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

This paper proposes a novel resonant circuit capable of PWM operation with zero switching losses. The resonant circuit is aimed at providing zero voltage intervals in the DC link of the PWM converter during the required converter device switching periods, and it gives minimum DC bus voltage stresses and minimum peak resonant current. It requires only two additional switches compared to a conventional PWM converter. It is observed that the resonant circuit guarantees the soft switching of all the switching power devices of converters including the switches for resonant operation. Simulation results and experimental results are presented to verify the operating principles. >

Resonant link bidirectional power converter. I. Resonant circuit

This paper describes the strategy to design and control of an axial flux SPM machine for achieving a wide flux-weakening operating region. By using a slotted stator with fractional slot windings and additional cores enclosing end windings, the axial flux machine satisfies the specification of a wide constant power speed range. The design procedure is presented for increasing flux-weakening capability while obtaining low harmonic back-electromotive-force and low cogging torque. This technique is applied to design an 8 Nm axial flux prototype machine that exhibits about 3:1 flux-weakening range. To the aim of exploiting full capability of the machine, a flux-weakening controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the flux- weakening region can be increased up to that of the six-step operation while maintaining the current control capability. The goodness of both design and control algorithm is proved by experimental tests on a prototype.

Design and Control of an Axial Flux Machine for a Wide Flux-Weakening Operation Region

Accurate measurement of phase current is crucial in a current-controlled PMSM drive system. Current measurement error directly deteriorates torque control performance. This paper analyzes effects of the current measurement error on the phase current and the output voltage of the current controller. Based on the analysis, a compensation method is proposed. It compensates the offset error and the scaling error separately without any additional hardware but using the output voltage reference of the current controller. The proposed method can be applied to general current-controlled PMSM drives in whole operation range. Experimental results verify the effectiveness of the proposed compensation method.

Compensation of current measurement error for current-controlled PMSM drives

A current source inverter (CSI) requires a capacitor filter for the commutation of switching device as well as for attenuating switching harmonics. Hence, the CSI-fed ac machine has a second-order system in the continuous time domain. This paper presents a design methodology for the closed-loop current controller of the CSI-fed ac machine drive system. A multiloop current controller design using a pole/zero cancellation method is employed with a transfer function matrix. To decouple the cross-coupling terms which cause mutual interferences between the d- and q-axes in the synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to enhance the stability of the system. A stability analysis in discrete-time domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed.

A Current Controller Design for Current Source Inverter-Fed AC Machine Drive System

In this paper, a new circuit for AC to AC power conversion is presented. The circuit is derived from the matrix converter topology, which has the capability of direct AC to AC power conversion without any DC link reactive component and input inductance except a small snubber. It consists of only unidirectional switches such as IGBTs with antiparallel diodes in contrast to the matrix power converter which consists of bi-directional switches. The input displacement power factor of the proposed scheme is unity and the overall power factor is near unity. The waveform of the input line currents is much alike with the diode a large DC-link reactor. The validity of the circuit and its operation is confirmed by experiments which uses a dynamic load-field oriented induction motor drive system.

Seung-Ki Sul

Papers

Resonant link bidirectional power converter. I. Resonant circuit

Design and Control of an Axial Flux Machine for a Wide Flux-Weakening Operation Region

Compensation of current measurement error for current-controlled PMSM drives

A Current Controller Design for Current Source Inverter-Fed AC Machine Drive System

AC to AC power conversion based on matrix converter topology with unidirectional switches