Adam Barkley

A High-Density, High-Efficiency, Isolated On-Board Vehicle Battery Charger Utilizing Silicon Carbide Power Devices

This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case.

Improved Online Identification of a DC–DC Converter and Its Control Loop Gain Using Cross-Correlation Methods

Recent progress in the identification of switching power converters using an all-digital controller has granted network analyzer functionality to the control platform. In particular, the cross-correlation technique provides a nonparametric identification of a converters small-signal control-to-output frequency response. The literature shows the viability of this technique as well as a few improvements to the basic technique. This online network analyzer functionality allows new flexibility in the areas of online monitoring and adaptive control. In this paper, several improvements to the cross-correlation method of system identification are proposed that aim to further improve the accuracy of the frequency response identification, particularly at high frequencies near the desired closed-loop bandwidth frequency. Additionally, an extension to the cross-correlation method is proposed that allows measurement of the control loop gain without ever opening the feedback loop. Thus, performance and stability margins may be evaluated while maintaining tight regulation of the output. Simulation and experimental results are shown to verify the proposed improvements and extension.

Improved online identification of switching converters using digital network analyzer techniques

Recent progress in the identification of switching power converters using an all-digital controller has granted network analyzer functionality to the control platform. In particular, the cross-correlation technique provides a nonparametric identification of a converterpsilas small-signal control-to-output frequency response. The literature shows the viability of this technique as well as a few improvements to the basic technique. This online network analyzer functionality allows new flexibility in the areas of online monitoring and adaptive control. In this paper, several improvements to the cross-correlation method of system identification are proposed which aim to further improve the accuracy of the frequency response identification, particularly at high frequencies near the desired closed-loop bandwidth. Additionally, an extension to the cross-correlation method is proposed which allows measurement of the control loop gain without ever opening the feedback loop. Thus, performance and stability margins may be evaluated while maintaining tight regulation of the output. Simulation and experimental results are shown to verify the proposed improvements.

Wide bandwidth system identification of AC system impedances by applying pertubations to an existing converter

A new approach is developed using an existing single-phase power electronics inverter to make a wideband impedance measurement at its interface using a pseudo-random binary sequence (PRBS) voltage perturbation and digital network analyzer techniques. Since the PRBS is an approximation to white noise, all frequencies of interest can be excited simultaneously. The perturbation at the interface is measured and cross-correlation techniques are applied to construct the wideband impedance of the system under test. Online monitoring of interface impedances is a key enabler for a number of smart-grid related capabilities, such as grid health monitoring, active filter re-tuning, identifying system interaction, and adaptive control of grid-connected switching converters. Knowledge of the converters surroundings enables smarter control actions, which lead to improved stability, performance and reliability of the smart grid.1

A 4H Silicon Carbide Gate Buffer for Integrated Power Systems

A gate buffer fabricated in a 2-μm 4H silicon carbide (SiC) process is presented. The circuit is composed of an input buffer stage with a push-pull output stage, and is fabricated using enhancement mode N-channel FETs in a process optimized for SiC power switching devices. Simulation and measurement results of the fabricated gate buffer are presented and compared for operation at various voltage supply levels, with a capacitive load of 2 nF. Details of the design including layout specifics, simulation results, and directions for future improvement of this buffer are presented. In addition, plans for its incorporation into an isolated high-side/low-side gate-driver architecture, fully integrated with power switching devices in a SiC process, are briefly discussed. This letter represents the first reported MOSFET-based gate buffer fabricated in 4H SiC.

Single Stage Brushless DC Motor Drive with High Input Power Factor for Single Phase Applications

This paper proposes a single stage topology suitable for small to medium power systems with high inertia loads such as home appliances. This approach features a single controlled power stage which implements both conventional brushless DC motor speed control and a novel power factor correction strategy. This approach eliminates the Boost Unity Power Factor (UPF) stage and bulk electrolytic capacitor typically used for single phase applications. With an appropriate current modulation strategy, the input current can be shaped and high input power factor can be obtained. Design equations are derived, a comparison with the conventional two-stage approach is performed and simulation and experimental results are presented.

Online Monitoring of Network Impedances Using Digital Network Analyzer Techniques

This paper presents an extension to the cross-correlation method for switching power converter identification which allows monitoring of Thévenin source and load impedances. This information can be used for fault localization, converter health monitoring, and load estimation. Additional insight into performance degradation due to subsystem interaction can also be obtained. To verify the proposed approach, impedances of three commonly encountered loads and an undamped input filter are measured and compared to results from a conventional network analyzer. Some practical techniques for improved high-frequency measurements are given, and a method to measure the Minor Loop Gain at an interface is proposed.

A UVLO Circuit in SiC Compatible With Power MOSFET Integration

The design and test of the first undervoltage lock-out circuit implemented in a low-voltage 4H silicon carbide process capable of single-chip integration with power MOSFETs is presented. The lock-out circuit, a block of the protection circuitry of a single-chip gate driver topology designed for use in a plug-in hybrid vehicle charger, was demonstrated to have rise/fall times compatible with a MOSFET switching speed of 250 kHz while operating over the targeted operating temperature range between 0°C and 200°C. Captured data show the circuit to be functional over a temperature range from -55°C to 300°C. The design of the circuit and test results is presented.

Fault protection and ride-through scheme for MVDC power distribution systems utilizing a supervisory controller

The paper proposes a protection scheme for zonal MVDC systems that allows fault isolation and ride-through of unfaulted zones. A Supervisory Controller coordinates the actions of mechanical contactors and a switching power converter to achieve the protection and reconfiguration function necessary in MVDC systems. Experimental results demonstrate the feasibility and performance of the approach.

Adaptive control of power converters using Digital Network Analyzer Techniques

We describe a new method for design of adaptive controls for switching power converters that leverages the information-rich frequency response data obtained using the correlation-based analysis dubbed Digital Network Analyzer Technique. Compared to existing single-frequency based adaptive control methods such as limit-cycle and relay-feedback based autotuning, this method provides a unified approach to target many distinct problems plaguing converter control designers. The major strength of this method is that a single adaptive controller structure is able to fix multiple converter problems with a generalized and online identification and adaptation procedure. Also, unlike the conservative nature of robust control, adaptive control attempts to maintain relatively high performance at each time instant whenever possible. A step-by-step procedure is given which explains how the control platform can use the converter to perturb the system, identify the non-parametric frequency response of the plant, fit the data to a parametric model, and synthesize a control which meets user specifications. Simulation results are provided for a comprehensive set of realistic scenarios, where each test case uniquely degrades the converter frequency response. In each case, the performance and stability degradation is mitigated through targeted control adaptation.