CN117526422A - Design and control method and system of wind-storage combined black start power supply - Google Patents
Design and control method and system of wind-storage combined black start power supply Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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Abstract
The invention belongs to the technical field of stable control of a black start power supply, and provides a design and stable control method and a system of a wind-storage combined black start power supply. And the distributed cooperative control based on the capacity consistency principle is adopted to control each black start power supply to generate a control instruction matched with the loadable capacity of the black start power supply, so that the load borne by each black start power supply is matched with the capacity of the black start power supply, and the black start power supply is favorable for executing the black start task.
Description
Technical Field
The invention belongs to the technical field of stable control of a black start power supply, and relates to a design and control method and system of a wind-storage combined black start power supply.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
In recent years, the permeability of new energy and power electronic devices in a power grid is continuously improved, so that the inertia and frequency modulation capacity of the power grid are reduced, and in addition, the influence of more extreme weather is added, so that a power system is at greater risk of blackout. Black start is the first step to restore power after a blackout, and more reliable black start power is required to restore power as soon as possible. However, in some areas lacking conventional black start power sources such as pumped storage power stations, it is necessary to consider the possibility of generating new energy sources such as wind power into the black start power sources.
In general, a black start power supply needs to provide stable power for a started unit, and establish stable voltage and frequency when a power grid fails greatly. However, due to the fluctuation of the wind power generation, the traditional permanent magnet direct-driven wind power generator cannot provide stable power to support black start, so that energy storage equipment is needed to be additionally arranged for the wind power generator, a coordination control method of a wind power generator set and energy storage is needed to be constructed, a control system of the wind power generator set is adjusted to capture wind power and output power to track the change of black start load, a wind storage combined system is proposed to be used as a black start power supply in literature, but the combination of an independent wind power system and an independent energy storage system is usually difficult to consider the difference of different energy response speeds and persistence, and coordination control of the wind power generator system during black start cannot be realized.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a design and control method and a system of a wind-storage combined black start power supply, which are beneficial to solving the problem that a new energy generator set is difficult to meet the requirements of fast networking and long-process stable operation at the same time, so that the new energy generator set is difficult to act as a black start power supply task after a power system blackout.
Firstly, the invention provides a design method of a novel black start power supply, and the wind-storage combined power supply obtained by the design method can coordinate four energy sources simultaneously, and the energy supply sources can be divided into four types: the method comprises the following steps of rotating reserve based on mechanical kinetic energy release of the permanent magnet synchronous wind turbine, reserved reserve based on overspeed pitch reduction and load shedding of the permanent magnet synchronous wind turbine, battery energy storage reserve based on electrochemical energy conversion and supercapacitor energy storage reserve based on capacitor charge and discharge. In order to fully coordinate the four energies, the invention connects the side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine generator to a common direct current bus, and then connects the direct current bus to a power grid through a grid side converter. The control system design for coordinating the four energy scheduling of the power supply is provided by considering the control requirements of the power supply under the working conditions of black start, grid connection, parallel operation with other types of power supplies and the like, so that the dominant role of the power supply in the black start scheduling process of the power supply is further played.
In order to achieve the above object, in a first aspect, the present invention provides a design method of a wind-storage combined black start power supply, including the following steps:
the machine side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine are connected to a common direct current bus, and then connected to a power grid through a grid side converter;
the battery energy storage is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine through a bidirectional DC/DC converter;
the super capacitor is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine through a bidirectional DC/DC converter;
the novel power supply is formed by the permanent magnet synchronous fan group, the battery energy storage and the super capacitor.
In a second aspect, the present invention provides a wind-powered, combined black-start power source constructed as in the method of the first aspect.
The utility model provides a wind stores up and unites black start power, includes synchronous fan group of permanent magnetism, battery energy storage and supercapacitor, wherein:
the machine side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine are connected to a common direct current bus, and then are connected to a power grid through a grid side converter;
the battery energy storage is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter;
The super capacitor is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter.
In a third aspect, the present invention provides a black start power supply stability control method based on the above structure. The permanent magnet synchronous wind turbine generator system is additionally provided with a black start control mode besides a traditional maximum power tracking (MPPT) mode. In this mode, the permanent magnet direct drive synchronous fan is allowed to run at an overspeed state to release additional rotor mechanical kinetic energy when needed. Meanwhile, the fan is controlled by variable pitch, and the permanent magnet direct-driven wind turbine generator is operated on a relationship curve of the tip speed ratio and the wind energy utilization coefficient of the load shedding in advance. The method aims at utilizing a certain rotor kinetic energy reserve and a load shedding reserve of the wind turbine generator when the system frequency is reduced due to load in the black start process, so that the power output of the wind turbine generator can be effectively increased.
A black start power supply stable control method comprises the following steps:
tip speed ratio adjustment: when the black start mode is started, the fan is set to run on a certain tip speed ratio through pitch control, so that the fan can run in a state lower than the maximum power under the condition that the wind speed is enough;
Presetting the rotor speed: presetting the rotor speed to be higher than the speed of the rotor in the maximum power tracking state so as to store certain mechanical energy;
frequency detection and response: when the system frequency is detected to be reduced, triggering the permanent magnet direct-drive synchronous fan to enter an emergency power output mode, and in the emergency power output mode, adjusting a control instruction of the permanent magnet direct-drive synchronous fan side converter to increase power output by utilizing pre-stored mechanical energy and current wind speed;
in an emergency power output mode, changing an active power reference value of a wind turbine generator side converter into a PI link self-adaptive decision based on a virtual frequency difference, and temporarily lifting a power set point of the wind turbine side converter along with the increase of the frequency difference caused by load sudden increase in black start so as to obtain power from a wind wheel more;
and controlling battery energy storage and supercapacitor equipment additionally arranged on the DC bus side of the converter based on the variation of the DC bus voltage, wherein the battery energy storage and the supercapacitor equipment adopt a constant DC voltage control mode to balance the output of the black start power supply and track unbalanced power when the black start load is tracked. The low-pass filtering link has the advantages that the battery energy storage response is slower than that of the super capacitor, the frequency is regulated without difference, the long-process energy compensation can be realized, and the secondary frequency modulation effect is realized. The super capacitor is regulated by frequency difference, can perform quick energy compensation, and plays roles of inertia response and primary frequency modulation.
The grid-type virtual synchronous machine is adopted to control a grid-side converter, and the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor is simulated into inertia, damping and frequency response characteristics of a synchronous generator.
As an alternative implementation manner, the specific process of using the virtual synchronous machine control network side converter to simulate the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor into inertia, damping and frequency response characteristics of a synchronous generator comprises the following steps: so that, seen from the power grid side to the grid side converter, it is as if it were a virtual inertiaJVirtual dampingVirtual frequency difference->-/>A characteristic virtual synchronous machine power supply, the comprehensive dynamic characteristic of which can be expressed by an equation:
wherein (1)>、/>、/>The virtual inertia is equivalent to the effects of the permanent magnet synchronous fan, the super capacitor and the battery pack respectively; />、/>、/>The functions of the permanent magnet synchronous fan, the super capacitor and the battery pack are equivalent for virtual damping; />Is a virtual angular frequency; />Is a rated angular frequency value;sis a Laplacian operator;P e to output electromagnetic power; order theI.e. +.>The active power reference value of the virtual synchronous machine is different from the active power reference value of the traditional virtual synchronous machine in that the active power reference value is formed by PI links based on virtual frequency difference, wherein +. >、/>Constant coefficients of a P (proportion) link and an I (integral) link respectively;
the active power reference value of the virtual synchronous machine control link of the grid-side converter is adaptively determined by the proportional integral link based on the virtual frequency difference, so that the running point of the wind turbine generator can be adaptively changed when the external load of the black start power supply suddenly changes, and the release and gradient utilization of wind energy, battery energy storage and super capacitors in black start can be better coordinated and controlled, and the energy use efficiency is optimized.
Alternatively, the specific process of tip speed ratio adjustment and rotor speed presetting includes:
obtaining a corresponding relation between the rotor speed and the capture power of the wind turbine generator set when the wind speed fluctuates based on the relation between the wind energy utilization coefficient and the tip speed ratio so as to guide the change of the capture power operating point of the wind turbine generator set when the wind power is started in black;
the mechanical power captured by the wind turbine generator set is expressed as:
wherein,the air density is indicated as such,ris the blade radius>Indicating wind speed, & lt & gt>Is the angular velocity of the rotor of the permanent magnet fan,representing wind energy utilization coefficient, which is related to tip speed ratio and pitch angle>Curve of (I)/(II)>For tip speed ratio->Is the pitch angle;
when the pitch angle is fixed, The curve approximates a sine curve; taking a certain point on the right side of the highest point on each approximate sine curve as an operating point, obtaining a wind energy utilization coefficient-tip speed ratio curve function through curve fitting, and recording as；
And the corresponding relation between the rotor rotating speed and the captured power of the wind turbine can be obtained by combining the real-time wind speed, so that the corresponding relation is used as a reference curve of the change of the captured power operating point of the wind turbine along with the wind speed and the rotating speed during black start.
As an alternative embodiment, the specific process of pitch control includes:
taking the input power of the virtual synchronous machine as a reference value of the capture power of the wind turbine, and obtaining a reference value of the rotating speed of the rotor of the wind turbine by a reference curve;
generating a pitch angle reference value by the rotating speed reference value through a PI link, and controlling the pitch angle through a servo system;
the change in pitch angle and rotational speed causes a change in captured power, which causes a change in rotational speed such that both rotor rotational speed and captured power reach the reference value.
As an alternative embodiment, the specific process of controlling the battery energy storage and super capacitor device additionally arranged on the direct current bus side of the converter based on the variation of the direct current bus voltage comprises the following steps: the method comprises the steps that a battery energy storage and a supercapacitor are connected to a direct current bus of a grid-connected converter of the wind turbine generator through a bidirectional DC/DC booster circuit, when direct current voltage fluctuation is caused by unbalanced wind power output and black start load, the battery energy storage and the supercapacitor change the output to enable the direct current voltage to be maintained at rated values, and unbalanced power is balanced when the wind power output tracks the black start load;
The battery energy storage and the super capacitor adopt a double-loop control mode of a voltage outer loop and a current inner loop;
the voltage outer loop control of the battery energy storage and the super capacitor adopts a Proportional Integral (PI) control mode of constant direct current voltage so as to eliminate the voltage deviation of the direct current bus:
wherein,the duty cycle of a boost circuit for the battery energy storage voltage or the supercapacitor; />For battery energy storage voltage or supercapacitor voltage, +.>、/>The actual voltage and the reference voltage on the direct current bus are respectively; />、/>The coefficients of the proportional link and the integral link of the control system are respectively;sis a laplace operator.
The battery energy storage and the current inner loop control of the super capacitor are different in their signal input links. The battery energy storage control link is to connect a low-pass filter in series with the output signal of the voltage outer ring as the signal input link of the current inner ring. The effect is that the low-pass filter generates a low-frequency time-varying current reference value to store energy for the battery, so that the battery energy storage will only compensate for long-term and steady-state unbalanced power. The supercapacitor takes the output signal of the low-pass filter link as the input link of the current inner loop signal subtracted from the output signal of the voltage outer loop. The effect is that the supercapacitor will be faced with a high frequency time-varying current reference, whereas its steady state current reference is 0, so that the supercapacitor will only compensate for the rapidly time-varying unbalanced power.
In a fourth aspect, the present invention provides a black start power stabilization control system, comprising:
the blade tip speed ratio adjusting unit is used for setting the fan to run on a certain blade tip speed ratio through pitch control when the black start mode is started, so that the fan can run in a state lower than the maximum power under the condition that the wind speed is enough;
a rotor speed presetting unit for presetting the rotor speed to be higher than the speed in the maximum power tracking state so as to store a certain mechanical energy;
the frequency detection and response unit is used for triggering the permanent magnet direct-drive synchronous fan to enter an emergency power output mode when the system frequency is detected to be reduced, and in the emergency power output mode, the side converter of the permanent magnet direct-drive synchronous fan adjusts a control instruction of the side converter so as to increase power output by utilizing pre-stored mechanical energy and current wind speed;
the wind turbine generator side converter control unit is used for changing an active power reference value of the wind turbine generator side converter into a PI link self-adaptive decision based on virtual frequency difference in an emergency power output mode, and the power set point of the wind turbine side converter is temporarily lifted along with the increase of the frequency difference caused by sudden load increase in black start so as to obtain power from a wind wheel more;
The energy storage and supercapacitor control unit is used for controlling battery energy storage and supercapacitor equipment additionally arranged on the DC bus side of the converter based on the variation of the DC bus voltage, and the battery energy storage and supercapacitor equipment and the supercapacitor equipment adopt a constant DC voltage control mode to balance the output of the black start power supply and track unbalanced power when the black start load is tracked;
the wind turbine generator grid side converter control unit is used for controlling the grid side converter by adopting a grid-structured virtual synchronous machine and simulating the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor into inertia, damping and frequency response characteristics of a synchronous generator.
In a fifth aspect, the present invention provides a method for stably controlling a long process of a black start power supply, which specifically includes the following steps:
judging whether a black start condition is met, if so, distributing a start task according to the state and capacity consistency principles of the wind turbine generator and the energy storage equipment;
performing starting control by using the black start power supply stable control method;
adopting distributed cooperative control of each black start power supply based on a capacity consistency principle;
and after the power system reaches a stable running state, synchronizing the black start power supplies, and smoothly connecting with an external power grid.
As an alternative embodiment, after judging whether the black start condition is satisfied, the recovery requirement of the power system when the external power source is lost is analyzed to ensure the value of the total load requirement to determine the optimal combination and number of the inverter type power sources constituting the black start power source.
In the starting control process, the wind turbine generator set which is subjected to network construction type modification by adopting the improved virtual synchronous machine control method is started in sequence according to a preset sequence, and a load is started and then connected to a power grid.
As an alternative embodiment, the specific process of performing the start-up control includes the steps of:
the wind wheel of the wind turbine generator drives the permanent magnet direct-driven fan to establish a side alternating voltage, an active power reference value is initially set, the rotor accelerates to the reference value, a side converter trigger pulse is unlocked, and the energy storage stable direct-current voltage is in a rated value;
after the machine side converter stably operates, unlocking a trigger pulse of the network side converter, and establishing network side alternating voltage, wherein an active power reference value is adaptively determined by a PI link based on virtual frequency difference;
closing a network side breaker, and accessing a transformer and a power transmission line;
closing a breaker of an auxiliary machine of the started power plant, starting accelerating an auxiliary machine rotor, absorbing active power and reactive power from a power grid, automatically adjusting an active reference value by utilizing the steps of the black start power supply stable control method, and controlling the capture power and the output power of a wind turbine generator to automatically track the change of a black start load;
The auxiliary machine is accelerated to the rated slip, the starting is completed, the power returns to the rated value, the thermal generator is started, and the black starting is completed.
As an alternative embodiment, when the black-start power supply is controlled stably, the output voltage or/and the output power of the black-start power supply is adjusted by adjusting the operating point voltage or/and the frequency of the black-start power supply according to the requirements of the load and the power grid frequency.
Further, the black-start power supply increases its output power when the load demand increases, and decreases its output power when the grid frequency increases.
As an alternative implementation mode, the specific process of adopting the distributed cooperative control of each black start power supply comprises the steps of obtaining the state and parameter information of each black start power supply, generating a control instruction matched with the loadable capacity of each black start power supply according to a capacity consistency principle, so that the load born by each black start power supply is matched with the capacity and the running state of the power supply of each black start power supply, and the added load task can be fairly and reasonably distributed among the black start power supplies according to the available capacity as weight, thereby being beneficial to the execution of the black start task.
In a sixth aspect, the present invention provides a black start power long process stability control system, comprising:
The judging unit is used for judging whether the black starting condition is met or not, and if so, the starting task is distributed according to the state and capacity consistency principles of the wind turbine generator and the energy storage equipment;
the black start power supply stable control system is used for performing black start control;
the distributed cooperative control unit is used for adopting the distributed cooperative control of each black start power supply based on the capacity consistency principle;
and the grid-connected unit is used for synchronizing the black start power supplies after the power system reaches a stable running state, and carrying out smooth grid connection with an external power grid.
As an optional implementation manner, the distributed cooperative control unit is configured to coordinate a coordination action between each black-start power supply, collect, through a communication network, status information of each black-start power supply in real time, and generate a corresponding control instruction based on a capacity consistency principle according to a load demand in black start.
Compared with the prior art, the invention has the beneficial effects that:
the invention connects the machine side converter, battery energy storage and super capacitor of the permanent magnet synchronous wind turbine generator to a common direct current bus, and then connects the machine side converter, battery energy storage and super capacitor to a power grid in a virtual synchronous machine control mode through the grid side converter. The designed novel power supply structure coordinates the dispatching of four types of energy, namely the rotor kinetic energy of the permanent magnet synchronous wind turbine, the load shedding standby of the permanent magnet synchronous wind turbine, the battery energy storage and the super capacitor, automatically tracks the frequency change of the system in the black start process in a virtual synchronous machine mode, adjusts the total output power to track the black start load, and finally enables the system frequency to return to the rated value again. The problem that the power output is difficult to be continuously stabilized under the impact of high amplitude and long-time load of the black start of the traditional new energy generator set is avoided.
Aiming at the problem that the traditional new energy generator set cannot bear the complex task of the black start long process, the invention carries out network construction transformation on the side converter of the wind turbine set based on the improved virtual synchronous machine technology; controlling the capture power and the output power of the wind turbine generator based on the corresponding relation between the rotor speed and the capture power of the wind turbine generator when the wind speed fluctuates, and tracking the power reference value of the virtual synchronous machine, namely tracking the change of the black start load; and an energy storage and supercapacitor device controlled by a constant direct current voltage is additionally arranged on the direct current bus side of the converter so as to balance wind power output and track unbalanced power when a black start load. The method solves the problem that the new energy generator set is difficult to simultaneously meet the capability requirements on the aspects of networking, frequency modulation, long-process stable operation and the like required by a black start power supply.
The invention reforms the permanent magnet direct-drive wind driven generator adopting the traditional control method, so that the permanent magnet direct-drive wind driven generator has black start capability, and the power output can automatically track the change of the black start load, thereby providing stable power for the started unit. The energy storage and supercapacitor device is used to compensate for unbalanced power, rather than the primary power source, reducing the requirements on its capacity.
The invention can realize the black start of the wind turbine generator, the energy storage and the super capacitor combined power generation system. Before practical application, the proposed black start power supply stability control method should be verified in a simulation environment, and after verification of the starting speed, coordination, stability and other aspects of the proposed scheme, the proposed scheme can be applied to an actual power system to realize quick starting and stable recovery of the power system.
In order to make the above objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a block diagram of a novel black start power supply;
fig. 2 is a schematic diagram of a grid-side converter control system;
FIG. 3 is a modified virtual synchronous machine control system;
FIG. 4 is an aerodynamic model and a rotating shaft transmission model of the permanent magnet direct drive wind driven generator;
FIG. 5 is a pitch angle control model of a wind turbine;
FIG. 6 is a graph of tip speed ratio versus wind energy utilization coefficient for a wind turbine;
FIG. 7 is a control model of a machine side converter in an embodiment of the invention;
FIG. 8 is a black start simulation model in an embodiment of the present invention;
FIG. 9 is a graph of wind speed variation for black start simulation in an embodiment of the present invention;
fig. 10 is a graph showing a change in the rotation speed of the auxiliary machine rotor in the embodiment of the present invention;
FIG. 11 is a graph of grid frequency variation in an embodiment of the present invention;
FIG. 12 is a graph of voltage amplitude variation at grid-tie points according to an embodiment of the present invention;
FIG. 13 is a graph of wind turbine capture power, output power, and active load variation in an embodiment of the invention;
FIG. 14 is a graph showing the change of the energy storage active output in the embodiment of the present invention;
FIG. 15 is a graph showing the change of the stored charge state in an embodiment of the present invention;
fig. 16a and 16b are graphs comparing grid frequencies under control of different virtual synchronous machines according to an embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the drawings and examples.
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Example 1
In recent years, a large number of new energy generator sets are connected in grid. Because the uncertainty of new energy power generation is high, the risk of power failure is increased. Black start is the first step in recovering power after a power outage. The general black start power supply should meet the following requirements: (1) having a self-starting capability; (2) capable of providing sufficient power to the activated unit; (3) keep the voltage and frequency stable during black start. Pumped storage is a traditional black start power supply. However, due to limitations of the installation location of the conventional black-start power supply, the conventional black-start power supply may be insufficient in some power grids where the generation ratio of new energy is high. Meanwhile, the new energy power generation has the characteristics of low starting power and high starting speed, and the recovery capability of the power grid after power failure can be improved. Therefore, it is necessary to consider making the new energy source a new black start power source.
However, the new energy generation unit has no automatic starting capability, and it is difficult to provide stable power to the started unit due to uncertainty and fluctuation of its output. In this regard, many researchers have suggested configuring energy storage for them to start new energy gensets and provide sufficient power. However, too relying on energy storage may result in too high energy storage cost, and coordination control of the new energy unit and the energy storage needs to be considered, so that the output of the new energy unit can track the change of the black start load.
The permanent magnet synchronous wind turbine generator is used as a new type black start power supply reconstruction object, and as a new type black start power supply, the permanent magnet synchronous wind turbine generator should have networking capability independent of independent operation of an external power grid, and a converter control system of the permanent magnet synchronous wind turbine generator needs to be reconstructed, so that the permanent magnet synchronous wind turbine generator can autonomously establish frequency-stable alternating voltage and has frequency modulation capability. The virtual synchronous machine is a net-structured control method, but when the virtual synchronous machine is independently net-structured, the degree of deviation of the power grid frequency from the rated value is greatly influenced by the accuracy of the active power reference value. A larger deviation of the active reference value from the actual active will result in a larger deviation of the grid frequency. Meanwhile, due to uncertainty of fluctuation of wind speed and load and time delay of the control center for adjusting the active reference value of the virtual synchronous machine, the traditional method for issuing the active power reference value by the control center inevitably leads to failure in returning frequency to the rated value and lower frequency minimum point in the black start process.
In one or more embodiments, a design method of a wind-storage combined black start power supply is disclosed, which comprises the following steps:
the permanent magnet synchronous fan, the battery energy storage and the super capacitor together form a novel power supply;
The machine side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine are connected to a common direct current bus, and then are connected to a power grid through a grid side converter;
the battery energy storage is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter;
the super capacitor is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter.
Based on this, in one or more embodiments, a black start power stabilization control method based on an improved virtual synchro-machine technique is disclosed. The black start power supply is the power supply obtained by the method, namely a novel black start power supply structure consisting of a permanent magnet direct drive wind generating set, an energy storage capacitor and a super capacitor, and is shown in figure 1.
The embodiment also provides a black start power supply stability control method based on the structure. The permanent magnet synchronous wind turbine generator system is additionally provided with a black start control mode besides a traditional maximum power tracking (MPPT) mode. In this mode, the permanent magnet direct drive synchronous fan is allowed to run at an overspeed state to release additional rotor mechanical kinetic energy when needed. Meanwhile, the fan is controlled by variable pitch, and the permanent magnet direct-driven wind turbine generator is operated on a relationship curve of the tip speed ratio and the wind energy utilization coefficient of the load shedding in advance. The method aims at utilizing a certain rotor kinetic energy reserve and a load shedding reserve of the wind turbine generator when the system frequency is reduced due to load in the black start process, so that the power output of the wind turbine generator can be effectively increased.
Mainly comprises the following steps:
tip speed ratio adjustment: when the black start mode is started, the fan is set to operate at a relatively low tip speed ratio through pitch control, so that the fan can operate in a state lower than the maximum power under the condition that the wind speed is sufficient.
Presetting the rotor speed: the rotor speed is preset to a speed slightly higher than that in the maximum power tracking state, so that some mechanical energy is stored.
Frequency detection and response: a frequency detection module is introduced. When the system frequency drop is detected, the module triggers the permanent magnet direct drive synchronous fan to enter an emergency power output mode.
Emergency power output mode: in this mode, the permanent magnet direct drive synchronous blower side converter adjusts its control command to increase power output using pre-stored mechanical energy and current wind speed.
The machine side converter controller of the permanent magnet synchronous wind turbine generator comprises: in the emergency power output mode, the active power reference value of the converter on the wind turbine generator side is adaptively determined by a PI link based on virtual frequency difference. As the frequency difference caused by the load dump increases in a black start, the power set point of the machine side converter will be temporarily raised in order to draw more power from the rotor.
The battery energy storage and supercapacitor control unit controls the battery energy storage and supercapacitor equipment additionally arranged on the DC bus side of the converter, the change amount of the DC bus voltage is fed back to the battery energy storage unit through a low-pass filtering link, the change amount of the DC bus voltage is directly fed back to the supercapacitor control unit, and the battery energy storage and supercapacitor control unit and the supercapacitor control unit adopt a constant DC voltage control mode to balance unbalanced power when the novel black start power supply outputs to track the black start load. The super capacitor is regulated by frequency difference, can perform quick energy compensation, and plays roles of inertia response and primary frequency modulation.
The grid-side converter control unit adopts a grid-structured virtual synchronous machine to control, and the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor is simulated into inertia, damping and frequency response characteristics of a synchronous generator through the control.
As a specific example, the present example builds its model on Matlab/Simulink. The control method disclosed by the embodiment relates to the control of a grid-side converter, a machine-side converter, a fan pitch angle control, a battery energy storage and a supercapacitor boost circuit of a permanent magnet synchronous wind turbine generator, and the specific control of each part is as follows:
1. Network-side converter control unit: the control of the network-structured virtual synchronous machine is adopted, and the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor is simulated into inertia, damping and frequency response characteristics of a synchronous generator through the control.
The network side converter is subjected to network construction transformation based on the improved virtual synchronous machine technology, and the overall control structure of the network side converter is shown in figure 2.
The virtual synchronous machine outputs the frequency of the grid-connected point voltage, the phase of the three-phase voltage is obtained through an integration link, and modeling of the part is shown in figure 3. The mechanical equations of motion simulated by a conventional virtual synchronous machine can be expressed as:
（1）
unlike conventional virtual synchronous machines, the mechanical equations of motion simulated by the modified virtual synchronous machine are expressed as:
（2）
wherein,is virtual inertia; />Is virtual damping; />Is a virtual angular frequency; />For angular frequency rating, 1 at per unit value;sis a Laplacian operator;P e to output electromagnetic power; the present embodiment uses a PI link based on virtual frequency differencesAn active power reference value instead of the conventional virtual synchronous machine, wherein +.>、/>Constant coefficients of the P (proportion) link and the I (integral) link, respectively.
During actual black start, the load side auxiliary machine starts to cause load power Rapidly rising, and due to communication problems, the reference value of the wind turbine capturing power is +.>Unresponsive to load power +.>But rather remains unchanged, which results in a drop in frequency. Virtual damping can naturally allow the frequency to settle but not return to nominal. For the improved virtual synchronous machine, on the one hand +.>The value of (2) will automatically increase, acting to reduce the rate of frequency decrease, on the other hand, the conversion of equation (2) into a pull-type function will result:
（3）
applying the final value theorem:
（4）
the final frequency is returned to the nominal value. The precondition that the formula (4) is establishedThe pole of (2) is located in the left half plane of the graph.
The frequency output by the improved virtual synchronous machine is integrated to obtain the phase of the three-phase voltage, and the phase is combined with the reference value of the amplitude of the grid-connected point voltage obtained by reactive droop to obtain the reference value of the three-phase voltage of the grid-connected point, and the reference value is modulated by the traditional voltage current inner ring and the traditional voltage current outer ring and the traditional PWM to output the trigger signal of the machine side converter.
2. Pitch angle control of the wind turbine generator: in the embodiment, an aerodynamic model, a rotating shaft transmission model and a pitch angle control model of the permanent magnet direct-drive fan are established on Matlab/Simulink. The invention is innovative in that the value of a rotor rotating speed reference value in a pitch angle control model is improved, the tracking of the fan capturing power to the black start load is realized, and the method concretely comprises the following steps:
Air flows through the surface of the fan blade, generates a thrust parallel to the rotation plane of the blade, and applies work to the blade to rotate the blade. The thrust force is related to air density, impeller radius, pitch angle, impeller rotational speed and wind speed. The mechanical power captured by the wind turbine generator set is as follows:
（5）
（6）
wherein,representing air density; />Representing wind speed; />Is the radius of the impeller; />The impeller rotating speed is similar to the rotor rotating speed for a direct-drive fan; />Is the tip speed ratio; />Is the pitch angle. />Representing the wind energy utilization coefficient, related to the pitch angle and the tip speed ratio, when the pitch angle is fixed,/->The curve approximates a sine curve.
The impeller of the direct-drive fan is connected with the generator only through the rotating shaft. Taking deformation of the rotating shaft into consideration, establishing a double-mass equivalent model of the rotating shaft transmission system:
（7）
（8）
（9）
wherein,、/>the inertia of the impeller and the inertia of the rotor are adopted; />、/>、/>The wind power torque, the mechanical torque at two ends of the rotating shaft and the output torque of the wind turbine generator set are adopted; />Is the rigidity of the shaft; />Is the damping coefficient. The aerodynamic model and the rotating shaft transmission model of the permanent magnet direct-drive wind driven generator built by the method are shown in figure 4.
According to the model, among factors related to the capture power of the wind turbine, the air density, the impeller radius and the wind speed are uncontrollable, the rotating speed is determined by wind torque, mechanical torque and output torque of the wind turbine, and the pitch angle is the most convenient method for controlling the capture power of the wind turbine.
The pitch angle control model of the wind turbine generator is shown in fig. 5. In the embodiment, a rotor rotation speed reference value generates a pitch angle reference value through a PI link, and the pitch angle is controlled through a servo system:
（10）
the reference value of the rotor rotational speed of the present embodiment is generated by the formula (11):
（11）
wherein,the virtual synchronous machine from the network side converter is an amount capable of tracking the black start load change, and is equal to the load in a steady state. />Is a manually set wind energy utilization coefficient-tip speed ratio relation curve, which is derived from the relation among tip speed ratio, pitch angle and wind energy utilization coefficient. Taking the pitch angle as each fixed value that increases from 0 degrees to 50 degrees in 2 degrees steps, the relationship between the tip speed ratio and the wind energy utilization coefficient is shown in fig. 6, and approximates a sinusoidal curve. And taking a certain point on the right side of the highest point on each curve as an operation point, so that the wind turbine generator is in an overspeed operation state. The operating points are subjected to curve fitting to obtain a wind energy utilization coefficient-tip speed ratio curve function, namely +.>. In FIG. 6 and->The intersecting curve isA curve.
In this embodiment, the cftool kit of Matlab is used to perform curve fitting, and the selected empirical formula is:
（12）
fitting results are:
（13）
In actual black start, the auxiliary engine starts to cause the active load to rise and the frequency to drop,will automatically increase the value of +.>Automatic tracking of the beginning of the increase in load change, as can be seen from FIG. 6 +.>And (3) rising, namely rising a rotor rotating speed reference value and falling a pitch angle. As can be seen from fig. 6, as the pitch angle decreases, the wind energy utilization factor increases, whereupon the mechanical power captured by the wind turbine increases and the rotor speed increases until it coincides with the speed reference, at which point the pitch angle stops decreasing. If the capture power of the wind turbine generator is equal to +.>If the rotor rotation speed is inconsistent, the rotor rotation speed is continuously changed, the pitch angle is also continuously changed, and finally, the rotor rotation speed and the captured power reach reference values. A detailed analysis of this process requires the machine side converter control after integration.
3. Side converter: in the embodiment, a rotor flux linkage directional control model of the machine side converter is established on Matlab/Simulink, as shown in fig. 7. The invention is innovative in that the value of the q-axis current reference value in the control model is improved, the tracking of the output power of the wind turbine generator to the black start load is realized, and the method concretely comprises the following steps:
the positive direction of the rotor flux linkage is taken as the positive direction of the d axis, and the stator voltage equation of the permanent magnet direct-drive wind driven generator is as follows:
（14）
、/>、/>、/>、/>、/>The voltage, current and inductance of the d and q axes of the permanent magnet direct drive wind driven generator are respectively,resistance of permanent magnet direct-drive wind driven generator>Rotor speed->For the magnitude of the induced magnetic flux of the rotor permanent magnets in the stator,pis a differential operator. Thereby, a rotor flux linkage directional control model of the machine side converter is obtained:
（15）
、/>、/>、/>the constant coefficients of the proportional link and the integral link of the directional control of the rotor flux linkage of the d-axis machine side converter and the q-axis machine side converter are respectively adopted. />Taking out zero and taking in->The value of (2) is represented by the active output reference value of the wind turbine generator system +.>The decision is that, assuming the stator resistance is sufficiently small, there are:
（16）
the wind energy utilization coefficient-tip speed ratio functionThe back-push is the tip speed ratio-wind energy utilization coefficient function, which is recorded as +.>，/>Can be expressed as:
（17）
when the rotational speed of the rotor is varied,corresponding changes result in a change of the q-axis current reference value, which in turn leads to +.>、Is a variation of (c). And after PWM modulation, a trigger signal of the generator side converter is formed to cause the change of the output power of the wind turbine generator. Due to the PI control, the q-axis current in steady state is equal to its reference value +.>The d-axis current is equal to zero, so that the active output of the wind turbine generator system. The +.11 of the formula (11)>Substituted into formula (17) to obtain->The active output of the wind turbine generator can track the black start load change. It is noted that in the actual black start process, with the auxiliary machine started, the virtual synchronous machine is responded first, and then +. >The rise of (2) causes the pitch angle to decrease and the captured power of the wind turbine to rise before the rotor begins to accelerate, causing +.>Rising. Therefore, the rise of the output power of the wind turbine generator is always delayed from the rise of the capture power, so that the stall problem is avoided, and the stable black start is facilitated. When the rotating speed of the rotor rises to the reference value, the pitch angle stops decreasing, and if the captured power of the wind turbine generator is inconsistent with the output power, the rotor speed continues to rise to exceed the reference value, the pitch angle increases, the captured power decreases, and finally, the captured power and the output power are balanced and are equal to the black start load.
4. Energy storage and supercapacitor control unit: in the embodiment, an energy storage and supercapacitor device controlled by a constant direct current voltage is additionally arranged on the direct current side of a converter so as to balance unbalanced power when wind power output tracks a black start load, and the method specifically comprises the following steps:
the battery energy storage is connected to a direct current bus of the grid-connected converter through a boost circuit, and the direct current voltage and the battery energy storage voltage meet the following relation:
（18）
wherein,for DC bus voltage +.>For battery energy storage voltage->The duty cycle of the boost circuit for battery energy storage is determined by equation (19):
（19）
Wherein,is the reference value of the DC bus voltage, +.>、/>The constant coefficients of the proportional and integral control links of the battery energy storage boost circuit are respectively obtained.
The super capacitor is connected to a direct current bus of the grid-connected converter through a boost circuit, and the direct current voltage and the super capacitor voltage meet the following relation:
（20）
wherein,for DC bus voltage +.>For supercapacitor voltage, ">The duty cycle of the boost circuit for the super capacitor is determined by the formula (21):
（21）
wherein,is the reference value of the DC bus voltage, +.>、/>The constant coefficients of the proportional and integral control links of the boost circuit of the super capacitor are respectively.
When the wind power output is smaller than the black start load, the direct current capacitor discharges, the direct current voltage decreases, the duty ratio of the energy storage capacitor and the super capacitor increases, and the direct current voltage is enabled to rise back to the rated value under the combined action of the energy storage capacitor and the super capacitor so as to balance the unbalanced power when the wind power output tracks the black start load.
The following examples are presented.
Taking a certain power grid in China as an example, a certain 200MW wind power plant as a black start power supply and a certain 300MW thermal power unit as a black start target unit, wherein a water feeding pump is an auxiliary machine with the largest capacity in the thermal power plant, and rated active power is 5.5MW. If the black start power supply can bear the impact of starting the water supply pump, the black start power supply is enough to start all auxiliary machines one by one to finish black start.
A black start simulation model is built on Matlab/Simulink, a wind farm is aggregated into 1 direct-drive fan, and a 5.5MW asynchronous motor is used as a water supply pump to be started. The parameters of a single direct-drive fan with the power of 1.5MW are shown in table 1, and a battery energy storage device with the power of 0.1MWh and a super capacitor with the power of 25F are connected in parallel on the direct-current side of the converter.
Table 11.5MW permanent magnet direct drive blower parameters
Simulation was performed according to the black start scheme described above:
when t=0s, the wind wheel drives the permanent magnet direct drive fan to establish the side alternating voltage, and the pitch angle controls the active reference valueAccelerating a rotor; triggering pulse of the unlocking machine side converter, and storing energy to stabilize the direct-current voltage at a rated value;
when t=2s, unlocking the trigger pulse of the network side converter, and establishing network side alternating voltage, wherein an active reference value is adaptively determined by a PI link based on virtual frequency difference; closing a network side breaker, and accessing a transformer and a power transmission line;
when t=5s, closing a breaker of the auxiliary machine, starting accelerating an auxiliary machine rotor, absorbing a large amount of active power and reactive power from a power grid, and causing power impact on a black start power supply;
the auxiliary machine accelerates to the rated slip, the starting is completed, the power returns to the rated value, the auxiliary machine stably operates, and the simulation is completed.
In the present embodiment, fluctuations are set for wind speed, as shown in fig. 9. FIGS. 10-15 are simulation results, wherein FIG. 10 is the rotational speed of the auxiliary machine rotor; FIG. 11 is a graph of grid frequency variation; FIG. 12 is a grid tie point voltage amplitude; FIG. 13 illustrates wind turbine generator set capture power Output power->Active load +.>The method comprises the steps of carrying out a first treatment on the surface of the FIG. 14 is an active power of the stored energy output; fig. 15 is an stored state of charge.
As can be seen from fig. 10, when t=5s, the auxiliary machine starts, the rotor starts accelerating, 15s reaches the rated value, and the auxiliary machine starts successfully, which indicates that the black start power supply under the control of the control method of the present invention is enough to bear the impact of the auxiliary machine start. In general, during the black start process, the power grid frequency drop caused by load access should not exceed 0.5Hz, and as can be seen from fig. 11, the lowest point of the power grid frequency is greater than 49.5Hz, so as to meet the black start requirement, and after the auxiliary machine is started, the frequency can return to the rated value. As can be seen from fig. 12, the voltage of the grid-connected point instantaneously drops by about 0.2p.u. due to the auxiliary machine starting, and then the voltage amplitude rapidly rises to the vicinity of the rated value, so as to meet the black start requirement. As can be seen from fig. 13, the captured power and the output power of the wind turbine generator can track the change of the black start load. When the auxiliary machine is started and the load is greatly increased, the output of the wind turbine generator is increased along with the increase; after the auxiliary engine is started, the load returns to the rated power of the auxiliary engine, the output of the wind turbine unit is reduced along with the load, and the load is stabilized near the load power. Although it can be seen from fig. 13 that there is a fluctuation in the wind turbine output, this is due to unavoidable fluctuations in wind speed. Unbalanced power caused by wind speed fluctuations and output changes delayed from load changes can be borne by the stored energy. As shown in fig. 14, when the wind power output is smaller than the black start load, the stored energy outputs active power; when the wind power output is larger than the black start load, the energy storage absorbs active power, and the unbalanced power is compensated. As can be seen from fig. 15, since the stored energy is not the main black start power source, only the task of compensating unbalanced power is carried out, so the change of the state of charge of the stored energy is not large during the black start process, which means that fewer stored energy can be configured, and the cost is reduced.
Comparing the control method of the invention with the traditional virtual synchronous machine, the power grid frequency change comparison diagrams under different control methods are shown in fig. 16a and 16 b. Obviously, the traditional virtual synchronous machine adopting the method of issuing the active power reference value by the control center is slower in response to the frequency, so that the lowest frequency point is lowered to 48.9Hz, the black start requirement is not met, the frequency cannot be raised to the rated value, and only differential adjustment can be achieved. It can be stated that the control method of the embodiment has stronger frequency response capability, can meet the requirement of black start, and realizes the long-process stable control of black start.
Example two
In one or more embodiments, a novel black start scheme based on the example one control method is disclosed, comprising the steps of:
(1) the wind wheel drives the permanent magnet direct-driven fan to establish a machine side alternating voltage, an active reference value is equal to zero, the rotor accelerates to the reference value, a machine side converter trigger pulse is unlocked, and the energy storage stable direct-current voltage is in a rated value;
(2) after the machine side converter stably operates, unlocking a trigger pulse of the network side converter, and establishing network side alternating voltage, wherein an active reference value is adaptively determined by a PI link based on virtual frequency difference;
(3) Closing a network side breaker, and accessing a transformer and a power transmission line;
(4) closing a breaker of an auxiliary machine of the started power plant, starting accelerating the rotor of the auxiliary machine, absorbing a large amount of active power and reactive power from a power grid, causing power impact on a black start power supply, and reducing the frequency of the power grid. The improved virtual synchronous machine automatically adjusts the active reference value and improves the output power. Meanwhile, the capturing power and the output power of the wind turbine generator are also used for automatically tracking the change of the black start load under the action of the control system;
(5) the auxiliary machine is accelerated to the rated slip, the starting is completed, the power returns to the rated value, the thermal generator is started, and the black starting is completed.
The specific implementation of the steps has been described in detail in the first embodiment, and will not be described in detail here.
Example III
A long-process stable control method of a black start power supply comprises the control links of self-start control, improved virtual synchronous machine control, power control, voltage control, distributed cooperative control and the like of the power supply.
Firstly, introducing self-starting control, and reasonably arranging the starting sequence of a power supply, a power grid and a load in the recovery process after a major power failure is very important. The new black start power should start before the conventional ac power and should start in a specific order. The starting sequence is to start the grid-structured wind turbine generator based on the improved virtual synchronous machine technology, then start the load and finally connect to the main power grid. Thus, the output voltage and the frequency stability of the wind turbine generator can be ensured.
The improved virtual synchronous machine control method is based on the control strategy of the improved virtual synchronous generator technology, and the characteristics similar to those of a synchronous generator are achieved through virtual inertia, virtual damping and virtual frequency difference technology, so that the frequency stability and the transient stability of a small system consisting of a black start power supply are improved.
In the power control step, the voltage and the frequency of the working point of the inverter are adjusted. The inverter should adjust the output power according to the requirements of the load and the grid frequency. When the load demand increases, the inverter should increase its output power, and when the mains frequency increases, the inverter should decrease its output power.
In the voltage control link, the black start power supply needs to be able to control its output voltage, and this embodiment can be implemented by adjusting the operating point voltage of the inverter, and the output voltage should be adjusted according to the requirement of the black start power supply for grid-connected point voltage control. The inverter should increase its output voltage when the grid-tie point voltage is lower than the reference value, and the inverter should decrease its output voltage when the grid-tie point voltage is higher than the reference value. Voltage control of the inverter may be achieved by adjusting the amplitude of the PWM signal.
And in the distributed cooperative control link, a distributed cooperative control strategy based on a capacity consistency principle can be adopted in the black start control process of various inverter type power supplies. The strategy can realize cooperative control among a plurality of black start power supplies, so as to optimize the start and stability performance of the system. In this embodiment, a distributed cooperative controller is introduced into the system, and is responsible for coordinating the actions between the inverters. The controller can collect the state and the available capacity information of the inverter in real time through a communication network, and generates corresponding control instructions by taking the available capacity as weight according to the system demand. This will help to achieve a coordinated operation between the various black start power supplies, further improving the start-up performance of the system. Of course, in some embodiments, a detecting and judging link is further included, that is, in the case that the system loses the external power supply, the distributed cooperative controller needs to detect the system state and judge whether the black start condition is satisfied.
In addition, the network construction control of the black start power supply comprises a start sequence, power control, voltage control and the like, so that the rapid start and stable recovery of the power system are realized. Under the condition that the black start condition is met, the distributed cooperative controller is required to distribute start tasks according to the capacity consistency principle on the basis of measuring the states of the wind turbine generator and the energy storage equipment of the novel black start power supply. First, an initial power supply is provided to the system using the energy storage device. Then, gradually starting the wind turbine generator to cooperatively operate with the energy storage equipment, and jointly realizing black start of the system.
Similarly, in the black start control process of the inverter-type power supplies, each controller needs to adjust the frequency and voltage of each black start power supply in real time according to the system requirements. The predictive control strategy can be adopted to predict the running state and performance index of the system in real time, so that the control strategy is optimized to improve the starting speed and stability of the system.
Preferably, some embodiments can design a long process coordination control strategy of a plurality of novel black start power supplies based on an optimization algorithm, and the strategy is used for carrying out long process coordination control on the plurality of novel black start power supplies, so that the speed and stability of recovery of the power system are improved.
The optimization targets of the optimization algorithm include: 1. maximizing the total available capacity: the total available capacity of all new black start power supplies is ensured to be maximized. 2. Minimizing response time: the power supply needs to respond to load changes in as short a time as possible.
Constraints of the optimization algorithm include: 1. black start power capacity limit: consider the maximum and minimum power out range for each black start power supply. 2. Network transmission constraints: consider the transmission capacity of the grid. 3. System stability constraints: the system voltage and frequency are within a specified range. 4. Capacity consistency constraint: and according to the proportion consistency principle of available capacity occupying the self capacity, the output of a plurality of power supplies is coordinated.
Novel black start power supply long process coordination control strategy: 1. prediction model: a model is built for predicting system load and power available capacity. 2. Real-time monitoring and adjustment: the available capacity of each power supply is monitored in real time and adjusted according to the prediction model. 3. And (5) distributing the output weight: the output of each power supply is dynamically distributed by calculating the ratio of the available capacity of each black start power supply to the self capacity of each black start power supply, so that the energy constraint of each black start power supply can be met before and after the output of each black start power supply.
The implementation steps are as follows:
1. and (3) data collection: all power and grid related data is collected.
2. Model establishment and verification: the historical data is used to build and validate the predictive model.
3. Optimization calculation and implementation of a long process coordination control strategy: and optimally calculating a multi-black start power supply long process coordination control strategy by adopting a mixed integer linear programming algorithm suitable for rapidly calculating linear constraint and objective function, and implementing the strategy in a control center.
4. Real-time monitoring and optimizing: and the output and system parameters of the black start power supply are adjusted in real time through an SCADA system or other real-time monitoring tools.
Through the long-process coordination control strategy of the black start power supply, a plurality of novel black start power supplies can be effectively coordinated, so that the recovery speed and stability of the power system are improved.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.
Claims (18)
1. The design method of the wind-storage combined black start power supply is characterized by comprising the following steps of:
the machine side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine are connected to a common direct current bus, and then connected to a power grid through a grid side converter;
the battery energy storage is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine through a bidirectional DC/DC converter;
the super capacitor is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine through a bidirectional DC/DC converter;
the novel power supply is formed by the permanent magnet synchronous fan group, the battery energy storage and the super capacitor.
2. The utility model provides a wind stores up and unites black start power, its characterized in that includes permanent magnet synchronous fan group, battery energy storage and supercapacitor, wherein:
The machine side converter, the battery energy storage and the super capacitor of the permanent magnet synchronous wind turbine are connected to a common direct current bus, and then are connected to a power grid through a grid side converter;
the battery energy storage is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter;
the super capacitor is connected in parallel to a direct current bus between a machine side converter and a grid side converter of the permanent magnet synchronous wind turbine generator through a bidirectional DC/DC converter.
3. A black start power supply stable control method is characterized by comprising the following steps:
tip speed ratio adjustment: when the black start mode is started, the fan is set to run on a certain tip speed ratio through pitch control, so that the fan can run in a state lower than the maximum power under the condition that the wind speed is enough;
presetting the rotor speed: presetting the rotor speed to be higher than the speed of the rotor in the maximum power tracking state so as to store certain mechanical energy;
frequency detection and response: when the system frequency is detected to be reduced, triggering the permanent magnet direct-drive synchronous fan to enter an emergency power output mode, and in the emergency power output mode, adjusting a control instruction of the permanent magnet direct-drive synchronous fan side converter to increase power output by utilizing pre-stored mechanical energy and current wind speed;
In an emergency power output mode, changing an active power reference value of a wind turbine generator side converter into a PI link self-adaptive decision based on a virtual frequency difference, and temporarily lifting a power set point of the wind turbine side converter along with the increase of the frequency difference caused by load sudden increase in black start so as to obtain power from a wind wheel more;
the method comprises the steps of controlling battery energy storage and supercapacitor equipment additionally arranged on the DC bus side of a converter based on the variation of the DC bus voltage, wherein a constant DC voltage control mode is adopted for balancing the unbalanced power of a black start power supply when the output of the black start power supply tracks a black start load;
the grid-type virtual synchronous machine is adopted to control a grid-side converter, and the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor is simulated into inertia, damping and frequency response characteristics of a synchronous generator.
4. The method for stably controlling a black start power supply according to claim 3, wherein the specific process of using a network-structured virtual synchronous machine to control a network-side converter to simulate the output power of a permanent magnet synchronous fan, a battery energy storage device and a super capacitor into inertia, damping and frequency response characteristics of a synchronous generator comprises the following steps: so that, seen from the power grid side to the grid side converter, it is as if it were a virtual inertia JVirtual dampingVirtual frequency difference->-/>A characteristic virtual synchronous machine power supply, the comprehensive dynamic characteristic of which can be expressed by an equation:
wherein,、/>、/>the virtual inertia is equivalent to the effects of the permanent magnet synchronous fan, the super capacitor and the battery pack respectively;、/>、/>the functions of the permanent magnet synchronous fan, the super capacitor and the battery pack are equivalent for virtual damping; />Is a virtual angular frequency; />Is a rated angular frequency value;sis a Laplacian operator;P e to output electromagnetic power; order theI.e. +.>The active power reference value of the virtual synchronous machine is different from the active power reference value of the traditional virtual synchronous machine in that the active power reference value is formed by PI links based on virtual frequency difference, wherein +.>、/>Constant coefficients of the P (proportion) link and the I (integral) link, respectively.
5. A black start power stabilizing control method according to claim 3, wherein the specific process of tip speed ratio adjustment and rotor speed presetting comprises:
obtaining a corresponding relation between the rotor speed and the capture power of the wind turbine generator set when the wind speed fluctuates based on the relation between the wind energy utilization coefficient and the tip speed ratio so as to guide the change of the capture power operating point of the wind turbine generator set when the wind power is started in black;
the mechanical power captured by the wind turbine generator set is expressed as:
Wherein,the air density is indicated as such,ris the blade radius>Indicating wind speed, & lt & gt>For the angular velocity of the permanent magnet fan rotor,/->Representing wind energy utilization coefficient, which is related to tip speed ratio and pitch angle>Curve of (I)/(II)>For the tip speed ratio,is the pitch angle;
when the pitch angle is fixed,the curve approximates a sine curve; taking a certain point on the right side of the highest point on each approximate sine curve as an operating point, obtaining a wind energy utilization coefficient-tip speed ratio curve function through curve fitting, and recording as；
And the corresponding relation between the rotor rotating speed and the captured power of the wind turbine can be obtained by combining the real-time wind speed, so that the corresponding relation is used as a reference curve of the change of the captured power operating point of the wind turbine along with the wind speed and the rotating speed during black start.
6. A black start power stabilizing control method according to claim 3, wherein the specific process of pitch control comprises:
taking the input power of the virtual synchronous machine as a reference value of the capture power of the wind turbine, and obtaining a reference value of the rotating speed of the rotor of the wind turbine by a reference curve;
generating a pitch angle reference value by the rotating speed reference value through a PI link, and controlling the pitch angle through a servo system;
the change in pitch angle and rotational speed causes a change in captured power, which causes a change in rotational speed such that both rotor rotational speed and captured power reach the reference value.
7. The method for stabilizing and controlling a black start power supply according to claim 3, wherein the specific process of controlling the battery energy storage and super capacitor device additionally arranged on the dc bus side of the converter based on the variation of the dc bus voltage comprises the steps of: the method comprises the steps that a battery energy storage and a supercapacitor are connected to a direct current bus of a grid-connected converter of the wind turbine generator through a bidirectional DC/DC booster circuit, when direct current voltage fluctuation is caused by unbalanced wind power output and black start load, the battery energy storage and the supercapacitor change the output to enable the direct current voltage to be maintained at rated values, and unbalanced power is balanced when the wind power output tracks the black start load;
the battery energy storage and the super capacitor adopt a double-loop control mode of a voltage outer loop and a current inner loop;
the voltage outer loop control of the battery energy storage and the super capacitor adopts a proportional integral control mode of constant direct voltage so as to eliminate the voltage deviation of the direct current bus:
wherein,the duty cycle of a boost circuit for the battery energy storage voltage or the supercapacitor; />For battery energy storage voltage or supercapacitor voltage, +.>、/>Respectively the actual voltage and the reference value on the direct current busA test voltage; />、/>The coefficients of the proportional link and the integral link of the control system are respectively; sIs a laplace operator.
8. The method for stabilizing and controlling a black start power supply according to claim 7, wherein the battery energy storage control step is to use a low-pass filter connected in series with the output signal of the outer ring of the voltage as the input step of the signal of the inner ring of the current; the supercapacitor takes the output signal of the low-pass filter link as the input link of the current inner loop signal subtracted from the output signal of the voltage outer loop.
9. A black start power stabilization control system, comprising:
the blade tip speed ratio adjusting unit is used for setting the fan to run on a certain blade tip speed ratio through pitch control when the black start mode is started, so that the fan can run in a state lower than the maximum power under the condition that the wind speed is enough;
a rotor speed presetting unit for presetting the rotor speed to be higher than the speed in the maximum power tracking state so as to store a certain mechanical energy;
the frequency detection and response unit is used for triggering the permanent magnet direct-drive synchronous fan to enter an emergency power output mode when the system frequency is detected to be reduced, and in the emergency power output mode, the side converter of the permanent magnet direct-drive synchronous fan adjusts a control instruction of the side converter so as to increase power output by utilizing pre-stored mechanical energy and current wind speed;
The wind turbine generator side converter control unit is used for changing an active power reference value of the wind turbine generator side converter into a PI link self-adaptive decision based on virtual frequency difference in an emergency power output mode, and the power set point of the wind turbine side converter is temporarily lifted along with the increase of the frequency difference caused by sudden load increase in black start so as to obtain power from a wind wheel more;
the energy storage and supercapacitor control unit is used for controlling battery energy storage and supercapacitor equipment additionally arranged on the DC bus side of the converter based on the variation of the DC bus voltage, and the battery energy storage and supercapacitor equipment and the supercapacitor equipment adopt a constant DC voltage control mode to balance the output of the black start power supply and track unbalanced power when the black start load is tracked;
the wind turbine generator grid side converter control unit is used for controlling the grid side converter by adopting a grid-structured virtual synchronous machine and simulating the output power of the permanent magnet synchronous fan, the battery energy storage and the super capacitor into inertia, damping and frequency response characteristics of a synchronous generator.
10. A black start power supply long process stable control method is characterized by comprising the following steps:
judging whether a black start condition is met, if so, distributing a start task according to the state and capacity consistency principles of the wind turbine generator and the energy storage equipment;
Performing start-up control using the black start power supply stabilization control method according to any one of claims 3 to 8;
adopting distributed cooperative control of each black start power supply based on a capacity consistency principle;
and after the power system reaches a stable running state, synchronizing the black start power supplies, and smoothly connecting with an external power grid.
11. The method for controlling the long-process stability of a black-start power supply according to claim 10, wherein after judging whether the black-start condition is satisfied, analyzing a recovery demand of the power system when the external power supply is lost to ensure a value of the total load demand to determine an optimal combination and number of inverter-type power supplies constituting the black-start power supply.
12. The method for stably controlling a black start power supply in a long process according to claim 10, wherein in the start control process, the wind turbine after the grid formation modification by using the improved virtual synchronous machine control method is started sequentially in a predetermined order, and the load is started and then connected to the power grid.
13. The method for controlling the long process stability of a black start power supply according to claim 10, wherein the specific process of performing the start control comprises the steps of:
The wind wheel of the wind turbine generator drives the permanent magnet direct-driven fan to establish a side alternating voltage, an active power reference value is initially set, the rotor accelerates to the reference value, a side converter trigger pulse is unlocked, and the energy storage stable direct-current voltage is in a rated value;
after the machine side converter stably operates, unlocking a trigger pulse of the network side converter, and establishing network side alternating voltage, wherein an active power reference value is adaptively determined by a PI link based on virtual frequency difference;
closing a network side breaker, and accessing a transformer and a power transmission line;
closing a breaker of an auxiliary machine of the started power plant, starting accelerating an auxiliary machine rotor, absorbing active power and reactive power from a power grid, automatically adjusting an active reference value by utilizing the steps of the black start power supply stable control method, and controlling the capture power and the output power of a wind turbine generator to automatically track the change of a black start load;
the auxiliary machine is accelerated to the rated slip, the starting is completed, the power returns to the rated value, the thermal generator is started, and the black starting is completed.
14. The method for controlling the long-process stability of a black-start power supply according to claim 10, wherein when the black-start power supply is controlled in a stable manner, the output voltage and/or the output power of the black-start power supply are/is adjusted by adjusting the operating point voltage and/or the operating frequency of the black-start power supply according to the requirements of a load and the power grid frequency.
15. The method of claim 14, wherein the black-start power supply increases its output power when the load demand increases, and decreases its output power when the grid frequency increases.
16. The method for stably controlling the long process of the black start power supply according to claim 10, wherein the specific process of adopting the distributed cooperative control of each black start power supply comprises the steps of obtaining the state and parameter information of each black start power supply, generating a control instruction matched with the loadable capacity of each black start power supply according to a capacity consistency principle, so that the load born by each black start power supply is matched with the capacity and the running state of the power supply of each black start power supply, and the added load task can be fairly and reasonably distributed among the black start power supplies according to the weight of the available capacity, thereby being beneficial to the execution of the black start task.
17. A black start power long process stability control system, comprising:
the judging unit is used for judging whether the black starting condition is met or not, and if so, the starting task is distributed according to the state and capacity consistency principles of the wind turbine generator and the energy storage equipment;
The black-start power stabilizing control system according to claim 9, for performing black-start control;
the distributed cooperative control unit is used for adopting the distributed cooperative control of each black start power supply based on the capacity consistency principle;
and the grid-connected unit is used for synchronizing the black start power supplies after the power system reaches a stable running state, and carrying out smooth grid connection with an external power grid.
18. The system of claim 17, wherein the distributed cooperative control unit is configured to coordinate a coordinated action between each of the black-start power supplies, collect status information of each of the black-start power supplies in real time through a communication network, and generate a corresponding control command based on a capacity consistency principle according to a load demand in black start.
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