John Shen

Efficiency-Oriented Optimal Design of the LLC Resonant Converter Based on Peak Gain Placement

The LLC resonant converter topology is widely used in dc-dc converter applications due to its advantages in achieving high efficiency and high power density. However, due to the complexity in the analysis, the converter lacks a clear design guideline on the selection of resonant tank parameters. In this paper, an optimization method is developed based on the operation mode analysis and peak gain placement. Following this approach, the converter can minimize the conduction loss while maintaining the required gain range. A 400-W, 400-V output and 25-38 V input LLC converter is built using the proposed method, which achieves above 98% peak efficiency. As a comparison, the conventional searching method is used to reselect the LLC parameters for the same specifications, and the experimental results show that the optimal design has better performance.

A Negative Sequence Compensation Method Based on a Two-Phase Three-Wire Converter for a High-Speed Railway Traction Power Supply System

This paper presents a negative sequence compensation system based on a novel two-phase three-wire converter to eliminate a negative sequence current for the high-speed railway traction power system with a three-phase V/V traction transformer. In this compensation system, the proposed two-phase three-wire converter is fed by two single-phase power sources formed with two step-down transformers connecting to the two feeder sections. The proposed converter contains three switch legs, one of which is connected to the common ground wire of two single-phase voltages. Hence, a switch leg is saved compared with two conventional single-phase converters, and the ratings of the power switches are not increased. In order to enhance the dynamic and steady-state performances of the compensation system, a compound control method composed of hysteresis control and dividing frequency control is presented. Simulation and experimental results are presented to demonstrate that the proposed compensator and its control strategy are very effective.

Railway Static Power Conditioners for High-speed Train Traction Power Supply Systems Using Three-phase V/V Transformers

In order to eliminate the negative-sequence and harmonic currents in the high-speed train traction systems with three-phase V/V transformers, a compensation strategy based on the railway static power conditioners (RPC) is proposed in this paper. An RPC contains two converters that are connected back to back by sharing the same dc link. In this paper, the structure and principle to compensate negative-sequence currents for the RPC with a three-phase V/V transformer are explained, and a strategy to provide the compensation references for negative-sequence and harmonic currents is proposed. Also, a method to separate active current, reactive current, and harmonic current references from the total negative-sequence and harmonic current references is given. Moreover, a controller is proposed to maintain the dc-link voltage and to compensate the negative-sequence and harmonic currents. Simulation and experimental results are provided to demonstrate that the proposed strategy is very effective.

Control strategy of a multi-port, grid connected, direct-DC PV charging station for plug-in electric vehicles

Photovoltaic modules have become a viable renewable energy source for energy systems in communications, commercial, and residential applications. Plug-in electric or hybrid vehicles appear in the market as an emerging technology to reduce carbon emissions and improve energy efficiency. PV modules and plug-in hybrid vehicles interact with the power grid as energy source and energy storage elements, respectively, however little was reported on energy conversion systems featuring three-way energy flow among the power grid, PV modules, and plug-in hybrid vehicles. This paper proposes a plug-in hybrid electric vehicle (PHEV) solar carport charging station concept featuring a multi-port power electronic interface among photovoltaic modules, PHEVs, and the power grid. A unique control strategy is implemented, allowing efficient energy transfer while reducing the conversion stages between the source and load. The system is designed to be modular to improve flexibility and allow for ease of expansion. In the proposed system, a single modular system will provide charging for two parking spaces.

Modeling of a hybrid electric vehicle powertrain test cell using bond graphs

A bond graph model of a hybrid electric vehicle (HEV) powertrain test cell is proposed. The test cell consists of a motor/generator coupled to a HEV powertrain and powered by a bidirectional power converter. Programmable loading conditions, including positive and negative resistive and inertial loads of any magnitude are modeled, avoiding the use of mechanical inertial loads involved in conventional test cells. The dynamics and control equations of the test cell are derived directly from the bond graph models. The modeling and simulation results of the dynamics of the test cell are validated through experiments carried out on a scaled-down system.

Maximum Energy Harvesting Control for Oscillating Energy Harvesting Systems

This paper presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.

System architecture of a modular direct-DC PV charging station for plug-in electric vehicles

Plug-in hybrid electric vehicles (PHEVs) are an emerging technology in the market and are helping to offset the negative effects of existing transportation methods that primarily rely on fossil fuel sources. As PHEVs are being introduced into the market, renewable energy sources such as solar power are taking a larger part in the energy sector. A need for high efficiency battery charging is required to decrease the amount of time it takes to charge these cars in order for them to become a viable means of transportation. A novel solar carport architecture is proposed that will provide a three port interface to PHEVs, solar panels and the utility grid to create a seamless power flow between the three ports. Current battery chargers rely heavily on AC/DC conversion from the grid to the car battery, however a direct DC/DC interface is made in this solar carport thus increasing the overall efficiency. This paper1 will prove this concept and show the improved performance over available battery charging schemes.

Series and Parallel Resonance Problem of Wideband Frequency Harmonic and Its Elimination Strategy

The extensive use of pulse width modulation control technology in smart grid will lead to prominent enlargement of high-frequency harmonics. The effects of the distributed capacitances of transmission line and transformer that are neglected previously will be very obvious. The performance of the traditional harmonic eliminating method for wideband harmonic is limited, which will lead to huge challenge to the analysis, evaluation, and elimination of harmonics as well as series and parallel resonance problem. In this paper, to accurately describe the influence of wideband harmonic on smart grid, the multiterminal analysis model of harmonic degradation in smart grid is established, especially the distributed capacitances of the transmission line and the transformer are considered. Then, a novel topology of hybrid active power filter (HAPF) for resonance damping and multitype harmonic eliminating is proposed. The resonance damping model of the new topology is established; analysis results indicate that the proposed HAPF has a good harmonic resonance damping characteristic. Both simulation and experimental results have validated the validity of the theoretical analysis in this paper.

Double Closed-Loop Control Method for Injection-Type Hybrid Active Power Filter

Injection-type hybrid active power filter (IHAPF) shows great promise in reducing harmonics and improving power factor with a relatively low capacity active power filter (APF), but suffers from fundamental current circulation that inadvertently impacts the compensation performance and stability of the IHAPF. In this paper, the control model of IHAPF is established first, and then the origin and harm of fundamental current circulation are analyzed. To solve this problem, a double closed-loop control method is proposed. In the double closed-loop control scheme, the outer control loop based on injection harmonic current detection is used to eliminate load harmonic current, while the inner control loop based on APF output current detection is used to ensure the secure operation of IHAPF. The new control method is compared to other IHAPF control methods. It is implemented in a 100-kVA IHAPF in the laboratory. Both simulation and experimental results show that the new double closed-loop control method is not only easy to implement, but also very effective in reducing harmonics. The fundamental current circulation issue was also resolved with the new design.

High efficiency current mode control for three-phase micro-inverters

Three-phase micro-inverters are critical to the success of AC modules in Mega Watt PV farms. A high performance micro-inverter must have high power density, high reliability, and low cost. Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) are derived from a proposed softswitching current mode control scheme which is based on the general half-bridge three-phase inverter topology. The frequency range and switch losses are compared and discussed. The VHCM has the highest efficiency at over 97.6%, while the CHCM has the narrowest frequency range. A hybrid control platform combining analog and logic units with DSP was designed and built to achieve the high-speed peak current control. A high frequency, high efficiency, and high power density micro-inverter was built for experimentation. The experimental results verify that the proposed control scheme is a promising solution for high performance three-phase micro-inverters.