73results about How to "Reduce output fluctuation" patented technology

The invention discloses a transmission and distribution coordinated dispatching target cascaded analysis method of a high-proportion renewable energy source power system. The transmission and distribution coordinated dispatching target cascaded analysis method of the high-proportion renewable energy source power system comprises a local scheduling layer which is a scheduling unit for performing joint output optimization on a distributed renewable energy source in the interior of one power distribution network; a power transmission network and a power distribution network which separately serves as autonomous main bodies for decoupling through border frequency and optimizing resources in zones separately and cooperating with each other to schedule a power transmission plan, wherein a powertransmission network scheduling layer is to perform uncertainty modeling on the renewable energy source based on the improved interval optimization method to construct an energy and standby coordinative optimization model, and the power distribution network scheduling layer is a local scheduling layer set for the distributed renewable energy sources and performs joint output optimization by utilizing a scene method and combining with an energy storage system, thereby constructing the distribution network layer sub-problems into a dynamic economic scheduling model with optimal economical efficiency and with a target of absorbing the distributed renewable energy source joint output in the local scheduling layer.

The invention discloses a joint pumped storage power station and wind power and solar power complementary system and an optimization method therefor, and belongs to the technical field a joint wind power and solar power energy storage power generation system. By transforming an available space of a waste mine, a hybrid power generation system, combined by an underground water-pumping energy-storage power station and a surficial wind power and solar power complementary power generation system, is established; by taking the operation indexes, such as the wind power and solar power complementary system, the water-pumping energy-storage power station, power grid transmission power and the like as constraint conditions, a configuration model with the minimum wind power and solar power complementary output fluctuation, the minimum joint system output fluctuation and an optimized tracking load curve is obtained; and finally, solving and optimization on the model is performed based on an improved simulated annealing algorithm. By taking full advantages of the energy storage and power generation capability of the underground water-pumping energy-storage power station and by combination with the complementary characteristics of the wind power and solar power resources, the joint system is higher in flexibility in output regulation, the total output tracking load curve is better in effect, and the system is higher in new energy consumption and utilization.

The object is to reduce an output fluctuation in an interconnection node. Provided is an operation control method of a wind power generation system including a step of obtaining the output data of each wind turbine, a step of determining a correlation between output fluctuations of adjacent wind turbines by using output data, and a step of shifting, if a strong correlation is exhibited, a phase of output fluctuation of either one of the adjacent wind turbines by a period at which the strong correlation is exhibited.

Provided is a voltage regulator capable of reducing fluctuation of an output current even when an output terminal thereof is short-circuited. In a case where the output terminal of the voltage regulator is short-circuited, an output current (Iout) of the voltage regulator is limited and fixed to a limit current value. When an output voltage (Vout) of the voltage regulator decreases to have a value equal to or smaller than not a detection voltage value (Vref3) of a reference voltage circuit (34) but a detection voltage value (Vref2) of a reference voltage circuit (31), a second limit operation in which the output voltage (Iout) is further limited to be decreased is set. Further, in a case where the output terminal is short-circuited and then reset, when the output voltage (Vout) has a value equal to or larger than not the detection voltage value (Vref2) but the detection voltage value (Vref3), the second limit operation is canceled.

The invention discloses a virtual inductor and virtual capacitor power distribution method of a three-port converter, and relates to a technology of distributing the power of a three-port converter which accesses a direct current micro power grid, for realizing reasonable distribution of the power for a hybrid energy storage system which accesses the direct current micro power grid through the three-port converter. The virtual inductor and virtual capacitor power distribution method of a three-port converter is characterized in that in an energy storage unit, when the voltage of a direct current bus is stable, the real-time current feedback values at the low voltage side of the three-port converter are used to form a virtual inductor and a virtual capacitor; after the virtual capacitor iscombined with sagging control, after constant voltage control, the virtual capacitor is combined with super capacitor voltage recovery control again to become the other input terminal of phase shift control; and the output terminal of phase shift control respectively acts on a switch tube Q1 to a switch tube Q12 in the three-port converter, so as to achieve reasonable distribution of hybrid energystorage power. The virtual inductor and virtual capacitor power distribution method of a three-port converter has the advantages of realizing reasonable distribution of power, and being suitable fora direct current hybrid energy storage system.

The invention relates to a method for controlling the steam temperature of an outlet of a DSG (Direct Steam Generation) trough type solar thermal collector, belonging to the field of thermal utilization of solar energy. The method comprises the following steps of: dividing a whole nonlinear working space into a plurality of subspaces, describing each subspace by using an accurate fixing model, and designing corresponding sub-controllers specific to the sub-models; and designing a switcher which is used for selecting an output of the corresponding controller of the model best matched with an object as the real controlled quantity of a system. The control method has the advantages of rapid response speed, astable deviation, little fluctuation of system output and reduction of model mismatchinfluence.

The invention discloses a wireless power transmission topology with strong anti-offset performance based on multi-frequency energy parallel transmission. A control module outputs a drive square wave signal of a high-frequency inverter, so that the output voltage of the high-frequency inverter is the mixed superposition of double-frequency or multi-frequency voltages. After through a primary side multi-frequency shared compensation network, double-frequency or multi-frequency current simultaneously excites a primary side transmitting coil, multi-frequency energy is transmitted to a receiving module in parallel through magnetic field coupling, the receiving module achieves double-frequency or multi-frequency energy separation and decoupling transmission, alternating-current voltage or current with the frequency being each frequency is outputted, and the alternating-current voltage or current is outputted to a load for power supply in a combined mode after being rectified and filtered respectively. Due to the design of resonance parameters, the output under different frequencies is inconsistent with the change trend of mutual inductance; after combined output, output voltage or current insensitive to mutual inductance change is obtained, output fluctuation caused by change of the relative positions of the transmitting coil and the receiving coil is greatly reduced, and stable output of the wireless power transmission system under the high-offset working condition is guaranteed.

The invention discloses a capacity configuration method of multiple types of assemblies of a photovoltaic power station by considering output characteristics. The method comprises steps of (1) selecting a photovoltaic assembly so as to obtain construction cost and maintenance cost of unit capacity of each type of photovoltaic assembly; (2) determining the total installed capacity of the photovoltaic power station; (3) obtaining the duty circle of typical weather days of each season of a planned year of a photovoltaic base; (4) carrying out recording on contribution processes of each type of the photovoltaic assembly based on periods according to the duty circle obtained in the step (3) so as to obtain the contribution process based on periods of each type of the photovoltaic assembly of unit capacity in each typical weather day of each month; (5) establishing a multi-target optimization model of capacity matching ratio of multiple types of the assemblies of the photovoltaic power station; and (6) using a multi-target optimization algorithm to solve the multi-target optimization model so as to obtain the optimal photovoltaic assembly capacity matching ratio. According to the invention, the optimal capacity matching ratio decision model of the combination of multiple types of the assemblies of the photovoltaic power station under a planned installed capacity is provided, and by use of the multi-target optimization algorithm to solve the model, the model calculation efficiency is improved.

The invention relates to an electric power system and an electric power market, and provides a bidding strategy, and can realize the following aspects: 1, the new energy consumption capability can beimproved, and the problems of "wind abandonment" and "photovoltaic abandonment" can be solved; 2, a day-ahead market bidding scheme can be provided for a VPP operator; and 3, the problems of low quantity of a single distributed power generation unit and poor coordination of multiple distributed power generation units can be solved. A production bidding organizational method of a virtual power plant in a day-ahead market is disclosed; a virtual power plant (VPP) is established by a wind generating set, a photovoltaic power generation unit, electric vehicles and an interruptible load in one dispatching region; by making full advantage of complementation characteristics of wind power and photovoltaic power, and by virtue of the wind and photovoltaic total output fluctuation suppression performance by batteries of the electric vehicles, the demand on the quantity of the electric vehicles can be lowered by adopting the interruptible load, and the VPP can be participated in the day-ahead market bidding; and equivalently, the electric energy production and time combined information of the further 24 time frames, and backup output and time combined information are submitted. The productionbidding organizational method is mainly applied to the electric power system and electric power market occasions.

A permanent magnet includes magnetic poles that are arranged so as to alternate in polarity in the circumferential direction of the axis of rotation. The magnet is attached to one of a pair of rotatable members. The rotatable members are relatively rotatable about an axis of rotation. A magnetic flux inducing ring, including an annular ring body and a plurality of protrusions protruding from the ring body, is attached to the other rotatable member. A plurality of magnetic sensors is arranged adjacent to the ring body. A first facing portion and a second facing portion, each for inducing a part of a magnetic flux of the ring body, are provided and do not rotate with the permanent magnet and the magnetic flux inducing ring.

A magnetic recording medium including a substrate, a nonmagnetic layer containing nonmagnetic powder and a binder, and a magnetic layer containing ferromagnetic powder and a binder, in this order, wherein the nonmagnetic layer has a thickness of from 0.5 to 2.5 μm, a specific surface area of from 20 to 120 m2 / ml, a pore volume of from 0.15 to 0.40 ml / ml, and a median pore radius of from 3 to 16 nm, and the nonmagnetic layer has particles having an average particle diameter of from 4 to 14 nm on a magnetic layer side.

The invention relates to a power source device of an electrophoresis system. The power source device of the electrophoresis system comprises an input unit, a pre-voltage-stabilization unit, a switch transduction unit and a high-voltage transformation output unit, wherein the input unit, the pre-voltage-stabilization unit, the switch transduction unit and the high-voltage transformation output unit are connected in sequence. Grid power frequency alternating voltage is converted into a programmable error-corrected direct current power source firstly, then the direct current power source is converted into high voltage pulse signals, and then the high voltage pulse signals are converted into high voltage direct voltage and a high voltage direct current, wherein the high voltage direct voltage and the high voltage direct current are needed by the electrophoresis system. The power source device of the electrophoresis system is characterized in that the pre-voltage-stabilization unit, the switch transduction unit and the high-voltage transformation output unit and a control unit construct closed loop feedback control. The closed loop feedback control can conduct self-adaption regulations according to power source requirements of the electrophoresis system, load changes of a buffer solution and output error analysis results of the high-voltage transformation output unit, and supply the stable high voltage direct voltage and the stable high voltage direct current for the electrophoresis system in a working method of constant voltage or constant current or constant power. The power source device of the electrophoresis system can be used for an electrophoresis system which is high in requirement for power source stability and can enable a potential of hydrogen (pH) gradient of the buffer solution in the electrophoresis system to be more stable.

A liquid crystal display (LCD) system comprising means for generating a plurality of LCD driving voltages, the driving voltage values ​​being symmetrical about a predetermined voltage value, said means having a buffer capacitor structure providing a buffer capacitance for each LCD driving voltage, The LCD system further includes an LCD driver circuit having matrix switching and control means for supplying voltages corresponding to said LCD driving voltages to the terminals of the LCD panel resulting in appropriate brightness levels for the pixels of the LCD panel. In order to define the LCD drive voltage value, at least one charge pump unit is provided with at least one pump capacitor and a switching element, wherein at least one charge pump unit is connected to a buffer capacitor.

An image shake correcting apparatus, optical equipment, and an imaging device are disclosed. The image shake correcting apparatus includes a movable member configured to hold an image shake correcting member; a fixed member configured to hold the movable member so as to be movable along a spherical surface centering on a rotational center point; and an electromagnetic drive unit configured to have a magnet and a coil provided in portions that are mutually opposed in the movable member and the fixed member, wherein the magnet and the coil are disposed with inclination from a direction perpendicular to an optical axis so that a direction of drive force that is generated when the coil is energized approximately conforms to a tangential direction of a spherical surface centering on the rotational center point.

The invention provides a method and a device for controlling the coordinated operation of a wind power and solar power complementary system. A maximum power output predication value of wind power anda maximum power output predication value of solar power are calculated at first; then wind power output dispatch instruction values and solar power output dispatch instruction values at various moments are determined through a multi-target optimization module; and then the actual power of a wind power plant and the actual power of a solar power plant in the wind power and solar power complementarysystem are controlled according to the wind power output dispatch instruction values and the solar power output dispatch instruction values at the various moments. By adopting the method and the device provided by the invention, the grid connection of renewable energy sources is promoted, the abandoned air volume is reduced, and the benefits of the grid connection are increased; the maximizing ofthe benefits of the grid connection of the wind power and solar power complementary system and the variance of the grid-connected output power are coordinated better, and the grid connection of the renewable energy sources and the friendly operation of the relative power grid are facilitated.

The invention relates to the technical field of microgrid scheduling, in particular to a microgrid time domain rolling optimization scheduling method based on DDR-MPC, and the method comprises the steps: building a day-ahead optimization scheduling model taking the lowest daily comprehensive operation cost as a target at a day-ahead scheduling stage based on differential price type demand response; in an intra-day scheduling stage, combining the differentiated demand response with a model prediction control method, and establishing an intra-day time domain rolling optimization scheduling modeltaking minimum rolling time domain comprehensive operation cost as a target based on DDR-MPC; and solving a microgrid time domain rolling optimization scheduling model by adopting a time domain rolling composite differential evolution algorithm. According to the method, DDR and MPC methods are combined, so that the comprehensive operation cost of the microgrid can be remarkably reduced, and the reliability of microgrid optimal scheduling is improved; the time domain rolling composite differential evolution algorithm provided by the invention can efficiently solve the model, can significantlyimprove the optimization convergence speed, and has good dynamic environment adaptability.

The invention discloses a cross-region wind power installed capacity coordinated planning method which includes the steps of obtaining related data, constructing a calculation model, calculating a wind power combination effective frontier curve, determining a planning result and the like. According to the cross-region wind power installed capacity coordinated planning method, the wind power installed capacity of different regions is planned in a united mode based on an investment combination theory, wind power total contribution fluctuation is effectively reduced, and total peak pitching capacity demands of a system are reduced. The wind power installed capacity of the various regions under the condition that wind power combination quality factors are maximum serves as final optimized results, and the credibility of the wind power capacity and wind power fluctuation are considered to the maximum degree. The top limitation and the bottom limitation of the wind power installed capacity of the various regions are set, conditions, such as electric power network structures, load levels and government policies, of the various regions are sufficiently considered, and the planning result is close to the reality.

The invention discloses a calculation method of matched energy storage capacity of a large-scale photovoltaic power station under power restriction requirements, and the method includes the followingsteps: S1, determining the total installed capacity of the photovoltaic power station; S2, determining the total installed capacity of the photovoltaic power station; S2, obtaining the time proportionof typical weather days in each month of the plan year of the photovoltaic base; S3, recording the power output process of the photovoltaic power station according to the time proportion obtained inthe step S2, and obtaining the power output process of the photovoltaic power station installed with the unit capacity in each typical weather day of each month by the time period; 4, selecting the type of the energy storage battery to obtain the service life and the investment cost of the unit capacity of the energy storage battery; S5, establishing an optimization model for calculating the capacity of the matching energy storage battery of the large-scale photovoltaic power station under the power restriction requirement; and S6, adopting an optimization algorithm to solve the model to obtain the optimal energy storage capacity of the large-scale photovoltaic power station under power restriction requirements. The invention provides an optimal capacity decision model for matched energy storage of a large-scale photovoltaic power station under power restriction requirements, and adopts the optimization algorithm to solve the model, thereby improving the calculation efficiency of the model.

The invention discloses a system for thermal power frequency modulation by combining super capacitor energy storage with lithium battery energy storage. The system comprises an energy storage system.The energy storage system is composed of a lithium iron phosphate battery, a super capacitor, a first PCS circuit, a second PCS circuit, a DC / DC converter and a medium-voltage transformer. The super capacitor, the second PCS circuit and the DC / DC converter constitute super capacitor energy storage of the system, and the lithium iron phosphate battery and the first PCS circuit constitute lithium battery energy storage of the system. The system has the beneficial effect that high-power charging and discharging can be achieved and high-power long-time charging and discharging can also be achieved. The super capacitor unit responds to a low-power frequency modulation instruction of a power grid to protect the battery energy storage subsystem, so that the lithium battery energy storage system can be charged and discharged at high power and at low rate, the service life of the system is prolonged, and the economy of the system is improved. The hybrid energy storage system can reduce the output fluctuation of a unit and improve the adjustment precision of a frequency modulation stable area.

The invention discloses a submarine low-power power supply system with a unit body structure. The submarine low-power power supply system comprises a plurality of microbial fuel cells and a fuel cell stack, wherein a whole pole plate structure is adopted by cathodes and anodes of the microbial fuel cells; a resistor and an electric wire are solidified in a pole plate; the fuel cell stack is formed by series connection, parallel connection or parallel-series connection of the microbial fuel cells; the anodes arranged at the lower parts of the unit body microbial fuel cells and the cathodes are arranged at the upper parts of the unit body microbial fuel cells; the anodes are arranged in an anaerobic sediment; and the cathodes are arranged in a liquid environment containing dissolved oxygen. The submarine low-power power supply system is good in invisibility, stable in output, fast in power supply response, long in running time, high in reliability and high in maneuverability, meets the special requirements of modern warfare put on an energy device, and has a wide application prospect in the field of military and a marine geological environment.

The invention relates to the technical field of wireless energy transmission, and discloses a double-pickup-coil wireless energy transmission device based on a full-bridge voltage-multiplying rectifier. The device comprises a transmitting part and a receiving part, wherein the transmitting part includes inverters Q1, Q2, Q3 and Q4, a transmitting coil Lp, a compensation capacitor Cp for compensating self-inductance of the transmitting coil, LCC resonance networks Lp, Cp, Lr and Cr of a primary side and system input DC voltage; the receiving part includes rectifiers D1, D2, D3 and D4, receivingend pickup coils S1 and S2, compensation capacitors Cs1 and Cs2 required for compensating inductance of the two pickup coils on the secondary side, voltage-multiplying rectifying capacitors C1 and C2, a voltage stabilizing capacitor and a load resistor on the direct-current output side of a rectifier, and mutual inductors Ms1 and Ms2 arranged between the transmitting coil and the pickup coils. According to the double-pickup-coil wireless energy transmission device based on the full-bridge voltage-multiplying rectifier, output fluctuation of the transmitting coil and the receiving coil under the offset condition can be reduced, cross coupling between the coils cannot be generated, and the current stress of the receiving coil is reduced.

The invention discloses a renewable energy cluster output distributed coordination control method considering uncertainty, and belongs to the field of power system optimization control. In order to cope with the adverse effect of wind and light energy uncertainty on regulation and control precision, aiming at the problem that the uncertainty of a traditional cluster output optimization model cannot be fully considered, an optimization model and strategy considering output uncertainty are constructed based on TSL distribution; meanwhile, in the aspects of information architecture and implementation mode on which coordination control depends, aiming at the defects of high calculation complexity, long data acquisition period, high communication pressure and the like existing in a traditional centralized mode, the invention provides a method for better adapting to the characteristics of frequent data interaction, high communication timeliness requirement and the like of a proposed optimization model considering uncertainty, distributed calculation solution is realized based on a multi-agent system theory, so that the calculation scale and the communication pressure are reduced, and fault separation and risk dispersion are realized. On the whole, the renewable energy cluster control precision, robustness and flexibility can be improved.

This invention provides a DC voltage-drop converter including: a first up arm switch circuit having an input end connected to a first supply input end and a control end connected to a first control signal source and the output end, a second up arm switch circuit having an input end connected to a second supply input end and a control end connected to a second control signal source and an output end connected to the first up arm switch output end, a down switch circuit having a first end connected to the output of the first up arm switch circuit and a second end connected to a reference supply and a filter circuit having an input end connected to the output of the first switch and an output end connected to the output of the supply, in which, the first up arm switch circuit and the second will not be conducted at the same time.

A power system includes a power generation system; an energy storage system which is provided with a super capacitor bank and a lithium battery device based on echelon utilization; a load system which is provided with a direct current quick charge interface; and an energy management system, wherein the energy storage system and the load system are respectively connected with the power generation system through a direct-current power transmission bus; the lithium battery device is connected to the direct-current power transmission bus through a first bidirectional direct-current chopper, and the super capacitor bank is connected to the direct-current power transmission bus through a second bidirectional direct-current chopper; the direct-current fast charging interface is connected to the direct-current power transmission bus through a load-side direct-current chopper; and the direct-current power transmission bus is connected to a main power grid through a power grid interaction device. According to the invention, by utilizing the renewable power generation resources and matching with the energy storage system composed of a decommissioned battery and a super capacitor, the power of a suburban charging station can be improved on the premise that the capacity of the existing power grid does not need to be expanded, and the popularization of new energy fast charging devices is promoted.

The invention discloses a hydraulic wave power generation system based on a volume adjusting principle. The hydraulic wave power generation system is characterized by comprising an energy capturing end, an energy storing end and an output end, the energy capturing end, the energy storing end and the output end are sequentially connected through medium pipelines, the energy capturing end converts wave energy into hydraulic energy and transmits the hydraulic energy to the energy storing end. The energy storing end converts the hydraulic energy with low frequency and high fluctuation into hydraulic energy with high and smooth frequency and then transmits the hydraulic energy with high and smooth frequency to the output end. The output end converts the stabilized hydraulic energy into high-quality electric energy. The multiplex control over hydraulic cylinder acting force, system working pressure and power generator rotating speed is realized in a volume adjusting manner, as a result, compared with a traditional throttling adjusting manner, throttling loss is avoided, conversion efficiency of the power generation system is improved, meanwhile power consumption and frequent pressure fluctuation caused by oil pressure fluctuation initiated by discrete and switching of a hydraulic valve are avoided, and the service life and reliability of all components in the system are increased.

An optical pick-up device comprising: at least two light sources for emitting laser beams of different wavelengths; a beam splitter for reflecting or transmitting the light beams from the light sources; the beam splitter including a wavelength selecting film which reflects substantially all of the light beam from one of the light sources and transmits substantially all of the light beam from the other light source, a collimator lens for collimating the light beams reflected or transmitted by the beam splitter; a rising mirror for reflecting the light beams collimated at the collimator lens for rising; an objective lens for transmitting the laser beams reflected at the rising mirror, at least two reflecting mirrors for reflecting, in advance, the light beam unnecessary for rising before entering the beam splitter, when the light beam is reflected at the rising mirror after being emitted from each light source and passing through the beam splitter and the collimator lens; and a front monitor PD for receiving the light beams and monitoring the quantity of light of the light beams reflected at the reflecting mirrors.

Disclosed is a concentrated solar energy wind power generation method. Heat generated by concentrated solar energy is used for heating air below a cylindrical high tower, hot air rises along an inner cavity of the high tower to generate convection, and wind generated through air convection drives a wind driven generator located on a top end opening of the high tower; a heat collection plate is adopted in solar energy concentration, and the heat collection plate is a conical cylinder with openings in the upper portion and the lower portion; an opening in the top is matched with an opening in the lower end of the high tower; the heat collection plate is composed of inner layer glass and outer layer glass, and the position between the inner layer glass and the outer layer glass is vacuum; the outer surface of the inner layer glass is coated with a spectral selective absorbing coating to absorb solar radiation energy; through sun irradiation, photons impact the coating, and the solar energy is converted into heat energy; the gathered solar energy heats air at the bottom of the high tower, the density of the hot air is small, the hot air is light and rises, cold air on the upper layer inside the cylindrical high tower is large in density, the cold air is heavy and sinks, vertical convection of the air is formed, the wind speed inside the higher tower is gradually increased, and the hotter the air is, the stronger the vertical hot convection is, and the larger the wind speed is; and the stable wind speed is formed, and the wind driven generator on the top is driven.

A low-offset bandgap circuit and a corrector are disclosed. The low-offset bandgap circuit comprises a core bandgap circuit and an offset elimination circuit. The low-offset bandgap circuit provides a reference potential at an output node. The core bandgap circuit comprises a core computation amplifier to generate a core current. The offset elimination circuit is coupled to two input ends of the core computation amplifier. The offset elimination circuit generates a compensation current according to the potential of the input ends of the core computation amplifier, in order to compensate an offset potential of the core computation amplifier. The reference potential is generated according to the core current and the compensation current. With the low-offset bandgap circuit and the corrector, output fluctuation caused by offset of the computation amplifier can be reduced, and stability of the output potential of the core bandgap circuit can be improved effectively.

The invention discloses a three-domain control system of an SAR satellite power supply Buck converter. The three-domain control system comprises a control domain I unit (linear domain), a control domain II unit (nonlinear multi-threshold hysteresis domain) and a control domain III unit (nonlinear slamming domain). The three control domains are selected according to the output voltage value. The control domain I unit adjusts the output voltage when the output voltage is near the steady-state value. And when the output voltage exceeds the steady-state amplitude limit, a control domain II unit adjusts the output voltage. And when the output voltage reaches the maximum allowable range, a control domain III unit adjusts the output voltage. The three-domain control combines the advantages of linear control and nonlinear control. According to the method, the optimization of steady-state precision and dynamic response of the Buck converter in the SAR satellite is achieved through the cooperation of the three control domains, high control precision is achieved in the steady state, and rapid dynamic response is achieved when the load dynamically changes in a large range.