CN102882383A - Direct power control method of modular multilevel wind power converter - Google Patents

Abstract

The invention discloses a direct power control method of a modular multilevel wind power converter. The direct power control method includes: computing active power and reactive power through a virtual magnetic linkage, equaling a power grid to an ideal voltage source, combining the ideal voltage source with converter input reactance, equaling a grid-side power source to a virtual alternating-current motor, and considering that grid-side voltage is generated by the virtual magnetic linkage by sensing. Compared with a voltage-oriented double-closed-loop control method, the direct power control method does not need design of a current inner loop and is rapid in dynamic response; and compared with a look-up-table direct power control method, the direct power control method does not need a grid-side voltage sensor and is rapid in dynamic response, constant in switching frequency and better in steady-state characteristic.

Description

A kind of direct Power Control method of modular multilevel wind electric converter

Technical field

The present invention relates to the Semiconductor Converting Technology field of offshore wind farm, relate in particular to a kind of direct Power Control method of modular multilevel wind electric converter.

Background technology

Being incorporated into the power networks on a large scale of the regenerative resources such as wind energy on the sea becomes the developing direction of Future Power System and intelligent grid application.Flexible DC power transmission (voltage source converter-high voltage direct current transmission based on voltage source converter, VSC-HVDC) technology, being applied to the marine wind electric field long-distance transmissions has become one of current research focus.The VSC-HVDC system has proposed high requirement to capacity and the electric pressure of voltage source converter.Modular multi-level converter (modular multilevel converter, MMC) possess the characteristics of cascade connection type current transformer, easily realizing more number of levels and modularized design, and can realize the back-to-back connection of DC side, is many level topological structure of a kind of VSC-HVDC of being applicable to.

Meritorious, the reactive power decoupling control method of traditional MMC mainly contain two kinds: one, based on the voltage oriented pair of closed loop control method (voltage oriented control, VOC) of VSC-HVDC system linear model.Two, based on the inquiry switch list direct Power Control method (Look-up-table direct power control, LUT-DPC) of VSC-HVDC system nonlinear model.

The voltage oriented control method that proposes in present disclosed document mainly is with the three-phase alternating current stream translation by the synchronous speed rotating coordinate transformation, be decomposed into meritorious, reactive power current component in the synchronous rotating frame, then pass through ratio-integration (PI) adjuster and implement independent control meritorious, the reactive power electric current, thereby realize decoupling zero control to instantaneous meritorious, the reactive power of MMC.But the method has the following disadvantages: one, the pi regulator design parameter is too much, adjusts difficulty.Adopt the engineering Tuning mostly based on ssystem transfer function, but this type systematic is comparatively complicated, mostly deviation is larger for the PI parameter that employing simplification transfer function Equivalent Calculation mode obtains, and need rely at the scene the artificial experience adjustment, and systematic function can't be guaranteed.Two, system parameters there is certain dependence, the ring feed forward architecture will be used the parameters such as system's inductance in adopting, the accuracy of these parameters is difficult to guarantee in real system, sometimes deviation is larger, and the difference along with system conditions, have certain variation, therefore, often cause actual motion performance and expected performance according to the pi regulator of nominal system parameter designing to have deviation.Three, HVDC light system Mathematical Modeling itself exists close coupling, the feature such as non-linear, and therefore pi regulator, can't guarantee dynamic performance according to the design of systematic steady state inearized model, and it is optimum that regulating effect can not reach.

The inquiry switch list direct Power Control method that proposes in present disclosed document comes from the thought of alternating current machine direct torque control, and is applied to adopt in the flexible DC power transmission system of MMC.The basic principle of this control method is: within a sampling period according to instantaneous meritorious, idle error and electrical network position signalling, in pre-determined voltage vector switch list, choose suitable current transformer output voltage vector, so that power output can be followed the tracks of its set-point quickly and accurately.With respect to VOC, the advantage of LUT-DPC mainly is that dynamic response is fast, has higher robustness.Yet its obvious deficiency is that the converter switches frequency is unstable, and steady-state characteristic is not as VOC, simultaneously, also because having used more transducer, cause system cost increase and bulky, and owing to lose sensor signal in the practical application, and be subject to noise jamming, cause systematic function to reduce.

Summary of the invention

For above-mentioned technical problem, the object of the present invention is to provide a kind of direct Power Control method of modular multilevel wind electric converter, its, reactive power meritorious by virtual flux linkage calculation, need not the line voltage transducer, need not ring in the design current, not only dynamic response is fast, and switching frequency is constant, and has better steady-state characteristic.

For reaching this purpose, the present invention by the following technical solutions:

A kind of direct Power Control method of modular multilevel wind electric converter comprises the steps:

A, according to the VSC-HVDC system configuration, set up the Mathematical Modeling of modular multilevel wind electric converter;

B, process the direct voltage set-point by pi regulator

Dc voltage detection value V with the modular multilevel wind electric converter _DcError, obtain the active current set-point

And with this active current set-point With dc voltage detection value V _DcProduct as active power set-point p ^*, wherein, reactive power set-point q ^*Be zero when unity power factor moves;

The three-phase alternating current signal I of C, modular multilevel wind electric converter AC that current sensor is obtained _{U, v, w}With and the output voltage v of each submodule _{Ju, v, w}, switch function S _{Ju, v, w}Process by virtual flux linkage calculation module, obtain the space bit angle setting γ of active power actual value p, reactive power actual value q and flux linkage vector _{ψ s}

D, with the active power set-point p among the step B ^*With reactive power set-point q ^*, and the active power actual value p among the step C and reactive power actual value q obtain the voltage reference signal u under the two-phase rotating coordinate system of direct Power Control device output by the power decoupled control module _RdAnd u _Rq

E, with the space bit angle setting γ of the flux linkage vector among the step C _{ψ s}With the voltage reference signal u among the step D _RdAnd u _RqBy three-phase/two-phase rotating coordinate transformation resume module, obtain three-phase voltage reference signal u ' _Ref, v ' _RefAnd w ' _Ref

F, with the three-phase voltage reference signal u ' in the step e _Ref, v ' _RefAnd w ' _RefControlled quentity controlled variable u with the output of MMC capacitance voltage mean value control module _Ave, v _AveAnd w _AveCarry out overlap-add procedure, obtain the three-phase voltage control signal u of modular multilevel wind electric converter _Ref, v _RefAnd w _Ref

G, with the three-phase voltage control signal u in the step F _Ref, v _RefAnd w _RefCapacitance voltage i with modular multilevel wind electric converter upper and lower bridge arm electric current, its each submodule _{Nu, v, w}, i _{Pu, v, w}, u _{Ju, v, w}Process by MMC trigger impulse generation module, obtain the switching signal of power device in the described modular multilevel wind electric converter of control.

Especially, the power device in the described modular multilevel wind electric converter adopts the MCC structure based on insulated gate bipolar transistor (IGBT).

Especially, the DC side of described modular multilevel wind electric converter adopts capacitance voltage stabilizing, and its AC is provided with reactor.

Especially, in the described steps A Mathematical Modeling of modular multilevel wind electric converter shown in formula (1):

$\left\{\begin{array}{c}{L}_{\mathrm{eq}}\frac{\mathrm{dp}}{\mathrm{dt}}=u_{\mathrm{sd}}^2-u_{\mathrm{rd}}\·u_{\mathrm{sd}}-\mathrm{\ω}\\ L_{\mathrm{eq}}\frac{\mathrm{dq}}{\mathrm{dt}}={u_{\mathrm{sq}}}^2+u_{\mathrm{rq}}\·u_{\mathrm{sd}}+\mathrm{\ω}\end{array}\right.---\left(1\right)$

Wherein, active power actual value p=u _SdI _Sd, reactive power actual value q=-u _SdI _Sq, u _SdAnd u _Sq, i _SdAnd i _Sq, u _RqAnd u _RqThe AC voltage that represents respectively voltage on line side, current on line side and this current transformer under the d-q coordinate system, L _EqThe equivalence of many level of representation moduleization wind electric converter input inductance, it comprises the inductance of AC reactor of this current transformer and the inductance of brachium pontis thereof.

Especially, described step C specifically comprises:

The bridge arm voltage u of C1, virtual many level of flux linkage calculation module computing moduleization wind electric converter _Ra, u _RbAnd u _Rc, wherein, u _Ra, u _RbAnd u _RcComputational process identical, with u _RaBe example, computational process is shown in formula (2):

$u_{\mathrm{ra}}=-{\mathrm{\Σ}}_{j=1}^n{v}_{\mathrm{ju}}\·S_{\mathrm{ju}}+{\mathrm{\Σ}}_{j=n+1}^{2n}{v}_j---\left(2\right)$

Wherein, v _JuBe the output voltage of described current transformer, S _JuBe corresponding switch function;

C2, virtual flux linkage calculation module are calculated virtual flux linkage vector Ψ under the alpha-beta coordinate system by following formula (3), (4) computing module _{S α}, Ψ _{S β}And space bit angle setting γ _{ψ s}

$\left\{\begin{array}{c}{\mathrm{\Ψ}}_{\mathrm{s\α}}=\∫\left(\frac{1}{\sqrt{6}}(2\·u_{\mathrm{ra}}-u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{ec}}\\ {\mathrm{\Ψ}}_{\mathrm{s\β}}=\∫\left(\frac{1}{\sqrt{2}}(u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{eq}}\·i_{\mathrm{L\β}}\end{array}\right.---\left(3\right)$

$\left\{\begin{array}{c}{\sin \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\β}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\\ {\cos \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\α}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\end{array}\right.---\left(4\right)$

Wherein, i _LaAnd i _{L β}Resultant vector for alternating current under the alpha-beta coordinate system;

C3, virtual flux linkage calculation module are by following formula (5), (6) many level of computing moduleization wind electric converter active power actual value p and reactive power actual value q; Wherein, according to this AC side of converter voltage relationship u _s=u _r+ u _L, i.e. ac grid voltage u _sEqual current transformer bridge arm voltage u _rWith voltage u on the reactor _LSum then can get electrical network magnetic linkage Ψ _rMagnetic linkage Ψ with this current transformer _sRelation, shown in formula (5);

Ψ _s＝L _eqi _L+Ψ _r (5)

$\left\{\begin{array}{c}p=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\β}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\α}})\\ q=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\α}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\β}})\end{array}\right.---\left(6\right)$

Wherein, i _LBe the resultant vector of alternating current, i _{S α}And i _{S β}Be the alternating current in the alpha-beta coordinate system.

Especially, the power decoupled control module adopts the feed forward decoupling control method to obtain the power control loop structure among the described step D.

Especially, MMC capacitance voltage mean value control module is used for voltage between the brachium pontis of many level of balance moduleization wind electric converter in the described step F, obtains controlled quentity controlled variable by following formula (7), (8)

$u_{\mathrm{ave}}^{*}=K_{p2u}(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})+K_{i2u}\∫(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})\mathrm{dt}---\left(7\right)$

$\left\{\begin{array}{c}{i}_{\mathrm{zu}}^{*}=K_{p1u}(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})+K_{i1u}\∫(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})\mathrm{dt}\\ i_{\mathrm{zu}}=C_{\mathrm{arm}}\frac{{\mathrm{du}}_{\mathrm{ave}}}{\mathrm{dt}}\end{array}\right.---\left(8\right)$

Wherein, K _P1u, K _I1u, K _P2u, K _I2uBe respectively ratio, integration multiplication factor, i _Zu,

Be change of current actual value and controlled quentity controlled variable, C _ArmBe the equivalent capacity of current transformer brachium pontis series connection, u _AveMean value for described capacitance voltage.

The present invention is meritorious by virtual flux linkage calculation, reactive power, realizes the direct Power Control to the modular multilevel wind electric converter, compares with VOC, of the present invention need not in the design current ring and dynamic response fast; Compare with LUT-DPC, the present invention need not the voltage on line side transducer, and not only dynamic response is fast, and switching frequency is constant, and has better steady-state characteristic.

Description of drawings

The offshore wind farm VSC-HVDC system construction drawing that Fig. 1 provides for the embodiment of the invention;

The modular multilevel wind electric converter topology diagram that Fig. 2 a provides for the embodiment of the invention;

Sub modular structure figure in the current transformer that Fig. 2 b provides for the embodiment of the invention;

The direct Power Control Method And Principle figure of the modular multilevel wind electric converter that Fig. 3 a provides for the embodiment of the invention;

The power decoupled control module schematic diagram that Fig. 3 b provides for the embodiment of the invention;

VSC-HVDC system active power and reactive power response curve that Fig. 4 a provides for the embodiment of the invention;

The VSC-HVDC system output response curve that Fig. 4 b provides for the embodiment of the invention;

System's output response curve when the electric power system that Fig. 4 c provides for the embodiment of the invention is broken down.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, the invention will be further described below in conjunction with drawings and Examples.

Please refer to shown in Figure 1, the offshore wind farm VSC-HVDC system construction drawing that Fig. 1 provides for the embodiment of the invention.Among the figure, VSC1 is the wind field side converter, and VSC2 is the net side converter.C1, C2 are dc capacitor.T1 is step-up transformer, wind field is exported send into the wind field side converter after voltage is increased to required numerical value.T2 is isolating transformer, and the net side converter is by this isolating transformer access electrical network, the effect of performance isolation and voltage matches.Wherein, wind field side converter and net side converter are the modular multilevel wind electric converter, and power device wherein adopts the MCC structure based on insulated gate bipolar transistor (IGBT).Through-put power P _DCTransmission direction for to be delivered to the net side by the wind field side.Need to prove, also be provided with reactor at the AC of described current transformer, play the effect that Ping Bo and dc capacitor voltage pump rise.

Shown in Fig. 2 a, the modular multilevel wind electric converter topology diagram that Fig. 2 a provides for the embodiment of the invention.Take net side converter VSC2 as example.By virtual magnetic linkage concept, net side power supply can be regarded as a virtual alternating current machine, shown in the part in the dotted line frame among the figure.Wherein, R ₀Be the stator resistance of described virtual alternating current machine, L ₀Be the inductance of described virtual alternating current machine, i _a, i _bAnd i _cBe current on line side, u ' _Rb, u ' _RbAnd u ' _RcThe AC voltage of this current transformer, u _Ra, u _RbAnd u _RcThe bridge arm voltage of current transformer.The submodule SMn of modular multilevel wind electric converter (n is positive integer) structure chart is shown in Fig. 2 b.

Shown in Fig. 3 a, the direct Power Control Method And Principle figure of the modular multilevel wind electric converter that Fig. 3 a provides for the embodiment of the invention.

In the present embodiment take a power system capacity as 40kVA, the VSC-HVDC system based on the modular multilevel wind electric converter of electric pressure 690V is example, each brachium pontis of this modular multilevel wind electric converter arranges four submodules, wind field side converter VSC1 controls direct voltage, and net side converter VSC2 controls active power.

Direct Power Control method based on the modular multilevel wind electric converter of virtual magnetic linkage comprises the steps:

Step S101, according to the VSC-HVDC system configuration, set up the Mathematical Modeling of modular multilevel wind electric converter.

In this Mathematical Modeling, wind field is partly used the synchronous generator equivalence, and the net side adopts ideal voltage source, and the wind field side transformer is step-up transformer, wind field is exported send into the wind field side converter after voltage is increased to required numerical value.The net side converter accesses electrical network through isolating transformer, and acting as of this side transformer isolated and voltage matches.The wind field side converter is connected DC side with the connection of long distance powedr transmission cable with the net side converter, cable model adopts

The simulation of type equivalent electric circuit.Wind field side converter and net side converter AC three-phase reactor adopt the three pole reactor module simulation.

The Mathematical Modeling of modular multilevel wind electric converter is shown in formula (1):

$\left\{\begin{array}{c}{L}_{\mathrm{eq}}\frac{\mathrm{dp}}{\mathrm{dt}}=u_{\mathrm{sd}}^2-u_{\mathrm{rd}}\·u_{\mathrm{sd}}-\mathrm{\ω}\\ L_{\mathrm{eq}}\frac{\mathrm{dq}}{\mathrm{dt}}={u_{\mathrm{sq}}}^2+u_{\mathrm{rq}}\·u_{\mathrm{sd}}+\mathrm{\ω}\end{array}\right.---\left(1\right)$

Wherein, active power actual value p=u _SdI _Sd, reactive power actual value q=-u _SdI _Sq, u _SdAnd u _Sq, i _SdAnd i _Sq, u _RqAnd u _RqThe AC voltage that represents respectively voltage on line side, current on line side and this current transformer under the d-q coordinate system, L _EqThe equivalence of many level of representation moduleization wind electric converter input inductance, it comprises the inductance of AC reactor of this current transformer and the inductance of brachium pontis thereof.

Step S102, process the direct voltage set-point by pi regulator

Dc voltage detection value V with the modular multilevel wind electric converter _DcError, obtain the active current set-point

And with this active current set-point

With dc voltage detection value V _DcProduct as active power set-point p ^*, wherein, reactive power set-point q ^*Be zero when unity power factor moves.

The three-phase alternating current signal I of step S103, modular multilevel wind electric converter AC that current sensor is obtained _{U, v, w}With and the output voltage v of each submodule _{Ju, v, w}, switch function S _{Ju, v, w}Process by virtual flux linkage calculation module, obtain the space bit angle setting γ of active power actual value p, reactive power actual value q and flux linkage vector _{ψ s}

The basic conception of described virtual flux linkage calculation module is drawn by virtual motor, its basic thought is that the electrical network equivalence is ideal voltage source, merge with the current transformer input reactance, net side power supply can be regarded a virtual alternating current machine as, thinks that voltage on line side is to be produced by virtual magnetic linkage induction.Virtual flux linkage calculation module specific works process is as follows:

The bridge arm voltage u of step S1031, virtual many level of flux linkage calculation module computing moduleization wind electric converter _Ra, u _RbAnd u _Rc, wherein, u _Ra, u _RbAnd u _RcComputational process identical, with u _RaBe example, computational process is shown in formula (2):

$u_{\mathrm{ra}}=-{\mathrm{\Σ}}_{j=1}^n{v}_{\mathrm{ju}}\·S_{\mathrm{ju}}+{\mathrm{\Σ}}_{j=n+1}^{2n}{v}_j---\left(2\right)$

Wherein, v _JuBe the output voltage of described current transformer, S _JuBe corresponding switch function.

Step S1032, virtual flux linkage calculation module are calculated virtual flux linkage vector Ψ under the alpha-beta coordinate system by following formula (3), (4) computing module _{S α}, Ψ _{S β}And space bit angle setting γ _{ψ s}

$\left\{\begin{array}{c}{\mathrm{\Ψ}}_{\mathrm{s\α}}=\∫\left(\frac{1}{\sqrt{6}}(2\·u_{\mathrm{ra}}-u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{ec}}\\ {\mathrm{\Ψ}}_{\mathrm{s\β}}=\∫\left(\frac{1}{\sqrt{2}}(u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{eq}}\·i_{\mathrm{L\β}}\end{array}\right.---\left(3\right)$

$\left\{\begin{array}{c}{\sin \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\β}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\\ {\cos \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\α}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\end{array}\right.---\left(4\right)$

Wherein, i _LaAnd i _{L β}Resultant vector for alternating current under the alpha-beta coordinate system.

Step S1033, virtual flux linkage calculation module are by following formula (5), (6) many level of computing moduleization wind electric converter active power actual value p and reactive power actual value q; Wherein, according to this AC side of converter voltage relationship u _s=u _r+ u _L, i.e. ac grid voltage u _sEqual current transformer bridge arm voltage u _rWith voltage u on the reactor _LSum then can get electrical network magnetic linkage Ψ _rMagnetic linkage Ψ with this current transformer _sRelation, shown in formula (5);

Ψ _s＝L _eqi _L+Ψ _r (5)

$\left\{\begin{array}{c}p=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\β}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\α}})\\ q=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\α}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\β}})\end{array}\right.---\left(6\right)$

Wherein, i _LBe the resultant vector of alternating current, i _{S α}And i _{S β}Be the alternating current in the alpha-beta coordinate system.

Known by formula (6), the Feedback of Power of system can be obtained by virtual flux linkage calculation, simultaneously by formula (3) as can be known, contain pure integral element in the flux linkage calculation process, its low-pass characteristic can improve the system rejection to disturbance performance, but initial value for integral is difficult to determine during practical application, affects systematic function, can adopt second order link 2 ω _c/ (s+ ω _c) ²Replace, its width of cloth phase frequency characteristic is similar to pure integral element, ω _cBe the system angle frequency.By formula (4) thus coordinate transform adopts flux linkage orientation to save system's AC voltage sensor as can be known.

Step S104, with the active power set-point p among the step S102 ^*With reactive power set-point q ^*, and the active power actual value p among the step S103 and reactive power actual value q obtain the voltage reference signal u under the two-phase rotating coordinate system of direct Power Control device output by the power decoupled control module _RdAnd u _Rq

The power decoupled control module schematic diagram that Fig. 3 b provides for the embodiment of the invention.Power decoupled control module and direct Power Control device form the current transformer power control loop.There are coupling in d, q axle variable, power decoupled control module employing feed forward decoupling control method acquisition power control loop structure as can be known by above-mentioned formula (1).

Step S105, with the space bit angle setting γ of the flux linkage vector among the step S103 _{ψ s}With the voltage reference signal u among the step S104 _RdAnd u _RqBy three-phase/two-phase rotating coordinate transformation resume module, obtain three-phase voltage reference signal u ' _Ref, v ' _RefAnd w ' _Ref

Step S106, with the three-phase voltage reference signal u ' among the step S105 _Ref, v ' _RefAnd w ' _RefControlled quentity controlled variable u with the output of MMC capacitance voltage mean value control module _Ave, v _AveAnd w _AveCarry out overlap-add procedure, obtain the three-phase voltage control signal u of modular multilevel wind electric converter _Ref, v _RefAnd w _Ref

MMC capacitance voltage mean value control module is used for voltage between the brachium pontis of many level of balance moduleization wind electric converter, and the method by stack balance component in the reference signal makes each submodule capacitance voltage follow the tracks of its set-point.Suppose that threephase load is symmetrical, only consider the circulation impact, MMC capacitance voltage mean value control module obtains controlled quentity controlled variable by following formula (7), (8)

$u_{\mathrm{ave}}^{*}=K_{p2u}(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})+K_{i2u}\∫(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})\mathrm{dt}---\left(7\right)$

$\left\{\begin{array}{c}{i}_{\mathrm{zu}}^{*}=K_{p1u}(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})+K_{i1u}\∫(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})\mathrm{dt}\\ i_{\mathrm{zu}}=C_{\mathrm{arm}}\frac{{\mathrm{du}}_{\mathrm{ave}}}{\mathrm{dt}}\end{array}\right.---\left(8\right)$

Wherein, K _P1u, K _I1u, K _P2u, K _I2uBe respectively ratio, integration multiplication factor, i _Zu, Be change of current actual value and controlled quentity controlled variable, C _ArmBe the equivalent capacity of current transformer brachium pontis series connection, u _AveMean value for described capacitance voltage.

Step S107, with the three-phase voltage control signal u among the step S106 _Ref, v _RefAnd w _RefCapacitance voltage i with modular multilevel wind electric converter upper and lower bridge arm electric current, its each submodule _{Nu, v, w}, i _{Pu, v, w}, u _{Ju, v, w}Process by MMC trigger impulse generation module, obtain the switching signal of power device in the described modular multilevel wind electric converter of control.

Shown in Fig. 4 a, VSC-HVDC system active power and reactive power response curve that Fig. 4 a provides for the embodiment of the invention.

Reactive power is given as zero in the present embodiment, and dc capacitor is precharged to 47kV (be 1.35Uf, Uf is the line voltage effective value of AC system).The VSC-HVDC system arranges net side active power set-point after starting, and is changed to 0.95p.u by the 0.65p.u step when t=1s, the verification system dynamic response performance.

Shown in Fig. 4 a, because meritorious, idle numerical difference between is larger, adopt perunit value output (with phase voltage peak value 28.6kV, power system capacity 20MVA carries out standardization to computational process), P ', Q ' are calculated by voltage, current measurement value among the figure, P, Q are based on virtual magnetic linkage algorithm and utilize formula (6) to calculate acquisition, and the two steady-state value is basically identical, shows among the present invention to have higher precision for the designed power estimation method of modular multilevel wind electric converter.

Shown in Fig. 4 b, the VSC-HVDC system output response curve that Fig. 4 b provides for the embodiment of the invention.Wherein, curve Vdc1 is direct Power Control algorithmic system output dc voltage of the present invention, curve Vdc2 is two closed-loop vector control algolithm systems output dc voltages, the startup stage dynamic property Vdc1 obviously be better than Vdc2, change moment in wind field side power output step, direct voltage only has very fuctuation within a narrow range, and two kinds of algorithm control performances are suitable, and system's dynamic response performance is good.

The transient state transient process often appears in electric power system, such as three-phase shortcircuit, shorted to earth etc., requires the flexible DC power transmission system to have certain antijamming capability.When t=1s was set, three relative ground circuit faults appearred in the net side, recovered normal behind the 0.12s, VSC-HVDC system responses curve shown in Fig. 4 c, large 0.6s tracing preset after fault recovery.Among Fig. 4 c, curve Vdc1 is direct Power Control algorithmic system output dc voltage of the present invention, curve Vdc2 is two closed-loop vector control algolithm systems output dc voltages, and the overshoot of Vdc1 is less than Vdc2, and performance of the present invention is better than two closed-loop vector controls in the transient process.

Technical scheme of the present invention is meritorious by virtual flux linkage calculation, reactive power, need not the line voltage transducer, need not ring in the design current, and not only dynamic response is fast, and switching frequency is constant, and has better steady-state characteristic.

Above-mentioned only is preferred embodiment of the present invention and institute's application technology principle, anyly is familiar with those skilled in the art in the technical scope that the present invention discloses, and the variation that can expect easily or replacement all should be encompassed in protection scope of the present invention.

Claims (7)

1. the direct Power Control method of a modular multilevel wind electric converter is characterized in that, comprises the steps:

A, according to the VSC-HVDC system configuration, set up the Mathematical Modeling of modular multilevel wind electric converter;

B, process the direct voltage set-point by pi regulator

Dc voltage detection value V with the modular multilevel wind electric converter _DcError, obtain the active current set-point

And with this active current set-point

With dc voltage detection value V _DcProduct as active power set-point p ^*, wherein, reactive power set-point q ^*Be zero when unity power factor moves;

The three-phase alternating current signal I of C, modular multilevel wind electric converter AC that current sensor is obtained _{U, v, w}With and the output voltage v of each submodule _{Ju, v, w}, switch function S _{Ju, v, w}Process by virtual flux linkage calculation module, obtain the space bit angle setting γ of active power actual value p, reactive power actual value q and flux linkage vector _{ψ s}

D, with the active power set-point p among the step B ^*With reactive power set-point q ^*, and the active power actual value p among the step C and reactive power actual value q obtain the voltage reference signal u under the two-phase rotating coordinate system of direct Power Control device output by the power decoupled control module _RdAnd u _Rq

E, with the space bit angle setting r of the flux linkage vector among the step C _{ψ s}With the voltage reference signal u among the step D _RdAnd u _RqBy three-phase/two-phase rotating coordinate transformation resume module, obtain three-phase voltage reference signal u ' _Ref, v ' _RefAnd w ' _Ref

F, with the three-phase voltage reference signal u ' in the step e _Ref, v ' _RefAnd w ' _RefControlled quentity controlled variable u with the output of MMC capacitance voltage mean value control module _Ave, v _AveAnd w _AveCarry out overlap-add procedure, obtain the three-phase voltage control signal u of modular multilevel wind electric converter _Ref, v _RefAnd w _Ref

G, with the three-phase voltage control signal u in the step F _Ref, v _RefAnd w _RefCapacitance voltage i with modular multilevel wind electric converter upper and lower bridge arm electric current, its each submodule _{Nu, v, w}, i _{Pu, v, w}, u _{Ju, v, w}Process by MMC trigger impulse generation module, obtain the switching signal of power device in the described modular multilevel wind electric converter of control.

2. the direct Power Control method of modular multilevel wind electric converter according to claim 1 is characterized in that, the power device in the described modular multilevel wind electric converter adopts the MCC structure based on insulated gate bipolar transistor (IGBT).

3. the direct Power Control method of modular multilevel wind electric converter according to claim 2 is characterized in that, the DC side of described modular multilevel wind electric converter adopts capacitance voltage stabilizing, and its AC is provided with reactor.

4. the direct Power Control method of modular multilevel wind electric converter according to claim 3 is characterized in that, the Mathematical Modeling of modular multilevel wind electric converter is shown in formula (1) in the described steps A:

$\left\{\begin{array}{c}{L}_{\mathrm{eq}}\frac{\mathrm{dp}}{\mathrm{dt}}=u_{\mathrm{sd}}^2-u_{\mathrm{rd}}\·u_{\mathrm{sd}}-\mathrm{\ω}\\ L_{\mathrm{eq}}\frac{\mathrm{dq}}{\mathrm{dt}}={u_{\mathrm{sq}}}^2+u_{\mathrm{rq}}\·u_{\mathrm{sd}}+\mathrm{\ω}\end{array}\right.---\left(1\right)$

Wherein, active power actual value p=u _SdI _Sd, reactive power actual value q=-u _SdI _Sq, u _SdAnd u _Sq, i _SdAnd i _Sq, u _RqAnd u _RqThe AC voltage that represents respectively voltage on line side, current on line side and this current transformer under the d-q coordinate system, L _EqThe equivalence of many level of representation moduleization wind electric converter input inductance, it comprises the inductance of AC reactor of this current transformer and the inductance of brachium pontis thereof.

5. the direct Power Control method of modular multilevel wind electric converter according to claim 4 is characterized in that, described step C specifically comprises:

The bridge arm voltage u of C1, virtual many level of flux linkage calculation module computing moduleization wind electric converter _Ra, u _RbAnd u _Rc, wherein, u _Ra, u _RbAnd u _RcComputational process identical, with u _RaBe example, computational process is shown in formula (2):

$u_{\mathrm{ra}}=-{\mathrm{\Σ}}_{j=1}^n{v}_{\mathrm{ju}}\·S_{\mathrm{ju}}+{\mathrm{\Σ}}_{j=n+1}^{2n}{v}_j---\left(2\right)$

Wherein, v _JuBe the output voltage of described current transformer, S _JuBe corresponding switch function;

C2, virtual flux linkage calculation module are calculated virtual flux linkage vector Ψ under the alpha-beta coordinate system by following formula (3), (4) computing module _{S α}, Ψ _{S β}And space bit angle setting γ _{ψ s}

$\left\{\begin{array}{c}{\mathrm{\Ψ}}_{\mathrm{s\α}}=\∫\left(\frac{1}{\sqrt{6}}(2\·u_{\mathrm{ra}}-u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{ec}}\\ {\mathrm{\Ψ}}_{\mathrm{s\β}}=\∫\left(\frac{1}{\sqrt{2}}(u_{\mathrm{rb}}-u_{\mathrm{rc}})\right)\mathrm{dt}+L_{\mathrm{eq}}\·i_{\mathrm{L\β}}\end{array}\right.---\left(3\right)$

$\left\{\begin{array}{c}{\sin \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\β}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\\ {\cos \mathrm{\γ}}_{\mathrm{\ψs}}=\frac{{\mathrm{\Ψ}}_{\mathrm{s\α}}}{\sqrt{{{\mathrm{\Ψ}}_{\mathrm{s\α}}}^2+{{\mathrm{\Ψ}}_{\mathrm{s\β}}}^2}}\end{array}\right.---\left(4\right)$

Wherein, i _LaAnd i _{L β}Resultant vector for alternating current under the alpha-beta coordinate system;

C3, virtual flux linkage calculation module are by following formula (5), (6) many level of computing moduleization wind electric converter active power actual value p and reactive power actual value q; Wherein, according to this AC side of converter voltage relationship u _s=u _r+ u _L, i.e. ac grid voltage u _sEqual current transformer bridge arm voltage u _rWith voltage u on the reactor _LSum then can get electrical network magnetic linkage Ψ _rMagnetic linkage Ψ with this current transformer _sRelation, shown in formula (5);

Ψ _s＝L _eqi _L+Ψ _r (5)

$\left\{\begin{array}{c}p=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\β}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\α}})\\ q=\mathrm{\ω}({\mathrm{\Ψ}}_{\mathrm{s\α}}{i}_{\mathrm{s\α}}-{\mathrm{\Ψ}}_{\mathrm{s\β}}{i}_{\mathrm{s\β}})\end{array}\right.---\left(6\right)$

Wherein, i _LBe the resultant vector of alternating current, i _{S α}And i _{S β}Be the alternating current in the alpha-beta coordinate system.

6. the direct Power Control method of modular multilevel wind electric converter according to claim 5 is characterized in that, the power decoupled control module adopts the feed forward decoupling control method to obtain the power control loop structure among the described step D.

7. the direct Power Control method of modular multilevel wind electric converter according to claim 6, it is characterized in that, MMC capacitance voltage mean value control module is used for voltage between the brachium pontis of many level of balance moduleization wind electric converter in the described step F, obtains controlled quentity controlled variable by following formula (7), (8)

$u_{\mathrm{ave}}^{*}=K_{p2u}(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})+K_{i2u}\∫(i_{\mathrm{zu}}^{*}-i_{\mathrm{zu}})\mathrm{dt}---\left(7\right)$

$\left\{\begin{array}{c}{i}_{\mathrm{zu}}^{*}=K_{p1u}(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})+K_{i1u}\∫(V_{\mathrm{dc}}-\underset{j=1}{\overset{2n}{\mathrm{\Σ}}}{v}_{\mathrm{ju}})\mathrm{dt}\\ i_{\mathrm{zu}}=C_{\mathrm{arm}}\frac{{\mathrm{du}}_{\mathrm{ave}}}{\mathrm{dt}}\end{array}\right.---\left(8\right)$

Wherein, K _P1u, K _I1u, K _P2u, K _I2uBe respectively ratio, integration multiplication factor, i _Zu,

Be change of current actual value and controlled quentity controlled variable, C _ArmBe the equivalent capacity of current transformer brachium pontis series connection, u _AveMean value for described capacitance voltage.

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