Research Highlights – Power Electronics and Magnetics Group

Resonant Loss Characterization of High Frequency Magnetic Components

Losses in magnetic components are nonlinear functions of frequency, especially at MHz frequencies and above. We propose two resonant approaches (series and parallel) to facilitate the ease of measuring a magnetic component’s losses, including the coupled effects of both windings in the case of transformers. The loss measurements obtained using these methods are found to correlate well against hand calculation, finite element analysis simulation, and calorimetric measurement.

- “Parallel Resonant Loss Characterization of High Frequency Magnetic Components” (JESTPE Journal – Sep 2024)
- “A Resonant Approach to Transformer Loss Characterization” (APEC 2022)

Double-Sided Conduction

Power converters are increasingly being operated in the high-frequency (HF) regime (3–30 MHz), where proximity-effect losses in transformers are difficult to contain. Litz wire does not scale well to multi-MHz operation where sub-skin-depth strands are prohibitive to manufacture. Interleaving is more scalable to HF and, in its best implementations, causes a current equal to the net current to flow on a single surface of a conductor or layer of conductors (e.g., a copper turn in a planar transformer), with no “negative” current or eddy currents. Double-sided conduction (DSC) is a field-shaping technique that results in the even distribution of current on two sides of each conductor layer, yielding two skin-depths worth of conduction. Double-sided conduction promises up to 50% improvement in copper losses in transformers wound with foil and solid wires, a scenario likely to be important as power converter operating frequencies exceed the useful range of Litz wire.

- “Double Sided Conduction in N:1 Transformers” (APEC 2024)
- “Double-Sided Conduction: A Loss-Reduction Technique for High Frequency Transformers” (APEC 2022)

High-Efficiency Wireless Inductive Power Transfer (IPT) Systems

Inductive power transfer (IPT) offers clear benefits over wired power transmission in battery charging, including safety, convenience, and automation. The efficiency of inductive power transfer (IPT) systems is strongly dependent on the load. We propose a dual-PWM control strategy, which enables zero voltage switching (ZVS) for all the power switches and optimization of the resonant tank power transfer efficiency (low reactive power) simultaneously. Compared to existing dual-phase-shift (DPS) control and triple-phase-shift (TPS) control, dual-PWM control achieves a higher efficiency across a wide load range. Another research direction to achieve constant current (CC) and constant voltage (CV) charging, and zero voltage switching (ZVS) of all switches is to use a variable inductor on the primary side . The system operates at a fixed frequency, eliminates the need for wireless communication and any secondary-side control, minimizing the complexity and cost of the secondary side especially. The cha charging current and voltage are well-regulated in their respective modes, while maintaining a high system efficiency.

- “Dual-PWM Control of Inductive Power Transfer Systems for High Efficiency Over Wide Load Ranges” (APEC 2024)
- “A Communication-less Wireless Battery Charger Based on Variable Inductor” (APEC 2024)

Switch-Mode & Synchronously Switched Active EMI Filters

Electromagnetic interference (EMI) in the 0.15-30 MHz frequency range is a key challenge. While passive LC filters can occupy up to 1/3 of the power supply’s volume, active EMI filters (AEFs) are effective in reducing filter size and current. Traditional AEFs use linear amplifiers to counteract ripple voltage or current, leading to limited bandwidth and high power consumption. We investigate switch-mode and synchronously switched AEFs as alternatives, which use high-frequency (30-300 MHz) amplifiers to achieve near-100% efficiency and avoid introducing additional interference in the regulated range.

Differential Power Processing Architecture for On-Vehicle Photovoltaics

On-vehicle integration of photovoltaics can extend the range of electric vehicles by a useful amount each day. However, partial shading can significantly limit PV power production even in stationary installations, and this is expected to be more severe in vehicles. Differential power processing (DPP) approaches can maximize PV output power despite partial shading. A PV-to-isolated-bus DPP architecture using extensible and inexpensive converter modules can leverage the vehicle’s existing low voltage battery as the common bus and reuse the existing onboard charger to interface the solar string to the high-voltage battery. The proposed converter module achieves maximum power point tracking (MPPT) for the cell(s) it is connected to without requiring any communication or power transfer across the isolation barrier while allowing bidirectional power with synchronous rectification. This offers high system efficiency, and simple control that scales easily to large numbers of DPP units.

- “Highly-Scalable Differential Power Processing Architecture for On-Vehicle Photovoltaics” (COMPEL 2023)

Compact Pulsed Power Systems Using GaN Devices and High-Efficiency Magnetic Structures

Pulsed power systems involve the transfer of massive amounts of energy at very high voltages and currents, in very short pulses with very fast rise times. They traditionally use reed switches and spark-gap mechanical switches. Modular pulsed power systems such as inductive voltage adders (IVAs) use multiple series-stacked modules, enabling the use of lower-voltage fast-switching semiconductor devices. Our initial work in this area involves characterizing GaN devices, which offer ultra-fast switching, superior electrical performance, and radiation hardness – making them a favorable choice for pulsed power applications. One potential drawback is their high on-resistance under switching conditions (dynamic Ron), which is not often publicly characterized by manufacturers. To study this, we propose a fast measurement approach with minimal additional circuitry – designed specifically for pulsed conditions. Using this approach, the dynamic Ron is measured for devices across several manufacturers, sizes (static Ron), blocking voltages and drain currents.

- “A Simple, High-Speed Measurement Technique for Dynamic on-resistance of GaN Devices for Hard-Switched Pulsed Power Applications” (COMPEL 2023)

Nonlinear Decentralized Control for Power Sharing in Modular DC-DC Converters

Modularity is an effective way to increase power converter capacity without increasing individual device stress. Its most significant impediment is control. Decentralized control of modular converters is preferable to centralized and distributed approaches because it scales more easily to large numbers of modules and it reduces the opportunity for global system failure. In this paper, we investigate a decentralized control approach wherein the increment or decrement of each module’s power at any time instant depends on the currently processing power. We highlight some issues appearing in experiments that are not seen in ideal theoretical analysis/simulation and propose solutions which are verified with experiments. We demonstrate the proposed control in a variety of configurations, including input-parallel-output-parallel, input-series-output-parallel, and a mixed input-series-parallel-output-parallel arrangement.