CN100588073C - Current control method and device of flexible DC power transmission current transformer - Google Patents

Current control method and device of flexible DC power transmission current transformer Download PDF

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Publication number
CN100588073C
CN100588073C CN200810038542A CN200810038542A CN100588073C CN 100588073 C CN100588073 C CN 100588073C CN 200810038542 A CN200810038542 A CN 200810038542A CN 200810038542 A CN200810038542 A CN 200810038542A CN 100588073 C CN100588073 C CN 100588073C
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current
phase
value
control
hysteresis
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CN101295878A (en
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李响
王志新
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/70Wind energy
    • Y02E10/76Power conversion electric or electronic aspects

Abstract

The invention relates to a current control method for a flexible DC transmission convertor and a device thereof, which pertains to the technical field of power transmission in wind power generation. The current control of the invention adopts a hysteresis loop comparator with the adjustable width of a hysteresis loop; the current bias is compared with the width of the hysteresis loop; when the current bias exceeds the width of the hysteresis loop, the hysteresis loop comparator outputs switching signals to change the switching tube state of the bridge circuit of the convertor and reduce the current bias so as to achieve the purpose of current tracing control; meanwhile, the closed loop control of switching signal frequency is brought in by the hysteresis loop comparator; the phase and theperiod of the switching signal are controlled to be equal to the phase and the period of a fixed clock signal by the dynamic regulation to the width of the hysteresis loop, thus causing the frequencyof the switching signal to be a fixed value. The method and the device promote the dynamic response speed and precision of the current tracing control of the flexible wind power DC transmission convertor on the sea, meanwhile, the switching frequency of the power tube of the convertor is kept to be fixed, switching stress and switching lose are reduced and the transmission efficiency is improved.

Description

The current control method of flexible DC power transmission current transformer and device
Technical field
The present invention relates to a kind of current control method and device of power transmission technology field, specifically is a kind of current control method and device of flexible DC power transmission current transformer of Oversea wind power generation electric power transfer.
Background technology
Along with the expansion day by day of marine wind electric field scale, wind energy turbine set is more and more far away apart from the distance of seashore, and capacity also rises to tens and even gigawatt.Flexible DC power transmission is a kind ofly to be novel technology of transmission of electricity fundamentally with voltage source converter (VSC), igbt (IGBT) and pulse-width modulation (PWM) technology, this technology have the active power that can power to passive network, can realize transmission system and reactive power independently control, need not additionally increase advantages such as reactive-load compensation equipment, meet the requirement of Oversea wind power generation head, become the one preferred technique of marine wind electric field networking apart from transmission of electricity.
Adopt traditional high-voltage AC transmission system with marine wind electric field and become owner of in the process of electrical network, because long distributed capacitance effect apart from the seabed ac cable causes the capacitance current in the cable excessive, and the reactive power compensation of AC system at sea is difficult to carry out, and makes traditional high-voltage AC transmission system can't use in the wind-powered electricity generation electric power transfer at sea.Flexible DC power transmission is a kind ofly to be novel technology of transmission of electricity fundamentally with voltage source converter, igbt and pulse modulation technology, this technology have the active power that can power to passive network, can realize transmission system and reactive power independently control, need not additionally increase advantages such as reactive-load compensation equipment, meet the requirement of Oversea wind power generation head, become the one preferred technique of marine wind electric field networking apart from transmission of electricity.Offshore wind power flexible DC power transmission current transformer is the key device of offshore wind power flexible DC power transmission system, and main effect is that the wind energy turbine set AC energy is converted to direct current energy quickly and accurately.Under the stable situation of wind energy turbine set voltage, the control of wind energy turbine set through-put power is actually control to wind energy turbine set output AC electric current, so the current control method of this part and device the performance index of flexible DC power transmission system have been determined.
The current control method of current transformer generally adopts the indirect current control method at present, and this method is controlled by PWM, generates the sine pulse width modulation (PWM) voltage of amplitude phase controlled in current transformer bridge circuit AC side; This PWM voltage and the acting in conjunction of AC network side electromotive force generate fundamental current in AC side of converter, and harmonic current is then by the filtering of current transformer net side inductance.This method is controlled the AC side output current indirectly by control bridge circuit PWM voltage, therefore has dynamic response slow, to the shortcoming of parameter sensitivity.At the deficiency of indirect current control, the someone has proposed to adopt the Direct Current Control method of current on line side closed-loop control, improves the dynamic and static performance of current on line side.
Find by prior art documents, Marian P, the Current ControlTechniques for Three-Phase Voltage-Source PWM Converters (three-phase voltage source PWM current transformer Current Control Technology) that people such as Kazmierkowski are delivered on IEEETransactions on Industrial Electronics, propose four kinds of Direct Current Control methods that adopt the current on line side closed-loop control, these four kinds of Direct Current Control methods can be summed up as fixed switching frequency PWM Current Control and hysteresis current PWM controls this two class.Wherein, the physical significance of fixed switching frequency PWM Current Control is clear, and it is convenient to realize, because switching frequency fixes, thereby net side transformer and filter inductance design be easier to, and help the limit switch loss.But the major defect of this method is that under the not high condition of switching frequency, the electric current dynamic response is slower, and the electric current dynamic deviation correspondingly changes with current changing rate.By contrast, the ring PWM Current Control that stagnates then has current response speed faster, and the electric current dynamic deviation is determined by hysteresis band.But the main deficiency of this scheme is embodied in switching frequency to be changed with the fluctuation of current changing rate, causes net side filter inductance difficult design, and power switch pipe stress and switching loss increase.At the high-power applications occasion of offshore wind power flexible DC power transmission current transformer, require the dynamic and static response of Current Control rapid, switching frequency should not be too high, and maintained switch fixed-frequency as much as possible, to reduce switch stress and switching loss.Therefore this two classes Direct Current Control method all is difficult to direct application.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, a kind of current control method and device of flexible DC power transmission current transformer is provided.The present invention has adopted the adjustable hysteresis comparator of a kind of hysteresis band h, current deviation Δ i and hysteresis band h are compared, when current deviation Δ i surmounts hysteresis band h, the hysteresis comparator output switching signal changes current transformer bridge circuit switching tube state reducing current deviation Δ i, thereby reaches the purpose of current tracking control; Insertion switch frequency closed-loop control is simultaneously controlled phase place and the cycle that the phase place of hysteresis comparator output switching signal and cycle equal a fixed clock signal by dynamic adjustment hysteresis band h, makes that the frequency of switching signal is a fixed value.
The present invention is achieved by the following technical solutions:
The current control method of flexible DC power transmission current transformer involved in the present invention comprises the steps:
The first step detects wind energy turbine set and exchanges voltage on line side and electric current, and calculates active power P, reactive power Q;
Second step is with active power P, reactive power Q reference value P corresponding with it Ref, Q RefRelatively, calculate acquisition active current command value i through pi regulator d *With reactive current i q *Command value;
The 3rd step is with current instruction value i d *, i q *After two rotation dq coordinates are tied to the coordinate transform of three phase static abc coordinate system, obtain three-phase current command value i a *, i b *, i c *, itself and the first step are detected the current on line side actual value i that obtains a, i b, i cRelatively, obtain three-phase current deviation signal Δ i a, Δ i b, Δ i c
In the 4th step, every phase hysteresis comparator is respectively with each phase current deviation and the relatively back output switching signal of hysteresis band separately;
The 5th step is with the switching signal f of every phase sAn and fixed clock signal f rBe input to hysteresis band estimating circuit separately, obtain the estimated value h of each phase hysteresis band r
The 6th step, whenever adopt a PLL phase-locked loop phase-control circuit to detect the phase difference of its switching signal and a fixed clock signal mutually, after pi regulator calculating, obtain the correction value h of hysteresis band p
The 7th step is with the estimated value h of each phase hysteresis band rWith correction value h pObtain actual hysteresis band value h after the addition, and feed back to hysteresis comparator separately, the frequency of controlling its output switching signal is a fixed value.After the end, the calculating of next time sampling.
Second step, described calculating through pi regulator obtained active current command value i d *With reactive current i q *Command value when its current instruction value of controlled current tracking, can realize the control to current transformer transmission active power, and to the compensation of wind energy turbine set reactive power.
The 4th step, described hysteresis comparator was a kind of hysteresis comparator of variable hysteresis band, and it adopts and becomes amplitude limiter circuit, changes hysteresis band h by direct change comparator output violent change.
Described fixed clock signal of the 5th step is that a duty ratio is 1/2, frequency, cycle changeless unit square-wave signal.With the frequency of this signal reference value as switching frequency, the phase place of control switch signal and cycle equated with the phase place and the cycle of this square-wave signal, just can realize the fixing of switching frequency.
The purpose of described hysteresis band estimating circuit of the 5th step is to be fixed reference in order to come the control switch cycle stability by the size of estimating hysteresis band, and its principle is by hysteresis band and switch periods relational expression:
h r T r = U dc 4 L ( 1 - e n 2 ) = h T s ⇒ h r = h T r T s = h f s f r
In the formula, T r=1/f rReference value (also being the fixed clock cycle) for the switching signal cycle; U DcBe the dc voltage value; L is a current transformer AC inductance value; e nBe AC side voltage perunit value; T s=1/f sDetected value for the switching signal cycle.
Described PLL phase-locked loop phase-control circuit of the 6th step makes the phase place of switching signal and the phase place of fixed clock signal keep homophase by revising the hysteresis band of hysteresis comparator.This correcting action has remedied the deficiency that described hysteresis band of the 5th step is estimated, has improved the stability of system.
Described hysteresis band estimating circuit of the 5th step and the described PLL phase-locked loop phase-control circuit parallel processing of the 6th step constitute the closed-loop control of switching frequency jointly, are realizing the Direct Current Control fast dynamic response simultaneously, have guaranteed the fixing of switching frequency.
The current control device of flexible DC power transmission current transformer involved in the present invention, comprise alternating voltage and current sensor, DSP digital signal processor, power computation module, coordinate transformation module, hysteresis comparator, hysteresis band estimating circuit, low pass filter, PLL phase-locked loop control circuit, wherein:
Alternating voltage, current sensor senses current transformer AC network side three-phase voltage value and current value, the AD conversion is after digital channel input dsp processor;
The power computation module of dsp processor inside can calculate the active power P and the reactive power Q of AC side of converter by the detected value of voltage, electric current, with itself and corresponding reference value P Ref, Q RefRelatively the back obtains the power difference, and the power difference obtains active current command value i after DSP internal digital PI regulates calculating d *With referenced reactive current value i q *, transfer to the intrinsic coordinates conversion module;
Coordinate transformation module is with biphase current command value i d *, i q *Be converted to three-phase current command value i a *, i b *, i c *, and with itself and three-phase electricity flow valuve i a, i b, i cCompare, obtain the three-phase current deviate;
Dsp processor exports the three-phase current deviate to hysteresis comparator with analog signal form after the DA conversion;
Hysteresis comparator with current deviation signal and hysteresis band relatively after, output switching signal acts on the current transformer brachium pontis; The switching signal and the fixed clock signal of hysteresis comparator output simultaneously input to the hysteresis band estimating circuit jointly, obtain the estimated value h of hysteresis band after low pass filter filtering r
PLL phase-locked loop phase-control circuit obtains the correction value h of hysteresis band by the phase difference between sense switch signal and fixed clock signal after pi regulator calculates pThe estimated value h of above-mentioned hysteresis band rWith correction value h pProduce hysteresis band actual value h after the addition, h is fed back to hysteresis comparator, form the closed-loop control of switching signal frequency.
Wherein:
Described hysteresis comparator adopts the change amplitude limit comparison circuit of variable hysteresis band, changes hysteresis band h by direct change comparator output violent change, and the frequency of the big more output switching signal of h is low more like this.
Described hysteresis band estimating circuit adopts a monostable oscillator, switching signal frequency f sThe pulse period of control generator output is T s, fixed clock signal frequency f rControl the width size of its output pulse, work as T r>T sShi Wufa reaches the pulsewidth adjustment, therefore introduces the detection gain 1/K (wherein K<1) of hysteresis band h.The pulse period of monostable oscillator output is T like this s, the width of pulse is KT r(less than T s).This pulse signal is used to control an analog switch, by duty ratio KT r/ T sRegulate the estimated value h of hysteresis band r
Described low pass filter is connected with hysteresis band estimating circuit circuit, is used for filtering hysteresis band estimated value h rIn the high frequency components component, improve the antijamming capability of anti-system.
Described PLL phase-locked loop control circuit is made up of PLL phase detecting circuit and a pi regulator, effective object is a hysteresis comparator, be used for sense switch signal and fixed clock phase difference between signals φ, export the correction value h of hysteresis band then by pi regulator p
According to the inventive method, only need carry out the independent control that a coordinate transform just can realize wind energy turbine set AC side active power and reactive power; Adopt the stagnant chain rate method of fixed frequency, only need calculate and just obtain active current and referenced reactive current value active power, reactive power, and do not need current tracking is done any numerical calculation, reduced the amount of calculation and the memory space of dsp processor, promoted overall system efficiency; Take the control method of switching frequency closed loop,, reduced the switch stress and the loss of power tube having kept original hysteresis current control rapidly, continuously, under the prerequisite of advantage such as accurate, fixed switching frequency.
With the present invention compared with the prior art, under identical switching frequency and condition of work, the current response time of the current tracking response time of structure control of the present invention than fixed switching frequency PWM Current Control structure has shortened 30%; During stable state, the error between actual current and the current instruction value is ± 2.4%, and its precision has improved nearly one times than the current PI controller structure in the fixed switching frequency PWM Current Control; The current on line side harmonic wave is little, harmonic wave resultant distortion THD<3.1% of phase current.Under the current response speed and current tracking precision conditions identical with hysteresis current PWM control structure, the switching signal frequency stabilization of hysteresis comparator output is in 100 ± 0.1% scopes in the structure of the present invention; And the frequency of the switching signal of hysteresis comparator output fluctuates between 30%~170% in the hysteresis current PWM control structure.The present invention is applicable to that also the offshore wind farm generate output arrives the electric power transfer of gigawatt greatly.
Description of drawings
Fig. 1 is a method flow diagram of the present invention;
Fig. 2 is the main circuit of flexible DC power transmission current transformer and the structural representation of control device of the present invention;
Fig. 3 is the structural representation of single-phase fixed hysteresis current frequently control in apparatus of the present invention;
Fig. 4 is the schematic diagram of variable-width hysteresis comparator in apparatus of the present invention;
Fig. 5 is the schematic diagram of hysteresis band estimating circuit in apparatus of the present invention.
Embodiment
Below in conjunction with accompanying drawing embodiments of the invention are elaborated: present embodiment is being to implement under the prerequisite with the technical solution of the present invention, provided detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.
Figure 1 shows that method flow diagram of the present invention, comprise the steps:
The first step detects wind energy turbine set and exchanges voltage on line side and electric current, and calculates active power P, reactive power Q;
Second step is with active power P, reactive power Q reference value P corresponding with it Ref, Q RefRelatively, calculate acquisition active current command value i through pi regulator d *With reactive current i q *Command value;
The 3rd step is with current instruction value i d *, i q *After two-phase rotation dq coordinate is tied to three phase static abc coordinate system and carries out coordinate transform, obtain three-phase current command value i a *, i b *, i c *, detect the wind energy turbine set AC network side current actual value i that obtains with the first step again a, i b, i cRelatively, obtain three-phase current deviation signal Δ i a, Δ i b, Δ i c
In the 4th step, every phase hysteresis comparator is respectively with each phase current deviation and the relatively back output switching signal of hysteresis band separately;
The 5th step is with the switching signal f of every phase sAn and fixed clock signal f rBe input to hysteresis band estimating circuit separately, obtain the estimated value h of each phase hysteresis band r
The 6th step, whenever adopt a PLL phase-locked loop phase-control circuit to detect the phase difference of its switching signal and a fixed clock signal mutually, after pi regulator calculating, obtain the correction value h of hysteresis band p
The 7th step is with the estimated value h of each phase hysteresis band rWith correction value h pObtain actual hysteresis band value h after the addition, and feed back to hysteresis comparator separately, the frequency of controlling its output switching signal is a fixed value.After the end, the calculating of next time sampling again.
The unitary sampling calculation process can be realized three closed-loop controls of power, electric current, switching frequency; Hysteresis band is estimated and PLL phase-locked loop phase control realizes parallel processing, has both improved the stability of whole system, has also improved the response speed of Current Control; Simultaneously, the closed-loop control of switching frequency is fixed on the control that a set-point is realized the fixed frequency hysteresis current with switching frequency.
As shown in Figure 2, the main circuit structure of flexible DC power transmission current transformer and the structure of control device of the present invention, wherein:
The main circuit structure of flexible DC power transmission current transformer comprises: wind energy turbine set three-phase net side electromotive force (e a, e be c), ac filter inductance L and three-phase equivalent resistance R form the AC network lateral circuit of current transformer; 6 IGBT bridge circuit switch (S k, k=1~6), 6 reverse parallel connection fly-wheel diode (VD k, k=1~6) and composition current transformer three-phase full-controlled bridge.
Current transformer three-phase bridge circuit DC side is received receiving end current transformer on the bank through submarine cable, simultaneously, DC side parallel filter capacitor C (capacitances in series and neutral ground connected mode that to adopt two capacitances be 2C make the neutral point voltage ripple disable, improve the stability of control system).The stability of the dc voltage of flexible DC power transmission system is realized by the direct voltage control of deciding of current transformer on the bank, therefore, can be a galvanic current kinetic potential with current transformer end equivalence on the bank.
Described ac filter inductance L, three-phase full-controlled bridge and dc filter capacitor C to the role and influence of transmission system are:
(1) ac filter inductance: during the VSC operate as normal, energy flows between AC network side and rectifier bridge, and portion of energy is stored on the inductance, is discharged into DC side by rectifier bridge then, realizes the PWM unsteady flow.Inductance is the necessary condition that guarantees the normal operation of three-phase VSC.
(2) three-phase full-controlled bridge: the power switched switch produces AC side voltage fast, controls the size and the phase place of its first-harmonic, thereby obtains desired ac-side current and power.
(3) dc filter capacitor: the element that mainly adopts for the voltage type PWM current transformer.Its effect is a stable DC side voltage, and filtering dc voltage ripple composition guarantees the current transformer operate as normal.Nth harmonic in the three-phase VSC output DC bus-bar voltage can produce the n+1 subharmonic through PWM modulation back in net side input current, so dc filter capacitor also helps to reduce the effect of Harmonics of Input.
Control device of the present invention comprises: exchange voltage on line side and current detection sensor, power computation module, coordinate transformation module, single-phase fixed ring control module and the switch drive of stagnating frequently, wherein:
Described alternating voltage, current sensor adopt contactless Hall type voltage, the current sensor of Switzerland LEM company, are used to detect three-phase voltage, the current value of current transformer AC network side.
Described dsp processor is the key control unit of control system, and inside programming realizes power computation module, digital pi regulator and coordinate transformation module.
Described power computation module, its principle are by formula P=eicos δ, Q=eisin δ, and wherein e is the phase voltage effective value; I is the phase current effective value; δ is the phase difference of voltage delay in electric current.
Described coordinate transformation module is the equivalent coordinate transformation module that two-phase rotation d-q coordinate is tied to three phase static abc coordinate system, is used for the command value i with biphase current d *, i q *Be transformed to the command value i of three-phase current a *, i b *, i c *Its transformation relation formula is as follows:
θ is the angle of current phasor and d between centers in the formula.
Power computation module, coordinate transformation module are realized by the dsp processor inside programming.Power computation module obtains active power value P and reactive power value Q after calculating by formula; With its respectively with active power reference value P RefAnd reactive power Q RefThe reference value comparison is after digital PI obtains active power command value i after regulating calculating d *With reactive power command value i q *Revolving dq by two-phase changes and can get three-phase current command value i after coordinate transformation module that coordinate is tied to three phase static abc coordinate system calculates a *, i b *, i c *Under the effect of single-phase fixed hysteresis current tracking Control frequently, the exportable threephase switch signal of hysteresis comparator S a, S b, S cChange the on off state of current transformer three-phase bridge circuit by switch driving circuit, make three-phase electricity flow valuve i a, i b, i cFollow its command value i rapidly a *, i b *, i c *, eliminate circuit deviations Δ i a, Δ i b, Δ i c, realize the flexible DC convertor control of offshore wind farm wind energy turbine set active power P, reactive power Q reference value P corresponding with it Ref, Q RefBetween floating follow control.
Below in conjunction with accompanying drawing 3, accompanying drawing 4 and accompanying drawing 5, realize the single-phase example that is applied as of deciding frequency hysteresis current tracking Control with the inventive method and device, technical scheme of the present invention is described in further detail (corresponding parameter omits subscript a, b, c during single-phase analysis).
Single-phase fixed hysteresis current control structure has frequently as shown in Figure 3 comprised hysteresis comparator, hysteresis band estimating circuit and PLL phase-locked loop phase-control circuit.It is used to export the switching signal of fixed frequency, by the effect of current transformer bridge circuit current deviation Δ i is controlled in the hysteresis band h.When switching frequency during, can be similar to and think a switch periods T much larger than mains frequency sInterior electrical network electromotive force e is invariable.If definition e n=2e/U DcCan derive T s = 4 hL / U dc ( 1 - e n 2 ) . Wherein: T sBe switch periods; L is an AC network side reactance value; U DcBe the dc voltage value.
As can be seen, if hysteresis band h fixes, and e nChange, then the PWM switch periods necessarily changes.In order to make the switch periods frequency constant, introduce a changeless reference data clock signal, its frequency is f r, the cycle is T rPeriod T when switching signal s=T rThe time, can get h = u dc T r ( 1 - e n 2 ) / 4 L . Obviously control hysteresis band h can maintained switch signal frequency f s=f r
Be illustrated in figure 4 as the schematic diagram of variable-width hysteresis comparator, adopt one to become amplitude limiter circuit, just can change hysteresis band h, realize the controlled hysteresis comparator of hysteresis band, the big more switching signal frequency f of this circuit h by direct change comparator output violent change sLow more.
For the control of the fixed frequency hysteresis current of single-phase brachium pontis, make switching frequency f sEqual a given fixed clock frequency f r, the control of its hysteresis band h should be considered from two aspects: on the one hand, should control h and make the period T of switching signal sPeriod T with the fixed reference clock signal rEquate; On the other hand, should control h and make the pulse train of switching signal equate with the phase place of fixed reference clock signal pulse sequence, also be phase difference=0.
Described control hysteresis band h makes the period T of switching signal sPeriod T with the fixed reference clock signal rEquating, is to realize by hysteresis band estimating circuit in apparatus of the present invention shown in Figure 5.It phase difference=0 of pulse train and fixed clock signal pulse sequence of switching signal is to realize by the PLL phase-locked loop phase-control circuit in the top frame of broken lines among Fig. 3 that described control hysteresis band h makes.
Below elaborate the embodiment of these two circuit:
Be illustrated in figure 5 as the schematic diagram of hysteresis band estimating circuit in apparatus of the present invention, adopt a monostable oscillator, switching frequency f sThe pulse period of controlling its output is T s, fixed clock frequency f rControl the width T of its output pulse rConsider T r>T sShi Wufa realizes pulse width control, introduces the detection gain 1/K (wherein K<1) of hysteresis band h.The pulse period of monostable oscillator output is T like this s, the width of pulse is KT r<T sThis pulse signal is used to control an analog switch, by duty ratio KT r/ T sRegulate the estimated value h of hysteresis band rFilter among the figure adopts low pass filter, the estimated value h of the filtering hysteresis band that is used for rHigh frequency components improves the stability of a system.Estimated value h with hysteresis band rThereby feed back to the closed-loop control that hysteresis comparator forms one-period, make the switching signal cycle stability of hysteresis comparator output at T r, increased the stability in large of whole system.
Described PLL phase-locked loop phase-control circuit is made up of PLL phase detecting circuit and a pi regulator, effective object is a hysteresis comparator, be used for sense switch signal and fixed clock frequency phase difference between signals φ, export the correction value h of hysteresis band then by pi regulator pCorrection value h with hysteresis band pWith estimated value h rObtain actual hysteresis band h after the addition and be input to hysteresis comparator, thereby form the closed-loop control of a phase place, make phase difference=0.

Claims (9)

1. the current control method of a flexible DC power transmission current transformer is characterized in that, may further comprise the steps:
The first step detects wind energy turbine set and exchanges voltage on line side and electric current, and calculates active power P, reactive power Q;
Second step is with active power P, reactive power Q reference value P corresponding with it Ref, Q RefRelatively, calculate acquisition active current command value i through pi regulator d *With referenced reactive current value i q *
The 3rd step is with current instruction value i d *, i q *After two-phase rotation dq coordinate is tied to the coordinate transform of three phase static abc coordinate system, obtain three-phase current command value i a *, i b *, i c *, itself and the first step are detected the current on line side actual value i that obtains a, i b, i cRelatively, obtain three-phase current deviation signal Δ i a, Δ i b, Δ i c
In the 4th step, every phase hysteresis comparator is respectively with each phase current deviation and the relatively back output switching signal of hysteresis band separately;
The 5th step is with the switching signal f of every phase s, actual hysteresis band value h and a fixed clock signal f rBe input to hysteresis band estimating circuit separately, obtain the estimated value h of each phase hysteresis band r
The 6th step, whenever adopt a PLL phase-locked loop phase-control circuit to detect the phase difference of its switching signal and a fixed clock signal mutually, after pi regulator calculating, obtain the correction value h of hysteresis band p
The 7th step is with the estimated value h of each phase hysteresis band rWith correction value h pObtain actual hysteresis band value h after the addition, and feed back to hysteresis comparator separately, the frequency of controlling its output switching signal is a fixed value, after the end, and the calculating of next time sampling.
2. the current control method of flexible DC power transmission current transformer according to claim 1 is characterized in that, second step, described calculating through pi regulator obtained active current command value i d *With referenced reactive current value i q *, when its current instruction value of controlled current tracking, realize the control of current transformer transmission active power and to the compensation of wind energy turbine set reactive power.
3. the current control method of flexible DC power transmission current transformer according to claim 1 is characterized in that, described hysteresis comparator of the 4th step is the hysteresis comparator that adopts the variable hysteresis band that becomes the amplitude limiter circuit realization.
4. the current control method of flexible DC power transmission current transformer according to claim 1, it is characterized in that, described fixed clock signal of the 5th step, be that a duty ratio is 1/2, frequency, cycle changeless unit square-wave signal, with the frequency of this signal reference value as switching frequency, the phase place of control switch signal and cycle equated with the phase place and the cycle of this square-wave signal, realized the fixing of switching frequency.
5. the current control method of flexible DC power transmission current transformer according to claim 1, it is characterized in that, it is fixed reference that described hysteresis band estimating circuit of the 5th step comes the control switch cycle stability by the size of estimating hysteresis band, described PLL phase-locked loop phase-control circuit of the 6th step is by revising the hysteresis band of hysteresis comparator, makes the phase place and the fixed clock signal f of switching signal rPhase place keep homophase, described hysteresis band estimating circuit of the 5th step and described PLL phase-locked loop phase-control circuit of the 6th step constitute the closed-loop control of switching frequency jointly, realize the Direct Current Control fast dynamic response simultaneously, guaranteeing the fixing of switching frequency.
6. the current control device of a flexible DC power transmission current transformer, it is characterized in that: comprise alternating voltage and current sensor, DSP digital signal processor, power computation module, coordinate transformation module, hysteresis comparator, hysteresis band estimating circuit, low pass filter, PLL phase-locked loop control circuit, wherein:
Alternating voltage, current sensor senses current transformer exchange voltage on line side, electric current, and the AD conversion is after digital channel is imported the DSP digital signal processor with three-phase voltage value and current value;
Power computation module calculates active power and reactive power after the internal digital pi regulator calculates active current command value and referenced reactive current value, and transfers to coordinate transformation module;
Coordinate transformation module is converted to the three-phase current command value with the biphase current command value, and itself and three-phase current detection value are compared, and obtains the three-phase current deviate;
The DSP digital signal processor exports the three-phase current deviate to hysteresis comparator with analog signal form after the DA conversion;
The hysteresis comparator output switching signal acts on current transformer three-phase brachium pontis, switching signal, actual hysteresis band value and the fixed clock signal f of hysteresis comparator output simultaneously rInput to the hysteresis band estimating circuit jointly and after low pass filter filtering, obtain the estimated value of hysteresis band;
The phase place and the fixed clock signal f of PLL phase-locked loop phase-control circuit sense switch signal rPhase place, and calculate the correction value of hysteresis band by its phasometer, produce the hysteresis band actual value after the estimated value of above-mentioned hysteresis band and the correction value addition and input to hysteresis comparator, form the closed-loop control of switching signal frequency.
7. the current control device of flexible DC power transmission current transformer according to claim 6, it is characterized in that, described hysteresis comparator, adopt the change amplitude limit comparison circuit of variable hysteresis band, change hysteresis band by direct change comparator output violent change, the frequency of the big more output switching signal of hysteresis band is low more like this.
8. the current control device of flexible DC power transmission current transformer according to claim 6, it is characterized in that, described hysteresis band estimating circuit, adopt a monostable oscillator, by the pulse period of its output of switching frequency signal controlling, by the width of its output pulse of fixed clock signal controlling, the pulse signal of this hysteresis band estimating circuit output is used to control an analog switch, the estimated value of recently regulating hysteresis band by duty.
9. the current control device of flexible DC power transmission current transformer according to claim 6, it is characterized in that, described PLL phase-locked loop control circuit, be composed in series by PLL phase detecting circuit and a pi regulator, effective object is a hysteresis comparator, this electric circuit inspection switching signal and fixed clock frequency phase difference between signals are calculated the correction value of exporting hysteresis band by pi regulator then.
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