Showing papers on "Power optimizer published in 1991"

Variable speed wind turbine with reduced power fluctuation and a static VAR mode of operation

Abstract: A wind turbine power converter is disclosed herein that smooths the output power from a variable speed wind turbine, to reduce or eliminate substantial power fluctuations on the output line. The power converter has an AC-to-DC converter connected to a variable speed generator that converts wind energy to electric energy, a DC-to-AC inverter connected to a utility grid, and DC voltage link connected to an electrical energy storage device such as a battery or a fuel cell, or a photovoltaic or solar cell. Also, an apparatus and method is disclosed herein for controlling the instantaneous current flowing through the active switches at the line side inverter to supply reactive power to the utility grid. The inverter can control reactive power output as a power factor angle, or directly as a number of VARs independent of the real power. Reactive power can be controlled in an operating mode when the wind turbine is generating power, or in a static VAR mode when the wind turbine is not operating to produce real power. To control the reactive power, a voltage waveform is used as a reference to form a current control waveform for each output phase. The current control waveform for each phase is applied to a current regulator which regulates the drive circuit that controls the currents for each phase of the inverter. Means for controlling the charge/discharge ratio and the regulating the voltage on the DC voltage link is also disclosed.

High frequency heating equipment

Abstract: The equipment includes a DC power supply comprising a power generator (20), an electric power generator (22) and a rectifying means (23), an inverter power supply (24) which boosts the output voltage of the DC power supply and drives a magnetron (28), and an inverter controlling part for controlling the inverter power supply (24) according to the output of a generator output detecting means (31) for detecting the output of the DC power supply. A function of dielectric heating can be exhibited stably by controlling the operating state of the inverter power supply (24) through the use of the output of the DC power supply.

HVDC tapping station: power tapping from a DC transmission line to a local AC network

Abstract: The authors describe a new concept for tapping off a small amount of power from a high voltage direct current (HVDC) transmission line to a local network. The proposed new concept for a series tapping implies power conversion in two steps from the line to a local AC network. This will make it possible to the use a single phase transformer between the DC line potential and ground. The converter bridge connected in series in the DC transmission is of the current source line-commutated type, while the other two converters are of the voltage-source forced-commutated type. The basic functions of the converter are described and illustrated by the results from simulations with the EMTP program.

The market for distributed power systems

Abstract: Distributed power architectures replace central power sources with one bulk power supply that is converted to the required voltages by DC/DC power converters at the point of need. The benefits and disadvantages of distributed power systems are summarized. In the last ten years, the design advantages of distributed power systems has spread to a variety of applications, including industrial controls, automotive applications, computer systems, medical electronics, and telecommunications. The market for distributed power architecture is a niche within the switching power supply industry. Approximately two-thirds of respondents among power supply vendors perceive growth in applications for distributed power architectures, although they differ on the rate of acceptance of this technology. Though most of the DC/DC power converters of distributed power architectures are currently used in military/aerospace and communications applications, the real potential for distributed power systems lies within the computer industry. >

Modelling, simulation and analysis of variable speed constant frequency wind energy conversion scheme using self excited induction generator

Abstract: Presents the dynamic modelling of variable speed constant frequency (VSCF) wind energy conversion scheme (WECS), employing self excited induction generator, connected to the utility grid through an AC-DC-AC converter scheme with uncontrolled rectifier and PWM inverter. The proposed scheme for regulating the flow of power through the link ensures reduced reactive power burden on the self excitation capacitor banks, reduced harmonic injection into the host power utility grid and efficient utilization of available wind energy. Modelling of the subsystems and simulation of the unified system with pulse width modulated (PWM) inverter control, to reduce harmonics injected into the utility grid are also presented. >

Wind turbine modelling and control

Abstract: The wind turbines discussed in the paper are upwind horizontal axis, grid-connected medium to large scale wind turbines. The configuration of wind turbine is the simplest possible comprising a three-blade rotor with rigid hub, gearbox and induction generator. The generator is connected directly to the grid thereby locking the speed of rotation of the rotor to the frequency of the grid which is of course fixed. For this reason this type of machine is called a constant speed wind turbine. There are two common methods of aerodynamic power limiting. The first is passive regulation. The rotor blades are designed to stall near rated windspeed. Hence, the power generated by the turbine does not rise further with windspeed. The second is active regulation. The torque induced on the rotor by the wind depends on the pitch angle of the blades. Hence, the torque may be reduced by feathering the blades and vice versa. During active regulation, above rated windspeed, the pitch of the blades are continuously set to the angle of pitch at which rated power is generated. The adjustment of pitch angle is usually made in response to power measurement. The capability to vary the pitch angle of the blades may be exploited to achieve much more than simply limiting the level of generation of power. The purpose of the paper is to report on an extensive investigation into the active control of constant speed wind turbines. >

High frequency link DC/AC converters using three phase output PWM cycloconverters for uninterruptible power supplies

Abstract: The authors propose a main circuit and a control method of a high-frequency link DC/AC power converter with three-phase output using a cycloconverter which converts a high-frequency voltage into a three-phase commercial frequency voltage. This DC/AC converter can control the flow of power bidirectionally, and can charge a DC power supply and compensate for instantaneous reactive power. Simulations and experiments were carried out to confirm the feasibility of the proposed method. >

Near-unity-power-factor single-phase AC-to-DC converter using a phase-controlled rectifier

Abstract: The authors describe a near unity power factor single-phase AC-to-DC power converter based on the line frequency phase controlled rectifier with an input capacitor. The method of achieving near unity power factor AC-to-DC conversion is presented, and the advantages and disadvantages of this conversion techniques are described. The converter was first simulated on a computer and then measured in the laboratory. Converter harmonics were minimized, and the converter purity factor was maximised by careful design of the rectifier. The converter displacement power factor was maximised by the input capacitor. The converter performs near unity power factor AC-to-DC conversion for the minimum input voltage, maximum output current condition in which the DC load approaches the rating of the service supplying it. >

Analysis of DC-DC converter for the maximum power point control of photovoltaic

Abstract: The authors describe the operating analysis and the experimental results of a DC-DC converter for the maximum power point control (MPP) of photovoltaic systems. When a DC-DC converter is used for the MPP control, it would connect to batteries. The analysis of the operation of this converter is carried out. As a result, the energy transference by the DC-DC converter was confirmed and the suitable circuit parameters were obtained. The experimental results of the MPP control of photovoltaic systems prove the usefulness of the MPP control. >

High-frequency heating apparatus mounted on a motor vehicle

Abstract: A DC power source constituted by a power generator (20), a dynamo (22) and a rectification means (23), an inverter power source (24) which boosts an output of the DC power source so as to drive a magnetron (28) and an inverter controller for controlling the inverter power source (24) by an output of a generated electric power output detecting means (31) for detecting the output of the DC power source are provided, whereby a required dielectric heating function can be stably achieved by controlling an operational state of the inverter power source (24) by the output of the DC power source.

Microcomputer control of DC/DC converters for photovoltaic applications

Abstract: Results obtained with an experimental system using microcomputer control of a Cuk converter fed from photovoltaic solar panels are presented. The control system maintains a constant output voltage regardless of the insolation and charge variations. Digital control has the advantages of avoiding reference values, ease of controller parameter adjustment, and the facility to cover a large number of working regimes of the solar panels and the DC/DC power converter. A proportional-integral-derivative (PID) algorithm is used for the converter. The PID parameters are easy to adjust from the user terminal keyboard and the output voltage can be fixed over a wide range of values. >

Test and evaluation of load converter topologies used in the Space Station Freedom power management and distribution dc test bed

Abstract: Power components hardware in support of the Space Station Freedom dc Electrical Power System were tested. One type of breadboard hardware tested is the dc Load Converter Unit, which constitutes the power interface between the electric power system and the actual load. These units are dc to dc converters that provide the final system regulation before power is delivered to the load. Three load converters were tested: a series resonant converter, a series inductor switchmode converter, and a switching full-bridge forward converter. The topology, operation principles, and tests results are described, in general. A comparative analysis of the three units is given with respect to efficiency, regulation, short circuit behavior (protection), and transient characteristics.

Output control method by adaptive control to wind power generating system

Abstract: For a wind power generating system in which resistive load is connected to the DC generator for load, the development of a control method which takes out wind energy effectively even when the system characteristic is unknown is considered. The control method is a hill-climbing method, and this method can follow the quasi-maximum output relatively easily only by the measurement of output. The effectiveness of output control by the hill-climbing method was confirmed for cases of both constant and fluctuating wind velocity. >

PV assisted DC and AC fluorescent lighting systems compared

Abstract: A comparison is made between efficient fluorescent lighting systems powered by AC and by DC with photovoltaic arrays providing a share of the load. The AC system requires an inverter on the photovoltaic array, and the DC system requires a DC power supply between the grid and the lighting circuit. More photovoltaic power is available for the lighting at all times when the sun is shining with the DC system. The total grid power consumed by each system is a function of power supply and inverter efficiencies, season, and TOD (time-of-day) benefits. The DC system appears to reduce summer utility peaks and summer customer demand charges further than an AC system would. >