Chengbin Ma

In recent years, high-frequency wireless power transfer (WPT), such as operating at 6.78 MHz (MHz), has attracted increasing attention due to its improved spatial freedom. In applications such as pipeline inspection robots and medical implants, the transmitting (Tx) coils are usually attached to curved surfaces, and the receiving device often undergoes multi-degree-of-freedom rotations during movement (i.e., positional and angular misalignment). Therefore, this article develops a staggered and overlapping curved Tx-coil array design to achieve a uniform magnetic field distribution in three-dimensional (3D) directions in cylindrical space. The staggered layout is periodic and spatially scalable, overcoming the spatial limitations of traditional designs; the overlapping of each individual curved Tx coil also suppresses the cross-coupling inside the coil array in the 3D direction. In addition, Tx input current phase modulation is applied to shape the magnetic field in the cylindrical space. Finally, the concept of the staggered curved coil array is implemented and verified in a 6.78 MHz WPT experimental system. The results show that the design greatly improves the spatial freedom of power transfer in 3D cylindrical space with a static and pre-optimized manner (i.e., no adaptation), especially showing high tolerance to rotations with position and angle misalignment. For instance, when charging a planar receiver with misaligned position and 20$^{\circ }$ titled angle, the coefficient of variation of the received output voltage is reduced to 6.5% over a 360$^{\circ }$ rotation.

With the emerging of large-capacity battery cells, the demand of high-current, high-conversion-ratio bidirectional dc-dc converters in energy storage systems (ESS) has also increased. Similarly, electric vehicle on-board chargers (OBC) face the same requirement when charging or discharging low-voltage (LV) batteries. Although conventional approaches such as inductor-inductor-capacitor converter (LLC) have provided good performance, their LV transistors still suffer from large switching stress during conversions from the LV side to the high-voltage (HV) side. In addition, due to the resonance, load transition response is slow and resonant amplitude oscillates during transients, which further increases the LV switching stress. To overcome these two shortcomings, an optimal trajectory control (OTC) based control for dual-active-bridge series-resonant converter (DBSRC) is proposed. It uses state-plane analysis (SPA) to find mode length solutions with the following two properties: First, for all the steady-state and transition solutions, zero-voltage switching (ZVS) always holds and the LV switching stress is constant and small; Second, transitions converge within one cycle and the resonant amplitude does not oscillate or overshoot. To validate the proposed solution, steady state tests, open-loop power transition tests and closed-loop load transition tests are conducted on a 3 kW prototype. In all tests, ZVS and small turn-off current are observed in every cycle, which is consistent with expectations. Besides, single-cycle convergence and fast load transition response are also verified.

This article presents a comprehensive impedance analysis of megahertz (MHz) wireless power transfer (WPT) systems considering load variations, coil misalignment and non-ideal factors including device parasitics and coil compensation error. The analysis shows that for the MHz operation, the above two non-ideal factors substantially enlarge the variation region of power amplifier's (PA) load impedance, which may adversely affect the stable operation of the MHz WPT systems in practical scenarios. This observation results in the development of a new region-to-region impedance matching network (IMN) design to enhance the robustness of the MHz WPT systems rather than existing ideal trajectory-to-trajectory or point-to-point impedance transformation. Specifically, the Möbius transformation is chosen as a tool to calculate the region-to-region IMN parameters due to its circularity-preserving property. The determination of initial and target PA impedance regions and solution of the Möbius transformation-based IMN design are further discussed from a system-level perspective. Experimental results show significantly improved stable operation of an actual 6.78 MHz WPT system with the proposed region-to-region impedance matching. With a $\pm 3\%$ coupled coil compensation error, the experimental MHz WPT system achieves a system efficiency of 82–87% under a 15-50 $\Omega$ dc load variation, and the system efficiency ranges between 81.18-87.50% with a varying mutual inductance coefficient $k$ between 0.086–0.161.

Mixed urinary incontinence, involving concurrent or diagnostically unclear components of urge- and stress-related dysfunction, remains poorly addressed by current therapeutic strategies. State-of-the-art electrostimulation relies primarily on sacral neuromodulation for urge-predominant symptoms, requiring bulky (~3 cm³) and costly (>$10,000) implants, while stress incontinence is largely managed by mechanical or surgical interventions that do not restore sphincter neuromuscular function. Here, we propose wireless-powered implanted programmable electrostimulation of sphincters (WIPES) that bypasses long nerve loops and provides on-site stimulation at the urethral sphincter. The adhesive-patch-like soft implant integrates wireless power receiving and tunable pulse generation, enabling long-term controlled stimulation with reduced size (<0.3 cm³) and weight (<0.9 g). In rats with experimentally induced urge or stress incontinence (in separate rat models of urge and stress incontinence established under the same experimental conditions), WIPES delivered free-moving stimulation and achieved average alleviation rates of 90.62% (UUI) and 97.92% (SUI) in voiding frequency and volume. WIPES was associated with peri-urethral neuromuscular remodeling and improved bladder–urethral functional outcomes, supporting its potential role in coordinated continence control.

Multiactive-bridge (MAB) converters are highly promising as energy routers in renewable energy applications. Their multiple-input multiple-output control challenges can be effectively addressed by a model predictive control (MPC) approach, which minimizes the interference between different ports and simplifies the controller design. However, during the optimization process, the input and output constraints are usually ignored to simplify the implementation, which may degrade the control performance and lead to large voltage overshoot/undershoot when the constraints are violated. Meanwhile, solving the constrained MPC problem within a short sampling time poses a huge computational challenge. To address these issues, in this article a continuous-control-set model predictive control (CCS-MPC) scheme is developed for the MAB converters, which incorporates input and output constraints to achieve over/under voltage protection. An MPC problem with multiple constraints is formulated and converted into a quadratic programming (QP) problem. Its real-time implementation on a low-cost microcontroller unit is further discussed including QP solver deployment, real-time certification, and delay compensation. Finally, the developed CCS-MPC scheme is experimentally verified by a four-port 500 W energy router prototype and well demonstrates the over/under voltage protection capability.

Compared with traditional energy systems, the scheduling and control of microgrids under dynamically changing power supply and demand is a major challenge. Although cloud-based microgrid management can provide long-term power prediction and scheduling, the prediction accuracy and communication quality strongly affect the reliability in practical applications. To address this problem, this paper develops a new joint cloud-local scheme to coordinate and switch between cloud-based energy management and its local counterpart. A multi-agent game among major local components is formulated to balance the power distribution inside a target home microgrid while referring to the cloud scheduling commands. An update of a relevant weight coefficient is also developed to enable a smooth transition from the cloud-local joint control to fully local control upon communication failures. A scaled-down testbed and a cloud scheduling platform are built to verify the proposed system architecture and joint control scheme. Results show that the proposed cloud-local joint control operates cost-effectively and reliably in both normal and failed communication scenarios. Compared with traditional rule-based control and cloud-based control, the total operating cost (i.e., the sum of electricity cost and battery degradation cost) is reduced by 18% and 29%, respectively.

Wireless power transfer systems operating at frequencies of several megahertz are of interest due to their high spatial freedom and compactness. Combining multiple transmitting (Tx) coils for magnetic field shaping has emerged as a promising candidate to further improve the spatial freedom of the power transfer. In this article, a new closed-loop-based scheme is developed for detecting the spatial position / orientation of multiple receivers (Rxs) and controlling the magnetic field distribution accordingly. Inspired by the orthogonal projection of visible light, this article proposes the concept of magnetic field projection to detect the position and orientation of multiple Rxs. Using a 2×2 Tx-coil array as an example, a coding-based detection approach is developed using the results of the magnetic field projections in the x, y, and z directions. A control flow is then proposed for determining the optimal phase combination of the power amplifier (PA) output currents to achieve the desired magnetic field shaping. Finally, the above concepts are experimentally realized and verified. Light-emitting-diode arrays were specially fabricated to visualize the actual magnetic field shaping results. It is found that the final system can accomplish the closed-loop detection of the three spatially distributed Rxs and the phase control of the PA output current within 25 ms. This article is accompanied by two video files to demonstrate the actual detection and control process.