CN111934307B - Flat operation control method and system for direct current power distribution network - Google Patents
Flat operation control method and system for direct current power distribution network Download PDFInfo
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Abstract
The invention discloses a flattened operation control method and system for a direct-current power distribution network, and belongs to the technical field of operation control of the direct-current power distribution network. The method comprises the following steps: modifying the original three-layer control architecture of the direct-current power distribution network into a flat control architecture comprising an upper-layer management system and a bottom-layer terminal; establishing an energy optimization model, and generating an optimal power command of the bottom terminal according to the energy optimization model; acquiring control characteristics of a bottom layer terminal, and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristics; and determining a droop coefficient, switching droop control modes of units of the bottom layer terminal according to the droop coefficient and a control strategy, and controlling the flat operation of the direct-current power distribution network. The invention can save the investment on the control system on one hand, and on the other hand, each bottom terminal in the system realizes the autonomous switching of control according to the established multi-segment active-voltage P-U characteristic curve, and can realize the plug and play function of the terminal layer.
Description
Technical Field
The invention relates to the technical field of operation control of a direct-current power distribution network, in particular to a flattened operation control method and system for the direct-current power distribution network.
Background
The direct current characteristics of the source end and the load end in the current power distribution system are more obvious, and the output of the energy storage port is also direct current. Therefore, in the traditional power distribution system, the loads such as direct-current photovoltaic, energy storage and electric vehicles in the area are managed and controlled by networking in a direct-current mode, and the method is an effective mode for improving the grid connection flexibility of each unit and improving the energy conversion efficiency of the system. On the other hand, bus voltage information in the direct current system reflects the balance condition of supply and demand power in the system, and compared with an alternating current system, the variable involved in the operation control of the direct current system is simpler. Therefore, the direct current power distribution has great economic and technical advantages in the aspects of high efficiency, low consumption, reliability, convenience for new energy access and the like.
At present, a large power grid multi-level control architecture which is continued from both a power distribution system and a microgrid system generally comprises a station control layer, a bay layer and a process layer from the secondary architecture. The direct current distribution system is networked based on a power electronic interface, the characteristic of power electronization of the power system is presented, a multi-level control framework is not beneficial to the requirement of quick response control after multi-converter grid connection, in addition, the key technology and application demonstration summary of the direct current distribution system published in Chinese Motor engineering newspaper indicates that droop control is a control strategy commonly adopted by the future direct current system, namely, each unit can carry out decentralized autonomous control based on local information, simultaneously, plug and play of a terminal is realized, in multi-machine parallel droop control, setting of a droop coefficient is a key for improving the overall control performance of the system, the power distribution precision among a plurality of units under peer-to-peer control is influenced, and the low-frequency oscillation of the system is also influenced.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for controlling flattened operation of a dc power distribution network, comprising:
acquiring the prediction information of the source and load sides of an upper management system in the flattened control architecture, establishing an energy optimization model according to the prediction information of the source and load sides, and generating an optimal power command of a bottom terminal in the flattened control architecture according to the energy optimization model;
the flattening processing architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
controlling the bottom layer terminal according to the optimal power command, acquiring the control characteristics of the bottom layer terminal, and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristics;
and determining a droop coefficient according to the multi-segment active-voltage P-U characteristic curve, and switching droop control modes of units of the bottom layer terminal according to the droop coefficient and a control strategy to control the flat operation of the direct-current power distribution network.
Optionally, after time domain analysis and frequency domain analysis are performed on the multi-segment active-voltage P-U characteristic curve, an optimal droop control coefficient is determined, and the flattening control operation of the direct-current power distribution network is optimized according to the optimal droop control coefficient.
Optionally, the bottom layer terminal includes: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage microgrid grid-connected converter and/or a load grid-connected converter.
Optionally, the control policy specifically includes:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct current power distribution network controls the interactive power to execute constant power control by an optimal execution command, or the converter station is used as a system main control unit to perform constant voltage control on the direct current bus voltage;
the method comprises the following steps that an energy storage power station in a direct-current power distribution network performs constant-power charging and discharging according to an optimal execution command, or performs constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement;
optionally, the generating the optimal power command of the bottom terminal according to the energy optimization model specifically includes:
respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage microgrid and a load grid-connected operation for droop control in an energy optimization model;
and determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command.
Optionally, determining the droop coefficient includes:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
and determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, performing frequency domain analysis on the output impedance, and determining the droop coefficient.
The invention also provides a flat operation control system for the direct-current power distribution network, which comprises the following components:
the command output module is used for acquiring the prediction information of the source and the load on two sides of an upper management system in the flat control architecture, establishing an energy optimization model according to the prediction information of the source and the load on two sides, and generating an optimal power command of a bottom terminal in the flat control architecture according to the energy optimization model;
the flat processing architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
the characteristic acquisition module is used for controlling the bottom layer terminal according to the optimal power command, acquiring the control characteristic of the bottom layer terminal and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristic;
and the control module determines a droop coefficient according to the multi-segment active-voltage P-U characteristic curve, switches a droop control mode of a unit of the bottom terminal according to the droop coefficient and a control strategy, and controls the flat operation of the direct-current power distribution network.
Optionally, after time domain analysis and frequency domain analysis are performed on the multi-segment active-voltage P-U characteristic curve, an optimal droop control coefficient is determined, and the dc distribution network flattening control operation is optimized according to the optimal droop control coefficient.
Optionally, the bottom layer terminal includes: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage microgrid grid-connected converter and/or a load grid-connected converter.
Optionally, the control policy specifically includes:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct current power distribution network controls the interactive power to execute constant power control by an optimal execution command, or the converter station is used as a system main control unit to perform constant voltage control on the direct current bus voltage;
the method comprises the following steps that an energy storage power station in a direct-current power distribution network performs constant-power charging and discharging according to an optimal execution command, or performs constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
and the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement.
Optionally, generating an optimal power command of the bottom-layer terminal according to the energy optimization model specifically includes:
Respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage micro-grid and a load grid in an energy optimization model during droop control operation;
and determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command.
Optionally, determining the droop coefficient includes:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
and determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, and performing frequency domain analysis on the output impedance to determine the droop coefficient.
The invention can save investment on a control system on one hand, and on the other hand, each bottom layer terminal in the system realizes the autonomous switching of control according to the formulated multi-segment P-U characteristic curve, and can realize the plug and play function of the terminal layer.
Drawings
Fig. 1 is a flow chart of a flat operation control method for a dc distribution network according to the present invention;
FIG. 2 is a diagram of a DC distribution network system according to an embodiment of the method for controlling the flattened operation of the DC distribution network of the present invention;
fig. 3 is a sectional active-voltage P-U characteristic curve according to an embodiment of a flattened operation control method for a dc power distribution network according to the present invention;
Fig. 4 is a control mode diagram of each terminal unit in an embodiment of a flat operation control method for a dc power distribution network according to the present invention;
fig. 5 is a control strategy diagram of an embodiment of a flat operation control method for a dc power distribution network according to the present invention;
fig. 6 is a two-layer flat control architecture diagram of an upper management system + a bottom terminal according to an embodiment of the flat operation control method for a dc power distribution network of the present invention;
fig. 7 is a structural diagram of a flattened operation control system for a dc distribution network according to the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including 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. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
The invention provides a flattening operation control method for a direct current distribution network, which comprises the following steps as shown in figure 1:
acquiring the prediction information of the source and load sides of an upper management system in the flattened control architecture, establishing an energy optimization model according to the prediction information of the source and load sides, and generating an optimal power command of a bottom terminal in the flattened control architecture according to the energy optimization model;
the flat processing architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
controlling the bottom layer terminal according to the optimal power command, acquiring the control characteristics of the bottom layer terminal, and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristics;
and determining a droop coefficient according to the multi-segment active-voltage P-U characteristic curve, and switching droop control modes of units of the bottom layer terminal according to the droop coefficient and a control strategy to control the flat operation of the direct-current power distribution network.
And (3) carrying out time domain analysis and frequency domain analysis on the multi-segment active-voltage P-U characteristic curve, determining an optimal droop control coefficient, and optimizing the flattening control operation of the direct-current power distribution network according to the optimal droop control coefficient.
An underlying terminal, comprising: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage micro-grid-connected converter and/or a load grid-connected converter.
The control strategy specifically comprises the following steps:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct-current power distribution network controls the interactive power to execute fixed power control by an optimal execution command, or the converter station is used as a system main control unit to control the direct-current bus voltage by fixed voltage;
the method comprises the following steps that an energy storage power station in a direct-current power distribution network carries out constant-power charging and discharging according to an optimal execution command, or carries out constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement;
optionally, generating an optimal power command of the bottom-layer terminal according to the energy optimization model specifically includes:
respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage microgrid and a load grid-connected operation for droop control in an energy optimization model;
and determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command.
Determining a droop coefficient, comprising:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
And determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, and performing frequency domain analysis on the output impedance to determine the droop coefficient.
The method and the system have the advantages that the preset function of the upper control system in the original three-layer control framework of the direct-current power distribution network is transferred to the grid-connected terminal of the direct-current power distribution network, and the flat control framework comprising the upper management system and the bottom terminal is modified.
The invention is further illustrated by the following examples:
as shown in fig. 2, the dc distribution system is characterized in that a converter VSC is connected to an ac system, the system includes a dc microgrid, two energy storage power stations, a photovoltaic power station, and a dc load, wherein the dc microgrid is intended to form a low-voltage area subnet, and is connected to the system through a bidirectional dc transformer, so as to meet the requirement of bidirectional interaction of active power, the energy storage power stations are used for balancing power in the system in real time, and the bidirectional dc transformer is also connected to the system, and the photovoltaic power station and the dc load are connected to the system through a unidirectional dc transformer;
modifying the original three-layer control architecture of the direct-current power distribution network into a flat control architecture comprising an upper-layer management system and a bottom-layer terminal;
the system-level control strategy of the flat architecture is related to the control strategy of each unit, and firstly, each converter in the system is defined to have the following control modes:
The photovoltaic power station has a maximum power point tracking control strategy MPPT, and outputs according to the maximum power all the time so as to improve the utilization rate of renewable energy;
the converter station VSC is used as an interface between a direct current system and an alternating current system, on one hand, the interaction power can be controlled to be executed according to an optimization instruction, namely, the power is fixed, and on the other hand, the converter station VSC can be used as a system main control unit to control the direct current bus voltage to be a fixed value, namely, the voltage is fixed;
the energy storage power station is used as the only inertia supporting unit of the direct current system, on one hand, the energy storage power station can control constant power charging and discharging according to an optimization instruction when being used as a slave control unit, and on the other hand, the energy storage power station can also be used as a master control unit to control constant voltage to maintain the voltage of a direct current bus to be constant;
the low-voltage microgrid grid-connected converter always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
and the load grid-connected converter performs constant power control according to the actual load requirement.
Therefore, according to the control characteristics of each terminal, the system can be described by using a multi-segment characteristic curve as shown in fig. 3, where the curve is divided into segments 1, 2, and 3, and the specific description is as follows:
in the 1 st section, a photovoltaic power station in the system generates enough power, an MPPT maximum power point tracking control strategy is adopted, energy storage is charged after the load requirement is met, a constant power control strategy is adopted for energy storage, a converter station is used as a main control unit for constant voltage control, a microgrid is regarded as a load with power capable of bidirectionally flowing, and a grid-connected converter adopts a constant low-voltage side voltage control strategy;
In the 2 nd droop section, when the photovoltaic power generation in the system is reduced or the load is increased, and the energy storage charging power is reduced to be below the maximum limit value and the soc is normal, the converter station is switched to be controlled by constant power, the bus voltage begins to drop, at the moment, the energy storage power station 1 and the energy storage power station 2 carry out peer-to-peer droop control to jointly bear the change of the system power so as to maintain the bus voltage in a normal range, and the photovoltaic maintains MPPT control and the microgrid grid-connected converter maintains a constant low-voltage side voltage control strategy;
in the 3 rd section, when the power generation in the system is further insufficient and the stored energy is discharged according to the maximum power, the voltage drop of the bus is further reduced, the converter station performs constant voltage control to meet the power requirement, the stored energy is converted into constant power control, the photovoltaic maintains MPPT control, and the microgrid grid-connected converter maintains a constant low-voltage side voltage control strategy.
In summary, each unit in the system will switch its own control mode from the master based on the multi-segment characteristic curve to achieve the purpose of power operation management, and this process does not need upper-layer system and communication.
In the above operation and control mode switching process, the specific control strategy of each unit based on the inner and outer rings of the converter is shown in fig. 4, and is specifically described as follows:
When the energy storage power station is used as a main control unit for droop control, the reference value U of the bus voltagedc-refAnd bus voltage measurement value UdcAnd port output current IdcThe value K after the proportion link is subjected to difference and then passes through a PI link and an amplitude limiting link Idc*Post and output current measurement value IdcObtaining a current reference value by performing difference, and generating a PWM signal after a PI link; when the stored energy is used as a slave control unit for constant power control, the power reference value Pess-refAnd a power measurement value PessAfter the difference is made, the current is measured with a current measurement value I after the PI and amplitude limiting links are carried outessGenerating a current reference value I after superpositioness-refAnd generating PWM signals through a PI link.
The method comprises the steps that a photovoltaic grid-connected converter always carries out Maximum Power Point Tracking (MPPT) control, a voltage reference value VMPPT corresponding to maximum tracking power is obtained through an MPPT link according to a measurement value of a photovoltaic port voltage Vpv and a current Ipv, and the voltage reference value VMPPT and the measurement value V correspond to the maximum tracking powerpvAnd finally generating a PWM signal through a PI link after the difference is made.
When the converter VSC is used as a main control unit to carry out constant voltage control, firstly, a bus voltage reference signal U is useddc-refAnd a voltage measurement value UdcAfter difference is made, the difference is respectively passed through upper amplitude limiting link and lower amplitude limiting link, then passed through PI link and multiplied by sin theta whose phase angle theta is passed through phase-locking link, then the multiplied value is mixed with current measuring value IdcObtaining a current reference value by performing difference, and generating a PWM signal through a PI link; when the converter is used as a slave control unit for constant power control, a power reference signal Pvsc-ref is multiplied by a sin theta obtained by subtracting a measurement value Pvsc through a PI link and a phase angle theta through a phase-locked link PLL, and then the multiplied product is multiplied by the current quantity Measured value IvscAnd obtaining a current reference value by performing difference, and generating a PWM signal through a PI link.
The microgrid grid-connected converter always runs on a DC bus voltage control strategy at a fixed low-voltage side, and a low-voltage side bus voltage reference value Udc-refAnd the measured value UdcAfter difference is made, the current passes through a PI link and is equal to the current two-side value IdcObtaining a current reference signal I after the differencedc-refAnd generating a PWM reference signal through a PI link.
Setting and calculating the droop coefficient under the condition that two energy storage power stations have equal droop control, and assuming the maximum voltage variation range U of the droop unitmax＝UM2、Umin＝UM3Resistance droop coefficient KESSiCan be obtained from the formula (1):
in the formula, Udc, Udcref and PESSi are respectively the port voltage of the converter, the bus voltage reference value and the output power.
In the formula PESSi maxFor storing the maximum output power, as shown in the formula (2), the output currents of the two energy storage units are inversely proportional to the resistive droop coefficient, i.e., IESS1/IESS2＝Kess2/Kess1. The line impedance Z of the grid connection of the unit is ignored at the momentliIn practice, when there is a small difference between the converter and the bus voltage, the voltage drop on the line will affect the deviation of the output power, and thus the accuracy of power distribution among the units, considering that the line impedance can be obtained by equation (1):
in the formula PESSiSatisfying the equality constraint:
in the formula,. DELTA.PloadThe resistive droop coefficients obtained by equations (3) and (4) are load variation values, do not consider the inner and outer ring control of the converter, belong to electromechanical transient, and cannot account for oscillation between network devices. Therefore, a small signal model is further established for the droop control converter for frequency domain analysis, and the droop control converter small signal model is shown in figure 5, wherein delta i is shown in the figure d(s)、Δubus(s)、Δun(s) the output current variation, the bus voltage variation and the no-load voltage variation of the droop converter, GU(s)、GI(s) are respectively a voltage controller and a current controller which are both PI controllers; gid(s)、Gud(s) transfer functions of converter current and voltage to duty cycle, respectively, gii(s) transfer function of input current to output current; zo(s) is the open-loop output impedance of the transformer, Δ u in the modelnWhen(s) is zero, the droop control converter output impedance ZD(s) is represented by formula (5);
to output impedance ZDAnd(s) calculating a Nyquist curve of the voltage-variable resistor to perform frequency domain analysis, wherein when a point (-1, j0) is not enclosed, the system is stable, the output impedance is the droop coefficient, and the droop coefficient is considered to be reasonable in value at the moment.
The system flattening control architecture is shown in fig. 6, the upper layer energy management system only makes a system min-level energy schedule according to power generation and load prediction information, the system min-level energy schedule comprises a day-ahead plan, rolling optimization and ultra-short-term scheduling, meanwhile, power instructions of all terminal units under the optimized scheduling are issued, and all terminal units receive the instructions and execute the instructions.
The present invention further provides a system 200 for controlling a dc distribution network to perform a flattened operation, as shown in fig. 7, including:
the command output module 201 is used for acquiring the prediction information of the source and load sides of the upper management system in the flat control architecture, establishing an energy optimization model according to the prediction information, and generating an optimal power command of the bottom terminal in the flat control architecture according to the energy optimization model;
The flat processing architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
the characteristic obtaining module 202 is used for controlling the bottom layer terminal according to the optimal control command, obtaining the control characteristic of the bottom layer terminal, and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristic;
and the control module 203 determines a droop coefficient according to the multi-segment active-voltage P-U characteristic curve, switches a droop control mode of the unit of the bottom-layer terminal according to the droop coefficient and a control strategy, and controls the flat operation of the direct-current power distribution network. And (3) carrying out time domain analysis and frequency domain analysis on the multi-segment active-voltage P-U characteristic curve, determining an optimal droop control coefficient, and optimizing the flattening control operation of the direct-current power distribution network according to the optimal droop control coefficient.
A bottom layer terminal, comprising: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage micro-grid-connected converter and/or a load grid-connected converter.
The control strategy specifically comprises the following steps:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct current power distribution network controls the interactive power to execute constant power control by an optimal execution command, or the converter station is used as a system main control unit to perform constant voltage control on the direct current bus voltage;
The method comprises the following steps that an energy storage power station in a direct-current power distribution network performs constant-power charging and discharging according to an optimal execution command, or performs constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement;
generating an optimal power command of the bottom terminal according to the energy optimization model, which specifically comprises the following steps:
respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage microgrid and a load grid-connected operation for droop control in an energy optimization model;
and determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command.
Determining a droop coefficient, comprising:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
and determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, performing frequency domain analysis on the output impedance, and determining the droop coefficient.
The method further comprises the step of transferring the preset function of the upper control system in the original three-layer control framework of the direct-current power distribution network to the grid-connected terminal of the direct-current power distribution network, and modifying the preset function into a flat control framework comprising the upper management system and the bottom terminal.
Compared with the existing common three-layer control architecture, the two-layer system adopting the upper-layer management system and the bottom-layer grid-connected terminal puts part of functions such as control mode switching and power management in the original upper-layer control system into each terminal unit to form a flat control method, so that the system control level and equipment can be effectively reduced, on one hand, the investment on the control system can be saved, on the other hand, each unit in the system realizes the autonomous switching of the control mode according to the established multi-segment P-U characteristic curve, and the cut-in and cut-out of a certain unit do not influence the cooperative mechanism, so that the plug-and-play function of the terminal layer can be realized. Meanwhile, a droop coefficient is designed, and on the basis of time domain analysis, a system impedance model is established based on a small signal model to carry out further frequency domain analysis on the droop coefficient, so that stable operation of the system under disturbance is ensured.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application 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 scheme in the embodiment of the application can be implemented by adopting various computer languages, such as object-oriented programming language Java and transliterated scripting language JavaScript.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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.
While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the present application.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Claims (10)
1. A method for controlling flattened operation of a dc distribution network, the method comprising:
Acquiring the prediction information of the source and the load of an upper management system in the flat control architecture, establishing an energy optimization model according to the prediction information of the source and the load, and generating an optimal power command of a bottom terminal in the flat control architecture according to the energy optimization model;
the flat control architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
controlling the bottom layer terminal according to the optimal power command, acquiring the control characteristics of the bottom layer terminal, and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristics;
determining a droop coefficient according to a multi-segment active-voltage P-U characteristic curve, switching droop control modes of units of a bottom layer terminal according to the droop coefficient and a control strategy, and controlling the flat operation of the direct-current power distribution network;
the generating of the optimal power command of the bottom-layer terminal according to the energy optimization model specifically includes:
respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage microgrid and a load grid-connected operation for droop control in an energy optimization model;
determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command;
The determining the droop coefficient according to the multi-segment active-voltage P-U characteristic curve comprises the following steps:
assuming maximum voltage variation range U of droop unitmax＝UM2、Umin＝UM3Resistance droop coefficient KESSiCan be obtained from the formula (1):
in the formula of Udc、Udcref、PESSiRespectively representing port voltage, bus voltage reference value and output power of the converter;
in the formula, PESSi maxFor storing the maximum output power, as shown in the formula (2), the output currents of the two energy storage units are inversely proportional to the resistive droop coefficient, i.e., IESS1/IESS2＝Kess2/Kess1(ii) a Considering the line impedance, it can be obtained from equation (1):
in the formula PESSiSatisfying the equality constraint:
in the formula,. DELTA.PloadThe resistive droop coefficient obtained by the formulas (3) and (4) is a load variation value, does not consider the control of an inner ring and an outer ring of a converter, belongs to electromechanical transient state, and cannot account for the oscillation between network equipment; therefore, a small signal model is further established for the droop control converter to carry out frequency domain analysis, and the small signal model of the droop control converter is delta id(s)、Δubus(s)、Δun(s) the change of the output current of the droop converter, the change of the bus voltage and the change of the no-load voltage, GU(s)、GI(s) are respectively a voltage controller and a current controller which are PI controllers; gid(s)、Gud(s) transfer functions of converter current and voltage to duty cycle, respectively, Gii(s) is the transfer function of the input current to the output current; z o(s) is the converter open loop output impedance, Δ u in the modelnWhen(s) is zero, the droop control converter outputs an impedance ZD(s) is represented by formula (5):
to output impedance ZD(s) calculating a Nyquist curve of the power amplifier to perform frequency domain analysis, and when the point (-1, j0) is not enclosed, the system is stable, and the output impedance is a droop coefficient.
2. The method according to claim 1, wherein the multi-segment active-voltage P-U characteristic curve is subjected to time domain analysis and frequency domain analysis, an optimal droop control coefficient is determined, and operation of flattening control of the direct-current power distribution network is optimized according to the optimal droop control coefficient.
3. The method of claim 1, the underlying terminal, comprising: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage micro-grid-connected converter and/or a load grid-connected converter.
4. The method according to claim 1, wherein the control strategy specifically includes:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct current power distribution network controls the interactive power to execute constant power control by an optimal execution command, or the converter station is used as a system main control unit to perform constant voltage control on the direct current bus voltage;
the method comprises the following steps that an energy storage power station in a direct-current power distribution network performs constant-power charging and discharging according to an optimal execution command, or performs constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
And the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement.
5. The method of claim 1, the determining a droop coefficient, comprising:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
and determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, performing frequency domain analysis on the output impedance, and determining the droop coefficient.
6. A flattened operational control system for a dc power distribution network, the system comprising:
the command output module is used for acquiring the prediction information of the source and the load on two sides of an upper management system in the flat control architecture, establishing an energy optimization model according to the prediction information of the source and the load on two sides, and generating an optimal power command of a bottom terminal in the flat control architecture according to the energy optimization model;
the flat control architecture is used for determining the associated control strategies of the upper management system and each terminal of the bottom terminal;
the characteristic acquisition module is used for controlling the bottom layer terminal according to the optimal power command, acquiring the control characteristic of the bottom layer terminal and generating a multi-segment active power-voltage P-U characteristic curve according to the control characteristic;
The control module determines a droop coefficient according to the multi-segment active-voltage P-U characteristic curve, switches a droop control mode of a unit of the bottom-layer terminal according to the droop coefficient and a control strategy, and controls the flat operation of the direct-current power distribution network;
the generating of the optimal power command of the bottom terminal according to the energy optimization model specifically includes:
respectively acquiring operation parameters of an energy storage power station, a photovoltaic power station, a low-voltage microgrid and a load grid-connected operation for droop control in an energy optimization model;
determining a PWM signal generated after droop control passes through a PI link according to the operation parameters, wherein the PWM signal is used as an optimal power command;
the control module determines the droop coefficient according to the multi-segment active power-voltage P-U characteristic curve, and the method comprises the following steps:
assuming maximum voltage variation range U of droop unitmax＝UM2、Umin＝UM3Resistance droop coefficient KESSiCan be obtained from the formula (1):
in the formula of Udc、Udcref、PESSiRespectively representing port voltage, bus voltage reference value and output power of the converter;
in the formula, PESSi maxFor storing the maximum output power, as shown in the formula (2), the output currents of the two energy storage units are inversely proportional to the resistive droop coefficient, i.e., IESS1/IESS2＝Kess2/Kess1(ii) a Considering the line impedance, it can be obtained from equation (1):
in the formula PESSiSatisfying the equality constraint:
In the formula,. DELTA.PloadThe load variation value is obtained from the equations (3) and (4)The resistive droop coefficient does not consider the control of an inner ring and an outer ring of a converter, belongs to electromechanical transient state, and cannot account for oscillation between network equipment; therefore, a small signal model is further established for the droop control converter to carry out frequency domain analysis, and the small signal model of the droop control converter is delta id(s)、Δubus(s)、Δun(s) the change of the output current of the droop converter, the change of the bus voltage and the change of the no-load voltage, GU(s)、GI(s) are respectively a voltage controller and a current controller which are both PI controllers; gid(s)、Gud(s) transfer functions of converter current and voltage to duty cycle, respectively, Gii(s) is the transfer function of the input current to the output current; zo(s) is the open-loop output impedance of the transformer, Δ u in the modelnWhen(s) is zero, the droop control converter output impedance ZD(s) is represented by formula (5):
to output impedance ZD(s) calculating a Nyquist curve of the power amplifier to perform frequency domain analysis, and when the point (-1, j0) is not enclosed, the system is stable, and the output impedance is a droop coefficient.
7. The system of claim 6, wherein the multi-segment active-voltage P-U characteristic curve is subjected to time domain analysis and frequency domain analysis, an optimal droop control coefficient is determined, and operation of flattening control of the direct current distribution network is optimized according to the optimal droop control coefficient.
8. The system of claim 6, the underlying terminal, comprising: the system comprises an energy storage power station, a photovoltaic power station, a low-voltage microgrid grid-connected converter and/or a load grid-connected converter.
9. The system of claim 6, wherein the control strategy specifically comprises:
outputting the photovoltaic power station in the direct-current power distribution network at the maximum power;
a converter station in the direct current power distribution network controls the interactive power to execute constant power control by an optimal execution command, or the converter station is used as a system main control unit to perform constant voltage control on the direct current bus voltage;
the method comprises the following steps that an energy storage power station in a direct-current power distribution network performs constant-power charging and discharging according to an optimal execution command, or performs constant-voltage control to maintain the voltage of a direct-current bus constant; the medium-low voltage microgrid grid-connected converter in the direct-current power distribution network always performs constant low-voltage side voltage control to maintain the constant voltage of the low-voltage microgrid bus;
and the load grid-connected converter in the direct-current power distribution network performs constant power control according to a preset requirement.
10. The system of claim 6, the determining a droop coefficient, comprising:
determining the maximum voltage variation range of the bottom layer terminal in a multi-segment active-voltage P-U characteristic curve, and determining the resistive droop coefficient of the bottom layer terminal;
and determining the output impedance of the bottom layer terminal according to the resistive droop coefficient, performing frequency domain analysis on the output impedance, and determining the droop coefficient.
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