System and method for controlling direct power of open-winding brushless double-fed wind driven generator

[0044] The present invention will be described in detail below in conjunction with the drawings:

[0045] Such as figure 1 As shown, the present invention provides a direct power control system for a composite rotor open-winding brushless doubly-fed wind power generator, which mainly includes a wind turbine 1, a brushless doubly-fed wind power generator 2, a bidirectional PWM frequency converter, and a central processing unit; The wind turbine 1 is connected to the brushless doubly-fed wind generator 2 through the speed increase box. The brushless doubly-fed wind generator 2 is connected to the bidirectional PWM inverter on the one hand, and connected to the transformer 6 through the grid switch 5 on the other hand. The aspect is connected to the central processing unit through the voltage and current signal detection unit and the input unit in turn; the two-way PWM frequency converter is connected to the transformer 6 through the filter, and the transformer 6 is connected to the power grid 7.

[0046] The central processing unit is also connected with a central monitoring system and a man-machine interface.

[0047] The two-way PWM inverter adopts a double-ended power supply type cascaded multilevel topology structure. When the two-way PWM inverter adopts a double-ended power supply type cascade multilevel topology structure, the brushless doubly-fed generator controls both ends of the open winding of the winding Power is directly supplied by two multi-level inverters respectively, forming a cascaded topology.

[0048] The brushless doubly-fed wind generator 2 includes a stator 8, a rotor 9 and a rotating shaft 11. Two sets of windings with different numbers of poles are embedded on the stator, namely the power winding 3 and the control winding 4, the number of poles being 2 respectively. p p And 2 p c , The control winding end is designed as an open winding structure; the rotor adopts (2 p p +2 p c ) The pole-radial laminated magnetic barrier and short-circuit cage bar composite new type rotor structure, the rotor laminations are laminated in the radial direction; a steel sleeve 10 is installed between the rotating shaft and the rotor, and the steel sleeve passes through the positioning pin on the rotating shaft and the rotating shaft Fixed together.

[0049] The power winding is connected to the power frequency grid through the grid-connected switch 5 and the transformer 6 for electric energy output, and the control winding is connected to the bidirectional PWM inverter, and is connected to the grid through the bidirectional PWM inverter, filter and transformer for AC excitation.

[0050] The control winding has an open winding structure, that is, the control winding is not connected in a star or angle shape, and its 6 terminals are all opened and led out.

[0051] In addition, the present invention also provides a composite rotor open-winding brushless doubly-fed wind power generator. As described above, the generator includes a stator 8, a rotor 9 and a rotating shaft 11. Two sets of windings with different numbers of poles are embedded on the stator. , Namely power winding 3 and control winding 4, the number of poles is 2 respectively p p And 2 p c , The control winding end is designed as an open winding structure; the rotor adopts (2 p p +2 p c ) The pole-radial laminated magnetic barrier and short-circuit cage bar composite new type rotor structure, the rotor laminations are laminated in the radial direction; a steel sleeve 10 is installed between the rotating shaft and the rotor, and the steel sleeve passes through the positioning pin on the rotating shaft and the rotating shaft Fixed together. The power winding is connected to the power frequency grid through the grid-connected switch 5 and the transformer 6 for electrical energy output, the control winding is connected to a bidirectional PWM frequency converter, and connected to the grid through a bidirectional PWM frequency converter, filter and transformer for AC excitation, the control winding It is an open winding structure, that is, the control winding is not connected in a star or angle shape, and all 6 terminals are opened and led out.

[0052] Specifically: figure 1 It is a schematic diagram of the structure of the brushless doubly-fed wind power generation system of the present invention. The wind turbine 1 is connected to the brushless doubly-fed wind turbine 2 through a speed increase box to drive the generator 2 to rotate. The power winding 3 of the brushless doubly-fed wind generator 2 is connected to the grid 7 through the grid-connected switch 5 and the transformer 6 for electric energy output; the control winding 4 of the brushless doubly-fed wind generator 2 is through a bidirectional PWM inverter and filter And the transformer 6 is also connected to the grid 7 for AC excitation. The voltage and current signal detection device provides input for the central processing unit, which is connected with the central monitoring system and the man-machine interface, and provides signals for the drive circuit to drive the bidirectional PWM inverter.

[0053] figure 2 with image 3 They are two structural schematic diagrams of the open-winding brushless doubly-fed wind power generator of the present invention. A steel sleeve 10 made of a non-magnetic material is installed between the rotating shaft 11 and the rotor 9, a stator 8 is arranged outside the rotor 9, and an organic shell 12 is arranged outside the stator 8.

[0054] Two sets of independent symmetrical windings with 8 poles and 4 poles are embedded on the iron core of the stator 8, namely the power winding 3 and the control winding 4, both of which are double-layer short-distance windings, that is, four layers are embedded in a slot Windings, the power winding 3 is at the top, and the control winding 4 is at the bottom.

[0055] Rotor 9 adopts ( p p + p c ) A new composite rotor structure with pole-radial laminated magnetic barriers and short-circuit cage bars. The rotor laminations are laminated in the radial direction, which can reduce the eddy current loss in the rotor core and improve the efficiency of the generator; the rotor 9 has ( p p + p c ) Salient poles, one half of each of the two adjacent salient poles together form a lamination group, which is composed of ( p p + p c ) A completely identical lamination group. This symmetrical structure realizes that only one type of lamination can be assembled into the entire rotor, thus greatly reducing the process cost and facilitating mass production; the lamination group is provided with a magnetic conductive layer 13 At least three layers of uniform magnetic barrier layers 14 with the same width are left on two adjacent salient pole magnetic conductive layers 13, and the width ratio between each magnetic barrier layer 14 and the magnetic conductive layer 13 is the same. Connected by radial connecting ribs to connect the magnetically conductive layers 13 into a whole; the magnetic barrier layer 14 is filled with epoxy resin or other high-temperature resistant non-magnetic materials, and is designed to have a uniform width and is a plurality of magnetic barrier layers , Its purpose is to increase quadrature-axis magnetic resistance, reduce direct-axis magnetic resistance, and facilitate the flow of magnetic flux along the trend that is conducive to magnetic field conversion. After adding the magnetic barrier layer 14, its magnetic field conversion ability is significantly improved, and the number of magnetic barrier layers The more the number, the more obvious the effect, but when there are many magnetic barrier layers, the cost will increase again. Therefore, the magnetic barrier layer should be selected as the appropriate number of layers; the conductive cage bar 15 is placed at the center line of the salient pole, and the rotor is placed in a total of one week ( p p + p c ) The conductive cage bar 15 adopts a layered design, the purpose is to overcome the skin effect of the induced current; the two ends of the conductive cage bar 15 are compressed with a conductive ring to realize a short-circuit connection, and these conductive cage bars are short-circuited with the end The rings are collectively referred to as short-circuit cage bars. In this way, a composite rotor structure of radial laminated magnetic barrier and short-circuit cage bar is formed. This type of rotor can be divided into two types according to the shape of the magnetic barrier: U-shaped radial laminated magnetic barrier and short-circuit cage composite rotor ( figure 2 ) And arc-shaped radial laminated magnetic barrier and short-circuit cage composite rotor ( image 3 ).

[0056] Figure 4 It is a schematic diagram of the open winding structure of the control winding of the novel brushless doubly-fed wind generator of the present invention. The control winding 4 of the brushless doubly-fed generator is all opened, and no star or angle connection is made, that is, all 6 terminals of the control winding 4 of the generator are led out to form an open winding structure.

[0057] Figure 5 It is a schematic diagram of the control method of the direct power control system of the novel open-winding brushless doubly-fed wind generator of the present invention, where v Is the wind speed; n r Is the generator speed; P Is active power; Q Is reactive power; u Is the voltage; i Is the current; sector_ Ψ c Indicates the sector where the flux linkage of the control winding 4 is located; Δ represents the error value of the corresponding quantity; superscript * represents the given value of the corresponding quantity; subscript p with c Respectively indicate the corresponding quantities of power winding 3 and control winding 4; subscript ABC Indicates that the corresponding quantity is static in three phases ABC Axis component in the coordinate system; subscript dq Indicates that the corresponding quantity is stationary in two phases dq The axis component in the coordinate system.

[0058] The control winding 4 of the brushless doubly-fed generator is an open winding structure, and its 6 terminals are all opened and led out. Two multi-level inverters are respectively connected to the two ends of the winding and supply power to the control winding 4 to form a double-ended power supply. Cascaded multilevel inverter 16 topology.

[0059] The excitation control method of the system adopts the direct power control method to realize the maximum power tracking control. The control idea is based on the active power of the power winding 3 of the brushless doubly-fed generator P And reactive power Q The error signal Δ P And Δ Q And the sector information (sector_ Ψ c ) To reformulate the switching voltage vector selection table, and directly and independently control the active power of the brushless doubly-fed generator by appropriately selecting the switching voltage vector P And reactive power Q , And then realize the maximum power tracking control.

[0060] Establish the mechanical power balance equation of the brushless doubly-fed generator as follows

[0061] (1)

[0062] Where P m Is the total mechanical power; P pm with P cm Are the mechanical power of the power winding 3 and the control winding 4 respectively; T e Is electromagnetic torque; Ω r Is the mechanical angular velocity of the rotor 9,; ω p with ω c Are the current angular frequencies of the power winding 3 and the control winding 4 respectively; p r Is the number of pole pairs of the rotor 9.

[0063] Equation (1) gives the respective mechanical power components of power winding 3 and control winding 4, while the direct power control strategy only considers the active power component of power winding 3 P pm. When neglecting the copper loss and the rate of change of energy storage in the magnetic field, the instantaneous electrical power is similar to the mechanical power, namely P p ≈ P pm.

[0064] In order to obtain the electromagnetic torque equation of the brushless doubly-fed generator, an intermediate quantity is introduced here-the flux linkage vector of the power winding 3 through the control winding 4 Ψ pc. Image 6 Gives a static in two phases dq Two sets of stator winding flux vector in reference coordinate system Ψ p with Ψ c And flux vector Ψ pc The relationship between the rotation speed and position. It is worth noting that the flux linkage vector Ψ pc Is to control the angular frequency of the current on the 4 sides of the winding ω c The speed of rotation, with the control winding 4 flux Ψ c Relatively static, not at the 3 side angular frequency of the power winding that produced it ω p This frequency change is caused by the modulation effect of the rotor 9 on the stator magnetomotive force waveform, which is also the basic mechanism of magnetic field coupling and torque generation in the brushless doubly-fed generator. Therefore, the electromagnetic torque equation of the brushless doubly-fed generator can be expressed as:

[0065] (2)

[0066] Where Is the magnetic flux leakage coefficient; L p with L c Are the self-inductance of the power winding 3 and the control winding 4 respectively; M pc Is the mutual inductance between two sets of stator windings; δ Is the flux vector Ψ pc versus Ψ c The angle between. From this we can see the connection between the brushless doubly-fed generator and the ordinary induction generator. Although their operating principles are different, from the perspective of generating electromagnetic torque, Y pc with Y c Respectively similar to the rotor and stator flux linkages of ordinary induction generators.

[0067] The flux linkage of power winding 3 in formula (2) Y p Can be expressed as

[0068] (3)

[0069] Where u p with i p These are the voltage vector and current vector of the power winding 3 respectively.

[0070] Voltage drop due to resistance of power winding 3 R p i p The impact on the voltage of the power winding 3 is very small and can be ignored. The power winding 3 is used as an electric energy output terminal, and its output is required to be a constant frequency and constant voltage, that is, voltage u p The amplitude and frequency remain unchanged, so it can be considered that the flux of power winding 3 Y p The amplitude and rotation speed are basically constant. Because of , So the flux linkage Y pc The amplitude of is also approximately constant. According to equations (1) and (2), it can be seen that by controlling the switching voltage vector applied to the control winding 4 u ck ( k = 0,1,…,7) to quickly change the magnetic link angle d Can reach the control active power P p the goal of. For reactive power Q p The control principle and P p Similar, but the logical relationship is different, so I won't repeat it here.

[0071] According to wind speed v And wind turbine operating characteristics, obtain the maximum absorbed power value, and then obtain the active power given value P *. It is detected that the power winding 3 of the brushless doubly-fed generator is stationary in three phases ABC Voltage and current values ​​in the coordinate system u pABC with i pABC. Since the direct power control method is based on two-phase static dq In the reference coordinate system, coordinate transformation is needed to make the three phases stationary ABC The voltage and current in the coordinate system are transformed to two-phase static dq In the coordinate system. Use two-phase static dq Voltage and current value of power winding 3 in the coordinate system u pdq with i pdq Calculate the actual value of active power and reactive power P with Q , As shown in formula (4), and their given values P * with Q * For comparison, the compared error value Δ P And Δ Q Input the hysteresis comparator 18 respectively. The reactive power change rate of the power winding 4 is used to estimate which sector the flux linkage vector of the control winding 4 is in. According to the output of the two hysteresis comparators 18 and the sector information (sector_ Ψ c ) Select a suitable switching voltage vector to drive the inverter 16.

[0072] (4)

[0073] The two control loops, one is the active power control loop, and the other is the reactive power control loop. Its function is to compare the given values ​​of active power and reactive power with their actual values, respectively, and the compared error value Input two hysteresis comparators respectively, the output of these two hysteresis comparators is used as the basis for selecting the switching voltage vector, and then correct the actual value of active power and reactive power to make it track the given value. The control winding magnetic The information of the sector where the chain is located is obtained from the rate of change of the reactive power of the power winding; the double-ended power supply type cascaded multi-level inverter uses this direct power control method for control to drive the brushless double-fed The generator realizes independent control of each phase current of the control winding.

[0074] Figure 7 It is a schematic diagram of the voltage vector and sector of the control winding switch of the present invention, Figure 8 It is a schematic diagram of the hysteresis comparison control principle of active power and reactive power of the present invention. Among them, ①~⑥represent six sectors; with They are respectively 1/2 of the total bandwidth of the hysteresis comparator 18 for active power and reactive power.

[0075] The output of the hysteresis comparator 18 is defined as

[0076] (5)

[0077] (6)

[0078] Table 1 shows the newly formulated control winding switch voltage vector selection table.

[0079]

[0080] Table 1 Control winding switch voltage vector selection table

[0081]

[0082] The proposed direct power control method does not depend on any parameters of the generator, only the voltage and current values ​​of the 7-side winding of the power grid (ie, the power winding 3), so it is more robust to parameter changes or inaccurate identification; The active power and reactive power of the brushless doubly-fed generator can be directly controlled independently. From the perspective of realizing the maximum power tracking of the wind power generation system, the structure of the controller is simpler and the calculation amount is greatly reduced; In terms of observation, the direct power control method only needs to obtain the information of the sector where the flux linkage of the control winding 4 is located, and does not need to observe its amplitude. The flux linkage position of the control winding 4 can be obtained from the detected reactive power of the power winding. The problem of poor real-time performance of the control system caused by the sensitivity of the flux linkage observer to the parameters is well solved.

[0083] The invention provides a direct power control system for a composite rotor open-winding brushless doubly-fed wind generator with simple structure, low cost, high operating performance and high wind power conversion efficiency.