Xudong Huang

Parasitic ringing and design issues of digitally controlled high power interleaved boost converters

High power boost converter has become the essential part of the distributed power system that enables energy to be fully utilized in fuel cell powered electric vehicles and stationary power systems. This paper presents analysis and design of a high-power multileg interleaved boost converter with a digital signal processor (DSP) based controller. A 20-kW converter was designed with coupled inductors to allow core-loss reduction and designed with high frequency switching to minimize the component size and eliminate the switching losses under discontinuous conducting mode operation. A dual-loop average current mode current control method implemented in DSP is employed to achieve the fast transient response. It was found through circuit analysis, simulation and experiment that the boost inductor interacted with the device parasitic capacitor and created unnecessary oscillating current whenever it reached zero current. Two high-power devices were used in both simulation and experiment to verify the analysis and design for a wide load range. Simulation and experiment results of the 20-kW boost converter under startup condition and load transient condition are also presented. Different anti-windup schemes for a typical PI-controller are evaluated. The results show that this typical controller with proper anti-windup scheme achieves better transient performance than without anti-windup scheme.

Inverter EMI modeling and simulation methodologies

A numerical prediction of electromagnetic interference (EMI) allows evaluation of EMI performances at the design stage and before prototyping. It can also help reduce the post-prototype electromagnetic compatibility cost by minimizing late redesign and modifications of a drive implementation. This paper describes two simulation approaches with time- and frequency-domain simulations and verifies them with experimental results. Both time- and frequency-domain simulation approaches are found effective as long as the noise source and propagation path are properly modeled. The three-dimensional (3-D) finite-element-analysis (FEA)-based parasitic parameter extraction tool-Ansoft Spicelink has been used substantially. To gain additional degree of confidence, the results obtained from FEA are verified with closed-form solutions and actual measurements.

A DSP based controller for high-power interleaved boost converters

High power boost converter has become the essential part of the distributed power system that enables energy to be fully utilized in fuel cell powered electric vehicles and stationary power systems. This paper presents a DSP-based fully digital control implementation for an interleaved high power DC-DC boost converter. A dual-loop average current mode current control method is employed to achieve the fast transient response. Different anti-wind up schemes for a typical PI-controller are evaluated through simulations and experiments. Simulation and experiment results of the 20-kW boost converter under a start-up condition and load transient condition are also presented. The results show that this typical controller with proper anti-wind up scheme achieves a better transient performance than without the anti-wind up scheme.

Three-phase inverter differential mode EMI modeling and prediction in frequency domain

This paper describes a frequency domain approach to the prediction of differential mode (DM) conducted electromagnetic interference (EMI) for a three-phase inverter at the early design stage. The approach is able to calculate the DM conducted EMI with more accurate noise source and parasitic path identification. The DM noise sources are identified as three device switching current and their frequency domain expressions are derived according to inverter operating principle. The parasitic components are identified using FEM analysis. The calculated DM EMI result is compared with experimental data and it can predict the high frequency resonant peak precisely. It is indicated that the frequency domain analysis with accurate noise source and parasitic modeling is an effective tool for DM EMI prediction for three-phase inverter circuit.

The role of parasitic inductance in high-power planar transformer design and converter integration

Planar transformers provide a distinct advantage over the traditional transformer. However, when the planar transformer is integrated into a power circuit, the interconnect parasitic effects arise that are not shown in a traditional wire-wound transformer. For typical soft-switching converters, a specific leakage inductance is generally needed to charge and discharge the device output capacitances to achieve zero-voltage turn on. This designated leakage inductance value needs to be large enough to extend the zero-voltage switching range. However, it was found that this hard-to-come-by leakage inductance in a planar structure may be overshadowed by the circuit interconnect parasitic inductance. This paper presents a design integration that incorporates the planar transformer and a full-bridge dc/dc converter. Through design calculation, finite element analysis, and experimental verification, it was proven that the role of the parasitic inductance is indeed far exceeding the transformer leakage inductance. Thus, for any design optimization, it is necessary to take into account the parasitic inductance in the integrated structure.

EMI characterization and simulation with parasitic models for a low-voltage high current AC motor drive

In this paper, a 12-V 1-kW permanent-magnet ac motor drive is tested extensively at a wide frequency range, and the frequency spectra are partitioned for identification of noise sources and their propagation paths. Switching characterization of the power MOSFET and its body diode reverse-recovery characterization are evaluated for circuit modeling. The parasitic components and common mode path are identified and measured with the time-domain reflectometry (TDR) method. The inverter circuit model is then constructed with major parasitic inductance and capacitance in device modules, passive components, leads, and interconnects. To verify the validity of the inverter model, a comparative study is performed with computer simulations and hardware experiments. The fundamental mechanisms by which the electromagnetic interference (EMI) noises are excited and propagated are analyzed, and the significant roles of parasitic elements coupling with device switching dynamics in EMI generation are examined. The results indicate that the identification of parasitic inductance through TDR measurement helps verify the voltage spike during turn-off, or vice versa. The conducted EMI noise caused by parasitic components of bus capacitor, dc bus, and devices is proven to be identifiable with the characterization and simulation techniques used in this paper.

Parasitic ringing and design issues of high power interleaved boost converters

High power boost converter has become the essential part of the distributed power system that enables energy to be fully utilized in fuel cell powered electric vehicles and stationary power systems. This paper presents analysis and design of a high-power multi-leg interleaved boost converter. A 20 kW converter was designed with coupled inductors to allow core-loss reduction and designed with high frequency switching to minimize the component size and eliminate the switching losses under discontinuous conducting mode (DCM) operation. Although the design challenges were mainly in optimization of device and component selection for cost and size reduction. It was found through circuit analysis, simulation and experiment that the boost inductor interacted with the device parasitic capacitor and created unnecessary oscillating current whenever it reached zero current. Two high-power devices were used in both simulation and experiment to verify the analysis and design for a wide load range.

High current SiC JBS diode characterization for hard- and soft-switching applications

A newly developed high-current silicon carbide (SiC) junction barrier Schottky (JBS) diode with a 1200 V, 15 A rating was characterized and evaluated for both hard- and soft-switching applications. Experimental results indicate that the conduction characteristics are comparable with, but the switching characteristic is far superior to, its silicon diode counterpart. The SiC JBS diode exhibits nearly zero reverse-recovery time and associated losses. When applied to hard-switching choppers, it reduces not only the reverse-recovery loss, but also the main switch turn-on loss. Using the MOSFET as the main switching device, the combination of switch turn-on loss and diode reverse-recovery loss shows more than a 70% reduction. When applied to soft-switching choppers, the SiC JBS diode is used as the auxiliary diode to avoid the voltage spike during auxiliary branch turn-off. With the conventional ultra-fast reverse-recovery Si diode, a voltage spike exceeds the switched-voltage transition by 100%, and the auxiliary circuit requires additional voltage clamping or snubbing to avoid overvoltage failure. With the SiC JBS diode, however, the voltage spike is reduced to less than 50% of the switched-voltage transition, and the additional voltage clamping circuit can be eliminated. Savings in soft-switching choppers using SiC JBS diodes can be realized in size and weight reduction, energy loss reduction, and reduced packaging complexity.

Analytical evaluation of modulation effect on three-phase inverter differential mode noise prediction

This paper presents the modulation effects on the differential mode (DM) conducted electromagnetic interference (EMI) for a three-phase inverter. The evaluation is to adopt a newly developed frequency-domain DM EMI prediction method with accurate noise source and parasitic path identification. Three different modulation schemes are studied and different DM noise sources expressions in frequency domain are derived. The parasitic components are identified using finite element analysis method (FEM). The calculated DM EMI results are compared with experimental data. It is indicated that the modulation schemes have significant impacts on EMI performance not only in switching frequency and its associated harmonics, but also in higher frequency regions.

EMI characterization with parasitic modeling for a permanent magnet motor drive

In this paper, a permanent magnet AC motor drive is tested extensively, and the prominent frequencies in EMI spectrum are identified for their relationship with the noise sources and their propagation paths. Switching characteristics of the power MOSFETs are evaluated by simulation and experiment for the noise source modeling. Major parasitic components and noise propagating mode paths are measured with a time-domain reflectometry method and verified with a 3-dimensional finite element analysis tool. The inverter circuit model is then constructed using pertinent parasitic inductance and capacitance values for the active device modules, the passive components, the leads, and the interconnects. To verify the validity of the inverter model, a comparative study is performed with computer simulations and hardware experiments. The fundamental mechanisms by which the EMI noises are excited and propagated are analyzed, and the significant roles of parasitic elements coupling with device switching dynamics in EMI generation are examined. The results indicate that the identification of parasitic inductance helps verify the noise peaking frequencies. The noise mitigation effects of added DC choke and RC snubbers are also characterized and proven with both simulation and measurement.