阅读说明：本技术 电机的谐波直接转矩控制 (Harmonic direct torque control of an electric machine ) 是由 N·M·A·弗赖雷 吴占元 于 2020-04-17 设计创作，主要内容包括：描述了一种用于生成发电机侧转换器部分(121)、特别是风力涡轮机(100)的发电机侧转换器部分(121)的转换器控制信号(265)的方法,所述发电机侧转换器部分(121)耦合到发电机(111)、特别地是永磁同步电机,所述方法包括：特别是基于谐波转矩需求(240)和转矩指示反馈信号(241,Fb),导出至少一个谐波转矩参考(245,Th*)；特别地基于谐波定子电压需求(246)和/或定子电压指示反馈信号(249,Vrms)导出至少一个谐波通量参考(251,psih*)；将所有的所述至少一个谐波转矩参考(245,Th*)加到基本转矩参考(253,Te*),并减去估计的发电机转矩(255,)以导出转矩误差(257)；将所有的所述至少一个谐波通量参考(251,psih*)加到基本通量参考(259,psis*),并减去估计的发电机通量(261,)以导出通量误差(263)；和基于转矩误差(257)和通量误差(263)导出转换器控制信号(265,135,Sabc)。(It is described a method for generating a converter control signal (265) of a generator-side converter section (121), in particular of a generator-side converter section (121) of a wind turbine (100), the generator-side converter section (121) being coupled to a generator (111), in particular a permanent magnet synchronous machine, the method comprising: deriving at least one harmonic torque reference (245, Th), in particular based on the harmonic torque demand (240) and the torque indication feedback signal (241, Fb); indicating a feedback signal (249, V) based on, inter alia, harmonic stator voltage demand (246) and/or stator voltagerms) to derive at least one harmonic flux reference (251, psih); adding all of the at least one harmonic torque reference (245, Th) to the base torque reference (253, Te), and subtracting the estimated generator torque (255, ) To derive a torque error (257); adding all of the at least one harmonic flux reference (251, psih) to the base flux reference (259, psis), and subtracting the estimated generator flux (261, ) To derive a flux error (263); and deriving a converter control signal (265, 135, Sabc) based on the torque error (257) and the flux error (263).)

1. Method for generating a converter control signal (265) of a generator-side converter section (121), in particular of a generator-side converter section (121) of a wind turbine (100), the generator-side converter section (121) being coupled to a generator (111), in particular a permanent magnet synchronous machine, the method comprising:

deriving at least one harmonic torque reference (245, Th), in particular based on the harmonic torque demand (240) and the torque indication feedback signal (241, Fb);

deriving at least one harmonic flux reference (251, psih), in particular based on a harmonic stator voltage demand (246) and a stator voltage indication feedback signal (249, Vrms);

adding all of the at least one harmonic torque reference (245, Th) to the base torque reference (253, Te)) And subtracting the estimated generator torque (255,) To derive a torque error (257);

adding all of the at least one harmonic flux reference (251, psih) to the base flux reference (259, psis), and subtracting the estimated generator flux (261,) To derive a flux error (263); and

a converter control signal (265, 135, Sabc) is derived based on the torque error (257) and the flux error (263).

2. The method according to the preceding claim, wherein the converter control signal (265) represents a switch state signal defining the switch states of a plurality of controllable switches of the generator-side converter section (121).

3. The method according to any of the preceding claims, wherein the stator voltage indication feedback signal (249, Vrms) is derived from the measured DC-link voltage (Vdc) and the switching state (Sabc), in particular involving applying an adaptive band-pass filter tuned to the harmonic of interest.

4. The method according to any of the preceding claims, wherein the torque error (257) and the flux error (263) are supplied to respective hysteresis controllers (268, 269), the outputs of which are supplied to a switch table (271) that outputs switch states (Sabc),

wherein the switching watch is further based on stator flux positioning in particularAnd outputting the switch state.

5. The method according to any one of the preceding claims, wherein both the torque error (357) and the flux error (363) are supplied to a predicted torque control (377) deriving the switch state (Sabc), the predicted torque control (377) comprising in particular model-based prediction and cost function minimization.

6. The method according to any one of the preceding claims 1 or 2,

wherein the torque error (457) is supplied to a torque controller (481), and in particular in parallel also to a harmonic torque controller (479, HTC), which operate in particular in one or more reference frames, a first voltage reference (483) is derived,

wherein the flux error (463) is supplied to a flux controller (485) and in particular in parallel also to a harmonic flux controller (487, HFC) which in particular operates in one or more reference coordinate systems, a second voltage reference (489) is derived,

wherein the converter control signal (Sabc) is derived based on the first voltage reference and the second voltage reference.

7. The method of the preceding claim, wherein both the first voltage reference (483) and the second voltage reference (489) are supplied to the output total voltage reference (492, uab |)A transformation module (491) in which a voltage reference (uab) is supplied to a space vector modulator (493) that derives a switch state signal (Sabc).

8. The method according to the preceding claim, wherein the stator voltage indication feedback signal (449, Vrms) is derived from a total voltage reference (uab, or udq).

9. Method according to any of the preceding claims, wherein the stator voltage (vs), in particular the reference stator, is based onThe voltage, and in particular the measured stator current (is), derives an estimated generator torque (255,) And the estimated generator flux (261,）。

10. method according to any of the preceding claims, wherein the basic torque reference (253, Te) and the basic flux reference (259,）。

11. the method according to any of the preceding claims, wherein the torque indicating feedback signal (241, Fb) comprises a sensor measurement signal, in particular a sensor measurement signal obtained by an accelerometer or a torque sensor or a microphone.

12. The method according to any of the preceding claims, wherein the harmonic torque reference (245, Th) is further derived based on an operating point (OP, 243) of the generator (111), the operating point in particular defining a rotational speed and a torque.

13. Method of controlling at least one generator-side converter section (121), in particular a generator-side converter section (121) of at least one wind generator (100), the at least one generator-side converter section (121) being coupled to at least one generator (111), in particular a permanent magnet synchronous machine, the method comprising:

-performing a method of generating a converter control signal (265, Sabc) according to any one of the preceding claims;

the converter control signal (265, Sabc) is supplied to the generator-side converter section (121).

14. Arrangement (150, 250, 350, 450) for controlling a generator-side converter section (121), in particular a generator-side converter section (121) of a wind turbine (100), the generator-side converter section (121) being coupled to a generator (111), in particular a permanent magnet synchronous machine, the arrangement being adapted to carry out a method according to any of the preceding claims.

15. Power generation system (100), in particular a wind turbine or a wind farm, comprising:

at least one generator (111);

at least one converter (119) comprising a generator-side converter portion (121), a DC link (123) and a utility converter portion (125), the generator-side converter portion being coupled to a generator (111); and

at least one arrangement (150, 250, 350, 450) according to the preceding claim.

Technical Field

The present invention relates to a method and an arrangement for generating converter control signals for a generator-side converter section coupled to a generator, in particular a generator-side converter section of a wind turbine. Furthermore, the invention relates to a power generation system comprising the arrangement and at least one generator and at least one converter.

Background

When operating generators, such as wind turbines, in particular permanent magnet synchronous machines, undesired harmonics of the fundamental electrical frequency interfere with efficient operation. The prior art discusses harmonic control of vector control drives.

Regarding torque ripple control in motor control with DTC (direct torque control), the prior art mainly addresses the estimation of electromagnetic torque with the aim of improving the estimation accuracy by means of more complex/accurate motor models and corresponding torque equations. These potentially high fidelity models require a large number of parameters that depend on load/saturation and rotor positioning and are difficult to measure/estimate. Thus, conventional approaches apply a number of simplifications to implementation and tuning, for example, ignoring load variations within given parameters and/or given operating ranges. As a feedback source, an accelerometer located in the stationary ring of the main bearing of the generator is used. Conventional harmonic control in FOC (field oriented control) is mainly based on Id and Iq currents.

However, it has been observed that the reduction of harmonics is not satisfactory when applying conventional methods.

Therefore, there may be a need for a method and arrangement for generating converter control signals for a generator-side converter section, wherein the harmonic control is improved. Further, there may be a need for a method of controlling at least one generator-side converter section, wherein converter control signals are generated according to a method according to an embodiment of the invention and supplied to the respective converter or generator-side converter section.

Disclosure of Invention

This need may be met by the subject matter according to the independent claims. The dependent claims describe advantageous embodiments of the invention.

According to an embodiment of the invention, there is provided a method of generating a converter control signal for coupling to a generator, in particular to a generator-side converter section of a permanent magnet synchronous machine (in particular to a generator-side converter section of a wind turbine), the method comprising: deriving at least one harmonic torque reference (e.g. Th @), in particular based on the harmonic torque demand and/or the torque indication feedback signal (e.g. Fb); deriving at least one harmonic flux reference (e.g., psih), in particular based on a harmonic stator voltage demand and/or a stator voltage indication feedback signal (e.g., Vrms); adding all of the at least one harmonic torque reference (e.g., Th) to the base torque reference (e.g., Te) and subtracting the estimated generator torque (e.g., Th)) To derive a torque error; adding all of the at least one harmonic flux reference (e.g., psih) to the base flux reference (e.g., psis) and subtracting the estimated generator flux (e.g., PSI)) To derive a flux error; and deriving a converter control signal (e.g., Sabc) based on the torque error and the flux error.

The method may be implemented in software and/or hardware. The method may in particular be performed by a wind turbine controller or generally by a converter controller controlling a generator-side converter section coupled to the generator.

The converter control signals may for example define the switching states of a plurality of controllable switches comprised in the generator-side converter section. The converter control signal may comprise a Pulse Width Modulation (PWM) signal. The method may be applicable to any number of harmonics, one or more, i.e. multiples of the fundamental electrical frequency. Thus, the method can be applied in parallel to several different harmonics of the fundamental electrical frequency.

The harmonic torque reference may be derived by a Torque Ripple Controller (TRC). The harmonic torque reference may be derived such that the torque complies with the harmonic torque demand when the converter sections are supplied with the respective converter control signals, e.g. the harmonic torque demand may be zero for one or more harmonics. The torque indicating feedback signal may comprise, for example, a sensor signal, such as derived from an accelerometer or microphone or a strain gauge.

The harmonic flux reference may be derived, for example, by a Harmonic Voltage Controller (HVC). The harmonic flux reference may be derived such that the stator voltage complies with the harmonic stator voltage requirements. The flux may be related to the magnetic flux of the magnetic field through the generator coil. The flux includes flux generated by the permanent magnet and flux generated by the armature reaction.

The base torque reference may be related to the desired dc torque. The fundamental flux reference may relate to the desired flux at the fundamental frequency, i.e. the stator flux, when viewed in a stationary reference frame.

The desired torque change as well as the desired flux change may be supplied as inputs to a switch table, which may output switch states as examples of converter control signals. According to an embodiment of the invention, the converter control signal represents a switch state signal defining the switch states of a plurality of controllable switches of the generator-side converter section.

The switch state signal may define which controllable switches comprised in the generator-side converter section are to be in a conducting state or a non-conducting state. Thereby, a conventional control method for the converter part is supported. The method may for example support a three-phase permanent magnet generator coupled to a generator-side converter section. The converter section may comprise two controllable switches connected in series for each phase.

According to an embodiment of the invention, the stator voltage indication feedback signal (e.g., Vrms) is derived from the measured DC link voltage (e.g., Vdc) and the switch state, in particular involving applying an adaptive bandpass filter tuned to the harmonic of interest. In the case when the reference voltage (or demand voltage) is not directly available, the reconstructed stator voltage is used.

The power generation system may comprise, in addition to the generator and the generator-side converter portion, a DC-link and a grid-side converter portion. The generator-side converter section may be substantially adapted to convert the variable frequency AC power stream to a substantially DC power stream on the DC link. The grid-side converter portion may be configured for converting a DC power flow into an AC power flow of substantially fixed frequency. From the DC link voltage and the switching state, the stator voltage can be estimated. Thus, a simple stator voltage indication feedback signal may be provided.

According to an embodiment of the invention, the torque error and the flux error are supplied to respective hysteretic controllers, the outputs of which (i.e. the desired torque change and flux change) are supplied to a switching table of output switching states, wherein the switching table is particularly further based on the stator flux positioning (e.g.,) And outputting the switch state.

The hysteresis controller may output either a positive or negative one or a positive or negative constant depending on whether the input exceeds the first threshold or is below the second threshold. The hysteretic controller may also be referred to as a "bang-bang" controller. Thereby, a simple way for deriving the switch state may be provided.

According to an embodiment of the invention, both the torque error and the flux error (and in particular also the total torque and flux reference and the stator voltage and current) are supplied to a predictive torque control deriving the switching state, which comprises in particular model-based prediction and cost function minimization.

According to an embodiment of the invention, the torque error is supplied to the torque controller, and in particular in parallel also to a harmonic torque controller (e.g. HTC), which in particular operates in one or more reference frames, deriving a first voltage reference, wherein the flux error is supplied to the flux controller, and in particular in parallel also to a harmonic flux controller (e.g. HFC), which in particular operates in one or more reference frames, deriving a second voltage reference, wherein the converter control signal (e.g. Sabc) is derived based on the first voltage reference and the second voltage reference.

Since the references to harmonic torque and harmonic flux are typically zero, the torque error and flux error of the harmonic controller will be derived primarily from harmonic feedback.

For both of the above approaches (i.e., hysteresis-based control and predictive control), the stator voltage indication feedback signal (e.g., Vrms) is derived from the measured DC-link voltage (e.g., Vdc) and the switch states.

According to an embodiment of the invention, both the first voltage reference and the second voltage reference are supplied to the output total voltage reference (e.g. uab;)A transformation module in which a voltage reference (e.g., uab) is supplied to a space vector modulator that derives a switch state signal (e.g., Sabc). Thus, conventional methods may be supported and conventional computing modules may be utilized.

According to an embodiment of the invention, the stator voltage indication feedback signal (e.g. Vrms) is derived from an overall voltage reference (e.g. uab, or udq).

According to an embodiment of the invention, the estimated generator torque (e.g. the generator torque)) And estimated generator flux (e.g. generator flux)) Is derived based on a stator voltage (e.g. vs), in particular a reference stator voltage, and a stator current (e.g. is), in particular measured.

A variety of flux/torque estimators may be employed, examples of which are given below:

。

according to an embodiment of the invention, the basic torque reference (e.g. Te) and the basic flux reference (e.g. psis) may be derived, for example, based on a stator voltage (in particular a reference stator voltage) and/or a stator current (in particular measured) and/or a DC link voltage.

According to an embodiment of the invention, the torque indicating feedback signal (Fb) comprises a sensor measurement signal, in particular obtained by a torque sensor and/or a microphone and/or an accelerometer. Thus, the feedback signal may for example be band pass filtered to indicate the actual torque at the harmonic considered.

According to an embodiment of the invention, alternatively, the harmonic torque reference (Th ×) may be derived from a look-up table based on the operating point of the generator, which particularly defines the rotational speed and the power output. The operating point may be measured, for example, by measuring, for example, rotational speed and power output and/or torque.

According to an embodiment of the invention, there is provided a method of controlling at least one generator-side converter section, in particular at least one generator-side converter section of at least one wind turbine, the at least one generator-side converter section being coupled to at least one generator, in particular a permanent magnet synchronous machine, the method comprising: performing a method of generating a converter control signal according to any of the preceding embodiments; the converter control signal is supplied to the generator-side converter section.

Thereby, the converter control signal is used to control the generator-side converter section. Thereby, the torque and/or voltage ripple of the generator may be effectively reduced. For example, harmonic fluxes may be generated to reduce voltage ripple.

It should be understood that features which are described, explained, provided or applied in any combination, individually or in any combination, to a method of generating converter control signals for a generator-side converter section are also applicable individually or in any combination to an arrangement for controlling a generator-side converter section according to an embodiment of the invention and vice versa.

According to an embodiment of the invention, an arrangement for controlling a generator-side converter section, in particular a generator-side converter section of a wind turbine, coupled to a generator, in particular a permanent magnet synchronous machine, is provided, which arrangement is adapted to carry out the method according to any of the preceding embodiments.

Furthermore, according to an embodiment, there is provided a power generation system, in particular a wind turbine or a wind farm, comprising: at least one generator; at least one converter comprising a generator-side converter portion, a DC link and a utility converter portion, the generator-side converter portion being coupled to a generator; and at least one arrangement according to the preceding embodiments.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Drawings

Embodiments of the present invention will now be described with reference to the accompanying drawings. The invention is not limited to the embodiments shown or described.

FIG. 1 schematically illustrates a power generation system, here implemented as a wind turbine, according to an embodiment of the invention;

2, 3, 4 schematically illustrate arrangements for controlling a generator side converter section according to different embodiments of the invention;

FIGS. 5, 6 and 7 illustrate implementations of harmonic controllers that may be employed in the arrangements illustrated in FIGS. 2 through 4; and

fig. 8 illustrates the simulation results.

Detailed Description

The illustrations in the drawings are in schematic form. It should be noted that in different figures, elements that are structurally and/or functionally similar or identical are provided with the same reference signs or with reference signs that differ only within the first digit. Descriptions of elements not described in one embodiment may be taken from a description of the elements in relation to another embodiment.

FIG. 1 illustrates, in schematic form, a wind turbine 100 as an example of a power generation system that provides electrical energy to a utility grid 101, according to an embodiment of the present invention.

The wind turbine comprises a hub 103, to which hub 103 a plurality of rotor blades 105 are connected. The hub is mechanically connected to a main shaft 107, the rotation of the main shaft 107 being transformed into the rotation of a secondary shaft 109 by a gearbox 108, wherein the gearbox 108 may be optional. The main shaft 107 or the secondary shaft 109 drives a generator 111, which generator 111 may in particular be a synchronous permanent magnet generator, which provides a power flow in three phases or windings 113, 115 and 117 to a converter 119, which converter 119 comprises a generator-side part (AC-DC part) 121, a DC link 123 and a grid-side part (DC-AC part) 125 for converting a variable AC power flow into a fixed frequency AC power flow, which fixed frequency AC power flow is provided in three phases or windings 127, 129, 131 to a wind turbine transformer 133, which wind turbine transformer 133 converts the output voltage into a higher voltage for transmission to the utility grid 101.

The converter 119 is controlled via a converter control signal 135, the converter control signal 135 being derived from and supplied by an arrangement 150 for controlling a generator-side converter section according to an embodiment of the invention, the arrangement 150 receiving at least one input signal 137, such as one or more reference values or one or more quantities indicative of the operation of the generator 111 or any component of the wind turbine 100.

The generator in fig. 1 comprises a single three-phase stator winding. The winding 113 thus carries the stator current I_aThe winding 115 carries the stator current I_bAnd winding 117 carries stator current I_c。

The arrangement 150 is adapted to cancel out torque and voltage harmonics (e.g. harmonics corresponding to six times the electrical frequency of the generator 111). According to an embodiment of the invention, the generator 111, the converter 119 and the arrangement 150 together form a generator system.

The arrangement 150 for controlling the generator-side converter section as comprised in the wind turbine power generation system 100 illustrated in fig. 1 receives an input signal 137, which input signal 137 may relate to the stator voltage, the stator current, may relate to a feedback signal, may relate to an operating point, as will be described in detail with reference to fig. 2 to 4. The control signal 135 is in particular a converter control signal for controlling the generator-side converter section 121 of the converter 119.

Fig. 2 schematically illustrates an arrangement 250 for controlling the generator side converter section, and fig. 3 and 4 illustrate respective embodiments 350, 450 of an arrangement for controlling the generator side converter section.

The input to the arrangement 250 is collectively referred to with reference numeral 237. The arrangement 250 comprises a torque pulse controller (TRC) 239 which receives as input a feedback signal 241 and/or a selectable signal 243 indicative of an operating point. The torque ripple controller 239 derives a harmonic torque reference 245 (Th) therefrom.

The arrangement 250 further comprises a Harmonic Voltage Controller (HVC) 247 that receives as input a stator voltage indication feedback signal 249 and derives therefrom a harmonic flux reference 251。

The torque ripple controller 239 and harmonic voltage controller 247 operate at specific harmonics of the fundamental frequency. If more than one fundamental frequency harmonic is to be processed, for each harmonic a respective torque ripple controller 239 and a respective harmonic voltage controller 247 may be provided. In the case of several harmonics to be dealt withIn this case, all harmonic torque references 245 are added to the base torque reference 253 (Te) at the summing element 254 and the estimated generator torque 255 is subtracted to derive the torque error 257. All harmonic flux references 251 are added to the fundamental flux reference 259 at the summing element 254And the estimated generator flux 261 is subtracted to derive a flux error 263. Desired flux changeAnd the desired torque change dTe is obtained as an output of the hysteresis control units 268, 269.

The converter control signal 265 is based on a desired torque change dTe and a desired flux changeAnd (4) deriving. Thus, the converter control signal 265 represents a switch state signal that defines the switching states of a plurality of controllable switches of the generator-side converter portion 121 (illustrated in fig. 1).

The stator voltage indication feedback signal 249 is derived from the measured DC link voltage Vdc and the switch state 265 using the calculation module 267. The calculated stator voltages may be band pass filtered to eliminate harmonics other than the harmonic on which harmonic voltage controller 247 is operating. According to the embodiment 250 illustrated in fig. 2, the torque error 257 and the flux error 263 are supplied to the respective hysteretic controllers 268, 269, the output of the hysteretic controllers 268, 269, the desired flux changeAnd the desired torque change dTe is supplied to the switch table 271 which outputs the switch state 265. In addition, switch table 271 receives stator flux positioning(273) And also derives the switch state 265 based on the stator flux position 273. Estimated generator torques 255 andthe estimated generator flux 261 is derived by a torque and flux estimator 275 based on the stator voltage vs, in particular the reference stator voltage and the stator current is.

Base torque reference 253 and base flux reference 259 are derived by base torque/flux reference calculation module 277 based on one or more of the following quantities: stator voltage "vs", stator current "is" and DC link voltage Vdc. As may be taken from fig. 2, the harmonic torque reference 245 (Th ″) is derived by the torque ripple controller 239 further based on the operating point 243 of the generator 111.

The arrangements 350, 450 illustrated in fig. 3 and 4 comprise modules similar or identical to the modules of the arrangement 250 illustrated in fig. 2, which modules are labeled with reference numerals that differ only in the first digit. However, the arrangement 350 for controlling the generator-side converter section according to an embodiment of the invention does not comprise the hysteresis controllers 268, 269 and the switch table 271, but instead comprises a predicted torque controller 377, which receives the torque error 357 and the flux error 363, and derives the converter control signal 365 therefrom.

Instead of the predicted torque control 377 or the hysteresis controllers 268, 269 and the switch table 271, the arrangement 450 illustrated in fig. 4 comprises a harmonic torque controller 479 and a basic torque controller 481, to which the torque error 457 is supplied and the outputs are added together using an adding element 480 to derive a first voltage reference 483. Still further, the arrangement 450 includes a primary flux controller 485 and a harmonic flux controller 487 to which the flux error 463 is supplied and whose outputs are summed by a summing element 480 to arrive at a second voltage reference 489. A first voltage reference 483 and a second voltage reference 489 are supplied toA transformation module 491The transform module 491 outputs a total voltage reference 492 uab. The total voltage reference 492 is supplied to the space vector modulationBlock 493, the space vector modulation block 493 derives the switch state 465 therefrom. As can be appreciated from fig. 4, the stator voltage indication feedback signal 449 is derived by module 467 based on the total voltage reference.

The harmonic torque controller 479 of fig. 4 and the torque ripple controllers 239, 339, 439 of fig. 2, 3, 4 are different controllers, but they may have the same structure (such as any of fig. 5-7) if suitable feedback signals are available. However, in case the feedback signal is not available to the torque ripple controller, it may be a look-up table with the Operating Point (OP) as input.

The torque controller 481 and the flux controller 485 in fig. 4) may be PI controllers for basic torque and flux. The converter control signal in fig. 4 is based on the conversion module by the inverse Park conversion voltage-adding modulatorIs derived from the input of (a).

High performance harmonic control in electric drives is important because it is a requirement of permanent magnet generators for several reasons: (1) the noise standard is met; (2) preventing excitation of structural modes and accelerated fatigue; (3) optimizing DC link voltage usage and system efficiency.

The Torque Ripple Controller (TRC) illustrated in fig. 2, 3 and 4 generates a harmonic torque reference (Th) which is added to the base torque reference (Te), modifying the reference torque to include errors in the estimated torque at the harmonic frequency of interest. The Harmonic Voltage Controllers (HVCs) illustrated in fig. 2, 3 and 4 generate harmonic flux references to minimize the corresponding harmonic voltages.

It is expected that the TRC and HVC will retain the advantages of direct torque control, i.e. fast dynamics due to decoupled control of torque and flux/voltage. Furthermore, the simplicity of implementation of the LUT-based approach is evident from fig. 2, since the internal flux and torque controllers (hysteretic controllers 268, 269) provide high bandwidth control without the need for additional parallel controllers.

The arrangement 350 illustrated in fig. 3 is another attractive solution, including a Predictive Torque Control (PTC) approach, which is endowed with high bandwidth flux and torque control, like LUT-based DTC (inner loop is composed of blocks for model-based prediction and cost function minimization).

In fig. 4, the TRC and HVC are integrated into direct torque control with space vector modulation. In contrast to the embodiments illustrated in fig. 2 and 3, in fig. 4 the voltage reference is readily available at the modulator input, i.e., at signal 492, but the lower bandwidth of the torque and flux controllers may require additional parallel controllers (HTC and HFC in fig. 4) to achieve high performance reference tracking of harmonic content and zero steady state error. Some approaches may be a resonant controller and a PI controller in multiple reference frames.

Vrms of the illustrated control method is calculated as follows:or. Vdq is readily available in DTC-SVM (sum of outputs of torque/flux controllers), while for DTC-LUT, the voltage is reconstructed using the switch state (Sabc) and dc link voltage (Vdc):

。

the harmonics of interest are extracted from Vrms by means of an adaptive BPF at the selected harmonics. It is emphasized that the embodiments focus on the external harmonic control loops shown in fig. 2, 3, 4, such as TRC and HVC, which modify the reference torque and flux required for any DTC-based control method. Thus, for the sake of completeness, different examples (LUT, prediction, SVM) presented in fig. 2, 3, 4 are given. However, the fast inner control loop may be implemented in other ways.

Fig. 5, 6 and 7 illustrate the harmonic controller as an implementation of the control blocks HVC, TRC, HTC, HFC illustrated in fig. 2, 3 and 4.

In particular, the torque ripple controllers 239, 339, 439 illustrated in fig. 2, 3, 4 may receive harmonic torque demand signals 240, 340, 440, respectively, that represent desired torques at the harmonics under consideration. The harmonic torque demand may be, for example, zero. Similarly, the harmonic voltage controller may receive as inputs the harmonic voltage demand signals 246, 346, 446 of fig. 2, 3, 4, respectively. The signal may represent a harmonic voltage requirement, and depending on the application, the requirement may be zero.

In all implementations of the controllers illustrated in fig. 5, 6, and 7, the harmonic error 504 is calculated from the demand harmonic value 502 and the feedback signal 503. In the implementation illustrated in fig. 5, the error 504 is shifted by 90 ° by a 90 ° phase shifter 506, and the output signal is supplied to a coordinate system transformation module 508. The coordinate system transformation module 508 transforms the error and the error of the 90 ° shift according to a coordinate system that rotates with the harmonic under consideration. The output is supplied to a PI regulator 510, the PI regulator 510 deriving an output signal so that the error is reduced to zero. Downstream of the regulator 510, a further coordinate system transformation module is arranged, which performs an inverse transformation to obtain the harmonic reference 545.

In fig. 6, the harmonic error 604 is supplied to trigonometric functions 612, 614 and the output is again supplied to the PI regulator 610, the output of the PI regulator 610 being multiplied by another trigonometric function 616, 618 and added together to obtain the harmonic reference 645.

In the implementation illustrated in fig. 7, the harmonic error 704 is supplied to the resonance adjuster 714 to obtain a harmonic reference 745.

The control blocks HVC, TRC, HTC, HFC in fig. 2, 3, 4 may all be implemented similarly and are in the following referred to as harmonic controllers. Different options for the harmonic controller are shown in figures 5, 6, 7. In all options, the harmonic error is calculated and a closed loop adjustment is performed. Thus, the regulator is used to control the harmonic error to 0. A harmonic regulator based on the vector control principle enables a simple PI controller as shown in fig. 5, 6. FIG. 7 shows a harmonic regulator using a resonant regulator with a typical transfer function where f1 is the resonant frequency, andis the damping of the controller. The block diagrams shown in fig. 5, 6, 7 assume that whenever necessary, an adaptive Band Pass Filter (BPF) is applied to the reference/feedback signal, and thus only the harmonic order of interest is given to the controller input. Alternatively, the BPF may be implemented in the harmonic error (Vn _ error) in fig. 5, 6 and 7.

。

Application to PM machines may allow noise and vibration to be reduced and also optimize hardware utilization. Noise and vibration reduction by minimizing torque ripple can be directly understood.

On the other hand, increasing hardware usage by controlling harmonic stator voltages/flux may not be as significant. The latter is explained by the fact that: in the presence of non-negligible voltage harmonics, it may be necessary to set a reduced (average) flux reference to avoid over-modulation of the converter, resulting in entering the flux weakened zone at a lower speed level and operating with increased phase current. The introduction of HVC enables the following possibilities: (1) an increase in the average stator flux reference; or (2) reduce the dc link voltage. In other words, the HVC allows for an extended operating range of the MTPA (maximum torque per amp), a reduced flux weakening range, and thus optimized drive efficiency.

One of the main advantages of the proposed control structure and corresponding feedback signal may be that the dependency on the accuracy of the flux and torque estimators is eliminated in relation to harmonic control. Note that the input to the TRC may not be limited to an accelerometer, and other signals such as a microphone and various sensors may be optional. Furthermore, the closed loop harmonic controller TRC may be replaced by a simple LUT with Operating Point (OP) information such as speed and torque as inputs, providing an inexpensive feed forward solution.

Fig. 8 illustrates simulation results of direct torque control based on a modified space vector modulator as illustrated in fig. 4. The control of the PM generator is achieved by implementing a DC link voltage controller for calculating the basic torque reference (Te) and a flux weakening control (also called basic voltage controller, since its aim is to keep the generator voltage below a given limit) for calculating the basic stator flux reference. With respect to harmonic control, measured or inferred torque ripple is used as a feedback signal with the controller in fig. 5 for the torque ripple controller, and harmonic voltage control uses the voltage ripple in Vrms as an input, and uses the controller structure as in fig. 5.

An abscissa 816 indicates time and an ordinate 818 indicates signal strength. Curve 820 illustrates the feedback torque, curve 822 illustrates the estimated torque, curve 824 depicts the modulation index, and curve 826 indicates the estimated flux. The torque pulse controller is activated at time point t =3s, i.e. at time point 828. It therefore results in an effective reduction of the measured torque ripple (the remaining oscillations are at uncontrolled low harmonic frequencies), while the sixth harmonic is imposed in the estimated/reference torque. The harmonic voltage control is enabled at time point 830, i.e. at t =5s, reducing the voltage ripple by applying the sixth harmonic in the reference flux. Thus, the converter operates further away from the flux weakening and/or overmodulation region.

According to an embodiment of the invention, the basic reference of current/torque/flux is calculated by means of a controller or look-up table, some examples being speed, power, torque, flux, voltage controllers and maximum torque per ampere methods. Such a controller provides Te andthey are typically DC signals during steady state operation.

The goal of the torque ripple controller is to control the torque ripple by using suitable sensors as feedback signals and generating a reference harmonic torque Th, which is a sinusoidal signal that varies at a given frequency or a combination of sinusoidal signals with different frequencies. The torque ripple controller may consist of various controllers (PI, search algorithms, etc.) and/or LUTs.

The goal of the harmonic voltage controller is to generate a reference harmonic flux by using the modulus of the reference voltage (Vrms) as feedback and generating a reference harmonic fluxTo control voltage ripple, reference harmonic fluxIs a sinusoidal signal that varies at a given frequency or a combination of sinusoidal signals having different frequencies. The harmonic voltage controller may be comprised of a variety of controllers.

The torque/flux controller may comprise a PI controller with a given bandwidth, intended to track the DC content of the torque and flux references.

The harmonic torque/flux controllers (HTC and HFC) may be controllers implemented by means of PI controllers, proportional resonant controllers in a harmonic reference frame, or any other suitable method.

The Park transformation may transform between a stationary coordinate system (ab) and a synchronously rotating coordinate system (dq), and vice versa. Similar techniques may be applied to the transformation between the synchronous rotating coordinate system and the harmonic reference coordinate system.

The voltage modulator generates a PWM (pulse width modulation) pattern using a reference voltage in a stationary coordinate system. The PWM signal is used to control power electronic switches, such as IGBTs, of the generator-side converter section. The hysteresis (bang-bang controller) may be considered as a controller for defining LUT entries in the DTC-LUT, typically using 2-level and/or 3-level controllers. The controller output determines whether the torque/flux is increasing, decreasing, or remaining constant.

The switch table determines the optimum voltage based on the desired action specified by the hysteretic controller in the LUT entry. The stator flux angle is also an entry of the LUT, which defines a given number of sectors.

The torque and flux estimator may use a machine model along with current measurements to estimate electromagnetic torque and stator flux. A reference voltage is typically used instead of the measurement voltage. A variety of models and observer structures can be used for estimation purposes.

Embodiments of the present invention may provide a control method for incorporating harmonic control capability into a direct torque control drive. The harmonic control may include torque ripple control and voltage ripple control. A control method for improving harmonic control performance in electric drives can be provided. Harmonic control may have little dependence on the accuracy of the torque ripple and flux chain ripple estimates, and may therefore be well robust. A control method may be well suited for the control of a permanent magnet generator of a wind turbine, which may provide an alternative to the more commonly used vector control methods. Embodiments of the present invention can reduce noise and vibration and increase a voltage control range and driving efficiency. A control method may be provided that is suitable for implementation in a frequency converter controller.

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Furthermore, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.