Rabiul Islam

A High-Frequency Link Multilevel Cascaded Medium-Voltage Converter for Direct Grid Integration of Renewable Energy Systems

Recent advances in solid-state semiconductors have led to the development of medium-voltage power converters (e.g., 6-36 kV) which could obviate the need for the step-up transformers of renewable power generation systems. The modular multilevel cascaded converters have been deemed as strong contenders for the development of medium-voltage converters, but the converters require multiple isolated and balanced dc supplies. In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed. The common high-frequency link generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues. An 11-kV system is designed and analyzed taking into account the specified system performance, control complexity, cost, and market availability of the power semiconductors. To verify the feasibility of the proposed system, a scaled down 1.73-kVA laboratory prototype test platform with a modular five-level cascaded converter is developed and explored in this paper, which converts a 210 V dc (rectified generator voltage) into three-phase 1 kV rms 50 Hz ac. The experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for future renewable generation systems and smart grid applications.

A Multilevel Medium-Voltage Inverter for Step-Up-Transformer-Less Grid Connection of Photovoltaic Power Plants

Recently, medium (0.1-5 MW) and large (>5 MW) scale photovoltaic (PV) power plants have attracted great attention, where medium-voltage grid connection (typically 6-36 kV) is essential for efficient power transmission and distribution. A power frequency transformer operated at 50 or 60 Hz is generally used to step up the traditional inverters low output voltage (usually ≤400 V) to the medium-voltage level. Because of the heavy weight and large size of the power frequency transformer, the PV inverter system can be expensive and complex for installation and maintenance. As an alternative approach to achieve a compact and lightweight direct grid connection, this paper proposes a three-phase medium-voltage PV inverter system. The 11-kV and 33-kV PV inverter systems are designed. A scaled down three-phase 1.2-kV test rig has been constructed to validate the proposed PV inverter. The experimental results are analyzed and discussed, taking into account the switching schemes and filter circuits. The experimental results demonstrate the excellent feature of the proposed PV inverter system.

A medium frequency transformer with multiple secondary windings for medium voltage converter based wind turbine power generating systems

Recent advances in magnetic materials have led to the development of compact and light weight, medium and high frequency transformers, which would be a possible solution to reducing the size and weight of wind turbine power generating systems. This paper presents the overall design and analysis of a Metglas amorphous alloy 2605SA1 based medium frequency transformer to generate the isolated balanced multiple DC supplies for medium voltage converter systems. A comprehensive electromagnetic analysis is conducted on the proposed design based on experimental results. The test stand, data analysis, and test results are discussed.

High-Frequency Magnetic-Link Medium-Voltage Converter for Superconducting Generator-Based High-Power Density Wind Generation Systems

Recent advances in solid-state semiconductors and magnetic materials have provided the impetus for high-frequency magnetic-link-based modular medium-voltage power conversion systems, which would be a possible solution to reduce further the weight and volume of superconducting generator-based wind generation systems. To verify this new concept, in this paper, a laboratory prototype of 5 kVA high-frequency magnetic-link modular power conversion system is developed for a scaled down 1.2 kV grid application. The design and implementation of the prototyping, test platform, and the experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for superconducting generator-based wind farm applications.

Multiple-input multiple-output medium frequency-link based medium voltage inverter for direct grid connection of photovoltaic arrays

Recent advances in magnetic materials and power semiconductor devices have led to the development of compact and lightweight medium voltage inverter with medium frequency-link, which would be a possible solution to reducing the weight and size of grid-connected photovoltaic (PV) inverter systems. This paper presents the design and analysis of a multiple-input multiple-output medium frequency-link based medium voltage inverters for step-up transformer-less direct grid connection of PV arrays. The multiple-output medium frequency-links generates multiple isolated and balanced dc supplies for all of the H-bridge inverter cells of modular multilevel cascaded (MMC) inverter. To verify the feasibility of the proposed system, a scaled down 1 kV laboratory prototype test platform with 5-level MMC inverter is developed. The design and implementation of the prototyping, test platform, and the experimental results are analyzed and discussed.

Observer-Based Load Frequency Control for Island Microgrid with Photovoltaic Power

As renewable energy is widely integrated into the power system, the stochastic and intermittent power generation from renewable energy may cause system frequency deviating from the prescribed level, especially for a microgrid. In this paper, the load frequency control (LFC) of an island microgrid with photovoltaic (PV) power and electric vehicles (EVs) is investigated, where the EVs can be treated as distributed energy storages. Considering the disturbances from load change and PV power, an observer-based integral sliding mode (OISM) controller is designed to regulate the frequency back to the prescribed value, where the neural network observer is used to online estimate the PV power. Simulation studies on a benchmark microgrid system are presented to illustrate the effectiveness of OISM controller, and comparative results also demonstrate that the proposed method has a superior performance for stabilizing the frequency over the PID control.

Surface plasmon polariton propagation modeling for graphene parallel pair sheets using FDTD

In this paper, a generalized approach of finite difference time domain (FDTD) modeling using surface boundary condition is presented for analyzing the properties of surface plasmon polaritons (SPPs) along straight and bent graphene parallel pairs. Incorporating intra-band conductivity into FDTD with perfectly matched layer absorbing boundary condition is used for SPP propagation modeling. Numerical results of straight and bent graphene parallel pairs for SPP propagation are provided to validate the proposed method.

Medium-frequency-link power conversion for high power density renewable energy systems

Recent advances in solid-state semiconductors and magnetic materials have provided the impetus for medium frequency-link based medium voltage power conversion systems, which would be a possible solution to reducing the weight and volume of renewable power generation systems. To verify this new concept, in this paper, a laboratory prototype of 1.73 kVA medium-frequency-link power conversion system is developed for a scaled down 1 kV grid applications. The design and implementation of the prototyping, test platform, and the experimental results are analyzed and discussed. It is expected that the proposed new technology would have great potential for future renewable and smart grid applications.

Improved direct torque control based modified torque controller for surface-mounted permanent magnet synchronous machines

In this paper, it proposes an improved space vector modulation (SVM) based direct torque control (DTC) algorithm with modified torque controller for surface-mounted permanent magnet synchronous machines (SPMSMs). First, it introduces the conventional SVM-DTC for SPMSM and then analyzes its potential shortcomings to be overcame. Second, an improved SVM-DTC control algorithm with a modified torque controller has been put forward to further enhance the drive performance of SPMSM, such as dynamic response and stable smoothness of torque. Third, with comparison of the conventional SVM-DTC algorithms, the SPMSM torque and flux ripples based on the new strategy are reduced obviously. Comprehensive simulations validate relevant theoretical analysis.