CN109412478B - Power droop control method of brushless doubly-fed motor - Google Patents

Power droop control method of brushless doubly-fed motor Download PDF

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CN109412478B
CN109412478B CN201811104778.1A CN201811104778A CN109412478B CN 109412478 B CN109412478 B CN 109412478B CN 201811104778 A CN201811104778 A CN 201811104778A CN 109412478 B CN109412478 B CN 109412478B
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CN109412478A (en
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陈宇
张德斌
苏靖媛
康勇
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/007—Control circuits for doubly fed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control

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Abstract

The invention belongs to the technical field of motor control, and discloses a grid-connected instantaneous power droop control method of a brushless double-fed motor, which can ensure that seamless switching of a power generation system from an independent operation mode to a grid-connected operation mode can be completed under any load working condition. The method is based on a brushless double-fed motor equivalent circuit model under control winding current orientation, each electric quantity information in the motor at the switching moment is sampled in real time, a droop coefficient is accurately designed according to the relation between active and reactive power and instantaneous impact current at the switching moment of an independent/grid-connected double mode, the sampled impact current and the droop coefficient are multiplied and then superposed on the control winding voltage of the brushless double-fed motor, so that the switching moment impact from independent operation to a grid-connected operation mode is reduced, and the safety and the stability of the system are improved.

Description

Power droop control method of brushless doubly-fed motor
Technical Field
The invention belongs to the technical field of motor control, and particularly relates to a power droop control method of a brushless double-fed motor.
Background
A brushless doubly-fed motor (BDFM) can realize variable-speed constant-frequency power generation only by rotating difference times of power capacity of a required frequency converter, and meanwhile, an electric brush and a slip ring are eliminated by adopting a special structural design, so that the operation reliability of the motor is improved, the maintenance and operation cost is reduced, and the BDFM has a wide application prospect in a power generation system.
In power generation applications, particularly in micro-grid applications such as wind power generation and ship shaft power generation, in order to improve power supply reliability, uninterrupted power supply to critical loads needs to be ensured, and a brushless double-fed motor simultaneously has the capabilities of carrying loads independently, carrying loads together with a power grid, and transferring loads to the power grid, so that a power generation system with independent/grid-connected dual-mode operation capability currently becomes a research hotspot. In the dual-mode power generation system, the control targets of independent and grid-connected operation are generally the amplitude and frequency of output voltage and active and reactive power respectively, so that different control systems are adopted under two working conditions according to different control targets. When the working condition changes and the system needs to be switched from independent operation to grid-connected operation, the instantaneous fluctuation of grid connection can seriously affect the voltage amplitude and frequency of a power grid, particularly a weak power grid, and even lead to grid connection failure and damage of system equipment. Therefore, in order to improve the overall reliability of the power generation system, the seamless switching control technology needs to be introduced into the power generation system at the moment of grid connection so as to reduce grid connection impact current and ensure the safety of the system.
At present, the seamless switching control technology at the moment of grid connection of a power generation system can be divided into several methods based on the characteristics of grid connection instant voltage difference, indirect current, direct torque control or power droop and the like.
For example, in a chinese patent application entitled "a grid-connected/off-grid seamless switching method for a microgrid converter", publication No. CN104319815A, published as 2015, 1, month, and 28, a strategy for implementing seamless switching based on a difference between a load voltage at an inverter switching time and a grid voltage expected value is proposed, seamless switching between grid-connected and off-grid is implemented according to a comparison result of a voltage difference in each switching period, and stability of an important load voltage is maintained.
For example, in the literature entitled "inductive Current controlled Based sensor Transfer of three-phase inverter in Distributed Generation", author z.liu, IEEE Transactions on power electronics 29(7), 2014: 3368-.
For example, a control strategy for realizing seamless switching of an independent/grid-connected mode based on Direct Torque Control (DTC) is proposed in a document named as a New smoothening Synchronization of Brushless double-Fed inductive generating and applying a position Machine Model, author r.sadghi, IEEETransactions on stable Energy 9(1), 2018: 371-.
At present, relevant researches on a droop control seamless switching technology are provided at home and abroad aiming at an inverter, a synchronous motor, a brush double-fed motor and the like, for example, a Chinese patent application named as 'a photovoltaic microgrid system grid-off/grid-connected control method based on inverse droop control', with a publication number of CN107257140A, published 2017, 10 and 17 is provided, and a current type controller is adopted aiming at a grid-connected inverter in a grid-off and grid-connected state for realizing seamless switching of the inverter from grid connection, so that grid-connected current impact is well reduced; the Chinese patent application entitled "improved droop control method for grid-side converter of permanent magnet synchronous generator set", publication No. CN105226720A, 2016, 1, 06, proposes a seamless switching strategy based on dynamically adjusting droop characteristic curve by calculating output active and reactive power and voltage change of direct current bus aiming at a synchronous motor, and can also realize grid-connection no-impact current switching; the Chinese patent application entitled 'control method and system of double-fed wind generating set', publication No. CN104201711B, 2016, 4, 20, provides power droop control based on different control quantities to obtain different regulating quantities for the double-fed wind generating set; the document entitled Analysis and observations of implementation Droop Control in DFIG-Based WindTimbines on Microgrid/Weak-Grid Stability, Author F.M. Mohammadrza, Exit IEEETransaction on Power Systems 30(1), 2015: 385-.
For the seamless switching of other three control strategies based on the power droop characteristic, the characteristics of a power generation system and power grid parameters are fully combined, the adaptability is high, the power sharing is ensured, the high-performance control can be realized, and the transient impact and oscillation phenomena during grid-connected switching are greatly improved, so that the method is widely applied. However, for the brushless double-fed motor and the power generation system thereof, no research has been made on a seamless switching strategy of the brushless double-fed motor based on the power droop characteristic; the brushless double-fed motor has larger differences with an inverter and a synchronous motor in structure, characteristics and models, and the physical characteristics and the mathematical model of the brushless double-fed motor are more complex than those of the brushless double-fed motor due to the special structure; with the improvement of the requirements of the power generation system, seamless switching under various operating conditions needs to be ensured, so that the existing method for seamless switching of the droop characteristics of the inverter and other motors is difficult to follow.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a brushless double-fed motor grid-connected instant seamless switching technology, and aims to solve the problem that the impact current is overlarge due to various non-ideal characteristics at the grid-connected instant.
In order to achieve the purpose, the invention provides a method for stably sampling each electric quantity of a system in amplitude following and phase locking stages before grid connection of a brushless double-fed motor under various working conditions, and calculating the electric quantity to obtain a droop control parameter to carry out grid connection instant droop control on the system.
The invention provides a power droop control method of a brushless doubly-fed motor, which comprises the following steps:
(1) series-parallel conversion of internal resistance and inductance of motor is carried out based on equivalent circuit of brushless doubly-fed motor, and simplified current equivalent resistance Z is obtained4；
(2) Detecting three-phase current of the control winding and carrying out ABC/dq coordinate conversion on the three-phase current to obtain a d-axis component i of the current of the control windingcdAnd q-axis component icq；
Detecting three-phase current of the power winding and carrying out ABC/dq coordinate conversion on the three-phase current to obtain a d-axis component i of the current of the power windingpdAnd q-axis component ipq；
Detecting three-phase line voltage of the power winding, converting the three-phase line voltage into phase voltage, and performing ABC/dq coordinate conversion on the phase voltage to obtain a d-axis component u of the voltage of the power windingpdAnd q-axis component upq；
(3) D-axis component i of power winding currentpdAnd q-axis component ipqAnd d-axis component u of power winding voltagepdAnd q-axis component upqConversion to control winding current orientation icqD-axis component of power winding voltage in 0 coordinate system
Figure GDA0002569036380000041
Component of q axis
Figure GDA0002569036380000042
And d-axis component of power winding current
Figure GDA0002569036380000043
Component of q axis
Figure GDA0002569036380000044
(4) Control winding voltage and control winding current coordinate system angle in brushless double-fed motor after control winding current orientation
Figure GDA0002569036380000045
The angles of the power winding voltage and the control winding current coordinate system and the electric quantity value in the step (3) obtain output active power P and reactive power Q;
and obtaining the steady state active power P when the steady state working point of the system is before grid connection according to the output active power P and the reactive power Q*Reactive power Q*；
(5) According to the steady state active power P*Reactive power Q*Obtaining output voltage before and after grid connection of the system and grid voltage phase deviation to obtain grid connection instant steady state power fluctuation delta P, delta Q and control winding voltage fluctuation delta ucd、ΔucqAnd obtaining a droop control coefficient Gd_q、Gq_q、Gq_dAnd the output delta u of the droop control link "cd、Δu”cq；
(6) According to the droop control coefficient Gd_q、Gq_q、Gq_dAnd the output delta u of the droop control link "cd、Δu”cqObtaining three-phase reference values of control winding voltage
Figure GDA0002569036380000046
And according to
Figure GDA0002569036380000047
Realize controlD, q axis component i of winding currentcd、icqFor control winding current d-axis reference value
Figure GDA0002569036380000048
And q-axis reference value
Figure GDA0002569036380000049
Closed loop tracking of (1).
Further, the step (2) includes the steps of,
(21) the mechanical angular speed omega of the motor rotor is obtained by mounting a code disc on the rotorm；
(22) According to the number of pole pairs p of the power windingpControl the number p of pole pairs of the windingcCurrent angular frequency of 100 pi rad/s of power winding and mechanical angular speed omega of rotormObtaining angular velocity ω of control windingc：
(23) Will control the winding current angular frequency omegacInputting an integral link to obtain an angle theta required by converting the control winding current to a unified reference dq coordinate systemcAnd is recorded as the control winding angle;
(24) detecting three-phase current i of control windingca、icb、iccAnd by thetacAs a coordinate transformation angle, converting the control winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a control winding current dq component icd、icq：
(25) According to the control winding angle theta in the step (23)cRotor position angle thetarObtaining a transformation angle θ for transforming power winding current from a stationary ABC coordinate to a unified reference dq coordinate systemp；
(26) Detecting three-phase current i of power windingpa、ipb、ipcAnd by thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a power winding current dq axis component ipd、ipq：
(27) Three-phase line voltage u of power winding to be detectedpab、upbc、upcaConverted into phase voltage upa、upb、upcAnd is given by thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a power winding voltage dq axis component upd、upq。
Further, the steady state active power P and the steady state reactive power Q are respectively:
Figure GDA0002569036380000051
wherein, P and Q are respectively steady-state active power and steady-state reactive power before the grid connection of the system; u. ofpIs a power winding voltage vector; u'cFor controlling the winding voltage vector, sp、scThe slip frequency of the power side and the control side are respectively; is the power winding voltage and control winding current coordinate system angle,
Figure GDA0002569036380000052
the control winding voltage and the control winding current coordinate system angle.
Further, the step (5) is specifically:
(51) in order to enable a system to realize linearization processing, the system power variation is expressed into a small signal form at the grid connection moment, and the output power fluctuates due to the error between the system output voltage and the grid voltage, the specific expression is as follows:
Figure GDA0002569036380000061
(52) subtracting the steady-state power formula in the step (4) from the formula in the step (51), eliminating steady-state quantity, and expressing power fluctuation as an output voltage and output current form, wherein the output voltage of the system is clamped to the voltage of a power grid after grid connection, and the droop control link output at the grid connection time is comprehensively obtained by:
Figure GDA0002569036380000062
wherein G isd_q、Gq_q、Gq_dIn order to control the droop control coefficient,
Figure GDA0002569036380000063
respectively outputting a d-axis fluctuation quantity and a q-axis fluctuation quantity of current for a control winding coordinate system;
(53) obtaining mechanical angular speed omega of motor rotor by mounting code disc on rotorm；
(54) Sampling the voltage frequency of the power winding in real time and obtaining the current angular frequency omega of the power windingp；
(55) According to the number of pole pairs p of the power windingpControl the number p of pole pairs of the windingcAngular frequency omega of the current of the power windingpAnd rotor mechanical angular velocity omegamObtaining angular velocity ω of control windingc；
(56) According to the control winding current orientation icqD-axis component of power winding voltage in 0 coordinate system
Figure GDA0002569036380000064
Component of q axis
Figure GDA0002569036380000065
Calculating the tangent value between two components in real time
Figure GDA0002569036380000066
(57) Real-time sampling control winding coordinate system output current d-axis fluctuation quantity
Figure GDA0002569036380000067
And q-axis fluctuation amount
Figure GDA0002569036380000068
(58) According to the angular frequency omega of the current of the obtained power windingpControlling the angular velocity omega of the windingcAnd tangent tan*Obtaining a droop control coefficient Gd_q、Gq_q、Gq_d；
(59) According to the obtained droop control coefficient Gd_q、Gq_q、Gq_dControlling the d-axis fluctuation of the output current of the winding coordinate system
Figure GDA0002569036380000071
Amount of q-axis fluctuation
Figure GDA0002569036380000072
And (S52) calculating to obtain the output delta u of the droop control link "cd、Δu”cq。
Further, the droop control coefficient G of step (58)d_q、Gq_q、Gq_dRespectively as follows:
Figure GDA0002569036380000073
wherein p ispIs the number of pole pairs, p, of the power windingcFor controlling the number of winding pole pairs, omegapIs the angular frequency, omega, of the current of the power windingrIs the angular velocity, tan, of the rotor winding*For controlling winding current orientation icqTangent value of q-axis component and d-axis component of power winding voltage under 0 coordinate system, X4The equivalent inductive reactance of the brushless doubly-fed motor is obtained.
Further, the step (6) is specifically:
(61) setting q-axis PI controller proportionality coefficient KpqAnd integral coefficient KiqValue K ofpq＝Kpd，Kiq＝KidWhere the proportionality coefficient K of the d-axis PI controllerpdAnd integral coefficient KidObtaining according to experience;
(62) will control the winding current d-axis reference value
Figure GDA0002569036380000074
And control winding current d-axis component icdDifference of (2)
Figure GDA0002569036380000075
Input d-axisThe PI controller obtains output PI of the d-axis controllerd(ii) a Will control the q-axis reference value of the winding current
Figure GDA0002569036380000076
And control winding current q-axis component icqDifference of (2)
Figure GDA0002569036380000077
Obtaining an output PI of a q-axis controller by an input q-axis PI controllerq；
(63) Obtaining a system current inner ring specific expression according to a brushless doubly-fed motor internal dq mathematical model:
Figure GDA0002569036380000078
Figure GDA0002569036380000079
wherein R issc、LscSingle-phase resistance, inductance, K, of the control winding of the brushless dual-feed machine1、K2And K3Respectively equivalent parameters obtained after the series connection and the parallel connection of the motor inductors,
(64) utilizing the angular velocity omega of the winding current controlled in the step (5)cIntegral derived control winding angle thetacReference values of d and q axis components of the control winding voltage
Figure GDA0002569036380000081
Obtaining a three-phase reference value u of the control winding voltage after Park inverse transformationca *、ucb *、ucc *And sending the signal to a pulse width modulation module to obtain a switch driving signal of a machine side converter, and driving the converter by using the signal to output a corresponding control winding three-phase voltage uca、ucb、uccThe closed-loop control of the winding current of the brushless dual-feeder control is realized; wherein the reference value of the d-axis component of the winding voltage is controlled
Figure GDA0002569036380000082
D-axis output delta u' for droop control link "cdOutput PI with d-axis controllerdSum, reference value of q-axis component of control winding voltage
Figure GDA0002569036380000083
Q-axis output delta u' for droop control link "cqOutput PI with q-axis controllerqAnd (4) summing.
Further, three-phase reference value u of control winding voltageca *、ucb *、ucc *Comprises the following steps:
Figure GDA0002569036380000084
wherein the content of the first and second substances,
Figure GDA0002569036380000085
to control the d-axis component reference of the winding voltage,
Figure GDA0002569036380000086
to control the q-component reference value of the winding voltage, θcAnd (4) controlling the winding angle obtained in the step (6).
Compared with the prior art, the technical scheme of the invention has the advantages that the seamless switching of grid connection under various working conditions is realized without changing the original independent operation control structure, so that the beneficial effect of greatly reducing the instantaneous current impact of grid connection can be achieved. Meanwhile, the beneficial effect of greatly simplifying the control difficulty can be achieved due to the linear processing of the system power control; the nonlinear problem of the system grid-connected instant power control is solved.
Drawings
FIG. 1 is a schematic diagram of the independent/grid-connected operation of a brushless doubly-fed motor;
FIG. 2 is an equivalent circuit of a brushless doubly-fed motor; wherein, (a) is a complete equivalent circuit of a grid-connected system; (b) an equivalent circuit is simplified for a grid-connected system;
FIG. 3 is a schematic diagram of obtaining a control winding current dq component in a unified reference dq coordinate system; wherein, (a) is a rotating coordinate system for controlling the winding current dq; (b) three-phase ABC to two-phase dq conversion is performed for controlling winding current;
FIG. 4 is a schematic diagram of obtaining voltage and current dq components of a power winding in a unified reference dq coordinate system; wherein, (a) is a power winding current dq rotation coordinate system; (b) three-phase ABC to two-phase dq conversion is performed on the electric quantity of the power winding;
FIG. 5 is a graph of the coordinate relationship of the windings for controlling winding current orientation required by the present invention;
FIG. 6 is a circuit diagram of a steady-state operating point before grid connection of a system;
FIG. 7 is a diagram of a system grid-connected instantaneous droop control relationship;
FIG. 8 is a schematic block diagram of a control winding current closed loop control system required by the present invention;
FIG. 9 is a grid-connected instantaneous waveform of a droop-free control system;
FIG. 10 is a grid-connected instantaneous waveform of a droop control system;
fig. 11 shows the active and reactive jump waveforms of the steady-state operation of the system.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a droop control strategy for a brushless double-fed motor at the grid connection moment to realize seamless switching at the grid connection moment, thereby finishing safe and quick grid connection control, meeting the requirements of uninterrupted power supply pair of critical loads and the requirements of a future wind power system operating in an independent mode and a grid connection mode.
In order to ensure uninterrupted power supply to critical loads, realize seamless switching from independent operation to grid-connected operation of a brushless double-fed power generation system and reduce impact and influence on the system, the invention provides a grid-connected instantaneous droop control method which is simple to realize, has strong control structure universality, is suitable for various load-carrying working conditions and industrial application occasions and various brushless double-fed motor types and fully utilizes the advantage of simplified design of the control winding current orientation commonly used in the existing brushless double-fed motor independent operation research, establishes a corresponding grid-connected instantaneous control system so as to reduce the switching instantaneous impact from the independent operation to the grid-connected operation mode and improve the system stability.
The droop control method is based on a brushless double-fed motor equivalent circuit model under the control winding current orientation, various electric quantity information inside a motor at the moment of switching is sampled in real time, a droop coefficient is accurately designed according to the relation between active and reactive power at the moment of switching in an independent/grid-connected mode and instantaneous impact current, the sampled impact current and the droop coefficient are multiplied and then superposed on the control winding voltage of the brushless double-fed motor, so that the droop control at the moment of grid-connected is realized, and the seamless switching of a power generation system from an independent operation mode to a grid-connected operation mode can be completed under any load working condition.
The method comprises the following specific steps:
(1) based on the equivalent circuit of the brushless doubly-fed motor shown in the diagram (a) in fig. 2, the series-parallel conversion of the internal resistance and inductance of the motor is performed to obtain a simplified circuit shown in the diagram (b) in fig. 2, and the simplified current equivalent resistance is as follows:
Figure GDA0002569036380000101
wherein r isp、r'r、r”cEquivalent resistances of a power winding, a rotor winding and a control winding are respectively; l ismp、L'σr、L”σcEquivalent inductances of a power winding, a rotor winding and a control winding are respectively; omegapIs the power winding angular frequency; sp、scThe slip frequencies of the power side and the control side are respectively;
therefore, the equivalent simplified circuit of the brushless double-fed grid-connected system can be obtained, and the simplified circuit can be represented as a connection form of a controlled voltage source and a constant voltage source through equivalent impedance;
(2) detecting three-phase currents of control windings, e.g. ica、icb、icc. According to the principle shown in FIG. 3, the winding is controlledConverting the current from a static three-phase ABC coordinate system to a unified reference dq coordinate system to obtain a d-axis component i of the control winding currentcdAnd q-axis component icq；
Detecting three-phase currents of power windings, e.g. ipa、ipb、ipc. According to the principle shown in FIG. 4, the power winding current is converted from a static ABC coordinate system to a reference dq coordinate system to obtain a d-axis component i of the power winding currentpdAnd q-axis component ipq；
Sensing three-phase line voltage of power winding, e.g. upab、upbc、upca. According to the principle shown in FIG. 4, the voltage of the power winding wire is converted into phase voltage, and then the d-axis component u of the voltage of the power winding is obtained by converting the phase voltage from a static ABC coordinate system into a unified reference dq coordinate systempdAnd q-axis component upq；
(3) D-axis component i of power winding currentpdAnd q-axis component ipqAnd d-axis component u of power winding voltagepdAnd q-axis component upqThe electric quantity is converted to the electric quantity under the control winding current directional coordinate system according to the electric quantity relation between the motors, which is shown in the principle of figure 5
Figure GDA0002569036380000111
(4) Based on the control winding current orientation, the angle of the control winding voltage in the brushless double-fed motor and the control winding current coordinate system is
Figure GDA0002569036380000112
The power winding voltage and the control winding current coordinate system have the angle, the relation is shown in fig. 6, the expression of output active power P and reactive power Q is deduced according to the equivalent circuit and the electric quantity value obtained in the step (3), and when the current inner loop and the current output outer loop track to a stable value due to the PI regulation function at the moment, the stable state working point before the grid connection of the system can be obtained through the expression;
(5) according to the steady-state active power P in the step (4)*Reactive power Q*Obtaining the phase deviation of the output voltage before and after the grid connection of the system and the voltage of the power grid to obtain the instantaneous steady-state power fluctuation delta P of the grid connection,Δ Q and control winding voltage fluctuation Δ ucd、ΔucqFurther deducing the relation between the grid-connected current and the grid-connected current fluctuation
Figure GDA0002569036380000113
And further neglecting the higher order term to obtain the output current fluctuation and the control winding voltage fluctuation Deltaucd、ΔucqThe droop coefficients are respectively G according to the relation expression of (1)d_q、Gq_q、Gq_dObtaining the output delta u of the droop control link "cd、Δu”cqAs shown in fig. 7;
(6) according to the principle shown in FIG. 8, a closed-loop control system for controlling the dq component of the winding current is constructed. Converting the electric quantity of the power side into a control winding coordinate system, and detecting the control winding current i obtained in the step (3)cd、icqWith corresponding closed-loop reference values
Figure GDA0002569036380000114
The error of (2) is inputted to a d-axis proportional-integral controller (PI controller); d. output PI of q-axis PI controllerd、PIqRespectively superposing output delta u of d-axis droop control link and q-axis droop control link "cd、Δu”cqTo obtain the reference value of the dq component of the control winding voltage
Figure GDA0002569036380000115
Obtaining a three-phase reference value of the control winding voltage through Park inverse transformation
Figure GDA0002569036380000116
Will be provided with
Figure GDA0002569036380000117
Inputting the pulse width modulation module to generate a driving signal of the machine side converter, and driving the machine side converter to generate the required three-phase voltage u of the control windingca、ucb、uccRealizing control of the winding current dq component icd、icqFor closed loop reference value
Figure GDA0002569036380000121
Closed loop tracking of (1); and meanwhile, the outer ring also adopts a PI controller to finish the quick control of the system.
The droop control method can complete seamless switching under two modes of system independent/grid-connected control, and the control performance of the system is improved.
The step (1) comprises the following steps, the principle of which is shown in fig. 2:
(11) according to the slip frequency of the circuit:
Figure GDA0002569036380000122
(12) the equivalent impedances of the control side, the rotor side and the power side obtained from the slip frequency are respectively as follows:
Figure GDA0002569036380000123
Figure GDA0002569036380000124
Zp＝rp+jωpLσp
(13) and connecting the equivalent circuit in series and parallel through impedance to obtain a grid-connected equivalent simplified model, wherein the series-parallel equivalence is as follows:
Figure GDA0002569036380000125
the step (2) comprises the following steps, the principle of which is shown in fig. 3:
(21) the mechanical angular speed omega of the motor rotor is obtained by mounting a code disc on the rotorm；
(22) The power winding voltage generated by the independent start of the brushless double-fed motor is constant at 50Hz, and the angular frequency omega ispConstant at a constant of 100 π rad/s. According to the operating characteristics of the brushless doubly-fed motor, the number p of pole pairs of the power winding is adjustedpControl the number p of pole pairs of the windingc"Gong" exerciseCurrent angular frequency of rate winding 100 pi rad/s, mechanical angular speed omega of rotormSubstituting formula (5) to obtain the angular frequency omega of the control winding currentc：
ωc＝(pp+pc)Ωm-100π……(5)
(23) Will omegacInputting an integral link to obtain an angle theta required by converting the control winding current to a unified reference dq coordinate systemcAnd is recorded as the control winding angle;
(24) detecting three-phase currents of control windings, e.g. ica、icb、icc(ii) a At thetacAs a coordinate transformation angle, converting the control winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a control winding current dq component icd、icq：
Figure GDA0002569036380000131
(25) Controlling the winding angle theta in the step (23)cRotor position angle thetarSubstituting equation (7) to obtain transformation angle theta for transforming power winding current from static ABC coordinate to unified reference dq coordinate systemp：θp＝(pp+pc)θr-θc……(7)
(26) Detecting three-phase currents of power windings, e.g. ipa、ipb、ipc(ii) a At thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a power winding current dq axis component ipd、ipq：
Figure GDA0002569036380000132
(27) Sensing three-phase line voltage of power winding, e.g. upab、upbc、upcaConvert it into phase voltage upa、upb、upc(ii) a At thetapAs coordinate transformation angles, by Park coordinate transformationConverting the current of the power winding from a static ABC coordinate to a unified reference dq coordinate system to obtain the voltage dq axis component u of the power windingpd、upq：
Figure GDA0002569036380000133
The step (3) includes the following steps, the principle of which is shown in fig. 5:
(31) by setting control winding current q-axis icqWhen the current of the control winding is equal to 0, the forced orientation is realized, and a reference coordinate system is determined;
(32) sensing three-phase line voltage of power winding, e.g. upab、upbc、upcaConvert it into phase voltage upa、upb、upcTaking the electric quantity of the power winding voltage two-phase static coordinate system
Figure GDA0002569036380000141
(33) Detecting three-phase currents of power windings, e.g. ipa、ipb、ipcTaking the electric quantity of the power winding current two-phase static coordinate system
Figure GDA0002569036380000142
(34) The relation of the electric quantity of the motor under a unified dq coordinate system of the brushless doubly-fed motor is obtained:
Figure GDA0002569036380000143
Figure GDA0002569036380000144
Figure GDA0002569036380000145
in the above formula Za、ZbRespectively, motor parameters, assumed to be known quantities.
(35) Due to the fact thatThe control winding current having been forced to orient, i.e. icqWhen the current amplitude of the control winding is measured, the angle of the power winding electric quantity transformed to the control winding current orientation coordinate system is obtained in a combined mode as follows:
Figure GDA0002569036380000146
in the above formula
Figure GDA0002569036380000147
(36) Substituting sine and cosine obtained in the step (35) into a d-axis component of the power winding voltage under the control winding current orientation obtained in the step (34)
Figure GDA0002569036380000148
Component of q axis
Figure GDA0002569036380000149
And d-axis component of power winding current
Figure GDA00025690363800001410
Component of q axis
Figure GDA00025690363800001411
The principle of the step (4) is shown in fig. 6:
(41) after the system adopts the orientation, the voltage vector of the control winding, the current of the control winding and the output voltage vector form a fixed angle. In order to continue to use the advantage of independent operation control winding current orientation, the whole grid-connected system still adopts a control winding current orientation control strategy, and the angle of a control winding voltage and control winding current coordinate system after orientation is
Figure GDA0002569036380000151
The power winding voltage and the control winding current coordinate system have the angle of;
(42) the brushless doubly-fed motor is in a steady state working condition, the integral impedance of the system becomes inductive, and Z in the step (13)4≈X4And simultaneously, according to the equivalent circuit diagram in the step (13), the active and reactive power steady-state working points P and Q are as follows:
Figure GDA0002569036380000152
wherein, P and Q are steady state active power and reactive power before the grid connection of the system respectively; u. ofpIs a power winding voltage vector; u'cFor controlling the winding voltage vector, sp、scThe slip frequency of the power side and the control side are respectively; a
Figure GDA0002569036380000153
In agreement with step (41).
The control winding current is directed downwards,
Figure GDA0002569036380000154
respectively are steady-state working points of the voltage d and q of the power winding;
Figure GDA0002569036380000155
respectively, the steady-state working points of the control winding voltage d and q, X4Is equivalent inductive reactance of brushless double-fed motor, sp、scAs can be obtained from step (11), the steady state power is further expressed as:
Figure GDA0002569036380000156
the step (5) includes the following steps, as shown in fig. 7:
(51) in order to enable a system to realize linearization processing, the system power variation is expressed into a small signal form at the grid connection moment, and the output power fluctuates due to the error between the system output voltage and the grid voltage, the specific expression is as follows:
Figure GDA0002569036380000161
(52) subtracting the formula (15) in the step (42) from the formula in the step (51), eliminating steady state quantity, and expressing power fluctuation as an output voltage and output current form, wherein the output voltage of the system is clamped to the voltage of a power grid after grid connection, and the droop control link output at the grid connection time is comprehensively obtained by arranging:
Figure GDA0002569036380000162
(53) the mechanical angular speed omega of the motor rotor is obtained by mounting a code disc on the rotorm；
(54) Sampling the voltage frequency of the power winding in real time to obtain the current angular frequency omega of the power windingp；
(55) According to the operating characteristics of the brushless doubly-fed motor, the number p of pole pairs of the power windingpControl the number p of pole pairs of the windingcAngular frequency omega of the current of the power windingpMechanical angular velocity omega of rotormTo obtain omegac；
(56) Orientation of current i according to control windingcqD-axis component of power winding voltage in 0 coordinate system
Figure GDA0002569036380000163
Component of q axis
Figure GDA0002569036380000164
Calculating in real time the tangent tan between the two components*：
Figure GDA0002569036380000165
(57) Real-time sampling control winding coordinate system output current d-axis fluctuation quantity
Figure GDA0002569036380000166
And q-axis fluctuation amount
Figure GDA0002569036380000167
(58) According to the angular frequency omega of the current of the obtained power windingpControlling the angular velocity omega of the windingcAnd tangent tan*Calculated droop controlCoefficient Gd_q、Gq_q、Gq_d；
Figure GDA0002569036380000168
(59) According to the obtained droop control coefficient Gd_q、Gq_q、Gq_dControlling the d-axis fluctuation of the output current of the winding coordinate system
Figure GDA0002569036380000171
Amount of q-axis fluctuation
Figure GDA0002569036380000172
And (S52) calculating to obtain the output delta u of the droop control link "cd、Δu”cq。
The step (6) comprises the following steps, as shown in fig. 8:
(61) setting the proportionality coefficient K of the d-axis PI controller according to design experiencepdAnd integral coefficient KidFor smaller value, q-axis PI controller proportionality coefficient KpqAnd integral coefficient KiqThe value is equal to the corresponding parameter of the d-axis controller according to the formula (17):
Kpq＝Kpd，Kiq＝Kid……(21)
(62) will control the winding current d-axis reference value
Figure GDA0002569036380000173
And control winding current d-axis component icdDifference of (2)
Figure GDA0002569036380000174
Inputting a d-axis PI controller, outputting PI by the d-axis controllerd(ii) a Will control the q-axis reference value of the winding current
Figure GDA0002569036380000175
And control winding current q-axis component icqDifference of (2)
Figure GDA0002569036380000176
Inputting a q-axis PI controller, wherein the output of the q-axis PI controller is PIq；
(63) Mathematical relation of formula (22) exists inside the mathematical model of the brushless doubly-fed machine, wherein Rsc、LscSingle-phase resistance, inductance, K, of the control winding of the brushless dual-feed machine1、K2And K3Respectively obtaining comprehensive parameters of the motor inductors through series-parallel connection:
Figure GDA0002569036380000177
therefore, on the basis that the control action of the arranged current inner ring PI controller is strong enough, the output of the current inner ring d axis and the output of the current inner ring q axis are superposed with the droop control quantity delta u'cd、Δu”cqI.e. d-axis reference value for the control winding voltage
Figure GDA0002569036380000178
And q-axis reference value
Figure GDA0002569036380000179
(64) Using the angular velocity ω of the control winding in step (5)cIntegral derived control winding angle thetacThe reference values of the d and q axis components of the winding voltage are controlled
Figure GDA00025690363800001710
Obtaining a three-phase reference value u of the control winding voltage through Park inverse transformationca *、ucb *、ucc *：
Figure GDA0002569036380000181
Will uca *、ucb *、ucc *Sending the signal into a pulse width modulation module to obtain a switch driving signal of a machine side converter, and driving the converter by using the signal to output a corresponding control winding three-phase voltage uca、ucb、uccAnd the closed-loop control of the control winding current of the brushless dual-feeder is realized.
Compared with the prior art, the grid-connected droop control method of the brushless double-fed motor power generation system has the following advantages:
(1) the method fully considers the operation condition of the brushless double-fed motor from no-load/loaded independent start operation to seamless switching to grid-connected condition, can effectively realize smooth grid connection under any load and any rotating speed, and reduces the influence of a grid-connected instant power generation system on a power grid;
(2) the method adopts control winding current orientation strategies for independent operation and grid-connected operation, the system has a uniform control framework, complex control algorithm switching during independent operation and grid-connected operation control is avoided, high adaptability is achieved, and control complexity is reduced;
(3) the grid-connected droop control method ingeniously utilizes system parameters and system steady-state electric quantity to control, only the original electric quantity of the system needs to be sampled to control, and therefore control cost is effectively reduced.
To further explain the power droop control method of the brushless doubly-fed machine provided by the embodiment of the present invention, the following detailed description is made with reference to specific examples:
the first embodiment is as follows:
the following takes a brushless doubly-fed machine with a 32kW wound rotor structure in a power generation mode as an example, and further details an implementation process of the present invention with reference to fig. 1 to 8.
The brushless doubly-fed machine is a nonlinear, strong-coupling and multivariable system, and in order to simplify analysis, only the action of the air gap fundamental wave magnetic field of the brushless doubly-fed machine is generally considered, and the following assumptions are made: (1) the influence of the tooth grooves of the stator and the rotor is not counted, the inner surface of the stator and the outer surface of the rotor are smooth, and the air gap is uniform; (2) the influences of ferromagnetic material saturation, magnetic hysteresis and eddy current are not counted, and parameters are linearized; (3) only the pole pair number P is considered in the magnetic field generated by the stator winding and the rotor windingpNumber of sum pole pairs PcThe effect of the fundamental wave ignores the influence of harmonic magnetic field.
When the brushless doubly-fed motor adopts a generator convention, a brushless doubly-fed motor mathematical model under a double synchronous rotation dq coordinate system can be obtained according to the coordinate transformation relation. Wherein the voltage equation is:
Figure GDA0002569036380000191
Figure GDA0002569036380000192
Figure GDA0002569036380000193
in the formula: u. ofpd、upq、ucd、ucqDq-axis voltage components of the power winding and the control winding respectively; i.e. ipd、ipq、icd、icq、ird、irqDq-axis current components of the power winding, the control winding and the rotor winding respectively; Ψpd、Ψpq、Ψcd、Ψcq、Ψrd、ΨrqDq-axis flux linkage components of the power winding, the control winding and the rotor winding respectively; rsp、Rsc、RrThe single-phase resistance values of the power winding, the control winding and the rotor winding are respectively; omegapThe angular frequency of the electric quantity of the power winding; omegamIs the mechanical angular frequency of the rotor; p is a radical ofp、pcThe pole pairs of the power winding and the control winding are respectively; s is the laplace operator.
The flux linkage equation is:
Figure GDA0002569036380000194
Figure GDA0002569036380000195
Figure GDA0002569036380000196
in the formula: l issp、Lsc、LrThe single-phase self-inductance values of the power winding, the control winding and the rotor winding are respectively; mpr、McrThe single-phase mutual inductance values of the power winding and the rotor winding and the single-phase mutual inductance values of the control winding and the rotor winding are respectively.
The electromagnetic torque equation is:
Figure GDA0002569036380000201
in the mathematical model of the double synchronous coordinate system, dq coordinate systems of the power winding, the control winding and the rotor winding are respectively represented by omegap、(pp+pc)Ωm﹣ωp、ωp﹣ppΩmIs rotated in space.
According to the mathematical model of the brushless doubly-fed motor, mathematical relations exist among all electric quantities. Under the simple closed-loop control of the control winding current, after independent no-load or on-load starting, the electric quantity steady-state value of the sampling system is utilized in the synchronous grid-connected stage, meanwhile, the rotating speed of the motor is sampled instantaneously, the droop coefficient of the motor is calculated, and the grid-connected instantaneous droop control of the brushless doubly-fed motor under the independent/grid-connected operation working condition is realized by combining simple mathematical calculation. The implementation process comprises the following steps:
an equivalent circuit diagram of a brushless doubly-fed motor power generation system is obtained according to the principle shown in FIG. 2.
(1) Converting the control winding and the rotor winding to the power winding side through the winding and simultaneously converting the electric quantity of the control winding and the electric quantity of the rotor winding from omegacAnd omegapConverting the obtained slip frequency to the power winding side through frequency conversion to obtain an equivalent mathematical model of the brushless doubly-fed motor, wherein the slip frequency is;
Figure GDA0002569036380000202
(2) and connecting the equivalent circuit in series and parallel through impedance to obtain a grid-connected equivalent simplified model, wherein the series-parallel equivalence is as follows:
Figure GDA0002569036380000203
Figure GDA0002569036380000204
Figure GDA0002569036380000205
Figure GDA0002569036380000211
in the above formula, the equivalent impedances at the control side, the rotor side and the power side are respectively:
Figure GDA0002569036380000212
Figure GDA0002569036380000213
Zp＝rp+jωpLσp
the control winding current dq component in the unified reference dq coordinate system is obtained as shown in principle in fig. 3.
(3) The mechanical angular speed omega of the motor rotor is obtained by mounting a code disc on the rotorm；
(4) According to the number of pole pairs p of the power windingpControl the number p of pole pairs of the windingcCurrent angular frequency of 100 pi rad/s of power winding and mechanical angular speed omega of rotormCalculating the angular frequency omega of the current of the control windingc：
ωc＝(pp+pc)Ωm-100π……(37)
(5) The calculated omegacInputting the integral link to obtain an angle thetacWherein s is the laplace operator:
Figure GDA0002569036380000214
(6) detection ofControlling three phase currents of windings, e.g. ica、icb、iccAt θcConverting the control winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate conversion as a coordinate conversion angle to obtain icd、icq：
Figure GDA0002569036380000215
According to the principle shown in FIG. 4, the voltage and current dq components of the power winding under the unified reference dq coordinate system are obtained.
(7) Mounting code disc on brushless double-fed motor rotor to obtain rotor position angle thetar；
(8) Combined power winding pole pair number ppControl the number p of pole pairs of the windingcIn the step (1), thetacRotor position angle thetarCalculating to obtain the angle thetap：θp＝(pp+pc)θr-θc……(40)
(9) Sensing three-phase line voltage of power winding, e.g. upab、upbc、upcaConverting it into a phase voltage upa、upb、upc(ii) a At thetapAs a coordinate transformation angle, the power winding voltage is transformed from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a component upd、upq：
Figure GDA0002569036380000221
(10) Detecting three-phase currents of power windings, e.g. ipa、ipb、ipc(ii) a At thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a component ipd、ipq：
Figure GDA0002569036380000222
According to the illustration of fig. 5, the power winding voltage, current d, q quantities are obtained in the control winding current orientation.
(11) Sensing three-phase line voltage of power winding, e.g. upab、upbc、upcaConvert it into phase voltage upa、upb、upcTaking the electric quantity of the two-phase static coordinate system
Figure GDA0002569036380000223
(12) Detecting three-phase currents of power windings, e.g. ipa、ipb、ipcTaking the electric quantity of the two-phase static coordinate system
Figure GDA0002569036380000224
(13) And obtaining the relation of the electric quantity of the motor under the unified dq coordinate system:
Figure GDA0002569036380000225
Figure GDA0002569036380000226
Figure GDA0002569036380000227
in the above formula Za、ZbRespectively, motor parameters, assumed to be known quantities.
(14) Since the control winding current has been forced to orient, i.e. icqWhen the current amplitude of the control winding is measured, the angle of the power winding electric quantity transformed to the control winding current orientation coordinate system is obtained in a combined mode as follows:
Figure GDA0002569036380000231
in the above formula
Figure GDA0002569036380000232
(15) Substituting the sine and cosine obtained in the step (14) into the formulas (44) and (45) to obtain the values of the voltage and the current d and the q of the power winding under the control winding current orientation
Figure GDA0002569036380000233
According to the figure 7, a control winding current closed-loop control system required by a brushless doubly-fed motor power generation system is built.
(16) Setting the proportionality coefficient K of the d-axis PI controller and the q-axis PI controller according to design experiencepd、KpqAnd integral coefficient Kid、KiqRespectively as follows: kpq＝Kpd＝3,Kiq＝Kid＝75……(48)
(17) The d-axis component i of the winding current will be controlledcdAnd a reference value
Figure GDA0002569036380000234
Comparing to obtain a difference value
Figure GDA0002569036380000235
Figure GDA0002569036380000236
And input into a d-axis PI controller to obtain an output PI of the d-axis PI controllerd：
Figure GDA0002569036380000237
The q-axis component i of the winding current will be controlledcqAnd a reference value
Figure GDA0002569036380000238
Comparing to obtain a difference value
Figure GDA0002569036380000239
And input into q-axis PI controller to obtain q-axis PI controller output PIq：
Figure GDA00025690363800002310
(18)Gd_q、Gq_qAnd Gq_dSampling to obtain the rotation speed, the d and q values of the power winding voltage and the fluctuation amount of the instantaneous output current for the droop coefficient
Figure GDA00025690363800002311
D-axis feedforward quantity delta u is obtained through calculation "cdAnd q-axis feedforward amount
Figure GDA00025690363800002312
(19) Separately superposed PId、PIqAnd Δ u "cd、Δu”cqCalculating d and q axis reference values of the control winding voltage
Figure GDA0002569036380000241
Comprises the following steps:
Figure GDA0002569036380000242
(20) using thetacAnd inverse Park transformation, consisting of
Figure GDA0002569036380000243
Obtaining three-phase reference values u of control winding voltageca *、ucb *、ucc *：
Figure GDA0002569036380000244
Will uca *、ucb *、ucc *Sending the signal into an SVPWM module to obtain a switch driving signal of a machine side converter, and driving the converter by using the signal to obtain a corresponding control winding three-phase voltage uca、ucb、uccApplying the voltage to a control winding of the brushless doubly-fed motor to realize closed-loop control on the current of the control winding;
the droop control principle analysis was performed as shown in fig. 7.
(21) According to the steps, the system works in a closed-loop running state, the brushless double-fed motor is made to run under the working conditions of no load and 400r/min of rotating speed, before grid connection is independently started, and G is maded_q＝Gq_q＝G q_d0, the feedforward quantity Deltu "cd＝Δu”cq0. Setting a reference value for the q-axis component of the control winding current
Figure GDA0002569036380000245
Realizing the control of the current orientation of the winding; controlling winding current d-axis component reference
Figure GDA0002569036380000246
And is output by the voltage amplitude PI regulator. And (3) obtaining the tangent values of the components d and q of the power winding voltage d and q under the control winding current orientation according to the formula (55) of the steady-state values of the power winding voltage d and q obtained in the step (15):
Figure GDA0002569036380000247
(22) and (3) carrying coefficients obtained in the steps (1), (2) and (21) into a system grid-connected instant droop control parameter obtained in the step (56):
Figure GDA0002569036380000251
wherein, the brushless double-fed motor is under the steady state working condition, and the whole impedance of the system becomes inductive, X4≈Z4；
(23) And (3) carrying the coefficient obtained in the step (22) into a system grid-connected instantaneous droop controller obtained in the step (57):
Figure GDA0002569036380000252
(24) therefore, the control process of grid connection instant droop under the power generation operation of the brushless doubly-fed motor is completed, and the smooth grid connection of the system can be completed under various working conditions by adding the control.
The second embodiment is as follows:
the motor parameters and experimental waveforms of the present example are given below with reference to fig. 9 to 11. The present embodiment consists of a wound rotor brushless double-fed motor, a load, a power grid, a back-to-back power electronic converter and a controller using the method of the present invention.
When the brushless doubly-fed motor is operated at 400 rpm, the grid connection moment is controlled by the droop control method.
Fig. 9 shows the grid-connected waveform after no-load starting and amplitude and phase locking when the brushless double-fed motor has no droop control, and fig. 10 shows the grid-connected waveform after no-load starting and amplitude and phase locking when the brushless double-fed motor has feed-forward control, so that the output current fluctuation at the grid-connected moment is obviously reduced after the droop control is adopted at the grid-connected moment, the seamless switching from independent operation to grid-connected operation is well completed, and the impact on a power grid is greatly reduced;
as shown in fig. 11, after the brushless doubly-fed machine is in grid-connected operation, the power controls the active and reactive jump waveforms. The instantaneous droop of grid connection is cut off from the inside of a program after seamless switching to grid connection, the switching of the instantaneous droop control of grid connection only switches the instantaneous adjustment quantity of droop control, the grid connection power control still adopts a scheme of controlling the winding current orientation during independent operation, the integral control framework of the system is not changed, and the regulation of the active power and the reactive power of the system is not influenced.
In conclusion, the droop control method can ensure that the grid connection of the system does not generate grid connection impact at the moment of grid connection under any load and any rotating speed, effectively improves the safety and the stability of the system, realizes the seamless switching of the independent and grid connection operation of the system, simultaneously controls the winding current to be oriented, does not generate any influence on the power control, does not change the original control scheme, and has great flexibility and adaptability.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. A power droop control method of a brushless doubly-fed motor is characterized by comprising the following steps:
(1) series-parallel conversion of internal resistance and inductance of motor is carried out based on equivalent circuit of brushless doubly-fed motor, and equivalent resistance Z of simplified circuit is obtained4；
(2) Detecting three-phase current of the control winding and carrying out ABC/dq coordinate transformation on the three-phase current to obtain a d-axis component i of the current of the control windingcdAnd q-axis component icq；
Detecting three-phase current of the power winding and carrying out ABC/dq coordinate transformation on the three-phase current to obtain a d-axis component i of the current of the power windingpdAnd q-axis component ipq；
Detecting three-phase line voltage of the power winding, converting the three-phase line voltage into phase voltage, and carrying out ABC/dq coordinate transformation on the phase voltage to obtain a d-axis component u of the voltage of the power windingpdAnd q-axis component upq；
(3) D-axis component i of power winding currentpdAnd q-axis component ipqAnd d-axis component u of power winding voltagepdAnd q-axis component upqCurrent orientation i converted to control winding by motor internal relationcqD-axis component of power winding voltage in 0 coordinate system
Figure FDA0002569036370000011
Component of q axis
Figure FDA0002569036370000012
And d-axis component of power winding current
Figure FDA0002569036370000013
Component of q axis
Figure FDA0002569036370000014
(4) Control winding voltage and control winding current coordinate system angle in brushless double-fed motor after control winding current orientation
Figure FDA0002569036370000015
The angles of the power winding voltage and the control winding current coordinate system and the electric quantity value in the step (3) obtain output active power P and reactive power Q;
and obtaining the steady state active power P when the steady state working point of the system is before grid connection according to the output active power P and the reactive power Q*Reactive power Q*(ii) a The steady state active power P and the steady state reactive power Q are respectively as follows:
Figure FDA0002569036370000021
wherein, P and Q are respectively steady-state active power and steady-state reactive power before the grid connection of the system; u. ofpIs a power winding voltage vector; u'cFor controlling the winding voltage vector, sp、scThe slip frequency of the power side and the control side are respectively; is the power winding voltage and control winding current coordinate system angle,
Figure FDA0002569036370000022
the angle of a coordinate system for controlling winding voltage and winding current;
(5) according to the steady state active power P*Reactive power Q*Obtaining instantaneous steady-state power fluctuation delta P and delta Q of the system caused by deviation of output voltage and power grid voltage before and after grid connection, clamping the output voltage after grid connection by the power grid voltage, further deducing the voltage fluctuation delta u of the output voltage and a control winding caused by output current fluctuationcd、ΔucqAnd obtaining a droop control coefficient Gd_q、Gq_q、Gq_dAnd the output delta u of the droop control link "cd、Δu”cq(ii) a The method specifically comprises the following steps:
(51) in order to enable a system to realize linearization processing, the system power variation is expressed into a small signal form at the grid connection moment, and the output power fluctuates due to the error between the system output voltage and the grid voltage, the specific expression is as follows:
Figure FDA0002569036370000023
wherein the content of the first and second substances,
Figure FDA0002569036370000024
and
Figure FDA0002569036370000025
respectively, the steady-state working points, X, of the d-axis component and the q-axis component of the control winding voltage4Equivalent inductive reactance of a brushless double-fed motor;
(52) subtracting the steady-state power formula in the step (4) from the formula in the step (51), eliminating steady-state quantity, and expressing power fluctuation as a control winding voltage and output current form, wherein the output voltage of the system is clamped to the grid voltage after grid connection, and the droop control link output at the grid connection time is comprehensively obtained by arranging:
Figure FDA0002569036370000031
wherein G isd_q、Gq_q、Gq_dIn order to control the droop control coefficient,
Figure FDA0002569036370000032
respectively outputting a d-axis fluctuation quantity and a q-axis fluctuation quantity of current for a control winding coordinate system;
(53) obtaining mechanical angular speed omega of motor rotor by mounting code disc on rotorm；
(54) Sampling the voltage frequency of the power winding in real time and obtaining the current angular frequency omega of the power windingp；
(55) According to the number of pole pairs p of the power windingpControl the number p of pole pairs of the windingcAngular frequency omega of the current of the power windingpAnd rotor mechanical angular velocity omegamObtaining angular velocity ω of control windingc；
(56) According to the control winding current orientation icqD-axis component of power winding voltage in 0 coordinate system
Figure FDA0002569036370000033
Component of q axis
Figure FDA0002569036370000034
Calculating the tangent value between two components in real time
Figure FDA0002569036370000035
(57) Real-time sampling control winding coordinate system output current d-axis fluctuation quantity
Figure FDA0002569036370000036
And q-axis fluctuation amount
Figure FDA0002569036370000037
(58) According to the angular frequency omega of the current of the obtained power windingpControlling the angular velocity omega of the windingcAnd tangent tan*Obtaining a droop control coefficient Gd_q、Gq_q、Gq_d(ii) a The droop control coefficient Gd_q、Gq_q、Gq_dRespectively as follows:
Figure FDA0002569036370000038
wherein p ispIs the number of pole pairs, p, of the power windingcFor controlling the number of winding pole pairs, omegapIs the angular frequency, omega, of the current of the power windingrIs the angular velocity, tan, of the rotor winding*For controlling winding current orientation icqTangent value of q-axis component and d-axis component of power winding voltage under 0 coordinate system, X4Equivalent inductive reactance of a brushless double-fed motor;
(59) according to the obtained droop control coefficient Gd_q、Gq_q、Gq_dControlling the d-axis fluctuation of the output current of the winding coordinate system
Figure FDA0002569036370000041
Amount of q-axis fluctuation
Figure FDA0002569036370000042
And (52) calculating to obtain the output delta u of the droop control link "cd、Δu”cq；
(6) According to the droop control coefficient Gd_q、Gq_q、Gq_dAnd the output delta u of the droop control link "cd、Δu”cqObtaining three-phase reference values of control winding voltage
Figure FDA0002569036370000043
And according to
Figure FDA0002569036370000044
Realizing control of d and q axis components i of winding currentcd、icqFor control winding current d-axis reference value
Figure FDA0002569036370000045
And q-axis reference value
Figure FDA0002569036370000046
Closed loop tracking of (1).
2. The power droop control method of claim 1, wherein step (2) comprises the steps of,
(21) the mechanical angular speed omega of the motor rotor is obtained by mounting a code disc on the rotorm；
(22) According to the number of pole pairs p of the power windingpControl the number p of pole pairs of the windingcCurrent angular frequency of 100 pi rad/s of power winding and mechanical angular speed omega of rotormObtaining angular velocity omega of control winding currentc：
(23) Will control the winding angular velocity omegacAfter an integration link is input, the integration link is converted into a unified reference dq coordinate system by the required angle thetacAnd is recorded as the control winding angle;
(24) detecting three-phase current i of control windingca、icb、iccAnd by thetacAs a coordinate transformation angle, converting the control winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a d-axis component i of the control winding currentcdAnd q-axis component icq：
(25) According to the control winding angle theta in the step (23)cRotor position angle thetarObtaining a transformation angle θ for transforming power winding current from a stationary ABC coordinate to a unified reference dq coordinate systemp；
(26) Detecting three-phase current i of power windingpa、ipb、ipcAnd by thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a power winding current d-axis component ipdAnd q-axis component ipq；
(27) Three-phase line voltage u of power winding to be detectedpab、upbc、upcaConverted into phase voltage upa、upb、upcAnd is given by thetapAs a coordinate transformation angle, converting the power winding current from a static ABC coordinate to a unified reference dq coordinate system through Park coordinate transformation to obtain a power winding voltage d-axis component updAnd q-axis component upq。
3. The power droop control method according to any one of claims 1-2, wherein the step (6) is specifically:
(61) setting q-axis PI controller proportionality coefficient KpqAnd integral coefficient KiqValue K ofpq＝Kpd，Kiq＝KidWhere the proportionality coefficient K of the d-axis PI controllerpdAnd integral coefficient KidObtaining according to experience;
(62) will control the winding current d-axis reference value
Figure FDA0002569036370000051
And control winding current d-axis component icdDifference of (2)
Figure FDA0002569036370000052
Obtaining output PI of d-axis controller by input d-axis PI controllerd(ii) a Will control the q-axis reference value of the winding current
Figure FDA0002569036370000053
And control winding current q-axis component icqDifference of (2)
Figure FDA0002569036370000054
Obtaining an output PI of a q-axis controller by an input q-axis PI controllerq；
(63) Obtaining a system current inner ring specific expression according to a brushless doubly-fed motor internal dq mathematical model:
Figure FDA0002569036370000055
Figure FDA0002569036370000056
wherein R issc、LscSingle-phase resistance, inductance, K, of the control winding of the brushless dual-feed machine1、K2And K3Equivalent parameters obtained after series connection and parallel connection of the motor inductors are respectively obtained;
(64) using the angular velocity ω of the control winding in step (5)cIntegral derived control winding angle thetacReference values of d and q axis components of the control winding voltage
Figure FDA0002569036370000057
Obtaining a three-phase reference value u of the control winding voltage after Park inverse transformationca *、ucb *、ucc *And sending the signal to a pulse width modulation module to obtain a switch driving signal of a machine side converter, and driving the converter by using the signal to output a corresponding control winding three-phase voltage uca、ucb、uccControl winding of the brushless dual-feeder is realizedClosed loop control of the group current; wherein the reference value of the d-axis component of the winding voltage is controlled
Figure FDA0002569036370000058
D-axis output delta u' for droop control link "cdOutput PI with d-axis controllerdSum, reference value of q-axis component of control winding voltage
Figure FDA0002569036370000059
Q-axis output delta u' for droop control link "cqOutput PI with q-axis controllerqAnd (4) summing.
4. The power droop control method of claim 3, wherein the control winding voltage three-phase reference value uca *、ucb *、ucc *Comprises the following steps:
Figure FDA0002569036370000061
wherein the content of the first and second substances,
Figure FDA0002569036370000062
to control the d-axis component reference of the winding voltage,
Figure FDA0002569036370000063
to control the q-component reference value of the winding voltage, θcAnd (4) controlling the winding angle obtained in the step (6).
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