DE102017201215A1 - Monitoring a torque of an asynchronous machine - Google Patents

Abstract

An electrical asynchronous machine (105) comprises several phases (U, V, W). A method (400) for determining a monitoring torque (M_E2) of the asynchronous machine (105) comprises steps of determining phase currents (Is) flowing through the phases (U, V, W) and a rotational speed (n) and / or Rotation angle of the asynchronous machine (105); transforming (405, 410) the phase currents (Is) from the uvw system to the dq system; and determining (430) the monitoring torque (M_E2) based on a q-component of the transformed phase currents.

Description

The invention relates to the monitoring of an asynchronous machine. In particular, the invention relates to the monitoring of a torque of a field-oriented controlled asynchronous machine.

An asynchronous machine can be controlled, for example, by means of a field-oriented control (FOR) or field-oriented control (FOS). If the asynchronous machine is used for a safety-relevant task, for example for driving a motor vehicle, then it must be ensured that the asynchronous machine precisely follows a control specification. A desired acceleration (driving or braking) must not be avoided and an unwanted acceleration (driving or braking) must not take place. A torque provided by the asynchronous machine must therefore be monitored to prevent a fault condition that may endanger an occupant of the motor vehicle or another road user outside the motor vehicle.

The torque can already be determined in the context of the FOS or FOR or can be determined with little effort from parameters of the control. The control plane of the asynchronous machine can also be called level 1. For safety reasons, the torque must still be determined on a separate level 2, wherein preferably only signals are used that come from sources that meet a predetermined safety requirement level. Such a stage may, for example, be determined according to the ASIL specifications (for example ASIL-A, ASIL-B or ASIL-C). By contrast, the signals of the first level can, according to the ASIL system, also be assigned to the level QM (quality management), for which no special conditions are to be met. The torque determined in level 2 is also called monitoring torque.

The determination of the torque of the asynchronous machine can be difficult under certain circumstances. For example, if the torque is determined based on stator magnitudes, a drastically inaccurate torque may be determined when an angular velocity of the rotor is close to zero. Similarly large errors can occur if a voltage applied to one phase of the asynchronous machine is very small, in particular in the region of a terminal voltage of a current valve used in the inverter. For example, the flow control valve may comprise an IGBT or FET type of semiconductor, and the turn-on voltage may be about 1V.

An object underlying the present invention is to provide an improved technique for determining a monitoring torque of an asynchronous machine. The invention solves this problem by means of the subject matters of the independent claims. Subclaims give preferred embodiments again.

An electrical asynchronous machine comprises several phases. A method for determining a monitoring torque of the asynchronous machine includes steps of determining phase currents flowing through the phases and a rotational speed and / or a rotational angle (rotor angle) of the asynchronous machine; transforming the phase currents from the uvw system to the dq system; and determining the monitoring torque based on a q component of the transformed phase currents.

It is assumed that the d-component of the current flowing through the asynchronous machine builds up the magnetic field in the machine and the q-component generates the torque. The q-component can be determined relatively simply by one or more appropriate transformations of the particular phase currents, so that the monitoring moment can be determined quickly and reliably. By using the rotational speed or the rotational angle or a variable derivable therefrom, the method can be improved in an improved manner.

The method can require only a few measured variables, so that it can be physically realized with manageable effort on an asynchronous machine. The implementation of the method is less complicated and can already be done by means of a processing device with manageable processing capacity. The method can thereby also be suitable for use in a real-time environment or be carried out by means of a cost-effective control device. In particular, the control device can also perform an additional control task, for example an FOS or FOR of the asynchronous machine.

Furthermore, the method uses analytical formulas instead of a heuristic or experimental values, so that modification or modification of input parameters can be easily made by appropriate adaptation of the processing. For example, the method may comprise converting the rotational speed or the rotational angle into an angular velocity. If instead of a speed or rotation angle sensor, a sensor used to scan the angular velocity, this step of the process can be easily eliminated. The speed and the angular velocity can in a conventional manner be determined from the angle of rotation (when, for example, a rotation angle sensor is used), for example, by time derivative.

The monitoring torque can additionally be determined on the basis of a magnetizing current and machine parameters of the asynchronous machine. The machine parameters may be considered constant in one embodiment of the invention. The magnetizing current can be easily formed, in particular based on the d-component of the transformed phase currents.

The phase currents can first be transformed from the uvw system into the aß system and from there into the dq system. The first transformation can be carried out by means of fixed quantities. For the second transformation, a transformation angle can be easily determined.

The transformation angle can in particular be determined by means of integration via a function which comprises the rotational speed, the q-component of the transformed phase currents, a magnetizing current and a machine parameter of the asynchronous machine. Through the step of integrating, the method can achieve improved robustness.

The machine parameter may comprise at least one of an inductance of the rotor, an electrical resistance of the rotor, an inductance of the stator or a number of pole pairs of the asynchronous machine. The one or more machine parameters may be fixedly predetermined for a given asynchronous machine in a simple embodiment. In another embodiment, at least one of the machine parameters can be tracked to a temperature of the asynchronous machine. For this purpose, a machine model of the asynchronous machine can be used so that the machine parameter can be determined on the basis of the determined temperature or a predetermined machine parameter can be adapted to the temperature.

The phase currents and the rotational speed or the rotational angle can each be determined on the basis of measured values from sensors which fulfill a predetermined safety requirement level. Such a security requirement level can be specified, for example, as an ASIL level. The method can thereby be used in particular for securing an asynchronous machine whose operation is safety-relevant for a person or a device. For example, the asynchronous machine can be used as a traction drive of a motor vehicle and the motor vehicle can be set up to carry a person or to operate in a traffic in which other people are or move.

It is further preferred that the speed of the asynchronous machine is below a predetermined threshold while the method is being performed. In other words, it is preferred that a determination of the torque takes place only below the speed threshold by means of the method described. As the speed increases above the speed threshold, the second level torque may be determined by another method that is more suitable for higher speeds and that operates on the basis of stator sizes, for example. If the speed drops below the speed threshold again, it is possible in reverse to switch back to the rotor flux-based method described above.

The method may further comprise determining an error condition if the monitoring torque deviates from a desired torque by more than a predetermined amount. The desired torque can be predefined in particular as the q component of a space vector in the dq system. The space pointer may be provided for controlling the asynchronous machine by means of an FOS or FOR.

The asynchronous machine can be controlled by means of a FOR, wherein as part of the field-oriented control, a torque of the asynchronous machine is determined and an error condition is determined if the specific torque deviates from the monitoring torque by more than a predetermined amount.

An apparatus for determining a monitoring torque of a multi-phase asynchronous machine comprises interfaces for sensors for sampling phase currents flowing through the phases and a rotational speed and / or a rotational angle of the asynchronous machine; and processing means adapted to transform the phase currents from the uvw system to the dq system; and determine the monitoring torque based on a q component of the transformed phase currents.

The processing device may be configured to perform at least part of the method described above. Furthermore, the processing device can comprise a programmable microcomputer or microcontroller and the method can run as a computer program product with program code means on the processing device or be stored on a computer-readable medium. Advantages or features mentioned or described with regard to the method can be transferred to the device and vice versa.

• 1 ein Schaltbild einer feldorientierten Regelung (FOR) für eine Asynchronmaschine;
• 2 ein System zur überwachten Steuerung einer Asynchronmaschine;
• 3 einen Stromzeiger in verschiedenen Koordinatensystemen;
• 4 ein Ablaufdiagramm eines Verfahrens zum Bestimmen eines Überwachungsmoments der Asynchronmaschine im System von 2; und
• 5 einen Zusammenhang zwischen Drehmoment und Schlupf an einer Asynchronmaschine

darstellt. The invention will now be described in more detail with reference to the attached figures, in which:

• 1 a circuit diagram of a field-oriented control (FOR) for an induction machine;
• 2 a system for supervised control of an asynchronous machine;
• 3 a current pointer in different coordinate systems;
• 4 a flowchart of a method for determining a monitoring torque of the asynchronous machine in the system of 2 ; and
• 5 a relationship between torque and slip on an asynchronous machine

represents.

1 shows an exemplary field-oriented control 100 for an asynchronous machine 105 , The asynchronous machine 105 can be provided for use in a motor vehicle, for example in an electric or hybrid powertrain, in a power steering or as a servomotor. Especially when using the asynchronous machine 105 in a safety-relevant application where a control error can cause material damage or personal injury, the field-oriented scheme should 100 be monitored as below with reference to 2 will be explained in more detail.

The asynchronous machine 105 includes a stator 110 in which three exemplary phases U . V and W attached, and a rotor 115 which is rotatable with respect to the stator 110 is stored. Every phase U . V . W (or 1, 2, 3) comprises a winding in the asynchronous machine 105 and is with an inverter 102 connected, which is preferably formed in B6 bridge circuit with three half-bridges to the phases U . V . W in each case alternately with a high and a low potential of an intermediate circuit voltage Udc to connect, so that, depending on a duty cycle, a predetermined voltage at the respective phase U . V . W established. The inverter 102 is preferably controlled by means of PWM signals (pulse width modulation signals), which in the illustrated embodiment by the field-oriented control 100 to be provided.

The field-oriented control can be used as a device 100 be executed to control the rotational behavior of the induction machine 105 perform on the basis of a predetermined space vector i in the manner of a vector control. These can be parts of the device 100 in particular from a programmable microcomputer and the processing can be carried out digitally. The illustrated function blocks are usually passed through sequentially. The illustrated field-oriented regulation 100 can thus also be used as a flow chart for a process 100 for field-oriented control of the asynchronous machine 105 be understood.

The space vector i is given in dq representation with components IsdRef and IsqRef and is present as an input variable. The d component of the space vector i is a magnetic flux, and the q component a torque of the asynchronous machine 105 assigned. Different coordinate systems for the space vector i will be discussed below with reference to FIG 3 described in more detail.

The components of the space vector i are transmitted to a transformation device via optional proportional-integral elements PI 120 passed, which transforms the input variables into three voltages Us1, Us2, Us3, which at the phases U . V . W the asynchronous machine 105 are to be adjusted. Optionally, the determined voltages may then be limited to valid values by means of a limiter before a PWM generator 125 based on the determined voltages PWM signals PWM1, PWM2, PWM3 for the inverter 102 determined to the desired voltages at the phases U . V . W the asynchronous machine 105 provide.

For the control, it is necessary to phase currents Is1, Is2, Is3, through the phases U . V . W flow, determine. For this, different approaches are possible. In the illustrated embodiment, the phase currents are detected by current sensors 135 sampled. The phase currents Is1, Is2, Is3 are calculated on the basis of a rotation angle ω of the asynchronous machine 105 transformed by a further transformation means 170 into the dq coordinate system. In the present case, the mechanical angle of rotation Θ _mech the asynchronous machine 105 by means of a position sensor 140 sampled, for example, as an arrangement of Hall sensors or incremental encoders on the rotor 115 can be appropriate. By multiplying the mechanical rotation angle Θ _mech with the number of pole pairs pz of the asynchronous machine 105 can be the electrical angle of rotation Θ _el . The mechanical rotation speed ω _mech can be determined by deriving the mechanical rotation angle Θ _mech after the time. If this value is multiplied by the number of pole pairs pz, the electric rotary speed ω _el results.

The transformed values Isd, Isq of the phase currents Is1, Is2, Is3 are added to the components Isd _ref and Isq _{ref of} the given space vector i, before the resulting sums are applied to the PI elements and then to the transformation means 120 be guided. The DC link voltage Udc used in various determination steps may be determined in any known manner.

Optionally, the components Isd, Isq fed back additively to the space vector i by means of a decoupler 145 decoupled from each other on the basis of the rotational speed ω _el and as EMKd and EMKq additive to the input of the transformation means 120 be guided. An optional position estimation model 150 On the basis of the PWM signals and the phase currents Is1, Is2, Is3, an estimated rotational speed _ω and an estimated rotational angle Θ of the asynchronous machine 105 ready.

Furthermore, a temperature sensor is preferred 155 at the asynchronous machine 105 intended. The temperature sensor 155 is preferred for determining the stator 110 prevailing temperature. The temperature sensor 155 and the current sensors 135 preferably satisfy a predetermined security requirement level, such as ASIL-A, ASIL-B or, preferably, ASIL-C.

The illustrated field-oriented regulation 100 is to be understood as an example. There are numerous variants and modifications of the illustrated scheme 100 However, all of them are based on the basic principle of vector control of the asynchronous machine 105 can be traced back. It should be noted that other concepts of regulation of the asynchronous machine 105 are possible, for example, the direct self-regulation (DSR), in which machine flow and torque can be controlled directly and independently.

2 shows a system 200 for controlling the asynchronous machine 105 , The system 200 includes the field-oriented control described above 100 as well as a device 205 or a procedure 210 for monitoring or evaluation of the field-oriented control 100 , The device 205 is preferably set up, a corresponding method 210 to perform monitoring and can be implemented in particular as a programmable microcomputer. Microcomputer, the field-oriented scheme 100 and the device 205 can be integrated with each other or separated from each other.

The field-oriented regulation 100 forms together with the asynchronous machine 105 and the inverter 102 a first level 215 of the system 200 , and the surveillance 205 respectively. 210 forms together with an evaluation 225 a second level 220 , The second level 220 is preferably set up the first level 215 to control or functionally monitor and is constructed by this as independently as possible, causing a malfunction in the first level 215 the function of monitoring the second level 220 if possible, not impaired. The evaluation 225 may also be considered as a method or device. The device 210 and the surveillance 225 are in this sense preferred by a common control device 228 includes or the method 210 and the evaluation 225 are preferably set up by means of the same processing device 228 to be carried out.

In the first level 215 becomes the asynchronous machine on the basis of a predetermined target torque M_Soll 105 controlled as above with respect to 1 is described in more detail. The nominal torque M_Soll may be predetermined in particular as the q-component of the space vector i, which is used to control the asynchronous machine 105 is predetermined. In the first level 215 is preferred by the field-oriented regulation 100 a first actual moment M_E1 that determines a calculation of the asynchronous machine 105 provided torque is expressed. The determination of the first actual moment M_E1 takes place on the basis of measurement and processing values of the field-oriented control 100 and optionally parameters of the asynchronous machine 105 ,

In the second level 220 that will be from the asynchronous machine 105 provided torque determined as M_E2. In this case, preferably only measurement and processing values are used which have been determined on the basis of secure sources, in particular sensors which fulfill a predetermined safety requirement level. In the illustrated embodiment, the device comprises 205 a first interface 230 for connection to the sensor 140 for sampling one at a speed of the asynchronous machine 105 indicative signal, such as a rotation angle, an angular velocity or the rotational speed; a second interface 235 for connection to the sensor 135 for sampling the phase currents Is or IsMeas at the phases U . V . W (corresponding to the currents Is1, Is2, Is3 or Isu, Isv, Isw) and optionally a third interface 240 for connection to the temperature sensor 155 for determining a temperature of the asynchronous machine 105 , in particular its stator 110 , The sensors 135 . 140 or 155 provide readings that are both the first level 215 as well as the second level 220 can be made available.

The evaluation 225 compare that to the second level 220 certain monitoring moment M_E2 with the target torque M_Soll or in the first level 215 certain actual moment M_E1 , In a further embodiment, the evaluation 225 also be set up to the target torque M_Soll with the monitoring moment M_E2 to compare. If one of the comparisons detects a deviation which is above a predetermined measure or threshold value, then an error may occur in the system 200 be determined. The threshold may be absolute, for example as a number of Nm (Newton by meter), or relative to the respective reference torque or maximum torque of the asynchronous machine 105 be determined. In the event of an error, a corresponding message can be output to handle the problem appropriately. The message may include the particular deviation and other parameters may be provided. It can also be an immediate reaction in the form of an intervention in the field-oriented control 100 be controlled, for example by the asynchronous machine 105 stopped or idle. For example, the inverter 102 be turned off, such as by the PWM inputs of the inverter 102 superimposed with suitable signals or outputs of the field-oriented control 100 be separated.

The regulations 205 . 210 the monitoring torque M_E2 and the evaluation 225 can by means of a common processing device 230 be performed. The processing device is preferably of a processing device for the field-oriented control 100 built differently, so that a common cause error ("common cause error") can be avoided. The processing device 230 In particular, it may comprise a programmable microcomputer, microcontroller or FPGA and be adapted to execute a method in the form of a computer program product. The method described in this application and the corresponding device are two versions of the same idea, so that features and advantages can each be assigned to the object of the other category.

3 shows a current vector i in different coordinate systems 300 , A fixed-stator coordinate system 305 is called ate coordinate system 305 and is relative to the stator 110 the asynchronous machine 105 Are defined. A rotor-fixed coordinate system 310 is also called kl-coordinate system 310 and is with respect to the rotor 115 the asynchronous machine 105 Are defined. A rotor flux-proof coordinate system 315 is also called dq coordinate system 315 and is in terms of a magnetic flux Ψ _rd in the rotor 115 the asynchronous machine 105 Are defined. A d-axis of the dq coordinate system 315 runs along the magnetic flux Ψ _rd .

Between the α-axis of the αβ-coordinate system 305 and the k-axis of the kl-coordinate system 315 is an angle θ _{r, el} . Between the α-axis of the αβ-coordinate system 305 and the d-axis of the dq-coordinate system 315, an angle θ _{s is} spanned. An angle θ _{i is} included between the current vector i and the α axis of the aβ coordinate system 305.

I _sd , the d component of the by the induction machine 100 flowing current, is called field-forming current, and I _sq , the q-component of the rotating field machine 100 flowing current, construed as a torque-forming current. It is proposed to transform the phase currents from the uvw system first into the aß system and from there into the dq system. The q-component of the transformed phase currents then corresponds to the torque of the asynchronous machine 105 , The first transformation can be performed by means of a constant transformation angle, for the second transformation first the angle θ _s between the α-axis of the aß coordinate system 305 and the d-axis of the dq coordinate system 315 has to be determined. It is suggested that the transformation angle θ _{s be} based on a magnetic flux in the rotor 115 the asynchronous machine 105 to determine.

4 shows a flowchart of a method 400 for determining the monitoring torque M_E2 the asynchronous machine 105 of the system 300 from 3 , The procedure 300 is a preferred implementation of the determination 205 210 in the system 300 , The procedure 300 especially on the device 205 of the system 200 be executed or by the process 210 includes his.

The procedure 400 is set up by the asynchronous machine 105 provided torque in the second level 220 to determine. For the determination, preferably only measured values are used whose collection each satisfies a predetermined safety requirement level. In particular, appropriately certified sensors can be used. For example, the security requirement level may be indicated as an ASIL level and may be about ASIL-A or higher (ASIL-B, ASIL-C, etc.). In the illustrated embodiment, the phase currents I _su , I _sv and I _sw and the rotational speed n or the rotational angle of the asynchronous machine are the reliable measured values 105 intended. In addition, a temperature TempSt of the asynchronous machine 105 , in particular its stator 110 , be used. Certain values of the second level 220 , ie intermediate results that are based on secured measured values or signals and thus can be considered as secured, are in the following marked with the index E2 or ASIL (cf. 2 ) and are preferably also considered secured.

In one step 405 an _aß transformation of the phase _currents I _{suvw is preferably} carried out. The general aß transformation is: $$\left[\begin{array}{c}{x}_{\alpha }\\ x\beta \end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}0& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]{\left[\begin{array}{c}{x}_u\\ x_v\\ x_w\end{array}\right]}_{,}$$

Here, x is a general quantity for which the phase current Is is used here.

In one step 410 the aß currents are transformed by a passive rotation (sinusoidal) into dq direct currents. $$\left[\begin{array}{c}{x}_d\\ x_q\end{array}\right]=\frac{2}{3}\left[\begin{array}{cc}\text{cos}{\theta }_s\left(t\right)& \text{sin}{\theta }_s\left(t\right)\\ -\text{sin}{\theta }_s\left(t\right)& \text{cos}{\theta }_s\left(t\right)\end{array}\right]{\left[\begin{array}{c}{x}_{\alpha }\\ x_{\beta }\end{array}\right]}_{,}$$

Again, x is a general quantity for which the phase current Is is used.

To carry out this rotation, the rotor flux angle θ _{s is} required (cf. 3 ), the determination of which is described in more detail below.

wobei L_r die Induktivität des Rotors 115 und R_r der elektrische Widerstand des Rotors 115 ist. Für die Berechnung des Magnetisierungsstroms wird folgender Zusammenhang ausgenutzt: $$\frac{d}{dt}{I}_{mE2}=\frac{1}{{\tau }_r}{\left(I_{sdE2}-I_{mE2}\right)}_{{}_{{}_{.}}}$$

In one step 415 a magnetizing _current I _{mE2 is} estimated. The following applies: ${\tau }_r=\frac{L_r}{R_{r_{.}}}$

where L _{r is} the inductance of the rotor 115 and R _{r is} the electrical resistance of the rotor 115 is. For the calculation of the magnetizing current, the following relationship is exploited: $$\frac{d}{dt}{I}_{me2}=\frac{1}{{\tau }_r}{\left(I_{sde2}-I_{me2}\right)}_{{}_{{}_{,}}}$$

wobei s der Laplace-Operator ist.In the Laplace area: $I_{m\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="DE102017201215A1\_0012.png"\; state="\{\{state\}\}">e</figure-callout>}2}=\frac{1}{s{\tau }_r+1}{I}_{s\mathrm{<figure-callout\; id="2"\; label="d\; e"\; filenames="DE102017201215A1\_0012.png"\; state="\{\{state\}\}">d\; </figure-callout>}e{2}_{{}_{{}_{.}}}}$

where s is the Laplace operator.

und ϑ_s=∫ω_sdt.In one step 420 the transformation angle θ _{s is} determined. The following applies: $$\frac{d}{dt}{\theta }_s={\omega }_s={\omega }_m+\frac{1}{{\tau }_r}\frac{I_{sqe2}}{I_{m\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="DE102017201215A1\_0012.png"\; state="\{\{state\}\}">e</figure-callout>}2}}$$

and θ _s = ∫ω _s dt.

Dabei ist pz die Polpaarzahl der Maschine 100.The required for this rotor angular frequency ω _m can be by means of a conversion factor K from the rotational speed of the polyphase machine 100 determine: $K=pz{\frac{2\pi }{60}}_{{}_{,}}$

Where pz is the number of pole pairs of the machine 100 ,

The torque calculation typically depends on the parameter quality of the induction machine 100 from. Their parameters, such as τ _r, L _r, L _{r m} or R may vary over time and in particular of a temperature of the engine 100 be dependent. It is therefore preferred that the temperature by means of the temperature sensor 155 is sampled that meets a predetermined safety requirement level, such as ASIL-A, ASIL-B or ASIL-C. The machine parameters can then be in one step 425 be determined or tracked. For the calculation of R _r , a rotor temperature model in level 2 can be used. The inductors L _r or L _m are preferably based on a saturation model of the machine 100 simulated.

The level 2 torque can then be in one step 430 be determined: $$M_{e2}=\frac{3}{2}pz\frac{L_m{}^2}{L_r}{I}_{me2}\cdot I_{sqe2}{}_{{}_{{}_{{}_{,}}}}$$

That in the second level 220 certain torque M _E2 can be determined in the manner shown completely on the basis of measured values recorded by means of sensors which fulfill a predetermined safety requirement level, for instance one of the steps ASIL-A to ASIL-D. The determination can be independent of that in the first level 215 so that a common source of error relevant to both determinations can be avoided.

The level 2 torque can be evaluated 225 used to verify the plausibility of level 1 torque. Dodge the specific torques M_E1 and M_E2 by more than a predetermined amount from each other, so an error can be determined. In this case, the induction machine can 100 be brought into a safe state, for example by switching off.

LIST OF REFERENCE NUMBERS

100

field-oriented regulation (device or method)

102

inverter

105

asynchronous

110

stator

115

rotor

120

transformation means

125

PWM generator

135

current sensor

140

position sensor

145

decoupler

150

Position estimation model

155

temperature sensor

AND MANY MORE

Phase or strand

200

system

205

Device for monitoring

210

Procedure for monitoring

215

first level (E1)

220

second level (E2)

225

evaluation

228

contraption

230

first interface (speed)

235

second interface (phase currents)

240

third interface (temperature)

M_Soll

target torque

M_E1

Actual moment from level 1

M_E2

Monitoring torque (= actual torque from level 2)

300

coordinate systems

305

fixed-stator coordinate system (αβ)

310

rotor-fixed coordinate system (kl)

315

rotor flux-fixed coordinate system (dq)

400

method

405

αβ-Transform

410

transform into dq DC currents

415

Estimate magnetizing current

420

Determine transformation angle (integrator)

425

Track machine parameters

430

Determine torque

Claims (11)

A method (400) for determining a monitoring torque (M_E2) of a multi-phase electrical induction machine (105) (U, V, W); wherein the method (400) comprises the steps of: determining phase currents (Is) flowing through the phases and a rotational speed (n) and / or a rotational angle of the asynchronous machine (105); Transforming (405, 410) the phase currents from the uvw system to the dq system; and determining (430) the monitoring torque (M_E2) based on a q-component of the transformed phase currents. Method (400) after Claim 1 in which the monitoring torque (M_E2) is additionally determined (425) on the basis of a magnetizing current (Im) and at least one machine parameter (L _r , R _r , L _m , z p) of the asynchronous machine (105). Method (400) after Claim 1 or 2 in which the phase currents (Is) are first transformed by the uvw system into the aß system (405) and from there into the dq system (410). Method (400) after Claim 3 wherein the transforming (410) is performed by means of a transformation angle ₍ θ _{s) determined} by integrating (415) a function including the rotational speed (n), the q-component of the transformed phase currents (Is), a magnetizing current (Im ) and a machine parameter (L _r , R _r , L _m , z p) of the asynchronous machine (105). Method (400) after Claim 4 wherein the machine parameter is at least one of an inductance of the rotor (L _r ), an electrical resistance (R _r ) of the rotor (115), an inductance (L _r ) of the stator (115) or a pole pair number (zp) of the asynchronous machine (105 ). Method (400) after Claim 5 , wherein at least one of the machine parameters (L _r , R _r , L _m , z p) a temperature (TempSt) of the asynchronous machine (105) is tracked. Method (400) according to one of the preceding claims, wherein the phase currents (Is) and the rotational speed (n) and / or the rotational angle are respectively determined on the basis of measured values from sensors (135, 140, 155) which fulfill a predetermined safety requirement level , Method (400) according to one of the preceding claims, wherein the speed (n) of the asynchronous machine (105) is below a predetermined threshold value. The method (400) of any one of the preceding claims, further comprising determining (225) an error condition if the monitoring torque (M_E2) deviates from a desired torque by more than a predetermined amount. Method (400) according to one of the preceding claims, wherein the asynchronous machine (105) by means of a field-oriented controller (100). is controlled, as part of the field-oriented control (100) a torque (M_E1) of the asynchronous machine (105) is determined and an error condition is determined if the specific torque (M_E1) by more than a predetermined amount of the monitoring torque (M_E2) deviates. Device for determining a monitoring torque (M_E2) of a multi-phase asynchronous machine (105), the device comprising: interfaces (230, 235, 240) for sensors (135, 140, 155) for sampling phase currents (Is) detected by the phases (U, V, W) flow, and a rotational speed (n) and / or a rotational angle of the asynchronous machine (105); and processing means (228) adapted to transform the phase currents (Is) from the uvw system to the dq system; and determine the monitoring torque (M_E2) based on a q component of the transformed phase currents.

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