ABSTRACT. This digest presents a 48V-to-1V stacked direct forward (SDF) dc-dc converter consisting of four 12V-to-1V direct forward (DF) modules connected in input-series output-parallel (ISOP) configuration. In each DF module, there is no secondary-side inductance, and a single-ended forward transformer is driven at high duty cycle to reduce the switch rms currents. An active clamp is employed on the primary side to reset the transformer, limit the switch voltage stress, and facilitate zero voltage switching. The approach is verified by simulation results on a 12V-to-1V, 50 A, 200 kHz prototype module using GaN devices and a planar transformer and having a peak efficiency of 93.9% and the full-load efficiency of 91.8%. Experimental results for a complete 48V-to-1V, 200A SDF converter prototype will be presented in the full paper.

ABSTRACT. This paper proposes an ultra-high-current 48-V-to-1-V hybrid switched-capacitor (SC) converter for next-generation digital loads (e.g., CPUs, GPUs, ASICs, etc.). The proposed topology can be viewed as two 2-to-1 SC converters merged with four 10-to-1 series-capacitor-buck (SCB) modules through four switching buses. Compared to the DC bus architecture, the switching bus architecture does not require bulky DC bus capacitors, reduces the number of required switches, and enables complete soft-charging operation. Compared to existing 48-V-to-1-V hybrid SC demonstrations, the proposed topology achieves the lowest normalized switch stress and the smallest normalized passive component volume, promising both higher efficiency and higher power density. 

ABSTRACT. This paper introduces a high conversion ratio multi-phase non-isolated DC-DC topology build from generic series-capacitor boost cells. Using a stand-alone LC cell, the approach contributes to a high modularity of the resulting converters and enables high conversion ratios. The unique interaction between the capacitor and the inductor result in a soft charging operation, which curbs the losses of the converter, and contributes to higher efficiency. The method was used to create a multiphase step-up DC-DC module for using in microinverters. The new converter significantly extends the effective duty ratio and lowers the voltage stress of the transistors and has inherent current sharing to balance the load between the phases. Experimental results of a modular interleaved two-phase prototype demonstrate an excellent proof of design methodology concept and agree well with the simulations and theoretical analyses developed in this study.

ABSTRACT. Wide-range switched-mode power amplifiers are desired that can work across a wide range of power levels and load impedances while maintaining high efficiency. Such designs would be valuable for emerging applications including plasma generation and wireless power transfer. We introduce a new wide-range switched-mode power amplifier architecture that can directly modulate its output voltage, enabling to output power modulation and compensate for resistive load variations. Dynamic frequency modulation is leveraged to address reactive load variations. The new architecture enables all the semiconductor switches to maintain zero-voltage switching across operating conditions.

ABSTRACT. This paper presents the design and implementation of a 13.56 MHz push-pull Class E power amplifier with broadband capabilities. The Class E amplifier utilizes SiC MOSFETs with a custom current source resonant gate driver. Because the amplifier is a push-pull structure, we design and implement a balun that converts the differential output into a ground-referenced output. This work experimentally demonstrates the proposed amplifier delivering over 1 kW power to a 50 Ω load impedance.

ABSTRACT. Piezoelectric devices have recently emerged as a promising candidate to replace magnetic components. Past research has explored different topologies and control strategies for dc-dc converters which only use a single piezoelectric resonator as the main energy-storage component. However, such converters exhibit relatively low efficiency when the voltage conversion ratio varies from its nominal value. This digest proposes a new merged switched-capacitor piezoelectric-resonator based dc-dc converter which can achieve high and flat efficiency across a wide voltage conversion ratio. In this converter, the switched-capacitor and the piezoelectric-resonator are combined to form a multi-level structure and controlled in a manner to achieve high efficiency across a wide voltage conversion ratio. The proposed topology and control strategy enables the switched-capacitor to be soft-charged by the current from the piezoelectric resonator and achieves zero-voltage-switching (ZVS) for all its switches. The steady-state operation of the proposed converter is analyzed in detail. Simulation and experimental results are presented to verify the advantages of the proposed converter. Finally, a method to derive a family of merged switched-capacitor piezoelectric-resonator based dc-dc converters based on the proposed principle is also presented.

ABSTRACT. Soft robots are enabling technologies for many emerging and important applications. The operation voltages of soft actuators, i.e., Macro Fiber Composites and Dielectric Elastomers, are usually in the range of hundreds or above a thousand volts. Each actuator in a soft robot needs to be controlled independently to perform useful functions. This paper presents the design and implementation of a flexible lightweight high voltage power converter for multi-actuator piezoelectric soft robots. A pulsed 1500 V, 1 W output can be generated from 7.4 V input voltage with less than 5 g of weight in power electronics. The flexible lightweight switched-capacitor-transformer dc-dc converter can be used in a wide range of piezoelectric soft robots with sophisticated control patterns.

ABSTRACT. Piezoelectric transformers (PTs) are a promising energy storage alternative to magnetics for power converter miniaturization. PTs offer galvanic isolation and voltage transformation like traditional magnetic transformers, but with superior power scaling properties at small size scales. Despite these advantages, most magnetic-less PT-based dc-dc converter designs have limited efficiencies and power densities. In this paper, we present a design framework for PTs that enables simultaneous achievement of maximum efficiency and maximum power density at a nominal operating point, while maintaining high-efficiency converter behaviors such as zero voltage switching (ZVS). We demonstrate this design process in the context of dc-dc power conversion, and the result suggests that significant gains in PT performance are possible with existing materials using these design strategies.

ABSTRACT. Piezoelectric devices recently have emerged as a viable alternative to replace magnetics. However, their applications have primarily been focused on dc-dc converters that utilize off-the-shelf piezoelectric devices. This paper introduces a class-e power amplifier that utilizes a newly developed piezoelectric transformer (PT) capable of scaling different conversion ratios. The proposed PT comprises a vertically stacked substrate quartz with PZT pieces mounted on the top and bottom surfaces of the quartz. The conversion ratio of the proposed device structure is established based on the constitutive equations of piezoelectric materials, and a design methodology is presented to achieve different voltage gains based on corresponding device parameters. A prototype PT is fabricated and tested to validate the proposed structure. Finally, a 13MHz class-e power amplifier is developed and tested using the proposed PT to demonstrate its advantage.

ABSTRACT. By operating resonant switched-capacitor converters precisely at the resonance timing between the LC tank comprised of the equivalent capacitance and inductance during each phase, zero current switching (ZCS) can be achieved to eliminate voltage-current overlap losses. Previous literature has shown that zero voltage switching (ZVS) can also be achieved to further reduce the switching losses and attain a higher peak efficiency by recovering the charge stored in the switches' parasitic output capacitance (Coss) every cycle.

Contrary to ZCS operation, even with ideal primary passive components, ZVS timing is highly dependent on load current. To maintain optimum ZVS timing through load changes and passive component variations, this paper proposes a novel digital feedback control technique that can dynamically track and achieve ZVS operation in a 2-to-1 resonant switched capacitor (ReSC) converter. The proposed concept is validated in a 48-V-to-24-V experimental hardware prototype, demonstrating up to 20% power loss reduction compared with conventional ZCS techniques.

ABSTRACT. This paper presents a novel decentralized start-up technique for cascaded converter setups in grid-forming applications. The proposed method controls each bidirectional cascaded converter as a rectifier unit that transfers power from the grid into the dc-side by modulating each module as a virtual resistor. Since resistors are agnostic to frequency and voltage, and simultaneously limit the current drawn from the grid, this method is not prone to over-currents and synchronizes inherently because of the series-current that is shared amongst the cascaded units. Provided the emulated resistances are within some theoretical limits, the localized PLL within each module is able to decipher the frequency, phase angle, and magnitude of the grid voltage. This information is then passed to the primary control (droop, virtual oscillator, or virtual synchronous machine) and we flip the direction of power flow as the system begins normal operation as a grid-forming unit. Compared to existing methods for start-up with a grid, this technique does not require external charging resistors or a centralized PLL to synchronize the series-connected modules. Furthermore, our approach achieves decentralized synchronization without any prior knowledge of the grid voltage, frequency, and phase. The proposed method is verified experimentally and in a simulation of a medium voltage application.

ABSTRACT. Grid-forming inverters are a promising technology for wide-scale implementation of renewable energy sources. As one of the key elements of grid-forming inverter control, the primary controller generates an internal reference voltage and angle. During contingencies in the grid such as faults, voltage drops, or frequency jumps, the inverter can be pushed into a current limiting operation, during which it is prone to lose synchronism with the connected grid. In this digest, we propose a synchronization method for grid-forming inverters such to maintain synchronism with the grid during current-limiting conditions. The method is illustrated for voltage and frequency jumps both in a SMIB and a network-wide EMT simulation.

ABSTRACT. Traditionally, power systems have been designed to operate with fixed frequency/voltage distribution systems. This frequency (0 Hz DC, 50 Hz European, 60 Hz, 400 Hz, or other) optimizes the system's performance. This approach has worked well throughout history, enabling the development of a design, analysis, and maintenance tool suite. Regulating the voltage this way results in additional control effort that can impact the system's performance. Not to mention that single-frequency operation could be considered sub-optimal in energy and power density. In particular, this is expected to be true for systems with highly stochastic sources or loads (e.g., PV, wind). For example, consider military power systems designed to source hotel loads and large pulsed electric loads (e.g., rail gun, electromagnetic launcher). Introducing electric weapons moves impedance matching/energy storage from mechanical/chemical based to electrical-based. By definition, these pulsed loads are multi-frequency and impossible to match impedance to the sources using traditional methods without incurring additional losses in the system. Such pulses can also result in significant voltage swings/transients on the bus. This paper will present the foundations of a generalized power-packet network (PPN) that represents a multi-frequency power system where power channels can be impedance matched independently of each other.