Multiplexed Supply of a MISO Wireless Power Transfer System for Battery-Free Wireless Sensors

Abstract

Multi-input single output wireless power transmission (MISO-WPT) systems have decisive advantages concerning flexible receiver position in comparison to single coil systems. However, the supply of the primary side brings a large uncertainty in case of variable positions of the secondary side. In this paper, a compact multiplexed primary side electronic circuit is proposed, which includes only one signal generator, a passive peak detector, a communication module, and a compensation capacitor. The novel approach has been studied and evaluated for a MISO-WPT system having a 16 coils on primary side and one coil on secondary side having the double diameter. Results show that a standard microcontroller, in this case an STM32, is sufficient for the control of the whole system, so that the costs and the energy consumption are significantly reduced. An activation strategy has been proposed, which allows to determine the optimal transmitting coil for each position of the receiving coil and to switch it on. The time-to-start-charging at different positions of the receiving coil and different number of neighbors has been determined. It remains in all cases under 2.5 s.This reduces the size of the supply circuit relative to the previous solutions. In [19], a multi-coil system with multiplexed solution is presented with a singular supply circuit. However, the selection of the appropriate coil requires dual MOSFET switches, which presents some similarity to a switch-based multi-coil system. Nevertheless, the control of the multi-coil system switches needs microcontrollers with a high number of pins. For that, in case of a big number of transmitting coils, an FPGA [22] is proposed as processing unit, leading to an increase of both energy consumption and costs.In this paper, we investigate the feasibility of a multiplexed circuit on the primary side supply approach, with the aim to reduce the circuit size and to control the system by a simple microcontroller with a limited number of pins. The main objective is to significantly decrease both energy consumption and system costs. To this end, we propose to use receiving coils having the double diameter of the transmitting coils. This is important to cover at least a singular transmitting coil for different possible positions on the top of the pad to power the device for all the possible positions. In order to enable the detection and the powering of even battery-free wireless sensor nodes, we propose that the communication between the transmitting and receiving coil is started from the transmitting side and supplied from the transferred energy on the secondary side.The paper is organized as follows: In Section 2, the primary side supply circuit for a system is presented. The description of the proposed multi-coil system control algorithm is detailed in Section 3. The experimental evaluation of the developed algorithm are reported in Section 4. Section 5 shows the analysis of the required time to start the charging process. A conclusion is provided in Section 6. Design of the Primar...

Energy-Aware System Design for Autonomous Wireless Sensor Nodes: A Comprehensive Review

“…This can be realized by controlling the system frequency [ 57 ], the system gain [ 58 ], the compensation capacitors [ 59 ] and the DC-DC rectifier [ 60 ]. To overcome misalignment effects, multiple input–single output (MISO) coil systems can be realized [ 61 ], which are composed of multiple transmitter coils connected in series [ 62 , 63 ] or parallel [ 64 , 65 ]. The sending coils can be activated simultaneously [ 62 ] or one-by-one independently [ 65 ] using multiple supply circuits [ 66 ], switches [ 64 , 67 ] or both [ 68 ].…”

“…To overcome misalignment effects, multiple input–single output (MISO) coil systems can be realized [ 61 ], which are composed of multiple transmitter coils connected in series [ 62 , 63 ] or parallel [ 64 , 65 ]. The sending coils can be activated simultaneously [ 62 ] or one-by-one independently [ 65 ] using multiple supply circuits [ 66 ], switches [ 64 , 67 ] or both [ 68 ]. The main difference between systems used to charge batteries and those to supply battery-free devices is the detection procedure.…”

“…The main difference between systems used to charge batteries and those to supply battery-free devices is the detection procedure. In fact, battery-free systems do not use communication for the activation of the transmitter side system due to lack of stored energy, which can be useful to activate communication procedure [ 65 ]. However, keeping the transmitter side ON to detect the presence of device for long times increases the energy losses.…”

“…However, keeping the transmitter side ON to detect the presence of device for long times increases the energy losses. In [ 65 ], the authors proposed a passive peak detector circuit of the receiver coil with controls the working circuit frequency to reduce the power consumption. When the device is detected, the system increases the working frequency to reach the resonance, which helps the system to deliver energy able to supply the circuit of the receiver side to communicate with the transmitter side.…”

A Novel Charging Method for Underwater Batteryless Sensor Node Networks

“…The objective of the authors requires that the load of the systems to charge varies depending on the total number of systems present in the charging area. In [ 18 ] is presented a multiple input multiple output WPT (MIMO–WPT) system for batteryless wireless sensors. Here the key point it is to maximize the energy received in the sensor node reducing the dependency of the energy transmitter.…”