CN113765122A - MMC converter valve control method and control system - Google Patents

MMC converter valve control method and control system Download PDF

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Publication number
CN113765122A
CN113765122A CN202110891759.3A CN202110891759A CN113765122A CN 113765122 A CN113765122 A CN 113765122A CN 202110891759 A CN202110891759 A CN 202110891759A CN 113765122 A CN113765122 A CN 113765122A
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value
voltage
actual
converter valve
increment
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Inventor
彭国平
孙文艺
周治国
张�浩
史奔
王红占
刘会民
李立冬
宋海军
徐元龙
白代兵
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Guangdong Anpu Electric Power Technology Co ltd
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Guangdong Anpu Electric Power Technology Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
    • 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
    • H02J3/36—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
    • 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • 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)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

A MMC converter valve control method and a control system thereof are provided, wherein the MMC converter valve control method comprises the following steps: calculating a direct-current voltage increment according to the actual frequency and the rated frequency, calculating an active given value according to the direct-current voltage rated value of the MMC converter valve, the direct-current voltage actual value of the MMC converter valve and the direct-current voltage increment, and further calculating an output voltage vector angle; calculating a voltage amplitude increment according to the actual output reactive power and a preset reactive power given value, and calculating an output voltage vector amplitude of the power grid side according to an alternating voltage modulus and the voltage amplitude increment; and carrying out space vector change on the vector angle and the vector amplitude of the output voltage to obtain the three-phase modulation wave. According to the invention, the working state of the power module in the MMC converter valve is adjusted according to the frequency change and the power change of the power grid side so as to adjust the output power and the frequency, thereby realizing the frequency support of the power grid without additionally increasing an energy storage device or carrying out variable pitch overspeed.

Description

MMC converter valve control method and control system
Technical Field
The invention belongs to the field of direct current transmission, and particularly relates to a control method and a control system for an MMC converter valve.
Background
With the development of the offshore wind power industry, the penetration rate of wind power generation to a power grid is continuously improved. In offshore wind power generation, if a traditional wind power plant alternating current grid-connected mode is adopted, due to the isolation effect of the wind power converter, the rotor motion of the wind turbine generator and the power grid frequency are decoupled, the equivalent inertia of the system is reduced, and the stability of the system frequency is seriously influenced.
Some research results show that the rapid change of the power grid frequency can be restrained to a certain extent by adding a virtual inertia control technology to the control of the fan converter. The virtual inertia control principle is shown as follows:
Figure BDA0003196178250000011
j is the rotational inertia of the virtual synchronous generator; omega is the electrical angular speed of the synchronous generator; theta is the electric gas phase angle of the synchronous generator; omega0Synchronizing the angular speed for the grid; t ismAnd TeMechanical and electromagnetic torques of the synchronous generator, respectively; d is a damping coefficient. Due to the existence of J and D, the converter has inertia to power and frequency.
However, the wind turbine generator has no extra power margin and does not have the primary frequency modulation capability on the power grid. In order to enable the wind turbine generator set to have primary frequency modulation capacity, the wind turbine generator set can be controlled to operate in an overspeed mode or change the pitch on the basis of virtual inertia control, and therefore a part of active power is reserved to be used as frequency modulation standby power of the system; or an energy storage device is additionally configured to be used as an active power standby of the fan unit, and the fan unit can be prevented from operating in a power reduction mode when participating in primary frequency modulation of the system.
However, both of the above two technical ways of implementing primary frequency modulation have limitations. For the virtual inertia control mode of overspeed variable pitch, although extra hardware equipment is not needed, the technical implementation cost is low, the fan unit needs to reduce power operation, the capacity of the fan unit participating in primary frequency modulation of a power grid is obtained at the cost of loss of generated energy, the utilization rate of the fan is reduced, and the economical efficiency is obviously reduced. Meanwhile, as the variable pitch system of the fan unit needs to frequently act to respond to the frequency change of the power grid, the fatigue accumulation of the wind wheel blade can be accelerated, and the service life of the blade is reduced. For a virtual inertia control mode based on an additional energy storage device, although the fan unit can still keep maximum power tracking, the generated energy is not lost, and the generating efficiency is improved, the energy storage device has the defects of higher equipment cost and large device size.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a control method of an MMC converter valve, which solves the problem that overspeed pitch changing or energy storage device increasing is needed when the frequency of the converter valve is modulated for the first time. The invention further provides an MMC converter valve control system.
The MMC converter valve control method according to the embodiment of the first aspect of the invention comprises the following steps:
calculating an output voltage vector angle: acquiring actual frequency and rated frequency of a power grid side, and calculating a direct-current voltage increment according to the actual frequency and the rated frequency; calculating an active given value according to a direct voltage rated value of the MMC converter valve, a direct voltage actual value of the MMC converter valve and the direct voltage increment; acquiring actual active power of a power grid side, and acquiring an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia and a preset virtual damping coefficient; calculating the vector angle of the output voltage according to the given angular velocity value and the synchronous angular velocity value of the power grid side;
calculating the vector amplitude of the output voltage: acquiring actual output reactive power of a power grid side, and calculating voltage amplitude increment according to the actual output reactive power and a preset reactive power given value; obtaining an alternating voltage modulus value of a power grid side, and calculating an output voltage vector amplitude value of the power grid side according to the alternating voltage modulus value and the voltage amplitude increment;
carrying out space vector change on the vector angle of the output voltage and the vector amplitude of the output voltage to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CAnd according to said three-phase modulated wave Vref_A、Vref_B、Vref_CAnd adjusting the MMC converter valve.
The MMC converter valve control method provided by the embodiment of the invention at least has the following technical effects: the output voltage vector angle and the output voltage vector amplitude comprise frequency information and amplitude information, and the three-phase modulation wave is generated by utilizing the output voltage vector angle and the output voltage vector amplitude, so that the control of the MMC converter valve can be realized by directly utilizing the three-phase modulation wave. According to the MMC converter valve control method provided by the embodiment of the invention, the working state of a power module in the MMC converter valve is adjusted according to the frequency change and the power change of the power grid side so as to adjust the output power and the frequency, thereby realizing the frequency support of the power grid without additionally increasing an energy storage device or carrying out variable pitch overspeed. In addition, the MMC converter valve control method provided by the embodiment of the invention can realize active power exchange with a power grid by controlling the direct-current voltage of the MMC converter valve, so that the MMC converter valve has certain primary frequency modulation capability when the frequency of the power grid fluctuates.
According to some embodiments of the invention, said calculating a dc voltage delta from said actual frequency and said nominal frequency comprises the steps of:
subtracting the actual frequency and the rated frequency to obtain a first direct current increment intermediate value;
performing hysteresis dead zone control on the first direct current increment intermediate value to obtain a second direct current increment intermediate value;
and multiplying the second direct current increment intermediate value by a preset first proportional coefficient to obtain the direct current voltage increment.
According to some embodiments of the present invention, after the hysteresis dead zone control is performed on the first dc increment intermediate value, the calculating a dc voltage increment according to the actual frequency and the rated frequency further includes:
and carrying out extreme value control on the second direct current increment intermediate value.
According to some embodiments of the present invention, the calculating an active set value according to the rated value of the dc voltage of the MMC converter valve, the actual value of the dc voltage of the MMC converter valve, and the dc voltage increment includes the following steps:
subtracting the rated value of the direct current voltage and the actual value of the direct current voltage to obtain a voltage difference value;
and adding the voltage difference value and the direct-current voltage increment, and outputting the voltage difference value and the direct-current voltage increment to a PI (proportional integral) regulating unit to obtain the active given value.
According to some embodiments of the present invention, the obtaining of the actual active power at the grid side and the obtaining of the given value of the angular velocity according to the actual active power, the given value of the active power, the preset virtual moment of inertia and the preset virtual damping coefficient include:
subtracting the actual active power and the active given value, and performing feedback regulation on the actual active power by utilizing an angular speed given value based on the virtual damping coefficient to obtain an intermediate regulating value;
and performing integral operation on the intermediate regulating value based on the virtual moment of inertia to obtain an angular speed given value.
According to some embodiments of the invention, said calculating said output voltage vector angle from said given value of angular velocity and said grid-side synchronous angular velocity value comprises the steps of:
adding the given angular velocity value and the synchronous angular velocity value to obtain an angular velocity correction parameter;
and performing integral operation on the angular velocity correction parameter to obtain the vector angle of the output voltage.
According to some embodiments of the present invention, the calculating the voltage amplitude increment according to the actual output reactive power and the preset reactive power given value comprises the following steps:
subtracting the actual output reactive power and the given reactive power value to obtain a first amplitude increment intermediate value;
performing hysteresis dead zone control on the first amplitude increment intermediate value to obtain a second amplitude increment intermediate value;
and multiplying the second amplitude increment intermediate value by a preset second proportionality coefficient to obtain the voltage amplitude increment.
According to some embodiments of the present invention, after the hysteresis dead zone control is performed on the first amplitude increment intermediate value, the step of calculating a voltage amplitude increment according to the actual output reactive power and a preset reactive power given value further includes:
and carrying out extremum control on the second amplitude increment intermediate value.
According to some embodiments of the invention, the space vector variation is performed on the output voltage vector angle and the output voltage vector magnitude to obtain a three-phase modulated wave Vref_A、Vref_B、Vref_CThe method comprises the following steps:
carrying out coordinate change on the output voltage vector angle and the output voltage vector amplitude to obtain a first modulation parameter and a second modulation parameter;
2/3 transformation is carried out on the first modulation parameter and the second modulation parameter to obtain the three-phase modulation wave Vref_A、Vref_B、Vref_C。
An MMC converter valve control system according to an embodiment of the second aspect of the present invention comprises:
the voltage vector angle calculation unit is used for obtaining the actual frequency and the rated frequency of the power grid side, calculating a direct current voltage increment according to the actual frequency and the rated frequency, calculating an active given value according to a direct current voltage rated value of an MMC converter valve, a direct current voltage actual value of the MMC converter valve and the direct current voltage increment, obtaining the actual active power of the power grid side, obtaining an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia and a preset virtual damping coefficient, and calculating the output voltage vector angle according to the angular velocity given value and a synchronous angular velocity value of the power grid side;
the voltage amplitude calculation unit is used for acquiring actual output reactive power of a power grid side, calculating a voltage amplitude increment according to the actual output reactive power and a preset reactive power given value, acquiring an alternating voltage modulus of the power grid side, and calculating an output voltage vector amplitude of the power grid side according to the alternating voltage modulus and the voltage amplitude increment;
a modulated wave generating unit for performing space vector variation on the output voltage vector angle and the output voltage vector amplitude to obtain a three-phase modulated wave Vref_A、Vref_B、Vref_CAnd according to said three-phase modulated wave Vref_A、Vref_B、Vref_CAnd adjusting the MMC converter valve.
The MMC converter valve control system provided by the embodiment of the invention at least has the following technical effects: the output voltage vector angle and the output voltage vector amplitude comprise frequency information and amplitude information, and the three-phase modulation wave is generated by utilizing the output voltage vector angle and the output voltage vector amplitude, so that the control of the MMC converter valve can be realized by directly utilizing the three-phase modulation wave. The MMC converter valve control system provided by the embodiment of the invention adjusts the working state of a power module in the MMC converter valve according to the frequency change and the power change of the power grid side so as to adjust the output power and the frequency, thereby realizing the frequency support of the power grid without additionally increasing an energy storage device or carrying out variable pitch overspeed. In addition, the MMC converter valve control system provided by the embodiment of the invention can realize active power exchange with a power grid by controlling the direct-current voltage of the MMC converter valve, so that the MMC converter valve control system has certain primary frequency modulation capability when the frequency of the power grid fluctuates.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a prior art MMC converter valve based DC power transmission system;
fig. 2 is a block diagram of a converter station of the dc transmission system of fig. 1;
fig. 3 is a block diagram of a sub-converter of the substation of fig. 2;
fig. 4 is a block diagram of an onshore converter platform of the dc transmission system of fig. 1;
FIG. 5 is a flow chart diagram of an MMC converter valve control method of an embodiment of the present invention;
FIG. 6 is a method flow diagram of an MMC converter valve control method of an embodiment of the present invention;
FIG. 7 is a block diagram of the MMC converter valve control system of an embodiment of the present invention.
Reference numerals;
converter station 100, rectifier transformer 110, converter 120, subconverter 121, smoothing reactor 122, function selection switch 123, alternating current filter 130, bypass switch 140,
A land converter platform 200, an MMC converter valve 210, a bridge arm smoothing reactor 211, a land transformer 220,
An ac auxiliary power system 300.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, if there are first, second, third, fourth, etc. described only for the purpose of distinguishing technical features, they are not to be interpreted as indicating or implying relative importance or implying number of indicated technical features or implying precedence of indicated technical features.
In the description of the present invention, unless otherwise explicitly defined, terms such as arrangement, connection and the like should be broadly construed, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the detailed contents of the technical solutions.
To better describe the MMC converter valve control method of an embodiment of the present invention, a DC power transmission system for performing the MMC converter valve control method of an embodiment of the present invention is presented herein.
As shown in fig. 1, the dc transmission system includes an onshore converter platform 200 and a plurality of converter stations 100.
Referring to fig. 1 and 2, each converter station 100 includes a rectifier transformer 110, a converter 120; the primary side of the rectifier transformer 110 is used for connecting an external power generation field, and the secondary side is connected with the input end of the converter 120; the converter 120 adopts a diode rectification structure. The rectifier transformer 110 comprises a plurality of groups of secondary sides, the converter 120 comprises a plurality of sub-converters 121 with the number consistent with that of the secondary sides of the rectifier transformer 110, and the secondary sides of the rectifier transformer 110 are connected with the input ends of the sub-converters 121 in a one-to-one correspondence manner; the output ends of the adjacent sub-converters 121 are sequentially connected to form a sub-converter series structure, and two output ends of the sub-converter series structure are respectively used as a positive voltage output end and a negative voltage output end of the converter 120.
The positive voltage output end and the negative voltage output end of the converter 120 are both connected with a smoothing reactor 122 and a function selection switch 123, and the function selection switch 123 is used for selecting the connection, disconnection or grounding of the circuit.
Referring to fig. 3, each of the plurality of sub-converters 121 adopts a three-phase bridge type six-pulse rectification structure, each sub-converter 121 includes an a-phase module, a B-phase module, and a C-phase module connected in parallel, each phase module includes a first diode valve string and a second diode valve string connected in series, and a common connection end of the first diode valve string and the second diode valve string is used for connecting an external ac power supply; the first diode valve string and the second diode valve string are both composed of a plurality of diode valves which are connected in parallel and/or in series. The specific number and connection of the diode valves is determined by the voltage and the current (the number in series depends on the voltage present and the number in parallel depends on the current present).
The diode valve in each phase module adopts the same structure and specifically comprises a first capacitor, a first resistor, a second resistor and a first diode; the first capacitor is connected with the cathode of the first diode in parallel after being connected with the first resistor in series, and the second resistor is connected with the first diode in parallel.
Referring to fig. 1 and 2, an input terminal of the rectifier transformer 110 is provided with an ac filter 130. The output end of the converter 120 is connected in parallel with the bypass switch 140, when a fault occurs, the bypass switch 140 is closed, the fault loop bypass can be communicated, and the function selection switch 123 is matched to play a better protection and fault troubleshooting role.
The input end of the converter station 100 is connected with an external power generation field, and the output end is connected with the input end of the onshore converter platform 200; the output of the onshore converter platform 200 is connected to the external ac grid and the onshore converter platform 200 is used for dc to ac conversion. The outputs of the plurality of converter stations 100 are serially connected in sequence and then connected to the onshore converter platform 200.
Referring to FIG. 4, the onshore converter platform 200 includes MMC converter valves 210, an onshore transformer 220; the input end of the MMC converter valve 210 is connected with the output end of the converter station 100, and the output end is connected with the input end of the land transformer 220; the output of the land transformer 220 is connected to an external ac power grid. The MMC converter valve 210 has an MMC structure, the MMC converter valve 210 includes 6 bridge arms, the 6 bridge arms include a plurality of power modules connected in series in sequence, and the plurality of power modules are all used for converting direct current to alternating current. 6 bridge arms of the MMC converter valve 210 are connected with a CT transformer and a bridge arm smoothing reactor 211.
Referring to fig. 1, in the power transmission system, an ac auxiliary power system 300 is further provided, an input end of the ac auxiliary power system 300 is connected to an output end of the onshore converter platform 200 or an external power source, and an output end is connected to an input end of the converter station 100 through a power distribution device; the alternating current auxiliary power supply system 300 is used for carrying out auxiliary power supply on an offshore wind farm; the ac auxiliary power supply system 300 is composed of an offshore ac cable and an auxiliary power supply device on the land side; the auxiliary power supply device is formed by sequentially connecting a first alternating current circuit breaker, a transformation device and a second alternating current circuit breaker in series, and the transformation device is used for voltage regulation.
An MMC converter valve control method according to an embodiment of the first aspect of the invention is described below with reference to fig. 1 to 7.
The MMC converter valve control method provided by the embodiment of the invention comprises the following steps of:
calculating an output voltage vector angle: obtaining the actual frequency F on the network siderefAnd rated frequency F0According to the actual frequency FrefAnd rated frequency F0Calculating a direct current voltage increment; DC voltage rating E according to MMC converter valve 210dcActual value U of direct-current voltage of MMC converter valve 210dcCalculating an active given value by the direct current voltage increment; obtaining the actual active power P of the power grid sidegObtaining an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia J and a preset virtual damping coefficient D; according to the given value of the angular speed and the synchronous angular speed value omega of the power grid side0Calculating an output voltage vector angle theta;
calculating the vector amplitude of the output voltage: obtaining actual output reactive power Q of power grid siderefAccording to the actual output reactive power QrefAnd a preset given value Q of reactive power0Calculating voltage amplitude increment; obtaining AC voltage modulus U of power grid side0According to the modulus U of the AC voltage0And voltageCalculating the output voltage vector amplitude U of the power grid side by the amplitude incrementm；
For output voltage vector angle theta and output voltage vector amplitude UmSpace vector variation is carried out to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CAnd according to a three-phase modulated wave Vref_A、Vref_B、Vref_CThe MMC converter valve 210 is adjusted.
Referring to fig. 1 to 6, when the dc transmission system is in operation, ac power generated by the offshore wind farm is rectified into dc power by the offshore converter station 100, and the active power is transmitted to the onshore converter station 200 by the high-voltage dc sea cable in a dc transmission manner. The MMC converter valve 210 inverts the dc power into ac power and transmits the active power to the onshore grid.
When the onshore power grid fluctuates severely, the actual frequency F of the power gridrefAnd rated frequency F0When the difference value exceeds the control range of the hysteresis dead zone, the actual frequency F is usedrefAnd rated frequency F0The difference in (c) generates a dc voltage delta. The DC voltage rating E of the MMC converter valve 210 is then obtaineddcAnd the actual value U of the DC voltage of the MMC converter valve 210dcAnd using a DC voltage rating EdcAnd the actual value U of the DC voltagedcAnd correcting the direct-current voltage increment, and further obtaining an active given value through PI operation. Then, based on the virtual moment of inertia J and the virtual damping coefficient D, the given value of the active power and the actual active power P are measuredgPerforming active-frequency control to obtain given angular velocity value, given angular velocity value and synchronous angular velocity value omega0After the addition operation is carried out, the vector angle theta of the output voltage can be obtained through the integral operation. It should be noted that the synchronous angular velocity value ω0Can be directly dependent on the rated frequency F of the power grid0The calculation yields, for example: rated frequency F050Hz, synchronous angular velocity value omega0Then an angular velocity value corresponding to 50 Hz.
Meanwhile, according to the actual output reactive power QrefAnd given value of reactive power Q0The voltage amplitude increment can be obtained, and further the AC voltage modulus value U can be obtained0And electricityObtaining the vector amplitude U of the output voltage of the power grid side by the voltage amplitude incrementm. Output voltage vector angle theta and output voltage vector amplitude UmThe amplitude, frequency and other information required by controlling the MMC converter valve 210 are included, and then the output voltage vector angle theta and the output voltage vector amplitude U are utilizedmGenerating a three-phase modulated wave Vref_A、Vref_B、Vref_CCan use three-phase modulated wave Vref_A、Vref_B、Vref_CThe control of the power module in the MMC converter valve 210 is completed. It should be noted that the vector angle θ of the output voltage depends on the actual frequency FrefAnd rated frequency F0The difference value of the direct current voltage control link is adjusted, so that the frequency support of the power grid can be realized when the active power output of the direct current voltage control link is changed by using the MMC converter valve 210 control method of the embodiment of the invention.
It should be noted that, in the MMC converter valve 210 control method according to the embodiment of the present invention, there is no current loop, and the output voltage vector magnitude UmThe MMC converter valve 210 may be controlled to externally present as a voltage amplitude of the voltage source, and the existence of the virtual moment of inertia J and the virtual damping coefficient D may make the MMC converter valve 210 have inertia for power and frequency.
According to the MMC converter valve control method provided by the embodiment of the invention, the vector angle theta of the output voltage and the vector amplitude U of the output voltagemIncluding frequency information and amplitude information, by using an output voltage vector angle theta and an output voltage vector amplitude UmAnd generating a three-phase modulation wave, and directly utilizing the three-phase modulation wave to realize the control of the MMC converter valve 210. According to the MMC converter valve control method provided by the embodiment of the invention, the working state of the power module in the MMC converter valve 210 is adjusted according to the frequency change and the power change of the power grid side so as to adjust the output power and the frequency, so that the frequency support of the power grid is realized, an additional energy storage device is not required, and variable pitch overspeed is not required. In addition, the MMC converter valve 210 control method of the embodiment of the present invention can realize active power exchange with the power grid by controlling the dc voltage of the MMC converter valve 210, so that the power grid has a certain primary frequency modulation capability when frequency fluctuation occurs in the power grid.
In some embodiments of the present invention, calculating the dc voltage delta based on the actual frequency and the nominal frequency comprises the steps of:
for actual frequency FrefAnd rated frequency F0Carrying out subtraction operation to obtain a first direct current increment intermediate value;
performing hysteresis dead zone control on the first direct current increment intermediate value to obtain a second direct current increment intermediate value;
the second direct current increment intermediate value and a preset first scale factor K are comparedbAnd performing multiplication operation to obtain the direct-current voltage increment.
The actual frequency F can be prevented by adding hysteresis dead zone controlrefAnd rated frequency F0When the difference is small, the direct current voltage increment needing to be adjusted is output. Specifically, a hysteresis dead zone range is set when the actual frequency FrefAnd rated frequency F0When the difference value of (d) is smaller than the hysteresis dead zone range, the increment of the output direct current voltage is directly made to be 0. In addition, the first scaling factor K is statedbWhen the whole direct current transmission system is determined, the determination can be carried out.
In some embodiments of the invention, hysteresis dead band control is performed on the first DC delta intermediate value according to the actual frequency FrefAnd rated frequency F0Calculating the direct current voltage increment, and further comprising the following steps:
and carrying out extreme value control on the second direct current increment intermediate value.
At the actual frequency FrefAnd rated frequency F0If the generated direct-current voltage increment is too large when the difference value is too large, if the direct-current voltage increment is used for generating a subsequent output voltage vector angle theta and further synthesizing a three-phase modulation wave, a fault occurs because a wind turbine generator set in a power generation field does not have enough power allowance for adjustment. After the extreme value control is set, the maximum value of the output direct current voltage increment can be limited, so that the regulation can be normally finished. For example: for a 50Hz grid, hysteresis dead band control may be performed if the frequency ripple does not exceed 0.1Hz, with a DC voltage delta output of 0, if the frequency ripple exceeds 0.1Hz but does not exceed 0.1HzIf the frequency fluctuation exceeds 1Hz, the direct current voltage increment can be normally output, if the frequency fluctuation exceeds 1Hz, the extreme value control needs to be executed, and after the extreme value control is executed, even if the actual frequency F isrefAnd rated frequency F0If the difference exceeds 1Hz, the output is also increased by a dc voltage corresponding to 1 Hz.
In some embodiments of the present invention, the DC voltage rating E is based on the MMC converter valve 210dcActual value U of direct-current voltage of MMC converter valve 210dcAnd calculating an active given value by the direct current voltage increment, and the method comprises the following steps:
for rated value E of DC voltagedcAnd the actual value U of the DC voltagedcCarrying out subtraction operation to obtain a voltage difference value;
and adding the voltage difference value and the direct-current voltage increment, and outputting the sum to a PI (proportional integral) regulating unit to obtain an active given value.
Calculating a DC voltage nominal value EdcAnd the actual value U of the DC voltagedcThe voltage difference value enables the adjustment to be needed in normal control, and then the final active given value can be obtained through addition operation with the direct current voltage increment and then through the Pl adjusting unit.
In some embodiments of the invention, the actual active power on the network side is obtained, based on the actual active power PgThe method comprises the following steps of obtaining an angular velocity given value by using an active given value, a preset virtual moment of inertia J and a preset virtual damping coefficient D:
to actual active power PgSubtracting the active given value, and performing feedback regulation on the actual active power by utilizing the angular speed given value based on the virtual damping coefficient to obtain an intermediate regulation value;
and performing integral operation on the intermediate regulating value based on the virtual moment of inertia J to obtain an angular speed given value.
Actual active power PgThe difference value between the active given value and the active given value is an intermediate regulating value, and the intermediate regulating value is subjected to integral operation based on the virtual moment of inertia J to obtain the angular speed given valueBefore the integral operation is carried out on the intermediate regulation value, negative feedback regulation is carried out by utilizing the virtual damping coefficient D, so that the stability of the output angular speed given value is ensured.
In some embodiments of the invention, the grid-side synchronous angular velocity value ω is determined from the angular velocity setpoint and the grid-side synchronous angular velocity value ω0Calculating an output voltage vector angle theta, comprising the following steps:
given value of angular velocity and synchronous angular velocity value omega0Performing addition operation to obtain an angular velocity correction parameter;
and performing integral operation on the angular velocity correction parameter to obtain an output voltage vector angle theta.
After obtaining the given value of angular velocity, the angular velocity value omega is synchronized0The angular velocity value which needs to be adjusted finally can be obtained by adding operation, and the vector angle theta of the output voltage which needs to be adjusted finally can be obtained by integrating the angular velocity value.
In some embodiments of the invention, the reactive power Q is output according to the actual outputrefAnd a preset given value Q of reactive power0Calculating the voltage amplitude increment, comprising the following steps:
to actual output reactive power QrefAnd given value of reactive power Q0Carrying out subtraction operation to obtain a first amplitude increment intermediate value;
performing hysteresis dead zone control on the first amplitude increment intermediate value to obtain a second amplitude increment intermediate value;
and multiplying the second amplitude increment intermediate value by a preset second proportionality coefficient to obtain the voltage amplitude increment.
By adding hysteresis dead zone control, the reactive power Q can be prevented from being actually outputrefAnd when the voltage fluctuates in a small range, the voltage amplitude increment needing to be adjusted is output. Specifically, a hysteresis dead zone range is set, and when the reactive power Q is actually outputrefWhen the fluctuation is smaller than the hysteresis dead zone range, the output voltage amplitude increment is directly output to a fixed value. In addition, it should be noted that the second proportionality coefficient KpWhen the whole direct current transmission system is determined, the determination can be carried out.
In some embodiments of the invention, the dead zone control is performed according to the actual output reactive power Q after the hysteresis dead zone control is performed on the first amplitude increment intermediate valuerefAnd a preset given value Q of reactive power0Calculating the voltage amplitude increment, and further comprising the following steps:
and carrying out extremum control on the second amplitude increment intermediate value.
At actual output reactive power QrefWhen the fluctuation is too large, the generated voltage amplitude increment is also too large, and at the moment, if the voltage amplitude increment is utilized to generate the subsequent output voltage vector amplitude UmAnd the wind turbine generator set in the power generation field does not have enough power allowance for adjustment, so that a fault occurs, and after the extreme value control is set, the maximum value of the output voltage amplitude increment can be controlled, so that the adjustment can be normally finished.
In some embodiments of the invention, the vector angle theta and the vector magnitude U are applied to the output voltagemSpace vector variation is carried out to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CThe method comprises the following steps:
for output voltage vector angle theta and output voltage vector amplitude UmCarrying out coordinate change to obtain a first modulation parameter and a second modulation parameter;
2/3 transformation is carried out on the first modulation parameter and the second modulation parameter to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_C。
Output voltage vector angle theta and output voltage vector amplitude UmIs the main basis for controlling the operation of the power module in the MMC converter valve 210, wherein the vector angle theta of the output voltage and the vector amplitude U of the output voltage are measuredmCoordinate change is carried out to obtain alpha and beta values of the output voltage of the power grid side under a two-phase static coordinate system, and then 2/3 transformation is carried out on the alpha and beta values to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CFurther, V can be usedref_A、Vref_B、Vref_CTo control the working state of the power module in each phase of the MMC converter valve 210 to achieve the purpose of adjusting the output powerRate, frequency effects.
An MMC converter valve control system according to an embodiment of the second aspect of the present invention comprises: the device comprises a voltage vector angle calculation unit, a voltage amplitude calculation unit and a modulation wave generation unit.
The voltage vector angle calculation unit is used for obtaining the actual frequency and the rated frequency of the power grid side, calculating a direct-current voltage increment according to the actual frequency and the rated frequency, calculating an active given value according to the direct-current voltage rated value of the MMC converter valve 210, the direct-current voltage actual value of the MMC converter valve 210 and the direct-current voltage increment, obtaining the actual active power of the power grid side, obtaining an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia and a preset virtual damping coefficient, and calculating an output voltage vector angle theta according to the angular velocity given value and the synchronous angular velocity value of the power grid side;
a voltage amplitude calculation unit for obtaining actual output reactive power Q of the power grid siderefAccording to the actual output reactive power QrefAnd a preset given value Q of reactive power0Calculating voltage amplitude increment, acquiring alternating voltage modulus at the power grid side, and calculating output voltage vector amplitude U at the power grid side according to the alternating voltage modulus and the voltage amplitude incrementm；
A modulated wave generation unit for generating an output voltage vector angle theta and an output voltage vector amplitude UmSpace vector variation is carried out to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CAnd according to a three-phase modulated wave Vref_A、Vref_B、Vref_CThe MMC converter valve 210 is adjusted.
Referring to fig. 1 to 7, when the dc transmission system is in operation, ac power generated by the offshore wind farm is rectified into dc power by the offshore converter station 100, and the active power is transmitted to the onshore converter station 200 by the high-voltage dc sea cable in a dc transmission manner. The MMC converter valve 210 inverts the dc power into ac power and transmits the active power to the onshore grid.
When the onshore power grid fluctuates severely, the actual frequency F of the power gridrefAnd rated frequency F0Difference value exceeding hysteresis loopIn the dead zone control range, the actual frequency F is usedrefAnd rated frequency F0The difference in (c) generates a dc voltage delta. The DC voltage rating E of the MMC converter valve 210 is then obtaineddcAnd the actual value U of the DC voltage of the MMC converter valve 210dcAnd using a DC voltage rating EdcAnd the actual value U of the DC voltagedcAnd correcting the direct-current voltage increment, and further obtaining an active given value through PI operation. Then, based on the virtual moment of inertia J and the virtual damping coefficient D, the given value of the active power and the actual active power P are measuredgPerforming active-frequency control to obtain given angular velocity value, given angular velocity value and synchronous angular velocity value omega0After addition operation, an output voltage vector angle theta can be obtained after integration. It should be noted that the synchronous angular velocity value ω0Can be directly dependent on the rated frequency F of the power grid0The calculation yields, for example: rated frequency F050Hz, synchronous angular velocity value omega0Then an angular velocity value corresponding to 50 Hz.
Meanwhile, according to the actual output reactive power QrefAnd given value of reactive power Q0The voltage amplitude increment can be obtained, and further the AC voltage modulus value U can be obtained0Obtaining the output voltage vector amplitude U of the power grid side by the sum voltage amplitude incrementm. Output voltage vector angle theta and output voltage vector amplitude UmThe amplitude, frequency and other information required by controlling the MMC converter valve 210 are included, and then the output voltage vector angle theta and the output voltage vector amplitude U are utilizedmGenerating a three-phase modulated wave Vref_A、Vref_B、Vref_CCan use three-phase modulated wave Vref_A、Vref_B、Vref_CThe control of the power module in the MMC converter valve 210 is completed. It should be noted that the vector angle θ of the output voltage depends on the actual frequency FrefAnd rated frequency F0The difference value of the direct current voltage control link is adjusted, so that the frequency support of the power grid can be realized when the active power output of the direct current voltage control link is changed by using the MMC converter valve 210 control method of the embodiment of the invention.
It should be noted that the MMC converter valve control method of the embodiment of the inventionIn the method, no current loop exists, and the vector amplitude U of the output voltagemThe MMC converter valve 210 may be controlled to externally present as a voltage amplitude of the voltage source, and the existence of the virtual moment of inertia J and the virtual damping coefficient D may make the MMC converter valve 210 have inertia for power and frequency.
According to the MMC converter valve control system provided by the embodiment of the invention, the vector angle theta of the output voltage and the vector amplitude U of the output voltagemIncluding frequency information and amplitude information, by using an output voltage vector angle theta and an output voltage vector amplitude UmAnd generating a three-phase modulation wave, and directly utilizing the three-phase modulation wave to realize the control of the MMC converter valve 210. The MMC converter valve control system of the embodiment of the invention adjusts the working state of the power module in the MMC converter valve 210 according to the frequency change and the power change of the power grid side so as to adjust the output power and the frequency, thereby realizing the frequency support of the power grid without additionally increasing an energy storage device or carrying out variable pitch overspeed. In addition, the MMC converter valve 210 control system of the embodiment of the present invention can realize active power exchange with the power grid by controlling the dc voltage of the MMC converter valve 210, so that the power grid has a certain primary frequency modulation capability when frequency fluctuation occurs in the power grid.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although the embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to the embodiments, and those skilled in the art will understand that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims (10)

1. The MMC converter valve control method is characterized by comprising the following steps of:
calculating an output voltage vector angle: acquiring actual frequency and rated frequency of a power grid side, and calculating a direct-current voltage increment according to the actual frequency and the rated frequency; calculating an active given value according to a direct voltage rated value of the MMC converter valve, a direct voltage actual value of the MMC converter valve and the direct voltage increment; acquiring actual active power of a power grid side, and acquiring an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia and a preset virtual damping coefficient; calculating the vector angle of the output voltage according to the given angular velocity value and the synchronous angular velocity value of the power grid side;
calculating the vector amplitude of the output voltage: acquiring actual output reactive power of a power grid side, and calculating voltage amplitude increment according to the actual output reactive power and a preset reactive power given value; obtaining an alternating voltage modulus value of a power grid side, and calculating an output voltage vector amplitude value of the power grid side according to the alternating voltage modulus value and the voltage amplitude increment;
carrying out space vector change on the vector angle of the output voltage and the vector amplitude of the output voltage to obtain a three-phase modulation wave Vref_A、Vref_B、Vref_CAnd according to said three-phase modulated wave Vref_A、Vref_B、Vref_CAnd adjusting the MMC converter valve.
2. The MMC converter valve control method of claim 1, wherein said calculating a DC voltage delta from said actual frequency and said nominal frequency comprises the steps of:
subtracting the actual frequency and the rated frequency to obtain a first direct current increment intermediate value;
performing hysteresis dead zone control on the first direct current increment intermediate value to obtain a second direct current increment intermediate value;
and multiplying the second direct current increment intermediate value by a preset first proportional coefficient to obtain the direct current voltage increment.
3. The MMC converter valve control method of claim 2, wherein said calculating a DC voltage delta from said actual frequency and said nominal frequency after said hysteresis dead band control of said first DC delta intermediate value, further comprises the steps of:
and carrying out extreme value control on the second direct current increment intermediate value.
4. The MMC converter valve control method of claim 1, wherein said calculating an active set value based on a DC voltage rating of the MMC converter valve, a DC voltage actual value of the MMC converter valve, and said DC voltage delta comprises the steps of:
subtracting the rated value of the direct current voltage and the actual value of the direct current voltage to obtain a voltage difference value;
and adding the voltage difference value and the direct-current voltage increment, and outputting the voltage difference value and the direct-current voltage increment to a PI (proportional integral) regulating unit to obtain the active given value.
5. The MMC converter valve control method of claim 1, wherein the obtaining of the actual active power at the grid side, the obtaining of the angular velocity set value according to the actual active power, the active set value, a preset virtual moment of inertia and a preset virtual damping coefficient, comprises the steps of:
subtracting the actual active power and the active given value, and performing feedback regulation on the actual active power by utilizing an angular speed given value based on the virtual damping coefficient to obtain an intermediate regulating value;
and performing integral operation on the intermediate regulating value based on the virtual moment of inertia to obtain an angular speed given value.
6. The MMC converter valve control method of claim 1, wherein said calculating said output voltage vector angle based on said angular velocity set point and said grid-side synchronous angular velocity value comprises the steps of:
adding the given angular velocity value and the synchronous angular velocity value to obtain an angular velocity correction parameter;
and performing integral operation on the angular velocity correction parameter to obtain the vector angle of the output voltage.
7. The MMC converter valve control method of claim 1, wherein calculating a voltage magnitude delta based on the actual output reactive power and a preset reactive power setpoint comprises:
subtracting the actual output reactive power and the given reactive power value to obtain a first amplitude increment intermediate value;
performing hysteresis dead zone control on the first amplitude increment intermediate value to obtain a second amplitude increment intermediate value;
and multiplying the second amplitude increment intermediate value by a preset second proportionality coefficient to obtain the voltage amplitude increment.
8. The MMC converter valve control method of claim 7, wherein after said hysteresis dead band control of said first magnitude delta intermediate value, said calculating a voltage magnitude delta from said actual output reactive power and a predetermined reactive power setpoint, further comprises the steps of:
and carrying out extremum control on the second amplitude increment intermediate value.
9. The MMC converter valve control method of claim 7, wherein the space vector variation of the output voltage vector angle and the output voltage vector magnitude to obtain a three-phase modulated wave Vref_A、Vref_B、Vref_CThe method comprises the following steps:
carrying out coordinate change on the output voltage vector angle and the output voltage vector amplitude to obtain a first modulation parameter and a second modulation parameter;
2/3 transformation is carried out on the first modulation parameter and the second modulation parameter to obtain the three-phase modulation wave Vref_A、Vref_B、Vref_C。
10. An MMC converter valve control system, characterized by comprising:
the voltage vector angle calculation unit is used for obtaining the actual frequency and the rated frequency of the power grid side, calculating a direct current voltage increment according to the actual frequency and the rated frequency, calculating an active given value according to a direct current voltage rated value of an MMC converter valve, a direct current voltage actual value of the MMC converter valve and the direct current voltage increment, obtaining the actual active power of the power grid side, obtaining an angular velocity given value according to the actual active power, the active given value, a preset virtual moment of inertia and a preset virtual damping coefficient, and calculating the output voltage vector angle according to the angular velocity given value and a synchronous angular velocity value of the power grid side;
the voltage amplitude calculation unit is used for acquiring actual output reactive power of a power grid side, calculating a voltage amplitude increment according to the actual output reactive power and a preset reactive power given value, acquiring an alternating voltage modulus of the power grid side, and calculating an output voltage vector amplitude of the power grid side according to the alternating voltage modulus and the voltage amplitude increment;
a modulated wave generating unit for performing space vector variation on the output voltage vector angle and the output voltage vector amplitude to obtain a three-phase modulated wave Vref_A、Vref_B、Vref_CAnd according to said three-phase modulated wave Vref_A、Vref_B、Vref_CAnd adjusting the MMC converter valve.
CN202110891759.3A 2021-08-04 2021-08-04 MMC converter valve control method and control system Pending CN113765122A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220224100A1 (en) * 2021-01-12 2022-07-14 Tianjin University Adaptive fault clearing scheme for mmc vsc-hvdc grid based on source-grid coordination

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220224100A1 (en) * 2021-01-12 2022-07-14 Tianjin University Adaptive fault clearing scheme for mmc vsc-hvdc grid based on source-grid coordination
US11444450B2 (en) * 2021-01-12 2022-09-13 Tianjin University Adaptive fault clearing scheme for MMC VSC-HVDC grid based on source-grid coordination

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