CN108847671A - Busbar voltage fluctuation suppressing method and system suitable for alternating current-direct current mixing micro-capacitance sensor - Google Patents
Busbar voltage fluctuation suppressing method and system suitable for alternating current-direct current mixing micro-capacitance sensor Download PDFInfo
- Publication number
- CN108847671A CN108847671A CN201810790651.3A CN201810790651A CN108847671A CN 108847671 A CN108847671 A CN 108847671A CN 201810790651 A CN201810790651 A CN 201810790651A CN 108847671 A CN108847671 A CN 108847671A
- Authority
- CN
- China
- Prior art keywords
- axis
- electric current
- current
- observation
- inverter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- 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
- H02J3/02—Circuit arrangements for ac mains or ac distribution networks using a single network for simultaneous distribution of power at different frequencies; using a single network for simultaneous distribution of ac power and of dc power
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
Abstract
The invention discloses a kind of busbar voltage fluctuation suppressing methods and system suitable for alternating current-direct current mixing micro-capacitance sensor, including：The observational equation that d axis AC output electric current and q axis AC output electric current is set separately in voltage dynamical equation of the side under dq rotating coordinate system is exchanged according to AC/DC inverter；The relationship between the observation and actual value of the relationship and q axis AC output electric current between the observation and actual value of d axis AC output electric current is respectively obtained according to observational equation；The relationship between the observation and actual value of the relationship and q axis AC output electric current between the observation and actual value of electric current is exported according to the response equation of busbar voltage, d axis AC, respectively obtain the d axis AF panel equation and q axis AF panel equation of AC/DC inverter, for eliminating disturbance of the AC/DC inverter exchange side output electric current to busbar voltage, to inhibit the fluctuation of busbar voltage.The present invention can effectively inhibit busbar voltage fluctuation, improve system stability.
Description
Technical field
The invention belongs to alternating current-direct current mixing micro-capacitance sensor control method for stably operating research fields, more particularly, to one kind
Busbar voltage fluctuation suppressing method and system suitable for alternating current-direct current mixing micro-capacitance sensor.
Background technique
In recent years, the heavy pressure of environmental protection and the increasingly exhausted of fossil energy to utilize clean reproducible energy
Distributed generation technology has become a hot topic of research.Micro-capacitance sensor be it is a kind of by distributed generation resource (Distributed Generation,
DG), load and energy storage device as a whole, can both be incorporated into the power networks or the novel power grid of isolated operation.Micro-grid connection operation
When, for power grid, micro-capacitance sensor is a whole interface, thus can be seen as independent unified controllable；Power grid
Failure or when needing to overhaul, micro-capacitance sensor off-network isolated operation maintains the continued power to important load.It is accessed according to micro-capacitance sensor
The difference of bus type, there are three types of structure types for micro-capacitance sensor：Alternating current and direct current and mixed type micro-capacitance sensor；Exchanging micro-capacitance sensor is most
Common micro-capacitance sensor tactic pattern；Direct-current grid energy conversion process is few, high-efficient, loss is low, without considering voltage-phase
And the control problem of frequency, these advantages greatly improve the controllability of direct-current grid and reliability, but exchange is negative at present
Lotus still accounts for the overwhelming majority；Alternating current-direct current mixing micro-capacitance sensor can meet simultaneously the needs of AC and DC load and efficiently utilize
The impact of DG, the stability for enhancing micro-capacitance sensor itself and reduction to main power grid, it is considered to be the following Efficient Development and utilization distribution
The preferred micro-capacitance sensor mode of the formula energy.Therefore, deep there is an urgent need to be carried out to alternating current-direct current mixing micro-capacitance sensor operation control technology
Research.
In isolated alternating current-direct current micro-grid system, it is prominent that busbar voltage is susceptible to power due to the not no support of bulk power grid
The disturbing influence of change, load is cut out, distributed generation resource is contributed, and change etc. can all cause AC/DC inverter in micro-capacitance sensor to export
Temporal variations occur for electric current, to influence the stabilization of busbar voltage.Simultaneously because system parameter variations, detection technique limitation etc. because
The influence of element is generally difficult to obtain the accurate model of control object, these Unmarried pregnancies also will lead to the generation of inverter voltage
Fluctuation.Especially under large disturbances, traditional inner ring PI (Proportional-Integral) control can not obtain ideal dynamic
Response characteristic acts trigger protection when serious, causes system crash.Therefore, the promotion of micro grid control system dynamic property
It is very crucial to the stable operation for guaranteeing microgrid.It is controlled and is replaced using PID (Proportion-Integral-Derivative)
Although PI controls the dynamic property that can improve system to a certain extent, the contradiction between its rapidity and overshoot is still
Need further to be solved.Other control strategies further include Sliding mode variable structure control, Active Disturbance Rejection Control and mixing nonlinear Control etc.,
But because of reasons such as sensibility of excessively complicated, arithmetic speed limitation and control parameter, in the application of real system and few.
It can be seen that the prior art can not effectively realize the two-way AC/DC inverter bus electricity of alternating current-direct current mixing micro-capacitance sensor
Pressure fluctuation inhibits, when external power disturbs it is excessive when even can deteriorate the stable operation of system, cause micro-grid system to collapse.
Summary of the invention
In view of the drawbacks of the prior art and Improvement requirement, the present invention provides a kind of suitable for alternating current-direct current mixing micro-capacitance sensor
Busbar voltage fluctuation suppressing method and system, it is intended that by the disturbance quantity of observation ac output current, it is correspondingly right
The ac output current disturbance of AC/DC inverter compensates, so that the voltage signal for AC/DC inverter provides accurate ginseng
Value is examined, and then inhibits the fluctuation of busbar voltage, improves the stability of alternating current-direct current mixing micro-capacitance sensor.
To achieve the above object, according to the invention a kind of to be suitable for alternating current-direct current mixing micro-capacitance sensor in a first aspect, providing
Busbar voltage fluctuation suppressing method, include the following steps：
(1) voltage dynamical equation of the side under dq rotating coordinate system is exchanged according to AC/DC inverter and d axis AC is set separately
Export the observational equation of electric current and q axis AC output electric current；
(2) according to d axis AC export electric current observational equation obtain d axis AC output electric current observation and actual value it
Between relationship, and according to q axis AC export electric current observational equation obtain q axis AC output electric current observation and actual value it
Between relationship；
(3) according to the response equation of busbar voltage, d axis AC output electric current observation and actual value between relationship with
And the relationship between the observation and actual value of q axis AC output electric current, respectively obtain the d axis AF panel of AC/DC inverter
Equation and q axis AF panel equation, for eliminating disturbance of the AC/DC inverter exchange side output electric current to busbar voltage, thus
Accurate reference value is provided for the voltage signal of AC/DC inverter, and then inhibits the fluctuation of busbar voltage.
Further, in step (1), the observational equation of set d axis AC output electric current is：
The observational equation of set q axis AC output electric current is：
Wherein,WithThe respectively observation of d axis AC output electric current and q axis AC output electric current, μdAnd μqIt is
The intermediate variable of observational equation, EdAnd EqRespectively d axis busbar voltage and q axis busbar voltage, idAnd iqThe respectively AC/DC change of current
Device exchanges the d shaft current and q shaft current of side, CfSide equivalent filter capacitor is exchanged for AC/DC inverter, ω is system angular frequency, ld
And lqThe respectively observation gain of d axis AC output electric current and q axis AC output electric current, and ld> 0, lq> 0.
Further, in step (2), d axis AC exports relationship and the friendship of q axis between the observation and actual value of electric current
Stream output electric current observation and actual value between relationship be respectively：
Wherein,WithThe observation of d axis AC output electric current and q axis AC output electric current respectively in the domain s,
i0d(s) and i0qIt (s) is respectively that d axis AC exports electric current in the domain s and q axis AC exports the actual value of electric current, T0dAnd T0qRespectively
D axis AC exports the observation time constant of electric current and q axis AC output electric current, and T0d=Cf/ld, T0q=Cf/lq。
Further, in step (3), the d axis AF panel equation G of AC/DC inverterfd(s) and q axis AF panel equation
Gfq(s) it is respectively：
Wherein, Gid(s) and GiqIt (s) is respectively AC/DC inverter exchange side d shaft current control loop and the control of q shaft current
The transmission function in circuit.
Second aspect according to the invention provides a kind of busbar voltage fluctuation suppression suitable for alternating current-direct current mixing micro-capacitance sensor
System processed, which is characterized in that including：D axis observer, q axis observer, d axis AF panel unit, q axis AF panel unit, d
Axis PI control unit, q axis PI control unit, d axis multiplier, q axis multiplier, the first plus-minus unit, the second plus-minus unit, third
Add and subtract unit and the 4th plus-minus unit；
The first input end of d axis observer is for receiving d axis busbar voltage Ed, the second input terminal of d axis observer is used for
Receive q axis busbar voltage Eq, the third input terminal of d axis observer is for receiving the d shaft current i of AC/DC inverter exchange sided；d
Axis observer is used to obtain the observation of d axis AC output electric current according to the signal received
The first input end of q axis observer is for receiving voltage Eq, the second input terminal of q axis observer is for receiving voltage
Ed, the third input terminal of q axis observer is for receiving the q shaft current i of AC/DC inverter exchange sideq；Q axis observer is used for basis
The signal received obtains the observation of q axis AC output electric current
The input terminal of d axis AF panel unit is connected to the output end of d axis observer；D axis AF panel unit is used for root
According to observationObtain compensation electric current icd, for eliminating the disturbance of AC/DC inverter exchange side d axis AC output electric current；
The input terminal of q axis AF panel unit is connected to the output end of q axis observer；Q axis AF panel unit is used for root
According to observationObtain compensation electric current icq, for eliminating the disturbance of AC/DC inverter exchange side q axis AC output electric current；
The first input end of first plus-minus unit is for receiving AC/DC inverter d shaft current reference value idref, the first plus-minus
Second input terminal of unit is for receiving electric current id, first plus-minus unit third input terminal be connected to d axis AF panel unit
Output end；First plus-minus unit is used for current reference value idrefWith electric current idSubtract each other and with compensation electric current icdIt is added, thus
Obtain electric current
The first input end of second plus-minus unit is for receiving AC/DC inverter q shaft current reference value iqref, the second plus-minus
Second input terminal of unit is for receiving electric current iq, second plus-minus unit third input terminal be connected to q axis AF panel unit
Output end；Second plus-minus unit is used for current reference value iqrefWith electric current iqSubtract each other and with compensation electric current icqIt is added, thus
Obtain electric current
The input terminal of d axis PI control unit is connected to the output end of the first plus-minus unit；D axis PI control unit is used for electricity
StreamProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side d shaft voltagedref；
The input terminal of q axis PI control unit is connected to the output end of the second plus-minus unit；Q axis PI control unit is used for electricity
StreamProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side q shaft voltageqref；
The input terminal of d axis multiplier is for receiving electric current id；D axis multiplier is used for electric current idAmplify ω LfTimes, thus
To voltage
The input terminal of q axis multiplier is for receiving electric current iq；Q axis multiplier is used for electric current iqAmplify ω LfTimes, thus
To voltage
The first input end of third plus-minus unit is for receiving voltage Ed, third plus-minus unit the second input terminal be connected to
The third input terminal of the output end of d axis PI controller, third plus-minus unit is connected to the output end of q axis multiplier；Third plus-minus
Unit is used for voltage EdReference value U is individually subtracteddrefAnd voltageTo obtain AC/DC inverter exchange side d shaft voltage Ud；
The first input end of 4th plus-minus unit is for receiving voltage Eq, the 4th plus-minus unit the second input terminal be connected to
The third input terminal of the output end of q axis PI controller, the 4th plus-minus unit is connected to the output end of d axis multiplier；4th plus-minus
Unit is used for voltage EqReference value U is individually subtractedqrefAnd voltageTo obtain AC/DC inverter exchange side q shaft voltage
Uq；
Wherein, LfSide equivalent filter inductance is exchanged for AC/DC inverter.
Further, d axis observer obtains the observation of d axis AC output electric current according to the signal receivedObservation
Equation is：
Q axis observer obtains the observation of q axis AC output electric current according to the signal receivedObservational equation be：
Wherein, μdAnd μqIt is the intermediate variable of observational equation, CfSide equivalent filter capacitor, ω are exchanged for AC/DC inverter
For system angular frequency, ldAnd lqThe respectively observation gain of d axis AC output electric current and q axis AC output electric current, and ld> 0, lq
> 0.
Further, d axis AF panel unit is according to observationObtain compensation electric current icdD axis AF panel equation
Gfd(s) and q axis AF panel unit is according to observationObtain compensation electric current icqQ axis AF panel equation Gfq(s) divide
It is not：
Wherein, T0dAnd T0qThe respectively observation time constant of d axis observer and q axis observer, and T0d=Cf/ld, T0q=
Cf/lq；Gid(s) and Giq(s) be respectively AC/DC inverter exchange side d shaft current control loop and q shaft current control loop biography
Delivery function.
In general, contemplated above technical scheme through the invention, can obtain following beneficial effect：
(1) the busbar voltage fluctuation suppressing method provided by the present invention suitable for alternating current-direct current mixing micro-capacitance sensor, according to mother
Line voltage and ac output current be set separately d axis AC output electric current and q axis AC output electric current observational equation, and according to
Set observational equation and alternating voltage control system equation difference d axis AC output electric current observation and actual value it
Between relationship and q axis AC output electric current observation and actual value between relationship, and further according to according to bus electricity
The sight of relationship and q axis AC output electric current between the response equation of pressure, the observation and actual value of d axis AC output electric current
Relationship between measured value and actual value respectively obtains the d axis AF panel equation and q axis AF panel equation of AC/DC inverter,
The disturbance being subject to for eliminating AC/DC inverter ac-side current.Therefore, method provided by the present invention can be handed over by observation
The disturbance quantity of stream output electric current simultaneously correspondingly compensates the electric current of AC/DC inverter exchange side, to be AC/DC inverter
Voltage signal accurate reference value is provided, and then effectively inhibit the fluctuation of busbar voltage.
(2) busbar voltage fluctuation provided by the present invention suitable for alternating current-direct current mixing micro-capacitance sensor inhibits system, in tradition
Two observers and two AF panel units are increased only on the basis of inner ring PI control, both without increasing capacitive/inductive electricity
Stream feedback inner ring reduces system design cost without additional sensors or the communication between other distributed generation resources is increased,
It will not influence the plug-and-play feature of distributed generation resource in alternating current-direct current mixing micro-capacitance sensor simultaneously.
Detailed description of the invention
Fig. 1 is alternating current-direct current mixing micro-capacitance sensor schematic diagram provided in an embodiment of the present invention；
Fig. 2 is two-way AC/DC inverter topological structure schematic diagram provided in an embodiment of the present invention；
Fig. 3 is traditional PI inner loop control system schematic；
Fig. 4 is that the busbar voltage fluctuation provided in an embodiment of the present invention suitable for alternating current-direct current mixing micro-capacitance sensor inhibits system to show
It is intended to；
Fig. 5 is using alternating current-direct current mixing micro-capacitance sensor active power curves when traditional control method；
Fig. 6 is bent using alternating current-direct current mixing micro-capacitance sensor active power when busbar voltage fluctuation suppressing method provided by the invention
Line；
Fig. 7 is the reactive capability curve using AC microgrids in alternating current-direct current mixing micro-capacitance sensor when traditional control method；
Fig. 8 is using AC microgrids in alternating current-direct current mixing micro-capacitance sensor when busbar voltage fluctuation suppressing method provided by the invention
Reactive capability curve；
Fig. 9 is ac bus frequency response curve under different control methods provided in an embodiment of the present invention；
Figure 10 is ac bus voltage effective value response curve under different control methods provided in an embodiment of the present invention；
Figure 11 is DC bus-bar voltage response curve under different control methods provided in an embodiment of the present invention.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.As long as in addition, technical characteristic involved in the various embodiments of the present invention described below
Not constituting a conflict with each other can be combined with each other.
In the examples below, the amount shaped like f indicates the current or voltage under time domain, and the amount shaped like f (s) indicates f through drawing
Current or voltage under the corresponding domain s obtained after Laplace transform.
Fig. 1 show an isolated alternating current-direct current mixing micro-capacitance sensor schematic diagram, including a two-way AC/DC inverter, m
A exchange micro battery DGA1~DGAmAnd n DC micro-electric source DGD1~DGDn.The topological structure of two-way AC/DC inverter is as schemed
Shown in 2, the voltage dynamical equation of the two-way AC/DC inverter exchange side is：
In formula (1), UabcAnd iabcRespectively indicate the three-phase voltage and three-phase current of AC/DC inverter exchange side, EabcTable
Show ac bus three-phase voltage, i0abcIndicate ac output current, Rf、LfAnd CfRespectively indicate AC/DC inverter exchange side etc.
Imitate filter resistance, equivalent filter inductance and equivalent filter capacitor；
The voltage dynamical equation under three-phase abc coordinate system shown in formula (1) dq rotation is converted to using Park transformation to sit
Voltage dynamical equation under mark system, can obtain：
Wherein, EdAnd EqRespectively d axis busbar voltage and q axis busbar voltage, UdAnd UqRespectively AC/DC inverter exchanges
The d shaft voltage and q shaft voltage of side, idAnd iqThe respectively d shaft current and q shaft current of AC/DC inverter exchange side, i0dAnd i0qPoint
Not Wei d axis AC export the actual value that electric current and q axis AC export electric current, ω is system angular frequency；
As shown in figure 3, in traditional traditional inner ring PI (Proportional-Integral) control, AC/DC inverter
After d shaft current reference value and q shaft current reference value are subtracted each other with AC/DC inverter d shaft current and q shaft current respectively, through overcurrent
Inner ring PI controls to obtain the reference input voltage of two-way AC/DC inverter；Since this method is by the d shaft current of AC/DC inverter
It is introduced into current control loop with q shaft current as feedback quantity, and realizes the quick tracking of reference quantity using PI controller, because
This can obtain following voltage governing equation：
Wherein, kpidAnd kiidThe respectively ratio control parameter and integration control of the PI controller of d shaft current control loop
Parameter, kpiqAnd kiiqThe respectively ratio control parameter and integration control parameter of the PI controller of q shaft current control loop；Simultaneous
(2), the transmission function G of AC/DC inverter exchange side d shaft current control loop can be obtained in (3)id(s) and q shaft current control loop
Transmission function Giq(s) it is respectively：
And then available busbar voltage response equation is：
D axis busbar voltage response equation E shown in formula (5)d(s) and q axis busbar voltage response equation EqIt (s) include two
A part, with d axis busbar voltage response equation Ed(s) for, wherein preceding two expressions AC/DC inverter d axis AC bus is electric
Pressure and d shaft current reference value idref(s) and q shaft current reference value iqref(s) relationship, rear two expression d axis ACs output electricity
Flow i0d(s) and q axis AC exports electric current i0q(s) to the disturbance characteristic of AC/DC inverter d axis AC busbar voltage；Q axis is female
Line voltage response equation Eq(s) component part is similar, and therefore not to repeat here.By formula (5) it is found that isolated alternating current-direct current mixes micro- electricity
The voltage for netting two-way AC/DC inverter is susceptible to the disturbing influence of external distributed generation resource changed power, and load is cut
Out, distributed generation resource power output change etc. can all cause AC/DC inverter output electric current that temporal variations occur, to influence voltage
Stablize, especially under high-power disturbance, Traditional control strategy can not obtain ideal dynamic response characteristic and effectively inhibit to change
Flow the impact and fluctuation of device voltage.
Based on above-mentioned analysis, the busbar voltage fluctuation suppressing method provided by the invention suitable for alternating current-direct current mixing micro-capacitance sensor
Include the following steps：
(1) voltage dynamical equation of the side under dq rotating coordinate system is exchanged according to AC/DC inverter and d axis AC is set separately
Export the observational equation of electric current and q axis AC output electric current；
In the present embodiment, according to paper " Sliding-mode control for systems with
Method disclosed in mismatched uncertainties via a disturbance observer " (2013) sets d
Axis AC exports the observational equation of electric current and q axis AC output electric current, specifically comprises the following steps：
(11) for the d axis AC voltage control system equation of formula (2-a) and (2-c) composition, system variable is taken：
For the nonlinear system indicated by following equation：
The disturbance-observer equation of disturbance quantity d (t) is
Wherein,It is disturbance estimated value, μ is the intermediate variable of disturbance observation link, and ρ (x) is the observation letter for needing to design
Number, is defined as ρ (x)=l1x1+l2x2+ ..., and l (x)=[l1 l2...] be disturbance observation link observation gain；To obtain
D axis AC output electric current observational equation be：
(12) for the q axis AC voltage control system equation of formula (2-b) and (2-d) composition, system variable is taken, according to same
The observational equation that the method for sample can obtain set q axis AC output electric current is：
Wherein, whereinWithRespectively the observation of d axis AC output electric current and q axis AC output electric current, ω are to be
System angular frequency, ldAnd lqThe respectively observation gain of d axis AC output electric current and q axis AC output electric current, and ld> 0, lq> 0；
Observe gain ldAnd lqIt being set according to performance requirement, observation gain is bigger, then the dynamic responding speed of viewer is faster, but if
Gain is excessive, and when running viewer, system may approach to saturation；
(2) according to d axis AC export electric current observational equation obtain d axis AC output electric current observation and actual value it
Between relationship, and according to q axis AC export electric current observational equation obtain q axis AC output electric current observation and actual value it
Between relationship；
In the present embodiment, according to paper " Sliding-mode control for systems with
Method disclosed in mismatched uncertainties via a disturbance observer " (2013), according to
Above-mentioned observational equation can obtain：
Thus the relationship and q axis AC output electric current between the observation and actual value of d axis AC output electric current are obtained
Observation and actual value between relationship be respectively：
Wherein,WithThe observation of d axis AC output electric current and q axis AC output electric current respectively in the domain s,
i0d(s) and i0qIt (s) is respectively that d axis AC exports electric current in the domain s and q axis AC exports the actual value of electric current, T0dAnd T0qRespectively
D axis AC exports the observation time constant of electric current and q axis AC output electric current, and T0d=Cf/ld, T0q=Cf/lq；
(3) according to the response equation of busbar voltage, d axis AC output electric current observation and actual value between relationship with
And the relationship between the observation and actual value of q axis AC output electric current, respectively obtain the d axis AF panel of AC/DC inverter
Equation and q axis AF panel equation, for eliminating disturbance of the AC/DC inverter exchange side output electric current to busbar voltage, thus
Accurate reference value is provided for the voltage signal of AC/DC inverter, and then inhibits the fluctuation of busbar voltage；
Consider in isolated alternating current-direct current micro-capacitance sensor, the suddenly change of external power will affect two-way AC/DC inverter voltage
Stabilization, and Traditional control strategy can not obtain ideal dynamic response characteristic to inhibit the fluctuation of inverter voltage；In this reality
It applies in example, the d axis AF panel equation G of AC/DC inverterfd(s) and q axis AF panel equation Gfq(s) it is respectively：
D axis AF panel equation Gfd(s) and q axis AF panel equation Gfq(s) current disturbing can be eliminated to inverter electricity
The impact of pressure to provide accurate reference value for inverter voltage signal, and enhances the dynamic response of inner ring PI control, this hair
It is disturbed suitable for the busbar voltage fluctuation suppressing method of alternating current-direct current mixing micro-capacitance sensor actually one kind based on voltage provided by bright
The dynamic improvement inner loop control method inhibited.
In conjunction with the busbar voltage fluctuation suppressing method provided by the present invention suitable for alternating current-direct current mixing micro-capacitance sensor, the present invention
A kind of busbar voltage fluctuation inhibition system suitable for alternating current-direct current mixing micro-capacitance sensor is additionally provided, as shown in figure 4, the system packet
It includes：D axis observer, q axis observer, d axis AF panel unit, q axis AF panel unit, d axis PI control unit, q axis PI control
Unit, d axis multiplier, q axis multiplier, the first plus-minus unit, the second plus-minus unit, third plus-minus unit and the 4th plus-minus processed
Unit；
The first input end of d axis observer is for receiving d axis busbar voltage Ed, the second input terminal of d axis observer is used for
Receive q axis busbar voltage Eq, the third input terminal of d axis observer is for receiving the d shaft current i of AC/DC inverter exchange sided；d
Axis observer is used to obtain the observation of d axis AC output electric current according to the signal received
The first input end of q axis observer is for receiving voltage Eq, the second input terminal of q axis observer is for receiving voltage
Ed, the third input terminal of q axis observer is for receiving the q shaft current i of AC/DC inverter exchange sideq；Q axis observer is used for basis
The signal received obtains the observation of q axis AC output electric current
The input terminal of d axis AF panel unit is connected to the output end of d axis observer；D axis AF panel unit is used for root
According to observationObtain compensation electric current icd, for eliminating the disturbance of AC/DC inverter exchange side d axis AC output electric current；
The input terminal of q axis AF panel unit is connected to the output end of q axis observer；Q axis AF panel unit is used for root
According to observationObtain compensation electric current icq, for eliminating the disturbance of AC/DC inverter exchange side q axis AC output electric current；
The first input end of first plus-minus unit is for receiving AC/DC inverter d shaft current reference value idref, the first plus-minus
Second input terminal of unit is for receiving electric current id, first plus-minus unit third input terminal be connected to d axis AF panel unit
Output end；First plus-minus unit is used for current reference value idrefWith electric current idSubtract each other and with compensation electric current icdIt is added, thus
Obtain electric current
The first input end of second plus-minus unit is for receiving AC/DC inverter q shaft current reference value iqref, the second plus-minus
Second input terminal of unit is for receiving electric current iq, second plus-minus unit third input terminal be connected to q axis AF panel unit
Output end；Second plus-minus unit is used for current reference value iqrefWith electric current iqSubtract each other and with compensation electric current icqIt is added, thus
Obtain electric current
The input terminal of d axis PI control unit is connected to the output end of the first plus-minus unit；D axis PI control unit is used for electricity
StreamProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side d shaft voltagedref；
The input terminal of q axis PI control unit is connected to the output end of the second plus-minus unit；Q axis PI control unit is used for electricity
StreamProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side q shaft voltageqref；
The input terminal of d axis multiplier is for receiving electric current id；D axis multiplier is used for electric current idAmplify ω LfTimes, thus
To voltage
The input terminal of q axis multiplier is for receiving electric current iq；Q axis multiplier is used for electric current iqAmplify ω LfTimes, thus
To voltage
The first input end of third plus-minus unit is for receiving voltage Ed, third plus-minus unit the second input terminal be connected to
The third input terminal of the output end of d axis PI controller, third plus-minus unit is connected to the output end of q axis multiplier；Third plus-minus
Unit is used for voltage EdReference value U is individually subtracteddrefAnd voltageTo obtain AC/DC inverter exchange side d shaft voltage Ud；
The first input end of 4th plus-minus unit is for receiving voltage Eq, the 4th plus-minus unit the second input terminal be connected to
The third input terminal of the output end of q axis PI controller, the 4th plus-minus unit is connected to the output end of d axis multiplier；4th plus-minus
Unit is used for voltage EqReference value U is individually subtractedqrefAnd voltageTo obtain AC/DC inverter exchange side q shaft voltage
Uq。
Wherein, d axis observer obtains the observation of d axis AC output electric current according to the signal receivedObservational equation
For：
Q axis observer obtains the observation of q axis AC output electric current according to the signal receivedObservational equation be：
D axis AF panel unit is according to observationObtain compensation electric current icdD axis AF panel equation Gfd(s), and
Q axis AF panel unit is according to observationObtain compensation electric current icqQ axis AF panel equation Gfq(s) it is respectively：
In system shown in Fig. 4, due to increasing observer and AF panel unit, busbar voltage response equation is：
By d axis AF panel equation Gfd(s) and q axis AF panel equation Gfq(s) it substitutes into formula (6), can obtain and be finally
The busbar voltage response equation of system is：
According to formula (7) it is found that it is defeated to eliminate exchange by the way that observer and AF panel unit are added in systems by the present invention
Impact of the current disturbing to inverter voltage out, so that accurate reference value is provided for inverter voltage signal, compared to tradition
Inner ring PI control is obtained, the dynamic response of control is effectively enhanced.
In order to verify the correctness and validity of control strategy presented here, build in PSCAD/EMTDC such as Fig. 1
Shown in isolate alternating current-direct current mixing micro-capacitance sensor structural topology.Wherein, the rated frequency of AC microgrids is 50Hz, voltage rating
380V, it includes two identical exchange micro battery DGA1And DGA2, the rated active power of each exchange micro battery is 40kW,
Rated reactive power is 10kVar；The voltage rating of direct-current grid is 700V, includes two identical DC micro-electric source DGD1With
DGD2, the rated power of corresponding each DC power supply is 40kW.Burden with power in AC and DC microgrid is all made of resistance
Type loads, and the load or burden without work in AC microgrids is loaded using inductive type.The structure of two-way AC/DC inverter is as shown in Fig. 2, it is handed over
Stream side equivalent filter inductance is Lf=0.005H, equivalent filter capacitor are Cf=10 μ F10 μ F.Each micro battery is using sagging in system
Control strategy, control system parameter estimator gain are ld=0.5, lq=0.1.In order to illustrate busbar voltage provided by the present invention
The superiority for fluctuating suppressing method, it is compared with traditional PI inner loop control method, and using control variable thought, i.e. bus
PI control parameter in voltage fluctuation suppressing method is identical as conventional PI control parameter.
Due to extraneous factor interference etc., system topology parameter is possible to change in the process of running, because
This superiority in order to embody mentioned busbar voltage fluctuation suppressing method, the present embodiment is with system topology Parameters variation work
For disturbing source, micro-grid system power distribution and busbar voltage fluctuation situation are observed.Specific disturbance is set as the two-way AC/DC change of current
The alternating current equivalent filter inductance L of devicef0.007H (variation of simulation system parameter) is changed to by 0.005H, and control parameter is constant.
System initial launch operating condition is that initial burden with power is 40kW in AC microgrids, load or burden without work 30kVar, and direct-current micro-grid is initial
Burden with power is 80kW.The transient disturbance of the present embodiment is set as after 4s, exchanges micro battery DGA1Due to originals such as failure or maintenance
It is thus out of service.System under busbar voltage fluctuation suppressing method and traditional PI inner loop control method that the present invention is mentioned responds
Comparing result is as shown in Figure 11-Figure 5.
It can be seen that from simulation result diagram 5-8 when the ac filter inductance parameters of two-way AC/DC inverter change
When, in the case where improving inner loop control, DG in entire micro-capacitance sensor is still proportional to undertake load power.After 4s, due to exchange
Micro battery DGA1Out of service, system distributes the biography of each power supply power output and two-way AC/DC inverter according to proportional principle again
Defeated power, i.e., each AC and DC micro battery respectively issue specified 40kW active power, and two-way AC/DC inverter does not transmit active
Power.But under conventional PI control, since filter inductance parameter changes and PI control parameter is not adjusted, distributed generation resource
Power output and the power of two-way AC/DC inverter be in mix, and by Fig. 9-11 it is found that alternating current-direct current busbar voltage frequency
It also is exceptional value.If thinking at this time, microgrid restores to stablize, it is necessary to PI control parameter is readjusted, and in systems in practice, system
Topological structure parameter does not ensure that completely accurate, can not accomplish PI control parameter system for tracking topologies change and real-time yet
Adjustment.Therefore, compared to traditional PI inner loop control method, busbar voltage fluctuation suppressing method provided by the present invention is significantly improved
The robust stability of system.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, not to
The limitation present invention, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should all include
Within protection scope of the present invention.
Claims (7)
1. a kind of busbar voltage fluctuation suppressing method suitable for alternating current-direct current mixing micro-capacitance sensor, which is characterized in that including walking as follows
Suddenly：
(1) voltage dynamical equation of the side under dq rotating coordinate system is exchanged according to AC/DC inverter and the output of d axis AC is set separately
The observational equation of electric current and q axis AC output electric current；
(2) it is obtained between the observation and actual value of d axis AC output electric current according to the observational equation that d axis AC exports electric current
Relationship, and obtained between the observation and actual value of q axis AC output electric current according to the observational equation that q axis AC exports electric current
Relationship；
(3) relationship and q between the observation and actual value of electric current are exported according to the response equation of busbar voltage, d axis AC
Axis AC exports the relationship between the observation and actual value of electric current, respectively obtains the d axis AF panel equation of AC/DC inverter
With q axis AF panel equation, disturbance of the electric current to busbar voltage is exported for eliminating AC/DC inverter exchange side, to be AC/
The voltage signal of DC inverter provides accurate reference value, and then inhibits the fluctuation of busbar voltage.
2. being suitable for the busbar voltage fluctuation suppressing method of alternating current-direct current mixing micro-capacitance sensor as described in claim 1, feature exists
In in the step (1), the observational equation of set d axis AC output electric current is：
The observational equation of set q axis AC output electric current is：
Wherein,WithThe respectively observation of d axis AC output electric current and q axis AC output electric current, μdAnd μqIt is observation side
The intermediate variable of journey, EdAnd EqRespectively d axis busbar voltage and q axis busbar voltage, idAnd iqRespectively AC/DC inverter exchanges
The d shaft current and q shaft current of side, CfSide equivalent filter capacitor is exchanged for AC/DC inverter, ω is system angular frequency, ldAnd lqPoint
Not Wei d axis AC export the observation gain that electric current and q axis AC export electric current, and ld> 0, lq> 0.
3. being suitable for the busbar voltage fluctuation suppressing method of alternating current-direct current mixing micro-capacitance sensor as claimed in claim 2, feature exists
In in the step (2), d axis AC exports relationship and q axis AC output electric current between the observation and actual value of electric current
Observation and actual value between relationship be respectively：
Wherein,WithThe observation of d axis AC output electric current and q axis AC output electric current, i respectively in the domain s0d
(s) and i0qIt (s) is respectively that d axis AC exports electric current in the domain s and q axis AC exports the actual value of electric current, T0dAnd T0qRespectively d
Axis AC exports the observation time constant of electric current and q axis AC output electric current, and T0d=Cf/ld, T0q=Cf/lq。
4. being suitable for the busbar voltage fluctuation suppressing method of alternating current-direct current mixing micro-capacitance sensor as claimed in claim 3, feature exists
In, in the step (3), the d axis AF panel equation G of AC/DC inverterfd(s) and q axis AF panel equation Gfq(s) respectively
For：
Wherein, Gid(s) and GiqIt (s) is respectively AC/DC inverter exchange side d shaft current control loop and q shaft current control loop
Transmission function.
5. a kind of busbar voltage fluctuation suitable for alternating current-direct current mixing micro-capacitance sensor inhibits system, which is characterized in that including：D axis is seen
Survey device, q axis observer, d axis AF panel unit, q axis AF panel unit, d axis PI control unit, q axis PI control unit, d
Axis multiplier, q axis multiplier, the first plus-minus unit, the second plus-minus unit, third plus-minus unit and the 4th plus-minus unit；
The first input end of the d axis observer is for receiving d axis busbar voltage Ed, the second input terminal use of the d axis observer
In reception q axis busbar voltage Eq, the third input terminal of the d axis observer is for receiving the d axis electricity of AC/DC inverter exchange side
Flow id；The d axis observer is used to obtain the observation of d axis AC output electric current according to the signal received
The first input end of the q axis observer is for receiving the voltage Eq, the second input terminal of the q axis observer is used for
Receive the voltage Ed, the third input terminal of the q axis observer is for receiving the q shaft current i of AC/DC inverter exchange sideq；
The q axis observer is used to obtain the observation of q axis AC output electric current according to the signal received
The input terminal of the d axis AF panel unit is connected to the output end of the d axis observer；The d axis AF panel list
Member is for according to the observationObtain compensation electric current icd, for eliminating AC/DC inverter exchange side d axis AC output electricity
The disturbance of stream；
The input terminal of the q axis AF panel unit is connected to the output end of the q axis observer；The q axis AF panel list
Member is for according to the observationObtain compensation electric current icq, for eliminating AC/DC inverter exchange side q axis AC output electricity
The disturbance of stream；
The first input end of the first plus-minus unit is for receiving AC/DC inverter d shaft current reference value idref, described first
Second input terminal of plus-minus unit is for receiving the electric current id, the third input terminal of the first plus-minus unit is connected to described
The output end of d axis AF panel unit；The first plus-minus unit is used for the current reference value idrefWith the electric current idPhase
Subtract and with the compensation electric current icdIt is added, to obtain electric current
The first input end of the second plus-minus unit is for receiving AC/DC inverter q shaft current reference value iqref, described second
Second input terminal of plus-minus unit is for receiving the electric current iq, the third input terminal of the second plus-minus unit is connected to described
The output end of q axis AF panel unit；The second plus-minus unit is used for the current reference value iqrefWith the electric current iqPhase
Subtract and with the compensation electric current icqIt is added, to obtain electric current
The input terminal of the d axis PI control unit is connected to the output end of the first plus-minus unit；The d axis PI control unit
For to the electric currentProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side d shaft voltagedref；
The input terminal of the q axis PI control unit is connected to the output end of the second plus-minus unit；The q axis PI control unit
For to the electric currentProportional integration operation is carried out, to obtain the reference value U of AC/DC inverter exchange side q shaft voltageqref；
The input terminal of the d axis multiplier is for receiving the electric current id；The d axis multiplier is used for the electric current idAmplification
ωLfTimes, to obtain voltage
The input terminal of the q axis multiplier is for receiving the electric current iq；The q axis multiplier is used for the electric current iqAmplification
ωLfTimes, to obtain voltage
The first input end of the third plus-minus unit is for receiving the voltage Ed, the second input of the third plus-minus unit
End is connected to the output end of the d axis PI controller, and the third input terminal of the third plus-minus unit is connected to the q axis multiplication
The output end of device；The third plus-minus unit is used for the voltage EdThe reference value U is individually subtracteddrefWith the voltageTo obtain AC/DC inverter exchange side d shaft voltage Ud；
The first input end of the 4th plus-minus unit is for receiving the voltage Eq, the second input of the 4th plus-minus unit
End is connected to the output end of the q axis PI controller, and the third input terminal of the 4th plus-minus unit is connected to the d axis multiplication
The output end of device；The 4th plus-minus unit is used for the voltage EqThe reference value U is individually subtractedqrefWith the voltageTo obtain AC/DC inverter exchange side q shaft voltage Uq；
Wherein, LfSide equivalent filter inductance is exchanged for AC/DC inverter.
6. inhibiting system suitable for the busbar voltage fluctuation of alternating current-direct current mixing micro-capacitance sensor as claimed in claim 5, feature exists
In the d axis observer obtains the observation of d axis AC output electric current according to the signal receivedObservational equation be：
The q axis observer obtains the observation of q axis AC output electric current according to the signal receivedObservational equation be：
Wherein, μdAnd μqIt is the intermediate variable of observational equation, CfSide equivalent filter capacitor is exchanged for AC/DC inverter, ω is to be
System angular frequency, ldAnd lqThe respectively observation gain of d axis AC output electric current and q axis AC output electric current, and ld> 0, lq> 0.
7. inhibiting system suitable for the busbar voltage fluctuation of alternating current-direct current mixing micro-capacitance sensor as claimed in claim 6, feature exists
In the d axis AF panel unit is according to the observationObtain compensation electric current icdD axis AF panel equation Gfd(s),
And the q axis AF panel unit is according to the observationObtain compensation electric current icqQ axis AF panel equation Gfq(s)
Respectively：
Wherein, T0dAnd T0qThe observation time constant of respectively described d axis observer and the q axis observer, and T0d=Cf/ld,
T0q=Cf/lq；Gid(s) and GiqIt (s) is respectively AC/DC inverter exchange side d shaft current control loop and q shaft current control loop
Transmission function.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810790651.3A CN108847671B (en) | 2018-07-18 | 2018-07-18 | Bus voltage fluctuation suppression method and system suitable for alternating current-direct current hybrid micro-grid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810790651.3A CN108847671B (en) | 2018-07-18 | 2018-07-18 | Bus voltage fluctuation suppression method and system suitable for alternating current-direct current hybrid micro-grid |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN108847671A true CN108847671A (en) | 2018-11-20 |
| CN108847671B CN108847671B (en) | 2020-09-08 |
Family
ID=64196294
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201810790651.3A Expired - Fee Related CN108847671B (en) | 2018-07-18 | 2018-07-18 | Bus voltage fluctuation suppression method and system suitable for alternating current-direct current hybrid micro-grid |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN108847671B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110729713A (en) * | 2019-10-16 | 2020-01-24 | 杭州电子科技大学 | Secondary voltage adjusting method suitable for direct-current microgrid |
| CN112003302A (en) * | 2020-08-21 | 2020-11-27 | 西安热工研究院有限公司 | Method for inhibiting voltage fluctuation of micro-grid bus |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103973143A (en) * | 2014-05-09 | 2014-08-06 | 浙江大学 | Control method for restraining point potential fluctuation in three-level grid-connected inverter |
| US20150280610A1 (en) * | 2014-04-01 | 2015-10-01 | Majid Pahlevaninezhad | Dc-bus controller for grid-connected dc/ac converters |
| CN105305402A (en) * | 2015-10-20 | 2016-02-03 | 天津大学 | Robust autonomous control method for bus voltage of DC micro grid |
| CN105790253A (en) * | 2016-03-29 | 2016-07-20 | 上海电气集团股份有限公司 | Double-loop control method |
| CN106300435A (en) * | 2016-08-29 | 2017-01-04 | 上海交通大学 | Isolated microgrid single-phase multi-inverter parallel system and distributed control method thereof |
-
2018
- 2018-07-18 CN CN201810790651.3A patent/CN108847671B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150280610A1 (en) * | 2014-04-01 | 2015-10-01 | Majid Pahlevaninezhad | Dc-bus controller for grid-connected dc/ac converters |
| CN103973143A (en) * | 2014-05-09 | 2014-08-06 | 浙江大学 | Control method for restraining point potential fluctuation in three-level grid-connected inverter |
| CN105305402A (en) * | 2015-10-20 | 2016-02-03 | 天津大学 | Robust autonomous control method for bus voltage of DC micro grid |
| CN105790253A (en) * | 2016-03-29 | 2016-07-20 | 上海电气集团股份有限公司 | Double-loop control method |
| CN106300435A (en) * | 2016-08-29 | 2017-01-04 | 上海交通大学 | Isolated microgrid single-phase multi-inverter parallel system and distributed control method thereof |
Non-Patent Citations (1)
| Title |
|---|
| CHENGSHAN WANG: "A Nonlinear-Disturbance-Observer-Based DC-Bus Voltage Control for a Hybrid AC/DC Microgrid", 《IEEE TRANSACTIONS ON POWER ELECTRONICS》 * |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110729713A (en) * | 2019-10-16 | 2020-01-24 | 杭州电子科技大学 | Secondary voltage adjusting method suitable for direct-current microgrid |
| CN110729713B (en) * | 2019-10-16 | 2021-05-18 | 杭州电子科技大学 | Secondary voltage adjusting method suitable for direct-current microgrid |
| CN112003302A (en) * | 2020-08-21 | 2020-11-27 | 西安热工研究院有限公司 | Method for inhibiting voltage fluctuation of micro-grid bus |
Also Published As
| Publication number | Publication date |
|---|---|
| CN108847671B (en) | 2020-09-08 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Lago et al. | Operation and control-oriented modeling of a power converter for current balancing and stability improvement of DC active distribution networks | |
| Wang et al. | Autonomous control of inverter-interfaced distributed generation units for harmonic current filtering and resonance damping in an islanded microgrid | |
| He et al. | An enhanced microgrid load demand sharing strategy | |
| CN104953606B (en) | Networked layered compensation method for voltage unbalance of PCC (Point of Common Coupling) of islanded microgrid | |
| Chittora et al. | Simple and efficient control of DSTATCOM in three‐phase four‐wire polluted grid system using MCCF‐SOGI based controller | |
| CN106532749B (en) | A kind of micro-capacitance sensor imbalance power and harmonic voltage compensation system and its application | |
| Dinh et al. | Adaptive notch filter solution under unbalanced and/or distorted point of common coupling voltage for three‐phase four‐wire shunt active power filter with sinusoidal utility current strategy | |
| Jia et al. | Fault characteristics and protection adaptability analysis in VSC‐HVDC‐connected offshore wind farm integration system | |
| dos Santos Alonso et al. | Distributed selective harmonic mitigation and decoupled unbalance compensation by coordinated inverters in three-phase four-wire low-voltage networks | |
| Rahmani et al. | Reciprocal effects of the distorted wind turbine source and the shunt active power filter: full compensation of unbalance and harmonics under ‘capacitive non‐linear load’condition | |
| Tummuru et al. | An improved current controller for grid connected voltage source converter in microgrid applications | |
| Wang et al. | An improved harmonic suppression control strategy for the hybrid microgrid bidirectional AC/DC converter | |
| Huber et al. | Analysis, design, and evaluation of three-phase three-wire isolated ac-dc converter implemented with three single-phase converter modules | |
| Dai et al. | A novel method for voltage support control under unbalanced grid faults and grid harmonic voltage disturbances | |
| Miret et al. | PI‐based controller for low‐power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags | |
| CN109617112A (en) | Modified DC voltage control strategy suitable for multiterminal flexible direct current system | |
| CN109473987A (en) | A kind of high-frequency harmonic paralleling compensating device based on silicon carbide | |
| CN108847671A (en) | Busbar voltage fluctuation suppressing method and system suitable for alternating current-direct current mixing micro-capacitance sensor | |
| CN108574276A (en) | A kind of direct-current grid power-sharing control method and system based on frequency injection | |
| CN110061504A (en) | A kind of slave power control method based on quasi- ratio resonance complex controll | |
| Sharma et al. | Affine projection sign algorithm based control for mitigation of distribution side power quality problems | |
| Sanjenbam et al. | Multi‐functional control strategy for power quality improvement of three‐phase grid using solar PV fed unified power quality conditioner | |
| Kanase et al. | Distribution static compensator for power quality improvement using PV array | |
| Wang et al. | A novel directional element for transmission line connecting inverter-interfaced renewable energy power plant | |
| D'Arco et al. | Harmonic compensation with active front-end converters based only on grid voltage measurements |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20200908 Termination date: 20210718 |
|
| CF01 | Termination of patent right due to non-payment of annual fee |