CN103208816A - Power collection and transmission system for wind power plant and voltage control method for alternating current generatrix of power collection and transmission system - Google Patents

Abstract

The invention discloses a power collection and transmission system for a wind power plant. The system comprises an alternating current generatrix, a wind generating set, a rectifier station and an inverter station, wherein the rectifier station comprises a rectifier and a converter transformer; the direct current side of the rectifier is connected with the direct current side of the inverter station, and the alternating current side of the rectifier is connected with one side of the converter transformer through a converter inductor; and the other side of the converter transformer is connected with the alternating current generatrix, and is grounded through a capacitor. The invention also discloses a voltage control method for the alternating current generatrix of the system. The voltage comprising the amplitude and frequency of the voltage of the alternating current generatrix of the system is integrally controlled by two control dimensions of the rectifier on a wind power plant side, so that the stability of the alternating current voltage of the power collection and transmission system of the wind power plant is ensured, and harmonic components of an alternating current system of the wind power plant are reduced.

Description

A kind of current collection transmission system of wind energy turbine set and ac bus voltage control method thereof

Technical field

The invention belongs to electric power system power transmission and distribution technical field, be specifically related to a kind of current collection transmission system and ac bus voltage control method thereof of wind energy turbine set.

Background technology

Along with energy scarcity and environmental change, wind energy receives very big concern, need utilize science and technology to develop wind energy, wind-powered electricity generation is one of them good approach, wind power generation develops rapidly, the construction of wind-powered electricity generation machine and wind energy turbine set is very fast, but because wind energy is unstable and uncertain, in order to guarantee the safety and stability of national grid operation, it is technical bottleneck and the difficult problem of the development of restriction wind-powered electricity generation that the wind energy turbine set safety and stability is incorporated into the power networks always, no matter be landwid electric field, or marine wind electric field, all can run into this problem.

Relevant wind farm grid-connected method mainly contains following several both at home and abroad at present: (1) wind energy turbine set slip ring system directly is incorporated into the power networks by alternating current circuit (cable or overhead wire); (2) the wind energy turbine set slip ring system is through rectifier, DC line (cable or overhead wire), inverter, i.e. flexible DC power transmission technology incoming transport electrical network.Second method just is incorporated into the power networks than first kind of alternating current circuit following advantage that directly has been incorporated into the power networks by flexible DC power transmission: 1. can realize long distance power transmission; 2. can provide the reactive power support for AC system by rectifier and inverter control, this has very important meaning for keeping AC system voltage to stablize; 3. wind energy turbine set slip ring system and AC system are relatively independent, exchange fault and advantage such as can directly not transmit.

When adopting flexible DC power transmission to be incorporated into the power networks, wind energy turbine set can run into a problem, i.e. the stable problem of wind energy turbine set slip ring system busbar voltage.Wind energy turbine set slip ring system and AC system are relatively independent, and wind energy turbine set slip ring system voltage is difficult to contact with external electrical network, only is associated with inner wind-driven generator and flexible DC power transmission system rectifier.Technology by wind-driven generator control slip ring system voltage also is not very perfect, add uncontrollability and the uncertainty of wind energy itself in addition, make wind-driven generator self exert oneself and electrical characteristic neither be very stable, therefore, it is comparatively suitable and appropriate to have flexible DC power transmission system rectifier to control wind energy turbine set slip ring system voltage.

People such as Huang Chuan, Wang Zhixin, Wang Guoqiang are marine wind electric field three level VSC-HVDC (the direct current transportation technology of voltage-source type) system emulation research (power electronic technology at title, 2011,45 (8), a kind of method of wind energy turbine set slip ring system busbar voltage has been proposed in the document 89～92), it exports reactive power by control wind energy turbine set side rectifier, thereby reaches the purpose of control slip ring system alternating voltage.Though this method can be controlled wind energy turbine set slip ring system alternating voltage amplitude to a certain extent, because it uses dimension of wind energy turbine set rectifier to control alternating voltage, can't play control action to the alternating voltage frequency.Wind energy turbine set slip ring system alternating voltage and whole wind electric field safe and stable operation are closely related, the instability of slip ring system alternating voltage frequency, can transmit at wind energy turbine set internal communication circuit, the system harmonics component of increasing exchanges, harmonic component can further be delivered to blower fan inside, the inner heating in winding of wind-powered electricity generation machine, influence electric elements useful life, produce very big infringement for the wind-powered electricity generation machine, in addition, harmonic wave also can bring more loss, and wind energy turbine set output energy efficiency reduces, and also can influence the stable operation of wind energy turbine set simultaneously.

Summary of the invention

At the above-mentioned technological deficiency of existing in prior technology, the invention provides a kind of current collection transmission system and ac bus voltage control method thereof of wind energy turbine set, can keep the stable of system's alternating voltage frequency, reduce the wind energy turbine set harmonic component.

A kind of current collection transmission system of wind energy turbine set comprises: ac bus, wind turbine generator, converting plant and Inverter Station; Wind turbine generator comprises many typhoons power generator, and described wind-driven generator links to each other with ac bus, and the interchange side of converting plant links to each other with ac bus, and the DC side of converting plant links to each other with the DC side of Inverter Station, and the interchange side of Inverter Station is connected with AC network.

Described converting plant comprises rectifier and converter transformer; The DC side of rectifier links to each other with the DC side of Inverter Station, and the interchange side of rectifier links to each other with a side of converter transformer by change of current inductance, and the opposite side of converter transformer links to each other with ac bus and passes through capacitor grounding.

Described rectifier adopts three-phase six brachium pontis structures, and each brachium pontis forms by several IGBT cascades.

The ac bus voltage control method of above-mentioned current collection transmission system comprises the steps:

(1) the three-phase input current I of collection converting plant _a～I _c, flow into the three-phase branch current I of converter transformer _Sa～I _ScAnd the three-phase bus voltage U of ac bus _a～U _c

(2) respectively to described three-phase branch current I _Sa～I _Sc, three-phase input current I _a～I _cWith the three-phase bus voltage U _a～U _cCarry out the dq conversion and obtain the d axle component I of three-phase branch current _SdWith q axle component I _Sq, three-phase input current d axle component I _dWith q axle component I _q, three-phase bus voltage d axle component U _dWith q axle component U _q

(3) make given d shaft voltage controlled quentity controlled variable U _DrefWith q shaft voltage controlled quentity controlled variable U _QrefDeduct the d axle component U of three-phase bus voltage respectively _dWith q axle component U _q, obtain d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _q

(4) to d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _Qref

(5) make described d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _QrefDeduct the d axle component I of three-phase branch current respectively _SdWith q axle component I _Sq, obtain d shaft current error signal Δ I _dWith q shaft current error signal Δ I _q

(6) to d shaft current error signal Δ I _dWith q shaft current error signal Δ I _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d axle modulation signal M _dWith q axle modulation signal M _q

(7) to d axle modulation signal M _dWith q axle modulation signal M _qCarry out the dq inverse transformation and obtain three-phase modulations signal M _a～M _c, and then according to described three-phase modulations signal M _a～M _cGenerate one group of pwm signal so that rectifier is controlled by SPWM (Sine Wave Pulse Width Modulation) technology.

In the described step (4), according to following formula to d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _qCarry out PI adjusting and feedforward decoupling compensation:

$I_{\mathrm{dref}}=(K_{p1}+\frac{K_{i1}}{s})\mathrm{\Δ}{U}_d+I_d-I_{\mathrm{Ld}}$

$I_{\mathrm{qref}}=(K_{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003018275100021.png"\; state="\{\{state\}\}">p</figure-callout>}2}+\frac{K_{i2}}{s})\mathrm{\&Delta;}{U}_q+I_q+I_{\mathrm{Lq}}$

Wherein: s is Laplacian, K _P1And K _P2Be given proportionality coefficient, K _I1And K _I2Be given integral coefficient, I _LdAnd I _LqBe d shaft current feedforward compensation amount and q shaft current feedforward compensation amount.

Described d shaft current feedforward compensation amount I _LdWith q shaft current feedforward compensation amount I _LqTry to achieve according to following formula:

I _Ld＝ωCU _q

I _Lq＝ωCU _d

Wherein: ω is angular frequency and the ω=2 π f of ac bus voltage, and f=50Hz, C are the appearance value of capacitor.

In the described step (6), according to following formula to d shaft current error signal Δ I _dWith q shaft current error signal Δ I _qCarry out PI adjusting and feedforward decoupling compensation:

$M_d=\frac{2[(K_{p3}+\frac{K_{i3}}{s})\mathrm{\&Delta;}{I}_d+U_d-U_{\mathrm{Ld}}]}{U_{\mathrm{dc}}}$

$M_q=\frac{2[(K_{p4}+\frac{K_{i4}}{s})\mathrm{\&Delta;}{I}_q+U_q+U_{\mathrm{Lq}}]}{U_{\mathrm{dc}}}$

Wherein: s is Laplacian, K _P3And K _P4Be given proportionality coefficient, K _I3And K _I4Be given integral coefficient, U _LdAnd U _LqBe d shaft voltage feedforward compensation amount and q shaft voltage feedforward compensation amount, U _DcDC bus-bar voltage for converting plant.

Described d shaft voltage feedforward compensation amount U _LdWith q shaft voltage feedforward compensation amount U _LqTry to achieve according to following formula:

U _Ld＝ωLI _sq

U _Lq＝ωLI _sd

Wherein: ω is angular frequency and the ω=2 π f of ac bus voltage, and f=50Hz, L are change of current inductance and the total inductance value of converter transformer leakage inductance.

Wind energy turbine set is when using flexible DC power transmission to be incorporated into the power networks, the difficult control of its wind energy turbine set slip ring system ac bus voltage, frequency also is difficult to stablize, and system's ac bus voltage has crucial effects for the safe and stable operation of wind energy turbine set and even whole wind-powered electricity generation grid-connected system.Adopt ac bus voltage control method of the present invention, can fully use two of wind energy turbine set side rectifier control dimensions, the ac bus voltage of control system on the whole comprises amplitude and the frequency of voltage, so useful technique effect of the present invention is:

(1) guarantees the stable of wind energy turbine set slip ring system alternating voltage, can reduce the harmonic component of wind energy turbine set AC system, prevent the damage that harmonic component brings for wind energy turbine set inside and even wind-powered electricity generation machine, minimizing is by the infringement of the caused wind-powered electricity generation machine of harmonic component internal electric element, comprise generator, transformer, transmission line and corresponding electric appliance element, thereby guarantee life-span and the normal operation thereof of electric equipment.

(2) reduce the harmonic component of wind energy turbine set AC system, can further reduce the wastage, reduce the supplementary load loss that generator and transformer and circuit produce because of harmonic component, reduce harmonic component in the power loss of electric component, take full advantage of place capacity, guarantee usage ratio of equipment, improve wind energy turbine set output energy efficiency.

(3) because wind power control system need be gathered wind energy turbine set slip ring system alternating voltage as the input signal amount, therefore, keep the stable of wind energy turbine set slip ring system voltage magnitude and frequency, even running for wind power control system also is very helpful, thereby guarantees wind energy turbine set and whole wind-powered electricity generation grid-connected system safe and stable operation.

Description of drawings

Fig. 1 is the structural representation of current collection transmission system of the present invention.

Fig. 2 is the principle process schematic diagram of system of the present invention ac bus voltage control method.

Fig. 3 is for adopting the waveform schematic diagram of system's ac bus voltage under the control method of the present invention.

Fig. 4 is for adopting the comparison schematic diagram of system's ac bus voltage harmonic component under prior art and the inventive method.

Embodiment

In order more specifically to describe the present invention, below in conjunction with the drawings and the specific embodiments technical scheme of the present invention and control method thereof are elaborated.

As shown in Figure 1, a kind of current collection transmission system of wind energy turbine set comprises: ac bus, wind turbine generator, converting plant and Inverter Station; Wind turbine generator comprises many typhoons power generator, and wind-driven generator is successively by total power converter, current collection inductance L _jAnd the mode of connection is the current collection transformer T of Δ/Y _jLink to each other with ac bus;

Converting plant comprises rectifier and converter transformer T; Rectifier adopts three-phase six brachium pontis structures, and each brachium pontis forms by several IGBT cascades; The DC side of rectifier links to each other with the DC side of Inverter Station by power transmission line, the interchange side of rectifier is that the side of the converter transformer T of Y/ Δ links to each other by change of current inductance L and the mode of connection, and the opposite side of converter transformer T links to each other with ac bus and by capacitor C ground connection.

Inverter Station adopts the inverter of three-phase six brachium pontis structures, and each brachium pontis forms by several IGBT cascades; The DC side of rectifier and the DC side of inverter all are parallel with dc-link capacitance, and the voltage at rectifier DC side two ends is the DC bus-bar voltage U of converting plant _Dc, the interchange side of inverter is by the transmission of electricity inductance L _sAnd the mode of connection is the transmitting transformer T of Δ/Y _sLink to each other with AC network.

As shown in Figure 2, the ac bus voltage control method of above-mentioned current collection transmission system comprises the steps:

(1) utilize the electric current and voltage Hall element to gather the three-phase input current I of converting plant _a～I _c, flow into the three-phase branch current I of converter transformer T _Sa～I _ScAnd the three-phase bus voltage U of ac bus _a～U _c

(2) respectively to three-phase branch current I _Sa～I _Sc, three-phase input current I _a～I _cWith the three-phase bus voltage U _a～U _cCarry out the dq conversion and obtain the d axle component I of three-phase branch current _SdWith q axle component I _Sq, three-phase input current d axle component I _dWith q axle component I _q, three-phase bus voltage d axle component U _dWith q axle component U _q

The dq transformation matrix is as follows:

$T_{\mathrm{abc}/\mathrm{dq}}=\frac{2}{3}\&CenterDot;\left[\begin{array}{ccc}\cos \mathrm{\&theta;}& \cos (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})& \cos (\mathrm{\&theta;}-\frac{4\mathrm{\&pi;}}{3})\\ \sin \mathrm{\&theta;}& \sin (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})& \sin (\mathrm{\&theta;}-\frac{4\mathrm{\&pi;}}{3})\end{array}\right]$

Wherein: θ is phase place and the θ=ω t of ac bus voltage, and ω is angular frequency and the ω=2 π f of ac bus voltage, and f=50Hz, t are the time.

(3) make given d shaft voltage controlled quentity controlled variable U _DrefWith q shaft voltage controlled quentity controlled variable U _QrefDeduct the d axle component U of three-phase bus voltage respectively _dWith q axle component U _q, obtain d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _qIn the present embodiment, U _Qref=0,

(4) according to following formula to d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _Qref $I_{\mathrm{dref}}=(K_{p1}+\frac{K_{i1}}{s})\mathrm{\&Delta;}{U}_d+I_d-I_{\mathrm{Ld}}$ I _Ld＝ωCU _q $I_{\mathrm{qref}}=({\mathrm{<figure-callout\; id="2"\; label="K\; p"\; filenames="HDA00003018275100021.png"\; state="\{\{state\}\}">K</figure-callout>}}_p+\frac{K_{i2}}{s})\mathrm{\&Delta;}{U}_q+I_q+I_{\mathrm{Lq}}$ I _Lq＝ωCU _d

Wherein: s is Laplacian, K _P1And K _P2Be given proportionality coefficient, K _I1And K _I2Be given integral coefficient, I _LdAnd I _LqBe d shaft current feedforward compensation amount and q shaft current feedforward compensation amount, C is the appearance value of capacitor; In the present embodiment, K _P1=K _P2=0.8, K _I1=20, K _I2=100, C=2 * 10 ^-3F.

(5) make d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _QrefDeduct the d axle component I of three-phase branch current respectively _SdWith q axle component I _Sq, obtain d shaft current error signal Δ I _dWith q shaft current error signal Δ I _q

(6) according to following formula to d shaft current error signal Δ I _dWith q shaft current error signal Δ I _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d axle modulation signal M _dWith q axle modulation signal M _q $M_d=\frac{2[(K_{p3}+\frac{K_{i3}}{s})\mathrm{\&Delta;}{I}_d+U_d-U_{\mathrm{Ld}}]}{U_{\mathrm{dc}}}$ U _Ld＝ωLI _sq $M_q=\frac{2[(K_{p4}+\frac{K_{i4}}{s})\mathrm{\&Delta;}{I}_q+U_q+U_{\mathrm{Lq}}]}{U_{\mathrm{dc}}}$ U _Lq＝ωLI _sd

Wherein: K _P3And K _P4Be given proportionality coefficient, K _I3And K _I4Be given integral coefficient, U _LdAnd U _LqBe d shaft voltage feedforward compensation amount and q shaft voltage feedforward compensation amount, L is change of current inductance and the total inductance value of converter transformer leakage inductance, U _DcDC bus-bar voltage for converting plant; In the present embodiment, K _P3=K _P4=5.2, K _I3=K _I4=50, C=5.2 * 10 ^-3F, U _Dc=100kV.

(7) to d axle modulation signal M _dWith q axle modulation signal M _qCarry out the dq inverse transformation and obtain three-phase modulations signal M _a～M _c, and then according to three-phase modulations signal M _a～M _cGenerate one group of pwm signal each IGBT in the rectifier is carried out switch control by the SPWM technology.

Dq inverse transformation matrix is as follows:

$T_{\mathrm{dq}/\mathrm{abc}}=\left[\begin{array}{cc}\cos \mathrm{\&theta;}& \sin \mathrm{\&theta;}\\ \cos (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})& \sin (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})\\ \cos (\mathrm{\&theta;}-\frac{4\mathrm{\&pi;}}{3})& \sin (\mathrm{\&theta;}-\frac{4\mathrm{\&pi;}}{3})\end{array}\right]$

In the present embodiment, wind energy turbine set is connected to the grid by the flexible DC power transmission system, and the wind energy turbine set slip ring system is connected with rectifier in the flexible DC power transmission system, is connected to inverter through 100km direct current transportation cable, then the incoming transport electrical network.System's rectifier is by two control dimension control wind energy turbine set slip ring system ac bus voltage magnitudes and frequency, and inverter is by two control dimension control flexible DC power transmission system's direct voltages and system's output reactive power.It is 35kV that expectation obtains ac bus line voltage effective value, and the no-load voltage ratio of converter transformer T is 35/110kV.The active power of output P=100MW of whole wind Electric field collector transmission system, output reactive power Q=0Mvar.

Behind the flexible DC power transmission wind-electricity integration slip ring system ac bus voltage control method of Fig. 3 for the employing present embodiment, the oscillogram of wind energy turbine set slip ring system three-phase alternating current busbar voltage.As can see from Figure 3, flexible DC power transmission wind-electricity integration slip ring system ac bus voltage is after using the present embodiment control method, three-phase alternating voltage amplitude, frequency conform to desired value, voltage magnitude and frequency are controlled effectively, the three phase sine waveform is clear, phase phasic difference 120 degree, wind-electricity integration slip ring system ac bus voltage control is stable.

Fig. 4 has the slip ring system ac bus voltage control method of control method and present embodiment now at the comparison schematic diagram of slip ring system ac bus voltage harmonic component THD value for employing.Two curves among Fig. 4 have represented respectively and have used existing control method and present embodiment at the wind farm grid-connected slip ring system ac bus of flexible DC power transmission voltage harmonic component THD value.As can see from Figure 4, adopt the existing resulting slip ring system ac bus of control method voltage harmonic component THD value to be about 0.042 and fluctuate bigger, adopt the resulting slip ring system ac bus of present embodiment voltage harmonic component THD value to be about 0.017 and comparatively stable near mean value, harmonic component has obtained suppressing and reducing to a great extent, reduced the influence of harmonic wave for wind energy turbine set inside and whole grid-connected system, reduce supplementary load loss, improve wind-electricity integration transmission energy efficiency, guaranteed the safe and stable operation of system.

Claims (7)

1. the current collection transmission system of a wind energy turbine set comprises: ac bus, wind turbine generator, converting plant and Inverter Station; Wind turbine generator comprises many typhoons power generator, and described wind-driven generator links to each other with ac bus, and the interchange side of converting plant links to each other with ac bus, and the DC side of converting plant links to each other with the DC side of Inverter Station, and the interchange side of Inverter Station is connected with AC network; It is characterized in that:

Described converting plant comprises rectifier and converter transformer; The DC side of rectifier links to each other with the DC side of Inverter Station, and the interchange side of rectifier links to each other with a side of converter transformer by change of current inductance, and the opposite side of converter transformer links to each other with ac bus and passes through capacitor grounding.

2. current collection transmission system according to claim 1 is characterized in that: described rectifier adopts three-phase six brachium pontis structures, and each brachium pontis forms by several IGBT cascades.

3. the ac bus voltage control method of a current collection transmission system as claimed in claim 1 or 2 comprises the steps:

(1) the three-phase input current I of collection converting plant _a～I _c, flow into the three-phase branch current I of converter transformer _Sa～I _ScAnd the three-phase bus voltage U of ac bus _a～U _c

(2) respectively to described three-phase branch current I _Sa～I _Sc, three-phase input current I _a～I _cWith the three-phase bus voltage U _a～U _cCarry out the dq conversion and obtain the d axle component I of three-phase branch current _SdWith q axle component I _Sq, three-phase input current d axle component I _dWith q axle component I _q, three-phase bus voltage d axle component U _dWith q axle component U _q

(3) make given d shaft voltage controlled quentity controlled variable U _DrefWith q shaft voltage controlled quentity controlled variable U _QrefDeduct the d axle component U of three-phase bus voltage respectively _dWith q axle component U _q, obtain d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _q

(4) to d shaft voltage error signal Δ U _dWith q shaft voltage error signal Δ U _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _Qref

(5) make described d shaft current controlled quentity controlled variable I _DrefWith q shaft current controlled quentity controlled variable I _QrefDeduct the d axle component I of three-phase branch current respectively _SdWith q axle component I _Sq, obtain d shaft current error signal Δ I _dWith q shaft current error signal Δ I _q

(6) to d shaft current error signal Δ I _dWith q shaft current error signal Δ I _qCarry out PI adjusting and feedforward decoupling compensation respectively successively, obtain d axle modulation signal M _dWith q axle modulation signal M _q

(7) to d axle modulation signal M _dWith q axle modulation signal M _qCarry out the dq inverse transformation and obtain three-phase modulations signal M _a～M _c, and then according to described three-phase modulations signal M _a～M _cGenerate one group of pwm signal so that rectifier is controlled by the SPWM technology.

4. ac bus voltage control method according to claim 3 is characterized in that: in the described step (4), according to following formula to d shaft voltage error signal Δ U _dWith _qShaft voltage error signal Δ U _qCarry out PI adjusting and feedforward decoupling compensation:

$I_{\mathrm{dref}}=(K_{p1}+\frac{K_{i1}}{s})\mathrm{\&Delta;}{U}_d+I_d-I_{\mathrm{Ld}}$

$I_{\mathrm{qref}}=(K_{p2}+\frac{K_{i2}}{s})\mathrm{\&Delta;}{U}_q+I_q+I_{\mathrm{Lq}}$

Wherein: s is Laplacian, K _P1And K _P2Be given proportionality coefficient, K _I1And K _I2Be given integral coefficient, I _LdAnd I _LqBe d shaft current feedforward compensation amount and q shaft current feedforward compensation amount.

5. ac bus voltage control method according to claim 4 is characterized in that: described d shaft current feedforward compensation amount I _LdWith q shaft current feedforward compensation amount I _LqTry to achieve according to following formula:

I _Ld＝ωCU _q

I _Lq＝ωCU _d

Wherein: ω is angular frequency and the ω=2 π f of ac bus voltage, and f=50Hz, C are the appearance value of capacitor.

6. ac bus voltage control method according to claim 3 is characterized in that: in the described step (6), according to following formula to d shaft current error signal Δ I _dWith q shaft current error signal Δ I _qCarry out PI adjusting and feedforward decoupling compensation:

$M_d=\frac{2[(K_{p3}+\frac{K_{i3}}{s})\mathrm{\&Delta;}{I}_d+U_d-U_{\mathrm{Ld}}]}{U_{\mathrm{dc}}}$

$M_q=\frac{2[(K_{p4}+\frac{K_{i4}}{s})\mathrm{\&Delta;}{I}_q+U_q+U_{\mathrm{Lq}}]}{U_{\mathrm{dc}}}$

Wherein: s is Laplacian, K _P3And K _P4Be given proportionality coefficient, K _I3And K _I4Be given integral coefficient, U _LdAnd U _LqBe d shaft voltage feedforward compensation amount and q shaft voltage feedforward compensation amount, U _DcDC bus-bar voltage for converting plant.

7. ac bus voltage control method according to claim 6 is characterized in that: described d shaft voltage feedforward compensation amount U _LdWith q shaft voltage feedforward compensation amount U _LqTry to achieve according to following formula:

U _Ld＝ωLI _sq

U _Lq＝ωLI _sd

Wherein: ω is angular frequency and the ω=2 π f of ac bus voltage, and f=50Hz, L are change of current inductance and the total inductance value of converter transformer leakage inductance.

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