CN111756071B - Full-power conversion wind turbine generator system with voltage source characteristic - Google Patents
Full-power conversion wind turbine generator system with voltage source characteristic Download PDFInfo
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- 238000012795 verification Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 4
- 230000006641 stabilisation Effects 0.000 claims description 4
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- 230000004069 differentiation Effects 0.000 claims description 2
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Classifications
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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
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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
- H02J3/002—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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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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
- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
Abstract
The invention provides a full-power conversion wind turbine generator with voltage source characteristics, which comprises the following components: a network side unit and a machine side unit; the net side unit is connected with the machine side unit; the mesh side unit includes: a grid-side converter; the grid-side converter controls direct-current side voltage; the grid-side converter includes: a grid-side converter control loop; the stable controller of the grid-side converter measures the direct-current voltage, and the output of the stable controller is superposed on the modulation voltage of the grid-side converter after passing through an amplifier and a high-pass filter. The stable controller of the machine side converter adds a three-stage first-order low-pass filter in an inertia transfer control loop of the original machine side converter. The phase of active power output by the machine side converter of the added three-stage low-pass filter can be adjusted in a smaller time scale, and the stability of the system is improved.
Description
Technical Field
The invention relates to the technical field of conversion wind turbines, in particular to a full-power conversion wind turbine with voltage source characteristics.
Background
With the increase of the inertia transfer coefficient KC, the running stability of the wind turbine in a weak power grid is reduced, and the oscillation instability of the wind turbine is easily caused. Therefore, it is necessary to study the stable control method of the voltage source type control wind turbine generator. In the prior art, a full-power conversion wind turbine generator set with voltage source characteristics is needed.
Patent document CN109378888B discloses a centralized high-voltage rectifying current distribution charging stack. The invention provides a safe and reliable centralized high-voltage rectifying current distribution charging pile. The invention comprises a high-voltage protection unit, a high-voltage rectifying transformer unit, a high-voltage rectifying unit and a charging pile group current distribution unit, and is characterized in that an output port of the high-voltage protection unit is connected with an input port of the high-voltage rectifying transformer unit, an output port of the high-voltage rectifying transformer unit is connected with an input port of the high-voltage rectifying unit, and an output port of the high-voltage rectifying unit is connected with an input port of the charging pile group current distribution unit. The patent still leaves room for improvement in terms of structure and performance.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a full-power conversion wind turbine with voltage source characteristics.
According to the invention, the full-power conversion wind turbine generator with the voltage source characteristic comprises the following components: a network side unit and a machine side unit; the net side unit is connected with the machine side unit; the mesh side unit includes: a grid-side converter; the grid-side converter controls direct-current side voltage; the grid-side converter includes: a grid-side converter control loop; DC side voltage (per unit value) in the grid side converter control loopThe output of the integrator is the phase theta of the modulating wave of the grid-side converter through the integrator with the gain being the grid angular frequency reference value omega Bg (namely 314.15926 rad/s); reference value (per unit value)/>, of reactive power of grid-side converterAnd feedback value (per unit value)/>The difference passes through a Proportional Integral (PI) regulator, and the sum of the output of the Proportional Integral (PI) regulator and the rated modulation voltage U t0 is the actual modulation voltage U t of the grid-side converter; a modulation signal of the grid-side converter is generated for Sinusoidal Pulse Width Modulation (SPWM) based on the actual modulation voltage U t and the phase θ.
Preferably, the gain of the integrator is a grid angular frequency reference value omega Bg; the grid angular frequency reference value ω Bg = 314.15926rad/s; DC side voltage (per unit value) in the grid side converter control loopThe output of the integrator is the phase theta of the modulating wave of the grid-side converter through the integrator with the gain being the grid angular frequency reference value omega Bg (namely 314.15926 rad/s); reference value (per unit value)/>, of reactive power of grid-side converterAnd feedback value (per unit value)/>The difference passes through a Proportional Integral (PI) regulator, and the sum of the output of the Proportional Integral (PI) regulator and the rated modulation voltage U t0 is the actual modulation voltage U t of the grid-side converter; a modulation signal of the grid-side converter is generated for Sinusoidal Pulse Width Modulation (SPWM) based on the actual modulation voltage U t and the phase θ.
Preferably, in order to make the direct current voltage only autonomously sense the change of the grid frequency and insensitive to the change of the grid voltage amplitude, a stabilizing and frequency sensing integrated controller is added in a control loop of the grid-side converter, the stabilizing and frequency sensing integrated controller measures the direct current voltage, and after the stabilizing and frequency sensing integrated controller passes through an amplifier K PSS and a high-pass filter with a time constant of T dc, the stabilizing and frequency sensing integrated controller outputs a modulation voltage which is superposed on the grid-side converter; the stabilizing and frequency sensing integrated controller can enable the direct-current voltage to only sense the change of the power grid frequency and is insensitive to the change of the amplitude of the power grid voltage. Since the high pass filter only allows the dynamic signal to pass, the combined stability and frequency sensing controller only works in a dynamic process.
Preferably, the parameters to be set by the integrated controller for stabilizing and frequency sensing include any one or more of the following parameters:
-a high pass filter time constant T dc;
-a stability control coefficient K PSS;
The stability and frequency perception integrated controller not only can enable the current voltage to only perceive the frequency change of the power grid, but also can enhance the operation stability of the weak power grid of the wind turbine.
The high-pass filter is used for enabling the resonant signal with the angular frequency omega res to pass through the high-pass filter, and the high-pass filtering time constant T dc>1/ωres;
For the stability control coefficient K PSS, the maximum value is limited by the maximum modulation ratio of the network side converter, and the maximum value K PSSmax of the K PSS is
Wherein: m max is the maximum value of the modulation ratio of the network side converter, and the value is 0.5 when SPWM modulation is adopted; The per unit value of the output voltage of the alternating current side of the grid-side converter; u Base is the base value of the alternating voltage; u dcB is the base value of the DC side voltage;
When setting the stability control coefficient K PSS, the value should be smaller than K PSSmax.
Preferably, the machine side unit includes: a machine side converter and a wind wheel;
a machine side converter is adopted to control wind power captured by a wind wheel;
The machine side converter adopts a vector control mode based on rotor flux linkage orientation;
the control method of the machine side converter comprises the following steps:
Generator rotating speed (per unit value) The product of the power factor k opt and the power factor k is used as the reference value (per unit value)/>, of the output power of the converter on the machine sideTo achieve inertia transfer control on the DC side, the DC side voltage (per unit value)/>After passing through a first-order low-pass filter with a time constant of T and a differentiation link with a gain of-K C, the output is/>Because a large amount of higher harmonics contained in the direct-current side voltage can cause system instability after being amplified by a differential link, a first-order low-pass filter in an inertia transfer control loop is used for reducing the influence of the differential link on the system stability. Active power reference value (per unit value)Output value (per unit value)/>, of inertia transfer control loopThe sum is used as the input of the active power controller of the machine side converter. The inertia transfer control loop can transfer the inertia of the wind wheel to the power grid side, and achieves the inertia response function of the wind turbine generator to the power grid.
Preferably, the machine side unit includes: a machine side converter control loop;
the machine side converter control loop includes: a machine side stabilization controller;
In order to enhance the running stability of a weak power grid of the wind turbine, a machine side stable controller is added in a machine side converter control loop, the machine side stable controller is a first-order low-pass filter with a three-stage time constant of T 2 added in an inertia transfer control loop, and the three-stage low-pass filters are connected in series.
Preferably, when the value of T 2 is selected, the adjusting time of the power system frequency change process is T s, the corresponding inertia time constant T iner is T s/4, and in order to enable the low-pass filter added on the machine side to more completely transmit the power grid frequency change signal, T 2<Tiner/10 needs to be satisfied.
Preferably, setting a network side stability control parameter of the network measurement unit;
setting a side stability control parameter of the side unit;
Step one: and establishing a state space model or a simulation model of a voltage source controlled wind turbine generator weak grid system, and judging the running stability of the wind turbine generator weak grid to obtain potential resonance frequency.
Step two: and (3) according to the potential resonant frequency of the wind turbine generator, the low-pass filtering time constant T 2 of side induced stability control of the setter.
Step three: and according to the potential resonance frequency, setting a high-pass filtering time constant T dc of the side stability control of the net. And determining the maximum value which can be taken by the K PSS according to the actual operation condition of the wind turbine.
Step four: and giving a value of a network side stability control coefficient K PSS, and substituting the value into a state space model to verify the validity of the designed parameter T 2、Tdc、KPSS. And constructing an electrical simulation model to further verify the validity of the set machine side and network side stable control parameters. If the electric oscillation is restrained, the stability control parameters of the machine side and the network side are designed; if the electrical oscillations are not suppressed, a net side stability control coefficient K PSS is redesigned, and theoretical verification and simulation verification are continued until the designed parameters stabilize the system.
Preferably, the grid-side unit performs low-voltage fault ride-through by adopting a method for blocking trigger pulses of the grid-side converter during grid faults;
three-phase symmetrical short circuit fault occurs at public connection point, and voltage amplitude of alternating current outlet end of wind turbine generator is detected And current amplitude/>The fault detector generates a short-circuit fault Flag bit, wherein the Flag is 0 in normal operation and 1 in three-phase short circuit. And the network side controller, the crowbar controller, the machine side controller and the variable pitch controller implement corresponding control schemes according to the fault Flag bit Flag.
Preferably, in the fault detector, the output current amplitude of the full power conversion wind turbine generator with voltage source characteristicsF I is 1 at p.u.; otherwise, F I is 0;
when the voltage amplitude of the common connection point When F U is 1; otherwise, F U is 0;
f I and F U pass through an OR gate, and the output of the OR gate is a short-circuit fault Flag bit;
to prevent malfunction of the fault detector, a falling edge delay is added between F I and the or gate, i.e. when F I changes from 0 to 1, the delay output immediately changes from 0 to 1; when F I goes from 1 to 0, the delay output goes from 1 to 0 after delay T F1 time;
here, T F1 takes 0.1s.
Preferably, in a grid-side converter for fault-ride-through,
The grid-side converter includes: a Flag-controlled, flag-controlled gating switch;
The Flag control is connected with a gating switch controlled by the Flag;
For gating switches SG2-SG4, in which Flag controls, the switch is in position 2 when the Flag value is 0; when Flag is 1, the switch is in position 1. When the three-phase short-circuit fault Flag of the power grid is changed from 0 to 1, the gating switches SG2-SG4 are changed from the position 2 to the position 1, s gabc are changed to 0, the triggering pulse of the grid-side converter is blocked, and the damage of overcurrent to a switching tube is avoided. The SG2 at position 2 means that the phase θ of the voltage at the common connection point is observed by the phase-locked loop, and the SG3 at position 2 reactive power control is cut off, so that the network side converter is restarted after the short circuit fault is removed. When the Flag is changed from 0 to 1 after the short-circuit fault is removed, the SG4 is switched to the position 2, and the network-side converter is restarted. After delay T F2, SG2 is switched from position 1 to position 2, and the grid-side converter is synchronized with the power grid according to the dynamic characteristic of direct current voltage. And switching from the position 1 to the position 2 after the SG3 delays T F3, and switching into reactive power control, wherein restarting of the network-side converter after fault removal is completed.
In a crowbar controller for fault ride-through, DC voltageThe output of the hysteresis comparator is used for determining whether the crow bar is put into the device or not. When/>The output of the hysteresis comparator is 1 when the hysteresis comparator is larger than the opening point u dc2, and the unloading circuit is put into reducing direct-current voltage; when/>The output of the hysteresis comparator is 0, and the unloading circuit is cut off from the direct current side. When the wind turbine generator system normally operates, flag is 1, and the on point u dc2 and the off point u dc1 of the hysteresis comparator are respectively 1.1p.u. and 0.9p.u.. When a short circuit fault occurs Flag is 0, the on point u dc2 and the off point u dc1 are set to 1.01p.u. and 0.99p.u., respectively, and the crowbar controller controls the dc voltage to be around the rated value because the machine side converter still emits power. After the fault clears, SC2, SC3 switch from position 1 to position 2 after delay T F2, the values of on point u dc2, off point u dc1 are again set to 1.1p.u. and 0.9p.u., respectively.
In the machine side converter controller for fault ride through, when a short-circuit fault occurrence Flag is 1, SM2 are switched from position 2 to position 1, inertia transfer control is switched out, and the machine side converter is changed from optimal power control to constant power control. Active power reference value of fault opportunity side converterThe purpose of setting to 0.05p.u. is to maintain the dc side voltage from dropping. When the short circuit fault is removed, SM1 switches from position 1 to position 2 after delay T F4, and the machine side converter switches back to optimal power control. SM2 switches from position 1 to position 2 after delay T F5, and inertia transfer control is put into operation.
In a pitch controller for fault ride through, when rotor speedThe machine side converter outputs active power/>When the set value is exceeded, the pitch angle beta is increased by the pitch controller, and wind power captured by the wind wheel is reduced. When the short circuit fault Flag is 1, the SP1 is switched from the position 2 to the position 1, the corresponding active power set value is changed from 1.2p.u. to 0, the output pitch angle beta of the variable pitch controller is increased, and the excessive increase of the rotating speed of the wind wheel caused by the reduction of the active power output by the machine side converter is reduced. After the fault is cleared, SP1 switches from position 1 to position 2 after delay T F6, the active power set point becomes 1.2p.u., and the pitch controller returns to normal.
Compared with the prior art, the invention has the following beneficial effects:
1. The invention discloses a full-power conversion wind turbine generator with a voltage source characteristic, which mainly comprises an autonomous power grid synchronous control of a grid-side converter, a control of direct-current voltage autonomous sensing power grid frequency change, an inertia transfer control, a stable controller of the grid-side converter, a stable controller of a machine-side converter, a design method of stable control parameters and a low-voltage fault ride-through control method;
2. The stable controller of the grid-side converter measures the direct-current voltage, and the output of the stable controller is superposed on the modulation voltage of the grid-side converter after passing through an amplifier and a high-pass filter. The stable controller of the machine side converter adds a three-stage first-order low-pass filter in an inertia transfer control loop of the original machine side converter. The phase of active power output by the side converter of the added three-stage low-pass filter can be adjusted in a smaller time scale, so that the stability of the system is improved;
3. according to the invention, on a larger time scale, the inertia response function of the wind turbine generator to the power grid can be realized better through the power grid frequency change signal. The parameter design method is provided according to the low-pass filter time constant of the system potential resonance frequency setter side stability controller, the high-pass filter time constant of the net side stability controller and the net side stability control coefficient. The low-voltage fault ride-through method is adopted to block the triggering pulse of the grid-side converter during the power grid fault period, and has the advantages of longer power grid short-circuit fault time tolerance, no frequency instability risk and stronger adaptability.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of a full power wind turbine system with voltage source characteristics according to the present invention.
Fig. 2 is a schematic diagram of a machine side stabilization control block of the present invention.
Fig. 3 is a schematic diagram of a network side stability control block of the present invention.
FIG. 4 is a schematic diagram of a parameter design flow of a machine side and network side stability controller of the present invention;
fig. 5 is a schematic diagram of a control frame of a low voltage fault ride through machine according to the present invention.
Fig. 6 is a schematic diagram of a fault detector control block of the present invention.
Fig. 7 is a schematic diagram of a control block diagram of the grid-side converter for low voltage fault ride through according to the present invention.
Fig. 8 is a schematic diagram of a crowbar control block for low voltage fault ride-through of the present invention.
Fig. 9 is a schematic diagram of a control block diagram of a machine side converter for low voltage fault ride through according to the present invention.
Fig. 10 is a schematic diagram of a pitch control block for low voltage fault ride through in accordance with the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
The structure of a grid-connected system of the full-power wind turbine generator set controlled by the voltage source is shown in figure 1, wherein a machine side converter adopts vector control based on rotor flux linkage orientation, and a grid side converter adopts 'inertial synchronization' control. In the grid-side converter control loop, the per unit value of the dc-side voltage is input to an integrating controller, the output of which is used for Pulse Width Modulation (PWM) as the phase θ of the grid-side converter output voltage ug. The reactive power output by the grid-side converter can be controlled by adjusting the amplitude of the modulation voltage. The PWM module generates a three-phase switching signal sabc based on θ and. The machine side converter adopts a double-loop control structure of a power outer loop and a current inner loop, and generates an optimal power reference value according to the rotating speed of the wind wheel so as to realize optimal power control.
In the control mode shown in fig. 1, the direct-current side voltage of the wind turbine generator can autonomously sense the frequency change of the power grid. The inertia transfer controller detects the change rate of the direct current voltage, multiplies the change rate by an inertia transfer coefficient KC, and the result is multiplied by-1 to obtain an output value of the inertia transfer controller. Plus the output value of the maximum power controller as the active power reference value.
The inertia transfer control loop in fig. 1 can transfer the inertia of the wind wheel to the power grid side, so that the inertia response function of the wind turbine generator to the power grid is realized. However, as the inertia transfer coefficient KC increases, the running stability of the wind turbine in the weak power grid decreases, and the oscillation instability of the wind turbine is easily induced. Therefore, it is necessary to study the stable control method of the voltage source type control wind turbine generator.
Referring to fig. 1, the present invention is a full-power wind turbine generator based on the voltage source type control shown in fig. 1, which does not limit the voltage level of a specific circuit, and a voltage source type pulse width modulation converter is generally adopted for a machine side converter and a grid side converter.
Referring to fig. 2, the machine side stabilization controller of the present invention. In the figure, the machine side stable controller is a first-order low-pass filter with a three-stage time constant of T2 added in an inertia transfer control loop, and the three-stage low-pass filters are connected in series. In general, the frequency change process of the power system can be equivalent by a first-order inertia link, the adjusting time is 6s-20s, and the corresponding inertia time constant Tiner is 1.5s-5s. In order for the side-applied low-pass filter to be able to more fully pass the grid frequency variation signal, the side low-pass filter time constant T2< Tiner/10 needs to be satisfied. In order to enable the phase lag of the first-order low-pass filter at the resonance frequency to be close to 90 degrees, the function of phase correction is realized, and the value of T2 cannot be too small. Here the T2 value takes 0.1s.
Referring to fig. 3, the web-side stability controller of the present invention. In the figure, the direct current voltage of the converter passes through a high-pass filter with a time constant of T dc, and then is used as additional modulation voltage through an amplifying link with a gain of K PSS, and is superimposed on the original voltage amplitude for sinusoidal pulse width modulation. In the network side stability control method, parameters to be set are a high-pass filter time constant T dc and a stability control coefficient K PSS. For a high pass filter that can pass signals with frequencies greater than 1/T dc rad/s, the T dc value here takes 0.1s for the resonant signal with angular frequency omega res to pass through the high pass filter, the high pass filter time constant T dc>1/ωres. For the stability control coefficient K PSS, increasing the value can enhance the damping coefficient of the grid-side converter and improve the running stability of the wind turbine generator. The maximum value of the stability control coefficient K PSS is limited by the maximum modulation ratio of the network side converter, and the maximum value K PSSmax of K PSS is as follows:
wherein: m max is the maximum value of the modulation ratio of the network side converter, and the value is 0.5 when SPWM modulation is adopted; The per unit value of the output voltage of the alternating current side of the grid-side converter; u Base is the base value of the alternating voltage; u dcB is a base value of the dc side voltage.
When setting the stability control coefficient K PSS, the value should be smaller than K PSSmax.
Referring to fig. 4, the machine side, network side stability controller parameter design flow chart of the present invention. In the figure, the stability control parameters of the designer side and the net side mainly comprise the following four steps:
Step one: and establishing a state space model or a simulation model of a voltage source controlled wind turbine generator weak grid system, and judging the running stability of the wind turbine generator weak grid to obtain potential resonance frequency.
Step two: and (3) according to the potential resonant frequency of the wind turbine generator, which is obtained in the step one, setting a side-induced stability control low-pass filtering time constant T 2, wherein the set T 2 is 0.1s.
Step three: according to the potential resonance frequency, the high-pass filtering time constant T dc of the side stability control of the tuning net is set, and T dc is selected to be 0.1s. And determining the maximum value which can be taken by the K PSS according to the actual operation condition of the wind turbine.
Step four: and giving a value of a network side stability control coefficient K PSS, and substituting the value into a state space model to verify the validity of the designed parameter T 2、Tdc、KPSS. And constructing an electrical simulation model to further verify the validity of the set machine side and network side stable control parameters. If the electric oscillation is restrained, the stability control parameters of the machine side and the network side are designed; if the electrical oscillations are not suppressed, a net side stability control coefficient K PSS is redesigned, and theoretical verification and simulation verification are continued until the designed parameters stabilize the system. The set K PSS value here is 1.57.
Referring to fig. 5, a control block diagram of a low-voltage fault ride through complete machine according to the invention is provided, a three-phase symmetrical short circuit fault occurs at a PCC point, and a voltage amplitude value of an alternating current outlet end of a wind turbine generator is detectedAnd current amplitude/>The fault detector generates a short-circuit fault Flag bit, wherein the Flag is 0 in normal operation and 1 in three-phase short circuit. And the network side controller, the crowbar controller, the machine side controller and the variable pitch controller implement corresponding control schemes according to the fault Flag bit Flag.
Referring to FIG. 6, a fault detector control block diagram of the present invention, when the wind turbine output current amplitude isF I is 1 at p.u.; otherwise, F I is 0. When PCC point voltage amplitude/>When F U is 1; otherwise, F U is 0.F I and F U pass through an OR gate, and the output of the OR gate is a short-circuit fault Flag. To prevent malfunction of the fault detector, a falling edge delay is added between F I and the or gate, i.e. when F I changes from 0 to 1, the delay output immediately changes from 0 to 1; when F I changes from 1 to 0, the delay output changes from 1 to 0 after delay T F1 time. Here, T F1 takes 0.1s.
Referring to fig. 7, a control block diagram of the network-side converter for low-voltage fault ride through according to the present invention, for the gating switches SG2-SG4 in which Flag is controlled, when the Flag value is 0, the switch is in position 2; when Flag is 1, the switch is in position 1. When the three-phase short-circuit fault Flag of the power grid is changed from 0 to 1, the gating switches SG2-SG4 are changed from the position 2 to the position 1, s gabc are changed to 0, the triggering pulse of the grid-side converter is blocked, and the damage of overcurrent to a switching tube is avoided. The SG2 at position 2 means that the PCC voltage phase θ is observed by the PLL, and the SG3 at position 2 reactive power control is cut off, facilitating restart of the GSC after the short circuit fault is removed. When Flag is changed from 0 to 1 after the short-circuit fault is removed, sg4 is switched to position 2 and gsc is restarted. After delay T F2, SG2 is switched from position 1 to position 2, and the grid-side converter is synchronized with the power grid according to the dynamic characteristic of direct current voltage. And switching from the position 1 to the position 2 after the SG3 delays T F3, and switching into reactive power control, wherein restarting of the network-side converter after fault removal is completed.
Referring to fig. 8, a crowbar control block diagram for low voltage fault ride through, dc voltage, of the present inventionThe output of the hysteresis comparator is used for controlling whether the crow bar is put into the device or not. When/>The output of the hysteresis comparator is 1 when the hysteresis comparator is larger than the opening point u dc2, and the unloading circuit is put into reducing direct-current voltage; when/>The output of the hysteresis comparator is 0, and the unloading circuit is cut off from the direct current side. When the wind turbine generator system normally operates, flag is 1, and the on point u dc2 and the off point u dc1 of the hysteresis comparator are respectively 1.1p.u. and 0.9p.u.. When a short circuit fault occurs Flag is 0, the on point u dc2, the off point u dc1 are set to 1.01p.u. and 0.99p.u., respectively, and the crowbar controller controls the dc voltage around the nominal value since the MSC is still delivering power. After the fault clears, SC2, SC3 switch from position 1 to position 2 after delay T F2, the values of on point u dc2, off point u dc1 are again set to 1.1p.u. and 0.9p.u., respectively.
Referring to fig. 9, a control block diagram of a machine side converter for low voltage fault ride through according to the present invention is such that when a short-circuit fault occurrence Flag is 1, SM2 are switched from position 2 to position 1, inertia transfer control is switched out, and the machine side converter is changed from optimal power control to constant power control. Active power reference value of fault opportunity side converterThe purpose of setting to 0.05p.u. is to maintain the dc side voltage from dropping. When the short circuit fault is removed, SM1 switches from position 1 to position 2 after delay T F4, and the machine side converter switches back to optimal power control. SM2 switches from position 1 to position 2 after delay T F5, and inertia transfer control is put into operation.
Referring to fig. 10, the pitch control block diagram for low voltage fault ride through of the present invention, when rotor speedThe machine side converter outputs active power/>When the set value is exceeded, the pitch angle beta is increased by the pitch controller, and wind power captured by the wind wheel is reduced. When the short circuit fault Flag is 1, the SP1 is switched from the position 2 to the position 1, the corresponding active power set value is changed from 1.2p.u. to 0, the output pitch angle beta of the variable pitch controller is increased, and the excessive increase of the rotating speed of the wind wheel caused by the reduction of the active power output by the machine side converter is reduced. After the fault is cleared, SP1 switches from position 1 to position 2 after delay T F6, the active power set point becomes 1.2p.u., and the pitch controller returns to normal.
In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
The foregoing describes specific embodiments of the present application. It is to be understood that the application is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the application. The embodiments of the application and the features of the embodiments may be combined with each other arbitrarily without conflict.
Claims (7)
1. A full power conversion wind turbine having voltage source characteristics, comprising: a network side unit and a machine side unit;
The net side unit is connected with the machine side unit;
The mesh side unit includes: a grid-side converter;
the grid-side converter controls direct-current side voltage;
the grid-side converter includes: a grid-side converter control loop;
the direct-current side voltage in the control loop of the grid-side converter passes through an integrator, and the output of the integrator is the phase of the modulating wave of the grid-side converter; the difference between the reference value and the feedback value of the reactive power of the grid-side converter passes through a proportional-integral regulator, and the sum of the output of the proportional-integral regulator and the rated modulation voltage is the actual modulation voltage of the grid-side converter; generating a modulation signal of the grid-side converter for sinusoidal pulse width modulation according to the actual modulation voltage and the phase;
the gain of the integrator is the grid angular frequency reference value omega Bg;
the grid angular frequency reference value ω Bg = 314.15926rad/s;
direct-current side voltage in the control loop of the grid-side converter The output of the integrator is the phase theta of the modulating wave of the grid-side converter through the integrator with the gain being the grid angular frequency reference value omega Bg; reference value/>, of reactive power of grid-side converterAnd feedback value/>The difference passes through a proportional integral regulator, and the sum of the output of the proportional integral regulator and the rated modulation voltage U t0 is the actual modulation voltage U t of the grid-side converter; generating a modulation signal of the grid-side converter for sinusoidal pulse width modulation according to the actual modulation voltage U t and the phase theta;
Setting a network side stability control parameter of the network side unit;
setting a side stability control parameter of the side unit;
Adding a stable and frequency sensing integrated controller into a control loop of the network-side converter;
the parameters to be set of the stabilizing and frequency sensing integrated controller comprise:
-a high pass filter time constant T dc;
-a stability control coefficient K PSS;
the high-pass filtering time constant T dc>1/ωres;
The maximum value K PSSmax of K PSS is:
Wherein m max is the maximum value of the modulation ratio of the network side converter, and the value is 0.5 when SPWM is adopted; The per unit value of the output voltage of the alternating current side of the grid-side converter; u Base is the base value of the alternating voltage; u dcB is a base value of the dc side voltage.
2. The full power conversion wind turbine of claim 1 having voltage source characteristics,
The stabilizing and frequency sensing integrated controller measures direct current voltage, and outputs modulation voltage which is overlapped on the grid-side converter after passing through an amplifier K PSS and a high-pass filter with a time constant of T dc; the stabilizing and frequency sensing integrated controller can enable the direct-current voltage to sense only the frequency change of the power grid.
3. The full power conversion wind turbine of claim 1 having voltage source characteristics,
When the stability control coefficient K PSS is set, the value of the stability control coefficient K PSS is set to be smaller than K PSSmax.
4. The full power conversion wind turbine of claim 1 having voltage source characteristics, wherein the machine side unit comprises: a machine side converter and a wind wheel;
a machine side converter is adopted to control wind power captured by a wind wheel;
The machine side converter adopts a vector control mode based on rotor flux linkage orientation;
the control method of the machine side converter comprises the following steps:
Rotation speed of generator The product of the power factor k opt and the power factor k opt is used as the reference value of the output power of the machine side converterDC side voltage/>After passing through a first-order low-pass filter with a time constant of T and a differentiation link with a gain of-K C, the output is/>
5. The full power conversion wind turbine of claim 1 having voltage source characteristics, wherein the machine side unit comprises: a machine side converter control loop;
the machine side converter control loop includes: a machine side stabilization controller;
The machine side stable controller is a first-order low-pass filter with three-stage time constant of T 2 added in an inertia transfer control loop, and the three-stage low-pass filters are connected in series.
6. The full power conversion wind turbine generator system with voltage source characteristics according to claim 5, wherein when the value of T 2 is selected, the adjustment time of the power system frequency change process is T s, and the corresponding inertia time constant T iner is T s/4.
7. The full power conversion wind turbine with voltage source characteristics of claim 1, wherein designing grid-side, machine-side stability control parameters comprises:
step one: establishing a state space model or a simulation model of a voltage source controlled wind turbine generator weak grid system, and judging the running stability of a wind turbine generator weak grid to obtain potential resonance frequency;
step two: according to the potential resonance frequency of the wind turbine generator, which is obtained in the first step, a low-pass filtering time constant T 2 of side induced stability control of the setter is set;
step three: according to the potential resonance frequency, setting a high-pass filtering time constant T dc of the network side stability control; determining the maximum value which can be taken by the K PSS according to the actual operation condition of the wind turbine;
Step four: giving a network side stability control coefficient K PSS value, substituting the value into a state space model to verify the validity of a designed parameter T 2、Tdc、KPSS; building an electrical simulation model to further verify the validity of the set machine side and network side stable control parameters; if the electric oscillation is restrained, the stability control parameters of the machine side and the network side are designed; if the electrical oscillations are not suppressed, a net side stability control coefficient K PSS is redesigned, and theoretical verification and simulation verification are continued until the designed parameters stabilize the system.
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