CN107947659B - A Stator Current Sinusoidal Control Method for DFIG-DC System - Google Patents

Abstract

The invention discloses a DFIG‑DC system stator current sinusoidal control method, which makes the stator current sinusoidal, reduces the harmonic current of the stator and rotor, and reduces the torque and power ripple at the same time; the invention does not use a voltage sensor, and directly uses the stator current to represent Stator voltage, and then the required rotor harmonic voltage is obtained through the doubly-fed motor model, and the rotor side is added with a suitable harmonic voltage to realize the sinusoidalization of the stator current. This control method can reduce the stator-rotor harmonic current loss and improve the operating efficiency of the system. It is an optimal control method that is very suitable for this topology.

Description

A Stator Current Sinusoidal Control Method for DFIG-DC System

technical field

The invention belongs to the technical field of new energy power generation, and in particular relates to a stator current sinusoidal control method of a DFIG-DC system.

Background technique

In the last ten years, DC microgrids based on new energy power generation equipment have been more and more researched and applied. The DC micro-grid has the advantages of high stability, simple grid connection, no reactive power loss, and wire cost saving, and most of the new energy generation units such as photovoltaics and wind power have DC ports, and most of the loads are DC loads, so for It is more economical, affordable and reliable to use DC micro-grid for these new energy power generation equipment.

In new energy power generation, wind power generation based on doubly-fed motors occupies a high proportion, so in the study of new energy DC grid-connected, it is of great significance to study doubly-fed motors DC-grid-connected. At present, most DC grid-connected DFIGs still adopt DC grid-connected topology based on VSC (Voltage Source Converter)-HVDC (High Voltage Direct Current Transmission). The advantage of this topology is that the control strategy of DFIG can be directly transplanted. In AC grid-connected, the disadvantage is that there are too many conversion stages, which leads to low efficiency, and requires a lot of transformers, which increases the cost. In the document "Research on DC Grid-connected Topology and Control Strategy Based on Doubly-fed Wind Power Generation System", scholar Yi Xilu proposed a double-fed wind turbine based on SSC (stator side converter)-RSC (rotor side converter) structure. Feed machine DC structure, this structure directly connects the bus bars of the rotor-side back-to-back converters in the traditional doubly-fed machine to the DC grid through the DC/DC converter. The advantage of this topology is that it reduces costs and expands The operating speed range of the doubly-fed motor. However, two converters are still required, and when the slip control is not optimal, the capacity of the two converters is greater than the capacity of the slip times the power, and the cost is still high. On this basis, Spanish scholar G.D.Marques and others proposed a DC grid-connected structure of doubly-fed motors based on single converter. The control rectifier bridge further reduces the cost of the topology structure, and only one converter needs to be controlled to further improve the reliability of the control; however, due to the uncontrolled rectifier bridge on the stator side, the stator and rotor currents are distorted, resulting in power and torque with great pulsation.

Contents of the invention

For the DFIG (Double-Fed Induction Generator, double-fed asynchronous wind generator)-DC topology structure, since the stator side is an uncontrolled rectifier bridge, it is very easy to cause stator current distortion, so the present invention provides a DFIG-DC system stator current sinusoidal The optimized control method can reduce the harmonic current of the stator and rotor, reduce the torque and power pulsation, improve the operating efficiency of the system, and improve the operating performance of the system, and it adopts a feedforward control strategy, avoiding the use of resonant controllers or repetitive controllers, and realizing stator The current sine can reduce the complexity of the algorithm and has a good application prospect.

A stator current sinusoidal control method of a DFIG-DC system, comprising the steps of:

(1) Collect the three-phase stator current I _sabc and the three-phase rotor current I _rabc of DFIG, and use the code disc to detect the speed ω _r and rotor position angle θ _r of DFIG at the same time;

(2) Use the stator flux phase-locked loop to estimate the current stator flux angle θ _s , subtract the rotor position angle θ _r from the stator flux angle θ _s to obtain the slip angle θ _slip , and then use the slip angle θ _slip Perform coordinate transformation on the three-phase rotor current I _rabc to obtain the d-axis component I _rd and q-axis component I _rq of the rotor current in the synchronous rotating coordinate system;

(3) The stator frequency reference value ω _ref is set as the rated frequency of the stator, and then the stator frequency error is obtained through PI control to obtain the rotor current d-axis reference value I _rdref ;

(4) According to the d-axis component I _rd and q-axis component I _rq of the rotor current, the d-axis reference value I _rdref of the rotor current and the given rotor current q-axis reference value I _rqref , the dq-axis errors of the rotor current are respectively controlled by PI Get the d-axis average component U _{d_PI} and the q-axis average component U _{q_PI} of the rotor voltage;

(5) Calculate the d-axis compensation amount ΔU _dr and the q-axis compensation amount ΔU _qr of the rotor voltage according to the d-axis component I _rd and the q-axis component I _rq of the rotor current;

(6) Determine the three-phase stator voltage U _sabc of DFIG according to the three-phase stator current I _sabc , make the three-phase stator voltage U _sabc pass through a 50Hz trap to obtain the three-phase stator harmonic voltage U _sabch , and then use the stator flux linkage The angle θ _s performs coordinate transformation on the three-phase stator harmonic voltage U _sabch to obtain the d-axis component U _sdh and q-axis component U _sqh of the stator harmonic voltage in the synchronous rotating coordinate system;

(7) Obtain the d-axis component U _rdh and q-axis component U _rqh of the rotor harmonic voltage through the rotor harmonic voltage generator according to the d-axis component U _sdh and q-axis component U _sqh of the stator harmonic voltage;

(8) Make U _{d_PI} + ΔU _dr + U _rdh get the rotor voltage d-axis modulation signal V _dr , make U _{q_PI} + ΔU _qr + U _rqh get the rotor voltage q-axis modulation signal V _qr , based on V _dr and V _qr through SVPWM ( Space Vector Pulse Width Modulation (Space Vector Pulse Width Modulation) technology is constructed to obtain a set of PWM signals to control the rotor converter of DFIG.

Further, in the step (2), the stator flux linkage angle θ _s at the current moment is estimated by using the stator flux linkage phase-locked loop, and the specific algorithm is as follows:

ψ _sq '＝L _s I _sq '+L _m I _rq ' θ _s = ∫ω _s '

Among them: L _s and L _m are the stator inductance and stator-rotor mutual inductance of DFIG respectively, K _ps and K _is the proportional coefficient and integral coefficient of the stator flux linkage phase-locked loop respectively, ψ _sq ' is the stator flux linkage q at the previous moment axis component, ω _s ' is the stator frequency at the previous moment, s is the Laplacian operator, I _rq ' and I _sq ' are the q-axis component of the rotor current and the q-axis component of the stator current at the previous moment, respectively.

Further, in the step (3), the stator frequency error is controlled by PI to obtain the rotor current d-axis reference value I _rdref through the following formula:

Among them: K _pf and K _if are the proportional coefficient and integral coefficient of the stator frequency control outer loop respectively, ω _s is the stator frequency at the current moment, and s is the Laplacian operator.

Further, in the step (4), the d-axis and q-axis errors of the rotor current are respectively controlled by PI to obtain the d-axis average component U _{d_PI} and the q-axis average component U _{q_PI} of the rotor voltage through the following formula:

Among them: K _pi and K _ii are the given proportional coefficient and integral coefficient respectively, s is the Laplacian operator.

Further, in the step (5), the d-axis compensation amount ΔU _dr and the q-axis compensation amount ΔU _qr of the rotor voltage are calculated by the following formula:

ΔU _dr ＝-ω _slip σL _r I _rq

ΔU _qr = ω _slip σL _r I _rd

Where: ω _slip is the slip speed and ω _slip = ω _s -ω _r , σ is the magnetic leakage coefficient of DFIG, and L _r is the rotor inductance of DFIG.

Further, in the step (6), the three-phase stator voltage U _sabc of DFIG is determined by the following expression:

Among them: U _sa , U _sb and U _sc respectively correspond to the A-phase, B-phase and C-phase stator voltages of DFIG, I _sa , I _sb and I _sc respectively correspond to the A-phase, B-phase and C-phase stator currents of DFIG, U _dc is the DC bus voltage of the DFIG-DC system.

Further, in the step (7), the d-axis component U _rdh and the q-axis component U _rqh of the rotor harmonic voltage are obtained through the following calculation expressions;

Among them: L _r and L _m are the rotor inductance and stator-rotor mutual inductance of DFIG respectively, ω _slip is the slip speed and ω _slip = ω _s -ω _r , ω _s is the stator frequency at the current moment, s is the Laplace calculation son.

The DFIG-DC system involved in the present invention mainly includes DFIG, rotor converter, stator uncontrolled rectifier bridge and DC power grid; the DFIG stator is connected to the DC power grid through the uncontrolled rectification bridge, and the DFIG rotor is simultaneously connected to the DC power grid through the rotor side converter , by controlling the rotor converter to provide excitation current to establish the stator voltage, the stator voltage makes the uncontrolled rectifier bridge on the stator side work in continuous conduction mode, and the uncontrolled rectifier bridge on the stator side realizes the conversion of AC current into DC power and transmission to the DC grid.

The advantage of the present invention in topological structure is that only one slip power inverter can realize the transmission of DFIG electric energy to the DC power grid, which can significantly reduce the cost of the topological structure. The advantage of the present invention in the control method is that for the stator and rotor current harmonics caused by the stator voltage distortion, the rotor harmonic voltage compensation is used to sine the stator current. This method is directly based on the mathematical model of DFIG and is obtained directly through the stator harmonic voltage. The required rotor voltage avoids the use of a set of resonant controllers or repetitive controllers, which reduces the parameter design work and reduces the complexity of the algorithm. Moreover, the stator voltage used in the present invention is obtained through the stator current based on the characteristics of the uncontrolled rectifier bridge, avoiding the use of voltage sensors, further reducing the complexity and cost of the control system, and having a good prospect in practical applications.

Description of drawings

FIG. 1 is a schematic diagram of the topology of the DFIG-DC system of the present invention.

Fig. 2 is a control block diagram of the stator current sinusoidal control method of the present invention.

Fig. 3 is a block diagram of the control structure of the stator flux linkage phase-locked loop of the present invention.

Fig. 4 is a structural block diagram of the rotor harmonic voltage generator of the present invention.

Fig. 5 is a schematic diagram of waveforms before and after stator current optimization of the DFIG-DC system of the present invention.

Detailed ways

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

As shown in Figure 1, the present invention is based on DFIG's DC grid-connected topology, including DFIG and DC grid, wherein the stator side of DFIG is connected to the DC grid through an uncontrolled rectification bridge, and the rotor is connected to the DC grid through the rotor converter. By controlling the rotor The converter generates a stable stator voltage to turn on the diode, and the uncontrolled rectifier bridge on the stator side converts the alternating current into direct current and inputs it to the direct current grid.

The controller is constructed by current sensors, encoders, drive circuits and DSP; among them, the current sensors are used to collect the three-phase stator current I _sa ~ I _sc and the three-phase rotor current I _ra ~ I _rc ; the encoder is used to detect the rotor current of DFIG The position angle obtains the rotational speed ω _r of DFIG, and the current sensor and encoder transmit the collected signals to the DSP after signal conditioning and analog-to-digital conversion. The DSP constructs a PWM signal through the corresponding control algorithm based on these signals and then amplifies the power of the drive circuit. Finally, the switching control of the IGBT in the rotor converter is carried out.

As shown in Figure 2, the stator current sinusoidal control method of the DFIG-DC system of the present invention includes the following steps:

(1) Use the current Hall sensor to collect the three-phase stator current signal I _sabc and the three-phase rotor current signal I _rabc , and use the encoder to detect the rotor position θ _r of DFIG, and then calculate the speed ω _r through the differentiator;

(2) Using the stator flux phase-locked loop to estimate the current stator flux angle θ _s , as shown in Figure 3, the specific calculation expression is as follows:

θ_s＝∫ω_s ψ _sq ＝L _s I _sq +L _m I _rq

θ _s = ∫ω _s

Where: ψ _sq is the q-axis component of the stator flux linkage, ω _s is the stator frequency, L _s is the stator inductance, L _m is the stator-rotor mutual inductance, K _ps and K _is the ratio and integral of the stator flux phase-locked loop, respectively Coefficient, s is the Laplacian operator.

Then, subtract the rotor position angle θ _r from the stator flux angle θ _s to obtain the slip angle θ _slip , and then use the slip angle θ _slip to perform coordinate transformation on the three-phase rotor current I _rabc to obtain the rotor current in the synchronous rotating coordinate system The d-axis component I _rd and the q-axis component I _rq , the specific transformation expressions are as follows:

θ _slip = θ _s - θ _r

(3) The stator frequency reference value is the rated frequency of the stator, and the stator frequency error is obtained through PI to obtain the rotor d-axis current reference value I _rdref , the specific calculation expression is as follows:

Among them: K _pf and K _if are the proportional and integral coefficients of the stator frequency control outer loop respectively, and ω _ref is the reference value of the stator frequency.

(4) The rotor d-axis current is the excitation current, the rotor q-axis current is the active current, and the rotor dq-axis current error is obtained by the PI regulator to obtain the average component of the rotor d-axis voltage U _{d_PI} and the average component of the q-axis voltage U _{q_PI} , the specific calculation expression as follows:

Among them: I _rdref is the rotor d-axis current reference value generated by the frequency outer loop, I _rqref is the given rotor q-axis current reference value, K _pi and K _ii are the given proportional coefficient and integral coefficient respectively.

(5) Calculate the rotor d-axis voltage compensation ΔU _dr and the rotor q-axis voltage compensation ΔU _qr according to the rotor dq-axis current and slip angular frequency. The specific calculation expressions are as follows:

ΔU _dr ＝-ω _slip σL _r I _rq

ΔU _qr = ω _slip σL _r I _rd

Among them: σ is the flux leakage coefficient, L _r is the rotor inductance, ω _slip = ω _s - ω _r is the slip speed.

(6) According to the relationship between the stator current and the stator voltage, the stator current is used to represent the stator voltage U _sabc , and the specific expression is as follows:

After the three-phase stator voltage U _{sabc is obtained, the three-phase stator harmonic voltage U sabch is} obtained through a 50Hz notch filter, and the three-phase stator harmonic voltage U _sabch is transformed by Park to obtain the dq vector U _sdqh of the stator harmonic voltage; and then the stator harmonic The dq vector U _sdqh of the wave voltage is obtained through the rotor harmonic voltage generator shown in Figure 4. The dq vector U _rdqh of the rotor harmonic voltage is obtained, and the specific calculation formula is as follows:

(7) Add the d-axis voltage average component U _{d_PI} of the rotor to the d-axis voltage compensation ΔU _dr and the rotor harmonic voltage d-axis component U _rdh to obtain the rotor d-axis voltage modulation signal V _dr , and the rotor q-axis voltage average component U _{q_} PI plus the q-axis voltage compensation ΔU _qr and the rotor harmonic voltage q-axis component U _rqh to obtain the rotor q-axis voltage modulation signal V _qr ; and then make the rotor voltage modulation signal through V _dr and V _qr to obtain a set of PWM through SVPWM technology construction signal to control the rotor converter.

As shown in Figure 5, the rotor harmonic voltage compensation is not used between 0.4 and 0.5s, the stator current has a high harmonic current, and the sine degree is very poor; after adding the rotor harmonic voltage compensation at 0.5s, the stator current The harmonic current of the motor is suppressed very well, and the sine degree of the stator current is greatly improved. It can be seen that the control method of the present invention can achieve a very good sine degree of the stator current, and has very good practical value in this DFIG-DC topology.

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above-mentioned embodiments, and apply the general principles described here to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention should fall within the protection scope of the present invention.

Claims (6)

1. a kind of stator current sine control method of DFIG-DC system, includes the following steps:

(1) the threephase stator electric current I of DFIG is acquired_sabcWith three-phase rotor current I_rabc, while turning for DFIG is detected using code-disc Fast ω_rWith rotor position angle θ_r；

(2) the stator magnet chain angle θ at current time is estimated using stator magnetic linkage phaselocked loop_s, make stator magnet chain angle θ_sSubtract rotor position Angle setting θ_rObtain slip angle θ_slip, and then utilize slip angle θ_slipTo three-phase rotor current I_rabcIt is coordinately transformed, is synchronized The d axis component I of rotating coordinate system lower rotor part electric current_rdWith q axis component I_rq；

(3) by stator frequency reference value ω_refIt is set as the rated frequency of stator, and then controls stator frequency error by PI Obtain rotor current d axis reference value I_rdref；

(4) according to the d axis component I of rotor current_rdWith q axis component I_rqAnd rotor current d axis reference value I_rdrefTurn with given Electron current q axis reference value I_rqref, so that rotor current dq axis error is passed through PI respectively and control to obtain the d axis average weight of rotor voltage U_{d_PI}With q axis average weight U_{q_PI}；

(5) according to the d axis component I of rotor current_rdWith q axis component I_rqCalculate the d axis compensation rate Δ U of rotor voltage_drWith q axis Compensation rate Δ U_qr；

(6) according to threephase stator electric current I_sabcDetermine the threephase stator voltage U of DFIG_sabc, make the threephase stator voltage U_sabcIt is logical The trapper for crossing 50Hz obtains threephase stator harmonic voltage U_sabch, and then utilize stator magnet chain angle θ_sTo threephase stator harmonic voltage U_sabchIt is coordinately transformed, obtains the d axis component U of stator harmonic voltage under synchronous rotating frame_sdhWith q axis component U_sqh；

(7) according to the d axis component U of stator harmonic voltage_sdhWith q axis component U_sqhRotor is obtained by rotor harmonic voltage generator The d axis component U of harmonic voltage_rdhWith q axis component U_rqh, specific calculation expression is as follows:

Wherein: L_rAnd L_mThe respectively inductor rotor of DFIG and rotor mutual inductance, ω_slipFor slip speed and ω_slip=ω_s- ω_r, ω_sFor the stator frequency at current time, s is Laplace operator；

(8) make U_{d_PI}+ΔU_dr+U_rdhObtain rotor voltage d axis modulated signal V_dr, make U_{q_PI}+ΔU_qr+U_rqhObtain rotor voltage q Axis modulated signal V_qr, it is based on V_drAnd V_qrOne group of pwm signal is obtained by SVPWM technical construction with the rotor current transformer to DFIG It is controlled.

2. stator current sine control method according to claim 1, it is characterised in that: utilized in the step (2) Stator magnetic linkage phaselocked loop estimates the stator magnet chain angle θ at current time_s, specific algorithm is as follows:

ψ_sq'=L_sI_sq'+L_mI_rq'

θ_s=∫ ω_s'

Wherein: L_sAnd L_mThe respectively stator inductance of DFIG and rotor mutual inductance, K_psAnd K_isRespectively stator magnetic linkage phaselocked loop Proportionality coefficient and integral coefficient, ψ_sq' be last moment stator magnetic linkage q axis component, ω_s' be last moment stator frequency, s For Laplace operator, I_rq' and I_sq' be respectively last moment rotor current q axis component and stator current q axis component.

3. stator current sine control method according to claim 1, it is characterised in that: pass through in the step (3) Following formula makes stator frequency error control to obtain rotor current d axis reference value I by PI_rdref:

Wherein: K_pfAnd K_ifThe respectively proportionality coefficient and integral coefficient of stator frequency control outer ring, ω_sFor the stator at current time Frequency, s are Laplace operator.

4. stator current sine control method according to claim 1, it is characterised in that: pass through in the step (4) Following formula makes rotor current dq axis error pass through PI respectively to control to obtain the d axis average weight U of rotor voltage_{d_PI}It is flat with q axis Divided dose U_{q_PI}:

Wherein: K_piAnd K_iiRespectively given proportionality coefficient and integral coefficient, s is Laplace operator.

5. stator current sine control method according to claim 1, it is characterised in that: pass through in the step (5) Following formula calculates the d axis compensation rate Δ U of rotor voltage_drWith q axis compensation rate Δ U_qr:

ΔU_dr=-ω_slipσL_rI_rq

ΔU_qr=ω_slipσL_rI_rd

Wherein: ω_slipFor slip speed and ω_slip=ω_s-ω_r, ω_sFor the stator frequency at current time, σ is the leakage field of DFIG Coefficient, L_rFor the inductor rotor of DFIG.

6. stator current sine control method according to claim 1, it is characterised in that: pass through in the step (6) Following formula determines the threephase stator voltage U of DFIG_sabc:

Wherein: U_sa、U_sbAnd U_scRespectively correspond the A phase for DFIG, B phase and C phase stator voltage, I_sa、I_sbAnd I_scRespectively correspond for A phase, B phase and the C phase stator current of DFIG, U_dcFor the DC bus-bar voltage of DFIG-DC system.

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