Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control

/pdf/overview-of-control-and-grid-synchronization-for-distributed-2nx31ovpe9.pdf

Overview of Control and Grid Synchronization for Distributed Power Generation Systems

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

This paper reviews the current status and implementation of battery chargers, charging power levels, and infrastructure for plug-in electric vehicles and hybrids. Charger systems are categorized into off-board and on-board types with unidirectional or bidirectional power flow. Unidirectional charging limits hardware requirements and simplifies interconnection issues. Bidirectional charging supports battery energy injection back to the grid. Typical on-board chargers restrict power because of weight, space, and cost constraints. They can be integrated with the electric drive to avoid these problems. The availability of charging infrastructure reduces on-board energy storage requirements and costs. On-board charger systems can be conductive or inductive. An off-board charger can be designed for high charging rates and is less constrained by size and weight. Level 1 (convenience), Level 2 (primary), and Level 3 (fast) power levels are discussed. Future aspects such as roadbed charging are presented. Various power level chargers and infrastructure configurations are presented, compared, and evaluated based on amount of power, charging time and location, cost, equipment, and other factors.

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Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and Hybrid Vehicles

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Current control techniques for three-phase voltage-source PWM converters: a survey

A new flux-weakening scheme for an Interior Permanent Magnet Synchronous Motor (IPMSM) is proposed. This control scheme enables the maximum torque operation for the fast acceleration in the constant power region according to the current and voltage limit condition. Especially the dynamic performance of the braking in the flux-weakening region is improved with the compensation of the stator resistance. Also since the onset of the flux weakening operation is adjusted according to the load conditions, the machine parameters. and whether motoring or braking region. the stable and precise transition operation into or out of the flux weakening region can be achieved. The effectiveness of the proposed scheme is verified through experiments with an IPMSM drive system.

Maximum Torque Operation of Interior Permanent Magnet Synchronous Motor in Flux-Weakening Control

Recently, integrated electric propulsion system has been vigorously adopted into naval vessels. To enhance effectiveness and efficiency of power management in these propulsion systems, this paper investigates necessity of energy storage devices and their operation strategies. By introducing the energy storage devices, engine can operate at higher efficiency point and accordingly costs for fuel and maintenance are significantly reduced. In addition, transient performance can also be improved with support of the devices and it leads to stable operation of shipboard power bus. To validate the proposal of this paper, computer simulation has been conducted with real load data of existing electric propulsion system.

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A Study on the Improving Effectiveness of Shipboard Electric Propulsion System with Ultra-capacitor Energy Storage Devices

This article discusses position estimation error in signal-injection sensorless control (SISC) induced by the current measurement noise of closed-loop Hall effect current sensor, when it is installed in an inverter system. For the first step, an equivalent circuit modeling of the current sensor in the inverter system is proposed, which includes the parasitic capacitances between the inverter and sensor. The presented modeling can explain how the high dv/dt of the inverter switching generates the leakage current through the parasitic capacitances, resulting in the measurement noise. The noise is sampled with analog to digital conversion, and it affects the rotor position estimation signal with the SISC algorithm. As a result, it is revealed that considerable position estimation error occurs from the noise. The experimental results are provided to verify the proposed theory and confirm the noise effects on the SISC performance.

Analysis of Position Estimation Error in Signal-Injection Sensorless Control Induced by Inverter dv/dt-Based Current Measurement Noise

The application of dc power systems to microgrids, such as the power system for vessels and islands, is gradually increasing. The major advantage of the dc system over the conventional ac system is the reduced fuel consumption and emission, which is mostly due to the variable speed operation of the diesel engine. It has been reported that the efficiency of the dc system can be maximized if the generation unit comprises a permanent magnet generator (PMG) and a diode rectifier. However, the fatal disadvantage of this composition is that the optimal efficiency operation of the variable speed engine may not be always possible unless the parameter of the PMG, specifically per-unit stator inductance, is within a specific range. The dc system design method proposed herein allows for a large voltage variation (e.g., 40%), and it is possible to operate engine along its optimum efficiency operating point even if the generator per-unit stator inductance does not have a specific range. At light-load conditions, in particular, the proposed method can reduce power converter switching loss and diesel engine fuel consumption. The validity of the proposed method was verified using computer simulations and small-scale experiments.

Variable DC Voltage Shipboard Power System With Permanent Magnet Generator and Diode Front End

Turbo compressors have been extensively used in the factory automation as a part of pneumatic manipulators. Authors developed a position sensorless super-high speed turbo compressor, and it has been installed and working at the industrial plants for years. But repeated failures have been reported at some specific sites. In this paper, the repeated failures are analyzed through experiments and theoretical approach and the remedy against the failures is proposed. Through the analysis, it is presented that there are current overshoots at the instances of voltage sags due to the time delay of dc-link voltage measurement, and the overshoots sometimes trip the inverter even after the voltage sags are cleared. And, the measurement circuit has been modified to reduce time delay. The proposed method has been applied to the failure sites, and the repeated failures have been disappeared.

Seung-Ki Sul

Papers

Maximum Torque Operation of Interior Permanent Magnet Synchronous Motor in Flux-Weakening Control

A Study on the Improving Effectiveness of Shipboard Electric Propulsion System with Ultra-capacitor Energy Storage Devices

Analysis of Position Estimation Error in Signal-Injection Sensorless Control Induced by Inverter dv/dt-Based Current Measurement Noise

Variable DC Voltage Shipboard Power System With Permanent Magnet Generator and Diode Front End

Voltage Sag Ride-Through of Super High-Speed Turbo Compressor