CN111668866A - Low voltage ride through control method based on rotation speed and reactive power joint optimization control - Google Patents

Low voltage ride through control method based on rotation speed and reactive power joint optimization control Download PDF

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CN111668866A
CN111668866A CN201910165041.9A CN201910165041A CN111668866A CN 111668866 A CN111668866 A CN 111668866A CN 201910165041 A CN201910165041 A CN 201910165041A CN 111668866 A CN111668866 A CN 111668866A
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grid
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wind turbine
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赵天乐
杨敏坤
都洪基
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Nanjing University of Science and Technology
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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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention discloses a low voltage ride through control method based on rotation speed and reactive power joint optimization control, which comprises the following steps of: a sectional type rotating speed control strategy is adopted to change the side control mode of the air intake machine; improving the reactive power control of the network side converter by adopting a network side multi-operation power control mode; and a combined control system is formed by combining the sectional type rotating speed control strategy of the fan side converter and the multi-operation mode reactive power control strategy of the network side converter. According to the invention, by analyzing the basic principle of realizing low voltage ride through of the direct-drive wind turbine generator, a combined control strategy of the double-end converter system of the direct-drive fan by adopting sectional type rotating speed control and network side multi-mode reactive power control is provided, so that the low voltage ride through capability of the direct-drive wind turbine generator and the reactive power supporting capability of a power grid are improved.

Description

Low voltage ride through control method based on rotation speed and reactive power joint optimization control
Technical Field
The invention belongs to the field of electric power systems and automation thereof, and particularly relates to a low-voltage ride-through control method based on rotation speed and reactive power joint optimization control.
Background
With the development of wind power technology in recent years, the single-machine capacity of a wind turbine generator is gradually improved, the scale of a wind power plant is gradually enlarged, and the interaction effect between the wind power plant and a traditional power grid is more and more obvious after the wind power is connected. For a low-permeability wind power system, a wind turbine generator can be immediately disconnected when the voltage of a power grid drops, and the condition can not cause bad influence on the system with lower wind power ratio; for a power system with high wind power permeability, the automatic off-grid of a large-scale fan can cause great impact on a power grid. The voltage stability and the frequency stability of the system are seriously threatened, and the negative benefit can hinder the large-scale development of the wind power industry. Therefore, on the background that the capacity of the wind turbine generator currently participating in grid connection accounts for a continuously increased proportion in the power grid, both new grid safety operation rules and wind power grid connection specifications require that the grid-connected wind turbine generator has certain low-voltage ride-through capability, namely, when the voltage of the power grid drops, the wind turbine generator can continuously run for a certain time in a grid connection mode and can provide reactive power support for the power grid.
The low voltage ride through means that when the voltage of the wind turbine generator connected to the power grid drops, the wind turbine generator can be connected with a power system, certain reactive power support can be provided for the power grid according to the voltage drop degree of the power grid, the power grid can be smoothly restored to a normal operation state, and therefore the wind turbine generator completes ride through operation within the low voltage time of the power grid. For grid-connected fans, low voltage ride-through is a specific operational functional requirement when a voltage drop occurs in the grid. At present, power related departments at home and abroad set detailed wind turbine generator grid-connected specifications and put different requirements on low-voltage ride-through operation according to various national conditions.
For a traditional fan operation mode, when a power grid fails, related protection measures are immediately implemented to disconnect the wind turbine generator from the power grid, the severity and duration of the power grid failure are not considered, the processing mode can guarantee the safety of the wind turbine generator to the maximum extent, and the method is feasible in a power system with low wind penetration rate. However, for an electric power system with a high proportion of wind power, if the off-grid operation mode of the wind power generator set is still adopted when the voltage of the power grid drops, the recovery difficulty of the whole power grid is increased, even the power grid fault is aggravated, the voltage of the power grid is finally collapsed, and larger-scale off-grid accidents of the generator set occur. Therefore, as the percentage of the installed capacity of the wind power to the installed capacity of the power system is continuously increased, the influence of the off-grid disconnection of the wind turbine generator on the safe and stable operation of the power grid is increased. In addition, the large-scale off-line of the wind turbine generator caused by the voltage drop of the power grid threatens the safety and stability of the power grid and causes great damage to the wind turbine generator. When the voltage of a power grid drops, the wind turbine generator set can generate unbalance of mechanical power and electromagnetic power, and the damage of related parts of the wind turbine generator set can be seriously influenced by overcurrent and overvoltage problems caused by the unbalance. The voltage drop is a common power grid disturbance condition in the actual operation of a power grid, so that the low voltage ride through capability is very important for the safe and stable operation of the power grid or the wind turbine generator.
Because the direct-drive wind turbine generator is connected with the power grid through the full-power converter system, decoupling is basically realized between the wind turbine and the power grid as well as between the synchronous generator and the power grid, if a special control means is adopted in the converter part, the direct-drive wind turbine generator can have low voltage ride through capability, and can be quickly recovered to a normal operation state after voltage disturbance is eliminated.
For voltage drops of different degrees of a power grid, safe and stable operation of a direct-drive wind power system cannot be guaranteed based on machine side and grid side conventional control strategies under an ideal steady-state working condition of the power grid, so that the control strategy of a converter system is further optimized and designed on the premise of not increasing an additional circuit and guaranteeing the operation safety of a wind turbine generator, and the important significance is achieved for fully exerting the adjusting capability of the wind turbine generator and a converter.
Disclosure of Invention
The invention aims to provide a low-voltage ride-through control method based on rotation speed and reactive power joint optimization control.
The technical scheme for realizing the purpose of the invention is as follows: a low voltage ride through control method based on rotation speed and reactive power joint optimization control comprises the following steps:
step 1, changing a side control mode of an air intake machine by adopting a sectional type rotating speed control strategy;
step 2, improving the reactive power control of the network side converter by adopting a network side multi-operation power control mode;
and 3, combining the fan side converter sectional type rotating speed control strategy and the network side converter multi-operation mode reactive power control strategy to form a combined control system.
Compared with the prior art, the invention has the following remarkable advantages: (1) according to the invention, the regulation capability of the wind turbine generator and the current converter can be fully exerted on the premise of not increasing extra hardware equipment such as a crowbar energy consumption circuit and the like and ensuring the operation safety of the wind turbine generator; (2) the direct-drive wind turbine generator combined control method combined with the fan side sectional type rotating speed control strategy and the grid side multi-operation mode control strategy can obviously improve the low voltage ride through capability of the direct-drive fan when the grid voltage drops, and ensure the safe and stable operation of the direct-drive wind turbine generator system; (3) when the voltage of a power grid is detected to drop, a control mode of converters at two ends of the direct-drive wind turbine generator is triggered to play a role, active power is output from a machine side and reactive power support is actively provided for the power grid, overvoltage of a direct-current bus in the voltage drop period of the power grid is restrained, and low voltage ride through capability of the direct-drive fan is improved.
Drawings
FIG. 1 is a flow chart of the low voltage ride through control strategy of the present invention.
Fig. 2(a), fig. 2(b) and fig. 2(c) are equivalent circuit diagrams of d-axis and q-axis ac systems and dc links of the grid-side converter according to the present invention, respectively.
FIG. 3 is a block diagram of outer ring segmented speed control of a machine side converter of the present invention.
Fig. 4 is a block diagram of the overall control of the machine side converter of the present invention.
Fig. 5 is a block diagram of the overall control of the grid-side converter of the present invention.
Detailed Description
With the increasing capacity of wind power merged into a power grid, the interaction effect between the wind power and the traditional power grid after the wind power is connected is more and more obvious. For a power system with high wind power permeability, the automatic off-grid of a large-scale fan can cause great impact on a power grid, and the voltage stability and the frequency stability of the system are seriously threatened. Under the background that the capacity of the wind turbine generator participating in grid connection is continuously improved at present, the new safe and stable operation rule of the power grid and the wind power grid connection standard require that the grid-connected wind turbine generator has certain low voltage ride through capability.
The invention provides a low voltage ride through control method based on rotation speed and reactive power combined optimization control according to the regulation capacity of a wind turbine generator and a current converter, as shown in figure 1, the method comprises the following steps:
analyzing a basic principle of realizing low voltage ride through of a direct-drive wind turbine generator, and adopting a control method at a converter part to realize the low voltage ride through capability of the direct-drive wind turbine generator;
changing the side control mode of the air intake machine by adopting a sectional type rotating speed control strategy;
improving the power control mode of the grid-side converter, and enhancing the reactive power supporting capability of the grid-side converter to the power grid during the voltage drop;
step four, a combined control system is formed by combining a fan side converter sectional type rotating speed control strategy and a network side converter multi-operation mode reactive power control strategy;
further, in the first step, because the direct-drive wind turbine generator is connected with the power grid through the full-power converter system, and the decoupling is basically realized between the wind turbine and the power grid as well as between the synchronous generator and the power grid, the direct-drive wind turbine generator can have low-voltage ride through capability by adopting a control strategy in the converter part, and can be quickly recovered to a normal operation state after voltage disturbance is eliminated.
The mathematical model of the grid-side converter under the dq synchronous rotation coordinate system is as follows:
Figure BDA0001986009660000041
in the formula (1), the current on the network side flows from the current converter to the power grid as the positive direction, and U issdAnd UsqD-axis and q-axis components of the grid voltage connected to the grid side respectively; u shapegdAnd UgqOutputting d-axis and q-axis components of the alternating voltage for the grid-side converter; i.e. isdAnd isqAre respectively the net sideD-axis and q-axis components of the current; omega is the fundamental angular frequency of the power grid; r and L are respectively an alternating current side circuit resistor and a filter inductor.
Therefore, according to the mathematical model of the grid-side converter under the dq two-phase synchronous rotating coordinate system, equivalent circuits of a d-axis and q-axis alternating current system and a direct current link of the grid-side converter can be obtained, as shown in fig. 2(a), 2(b) and 2 (c).
If losses in the network side converter and the reactor are neglected, it can be seen from fig. 2 that active power P injected into the grid through the network side converterinvCan be expressed as:
Figure BDA0001986009660000042
with grid voltage oriented on the d-axis, there is UsqWhen 0, formula (2) can be rewritten as:
Figure BDA0001986009660000043
and the output active power P of the machine side converterrecComprises the following steps:
Prec＝Udcirec(4)
during normal operation, direct current voltage keeps invariable, and according to the power balance principle, the power of direct current bus both sides equals, promptly:
Figure BDA0001986009660000044
the energy Δ P flowing through the dc-side capacitor can then be expressed as:
Figure BDA0001986009660000045
in a steady state, the power of the machine-side and grid-side converters is equal, so Δ P is equal to 0, the dc voltage is constant at the reference value, and no current flows through the capacitor.
When the power grid is in fault, under the condition that the current limitation of the converter is not considered in an ideal state, the power grid voltage is limited by UsdInstantly falls to U'sdBecause the wind turbine generator and the power grid are basically isolated through the grid-connected converter system, the active power output by the machine side converter is basically kept constant, and in order to maintain the active power balance of the converters on two sides, the d-axis current of the grid side converter also needs to be isdIs increased to i'sdNamely, the following steps are provided:
Figure BDA0001986009660000051
in actual operation, the grid-side converter has certain current limiting measures, the passing current is not allowed to increase infinitely, the current limiting effect of the limiter is considered, and the actual instantaneous d-axis current at the moment is set as i ″sdAnd i ″)sd＜i′sdThen, there are:
Figure BDA0001986009660000052
Prec＝P′inv+ΔP (9)
p 'in the formula (8)'invThe actual active power of the network side is obtained when the voltage of the power grid drops.
From the above analysis, it can be known that the grid voltage drop causes PinvThe direct-current bus voltage U is directly caused by charging the capacitordcRises rapidly. If effective measures are not taken timely, the large fluctuation of the direct current voltage can cause the damage of the direct current bus capacitor and the full-power converter. Therefore, the safe and stable operation of the direct-drive wind power system cannot be ensured based on the conventional machine side and grid side control strategies under the ideal steady-state working condition of the power grid, and the control strategy of the current conversion system needs to be further optimally designed.
Furthermore, in the second step, because the imbalance of the active power on the two sides of the direct current bus is the main reason for causing the overvoltage of the direct current bus when the voltage of the power grid drops, and the drop of the active power on the power grid side is generally uncontrollable, the inertia energy storage system of the rotor of the permanent magnet synchronous generator is utilized, and the active power output by the wind turbine generator is controlled by adjusting the rotating speed of the wind turbine generator, so that the change trend of the active power on the power grid side can be actively tracked, and the control target of restraining the fluctuation of the direct current voltage by reducing the imbalance of the active power on the two sides of the.
According to the mathematical model of the direct-drive fan shafting transmission mechanism and in combination with the power transmission between the wind turbine generator and the converter system, the power transmission model of the shafting part of the wind turbine generator is obtained as follows:
Figure BDA0001986009660000053
in the formula (10), PmIs the output power of the wind turbine, PeRepresenting the active power output by the generator, JeqIs the moment of inertia of the rotor, omegagRepresenting the generator speed, and deltap representing the mechanical energy stored in the generator rotor.
Under the condition of steady state of the system and neglecting winding impedance and loss of converter devices, active power on two sides of the direct current bus keeps balance, namely Pe＝PsIn which P issFor the net side active power, the formula (10) is replaced by:
Figure BDA0001986009660000061
from equations (10) and (11), integrating the two sides of the equation over the same time period T, respectively, can obtain:
Figure BDA0001986009660000062
Figure BDA0001986009660000063
through the combined vertical type (12) and the formula (13), the active state of the network side in voltage drop can be reflected to the machine side, namely the active unbalance at two ends of the back-to-back converter system is equivalently converted into the unbalanceThe imbalance between the mechanical power and the electromagnetic power of the machine side is stored in the form of mechanical energy of the rotor of the generator, so that a corrected reference value omega of the generator speed during low voltage of the grid is obtained according to equations (12) and (13)grefComprises the following steps:
Figure BDA0001986009660000064
the formula (14) shows that in the period of grid voltage drop, the imbalance of active power of the machine side and the grid side is taken as a control target, the rotating speed of the generator can be improved by correcting the reference value of the rotating speed of the generator, the energy storage of the rotor is increased, the active power of the machine side injected into a direct current link is limited, and the control target of suppressing the overvoltage of a direct current bus is achieved.
In the conventional control strategy of the machine side, the rotation speed controller takes the maximum wind power tracking as a control target, and the change of the network side active power cannot be synchronously tracked during the fault period, so that the machine side active power and the network side active power are unbalanced. Therefore, the invention provides a sectional type rotating speed control strategy, and the rotating speed reference values are respectively defined by adopting a sectional control mode under different working conditions of 'steady state-low voltage'. Under a steady state working condition, taking the optimal rotating speed for realizing the tracking of the maximum wind power as a rotating speed reference value; under the condition of grid voltage drop, the synchronous change of machine side active power and grid side active power is realized, the unbalance of the active power on two sides is restrained as a control target, the reference value of the rotating speed during the fault period is corrected according to the formula (14), the unbalance of the active power on two sides of the direct current bus is converted into the unbalance of the mechanical power and the electromagnetic power in the wind turbine generator, namely the rotating speed omega of the generator is adjusted through the controllergThe unbalanced power is stored in the permanent magnet synchronous generator in a rotor kinetic energy mode, the rotating speed energy storage item is increased, active power injected into a direct current system by the machine side is limited, and the imbalance of the active power of the machine side and the active power of the network side during the fault period is restrained. The control block diagram of the outer ring segmented speed control part of the machine side converter designed by the method is shown in figure 3.
In FIG. 3,. omega.gref1Representing the optimal rotating speed reference value taking maximum power tracking as a control target under the normal working condition; omegagref2Indicating fault periods to inhibit DC systemThe two sides of the rotor are in active unbalance and are used as corrected rotating speed reference values of a control target; u shapeacAnd UacrefRespectively calculating the actual value and the rated value of the alternating voltage at the network side, triggering a judging module of a machine side rotating speed control link to switch a control mode when the voltage drop exceeds 20 percent by calculating the voltage drop degree at the network side, and introducing a rotating speed correction reference value; omegagrefIn order to finally input the rotating speed reference value of the outer ring part of the machine side controller, the value of the rotating speed reference value is ensured not to exceed the safe operation range of the rotating speed through an amplitude limiting link, and the rotating speed range is set to be 0 to a rated rotating speed value; i.e. iqrefIs the q-axis current reference value of the final input current inner loop control part. Under the normal operation condition, the control target of the machine side of the wind turbine generator set is the maximum wind power tracking, and the machine side controller is used for adjusting the rotating speed to be the optimal rotating speed value, namely omegagref＝ωgref1(ii) a During the voltage drop of the power grid, the inertia energy storage characteristic of the rotor of the permanent magnet synchronous generator is utilized, the active power of the direct current link injected into the middle of the fan side is changed by adjusting the rotating speed of the generator during the voltage drop, the imbalance of the active power at two sides of the direct current bus during the power grid fault is reduced, and the rotating speed reference value omega of the generator is changed under the modegref＝ωgref2。
In summary, the overall control structure of the machine side inverter is shown in fig. 4. The machine side converter adopts a double closed loop decoupling control structure, wherein a reactive power reference value QrefSetting the power factor to be 0, so that the wind turbine generator operates in a unit power factor state, and utilizing the rated capacity of the wind turbine generator to the maximum extent; omegagrefAnd respectively adopting different rotating speed reference values for the rotating speed reference values output by the sectional type rotating speed control module according to the operating conditions of the power grid.
Further, in the third step, a network side converter reactive power control strategy with different working modes is provided. When the grid voltage drops due to a short-circuit fault or the like, the grid-side converter generally does not consider the reactive support of the converter on the grid under the conventional control condition, so the reference value of the reactive power is generally set to 0. During the voltage drop of the power grid, the reactive power injected into the power grid by the grid-side converter is passively changed due to the change of the active power on the grid side, and the reactive support capability of the PWM voltage source type converter is not fully utilized. Therefore, in order to provide reactive support to the grid during grid faults, q-axis reactive control of the grid-side converter needs to be dominant, and the reactive power regulation capability of the grid-side converter needs to be fully exerted.
Under the normal operation state of the system, the reference value of the network side reactive power control is 0, the reference value of the q-axis current is also 0, and the unit power factor operation mode is kept; under the condition that voltage drop occurs on a network side, according to the voltage drop degree, a q-axis outer ring calculates a reference value of q-axis current of an inner ring through a proportional control link, the faster the proportional control is, the q-axis current can be quickly regulated during the power grid fault, the inner ring still adopts a PI control mode, the current reference value can be quickly and accurately tracked, the d-axis current reference value is not calculated through an outer ring direct current voltage PI controller any more, but is obtained through calculation according to a maximum current threshold value of a network side converter and the q-axis current reference value, the reference current is limited, namely, the q-axis reactive power control plays a leading role during the power grid voltage drop, reactive power support is provided for a power grid, and the voltage drop degree of the power grid is reduced.
Reference value i of q-axis inner loop current during grid voltage dropsqrefCalculated by equation (15):
isqref＝λ(Uacref-Uac) (15)
in the formula (15), the q-axis current reference value is obtained when the grid-side converter works in the reactive support control mode; u shapeacrefAnd UacRespectively a rated value and an actual value of the net side voltage effective value; and lambda is the proportional control coefficient of the outer ring.
Because the direct current bus generates overvoltage during the low voltage period of the power grid, the d-axis control link of the grid side converter loses effective control on the direct current voltage, and in order to ensure that the q-axis reactive power control dominates the prior position during the fault period, the reference value i of the d-axis inner loop currentsdrefCalculated by equation (16):
Figure BDA0001986009660000081
in formula (16), imaxFor side exchange of netThe maximum current threshold of the current device is set to be 1.1 pu; i.e. isqrefIs a q-axis current reference value.
In summary, the structure of the network-side improved multi-operation mode controller is shown in fig. 5. In FIG. 5, QsrefAnd QsRespectively a network side reactive reference value and a measured value; u shapedcrefAnd UdcRespectively representing a direct current voltage reference value and an actual measurement value; ctrl is a control mode switching signal determined according to the network side voltage drop degree, when the network voltage drop exceeds 20%, Ctrl is made to be 1 by adjusting the q-axis and d-axis current reference values, and the network side converter is switched to a reactive support control mode so as to realize reactive control of the network side converter under different working modes.
And furthermore, in the fourth step, a machine side converter sectional type rotating speed control strategy and a network side converter multi-operation mode reactive power control strategy which are respectively designed in the second step and the third step are combined to form a combined control system, when the voltage of the power grid is detected to drop, the machine side sectional type rotating speed control strategy and the network side multi-operation mode control strategy play a role simultaneously, and the overvoltage of a direct current bus during the voltage drop of the power grid is restrained by limiting machine side output active power and actively providing reactive power support for the power grid, so that the low voltage ride through capability of the direct drive fan is improved.

Claims (4)

1. A low voltage ride through control method based on rotation speed and reactive power combined optimization control is characterized by comprising the following steps:
step 1, changing a side control mode of an air intake machine by adopting a sectional type rotating speed control strategy;
step 2, improving the reactive power control of the network side converter by adopting a network side multi-operation power control mode;
and 3, combining the fan side converter sectional type rotating speed control strategy and the network side converter multi-operation mode reactive power control strategy to form a combined control system.
2. The low voltage ride through control method based on rotation speed and reactive power combined optimization control according to claim 1, wherein in the step one, an inertial energy storage system of a rotor of the permanent magnet synchronous generator is utilized during grid voltage sag, and active power output by the wind turbine generator is controlled by adjusting the rotation speed of the wind turbine generator so as to actively track the change trend of the active power on the grid side, so that the imbalance of the active power on two sides of the direct current bus is reduced.
3. The low voltage ride through control method based on rotation speed and reactive power combined optimization control according to claim 2, wherein the first step is specifically:
according to the mathematical model of the direct-drive fan shafting transmission mechanism and in combination with the power transmission between the wind turbine generator and the converter system, the power transmission model of the shafting part of the wind turbine generator is obtained as follows:
Figure FDA0001986009650000011
in the formula, PmIs the output power of the wind turbine, PeRepresenting the active power output by the generator, JeqIs the moment of inertia of the rotor, omegagRepresenting the generator speed, Δ P representing the mechanical energy stored in the generator rotor;
under the condition of steady state of the system and neglecting winding impedance and loss of converter devices, active power on two sides of the direct current bus keeps balance, namely Pe＝PsIn which P issThe network side active power is obtained by substituting the formula (1):
Figure FDA0001986009650000012
according to the equations (1) and (2), the two sides of the equation are integrated in the same time period T, respectively, and the following can be obtained:
Figure FDA0001986009650000013
Figure FDA0001986009650000014
through the combined vertical type (3) and the formula (4), the active state of the network side during voltage drop can be reflected to the machine side, namely the active unbalance at two ends of the back-to-back converter system is equivalently converted into unbalance between the mechanical power and the electromagnetic power of the machine side, the unbalance power is stored in a mode of mechanical energy of a generator rotor, and therefore the corrected reference value omega of the rotating speed of the generator during the low voltage period of the power grid can be obtained according to the formula (3) and the formula (4)grefComprises the following steps:
Figure FDA0001986009650000021
4. the method for controlling low voltage ride through based on rotation speed and reactive power combined optimization control according to claim 1, wherein in the second step, by using the reactive support capability of the PWM voltage source converter itself, the q-axis reactive control function of the grid-side converter is exerted during the grid fault, and the reference values of the grid-side active current and the reactive current are recalculated and distributed according to the grid voltage drop degree, so as to limit the active current, specifically:
reference value i of q-axis inner loop current during grid voltage dropsqrefCalculated by equation (6):
isqref＝λ(Uacref-Uac) (6)
in the formula isqrefA q-axis current reference value when the grid-side converter works in a reactive support control mode is obtained; u shapeacrefAnd UacRespectively a rated value and an actual value of the net side voltage effective value; lambda is the proportional control coefficient of the outer ring;
d-axis inner ring current reference value isdrefCalculated by equation (7):
Figure FDA0001986009650000022
in the formula imaxSetting the maximum current threshold of the grid-side converter as 1.1 pu; i.e. isqrefIs a q-axis current reference value.
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Application publication date: 20200915