CN112234643A - Control system and method for interconnecting two regional power grids based on flexible direct-current transmission - Google Patents

Control system and method for interconnecting two regional power grids based on flexible direct-current transmission Download PDF

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CN112234643A
CN112234643A CN202011061121.9A CN202011061121A CN112234643A CN 112234643 A CN112234643 A CN 112234643A CN 202011061121 A CN202011061121 A CN 202011061121A CN 112234643 A CN112234643 A CN 112234643A
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voltage
current
converter
module
frequency
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CN112234643B (en
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朱介北
王晓南
刘迎澍
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Tianjin University
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Tianjin University
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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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • 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
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a control system based on flexible direct current transmission interconnection two-area power grid, which comprises a first synchronous generator area power system, a second synchronous generator area power system and a voltage source type converter high-voltage direct current transmission system, wherein the first synchronous generator area power system and the second synchronous generator area power system are sequentially connected; the alternating current side of the first converter is connected with a first synchronous generator regional power system; the alternating current side of the second converter is connected with a second synchronous generator regional power system; the direct current sides of the first converter and the second converter are respectively connected with a capacitor in parallel and connected through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the first converter controller is provided with a power outer ring module; a controller of the second converter is provided with a voltage outer ring module; the power outer loop module comprises a power grid frequency calculation module, a comparison gating module, a remote control module and a local control module; the voltage outer loop module comprises a direct current voltage-frequency droop control module. The invention can adaptively realize the stability of the system.

Description

Control system and method for interconnecting two regional power grids based on flexible direct-current transmission
Technical Field
The invention relates to the field of alternating current and direct current interconnected power grids, in particular to a control system and method for interconnecting two regional power grids based on flexible direct current transmission.
Background
At present, the share proportion of renewable energy and natural gas in primary energy is higher and higher, the consumption proportion of coal quantity is reduced year by year, clean energy with superiority in environmental protection also brings opportunities and challenges to a power system, the problems of inherent intermittency and randomness, uneven distribution of countries and regions and the like are mainly reflected, and in order to balance the distribution and consumption problems of renewable energy, the interconnection of an alternating current power grid and a direct current power grid becomes an important method for efficiently utilizing new energy. In the interconnection of power grids, the advantages of the flexible direct current transmission technology, such as current self-turn-off, flexibility and convenience in control, application of the pulse width modulation technology, and the like, are widely applied, but the defects are that the flexible direct current externally presents low inertia and weak damping, cannot actively participate in power grid adjustment, and cannot provide damping for the interconnected power grids to suppress disturbance. Meanwhile, when one port of the interconnected power grid has frequency change, the power system on the other port side cannot support the frequency change.
One control method commonly used in current converter stations is vector control, which generally controls a target through a voltage outer loop and a current inner loop. The voltage outer ring generates a control signal to be transmitted to the current inner ring through processing the reference value transmitted by receiving the system level control, and the current inner ring generates a voltage reference value expected to be output after processing and transmits the voltage reference value to the trigger level controller. The vector control has a good control effect, and can realize overcurrent control and high-power application occasions. Most of the existing documents compensate for single-ended system inertia and damping, that is, only the power system applying inertia compensation can self-sufficient inertia and damping for the interconnected power network, and no attention is paid to whether other interconnected systems possess virtual inertia, which is very disadvantageous for frequency support of two-ended systems or multi-ended systems. In order to compensate the reduced equivalent system inertia, improve the dynamic characteristic of the converter and improve the mutual supporting capacity of systems at two ends, a related scholars designs a relational equation of frequency and direct current voltage by comparing an energy equation of direct current capacitance with a motion equation of a rotor, so that the stability of the system is improved by using capacitance energy, but the scheme of the method has higher requirement on capacitance value and needs certain consideration for actual occupied space. The students design the method of using master-slave control and average current control to make mutual connection of two-terminal systems, but the method needs a communication mechanism to share information of each distributed power supply or energy storage battery, however, the methods are high in cost and the stability of the methods depends on the effectiveness of communication.
Disclosure of Invention
The invention provides a control system and a control method based on flexible direct current transmission interconnected two-area power grid, aiming at solving the technical problems in the prior art.
The technical scheme adopted by the invention for solving the technical problems in the prior art is as follows: a control system based on flexible direct current transmission interconnection two-area power grids comprises a first synchronous generator area power system, a second synchronous generator area power system and a voltage source type converter high-voltage direct current transmission system which are sequentially connected; the voltage source type high-voltage direct-current transmission system comprises a first converter and a second converter; the alternating current side of the first converter is connected with a first synchronous generator regional power system; the alternating current side of the second converter is connected with a second synchronous generator regional power system; the direct current sides of the first converter and the second converter are respectively connected with a capacitor in parallel and connected through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer ring module, a first current inner ring module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; the power outer ring module outputs a reference current to the first current inner ring module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; the voltage outer ring module outputs a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
outside of powerThe loop module comprises a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a side capacitor of the first current converter and actual current of the direct current bus, converts the voltage signals into frequency signals, and the frequency signals are set to be f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a The comparison gating module comprises a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both comprising a virtual inertial damper for damping frequency oscillations, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the first synchronous generator regional power system and then outputting the reference active power, and setting PACAnd PAC *Corresponding to the actual active power and the reference active power of the electric power system of the first synchronous generator area; first PI controller input PACAnd PAC *Outputting a reference current to the input end of the first current inner loop module;
the voltage outer ring module comprises a third PI controller and a direct current voltage-frequency droop control module; the direct current voltage-frequency droop control module inputs the difference value between the actual frequency and the rated frequency of the second synchronous generator regional power system, converts the difference value into the reference voltage of the direct current bus, limits the amplitude extreme value of the reference voltage and outputs the limited reference voltage; the third PI controller inputs the difference between the voltage at two ends of a capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module; and outputting the reference current to the second current inner loop module.
Further, the DC voltage-frequency droop control module comprises a first amplifier and a voltage limiter; let the actual frequency of the second synchronous generator regional power system be f2(ii) a First amplifier input f2And f0Is set to be U, the output signal of the first amplifier is set to be Udc'; setting the rated voltage of the DC bus as Udc0(ii) a Setting a maximum value and a minimum value of the voltage amplitude of the direct current bus; voltage limiter of input Udc' and Udc0And outputting the direct current bus reference voltage, wherein the direct current bus reference voltage is used for firstly carrying out proportional amplification on the input signal, and then limiting the signal after proportional amplification between a maximum value and a minimum value and then outputting the signal.
Further, the grid frequency calculation module comprises a second amplifier and a third amplifier, and the voltage signal U is set at two ends of the capacitor at the side of the first converterdc1Setting the actual current of the direct current bus as I; a second amplifier input I, the output signal of which is set to Ud(ii) a Will Udc1Subtracting U in sequencedAnd Udc0Then the difference is obtained and input to a third amplifier, f0Added to the output signal of the third amplifier to give a sum f2’。
Further, the virtual inertia damper comprises a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier and a multi-input adder; frequency slope calculator input fsOutput fsSlope-to-frequency slope limiter of (1), setting fsThe frequency slope limiter limits the frequency slope to a maximum value and a minimum value of the slope ofsThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then output to the virtual inertia amplifier, and the output signal of the virtual inertia amplifier is set to be delta P1(ii) a Virtual damping amplifier input fsAnd f0Let the output signal of the virtual damping amplifier be Δ P2(ii) a Let the mechanical power input by the synchronous generator be PM(ii) a The multi-input adder comprises two negative input ends and one positive input end, and the multi-input adder comprises two negative input ends and one positive input endIn, a negative input terminal input Δ P1And the other negative input terminal is input with delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *。
Further, the power outer loop module further comprises a second PI controller, the second PI controller inputs the difference between the reactive power actual value and the reactive power reference value of the first synchronous generator regional power system, and outputs reactive reference current to the input end of the first current inner loop module.
The invention also provides a control method for interconnecting two regional power grids based on flexible direct-current transmission, which comprises the following steps:
connecting a first synchronous generator regional power system and a second synchronous generator regional power system through a voltage source type converter high-voltage direct-current transmission system; the voltage source type high-voltage direct-current transmission system is provided with a first converter and a second converter; connecting the ac side of the first converter to the first synchronous generator regional power system; connecting the ac side of the second converter to a second synchronous generator regional power system; connecting the direct current sides of the first converter and the second converter in parallel with a capacitor respectively and connecting the capacitors through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer loop module, a first current inner loop module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; enabling the power outer loop module to output a reference current to the first current inner loop module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; enabling the voltage outer ring module to output a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
the power outer loop module is provided with a power grid frequency calculation module, a comparison gating module,The remote control module, the local control module and the first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a capacitor at the side of the first current converter and actual current of the direct current bus and converts the voltage signals and the actual current to generate frequency signals; setting the frequency signal generated by the power grid frequency calculation module as f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a The comparison gating module is provided with a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both provided with a virtual inertial damper for suppressing frequency oscillation, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the electric power system of the first synchronous generator area; after the difference between the actual active power and the reference active power of the first synchronous generator area electric power system is subjected to proportional integral regulation through a first PI controller, the difference is used as reference current and is input into a first current inner ring module;
and the voltage outer ring module is internally provided with a direct current voltage-frequency droop control module, and the direct current voltage-frequency droop control module is used for converting the difference value between the actual frequency and the rated frequency of the regional power system of the second synchronous generator to generate the reference voltage of the direct current bus, limiting the amplitude extreme value of the reference voltage and outputting the reference voltage, and performing proportional integral adjustment on the difference value between the voltage at two ends of the capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module through a third PI controller to be used as a reference current and input the reference current to the second current inner ring module.
Further, the direct current voltage-frequency droop control module is provided with a first amplifier and a voltage amplitude limiter; let the actual frequency of the second synchronous generator regional power system be f2(ii) a Let the first amplifier input f2And f0The difference of (a), the amplification factor of the first amplifier is equal to the droop coefficient of the direct current voltage-frequency; setting the output signal of the first amplifier to Udc'; setting the rated voltage of the DC bus as Udc0(ii) a Setting a maximum value and a minimum value of the voltage amplitude of the direct current bus; making the voltage limiter input Udc' and Udc0And outputting the direct current bus reference voltage to amplify the input signal in proportion, and then limiting the amplified signal between a maximum value and a minimum value and outputting the amplified signal.
Furthermore, the power grid frequency calculation module is provided with a second amplifier and a third amplifier, so that the second amplifier inputs the actual current of the direct current bus, and the amplification factor of the second amplifier is equal to the equivalent resistance of the direct current bus; setting a voltage signal U across a side capacitor of a first converterdc1(ii) a Let the output signal of the second amplifier be Ud(ii) a Will Udc1Subtracting U in sequencedAnd Udc0Then the obtained difference value is input into a third amplifier, so that the amplification factor of the third amplifier is equal to the reciprocal of the droop coefficient of the direct current voltage-frequency; output of the third amplifier and f0The sum of the additions is f2’。
Furthermore, the virtual inertia damper is provided with a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier and a multi-input adder; let the frequency slope calculator input fsOutput fsSlope-to-frequency slope limiter of (1), setting fsIs made to be the maximum and minimum of the slope of (a), so that the frequency slope limiter will limit fsThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then is output to the virtual inertia amplifier, so that the amplification coefficient of the virtual inertia amplifier is an inertia time constant, and the output signal of the virtual inertia amplifier is delta P1(ii) a Make the virtual damping amplifier input fsAnd f0Difference of (2)The amplification coefficient of the virtual damping amplifier is set as the damping coefficient, and the output signal of the virtual damping amplifier is delta P2(ii) a Let the mechanical power input by the synchronous generator be PM(ii) a The multi-input adder comprises two negative input ends and a positive input end, wherein one negative input end inputs delta P1And the other negative input terminal is input with delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *。
Furthermore, the power outer ring module is also provided with a second PI controller, and after the difference between the actual reactive power value and the reference reactive power value of the electric power system in the area of the first synchronous generator is subjected to proportional integral adjustment through the second PI controller, the reference current is output to the input end of the first current inner ring module.
The invention has the advantages and positive effects that:
(1) the converter at the second synchronous generator area power system end adopts frequency droop control, and carries out amplitude limiting on direct current voltage, so that on one hand, effective control on the direct current voltage can be achieved, and on the other hand, related control of physical quantity is adopted by the converter and the first synchronous generator area power system, so that the use of communication equipment is reduced, the cost is saved, and the transmission efficiency and accuracy are improved.
(2) Inertia and damping are added into a control scheme of a converter at the end of a power system of a first synchronous generator area, so that the stability of the power system of the first synchronous generator area can be effectively improved, and power support can be performed on the frequency change of the power system of a second synchronous generator area.
(3) The power outer loop module is provided with a local remote control module and a local control module, the remote control module and the local control module are provided with virtual inertia dampers for inhibiting frequency oscillation, and the flexible selection of inertia and damping can realize the stability of the system in a self-adaptive manner.
(4) The power outer loop module improves the stability of the electric power system of the first synchronous generator area by adopting the power grid frequency calculation module and the comparison gating module.
Drawings
Fig. 1 is a schematic structural diagram of a control system based on a flexible direct-current transmission interconnected two-area power grid according to the invention.
Fig. 2 is a control schematic of the first converter of the present invention.
Fig. 3 is a control diagram of a second converter according to the invention.
FIG. 4 is a flow chart of the operation of a comparison gating module in the present invention.
Fig. 5 is a schematic diagram of frequency selection when frequency changes occur in a one-sided system.
Fig. 6 is a schematic diagram of frequency selection when frequency changes occur in a two-sided system.
In FIG. 1, Udc1Representing the dc voltage across the first converter side capacitor; u shapedc2Representing the dc voltage across the second converter side capacitor; i represents the actual current of the dc bus. The voltage across the side capacitor of the second converter is Udc2。
In FIG. 2, Udc1Representing the dc voltage across the first converter side capacitor; i represents the actual current of the direct current bus; r represents the equivalent resistance of the direct current bus; u shapedRepresenting the output signal of the second amplifier; u shapedc2Representing the dc voltage across the second converter side capacitor; u shapedc0Indicating the rated voltage of the direct current bus; k represents a droop coefficient of dc voltage-frequency; f. of0Representing rated frequencies of a first synchronous generator region power system and a second synchronous generator region power system; f. of2' denotes a frequency on the second synchronous generator area electric power system side obtained by calculation; f. of1Representing an actual frequency of the first synchronous generator area power system; f. ofSRepresenting the frequency signal output by the comparison gating module; on represents a control signal of the multiplexer; h represents an inertia time constant; d represents a damping coefficient; pMRepresenting the mechanical power input by the synchronous generator; delta P1Representing a virtual inertia amplifier output signal; delta P2Represents the virtual damping amplifier output signal is; pACRepresenting the actual active power of the first synchronous generator area power system; pAC *Representing a reference active power of the first synchronous generator area power system; q1Representing an actual value of reactive power of the electric power system of the first synchronous generator area; q1 *A reactive power reference value representing a first synchronous generator area power system; u. ofabc1And iabc1Correspondingly representing three-phase alternating current voltage and alternating current at an alternating current-direct current coupling point at the side of the first converter; u. ofabc1 *Representing three-phase alternating voltage and alternating current reference values at a direct current coupling point of the first converter side; u. ofdq1And idq1Correspondingly representing the voltage and the current of the first converter side under the dq axis after park transformation; u. ofdq1 *And idq1 *Correspondingly representing a reference voltage and a reference current under a dq axis of the first converter side; PLL stands for phase locked loop; theta represents the phase angle output by the phase-locked loop and used for carrying out park conversion; PWM denotes a pulse width modulator; i.e. id1 *And iq1 *Correspondingly representing active reference current and reactive reference current input by the first current inner loop module; u. ofd1 *And uq1 *And correspondingly representing the active reference voltage and the reactive reference voltage output by the first current inner loop module.
In FIG. 3, f2Representing the actual frequency of the second synchronous generator area power system; f. of0Representing rated frequencies of a first synchronous generator region power system and a second synchronous generator region power system; k represents a droop coefficient of dc voltage-frequency; u shapedc0Indicating the rated voltage of the direct current bus; u shapedc2 *The direct current bus reference voltage generated by the conversion of the direct current voltage-frequency droop control module is represented; u shapedc' denotes the output signal of the first amplifier; q2Representing an actual value of reactive power of the second synchronous generator area power system; q2 *A reactive power reference value representing a second synchronous generator area power system; u. ofabc2And iabc2Correspondingly representing the three-phase alternating voltage and the alternating current at the alternating-current and direct-current coupling point of the second converter side; u. ofabc2 *Representing three-phase alternating voltage and current at a dc coupling point on the second converter sideA reference value; u. ofdq2And idq2Correspondingly representing the voltage and the current of the second converter side under the dq axis after park transformation; u. ofdq2 *And idq2 *Correspondingly representing a reference voltage and a reference current under a dq axis of the second converter side; PLL stands for phase locked loop; θ represents a phase signal on the ac side of the first converter; PWM denotes a pulse width modulator; i.e. id2 *And iq2 *Correspondingly representing active reference current and reactive reference current input by the second current inner loop module; u. ofd2 *And uq2 *And correspondingly representing the active reference voltage and the reactive reference voltage output by the second current inner loop module.
In FIGS. 4 to 6, f1And f2Correspondingly representing the actual frequency of the power system of the first synchronous generator area and the second synchronous generator area; df is a1Dt and df2The frequency f is represented by the correspondence of/dt1And frequency f2The rate of change of (c); f. ofDLA minimum value representing the frequency; f. ofDHA maximum value representing a frequency; [ f ] ofDL，fDH]Is the allowable variation range of the frequency; t/s represents the time of output lock; k is a radical ofaAnd kbCorresponding representation f1And f2The slope of the frequency curve of (a), i.e., the rate of change of frequency; f. of0The rated frequencies of the first and second synchronous generator region power systems are shown.
Detailed Description
For further understanding of the contents, features and effects of the present invention, the following embodiments are enumerated in conjunction with the accompanying drawings, and the following detailed description is given:
referring to fig. 1 to 6, a control system based on a flexible dc power transmission interconnection two-area power grid includes a first synchronous generator area power system, a second synchronous generator area power system, and a voltage source converter high-voltage dc power transmission system, which are connected in sequence; the voltage source type high-voltage direct-current transmission system comprises a first converter and a second converter; the alternating current side of the first converter is connected with a first synchronous generator regional power system; the alternating current side of the second converter is connected with a second synchronous generator regional power system; the direct current sides of the first converter and the second converter are respectively connected with a capacitor in parallel and connected through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer ring module, a first current inner ring module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; the power outer ring module outputs a reference current to the first current inner ring module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; the voltage outer ring module outputs a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
the power outer loop module comprises a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a side capacitor of the first current converter and actual current of the direct current bus, converts the voltage signals into frequency signals, and the frequency signals are set to be f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a The comparison gating module comprises a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; setting the control signal of the multi-way selection switch as on, namely the control signal of the multi-way selection switch is the selection comparator pair f2' and f1And outputting a judgment result signal after the comparison and judgment. If the selection result is f2' then the control signal on of the multi-way selection switch drives the multi-way switchWay selection switch makes f2The signal end is communicated with the output port of the comparison gating module; if the selection result is f1Then the control signal on of the multi-way selection switch drives the multi-way selection switch to enable f1The signal end is communicated with the output port of the comparison gating module.
Let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both comprising a virtual inertial damper for damping frequency oscillations, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the first synchronous generator regional power system and then outputting the reference active power, and setting PACAnd PAC *Corresponding to the actual active power and the reference active power of the electric power system of the first synchronous generator area; first PI controller input PACAnd PAC *Outputting a reference current to the input end of the first current inner loop module; the reference current output by the first PI controller can be used as an active current reference signal input by the first current inner loop module.
The voltage outer ring module comprises a third PI controller and a direct current voltage-frequency droop control module; the direct current voltage-frequency droop control module inputs the difference value between the actual frequency and the rated frequency of the second synchronous generator regional power system, converts the difference value into the reference voltage of the direct current bus, limits the amplitude extreme value of the reference voltage and outputs the limited reference voltage; let the voltage across the side capacitor of the second converter be Udc2(ii) a The third PI controller inputs the difference between the voltage at two ends of a capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module; and outputting the reference current to the second current inner loop module. The reference current output by the third PI controller can be used as an active current reference signal input by the second current inner loop module.
Preferably, the dc voltage-frequency droop control module may include a first amplifier and a voltage limiter; can be provided with a second synchronous hairThe actual frequency of the electric system of the motor area is f2(ii) a The first amplifier can input f2And f0The amplification factor of the first amplifier is equal to the droop factor K of the dc voltage-frequency, and the output signal of the first amplifier can be set to Udc'; rated voltage capable of setting DC bus as Udc0(ii) a The maximum value and the minimum value of the voltage amplitude of the direct current bus can be set; voltage limiter of input Udc' and Udc0And outputting the direct current bus reference voltage, wherein the direct current bus reference voltage is used for firstly carrying out proportional amplification on the input signal, and then limiting the signal after proportional amplification between a maximum value and a minimum value and then outputting the signal. Can be provided with UDLThe minimum value of the set DC bus voltage can be set as UDHIndicates the maximum value of the set DC bus voltage, [ U ]DL，UDH]The output value of the voltage limiter is [ U ] within the allowable variation range of the DC bus voltageDL，UDH]In the meantime.
Preferably, the grid frequency calculation module may comprise a second amplifier and a third amplifier, and the voltage signal U across the first converter side capacitor may be setdc1The actual current of the direct current bus can be set as I; a second amplifier input I with an amplification factor equal to the equivalent resistance R of the DC bus and an output signal Ud，UdRI; can be combined with Udc1Subtracting U in sequencedAnd Udc0Then the difference is input to a third amplifier, the amplification factor of the third amplifier can be equal to the reciprocal of the droop coefficient K of the direct current voltage-frequency, f0Added to the output signal of the third amplifier to give a sum f2’。
Preferably, the virtual inertial damper may include a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier, and a multi-input adder; the frequency slope calculator can input fsOutput fsThe slope-to-frequency slope limiter of (1), can set fsThe frequency slope limiter limits the frequency slope to a maximum value and a minimum value of the slope ofsThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then output to the virtual inertia amplifier, and the output signal of the virtual inertia amplifier can be set to be delta P1(ii) a Virtual damping amplifier input fsAnd f0The difference of (a) can be set as Δ P2(ii) a The mechanical power input by the synchronous generator can be set to be PM(ii) a The multi-input adder may include two negative input terminals and one positive input terminal, wherein one negative input terminal may input Δ P1The other negative input terminal can input delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *. The amplification factor of the virtual inertia amplifier may be set to the inertia time constant H, and the amplification factor of the pseudo-damping amplifier may be set to the damping factor D.
Preferably, the power outer loop module may further include a second PI controller, and the second PI controller may input a difference between an actual value of reactive power of the first synchronous generator area power system and a reference value of reactive power, and may output a reference current of reactive power to an input terminal of the first current inner loop module. The first current inner loop module can input the active reference current from the first PI controller and the reactive reference current from the second PI controller according to the actual current and the actual voltage input to the AC side of the first converter; output active reference voltage ud1 *And a reactive reference voltage uq1 *And after inverse park transformation, generating a three-phase alternating voltage and an alternating current reference value u at a direct-current coupling point of the first converter sideabc1 *And then output to the first pulse width modulator.
Preferably, the voltage outer loop module may further include a fourth PI controller, and the fourth PI controller may input a difference between the reactive power actual value and the reactive power reference value of the second synchronous generator area power system and may output the reactive reference current to an input terminal of the second current inner loop module. The second current inner loop module can input the active reference current from the third PI controller and the reactive reference current from the fourth PI controller into the actual current and the actual voltage of the AC side of the second converter; output active reference voltage ud2 *And a reactive reference voltage uq2 *And after park inverse transformation, generating three-phase AC at the DC coupling point of the second converter sideReference value u of current voltage and alternating currentabc2 *And then output to the second pulse width modulator.
The invention also provides an embodiment of a control method for interconnecting two regional power grids based on flexible direct-current transmission, which comprises the following steps:
connecting a first synchronous generator regional power system and a second synchronous generator regional power system through a voltage source type converter high-voltage direct-current transmission system; the voltage source type high-voltage direct-current transmission system is provided with a first converter and a second converter; connecting the ac side of the first converter to the first synchronous generator regional power system; connecting the ac side of the second converter to a second synchronous generator regional power system; connecting the direct current sides of the first converter and the second converter in parallel with a capacitor respectively and connecting the capacitors through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer loop module, a first current inner loop module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; enabling the power outer loop module to output a reference current to the first current inner loop module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; enabling the voltage outer ring module to output a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
the power outer loop module is provided with a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a capacitor at the side of the first current converter and actual current of the direct current bus and converts the voltage signals and the actual current to generate frequency signals; setting the frequency signal generated by the power grid frequency calculation module as f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a Comparison gating moduleThe block is provided with a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; setting the control signal of the multi-way selection switch as on, namely the control signal of the multi-way selection switch is the selection comparator pair f2' and f1And outputting a judgment result signal after the comparison and judgment. If the selection result is f2' if so, the control signal on of the multi-way selection switch drives the multi-way selection switch to enable f2The signal end is communicated with the output port of the comparison gating module; if the selection result is f1Then the control signal on of the multi-way selection switch drives the multi-way selection switch to enable f1The signal end is communicated with the output port of the comparison gating module.
Let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both provided with a virtual inertial damper for suppressing frequency oscillation, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the electric power system of the first synchronous generator area; and after the difference between the actual active power and the reference active power of the first synchronous generator area power system is subjected to proportional integral regulation through a first PI controller, the difference is used as reference current and input to a first current inner ring module.
Can be selected according to the frequency control requirements of the first and second synchronous generator regional power systems, can set the allowable frequency variation range of the first and second synchronous generator regional power systems, and then f is adjusted2' and f1Compared with the allowable variation range of the frequency, the relative selection is more suitableWith a preferred frequency as fsOutputting; can also compare f2' and f1The magnitude of the change rate of (2), and selecting a relatively suitable frequency as fsAnd (6) outputting.
Referring to FIG. 4, the allowable variation range [ f ] of the frequency can be setDL，fDH]When f is1And f2' when both are within the variation allowable range, the frequency can be selected1Input into virtual inertial dampers, i.e. fsIs f1(ii) a When one side of the system frequency in the first synchronous generator area electric power system and the second synchronous generator area electric power system exceeds the frequency allowable variation range, selecting the frequency exceeding the range as the input of the virtual inertia damper, namely fsOut of range frequencies; when the frequency of the first synchronous generator area power system and the frequency of the second synchronous generator area power system both change and both exceed the allowable change range, f is paired1And f2' comparison of absolute magnitude of rate of change when df1/dt≥d f2'/dt, the first synchronous generator region power system side frequency is selected as the input to the virtual inertial damper, i.e., fsIs a frequency f1(ii) a When df1/dt<d f2When'/dt, select f2' as input to a virtual inertial damper, i.e. fsIs a frequency f2'; the output lock time T/s is maintained after the determined frequency is selected to ensure continuous control of the local or remote, with specific selection flow diagrams and comparison principles as shown in fig. 4-6.
And the voltage outer ring module is internally provided with a direct current voltage-frequency droop control module, and the direct current voltage-frequency droop control module is used for converting the difference value between the actual frequency and the rated frequency of the regional power system of the second synchronous generator to generate the reference voltage of the direct current bus, limiting the amplitude extreme value of the reference voltage and outputting the reference voltage, and performing proportional integral adjustment on the difference value between the voltage at two ends of the capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module through a third PI controller to be used as a reference current and input the reference current to the second current inner ring module.
Preferably, the dc voltage-frequency droop control module may be configured with a first amplifier and a voltage limiter; the actual frequency of the second synchronous generator regional power system can be set to f2(ii) a The first amplifier input f can be made2And f0The difference of (a), the amplification factor of the first amplifier can be made equal to the droop coefficient of the direct-current voltage-frequency; setting the output signal of the first amplifier to Udc'; setting the rated voltage of the DC bus as Udc0(ii) a The maximum value and the minimum value of the voltage amplitude of the direct current bus can be set; can make the input U of the voltage limiterdc' and Udc0And outputting the direct current bus reference voltage, so that the direct current bus reference voltage can be used for firstly carrying out proportional amplification on the input signal, and then limiting the signal after proportional amplification between a maximum value and a minimum value and then outputting the signal.
Preferably, the grid frequency calculation module may be provided with a second amplifier and a third amplifier, so that the second amplifier may input the actual current of the dc bus, and the amplification factor of the second amplifier may be equal to the equivalent resistance R of the dc bus; a voltage signal U can be set at two ends of the side capacitor of the first converterdc1(ii) a The output signal of the second amplifier can be set to Ud(ii) a Can be combined with Udc1Subtracting U in sequencedAnd Udc0Then the difference value is input into a third amplifier, so that the amplification factor of the third amplifier is equal to the reciprocal of the droop coefficient K of the direct current voltage-frequency; output of the third amplifier and f0The sum of the additions is f2’。
Preferably, the virtual inertia damper can be provided with a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier and a multi-input adder; may make the frequency slope calculator input fsOutput fsThe slope-to-frequency slope limiter of (1), can set fsThe maximum and minimum of the slope of (a) can be such that the frequency slope limiter will besThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then is output to the virtual inertia amplifier, so that the amplification coefficient of the virtual inertia amplifier is an inertia time constant H, and the output signal of the virtual inertia amplifier is delta P1(ii) a Can make the input f of the virtual damping amplifiersAnd f0A difference of (2) to make a virtual resistanceThe amplification factor of the amplifier is damping coefficient D, and the output signal of the virtual damping amplifier can be set to be delta P2(ii) a The mechanical power input by the synchronous generator can be set to be PM(ii) a The multi-input adder can be provided with two negative input ends and one positive input end, wherein one negative input end can input delta P1The other negative input terminal can input delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *。
Preferably, the power outer loop module may further include a second PI controller, and the second PI controller may be configured to input a difference between an actual value of reactive power of the first synchronous generator regional power system and a reference value of reactive power, and may be configured to output a reference current of reactive power to the input terminal of the first current inner loop module. i.e. id1 *And iq1 *Correspondingly representing active reference current and reactive reference current input by the first current inner loop module; u. ofd1 *And uq1 *And correspondingly representing the active reference voltage and the reactive reference voltage output by the first current inner loop module. The first current inner loop module can input an active reference current i from the first PI controllerd1 *And a reactive reference current i of the second PI controllerq1 *Inputting the actual current and the actual voltage of the AC side of the first converter; output active reference voltage ud1 *And a reactive reference voltage uq1 *And after inverse park transformation, generating a three-phase alternating voltage and an alternating current reference value u at a direct-current coupling point of the first converter sideabc1 *And then output to the first pulse width modulator.
Preferably, the voltage outer loop module may further include a fourth PI controller, and the fourth PI controller may be configured to input a difference between an actual value of reactive power of the second synchronous generator regional power system and a reference value of reactive power, and may be configured to output a reference current of reactive power to an input terminal of the second current inner loop module. The second current inner loop module can input the active reference current from the third PI controller, the reactive reference current from the fourth PI controller and the actual current on the AC side of the second converterCurrent and actual voltage, and output active reference voltage ud2 *And a reactive reference voltage uq2 *And after inverse park transformation, generating a three-phase alternating voltage and alternating current reference value u at the direct current coupling point of the second converter sideabc2 *And then output to the second pulse width modulator.
The first and second converters, the capacitor, the first and second pulse width modulators, the first and second current inner loop modules, the grid frequency calculation module, the virtual inertial damper, the remote control module, the local control module, the dc voltage-frequency droop control module, the first to fourth PI controllers, the selection comparator, the multiplexer, the first to third amplifiers, the voltage limiter, the frequency slope calculator, the frequency slope limiter, the virtual inertia amplifier, the virtual damping amplifier, the multi-input adder, and other functional devices and modules may be implemented by using functional devices and modules in the prior art, or implemented by using software in the prior art and using conventional technical means.
The working principle of the invention is further explained below with reference to the attached drawings:
fig. 1 is a schematic structural diagram of a control system based on a flexible dc power transmission interconnection two-area power grid, which includes a first synchronous generator area power system, a second synchronous generator area power system and a voltage source converter high-voltage dc power transmission system connected in sequence; the voltage source type high-voltage direct-current transmission system comprises a first converter and a second converter; the alternating current side of the first converter is connected with a first synchronous generator regional power system; the alternating current side of the second converter is connected with a second synchronous generator regional power system; the direct current sides of the first converter and the second converter are respectively connected with a capacitor in parallel and connected through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer ring module, a first current inner ring module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; the power outer ring module outputs a reference current to the first current inner ring module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; the voltage outer ring module outputs a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters
The first synchronous generator area power system comprises two sets of synchronous generators with the same capacity, an excitation system and a transformer thereof. The first synchronous generator area power system comprises a set of synchronous generators, an excitation system and a transformer thereof. The first converter adopts an active power regulation converter, and the second converter adopts a direct-current voltage regulation converter; the voltage source type converter high-voltage direct-current transmission system becomes a flexible direct-current transmission system which is connected with a first synchronous generator area power system and a second synchronous generator area power system, capacitors are respectively connected in parallel on the connected direct-current sides of the first converter and the second converter, and a specific topological diagram is shown in figure 1.
The first converter and the second converter are respectively controlled according to the following control principle:
1. control principle of the first converter:
the first converter is an active power regulating converter, the active power regulating converter is abbreviated as PR-VSC in English, in the traditional active power-frequency droop control, a virtual inertia time constant and a damping coefficient are added, wherein the inertia time constant is multiplied by the slope of frequency, the damping coefficient has the effect of the droop coefficient, the first converter can be regarded as a local load when compensating the change of the local frequency, and the first converter can be regarded as a generator when compensating the frequency of a remote second synchronous generator regional power system. The frequency input by the virtual inertial damper not only is the frequency of the first synchronous generator regional power system, but also includes the grid frequency data of the second synchronous generator regional power system, and then the local or remote control mode selection is performed, and the specific block diagram is shown in fig. 2. And after the mode selection is finished, the control signal of the current converter is obtained through the processing of the first current inner loop module and the PWM of the first pulse width modulator, so that the inertia and damping simulation control of the first current converter is realized. The power outer loop module of the first converter adopts inertia and damping simulation control and reactive power control, and obtains a control signal of the converter through the control of the first current inner loop module and the modulation of the PWM (pulse width modulation) of the first pulse width modulator to realize the droop control of the first converter, and a control block diagram of the droop control is shown in figure 2, and a calculation expression of active power is as follows:
Figure BDA0002712405190000141
let the three-phase AC voltage and AC current at the AC-DC coupling point on the first converter side correspond to uabc1And iabc1(ii) a Let u be obtained by a phase-locked loop PLL from a phase signal theta on the AC side of the first converterabc1And iabc1And theta is input to the three-phase AC voltage and current signal u of the signal in the abc-dq park converterabc1And iabc1And phase signal theta, abc-dq park converter output signal udq1And idq1，udq1And idq1Correspondingly representing the voltage and the current of the first converter side under the dq axis after park transformation; which is connected with a reference current signal i generated by a power outer loop moduledq1 *Are input together to a second current inner loop module udq1 *And idq1 *Correspondingly representing a reference voltage and a reference current under a dq axis of the first converter side; second current inner loop module output udq1 *Generating a reference AC voltage value u after dq-abc park inverse transformationabc1 *，uabc1 *Representing three-phase alternating voltage and alternating current reference values at a direct current coupling point of the first converter side; the input of the pulse width modulator PWM is a reference AC voltage value uabc1 *And the output signal controls the on-off of a power switch of the first converter.
The power outer loop module comprises a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller. A remote control module, a local control module, both comprising a virtual inertial damper for damping frequency oscillations, wherein:
the working principle of the power grid frequency calculation module is as follows: when the second converter adopts DC voltage-frequency droop control, the frequency f of the power system side of the second synchronous generator area2When the change occurs, the direct current voltage U of the electric power system side of the second synchronous generator areadc2And therefore also the direct voltage U on the side of the power system via the first synchronous generator area can be changed using kirchhoff's current lawdc1And calculating to obtain a direct current voltage value U of the electric power system side of the second synchronous generator areadc2Then, the voltage is converted by the direct current voltage-frequency droop control to obtain Udc1And f2The specific block diagram is shown in the upper left corner of fig. 2, and the grid frequency calculation module is specifically represented as follows:
Figure BDA0002712405190000151
local or remote control mode selection: the frequency input into the virtual inertia damper is selected through a remote control module and a local control module, and is equivalent to the corresponding frequency control of a first synchronous generator area power system or a second synchronous generator area power system;
the selection has the following principle: setting the allowable variation range of frequencyDL，fDH]When f is1And f2All within the allowable variation range, selecting the frequency f1Inputting the frequency into a virtual inertia damper, and when one side system frequency in the first synchronous generator area electric power system and the second synchronous generator area electric power system exceeds a frequency allowable variation range, selecting the frequency exceeding the range as the input of the virtual inertia damper, namely fsFor frequencies outside the range(ii) a When the frequency of the first synchronous generator area power system and the frequency of the second synchronous generator area power system both change and both exceed the allowable change range, f is paired1And f2Comparing absolute values of the rates of change when df1/dt≥df2At/dt, the first synchronous generator region power system side frequency is selected as the input to the virtual inertial damper, i.e., fsIs a frequency f1(ii) a When df1/dt<df2At dt, then select f2As input to a virtual inertial damper, i.e. fsIs a frequency f2(ii) a The output lock time T/s is maintained after the determined frequency is selected to ensure continuous control of the local or remote, with specific selection flow diagrams and comparison principles as shown in fig. 4-6. In FIGS. 4 to 6, f1And f2Correspondingly representing the actual frequency of the power system of the first synchronous generator area and the second synchronous generator area; df is a1Dt and df2The frequency f is represented by the correspondence of/dt1And frequency f2The rate of change of (c); f. ofDLA minimum value representing the frequency; f. ofDHA maximum value representing a frequency; [ f ] ofDL，fDH]The allowable change range of the frequency is also a dead zone of frequency selection, and the comparison of the frequency magnitude or the comparison of the absolute value of the frequency change rate is carried out after the allowable change range of the frequency is exceeded; t/s represents the time of output lock; k is a radical ofaAnd kbCorresponding representation f1And f2The slope of the frequency curve of (a), i.e., the rate of change of frequency; f. of0Representing rated frequencies of a first synchronous generator region power system and a second synchronous generator region power system; when the frequency f1After the deadband is exceeded, the frequency will lock onto it until the deadband internal value is restored.
If the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both comprising a virtual inertial damper for damping frequency oscillations, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the first synchronous generator regional power system and then outputting the reference active power, and setting PACAnd PAC *Corresponding to the first synchronous generator zoneActual active power and reference active power of the force system; first PI controller input PACAnd PAC *Outputting a reference current to the input end of the first current inner loop module; the above principle can be shown by the following formula:
Figure BDA0002712405190000161
Figure BDA0002712405190000162
wherein H represents an inertia time constant; d represents a damping coefficient; pMRepresenting the mechanical power input by the synchronous generator and deltap representing the damping power.
2. Second converter control principle:
second transverter direct current voltage regulation transverter, DR-VSC for short in English, it adopts direct current voltage-frequency droop control and decides reactive power control, carries out amplitude limiting control to direct current voltage simultaneously, and this is outer loop control, obtains the control signal of transverter through the control of electric current inner loop and PWM modulation once more, realizes the droop control of second transverter, and its control diagram is shown in fig. 3, and droop control and reactive power's calculation concrete expression is:
Vdc2*-Vdc0＝k·(f2-f0)
Figure BDA0002712405190000163
let u be the three-phase AC voltage and current corresponding to the AC side of the second converterabc2And iabc2(ii) a Let θ be a phase signal obtained by a phase locked loop PLL, and a three-phase AC voltage and current signal u input to an abc-dq interconverterabc2And iabc2And a phase signal theta, where the output signal of the abc-dq interconverter is set to udq2And idq2Which is coupled to a reference current signal i generated by a voltage outer loopdq2*Input into the second current inner loop module, and set the voltage reference value output by the second current inner loop module as udq2 *Generating a reference AC voltage value u after passing through a dq-abc converterabc2 *The input of the pulse width modulator is a reference AC voltage value uabc2 *And the output signal controls the converter.
The above-mentioned embodiments are only for illustrating the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and to carry out the same, and the present invention shall not be limited to the embodiments, i.e. the equivalent changes or modifications made within the spirit of the present invention shall fall within the scope of the present invention.

Claims (10)

1. A control system based on flexible direct current transmission interconnection two-area power grids is characterized by comprising a first synchronous generator area power system, a second synchronous generator area power system and a voltage source type converter high-voltage direct current transmission system which are sequentially connected; the voltage source type high-voltage direct-current transmission system comprises a first converter and a second converter; the alternating current side of the first converter is connected with a first synchronous generator regional power system; the alternating current side of the second converter is connected with a second synchronous generator regional power system; the direct current sides of the first converter and the second converter are respectively connected with a capacitor in parallel and connected through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer ring module, a first current inner ring module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; the power outer ring module outputs a reference current to the first current inner ring module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; the voltage outer ring module outputs a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
the power outer loop module comprises a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a side capacitor of the first current converter and actual current of the direct current bus, converts the voltage signals into frequency signals, and the frequency signals are set to be f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a The comparison gating module comprises a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both comprising a virtual inertial damper for damping frequency oscillations, both inputting f0And input f by a multi-way selector switchsConverting and generating reference active power of the first synchronous generator regional power system and then outputting the reference active power, and setting PACAnd PAC *Corresponding to the actual active power and the reference active power of the electric power system of the first synchronous generator area; first PI controller input PACAnd PAC *Outputting a reference current to the input end of the first current inner loop module;
the voltage outer ring module comprises a third PI controller and a direct current voltage-frequency droop control module; the direct current voltage-frequency droop control module inputs the difference value between the actual frequency and the rated frequency of the second synchronous generator regional power system, converts the difference value into the reference voltage of the direct current bus, limits the amplitude extreme value of the reference voltage and outputs the limited reference voltage; the third PI controller inputs the difference between the voltage at two ends of a capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module; and outputting the reference current to the second current inner loop module.
2. The flexible direct current power transmission interconnection two-area power grid-based control system is characterized in that the direct current voltage-frequency droop control module comprises a first amplifier and a voltage limiter; let the actual frequency of the second synchronous generator regional power system be f2(ii) a First amplifier input f2And f0Is set to be U, the output signal of the first amplifier is set to be Udc'; setting the rated voltage of the DC bus as Udc0(ii) a Setting a maximum value and a minimum value of the voltage amplitude of the direct current bus; voltage limiter of input Udc' and Udc0And outputting the direct current bus reference voltage, wherein the direct current bus reference voltage is used for firstly carrying out proportional amplification on the input signal, and then limiting the signal after proportional amplification between a maximum value and a minimum value and then outputting the signal.
3. The flexible direct current power transmission interconnected two-area power grid-based control system according to claim 1, wherein the grid frequency calculation module comprises a second amplifier and a third amplifier, and the voltage signal U across the first converter side capacitor is setdc1Setting the actual current of the direct current bus as I; a second amplifier input I, the output signal of which is set to Ud(ii) a Will Udc1Subtracting U in sequencedAnd Udc0Then the difference is obtained and input to a third amplifier, f0Added to the output signal of the third amplifier to give a sum f2’。
4. The flexibly direct-current power transmission interconnected two-area power grid-based control system according to claim 1, wherein the virtual inertial damper comprises a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier and a multi-inputAn adder; frequency slope calculator input fsOutput fsSlope-to-frequency slope limiter of (1), setting fsThe frequency slope limiter limits the frequency slope to a maximum value and a minimum value of the slope ofsThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then output to the virtual inertia amplifier, and the output signal of the virtual inertia amplifier is set to be delta P1(ii) a The difference between the input fs and f0 of the virtual damping amplifier, let the output signal of the virtual damping amplifier be Δ P2(ii) a Let the mechanical power input by the synchronous generator be PM(ii) a The multi-input adder comprises two negative input ends and a positive input end, wherein one negative input end inputs delta P1And the other negative input terminal is input with delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *。
5. The flexible direct current power transmission interconnection two-area power grid-based control system according to claim 1, wherein the power outer loop module further comprises a second PI controller, and the second PI controller inputs a difference between an actual reactive power value and a reference reactive power value of the first synchronous generator area power system and outputs a reference reactive current to an input end of the first current inner loop module.
6. A control method based on flexible direct current transmission interconnection two-area power grid is characterized by comprising the following steps:
connecting a first synchronous generator regional power system and a second synchronous generator regional power system through a voltage source type converter high-voltage direct-current transmission system; the voltage source type high-voltage direct-current transmission system is provided with a first converter and a second converter; connecting the ac side of the first converter to the first synchronous generator regional power system; connecting the ac side of the second converter to a second synchronous generator regional power system; connecting the direct current sides of the first converter and the second converter in parallel with a capacitor respectively and connecting the capacitors through a direct current bus; the first converter and the second converter are driven and controlled by a double closed-loop controller; the controller of the first converter is provided with a power outer loop module, a first current inner loop module and a first pulse width modulator; the controller of the second converter is provided with a voltage outer ring module, a second current inner ring module and a second pulse width modulator; enabling the power outer loop module to output a reference current to the first current inner loop module; the first current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the first converter and outputting a pulse width control signal to the pulse width modulator; enabling the voltage outer ring module to output a reference current to the second current inner ring module; the second current inner loop module is also used for inputting the actual current and the actual voltage at the alternating current side of the second converter and outputting a pulse width control signal to the second pulse width modulator; the first and second pulse width modulators control the operation of the first and second converters; wherein:
the power outer loop module is provided with a power grid frequency calculation module, a comparison gating module, a remote control module, a local control module and a first PI controller; the power grid frequency calculation module inputs voltage signals at two ends of a capacitor at the side of the first current converter and actual current of the direct current bus and converts the voltage signals and the actual current to generate frequency signals; setting the frequency signal generated by the power grid frequency calculation module as f2'; let the actual frequency of the first synchronous generator regional power system be f1(ii) a The comparison gating module is provided with a selection comparator and a multi-path selection switch, and the multi-path selection switch is provided with a data input end and a plurality of data output ends; selection comparators to which f is input2' and f1And to f2' and f1Performing comparison judgment, and selecting f according to the judgment result2' and f1One of the signals is output to a data input end of the multi-path selection switch, and meanwhile, a judgment result signal is output to a control end of the multi-path selection switch as a control signal; let the signal output by the selection comparator be fs(ii) a Two data output ends in the multi-path selection switch are respectively and correspondingly connected with the input ends of the remote control module and the local control module; if the rated frequencies of the first and second synchronous generator regional power systems are both f0(ii) a A remote control module and a local control module, both provided with a virtual inertial damper for suppressing frequency oscillation, both inputting f0And input f by a multi-way selector switchsConversion to generate the first syncsThe reference active power of a power system of a step generator region; after the difference between the actual active power and the reference active power of the first synchronous generator area electric power system is subjected to proportional integral regulation through a first PI controller, the difference is used as reference current and is input into a first current inner ring module;
and the voltage outer ring module is internally provided with a direct current voltage-frequency droop control module, and the direct current voltage-frequency droop control module is used for converting the difference value between the actual frequency and the rated frequency of the regional power system of the second synchronous generator to generate the reference voltage of the direct current bus, limiting the amplitude extreme value of the reference voltage and outputting the reference voltage, and performing proportional integral adjustment on the difference value between the voltage at two ends of the capacitor at the side of the second converter and the output signal of the direct current voltage-frequency droop control module through a third PI controller to be used as a reference current and input the reference current to the second current inner ring module.
7. The control method based on the flexible direct current transmission interconnected two-area power grid according to claim 6, wherein the direct current voltage-frequency droop control module is provided with a first amplifier and a voltage limiter; let the actual frequency of the second synchronous generator regional power system be f2(ii) a Let the first amplifier input f2And f0The difference of (a), the amplification factor of the first amplifier is equal to the droop coefficient of the direct current voltage-frequency; setting the output signal of the first amplifier to Udc'; setting the rated voltage of the DC bus as Udc0(ii) a Setting a maximum value and a minimum value of the voltage amplitude of the direct current bus; making the voltage limiter input Udc' and Udc0And outputting the direct current bus reference voltage to amplify the input signal in proportion, and then limiting the amplified signal between a maximum value and a minimum value and outputting the amplified signal.
8. The method according to claim 6, wherein the grid frequency calculation module is configured to set the second amplifier and the third amplifier such that the second amplifier inputs the actual current of the dc bus and the amplification factor of the second amplifier is equal to the amplification factor of the dc busThe equivalent resistance of (2); setting a voltage signal U across a side capacitor of a first converterdc1(ii) a Let the output signal of the second amplifier be Ud(ii) a Will Udc1Subtracting U in sequencedAnd Udc0Then the obtained difference value is input into a third amplifier, so that the amplification factor of the third amplifier is equal to the reciprocal of the droop coefficient of the direct current voltage-frequency; output of the third amplifier and f0The sum of the additions is f2’。
9. The control method based on the flexible direct current transmission interconnected two-area power grid according to claim 6, wherein the virtual inertial damper is provided with a frequency slope calculator, a frequency slope limiter, a virtual inertia amplifier, a virtual damping amplifier and a multi-input adder; let the frequency slope calculator input fsOutput fsSlope-to-frequency slope limiter of (1), setting fsIs made to be the maximum and minimum of the slope of (a), so that the frequency slope limiter will limit fsThe slope of the virtual inertia amplifier is limited between a maximum value and a minimum value and then is output to the virtual inertia amplifier, so that the amplification coefficient of the virtual inertia amplifier is an inertia time constant, and the output signal of the virtual inertia amplifier is delta P1(ii) a Make the virtual damping amplifier input fsAnd f0The amplification factor of the virtual damping amplifier is a damping factor, and the output signal of the virtual damping amplifier is delta P2(ii) a Let the mechanical power input by the synchronous generator be PM(ii) a The multi-input adder comprises two negative input ends and a positive input end, wherein one negative input end inputs delta P1And the other negative input terminal is input with delta P2Positive input terminal input PM(ii) a Multiple input adder output PAC *。
10. The control method based on the flexible direct current transmission interconnected two-area power grid according to claim 6, characterized in that the power outer loop module is further provided with a second PI controller, and the difference between the actual reactive power value and the reference reactive power value of the first synchronous generator area power system is subjected to proportional-integral regulation through the second PI controller, and then the reference current is output to the input end of the first current inner loop module.
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