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.

/pdf/review-of-battery-charger-topologies-charging-power-levels-85yy2igx2w.pdf

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

In this paper, an LQG based speed controller for torsional vibration suppression in a 2-mass motor drive system is proposed. Because of the difficulty of measuring the load speed and the shaft torque, the Kalman filter as an optimal full order estimator is used. The Kalman filter can also estimate the load torque disturbance as well as unknown states. The details of the determination of the control parameters of a LQG based speed controller with load torque feedforward compensation is explained, and how the control response is affected based on the selection of each weighting in the performance index is also considered. Simulations are carried out to verify this algorithm in comparison with a conventional PI controller. >

LQG based speed controller for torsional vibration suppression in 2-mass motor drive system

A new approach to the position sensor elimination of permanent magnet synchronous machine (PMSM) drives for low-speed operation is presented in this paper. Using the position sensing characteristics of the PMSM itself, the actual rotor position, as well as the machine speed, can be obtained even in the transient state. Since the essential back-EMF information is obtained from direct measurement during a special test cycle called MCDI, the operating speed range of the sensorless drives can be extended to 10 RPM. Moreover, the chronic starting problem of PMSM drives can be simply settled by the proposed algorithm. In order to verify the feasibility of the proposed scheme, experimental results in the low-speed range of about 10/spl sim/100 RPM are also presented.

New approach for the low speed operation of the PMSM drives with rotational position sensors

In this study, the advanced gear shifting and clutching strategy for parallel hybrid electric vehicle with automated manual transmission (AMT) is proposed. The efficient gear shift point considering the fuel consumption of a diesel engine and the efficiency of induction machine can be determined by means of optimization technique, and automatic gear shift can be realized by controlling the AMT. Performing the speed control of the induction machine and the diesel engine, the synchronization at gear shift is guaranteed and it enables reduction of the shift shock and shortens the shifting time. Hence, it results in the improvement of shift quality and the driving comfort of the vehicle. Dynamo-based experiments are carried out to prove the validity of the proposed transmission control strategy.

Advanced gear shifting and clutching strategy for parallel hybrid vehicle with automated manual transmission

The cutoff frequency of a LC output filter for dynamic voltage restorers (DVR) limits the control bandwidth of a DVR system and the attenuation factor against the inverter switching ripples. For a selected cutoff frequency of a LC output filter, infinite number of L-C combinations is possible. Although different L-C combination has different filter characteristics, the filter design on L-C combination has been depended on field experiences without clear analysis. This paper proposes a design criterion and a design example for the L-C filter combination considering the control characteristics and the size of DVRs. An experimental DVR system based on the proposed LC output filter design methodology is built and tested.

A design consideration of output filters for dynamic voltage restorers

Trapezoidal voltages can be used to compensate for the inverter nonlinearity. In particular, the modulating shape of these voltages facilitates the adaptation of the compensation to various operating conditions. In this paper, practical implementation schemes are proposed to improve the performance of the compensation method based on the trapezoidal voltage. After the implementation schemes are detailed, their effectiveness is discussed with experimental results. It has been proved that the proposed schemes are useful for the robust compensation.

Seung-Ki Sul

Papers

LQG based speed controller for torsional vibration suppression in 2-mass motor drive system

New approach for the low speed operation of the PMSM drives with rotational position sensors

Advanced gear shifting and clutching strategy for parallel hybrid vehicle with automated manual transmission

A design consideration of output filters for dynamic voltage restorers

Implementation Schemes to Compensate for Inverter Nonlinearity Based on Trapezoidal Voltage