Showing papers on "Power optimizer published in 1995"

AC/DC/AC PWM converter with reduced energy storage in the DC link

Abstract: The paper introduces the family of quasi-direct converters, i.e., forced-commutated AC/DC/AC power converters including small energy storage devices in the DC link. In particular, the case of the three-phase to three-phase quasi-direct power converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported. >

On lossless switched-capacitor power converters

Abstract: This paper addresses the design of efficient switched-capacitor power converters. The discussion starts with a review of the fundamental limitation of switched-capacitor circuits which shows that the topology of such circuits and the "forced" step changes of capacitor voltages are the inherent attributes of power loss. Although the argument follows from a rather trivial result from basic circuit theory, it addresses an important issue on the maximum efficiency achievable in a switched-capacitor power converter circuit. Based on the observed topological constraint of switched-capacitor power converter circuits, the simplest lossless topology for AC/DC power conversion is deduced. Also discussed is a simple version of lossless topology that achieves isolation between the source and the load. Finally, an experimental AC/DC switched-capacitor power converter, based on the proposed idea, is presented which demonstrates an improved efficiency over other existing switched-capacitor power converters. The proposed AC/DC power converter contains no inductors and thus is suitable for custom IC implementation for very low power applications. >

Fuzzy logic integrated electrical control to improve variable speed wind turbine efficiency and performance

Abstract: A control system utilizing fuzzy logic adaptive control to control the operation of a wind turbine driven electric power generator to control power generator speed and hence power frequency while maximizing the power output of the power generator. Wind turbulence effects are eliminated and airgap magnetic flux of the power generator is controlled.

Uninterruptible power supply with AC and DC power inputs

Abstract: An uninterruptible power supply includes first and second inputs for receiving AC and DC power respectively, first and second switching circuits, an auxiliary power supply, a transformer, a selection circuit, an A to DC converter and a hold-up capacitor. The hold-up capacitor can provide energy storage for both AC and DC operation.

Power quality of wind turbines and their interaction with the grid

Abstract: The interaction of wind turbines (WT) with the grid has an evident influence on the voltage of the grid. The loss of power quality is depending directly on the intensity of the interference related to the capacity of the grid. In near future a certificate for power quality will be claimed by German utilities. This certificate will demonstrate the quality of power generation of a WT with respects to harmonics, power peaks, power factor and flicker for normal operation as well as for extreme and switching operation conditions. In this paper we present examples of the measurements according to the guideline. We show the grid interactions occurring during the operation of different WTs and how they possibly could be diminished. In addition the interaction effects of single WTs and wind farms will be compared.

Optimizing small wind turbine performance in battery charging applications

Abstract: Many small wind turbine generators (10 kW or less) consist of a variable speed rotor driving a permanent magnet synchronous generator (alternator). One application of such wind turbines is battery charging, in which the generator is connected through a rectifier to a battery bank. The wind turbine electrical interface is essentially the same whether the turbine is part of a remote power supply for telecommunications, a standalone residential power system, or a hybrid village power system, in short, any system in which the wind generator output is rectified and fed into a DC bus. Field experience with such applications has shown that both the peak power output and the total energy capture of the wind turbine often fall short of expectations based on rotor size and generator rating. In this paper, the authors present a simple analytical model of the typical wind generator battery charging system that allows one to calculate actual power curves if the generator and rotor properties are known. The model clearly illustrates how the load characteristics affect the generator output. In the second part of this paper, the authors present four approaches to maximizing energy capture from wind turbines in battery charging applications. The first of these is to determine the optimal battery bank voltage for a given WTG. The second consists of adding capacitors in series with the generator. The third approach is to place an optimizing DC/DC voltage converter between the rectifier and the battery bank. The fourth is a combination of the series capacitors and the optimizing voltage controller. They also discuss both the limitations and the potential performance gain associated with each of the four configurations.

Photovoltaic systems for small-scale remote power supplies

Abstract: This article considers the technical aspects of using photovoltaic systems for small power supplies where a connection from a main electricity distribution network is not appropriate. The technology of the various components of a photovoltaic power system is discussed and the overall system design considered. Typical applications of photovoltaic systems are described.

Grid connected bi-directional converter including a pwm, dc-dc chopper, and energy storage/supply device

Abstract: A bi-directional converter (i.e., AC- > DC or DC- > AC) for transferring electrical energy between a high voltage AC power grid (12) and a DC energy storage/supply (22) (such as a battery or a series of photovoltaic or fuel cells). The converter includes a PWM inverter (20) coupled to the grid (12), and a DC-DC chopper (21) coupled between the PWM inverter (20) and a DC energy storage/supply (22). The PWM inverter (20) includes a switching circuit (26) having high speed electrical switches arranged in pairs coupled between the AC grid phase voltage rails and DC-DC chopper voltage rails. An inverter control unit (24) includes a DC bus voltage regulator (40) to regulate the voltage on the DC side of the PWM inverter (20), and a reactive power controller (42). A DC control unit (23) includes a real power controller (41) that controls the real power flow by controlling the current flow of the DC energy storage/supply (22). By modulating the DC switches (25) in the DC-DC chopper (21), the DC current to the DC energy storage/supply (22) is controlled to provide a desired real power flow through the DC-DC chopper (21), independent of the voltage (VDC) of the energy storage/supply (22).

Current sharing of redundant DC-DC converters in high availability systems-a simple approach

Abstract: DC-DC power converters operating in parallel, redundant configurations can produce high availability systems, which can tolerate the failure of one or more of the power converters involved. This paper details a simple but effective method for insuring current sharing in paralleled modules, which can be applied to power convertor modules from many different manufactures. >

Controllable converter power supply

Abstract: In accordance with the present invention a power supply for providing an ac/dc output to a load is disclosed. The power supply includes a first source of dc power and an inverter that provides an ac output to the load. A second source of dc power is provided and selectably connects the first and second sources of dc power in series with the load when the output current reverses. In one embodiment the power sources are connected in series with every output current reversal. The first source of dc power is controllable and the magnitude of the dc current is responsive to a current reference signal. A control circuit provides the current reference signal, wherein the current reference signal is pulsed immediately prior to the ac output reversing polarity. The first source of dc power source preferably includes a buck converter that is switched at a variable frequency, depending upon the desired output current. In the event the user selects either an ac or dc electrode negative output a period of electrode positive dc energy is provided at start up to help establish the arc.

Characteristics of a parallel-module high power-factor AC-to-DC converter system with current-balancing controllers

Abstract: Characteristics of a parallel-module high power-factor AC-to-DC power converter system using current-balancing controllers are presented. Problems caused by the parallel connection of power factor correction (PFC) power converter modules are discussed. Two types of current-balancing controllers, i.e. conventional and improved, are applied to the parallel-module PFC system to share the load current between the power converter modules. The effectiveness of the current-balancing controllers for the PFC power converter system is confirmed by experiment. The current-balancing controller improved here has fast transient response to load current sharing under dynamic conditions.

Dc power source system

Abstract: PURPOSE: To provide a DC power source system capable of supplying a required minimum of load by converting the output of a storage battery to AC power by high efficiency even when the storage battery having small capacity is mounted as an emergency power source. CONSTITUTION: In a DC power source system, a storage battery 7 having small capacity is connected to the output terminal of a DC power source 1 made of a solar cell via a charge/discharge controller 6, a small-capacity inverter 8 having lower rated output than that of a main inverter 2 is connected between the controller 6 and the battery 7, and an emergency plug socket 9 is connected to the output terminal of the inverter 8.

Investigation of power distribution architectures for distributed avionics loads

Abstract: Advanced aircraft will require electrical power to service diverse loads such as solid-state radars (which are pulsed loads) and digital loads which may require voltages of 1.5 V DC or lower. In this paper several alternative power distribution architectures capable of supplying the needed power to avionics loads are compared with regard to weight, size, cost, reliability, and efficiency. Versatile spreadsheet tools were developed that allow rapid and accurate comparison of alternative distribution schemes. Centralized and several types of decentralized architectures are compared assuming use of either existing or of advanced power converter technology. >

Space-vector modulated PWM converters for photo-voltaic interface applications: analysis, power management and control issues

Abstract: This paper presents new power management and control concepts for power converters that interface a photovoltaic (PV) system to an electric utility power system. The interface circuit is a space-vector modulated (SVM), high-frequency, 3/spl phi/, PWM buck-type inverter. Decoupled control of DC voltage for peak power tracking, and the quadrature component of AC output current for reactive power flow control is achieved. The inner current loop maintains a preset flow of reactive power from the power converter to the local load and the utility power system. The peak power tracking loop sets the reference value of the outer voltage loop. Small-signal model of the switching power converter, derived in rotating d-q coordinates is used to design the control loops. >

A high power factor operating self-resonant-PWM forward converter

Abstract: This paper presents a new soft commutation forward converter operating with almost unity power factor. The proposed approach allows building of a converter with high power density and high operation efficiency. Moreover, sinusoidal input current can also be obtained satisfying the IEC555-2 standards. The operating principle, theoretical analysis, relevant equations, simulation and experimental results for the converter are presented. >

Method and apparatus for protecting an inverter power supply

Abstract: In accordance with the present invention a power supply for providing an ac/dc output to a load is disclosed. The power supply includes a first source of dc power and an inverter that provides an ac output to the load. A second source of dc power is provided and selectably connects the first and second sources of dc power in series with the load when the output current reverses. In one embodiment the power sources are connected in series with every output current reversal. The first source of dc power is controllable and the magnitude of the dc current is responsive to a current reference signal. A control circuit provides the current reference signal, wherein the current reference signal is pulsed immediately prior to the ac output reversing polarity. The first source of dc power source preferably includes a buck converter that is switched at a variable frequency, depending upon the desired output current. In the event the user selects either an ac or dc electrode negative output a period of electrode positive dc energy is provided at start up to help establish the arc.

Controllable power supply

Abstract: A power supply for providing an AC/DC output to a load, particularly for us in GTAW welding includes a first source (111) of DC power and an inverter (117) that provides an AC output to the load. A second source of DC power (121) is provided and the power supply selectably connects the first (111) and second (121) sources of DC power in series with the load when the output current reverses. In one embodiment the power sources (111, 121) are connected in series with every output current reversal. The first source (111) of DC power is controllable and the magnitude of the DC current is responsive to a current reference signal. A control circuit (120) provides the current reference signal, wherein the current reference signal is pulsed immediately prior to the AC output reversing polarity. The first source (111) of DC power preferably includes a buck converter (112) that is switched at a variable frequency, depending upon the desired output current. In the event the user selects either an AnC or DC electrode negative output a period of electrode positive DC energy is provided at start up to help establish the arc.

Variable speed operation of generators with rotor-speed feedback in wind power applications

Abstract: The use of induction generators in wind power applications has been common since the early development of the wind industry. Most of these generators operate at fixed frequency and are connected directly to the utility grid. Unfortunately, this mode of operation limits the rotor speed to a specific rpm. Variable-speed operation is preferred in order to facilitate maximum energy capture over a wide range of wind speeds. This paper explores variable-speed operating strategies for wind turbine applications. The objectives are to maximize energy production, provide controlled start-up and reduce torque loading. This paper focuses on optimizing the energy captured by operating at maximum aerodynamic efficiency at any wind speed. The control strategy we analyze uses rotor speed and generator power as the feedback signals. In the normal operating region, rotor speed is used to compute a target power that corresponds to optimum operation. With power as the control objective, the power converter and generator are controlled to track the target power at any rpm. Thus, the torque-speed characteristic of the generator is shaped to optimize the energy capture. The target power is continuously updated at any rpm. in extreme areas of the operating envelope, during start-up, shutdown, generator overload, or overspeed, different strategies driven by other system considerations must be used.

Controllable power system

Abstract: A power supply for providing an AC/DC output to a load, particularly for us in GTAW welding includes a first source (111) of DC power and an inverter (117) that provides an AC output to the load. A second source of DC power (121) is provided and the power supply selectably connects the first (111) and second (121) sources of DC power in series with the load when the output current reverses. In one embodiment the power sources (111, 121) are connected in series with every output current reversal. The first source (111) of DC power is controllable and the magnitude of the DC current is responsive to a current reference signal. A control circuit (120) provides the current reference signal, wherein the current reference signal is pulsed immediately prior to the AC output reversing polarity. The first source (111) of DC power preferably includes a buck converter (112) that is switched at a variable frequency, depending upon the desired output current. In the event the user selects either an AC or DC electrode negative output a period of electrode positive DC energy is provided at start up to help establish the arc.

A Predictive Control Based Photovoltaic Power Generation for Air Conditioning System

Abstract: In this paper an auxiliary power supply scheme using photovoltaic power generation for air-conditioning system and its novel control strategy are proposed The proposed auxiliary power supply system employs a boost converter, a bidirectional power converter and photovoltaic arrays The boost converter controlled by a predictive control strategy provides maximum power track (MPT) state on the photovoltaic(PV) arrays as well as power generation facility function on the ac utility grid Furthermore the bidirectional power converter controls the power flow balance between the loads and two different power sources according to the condition of the load power and the supplied power from photovoltaic arrays It is shown that the maximum power tracking of the PV arrays, the unit power factor of ac utility grid and the descent input dc voltage regulation of the air-conditioning system are achieved by the proposed predictive control strategy The proposed switching strategy for the boost converter and the bidirectional power converter are based on the predictive control with ac line current and output voltage of the PV arrays The bidirectional power converter is suitably modulation controlled to rectify the ac source during the power shortage under the poor power generation of PV arrays or over load conditions of airconditioner During the opposite state, the bidirectional power converter is gated to function as a regeneration inverter Controller design procedure for the proposed approach to achieve near sinusoidal input currents under the inverter mode and the rectifier mode is detailed Simulation results on a laboratory proto-type system are discussed Experimental results from the laboratory proto-type system will be presented in the near future

Modeling of DC spacecraft power systems

Abstract: Future spacecraft power systems must be capable of supplying power to various loads This delivery of power may necessitate the use of high-voltage, high-power dc distribution systems to transmit power from the source to the loads Using state-of-the-art power conditioning electronics such as dc-dc converters, complex series and parallel configurations may be required at the interface between the source and the distribution system and between the loads and the distribution system This research will use state-variables to model and simulate a dc spacecraft power system Each component of the dc power system will be treated as a multiport network, and a state model will be written with the port voltages as the inputs The state model of a component will be solved independently from the other components using its state transition matrix A state-space averaging method is developed first in general for any dc-dc switching converter, and then demonstrated in detail for the particular case of the boost power stage General equations for both steady-state (dc) and dynamic effects (ac) are obtained, from which important transfer functions are derived and applied to a special case of the boost power stage

Soft on power system and method

Abstract: A computer power system with a keyboard, a computer housing, and a single AC to DC power converter that generates a DC power signal as long as it is energized by an AC power source. The power system is digitally controllable by the central processing unit (CPU) or from soft on/off switches on the keyboard and computer housing. This is made possible by a soft on/off controller that receives soft on/off control signals from the CPU and the soft on/off switches and in response generates a power transition signal that triggers shaping circuits to connect (soft on) or disconnect (soft off) power system output lines and power lines from the converter. The shaping circuits also ensure that the rising edge of a digitally switched power system output signal resembles the rising edge of the converter's cold-start power signal. Following a soft off event, the power system is in a low power standby state as power is not being supplied to the computer's power hungry components even though the converter is still generating a power signal.

Studies on Wind-Turbine Performance and New Power System

Abstract: The wind turbine performances and its relevent working states are introduced first Then two fundamental test methods: the force-measured method and the accelerationmeasured method,which are applied to the rotor property test in the wind tunnel,are described The problems and restrictions appeared in the application of the two test methods are discussed Especially,the restrictions produced by the applied power systems affecting on the measure ment of the wind trubine performance are further discussed On these bases is established a novel power system,which adopts the pulse-width modulation technique and consists of a bi-closed-loop controlled system, a current controlled inner-loop and a revolution controlled outer-loop The test results of the aerodynamic characteristics of the wind turbine by using the novel power system show that this power system is able to meet the need of all performance tests and various states at a specific wind speed As the result,this novel power system delivers a powerful tool for the wind turbine performance test in the wind tunnel

A Self-tuning Maximum Power Tracking Method of Photovoltaic Power Generator

Abstract: It is a big advantage of a photovoltaic power system to be able to generate power even in a small sized installation. A residential photovoltaic power generator makes the most of this advantage. In this case the controller for the maximum power tracking is required to be compact because space for the control installation can not be easily obtained. For this reason the development of a high frequency controller is essential. However the dynamic characteristics of a solar cell module are different from a static one owing to the presence of hysteresis at a high frequency. In such a high frequency region the conventional tracking method based on no hysteresis can not be responsible for control of the power system. In this paper the authors propose a new self-tuning maximum power tracking method for adjusting the control parameters of the power system at the high operating frequency. This method is distinguished by the fact that the control parameters are adjusted by the estimated value on the dynamic equivalent circuit of the solar cell module. The computer simulation and experimental results of the power system controlled by the proposed method shows excellent performances.