CN109861262A - A kind of control flexible direct current and the stable method and system of weak AC network - Google Patents
A kind of control flexible direct current and the stable method and system of weak AC network Download PDFInfo
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Abstract
The invention discloses a kind of control flexible direct currents and the stable method and system of weak AC network, belong to field of power system.The method of the present invention comprises determining that operating point in AC network power transfer characteristic curve Us‑PsWith flexible direct current power characteristic Us‑PcPosition；Determine that operating point position, including operating point are located at Us‑PcConsecutive variations section, operating point are located at Us‑PcForce revert section or without different situations such as operating points；When flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage UsLower than setting threshold value Usth, then FRTS parameter I is resetcdF；Operating status after real-time monitoring direct current and weak AC network combined hybrid system fault disturbance stops i when causing dynamic instability because of electric current recoverycdAnd icqIncrease；If UsIt is still below UsthAnd the duration is more than Ts, then drop dc power △ P is returnedcTo promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.The present invention can restore combined hybrid system stable operation.
Description
Technical field
The present invention relates to field of power systems, and more particularly, to a kind of control flexible direct current and weak AC network
Stable method and system.
Background technique
Voltage source converter (Voltage Source Converter, VSC) is flexible DC transmission (VSC-HVDC) system
Core component in system, the extensive use under different scenes become the weight for pushing the development of electric system power electronicsization
Want form.VSC response characteristic after disturbed, by remarkable effect in the Multiple Time Scales dynamic behaviour of alternating current-direct current combined hybrid system.For
Weak AC network, this effect is more prominent, is affected by this, system stability characteristic (quality) will be increasingly complex.For this purpose, surrounding flexible direct current
With the operation characteristic of weak AC network combined hybrid system and the research of stability contorting, it has also become the hot spot of current electric system research with
Emphasis.
The operation characteristic of VSC-HVDC and weak AC network combined hybrid system, are related to Steady, small disturbed stability
With 3 main aspects of large disturbance stability.Wherein, compared with small disturbance stability Journal of Sex Research, for VSC-HVDC and weak alternating current
The large disturbances stability characteristic (quality) research of net combined hybrid system, relatively lags behind.And in ongoing large disturbances stability characteristic (quality) research, greatly
Multi-focus combined hybrid system frequency stabilization and relevant control problem caused by active imbalance.
Under large disturbances impact, current limit, fault traversing strategy etc. control link of protection, will significantly affect the disturbed sound of VSC
Characteristic is answered, keeps alternating current-direct current combined hybrid system security and stability increasingly complex, stability contorting faces new requirement.
Summary of the invention
In view of the above-mentioned problems, the invention proposes a kind of control flexible direct current and the stable method of weak AC network, it is described
Method includes:
Forecast failure scanning is carried out to flexible direct current and weak AC network combined hybrid system, determines significant reduction direct current and weak friendship
The failure of galvanic electricity net combined hybrid system intensity, grid power transmits after obtaining flexible direct current and weak AC network combined hybrid system large disturbances
Characteristic curve Us-PsWith flexible direct current power characteristic Us-PcOperating point, and determine operating point AC network power pass
Defeated characteristic curve Us-PsWith flexible direct current power characteristic Us-PcPosition:
Determine operating point position, including Us-PcConsecutive variations section, operating point are located at Us-PcForce revert section or without fortune
The different situations such as row point, when flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage UsLower than setting
Set threshold value Usth, then FRTS parameter I is resetcdF；
Operating status after real-time monitoring direct current and weak AC network combined hybrid system fault disturbance causes when because of electric current recovery
When dynamic instability, stop icdAnd icqIncrease；
If UsLower than setting threshold value UsthAnd the time is more than TD, then apply superposition watt current Perturbation △ icdrefIf Us
It hovers in UsL2With UsHBetween unstable equilibrium point, combined hybrid system operating point can be made voluntarily to slide under VSC controller action
Us-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than TS, then drop dc power △ P is returnedc
To promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
Optionally, operating point is located at Us-PcWhen consecutive variations section, applies the small size Perturbation of VSC reference current, make to transport
Row point transits to stable equilibrium point.
Optionally, operating point is located at Us-PcWhen force revert section, make U by large disturbances impacts<UsL1Later, in mixed connection
During system dynamic trajectory rises, Us>UsHWhen, FRTS is exited, and works as UsLess than UsL2When, FRTS will force to limit i againcd
For IcdF, according to formula:
Or
Us≤Usth (2)
As icdAnd icqRestore the stopping criterion increased, maintains PcMaximum power transfer or UsTo set voltage Usth。
Optionally, Us-PsWith Us-PcWhen without public operating point, if UsThere is solution, correspondence system reference capacity and VSC benchmark hold
Value is S to amount respectivelyB、SVSCXsAnd IcdF, the XsAnd IcdFMeet following formula:
Xs≤EsSB/IcdFSVSC (3)
IcdF≤EsSB/XsSVSC (4)
Work as UsReach setting threshold value Usth, corresponding set Xs, can adjust IcdFIt is arranged, then XsAnd IcdFMeet following public
Formula:
The present invention also provides a kind of control flexible direct current and the stable system of weak AC network, present system includes:
Get parms module, carries out forecast failure scanning to flexible direct current and weak AC network combined hybrid system, determines significant
The failure of direct current and weak AC network combined hybrid system intensity is weakened, flexible direct current and weak AC network combined hybrid system large disturbances are obtained
Grid power transfer curve U afterwardss-PsWith flexible direct current power characteristic Us-PcOperating point, and determine operating point exist
AC network power transfer characteristic curve Us-PsWith flexible direct current power characteristic Us-PcPosition:
It determines malfunctioning module, determines operating point position, including Us-PcConsecutive variations section, operating point are located at Us-PcIt forces
Restore section or without different situations such as operating points；
First control module, when flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage Us
Lower than setting threshold value Usth, then FRTS parameter I is resetcdF；
Operating status after second control module, real-time monitoring direct current and weak AC network combined hybrid system fault disturbance, when
When causing dynamic instability because of electric current recovery, stop icdAnd icqIncrease；
Third control module, if UsLower than setting threshold value UsthAnd the time is more than TD, then apply superposition watt current perturbation
Measure △ icdrefIf UsIt hovers in UsL2With UsHBetween unstable equilibrium point, can make combined hybrid system operating point VSC controller make
U is voluntarily slided unders-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than TS, then drop is returned
Dc power △ PcTo promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
The present invention corresponds to the varying strength of AC network after large disturbances impact, and VSC-HVDC and AC network combined hybrid system can
There are a variety of wild effects, including microvariations are unstable, Dynamic- Recovery is unstable, and without steady operation point etc., stablize machine
It manages different.
The present invention adjusts and reduce VSC current limiting low-voltage value in advance, or according to VSC working voltage U after fault disturbancesAnd power PcIt is quiet
State and behavioral characteristics implement current reference value control, can restore combined hybrid system stable operation.
Detailed description of the invention
Fig. 1 is a kind of control flexible direct current and the stable method VSC-HVDC of weak AC network and AC network combined hybrid system
Equivalent model figure；
Fig. 2 is combined hybrid system under a kind of control flexible direct current and the stable method AC network varying strength of weak AC network
Typical operating condition curve graph；
Fig. 3 is that a kind of control flexible direct current and the stable method microvariations wild effect of weak AC network and electric current perturb
Control effect curve graph；
Fig. 4 is a kind of control flexible direct current and weak AC network stable method dynamic instability phenomenon and restoring current control
Effect curve figure processed；
Fig. 5 is a kind of control flexible direct current and the stable method of weak AC network without steady-state operation point phenomenon and resetting IcdF
Control effect curve graph
Fig. 6 is a kind of control flexible direct current and the stable method flow diagram of weak AC network；
Fig. 7 is a kind of control flexible direct current and the stable system construction drawing of weak AC network.
Specific embodiment
Exemplary embodiments of the present invention are introduced referring now to the drawings, however, the present invention can use many different shapes
Formula is implemented, and is not limited to the embodiment described herein, and to provide these embodiments be at large and fully disclose
The present invention, and the scope of the present invention is sufficiently conveyed to person of ordinary skill in the field.Show for what is be illustrated in the accompanying drawings
Term in example property embodiment is not limitation of the invention.In the accompanying drawings, identical cells/elements use identical attached
Icon note.
Unless otherwise indicated, term (including scientific and technical terminology) used herein has person of ordinary skill in the field
It is common to understand meaning.Further it will be understood that with the term that usually used dictionary limits, should be understood as and its
The context of related fields has consistent meaning, and is not construed as Utopian or too formal meaning.
The present invention provides a kind of control flexible direct currents and the stable method of weak AC network, as shown in Figure 6, comprising:
Forecast failure scanning is carried out to flexible direct current and weak AC network combined hybrid system, determines significant reduction direct current and weak friendship
The failure of galvanic electricity net combined hybrid system intensity, grid power transmits after obtaining flexible direct current and weak AC network combined hybrid system large disturbances
Characteristic curve Us-PsWith flexible direct current power characteristic Us-PcOperating point, and determine operating point AC network power pass
Defeated characteristic curve Us-PsWith flexible direct current power characteristic Us-PcPosition:
As shown in Figure 1, in figure, Uc、PcdRespectively VSC outlet side voltage and active；Pc、QcAnd Ps、QsRespectively VSC is defeated
Out and injection AC network it is active with it is idle；UsFor change of current busbar voltage；ud、id、IcRespectively VSC DC voltage, electricity
Stream and ac-side current；Rc、LcAnd CdRespectively commutating reactor resistance, inductance and DC bus capacitor；XsiAnd XseRespectively
For the Thevenin's equivalence reactance of receiving end power grid and external communication power grid；EsFor AC network Thevenin's equivalence potential.
Subtract if large disturbances failure, the receiving end equivalence AC network intensity such as broken string occur for portion of external interconnection AC channel
Weak, combined hybrid system operating condition will change.Whether combined hybrid system is stablized, on the one hand, depend on VSC power characteristic after disturbance
Whether curve and AC network power characteristic have intersection point, i.e., whether have equalization point；On the other hand, VSC is depended on to control
Can system dynamic regulation processed, make combined hybrid system transit to stable equilibrium point.
VSC is counted and amplitude limit link and fault traversing strategy using determine active power, determines Reactive Power Control mode, then right
Answer the nose-shaped set of curves U of AC network power transfer characteristic of varying strength after large disturbancess-PsAnd VSC large disturbances power characteristic
Curve Us-PcAs shown in Figure 2.
When determining that operating point is located at Us-PcConsecutive variations section, operating point are located at Us-PcForce revert section or without operation
When point, when flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage UsLower than setting threshold value
Usth, then FRTS parameter I is resetcdF；
After failure, AC network power transfer characteristic curve Us-PsWith flexible direct current power characteristic Us-PcIntersection point
Oβ, when being located at the consecutive variations section the latter a'b, due to OβIn Us-PsThe low-voltage and high-current of nose-shaped curve lower half portion is run
State, VSC export icdBy fault traversing strategy (Fault Ride Through Strategy, FRTS) clipping.Under the state,
If combined hybrid system is made U by microvariationssIncrease, is then determining PcUnder controller action, icdTo accordingly it reduce, reduced icdEffect
U will be further increased in AC networks, and then persistently reduce icd.The corresponding process, the operating point of combined hybrid system will be by OβFrom
It is dynamic to slide to identical PcCorresponding high voltage low current state, i.e. O'βPoint, as shown in Figure 2.Therefore, OβFor microvariations unstable equilibrium
Point, O'βIt is then post-fault stable equalization point.
Operating status after real-time monitoring direct current and weak AC network combined hybrid system fault disturbance causes when because of electric current recovery
When dynamic instability, stop icdAnd icqIncrease；
Make U by large disturbances impacts<UsL1Later, during combined hybrid system dynamic trajectory rises along o " c, c is crossed
Point is Us>UsHWhen, FRTS is exited, icdAnd icqIt will be under recovery policy effect, by setting rate IcuplimLinear increase.icdAnd icq
And its act on AC network XsThe U of formations, codetermine VSC output power Pc, PcDynamic trajectory is along AC network Us-PsBecome
Change.
As shown in Fig. 2, increasing with VSC Injection Current, when dynamic trajectory is located at Us-PsWhen curve top half 3., PcIncrease
Big UsIt reduces, after crossing inflection point, PcReduce UsIt is then still lasting to reduce, work as UsLess than UsL2When, FRTS will force to limit i againcdFor
IcdF.The corresponding process, PcDynamic trajectory will be in Us-PcWith Us-PsUsL2And UsHInterval period alternately switches, combined hybrid system
Steady-state operation point can not be established.For this purpose, can applying equation (1) or formula (2) be used as icdAnd icqRestore the stopping criterion increased, with dimension
Hold PcMaximum power transfer or UsTo set voltage Usth。
Us≤Usth (2)
If UsLower than setting threshold value UsthAnd the time is more than TD, then apply superposition watt current Perturbation △ icdrefIf Us
It hovers in UsL2With UsHBetween unstable equilibrium point, combined hybrid system operating point can be made voluntarily to slide under VSC controller action
Us-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than TS, then drop dc power △ P is returnedc
To promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
After large disturbances impact, if Us-PsWith Us-PcWithout public operating point, corresponding combined hybrid system will be without steady-state operation point.If Us
There is solution, correspondence system reference capacity and VSC reference capacity difference value are SB、SVSCXsAnd IcdF, should meet respectively formula (3) and
Relationship shown in formula (4).
Xs≤EsSB/IcdFSVSC (3)
IcdF≤EsSB/XsSVSC (4)
Corresponding UsReach setting threshold value UsthOr more, then XsAnd IcdFFormula (5) and formula (6) should be met respectively.
After failure, if AC network XsSignificantly increasing makes Us-PsWith Us-PcWithout intersection point, as in Fig. 2 curve 4. shown in, then mix
Connection system will be unable to stable operation.Stablize for recovery system, corresponding set Xs, can adjust IcdFSetting meets it such as formula
(5) or formula (6).
As shown in Figure 1, investigating exchange Transmission Corridor and cut-offfing leads to XsIncrease the steady of corresponding various operating conditions in various degree
It is qualitative, and the validity of corresponding control strategy.Wherein, VSC, which is used, determines active power and determines Reactive Power Control mode, PcWith
QcRespectively 1250MW, 200MVar, FRTS major parameter are set as UsL1=0.8pu, UsL2=0.5pu, UsH=0.9pu, IcdF
=0.4pu.The reference capacity S of AC network and VSCB、SVSCValue is 100MVA and 1250MVA respectively.In addition, UsthValue is examined
Consider is the different situations such as 0.8pu, 0.85pu and 0.9pu, TDAnd TSRespectively 2.0s and 3.0s.
(1) microvariations wild effect and stability contorting effect
For system shown in Figure 1, after fault disturbance, if XsTransition is to 0.075pu, Us-PsWith Us-PcIntersection point will be located at before
Person lower half portion, as in Fig. 2 curve 2. shown in, combined hybrid system be in low-voltage and high-current operation microvariations unstable equilibrium
Point.
Due to U after disturbancesFor 0.59pu, it is suspended in UsthHereinafter, for this purpose, applying electric current △ icdrefPerturbation control.Such as Fig. 3
It is shown, after perturbation control, combined hybrid system can fast transition to identical PcThe stable equilibrium point of corresponding high voltage low current, UsFor
0.97pu。
(2) dynamic instability phenomenon and stability contorting effect
For system shown in Figure 1, after fault disturbance, if XsTransition is to 0.08pu, Us-PsU will be intersected ats-PcDynamic it is extensive
Multiple area, as in Fig. 2 curve 3. shown in.With this condition, disturbed rear combined hybrid system transient response is as shown in Figure 4, it can be seen that extensive
Multiple period icdIt is linear to be promoted, corresponding PcAlong Us-PsIt is gradually reduced after rising to maximum value inflection point, UsIt is then dull to reduce, and meeting
Us<UsL2When icdI is reduced to by FRTS limitation againcdF。icdReduction makes UsGo up rapidly, and be again introduced into Dynamic- Recovery area, so
Each electrical quantity of combined hybrid system forms periodic swinging, is unable to operate stably.When meeting maximum transmission power criterion shown in formula (1),
Or shown in formula (2) when voltage threshold value criterion, stop VSC and export current boost, then restorable system is stablized, as shown in figure 4, figure
Middle UsthRespectively 0.8pu and 0.9pu.
(3) without steady-state operation point phenomenon and stability contorting effect
After fault disturbance, if XsTo 0.2pu, corresponding AC network is obviously reduced for transition, then is occurred such as curve 4. institute in Fig. 2
Show Us-PsWith Us-PcOperating condition without public operating point, combined hybrid system will be unable to run.When detecting XsWhen being unsatisfactory for formula (5), benefit
Corresponding U can be calculated with formula (6)sthFor the I of 0.8pu and 0.85pucdFMaximum value is respectively 0.24pu and 0.211pu.It is mixed
The transient response and operating point variation for contacting system are as shown in figure 5, resetting IcdFValue limits VSC power transmission power, can make mixed connection system
System maintains to stablize, and voltage is able to ascend to Usth。
The above time-domain simulation results, after demonstrating large disturbances impact, VSC-HVDC and weak AC network combined hybrid system exist
The wild effect of variform can maintain system to stablize according to combined hybrid system operating status.
The present invention also provides a kind of control flexible direct currents and the stable system 200 of weak AC network, as shown in fig. 7, system
200, comprising:
The module that gets parms 201 carries out forecast failure scanning to flexible direct current and weak AC network combined hybrid system, determines aobvious
The failure of reduction direct current and weak AC network combined hybrid system intensity is write, flexible direct current is obtained and is disturbed greatly with weak AC network combined hybrid system
Grid power transfer curve U after dynamics-PsWith flexible direct current power characteristic Us-PcOperating point, and determine operating point
In AC network power transfer characteristic curve Us-PsWith flexible direct current power characteristic Us-PcPosition:
It determines malfunctioning module 202, determines operating point position, including Us-PcConsecutive variations section, operating point are located at Us-PcBy force
System restores section or without different situations such as operating points；
First control module 203, when flexible direct current and weak AC network combined hybrid system are electric without steady-state operation point or operating point
Press UsLower than setting threshold value Usth, then FRTS parameter I is resetcdF；
Operating status after second control module 204, real-time monitoring direct current and weak AC network combined hybrid system fault disturbance,
When causing dynamic instability because of electric current recovery, stop icdAnd icqIncrease；
Third control module 205, if UsLower than setting threshold value UsthAnd the time is more than TD, then apply superposition watt current and take the photograph
Momentum △ icdrefIf UsIt hovers in UsL2With UsHBetween unstable equilibrium point, combined hybrid system operating point can be made in VSC controller
U is voluntarily slided under effects-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than TS, then return
Dc power △ P dropscTo promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
The present invention corresponds to the varying strength of AC network after large disturbances impact, and VSC-HVDC and AC network combined hybrid system can
There are a variety of wild effects, including microvariations are unstable, Dynamic- Recovery is unstable, and without steady operation point etc., stablize machine
It manages different.
The present invention adjusts and reduce VSC current limiting low-voltage value in advance, or according to the quiet of VSC working voltage Us after fault disturbance and power P c
State and behavioral characteristics implement current reference value control, can restore combined hybrid system stable operation.
Claims (5)
1. a kind of control flexible direct current and the stable method of weak AC network, which comprises
Forecast failure scanning is carried out to flexible direct current and weak AC network combined hybrid system, determines significant reduction direct current and weak alternating current
The failure of net combined hybrid system intensity obtains grid power transmission characteristic after flexible direct current and weak AC network combined hybrid system large disturbances
Curve Us-PsWith flexible direct current power characteristic Us-PcOperating point, and determine that operating point is special in AC network power transmission
Linearity curve Us-PsWith flexible direct current power characteristic Us-PcPosition, wherein UsIt is female for flexible direct current and AC network interface
Voltage, the P of linesFor active power, the P for injecting AC networksFor flexible direct current active power of output:
Determine operating point position, including Us-PcConsecutive variations section, operating point are located at Us-PcForce revert section or without operating point
Etc. different situations；
When flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage UsLower than setting threshold value Usth,
Then reset watt current clipping parameter I in FRTScdF；
Operating status after real-time monitoring direct current and weak AC network combined hybrid system fault disturbance causes dynamically when because of electric current recovery
When unstable, stop watt current icdWith reactive current icqIncrease；
If UsLower than setting threshold value UsthAnd the time is more than setting delay TD, then apply superposition watt current Perturbation △ icdref,
If UsIt hovers in setting value UsL2With UsHBetween unstable equilibrium point, can make combined hybrid system operating point under VSC controller action
Voluntarily slide to Us-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than setting delay Ts, then
Return drop dc power △ PcTo promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
2. according to the method described in claim 1, the operating point is located at Us-PcWhen consecutive variations section, apply VSC reference
The small size Perturbation of electric current, makes operating point transit to stable equilibrium point.
3. according to the method described in claim 1, the operating point is located at Us-PcWhen force revert section, rushed by large disturbances
Hitting makes Us<UsL1Later, during combined hybrid system dynamic trajectory rises, Us>UsHWhen, FRTS is exited, and works as UsLess than UsL2When,
FRTS will force to limit i againcdFor IcdF, according to formula:
Or
Us≤Usth (2)
As icdAnd icqRestore the stopping criterion increased, maintains PcMaximum power transfer or UsTo set voltage Usth。
4. according to the method described in claim 1, large disturbances impact after, if Us-PsWith Us-PcWithout public operating point, if UsThere is solution,
Correspondence system reference capacity and VSC reference capacity difference value are SB、SVSCXsAnd IcdF, the XsAnd IcdFMeet following public
Formula:
Xs≤EsSB/IcdFSVSC (3)
IcdF≤EsSB/XsSVSC (4)
Work as UsReach setting threshold value Usth, corresponding set Xs, can adjust IcdFIt is arranged, then XsAnd IcdFMeet following formula:
5. a kind of control flexible direct current and the stable system of weak AC network, the system comprises:
Get parms module, carries out forecast failure scanning to flexible direct current and weak AC network combined hybrid system, determines significant reduction
The failure of direct current and weak AC network combined hybrid system intensity obtains electricity after flexible direct current and weak AC network combined hybrid system large disturbances
Net power transfer characteristic curve Us-PsWith flexible direct current power characteristic Us-PcOperating point, and determine operating point exchanging
Grid power transfer curve Us-PsWith flexible direct current power characteristic Us-PcPosition:
Determine that malfunctioning module, including operating point are located at Us-PcConsecutive variations section, operating point are located at Us-PcForce revert section or
Without different situations such as operating points；
First control module, when flexible direct current and weak AC network combined hybrid system are without steady-state operation point or operating point voltage UsIt is lower than
Set threshold value Usth, then FRTS parameter I is resetcdF；
Operating status after second control module, real-time monitoring direct current and weak AC network combined hybrid system fault disturbance, when because of electricity
When stream restores to cause dynamic instability, stop icdAnd icqIncrease；
Third control module, if UsLower than setting threshold value UsthAnd the time is more than TD, then apply superposition watt current Perturbation △
icdrefIf UsIt hovers in UsL2With UsHBetween unstable equilibrium point, can make combined hybrid system operating point under VSC controller action
Voluntarily slide to Us-PsThe stable equilibrium point of curve top half, if UsIt is still below UsthAnd the duration is more than TS, then drop direct current is returned
Power △ PcTo promote Us, wherein FDFor the marker bit for avoiding electric current perturbation control frequent movement.
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| 郑超等: "基于实际工程控制系统的直流受扰特性分析-电压快速波动下整流端特性及其优化", 《高电压技术》 * |
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| CN109861262B (en) | 2021-03-02 |
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