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 analyzes the inverter nonlinearity effect resulting in issues such as narrow pulses and the even order harmonics in three-level T-type inverters. These issues make the compensation of the inverter nonlinearity be difficult. Based on the analysis of the output voltage distortion, carrier-based PWM methods to avoid these issues and to balance dc-link voltages simultaneously are proposed using the concept of the offset voltage. The proposed PWM methods can be easily implemented by adding appropriate offset voltages to output voltage references. Also, a compensation method to alleviate inverter nonlinearity effects is proposed based on the modeling of the inverter nonlinearity. The effectiveness of proposed methods is verified by experimental results. Through the proposed algorithms, not only even harmonics but also 5th and 7th harmonic components of current are conspicuously reduced. At the same time, the neutral voltage of the inverter can be balanced effectively by the proposed PWM methods.

Analysis and compensation of inverter nonlinearity for three-level T-type inverters

This paper describes boundary conditions for phase current reconstruction of a three current-shunt inverter and suggests a voltage injection method to expand the measurable areas The boundary conditions are derived on voltage vector plane for symmetric space vector PWM For the expansion of the areas, different voltages are injected depending on the position of the voltage vector with double sampling When voltage vector is located in the insensible area, additional voltage is injected to place the voltage vector in the measurable area during next half of switching period and compensation voltage is added in the other half period Voltages with minimum magnitudes are chosen to minimize the current ripples Simulation results are presented to support the effectiveness of boundary condition derivation and proposed voltage injection method

Voltage injection method for boundary expansion of output voltages in three shunt sensing PWM inverters

In this paper, the design and control aspects of a multispan tension simulator are presented. The simulator consists of four driven rolls, including unwinder, winder, and two bridle rolls. Some relationships between design parameters and characteristics of the simulator are explained as a design guide of a multispan system. A new control algorithm of continuous load balance control is proposed for the control of speed and tension in the multispan system. The strip tension is controlled by the continuous balancing of the load torque of rolls without a tension sensor. The simulation and experimental results reveal conspicuous improvement of tension control performance by the proposed algorithm.

Design and control of multispan tension simulator

This paper presents a control scheme for the Modular Multilevel Converter (MMC) to drive a variable-speed AC machine, especially focusing on improving dynamic performance. Theoretically, the energy balance in the cell capacitors is prone to be unstable at startup and low frequency operation. Therefore, the MMC topology essentially requires advanced strategies for energy balancing so as to suppress the voltage pulsation of each cell capacitor. The pulsation is getting larger as the output frequency of MMC is getting lower. This paper proposes a strategy for robust dynamic response even at zero output frequency of MMC employing leg offset voltage injection. With this proposed strategy, an AC machine has been driven from standstill to rated speed without excessive cell capacitor voltage ripples. The experimental results verify that stable operation is guaranteed for both a 15r/min operation with 40% step load torque and the entire frequency operation with varying load torque.

Control strategy for improved dynamic performance of variable-speed drives with the Modular Multilevel Converter

In a relative position control system, where feedfoword control can not be applied and the position control performance is restricted only by the bandwidth of the position controller, a disturbance observer are used actively to enhance the control performance. The position reference is considered as a disturbance by the proposed method. Therefore, the relative position control is performed by the disturbance observer as well as by the position controller. As a result, the position control performance is enhanced up to about 33 [%] compared to that of the conventional method with the disturbance observer. The feasibility of the proposed method has been verified by the experimental results using a high precision linear motion control system as well as by the analysis based on Bode plot.

Seung-Ki Sul

Papers

Analysis and compensation of inverter nonlinearity for three-level T-type inverters

Voltage injection method for boundary expansion of output voltages in three shunt sensing PWM inverters

Design and control of multispan tension simulator

Control strategy for improved dynamic performance of variable-speed drives with the Modular Multilevel Converter

Application of a disturbance observer for a relative position control system