Showing papers by "Fang Zheng Peng published in 2018"

State-of-Charge Balancing Control for a Battery-Energy-Stored Quasi-Z-Source Cascaded-Multilevel-Inverter-Based Photovoltaic Power System

Abstract: A battery-energy-stored quasi-Z-source cascaded multilevel inverter (qZS-CMI)-based photovoltaic (PV) power generation system combines advantages of a qZS inverter, a CMI, and a battery energy storage system. However, unbalanced battery state of charge (SOC) between cascaded H-bridge inverter modules will degrade an entire system's performance and shorten battery lifespan. This paper proposes a control method to balance battery SOCs of all modules, no matter the intermittent states of each module's PV power. The method is on the basis of battery SOCs, SOC limits of each module, and the total power injected into the power grid. Simulation and experimental results verify the proposed control method that ensures identical SOCs for the battery-energy-stored qZS-CMI PV system.

Effect of Gate-Oxide Degradation on Electrical Parameters of Power MOSFETs

Abstract: Gate oxide in power metal–oxide–semiconductor field effect transistors (MOSFETs) degrades over time The degradation leads to an accumulation of oxide-trapped charges within the gate oxide and an accumulation of interface-trapped charges at the oxide–semiconductor surface of power MOSFETs Overtime, such charges significantly alter the electrical parameters of power MOSFETs; to observe this, the electrical parameters are utilized as precursors of gate-oxide degradation The purpose of this paper is threefold: 1) to propose a new online precursor of gate-oxide degradation—the gate plateau time; 2) to demonstrate a simultaneous dip-and-rebound variation pattern of four precursors of gate-oxide degradation: threshold voltage, gate plateau voltage, gate plateau time, and on-resistance; and 3) to compare the shift tendencies of each precursor over the course of gate-oxide degradation The existing studies of gate-oxide degradation mechanisms and their effects on threshold voltage and mobility reduction were extended to correlate a variation of all four precursors using analytical expressions The variation patterns were experimentally verified using high-electric field stressing in two different commercial power MOSFETs The new precursor, the gate plateau time, was found to be a competitive gate-oxide degradation precursor, as it had a higher positive shift than threshold voltage and gate plateau voltage In addition, the threshold voltage was found to be the most sensitive indicator of the negative shift (dip), while the on-resistance and gate plateau time were found to be the most sensitive indicators of the positive shift (rebound)

An H-Bridge-Based Single-Phase VAr Generator With Minimum DC Capacitance

Abstract: Conventional single-phase H-bridge applications have second-order harmonic ripple power on the dc bus. The second-order harmonic power is usually filtered by a bulk capacitor on the dc bus to maintain a constant dc-bus voltage, which results in low power density. However, in applications like VAr generator, a larger dc-bus voltage fluctuation is acceptable since the dc bus connects to no load. This paper releases the constraints on dc-bus voltage fluctuation so that the dc-bus capacitor can be fully utilized. Based on this idea, an H-bridge-based single-phase VAr generator with minimum dc capacitance is proposed, which reduces the dc-bus capacitor to 1/10th of the size compared to that of the sinusoidal pulse width modulation (SPWM)-modulated H-bridge inverter, without increasing components’ count. A general modulation method of the proposed VAr generator is derived to utilize the fluctuating dc-bus voltage. The system volume and power loss are assessed to compare with the conventional SPWM-modulated H-bridge and the circuits with power-decoupling cells. A proportional-integral controller is applied to the system to control the input ac current. The analysis and design are validated by simulations and experiments.

A 25kW SiC Universal Power Converter Building Block for G2V, V2G, and V2L Applications

Abstract: This paper presents a universal power converter building block (PCBB) with isolation transformer which can perform various functionalities such as charging (G2V), vehicle to grid (V2G) regenerative capability, and vehicle to load (V2L) feature. This converter can output different types of voltage, such as AC or DC, high voltage or low voltage, singlephase or three-phase. With different combinations of modularized PCBB, various voltage and power rating can also be achieved. The control algorithms for each operation mode are explained, including G2V, V2G, and V2L. Simulation results are accompanied to validate its capability. To achieve high power density, SiC MOSFET power module with high frequency switching is adopted along with the isolation transformer of nanocrystalline core. Overall, this paper extends a promising circuit topology of multiple practical and essential features for vehicle electrification.

Precursors of Gate-Oxide Degradation in Silicon Carbide MOSFETs

Abstract: Gate-oxide degradation is more critical in Silicon Carbide (SiC) MOSFETs than in Silicon (Si) MOSFETs. This is because of the smaller gate-oxide thickness and the higher electric field that develops across this thinner gate oxide in SiC MOSFETs. While multiple precursors (indicators) have been identified for monitoring the gate-oxide degradation process in Si MOSFETs, very few have been identified for their SiC counterparts. The purpose of this digest is to demonstrate that the gate-oxide degradation precursors used in Si MOSFETs: a) gate plateau voltage and b) gate plateau time, can also be used as precursors for SiC MOSFETS. Moreover, the precursors are found to exhibit a simultaneous increasing trend (during the stress time) leading to an increase in on-state loss, switching loss and switching time of the SiC MOSFET. The existing studies of gate-oxide degradation mechanisms in SiC MOSFETs, and their effects on threshold voltage and mobility were extended to correlate a variation of precursors using analytical expressions. The increasing trends of precursors were experimentally confirmed by inducing gate-oxide degradation in a commercial SiC MOSFET.

High Power Density Z-Source Resonant Wireless Charger With Line Frequency Sinusoidal Charging

Abstract: Wireless charger for electric vehicles (EVs) is an offline application and it needs power factor correction (PFC) function, which usually consists of a front-end boost PFC and a cascaded dc–dc converter. Z-source resonant converter (ZSRC), a single-stage solution with low cost and high efficiency, was proposed for EV wireless charger lately. The Z-source capacitors in the ZSRC are designed to absorb the double-line frequency ripple in this single-phase application. Sinusoidal charging, which allows the double-line frequency ripple propagate to the output, is another solution aiming at reducing the bulky capacitors. Recently, a comparison of low-frequency (120 Hz) sinusoidal charging and dc charging shows a negligible impact on Li-ion batteries’ performance. Therefore, the ZSRC's capacitor, the biggest component, can be reduced dramatically from millifarad to several microfarads with a sinusoidal charging technique, which features the ZSRC high power density. Also, it keeps the Z-source's benefit of boost ability and being immune to shoot-through problems. In this paper, the sinusoidal charging behavior for the ZSRC is modeled, and a control scheme that has both PFC function and load regulation for sinusoidal charging is proposed. This control scheme can pass IEC61000-3-2 Class A criterion. Experimental results based on a 1-kW prototype with 20 cm air gap between the primary and secondary side are presented to illustrate the proposed control scheme.

Non-linear capacitor based variable capacitor for self-tuning resonant converter in wireless power transfer

Abstract: In wireless power transfer (WPT) system, the resonant frequency of primary side and secondary side should be matched to maximize the power transferred and efficiency. However, in mass production, the variation of each component in the resonant circuit results in poor matching. One solution is to utilize a variable capacitor for self-tuning to compensate the variation. To implement a variable capacitor on a linear capacitor in power converters, most of the solutions chop part of the rated current by an auxiliary circuit. Therefore, the power rating of the auxiliary circuit is proportional to the percentage of capacitance variation, which generates considerable loss. On the other hand, non-linear capacitor, ceramic capacitor as an example, can change capacitance by varying DC bias. The auxiliary circuit to hold the DC bias only needs to supply the leakage current of the nonlinear capacitor, which is negligible. In this paper, an almost lossless auxiliary circuit for continuously varying DC bias is proposed. It is suitable for high power applications such as electric vehicles wireless charger. Experimental results based on a 100-W scale-down series resonant converter (SRC) with 20-cm air gap between the primary and secondary side are presented to illustrate the mechanism of this method.

Comprehensive Design and Control of Electric Powertrain Evaluation Platform for Next Generation EV/HEV Development

Abstract: Electric powertrain or power control unit, which is the integral part of the EV/HEV, is consisting of the high voltage battery, DC/DC converter, inverter, and electric motor To evaluate the powertrain performance is a crucial stage for its development In this paper, a peak 150-kW powertrain evaluation system with 2006 Toyota Prius as the evaluated target is designed along with its control technique being elaborated This system is constructed as grid-connected back-to-back inverters driving a 55kW IPM machine to work as the load to the Prius’s powertrain Operation modes of the system and the data collection are presented in the end Overall, this platform extends an energy-saving solution for powertrain evaluation with the capability of sending the energy from the evaluated vehicle back to the grid compared to traditional dyno system which only dumps the power a passive load

Wireless Power Transfer with Additional Third Harmonic: Theoretical Analysis, Design, and Demonstration

Abstract: The power rating for Electric Vehicles wireless charger keeps increasing as the technology develops. With limited space and volume, the maximum transferring power has reached a bottle neck even with an optimized coupling winding design. It is well known that third harmonic injection can increase the maximum power transfer for line-frequency inverter. However, for high frequency resonant converters, it is a big challenge to utilize third harmonic as the resonant network is a band-pass filter for fundamental frequency only. Also, the switching frequency is closed to resonant frequency and the phase relationship between fundamental and third harmonic mostly relies on impedance match. This paper explores the feasibility of third harmonic injection in resonant converters, and theoretically proves the additional third harmonic can lead to a maximum 40% extra output power. A W-filter which is low impedance for both fundamental and third harmonic is proposed. To adjust the phase relationship, a dither feedback across the nonlinear output diode rectifier is proposed. A minimum system and a wireless power transfer (WPT) system have been constructed by W-filters in simulation. Experimental results based on a 20-W scale-down prototype are presented to illustrate the proposed system.

First order frequency-domain analytical model for resonant converters in CCM

Abstract: Fundamental harmonic approximation (FHA) is a general analysis method for diode-bridge rectifier in resonant converters. However, the accuracy of FHA is low in some wireless power transfer (WPT) applications, as the current has distortions due to different compensation networks. Also, there are researches on increasing the power density of resonant converters by injecting third harmonic. In such case, FHA no longer holds true. As the diode-bridge rectifier is a well-known harmonic source, numerous modeling methods for Grid connected AC/DC converters have been addressed. However, most of them have all kinds of limitations and cannot be applied to resonant converter directly. This paper proposes a frequency-domain analytical model for resonant converters in CCM, considering any load and source situation. The advantage of the proposed model is a truly first order solution and a general model for all resonant converters. Two test systems have been constructed in simulation and calculation to verify the proposed model. One is a resonant converter with both fundamental and third harmonic components, the other one is an LCC compensated wireless charger.

Precursors of gate oxide degradation in SiC power MOSFETs

Abstract: Gate oxide degradation is more critical in Silicon-Carbide (SiC) MOSFETs than in Silicon (Si) MOSFETs. This is because of the smaller gate oxide thickness and the higher electric field that develops across the gate oxide in SiC MOSFETs. While multiple precursors have been identified for monitoring the gate oxide degradation in Si MOSFETs, very few precursors have been identified for SiC MOSFETs. The purpose of this paper is to demonstrate that gate oxide degradation precursors used in Si MOSFETs: a) threshold voltage, b) gate plateau voltage and c) gate plateau time, can also be used as precursors for SiC MOSFETS. Moreover, all three precursors are found to exhibit a simultaneous increasing trend (during the stress time) leading to an increase in on-state loss, switching loss and switching time of the SiC MOSFET. The existing studies of gate oxide degradation mechanisms in SiC MOSFETs, and their effects on threshold voltage and mobility were extended to correlate a variation of all three precursors using analytical expressions. The increasing trends of precursors were experimentally confirmed by inducing gate oxide degradation in commercial SiC MOSFET samples.

A carrier magnitude varying modulation for distributed static series compensator to achieve a maximum reactive power generating capability

Abstract: Conventional single-phase H-bridge applications have second-order harmonic ripple power on the dc bus. However, in applications like a voltage source inverter (VSI) module of a Distributed Static Series Compensator (DSSC), a larger dc bus voltage fluctuation is acceptable since the dc bus connects to no load. This paper releases the constraints on dc bus voltage ripples so that the dc-bus capacitor can be fully utilized. Based on this idea, a carrier magnitude varying modulation is proposed, in which the VSI can generate ten times the reactive power of a conventional SPWM based VSI. The system reactive power generating capability is assessed to compare with the conventional SPWM based VSI and the constant duty cycle control based VSI. A PI controller is applied to the system to regulate the ac current. The analysis and design are validated by simulation and experiments.