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This article presents a coordinated control method used for wireless power transfer (WPT) systems. This method can improve WPT system transmission efficiency while maintaining the constant output voltage. First, the topology of the DC–DC converter is selected and the equivalent circuit model of the WPT system is established. Then, the WPT system characteristics are discussed and the mutual inductance estimation process is presented. Furthermore, the coordinated control method is proposed, where the constant voltage output is achieved by connecting the Buck–Boost converter after the diode rectifier. Meanwhile, the optimal phase shift angle is calculated and sent to the controller to achieve maximum transmission efficiency tracking control, according to the measured load voltage and current. Finally, simulations and experiments are adopted to verify the proposed coordinated control method. The experimental results indicate that the average system transmission efficiency is increased by 1.80% and the efficiency fluctuation is decreased by 2.67% when the system load resistance varies, while the average system transmission efficiency is increased by 1.80%, and the efficiency fluctuation is decreased by 3.14% when the mutual inductance changes. This means the proposed coordinated control method is effective under the conditions of the WPT load and mutual inductance variations. [ABSTRACT FROM AUTHOR]

This paper introduces a novel power supply voltage adjustment strategy that can determine the optimum voltage value based on the amount of absorbed power. The novel automatic voltage adjustment technique was called inverse maximum power point tracking (iMPPT). The proposed control strategy consists of a modified maximum power point tracking (MPPT) algorithm (more precisely the P&O method). In this case, the modified MPPT technique establishes the minimum value of the input absorbed power of a consumer load served by a switched-mode power supply (SMPS). The iMPPT adjusts the input power by modifying the input voltage of the main power supply. The served loads are connected to the variable power supply via an interfacing power electronics converter that performs the automatic voltage regulation function (AVR). The optimal value of the input voltage level can be achieved when the input power of the automatic voltage regulation converter is at a minimum. In that case, the energy conversion efficiency ratio is at a maximum, and the overall losses related to the front-end power stage are at a minimum. The proposed technique can also be considered a Maximum Efficiency Tracking (MET) method. By performing the inverse operation of a maximum power point tracking algorithm on the input demanded power of a switched mode power supply (SMPS), the optimum input voltage level can be determined when the maximum energy conversion ratio (related to a given load level) is achieved. The novel proposed iMPPT method can improve the energy conversion ratio from 85% up to approximately 10% in the case of an output power level of 800 W served by a synchronous buck converter at the input voltage level of 350 V. The total amount of recovered power in this situation can be approximately 100 W.

This paper introduces a novel power supply voltage adjustment strategy that can determine the optimum voltage value based on the amount of absorbed power. The novel automatic voltage adjustment technique was called inverse maximum power point tracking (iMPPT). The proposed control strategy consists of a modified maximum power point tracking (MPPT) algorithm (more precisely the P&O method). In this case, the modified MPPT technique establishes the minimum value of the input absorbed power of a consumer load served by a switched-mode power supply (SMPS). The iMPPT adjusts the input power by modifying the input voltage of the main power supply. The served loads are connected to the variable power supply via an interfacing power electronics converter that performs the automatic voltage regulation function (AVR). The optimal value of the input voltage level can be achieved when the input power of the automatic voltage regulation converter is at a minimum. In that case, the energy conversion efficiency ratio is at a maximum, and the overall losses related to the front-end power stage are at a minimum. The proposed technique can also be considered a Maximum Efficiency Tracking (MET) method. By performing the inverse operation of a maximum power point tracking algorithm on the input demanded power of a switched mode power supply (SMPS), the optimum input voltage level can be determined when the maximum energy conversion ratio (related to a given load level) is achieved. The novel proposed iMPPT method can improve the energy conversion ratio from 85% up to approximately 10% in the case of an output power level of 800 W served by a synchronous buck converter at the input voltage level of 350 V. The total amount of recovered power in this situation can be approximately 100 W. [ABSTRACT FROM AUTHOR]

This article presents a coordinated control method used for wireless power transfer (WPT) systems. This method can improve WPT system transmission efficiency while maintaining the constant output voltage. First, the topology of the DC–DC converter is selected and the equivalent circuit model of the WPT system is established. Then, the WPT system characteristics are discussed and the mutual inductance estimation process is presented. Furthermore, the coordinated control method is proposed, where the constant voltage output is achieved by connecting the Buck–Boost converter after the diode rectifier. Meanwhile, the optimal phase shift angle is calculated and sent to the controller to achieve maximum transmission efficiency tracking control, according to the measured load voltage and current. Finally, simulations and experiments are adopted to verify the proposed coordinated control method. The experimental results indicate that the average system transmission efficiency is increased by 1.80% and the efficiency fluctuation is decreased by 2.67% when the system load resistance varies, while the average system transmission efficiency is increased by 1.80%, and the efficiency fluctuation is decreased by 3.14% when the mutual inductance changes. This means the proposed coordinated control method is effective under the conditions of the WPT load and mutual inductance variations.

For the typical magnetically coupled wireless power transmission system, power consumption is often caused by the impedance effect of the primary and secondary sides, the loss and heat generation of the actual semiconductor devices and the change of the coupling coefficient caused by distance. The uncertainty of frequency tracking efficiency caused by high enough coil transmission with low load receiving efficiency and load impedance changes makes it difficult to stabilize the output of the optimal efficiency point of the system. In order to solve this problem, a wireless power transmission system is proposed based on the traditional wireless power transmission system a wireless power transmission system is proposed to predict and stabilize the variable impedance, so as to stably track the efficiency of the system in the resonant frequency range. It is not affected by load jitter, actual circuit parameters and environmental disturbance. The test results show that the transmission efficiency of tracking frequency and predicting impedance can be realized at a certain distance, and the difference between the prediction error and the actual efficiency is about 1%–3%.

This paper presents a novel compensation parameter design methodology and maximum efficiency tracking (MET) control strategy for inductive power transfer (IPT) system with an inductance and double capacitance-series (LCC-S) compensation topology. The compensation parameters of a conventional IPT converter are designed for the required output voltage by considering the fluctuation ranges of the battery voltage and coupling coefficient, but without considering the efficiency characteristics of the IPT converter. Additionally, the IPT system efficiency fluctuates with the load, because the battery equivalent resistance continuously changes according to the state-of-charge. To address these problems, this paper presents a compensation parameter design methodology based on a loss analysis of the IPT converter. The losses of the transmitter and receiver in the IPT converter with the optimal compensation parameters are compared and analyzed according to the load. Based on these analyses, a control strategy is proposed for tracking the maximum efficiency according to the load without real-time communication. To validate the proposed compensation parameter design methodology and maximum-efficiency tracking control strategy, a 1.85 kW experimental prototype is configured.

With the application of electrical equipment, magnetically coupled resonant (MCR) wireless power transfer (WPT) technology has become an effective means to improve equipment intelligence. The MCR‐WPT system is a loosely coupled system, and the resonant frequency may be split or detuned due to the changes of load or transferring distance, resulting in the system transfer efficiency (TE) greatly reduced. To solve the problems of limited speed and accuracy in the existing frequency tracking methods, this paper analyzes the relation between the detuning rate and the system TE, proposing an adaptive frequency tracking control method based on fuzzy radial basis function neural network control. The neural network outputs proportion–integration–differentiation parameters to adjust the inverter drive circuit, and the frequency of inverter drive circuit is adjusted nonlinearly in real time to ensure the accurate frequency tracking of the MCR‐WPT system. The simulation and experimental results show that the proposed method can enhance the tracking ability of the resonant frequency, and effectively improve the system TE. [ABSTRACT FROM AUTHOR]

Induction Hardening (IH) process contributes to the improvement of the mechanical properties of the steel. In this application, the inverter operates at resonant frequency for high operating performances. However, this is usually accompanied by steel characteristics variation under temperature effect especially the magnetic permeability. This paper proposes two approaches for resonance frequency adaptation. The first is based on maximum efficiency tracking (MET) scheme. In this context, simulation with an algorithm for control is developed to find in real-time the adequate frequency based on current and voltage sensor. This approach is found effective but requires a constant determination of the input and the output power. Hence, it makes it difficult for implementation. To alleviate this drawback, advanced technique based on deep learning (DL) algorithm is proposed. Thus, an experimental prototype is built to determine the experimental Temperature-Frequency data profiles up to the hardening for two metal bars. Hence, a neural network (NN) based model control is elaborated. After a careful selection of NN parameters, a trained model is obtained with satisfactory accuracy leading to the predict model. This was easily implemented in real time on raspberry pi 3 + and allows the system to perform continuously under high efficiency for hardening purposes.

In the underwater wireless power transfer system for the marine vehicle, the system transfer efficiency is influenced by factors including coupling state and load condition. To solve the problem of transfer efficiency decrease caused by the dynamic changes of coupling coefficient and load conditions, a maximum efficiency tracking method based on the dynamic identification of optimal output voltage and coupling coefficient is proposed. Moreover, the approximation characteristic to the nonlinear function of artificial neural networks is used to dynamically adjust the output voltage of DC/DC converter, and the deviation between the output voltage and optimal voltage can be kept within the allowable error range leading to maximum efficiency tracking. The experimental results show that the control method can calculate the optimal output voltage correctly, adjust the output voltage quickly and accurately, and achieve the maximum efficiency of the wireless power transfer system when the coupling coefficient and load conditions change dynamically. [ABSTRACT FROM AUTHOR]

Efficiency is very important in inductively coupled power transfer (ICPT) systems. To maintain a high efficiency, a maximum efficiency tracking (MET) method based on parameter detection is proposed in the paper. The basic idea is to convert the load value to the active short-circuit (ASC) time interval for the semi-controlled rectifier on the pick-up side. The ASC time interval and the transmitting coil current are detected to calculate the load and mutual inductance values on the transmitting side. According to the detected parameters, the output voltage of the high-frequency inverter that makes the system run at its maximum efficiency can be calculated and controlled. In addition, the load voltage is controlled by the high-frequency rectifier on the pick-up side. Simulation and experimental results show that this method can quickly achieve MET without wireless communication. Furthermore, the difference between the experimental maximum efficiency and the theoretical maximum efficiency is no more than 2%. [ABSTRACT FROM AUTHOR]

This paper proposes a discontinuous charging technique for switched-capacitor converters that improves the power conversion efficiency (PCE) at low power levels and extends the input power harvesting range at which high PCE is achievable. Discontinuous charging delivers current to energy storage only during clock non-overlap time. This enables tuning of the output current to minimize converter losses based on the available input power. Based on this fundamental result, an input power-aware, two-dimensional efficiency tracking technique for Wireless Sensor Network (WSN) nodes is presented. In addition to conventional switching frequency control, clock non-overlap time control is introduced to adaptively optimize PCE according to the sensed ambient power levels. The proposed technique is designed and simulated in 90nm CMOS with post-layout extraction. Under the same input and output conditions, the proposed system maintains at least 45% PCE at 4μW input power, as opposed to a conventional continuous system which requires at least 18.7μW to maintain the same PCE. Therefore, the input power harvesting range is extended by 1.5x. The technique is applied to a wearable WSN implementation utilizing the IEEE 802.15.4-compatible GreenNet communications protocol. This allows the node to meet specifications and achieve energy autonomy when deployed in environments where the input power is 49% lower than what is required for conventional operation.

Wireless power transfer (WPT) technology has drawn much attention due to its advantages such as safety, convenience, and non-contact. For some movable devices such as intelligent inspection robot, the constant output voltage is very important to ensure its normal operation. In order to improve the system efficiency and steadiness of output voltage, a maximum efficiency tracking and constant voltage charging method is proposed for the dynamic WPT system. In this method, the mutual inductance and optimal input voltage can be estimated accurately no matter the coupling coefficient and equivalent load change or not. The simulation and experimental results have shown that the WPT system realize maximum efficiency tracking and constant voltage charging when the resistance is changed from 10Ω to 5Ω, and the same result was achieved when the mutual inductance is altered from 20μH to 10μH.

This article presents a closed-loop transmitter for wireless power transfer with automatic resonance frequency tracking to maintain high power transfer efficiency in the over-coupled region. The transmitter consists of a source oscillator, power amplifier (PA), PA driver, matching network, and feedback circuitry. By injecting the resonant output of coupled antenna coils into a source oscillator to form a positive feedback loop, the source oscillator is injection-locked and the closed-loop transmitter functions as a power oscillator with the oscillation frequency determined by the resonance of the coupled coils. The proposed resonant frequency tracking minimizes the change in the input impedance presented to the PA, and hence mitigates mismatch that causes a sharp drop in the PA efficiency of conventional transmitters. Implemented in 0.13 μm Bipolar–CMOS–DMOS (BCD) technology, the prototype maintains PA efficiency above 60% even at highly over-coupled spacings (10 mm), which is significantly below the critical coupling spacing (40 mm). Compared to a transmitter without feedback (i.e., running in open loop), the transfer efficiency at a coupling distance of 10 mm is improved by 6.6 times and the charging range with power transfer efficiency over 50% is also doubled. [ABSTRACT FROM AUTHOR]

We propose a maximum efficiency tracking for a multiple-transmitter system that optimizes both the current ratios of transmitter (Tx) coils and the effective Rx load. It is found that unlike the single-Tx case, the optimal load impedance of multiple-Tx system depends on the current ratios among Tx coils. Meanwhile, the Tx current ratios should be controlled to be the same with magnetic coupling ratios between each Tx and Rx. Hence, we propose a two-step tracking method that first optimizes the Tx current ratios and then optimizes the Rx load impedance. To match the Tx current ratio with the magnetic coupling ratio, it is analyzed that the reflected resistances at every Tx become identical to each other when the Tx coil current ratios are equal to the magnetic coupling ratios. It is also revealed that the reflected resistance at specific Tx is reduced (increased) when its Tx current is increased (reduced) relative to other Tx currents. The proposed feedback equalizes all reflected resistances based on this property. The second step of the proposed tracking is to optimize the Rx load while fixing the Tx current ratios by globally scaling up or down the strengths of whole Tx currents. Maximum of 478 W is delivered at 79% efficiency. The algorithm does not have a limit on the number of Txs except the small standby power consumption. The proposed theoretic analysis and control method enable the first-ever maximum efficiency tracking for multiple-Tx system, where the first step optimizes the relative Tx current ratios and the second step optimizes the load impedance. [ABSTRACT FROM AUTHOR]

Inductive coupled power transfer (ICPT) systems are now more desired to provide constant output voltage with the highest efficiency, which will be affected by source (input voltage) and load (load resistance) conditions. To address this issue, an integrated control method is proposed in this study, which is realised by using the active impedance matching technology based on the buck ‐boost circuit on the load side and the robust H∞ control technology on the inverter side. This control scheme allows both two technologies to be applied simultaneously and independently operated. The bilateral inductor ‐capacitor ‐inductor ICPT compensation system is used here to test the proposed method, which is representative, and it is also applicable to other typical compensation topologies and has a certain universality. Finally, an experimental platform is established. Experimental results show that the system can achieve 24 V constant output voltage and 84.53% efficiency tracking under the condition of simultaneous 20% input voltage disturbance and 50% load change, which shows the effectiveness of the proposed integrated control method. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Correlation between the maximum driving efficiency and the minimum current was experimentally validated. • Extremum Seeking Control (ESC) technique was utilized to track optimum driving frequency using current feedback. • For output power control, preload control had a wider operating range compared to voltage amplitude control. Abstract Despite their great features, ultrasonic motors' (USM) driving schemes still suffer from suboptimum driving efficiencies and limited operating range. The driving efficiency and operation range are mainly functions of the vibration amplitude and the preload. Vibration amplitude is generally controlled by means of adjusting the driving frequency. Unfortunately, there exists a narrow frequency band where efficiency is maximized resulting in a limited output power range. Due to temperature rise, this frequency is continuously shifting which necessitates dynamic tracking of the optimum state. Fortunately, maximum driving efficiency was experimentally confirmed to have good correspondence with minimum current. Current feedback was thus utilized within an Extremum Seeking Control (ESC) loop to track maximum efficiency. Besides driving frequency control, voltage amplitude and preload can be controlled to realize the desired output power while maintaining maximum efficiency. Using ESC technique, the maximum efficiency was successfully located and tracked under different voltage amplitudes and preloads. The output power under optimum condition was found to have a wider control range with preload control than with voltage amplitude control. [ABSTRACT FROM AUTHOR]

Charging current and efficiency of a wireless power transfer system depend on the equivalent load resistance of supercapacitor load, which varies during charging. To achieve constant current (CC) charging and maximized efficiency under variable loads, control method that employs primary-side phase shift H-bridge inverter and secondary-side semiactive rectifier are proposed. The proposed secondary-side control method not only achieves CC charging, but also ensures no reactive impedance seen into the semiactive rectifier. Furthermore, the maximum efficiency tracking is based on searching the minimum system dc input current for any given output power. It is realized by phase shift H-bridge inverter that is controlled by the perturbation and observation algorithm. Simulation and experimental results validate the feasibility of the proposed control method. During CC charging of 3 A, the maximum efficiency is 81% and largest efficiency improvement is 15.2% at light load. The proposed control method improves the system performance and is suitable for the applications that require compact receiver and no wireless communication link between the transmitter and the receiver. [ABSTRACT FROM AUTHOR]

Maximum efficiency tracking is an important issue for wireless power transfer (WPT) system. Traditional maximum efficiency tracking method normally focuses on load impedance matching with fixed coupling condition. However, WPT system is a loosely coupling system, the coupling coefficient varies due to relative movement between the primary and secondary sides. Unknown to this variation may result in failure of the tracking. In this paper, a novel maximum efficiency tracking method is proposed with integrated dynamic coupling coefficient estimation. This method can take almost all requirements for maximum efficiency tracking into account including adaption for coupling coefficient and load variation, and output controllability. The tracking method is easy to implement because no additional circuitry or measurement is required. Experimental results have verified the correctness of the proposed coupling coefficient estimation method. And the maximum efficiency tracking results show the system can achieve a good performance against coupling coefficient and load variation with the proposed tracking method. [ABSTRACT FROM AUTHOR]

In this paper, the loading effect of a Class E power amplifier (PA) driven 6.78 megahertz (MHz) wireless power transfer (WPT) system is analyzed at both circuit and system levels. A buck converter is introduced and controlled to track an optimal equivalent load that maximizes the system efficiency under uncertainties in the relative position of coils and the final load. For power control, an additional degree of freedom is provided by adding an ultracapacitor bank. A control strategy is proposed to track the maximum efficiency and charge/discharge the ultracapacitor bank through the on/off control of the Class E PA. Thus, high system efficiency can be maintained under various uncertainties and load power demands. Finally, the theoretical analysis and the control scheme are validated in experiments. The results show that the proposed Class E PA-driven MHz WPT system can stably achieve a high efficiency under different coil distances and various constant/pulsed power profiles. The measured highest system efficiency can reach 72.1% at a load power level of 10 W. [ABSTRACT FROM AUTHOR]

Switch conductance modulation techniques are demonstrated in a fully integrated multi-ratio switched-capacitor voltage regulator with hysteretic control, in 22 nm tri-gate CMOS with high-density MIM capacitor. We present (i) an adaptive switch-size scaling scheme for maximum efficiency tracking across a wide range of voltages and currents, governed by a frequency-based control law that is experimentally validated across multiple dies and temperatures and, (ii) a simple active ripple mitigation technique that modulates the gate drive of select MOSFET switches effectively in all conversion modes. Efficiency improvements up to 15% are measured under low output voltage and load conditions. Load-independent output ripple of < 50 mV is achieved, enabling reduced interleaving. Test chip implementations and measurements demonstrate ease of integration in SoC designs, power efficiency benefits and EMI/RFI improvements. [ABSTRACT FROM PUBLISHER]