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

To obtain phase currents information in AC drives, shunt sensing technology is known to show great performance in cost-effectiveness and therefore it is widely used in low cost applications. However, shunt sensing methods are unable to acquire phase currents in certain operation conditions. This paper deals with the derivation of the boundary conditions for phase current reconstruction in three-shunt sensing inverters and proposes a voltage injection method to expand the measurable areas. As the boundary conditions are deeply dependent on the switching patterns, they are typically analyzed on the voltage vector plane for space vector pulse width modulation (SVPWM) and discontinuous pulse width modulation (DPWM). In the proposed method, the voltage injection and its compensation are conducted within one sampling period. This guarantees fast current reconstruction and the injected voltage is decided so as to minimize the current ripple. In addition to the voltage injection method, a sampling point shifting method is also introduced to improve the boundary conditions. Simulation and experimental results are presented to verify the boundary condition derivation and the effectiveness of the proposed voltage injection method.

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Analysis of the Phase Current Measurement Boundary of Three Shunt Sensing PWM Inverters and an Expansion Method

This paper introduces a new maximum efficiency operation method of Synchronous Reluctance Machine (SynRM) based on a signal injection. To control SynRM in the maximum efficient operating point, the sum of the copper losses and the iron losses should be minimized. Although many kinds of efficient operating method had been introduced, most of them were dependent upon the machine parameters. The inaccuracy of the machine parameters, especially d-/q-axis inductances which are known to vary extremely according to the operating condition, makes the maximum efficiency operating point be out of the target. In this paper, a new maximum efficiency operating method of SynRM is proposed. Adopting the high frequency signal injection concept, the maximum efficiency operating point can be traced without dependency on the machine parameters. The effectiveness of the method is verified by experimental results.

Maximum efficiency operation of Synchronous Reluctance Machine using signal injection

In this article, a method to estimate the temperature of an NdFeB magnet in an interior permanent magnet synchronous motor (IPMSM) has been developed in medium and high speed operating conditions. Fundamental reactive energy is newly brought out and directly used in the developed method to estimate the magnet temperature accurately, which results in higher sensitivity with respect to the magnet temperature variation compared to the conventional methods. It is because the variation of the reactive energy caused by the magnet temperature includes variations of inductances in addition to that of the magnet flux linkage. In the proposed method, a stator resistance error effect caused by a stator temperature is inherently removed without any additional temperature sensor on stator winding. Moreover, the proposed method is robust to an inverter nonlinearity effect and ac resistance effect. As a result, the proposed method can estimate the magnet temperature accurately in real time, even in load variation, regardless of the stator temperature variation. The magnet temperature estimation error has been less than 3.7 °C in the online estimation for 10 000 s under wide speed and torque variations.

Temperature Estimation of IPMSM by Using Fundamental Reactive Energy Considering Variation of Inductances

The concept of a 4-wheel drive system for an electric vehicle is presented This drive concept with four induction motors, one driving each wheel, allows the omission of the rear axle including the conventional differential gears The drive has characteristics which can be compared with a 4-wheel steering system The investigation of a single-track model of the vehicle leads to very similar transfer functions for both systems A yaw motion control is implemented together with a drag-torque control of the wheels Each block of the control is part of a hierarchy Simulations performed with a more detailed nonlinear model show very good correspondence with the simplified model, and performance evaluation is based on an experimental study on a 4-wheel drive electric vehicle

Torque steering control of 4-wheel drive electric vehicle

This paper presents an active Anti-Islanding Detection (AID) method using Negative Sequence Voltage (NSV) injection to electrical grid through a three-phase photovoltaic (PV) inverters. Because islanding operation mode can cause a variety of problems, the islanding detection of grid-connected PV inverter is the mandatory feature. The islanding mode is detected by measuring the magnitude of Negative Sequence Impedance (NSI) calculated by the negative sequence voltage and current at the point of common coupling (PCC). Simulation and experiment are performed to verify the effectiveness of the proposed method which can detect the islanding mode in the specified time. The test has been done in accordance with the condition on IEEE Std 929–2000.

Seung-Ki Sul

Papers

Analysis of the Phase Current Measurement Boundary of Three Shunt Sensing PWM Inverters and an Expansion Method

Maximum efficiency operation of Synchronous Reluctance Machine using signal injection

Temperature Estimation of IPMSM by Using Fundamental Reactive Energy Considering Variation of Inductances

Torque steering control of 4-wheel drive electric vehicle

Anti-islanding detection method using Negative Sequence Voltage