CN107968424A - Flexible DC power transmission hierarchical control method - Google Patents
Flexible DC power transmission hierarchical control method Download PDFInfo
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- H02J13/0079—
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The present invention relates to a kind of flexible DC power transmission hierarchical control method, belong to flexible direct-current transmission field.Control system is divided into system-level control, the control of change of current station level and converter valve level and controls three layers.System-level key-course is divided into active class control and the control of idle class, and active power class controls the method for including active power controller, FREQUENCY CONTROL and DC voltage control, and reactive power class controls the method for including Reactive Power Control and alternating voltage control.Change of current Substation level is divided into two major class of current indirect control and Direct Current Control, current indirect control is to be input to control module by the deviation for the reference value for exporting real-time acquisition state amount and system, phase shifting angle δ and modulation ratio M are obtained by pi regulator, and Direct Current Control mode is divided into inner ring current control and outer loop voltag controls two parts, inner ring Current Control Strategy is double closed-loop control system, and current status feedback control is introduced in current inner loop can realize the decoupling of watt current and reactive current.
Description
Technical field
The present invention relates to flexible direct-current transmission field, more particularly to a kind of flexible DC power transmission hierarchical control method.
Background technology
Flexible DC power transmission (HVDC Flexible) is one kind with voltage source converter (Voltage Source
Converter, VSC), based on the technology such as self-turn-off device and pulsewidth modulation (Pulse Width Modulation, PWM)
New Technologies of Electric Power Transmission.
Based on voltage source converter and pulse width modulating technology voltage-source type high voltage dc transmission technology (VSC-
HVDC), it can realize the independent control of active power and reactive power, there is dynamic passive compensation and improve the spy of power quality
Point, and control flexibly, energy transportation problem can be efficiently solved, has been obtained in existing high voltage direct current transmission project wide
General application.The transverter used based on early the high voltage direct current transmission project of voltage source converter is mostly two level, two poles
Three level or Cascade H bridge type topological structure of pipe clamp, switching frequency is low, and loss is big, there are dynamic static state voltage equipoise and is difficult to realize
The problems such as modularized design, with the expansion of power grid scale and the increase of new-energy grid-connected capacity, traditional voltage-source type change of current
Device can not meet the requirement of HVDC engineerings.German scholar R.Marquart and A.Lesniar proposed Novel electric potential source in 2001
Type current converter modularization multilevel converter (Modular Multilevel Converter, MMC), in generation of electricity by new energy simultaneously
The fields such as net, Power System Interconnection and urban distribution network capacity-increasing transformation have great application prospect, and are changed compared to two level or three level
Device is flowed, MMC has the advantages that output voltage waveforms harmonic wave is few, switching loss is low, be easy to modularized design and autgmentability is strong.MMC
It is to approach sine wave, control system therein by controlling the control signal of bridge arm submodule wholly-controled device to produce staircase waveform
Operation for MMC plays a crucial role, and the emphasis of modularization multi-level converter technology is that solution transverter
Control problem.
The content of the invention
It is an object of the invention to provide a kind of flexible DC power transmission hierarchical control method, solve existing in the prior art
Control function boundary between controller is unclear, the problems such as controlling of bypassing the immediate leadership.The present invention uses the hierarchical design principle of control system, point
Into three layers of system-level key-course, change of current Substation level and converter valve level key-course.
System-level key-course is divided into active class control according to the property of its controlled quentity controlled variable and idle class controls.Active power class control
System mainly includes work(Power Control, FREQUENCY CONTROL, DC voltage control and DC current control, and the control of reactive power class is led
To include Reactive Power Control, alternating voltage controls.
Change of current Substation level can be mainly divided into two major class of current indirect control and Direct Current Control.Indirect Electro flow control
System is the reference value by the way that the active power gathered in real time, DC voltage, DC current or frequency are exported with system-level control
Between deviation be input to corresponding control module, by pi regulator obtain valve level control needed for phase shifting angle δ, by idle work(
Deviation between rate or alternating voltage and the reference value of system-level control output is input to corresponding control module, is adjusted by PI
Device obtains the modulation ratio M needed for the control of valve level；And Direct Current Control mode is divided into inner ring current control and the control of outer loop voltag
Two parts.
Valve level key-course is broadly divided into switch modulation, capacitor voltage balance control and pulse-triggered technology.Switch modulation master
There are two kinds, one kind is pulse width modulation, and another kind is that nearest level approaches modulation；Capacitor voltage balance control, which uses, to be based on
The capacitor voltage balance control strategy of prime factorization method；Pulse-triggered technology is considered to use the follow-on mixing of submodule
MMC, with half-bridge submodule (Half Bridge Sub-module, HBSM) and full-bridge submodule (Full Bridge Sub-
Module, FBSM) be used in mixed way in case of be illustrated.
The above-mentioned purpose of the present invention is achieved through the following technical solutions：
Flexible DC power transmission hierarchical control method, step are as follows：
(1) control system is divided into system-level key-course, change of current Substation level and converter valve level key-course；
(2) system-level key-course is divided into active class control according to the property of its controlled quentity controlled variable and idle class controls；
(3) change of current Substation level is divided into two major class of current indirect control and Direct Current Control；
(4) converter valve level key-course is divided into switch modulation, capacitor voltage balance control and pulse triggering method.
The system-level key-course is divided into active class control according to the property of its controlled quentity controlled variable and idle class controls, comprising such as
Lower control model：
2.1) real power control pattern；
2.2) idle control model；
2.3) alternating voltage control model；
2.4) DC voltage control pattern；
2.5) FREQUENCY CONTROL pattern；
2.6) passive alternating voltage control model.
The change of current Substation level is divided into two major class of current indirect control and Direct Current Control, includes following control
Method：
3.1) current indirect control method；
3.2) the inner ring current control in Direct Current Control；
3.3) open sea wharf in Direct Current Control；
3.4) the outer shroud DC voltage control in Direct Current Control；
3.5) the outer shroud FREQUENCY CONTROL in Direct Current Control；
3.6) the passive alternating voltage control in Direct Current Control.
The converter valve level key-course is divided into switch modulation, capacitor voltage balance control and pulse-triggered, containing as follows
Control method：
4.1) capacitor voltage balance algorithm grouping process of the capacitor voltage balance control based on prime factorization method；
4.2) capacitor voltage balance control optimized control method flow；
4.3) capacitance voltage equal pressure sequence algorithm when HBSM and FBSM is used in mixed way in the mixing MMC of pulse triggering method.
The beneficial effects of the present invention are：So that current conversion station control limits at different levels are clear, every layer of controller completes this layer
The control function of level, each layer can have quick responding ability according to the response speed of setting.
Brief description of the drawings
Attached drawing described herein is used for providing a further understanding of the present invention, forms the part of the application, this hair
Bright illustrative example and its explanation is used to explain the present invention, does not form inappropriate limitation of the present invention.
Fig. 1 is flexible direct current hierarchical control schematic diagram；
Fig. 2 is the operational mode of current conversion station；
Fig. 3 is current indirect control schematic diagram；
Fig. 4 is the VSC-HVDC controller architecture schematic diagrames based on vector controlled；
Fig. 5 is the control system architecture schematic diagram of voltage source converter；
Fig. 6 is the inner ring current controller of VSC；
Fig. 7 is the VSC control system architecture figures using Current Decoupling and voltage feedforward control；
Fig. 8, Fig. 9 are outer shroud active power and reactive power controller；
Figure 10 is constant DC voltage control device；
Figure 11 is frequency controller；
Figure 12 determines AC voltage controller for inactive side；
Figure 13 is the capacitor voltage balance algorithm grouping process based on prime factorization method；
Figure 14 is optimal method control flow；
Figure 15 is sub-modular structure figure；
Figure 16 is the MMC based on HBSM and FBSM mixing submodules；
Figure 17 is the equal pressure sequence algorithm flow chart of capacitance voltage.
Embodiment
The detailed content and its embodiment of the present invention is further illustrated below in conjunction with the accompanying drawings.
The method of the flexible DC power transmission hierarchical control of the present invention, is divided into system-level control, change of current station level by control system
Control and converter valve level control three layers.System-level key-course is divided into active class control and idle class according to the property of its controlled quentity controlled variable
Control, the main method for describing active power controller, FREQUENCY CONTROL and DC voltage control of active power class control, and it is idle
The main method for describing Reactive Power Control and alternating voltage control of power class control.Change of current Substation level can mainly divide
For two major class of current indirect control and Direct Current Control, current indirect control is by the way that real-time acquisition state amount and system is defeated
The deviation of the reference value gone out is input to control module, and phase shifting angle δ and modulation ratio M are obtained by pi regulator, and Direct Current control
Mode processed is divided into inner ring current control and outer loop voltag controls two parts, and inner ring Current Control Strategy is double closed-loop control system,
Current status feedback control is introduced in current inner loop can realize the decoupling of watt current and reactive current.Valve level key-course master
Being divided into switch modulation, capacitor voltage balance control and pulse-triggered technology, switch modulation mainly has two kinds, and one kind is that pulse is wide
Degree modulation, another kind are that nearest level approaches modulation, and capacitor voltage balance control is using the capacitance electricity based on prime factorization method
Weighing apparatus control strategy is flattened, pulse-triggered technology take into account a kind of situation of mixing MMC, i.e., using half-bridge submodule and full-bridge
The situation that module is used in mixed way.
Referring to shown in Fig. 1 to Figure 17, flexible DC power transmission hierarchical control method of the invention, using hierarchical design principle,
It is as shown in Figure 1 to be divided into system-level key-course, change of current Substation level and converter valve level key-course, hierarchical control principle.
1. system-level key-course
The common control mode of flexible direct current transmission converter station can be divided into two major classes according to the property of its controlled quentity controlled variable：
(1) active power quasi-controller, major function are to directly control to be injected into the active of AC system by current conversion station
Power or indirectly adjusting and the relevant physical quantity of active power, such as DC voltage, DC current and AC system frequency.Mainly
Including：1. active power controller, 2. DC voltage control, 3. DC current control, 4. FREQUENCY CONTROL.
(2) reactive power quasi-controller, major function are to directly control to be injected into the idle of AC system by current conversion station
Power is adjusted and the relevant physical quantity of reactive power indirectly.Mainly include：1. Reactive Power Control, 2. alternating current is voltage-controlled
System.
It should be noted that either two end systems or multi-terminal system, it is necessary to have a current conversion station using determining DC voltage
Control, with ensure system respectively station between active power balance.
It is, in general, that the basic operational mode of subregion interconnect device one end current conversion station have it is following several：
(1) real power control pattern
Such as Fig. 2 (a), active power controller module receives active power dispatch instruction PsetWith for power oscillation damping and realization
The purpose of emergency DC power support, modulates marker signal Pm, they pass through active command governing loop (Active Power
Reference Regulation) generation active power reference signal Pref.Different active commands can be designed as needed
Governing loop and upper lower limit value.
(2) idle control model
Such as Fig. 2 (b), Reactive Power Control module receives Reactive Power Dispatch instruction QsetWith fast reactive QmThe signals such as change, it
By reactive command governing loop (Reactive Power Reference Regulation) generation reactive power reference
Signal Qref.Idle modulation can be used for suppressing the flickering of voltage with fast reactive change, improve the occasions such as power quality.According to
Need that different reactive command governing loops and limit value can be designed.
(3) alternating voltage control model
In many occasions, the control targe of VSC current conversion stations is the alternating voltage adjusted on certain busbar.Such as Fig. 2 (c) institutes
Show, alternating voltage control module receives superior instructions Uacset, by alternating voltage governing loop (AC Voltage Reference
Regulation), according to the information such as system conditions, generation alternating voltage reference signal Uacref。
(4) DC voltage control pattern
DC voltage control is extremely important in VSC-HVDC, and for two end systems, wherein one end must use straight
Flow voltage mode control.As shown in Fig. 2 (d), DC voltage control module receives higher level's DC voltage command value Udcset, by straight
Galvanic electricity pressure governing loop (DC Voltage Regulation), according to system running state, generates direct voltage reference value
Udcref。
(5) FREQUENCY CONTROL pattern
Mains frequency is adjusted in application VSC-HVDC, and is supplied to large-scale speed regulating motor power supply on offshore drilling platform etc.
When electric field closes, frequently with FREQUENCY CONTROL pattern.As shown in (e) part in Fig. 2, frequency control module receives higher level's frequency instruction value
fset, by frequency governing loop (Frequency Regulation), according to system running state, generate frequency reference
fref。
(6) passive alternating voltage control model etc.
When VSC-HVDC is connected to light current Force system either passive network or when wind power plant passes through VSC-HVDC
When grid-connected, VSC-HVDC is the unique power source of receiving-end system or VSC-HVDC is injected into the active power of receiving-end system and occupies master
When wanting share, ensured to be stablized by end station system using the control of passive alternating voltage by end station.
System-level control can also be controlled manually in addition to receiving and dispatching by operations staff.System-level control generation instruction letter
Number Pref、 Qref、UacrefAnd Udcref, and it is transmitted to the outer ring controller of Converter controller.System-level control is higher level
Control, which kind of topological structure of its selection with transverter is unrelated, i.e., is all suitable to two level and modularization multi-level converter
.
2. change of current Substation level
The reference value that the control of flexible direct current converter station level is exported by receiving the control of upper system level, obtains reference signal
Waveform.The control mode of change of current station level can be mainly divided into two major class of current indirect control and Direct Current Control.
2.1 current indirect control
Current indirect control reaches control mesh by controlling amplitude and the phase of transverter exchange side fundamental voltage output of voltage
The characteristics of mark, this control mode is simple in structure, but ac-side current dynamic response is slow, and is difficult to realize excess current control,
Current control schematic diagram is connect as shown in figure 3, x and y represents active power class physical quantity and reactive power class physical quantity respectively in figure,
Similar to above, active class physical quantity can select active-power P, DC voltage U as neededdc, DC current IdcWith system frequency
Rate f, idle class physical quantity can select reactive power Q and alternating voltage U as neededac.Subscript ref is expressed as reference value, under
Mark m represents measured value, and δ and M are respectively phase shifting angle and modulation ratio.
By current indirect control schematic diagram as it can be seen that the current indirect control of flexible DC power transmission by that will gather in real time
Deviation between active power, DC voltage, DC current or frequency and the reference value of system-level control output is input to accordingly
Control module, obtain the phase shifting angle δ needed for the control of valve level by pi regulator, by reactive power or alternating voltage with it is system-level
Control the deviation between the reference value of output to be input to corresponding control module, obtained by pi regulator needed for the control of valve level
Modulation ratio M.
2.2 Direct Current Control
Alternating current-direct current side control technology in the design of converter Control layer, it is vector controlled (Vector to occupy an leading position at present
Control) technology, also referred to as-Direct Current Control ", usually by outer shroud (Outer loop) Power Control and inner ring
Two rings of (Inner loop) current control are formed, and have quick current response characteristic, therefore be subject to industrial quarters and academia
Common concern.Meanwhile vector controlled has inherent current limiting capacity, therefore be well suited for being applied to high-power occasion well
VSC-HVDC systems, and use flexible DC power transmission Baseline Control Strategy.
Vector controlled structure using inner ring current control and open sea wharf is in current flexible DC transmission technology
Most widely employed control mode.The Control system architecture of both ends flexible direct current power transmission system is as shown in Figure 4.
The Control system architecture of VSC-HVDC both sides transverter is symmetrical, mainly by inner ring current controller, exterior ring power control
Several part compositions such as device, Phase-Locked Synchronous link (not marked in figure) and trigger pulse generation link processed.Wherein, common outer shroud
Controller form has：Constant DC voltage control, determine active power controller, determine Reactive Power Control, determine alternating voltage control etc., outside
The reference signal that ring controller meeting tracking system level controller gives.In order to keep the active power balance of system, system is necessary
There is side transverter to use constant DC voltage control, and opposite side uses and determines active power controller；Meanwhile according to VSC current conversion stations
Specific control targe, current conversion station controls it is also an option that determine alternating voltage at the same time or determines Reactive Power Control.But to nothing
In the VSC-HVDC systems of source network power supply, rectification side generally use constant DC voltage control, and inverter side uses and determines alternating current
Voltage-controlled system.
One end VSC Control system architectures are as shown in figure 5, it is identical by inner ring current controller, exterior ring power adjuster, lock
Walk the link composition (belonging to valve key-course) such as link and trigger pulse generation.Inner ring current controller realizes transverter exchange side electricity
Stream waveform and phase directly control, with quick track reference electric current.Open sea wharf is then according to the system-level controls of VSC-HVDC
Target processed can realize constant DC voltage control, determine active power controller, determines FREQUENCY CONTROL, determine Reactive Power Control and exchanged with fixed
The control targes such as voltage control.The phase signal of phaselocked loop section output is used to provide voltage vector oriented control and trigger pulse life
Into required reference phase.Trigger pulse generation link is produced using the reference voltage and synchronous phase signal of electric current loop output
The trigger pulse of each bridge arm of transverter.
(1) inner ring current control
Inner ring current controller is designed with a variety of implementations, below main introduce the current inner loop control based on PI links
Mode processed.
Mathematical model under transverter exchange side two-phase rotating coordinate system is：
Above formula shows that d, q shaft current remove controlled amount vd、vqInfluence outside, be also subject to current cross coupling terms ω Lisd、
ωLisqWith network voltage usd、usqInfluence.To eliminate current coupling and grid disturbances between d, q axis, now by above formula
It is rewritten as
Wherein,
v′d、v′qIt is and i respectivelysd、isqComponent of voltage with first differential relation.Obviously, this decoupling item can be adopted
Realized with proportional integration link, to compensate the voltage drop on equivalent reactance device.By introducing d, q shaft voltage compensating for coupling item
ud、 uq, nonlinear equation is realized decoupling, while by grid disturbance voltage usd、usqFeedforward compensation is taken, is not only realized
D, the independent decoupling control of q shaft currents, and also improve the dynamic property of system.From the point of view of control principle, before being introduced in formula
Feedback compensation is actually to go to compensate measurable disturbing signal using open loop control mode.
In formula,The respectively reference value of watt current and reactive current.
Therefore, current decoupled control device as shown in Figure 6 can be obtained from above.Current controller output quantity vdref、vqrefIt is right respectively
Answer the d axis and q axis components of the sinusoidal reference fundamental voltage of VSC desired outputs.According to Voltage Reference component and electric network voltage phase
Signal, the trigger pulse of each bridge arm can be obtained by space vector pulse width modulation.Current reference value in figureFrom outer shroud
Controller output obtains.Inner ring current control uses current feedback and voltage feed-forward control, improves the tracking of current controller
Response characteristic, while eliminate further through pi regulator the steady-state error of current tracking.
The above analysis, can obtain changing based on the VSC containing Current Decoupling double-closed-loop control device under synchronously rotating reference frame
Stream station system structure, as shown in Figure 7.
After above-mentioned decoupling control, the d axis and q axis of its current controller become two independent control rings.Using d axis as
Example, its open-loop transfer function G (s) are：
Required according to the dynamic response characteristic of inner ring current controller, while in view of the delay on system stability of control
Influence, suitable k can be selectedp, ki。
(2) open sea wharf
VSC-HVDC systems mainly have constant DC voltage control, determine active power controller, determine Reactive Power Control, fixed exchange
The basic control modes such as voltage control, FREQUENCY CONTROL, the control of passive alternating voltage.In order to keep system active balance and direct current
Pressure is stablized, and must have a transverter to use constant DC voltage control in VSC-HVDC systems, and other current conversion stations can use
Determine active power controller or FREQUENCY CONTROL etc..The outer ring controller structure under each control mode is designed separately below.
Under three-phase power grid voltage equilibrium condition, network voltage vector U is takensDirection be d direction of principal axis, have usd=Us(UsFor
The modulus value of network voltage space vector), usq=0, then power can be reduced to：
Therefore i can be passed throughsdAnd isqP and Q is controlled respectively, so as to fulfill the separately adjustable of active power and reactive power.
In order to eliminate steady-state error, pi regulator is introduced, then Active Power Controller and reactive power controller structure are as shown in Figure 8.
The deviation of active power and active power command value is adjusted through PI, is converted to the reference quantity of watt currentIt is idle
The deviation of power and reactive power command value is adjusted through PI, is converted to the reference quantity of reactive current
Inverse steady state model design Active Power Controller and reactive power controller can also be introduced.According to above formula, can obtain
The discreet value of watt current and reactive current is respectively：
In order to eliminate steady-state error, pi regulator is introduced, then active and reactive power controller and power controller structure be such as
Shown in Fig. 9.
The deviation of active power and active power command value is adjusted through PI, is converted to isdCorrection amount △ id, △ idWith it is inverse
The discreet value i ' of model outputsdIt is added the reference quantity as watt currentSimilarly, reactive power and reactive power command value
Deviation adjusted through PI, be converted to isqCorrection amount △ iq, △ iqWith the discreet value i ' of inversion model outputsqIt is added as idle
The reference quantity of electric currentActive Power Controller and reactive power controller are combined using inverse steady state model and pi regulator,
The response characteristic of controller can be improved and eliminate static difference.
(3) outer shroud DC voltage control
As it was previously stated, using the transverter of constant DC voltage control pattern can be used for balance straight-flow system it is active and keep
DC-side Voltage Stabilization.When ignoring R and transverter is lost, the active holding balance of transverter alternating current-direct current both sides, i.e.,：
During stable state,
When VSC alternating current-direct currents both sides it is active uneven when, the fluctuation of DC voltage will be caused, watt current then will be at this time
DC bus capacitor charging (or electric discharge), until DC voltage stability is in setting value.Therefore the change of current for constant DC voltage control
For device, equivalent to one active balance node.The design of constant DC voltage control device is as shown in Figure 10.Determine direct current in designed
In voltage controller, the reference value of DC voltage and DC voltage instruction deviation after PI is adjusted as watt current
(4) outer shroud FREQUENCY CONTROL
Different control modes can be selected in different application scenarios by determining FREQUENCY CONTROL, and control mode is as follows：
Frequency control system 1：
If the frequency for only having transverter to carry out regulating system in passive system, can directly make and be changed with what passive system interconnected
Flow deviceEqual to system nominal frequency, as shown in Figure 11 (a), this transverter can also be used for controlling alternating voltage at the same time.
Frequency control system 2：
Since the energy of direct current capacitors storage is：
When ignoring the loss of transverter,
In formula, Prec, PinvTo flow into the power of flexible direct current power transmission system rectification side, and the power of inverter side outflow, root
According to the power versus frequency characteristic of interconnected electric power system, frequency control system 2 can be selected such as following formula：
In formula, f0For system nominal frequency, kfIt is gain coefficient, Udc0And UdcRespectively DC voltage rated value and reality
Measured value.This frequency controller is a proportional controller, as shown in Figure 11 (b).
Frequency control system 3：
According to active-frequency relation of electric system, shown in block diagram such as Figure 11 (c) of frequency control system, wherein f comes from
The estimation of PLL, can use PI links to eliminate steady-state error.
(5) passive alternating voltage control
It can power and tie up to passive network for wind power integration, to the application scenarios such as island with power, flexible DC power transmission
Hold the alternating-voltage stabilization of inactive side.According to the basic principle for the both ends VSC-HVDC systems powered to passive network, for nothing
Source devises passive alternating voltage control, its controller design is as shown in figure 12.
The control of inverter side alternating voltage is completed by a voltage governing loop.First by inverter side three-phase alternating voltage
Measured value uabcAfter dq0 coordinate transforms with alternating voltage reference value urefCompare, uref=[1,0,0]T, three elements point
U is not representedrefD, q, 0 each axis component, relatively after error respectively obtain u through pi regulatord、uq、u0Component, ultimately forms arteries and veins
Rush the input signal u of generatorcdq0, and produce pulse and transverter is adjusted, maintain AC system voltage permanent so as to reach
Fixed purpose.
3. converter valve level controls
Last layer of flexible direct current power transmission system control system is the control of converter valve level, and the main of valve level control is appointed
Business is to receive the output signal that the control of change of current station level produces, and turns off electric power by the way that appropriate modulation system trigger mode is in the block
Electronic device.Therefore the control of valve level is broadly divided into switch modulation, capacitor voltage balance control and pulse-triggered technology.
3.1 switch modulation
Switch modulation mode mainly has two kinds, one kind be pulse width modulation (Pulse Width Modulation,
PWM), another kind is that nearest level approaches modulation (Nearest Level Modulation, NLM).Led in D.C. high voltage transmission
Domain, is limited by the voltage endurance capability that can turn off power electronic devices (such as IGBT), flexible straight in order to realize higher transmission capacity
The mode of stream transmission system generally use a module-cascades up to a hundred improves transmission voltage class, since number of modules is very much, output
Voltage waveform is similar to the sine wave of standard.Based on the switch modulation of PWM technologies, frequent movement is switched, caused device is opened
Closing loss can be bigger, and in the case where submodule number is relatively more, the total losses of current conversion station will also significantly increase.Therefore high pressure
Flexible direct-current transmission field is more using the switch modulation based on NLM.
NLM also referred to as quantifies rounding method, and principle is similar with the A/D changes in digital circuit, its working mechanism is from the change of current
Station level control system receives reference wave, is selected and the immediate conduct of reference wave sampled value in the level that can be generated from transverter
Control instruction, the submodule for then triggering respective number produce required level output.NLM is selecting closest level moment base
Obtained in the following formula：
N (t)=[uref/UCref] (3-1)
In formula, N (t) is that bridge arm needs the submodule number that puts into, UCrefFor submodule capacitor voltage reference value, urefFor
Bridge arm voltage reference value, [] symbol are meant that to the data round off principle rounding in [].
, it is necessary to generation into line triggering pulse after obtaining bridge arm and needing the submodule number that puts into.Trigger pulse is given birth to
Into there is following several requirements：
(1) during each trigger action, the submodule number that switching state needs to change in bridge arm will be lacked as far as possible.On the one hand it is
On the other hand it is due to that the switching characteristic of power electronic devices has differences and during dead band to reduce the switching frequency of device
Between introducing, the inputs of different submodules and excision can not possibly fully synchronized progress, so as to cause DC voltage fluctuation, during switching
Need the submodule number that changes more, the fluctuation of DC voltage is more violent.
(2) triggering control needs and capacitor voltage balance control is engaged.
3.2 capacitor voltage balances control
The present invention use the capacitor voltage balance control strategy based on prime factorization method, be detailed below based on matter because
The submodule grouping process of sub- decomposition method：
Assuming that single bridge arm submodule number is N, prime factorization is carried out to it, is thought according to the prime factorization method of integer
Think, N can be written as：
N=m1×m2×L×mn+1(1 ＜ m1,m2,L,mn+1＜ N) (3-2)
In formula, m1、m2…mnThe group number decomposited when being grouped for each layer；mn+1For in n-th layer packet group after progress n-layer packet
Submodule number.It should be noted that m1、m2…mn+1It is that N decomposites the prime number come.
Submodule is grouped according to the decomposable process of prime factorization method, as shown in figure 13.First, N number of submodule exists
First layer has been divided into m in equal size1Group.Then, first layer m1Submodule carries out average packet, quilt again in the second layer in group each group
It divide into m2Group.And so on, during to n-th layer, the submodule in last layer each group is divided into mnGroup, then got in every group
Submodule number is mn+1.Meanwhile in order to maintain the balance of voltage between each group, in each layer of grouping process, all using electric between group
Pressure balanced algorithm carries out the distribution of conducting submodule number.The assigning process of whole conducting submodule number can be retouched with equation below
State：
In formula, NonThe submodule number that need to be turned on for bridge arm；N1、N2…Nn-1And NnRespectively first layer, the second layer ...
The n-1 layers of conducting submodule number for matching somebody with somebody gained with n-th layer each component, the conducting submodule number that each component is matched somebody with somebody at most are differed as 1；Q1、
Q2…Qn-1And QnRespectively Non、N1…Nn-1Divided by place layer packet when institute packet count (m1、m2...mn) obtained by business； R1、
R2…Rn-1And RnRespectively corresponding remainder.Distribution conducting submodule number, according to balance of voltage algorithm between group, by each layer of institute
Remainder is obtained to be sequentially allocated to the packet for meeting distributive condition, therefore, the conducting submodule that every layer of some packet distribution obtains
Number matches somebody with somebody obtained conducting submodule number and adds 1 again for corresponding business for business, remaining each component obtained by last layer divided by group number.NonA need
For the submodule number of conducting by being grouped layer by layer, final allocation result is that last layer has RnGroup needs to turn on Qn+ 1 submodule
Block, and remaining group need to turn on QnA submodule.
It is N to assume initially that single bridge arm submodule number, and n-layer packet is carried out to it, writeable according to the decomposition method thought N of integer
For：
N=m1×m2×L mi×L×mn+1(1 ＜ m1,m2,L mi,L,mn+1＜ N) (3-4)
In formula, m1、m2…mi…mnThe group number decomposited when being grouped for each layer, wherein at least one number are non-prime；
mn+1For submodule number in n-th layer packet group after progress n-layer packet.In the case of this packet, when considering multilayer packet, repeatedly
The required sequence number of distribution of conducting submodule number, and submodule in n-th layer each group are carried out using balance of voltage algorithm between group
Block is ranked up required sequence number using traditional algorithm, then the sequence number of multilayer packet is：
It is assumed that mi, can be to m for non-primeiOnce decomposed again, you can be rewritten as formula (2-27)：
N=m1×L×mi-1×mi1×mi2×mi+1×L×mn+1 (3-6)
Then the sequence number after decomposition is：
In formula：TiFor miBridge arm sequence number after decomposition；mi1、mi2For miThe integer come is decomposited, and meets 1<mi1、 mi2<
N。
Formula (3-2) subtracts formula (3-4) and obtains：
From formula (3-5), Δ Ti>0, i.e., i-th layer is divided again, sequence number can be reduced further.The rest may be inferred,
If each layer can be divided to be grouped again again to all, until can not be further divided into only, bridge arm sequence number is minimum, multilayer packet at this time
Form conforms exactly to the decomposition result of prime factorization method.So it may be concluded that：Multilayer packet is carried out to bridge arm submodule, can
The further reduction sequence number on the basis of improved method, and the sequence number of the multilayer block form based on prime factorization method
At least.
After bridge arm submodule determines the block form of prime factorization, each layer order of packets has different selections, and different
The sequence number that calculates of order of packets difference.By taking 20 submodules as an example, carrying out prime factorization can obtain：20=
5×2×2.20 submodules first can be divided into 5 groups during packet, then 4 submodules in every group are divided into 2 groups, sequence number passes through
Formula (3-7) is calculated as 25；Also 2 groups can be first divided into, then every group of 10 submodules are divided into 5 groups, sequence number passes through formula (3-7)
It is calculated as 31.And then chosen using Lagrange's multiplier, Lagrangian object function is：
λ represents Lagrange's multiplier in formula.Successively to m in formula1、m2…mn+1, λ seek partial derivative, can obtain：
Solution formula (3-7) can obtain：
By the m in formula (3-8)iItem subtracts mi+1：
Due to mi+1>1, so there is mi>mi+1.But gained limit is calculated by formula (3-9) and not fully meets prime factor point
Group form, the reason is that in the block form determined by formula (3-1), it is possible that prime factor index is not 1 situation, is decomposed
Some prime factors out are identical.Therefore in order to meet prime factor block form, while formula (3- can be met as much as possible again
9) result of calculation, it is allowed to mi=mi+1, i.e. the inequality relation of the two is changed into mi≥mi+1.And so on understand, m1、m2…mn+1
It should meet that latter is not more than the inequality relation of previous item, i.e.,：
m1≥m2≥L≥mn≥mn+1 (3-13)
So in the case of definite bridge arm block form, minimum value is obtained for formula (3-6), it is necessary to make m1、m2…mn+1
Meet formula (3-10), i.e., when carrying out multilayer packet to bridge arm submodule, after determining block form by prime factorization method, each layer is pressed
The order of packets of prime factor from big to small is successively grouped, and bridge arm sequence number can be made minimum.
This capacitor voltage balance method is known as to the optimal method of capacitor voltage balance packet sequencing, it is referred to as optimal
Change method, specific implementation step are as follows：
(1) prime factorization is carried out to single bridge arm submodule number, determines the block form of bridge arm submodule multilayer packet；
(2) after moment bridge arm conducting submodule number is calculated, successively it is grouped by the order of prime factor from big to small, often
Once it is grouped, according to the group divided again by distributing gained conducting submodule number during upper-layer packet, by balance of voltage algorithm between group,
Reallocate to conducting submodule number, until can not be further divided into only, first layer packet bridge arm according to determined by modulation strategy
Turn on submodule number distribution；
(3) last layer point each group is according to the conducting submodule number finally distributed, traditionally to submodule in group
Pressed, so as to complete the execution step of whole optimal method.
The specific control flow chart of optimal method is as shown in figure 14.By taking single bridge arm submodule number N=216 as an example, according to most
Optimization method understands that 216 prime factorization form is 3 × 3 × 3 × 2 × 2 × 2, by this order of packets to single bridge arm
216 submodules are successively grouped, and sequence number at this time is minimum.Calculate the sequence time of single bridge arm under optimal method
Number, and table 3-1 is relatively obtained with improved method and traditional algorithm, order of packets presses the prime factor arrangement of block form in table 3-1
Order is successively grouped.
Table 3-1 sequence numbers compare
, it is apparent that improved method can substantially reduce bridge arm sequence number from table 3-1, and optimal method can be real
Now further optimization, makes bridge arm sequence number minimum, at utmost reduces operand.
Further, being capable of the further row of reduction if Shell sorting will be changed to based on the bubble sort in prime factor algorithm
Order number, improves sequence efficiency, and then reduces the requirement to system hardware.
3.3 Pulse-trigger control
MMC maximums feature based on half-bridge submodule (Half Bridge Sub-module, HBSM) is simple for topology, warp
Ji property is high, but does not possess DC Line Fault Scavenging activity；And based on full-bridge submodule (Full Bridge Sub-module,
FBSM), single clamp submodule (Clamp Single Sub-module, CSSM), double clamp submodule (Clamp Double
Sub-module, CDSM), series connection Shuangzi module (Series Double Sub-module, SDSM), improve compound submodule
The MMC of (Improved Hybrid Sub-module, IHSM) then contrasts, therefore scholars propose to combine both again
To form mixing MMC, the complementation that advantage is changed to greatest extent, various sub-modular structures are as shown in figure 15, working status such as table 3-2
Shown in table 3-7.
The working status of table 3-2 HBSM
(note：1 represents open-minded, and 0 represents shut-off, and+expression electric current is positive direction, and-expression electric current is negative direction)
The working status of table 3-3 FBSM
The working status of table 3-4 CSSM
The working status of table 3-5 CDSM
The working status of table 3-6 SDSM
The working status of table 3-7 IHSM
By taking the mixing submodule that HBSM and FBSM is formed as an example, MMC topologys are then mixed as shown in figure 16.
For mixing MMC, it is contemplated that FBSM when HBSM and FBSM in mixing MMC are mixed has the energy of negative voltage output
Power, mixed type MMC can run on ovennodulation state, it is therefore desirable to the equal pressure sequence algorithm of capacitance voltage of mixed type MMC into
Row is introduced.Capacitance voltage presses sequence step as follows：
(1) input submodule number N needed for calculatingref=vpa/Uc；
(2) bridge arm voltage v in judgementpaIt is positive and negative；
(3) bridge arm current I is judgedarmIt is positive and negative；
(4) if vpa>=0 and Iarm>=0, positive input voltage is minimum | Nref| a FBSM and HBSM submodules；If vpa
>=0 and Iarm＜ 0, positive input voltage are highest | Nref| a FBSM and HBSM submodules；If vpa＜ 0 and Iarm>=0, positive input
Voltage is minimum | Nref| a FBSM submodules；If vpa＜ 0 and Iarm＜ 0, positive input voltage are highest | Nref| a FBSM submodules
Block.
Above step is capacitance voltage sequencer procedure, the equal pressure sequence algorithm such as Figure 17 institutes of capacitance voltage of its valve level triggering
Show.
Above content is the specific embodiment of the invention, is described in detail by system-level key-course, the control of change of current station level
The specific embodiment of layer and converter valve level key-course, it is proposed that complete flexible DC power transmission hierarchical control mode.
The foregoing is merely the preferred embodiment of the present invention, it is not intended to limit the invention, for the technology of this area
For personnel, the invention may be variously modified and varied.All any modification, equivalent substitution, improvement and etc. made for the present invention,
It should all be included in the protection scope of the present invention.
Claims (4)
- A kind of 1. flexible DC power transmission hierarchical control method, it is characterised in that：Step is as follows：（1）Control system is divided into system-level key-course, change of current Substation level and converter valve level key-course；（2）System-level key-course is divided into active class control according to the property of its controlled quentity controlled variable and idle class controls；（3）Change of current Substation level is divided into two major class of current indirect control and Direct Current Control；（4）Converter valve level key-course is divided into switch modulation, capacitor voltage balance control and pulse triggering method.
- 2. flexible DC power transmission hierarchical control method according to claim 1, it is characterised in that：The system-level control Layer is divided into active class control according to the property of its controlled quentity controlled variable and idle class controls, and includes following control model：2.1）Real power control pattern；2.2）Idle control model；2.3）Alternating voltage control model；2.4）DC voltage control pattern；2.5）FREQUENCY CONTROL pattern；2.6）Passive alternating voltage control model.
- 3. flexible DC power transmission hierarchical control method according to claim 1, it is characterised in that：The change of current station level control Preparative layer is divided into two major class of current indirect control and Direct Current Control, includes following control method：3.1）Current indirect control method；3.2）Inner ring current control in Direct Current Control；3.3）Open sea wharf in Direct Current Control；3.4）Outer shroud DC voltage control in Direct Current Control；3.5）Outer shroud FREQUENCY CONTROL in Direct Current Control；3.6）Passive alternating voltage control in Direct Current Control.
- 4. flexible DC power transmission hierarchical control method according to claim 1, it is characterised in that：The converter valve level Key-course is divided into switch modulation, capacitor voltage balance control and pulse-triggered, containing following control method：4.1）Capacitor voltage balance controls the capacitor voltage balance algorithm grouping process based on prime factorization method；4.2）Capacitor voltage balance controls optimized control method flow；4.3）Capacitance voltage equal pressure sequence algorithm when HBSM and FBSM is used in mixed way in the mixing MMC of pulse triggering method.
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