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

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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

This paper presents a resonance suppression method that reduces current oscillation incurred by the LCL -filtered grid-connected converter’s discontinuous PWM (DPWM). First, the cause of LCL resonance is analyzed with an aspect of frequency and time domain for DPWM scheme. Then, voltage references are manipulated to decrease the resonance problem. In the proposed method, pole voltage references at the edge of offset voltage are slightly adjusted to reduce the current oscillation. In addition, a perturb and observe (P&O) technique is adopted to search the magnitude of an edge voltage. Through the simulation and experimental tests, the current oscillation is dramatically reduced while keeping the advantages of DPWM scheme. The proposed method can minimize the switching frequency under the grid harmonics regulation.

/pdf/resonance-suppression-method-for-grid-connected-converter-1llq2isqn5.pdf

Resonance Suppression Method for Grid-Connected Converter With LCL Filter Under Discontinuous PWM

This paper proposes an identification scheme of interior permanent-magnet synchronous motor (IPMSM) flux-linkage through experimental tests considering the magnetic saturation and spatial harmonics. In proposed scheme, flux-linkage is identified based on the voltage equation of IPMSM. The electro-motive force in rotor reference frame is obtained in real time by applying discrete Fourier transform on the voltage reference of proportional integral and resonant current controller, with precise compensation of the time delay from digital control and PWM on fundamental and harmonic components. The effect of the inverter nonlinearity is compensated using experimentally obtained look up table. Simulation model is constructed using the identified flux-linkage map. The effectiveness of the proposed flux-linkage identification scheme in simulating IPMSM control algorithms is verified through the comparison of simulation and experimental results.

Experimental Identification of IPMSM Flux-Linkage Considering Spatial Harmonics for High-Accuracy Simulation of IPMSM Drives

This paper proposes the control algorithm for a Surface Mounted Permanent Magnet Synchronous Motor(SMPMSM) drive system running at 116,000 r/min. Hall sensors are employed to measure the rotor position, and a speed observer is used to enhance the dynamic performance of the drive system. And in order to extend the output power capacity in the high-speed operating region, a flux-weakening controller, integrated with an anti-windup controller, is implemented. Through the simulations and experiments, it is validated that both high speed operation and fast acceleration has achieved with the proposed methods.

Implementation of super high-speed permanent magnet synchronous machine drive

Drive Circuit of 4-Level Inverter for 42V Power System

This paper presents a power converter configuration for the compound type hybrid excavator with an ultra capacitor, which is directly connected in parallel to dc-link capacitor without DC/DC converter. With this structure, the efficiency of the system has been improved compared to the conventional compound type hybrid excavator where an ultra capacitor was connected via DC/DC converter. And, a power control strategy for the suggested configuration is described. To suppress the oscillation of the voltage of the ultra capacitor, an observer for the internal voltage of the ultra capacitor is devised. To evaluate the effectiveness of the proposed configuration and power control strategy, extensive computer simulations have been performed and the results are discussed. The feasibility of the simulation results is experimentally verified based on mid-sized excavator.

Seung-Ki Sul

Papers

Resonance Suppression Method for Grid-Connected Converter With LCL Filter Under Discontinuous PWM

Experimental Identification of IPMSM Flux-Linkage Considering Spatial Harmonics for High-Accuracy Simulation of IPMSM Drives

Implementation of super high-speed permanent magnet synchronous machine drive

Drive Circuit of 4-Level Inverter for 42V Power System

System configuration and control strategy for compound type hybrid excavator with ultra capacitor