Showing papers on "Power optimizer published in 2003"

DC distribution for industrial systems: opportunities and challenges

Abstract: This paper investigates the opportunities and challenges associated with adopting a DC distribution scheme for industrial power systems. A prototype DC distribution system has been simulated to investigate the issues. One of the issues focused is the interaction between power converters that are used to convert AC to DC and DC to AC. Another challenging issue investigated is the system grounding. These issues become challenging mainly due to the neutral voltage shift associated with the power converters. The paper shows that converter interactions can be minimized with proper filtering and control on the converters. The paper also proposes a grounding scheme and shows that this scheme provides an effective solution by keeping the neutral voltages low under normal conditions and by limiting the fault currents during fault conditions. With these features, DC distribution provides very reliable and high-quality power.

A novel high-performance utility-interactive photovoltaic inverter system

Abstract: This paper presents a novel photovoltaic inverter that cannot only synchronize a sinusoidal AC output current with a utility line voltage, but also control the power generation of each photovoltaic module in an array. The proposed inverter system is composed of a half-bridge inverter at the utility interface and a novel generation control circuit which compensates for reductions in the output power of the system that are attributable to variations in the generation conditions of respective photovoltaic modules. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the half-bridge inverter, across the photovoltaic modules. Consequently, the output power of the system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.

DC bus voltage control for a distributed power system

Abstract: This paper addresses voltage control of distributed DC power systems. DC power systems have been discussed as a result of the introduction of renewable, small-scale power generation units. Also, telecommunication power systems featuring UPS properties might benefit from a broader introduction of DC power systems. Droop control is utilized to distribute the load between the source converters. In order to make the loading of the source converters equal, in per unit, the voltage control algorithm for each converter has to be designed to act similar. The DC side capacitor of each converter, needed for filtering, is also determined as a consequence. The root locus is investigated for varying DC bus impedance. It is found that the risk of entering converter over-modulation is a stronger limitation than stability, at least for reasonable DC bus cable parameters. The stationary and dynamic properties during load variations are also investigated.

Wind Turbine Operation in Electric Power Systems

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Cascaded H-bridge multilevel converter for grid connected photovoltaic generators with independent maximum power point tracking of each solar array

Abstract: This paper introduces a new control method and proportional PWM modulation of the cascaded H-bridge multilevel converter for grid-connected photovoltaic systems. This control makes each H-bridge module supply different power levels, allowing therefore for each module an independent maximum power point tracking of the corresponding photovoltaic array.

Multi-mode renewable power converter system

Abstract: A multi-mode renewable power converter system is disclosed. The system includes a control unit, a boost converter, an inverter and optional bi-directional charger, wherein the boost converter converts DC output of a solar cell or a renewable source to high DC bus voltage, and the inverter converts this DC bus voltage to an AC output. This power converter can be used to support standalone load or grid-connected system with a dynamic maximum power point tracking (MPPT) circuit. The MPPT circuit detects the current and voltage from the solar cell and indicates to the inverter to provide power to the load connected. When the optional bi-directional charger is installed, the MPPT signal is also fed to this charger to make the power efficiency maximized for the system.

Implementation and control of grid connected AC-DC-AC power converter for variable speed wind energy conversion system

Abstract: 30 kW electrical power conversion system is developed for a variable speed wind turbine system. In the wind energy conversion system (WECS) a synchronous generator converts the mechanical energy into electrical energy. As the voltage and frequency of generator output vary along the wind speed change, a DC-DC boosting chopper is utilized to maintain constant DC link voltage. The input DC current is regulated to follow the optimized current reference for maximum power point operation of turbine system. Line side PWM inverter supply currents into the utility line by regulating the DC link voltage. The active power is controlled by q-axis current whereas the reactive power can be controlled by d-axis current. The phase angle of utility voltage is detected using software PLL (phased locked loop) in d-q synchronous reference frame. Proposed scheme gives a low cost and high quality power conversion solution for variable speed WECS.

Offshore wind turbine

Abstract: A wind energy conversion system optimized for offshore application. Each wind turbine includes a semi-submersible hull with ballast weight that is moveable to increase the system's stability. Each wind turbine has an array of rotors distributed on a tower to distribute weight and loads and to improve power production performance where windshear is high. As much of the equipment associated with each rotor as possible is located at the base of the tower to lower the metacentric height. The equipment that may be emplaced at the bottom of the tower could include a power electronic converter, a DC to AC converter, or the entire generator with a mechanical linkage transmitting power from each rotor to the base of the tower. Rather than transmitting electrical power back to shore, it is contemplated to create energy intensive hydrogen-based products at the base of the wind turbine. Alternatively, there could be a central factory ship that utilizes the power produced by a plurality of wind turbines to create a hydrogen-based fuel. The hydrogen-based fuel is transported to land and sold into existing markets as a value-added 'green' product.

Grid-connected power systems having back-up power sources and methods of providing back-up power in grid-connected power systems

Abstract: A grid-connected power system includes a primary power source, a back-up power source, a DC/AC inverter and a DC/DC converter. Direct current from the primary power source is supplied to the DC/AC inverter to obtain an alternating current output supplied to a utility grid when power from the utility grid is available to power a load. The output of the inverter is supplied to a selected portion of the load when power from the utility grid is unavailable to the load. Direct current from the back-up power source is supplied to the inverter through a DC/DC converter when power from the utility grid is unavailable to the load. The DC/DC converter converts the voltage of direct current from the back-up power source to direct current having a voltage compatible with the voltage of the primary power source and the inverter. The back-up power source may be charged by the primary power source or by the utility grid. Methods of providing back-up power include converting the voltage of direct current from a back-up power source to direct current of converted voltage and supplying the direct current of converted voltage to a DC/AC inverter.

Monopolar DC to bipolar DC to AC converter

Abstract: This invention improves the performance and lowers the cost of DC to AC inverters and the systems where these inverters are used. The performance enhancements are most valuable in renewable and distributed energy applications where high power conversion efficiencies are critical. The invention allows a variety of DC sources to provide power thru the inverter to the utility grid without a transformer and at very high power conversion efficiencies. The enabling technology is a novel inverter circuit topology where the DC source is connected directly to the positive bus of the DC to AC converter and where a negative bus is generated from the positive bus with a flyback converter. The inverter power topology does include or require a transformer. The AC inverter output configuration can be either single-phase or three-phase. The AC inverter output can be either utility interactive or directly supply loads.

Dc to ac inverter with single-switch bipolar boost circuit

Abstract: This invention improves the performance and lowers the cost of DC to AC inverters and the systems where these inverters are used. The performance enhancements are most valuable in renewable and distributed energy applications where high power conversion efficiencies are critical. The invention allows a variety of DC sources to provide power thru the inverter to the utility grid or directly to loads without a transformer and at very high power conversion efficiencies. The enabling technology is a novel boost converter stage that regulates the voltage for a following DC to AC converter stage and uses a single semiconductor switching device. The AC inverter output configuration is either single-phase or three-phase.

Continuous reactive power support for wind turbine generators

Abstract: Real and reactive power control for wind turbine generator systems. The technique described herein provides the potential to utilize the total capacity of a wind turbine generator system (e.g., a wind farm) to provide dynamic VAR (reactive power support). The VAR support provided by individual wind turbine generators in a system can be dynamically varied to suit application parameters.

Double-input PWM DC/DC converter for high/low voltage sources

Abstract: A novel double-input PWM DC/DC converter for high/low voltage sources is proposed in this paper With PWM control, the proposed converter can draw power from two different voltage sources simultaneously or individually The operation modes and the steady-state analysis of the proposed double-input DC/DC converter are introduced in detail The control scheme for the power flow balancing is also presented By using a single passive lossless soft-switching cell, switching losses of all power switches can be reduced significantly Finally, experimental measurements are demonstrated to verify the feasibility of the proposed converter

Portable wind power apparatus for electric vehicles

Abstract: A device for converting wind energy into electrical energy for powering a vehicle, the device including a wind turbine positioned on the vehicle and a generator positioned within the vehicle and connected between the wind turbine and systems of the vehicle. When the vehicle is in motion, wind impinges on the wind turbine and causes the wind turbine to rotate. The generator converts rotational energy of the wind turbine into electrical energy. The electrical energy is provided to power the systems of the vehicle and the batteries of the vehicle are recharged.

Wind farm electrical system

Abstract: An approach to wind farm design using variable speed wind turbines with low pulse number electrical output. The output of multiple wind turbines are aggregated to create a high pulse number electrical output at a point of common coupling with a utility grid network. Power quality at each individual wind turbine falls short of utility standards, but the aggregated output at the point of common coupling is within acceptable tolerances for utility power quality. The approach for aggregating low pulse number electrical output from multiple wind turbines relies upon a pad mounted transformer at each wind turbine that performs phase multiplication on the output of each wind turbine. Phase multiplication converts a modified square wave from the wind turbine into a 6 pulse output. Phase shifting of the 6 pulse output from each wind turbine allows the aggregated output of multiple wind turbines to be a 24 pulse approximation of a sine wave. Additional filtering and VAR control is embedded within the wind farm to take advantage of the wind farm's electrical impedence characteristics to further enhance power quality at the point of common coupling.

Predictive DC voltage control of single-phase PV inverters with small DC link capacitance

Abstract: This paper proposes a novel control method for DC voltage in single-phase voltage-source inverters fed by constant-current or constant-power sources. The technique predicts the inverter power require to correct a DC voltage error within one fundamental AC cycle. This is based on the power balance between DC input and AC output, and the energy stored in the DC link capacitor. The fast response means a smaller capacitor can be used, and operation with a large double-line-frequency ripple on the DC bus is possible without causing distortion of the AC output current. This scheme is suitable for applications where substantial DC link buffer energy is unnecessary, e.g.: grid-connected photovoltaic generators. The reliability and lifetime of the inverter can be significantly improved if a non-electrolytic type capacitor is used. Experimental results are presented that verify the inverter operation.

Maximum power point tracking of coupled inductor interleaved boost converter supplied PV system

Abstract: A photovoltaic generator exhibits nonlinear voltage-current characteristics and its maximum power point varies with solar radiation. A two-cell interleaved boost converter with coupled inductors is used to match the photovoltaic system to the load and to operate the solar cell array at maximum power point. A maximum power point tracking algorithm is developed using only load voltage information, eliminating the array current detection. The present converter system has the advantages of low ripple content, both on the load and source side, improved efficiency and reduced switch stress, as compared to noncoupled two-cell interleaved converters. As a result, a lower value of array capacitance is sufficient for smoothing the array voltage and current. Analytical expressions for the photovoltaic source and interleaved boost converter, corresponding to maximum power point operation of the SCA, are derived. Experimental results are presented to demonstrate the suitability of this converter system. Few experimental observations are also presented for partial shading conditions. Further, a comparative study of coupled and noncoupled interleaved boost converters for photovoltaic applications is made. These studies reveal that, by introducing coupling among the parallel branch inductors, it is possible to improve steady-state performance while maintaining the dynamic performance of the photovoltaic system.

Power control interface between a wind farm and a power transmission system

Abstract: A power control interface between an unstable power source such as a wind farm and a power transmission line employs an Electrical Energy Storage, Control System, and Electronic Compensation Module which act together like an 'electronic shock absorber' for storing excess power during periods of increased power generation and releasing stored energy during periods of decreased power generation due to wind fluctuations. The Control System is provided with a 'look ahead' capability for predicting power output (wind speed conditions) and maintaining energy storage or release over a 'narrow-band' range despite short duration fluctuations. The Control System uses data derived from monitoring the wind farm power output and the power transmission line, and employs system-modeling algorithms to predict narrow-band wind speed conditions. The power control interface can also use its energy storage capacity to provide voltage support at the point of injection into the power transmission system, as well as fault clearance capability for 'riding out' transient fault conditions occurring on the power transmission line.

Is the answer blowing in the wind

Abstract: Wind power is the most rapidly growing technology for renewable power generation. However, fundamental differences exist between conventional thermal, hydro, and nuclear generation and wind power. These differences are reflected in the specific interaction of wind turbines with the power system. Further, there are differences between the various wind turbine types, which also affect their system interaction. In this article, first the current status and the technology of wind power are briefly discussed. The general working principles are explained and the different wind turbine types are described. Then, the differences between wind power and conventional power generation are highlighted as well as their consequences for interaction with the power system, both locally and on a system level.

Voltage recovery of grid-connected wind turbines after a short-circuit fault

Abstract: A simulation model of a MW-level wind turbine with dynamic slip control and pitch control is developed in the simulation tool of PSCAD/EMTDC and stability investigations are carried out with respect to a short circuit fault in the external power system. After the fault has been cleared, the voltage at the wind turbine terminal has to be re-established, and the wind turbine should restore its normal operating condition. Controlling the generator slip and pitch angle can adjust the electromagnetic torque and the aerodynamic torque of wind turbine, which helps to rebuild the voltage at the wind turbine terminal. Simulation results prove that dynamic slip control and pitch control are effective methods to improve the voltage and maintain power system stability.

Modeling wind farms for power system stability studies

Abstract: Wind energy conversion systems comprise mechanical and electrical equipment and their controls. Modeling these systems for power system stability simulation studies requires careful analysis of the equipment and controls to determine the characteristics that are important in the timeframe and bandwidth of such studies. Just as important, the characteristics must be reviewed to put aside factors that can be important for wind turbine/wind farm design but do not play a decisive role for the wind turbine/wind farm response from a system standpoint or whose characteristics are not relevant to the frequency range typical for power system stability performance. With this in mind, models of wind turbine units and wind farms are being developed for a commercial power system load flow and stability simulation package. All significant air-dynamical, mechanical, and electrical factors have been reviewed and are modeled appropriately. Load flow models allow aggregation of wind farms comprising tens to hundreds of wind turbine units and easy addition of an equivalent of the wind farm to the model of the existing system. Dynamic models represent different types of constant speed and variable speed technologies currently employed by manufacturers, with their controls.

Programmable power supply capable of receiving AC and DC power input

Abstract: A power supply capable of receiving an AC or DC input power signal and converting the received input power signal into a DC output power signal includes retractable AC and DC input plugs as well as a retractable output cable. One or more interchangeable tips may be attached to the end of the output cable to change a characteristic of the output power to meet a power requirement of an electronic device to which power is being supplied. The tips may be stored in a recess in the outer housing of the power supply.

1/spl phi/ 3W grid-connection PV power inverter with partial active power filter

Abstract: This paper presents a single-phase three-wire (1/spl phi/ 3W) grid-connection photovoltaic (PV) power inverter with a of partial active power filter (PAPF) feature, which can not only deal with PV power but filter current harmonics and improve power factor. Once the processed power exceeds the switch ratings, the inverter can reduce its output reactive power and harmonic power, while still supplying the maximum real power generated by the PV arrays. In the derivation of control laws, a limit circle is defined to confine the output power of the inverter. To determine the power that the inverter can process, the instantaneous reactive power of a 1/spl phi/ 3W system is defined and used to calculate reactive power, which can avoid complex detections of phase angle and magnitude of the fundamental component of a nonlinear load current. Simulation results and experimental measurements have verified the proposed algorithm and the feasibility of the inverter.

Photo-voltaic power converter with a simple maximum-power-point-tracker

Abstract: A simple power conditioner to convert the power available from solar panels for feeding into 60 Hz AC mains is described. The output from the solar panels will be converted into a regulated DC voltage using a boost converter and a large capacitor. The DC output will then be converted to 60 Hz AC using a bridge inverter. The ratio between the load current and the short-circuit current of a PV panel at maximum power point is nearly constant for different insolation (light) levels and this property is utilized in designing a simple maximum power point tracking (MPPT) controller. The results obtained on an experimental converter are presented.

Generator with DC boost and split bus bidirectional DC-to-DC converter for uninterruptible power supply system or for enhanced load pickup

Abstract: A local power generation system generates a substantially DC voltage at an inverter input, which is modulated to generate a resulting output AC power signal to a load. The inverter input voltage may be obtained from an engine generator, providing an AC power signal that is rectified. An energy storage device helps maintain the DC voltage at the inverter input when load power draw increases or during engine startup or acceleration, for example, until the engine accommodates the increased power demand. The system may also be used in an uninterruptible power supply (UPS) application, in which the load draws power from a utility-provided AC power source until a fault condition appears. When the fault condition appears, the load switches its power draw from the utility-provided AC power source to the inverter output. The energy storage device is charged through a bidirectional DC-to-DC converter and through an inverter that operates in a rectifier mode to rectify a utility-provided AC electrical power signal.

A simple maximum power point tracker for grid connected variable speed wind energy conversion system with reduced switch count power converters

Abstract: In this paper, a simple control strategy for an optimal extraction of output power from grid connected variable speed wind energy conversion system (VSWECS) with reduced switch count power converters is presented. In order to improve the overall efficiency and to reduce the cost, B-4 PWM converters are used. The system consists of a variable speed wind turbine coupled to a permanent magnet synchronous generator (PMSG) through a gear box, two PWM B4-power converters. Output power from PMSG is first converted into DC and then it is fed to the grid. Both the power conversions are performed at unity power factor and the DC link voltage is maintained constant. The MPPT extracts optimum power from the wind turbine from cut-in to rated wind velocity by sensing only the turbine output power. The complete system has been simulated for various wind velocities. The control algorithm is implemented on TMS320F243 DSP and the simulated results are validated by experimental results.

Integrated mobile tool and welder power supply system

Abstract: An integrated mobile tool and welder power supply system includes a primary DC power source coupled to a power supply chassis for supplying DC power to DC-operated power equipment such as welders and AC power to AC-powered equipment such as standard AC power tools. The power supply chassis houses a power inverter for transforming DC power from the primary DC power source into AC power and one or more power converters for supplying a recharging current to the primary DC power source from one or both of an external AC power source or an external DC power source. The power supply system can be configured such that if an external AC power source is available, that AC power source is electrically coupled to an AC output terminal for supplying AC-powered tools. In one embodiment, the switching of AC output power from the power inverter to the external AC power source may be overridden by means of an AC output mode selection switch. In another embodiment, the system is equipped with a DC transfer switch, a motor drive output and a motor demand indicator input so that a DC motor (e.g., the welding wire spool feed motor DC welder) may be driven from a regulated DC power source as opposed to the unregulated primary DC power source.