Method for controlling power converter system and power converter system

Abstract

A method for controlling a power converter system and a power converter system, the power converter system comprising a first power converter (10) connected to a first stator winding of an induction motor (30) and a second power converter (20) connected to a second stator winding of the induction motor (30), the induction machine (30) has a rotor, a first stator winding, and a second stator winding, the first power converter (10) being configured to transmit a slip angle estimate to the second power converter (20), and the second power converter (20) is configured to determine a slip angle reference based on the slip angle estimate transmitted from the first power converter (10) and a predetermined phase shift between the second stator winding and the first stator winding, and to determine a rotor flux angle estimate based on the determined slip angle reference and a mechanical angle of the rotor.

Description

Technical Field

[0001] The invention relates to a method for controlling a power converter system. Background Art

[0002] A multi-winding induction machine is an electrical machine, such as an electric motor, having two or more stator windings. Each stator winding can be connected to a separate power converter device, one for each winding, which converter devices can be controlled substantially independently. There is a predetermined (multiple) phase shift between the two or more stator windings.

[0003] Figure 1 An example of a configuration is shown in which a three-phase dual (two) winding induction motor 30 is connected to two power converter devices 10, 20, wherein both power converters 10, 20 include inverters. In this example, the two stator windings can be controlled by two respective inverters, which receive the same torque reference from, for example, a PLC 40 that can control the torque and / or speed of the entire induction motor.

[0004] A challenge associated with the exemplary configuration is how to synchronize the field direction between the two inverters, e.g., to have the fundamental components of the winding currents in balance and correctly phase-shifted to match the actual phase shift between the windings. In particular, in the case of an induction machine, it may be difficult to synchronize the direction even if the mechanical position of the machine rotor is provided to both inverters. This is due to the fact that the slip angle may be changing all the time if the machine is loaded. Therefore, the position of the machine rotor, e.g., from a rotary encoder coupled to the rotor, cannot be used for field direction synchronization.

[0005] One possible solution is to send the magnetic field direction, or rotor flux angle, directly from one converter device acting as a master to another converter device acting as a slave. However, one problem associated with this solution is that a high bandwidth communication link operating at at least high speed is required between the converter devices, and such a high bandwidth communication link may not be readily available and / or may be difficult or expensive to arrange in practice. Furthermore, even if there is a fast communication link between the converter devices, sending an additional fast signal over it may significantly reduce the bandwidth available for other signals in the communication link and / or increase the CPU load of the converter devices and system components providing the communication link between them, which is undesirable. Summary of the invention

[0006] Therefore, the object of the present invention is to provide a method and an apparatus for implementing the method in order to overcome the above problems or at least alleviate the above problems. The object of the present invention is achieved by a method and a power converter system characterized by what is stated in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The present invention is based on the following idea: in a first power converter, a first slip angle estimate of the rotor is determined based on an estimated rotor flux and a mechanical angle of the rotor, and the determined first slip angle estimate is transmitted from the first power converter to each second power converter; thereby, in each second power converter, a slip angle reference can be determined based on the first slip angle estimate transmitted from the first power converter and a predetermined phase shift between the second stator winding and the first stator winding, and then the rotor flux angle estimate can be determined based on the determined slip angle reference and the mechanical angle of the rotor.

[0008] An advantage of the solution of the invention is that, since the slip angle usually changes rather slowly, its transmission consumes less bandwidth of the communication link between the converter devices, so that a high-speed communication link between the converter devices is not necessarily required. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Hereinafter, the present invention will be described in more detail by way of preferred embodiments with reference to the accompanying drawings, in which

[0010] Figure 1 An example of a system is illustrated;

[0011] Figure 2 An example of a system according to an embodiment is illustrated;

[0012] Figure 3 illustrates an example of a power converter system according to an embodiment;

[0013] Figure 4 illustrates a block diagram according to an embodiment;

[0014] Figure 5 illustrates an example of a power converter system according to an embodiment;

[0015] Figure 6 illustrates a block diagram according to an embodiment;

[0016] Figure 7 illustrates an example of a power converter system according to an embodiment; and

[0017] Figure 8 A block diagram according to an embodiment is illustrated. DETAILED DESCRIPTION

[0018] The following embodiments are exemplary. Although the description may mention "one", "an" or "some" embodiments in multiple locations, this does not necessarily mean that each such mention points to the same embodiment, or that the features are only applicable to, for example, a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments. Different embodiments and embodiments may be described below using a single unit, model and device without limiting the embodiment / embodiment to such a solution. Generally, all terms and expressions used should be interpreted broadly, and they are intended to illustrate rather than limit the embodiments. Only the necessary components for understanding the various embodiments are shown in the figure. For example, the number and / or configuration of the various elements and generally their implementation may be different from the examples shown in the figure. It should be noted that the use of the embodiments described herein is not limited to, for example, devices or systems using any specific base frequency or any specific voltage level.

[0019] Various embodiments described herein are generally applicable to and connected to various power converter devices and systems thereof. An example of a power converter device (device) is an electric drive, which generally refers to an electronic device that can be used to adjust the performance of, for example, a motor in this article. For example, an electric drive (AC drive, variable frequency drive, variable speed drive) can control the power, frequency and / or current provided to the motor. One or more electric drives and a motor controlled by one or more electric drives can form an electric drive system. The electric drive may include one or more power converter units or modules, such as a rectifier, an inverter and / or a frequency converter, which may include various power semiconductor devices. The term "inverter" herein generally refers to an electronic device or circuit that can convert direct current (DC) into alternating current (AC). An example of an inverter is a semiconductor bridge implemented by a controllable semiconductor switch, such as an IGBT (insulated gate bipolar transistor) or a FET (field effect transistor), which is controlled according to the modulation or control scheme used. The control of the motor can be implemented by means of an electric drive, for example, the motor implements the required speed and / or torque command. For example, the control method of the electric drive includes flux vector control and direct torque control.

[0020] According to an embodiment, a power converter system includes a first power converter configured to be connected to a first stator winding to control the first stator winding of an induction motor having a rotor, a first stator winding and at least one second stator winding, wherein the first stator winding and the at least one second stator winding are multi-phase windings. The power converter system also includes at least one second power converter configured to be connected to a corresponding second stator winding to control a corresponding second stator winding of the induction motor.

[0021] Figure 2 An example of a system according to an embodiment is illustrated. Figure 2is a simplified block diagram of an exemplary system, which shows some devices (e.g., instruments, devices, nodes) and functional entities, the implementation and / or number and / or configuration of which may vary from Figure 2 The example is different. The actual physical connection between different elements may be different from the example shown. For example, such a system may also include other devices, functional entities and / or structures. Similarly, for example, any communication protocol used may be different and may depend on system characteristics, for example. The exemplary system includes a first (master) power converter 10 and a second (slave) power converter 20. The exemplary system also includes an induction motor 30, which has two three-phase stator windings. There is a predetermined phase shift between the two stator windings. The first power converter 10 is connected to the first stator winding of the induction motor 30, and the second power converter 20 is connected to the second stator winding of the induction motor 30. According to an embodiment, the first power converter 10 and the second power converter 20 each include at least one inverter 100, 200, wherein the output of the inverter 100 of the first power converter 10 can be connected to the first stator winding of the induction motor 30, that is, its three phases, and the output of the inverter 200 of the second power converter 20 can be connected to the second stator winding of the induction motor 30, that is, its three phases. The figure also shows a first control device 11, which can be configured to control, for example, the operation of the first power converter 10 and its components, such as its inverter 100, and a second control device 21, which can be configured to control, for example, the operation of the second power converter 20 and its components, such as its inverter 200. For example, the first control device 11 and / or the second control device 21 can include one or more physical units and can be configured to perform one or more functions of any embodiment described herein. The induction motor 30 can be any kind of multi-winding multi-phase induction motor (asynchronous AC motor), such as a squirrel cage rotor induction motor. For example, in an embodiment, the number of stator windings of the induction motor 30 can be greater than two, with any predetermined phase shift between the windings and / or the stator windings of the induction motor 30. According to an embodiment, when the number of stator windings of the induction motor 30 is greater than two, the system includes a corresponding number of second (driven) power converters, so that there is a power converter connected to each stator winding of the induction motor 30, respectively.

[0022] Figure 2The exemplary system also includes an encoder 50, such as a rotary encoder, which can be directly or indirectly connected or coupled to the rotor shaft of the induction motor 30. The encoder 50 can be configured to provide the mechanical angle of the rotor of the induction motor 30 to at least the first power converter 10 and the second power converter 20, or indicate its amount, for example, as shown in the embodiment, via a signal separator unit 60. The encoder 50 can be an incremental encoder, for example, using a Z pulse, thereby providing output signals A, B and Z in a manner known per se. The encoder 50 can also be another type of absolute encoder, for example. Therefore, the converter devices 10, 20 receive the mechanical angle θm from the encoder 50. In other words, the same absolute angle is transmitted to both (all) converter devices substantially at the same time, so that both (all) converter devices receive the same signal from the encoder 50. It is worth noting that the mechanical angle θm in the figure is assumed to be converted into an electrical angle taking into account the number of pole pairs (i.e., the number of poles / 2) of the induction motor 30.

[0023] Figure 2 The exemplary system further illustrates a connection between a first (master) power converter 10 and a second (slave) power converter 20, by which slip angle θslip1 data may be transmitted from the first power converter 10 to the second power converter 20, as will be described in more detail below. Although in the illustrated example, the connection is through an exemplary PLC (programmable logic controller) 40, which may also control the torque and / or speed of the induction motor 30, for example, via a torque control signal Tref to the power converter devices 10, 20, it should be noted that the connection by which slip angle data may be transmitted from the first power converter 10 to the second power converter 20 may be any type of wired or wireless connection. Or a combination thereof, using any suitable communication protocol. It should also be noted that, for example, the converter devices 10, 20 may be from a plurality of communication protocols other than the exemplary Figure 2 Another control entity shown receives its control for controlling the induction motor 30 .

[0024] According to an embodiment, a method includes controlling a first stator winding of an induction motor 30 by a first power converter 10 and controlling each second stator winding of the induction motor 30 by a corresponding second power converter 20. The method also includes receiving a mechanical angle of a rotor of the induction motor 30 in the first power converter 10 and each second power converter 20. The method also includes determining, in the first power converter 10, a first slip angle estimate of the rotor based on an estimated rotor flux and the mechanical angle of the rotor of the induction motor 30. The method also includes transmitting the determined first slip angle estimate from the first power converter 10 to each second power converter 20. The method also includes, in each second power converter 20, determining a slip angle reference based on the first slip angle estimate transmitted from the first power converter 10 and a predetermined phase shift between the second stator winding and the first stator winding, and determining a rotor flux angle estimate based on the determined slip angle reference and the mechanical angle of the rotor. Reference is made below to Figures 3 to 8 Examples of possible embodiments are given. It should be noted that although Figures 3 to 8 The example in FIG. 1 shows only one second (driven) converter device 20, but there may be any number of such second (driven) converter devices, each connected to a respective second winding of the induction motor 30. In this case, Figures 3 to 8 The functionality of the illustrated single second converter device 20 may be implemented individually in each such second converter device.It should be noted that the exemplary figures only show functionality relevant for implementing and understanding the various embodiments.

[0025] Figure 3 An example of a power converter system is shown, the system including a first (master) power converter 10 and a second (slave) power converter 20 and generally corresponding to Figure 2 The encoder 50 and the distributor 60 of the system. For the sake of clarity, the induction motor 30 and any inverter units 100 and 200 are not shown. Figure 3 is shown in . In an embodiment, the first (main) power converter 10 includes a control device 11 and some of its possible functions, such as a motor model block 110, are shown in more detail. The "motor model" here generally refers to a calculated motor model, which can use various measured or otherwise obtained quantities such as motor current, voltage and / or rotor angle as source information to determine or estimate information related to the rotation of the motor, such as motor speed, (electrical) position, torque and / or flux. For example, such a motor model block may include the functionality of a flux observer. The information determined or estimated by the motor model can then be used to control the converter device and the motor connected to it, such as speed and / or torque control.

[0026] In the example described, the first (main) power converter 10 further comprises a measuring device 12, which is configured to perform the required measurements, or at least receive measurement data from one or more possible separate measurement units. As an example, the measuring device 12 can measure the motor current, i.e. the stator current i of the first stator connected to the first power converter 10. s1 , and / or the motor voltage, ie, the stator voltage u connected to the first stator of the first power converter 10 s1 Such measurements may be performed from the output of the inverter 100 of the power converter 10 connected to the first stator of the induction motor 30, with suitable current and / or voltage measuring equipment, such as may be implemented within the power converter device 10. For example, the three output phase currents i of the inverter 100 may be measured. a 、i b 、i c , and can be appropriately converted from the three-phase abc reference system to a two-phase representation by a three-phase to two-phase (abc to xy) transformation (Clarke transformation) in a manner known per se, by means of the measuring device 12. Assuming that the three phase currents i a 、i b 、i c is substantially symmetrical, it is sufficient to measure only two of the three output phase currents of the inverter 100, since the third current can be calculated from the other two. Thus, the measuring device 12 can output a single (vector) quantity, namely the stator current i of the first stator of the induction motor 30. s1 In a similar manner, the three output phase voltages u of the inverter 100 can be measured by the measuring device 12. a 、u b 、u c , and appropriately converted from the three-phase abc reference frame to a two-phase representation and output as a single (vector) quantity, namely the stator voltage u of the first stator of the induction motor 30 s1 .

[0027] In the example, the first power converter 10 also includes a transmitter (Tx) 13, which is configured to send at least the slip angle θslip1 data to one or more second power converter devices. The exemplary first power converter 10 also includes an encoder interface block 14, which is configured to receive data from the encoder 50 and extract the mechanical angle θm, etc. from the received data. Figure 3 In the example of FIG. 2 , the second (slave) power converter 20 comprises a control device 21 and shows some of its possible functions in more detail, such as a motor model block 210. Furthermore, the second power converter 20 comprises a measuring device 22, which may essentially correspond to the measuring device 12 of the first power converter 10, but may measure the motor current, i.e. the stator current i of the second stator connected to the second power converter 20.s2 , and / or the motor voltage, ie, the stator voltage u of the second stator connected to the second power converter 20 s2 . In the example, the second power converter 20 also includes a receiver (Rx) 23, which is configured to receive at least the slip angle θslip1 data from the first power converter device 10. The exemplary second power converter 20 also includes an encoder interface block 24 corresponding to the encoder interface block 14 of the first power converter 10. In addition, the exemplary second power converter 20 includes a phase shift block 25, which can provide a (predetermined) value of the phase shift between the second stator connected to the second power converter 20 and the first stator connected to the first power converter 10.

[0028] exist Figure 3 In the example of FIG. 1 , the motor model block 110 of the first (main) power converter 10 is configured to determine the estimated rotor flux (vector) ψ R1 As an example, the motor model block 110 of the first power converter 10 may be configured to be based on the stator current i of the induction motor 30 s1 , stator voltage u s1 and the rotor mechanical angle θm to determine the estimated rotor flux (vector) ψ R1 As another example, the motor model block 110 of the first power converter 10 may be configured to be based on the stator current i s1 and stator voltage u s1 (ie, without considering the mechanical angle θm of the rotor of the induction motor 30) to determine the estimated rotor flux (vector) ψ R1 .

[0029] This allows the calculation of the rotor flux ψ in the stator reference frame in the variable (arg) block. R1The estimated angle θR1 of the induction motor 30 is calculated by subtracting the measured mechanical angle θm from the estimated rotor flux angle θR1 in the first power converter 10. A first slip angle estimate θslip1 can then be determined by subtracting the measured mechanical angle θm from the estimated rotor flux angle θR1 in the first power converter 10. The first slip angle estimate θslip1 is then sent to (each) the second power converter 20 (e.g., via the PLC 40). In the second power converter 20, the winding-to-winding phase shift (between the first winding and the corresponding second winding of the induction motor 30) provided by block 25 is added to the first slip angle estimate θslip1, thereby producing a phase shift-corrected slip angle reference θslip_ref. Based on the measured rotor mechanical angle θm and the slip angle reference θslip_ref, the motor 210 of the second power converter 20 can be modified to align the magnetic field directions in the two power converters 10, 20. This in turn enables, for example, balancing the current vector dq components that produce flux and torque, because they can be calculated using the same reference frame in the two power converters 10, 20. For example, depending on how the machine model is implemented, there are many ways to correct the field direction of the second power converter to correspond to the field direction of the first power converter. A more detailed example is given below.

[0030] According to an embodiment, in each second power converter 20, the determination of the rotor flux angle estimate comprises determining the rotor flux angle estimate based on the determined flux angle reference θslip_ref, the mechanical angle θm of the rotor and the stator current i of the corresponding second stator winding s2 .

[0031] According to an embodiment, in each second power converter 20, the determination of the rotor flux angle estimate includes determining the second flux angle estimate based on the determined flux angle reference and the stator current of the corresponding second stator winding, and determining the rotor flux angle estimate based on the determined second flux angle estimate and the mechanical angle of the rotor. As an example, the control of the second power converter 20 can be based only on the current model, that is, the motor model 210 of the second power converter receives the measured current i of the corresponding second stator winding. s2 , the rotor mechanical angle θm and the slip angle reference θslip_ref as input signals, such as Figure 3 The control scheme may include a slip angle estimator that can be corrected directly based on the slip angle reference. Figure 4 It is shown in more detail how slip correction is performed according to an embodiment.

[0032] exist Figure 4 In the example, according to Figure 3 The example of FIG. 1 illustrates the functions that may be performed in the motor model block 210 of the second power converter 20, converting the measured stator current i s2Transform to the rotor flux reference frame (xy to dq or Park transformation) to obtain the d-axis and q-axis components of the current is2d, is2q. The d component is2d is low-pass filtered, and the filtering time constant is equal to the rotor time constant. The filtered magnetizing current component im is multiplied by the main inductance Lm to obtain the rotor flux amplitude estimate ψ R2 The slip frequency can be estimated by dividing the q-axis stator current component is2q by the rotor flux amplitude ψ R2 , and then multiplied by the rotor resistance RR. The slip frequency estimate ωslip is corrected by the slip frequency correction term ωslip_corr, and then further integrated to calculate the second slip angle estimate θslip2. The calculation of the slip frequency correction term ωslip_corr is proportional to the difference between the slip angle reference θslip_ref and the second slip angle estimate θslip2. Therefore, as an example, if the slip angle estimate θslip2 lags behind the slip angle reference θslip_ref, the slip frequency is increased to catch up with the reference, and vice versa. Finally, the slip angle estimate θslip2 is added to the mechanical angle θm of the rotor to obtain the respective rotor flux angle estimates θR2 (i.e., magnetic field direction), which can be used for the Park transformation of the stator current in the second power converter 20. Therefore, the rotor flux angle estimate θR2 of the second power converter 20 will follow the rotor flux angle estimate θR1 of the first power converter 10, because the slip angle and mechanical angle 10, 20 between the power converters are synchronized.

[0033] According to an embodiment, in each second of the power converter 20, the determination of the rotor flux angle estimate includes determining a rotor flux angle reference based on a determined slip angle reference and a mechanical angle of the rotor; determining a second flux angle estimate based on the determined rotor flux angle reference and a stator current of a corresponding second stator winding, and determining a rotor flux angle estimate based on the determined second flux angle estimate and the mechanical angle of the rotor. For example, the magnetic field directions of the power converters 10, 20 may also be synchronized by corrections based on rotor flux angle errors (rather than slip angle errors). This would only require minor modifications to the above-described controls based on the current model. Figure 5 and Figure 6 An example of the overall concept is shown. Figure 5 For Figure 3 The corresponding power converter system example, except that Figure 5 In the example, in the second power converter 20, the slip angle reference θslip_ref is added to the measured mechanical angle θm to obtain the rotor flux angle reference θR_ref of the motor model block 210. The motor model block 210 also receives the mechanical angle θm as input as shown in the figure.

[0034] exist Figure 6 In the example, according to Figure 5The example illustrates the functions that may be performed in the motor model block 210 of the second power converter 20, which corrects the slip frequency estimate ωslip based on the difference between the rotor flux angle reference θR_ref and the rotor flux angle estimate θR2 to align it with the reference. In other words, the motor model 210 directly compares the magnetic field direction (rather than the slip angle). Otherwise, Figure 6 The functions shown in will be the same as explained above Figure 4 corresponds to the functions shown in .

[0035] According to an embodiment, in each second power converter 20, the determination of the rotor flux angle estimate comprises determining the rotor flux angle estimate based on the determined slip angle reference, the mechanical angle of the rotor, the stator current of the corresponding second stator winding, and the stator voltage of the corresponding second stator winding. According to an embodiment, in each second power converter, the determination of the rotor flux angle estimate comprises determining the rotor flux angle reference based on the determined slip angle reference and the mechanical angle A1 of the rotor, and determining the rotor flux angle estimate based on the determined rotor flux angle reference, the stator current of the corresponding second stator winding, and the stator voltage of the corresponding second stator winding.

[0036] In the above Figure 3-6 The concept of field-oriented synchronization is generally based on a current model. However, it can also be used for flux observers that are generally based on a voltage model, using the motor voltage as input signal instead of the mechanical speed or angle. Figure 3-6 Unlike the general concept shown, this control scheme does not require separate slip angle and flux amplitude estimators, for example.

[0037] Instead, the rotor flux can be estimated directly as a vector that can be corrected to align it with the rotor flux angle reference θR_ref. This means that, for example, Figure 7 In the example shown, only the stator voltage u connected to the second stator of the second power converter 20 is s2 and the stator current i s2 And the rotor flux angle reference θR_ref can be used as the input of the motor model block 210 of the second power converter 20. In addition, Figure 7 The system basically corresponds to the one explained above Figure 3 and Figure 5 The example shown in .

[0038] exist Figure 8 In the example, according to Figure 7 The example of FIG. 2 illustrates the functions that may be performed by the motor model block 210 of the second power converter 20. The stator flux can be estimated using the following voltage model equation (the voltage will be corrected below):

[0039] ψ s =∫(us2 -R s i s2 +u corr )dt, (1)

[0040] Among them, ψ s = stator flux estimation

[0041] u s2 = stator voltage of the second stator connected to the second power converter 20

[0042] i s2 = stator current of the second stator connected to the second power converter 20

[0043] u corr = Voltage correction term

[0044] R s = stator resistance 20 connected to the second stator of the second power converter

[0045] In the second power converter 20, the stator flux is estimated by subtracting the leakage flux (i.e., the leakage inductance L σ The product of the stator current and the rotor flux ψ can be calculated. R2 , as shown below:

[0046] ψ R2 =ψ s -L σ i s2 (2)

[0047] The bold symbols here represent vectors; therefore, the rotor flux estimate ψ R2 With amplitude ψ R2 The voltage integrated in Equation 1 can be corrected by a small correction to the stator flux and angle θR2. The magnitude of the correction may be proportional to the correction gain G and the difference between the rotor flux angle reference θR_ref and the rotor flux angle estimate θR2. The correction angle γ may be calculated relative to the estimated rotor flux angle θR2, so that the actual voltage is corrected to:

[0048] u corr =G(θ R_ref -θ R2 ) jγ (3)

[0049] For example, G and γ are parameters that can be appropriately selected to better maintain the stability of the model and make the angular error θR_ref-θR2 of all working points close to zero.

[0050] It should be noted that there is substantially no limitation on the implementation of the motor model 110 of the first power converter 10 or any corresponding function therein, since only the estimated rotor flux angle θR1 is extracted from the motor model 110 to calculate the first slip angle estimate θslip1, which is then sent as a reference signal to the second power converter 20. Therefore, the motor model 110 of the first power converter 10 can be implemented in a variety of ways, such as using a closed-loop or open-loop vector control scheme, with voltage, current and / or speed (or the mechanical angle of the rotor (shaft), speed representing the rate of change of the mechanical angle with respect to time) as input to the model. In the open-loop case, only voltage and current may be required, while closed-loop operation may be based only on current and speed, for example. The motor model 210 that may exist for the second power converter 20, or any corresponding function or entity within the control device 21 of the second power converter 20, may be supplemented according to any of the embodiments described herein.

[0051] According to an embodiment, the rotor flux angle estimate θR2 determined in the (multiple) second power converter 20 according to any of the embodiments described herein may be used in each second power converter 20 to control the corresponding second stator winding of the induction motor 30. As an example, the rotor flux angle estimate θR2 may be used in the second power converter 20 to transform various quantities, such as current and / or voltage quantities, between different reference frames, for example in a manner known per se. Examples of such transformations include Park transformations and inverse (reverse) Park transformations, as well as direct quadrature zero (abc to dq) transformations and their inverse transformations.

[0052] According to an embodiment, a power converter system includes a first power converter configured to be connected to a first stator winding to control the first stator winding of an induction motor having a rotor, a first stator winding and at least one second stator winding, wherein the first stator winding and the at least one second stator winding are multi-phase windings; and at least one second power converter configured to be connected to a corresponding second stator winding to control the corresponding second stator winding of the induction motor. The first power converter includes a device configured to receive a mechanical angle of a rotor of the induction motor, a device configured to determine a first slip angle estimate of the rotor based on an estimated rotor flux and the mechanical angle of the rotor, and a device configured to transmit the determined first slip angle estimate to at least one second power converter. At least one second power converter includes: a device configured to receive a mechanical angle of a rotor of the induction motor, a device configured to receive a first slip angle estimate determined by the first power converter; a device configured to determine a slip angle reference based on the first slip angle estimate received from the first power converter and a predetermined phase shift between the corresponding second stator winding and the first stator winding, and a device configured to determine a rotor flux angle estimate based on the determined slip angle reference and the mechanical angle of the rotor.

[0053] The first control device 11 and / or the second control device 21 or other means for realizing at least part of the function according to any one of the embodiments herein or a combination thereof can be realized as a physical unit or as two or more independent physical units configured to realize the function. Here, the term "unit" generally refers to a physical or logical entity, such as a physical device or a part thereof or a software routine. The first control device 11 and / or the second control device 21 or other means for realizing at least part of the function according to any one of the embodiments herein can be realized at least in part by, for example, one or more computers or corresponding digital signal processing (DSP) devices equipped with suitable software. The computer or digital signal processing device preferably includes at least a working memory (RAM) providing a storage area for arithmetic operations and a central processing unit (CPU) such as a general-purpose digital signal processor. The CPU may include a set of registers, an arithmetic logic unit and a control unit. The central processing unit control unit is controlled by a sequence of program instructions transmitted from the RAM to the central processing unit. The CPU control unit may include some microinstructions for basic operations. The implementation of the microinstructions may vary depending on the CPU design. The program instructions may be encoded in a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language or an assembly language. The computer may also have an operating system, which may provide system services to computer programs written in the program instructions. The computer or other device implementing the various embodiments, or a portion thereof, may further include appropriate input means for receiving, for example, measurement and / or control data, and output means for outputting, for example, control or any other data, such as a determined heat load. One or more specific integrated circuits, such as application specific integrated circuits (ASICs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), and / or discrete electronic components and devices may also be used to implement the functions according to any one of the embodiments.

[0054] Many electrical devices, such as power converters and components thereof, may include processors and memories that can be used to implement functions according to various embodiments described herein. Therefore, at least some modifications and configurations that may be required to implement the embodiments may be performed as software routines, which may be implemented as added or updated software routines. If at least part of the functions of any embodiment are implemented by software, the software may be provided as a computer program product containing computer program code, which, when run on a computer, causes the computer or corresponding device to perform the functions according to the embodiments described herein. Such computer program code may be stored or generally contained on a computer-readable medium, such as a suitable memory, such as flash memory or optical memory, from which it may be loaded to a unit or units that execute the program code. In addition, such computer program code that implements any embodiment may be loaded to a unit or units that execute the computer program code via, for example, a suitable data network, and it may replace or update a program code that may exist. An embodiment may provide a computer program embodied on any client-readable distribution / data storage medium or storage unit or manufactured part, including program instructions executable by one or more processors / computers, which, when loaded into a device, constitute a monitoring device, or any corresponding unit or entity that provides the corresponding function, or at least partially provide the corresponding function. Programs, also called program products, include software routines, program fragments constituting "program libraries", applets and macros, which can be stored in any medium and can also be downloaded to a device. In other words, each or some or one possible unit / subunit and / or algorithm for one or more of the above functions / operations, for example, by Figures 1 to 8 Any of the methods and any combination thereof may be an element comprising one or more arithmetic logic units, multiple special registers and control circuits.

[0055] It is obvious to those skilled in the art that, as technology advances, creative concepts can be implemented in various ways. In addition, it is clear to those skilled in the art that the described exemplary embodiments can, but need not, be combined with other exemplary embodiments in various ways. The present invention and its embodiments are not limited to the above examples, but can be varied within the scope of the claims. If any exemplary embodiments and / or features described herein do not fall within the scope of the independent claims, they are interpreted as examples that help understand the various embodiments of the present invention.

Claims

1. A method for controlling a power converter system, the power converter system comprising: An induction motor having a rotor, a first stator winding and at least one second stator winding, wherein the first stator winding and the at least one second stator winding are multi-phase windings; as well as a first power converter connected to the first stator winding and, for each second stator winding, a respective second power converter connected to the second stator winding, The method comprises: controlling the first stator winding of the induction motor via the first power converter; controlling each second stator winding of the induction motor via the corresponding second power converter; receiving, in the first power converter and each second power converter, a mechanical angle of the rotor of the induction motor; In the first power converter, determining a first slip angle estimate of the rotor based on an estimated rotor flux and the mechanical angle of the rotor; transmitting the determined first slip angle estimate from the first power converter to each second power converter; and In each second power converter: determining a slip angle reference based on the first slip angle estimate transmitted from the first power converter and a predetermined phase shift between the second stator winding in question and the first stator winding; and A rotor flux angle estimate is determined based on the determined slip angle reference and the mechanical angle of the rotor.

2. The method of claim 1 , wherein determining the rotor flux angle estimate in each second power converter comprises: The rotor flux angle estimate is determined based on the determined first slip angle reference, the mechanical angle of the rotor, and a stator current of the corresponding second stator winding.

3. The method of claim 2, wherein determining the rotor flux angle estimate in each second power converter comprises: determining a second slip angle estimate based on the determined slip angle reference and the stator current of the corresponding second stator winding, and The rotor flux angle estimate is determined based on the determined second slip angle estimate and the mechanical angle of the rotor.

4. The method of claim 2, wherein determining the rotor flux angle estimate in each second power converter comprises: determining a rotor flux angle reference based on the determined slip angle reference and the mechanical angle of the rotor; determining a second slip angle estimate based on the determined rotor flux angle reference and the stator current of the corresponding second stator winding; The rotor flux angle estimate is determined based on the determined second slip angle estimate and the mechanical angle of the rotor.

5. The method of claim 1 , wherein determining the rotor flux angle estimate in each second power converter comprises: The rotor flux angle estimate is determined based on the determined slip angle reference, the mechanical angle of the rotor, a stator current of the corresponding second stator winding, and a stator voltage of the corresponding second stator winding.

6. The method of claim 5, wherein determining the rotor flux angle estimate in each second power converter comprises: determining a rotor flux angle reference based on the determined slip angle reference and the mechanical angle of the rotor; as well as The rotor flux angle estimate is determined based on the determined rotor flux angle reference, the stator current of the corresponding second stator winding, and the stator voltage of the corresponding second stator winding.

7. A method according to any one of claims 1 to 6, wherein the determined rotor flux angle estimate is used in each second power converter to control the respective second stator winding.

8. A method according to any one of claims 1 to 6, wherein the first stator winding is controlled by the first power converter and each second stator winding is controlled by the respective second power converter according to a common torque reference.

9. A power converter system comprising: a first power converter configured to be connected to a first stator winding to control the first stator winding of an induction motor having a rotor, the first stator winding, and at least one second stator winding, wherein the first stator winding and the at least one second stator winding are multi-phase windings; as well as at least one second power converter configured to be connected to a corresponding second stator winding to control the corresponding second stator winding of the induction motor, The first power converter comprises: means configured to receive a mechanical angle of said rotor of said induction motor; means configured to determine a first slip angle estimate of the rotor based on the estimated rotor flux and the mechanical angle of the rotor; and means configured to communicate the determined first slip angle estimate to the at least one second power converter; and wherein the at least one second power converter comprises: means configured to receive the mechanical angle of the rotor of the induction motor; means configured to receive the determined first slip angle estimate from the first power converter; means configured to determine a slip angle reference based on the first slip angle estimate received from the first power converter and a predetermined phase shift between the corresponding second stator winding and the first stator winding; and Means are configured to determine a rotor flux angle estimate based on the determined slip angle reference and the mechanical angle of the rotor.

10. The power converter system of claim 9, wherein the means configured to determine the rotor flux angle estimate comprises means configured to determine the rotor flux angle estimate based on the determined slip angle reference, the mechanical angle of the rotor, and the corresponding second stator winding.

11. The power converter system of claim 10, wherein the means configured to determine the rotor flux angle estimate comprises: means configured to determine a second slip angle estimate based on the determined slip angle reference and said stator current of said corresponding second stator winding; as well as Means configured to determine the rotor flux angle estimate based on the determined second slip angle estimate and the mechanical angle of the rotor.

12. The power converter system of claim 10, wherein the means configured to determine the rotor flux angle estimate comprises: means configured to determine a rotor flux angle reference based on the determined slip angle reference and the mechanical angle of the rotor; means configured to determine a second slip angle estimate based on the determined rotor flux angle reference and the stator current of the corresponding second stator winding; as well as Means configured to determine the rotor flux angle estimate based on the determined second slip angle estimate and the mechanical angle of the rotor.

13. The power converter system of claim 9, wherein the device configured to determine the rotor flux angle estimate comprises a device configured to determine the rotor flux angle estimate based on the determined slip angle reference, the mechanical angle of the rotor, the stator current of the corresponding second stator winding, and the stator voltage of the corresponding second stator winding.

14. The power converter system of claim 13, wherein the means configured to determine the rotor flux angle estimate comprises: means configured to determine a rotor flux angle reference based on the determined slip angle reference and the mechanical angle of the rotor; as well as means configured to determine the rotor flux angle estimate based on the determined rotor flux angle reference, the stator current of the corresponding second stator winding, and the stator voltage of the corresponding second stator winding.

15. A power converter system according to any one of claims 9 to 14, wherein the power converter system comprises means configured to measure the mechanical angle of the rotor of the induction motor.

16. A power converter system according to any one of claims 9 to 14, wherein the power converter system comprises an induction machine having a rotor, a first stator winding and at least one second stator winding, wherein the first stator winding and the second stator winding are multi-phase windings, Wherein the first power converter is connected to the first stator winding of the induction motor, and the at least one second power converter is connected to a corresponding second stator winding of the induction motor.

17. The power converter system of claim 16, wherein the first power converter comprises a first inverter, wherein an output of the first inverter is connected to the first stator winding of the induction motor, and the second power converter comprises a second inverter, wherein an output of the second inverter is connected to the second stator winding of the induction motor.

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