Device and method for determining the rotation of an induction machine

文档序号：954941 发布日期：2020-10-30 浏览：2次中文

阅读说明：本技术 用于确定感应电机的转动的装置和方法 (Device and method for determining the rotation of an induction machine ) 是由安西·西内尔沃于 2020-04-20 设计创作，主要内容包括：本发明提出了一种用于估计感应电机的转动速度和/或转动方向的装置。该装置控制感应电机的定子电压(uu、uv、uw),使得由定子电压构成的电压空间矢量具有固定方向,并且由感应电机的定子电流(iu、iv、iw)构成的电流空间矢量具有预定长度或预定的d分量。基于电流空间矢量的q分量的波形来估计转动速度和/或转动方向,其中,电流空间矢量的d分量与电压空间矢量平行,并且电流空间矢量的q分量与电压空间矢量垂直。该装置在感应电机没有足够的磁通量用于对转动速度和/或转动方向进行基于通量的确定时是可用的。(The present invention proposes an apparatus for estimating the rotational speed and/or rotational direction of an induction motor. The device controls the stator voltage (u) of an induction machine u 、u v 、u w ) So that a voltage space vector composed of the stator voltage has a fixed direction and is composed of a stator current (i) of the induction motor u 、i v 、i w ) The resulting current space vector has a predetermined length or a predetermined d-component. Based on current spaceThe waveform of the q-component of the vector, where the d-component of the current space vector is parallel to the voltage space vector and the q-component of the current space vector is perpendicular to the voltage space vector, is used to estimate the rotational speed and/or rotational direction. The arrangement is usable when the induction machine does not have sufficient magnetic flux for flux-based determination of the speed and/or direction of rotation.)

1. An apparatus (101), comprising a processing system (102) implemented with one or more processor circuits, the processing system (102) configured to:

-controlling the stator voltage (u) of the induction machine (105)_u、u_v、u_w) To form a voltage space vector having a fixed direction with respect to a stator of the induction machine,

-controlling the length of the voltage space vector to adjust the stator current (i) of the induction machine_u、i_v、i_w) Satisfying a condition that a current space vector composed of the stator currents has a predetermined length; and

-estimating, based on the waveform of the q-component of the current space vector, at least one of: a rotational speed of a rotor (106) of the induction machine, a rotational direction of the rotor,

wherein a d-component of the current space vector is parallel to the voltage space vector and a q-component of the current space vector is perpendicular to the voltage space vector.

2. The apparatus of claim 1, wherein the processing system is configured to: detecting a direction of change of a q-component of the current space vector at the start of satisfying a condition related to the stator current, and determining the rotation direction based on the detected direction of change.

3. The apparatus of claim 1 or 2, wherein the processing system is configured to: detecting a polarity of a first local extremum of a waveform of a q-component of the current space vector occurring after a condition related to the stator current starts to be satisfied, and determining the rotational direction based on the detected polarity.

4. The apparatus of any one of claims 1-3, wherein the processing system is configured to: measuring a first time value indicating a time elapsed from when the condition related to the stator current starts to be satisfied to a time when a waveform of a q-component of the current space vector reaches a first local extremum after the condition related to the stator current starts to be satisfied, and estimating the rotational speed based on the measured first time value.

5. The apparatus of any of claims 1-4, wherein the processing system is configured to: measuring at least one second time value indicative of an elapsed time between two local maxima or two local minima of the waveform of the q-component of the current space vector, and estimating the rotational speed based on the measured at least one second time value.

6. The apparatus of any one of claims 1-5, wherein the processing system is configured to: the rotational speed is estimated based on the waveform of the q-component of the current space vector, and then the stator voltage is controlled to rotate the current space vector at the estimated rotational speed.

7. The apparatus of claim 6, wherein the processing system is configured to: estimating a flow direction of air gap power of the induction machine based on the stator voltage, the stator current and a stator resistance when the current space vector is rotating to decrease a rotational speed of the current space vector when the estimated flow direction is towards a rotor of the induction machine and to increase the rotational speed of the current space vector when the estimated flow direction is out of the rotor of the induction machine.

8. The apparatus of any one of claims 1-7, wherein the processing system is configured to:

-monitoring whether the waveform of the q-component of the current space vector reaches a local extremum within a predetermined time period after the condition related to the stator current starts to be fulfilled, and

-estimating, in response to a condition that a q-component of the current space vector does not reach a local extremum within the predetermined time period, at least one of the following based on a behavior of the induction machine with a magnetic flux generated during the predetermined time period: rotational speed, rotational direction.

9. The apparatus of any one of claims 1-8, wherein the condition related to the stator current is: the current space vector has a predetermined length, and the predetermined length is in a range of 30% to 100% of a peak value of a nominal current of the induction motor.

10. The apparatus of any one of claims 1-8, wherein the condition related to the stator current is: the current space vector has a predetermined d-component, and the predetermined d-component is in a range of 20% to 70% of a peak value of a nominal current of the induction machine.

11. A power electronic converter (100), comprising:

a converter stage (104) for forming a stator voltage for an induction machine (105),

a controller (103) for controlling the stator voltage based at least partly on a stator current of the induction machine, an

An apparatus (101) according to any one of claims 1-10, the apparatus being configured to estimate at least one of: a rotational speed of a rotor (106) of the induction machine, a rotational direction of the rotor.

12. A method, characterized in that the method comprises:

-controlling (301) a stator voltage (u) of the induction machine (105)_u、u_v、u_w) To form a voltage space vector having a fixed direction with respect to a stator of the induction machine,

-controlling (302) the length of the voltage space vector to adjust the stator current (i) of the induction machine_u、i_v、i_w) Satisfying a condition that a current space vector composed of the stator currents has a predetermined length; and

-estimating (303), based on the waveform of the q-component of the current space vector, at least one of: a rotational speed of a rotor (106) of the induction machine, a rotational direction of the rotor,

wherein a d-component of the current space vector is parallel to the voltage space vector and a q-component of the current space vector is perpendicular to the voltage space vector.

13. A computer program, characterized in that the computer program comprises computer-executable instructions for controlling a programmable processor to perform the actions of:

-controlling the stator voltage (u) of the induction machine (105)_u、u_v、u_w) To form a voltage space vector having a fixed direction with respect to a stator of the induction machine,

-estimating, based on the waveform of the q-component of the current space vector, at least one of: a rotational speed of a rotor (106) of the induction machine, a rotational direction of the rotor,

wherein a d-component of the current space vector is parallel to the voltage space vector and a q-component of the current space vector is perpendicular to the voltage space vector.

14. A non-transitory computer readable medium encoded with the computer program of claim 13.

Technical Field

The present disclosure relates to an apparatus and method for estimating a rotational speed and/or a rotational direction of an induction motor. The arrangement is usable when the induction machine does not have sufficient magnetic flux for flux-based determination of the speed and/or direction of rotation. Furthermore, the present disclosure relates to a power electronic converter for driving an induction machine. Furthermore, the present disclosure relates to a computer program for estimating the rotational speed and/or rotational direction of an induction machine.

Background

In many cases, it is necessary to energize a rotating induction motor whose rotational speed is not measured and which does not have sufficient magnetic flux for flux-based determination of rotational speed and/or rotational direction. This scenario arises in applications where there is no tachometer or other speed measuring device and the induction machine restarts after the power has been removed before the rotor stops rotating but after the magnetic flux has disappeared. In applications of the above type, a device that supplies power to the induction machine (such as, for example, a power electronic converter) magnetizes the induction machine with the voltage that constitutes the rotating voltage space vector. If the direction and/or speed of rotation of the voltage space vector differs too much from the direction and speed of rotation of the rotor, large currents may be generated, which may damage the induction motor and/or the devices supplying the induction motor. The situation may be particularly problematic when the voltage space vector and the rotor of the induction machine have opposite directions of rotation. Therefore, it is necessary to estimate the direction of rotation of the rotor, and advantageously also the speed of rotation of the rotor, before starting to magnetize the induction machine with the voltages constituting the voltage space vector of the rotation.

Known methods for estimating the rotational speed and/or rotational direction of an induction machine include: the stator windings of the induction machine are supplied with direct current pulses and the stator voltage is measured as a function of the direction and speed of rotation. The challenges associated with this approach are that the rotation dependent component of the stator voltage is small and the stator voltage has switching ripple and other components related to stator resistance and stator stray inductance. Therefore, based on the above-described stator voltage, it is difficult to estimate the rotational speed and/or the rotational direction with sufficient reliability.

Publications JP2007274900 and EP1536552 describe methods for determining the rotational speed and direction of a free-running induction motor. The method is based on the act of supplying a direct current to a stator of the induction machine in a first space vector direction and detecting a current induced in a second space vector direction perpendicular to the first space vector direction.

Publication US2012098472 describes a mechanism for a motor controller for engaging a rotary electric machine. The power section is configured to provide power to the motor. The control is configured to control the power section. The control is configured to search for a motor frequency of the motor by applying a small excitation voltage to the motor, and initially apply the excitation voltage at a voltage frequency that is a maximum frequency. The control is configured to track the motor frequency until the motor frequency is below the equivalent speed command and engage the motor by applying a higher voltage to the motor.

Publication EP1049243 describes a system comprising means for determining a stator voltage vector, for measuring a stator winding current vector, for deriving an estimated or modeled stator flux vector based on the current and voltage vectors, and for deriving a stator current vector demand value based on the flux vector. The current regulator generates a value that applies the stator voltage vector such that the stator current is regulated to a desired value.

The publication Kondo Keiichiro "Re-standing technologies for relating to rotating controlled AC motors at the rotating stands" (10 th Asia control conference (ASCC) 2015, IEEE 2015 5 months 31 days, pages 1-6) describes a restart method associated with a rotating sensorless control method for induction motors and permanent magnet synchronous machines.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of various inventive embodiments. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplary and non-limiting embodiments of the invention.

According to the present invention, a novel apparatus is provided that estimates the speed and/or direction of rotation of an induction machine when the induction machine does not have sufficient magnetic flux for flux-based determination of the speed and/or direction of rotation. An apparatus according to the invention comprises a processing system implemented with one or more processor circuits, the processing system configured to:

-controlling the stator voltage of the induction machine to constitute a voltage space vector having a fixed direction with respect to the stator of the induction machine,

-controlling the length of the voltage space vector to adjust the stator current of the induction machine to meet the condition that the current space vector formed by the stator currents has a predetermined length; and

-estimating, based on the waveform of the q-component of the current space vector, at least one of: the rotational speed of the rotor of the induction motor, the rotational direction of the rotor,

wherein a d-component of the current space vector is parallel to the voltage space vector and a q-component of the current space vector is perpendicular to the voltage space vector.

The stator current is inherently filtered by the windings of the induction machine, and therefore, compared to voltage-based methods, the waveform based on the q-component of the current space vector is easier to form a sufficiently reliable estimate of the rotational speed and/or rotational direction of the induction machine.

According to the present invention, there is also provided a novel power electronic converter, comprising:

a converter stage for forming a stator voltage for an induction machine,

a controller for controlling the stator voltage based at least partly on a stator current of the induction machine, an

-an apparatus according to the invention for estimating at least one of: a rotational speed of a rotor of the induction motor, a rotational direction of the rotor.

According to the present invention, a new method is also provided for estimating the speed and/or direction of rotation of an induction machine when the machine does not have sufficient magnetic flux for flux-based determination of speed and/or direction of rotation. The method according to the invention comprises the following steps:

-controlling a stator voltage of an induction machine to constitute a voltage space vector having a fixed direction with respect to a stator of the induction machine,

-estimating, based on the waveform of the q-component of the current space vector, at least one of: a rotational speed of a rotor of the induction motor, a rotational direction of the rotor.

According to the present invention, there is also provided a novel computer program for estimating the speed and/or direction of rotation of an induction machine when the machine does not have sufficient magnetic flux for flux-based determination of speed and/or direction of rotation. The computer program according to the invention comprises computer-executable instructions for controlling a programmable processor to perform the following actions:

-controlling a stator voltage of an induction machine to constitute a voltage space vector having a fixed direction with respect to a stator of the induction machine,

-estimating, based on the waveform of the q-component of the current space vector, at least one of: a rotational speed of a rotor of the induction motor, a rotational direction of the rotor.

According to the present invention, a new computer program product is also provided. The computer program product comprises a non-volatile computer-readable medium, such as a compact disc "CD", encoded with a computer program according to the invention.

Various exemplary and non-limiting embodiments are described in the accompanying dependent claims.

The exemplary and non-limiting embodiments, both as to organization and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplary embodiments when read in connection with the accompanying drawings.

The verbs "comprise" and "comprise" are used in this document as open-ended limitations that neither exclude nor require the presence of unrecited features. The features recited in the dependent claims may be freely combined with each other, unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" throughout this document (i.e., in the singular) does not exclude a plurality.

Drawings

Exemplary and non-limiting embodiments and advantages thereof are described in more detail below with reference to the accompanying drawings, in which:

fig. 1 shows a power electronic converter comprising an apparatus according to an exemplary and non-limiting embodiment for estimating the rotational speed and/or rotational direction of an induction machine when the induction machine does not have sufficient magnetic flux for flux-based determination of the rotational speed and/or rotational direction,

Figure 2a shows a functional block diagram of an apparatus according to an exemplary and non-limiting embodiment,

FIG. 2b shows a functional block diagram of an apparatus according to another exemplary and non-limiting embodiment, an

Fig. 3 shows a flow diagram of a method for estimating a rotational speed and/or a rotational direction of an induction motor when the induction motor does not have sufficient magnetic flux for a flux-based determination of the rotational speed and/or the rotational direction, according to an exemplary and non-limiting embodiment.

Detailed Description

The specific examples provided in the following description should not be construed as limiting the scope and/or applicability of the appended claims. The list and set of examples provided in the following detailed description are not exhaustive unless explicitly stated otherwise.

FIG. 1 illustrates a power electronics converter according to an exemplary and non-limiting embodimentA transducer 100. The power electronic converter 100 comprises a converter stage 104 for forming a stator voltage for an induction machine 105. For illustrative purposes, the number of phases of induction motor 105 is three, but different numbers of phases are possible. In fig. 1, the stator phase voltage is denoted u_u、u_vAnd u_w. In the exemplary case shown in fig. 1, the input voltage of the power electronic converter 100 is a direct current "DC" voltage U _DC. It is also possible that the input voltage is, for example, a three-phase alternating "AC" voltage. In this exemplary case, the power electronic converter may comprise, for example, a rectifier and a DC voltage intermediate circuit between the rectifier and the converter stage 104. The converter stage 104 may be configured to employ, for example, pulse width modulation ("PWM") to convert the DC voltage U_DCConverted into stator voltage u_u、u_vAnd u_w. However, it is also possible that the converter stage 104 is a matrix converter stage for performing a conversion from e.g. a three-phase input AC voltage to the stator voltage u of the induction machine 105_u、u_vAnd u_wDirect conversion of (2). Power electronic converter 100 further includes a stator voltage u for controlling induction machine 105_u、u_vAnd u_wThe controller 103. In fig. 1, a set of switch control values transmitted by the controller 103 to the converter stage 104 is denoted by s. The controller 103 may include means for implementing different control modes such as one or more vector control modes and scalar control modes. In the vector control mode, the controller 103 may be based at least in part on the stator current i of the induction machine 105_uAnd i_vAnd controls the stator voltage u based on machine parameters, i.e. the inductance and resistance of the induction machine 105_u、u_vAnd u_w. In the exemplary case shown in fig. 1, it is assumed that the stator current i _u、i_vAnd i_wThe sum is zero, and since i_w＝-i_u-i_vThus, the controller 103 only needs two stator currents i_uAnd i_v。

The power electronic converter 100 also includes, according to an exemplary and non-limiting embodiment, a device 101 for providing sufficient magnetic flux at the induction machine 105 for balancingRotational speed omega_rAnd/or rotational direction estimating rotational speed ω of induction motor 105 based on the flux determination_rAnd/or the direction of rotation.

FIG. 2a shows when the processing system 102 of the apparatus 101 is estimating the rotational speed ω of the induction motor 105_rAnd/or an exemplary functional block diagram corresponding to processing system 102 when turning directions. The processing system 102 is configured to control a stator voltage u of the induction machine 105_u、u_vAnd u_wTo form a voltage space vector having a fixed direction relative to the stator of induction machine 105. The voltage space vector is defined as (2/3) (u)_u+au_v+a²u_w) Wherein, in the step (A),

where j is an imaginary unit. In fig. 2a, the direction of the voltage space vector is represented by the d-axis of the dq coordinate system fixed to the stator of induction machine 105, because the voltage space vector has a fixed direction relative to the stator. Thus, the voltage space vector is u_d. The processing system 102 is configured to implement a function block 211 that converts the voltage space vector into a reference stator voltage u _uref、u_vrefAnd u_wrefSo that u is_uref＝u_dcos(θ)，u_vref＝u_dcos (theta-120 DEG), and u_wref＝u_dcos (θ -240 °), where θ is the angle between the d-axis of the dq coordinate system and the magnetic axis of phase u of the stator winding. The angle θ may be expressed as an electrical angle or an electric arc, for example. The function block 212 implemented by the controller 103 shown in fig. 1 will reference the stator voltage u_uref、u_vrefAnd u_wrefInto a set of switch control values s which are passed to the converter stage 104.

The processing system 102 is configured to implement a function block 213, the function block 213 calculating a stator current i_u、i_vAnd i_wThe d and q components of the constructed current space vector are such that:

and is

Wherein i_w＝-i_u-i_vAnd d component i of the current space vector_dParallel to the voltage space vector, and the q-component i of the current space vector_qPerpendicular to the voltage space vector. Without limiting generality, the fixed direction of the voltage space vector may be chosen to be the direction of the magnetic axis of phase u, i.e., θ is 0. In this example case:

i_d＝(2/3)(i_u-i_v/2-i_w/2) and

the processing system 102 is configured to implement: a function block 217, the function block 217 calculating a length i of the current space vector_abs(ii) a And a function block 210, the function block 210 controlling a length of the voltage space vector such that the stator current i_u、i_vAnd i_wSatisfies that the current space vector has a predetermined length i _abs，refThe conditions of (1). The function block 210 may be, for example, a proportional "P" regulator, a proportional and integral "PI" regulator, a proportional, integral and derivative "PID" regulator, or some other suitable regulator. Predetermined length i of current space vector_abs，refMay for example be in the range of 30% to 100% of the peak value of the nominal current of the induction machine 105.

The processing system 102 is configured to implement a function block 214, the function block 214 based on a q-component i of a current space vector_qTo estimate the direction of rotation and/or the speed of rotation omega_r. The following describes estimating the rotational direction and/or rotational speed ω_rExemplary manner of (a).

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to meet the above at the outsetCondition i_abs＝i_abs，refTime-detecting q-component i_qAnd the direction of rotation is determined based on the detected direction of change. As shown in the exemplary waveform 215 of fig. 2a, if the q component i_qFirst, the rotation direction is determined to be positive. Accordingly, as shown in the exemplary waveform 216 shown in FIG. 2a, if the q component i_qFirst, the direction of rotation is determined to be negative.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to: detecting satisfaction of condition i at the beginning _abs＝i_abs，refQ component i appearing later_qAnd determining the direction of rotation based on the detected polarity. As shown in the exemplary waveform 215 shown in fig. 2a, if the first local extremum is a negative value, the direction of rotation is determined to be positive. Accordingly, as shown in the exemplary waveform 216 shown in FIG. 2a, if the first local extremum is a positive value, then the direction of rotation is determined to be negative.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to: measuring a first time value T₁First time value T₁Indicating satisfaction of condition i from the beginning_abs＝i_abs，refTo q component i_qThe time elapsed at the moment the waveform of (a) reaches its first local extremum. The processing system 102 is configured to determine a first time value T based on the measured time value₁To estimate the rotational speed omega_rSo that ω is_r，estimate＝π/T₁Where p is the number of pole pairs of the induction machine 105.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to: measuring at least one second time value T₂A second time value T₂Indicating q component i_qThe time elapsed between two consecutive local maxima or between two consecutive local minima of the waveform of (a). The processing system 102 is configured to determine a second time value T based on the measured time value ₂To form a counter-rotational speed omega_rSo that ω is_r，estimate＝2π/T₂/p。

At the rootIn an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to apply two or more of the above-described exemplary ways to estimate the direction of rotation and/or the speed of rotation ω_r. Albeit by observing the q-component i_qA number of local maxima and/or a number of local minima of the waveform of (a) may be such as to impart a relative rotational speed ω_rIs more accurate, but this increases the time required to obtain the estimate.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to estimate the rotational speed ω in one or more of the manners described above_rThen controlling the stator voltage u_u、u_vAnd u_wThe current space vector is caused to rotate at the estimated rotational speed. The current space vector may be rotated, for example, such that the voltage space vector (2/3) (u) is controlled_u+au_v+a²u_w) To control the current space vector (2/3) (i)_u+ai_v+a²i_w) And the rotational speed of the current space vector is controlled by controlling the rotational speed of the voltage space vector.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to be based on a stator voltage u_u、u_vAnd u_wStator current i_u、i_vAnd i _wAnd stator resistance as the current space vector rotates to estimate the air gap power P of the induction machine 105_agThe direction of flow of (a). The processing system 102 is configured to decrease the rotational speed of the current space vector when the estimated flow direction is towards the rotor 106 of the induction machine and to increase the rotational speed of the current space vector when the estimated flow direction is out of the rotor of the induction machine. When the magnetic energy contained by the induction machine 105 is substantially constant, the air gap power can be estimated as:

P_ag＝u_ui_u+u_vi_v+u_wi_w-R_s(i_u ²+i_v ²+i_w ²)，

wherein R is_sIs to make sureA sub-resistance. If the estimated air gap power flows towards the rotor, the induction machine 105 acts as a motor and the estimation of the rotational speed, i.e. the rotational speed of the current space vector, is too high. Accordingly, if the estimated air gap power flows from the rotor, the induction machine 105 acts as a generator and the estimation of the rotational speed (i.e., the rotational speed of the current space vector) is too low.

In an apparatus according to an exemplary and non-limiting embodiment, the processing system 102 is configured to monitor that the above condition I is met at the beginning_abs＝I_abs，refQ component i in a predetermined period of time thereafter_qWhether the waveform of (a) reaches a local extremum. If the rotor is rotating so slowly that the q-component i is present in the above-mentioned time period _qIf the local extremum is not reached, the rotor will be magnetized by the stator current, and a suitable known speed detection method for a magnetized rotor may be used after the above-mentioned time period. In other words, the processing system 102 may be configured to estimate the rotational speed ω based on behavior of the induction machine 105 with magnetic flux generated during the time period in response to a condition that the local extremum is not reached within the time period_rAnd/or the direction of rotation. Speed detection methods for magnetized rotors may include, for example: arranging a series of stator shorts; measuring the short-circuit current of the stator; and estimating the speed and/or the direction of rotation based on the measured short-circuit current.

Fig. 2b shows an exemplary functional block diagram corresponding to a processing system of an apparatus according to an exemplary and non-limiting embodiment. The functional block diagram shown in FIG. 2b corresponds to when the processing system is estimating the rotational speed ω of the induction motor 105_rAnd/or a handling system while turning. In this exemplary case, the processing system is configured to control the length of the voltage space vector such that the stator current i_u、i_vAnd i_wThe following conditions are satisfied: the current space vector having a predetermined d-component i _d，refI.e. i_d＝i_d，ref. Predetermined d-component i of current space vector_d，refMay for example be in the range of 20% to 70% of the peak value of the nominal current of the induction machine 105. The functional blocks 210b, 211b, shown in FIG. 2b,212b, 213b and 214b may be similar to the function blocks 210 and 211, respectively, shown in fig. 2 a. The exemplary embodiment shown in fig. 2b requires less computation than the exemplary embodiment shown in fig. 2a, because the length of the current space vector is not computed in the exemplary embodiment shown in fig. 2 b. However, in some cases, the exemplary embodiment shown in FIG. 2a may provide better results because, for example, the saturation state of induction machine 105 may be better controlled when using the exemplary embodiment shown in FIG. 2 a.

The processing system 102 shown in fig. 1 may be implemented with one or more processor circuits, each of which may be a programmable processor circuit provided with appropriate software, a special purpose hardware processor (e.g., an application specific integrated circuit "ASIC"), or a configurable hardware processor (e.g., a field programmable gate array "FPGA"). Further, the processing system may include one or more memory devices, each of which may be, for example, a random access memory "RAM" circuit. In many power electronic converters, the means for estimating the speed and/or direction of rotation according to exemplary and non-limiting embodiments may be implemented using hardware of the control system of the power electronic converter.

The above-described apparatus 101 is an example of an apparatus including:

-means for controlling the stator voltage of the induction machine to form a voltage space vector having a fixed direction with respect to the stator of the induction machine,

-means for controlling the length of the voltage space vector to adjust the stator current of the induction machine to meet a condition, which is one of the following conditions: a) a current space vector consisting of stator currents has a predetermined length; b) the current space vector has a predetermined d-component parallel to the voltage space vector, an

-means for estimating the rotational speed of the rotor and/or the rotational direction of the rotor of the induction machine based on the waveform of the q-component of the current space vector, which q-component is perpendicular to the voltage space vector.

-action 301: controlling a stator voltage of the induction machine to form a voltage space vector having a fixed direction with respect to the stator of the induction machine,

-an action 302: controlling the length of the voltage space vector to adjust the stator current of the induction machine to satisfy a condition, the condition being one of: a) a current space vector consisting of stator currents has a predetermined length; b) the current space vector has a predetermined d-component parallel to the voltage space vector, an

-action 303: the rotational speed of the rotor of the induction motor and/or the rotational direction of the rotor is estimated based on the waveform of the q component of the current space vector, which is perpendicular to the voltage space vector.