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This paper investigates a new method to model and control variable-frequency power converters in a switching-synchronized sampled-state space for cycle-by-cycle digital control. There are a number of significant benefits in comparison to other methods including fast dynamic performance together with ease of design and implementation. Theoretical results are presented and verified through hardware, and simulations of a current-mode buck converter with constant on-time and a current-mode boost converter with constant off-time. Dynamic voltage scaling for microprocessors and LiDAR are among the applications that can benefit.

Wireless power transfer (WPT) is emerging as the preeminent way to charge electric vehicles, but there appears to be no fair way to measure the power transfer. In this article, Faraday coil transfer-power measurement (FC-TPM) is presented. FC-TPM employs non-contact, open-circuited sense coils to measure the electromagnetic field from WPT and calculates the real power propagating through the air gap between the transmitter and receiver coils. What is measured is the real electromagnetic power, representing the pure dispensation of energy that unambiguously demarcates the losses on either side. FC-TPM was demonstrated to be 0.1% accurate in hardware over an Rx coil misalignment of up to 10 cm using a 1-kW WPT system. Fair metering incentivizes businesses and individuals to make choices that conserve energy and advance technology by providing more information and by properly assigning the financial loss. This article is accompanied by a video highlighting the essential contributions of this article.

This paper introduces a 4kV/120A solid-state DC circuit breaker (DCCB) based on discrete SiC MOSFETs. The DCCB is designed in a 5-layer tower structure. Each layer consists of a circular main conduction branch and an attached gate driver. There are two primary benefits in the proposed DCCB. First, it reduces conduction loss with multiple devices in parallel. Second, it achieves an ultrafast response speed with SiC MOSFETs. Moreover, the gate drivers of the DCCB are powered by a domino inductive power transfer (IPT) system. It achieves the load-independent constant-voltage output characteristics, which means the outputs are immune to load variations. An IPT system prototype is implemented to test the power transfer performance. At 500kHz frequency, the total output power reaches 15.73W that is sufficient to power on 5 gate drivers, with a peak transfer efficiency of 75.4%. The IPT system is tested to power a 4kV/120A DCCB prototype. It validates that the DCCB is effective to turn off 120A current within 3.5s.

Foreign objects near wireless power transfer (WPT) systems are fire hazards that must be detected. In this article, a new accurate method is presented for foreign object detection based on an electromagnetic model for WPT. Foreign objects are detected by quantifying the deviation from a normal model. This deviation is caused by the foreign object's additional electromagnetic coupling. Advantages of this new method include invariance to receiver coil misalignment, and power level, allowing low-power detection prior to startup. Electromagnetic model-based foreign object detection was demonstrated in hardware to detect a 2 cm diameter U.S. nickel coin, a small disposable lighter, and a saline proxy for a living animal in a kilowatt-level wireless power transfer system, using a prestartup power of only 7 W. Furthermore, foreign objects can be detected regardless of an Rx coil misalignment of up to 10 cm. This article is accompanied by an instructional video.

Ultrafast and isolated gate drivers advance the development of pulse and very high frequency power electronics for applications that include LiDAR, space systems, miniaturized hardware, and testing of emerging ultrafast devices. The isolated ultrafast gate driver in this letter achieves a gate voltage slew rate above 12 GV/s with rise and fall times below 260 ps with the proper choice of components. Magnetic isolation provides transient immunity and positive feedback enables dynamic dc restoration to allow arbitrarily long on - and off -times and preserve variable duty cycles. With the isolated ultrafast gate driver, an EPC 2038 GaN FET achieves a drain voltage slew rate of over 37 GV/s when hard-switching and improves total efficiency by 8% (including gating loss) with a careful choice of logic inverters in a symmetric 100 MHz current-mode class D (CMCD) wireless power transfer system. The ultrafast gate driver with isolation and positive feedback was implemented with a commercial radio frequency signal transformer and discrete logic inverters and validated in a hard-switching double pulse test, a narrow pulse test repeating at 165 MHz, and a 100 MHz soft-switching CMCD resonant converter.

DC-DC converters with low EMI and fast dynamic voltage scaling capability can significantly benefit the distributed computing and sensing devices in the Internet of things (IoT). However, the classic power converters have to tradeoff between fast transient response and small current ripple. We overcome this limitation by utilizing a programmable saturating inductor. In this paper, we investigate a ripple-programming architecture with compact volume, maximum power consumption of 1% of the power stage, and a ripple settling time below 1ms. The architecture includes a low-cost load estimation method with an error below 8% over the entire load range. We implement this ripple-programming architecture on a 1 MHz constant on-time buck converter prototype with a peak power of 30W. The inductor ripple can be effectively reduced by 40%.

The explosive growth of electric vehicles (EVs) is leading to a surge in retired EV batteries, which are typically recycled despite having nearly 80% available capacity. Repurposing automotive batteries for second-use battery energy storage systems (2-BESS) has both economical and environmental benefits. The challenge with second-use batteries is the heterogeneity in their state of health. This paper introduces a new strategy to optimize 2-BESS performance despite the heterogeneity of individual batteries while reducing the cost of power conversion. In this paper, the statistical distribution of the power heterogeneity in the supply of batteries is used to optimize the choice of power converters and design the power flow within the battery energy storage system (BESS) to optimize power capability. By leveraging a new lite-sparse hierarchical partial power processing (LS-HiPPP) approach, we study how a hierarchy in partial power processing (PPP) partitions power converters to significantly reduce converter ratings, process less power to achieve high system efficiency with lower cost (lower efficiency) converters, and take advantage of economies of scale by requiring only a minimal number of sets of identical converters. Our results demonstrate that LS-HiPPP architectures offer the best tradeoff between battery utilization and converter cost and have higher system efficiency than conventional partial power processing (C-PPP) in all cases., Comment: typos corrected, references added, title, abstract and introduction revised, DOI updated, results unchanged

The heterogeneity in pack voltages and capacity of aged packs limits the performance and economic viability of second-use battery energy storage systems (2-BESS) due to issues of reliability and available energy. Overcoming these limitations could enable extended use of batteries and improve the environmental impacts of electric vehicles by reducing the number of batteries produced. This paper compares Lite-Sparse Hierarchical Partial Power Processing (LS-HiPPP), a new method for power processing in 2-BESS, to conventional power processing architectures using a stochastic EV charging plaza model. This method for performance evaluation allows a fair comparison among power processing architectures for 2-BESS. Results show that LS-HiPPP increases the battery energy utilization to 94% as compared to 78% for conventional partial power processing (C-PPP) and 23% for full power processing. These results were obtained with 25% heterogeneity in individual battery capacities and 20% power processing within the 2-BESS. Derating and captured value are two derived performance metrics for comparing LS-HiPPP and C-PPP in this work. The derating for LS-HiPPP is 84.3% in comparison to 63.1% for C-PPP. The captured value for LS-HiPPP is 79.8% versus 51% for C-PPP., Comment: typos corrected, references added, several sections from the previous version were omitted because it is out of scope for the journal submission, title, abstract and introduction revised, results unchanged

Wireless power transfer for lightweight unmanned aerial vehicles (UAV) and agile robots require relatively long transfer distances, tolerance to misalignment, light weight, and high power. In this paper, we show that operating at VHF (very-high-frequency) together with segmenting air-core coils using discrete capacitors and driving each segment separately is an effective method to achieve these goals. An active-to-passive segmented (APS) WPT system with eight primitive current-mode class D (CMCD) converters was demonstrated to operate at 100 MHz with 6W output power with 69% end-to-end drain (dc-dc) efficiency; 10W output power with 65% end-to-end drain (dc-dc) efficiency both at 4 cm transfer distance using an active segmented CMCD inverter and a passive segmented CMCD rectifier.

A modular approach to the complex robotic systems is desireable due to advantages such as ease of development, reconfigurability, and re-usability. Powering these dynamic structures while maintaining ease of assembly and versatile form-factor is a challenge. One promising solution is to exchange energy between modules which each have a small battery. Performing this exchange of energy using mechanical connections is not only unreliable but also limits the reconfigurability of the modules. In this paper, we present a bidirectional capacitive wireless power transfer scheme for energy balancing between different robot modules. A modified CMCDE topology is also presented to make the power transfer resilient to the changes in the robot dimensions. The concept is verified by demonstrating 20 W of power transfer between two modules at 13.56 MHz achieving a dc-dc efficiency of 79 % that is resilient to the changes in the track length.

Power conversion at 100MHz is important to miniaturization and integration, which is critical in wireless power transfer (WPT) for Peer-to-Peer (P2P) charging in consumer electronics and Internet of Things (IoT). Design and implementation at this frequency is challenging in selecting active devices, passive components, gate drivers, and circuit topologies along with compensation networks, which are crucial for WPT systems capable of a wide load range.This paper articulates the design of a 100MHz inductive wireless power transfer system using current-mode class D converters both for the transmitter and receiver. An equivalent model for the symmetric CMCD WPT system is derived and used to show purely resistive input impedance, wide load range, and constant output current with the tuned compensation networks obtained from the previously published current-controlled-voltage-source (CCVS) model. Uniqueness of solution and sensitivity to parameters is analyzed for the compensation networks, which provides a guide for hardware designers. Finally, a prototype of a 100MHz symmetric CMCD WPT system is built and used to verify the characteristics with the designed compensation networks under different loading conditions and input voltages. A prototype of a symmetric CMCD WPT system was demonstrated to achieve 2.7W output power, nearly 70% end-to-end drain efficiency, and nearly 60% total efficiency when including gating loss.

Dynamic voltage scaling is needed to support efficient operation despite rapidly fluctuating power demand, which is exemplified in the automatic power control of LiDAR (Light Detection and Ranging) for autonomous ground and airborne vehicles. This is especially challenging in boost converters because of more complicated dynamics. A current-mode boost converter using constant-off-time (variable-frequency) is particularly advantageous because inductor current settles in one switching cycle. Digital control is needed for programmable flexibility over a wide operating range. However, variable frequency power conversion and high speed digital control are difficult to combine in a traditional digital control framework. In this paper, we apply and demonstrate in hardware a recently published theoretical framework for cycle-by-cycle digital control of variable frequency power converters. The prototype variable-frequency boost converter with a 3 MHz peak switching frequency shows an exceptionally fast dynamic response over a wide operating range.

Maximum power point tracking (MPPT) is one of the main challenges in solar photovoltaic systems, especially under partial shading conditions in which solar panels do not receive uniform solar irradiance. The diffusion charge redistribution (DCR) technique is an approach which uses the intrinsic diffusion capacitance of solar cells together with semiconductor switches to balance the voltage among the cells. Using this technique enables us to apply MPPT with cell-level granularity using a single module-level converter. The differential DCR (dDCR) structure is a modification to the conventional DCR structure to enable differential power processing, which leads to low insertion loss because only the mismatch power is processed by every switch. The dDCR architecture has two outputs and needs a two-port converter. This paper examines a two-port up/down dc-dc converter which is capable of doing two-dimensional MPPT of dDCR solar panels. An emulator is also presented to replicate the averaged behavior of dDCR solar panels for evaluating the converter. Prototypes of the converter and the emulator were built and a coordinate ascent method was used as the two-dimensional MPPT algorithm; the capability of the converter to do two-dimensional MPPT of dDCR solar panels was demonstrated.

The fastest transient response of dc-dc converters, which is a dominant performance criterion for dynamic voltage scaling (DVS), is fundamentally limited by the inductor current slew rate. We employ a saturating inductor with a systematic control design to increase the slew rate without introducing extra hardware. The resulting 5 MHz saturating inductor current-mode buck converter using constant-on-time (CM-COT buck converter) controlled by a high-speed cycle-by-cycle digital controller that is designed under the switching-synchronized sampled-state space (5S) control framework exhibits a 2.6 μs large-signal voltage risetime (10%-90%) with no overshoot. Furthermore, we extend the 5S control framework to this nonlinear converter plant by utilizing singular perturbation theory. The resulting controller exhibits a large-signal stability and an ability to handle a peak slew current that is 11 times the steady-state average current in a 30 W saturating inductor CM-COT buck converter prototype.