CN112600232B - Extra-high voltage direct current transmission system converter station control system based on virtual synchronous machine - Google Patents
Extra-high voltage direct current transmission system converter station control system based on virtual synchronous machine Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
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- 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
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- 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]
Abstract
A virtual synchronizer-based converter station control system of an extra-high voltage direct current transmission system is characterized in that a virtual synchronizer VSG1 on a rectification side is connected with a transmitting-end power grid through a switch, and a virtual synchronizer VSG2 on an inversion side is connected with a receiving-end power grid through a switch; the system also comprises a reactive power regulation module, an active power regulation module, a virtual rotor module and an electrical module, and the system can simulate the electromagnetic and operating characteristics of the traditional synchronous generator, so that the ultra-high voltage direct current transmission system has the characteristics of rotational inertia, damping coefficient, frequency modulation and voltage regulation similar to the traditional synchronous generator, the stability of a transmitting end system and a receiving end system is enhanced, and the frequency of an alternating current system can be regulated in a non-differential mode through a non-differential frequency modulation link.
Description
Technical Field
The invention relates to a control system of a converter station of an extra-high voltage direct current transmission system.
Background
The ultra-high voltage direct current transmission technology is an international advanced transmission technology at present, has the advantages of long distance, large capacity, low loss, small occupied area and the like compared with the alternating current transmission technology, and has important significance for promoting the development of clean energy, changing the development mode of energy, accelerating the structure adjustment and pulling the economic growth.
Due to the fact that the transmission power of the ultra-high voltage direct current transmission system is greatly increased compared with that of a traditional transmission system, and due to the continuous development of an alternating current-direct current transmission parallel system, the performance of a control system of the ultra-high voltage direct current transmission system has important influence on the stability and reliability of the whole system. At present, extra-high voltage direct current transmission mostly adopts constant power control, namely, a rectification side adopts direct current control, and an inversion side adopts a control mode of direct current voltage control, and the control can not make corresponding response to the voltage and the frequency of an alternating current system. And as the converter does not have the characteristics of rotational inertia and damping similar to those of the traditional synchronous generator, primary frequency modulation support cannot be provided for an alternating current system, and as the permeability of power electronic devices in a high-voltage direct current transmission system and the like in a power grid is continuously increased, the equivalent rotational inertia and damping of the power system are correspondingly reduced, so that the frequency modulation capability of the system is reduced, and great challenges are provided for the safe and stable operation of the power system.
In recent years, due to the continuous development of virtual synchronous machine (VSG) technology, an inverter control method based on the VSG technology is gradually applied to systems for distributed energy, new energy power generation, and the like. The technology can simulate the rotational inertia and the damping characteristic of the synchronous generator through a certain control strategy, and enables the inverter to have the frequency modulation and voltage regulation functions, so that the operation characteristic of the synchronous generator is shown, and the frequency modulation capability of the system is further enhanced. However, most of the research on the VSG is focused on the frequency modulation and voltage regulation characteristics of a single inverter, the dc side is usually replaced by a dc voltage source, and further research is needed how to apply the VSG to an extra-high voltage dc power transmission system and realize the frequency modulation of an ac system and the control of the dc voltage.
Disclosure of Invention
The invention aims to provide a Virtual Synchronous Generator (VSG) -based control system for a converter station of an extra-high voltage direct-current transmission system, which has the voltage regulation and primary frequency modulation characteristics similar to those of a synchronous generator by simulating the rotational inertia and damping characteristics of the synchronous generator, and increases a no-difference frequency modulation and direct-current voltage control module on the basis, thereby improving the running stability of a transmitting end alternating-current system and a receiving end alternating-current system.
In order to achieve the purpose, the invention provides the following scheme:
the invention relates to a virtual synchronous machine (VSG) -based control system of a converter station of an extra-high voltage direct current transmission system, wherein a virtual synchronous machine VSG1 at a rectification side is connected with a transmitting-end power grid, and a virtual synchronous machine VSG2 at an inversion side is connected with a receiving-end power grid; the control system also comprises a reactive power adjusting module, an active power adjusting module, a virtual rotor module and an electric module; in an active power regulation module of a virtual synchronous machine VSG1 at a rectification side, an active-frequency droop controller obtains corresponding power delta P of frequency droop at the rectification side according to frequency change of an alternating current system at the rectification side D2 The frequency deviation-free regulator on the rectifying side is based on the frequency variation of the AC system on the rectifying side and the DC voltage reference value U dcref Obtaining the equivalent reference value of DC voltage
The DC voltage controller on the rectifying side is based on
And the actual value U of the DC voltage dc Obtaining the corresponding power delta P of the DC voltage regulation 2 The active power controller at the rectification side utilizes the frequency droop corresponding power delta P at the rectification side D2 Regulating corresponding power delta P by DC voltage 2 And a transmission power offset value deltap c Adjusting the input mechanical power P at the rectification side mc2 (ii) a In an active power adjusting module of the VSG2 of the virtual synchronous machine at the inversion side, an active-frequency droop controller obtains corresponding power delta P of the frequency droop at the inversion side according to the frequency change of an alternating current system at the inversion side D1 The inverter side frequency deviation-free regulator obtains the inverter side according to the frequency change of the inverter side alternating current systemCorresponding power delta P of frequency indifference regulation 1 The inverter side active power controller utilizes the inverter side frequency to droop the corresponding power delta P D1 The frequency of the inversion side is adjusted without difference to corresponding power delta P 1 And a transmission power offset value deltap c Adjusting the mechanical power P input to the inverter side mc1 (ii) a According to the mechanical power P input from the inversion side mc1 And the mechanical power P input at the rectification side mc2 Determining input mechanical power P of VSG converter m And then the virtual rotor module inputs mechanical power P by utilizing VSG converter m Obtaining the electrical angle theta of the VSG alternating current system; in the reactive power regulation module, a reactive power-voltage droop controller obtains a reactive power deviation corresponding regulation voltage value delta V according to the voltage change of the VSG alternating current system Q The virtual excitation regulator correspondingly regulates the voltage value delta V by utilizing the reactive deviation Q And finally, obtaining an equivalent direct axis command voltage by the electrical module by using the obtained VSG alternating current system electrical angle theta and the command voltage value E
And equivalent quadrature axis command voltage
And further controlling the VSG output signal of the virtual synchronous machine.
The invention is also characterized in that:
according to the invention, a rectification side virtual synchronous machine VSG1 control strategy is adopted on a rectification side of an extra-high voltage direct current transmission system converter station based on a virtual synchronous machine, an inversion side virtual synchronous machine VSG2 control strategy is adopted on an inversion side, and a rectification side pole-end converter and a ground-end converter respectively input command voltage values with different electrical angles.
When no-difference frequency modulation is needed, the frequency error regulator is connected to the active power regulation module, and the no-difference frequency modulation of the VSG alternating current system is achieved.
The calculation of the angular frequency of the VSG alternating current system in the virtual rotor link is more accurate.
The work process of the converter station control system of the extra-high voltage direct current transmission system based on the virtual synchronous machine is as follows:
1.1 Transmission Power reference value P of Extra-high Voltage direct Current Transmission System in the control System of the converter station of the Extra-high Voltage direct Current Transmission System based on the virtual synchronizer according to the present invention set And the actual transmission power P e Determining a transmission power offset value:
ΔP＝P set -P e (1)
in the formula,. DELTA.P c Is a transmission power offset value, P set For a given active power reference value, P e And outputting the actual output power of the extra-high voltage direct current transmission system.
1.2 according to the change of the angular frequency of the inverter side alternating current system, determining the power corresponding to the inverter side frequency droop and the power corresponding to the inverter side frequency no-difference regulation through simulating the droop relation of the active power and the frequency of the synchronous generator:
ΔP D1 ＝D p (w n -w 1 ) (2)
in the formula, H w (s) is the transfer function of the inverter-side frequency-error-free regulator, w 1 For the angular frequency, w, of the AC system on the inverting side n At a nominal angular frequency, D p Is the active-frequency droop coefficient, Δ P D1 For inverting the power corresponding to the side frequency droop, Δ P 1 Corresponding power is adjusted for the inverter side frequency no difference, when only the primary frequency modulation characteristic of the synchronous generator needs to be simulated, the inverter side frequency no difference adjuster stops running, and the value is 0; when an inverter-side frequency non-difference regulator is used, the inverter sideCorresponding power delta P of frequency indifference regulation 1 Is adjusted according to the frequency deviation.
The active-frequency droop coefficient and the rotational inertia are in the following relationship:
D p ＝w 1 D (4)
wherein D is a VSG damping parameter.
1.3, determining the input mechanical power of an inversion side, and distributing the power of an inversion side series current converter according to an inversion side structure of a converter station of an ultra-high voltage direct current transmission system:
P mc1 ＝ΔP c +ΔP D1 +ΔP 1 (5)
P m1 ＝P mc1 /4 (6)
in the formula, P mc1 For the mechanical power input on the inverting side, P m1 Inputting mechanical power, Δ P, for the inverter-side converter c For transmission power offset value, Δ P 1 And adjusting the corresponding power for the frequency of the inversion side without difference.
1.4 according to the deviation value of the actual angular frequency and the rated angular frequency of the rectification side AC system, obtaining the power delta P corresponding to the droop of the rectification side frequency through a link of simulating the droop relation of the active power and the frequency of the synchronous generator D2 ：
ΔP D2 ＝D p (w n -w 2 ) (7)
In the formula,. DELTA.P D2 For rectifying the power corresponding to the side frequency droop, w n At nominal angular frequency, w 2 Is the rectified side ac system angular frequency.
1.5 obtaining the deviation value of the actual angular frequency and the rated angular frequency of the rectification side AC system through a non-difference frequency adjusting link and a DC voltage controller to obtain the corresponding power delta P of the DC voltage adjustment 2 ：
Wherein, the first and the second end of the pipe are connected with each other,
in the formula,. DELTA.P 2 Regulating the corresponding power, w, for the DC voltage 2 For rectifying the angular frequency, H, of the side AC system dc (s) is the dc voltage controller transfer function,
is a DC voltage equivalent reference value, U dc Is the actual value of the DC voltage, U dcref Is a DC voltage reference value, K w-dc Is the direct current voltage and the frequency proportionality coefficient, w, of the rectified side alternating current system n At nominal angular frequency, w 2 Is the rectified side ac system angular frequency.
1.6, determining the input mechanical power of the rectification side of the converter station of the ultra-high voltage direct current transmission system, and distributing the power of the series converters at the rectification side according to the rectification side structure of the converter station of the ultra-high voltage direct current transmission system:
P mc2 ＝ΔP c +ΔP D2 +ΔP 2 (10)
P m2 ＝P mc2 /4 (11)
in the formula, P mc2 For the input of mechanical power on the rectifying side, P m2 Inputting mechanical power, Δ P, for the rectifier-side converter D2 For rectifying side frequency droop active power, Δ P 2 Adjusting the corresponding power, Δ P, for the DC voltage c Is the transmission power offset value.
Let VSG converter input mechanical power be P m Then, there are:
wherein, P m Inputting mechanical power, P, to VSG converters m2 For inputting mechanical power, P, to the rectifier-side converter m1 Mechanical power is input to the inverter side converter.
Step 2, inputting mechanical power P by using the VSG converter obtained in the step 1 m VSG intersection is obtained by simulating the rotational inertia of the synchronous generatorAngular frequency w and electrical angle θ of the flow system;
2.1 input mechanical Power P Using the VSG converter obtained m And obtaining the primary approximate angular frequency w' of the VSG alternating current system:
wherein w' is the primary approximate angular frequency of the VSG AC system, J is the virtual moment of inertia of VSG, P m Mechanical power is input to the VSG inverter.
2.2 substitution of the nominal angular frequency w in equation (13) with the primary approximate angular frequency w' of the VSG AC System n And obtaining a secondary approximate angular frequency w 'of the VSG alternating current system, and taking the secondary approximate angular frequency w' as the angular frequency w of the VSG alternating current system:
where w is the angular frequency of the VSG ac system, and w ″ is the quadratic approximation angular frequency of the VSG ac system, the following are:
θ＝∫wdt (15)
in the formula, θ represents VSG ac system electrical angle.
3.1 according to the deviation between the actual value of the VSG output reactive power and the set value, obtaining a reactive deviation corresponding regulating voltage value through a reactive-voltage droop controller:
in the formula,. DELTA.V Q Adjusting the voltage value for the reactive deviation, D q Is the reactive-voltage droop coefficient, Q set For a given reactive power reference value, Q e The reactive power value is actually output.
3.2 adjusting the voltage value DeltaV corresponding to the obtained reactive deviation Q And the difference value delta V between the VSG output voltage rated value and the actual value, and the virtual excitation current is regulated by the virtual excitation regulator:
i f ＝H V (s)(ΔV+ΔV Q ) (17)
wherein i f For a virtual field current, H V (s) is the virtual excitation regulator transfer function, Δ V is the difference between the VSG output voltage nominal value and the actual value, i.e.:
ΔV＝V n -V (18)
in the formula, V n And V is the rated output voltage value of VSG, and the actual output voltage value of VSG.
3.3, the magnitude of the voltage e in the VSG is changed by regulating the obtained virtual exciting current, and the magnitude of the voltage at the output end of the VSG is indirectly regulated, wherein the corresponding relation is as follows:
E＝K f i f (19)
wherein E is a command voltage value, K f To the excitation coefficient, K f The proportional relationship of the virtual exciting current and the VSG output voltage is reflected.
Step 4, obtaining direct axis and quadrature axis command voltages E through coordinate transformation by using the command voltage value E obtained in the step 3 and the VSG alternating current system electrical angle theta obtained in the step 2 d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage and equivalent quadrature axis command voltage through the electric module
And
thereby controlling the VSG output signal.
4.1 utilize command voltage value E and VSG alternating current system electrical angle theta, obtain rectification side extreme transverter and contravariant side transverter three-phase command voltage:
in the formula, e a1 、e b1 、e c1 Three-phase command voltage, e, of rectifying-side and inverting-side pole-end converters 1 Is its vector value.
4.2 in order to suppress the fluctuation range of the direct-current voltage, in the control strategy of the rectification side, the three-phase command voltage of the extreme converter is lagged by 30 degrees to be used as the command voltage of the ground-end converter:
in the formula, e a2 、e b2 、e c2 Three-phase command voltage, e, of the rectifier side ground converter 2 For its vector value, E is the command voltage value.
4.3 coordinate-transforming the three-phase command voltage of each converter to obtain direct-axis command voltage and quadrature-axis command voltage e d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage and equivalent quadrature axis command voltage through the electric module
And
thereby controlling the VSG output signal.
And
the calculating method comprises the following steps:
in the formula (I), the compound is shown in the specification,
and
respectively an equivalent direct axis command voltage, an equivalent quadrature axis command voltage, e d And e q Respectively a direct axis command voltage, a quadrature axis command voltage, i d And i q Respectively the direct and quadrature components, R, of the VSG output current V And L V Respectively a virtual resistor and a virtual inductor.
The invention has the beneficial effects that: the synchronous generator has the voltage regulation and primary frequency modulation characteristics similar to those of the synchronous generator by simulating the rotational inertia and the damping characteristics of the synchronous generator, and on the basis, a no-difference frequency modulation and direct-current voltage control module is added, so that the running stability of a sending end alternating-current system and a receiving end alternating-current system is improved.
Drawings
FIG. 1 is a simplified structural schematic diagram of an extra-high voltage DC power transmission system according to the present invention;
fig. 2 is a schematic diagram of a virtual synchronous control system of the extra-high voltage direct-current transmission system.
Detailed Description
The invention will be further explained with reference to the drawings and the detailed description.
As shown in fig. 1, in the control system of the converter station of the extra-high voltage direct current transmission system based on the virtual synchronous machine, the virtual synchronous machine VSG1 at the rectification side is connected with a transmitting-end power grid through a switch, the virtual synchronous machine VSG2 at the inversion side is connected with a receiving-end power grid through a switch, and the double-end VSG can be connected with a load with a certain capacity.
As shown in fig. 2, the control system of the control structure further comprises a reactive power regulating module, an active power regulating module, a virtual rotor module and an electrical module; in the active regulation module, an inverter side frequency homodyne regulator is connected with an active power controller through a switch S1, and a rectification side frequency homodyne regulatorThe regulator is connected with a direct current voltage controller through a switch S3, and the direct current voltage controller is connected with an active power controller through a switch S2. When the system is used for simulating the rotational inertia, the damping characteristic and the frequency and voltage modulation characteristic of the synchronous generator, the switches S1, S2 and S3 are in an open state, a closed state and a disconnected state respectively, the active adjusting module of the virtual synchronous machine VSG2 at the inversion side obtains a corresponding power adjusting value through the active-frequency droop controller, and then the active power controller adjusts the mechanical power P input by the inverter side converter m1 The VSG2 active adjusting module of the virtual synchronous machine on the rectifying side respectively obtains corresponding power adjusting values through an active-frequency droop controller and a direct-current voltage controller, and then adjusts the input mechanical power P of a converter on the rectifying side through an active power controller m2 When the frequency needs to be adjusted in a non-differential mode, the switches S1, S2 and S3 are all in a closed state, wherein the active adjusting module of the virtual synchronous machine VSG2 at the inversion side respectively obtains corresponding power adjusting values through the active-frequency droop controller and the frequency non-differential adjuster, and then adjusts the mechanical power P input by the inverter side converter through the active power controller m1 The VSG2 active regulation module of the virtual synchronous machine at the rectification side respectively obtains corresponding power regulation values through an active-frequency droop controller, a direct-current voltage controller and a frequency differential-free regulator, and regulates the input mechanical power P of a converter at the rectification side through an active power controller m2 According to the input mechanical power P of the rectifier-side converter m2 And the mechanical power P input by the inverter side converter m1 Determining input mechanical power P of VSG converter m (ii) a Virtual rotor module utilization P m Obtaining the electrical angle theta of the VSG alternating current system; the reactive power regulation module obtains an instruction voltage E through a reactive power-voltage droop controller and a virtual excitation regulator, and finally, the electrical module obtains an equivalent direct axis instruction voltage and an equivalent quadrature axis instruction voltage by using the obtained VSG alternating current system electrical angle theta and the instruction voltage E
And
and then controls the VSG output signal.
The work process of the extra-high voltage direct current transmission system converter station control system based on the virtual synchronous machine is as follows:
1. simulating the rotational inertia J and the damping characteristic D of the synchronous generator according to the formulas (2) and (13) by a control method of combining an active power controller, an active-frequency droop controller and a frequency non-difference regulator on an inversion side and a control method of combining the active-frequency droop controller, the frequency non-difference regulator and a direct-current voltage controller on a rectification side, and inputting mechanical power P to the VSG converter m Regulated, VSG converter input mechanical power P m Determined by formula (6), formula (11), and formula (12);
2. inputting mechanical power P by using obtained VSG converter m Obtaining the angular frequency w and the electrical angle theta of the VSG alternating current system according to the formulas (14) and (15) through a virtual rotor link;
3. regulating the VSG output internal potential E by a control method combining a reactive-voltage droop controller and a virtual excitation regulator to obtain a command voltage value E;
4. obtaining direct-axis and quadrature-axis command voltages E through coordinate transformation by using the obtained command voltage value E and the VSG alternating current system electrical angle theta d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage and equivalent quadrature axis command voltage through electrical link
And
thereby controlling the VSG output signal.
Example 1
The active module of the inversion side VSG adopts an active power controller and an active-frequency droop controller, the active module of the rectification side VSG adopts a method of combining the active power controller, the active-frequency droop controller and a direct-current voltage controller, and the working process of the control system specifically comprises the following steps:
At this time, because the control system of the converter station of the ultra-high voltage direct current transmission system based on the virtual synchronous machine is in a primary frequency modulation state, at this time, the following steps are carried out:
ΔP 1 ＝0 (3)
step 2, utilizing the input VSG converter mechanical power P obtained in the step 1 m Obtaining the angular frequency w and the electrical angle theta of the VSG alternating-current system by simulating the rotational inertia of the synchronous generator;
step 4, obtaining direct axis command voltage and quadrature axis command voltage E through coordinate transformation by using the command voltage value E obtained in the step 3 and the VSG alternating current system electrical angle theta obtained in the step 2 d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage and equivalent quadrature axis command voltage through an electrical link
And
thereby controlling the VSG output signal.
Example 2
The active module of the inversion side VSG adopts a method of combining an active power controller, an active-frequency droop controller, a direct-current voltage controller and a frequency non-difference regulator, and the active module of the rectification side VSG adopts a method of combining an active power controller, an active-frequency droop controller, a direct-current voltage controller and a frequency non-difference regulator, wherein the control method specifically comprises the following steps:
At this time, because the converter station control system of the ultra-high voltage direct current transmission system based on the virtual synchronous machine is in a no-difference frequency modulation state, at this time, the following steps are carried out:
ΔP 1 ＝H w (s)(w n -w 1 ) (3)
step 2, converting the VSG obtained in the step 1 into the input mechanical power P m By simulating synchronous generatorsObtaining angular frequency w and an electrical angle theta of the VSG alternating current system through the rotational inertia;
step 4, obtaining direct axis command voltage and quadrature axis command voltage E through coordinate transformation by using the command voltage value E obtained in the step 3 and the VSG alternating current system electrical angle theta obtained in the step 2 d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage and equivalent quadrature axis command voltage through an electrical link
And
thereby controlling the VSG output signal.
The invention relates to an extra-high voltage direct current transmission system converter station control system based on a virtual synchronous machine, which comprises a rectification side virtual synchronous machine control system and an inversion side virtual synchronous machine control system, wherein the rectification side virtual synchronous machine VSG1 is connected with a transmitting end power grid G1, the inversion side virtual synchronous machine VSG2 is connected with a receiving end power grid G2, and the rectification side virtual synchronous machine VSG1 is used for adjusting input mechanical power to maintain system power balance by detecting direct current voltage change; the VSG2 copes with load variations by adjusting the output power. The rectification-side virtual synchronous machine VSG1 and the inversion-side virtual synchronous machine VSG2 also have the function of adjusting the frequencies of the respective ac systems.
As shown in fig. 2, when the load on the inverter side suddenly increases, the transmission power of the virtual synchronous machine VSG2 on the inverter side increases, and a certain power shortage occurs at this time, after the virtual rotor link, the frequency of the ac system on the inverter side slowly decreases, and meanwhile, due to the decrease of the frequency, under the effect of the damping link, the power shortage decreases, and the output power of the virtual synchronous machine VSG2 on the inverter side slowly increases. The direct-current line voltage U in the extra-high voltage direct-current transmission system is increased due to the VSG2 output power of the inversion side virtual synchronous machine dc Will reduceAt this time, the virtual synchronous machine VSG1 on the rectification side adjusts the dc voltage value by adjusting the input mechanical power, so that the dc voltage value is stabilized within a certain range. Therefore, the converter station control system of the extra-high voltage direct current transmission system based on the virtual synchronous machine can enhance the rotational inertia and damping characteristics of the extra-high voltage direct current transmission system, inhibit the rapid change of the system frequency and ensure the stability of the system frequency.
When the frequency is required to be adjusted without difference, the switches S1 and S3 are closed, and at the moment, the frequency non-difference adjuster of the virtual synchronous machine VSG1 at the rectifying side and the virtual synchronous machine VSG2 at the inverting side is accessed into the system, wherein the virtual synchronous machine VSG2 at the inverting side adjusts the output power of the virtual synchronous machine VSG2 according to the frequency difference value at the inverting side to maintain the stability of the frequency; the virtual synchronous machine VSG1 on the rectifying side adjusts input power according to the frequency difference value on the rectifying side to maintain the frequency stability, and plays a role in no-difference frequency modulation.
If the reactive load on the inversion side is suddenly increased, the virtual excitation current is adjusted to indirectly adjust the internal potential of the VSG output under the action of a reactive-voltage droop controller of the reactive power adjusting module and the virtual excitation adjuster, so that the stability of the output voltage is ensured.
Claims (7)
1. A virtual synchronous machine-based converter station control system of an extra-high voltage direct current transmission system is characterized in that: in the control system, a virtual synchronous machine VSG1 at a rectification side is connected with a transmitting end power grid, and a virtual synchronous machine VSG2 at an inversion side is connected with a receiving end power grid; the control system also comprises a reactive power regulation module, an active power regulation module, a virtual rotor module and an electric module; in an active power regulation module of a virtual synchronous machine VSG1 at a rectification side, an active-frequency droop controller obtains power delta P corresponding to frequency droop at the rectification side according to frequency change of an alternating current system at the rectification side D2 The frequency deviation-free regulator on the rectifying side is based on the frequency variation of the AC system on the rectifying side and the DC voltage reference value U dcref Obtaining the equivalent reference value of DC voltage
The DC voltage controller on the rectifying side is equivalent according to the DC voltageReference value
And the actual value U of the DC voltage dc Obtaining the corresponding power delta P of the DC voltage regulation 2 The active power controller at the rectification side utilizes the corresponding power delta P of the frequency droop at the rectification side D2 Regulating corresponding power delta P by DC voltage 2 And a transmission power offset value deltap c Adjusting the input mechanical power P at the rectification side mc2 (ii) a In an active power adjusting module of the VSG2 of the virtual synchronous machine at the inversion side, an active-frequency droop controller obtains corresponding power delta P of the frequency droop at the inversion side according to the frequency change of an alternating current system at the inversion side D1 The inverter side frequency differential-free regulator obtains the corresponding power delta P of the inverter side frequency differential-free regulation according to the frequency change of the inverter side alternating current system 1 The inverter side active power controller utilizes the inverter side frequency to droop the corresponding power delta P D1 The frequency of the inversion side is adjusted without difference to corresponding power delta P 1 And a transmission power offset value deltap c Adjusting the mechanical power P input to the inverter side mc1 (ii) a According to the mechanical power P input from the inversion side mc1 And the mechanical power P is input at the rectification side mc2 Determining input mechanical power P of VSG converter m And then the virtual rotor module inputs mechanical power P by using the VSG converter m Obtaining the electrical angle theta of the VSG alternating current system; in the reactive power regulation module, the reactive power-voltage droop controller obtains a reactive power deviation corresponding regulation voltage value delta V according to the voltage change of the VSG alternating current system Q Virtual excitation regulator corresponding to regulated voltage value DeltaV by using reactive deviation Q And the difference value delta V between the rated value and the actual value of the VSG output voltage to obtain a command voltage value E, and finally, the electrical module obtains an equivalent command voltage by using the obtained VSG alternating current system electrical angle theta and the command voltage value E
And
and then controls the VSG output signal.
2. The virtual synchronous machine-based extra-high voltage direct current transmission system converter station control system of claim 1, characterized in that: the control system works as follows:
step 1, according to the angular frequency change of a VSG alternating current system and the VSG output power change, the input mechanical power P of the VSG converter is adjusted on the inverting side through a control method of combining an active power controller, an active-frequency droop controller and a frequency non-difference regulator, and on the rectifying side through a control method of combining the active power controller, the active-frequency droop controller, the frequency non-difference regulator and a direct current voltage controller m ；
Step 2, inputting mechanical power P by using the VSG converter obtained in the step 1 m Obtaining the angular frequency w and the electrical angle theta of the VSG alternating current system by simulating the rotational inertia of the synchronous generator;
step 3, regulating the internal potential E output by the VSG by a control method combining a reactive-voltage droop controller and a virtual excitation regulator to obtain a command voltage value E;
step 4, obtaining the direct axis instruction voltage E through coordinate transformation by using the instruction voltage value E obtained in the step 3 and the VSG alternating current system electrical angle theta obtained in the step 2 d And quadrature axis command voltage e q (ii) a Using the resultant command voltage e d And e q Obtaining the equivalent direct axis command voltage through the electric module
And equivalent quadrature axis command voltage
And the VSG outputs a signal.
3. The virtual synchronous machine-based extra-high voltage direct current transmission system converter station control system according to claim 2, characterized in that: the control method of the inversion side combining the active power controller, the active-frequency droop controller and the frequency no-difference regulator in the step 1 comprises the following steps:
1.1 according to the transmission power reference value P of the extra-high voltage direct current transmission system in the extra-high voltage direct current transmission system converter station control system based on the virtual synchronous machine set And the actual transmission power P e Determining a transmission power offset value:
△P c ＝P set -P e (1)
in the formula,. DELTA.P c Is a transmission power offset value, P set For a given active power reference value, P e Actual output power of the extra-high voltage direct current transmission system is obtained;
1.2 according to the change of the angular frequency of an inverter side alternating current system, determining the power corresponding to the inverter side frequency droop and the power corresponding to the inverter side frequency no-difference regulation by simulating the droop relation of the active power and the frequency of a synchronous generator:
△P D1 ＝D p (w n -w 1 ) (2)
in the formula, H w (s) is the transfer function of the inverter-side frequency-differential-free regulator, w 1 For the angular frequency, w, of the AC system on the inverting side n At a nominal angular frequency, D p As active-frequency droop coefficient, Δ P D1 For inverting the power corresponding to the side frequency droop, Δ P 1 Corresponding power is adjusted for the inverter side frequency no difference, when only the primary frequency modulation characteristic of the synchronous generator needs to be simulated, the inverter side frequency no difference adjuster stops running, and the value is 0; when an inverter-side frequency non-differential regulator is used, Δ P 1 The value of (c) is adjusted according to the frequency deviation;
the active-frequency droop coefficient and the rotational inertia are in the following relationship:
D p ＝w 1 D (4)
in the formula, D is a VSG damping parameter;
1.3, determining the input mechanical power of an inversion side, and distributing the power of an inversion side series converter according to an inversion side structure of a converter station of the ultra-high voltage direct current transmission system:
P mc1 ＝△P c +△P D1 +△P 1 (5)
P m1 ＝P mc1 /4 (6)
in the formula, P mc1 For the mechanical power input on the inverting side, P m1 For input of mechanical power, Δ P, to the inverter-side converter c For transmission power offset value, Δ P D1 For inverting the power corresponding to the side frequency droop, Δ P 1 And adjusting the corresponding power for the frequency of the inversion side without difference.
4. An extra-high voltage direct current transmission system converter station control system based on a virtual synchronous machine according to claim 3, characterized in that in the step 1, a control method that an active power controller, an active-frequency droop controller, a frequency no-difference regulator and a direct current voltage controller are combined on a rectification side is adopted, and the steps are as follows:
1.4 according to the deviation value of the actual angular frequency and the rated angular frequency of the rectification side alternating current system, a corresponding power value delta P is obtained through a link of simulating the droop relation of the active power and the frequency of the synchronous generator D2 ：
ΔP D2 ＝D p (w n -w 2 ) (7)
In the formula,. DELTA.P D2 For rectifying the power corresponding to the side frequency droop, w n At nominal angular frequency, w 2 Is the angular frequency of the rectification side AC system;
1.5 obtaining the corresponding power delta P of the direct-current voltage regulation through a non-difference frequency regulation link and a direct-current voltage controller according to the deviation value of the actual angular frequency and the rated angular frequency of the rectification side alternating-current system 2 ：
Wherein, the first and the second end of the pipe are connected with each other,
in the formula,. DELTA.P 2 Regulating the corresponding power for the DC voltage, H dc (s) is the dc voltage controller transfer function,
is a DC voltage equivalent reference value, U dc Is the actual value of the DC voltage, U dcref Is a DC voltage reference value, K w-dc Is the proportional coefficient of the DC voltage and the frequency of the AC system on the rectification side, w n At nominal angular frequency, w 2 The angular frequency of the AC system at the rectification side;
1.6, determining the input mechanical power of the rectification side of the converter station of the extra-high voltage direct current transmission system, and distributing the power of the series converters on the rectification side according to the rectification side structure of the converter station of the extra-high voltage direct current transmission system:
P mc2 ＝ΔP c +ΔP D2 +ΔP 2 (10)
P m2 ＝P mc2 /4 (11)
in the formula, P mc2 For the rectified side input of mechanical power, P m2 For input of mechanical power, Δ P, to the rectifier-side converter D2 For rectifying the power corresponding to the side frequency droop, Δ P 2 Regulating the corresponding power, Δ P, for a DC voltage c Is a transmission power offset value;
let VSG converter input mechanical power be P m Then, there are:
wherein, P m Mechanical power is input to the VSG inverter.
5. The virtual synchronous machine-based extra-high voltage direct current transmission system converter station control system according to claim 2, wherein the method for obtaining the angular frequency w of the VSG alternating current system by simulating the moment of inertia of the synchronous generator in the step 2 is as follows:
2.1 input mechanical Power P with VSG converter obtained m And obtaining a primary approximate angular frequency w' of the VSG alternating current system:
wherein w' is the first order approximate angular frequency of VSG AC system, J is VSG virtual moment of inertia, P m Inputting mechanical power for the VSG converter;
2.2 substitution of the nominal angular frequency w in equation (13) with the primary approximate angular frequency w' of the VSG AC System n And obtaining a VSG alternating current system quadratic approximate angular frequency w', and taking the angular frequency w as the VSG alternating current system angular frequency w:
where w is the angular frequency of the VSG ac system, and w ″ is the quadratic approximate angular frequency of the VSG ac system, then:
θ＝∫wdt (15)
in the formula, θ represents a VSG ac system electrical angle.
6. The virtual synchronous machine-based extra-high voltage direct current transmission system converter station control system according to claim 2, wherein the method for indirectly adjusting the internal potential e of the VSG output by adjusting the virtual excitation current through the control method of combining the reactive-voltage droop controller and the virtual excitation regulator in step 3 is as follows:
3.1 according to the deviation between the actual value of the VSG output reactive power and the set value, obtaining a reactive deviation corresponding regulating voltage value through a reactive-voltage droop controller:
in the formula,. DELTA.V Q Is made ofWork deviation corresponds to the regulated voltage value, D q Is the reactive-voltage droop coefficient, Q set For a given reactive power reference value, Q e Outputting a reactive power value for the actual;
3.2 correspondingly adjusting the voltage value DeltaV by using the obtained reactive deviation Q And the difference value delta V between the VSG output voltage rated value and the actual value, and the virtual excitation current is regulated by a virtual excitation regulator:
i f ＝H V (s)(ΔV+ΔV Q ) (17)
wherein i f For virtual excitation current, H V (s) is the virtual excitation regulator transfer function, Δ V is the difference between the VSG output voltage nominal value and the actual value, i.e.:
△V＝V n -V (18)
in the formula, V n The voltage is a VSG rated output voltage value, and V is a VSG actual output voltage value;
3.3, the magnitude of the voltage e in the VSG is changed by adjusting the obtained virtual exciting current, and the magnitude of the voltage at the output end of the VSG is indirectly adjusted, wherein the corresponding relation is as follows:
E＝K f i f (19)
wherein E is a command voltage value, K f To the excitation coefficient, K f The proportional relation between the virtual exciting current and the command voltage value is reflected.
7. The virtual synchronous machine-based extra-high voltage direct current transmission system converter station control system according to claim 2, characterized in that: and 4, obtaining direct-axis command voltage and quadrature-axis command voltage E through coordinate transformation by using the command voltage value E obtained in the step 3 and the VSG alternating current system electrical angle theta obtained in the step 2 d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining equivalent direct axis command voltage through the electric module
And equivalent quadrature axis command voltage
And further controlling the VSG output signal as follows:
4.1 obtaining three-phase command voltage of the rectification side pole-end converter and the inversion side converter by using the command voltage value E and the VSG alternating current system electrical angle theta:
in the formula, e a1 、e b1 、e c1 Three-phase command voltage, e, of rectifying-side and inverting-side pole-end converters 1 Is its vector value;
4.2 in order to suppress the fluctuation range of the direct-current voltage, in the control strategy of the rectification side, the three-phase command voltage of the extreme converter is lagged by 30 degrees to be used as the command voltage of the ground-end converter:
in the formula, e a2 、e b2 、e c2 Three-phase command voltage, e, of the rectifier side ground converter 2 Is its vector value, E is the command voltage value;
4.3 coordinate-transforming the three-phase command voltage of each converter to obtain direct-axis command voltage and quadrature-axis command voltage e d And e q (ii) a Using the obtained direct axis command voltage and quadrature axis command voltage e d And e q Obtaining the equivalent direct axis command voltage through the electric module
And equivalent quadrature axis command voltage
Further controlling the VSG to output signals; equivalent direct axis command voltage
And equivalent direct axis command voltage
The calculating method comprises the following steps:
in the formula (I), the compound is shown in the specification,
and
respectively an equivalent direct axis command voltage, an equivalent quadrature axis command voltage, e d And e q Respectively a direct axis command voltage, a quadrature axis command voltage, i d And i q Respectively, the direct and quadrature components, R, of the VSG output current V And L V Respectively a virtual resistor and a virtual inductor.
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