Operating Frequency Range of Air Core Magnetic Inductors for Very High Frequency Power Converters

In power converters, current sensing is essential for control and protection. This paper employs tunnel magnetoresistance (TMR) to non-invasively measure the PCB trace current in high frequency power converters. The operating principle of the TMR sensor is briefly introduced. Then we discuss the influence of skin effect on TMR measurement delay and bandwidth. Based on the finite element method (FEM) simulations, optimal install locations of the TMR sensor are found to avoid the influence of skin effect. An empirical formula is provided to summarize the optimal install locations under different trace widths. By putting the TMR sensor at the optimal location, the measurement delay is reduced from 517ns to 102ns according to experimental results. Next, a comb-shaped shield is proposed to suppress the switching spikes of TMR sensor output caused by common mode noise. The parameters of the comb-shield are chosen such that the electric field are shielded without affecting the magnetic field distribution. With the proposed comb-shaped shield, the TMR output spikes is reduced from 0.20V to 0.05V, whereas the measurement delay is almost not affected (W/O-102ns, with114ns).

The nature of reverse recovery losses is examined in hard-switched and soft-switched converters, using silicon (Si), silicon carbide (SiC), or gallium nitride (GaN) devices. A loss model and experimental results with a prototype 150-to-400 V, 150 W, boost converter operated at switching frequencies between 500 kHz and 2 MHz are used to characterize and quantify losses related to diode reverse recovery. It is found that reverse-recovery related losses with Si diodes cannot be neglected even when the converter is soft switched, with zero-current switching of the diode and zero-voltage switching of the transistor. The switching losses with SiC or GaN diodes are substantially smaller in all cases considered, and can be reduced to negligible values when the converter is soft switching.

Paralleling converters is a good choice for designing high frequency and high power converters. Nevertheless there must be a mechanism to share the load among phases to achieve all the benefits of parallel operation. A simple method to achieve current sharing is paralleling converters with high impedance. The ZVT Boost converter has interesting properties: Zero Voltage Transition, less semiconductors stress and high input impedance, what can be used as a passive lossless current sharing method. It has been analyzed in this paper, getting a complete model, where the impedance has been studied. A 2-stages 600 W prototype has been designed to test the current sharing.

Due to the modulator free structure, the finite-control-setmodel predictive control (FCS-MPC) needs a high sampling frequency/interrupt frequency (20–50 kHz) for power converters application, while the typical converter switching frequency is around 20–25% of the sampling frequency. To obtain a high switching frequency, it is not always practical to increase the sampling rate by considering the computational burden in a digital processor. Therefore, increasing the switching frequency without using a high sampling frequency is a critical task for FCS-MPC, particularly applied to silicon carbide and gallium nitride-based high switching frequency power converters. To solve this problem, this article proposes the multirate FCS-MPC (MRFCS-MPC), where the control frequency is allowed to be higher than the sampling frequency. Consequently, the switching frequency can be significantly increased without changing the sampling frequency. The proposed scheme inherits the ability to handle complex control objectives from the traditional FCS-MPC. The lifting model is built to predict the fast rate information of state variables based on the low sampling output. Then, the fast rate control inputs within one sampling interval are solved efficiently with a good tradeoff between computational burden and optimized system performance. The experimental motor drive system tests are carried out to verify the effectiveness of the proposed MRFCS-MPC.

High density high switching frequency power converter conducted EMC had been analysed, modelling the noise source and noise path, while providing accurate conducted EMC noise limits comparable to accredited noise measurements up to 100 MHz. The military specified DC-DC converters are applicable, spanning from 100 W handheld power managers up to 2 kW DC-DC battery chargers. The Step-Down converter, Step-Up converter and their multi-phase derivatives were analysed and modelled. Some techniques to reduce conducted EMI, such as phase dithering, were also analysed. Circuit layout high frequency effects as well as high frequency impedances of the power components were characterised. At first, a trapezoidal noise source and lumped element noise path model was adopted, showing the high frequency limitations of this technique. A mathematical model was also presented. Thereafter, a high frequency lumped element model including switching elements, was created by using equivalent impedance circuits obtained by measurement from an impedance analyser performed on individual components and traces. A time domain transient model circuit analysis was investigated to represent noncompliance circuit noise as measured with a LISN. Various affordable software packages were evaluated to be considered as a high frequency conducted EMC tool, noting accuracy and ease of use. The accuracy of these modelling tools was compared to accredited measurements. A compact LISN was manufactured and a measurement bench was set up and calibrated against an accredited LAB to perform these practical verification tests. Noise signals were recorded in a simultaneous digital manner so as to be able to perform a detailed post analysis as well as diagnostic calculations, such as common mode and differential mode separation, calibrated with an EMC ETS-Lindgren current probe. Good and workable model accuracies were achieved with the basic Step-Up and Step-Down circuits over the conducted emission frequency band and beyond. Prominent noise effects occur up to this frequency when high density and high switching speed converters are analysed.

Raman frequency conversion of high average power pulsed Nd:YAG laser radiation into the near IR spectral region in a barium nitrate Raman laser was studied with the emphasis on thermal effects inside the Raman-active medium. The probe-beam technique together with numerical reconstruction, done by integrating the transient heat conduction and paraxial wave equations, revealed dynamics of the induced distortions featuring high-order optical aberrations. By utilizing the Zernike expansion of the reconstructed phase profile and implementing a special focusing geometry of the pump beam, partial compensation of the distortions was realized in a stable configuration of the Raman cavity. Generation of the first-, second-, and third-order Stokes radiation with output power of 17, 9.5, and 5.5 W corresponding to a quantum conversion efficiency of 32, 21, and 13% is reported.

This paper presents a design procedure for inductors based on low-permeability magnetic materials, for use in very high frequency power conversion. The proposed procedure offers an easy and fast way to compare different magnetic materials based on Steinmetz parameters and quickly select the best among them, to estimate the achievable inductor quality factor and size, and to design the inductor. Approximations used in the proposed methods are discussed. Geometry optimization of magnetic-core inductors is also investigated. The proposed design procedure and methods are verified by experiments.

A new microtransformer (1:1) for high frequency power or signal conversion has been designed, fabricated and characterized in this work. An innovative laterally laminated-core structure has been adopted and implemented by using new micromachining techniques. Using the fabricated microtransformer, a voltage gain of -4 dB has been achieved over the frequency range of 7-11 MHz. The coupling coefficient between the primary and secondary coils is higher than 0.9 up to 5 MHz. The transformer realized in this research functionally works as a basic transformer for power or signal conversion.

The recent advancement in the technology of SiC MOSFETs has spurred interest in designing compact and high switching frequency (10–20 kHz) power converters. However, grid-integration of these power converters at medium voltage (MV) scale would require a conventional transformer. With the development of new high voltage (HV) 10 kV and 15 kV SiC MOSFETs, these converters can directly interface with medium voltage (MV) grids without the need for line-frequency transformers, using simple two-level and three-level topologies. The application of these devices is currently being explored in all MV Applications (8 kV to 30 kV) like Solid State Transformer, MV Drives, Power Conditioning Systems, and MVDC isolators. This paper discusses application of 10 kV SiC MOSFETs and JBS Diodes for enabling Asynchronous Microgrid Power Conditioning System (AMPCS). This medium voltage power converter is enabled by series-connection of devices, in a Three-Level Neutral Point Clamped (3L-NPC) configuration. The voltage balancing of these series-connected devices is achieved by using R C-snubbers. This paper addresses the different conduction modes and switching sequences of a 3L-NPC pole, which is used as building block for the three-phase converter. The switching loss analysis, for various snubber values, is presented for the MOSFETs and the clamping diodes along with experimental results. This research helps in providing an overview of switching losses that are disspated through the device (and heatsink) and through the snubber resistor in a 3L-NPC convertor pole.

Both high switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) topology allows zero voltage soft switching (ZVS) under all line and load conditions, eliminates leakage inductance and snubber losses, and enables high frequency and high power density power conversion. Traditional ACF ZVS operation relies on the resonance between leakage inductance and a small primary-side clamping capacitor, which leads to increased rms current and high conduction loss. This also causes oscillatory output rectifier current and impedes the implementation of synchronous rectification. This paper proposes a secondary-side resonance scheme to shape the primary current waveform in a way that significantly improves synchronous rectifier operation and reduces primary rms current. The concept is verified with a 25-W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> high-density 45-W adapter prototype using a monolithic gallium nitride power IC. Over 93% full-load efficiency was demonstrated at the worst case 90-V ac input and maximum full-load efficiency was 94.5%.

Technologies enabling the development of compact systems for wireless transfer of power through radio frequency waves (RF) continue to be important for future space-based systems. A typical wireless power receiver (WPR) consists of an antenna array and an RF to DC power conversion network. The physical size of a WPR is inversely proportional to its frequency of operation and directly depends on its power delivery capacity. The smaller form factor of the higher frequency WPRs makes them more attractive for space systems. However, they have to deal with: 1) Availability of high frequency power conversion components; and 2) Overall efficiencies in antenna arrays and power conversion networks. In this paper we present a new, compact, scalable, and low-cost slot antenna array technology for efficient receipt and conversion of power using RF waves at 94 GHz. Simulation of the performance of an individual slot suggests that the antenna can capture 93% of the RF energy. In an array form, this efficiency is also a function of the packing density of the slots and the ratio of energy stored in the antenna side lobes. Antenna simulation results suggest that the energy of the side lobes of each slot is more than 20 dB lower than that of the main lobe. As a result, slots can be placed very close to each other. A very small network located adjacent to each individual slot differentially converts the RF to DC power. This network consists of a coupling electrode, bypass capacitors, a matching transmission line, a rectifier, a low pass filter, and a DC storage capacitor. Details of the network and its fabrication over the slot array using additional layers of SiO2 and Au are described. Simulation results are also presented, which suggest that this technology is capable of realizing overall conversion efficiencies greater than 72%.

The higher switching frequency in combination with di/dt loops and dv/dt nodes in the power stages of high frequency power converters generates higher order harmonics which cause Electro Magnetic Interference (EMI). It is commonly perceived that high frequency converters are more vulnerable to radiated EMI, thus, it is very important to analyze the radiated emission of these converters. According to the author's knowledge, the analysis of the radiated emission of power converters switching in the MHz frequency region has not been presented until now. Therefore, in this paper, the measurements, and analysis of the near field radiated emissions of these emerging power converters is presented. These measurements are beneficial in the early design stage of power converters. Both E-field and H-field and captured and analyzed for a half bridge converter switching at 3 MHz and at the output power level of 25 W. The effects of the magnetic and electric field emissions with the addition of a Y-capacitor and secondary side common mode choke are analyzed.

In a high-frequency power converter above MHz, the loss caused by the AC resistance of the transformer winding becomes the bottleneck restricting the efficiency of the converter. A new half-turn matrix planar transformer structure is proposed for the half-bridge LLC resonant converter which is commonly used in high-frequency power converter to solve this problem. Compared with traditional planar transformers, the minimum turns ratio of the winding is shifted from n: to 0.5n: 0.5, and the AC loss of the primary and secondary windings is reduced to half of the original. Moreover, the proposed transformer also uses the principle of magnetic flux cancellation to reduce the core loss and it is more convenient for the termination of the secondary windings and the synchronous rectifiers, reducing the termination loss and via loss. Different half-turn matrix transformer structures are studied in this paper and the optimized design methods are proposed. Based on ANSYS Maxwell simulation, the transformer loss is reduced compared with the traditional one under 1 MHz frequency and 1kW power condition and the flux balance is achieved.

Pulsed electrolysis has become a promising research topic in recent decades due to advances in solid-state semiconductor devices. These technologies have enabled the design and construction of simpler, more efficient, and less costly high-voltage and high-frequency power converters. In this paper, we study high-voltage pulsed electrolysis considering variations in both power converter parameters and cell configuration. Experimental results are obtained for frequency variations ranging from 10 Hz to 1 MHz, voltage changes from 2 V to 500 V, and electrode separations from 0.1 to 2 mm. The results demonstrate that pulsed plasmolysis is a promising method for decomposing water for hydrogen production.

The dv/dt switching limitations of power semiconductor devices are evaluated in a boost (PFC) power converter using circuit simulations. State-of-the-art commercial silicon CoolMOS devices, commercial Silicon Carbide (SiC) Junction Barrier Schottky (JBS) diodes, and emerging Gallium Nitride (GaN) lateral power transistors are considered. It is shown that although SiC and GaN power devices have low stored charge and small capacitances, they experience high switching dv/dt stresses which may pose serious switching limitations especially in high-frequency power converters. This problem is likely to be further exacerbated by the presence of a high density of crystal defects in SiC and GaN materials which will manifest in the form of poor field-reliability. Specific guidelines for device selection are recommended in order to optimize both performance and field-reliability.