阅读说明：本技术 控制多通道多相电机的方法 (Method for controlling a multi-channel polyphase machine ) 是由 P·戈德里奇 Y·胡 A·托马斯 Z-Y·吴 于 2019-01-11 设计创作，主要内容包括：本发明描述了一种控制多通道多相电机(3)的方法,该多通道多相电机包括多个通道(C1、C2、……),每个通道具有连接到转换器(M1、M2、……)的一组相绕组(WA1、WB1、WC1；WA2、WB2、WC2；……),该方法包括以下步骤：操作转换器(M1、M2)以使通道(C1、C2、……)电气地相移；在旋转参考坐标系中基于电气量(V<Sub>dq</Sub>、I<Sub>dq</Sub>)来计算主要谐波的谐波注入电流(I<Sub>d6</Sub>、I<Sub>q6</Sub>)；基于谐波注入电流(I<Sub>d6</Sub>、I<Sub>q6</Sub>)来确定主要谐波的谐波电压参考(V<Sub>d6*</Sub>、V<Sub>q6*</Sub>)；以及根据基波电压参考(V<Sub>d*</Sub>、V<Sub>q*</Sub>)和谐波电压参考(V<Sub>d6*</Sub>、V<Sub>q6*</Sub>)来调节通道(C1、C2、……)的AC输出电压(Vc)。本发明还描述了一种多通道多相电机(3)的控制装置(1)；一种风力涡轮机；以及一种计算机程序产品。(The invention describes a method of controlling a multi-channel multi-phase electric machine (3) comprising a plurality of channels (C1, C2, … …), each channel having a set of phase windings (WA 1, WB1, WC 1; WA2, WB2, WC 2; … …) connected to a converter (M1, M2, … …), the method comprising the steps of: operating the converters (M1, M2) to electrically phase shift the channels (C1, C2, … …); based on an electrical quantity (V) in a rotating reference frame dq 、I dq ) To calculate the harmonic injection current (I) of the main harmonic d6 、I q6 ) (ii) a Based on harmonic injection current (I) d6 、I q6 ) To determine the harmonic voltage reference (V) of the primary harmonic d6* 、V q6* ) (ii) a And from the fundamental voltage reference (V) d* 、V q* ) And harmonic voltage reference (V) d6* 、V q6* ) To regulate the AC output voltage (Vc) of the channels (C1, C2, … …). The invention also describes a control device (1) for a multi-channel multi-phase motor (3); a wind turbine; and a computer program product.)

1. A method of controlling a multi-channel multi-phase electric machine (3) comprising a plurality of channels (C1, C2, … …), each channel having a set of phase windings (WA 1, WB1, WC 1; WA2, WB2, WC 2; … …) connected to a converter (M1, M2, … …), the method comprising the steps of: operating the converters (M1, M2, … …) to electrically phase shift the channels (C1, C2, … …); (ii) a And, for each channel:

based on an electrical quantity (V) in a rotating reference frame_dq、I_dq) To calculate the harmonic injection current (I) of the main harmonic_d6、I_q6) Wherein a target fluctuation value (P6 _ ref, V6_ ref, R) based on the primary harmonic (6 f)₆) To calculate the injection current (I)_d6、I_q6) The target fluctuation value (P6 _ ref, V6_ ref, R)₆) Including a target power fluctuation component and a target voltage fluctuation component;

-injecting a current (I) based on said harmonics_d6、I_q6) To determine a harmonic voltage reference (V) of the primary harmonic_d6*、V_q6*) (ii) a And

-from a fundamental voltage reference (V)_d*、V_q*) And the harmonic voltage reference (V)_d6*、V_q6*) To regulate the AC output voltage (V) of the channel (C1, C2, … …) of the multi-channel multi-phase motor (3)_C）。

2. Method according to claim 1, wherein the harmonic injection current (I) is calculated using a model relating generator electrical values (P6, V6) to generator speed (ω)_d6、I_q6）。

3. Method according to claim 1 or claim 2, wherein the injection current (I) is calculated using a feed forward control method_d6、I_q6）。

4. Method according to claim 3, wherein the injection current (I) is calculated from a target ripple specified for the motor output voltage and power_d6、I_q6）。

5. Method according to claim 1 or claim 2, wherein the harmonic injection current (I) is calculated using a decoupled feedback control method_d6、I_q6）。

6. Method according to claim 1 or claim 2, wherein the harmonic injection current (I) is calculated using a multivariate feedback control method_d6、I_q6）。

7. Method according to any of the preceding claims, wherein the steps of the method are for controlling a dual three-phase motor (3), wherein there is a 30 ° phase shift between the two channels (C1, C2) of the motor (3).

8. The method of claim 7, wherein the primary harmonic is a sixth harmonic (6 f).

9. A control device (1) of a multi-channel, multi-phase electric machine (2), the control device comprising:

-a voltage reference generator (11) realized to generate a fundamental voltage reference (V) for the motor frequency_d*、V_q*）；

-a harmonic voltage reference generator (10) realized to generate a harmonic voltage reference (V) for a major harmonic (6 f) of the motor frequency_d6*、V_q6*) (ii) a And

-an output voltage controller (12) implemented to be based on the fundamental voltage reference (V)_d*、V_q*) And the harmonic voltage reference (V)_d6*、V_q6*) To control the motor output voltage (V); and wherein the harmonic voltage reference generator (10) comprises:

-a calculation module (101 _ P, 101_ V) realized to be based on an electrical quantity (V) in a rotating reference frame_dq、I_dq) To calculate a generator power value (P6) and a generator voltage value (V6); and

-an injection current calculation module (102) realized as a target fluctuation value (P6 _ ref, V6 ref, R) based on the primary harmonic (6 f)₆) To calculate the injection current (I) of said primary harmonic (6 f)_d6、I_q6) (ii) a And

-a harmonic current controller (103) realized to inject a current (I) in dependence of the harmonic_d6、I_q6) To calculate the harmonic voltage reference (V)_d6*、V_q6*）。

10. The control device according to claim 9, wherein the injection current calculation module (102) comprises a ripple minimization module (1021).

11. The control device according to claim 9, wherein the injection current calculation module (102) comprises a harmonic power regulator (102 _ P) and a harmonic voltage regulator (102 _ V).

12. The control apparatus of claim 9, wherein the injection current calculation module (102) comprises a multivariable regulator (1028).

13. A wind turbine, comprising:

-a multi-channel multi-phase generator (3); and

-a wind turbine controller comprising a control device (1) according to any of claims 9 to 12.

14. Computer program product comprising a computer program which is directly loadable into a memory of a control device (1) of a multi-channel multi-phase electric machine (3) and comprising program elements for calculating a harmonic voltage reference (Vd) for use in a method according to any of claims 1-8 when the computer program is executed by the controller of the multi-channel multi-phase electric machine (3)_6*、V_q6*）。

Technical Field

The invention describes a method of controlling a multi-channel multi-phase motor; a control device for a multi-channel multi-phase motor; and a wind turbine comprising a multi-channel multi-phase generator.

Background

Multiphase electrical machines such as generators or motors rarely operate ideally and there is generally a degree of fluctuation (ripple) in one or more of the output variables. For example, a multiphase generator may exhibit torque ripple as well as fluctuations in its output voltage and output power. The magnetic flux distribution in the air gap is determined to a large extent by the generator design. Harmonics in the magnetic flux cause fluctuations in the electromagnetic torque, the electrical power and the terminal voltage of the machine (i.e., the three-phase voltage of each channel of the machine).

For various reasons, different kinds of fluctuations are problematic. The torque ripple causes vibrations of the motor and must be reduced in order to avoid material fatigue. The vibration caused by the torque fluctuation causes acoustic noise. In particular in the case of wind turbines, measures must be taken to reduce the torque fluctuations in order to comply with often very strict acoustic regulations. Various control methods known from the prior art (e.g. as described in EP3223422a1 and EP2043255a 2) are limited to reducing acoustic noise caused by torque fluctuations.

Voltage fluctuations are mainly generated by harmonics in the motor EMF and phase currents. In the presence of voltage fluctuations, the voltage usage for controlling such a motor may have to be reduced when fed from a voltage source converter. This is because, for a typical three-phase voltage source converter, the DC link voltage has a limit on the maximum value of the terminal voltage. This effectively defines the saturation level of the modulation depth. However, a high modulation depth is necessary to operate such motors efficiently. In general, a margin is left between the design value and the maximum value in view of the current control dynamics. If there is a fluctuation in the control voltage, the level of the average voltage must be lowered to keep it below the saturation level. This corresponds to a reduction in modulation depth. In the prior art, this problem has been addressed by applying harmonic current injection techniques to reduce torque ripple. This known harmonic current injection method is typically accomplished by current injection along the q-axis. It is also possible to minimize voltage and torque ripple by harmonic current injection along the d-axis.

However, fluctuations in the electrical power of the motor (or simply "power fluctuations") are not reduced by harmonic current injection along the d-and q-axes, and may even increase instead. The power fluctuations will be transferred to the DC-link and will generate heat in the capacitors of the DC-link, thereby shortening its useful life. The capacitor requires cooling, which is difficult to implement and increases overall cost. The DC link may also include a battery and any power fluctuations will also generate heat in the battery, thereby shortening its useful life.

It should also prevent power fluctuations from being transferred to the grid, as harmonics may violate grid regulations and may cause control instabilities in the grid converter. This is especially important for large generators, such as wind turbines that produce power in the megawatt range, as power fluctuations can reach an amplitude of 100 kW.

Disclosure of Invention

It is therefore an object of the present invention to provide an improved way of controlling a motor to reduce ripple while overcoming the problems outlined above.

This object is achieved by: a method of controlling a multi-channel, multi-phase electric machine according to claim 1; the control device of claim 9; the wind turbine of claim 14; and the computer program product of claim 15.

The inventive method is provided for controlling a multi-channel multi-phase motor comprising a plurality of channels, each channel having a set of phase windings connected to a converter. In the following it will be assumed that the motor is designed to electromagnetically phase shift the channels. According to the invention, the method comprises the following steps: operating the converter to phase shift the channels electrically accordingly; and then, for each channel, calculating a harmonic injection current of a specific harmonic based on the electrical quantity in the rotating reference frame. Hereinafter, the injection current may also be referred to as an injection current reference or an injection current demand. The injection current is calculated based on a target fluctuation value of the primary harmonic, the target fluctuation value including a target power fluctuation component and a target voltage fluctuation component. Then, a harmonic voltage reference (or "harmonic voltage demand") for the particular harmonic is calculated based on the harmonic injection current, and then the AC output voltage of the channel is calculated based on the harmonic voltage reference and the fundamental voltage reference.

In order to simplify the control of a multi-channel, multi-phase motor, suitable transformations are usually performed so that an AC variable whose value is altered in dependence on the rotating magnetic field can be treated as a DC variable. This greatly simplifies the calculation. For example, as will be known to the skilled person, a dq0 transformation or Park transformation may be performed on the AC voltage and current values to obtain voltage and current vectors in a rotated dq0 reference coordinate system (also referred to as dq reference coordinate system). In the context of the present invention, the term "injected current" will be understood as a current vector comprising a d-axis component and a q-axis component in a rotating reference frame.

In the context of the present invention, a specific harmonic is the dominant harmonic. Master and slaveThe harmonic is a certain multiple of the electrical frequency of the motor and depends on the number of phases in the channel. For example, in a three-phase machine, the primary harmonic is six times the electrical frequency, i.e. the sixth harmonic is in the frequency spectrum at the fundamental or machine frequency f₀Six times higher. This harmonic may be referred to simply as the "6 f harmonic". The invention is based on the insight that: in a multi-channel multi-phase motor with electromagnetic phase shift between the channels, torque fluctuations at the major harmonics can be cancelled out. Although the invention can be used with substantially any multi-channel multi-phase motor, for simplicity it will be assumed hereinafter: the motor has two channels, each with three phases, and there is a 30 ° phase shift between the two channels. A motor having two three-phase channels is generally referred to as a dual three-phase motor. In a dual three-phase machine with a 30 ° phase shift between the two channels, the torque ripple at the 6f harmonic is cancelled out.

The advantage of the control method according to the invention is that the additional degree of freedom of control is caused by effectively eliminating the 6f torque ripple by phase shifting the two channels. Since the 6f torque ripple has been dealt with, the motor can better tolerate the presence of the 6f harmonic in the phase currents. In other words, it is not necessary to design the motor to prevent the development of the 6f flux linkage represented in the rotating reference frame. Instead, it is possible to apply a relatively simple control method to eliminate or at least reduce 6f voltage fluctuations as well as 6f power fluctuations very significantly.

When the inventive control method is used by an electrical machine, such as a wind turbine generator, reducing the 6f power fluctuation to an advantageously low level or even eliminating it altogether results in a higher bandwidth for DC link control. Increasing the DC link bandwidth significantly improves the power flow between the generator and the grid. An additional advantage of reducing or eliminating 6f power fluctuations is that the size of the DC link capacitor can be reduced and the cost of the smaller capacitor is lower, so that the overall cost of the wind turbine can be reduced.

According to the invention, a control device for a multi-channel, multi-phase electric machine comprises: a voltage reference generator implemented to generate a fundamental voltage reference for a motor frequency; a harmonic voltage reference generator implemented to generate a harmonic voltage reference for a selected major harmonic of the motor frequency; and an output voltage controller implemented to control the motor output voltage based on the fundamental voltage demand and the harmonic voltage demand.

The inventive control device can advantageously be implemented in any controller of an already existing multi-channel multi-phase motor (e.g. a double three-phase motor with a 30 ° electromagnetic phase shift between the channels), so that the performance of the already existing motor can be improved.

In the context of the present invention, it may be assumed that: the converter is controlled by Pulse Width Modulation (PWM) and the fundamental and harmonic voltage references are input to a PWM controller which determines the generator output voltage. The voltage reference generator may also be referred to as a fundamental controller because it generates a voltage reference for the motor frequency or the fundamental frequency.

According to the invention, a wind turbine comprises: a multi-channel multi-phase generator, preferably a dual three-phase generator; and a controller implementing an embodiment of the control device of the present invention. An advantage of the inventive wind turbine is that the power in the power flow between the generator and the grid can be improved (compared to a wind turbine not implementing the inventive control method), since the reduced 6f power fluctuation results in a higher bandwidth for the DC link control. Furthermore, the inventive wind turbine may be constructed at lower cost, since the DC link capacitor may be smaller than a comparable wind turbine not implementing the inventive control method.

According to the invention, the computer program product comprises a computer program which can be directly loaded into a memory of a controller of the multi-channel multi-phase electric machine and comprises program elements for calculating a harmonic voltage reference for use in the control method of the invention when said computer program is executed by the controller of the multi-channel multi-phase electric machine.

The units or modules of the computer program product may be fully or partially implemented as software modules running on the processor of the controller.

Particularly advantageous embodiments and features of the invention are given by the dependent claims, as disclosed in the following description. Features from different claim categories may be combined as appropriate to give further embodiments not described herein.

As indicated above, the inventive method is applicable to any multi-channel multi-phase motor, for example a four (four-channel) three-phase motor with a 15 ° phase shift between the channels. However, for the sake of clarity, and without limiting the invention in any way, it may be assumed that the electrical machine is a dual three-phase wind turbine generator. Again, without limiting the invention in any way, it may be assumed that the generator is implemented as a fractional-slot concentrated winding generator.

In the control method of the present invention, for each channel, the harmonic injection current is preferably calculated using a model that relates generator electrical values to generator speed. The advantage of this method is that the generator electrical value and the generator speed are quantities that can be measured relatively easily, and the wind turbine controller will typically already comprise some means of measuring these quantities.

According to the invention, the injection current is calculated for each channel based on a target fluctuation value or a target fluctuation reference of the primary harmonic. For example, the target fluctuation value may include a target power reference and a target voltage reference. Alternatively, the target fluctuation value may be in the form of a vector having a target power fluctuation component and a target voltage fluctuation component. For example, the target fluctuation vector may include sine and cosine terms of power fluctuation and voltage fluctuation.

According to the present invention, a harmonic voltage reference generator includes: a calculation module implemented to calculate a generator power value and a generator voltage value based on the electrical quantity in the rotating reference frame; an injection current calculation module implemented to calculate an injection current reference for a primary harmonic (an "injection current demand") based on the generator power value and the generator voltage value; and a harmonic current controller implemented to calculate a harmonic voltage reference from the harmonic injection current reference to obtain a final control voltage for the PWM operation.

The harmonic voltage reference generator of the control device of the present invention includes a harmonic current controller that outputs harmonic voltage reference components, i.e., a d-axis component and a q-axis component of a harmonic voltage reference vector. The harmonic voltage reference component is then passed to the PWM controller, which adds it to the fundamental voltage reference component to determine the generator output voltage for that channel, as explained above. The generator output or terminal voltage of each channel will have advantageously low or negligible voltage fluctuations.

There are various possible ways of calculating the 6f injection current reference when implementing the method of the invention. In the first method, the harmonic injection current is calculated using a feed forward control method. In this method, the injection current calculation module is implemented to calculate a reverse-working 6f current reference from expected or target fluctuations specified for the motor output voltage and power. The relationship between torque ripple, voltage ripple and power ripple is roughly estimated using a motor model.

In a second approach, the harmonic injection current is calculated using a decoupled feedback control method that implements a harmonic power regulator and a harmonic voltage regulator. In the method, an injection current calculation module includes a 6f power regulator and a 6f voltage regulator. The 6f power regulator receives the 6f generator power value and the 6f power fluctuation reference and calculates a d-axis injection current value and a q-axis injection current value. The 6f voltage regulator receives the 6f generator voltage value and the 6f voltage ripple reference and calculates a q-axis injection current value and a d-axis injection current value. The d-axis components are added, the q-axis components are added, and the resulting d-axis and q-axis injection current values are passed to a harmonic current controller.

In a third method, a multivariate feedback control method is used to calculate the harmonic injection current. In this approach, the injection current calculation module implements a multivariable regulator that is implemented to optimize a particular term formed by normalized voltage and power fluctuations. Since the goal is to minimize this single term, the adjustment techniques used in the feedback control above can be applied and the desired I can be generated_d6*And I_q6*Values and feed them to a harmonic current controllerA voltage requirement is obtained.

Drawings

Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

Figure 1 shows a simplified electrical diagram of a dual three-phase motor;

figure 2 illustrates the electromagnetic phase shift between the windings of the first channel and the windings of the second channel of the machine of figure 1;

FIG. 3 illustrates an exemplary frequency spectrum of a dual three-phase motor;

FIG. 4 shows a simplified block diagram of the control device of the present invention;

FIG. 5 shows a block diagram of a first embodiment of an injection current calculation module for the control device of FIG. 4;

FIG. 6 shows a block diagram of a second embodiment of an injection current calculation module for the control device of FIG. 4;

FIG. 7 shows a block diagram of a harmonic regulator implemented in the control device of FIG. 6;

FIG. 8 shows a block diagram of a third embodiment of an injection current calculation module for the control device of FIG. 4;

FIG. 9 shows a 6f ripple waveform produced by the control method of the present invention;

fig. 10 to 12 show 6f fluctuation waveforms observed in the prior art control method;

fig. 13 shows a block diagram of a prior art controller.

In the drawings, like numbers refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale.

Detailed Description

Fig. 1 shows a simplified electrical diagram of a dual three-phase generator. On the right side two channels C1, C2 of the generator are indicated. The terminal voltage of each channel C1, C2 is controlled by a motor side converter M1, M2. DC link capacitors D1, D2 are arranged in the DC link between the motor side converters M1, M2 and the grid side converters G1, G2. The grid-side converters G1, G2 are connected to the transformer T via line reactors R1, R2.

Fig. 2 illustrates the 30 ° phase shift between the first and second channels of fig. 1 by superimposing a phasor diagram of the channel currents on a simplified representation of the stator. The first channel C1 is represented by three windings WA1, WB1, WC1, and the second channel C2 is represented by three windings WA2, WB2, WC 2. Here, the windings are connected in a star configuration (a delta configuration is likewise possible). The 30 ° phase shift between the first channel C1 and the second channel C2 has been shown to have various advantages, one of which is to effectively cancel out the 6f torque ripple.

Fig. 3 shows an exemplary frequency spectrum of a dual three-phase motor controlled using a conventional control method. The diagram indicates the fundamental wave f₀(at the electrical frequency of the motor) and several harmonics. In a double three-phase machine, the sixth harmonic 6f (at six times the electrical frequency of the machine) is the largest (dominant) and therefore also the most problematic harmonic. Amplitude of harmonics in the spectrum (relative to the fundamental f)₀Of) corresponds to the amplitude of the ripple component superimposed on the output voltage or output power.

Fig. 4 shows a simplified block diagram of the inventive control device 1. As will be known to the skilled person, a transformation has been performed on the measured currents to obtain a vector I in the rotated dq0 reference frame_dqAnd V is_dqIs from I_dqA voltage vector derived by a current controller (not shown). Vector I_dq、V_dqIs passed to a fundamental wave controller 11 which generates a voltage reference V for a PWM control unit 12_d*、V_q*The PWM control unit determines or regulates the output voltage V of the channel_COr terminal voltage V_C. Current vector I_dqShould be understood to include the d-axis component I in the rotating reference frame_dAnd q-axis component I_q. The same applies to the voltage vector V_dqIt is to be understood as also including the d-axis component V in the rotating reference frame_dAnd q-axis component V_q. Conventional control devices typically include only a fundamental controller and a PWM control unit that uses only a fundamental voltage reference V_d*、V_q*To determine or regulate terminal voltage V_C。

In the control device of the invention, the vector I_dq、V_dqIs also passed to a harmonic voltage reference calculation module 10, which may be implemented in one of several ways as will be explained below, and comprises a 6f reference calculation module providing a fundamental voltage reference V to be added by the PWM control unit_d*、V_q*Harmonic voltage reference V of_d6*、V_q6*. Harmonic voltage reference calculation module 10 is implemented to provide a 6f voltage reference V_d6*、V_q6*I.e. a voltage reference that will result in minimizing 6f fluctuations in the motor output voltage and output power. In the control device 1 of the present invention, the PWM control unit 12 for the channel is based not only on the fundamental voltage reference V_d*、V_q*But also by taking into account the harmonic voltage reference V_d6*、V_q6*The generator output voltage V is determined such that major harmonic fluctuations in the output power and voltage of the channel can be minimized or even eliminated.

Fig. 5, 6 and 7 show various possible embodiments of the 6f reference calculation module 102 of the harmonic voltage reference calculation module 10. In each case, the generator power calculation module 101_ P is based on the vector I_dq、V_dqTo calculate the value of the generator power sixth harmonic P6, and the generator voltage calculation module 101_ V is based on the vector I_dq、V_dqTo calculate the value of the generator voltage sixth harmonic V6. Each calculation module 101_ P, 101_ V comprises a velocity dependent band pass filter to pass only the sixth harmonic frequency. Injection of reference I_d6*、I_q6*Calculated in the injection current calculation module 102 and passed to the harmonic current controller 103, which in turn generates the 6f voltage reference V_d6*、V_q6*. In fig. 5, the injection current calculation module 102 is implemented as a ripple control module 1021 (or "ripple minimization module") using a feed forward method. At a given operating point with a specific speed and a specific load, the 6f power fluctuates P₆Can be expressed as:

where ω is the speed or electrical angular frequency of the motor; i is_d、I_q、V_dAnd V_qIs a vector I_dq、V_dqD-axis and q-axis components of (1); and I_d6And I_q6Will be injected with current_d6And_q6the harmonic current vector injected by the corresponding phase angle. Psi_pm0Is the DC value from the flux linkage of the permanent magnet, and psi is derived from the 6f harmonic values in the d-axis and q-axis permanent magnet flux linkages according to the following equation_pm6aAnd psi_pm6b：

At this operating point, the 6f voltage fluctuates V_d6、V_q6Can be expressed as:

and the rms voltage 6f fluctuates v_rms6Can be expressed as:

wherein v is_rms0Is the fundamental rms (root mean square) voltage. Then, the current is injected into vector I_injCan be defined as:

6f Power fluctuation P₆And 6f rms voltage fluctuation v_rms6It can also be expressed as:

wherein the relationship between the current injection vector and the output fluctuation vector is expressed as:

where matrices a and B are related only to the motor parameters and fundamental electrical quantities and can be derived using the equations presented above. For example,

outputting a fluctuation vector R₆Can fluctuate by 6f power P₆And 6f Voltage fluctuation V₆The sine and cosine terms are combined into:

allowing the term P to be established for equations (6) and (7)_{6_cos}、P_{6_sin}、V_{6_cos}、V_{6_sin}For example, if the target 6f power fluctuation and the target 6f voltage fluctuation are each zero, the fluctuation vector is a null entry 4 × 1 vector in the case where the fluctuation vector is established and the closed form of matrices A and B are derived from the motor parameters and the fundamental electrical quantity, the 6f power fluctuation P can be calculated₆And 6frms Voltage fluctuation V_rms6The value of (c).

Subsequently, using equation (1), the required harmonic current I can be calculated from the target power fluctuation and the target rms voltage fluctuation_d6、I_q6. Since power fluctuations can also be expressed in terms of voltage or current fluctuations, this motor parameter dependency can be removed. Fig. 6 shows a block diagram of a second embodiment of the injection current calculation module 102 for the control device of fig. 4. Here, the harmonic current I is calculated using a pair of harmonic power and voltage regulators 102_ P, 102_ V connected in a feed forward arrangement_d6、I_q6. Harmonic power regulator 102_ P receives 6f power fluctuation P from generator power calculation module 101_ P₆And receiving a power reference P6_ ref (e.g., zero), and calculating a d-axis current reference component I_d6*And q-axis current reference componentI_q6*. The value of the power reference P6_ ref may be zero since the major harmonic power fluctuations will be minimized.

The harmonic voltage regulator 102_ V receives the 6f voltage fluctuation V from the generator voltage calculation module 101_ V₆And receiving a voltage reference V6_ ref (e.g., zero), and calculating a d-axis current reference component I_d6*And q-axis current reference component I_q6*. Also in this case, the value of the voltage reference V6_ ref may be zero since major harmonic voltage fluctuations will be minimized.

Adding the d-axis components to obtain a d-axis current reference I_d6*. Adding the q-axis components to obtain a q-axis current reference I_q6*. Then, the current is referenced I_d6*、I_q6*Is passed to a harmonic current controller 103 which generates a 6f voltage reference V_d6*、V_q6*。

Fig. 7 shows an exemplary block diagram of the harmonic power regulator 102_ P of fig. 5 (the harmonic voltage regulator 102_ V is identically constructed and only the relevant signals must be replaced). The feedback signal P6 is subtracted from the reference signal P6_ ref. The result is passed to a 90 ° phase shifter 1021 and also to a coordinate system transformation module 1022 which performs a non-phase-shifting transformation of the phase shifted signal from the dq-rotated reference frame to a coordinate system rotated at a frequency of 6 f. The output of the coordinate system transformation module 1022 is passed to two proportional-integral controllers 1023, which in turn are passed to a second phase transformation module 1024, which generates a d-axis current reference component I_d6*And q-axis current reference component I_q6*。

Fig. 8 shows a block diagram of a third embodiment of the injection current calculation module 102 for the control device of fig. 4. Here, the multivariable regulator 1028 receives the 6f power fluctuation P from the generator power calculation module 101_ P₆And receiving the 6f voltage fluctuation V from the generator voltage calculation module 101_ V₆. The multivariable regulator 1028 is also given weighting factors λ, μ. The multivariable regulator 1028 is implemented to optimize the following equation:

where y is the slave power fluctuation and the voltage fluctuation (P)₆、V₆) And the slave power and voltage (P)₀、V₀) A DC value of (a). Since the objective is to minimize y, the conditioning technique shown in FIG. 6 can be applied, and I can be generated_d6*And I_q6*And then passes them to the HCC controller to calculate the voltage requirements.

Fig. 9 illustrates the simultaneous minimization of all three 6f fluctuations when the inventive method is applied in the control of a dual three-phase motor in which the two channels C1, C2 are electromagnetically phase-shifted by 30 °. The upper part of the figure shows the 6f torque ripple T of the first passage C1₆₁And 6f torque ripple T of second channel C2₆₂. 6f Torque ripple T₆₁、T₆₂Each located in the range of ± 45 kNm. Since the two channels C1, C2 have been phase shifted by 30 °, the 6f torque ripple T₆₁、T₆₂Cancel each other out such that the net 6f torque ripple T₆Is 0 Nm.

The middle part of the figure shows the 6f power fluctuation P₆And the lower part of the figure shows the 6f Vrms voltage fluctuation V of either of the two channels C1, C2₆. With the method of the present invention, 6f power fluctuation P using any of the three methods described above with the aid of FIGS. 4-7₆Has been reduced to a very favourable level of significantly less than 0.01 kW and a 6f voltage fluctuation V₆Has been reduced to a very favorable level close to zero volts. FIGS. 10 to 12 show the passage I_qHarmonic current injection control (i.e., by harmonic current injection along the q-axis) minimizes the typical waveform that results when one type of ripple is present, as practiced in the prior art. The controlled electrical machine is a dual three-phase generator of a wind turbine. For either of the two channels C1, C2, the graphs show the 6f ripple on each of torque, power and rms voltage for rotor electrical angle (in radians). When only one type of 6f fluctuation is maximizedThe other two 6f fluctuation types showed significantly higher levels when miniaturized.

In FIG. 10, through I_qHarmonic current injection only minimizes torque ripple. Now, the torque ripple T of 6f₁₀In the advantageously low range of-0.2 to 0.2 kNm. However, 6f power fluctuation P₁₀Is relatively high, reaching 300 kW. Similarly, the 6f voltage fluctuation V₁₀Also relatively high, reaching ± 80V.

In fig. 11, only power fluctuation is minimized by Iq harmonic current injection, and 6f power fluctuation P₁₁In the advantageously low range of ± 3 kW. However, the 6f voltage fluctuation V₁₁Also relatively high, reaching ± 18V. 6f Torque ripple T₁₁Is relatively high, reaching + -45 kNm.

In fig. 12, only the voltage ripple is minimized by Id harmonic current injection, and the 6f voltage ripple V₁₂Now not exceeding 0.02V. However, 6f power fluctuation P₁₂Is also relatively high, reaching + -80 kW. 6f Torque ripple T₁₂Is relatively high, reaching + -50 kNm.

These figures illustrate that: known methods for reducing or eliminating fluctuations are beneficial only from the perspective of reduced fluctuations, but the problems associated with the other two types of fluctuations may offset those benefits.

Fig. 13 shows a simple block diagram of a prior art controller for the first channel of a dual three-phase motor. The Id current controller 70d receives the Id reference Id1_ ref and the measured Id value Id1 and calculates the d-axis voltage reference Vd 1. The Iq current controller 70q receives the Iq reference Iq1 — ref and the measured Iq value Iq1 and calculates the q-axis voltage reference Vq 1.

The harmonic current controller 71 provides harmonic voltage references Vqh1, Vdh1 for specific harmonics (e.g., major harmonics). Inputs to harmonic current controller 71 are received from three modules: a voltage fluctuation control module 710 that receives a generator Vrms value; a power fluctuation control module 711 that receives the generator power value; and a torque ripple control module 712 that receives the generator torque value. Referencing each harmonic to Vqh 1%,Vdh1 is added to the corresponding voltage references Vq1, Vd1 and the added signal is passed to the PWM unit 72 which uses the added signal to control the terminal voltage V of the first channel_C1。

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. The invention is applicable to motors with different numbers of channels and different numbers of phases. For example, the motor may have three channels, each having three phases, with a 20 ° phase shift between the channels. If the motor has four channels, each with three phases, a 15 ° phase shift is used between the channels. For a three-phase motor, the 6f harmonic is dominant and needs to be dealt with using the method of the present invention. Similarly, the motor may have two/three/four channels, each with five phases, with 18/12/9 phase shifts between the channels. In this case, the 10f (tenth) harmonic is dominant and needs to be processed using the method of the present invention. For a motor with two/three/four channels (seven phases per channel) and a 12.86/8.57/6.42 phase shift between the channels, the 14f (fourteen) harmonic is dominant and needs to be processed using the method of the present invention.

For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. Reference to "a unit" or "a module" does not preclude the use of more than one unit or module.