Showing papers on "Power optimizer published in 2002"

General model for representing variable speed wind turbines in power system dynamics simulations

Abstract: A tendency to erect ever more wind turbines can be observed in order to reduce the environmental consequences of electric power generation. As a result of this, in the near future, wind turbines may start to influence the behavior of electric power systems by interacting with conventional generation and loads. Therefore, wind turbine models that can be integrated into power system simulation software are needed. In this contribution, a model that can be used to represent all types of variable speed wind turbines in power system dynamics simulations is presented. First, the modeling approach is commented upon and models of the subsystems of which a variable speed wind turbine consists are discussed. Then, some results obtained after incorporation of the model in PSS/E, a widely used power system dynamics simulation software package, are presented and compared with measurements.

Multi-input DC/DC converter based on the multiwinding transformer for renewable energy applications

Abstract: A multi-input DC/DC power converter based on the flux additivity is proposed in this paper. Instead of combining input DC sources in the electric form, the proposed converter combines input DC sources in magnetic form by adding up the produced magnetic flux together in the magnetic core of the coupled transformer. With the phase-shifted pulsewidth-modulation (PWM) control, the proposed converter can draw power from two different DC sources and deliver it to the load individually and simultaneously. The operation principle of the proposed converter has been analyzed in detail. The output voltage regulation and power flow control can be achieved by the phase-shifted PWM control. A prototype converter with two different DC voltage sources has been successfully implemented. Computer simulations and hardware experimental results are presented to verify the performance of the proposed multi-input DC/DC power converter.

Current-sensing techniques for DC-DC converters

Abstract: Current sensing is one of the most important functions on a smart power chip. Conventional current-sensing methods insert a resistor in the path of the current to be sensed. This method incurs significant power losses, especially when the current to be sensed is high. Lossless current-sensing methods address this issue by sensing the current without dissipating the power that passive resistors do. Six available lossless current sensing techniques are reviewed. A new scheme for increasing the accuracy of current sensing when the discrete elements are not known is introduced. The new scheme measures the inductor value during the DC-DC controller startup.

Maximum power tracking for photovoltaic power system

Abstract: The electric power supplied by a photovoltaic power generation system depends on the solar radiation and temperature. Designing efficient PV systems heavily emphasizes tracking the maximum power operating point. This work develops a novel three-point weight comparison method that avoids the oscillation problem of the perturbation and observation algorithm which is often employed to track the maximum power point. Furthermore, a low cost control unit is developed, based on a single chip to adjust the output voltage of the solar cell array. Finally, experimental results confirm the superior performance of the proposed method.

Method for operating a wind park

Abstract: The invention relates to a method for operating a wind park; consisting of several wind power plants. The wind part is connected to an electric supply network into which the power produced by the wind park is fed and the wind park and/or at least one of the wind power plants of the wind park is provided with a control input which is used to adjust the electric power of the wind park or one or several individual wind plants within a range of 0-100 % of the respectively provided power, especially the nominal output thereof. A data processing device is connected to the control input and is used to adjust the control value within a range of 0-100 % according to the amount of power available from the entire wind part at the output where it is fed into the power network. The operator (EVU) of the electric power supply network to which the wind park is connected can adjust the power provided by the wind park via the control input.

Multiple-input DC-DC power converter for power-flow management in hybrid vehicles

Abstract: The search for a compact, lightweight, and efficient energy storage system (battery and/or combination of other emerging technologies, including ultracapacitors, flywheel energy storage system, advanced batteries, and fuel cells) that is both affordable and has acceptable cycle life remains the major roadblock to large-scale production of EVs and HEVs. In this paper a multiple input DC-DC power converter (MI-PEC) devoted to combine the power flowing from combined on-board energy sources is presented; the proposed arrangement for the propulsion system includes electric generator (EG), ultracapacitor tank (UC) and battery systems.

A new green power inverter for fuel cells

Abstract: This paper presents a new grid connected inverter for fuel cells. It consists of a two stage power conversion topology. Since the fuel cell operates with a low voltage in a wide voltage range (25 V-45 V) this voltage must be transformed to around 350-400 V in order to invert this DC power into AC power to the grid. The proposed converter consists of an isolated DC-DC converter cascaded with a single phase H-bridge inverter. The DC-DC converter is a current-fed push-pull converter. A new dedicated voltage mode startup procedure has been developed in order to limit the inrush current during startup. The inverter is controlled as a power factor controller with resistor emulation. Experimental results of converter efficiency, grid performance and fuel cell response are shown for a 1 kW prototype. The proposed converter exhibits a high efficiency in a wide power range (higher than 92%) and the inverter operates with a near unity power factor and a low current THD.

A research on photovoltaic energy controlling system with maximum power point tracking

Abstract: This paper introduces a photovoltaic energy system, controlled by a DC-DC converter and a single phase bi-directional PWM converter to realize the inversion. A current controlling (MPPT) method of tracking the maximum power point and forcing the system to operate close to this point is used. An artificial neural network is used in the MPPT system and its robustness and insensitivity to the intermittent weather conditions is enhanced. Uc3854 is used as an inversion current controller, which has a high performance in harmonics and power factor.

A 31-level cascade inverter for power applications

Abstract: Power inverter modules fed with separate DC voltage sources of voltage ratio 1:2:4:8 are connected to form a cascade multilevel inverter. This new proposal combines the advantages of the static phase-shifter and chain-cell converter concept. Using the same number of power devices as a standard nine-level inverter, the proposed converter operates as a high-power digital-to-analog converter with 31-level resolution. Electrolytic capacitors used in the proposed inverter for providing the DC voltage sources will never be connected in opposite polarity in all cases, thus ensuring high reliability. The proposal has the potential for uninterruptible power supply and flexible AC transmission applications.

Distributed power system

Abstract: A power generation system is disclosed. In one embodiment, the power generation system includes a fuel source, a turbogenerator coupled to the fuel source, and a power controller coupled to the turbogenerator. The power controller includes an AC/DC power converter that converts AC power generated by the turbogenerator to DC power on output lines for supplying a DC load. The power controller regulates the fuel to the turbogenerator, independent of a DC voltage on the output lines. A capacitor such as an electrochemical capacitor or a hybrid capacitor, coupled across the output lines, sources power to and/or sinks power from the output lines due to load changes by the DC load. In a further embodiment, the power controller includes an additional DC/DC power converter. In yet a further embodiment, the power controller includes a second additional DC/DC power converter to controllably couple the capacitor to a DC bus.

Data processor controlled DC to DC converter system and method of operation

Abstract: A flexible, reliable and economical DC to DC power converter system includes a plurality of DC to DC converter units, a pulse width modulation current share bus interconnecting the DC to DC converter units and a synchronization signal connected to each of the DC to DC converter units to synchronize each of the DC to DC converter units to the same frequency. Each DC to DC converter unit includes a power section, a controller and a standard universal interface connecting the power section to the controller such that the power section can be changed to accommodate different input voltages, output voltages and current loads without making significant hardware changes in the controller. The controller includes a digital signal processor having a calibration table matching control parameters to the specific circuit characteristics of the power section. The digital signal processor has a clock signal synchronized to the synchronization signal, resolves master/slave contention for controlling the output voltage in response to signals sent and received over the current share bus and generates pulse width modulation power switch control signals controlling the power section to operate in either dual or single converter mode at different frequencies in response to varying system output current demands.

AC/DC cascaded power converters having high DC conversion ratio and improved AC line harmonics

Abstract: AC/DC cascaded power converters having high DC conversion ratio and improved AC line harmonics provide low input harmonic currents, high power factor and efficient operation for low voltage DC outputs when coupled directly to a source of unfiltered rectified AC voltage. The power converter incorporates an intermediate storage element that provides most or all of the energy storage capacitance within the power converter and a blocking device that enables continuous energy transfer from AC line to output to achieve unity power factor and regulated output while maintaining low AC input current ripple.

Prediction-data-based maximum-power-point-tracking method for photovoltaic power generation systems

Abstract: A new maximum-power-point-tracking (MPPT) method for a photovoltaic (PV) power generation system was studied which can efficiently generate PV power even under changing weather conditions. In order to research a method suitable for the actual photovoltaic power system, PV characteristics of the maximum power point were measured for more than six months using a PV curve tracer. The actual maximum power points vary with conditions such as the surface temperature and the quantity of solar radiation. So, relationships between the maximum power point and circuit variables such as open circuit voltage and short circuit current were examined under various conditions appearing in the PV power generation system. It was found through measurements that the relationship between the maximum power and the current that the output power was almost a linear function in the actual solar arrays, regardless of the weather conditions. The MPPT method was proposed based on the obtained findings. It was verified through simulations and experiments that the proposed method enables the solar arrays to quickly generate the maximum power as determined by weather conditions at the time.

A new maximum power point tracking control scheme for wind generation

Abstract: According to the aerodynamical characteristic of the wind turbine, a maximum power point tracking (MPPT) is necessary to get high efficiency for wind power conversion, which means that the rotating speed of wind turbine should be adjusted in the real time to capture maximum wind power. Because of the fast variation of wind speed and the heavy inertia of generator, the MPPT control of wind generation is much challengeable. A new MPPT control scheme has been developed for permanent magnetic (PM) generator driven by a three-phase inverter to generate 350 V direct current power to the DC bus line. The main differences between the method used in the proposed MPPT system and other techniques used in the past are as follows: (1) the tracking step is variable according to the change of wind speed; (2) in order to avoid the dead time effect of the inverter the MPPT control is synchronized to the rotating speed of the generator; (3) a low pass filter is used at the output of the MPPT controller to decrease the fluctuation of the rotating speed reference. The resulting system has high-efficiency, lower-cost and fast, stable tracking speed. The experimental results show that it can track as fast as 0.2Hz variation of wind speed and increases the output wind power as much as 48%. As a result, the efficiency of the generation has been improved evidently.

Utility-connected power converter for maximizing power transfer from a photovoltaic source while drawing ripple-free current

Abstract: This paper presents a power converter for coupling photovoltaic arrays to the utility grid. The converter draws a programmable, ripple-free DC current from the photovoltaic array and injects power into the grid at unity power factor. The programmable input current feature makes this converter ideal for use with maximum power point tracking technology. The proposed converter has an additional unique feature in that the internal dc link carries a large (approximately 25%) ripple voltage. Allowing a large ripple on the DC link reduces the required size of the link capacitor. This paper includes basic system information, analysis of filter requirements, controller design and preliminary hardware results.

Apparatus and method of detecting ground fault in power conversion system

Abstract: In a power conversion system having a DC power supply which has an almost fixed DC voltage to ground and a predetermined stray capacitance to ground and outputs a DC power, and a power converter which converts the DC power output from the DC power supply into an AC power by switching, the phase of an AC voltage to ground generated in the DC power supply by switching is detected, the phase of an AC ground fault current that flows through the stray capacitance to ground and the ground fault resistance of the DC power supply is detected, and the difference between the two detected phases is compared with a predetermined threshold value, thereby determining a DC ground fault in the DC power supply. With this arrangement, the ground fault state of the DC power supply can more accurately be detected. In addition, the operation efficiency of the power conversion system can be increased.

Method for operating a wind farm

Abstract: The method involves setting the electrical power of the wind park or one or more wind power systems in a range of 0 to 100 per cent of the available power by means of a data processing device connected to at least one wind power system control input. The demanded power is set depending on the total available power of the wind park. The controller of the supply system can set the power output by the wind park. An independent claim is also included for the following: a wind park and a wind power system.

Power slope targeting for DC generators

Abstract: A simple feedback control loop, in conjunction with an improved maximum power point tracking intermediate controller, can be used ensure efficient operation of a power generator. The improved maximum power point tracking controller operates the generator at its maximum allowable power point. A power output of the generator is measured and compared to a power output setpoint. Operating characteristics of the generator are then adjusted to cause the maximum allowable power point and measured power output to approximate the power output setpoint. Although applicable to all types of generators, this is particularly beneficial in fuel cell generator systems and other systems where damage to generator components can occur if operated above a maximum allowable power output level. In other systems, the maximum allowable power output may approach or equal a maximum power point (or maximum possible power point).

DC Distributed Power Systems - Analysis, Design and Control for a Renewable Energy System

Abstract: Renewable energy systems are likely to become wide spread in the future due to environmental demands. As a consequence of the dispersed nature of renewable energy systems, this implies that there will be a distributed generation of electric power. Since most of the distributed electrical energy sources do not provide their electric power at line frequency and voltage, a DC bus is a useful common connection for several such sources. Due to the differences in output voltage among the sources, depending on both the type of source and their actual operating point, the sources are connected to the DC power system via power electronic converters. The intention behind the presented work is not to replace the existing AC power system, but to include local DC power systems. The AC and DC power systems are connected at some points in the network. The renewable energy sources are weak compared to the present hydro power and nuclear power plants, resulting in a need of power conditioning before the renewable energy is fed to the transmission lines. The benefit of such an approach is that power conditioning is applied on a central level, i.e. at the interface between the AC and DC power systems. Present DC transmission systems are discussed and investigated in simulations. Then, different methods for load sharing and voltage control are discussed. Especially, the voltage droop control scheme is examined thoroughly. Since the droop control method does not require any high-speed communication between sources and loads, this is considered the most suitable for DC distributed power systems. The voltage feed back design of the controller also results in a specification of the DC bus capacitors (equivalents to DC link capacitors of single converters) needed for filtering. If the converters in the DC distribution system are equipped with capacitors selected from this design criterion and if the DC bus impedance is neglected, the source converters share the total load equally in per unit. The same DC distribution bus configuration is studied in a wind power application. Especially the dynamic properties of load-source interactions are highlighted. They are interesting since the sources are considered weak for a distributed power system. This is illustrated with simulations where the power is fed from wind turbines only and constant power loads are controlled at the same time as the DC bus voltage level. Personal safety and prevention of property damage are important factors of conventional AC power systems. A grounding scheme for the DC distribution system together with algorithms for detection of ground faults, are presented. The proposed method detects ground faults on both the AC and DC sides and is extended to cover short circuit faults with a minor work effort. Experimental verifications follow the theoretical investigations introduced above. First, dynamic properties are studied and the behavior predicted from theoretical analysis and simulations is verified. Then, load sharing is investigated. Also in this investigation, the experimental results agree with the simulated. (Less)

Power converter control for automatic maximum power point tracking

Abstract: The invention concerns a method and a circuit for maximum power point tracking of a variable power source from a comparison of an image of the power (P) supplied by the power source, the circuit comprising two elements (14, 31) providing different propagating delays to a physical quantity proportional to the power image, a comparator (16) of the outputs of the delaying elements to control a trigger (17) supplying a signal (Q) with two automatic control states to a static power converter, and means (33) for detecting a transitory operating condition from variations in oscillations of an established operating condition and means (32) for modifying the delay input by the slower delaying element (31).

User-configurable power architecture with hot-pluggable power modules

Abstract: A power management system for use in a power-consuming system is disclosed. The system comprises one or more power module bays each adapted to have a power module hot-pluggably installed therein, the power module comprising an uninterruptible power supply (UPS) power module and a power supply unit (PSU) power module each adapted to be installed in the one or more power module bays; and a power module interface that connects power signals generated by installed power modules with one or more power buses in the system.

Modelling and Analysing Impacts of Wind Power on Transient Stability of Power Systems

Abstract: This paper considers the impact of increasingly large numbers of wind turbine generators on the stability of power grid networks. Most modern wind turbines do not have conventional grid coupled synchronous generators, as is the case with most other technologies for electrical power generation. Instead, squirrel cage induction generators are used, or generators that are grid coupled with power electronic converters. Consequently, wind turbines interact with the power system in a way that differs from conventional generators. In the paper, the interaction between wind turbines and the power system is investigated using simulations of a widely used representative dynamics test system in which a high wind power penetration is assumed. It is concluded that the impact of wind power on power system transient stability varies much when either constant or variable speed wind turbines are used.

Aggregated modelling of wind parks with variable speed wind turbines in power system dynamics simulations

Abstract: More and more wind turbines are made part of electrical power systems, in order to reduce the adverse environmental impact of conventional electrical power generation. A tendency to erect these turbines in wind parks, that are connected to the high voltage transmission grid can be observed. To facilitate the investigation of the impact of a wind park on the dynamics of the power system to which it is connected, an adequate model is required. In order to avoid the necessity of developing a detailed model of a wind park with tens or hundreds of wind turbines and their interconnections, aggregated wind park models are needed. A further advantage of aggregated models is a substantial reduction of computation time. In this paper, an aggregated model for a wind park equipped with variable speed wind turbines is developed and it is shown that the results yielded by the aggregated model and a detailed model show a high degree of correspondence.

High frequency low cost DC-AC inverter design with fuel cell source for home applications

Abstract: This paper presents a new design of high frequency DC/AC inverter for home applications using fuel cells or photovoltaic array sources. A battery bank parallel to the DC link is provided to take care of the slow dynamic response of the source. The design is based on a push-pull DC/DC converter followed by a full-bridge PWM inverter topology. The nominal power rating is 10 kW. Actual design parameters, procedure and experimental results of a 1.5 kW prototype are provided. The objective of this paper is to explore the possibility of making renewable sources of energy utility interactive by means of low cost power electronic interface.

Transient ride-through or load leveling power distribution system

Abstract: A power generation system includes a turbogenerator having a motor/generator and a turbine coupled to a common shaft, and generates AC power. A first power converter is coupled to the turbogenerator and a DC bus and converts the AC power to DC power on the DC bus. A second power converter is coupled to the DC bus and is couple-able to a load. The second power converter converts the DC power on the DC bus to an output power for coupling to the load. Also coupled to the DC bus are a battery and a capacitor to stabilize a DC voltage on the DC bus during load changes. The power generation system further includes a power controller coupled to the turbogenerator and the first and second power converters. The power controller regulates a speed of the turbine, independent of the DC voltage on the DC bus.

DC power supply device

Abstract: A DC power supply device comprises an AC/DC converter 1, a DC/DC converter 2, and a DC converter 3 converting DC power from a battery 4 to DC voltage for connecting to output terminals of the AC/DC converter. The DC power supply device is provided with a controlling circuit 100 which observes a charging control level and a load sharing level, impresses a charging command on a UPS controlling part controlling the DC converter, and simultaneously provides a PFC controlling part controlling the AC/DC converter with a current command when a voltage level is less than the charging control level, stops only the charging command when the voltage level is more than the charging level and less than the load sharing level, and provides the UPS controlling part and the PFC controlling part with current commands when the voltage level is more than the load sharing level. The AC/DC converter and the DC converter supply power in parallel when a load is more than a prescribed value, and the DC converter supplies power as a backup when a trouble is present in an AC power input.

Power generation system having transient ride-through/load-leveling capabilities

Abstract: A power generation system includes a turbogenerator having a motor/generator and a turbine coupled to a common shaft, and generates AC power A first power converter is coupled to the turbogenerator and a DC bus and converts the AC power to DC power on the DC bus A second power converter is coupled to the DC bus and is couple-able to a load The second power converter converts the DC power on the DC bus to an output power for coupling to the load Also coupled to the DC bus are a battery and a capacitor to stabilize a DC voltage on the DC bus during load changes The power generation system further includes a power controller coupled to the turbogenerator and the first and second power converters The power controller regulates a speed of the turbine, independent of the DC voltage on the DC bus

A comparison of various buck-boost converters and their application to PFC

Abstract: The conventional boost converters are generally used for rectifier circuits with power factor correction, and as a result the output voltage becomes limited. To expand the controlled voltage range, buck-boost or Cuk converter types should be utilized. This paper presents a circuit configuration with power factor correction by a third type of buck boost converter, termed a 'CSC, canonical switching cell'. Single-phase power factor correction using a buck boost converter can control the output voltage over a wide range, because it has the ability to step-up and step-down the output voltage. Firstly, this paper compares the mechanisms of the power transmission and the characteristics based on total stored energy. Secondly, CSC converter is applied to the single-phase power factor correction. It is presented that this converter is suitable for power factor correction.

Hybrid vehicle and control method therefor

Abstract: A hybrid vehicle and a control method of the hybrid vehicle is provided, capable of suppressing discharge of the battery at the time of starting a DC/DC converter and suppressing temporal voltage drop of the battery. When the engine is in the idle state and the power generated by the motor is not sufficient, the motor controller starts the DC/DC converter at a low output voltage state, and the amount of power generated by the motor is gradually increased at a speed without disturbing the idle rotation of the engine, and when it is determined that the power generation by the motor is sufficiently high by comparing the amount of power generation with the amount of power consumption at the output of the DC/DC converter, the operation mode of the output variable DC/DC converter is switched from the low voltage mode to the high voltage mode.

Power supply and inverter used therefor

Abstract: This invention relates to a power supply that integrates a rectifier/filter's circuitry and a converter's circuitry with an inverter to reduce space occupied and increase power efficiency. The power supply includes: a rectifier/filter, a DC-DC converter and a DC-AC inverter. The rectifier/filter, connected to an alternating current (AC) input terminal, converts the input AC into a direct current (DC). The DC-DC converter and the DC-AC inverter are parallel to each other with one end concurrently connected to the rectifier/filter's output and the other end respectively outputting the desired powers. As such, DC-DC converter reduces the converted DC voltage to lower DC voltages to power all circuits except for the lamp and DC-AC inverter converts the converted DC voltage into higher AC voltage output to drive the lamp.