Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems
Near-field interfaces with miniaturized coil systems and low output power levels, such as applied in biomedical sensor systems, can suffer from severe efficiency degradation due to dynamic impedance mismatches, reducing battery life of the power transmitter unit and requiring to increase the level o...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-03-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/21/6/2023 |
| _version_ | 1827697880354258944 |
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| author | Sebastian Stoecklin Adnan Yousaf Gunnar Gidion Leonhard Reindl Stefan J. Rupitsch |
| author_facet | Sebastian Stoecklin Adnan Yousaf Gunnar Gidion Leonhard Reindl Stefan J. Rupitsch |
| author_sort | Sebastian Stoecklin |
| collection | DOAJ |
| description | Near-field interfaces with miniaturized coil systems and low output power levels, such as applied in biomedical sensor systems, can suffer from severe efficiency degradation due to dynamic impedance mismatches, reducing battery life of the power transmitter unit and requiring to increase the level of electromagnetic emission. Moreover, the stability of weakly-coupled power transfer systems is generally limited by transient changes in coil alignment and load power consumption. Hence, a central research question in the domain of wireless power transfer is how to realize an adaptive impedance matching system under the constraints of a simultaneous power feedback to increase the system’s efficiency and stability, while maintaining circuit characteristics such as small size, low power consumption and fast reaction times. This paper presents a novel approach based on a two-stage control loop implemented in the primary-side reader unit, which uses a digital PI controller to maintain the rectifier output voltage for power feedback and an on-top perturb-and-observe controller configuring the setpoint of the voltage controller to maximize efficiency. The paper mathematically analyzes the AC and DC transfer characteristics of a resonant inductive link to design the reactive AC matching network, the digital voltage controller and ultimately the DC-domain impedance matching algorithm. It was found that static reactive L networks result in suitable efficiency levels for coils with sufficiently high quality factor even without adaptive tuning of operational frequency or reactive components. Furthermore, the regulated output voltage of the rectifier is a direct measure of the DC load impedance when using a regular DC/DC converter to supply the load circuits, so that this quantity can be tuned to maximize efficiency. A prototype implementation demonstrates the algorithms in a 40.68 MHz inductive link with load power levels from 10 to 100 mW and tuning time constants of 300 ms, while allowing for a simplified receiver with a footprint smaller than 200 mm<sup>2</sup> and a self-consumption below 1 mW. Hence, the presented concepts enable adaptive impedance matching with favorable characteristics for low-energy sensor systems, i.e., minimized footprint, power level and reaction time. |
| first_indexed | 2024-03-10T13:17:56Z |
| format | Article |
| id | doaj.art-f475fc3d7e5648eab9056cc3d1e6689b |
| institution | Directory Open Access Journal |
| issn | 1424-8220 |
| language | English |
| last_indexed | 2024-03-10T13:17:56Z |
| publishDate | 2021-03-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Sensors |
| spelling | doaj.art-f475fc3d7e5648eab9056cc3d1e6689b2023-11-21T10:18:37ZengMDPI AGSensors1424-82202021-03-01216202310.3390/s21062023Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer SystemsSebastian Stoecklin0Adnan Yousaf1Gunnar Gidion2Leonhard Reindl3Stefan J. Rupitsch4Laboratory for Electrical Instrumentation and Embedded Systems, Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, GermanyLaboratory for Electrical Instrumentation and Embedded Systems, Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, GermanyLaboratory for Electrical Instrumentation and Embedded Systems, Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, GermanyLaboratory for Electrical Instrumentation and Embedded Systems, Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, GermanyLaboratory for Electrical Instrumentation and Embedded Systems, Department of Microsystems Engineering, University of Freiburg, 79110 Freiburg, GermanyNear-field interfaces with miniaturized coil systems and low output power levels, such as applied in biomedical sensor systems, can suffer from severe efficiency degradation due to dynamic impedance mismatches, reducing battery life of the power transmitter unit and requiring to increase the level of electromagnetic emission. Moreover, the stability of weakly-coupled power transfer systems is generally limited by transient changes in coil alignment and load power consumption. Hence, a central research question in the domain of wireless power transfer is how to realize an adaptive impedance matching system under the constraints of a simultaneous power feedback to increase the system’s efficiency and stability, while maintaining circuit characteristics such as small size, low power consumption and fast reaction times. This paper presents a novel approach based on a two-stage control loop implemented in the primary-side reader unit, which uses a digital PI controller to maintain the rectifier output voltage for power feedback and an on-top perturb-and-observe controller configuring the setpoint of the voltage controller to maximize efficiency. The paper mathematically analyzes the AC and DC transfer characteristics of a resonant inductive link to design the reactive AC matching network, the digital voltage controller and ultimately the DC-domain impedance matching algorithm. It was found that static reactive L networks result in suitable efficiency levels for coils with sufficiently high quality factor even without adaptive tuning of operational frequency or reactive components. Furthermore, the regulated output voltage of the rectifier is a direct measure of the DC load impedance when using a regular DC/DC converter to supply the load circuits, so that this quantity can be tuned to maximize efficiency. A prototype implementation demonstrates the algorithms in a 40.68 MHz inductive link with load power levels from 10 to 100 mW and tuning time constants of 300 ms, while allowing for a simplified receiver with a footprint smaller than 200 mm<sup>2</sup> and a self-consumption below 1 mW. Hence, the presented concepts enable adaptive impedance matching with favorable characteristics for low-energy sensor systems, i.e., minimized footprint, power level and reaction time.https://www.mdpi.com/1424-8220/21/6/2023wireless power transfermaximum efficiency point trackingadaptive impedance matchingpower feedbackbiomedical systemswireless microsytems |
| spellingShingle | Sebastian Stoecklin Adnan Yousaf Gunnar Gidion Leonhard Reindl Stefan J. Rupitsch Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems Sensors wireless power transfer maximum efficiency point tracking adaptive impedance matching power feedback biomedical systems wireless microsytems |
| title | Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems |
| title_full | Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems |
| title_fullStr | Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems |
| title_full_unstemmed | Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems |
| title_short | Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems |
| title_sort | simultaneous power feedback and maximum efficiency point tracking for miniaturized rf wireless power transfer systems |
| topic | wireless power transfer maximum efficiency point tracking adaptive impedance matching power feedback biomedical systems wireless microsytems |
| url | https://www.mdpi.com/1424-8220/21/6/2023 |
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