CN113054686A - Low voltage ride through control method and device for permanent magnet wind turbine generator - Google Patents
Low voltage ride through control method and device for permanent magnet wind turbine generator Download PDFInfo
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- CN113054686A CN113054686A CN202110510105.1A CN202110510105A CN113054686A CN 113054686 A CN113054686 A CN 113054686A CN 202110510105 A CN202110510105 A CN 202110510105A CN 113054686 A CN113054686 A CN 113054686A
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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
- 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 relates to a low voltage ride through control method and device of a permanent magnet wind turbine generator. When the permanent magnet wind turbine generator is in a low voltage ride through state, the active power and the reactive power of the permanent magnet wind turbine generator are set by controlling the converter on the generator side and the converter on the grid side, and the unloading resistor is adopted on the direct current side, so that the risk of overspeed grid disconnection of the permanent magnet wind turbine generator during the low voltage ride through period can be reduced, and the reactive power support can be provided for a power grid according to the requirements of the national standard GB/T36995-2018 wind turbine generator fault voltage ride through capability test regulation during the low voltage ride through period, so that the low voltage ride through of the permanent magnet wind turbine generator is realized.
Description
Technical Field
The invention relates to the technical field of wind power generation, in particular to a low-voltage ride through control method and device of a permanent magnet wind turbine generator.
Background
The existing wind power integration is mainly carried out in a centralized mode, and a wind power group is disconnected under the influence of power grid faults, so that power impact is brought to a connected power grid, and the safe operation of a wind power-containing power system can be endangered in severe cases. The wind turbine generator set does not have low voltage ride-through (LVRT) is considered to be a main cause of the grid disconnection. Therefore, the LVRT control method of the wind turbine generator is generally regarded as important.
The permanent magnet wind turbine generator is one of main power units adopted by wind power at present, based on the existing LVRT control method, the permanent magnet wind turbine generator can realize LVRT under the non-rated working condition, but the risk of overspeed disconnection still exists under the rated working condition.
Therefore, how to design a low voltage ride through control method and device for a permanent magnet wind turbine generator, which can reduce the risk of overspeed and grid disconnection, becomes a problem to be solved in the field at present.
Disclosure of Invention
The invention aims to provide a low voltage ride through control method and a low voltage ride through control device for a permanent magnet wind turbine generator.
In order to achieve the purpose, the invention provides the following scheme:
a low voltage ride through control method of a permanent magnet wind turbine generator comprises the following steps:
acquiring a power grid voltage;
judging the running state of the permanent magnet wind turbine generator according to the power grid voltage;
when the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low voltage ride through state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter are unbalanced, and a second direct current side capacitor voltage is obtained through the control of the generator side converter and the control of the grid side converter;
judging whether the second direct current side capacitor voltage is larger than an action threshold value, wherein the action threshold value is the value of input unloading resistance and is 1.1 times of the rated value of the first direct current side capacitor voltage;
if not, returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter;
if so, inputting an unloading resistor at the direct current side to obtain a third direct current side capacitor voltage;
judging whether the third direct current side capacitor voltage is larger than the action threshold value;
if yes, keeping the unloading resistor input;
and if not, removing the unloading resistor, and returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter.
Optionally, the method further includes determining a power reference value of the generator-side converter, specifically including:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, setting an active power reference value of a generator side converter as maximum wind energy capture power; in order to reduce the copper consumption of the stator winding, the reactive power reference value of the generator-side converter is set to be 0;
when the permanent magnet wind turbine generator is in a low voltage ride through state, the active power reference value P of the generator side convertersminThe calculation process of (2) is as follows:
the equation of motion of the rotor of the permanent magnet generator is as follows:
wherein: omegarIs the rotor speed; t is time; omegarIs the synchronous angular velocity; t isjIs inertiaA time constant; t ismIs a mechanical torque; t iseIs an electromagnetic torque; superscript represents a per unit value;
when t is increased from 0 to t1Then, t is obtained according to the equation of motion of the rotor of the permanent magnet generator1The moment rotor speed omegar(t1) Comprises the following steps:
when t is1∈[0，0.625]When there is Te *＝Ps *，PsActive power of a converter at the generator side;
when t is1When 0.625, rotor speed Ωr(0.625) is:
if the permanent magnet wind turbine generator does not overspeed and is off-grid during the low voltage ride through period, the following steps are carried out: omegar(0.625)≤Ωrlim，ΩrlimSetting a value for overspeed protection of the permanent magnet wind turbine generator;
this gives:
namely:
when in use
When the temperature of the water is higher than the set temperature,
when in use
When the temperature of the water is higher than the set temperature,
P* smin＝0 (7)。
optionally, the method further includes determining a power reference value of the grid-side converter, specifically including:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the grid-side converter works in a unit power factor state, and a reactive power reference value of the grid-side converter is set to be 0;
when the permanent magnet wind turbine generator is in a low voltage ride through state, the calculation process of the active power reference value and the reactive power reference value of the grid-side converter is as follows:
during the low voltage ride through period, according to the national standard GB/T36995 of the people's republic of China and 2018 wind generating set fault voltage ride through capability test regulations, under the condition that an additional reactive compensation device is not considered, the dynamic reactive current I provided by the permanent magnet wind generating set to the power gridTCSatisfies the following conditions:
ITC≥1.5×(0.9-UT)In (8)
wherein: i isTCDynamic reactive current, I, supplied to the grid by a permanent magnet wind turbinenRated current, U, of the wind turbineTIs the voltage per unit value of the test point line of the wind turbine generator, 0.2<UT<0.9；
According to the formula (8), during low voltage ride through, the reactive current reference value I of the grid-side convertergqrefComprises the following steps:
I* gqref＝1.5×(0.9-UT)In * (9)
from this, the reference value Q of the reactive power of the grid-side converter during low voltage ride through can be derivedgrefComprises the following steps:
Q* gref＝UT×I* gqref (10)
the reference value of active current obtained by the control of the DC side capacitor voltage is I* gdref1；
Maximum allowable current I of the grid-side convertermaxThe obtained active current reference value is Igdref2；
Get Igdref1And Igdref2The minimum value of the voltage-measuring current is used as a reference value of the active current of the grid-measuring converter during the low-voltage ride-through period, namely:
I*gdref＝min(I*gdref1，I*gdref2) (12)；
wherein: min (I)gdref1，I*gdref2) Is expressed by taking Igdref1And Igdref2Minimum value of (d);
it can thus be derived the active power reference P of the grid-side converter during low voltage ride throughgrefComprises the following steps:
P* gref＝UT×I* gdref (13)。
optionally, the controlling the generator-side converter specifically includes:
the generator side converter is controlled by a double closed loop;
the q-axis sends a difference value obtained by comparing the active power reference value of the generator-side converter with the active power actually sent by the generator-side converter into a PI1 regulator;
the d-axis sets a reactive current reference value of the generator-side converter to 0;
comparing the reference values of the d-axis current and the q-axis current with the actual values, and regulating the current difference value into a voltage control quantity through PI2 and PI3 regulators;
and the q axis is added with the generated no-load induced electromotive force, and the d axis and the q axis are respectively added with the coupling phases of respective voltage components to obtain the rotor voltage control quantity under the dq coordinate system, and the control quantity of the three-phase voltage of the rotor of the permanent magnet generator is obtained through coordinate transformation.
Optionally, the controlling the grid-side converter specifically includes:
acquiring d-axis and q-axis current reference values of the grid-side converter;
comparing the d-axis and q-axis current reference values of the grid-side converter with actual values, and obtaining voltage control quantities through PI5 and PI6 regulators;
and the d-axis and the q-axis are added with respective power grid voltage feed-forward phases and coupling phases of voltage components to obtain voltage control quantity at the port of the grid-side converter, and then the control quantity of the three-phase voltage is obtained through coordinate transformation.
Optionally, the unloading resistor has a resistance value:
wherein R is an unloading resistor; u shapedcmaxThe maximum voltage that the direct current side capacitor can bear; delta PmaxThe maximum unbalanced power to be borne by the unloading resistor.
Optionally, when the active power actually emitted by the generator-side converter and the active power actually emitted by the grid-side converter cannot be balanced, the unbalanced power to be borne by the unloading resistor is a difference between the active power output by the generator-side converter and the active power output by the grid-side converter after being controlled by the generator-side converter and the side grid converter.
The invention also provides a low voltage ride through control device of the permanent magnet wind turbine generator, which comprises:
the power grid voltage acquisition unit is used for acquiring power grid voltage;
the first judgment unit is used for judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low voltage ride through state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter are unbalanced, and a second direct current side capacitor voltage is obtained through the control of the generator side converter and the control of the grid side converter;
a second determination unit configured to determine whether or not the second dc-side capacitor voltage is greater than an operation threshold value, where the operation threshold value is a value of an input unloading resistor and is 1.1 times a rated value of the first dc-side capacitor voltage;
if not, returning to the first judgment unit;
if so, inputting an unloading resistor at the direct current side to obtain a third direct current side capacitor voltage;
a third determining unit, configured to determine whether the third dc-side capacitor voltage is greater than the action threshold;
if yes, keeping the unloading resistor input;
and if not, removing the unloading resistor and returning to the first judgment unit.
Optionally, the power supply further includes a generator-side converter power reference value determining unit, where the generator-side converter power reference value determining unit specifically includes:
the first judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the first normal operation state module is used for setting an active power reference value of the generator side converter as maximum wind energy capture power when the permanent magnet wind turbine generator is in a normal operation state;
the first reactive power reference value setting module is used for setting the reactive power reference value of the generator side converter to 0 in order to reduce the copper consumption of the stator winding;
and the first power reference value calculating module is used for calculating an active power reference value of the generator side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
Optionally, the system further includes a grid-side converter power reference value determining unit, where the grid-side converter power reference value determining unit specifically includes:
the second judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the second normal operation state module is used for enabling the grid-side converter to work in a unit power factor state when the permanent magnet wind turbine generator is in a normal operation state;
the second reactive power reference value setting module is used for setting the reactive power reference value of the grid-side converter to 0;
and the second power reference value calculating module is used for calculating an active power reference value and a reactive power reference value of the grid-side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a low voltage ride through control method and a device of a permanent magnet wind turbine generator, which can reduce the risk of overspeed off-grid of the permanent magnet wind turbine generator during low voltage ride through and ensure that the permanent magnet wind turbine generator provides reactive power support for a power grid during low voltage ride through according to the requirements of national standard GB 201t 36995 of the people's republic of China-.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a flowchart of a low voltage ride through control method for a permanent magnet wind turbine generator according to embodiment 1 of the present invention;
FIG. 2 is a block diagram of the control of a generator side converter;
fig. 3 is a control schematic block diagram of a grid-side converter;
fig. 4 is a block diagram of a low voltage ride through control device of a permanent magnet wind turbine generator according to embodiment 2 of the present invention.
Description of the symbols: 1. a power grid voltage acquisition unit; 2. a first judgment unit; 3. a second judgment unit; 4. and a third judging unit.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a low-voltage ride through control method and device for a permanent magnet wind turbine generator. Under the control of the grid-side converter, the DC-side capacitor voltage is stabilized at its reference value. During the low voltage ride through period, active power between the generator side converter and the grid side converter is unbalanced, the unbalanced power enables the direct current side capacitor voltage to be increased, and the direct current side capacitor voltage can exceed a safety threshold value in serious conditions, so that the wind turbine generator is off-grid. Therefore, in order to reduce the risk of the wind turbine generator off-grid, the direct current side adopts an unloading resistor. By controlling the generator-side converter and the grid-side converter, if the dc-side capacitor voltage exceeds an operation threshold, the load-relieving resistor is put in, and unbalanced power between the generator-side converter and the grid-side converter is consumed, so that the dc-side capacitor voltage is maintained within a safe range.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1:
referring to fig. 1, a low voltage ride through control method for a permanent magnet wind turbine generator according to embodiment 1 of the present invention includes the following steps:
s1: obtaining the voltage of the power grid.
Before step S1, determining a power reference value of the generator-side converter, specifically including:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the active power reference value of the generator side converter is set as the maximum wind energy capture power. To reduce the stator winding copper losses, the generator-side converter reactive power reference is set to 0.
When the permanent magnet wind turbine generator is in a low-voltage ride-through state, the minimum value P of the active power of the generator set for ensuring that the permanent magnet wind turbine generator does not generate overspeed and offline can be deduced according to the equation of motion of the rotor of the permanent magnet generatorsminA 1 is to PsminAs an active power reference value for the generator side converter during low voltage ride through. PsminThe calculation process is as follows:
the equation of motion of the rotor of the permanent magnet generator is as follows:
wherein: omegarIs the rotor speed; t is time; omegarIs the synchronous angular velocity; t isjIs the inertia time constant; t ismIs a mechanical torque; t iseIs an electromagnetic torque; superscript denotes per unit value.
When t is increased from 0 to t1(t1>0) Then, according to the rotor motion equation, t can be obtained1The moment rotor speed omegar(t1) Comprises the following steps:
when t is1∈[0，0.625]When there is Te *＝Ps *，PsThe active power of the converter at the generator side.
When t is1When 0.625, rotor speed Ωr(0.625) is:
if the permanent magnet wind turbine generator does not overspeed and is off-grid during the low voltage ride through period, the following steps are performed: omegar(0.625)≤Ωrlim，ΩrlimAnd setting the overspeed protection constant value for the permanent magnet wind turbine generator.
This gives:
namely:
when in use
When the temperature of the water is higher than the set temperature,
when in use
When the temperature of the water is higher than the set temperature,
P* smin＝0 (7)。
specifically, before step S1, determining a power reference value of the grid-side converter further includes:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the grid-side converter worksIn a unit power factor state, a reactive power reference value of the grid-side converter is set to be 0; the active power of the grid-side converter is controlled by the voltage of a direct-current side capacitor and the maximum allowable current I of the grid-side convertermaxAnd determining that the active power reference value of the grid-side converter does not need to be set independently.
When the permanent magnet wind turbine generator is in a low voltage ride through state, the calculation process of the active power reference value and the reactive power reference value of the grid-side converter is as follows:
during the low voltage ride through period, according to the national standard GB/T36995 of the people's republic of China and 2018 wind generating set fault voltage ride through capability test regulations, under the condition that an additional reactive compensation device is not considered, the dynamic reactive current I provided by the permanent magnet wind generating set to the power gridTCSatisfies the following conditions:
ITC≥1.5×(0.9-UT)In,(0.2≤UT≤0.9) (8)
wherein: i isTCDynamic reactive current, I, supplied to the grid by a permanent magnet wind turbinenRated current, U, of the wind turbineTAnd the voltage per unit value of the test point line of the wind turbine generator is obtained.
According to the formula (8), during low voltage ride through, the reactive current reference value I of the grid-side convertergqrefComprises the following steps:
I* gqref＝1.5×(0.9-UT)In * (9)
from this, the reference value Q of the reactive power of the grid-side converter during low voltage ride through can be derivedgrefComprises the following steps:
Q* gref＝UT×I* gqref (10)
active current reference value I of the grid-side convertergdrefThe maximum allowable current I of the grid-side converter is controlled by the voltage of a direct-current side capacitormaxAnd (6) determining. The active current reference value obtained by controlling the direct current side capacitor voltage is I* gdref1(ii) a Maximum allowable current I of the grid-side convertermaxThe obtained active current reference value is Igdref2；
Get Igdref1And Igdref2The minimum value of the voltage-measuring current is used as a reference value of the active current of the grid-measuring converter during the low-voltage ride-through period, namely:
I*gdref＝min(I*gdref1，I*gdref2) (12)；
wherein: min (I)gdref1，I*gdref2) Is expressed by taking Igdref1And Igdref2Minimum value of (d);
it can thus be derived the active power reference P of the grid-side converter during low voltage ride throughgrefComprises the following steps:
P* gref＝UT×I* gdref (13)。
as a possible implementation manner, the controlling of the generator-side converter specifically includes:
fig. 2 shows a control schematic block diagram of the generator-side converter.
The voltage equation of the permanent magnet generator is as follows:
wherein: u. ofsdIs the d-axis component of the generator outlet voltage; u. ofsqIs the q-axis component of the generator outlet voltage; i.e. isdIs the d-axis component of the generator outlet current; i.e. isqIs the q-axis component of the generator outlet current; l isdA stator d-axis inductance; l isqA stator q-axis inductance; rsIs a stator resistor; omegasIs the generator speed; ΨfIs a permanent magnetic flux.
The generator side converter is controlled by adopting double closed loops, a q-axis outer loop is a generator output active power control loop, and a difference value obtained by comparing an active power reference value of the generator side converter with an active power actually sent by the generator side converter is sent to a PI1 regulator. And the d-axis sets the reactive current reference value of the generator side converter to be 0, so that the reactive power reference value can be ensured to be 0.
The inner ring is a current control ring, after the reference values of the currents of the d axis and the q axis are compared with actual values, the current difference value is adjusted into a voltage control quantity through PI2 and PI3 regulators, the q axis is added with the no-load induced electromotive force of power generation, the d axis and the q axis are respectively added with the coupling phases of respective voltage components, the rotor voltage control quantity under a dq coordinate system can be obtained, and then the control quantity of the three-phase voltage of the rotor of the permanent magnet generator is obtained through coordinate transformation.
As a possible implementation manner, the controlling of the grid-side converter specifically includes:
as shown in fig. 3, a control schematic block diagram of the grid-side converter is shown.
Under the dq synchronous rotation coordinate system, the active power and the reactive power output by the grid-side converter are as follows:
wherein: u. ofgdIs the d-axis component of the grid voltage; u. ofgqIs the q-axis component of the grid voltage; i.e. igdIs the d-axis component of the grid current; i.e. igqIs the q-axis component of the grid current; pgActive power, Q, output for a grid-side convertergThe reactive power is output by the grid-side converter.
Oriented by the grid voltage vector, the d-axis voltage component is:
ugd＝ug (16)
wherein u isgThe effective value of the grid line voltage is obtained;
the q-axis voltage component is:
ugq＝0 (17)
the active and reactive power output by the grid-side converter can be represented again as:
therefore, active and reactive decoupling control of the grid-side converter can be realized.
An outer ring acquires d-axis and q-axis current reference values of the grid-side converter;
the inner ring compares the d-axis and q-axis current reference values of the grid-side converter with actual values, and obtains voltage control quantity through PI5 and PI6 regulators;
and the d-axis and the q-axis are added with respective power grid voltage feed-forward phases and coupling phases of voltage components to obtain voltage control quantity at the port of the grid-side converter, and then the control quantity of the three-phase voltage is obtained through coordinate transformation.
S2: judging the running state of the permanent magnet wind turbine generator according to the power grid voltage;
it should be noted that when the grid voltage is lower than 0.9p.u., the permanent magnet wind turbine is in a low voltage ride through state, otherwise, the permanent magnet wind turbine is in a normal operation state.
When the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low-voltage ride-through state, the active power actually sent by the generator side converter and the active power actually sent by the grid side converter are unbalanced, and second direct-current side capacitor voltage is obtained through control over the generator side converter and control over the grid side converter.
S3: and judging whether the second direct current side capacitor voltage is larger than an action threshold value, wherein the action threshold value is the value of input unloading resistance and is 1.1 times of the rated value of the first direct current side capacitor voltage.
If not, returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter;
and if so, inputting an unloading resistor on the direct current side to obtain a third direct current side capacitor voltage.
The unbalanced power delta P born by the unloading resistor is the active power P output by the generator side converter after being controlled by the generator side converter and the side grid convertersAnd active power P output by the grid-side convertergThe difference between them, i.e. Δ P ═ Ps-Pg。
The magnitude of the unloading resistance value of the direct current side is the maximum unbalanced power delta P born by the unloading resistancemaxMaximum voltage U bearable by DC side capacitordcmaxAnd (4) jointly determining. When the nonlinear element in the circuit is not considered, the expression of the unloading resistance is:
wherein R is an unloading resistor; u shapedcmaxThe maximum voltage that the direct current side capacitor can bear; delta PmaxThe maximum unbalanced power to be borne by the unloading resistor.
S4: judging whether the third direct current side capacitor voltage is larger than the action threshold value;
if yes, keeping the unloading resistor input;
and if not, removing the unloading resistor, and returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter.
By the method, when the permanent magnet wind turbine generator normally operates, active power between the generator side converter and the grid side converter is kept balanced. Under the control of the grid-side converter, the DC-side capacitor voltage is stabilized at its reference value. During the low voltage ride through period, active power between the generator side converter and the grid side converter is unbalanced, the unbalanced power enables the direct current side capacitor voltage to be increased, and the direct current side capacitor voltage can exceed a safety threshold value in serious conditions, so that the wind turbine generator is off-grid. Therefore, in order to reduce the risk of the wind turbine generator off-grid, the direct current side adopts an unloading resistor. After the control of the generator side converter and the control of the side grid converter, if the direct current side capacitor voltage exceeds an action threshold value, an unloading resistor is put into the converter, unbalanced power between the generator side converter and the grid side converter is consumed, and the direct current side capacitor voltage is maintained in a safe range.
Example 2:
referring to fig. 4, the present invention further provides a low voltage ride through control device for a permanent magnet wind turbine, the device includes:
the power grid voltage acquisition unit 1 is used for acquiring power grid voltage;
the first judgment unit 2 is used for judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low voltage ride through state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter are unbalanced, and a second direct current side capacitor voltage is obtained through the control of the generator side converter and the control of the grid side converter;
a second determination unit 3, configured to determine whether the second dc-side capacitor voltage is greater than an operation threshold, where the operation threshold is a value of the input unloading resistance and is 1.1 times a rated value of the first dc-side capacitor voltage; if not, returning to the first judgment unit 2;
if so, inputting an unloading resistor at the direct current side to obtain a third direct current side capacitor voltage;
the third judging unit 4 is configured to judge whether the third dc-side capacitor voltage is greater than the operation threshold;
if yes, keeping the unloading resistor input;
if not, the unloading resistor is removed, and the operation returns to the first judgment unit 2.
Specifically, the power generation system further comprises a power reference value determining unit of the generator-side converter, wherein the power reference value determining unit of the generator-side converter specifically comprises:
the first judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the first normal operation state module is used for setting an active power reference value of the generator side converter as maximum wind energy capture power when the permanent magnet wind turbine generator is in a normal operation state;
the first reactive power reference value setting module is used for setting the reactive power reference value of the generator side converter to 0 in order to reduce the copper consumption of the stator winding;
and the first power reference value calculating module is used for calculating an active power reference value of the generator side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
Specifically, the method further includes a grid-side converter power reference value determining unit, where the grid-side converter power reference value determining unit specifically includes:
the second judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the second normal operation state module is used for enabling the grid-side converter to work in a unit power factor state when the permanent magnet wind turbine generator is in a normal operation state;
the second reactive power reference value setting module is used for setting the reactive power reference value of the grid-side converter to 0;
and the second power reference value calculating module is used for calculating an active power reference value and a reactive power reference value of the grid-side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
By the device, the risk of overspeed disconnection of the permanent magnet wind turbine generator during low voltage ride through can be reduced, and the permanent magnet wind turbine generator can provide reactive power support for a power grid during low voltage ride through according to the requirements of national standard GB/T36995-.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. A low voltage ride through control method of a permanent magnet wind turbine generator is characterized by comprising the following steps:
acquiring a power grid voltage;
judging the running state of the permanent magnet wind turbine generator according to the power grid voltage;
when the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low voltage ride through state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter are unbalanced, and a second direct current side capacitor voltage is obtained through the control of the generator side converter and the control of the grid side converter;
judging whether the second direct current side capacitor voltage is larger than an action threshold value, wherein the action threshold value is the value of input unloading resistance and is 1.1 times of the rated value of the first direct current side capacitor voltage;
if not, returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter;
if so, inputting an unloading resistor at the direct current side to obtain a third direct current side capacitor voltage;
judging whether the third direct current side capacitor voltage is larger than the action threshold value;
if yes, keeping the unloading resistor input;
and if not, removing the unloading resistor, and returning to the step of obtaining a second direct-current side capacitor voltage through the control of the generator side converter and the control of the grid side converter.
2. The method for controlling the low voltage ride through of the permanent magnet wind turbine generator set according to claim 1, further comprising determining a power reference value of the generator-side converter, specifically comprising:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, setting an active power reference value of a generator side converter as maximum wind energy capture power; in order to reduce the copper consumption of the stator winding, the reactive power reference value of the generator-side converter is set to be 0;
when the permanent magnet wind turbine generator is in a low voltage ride through state, the active power reference value P of the generator side convertersminThe calculation process of (2) is as follows:
the equation of motion of the rotor of the permanent magnet generator is as follows:
wherein: omegarIs the rotor speed; t is time; omegarIs the synchronous angular velocity; t isjIs the inertia time constant; t ismIs a mechanical torque; t iseIs an electromagnetic torque; superscript represents a per unit value;
when t is increased from 0 to t1Then, t is obtained according to the equation of motion of the rotor of the permanent magnet generator1The moment rotor speed omegar(t1) Comprises the following steps:
when t is1∈[0，0.625]When there is Te *＝Ps *，PsActive power of a converter at the generator side;
when t is1When 0.625, rotor speed Ωr(0.625) is:
if the permanent magnet wind turbine generator does not overspeed and is off-grid during the low voltage ride through period, the following steps are carried out: omegar(0.625)≤Ωrlim，ΩrlimSetting a value for overspeed protection of the permanent magnet wind turbine generator;
this gives:
namely:
when in use
When the temperature of the water is higher than the set temperature,
when in use
When the temperature of the water is higher than the set temperature,
P* smin＝0 (7)。
3. the method for controlling the low voltage ride through of the permanent magnet wind turbine generator according to claim 1, further comprising determining a power reference value of the grid-side converter, specifically comprising:
judging the running state of the permanent magnet wind turbine generator;
when the permanent magnet wind turbine generator is in a normal operation state, the grid-side converter works in a unit power factor state, and a reactive power reference value of the grid-side converter is set to be 0;
when the permanent magnet wind turbine generator is in a low voltage ride through state, the calculation process of the active power reference value and the reactive power reference value of the grid-side converter is as follows:
during the low voltage ride through period, according to the national standard GB/T36995 of the people's republic of China and 2018 wind generating set fault voltage ride through capability test regulations, under the condition that an additional reactive compensation device is not considered, the dynamic reactive current I provided by the permanent magnet wind generating set to the power gridTCSatisfies the following conditions:
ITC≥1.5×(0.9-UT)In (8)
wherein: i isTCDynamic reactive current, I, supplied to the grid by a permanent magnet wind turbinenRated current, U, of the wind turbineTIs the voltage per unit value of the test point line of the wind turbine generator, 0.2<UT<0.9；
According to the formula (8), during low voltage ride through, the reactive current reference value I of the grid-side convertergqrefComprises the following steps:
I* gqref＝1.5×(0.9-UT)In * (9)
from this, the reference value Q of the reactive power of the grid-side converter during low voltage ride through can be derivedgrefComprises the following steps:
Q* gref＝UT×I* gqref (10)
the reference value of active current obtained by the control of the DC side capacitor voltage is I* gdref1；
Maximum allowable current I of the grid-side convertermaxThe obtained active current reference value is Igdref2；
Get Igdref1And Igdref2The minimum value of the voltage-measuring current is used as a reference value of the active current of the grid-measuring converter during the low-voltage ride-through period, namely:
I*gdref＝min(I*gdref1，I*gdref2) (12)；
wherein: min (I)gdref1，I*gdref2) Is expressed by taking Igdref1And Igdref2Minimum value of (d);
it can thus be derived the active power reference P of the grid-side converter during low voltage ride throughgrefComprises the following steps:
P* gref＝UT×I* gdref (13)。
4. the method for controlling the low voltage ride through of the permanent magnet wind turbine generator set according to claim 1, wherein the controlling of the generator-side converter specifically comprises:
the generator side converter is controlled by a double closed loop;
the q-axis sends a difference value obtained by comparing the active power reference value of the generator-side converter with the active power actually sent by the generator-side converter into a PI1 regulator;
the d-axis sets a reactive current reference value of the generator-side converter to 0;
comparing the reference values of the d-axis current and the q-axis current with the actual values, and regulating the current difference value into a voltage control quantity through PI2 and PI3 regulators;
and the q axis is added with the generated no-load induced electromotive force, and the d axis and the q axis are respectively added with the coupling phases of respective voltage components to obtain the rotor voltage control quantity under the dq coordinate system, and the control quantity of the three-phase voltage of the rotor of the permanent magnet generator is obtained through coordinate transformation.
5. The method for controlling the low voltage ride through of the permanent magnet wind turbine generator according to claim 1, wherein the controlling of the grid-side converter specifically comprises:
acquiring d-axis and q-axis current reference values of the grid-side converter;
comparing the d-axis and q-axis current reference values of the grid-side converter with actual values, and obtaining voltage control quantities through PI5 and PI6 regulators;
and the d-axis and the q-axis are added with respective power grid voltage feed-forward phases and coupling phases of voltage components to obtain voltage control quantity at the port of the grid-side converter, and then the control quantity of the three-phase voltage is obtained through coordinate transformation.
6. The low voltage ride through control method of the permanent magnet wind turbine generator set according to claim 1, wherein the unloading resistor has a resistance value of:
wherein R is an unloading resistor; u shapedcmaxThe maximum voltage that the direct current side capacitor can bear; delta PmaxThe maximum unbalanced power to be borne by the unloading resistor.
7. The method according to claim 1, wherein when the active power actually generated by the generator-side converter and the active power actually generated by the grid-side converter cannot be balanced, the unbalanced power to be borne by the unloading resistor is a difference between the active power output by the generator-side converter and the active power output by the grid-side converter after the generator-side converter is controlled and the grid-side converter is controlled.
8. The utility model provides a low voltage ride through controlling means of permanent magnetism wind turbine generator system which characterized in that includes:
the power grid voltage acquisition unit is used for acquiring power grid voltage;
the first judgment unit is used for judging the running state of the permanent magnet wind turbine generator according to the power grid voltage;
when the permanent magnet wind turbine generator is in a normal operation state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter keep balance; the voltage of the first direct current side capacitor is stabilized at a reference value, and the reference value is a value of the permanent magnet wind turbine generator set during normal operation;
when the permanent magnet wind turbine generator set is in a low voltage ride through state, the active power actually sent out by the generator side converter and the active power actually sent out by the grid side converter are unbalanced, and a second direct current side capacitor voltage is obtained through the control of the generator side converter and the control of the grid side converter;
a second determination unit configured to determine whether or not the second dc-side capacitor voltage is greater than an operation threshold value, where the operation threshold value is a value of an input unloading resistor and is 1.1 times a rated value of the first dc-side capacitor voltage;
if not, returning to the first judgment unit;
if so, inputting an unloading resistor at the direct current side to obtain a third direct current side capacitor voltage;
a third determining unit, configured to determine whether the third dc-side capacitor voltage is greater than the action threshold;
if yes, keeping the unloading resistor input;
and if not, removing the unloading resistor and returning to the first judgment unit.
9. The low voltage ride through control device of the permanent magnet wind turbine generator according to claim 8, further comprising a generator-side converter power reference value determining unit, wherein the generator-side converter power reference value determining unit specifically includes:
the first judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the first normal operation state module is used for setting an active power reference value of the generator side converter as maximum wind energy capture power when the permanent magnet wind turbine generator is in a normal operation state;
the first reactive power reference value setting module is used for setting the reactive power reference value of the generator side converter to 0 in order to reduce the copper consumption of the stator winding;
and the first power reference value calculating module is used for calculating an active power reference value of the generator side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
10. The low voltage ride through control device of the permanent magnet wind turbine generator according to claim 8, further comprising a grid-side converter power reference value determining unit, wherein the grid-side converter power reference value determining unit specifically includes:
the second judgment module is used for judging the running state of the permanent magnet wind turbine generator;
the second normal operation state module is used for enabling the grid-side converter to work in a unit power factor state when the permanent magnet wind turbine generator is in a normal operation state;
the second reactive power reference value setting module is used for setting the reactive power reference value of the grid-side converter to 0;
and the second power reference value calculating module is used for calculating an active power reference value and a reactive power reference value of the grid-side converter when the permanent magnet wind turbine generator is in a low voltage ride through state.
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