CN103401231B - A kind of DFIG direct current grid-connected system based on RMC and flux linkage orientation control method thereof - Google Patents

Abstract

The invention discloses an RMC-based DFIG DC grid-connected power generation system, which includes multiple DFIGs and a high-voltage DC grid; each DFIG is connected with a stator RMC converter and a rotor RMC converter; the stator RMC converter and the rotor RMC The converters are connected with a controller. Among them, the stator RMC converter plays the role of converting the AC output of DFIG into DC and boosting it to the voltage level of HVDC, and at the same time realizes the maximum wind energy tracking operation of DFIG; the role of rotor RMC commutation is to provide excitation for the DFIG rotor and achieve stability at the same time DFIG stator terminal voltage control. The invention also discloses the flux linkage directional control method of the above system, which directly changes the power from AC transmission to high-voltage DC transmission through the RMC converter on the stator side. The system structure is simple and the operation performance is stable, so that the control of DFIG and DC transmission itself has been simplified.

Description

An RMC-based DFIG DC grid-connected power generation system and its flux linkage directional control method

technical field

The invention belongs to the technical field of wind power grid-connected power generation, in particular to an RMC (reduced matrix converter)-based DFIG DC grid-connected power generation system and a flux linkage directional control method thereof.

Background technique

With the increase of population and the development of economy, human beings' demand for energy is also increasing, and the traditional energy reserves are becoming increasingly exhausted, thus bringing about the problem of energy shortage. With the depletion of traditional energy sources, wind energy has become a very promising new energy source. In today's society, the wind power industry has become a pillar industry in the field of new energy sources.

With the wide application of onshore wind farms, offshore wind farms are also developing continuously. Compared with onshore wind farms, offshore wind power has become an important sustainable energy source due to its advantages of high wind speed, low wind shear, low eddy current, and high output. With the increase of the scale of offshore wind farms and the offshore distance of wind farms, AC transmission is affected by the charging current of AC cables, and the transmission capacity and transmission distance are limited, which cannot meet the grid-connected requirements of offshore wind farms. HVDC (High Voltage Direct Current Transmission) has become an ideal way to connect large-scale offshore wind farms to the grid due to its many advantages.

The traditional double-fed wind turbine HVDC grid-connected structure is shown in Figure 1. It is mainly composed of multiple DFIGs. Each DFIG (double-fed asynchronous wind turbine) is connected to the rotor converter, grid-side converter, filter, and transformer in sequence. Then connect to the DC bus through the sending end station. This grid-connected system must use the sending end station to change the DFIG output power from AC transmission to DC transmission, and the sending end station needs to maintain a stable motor stator terminal voltage under different working conditions. The system structure is complex and the control is difficult. In addition, the traditional converters used in HVDC have many conversion stages, which increases energy loss, and the use of electrolytic capacitors for voltage stabilization increases the volume and weight of the system, while reducing the reliability of the system.

Therefore, it is necessary to develop a new wind power HVDC grid-connected system topology, combined with the relevant characteristics of the DFIG wind turbine control system, to simplify the structure of the system while ensuring the grid-connected effect, reduce its construction cost, improve its operating performance, and achieve Better research and practical engineering applications.

Contents of the invention

Aiming at the above-mentioned technical problems existing in the prior art, the present invention provides an RMC-based DFIG DC grid-connected power generation system and its flux linkage oriented control method, which has a simple structure and low cost, and a control strategy through air gap potential and flux linkage orientation , to ensure the stable performance of the system.

An RMC-based DFIG DC grid-connected power generation system, including multiple DFIGs and high-voltage DC grids, each DFIG is connected with a stator RMC converter and a rotor RMC converter; the stator RMC converter and rotor RMC converter The streamers are connected to a controller.

The stator RMC converter includes RMC, single-phase high-frequency transformer and single-phase full-bridge uncontrolled converter; wherein: the RMC is used to convert the three-phase stator voltage of DFIG into positive and negative alternating Pulse voltage, which is boosted by a single-phase high-frequency transformer and then converted into direct current by a single-phase full-bridge uncontrolled converter. Part of the direct current supplies power to the rotor RMC converter, and the other part is injected into the high-voltage direct current grid.

The rotor RMC converter includes an RMC, a single-phase high-frequency transformer and a single-phase full-bridge fully-controlled converter; wherein: the single-phase full-bridge fully-controlled converter is used to convert the DC The voltage is converted into a positive and negative alternating square wave voltage. The square wave voltage is stepped down by a single-phase high-frequency transformer and then converted into a three-phase alternating current by RMC to provide excitation for the DFIG rotor to control the air gap potential of the DFIG as a three-phase symmetrical sine wave. Wave.

The controller is used to collect the three-phase stator current, three-phase rotor current and rotational speed of DFIG, and construct two sets of PWM signals to control the stator RMC converter and the rotor RMC converter respectively according to these signals.

The DFIG has three-phase stator windings and three-phase rotor windings; the three-phase stator windings are respectively connected to the three-phase AC side of the RMC in the stator RMC converter, and the three-phase rotor windings are respectively connected to the rotor RMC The three-phase AC side of the RMC in the converter is connected correspondingly, and the DC side of the single-phase full-bridge uncontrolled converter is correspondingly connected to the DC side of the single-phase full-bridge fully-controlled converter, and then connected to the high-voltage direct current net.

Preferably, the DC side of the single-phase full-bridge uncontrolled converter and the DC side of the single-phase full-bridge fully-controlled converter are connected in parallel with a bus filter capacitor; a constant DC voltage can be maintained.

The RMC is a three-phase six-arm structure, each of which is constructed by a bidirectional power switch; the bidirectional power switch is composed of _two IGBT tubes T1 _- T2; wherein, the set _of IGBT tubes T1 _The electrode is _one end of the bidirectional power switch, the emitter of the IGBT tube T1 is connected to the emitter of the IGBT tube T2, the collector of the IGBT tube T2 is the other end _of the bidirectional power switch, and the _two IGBT tubes T1 ~ _T2 The gate receives the PWM signal provided by the controller.

The flux linkage oriented control method of the above-mentioned DFIG DC grid-connected power generation system is as follows:

For the control of the rotor RMC converter, the following steps are included:

A1. Collect the three-phase stator current, three-phase rotor current and rotational speed of DFIG; respectively perform dq transformation on the three-phase stator current and three-phase rotor current to obtain the d-axis component I _ds and q-axis component I _qs of the three-phase stator current and The d-axis component I _dr and the q-axis component I _qr of the three-phase rotor current;

A2. Calculate the equivalent excitation current I _m of DFIG and the d-axis compensation amount ΔU _dr and the q-axis compensation amount ΔU _qr of the rotor voltage according to the signal obtained in step A1;

A3. Calculate the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr through PI adjustment and compensation according to the signal calculated in step A2;

A4. According to the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr , a set of PWM signals is constructed by PN-SVM (positive and negative alternating space vector modulation) technology to control the RMC in the rotor RMC converter. to control;

For the control of the stator RMC converter, the following steps are included:

B1. Collect the three-phase stator current and three-phase rotor current of DFIG; respectively perform dq transformation on the three-phase stator current and three-phase rotor current to obtain the d-axis component I _ds and q-axis component I _qs of the three-phase stator current and the three-phase The d-axis component I _dr and the q-axis component I _qr of the rotor current;

B2. Calculate the d-axis component E _dm and the q-axis component E _qm of the DFIG air gap potential and the d-axis compensation ΔU _ds and the q-axis compensation ΔU _qs of the stator voltage according to the signal obtained in the step B1;

B3. Calculate the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs through PI adjustment and compensation according to the signal calculated in step B2;

B4. According to the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs , a set of PWM signals is obtained through PN-SVM technology to control the RMC in the stator RMC converter.

In the step A2, the equivalent excitation current I _m and the d-axis compensation ΔU _dr and the q-axis compensation ΔU _qr of the rotor voltage are calculated according to the following formula:

ψ _dm =L _m I _ds +L _m I _dr

I _m = ψ _dm /L _m

ΔU _dr ＝-ω _s L _σr I _qr

ΔU _qr = ω _s L _σr I _dr + ω _s L _m I _m

Where: ω _s is the slip angular velocity and ω _s =ω ₁ -ω, ω ₁ =2πf, f is the power frequency, ω is the speed of DFIG; L _σr is the rotor leakage inductance and L _σr =L _r -L _m , L _m is the stator-rotor mutual inductance of DFIG, and L _r is the rotor inductance of DFIG.

In the step A3, the specific method of calculating the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr through PI adjustment and compensation is as follows:

First, subtract the equivalent excitation current I _m and the q-axis component I _qr of the three-phase rotor current from the preset current value i _m and current value i _qr respectively to obtain the excitation current error ΔI _m and the rotor q-axis current error ΔI _qr ;

Then, PI adjustment is performed on the excitation current error ΔI _m to obtain the current value i _dr , and the current value i _dr is subtracted from the d-axis component I _dr of the three-phase rotor current to obtain the rotor d-axis current error ΔI _dr ;

Finally, according to the following formula, the rotor d-axis current error ΔI _dr and the rotor q-axis current error ΔI _qr are adjusted and compensated by PI, and the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr are obtained;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pr</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pr</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}$

Among them: K _pr and K _ir are the rotor proportional coefficient and the rotor integral coefficient respectively, s is the Laplacian operator.

In the described step A4, the specific method of constructing PWM signal by P-N-SVM technology is as follows:

Firstly, according to the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr , determine the sector where the required reference input voltage vector is located in the stationary α-β coordinate system;

Then, calculate the action time t _x , _ty and t ₀ corresponding to the adjacent basic voltage vectors V _x and V _y on the left and right sides of the sector and the zero voltage vector V ₀ ;

Finally, in the first half of the modulation cycle, a set of PWM signals is constructed according to the switch combination of the voltage vectors V _x , V _y and V ₀ and the action time to control the RMC in the rotor RMC converter; in the second half of the modulation cycle , according to the switch combination of voltage vectors -V _x , -V _y and V ₀ and the action time to construct a set of PWM signals to control the RMC in the rotor RMC converter; where the voltage vector V _x and -V _x pole The opposite action time is equal, and the voltage vector V _y and -V _y polarity opposite action time are equal.

In the step B2, the d-axis component E _dm and the q-axis component E _qm of the DFIG air gap potential and the d-axis compensation ΔU _ds and the q-axis compensation ΔU _qs of the stator voltage are calculated according to the following formula:

E _dm ＝-ω ₁ L _m (I _qs +I _qr )

E _qm ＝ω ₁ L _m (I _ds +I _dr )

ΔU _ds =E _dm -ω ₁ L _σs I _qs

ΔU _qs ＝E _qm +ω ₁ L _σs I _ds

Where: ω ₁ =2πf, f is the power frequency, L _σs is the stator leakage inductance and L _σs =L _s -L _m , L _m is the stator-rotor mutual inductance of DFIG, and L _s is the stator inductance of DFIG.

In the step B3, the specific method of calculating the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs through PI adjustment and compensation is as follows:

First, subtract the d-axis component I _ds and q-axis component I _qs of the three-phase stator current from the preset current value i _ds and current value i _qs respectively, and obtain the stator d-axis current error ΔI _ds and the stator q-axis current error ΔI _qs ;

Then, according to the following formula, the stator d-axis current error ΔI _ds and the stator q-axis current error ΔI _qs are adjusted and compensated by PI, and the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs are obtained;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ps</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; is</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ps</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; is</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}$

Among them: K _ps and K _is respectively the stator proportional coefficient and the stator integral coefficient, s is the Laplacian operator.

In the described step B4, the concrete method of constructing PWM signal by P-N-SVM technology is as follows:

Firstly, according to the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs , determine the sector where the required reference input voltage vector is located in the stationary α-β coordinate system;

Then, calculate the action time t _x , _ty and t ₀ corresponding to the adjacent basic voltage vectors V _x and V _y on the left and right sides of the sector and the zero voltage vector V ₀ ;

Finally, in the first half of the modulation cycle, a set of PWM signals is constructed according to the switch combination of the voltage vectors V _x , V _y and V ₀ and the action time to control the RMC in the stator RMC converter; in the second half of the modulation cycle , according to the switch combination of voltage vectors -V _x , -V _y and V ₀ and the action time to construct a set of PWM signals to control the RMC in the stator RMC converter; where the voltage vector V _x and -V _x pole The opposite action time is equal, and the voltage vector V _y and -V _y polarity opposite action time are equal.

The system of the present invention mainly includes DFIG, rotor RMC converter, stator RMC converter and high-voltage DC power grid; in the RMC converter structure connected to the DFIG rotor winding, it directly connects the DC power required by the DC bus to the stable DC power grid. The stator RMC converter converts the AC output of DFIG into DC and boosts it to the voltage level of HVDC. At the same time, it realizes the maximum wind energy tracking operation of DFIG and the end station function of wind farm side transmission. The role of the rotor RMC converter is to provide excitation for the DFIG rotor and at the same time realize stable DFIG stator terminal voltage control. The DC power grid in the present invention is equivalent to an infinite DC source with stable voltage, and can directly transmit electric energy to remote areas through high-voltage DC transmission.

The stator RMC converter of the DFIG of the present invention adopts an indirect air gap potential orientation strategy, and the rotor RMC converter adopts an indirect air gap flux linkage orientation control method. In the traditional DFIG AC grid-connected model, the output of the fan stator end is directly connected to the grid, and the voltage on the stator side is a stable and symmetrical three-phase AC, which provides a stable stator flux orientation or stator voltage orientation reference for DFIG vector control. However, in the DFIG DC grid-connected system of the present invention, the stator of DFIG is connected with the stator RMC converter, so in order to ensure the precise positioning of its vector control, it is necessary to control the rotor RMC converter to ensure that the air gap potential is three-phase symmetrical sinusoidal , and then control the stator RMC converter to realize the maximum wind energy tracking operation of the DFIG unit.

The beneficial effects of the present invention are: in the DFIG wind power system, the power is directly changed from AC transmission to DC transmission through the stator RMC converter, wherein the high-frequency transformer in the RMC converter directly increases the DC bus voltage to the HVDC voltage level , compared with the power frequency transformer in the traditional DFIG grid-connected system, it is smaller in size and lighter in weight. On the one hand, the P-N-SVM modulation technology realizes the above-mentioned control objectives of the stator-rotor RMC converter, and on the other hand, it also ensures that the input side voltage of the high-frequency transformer is a high-frequency square wave pulse with alternating positive and negative; at the same time, for the DFIG system Said that the number of stages of the converter is reduced, and at the same time, the larger voltage stabilizing capacitor is replaced by a smaller volume and weight filter capacitor. The system structure is simple and the operation performance is stable, which simplifies the control of DFIG and DC transmission itself.

Description of drawings

Figure 1 is a schematic structural diagram of a traditional DC grid-connected power generation system based on DFIG.

Fig. 2 is a schematic structural diagram of the RMC-based DFIG DC grid-connected power generation system of the present invention.

Figure 3(a) is a schematic diagram of the topology of the stator RMC converter.

Figure 3(b) is a schematic diagram of the topology of the rotor RMC converter.

Fig. 3(c) is a schematic structural diagram of a bidirectional power switch.

Fig. 4 is a schematic flowchart of the control principle of the rotor RMC converter.

Fig. 5 is a schematic flowchart of the control principle of the stator RMC converter.

Fig. 6(a) is a simulation waveform diagram of the grid-connected power generation system of the present invention in a steady state.

Fig. 6(b) is a simulation waveform diagram of the grid-connected power generation system of the present invention under the condition of DFIG rotation speed variation.

Detailed ways

In order to describe the present invention more specifically, the technical solution and its control method of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 2, an RMC-based DFIG DC grid-connected power generation system includes multiple DFIGs and a high-voltage DC grid. Each DFIG is connected with a stator RMC converter and a rotor RMC converter; the stator RMC converter and the The rotor RMC converter is connected with a controller; DFIG has three-phase stator windings and three-phase rotor windings, and the three-phase stator windings and three-phase rotor windings are all connected in a star connection; where:

As shown in Fig. 3(a), the stator RMC converter includes RMC, single-phase high-frequency transformer T and single-phase full-bridge uncontrolled converter. The three-phase AC side of RMC is connected to the three-phase stator winding of DFIG ; Among them: RMC is used to convert the three-phase stator voltage of DFIG into positive and negative alternating pulse voltage, the pulse voltage is boosted by single-phase high-frequency transformer T and then converted into direct current by single-phase full-bridge uncontrolled converter , part of the direct current powers the rotor RMC converter, and the other part is injected into the high voltage direct current grid.

As shown in Fig. 3(b), the rotor RMC converter includes RMC, single-phase high-frequency transformer T and single-phase full-bridge fully-controlled converter. The three-phase AC side of RMC is connected to the three-phase rotor winding of DFIG correspondingly ; Among them: the single-phase full-bridge fully-controlled converter is used to convert the DC voltage on the high-voltage DC grid into a positive and negative alternating square wave voltage. The square wave voltage is stepped down by the single-phase high-frequency transformer T and converted to The three-phase alternating current provides excitation for the DFIG rotor to control the air-gap potential of the DFIG to be a three-phase symmetrical sine wave.

The DC side of the single-phase full-bridge uncontrolled converter is connected to the DC side of the single-phase full-bridge fully-controlled converter correspondingly and then connected to the high-voltage DC grid; the DC sides of the two converters are connected in parallel with a bus filter capacitor c.

In this embodiment, the RMC is a three-phase six-leg structure, each of which is constructed by a bidirectional power switch; as shown in Figure 3(c), the bidirectional power switch consists of two IGBT tubes T ₁ ~ T ₂ ; Among them, the collector of IGBT tube T1 is _one end _of the bidirectional power switch, the emitter of IGBT tube T1 is connected to the emitter of _IGBT tube _T2 , and the collector of IGBT tube T2 is the other end of the bidirectional power switch. The gates of IGBT tubes T ₁ ~ T ₂ receive the PWM signal provided by the controller; the power switching device of the bridge arm of the single-phase full-bridge uncontrolled converter adopts diodes, and the bridge arm of the single-phase full-bridge fully controlled converter The power switching device adopts IGBT.

The controller is used to collect the three-phase stator current I _as ～I _cs , the three-phase rotor current I _ar ～I _cr and the speed ω of DFIG, and construct two sets of PWM signals to convert the stator RMC converter and the rotor RMC respectively according to these signals. flow control. In this embodiment, the controller is constructed by a current sensor, an encoder, a drive circuit, and a DSP; wherein, the current sensor is used to collect current signals; the encoder is used to detect the rotor position angle and rotational speed of DFIG, and the current sensor and encoder will collect The received signals are sent to the DSP after signal conditioning and analog-to-digital conversion, and the DSP constructs two sets of PWM signals through the corresponding control algorithm according to these signals, and then amplifies the power of the drive circuit to respectively amplify the stator RMC converter and the rotor RMC converter. The bidirectional power switch of the RMC in the middle performs switching control.

As shown in Figure 4, the control method of the rotor RMC converter in this embodiment includes the following steps:

(1) Use the current sensor to collect the three-phase stator current I _as ~ I _cs and the three-phase rotor current I _ar ~ I _cr of DFIG, and use the encoder to obtain the speed ω of DFIG by detecting the rotor position angle θ;

According to the indirect air-gap flux orientation principle, the d-axis is set in the direction of the stator flux linkage, and the dq transformation is performed on the three-phase stator current I _as ~ I _cs and the three-phase rotor current I _ar ~ I _cr respectively, and the three-phase stator current is obtained The d-axis component I _ds and the q-axis component I _qs and the d-axis component I _dr and the q-axis component I _qr of the three-phase rotor current;

Among them, the air-gap flux linkage space angle θ _e =∫ω ₁ dt required for dq transformation, ω ₁ is the rotational angular velocity of the stator flux linkage, which is obtained according to the formula ω ₁ =2πf, and f takes the power frequency of 50Hz.

(2) According to the signal obtained in step (1), the equivalent excitation current I _m of DFIG and the d-axis compensation ΔU _dr and q-axis compensation ΔU _qr of the rotor voltage are calculated by the following formula;

ψ _dm =L _m I _ds +L _m I _dr

I _m = ψ _dm /L _m

ΔU _dr ＝-ω _s L _σr I _qr

ΔU _qr ＝ω _s L _σr I _dr +ω _s L _m I _m where: ω _s is slip angular velocity and ω _s =ω ₁ -ω, L _σr is rotor leakage inductance and L _σr =L _r -L _m , L _m is the stator-rotor mutual inductance of DFIG, L _r is the rotor inductance of DFIG; in this embodiment, L _r =3.907pu, L _m =3.78pu.

(3) According to the signal calculated in step (2), the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr are calculated through PI adjustment and compensation;

First, subtract the equivalent excitation current I _m and the q-axis component I _qr of the three-phase rotor current from the preset current value i _m and current value i _qr respectively to obtain the excitation current error ΔI _m and the rotor q-axis current error ΔI _qr ; In this embodiment, the current value i _m is obtained according to the formula i _ms =E _m /ω ₁ L _m , and the current value i _qr =-I _qs ; wherein, E _m is a given value of the DFIG air gap potential amplitude and Em= _1pu .

Then, perform PI adjustment on the excitation current error ΔI _m according to the following formula to obtain the current value i _dr , and subtract the d-axis component I _dr of the three-phase rotor current from the current value i _dr to obtain the rotor d-axis current error ΔI _dr ;

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}$

Wherein: K _p and K _i are excitation proportional coefficient and excitation integral coefficient respectively, in this embodiment, K _p =4, K _i =50.

Finally, according to the following formula, the rotor d-axis current error ΔI _dr and the rotor q-axis current error ΔI _qr are adjusted and compensated by PI, and the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr are obtained;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pr</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; dr</span>}}$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pr</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; qr</span>}}$

Wherein: K _pr and K _ir are the rotor proportional coefficient and the rotor integral coefficient respectively, and in this embodiment, K _pr =5, and K _ir =50.

(4) According to the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr , a set of PWM signals are obtained through PN-SVM technology to control the rotor RMC converter:

Firstly, the rotor d-axis voltage modulation signal V _dr and the rotor q-axis voltage modulation signal V _qr are transformed into the rotor α-axis voltage modulation signal V _αr and the rotor β-axis voltage modulation signal in the stationary α-β coordinate system by inverse Park transformation V _βr ;

Then, according to the modulation signals V _αr and V _βr , determine the sector where the required reference input voltage vector is located in the static α-β coordinate system, and the angle between the reference input voltage vector and the adjacent basic voltage vector on the right side of the sector θ _svm ;

Then, according to θ _svm , calculate the action time t _x , t _y and t ₀ corresponding to the adjacent basic voltage vectors V _x and V _y on the left and right sides of the sector and the zero voltage vector V ₀ ; the specific calculation formula is as follows:

t _x ＝(T _pwm /2)*msin(60°-θ _svm )

t _y ＝(T _pwm /2)*msinθ _svm

t _x ＝ T _pwm /2-t _x -t _y

Among them: T _pwm is the modulation period, m is the voltage modulation degree;

Finally, in the first half of the modulation cycle, a set of PWM signals is constructed according to the switch combination of the voltage vectors V _x , V _y and V ₀ and the action time to control the RMC in the rotor RMC converter; in the second half of the modulation cycle, According to the switch combination of voltage vectors -V _x , -V _y and V ₀ and the action time, a set of PWM signals is constructed to control the RMC in the rotor RMC converter; the voltage vector V _x is opposite to -V _x in polarity The action time is equal, and the voltage vector V _y and -V _y polarity are opposite and the action time is equal.

As shown in Figure 5, the control method of the stator RMC converter in this embodiment includes the following steps:

(1) Use the current sensor to collect the three-phase stator current I _as ~ I _cs and the three-phase rotor current I _ar ~ I _cr of DFIG;

According to the air gap potential vector orientation principle, the d-axis is set in the direction of the air gap potential vector, and the three-phase stator current I _as ~ I _cs and the three-phase rotor current I _ar ~ I _cr are subjected to dq transformation respectively to obtain the three-phase stator current The d-axis component I _ds and the q-axis component I _qs and the d-axis component I _dr and the q-axis component I _qr of the three-phase rotor current; where the air gap potential vector space angle θ _v = θ _e + π/ 2.

(2) According to the signal obtained in step (1), the d-axis component E _dm and q-axis component E _qm of the DFIG air gap potential and the d-axis compensation ΔU _ds and q-axis compensation ΔU of the stator voltage are calculated by the following formula _qs ;

E _dm ＝-ω ₁ L _m (I _qs +I _qr )

E _qm ＝ω ₁ L _m (I _ds +I _dr )

ΔU _ds =E _dm -ω ₁ L _σs I _qs

ΔU _qs ＝E _qm +ω ₁ L _σs I _ds

Wherein: L _σs is stator leakage inductance and L _σs =L _s -L _m , L _s is stator inductance of DFIG; in this embodiment, L _s =3.91pu.

(3) According to the signal calculated in step (2), the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs are calculated through PI adjustment and compensation:

First, subtract the d-axis component I _ds and q-axis component I _qs of the three-phase stator current from the preset current value i _ds and current value i _qs respectively, and obtain the stator d-axis current error ΔI _ds and the stator q-axis current error ΔI _qs ; in this embodiment, the current value i _qs =0, and the current value i _ds is obtained according to the formula i _ds =K _w ω ³ /U _ds ; where K _w is a given maximum wind energy tracking coefficient and K _w =0.5 , U _ds is the d-axis component of the three-phase stator voltage.

Then, according to the following formula, the stator d-axis current error ΔI _ds and the stator q-axis current error ΔI _qs are adjusted and compensated by PI, and the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs are obtained;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ps</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; is</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; ds</span>}}$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; ps</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; is</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}_{\mathrm{<span\; class="notranslate">\; qs</span>}}$

Where: K _ps and K _is respectively the stator proportional coefficient and the stator integral coefficient, in this embodiment, K _ps =4, K _ir =50.

(4) According to the stator d-axis voltage modulation signal V _ds and the stator q-axis voltage modulation signal V _qs , a set of PWM signals is obtained through PN-SVM technology to control the RMC in the stator RMC converter.

The following is a simulation analysis of this embodiment; the rated frequency of the high-frequency transformer is 3kHz, the voltage ratio is 1.15:10kV, and the DFIG parameters are shown in Table 1:

Table 1

Motor parameters parameter value

Rated power _Pn 3MW Rated voltage U _n 220V Rated frequency f _n 50Hz Torque speed ω _n 0.9pu Stator phase resistance R _s 0.00586pu Stator inductance L _s 3.91pu Rotor inductance L _r 3.907pu Motor mutual inductance L _m 3.78pu number of pole pairs p 3

Fig. 6 is a simulation waveform diagram of controlling the DFIG grid-connected system in this embodiment, including three-phase air gap potentials E _am to E _cm , three-phase stator currents I _as to I _cs , and three-phase rotor currents I _ar to I _cr The waveform and the stator output active and reactive waveforms.

In Fig. 6(a), the active power given value of our target output is 2.1MW (0.7pu). It can be seen from the simulation results that the air gap potential and phase current waveforms are good. The actual output active power value P also fluctuates around 2.1MW, and the fluctuation range is ±5%. At this time, the active current component _Isd and the reactive current component _Isq of the stator are both in a stable state; in the simulation, the high-voltage DC bus voltage is set to 10kV.

In Fig. 6(b), we simulate the situation when the fan speed changes. When t=0～0.2s, the rotating speed of DFIG is 0.8pu. When t=0.2～0.4s, the rotational speed of DFIG increases linearly to 1.2pu, and when t=0.4～0.6s, the rotational speed of DFIG runs stably at 1.2pu. So far, the rotational speed of DFIG changes from sub-synchronous to super-synchronous. The reactive power output setting is set to 0, and the stator converter operates under unity power factor. It can be seen from the simulation results that the terminal voltage and phase current waveforms are good; the actual output active power value P changes with the cubic law of the DFIG speed, and the overshoot is small. Since the current frequency on the rotor side is related to the absolute value of the slip, the rotor current frequency also changes continuously when the fan speed changes (t=0.2-0.4s). The amplitude of the stator and rotor current increases with the increase of power, the amplitude of the air gap potential is stable, and the control performance is good.

Claims (5)

1., based on a flux linkage orientation control method for the DFIG direct current grid-connected system of RMC, described DFIG direct current grid-connected system comprises multiple stage DFIG and high-voltage direct current power grid, and every platform DFIG is connected with stator RMC converter and rotor R MC converter; Described stator RMC converter and rotor R MC converter are connected with a controller altogether;

Described stator RMC converter comprises RMC, single-phase high frequency transformer and single-phase full bridge and does not control type current transformer; Wherein: the pulse voltage of the RMC in stator RMC converter for by the threephase stator voltage transitions of DFIG being positive and negative alternation, this pulse voltage is converted to direct current by not controlling type current transformer by single-phase full bridge after single-phase high frequency transformer boost, this direct current part powers to rotor R MC converter, and another part injects high-voltage direct current power grid;

Described rotor R MC converter comprises RMC, single-phase high frequency transformer and single-phase full bridge full-control type current transformer; Wherein: described single-phase full bridge full-control type current transformer is used for square-wave voltage direct voltage online for high voltage direct current being converted to positive and negative alternation, this square-wave voltage is converted to three-phase alternating current for DFIG rotor by the RMC in rotor R MC converter and provides excitation, with the air gap electromotive force of control DFIG for three-phase symmetrical is sinusoidal wave after single-phase high frequency transformer pressure-reducing;

Described controller for gathering the threephase stator electric current of DFIG, three-phase rotor current and rotating speed, and goes out two groups of pwm signals according to these signal configuration and controls stator RMC converter and rotor R MC converter respectively;

RMC in stator RMC converter and rotor R MC converter is three-phase six bridge arm structure, and its each brachium pontis is built by a two-way power switch; Described two-way power switch is by two IGBT pipe T ₁~ T ₂composition; Wherein, IGBT pipe T ₁one end of current collection very two-way power switch, IGBT pipe T ₁emitter and IGBT pipe T ₂emitter be connected, IGBT pipe T ₂the other end of current collection very two-way power switch, two IGBT pipe T ₁~ T ₂gate pole the pwm signal that provides of controller is provided;

Described flux linkage orientation control method is as follows:

For the control of rotor R MC converter, comprise the steps:

A1. the threephase stator electric current of DFIG, three-phase rotor current and rotating speed is gathered; Respectively dq conversion is carried out to threephase stator electric current and three-phase rotor current, obtain the d axle component I of threephase stator electric current _dswith q axle component I _qsand the d axle component I of three-phase rotor current _drwith q axle component I _qr;

A2. gone out the equivalent exciting current I of DFIG by following formulae discovery according to the signal obtained in steps A 1 _mand the d axle compensation rate Δ U of rotor voltage _drwith q axle compensation rate Δ U _qr;

ψ _dm＝L _mI _ds+L _mI _dr

I _m＝ψ _dm/L _m

ΔU _dr＝-ω _sL _σrI _qr

ΔU _qr＝ω _sL _σrI _dr+ω _sL _mI _m

Wherein: ω _sfor slip angular velocity and ω _s=ω ₁-ω, ω ₁=2 π f, f are power frequency, and ω is the rotating speed of DFIG; L _{σ r}for rotor leakage inductance and L _{σ r}=L _r-L _m, L _mfor the rotor mutual inductance of DFIG, L _rfor the inductor rotor of DFIG;

A3. according to the signal calculated in steps A 2, compensation calculation is regulated to go out rotor d shaft voltage modulation signal V by PI _drwith rotor q shaft voltage modulation signal V _qr;

A4. according to rotor d shaft voltage modulation signal V _drwith rotor q shaft voltage modulation signal V _qrone group of pwm signal is obtained to control the RMC in rotor R MC converter by P-N-SVM technical construction;

For the control of stator RMC converter, comprise the steps:

B1. threephase stator electric current and the three-phase rotor current of DFIG is gathered; Respectively dq conversion is carried out to threephase stator electric current and three-phase rotor current, obtain the d axle component I of threephase stator electric current _dswith q axle component I _qsand the d axle component I of three-phase rotor current _drwith q axle component I _qr;

B2. calculated the d axle component E of DFIG air gap electromotive force by following formula according to the signal obtained in step B1 _dmwith q axle component E _qmand the d axle compensation rate Δ U of stator voltage _dswith q axle compensation rate Δ U _qs;

E _dm＝-ω ₁L _m(I _qs+I _qr)

E _qm＝ω ₁L _m(I _ds+I _dr)

ΔU _ds＝E _dm-ω ₁L _σsI _qs

ΔU _qs＝E _qm+ω ₁L _σsI _ds

Wherein: L _{σ s}for stator leakage inductance and L _{σ s}=L _s-L _m, L _sfor the stator inductance of DFIG;

B3. according to the signal calculated in step B2, compensation calculation is regulated to go out stator d shaft voltage modulation signal V by PI _dswith stator q shaft voltage modulation signal V _qs;

B4. according to stator d shaft voltage modulation signal V _dswith stator q shaft voltage modulation signal V _qsone group of pwm signal is obtained to control the RMC in stator RMC converter by P-N-SVM technical construction.

2. flux linkage orientation control method according to claim 1, is characterized in that: in described steps A 3, regulates compensation calculation rotor d shaft voltage modulation signal V by PI _drwith rotor q shaft voltage modulation signal V _qrconcrete grammar as follows:

First, the current value i preset is made _mwith current value i _qrdeduct equivalent exciting current I respectively _mwith the q axle component I of three-phase rotor current _qr, obtain exciting current error delta I _mwith rotor q shaft current error delta I _qr;

Then, to exciting current error delta I _mcarry out PI adjustment and obtain current value i _dr, make current value i _drdeduct the d axle component I of three-phase rotor current _dr, obtain rotor d shaft current error delta I _dr;

Finally, according to following formula to rotor d shaft current error delta I _drwith rotor q shaft current error delta I _qrcarry out PI and regulate compensation, obtain rotor d shaft voltage modulation signal V _drwith rotor q shaft voltage modulation signal V _qr;

Wherein: K _prand K _irbe respectively rotor proportionality coefficient and rotor integral coefficient, s is Laplacian.

3. flux linkage orientation control method according to claim 1, is characterized in that: in described steps A 4, as follows by the concrete grammar of P-N-SVM technical construction pwm signal:

First, according to rotor d shaft voltage modulation signal V _drwith rotor q shaft voltage modulation signal V _qrdetermine the sector that required reference input voltage vector is residing in static alpha-beta coordinate system;

Then, the adjacent basic voltage vectors V in this left and right sides, sector is calculated _xand V _yand Zero voltage vector V ₀corresponding t action time _x, t _yand t ₀;

Finally, in front half modulation period, according to voltage vector V _x, V _yand V ₀switch combination and construct one group of pwm signal action time to control the RMC in rotor R MC converter; In rear half modulation period, according to voltage vector-V _x,-V _yand V ₀switch combination and construct one group of pwm signal action time to control the RMC in rotor R MC converter; Wherein, voltage vector V _xwith-V _xthe polarity adverse effect time is equal, voltage vector V _ywith-V _ythe polarity adverse effect time is equal.

4. flux linkage orientation control method according to claim 1, is characterized in that: in described step B3, regulates compensation calculation stator d shaft voltage modulation signal V by PI _dswith stator q shaft voltage modulation signal V _qsconcrete grammar as follows:

First, the current value i preset is made _dswith current value i _qsdeduct the d axle component I of threephase stator electric current respectively _dswith q axle component I _qs, obtain stator d shaft current error delta I _dswith stator q shaft current error delta I _qs;

Then, according to following formula to stator d shaft current error delta I _dswith stator q shaft current error delta I _qscarry out PI and regulate compensation, obtain stator d shaft voltage modulation signal V _dswith stator q shaft voltage modulation signal V _qs;

Wherein: K _psand K _isbe respectively stator proportionality coefficient and stator integral coefficient, s is Laplacian.

5. control method according to claim 1, is characterized in that: in described step B4, as follows by the concrete grammar of P-N-SVM technical construction pwm signal:

First, according to stator d shaft voltage modulation signal V _dswith stator q shaft voltage modulation signal V _qsdetermine the sector that required reference input voltage vector is residing in static alpha-beta coordinate system;

Then, the adjacent basic voltage vectors V in this left and right sides, sector is calculated _xand V _yand Zero voltage vector V ₀corresponding t action time _x, t _yand t ₀;

Finally, in front half modulation period, according to voltage vector V _x, V _yand V ₀switch combination and construct one group of pwm signal action time to control the RMC in stator RMC converter; In rear half modulation period, according to voltage vector-V _x,-V _yand V ₀switch combination and construct one group of pwm signal action time to control the RMC in stator RMC converter; Wherein, voltage vector V _xwith-V _xthe polarity adverse effect time is equal, voltage vector V _ywith-V _ythe polarity adverse effect time is equal.