Xiaofeng Lyu

A SiC-Based High Power Density Single-Phase Inverter With In-Series and In-Parallel Power Decoupling Method

This paper presents an in-series and in-parallel combination power decoupling method for the single-phase inverter. With basic power equation derivation, the proposed method is analyzed and compared with other methods in theory. The operating principles and the control strategy are introduced. The circuit parameters based on silicon carbide device are designed in detail, and the power losses are evaluated for the circuit. To verify the theoretical analysis, a PLECS simulation model is built. Based on the simulation results, both the proposed method and the in-series method can achieve a more than 89% reduction of the dc-link capacitance compared with the traditional inverter. Furthermore, the proposed method is superior to the in-series method, with a more than 68% reduction of the extra circuits capacitance. Finally, a 2-kW prototype with a size of 7.25 × 3.6 × 1.4 in3 and a power density of ~55 W/in3 is developed. Compared with the in-series method, the extra capacitance can be reduced by about 64% for the proposed power decoupling method. The experimental results are almost consistent with the simulation results. The efficiency for the proposed method is higher than 95%.

A Zero-Current-Switching High Conversion Ratio Modular Multilevel DC-DC Converter

As the demand of dc–dc converter for medium and high voltage application is increasing in recent years, more and more attention has been paid to modular multilevel converters (MMC). This paper proposes a novel transformerless MMC to achieve high-conversion-ratio DC–DC power conversion purpose. This converter can be used in Medium Voltage Direct Current (MVDC) system, as a high step-up ratio solid-state transformer (SST). The proposed converter possesses scalability, simplicity as well as inherent voltage balancing capability. No complex control algorithm is needed to balance the voltages in each submodule. By using the MMC concept, N low voltage submodules are connected in series to generate a high voltage output. The conversion ratio can be regulated by the phase-shifted control. Two kinds of submodules are outlined to build the MMC. By utilizing stray inductance distributed on wire, the bulky inductors with high power loss can be removed from the system. Resonant operation between wire stray inductance and submodule capacitors assists the converter to work under ZCS mode at high efficiency. A design example with 11-time step-up ratio is analyzed and simulated. And a 200W scaled down lab prototype with 7-time voltage step-up capability has been built to verify the proposed concept.

Multilevel modular converter with reduced device count for hybrid and electric vehicle

This paper presents a low cost multilevel modular switched capacitor dc-dc converter for high power and high voltage conversion ratio application with reduced device count. The switching devices number of the traditional multilevel modular switched capacitor dc-dc converter is increasing fast with the increase of conversion ratio. Large number of switching devices means more gate drive circuit, more complex and higher cost. The proposed circuit has low device number, low device voltage stress and current stress. The proposed circuit also inherits the modular structure, simple control, low conduction loss, high switching frequency operation capability, and soft switching features from the traditional multilevel modular switched capacitor dc-dc converter. Therefore, a high voltage conversion ratio switched capacitor dc-dc converter with low cost and simple structure can be built using the proposed circuit. Simulation results are provided to validate the operating principle and features of the circuit.

A high power density single-phase inverter with in-series and -parallel power decoupling method

In this paper, in order to improve the in-series power decoupling circuit, an in-series and -parallel method is proposed to further reduce the extra capacitor without performance penalty. Based on DC-side in-series method and AC-side three-leg method, a novel way is given to not only reduce the DC-link capacitor but also to decrease the extra capacitor. Thus, it could further make the system high power density and long lifetime. Simulation results are presented to show the performance of this proposed method.

A high voltage gain modular multilevel DC-DC converter

This Paper presents a new modular multilevel converter (MMC) concept to achieve high ratio DC-DC power conversion purpose. This converter can be deployed in High-voltage direct current (HVDC) system, or it can be used as a Solid-state Transformer (SST). The proposed converter is flexible, reliable and it possesses scalability and simplicity. The conversion ratio can be regulated by the phase-shifted control, without any hardware modification. Using the MMC concept, this converter can be implemented with lower voltage rating switching devices instead of much higher voltage rating switches, which is usually unavailable. Two kinds of submodules are outlined for building the MMC. By utilizing inductance distributed on wire/trace and equivalent series inductance (ESL) of the capacitors, no inductors are needed to build the converter. Resonant operation between wire/trace inductance, ESL of capacitors and submodule capacitors assists the converter work under ZCS mode for higher efficiency. The operation principle as well as simulation results of a 20kW converter are presented in this paper.

A High-Efficiency Linear LED Driver With Concave Current Control for Low-Power Application

This paper presents a linear light-emitting diode (LED) driver with concave current control method for low-power applications. In order to achieve a high efficiency of the linear LED driver, control methods with three different current shapes, namely, traditional flat current shape, convex current shape, and the proposed concave current shape, have been discussed and compared via theoretical analyses, numerical simulations, and experiments in this paper. It is concluded that the proposed concave current control method has the highest efficiency among these three methods for universal input voltage conditions. The operation principles and design considerations of the control method have been provided. It is verified by the experimental results that the proposed concave current control method has a 10% efficiency improvement when compared with the flat and convex current control methods. Furthermore in order to limit the peak current of the concave current for practical considerations, a revised cut-top current control method is presented by adding a limited current. Both simulation and experimental results show that a 37% reduction of the peak current is obtained for the cut-top current control method. On the other hand, a 5% improvement of the efficiency can be achieved by the revised cut-top current than flat and convex current control methods.

Multilevel modular switched-capacitor resonant converter with voltage regulation

This paper presents a novel modular multilevel switched-capacitor based resonant converter (MMSCRC) to achieve dc-dc power conversion function. In comparison to existing multilevel modular switched-capacitor circuits, the proposed switched-capacitor resonant converter (SCRC) possess voltage regulation capability. Its modular structure accomplishes voltage conversion function and proposed closed-loop phase-shift control regulates the output voltage. Meanwhile, zero-voltage switching (ZVS) operation can be accomplished. By increasing switching frequency of wide bandgap device and reducing inductance in the circuit, magnetic components can be minimized. Hence, high power density and high efficiency of the proposed converter can be achieved. This paper includes circuit operation, steady-state characteristics as well as in-depth analysis for ZVS operation. Simulation results are provided to verify the operation principle of the proposed MMSCRC. A 600W lab prototype with 6:1 conversion ratio has been built. Experimental result are also provided to validate the theoretical analysis.

A high-power-density single-phase inverter with pulse current injection power decoupling method

This paper presents high-power-density inverter with pulse current injection power decoupling method. In order to reduce the dc-link capacitor significantly, dc-link current is fully analyzed with double Fourier method in theory. Compared with the traditional 2nd harmonic power decoupling method, the pulse current injection method considers not only 2nd order harmonic but also the higher order harmonics. As a result, it can further reduce the dc-link capacitor value. The relationship between the dc-link capacitor value and different order harmonics has been investigated and analyzed. It shows that when dc-link capacitor value is reduced to one critical value, traditional 2nd harmonic power decoupling method is limited. Finally, one novel pulse current injection method is proposed and verified by simulation.

A resonant modular multilevel DC-DC converter with zero current switching for MVDC application

This paper presents a modular multilevel dc-dc converter (MMC) with zero-current switching (ZCS) feature and its analysis for medium-voltage direct current (MVDC) applications. The main focus of this paper is analyzing the overall efficiency of the proposed MMC and experimentally verifying the theoretical analysis on operating principle. Furthermore, in order to achieve high efficiency, the proposed MMC has the capability to maintain ZCS operation at different load conditions. In this paper, the proposed MMC with maximum 200kW power output is used to perform the efficiency analysis. Simulation uses the same parameters that are used to analyze efficiency and displays waveforms when the MMC operates at 66kW. At last, a 200W lab prototype has been built. And operating characteristics of the MMC are validated through experimental results.

DC-Link RMS Current Reduction by Increasing Paralleled Three-Phase Inverter Module Number for Segmented Traction Drive

This paper presents a three-phase inverter dc-link capacitor root-mean-square (RMS) current reduction method. The proposed method is especially suitable for high current electric drive applications while multiple switching devices have to be connected in parallel at the package level, such as Toyota Camry or Tesla Model S. This paper analyzed the proposed method theoretically using double Fourier analysis, and derived the optimal operating point. Furthermore, the effectiveness of the proposed method is also verified by simulation under different PWM strategies (SPWM, SVPWM, and DPWM1), carrier shapes (triangle and sawtooth), and power factors. The proposed dc-link capacitor current cancellation method could lead to smaller dc-link capacitor design; the system volume reduction and cost are also estimated with different number of device packages in parallel. The experimental results are also provided using a 6 kW SiC-based inverter prototype assuming three paralleled devices in each phase leg, which are consistent with the theoretical analysis and simulation results.