strategy (DCS) is proposed in [20], adjusting the operating frequency of the highfrequency power amplifer and the duty cycle of the switching voltage to adapt to changes in distance between coils or output load changes, ensuring that the system can track the maximum power point under the optimal ZVS conditions. Reference [21] proposes an autonomous pulse frequency modulation scheme (APFM) for WPT battery charging; by extracting and processing the current signal on the primary side, the WPT system can adjust its output power by changing its duty cycle, achieving reliable ZVS.…”

Maximum Wireless Power Transmission Using Real-Time Single Iteration Adaptive Impedance Matching

“…To compensate for η W P T reduction, a range-adaptive control technique can be employed, especially for the short coilto-coil distance cases, where a large impedance mismatch occurs. Two main compensation methods are reported in the literature: (i) frequency tracking approaches in which the input power supply frequency is adjusted adaptively to the coilto-coil distance [12], [13], [15], [16], [17], [18], [19], and (ii) impedance matching (IM) techniques, such as coupling manipulation [8], [10], [11], lossless IM-networks [1], [2], [9], and IM ability of DC/DC converters [20]. In [15], the reference value for the WPT system input voltage against coupling variations was achieved by tracking split frequencies in the strongly coupled region using a Voltage Controlled Oscillator (VCO).…”

“…In [15], the reference value for the WPT system input voltage against coupling variations was achieved by tracking split frequencies in the strongly coupled region using a Voltage Controlled Oscillator (VCO). To track the maximum power transmitted point, manual and automatic frequency control of the input power supply were employed in [13] and [19], respectively. Another automated frequency control technique was introduced in [16], which monitored η W P T using out-band wireless communication and adjusted the frequency of the input power supply using a Phase-Locked Loop (PLL) to achieve η W P T goal higher than 70%.…”