CN105529731B - Based on flexible direct-current transmission system converter station grade modified control strategy - Google Patents
Based on flexible direct-current transmission system converter station grade modified control strategy Download PDFInfo
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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
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- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The problems such as the invention discloses the electric current dynamic response for solving flexible direct current transmission converter station grade control system is slow, and control system is complicated, robustness；For the Direct Current double-closed-loop control that traditional flexible DC transmission technology uses, simplifies inner loop control mathematical model on the basis of conventional vector control theory by improving inner ring current Control Algorithm and replaced with predictive control model, without decoupling link；The control strategy has the advantage that possess control structure simple, consumes the less calculating time, dynamic response is fast, quick track reference value and output voltage stabilization.The present invention, by changing the control strategy of converter station, improves stability and rapidity, makes system operation more preferably, realize process easily and simply, equipment cost is greatly saved while guaranteeing flexible HVDC transmission system stable operation.
Description
Technical field
The present invention relates to the modified control strategies based on flexible HVDC transmission system, belong to technical field of electric power.
Background technique
Flexible direct-current transmission system converter station grade controls and receives system-level active and idle class physical quantity reference value, and obtains
To the modulation ratio M and phase shifting angle of SPWM signalIt is supplied to the trigger pulse Risk factor of converter valve grade control.By flexible direct current
Basic regulative mode it is found thatVariation mainly influence active power, the variation of M mainly influences reactive power, andIt is smaller this
Relationship is more obvious.It therefore, can be by changing phase angleActive power is controlled, it is to control idle by changing modulation ratio M
Power.
There are many implementations of change of current station level control, such as directly controls, vector controlled and self adaptive control etc..Tradition
On, following several control methods are generally taken for the converter station of flexible HVDC transmission system: 1. directly controlling also known as " Indirect Electro
Flow control " receives the instruction of system-level controller, reaches adjusting inverter with phase shifting angle by control modulation ratio and exchanges side
The amplitude of output voltage and the purpose of phase.This control mode is simple, and directly, but response speed is slow, it is not easy to realize
Current control.2. vector controlled is also known as " Direct Current Control ", double -loop control is generallyd use, i.e., outer loop voltag control and inner ring electricity
Flow control.Vector controlled is relatively simple for structure, fast response time, and the control such as overcurrent easy to accomplish is suitable for flexible direct current
Application.But vector controlled needs complicated coordinate transformation process, needs complicated decoupling algorithm, and closed loop design is key,
Parameter tuning is cumbersome, and coordinate orientation is easy to be distorted to influence by network pressure.3. new control strategy also continuously emerges, such as repeat
Control, adaptive control, sliding mode control etc..But these general control strategies are chiefly used in medium and small power occasions.
In flexible HVDC transmission system, the control of change of current station level is the core in flexible HVDC transmission system control,
How to make converter station that there is quick dynamic response, it is stable defeated to realize that high power factor obtains for simplified Control system architecture
Voltage is the research emphasis of the invention patent out.
Summary of the invention
While it is an object of the invention to guarantee that flexible direct-current transmission system converter station exports stable voltage, based on biography
On the basis of the vector controlled of system, by improving inner ring current Control Algorithm, active class reference quantity and idle class reference quantity are passed through
Outer ring controller generates meritorious reference current, idle reference current；Reference current, DC voltage electric current is by inner ring prediction electricity
Flow control generates the modulating wave in PWM trigger；Last PWM trigger output pulse makes switch motion.Guaranteeing flexible direct current
While transmission system stable operation, by the control strategy of change converter station, the stability and rapidity of system operation are improved,
Make system operation more preferably, realizes process easily and simply.
Technical characteristic of the invention is as follows:
(1) improved inner ring predictive-current control is to convert the current error in this period within the fixed sampling period
Next period actual current track reference electric current is enabled, to make change of current utensil as the given value of valve grade control for voltage signal
There is quick dynamic response, realizes high power factor, obtain stable output voltage.
(2) improved inner ring predictive-current control strategy is with this sampling actual current and next sampling instant
Predicted current is compared, and finds out optimum control voltage and space vector of voltage so that current error is minimum, forces next
The actual current of sampling instant tracks this moment reference current with optimal properties.There is no coupled relation, nothing between control variable
Decoupling control is needed, mathematical model is greatly simplified, so that control structure is simple and easy, simplifies change of current station level control system
Design.
(3) follow-on predictive-current control strategy is applied to flexible HVDC transmission system, the quick regulating system of energy
Active power and reactive power, real-time is good, is easy Digital Realization, has good robustness.
The beneficial effect is that:
Primary study of the present invention is directed to flexible direct-current transmission system converter station grade modified control strategy, by conventional vector control
Inner ring current control is modified to predictive-current control in system.
(1) flexible direct-current transmission system converter station grade modified control strategy simplifies the control system knot of change of current station level
Structure improves system dynamic responding speed, save the cost.
(2) follow-on predictive-current control strategy is applied to having for the flexible HVDC transmission system quick regulating system of energy
Function power and reactive power, real-time is good, is easy Digital Realization, has good robustness；To improve the economy of system
Benefit and Practical Benefit.
Detailed description of the invention
Fig. 1 is improved inner ring predictive-current control system structure design figure.
Fig. 2 is converter station using the whole control structure design drawing for improving control strategy.
Fig. 3 is the structure chart of flexible HVDC transmission system.
Specific embodiment
The invention will be further described with specific implementation process with reference to the accompanying drawing.
Referring to Fig. 1, based on improvement inner ring current Control Algorithm on the basis of traditional vector controlled, it is assumed that systematic sampling week
Phase is Ts, and the prediction at phase current t=(K+1) Ts moment can be obtained by the dynamic mathematical models expression formula such as formula (1) of converter station (VSC)
Model is formula (2).
Equivalent circuit usa,usb,uscThe three-phase voltage of exchange side system is respectively indicated, wherein three-phase voltage keeps balance full
Sufficient usa+usb+usc=0；Wherein uca,ucb,uccThe three-phase phase voltage exported for the VSC using PWM modulation；N indicates DC side
Bus neutral point；L indicates equivalent reactance；R indicates substitutional resistance.
Make line current track reference electric current in a switch periods, meets above-mentioned (1) formula it can be concluded that fixed switch frequency
The predictive-current control rule of rate are as follows:
Wherein vj(k) it indicates the control signal mutually exported in t=KT moment jth, meets -1≤vj(k)≤1, j=a, b, c；
udc(k) in t=nT moment DC side busbar voltage；a1=Ln/Ts；a2=Rn；LnAnd RnRespectively indicate R in equivalent circuit Fig. 2
With the value of L；T is the sampling period when the sampling period is sufficiently small, can be approximately considered ij(k+1)=ijref(k)；ijIt (k+1) is mutually electricity
Flow the predicted value of subsequent time；Therefore available corresponding current inner loop transmission function are as follows:
G (z)=ij(Z)/ijref(z)=1/z (3)
Therefore the function of available predictive-current control device are as follows:
Inner ring current control structure Fig. 1 of corresponding predictive-current control device can be designed by formula (4).
Referring to fig. 2, converter station is based on modified predictive-current control block diagram.PLL indicates that phaselocked loop makes output voltage signal
It is synchronous with exchange side voltage holding.Active class and idle class reference value are by outer ring controller generation meritorious reference current idref,
Idle reference current iqref；The reference current of generation is transformed in three-phase current and DC voltage electric current process by dq coordinate
Ring predictive-current control device generates the modulating wave in PWM trigger；Last PWM trigger output pulse makes switch motion.Wherein
Active class reference value mainly includes active power, DC voltage, frequency；Idle class reference value mainly includes reactive power, is handed over
Galvanic electricity pressure.
It is the structure chart of both ends flexible HVDC transmission system, by exchanging side power supply, converter reactor, the change of current referring to Fig. 3
It stands, DC power transmission line composition；Wherein change of current station level control uses follow-on control method.
The active class reference quantity and idle class reference quantity generated by system-level controller generates active electricity through outer ring controller
Flow reference value idrefWith reactive current reference value iqref；The control of converter valve is by reference current, and ac-side current passes through (4) formula
Inner ring predictive-current control device by obtain inner loop control device output voltage d, q axis component desired value Udref, Uqref, lead to
It crosses PWM modulation and generates, usually by changing modulation ratio M and phase shift angleTo realize.As known Udref, UqrefWhen, modulation
Than M and phase shifting angleIt is calculated by formula (5):
Modulation ratio M determines the amplitude of sinusoidal modulation wave signal, and initial phase is by phase shifting angleIt determines, and carrier wave is generally
Isosceles triangle wave.For every phase, when modulating wave is greater than carrier wave, upper bridge arm conducting, on the contrary then lower bridge arm are connected.Therefore modulation ratio M
And phase shifting angleIt just determines the trigger pulse of every phase bridge arm, and then determines the voltage waveform of converter station output.
Claims (2)
1. being directed to the change of current station level modified control strategy of flexible HVDC transmission system, it is characterised in that: controlled in conventional vector
On the basis of, inner ring current control is replaced with prediction model current diffusion limited model, is carried out specific to the mathematical model of converter station
It derives, obtains the expression formula of inner ring predictive-current control to substitute traditional inner ring current control mode, inner ring predicted current control
Device processed exports three-phase voltage desired value, controls to obtain modulation degree M and phase shifting angle by valve gradeThe inner ring predictive-current control
Obtain the predictive-current control formula of fixed switching frequency are as follows:
Wherein vj(k) it indicates the control signal mutually exported in t=KT moment jth, meets -1≤vj(k)≤1, j=a, b, c, udc
(k) in t=nT moment DC side busbar voltage, a1=Ln/Ts, a2=Rn, LnAnd RnRespectively indicate R and L in equivalent circuit
Value, T are the sampling period when the sampling period is sufficiently small, can be approximately considered ij(k+1)=ijref(k), ij(k+1) under phase current
The predicted value at one moment, available corresponding current inner loop transmission function are as follows: G (z)=ij(Z)/ijref(z)=1/z
To obtain the function of predictive-current control device are as follows:
2. the change of current station level modified control strategy according to claim 1 for flexible HVDC transmission system, application
To flexible HVDC transmission system, it is characterised in that: change of current station level inner ring predictive-current control is not necessarily to feed forward decoupling control, is suitable for
All flexible DC transmission engineerings, including two traditional level, three level VSC-HVDC systems and modular multilevel MMC-
HVDC。
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103036460A (en) * | 2012-11-26 | 2013-04-10 | 天津大学 | Model prediction control method for three-level voltage-source-type converter |
| CN104393773A (en) * | 2014-12-02 | 2015-03-04 | 天津航空机电有限公司 | Three-phase voltage pulse width modulation rectifier prediction current control method |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103036460A (en) * | 2012-11-26 | 2013-04-10 | 天津大学 | Model prediction control method for three-level voltage-source-type converter |
| CN104393773A (en) * | 2014-12-02 | 2015-03-04 | 天津航空机电有限公司 | Three-phase voltage pulse width modulation rectifier prediction current control method |
Non-Patent Citations (3)
| Title |
|---|
| 3电平VSC-HVDC系统模型预测控制策略;谭国俊等;《高电压技术》;20131130;第39卷(第11期);第2737-2742页 |
| VSC-HVDC海上风电输电变流器预测电流控制策略研究;李爽等;《太阳能学报》;20120930;第33卷(第9期);第1516-1523页 |
| 模块化多电平变流器HVDC系统的模型预测控制;朱玲等;《电力系统保护与控制》;20140816;第42卷(第16期);第1-8页 |
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