DE102015223365A1 - Method for determining a d and q current for controlling a permanent-magnet synchronous machine - Google Patents

Abstract

The invention relates to a method and a control device (6) for determining a collar of a q-current (id, iq) for driving a permanent-magnet synchronous machine (1), so that this outputs a predetermined torque (T). Starting from a first d-current (id1) for adjusting the torque (T) at an MTPA operating point (P1) of the synchronous machine (1) and starting from a second d-current (id2) for adjusting the torque (T) at a MTPV operating point (P2) of the synchronous machine (1), the d and q current (id, iq) for driving the synchronous machine (1) by means of an approximation method iteratively determined.

Description

The invention relates to a method for determining a d-current and a q-current for driving a permanent-magnet synchronous machine (PMSM, "permanent magnet synchronous motor"), so that it outputs a predetermined torque. The invention also relates to a control device for controlling an inverter by means of which a permanent-magnet synchronous machine is supplied with electric current, so that it outputs a predetermined torque to the control unit, wherein the control device has a determination module, which is designed to d and a q current the synchronous machine required to output the predetermined torque.

For example, from the US 6,936 / 991 B2 a method and a control device for determining a d-current and a q-current for driving a permanent-magnet synchronous machine is known.

The object of the invention is to provide a simplified method and control device for determining the d- and q-current for driving a permanent-magnet synchronous machine.

This object is achieved by a method and a control device having the features of the main claims. Preferred embodiments can be taken from the respective dependent claims.

Accordingly, a method is proposed in which the d- and q-current for controlling a permanent-magnet synchronous machine is determined so that they have a predetermined, d. H. desired, outputs torque. Starting from a first d-current and possibly the first q-current for setting the torque at an MTPA operating point of the synchronous machine and starting from a second d-current and possibly second q-current for adjusting the torque at an MTPV Operating point of the synchronous machine, the d- and q-current to control the synchronous machine by means of an approximate method iteratively determined.

Accordingly, a control device for controlling an inverter by means of which a permanent-magnet synchronous machine is supplied with electric current, so that it outputs a predetermined torque to the control unit proposed. In this case, the control unit has a determination module which is designed to iteratively determine the d and q current of the synchronous machine which is required for it to output the predetermined torque by means of an approximation method. In this case, the determination module is designed to generate the d- and q- starting from the first d-current for setting the torque at a MTPA operating point of the synchronous machine and starting from the second d-current for adjusting the torque at a MTPV operating point of the synchronous machine. Determine current to control the synchronous machine.

The d and q currents form the proportions of the electrical (total) current flowing through the synchronous machine in a d-q coordinate system moved together with the magnetic rotor flux or the rotor of the synchronous machine.

In the proposed approximation method, therefore, two starting points will be specified as starting conditions, namely the MTPA operating point and the MTPV operating point of the synchronous machine, in each case at the predetermined torque. MTPA = maximum torque per ampere and MTPV = maximum torque per voltage. MTPA and MTPV each form a known curve in the d-q coordinate system. Likewise, the predetermined torque forms a per se known curve in the d-q coordinate system, in detail a hyperbola. The curves of the MTPA and MTPV intersect the curve of the given torque in the d-q coordinate system at (exactly) one point, respectively, defined by a d and q current. These intersections or the currents there are therefore determinable. Each intersection forms a particular operating point of the synchronous machines, the MTPA operating point and the MTPV operating point.

A suitable method for determining the points of intersection, ie the MTPA and MTPV operating point, or the respective d and q currents is, for example, the non-prepublished patent application DE 10 2015 209 624.6 the applicant can be removed. These currents serve as starting points for the approximation process. The approximation method is iterative, that is, it gradually approximates the optimum for the d and q currents for the given torque.

The number of iteration steps carried out, ie the termination of the approximation method, is linked in particular to the presence of predetermined conditions, such as, for example, the achievement of a maximum number of iteration steps performed or undershooting a difference between the results of two immediately consecutive iteration steps (interval size).

At least the d-current and optionally the q-current for setting the torque at the MTPA operating point of the synchronous machine as well as the d-current and optionally the q-current for setting the torque at the MTPV are preferably used as starting conditions for a first iteration step. Operating point of the synchronous machine specified. Based on this, the q-current and the d-current are then iteratively determined to set the torque.

ermittelt, mit

T

= vorgegebenes Drehmoment,

z_p

= Polpaarzahl der Synchronmaschine,

Ψ_PM

= Polradfluss der Synchronmaschine,

L_d

= Induktivität der Synchronmaschine in d-Richtung,

L_q

= Induktivität der Synchronmaschine in q-Richtung.

Preferably, the q-current for driving the synchronous machine is based on:

determined with

T

= predetermined torque,

z _p

= Pole pair number of the synchronous machine,

Ψ _PM

= Pole wheel flux of the synchronous machine,

L _d

= Inductance of the synchronous machine in the d-direction,

L _q

= Inductance of the synchronous machine in q-direction.

Particularly suitable approximation methods have been the bisection (also called "interval bisection method") and the method of the golden section (also called "Golden section search method" or "golden section search"). In the proposed control unit, the determination module is accordingly designed to carry out at least one of these approximation methods. It can also be provided that it is designed to carry out (at least or exactly) both of these approximation methods and, if necessary, the respectively more favorable one, d. H. faster and / or more accurate and / or less compute-intensive, etc., selects approximate methods.

The thus determined d and q currents can be used for field-oriented control (FOR) or field-oriented control (FOS) of the synchronous machine, i. H. the synchronous machine can be vector controlled or vector controlled. The proposed control unit may therefore in particular be a control unit that controls the synchronous machine in a field-oriented manner (FOR control device) or controls (FOS control device).

In the following the invention will be explained in more detail with reference to figures, from which further preferred embodiments and features of the invention can be removed. Here are shown in a schematic representation:

1 , a structure of a drive system with a permanent-magnet synchronous machine,

2 , Operating points of a permanent-magnet synchronous machine in the dq coordinate system of the synchronous machine,

3 , Operating points of a permanent-magnet synchronous machine in the dq coordinate system of the synchronous machine,

4 , Operating points of a permanent-magnet synchronous machine in the dq coordinate system of the synchronous machine,

5 , a flow chart of a method for determining a d and q current for driving a permanent-magnet synchronous machine using the bisection,

6 FIG. 5 is a flow chart of a method for determining a d and q current for driving a permanent magnet synchronous machine using the golden section method.

In particular, the invention relates to finding the optimum reference currents for a field-oriented controlled or controlled permanent magnet synchronous machine. For this purpose, the optimum reference currents are determined in a rotor flux-fixed qd coordinate system. According to these reference currents, a Inverter can be actuated to control the synchronous machine, ie it can accordingly be the power semiconductors operated in the inverter (switched on and off), so that adjust the currents in the synchronous machine.

1 shows a typical structure of a field-oriented control (FOR) or field-oriented control (FOS) running drive system of a permanent-magnet synchronous machine 1 ,

The drive system is supplied with a predetermined torque T. This torque T should at the permanent magnet synchronous machine 1 are output, ie, the synchronous machine is to deliver this torque T to an output shaft, for example, to drive a vehicle or a machine with this torque T. The torque T may, for example, be predetermined by an operator of the drive system, such as a vehicle driver or a machine operator. It can also be requested by a higher-level control or regulation.

This is a determination module 2 provided, which determines from the torque T a corresponding d-current and q-current i _d , i _q . If a regulation (FOR) is present, actual values of the d-current and q-current can be used for this purpose i * / d, i * / q added and each supplied to a PI controller. If there is a control (FOS), the addition of the actual values is no longer necessary i * / d, i * / q as well as the PI controllers.

The currents i _d , i _q become a decoupling network 3 fed from the then decoupled currents a PWM generator 4 be fed (PWM = pulse width modulation). This generates from the decoupled currents the PWM signals PWM1, PWM2, PWM3 for the pulse width modulated control of power semiconductors of an inverter 5 to the d and q currents i _d , i _q in the synchronous machine 1 adjust. Alternatively, pulse frequency modulated (PFM) signals could also be generated by the generator 4 to be provided.

The modules 2 . 3 . 4 especially in a control unit 6 (Dashed frame) spatially be housed together, for example in the form of an integrated circuit. The control unit 6 For example, from the inverter 5 be physically separated. The control unit 6 can also be on the inverter 5 be placed, that is arranged on it. So can the controller 6 and the inverter 5 just share a common cooling circuit.

There are various possibilities for choosing the d and q currents i _d , i _{q on} the basis of the torque T. Typically, at the base speed of the synchronous machine 1 the d and q currents are chosen so that the stator current is minimal to minimize losses in the copper windings of the stator (copper losses). These are the dominant loss factors in the low speed range. At higher speeds, the d and q currents can be chosen so that the stator flux is minimal to minimize losses due to magnetic saturation of the iron components of the stator (iron losses). These are the dominating loss factors in the high speed range.

In the higher speed range, in field weakening mode of the synchronous machine 1 However, the lying on the MTPA curve operating points, however, due to the physical limitation of the magnetic stator flux in the synchronous machine 1 not (all) be approached. This natural limit caused by the voltage limitation should be used in determining the d and q current in the determination module 2 therefore be taken into account.

2 shows operating points P1, P2 of a permanent-magnet synchronous machine in a dq coordinate system of the synchronous machine. It may be in accordance with 1 controlled synchronous machine 1 act. The vertical axis represents the q-current and the horizontal axis the d-current of the synchronous machine. The dq coordinate system is co-rotating in a manner known per se with the magnetic rotor flux or the rotor of the synchronous machine. The currents in the d and q directions (ie the d and q currents) together form the vectorial stator current of the synchronous machine.

In the dq coordinate system the MTPA and MTPV curves are shown. These are the curves for "maximum torque per ampere" and "maximum torque per voltage", ie for a curve representing the maximum torque delivered per electric current supplied and a curve representing the maximum torque delivered per input represents electrical voltage. These curves are machine specific and can be assumed to be known. Likewise, a torque curve T (hyperbola) is shown in the dq coordinate system. Along this curve, the torque T is constant. The MTPA and MTPV curves have exactly one point of intersection P1, P2 with the torque curve T in the considered range. When the torque is specified, ie the torque curve T is known, and also the MTPA and MTPV curves are known, the points of intersection P1, P2 can be determined relatively easily, for example by means of the non-prepublished patent application DE 10 2015 209 624.6 the applicant described method.

The intersection P2 is an operating point at which the torque T is optimum with respect to an electric voltage supplied to the synchronous machine, and the intersection P1 is an operating point at which the torque T is optimum with respect to an electric current supplied to the synchronous machine is. The supplied electrical voltage is applied, in particular, to a DC link capacitor of the inverter driving the synchronous machine. It is then an intermediate circuit voltage of the inverter.

In 2 are also the stator currents i ₁ , i ₂ indicated, which must be applied to the synchronous machine, so that it is operated in the respective operating point P1, P2. The stator currents i ₁ , i ₂ are each divided into a d-current i _d1 , i _d2 , that is to say a d-portion of the total current i ₁ , i ₂ , and a q-current i _q1 , i _q2 therefore a q-component of the total current i ₁ , i ₂ , on.

U

= an der Synchronmaschine anliegende Spannung, insbesondere Zwischenkreisspannung eines die Synchronmaschine ansteuernden Wechselrichters, und

ω_e

= jeweilige elektrische Winkelgeschwindigkeit.

3 corresponds essentially to the presentation 2 , where the MTPA and MTPV curves and P2 are not shown. Instead, ellipses for different electrical angular velocity ω ₁ , ω _{2 of} the synchronous machine are shown. The angular velocities ω ₁ , ω ₂ determine the magnetic stator flux λ in the synchronous machine according to:

U

= voltage applied to the synchronous machine, in particular DC link voltage of an inverter driving the synchronous machine, and

ω _e

= respective electrical angular velocity.

The ellipses indicate the limit for the magnetic stator flux λ in the synchronous machine. Outside the ellipse, the stator flux λ would exceed the magnetic saturation. An operation of the synchronous machine in operating points that are outside the respective ellipse is therefore not possible.

Due to the limited magnetic stator flux λ, the synchronous machine is therefore not always operable in the optimal operating points P1 or P2. In 3 For example, an ellipse for the angular velocity ω _{1 is} shown, in which the synchronous machine is still operable at the operating point P1 (P1 lies within the ellipse for ω ₁ ). The current i ₁ required to provide the torque T is minimal since P1, as in FIG 2 shown forms the intersection between the MTPA curve and the torque curve T.

At higher angular velocities, the ellipse shrinks, since the resulting magnetic stator flux λ reaches the range of the magnetic saturation of the stator and can not exceed it. The synchronous machine is thus no longer operable at the angular velocity ω ₂ at the operating point P1 (P1 is outside the ellipse for ω ₂ ). The operating point at which the synchronous machine is still operable on the one hand and on the other hand the torque with respect to the electrical current supplied to the synchronous machine is optimal, is now shifted along the torque curve T and lies in PX. There, the ellipse of the angular velocity ω ₂ intersects with the torque curve T.

Out 3 It can be seen that the electric current i required for the operating point PX is greater in magnitude than the electric current i ₁ required for the operating point P1 (the circle with the radius i is larger than the circle with the radius i ₁ ). Likewise, the d and q portions of the currents i and i _{1 are} significantly different. According to 3 can be generated at the angular velocity ω ₂ no torque in the synchronous machine with the current i ₁ , since this would be completely outside the ellipse for ω ₂ and therefore is not adjustable.

The determination of the intersection between the torque curve T (hyperbola) and the curve of the prevailing or desired angular velocity ω _e or ω ₁ , ω ₂ (ellipse) is a highly nonlinear problem. An analytic solution thus required a very powerful controller.

In the present case, it is therefore proposed to iteratively determine the d and q currents for driving the synchronous machine by means of an approximation method. This approach favors the use of low-power and therefore cost-effective ECUs. Here, from the MTPA operating point P1 and the MTPV operating point P2. Preferably, these and the respective d and q currents by means of the non-prepublished patent application DE 10 2015 209 624.6 determined by the applicant.

Within the scope of the method, the maximum possible magnetic stator flux λ should be taken into account in order to exclude results which the synchronous machine can not achieve at the respectively present angular velocity ω _e .

4 corresponds to the presentation 2 and 3 , Out 4 is an operating point PX removable, by which the requested torque T can be provided and on the one hand at the present angular velocity ω _{e is} just reached and on the other hand with respect to the required stator current i is optimal, ie the stator current i is minimal. Although the operating point P1 would be better with respect to the required stator current (i ₁ <i), this can not be achieved at the present angular velocity ω _e due to the limited magnetic stator flux λ.

As in 4 is recognizable, is the desired operating point PX between the MTPA operating point P1 and the MTPV operating point P2. These points P1, P2 are therefore suitable as starting points (starting conditions) for the approximation method. For a first iteration step, therefore, the d and q currents present at these operating points P1, P2 (cf. 2 ). These are then gradually approximated to the desired operating point PX or the d and q currents present there.

Out 5 By way of example, a method can be inferred in which the bisection is used as an approximation method. Here, the interval between the solutions / currents determined in each iteration step is gradually reduced, until a sufficient approximation is found. 5 shows a flowchart of the method.

In a step S0 (= initialization step), the quantities or values i _d1 , i _q1 , i _d2 , i _{q2 are} initialized. The first d and q currents i _d1 , i _q1 define the MTPA operating point P1 and the second d and q _currents i _d2 , i _q2 the MTPV operating point P2. The points P1 and P2 thus form the starting conditions for the approximation method. These values were determined in advance in particular. They can then, for example, be taken from a table or a characteristic curve or a characteristic field. They could also be calculated analytically or approximately. In particular, in step S0, the memory areas of a data memory provided in a control unit for the values i _d1 , i _q1 , i _d2 i _{q2 are} respectively initialed or initialized with the respective value.

In a subsequent step S1, iteration step (s), i _{d is} based on: i _d = 0.5 (i _d1 + i _d2 ) determined.

ermittelt, mit

T

= vorgegebenes Drehmoment,

z_p

= Polpaarzahl der Synchronmaschine,

Ψ_PM

= Polradfluss der Synchronmaschine,

L_d

= Induktivität der Synchronmaschine in d-Richtung,

L_q

= Induktivität der Synchronmaschine in q-Richtung.

Based on i _d , i _q will also be based on:

determined with

T

= predetermined torque,

z _p

= Pole pair number of the synchronous machine,

Ψ _PM

= Pole wheel flux of the synchronous machine,

L _d

= Inductance of the synchronous machine in the d-direction,

L _q

= Inductance of the synchronous machine in q-direction.

U

= an der Synchronmaschine anliegende Spannung, insbesondere Zwischenkreisspannung eines die Synchronmaschine ansteuernden Wechselrichters,

ω_e

= elektrische Winkelgeschwindigkeit der Synchronmaschine,

And it becomes a value f (i _d , i _q ) based on: f (i _d , i _q ) = λ 2 / limit - [L _d i _d + Ψ _PM ) ² + (L _q i _q ) ² ] determined with

U

= voltage applied to the synchronous machine, in particular DC link voltage of an inverter driving the synchronous machine,

ω _e

= electrical angular velocity of the synchronous machine,

If this value f (i _d , i _q ) is positive, the operating point defined by i _d and i _q lies within the possible magnetic stator flux λ. The operating point would thus be represented in principle, ie the synchronizing machine operable in this operating point. On the other hand, if this value f (i _d , i _q ) is negative, the operating point defined by i _d and i _q lies outside the limit for the magnetic stator flux λ. The operating point would therefore not be represented in principle, ie the synchronous machine can not be operated at this operating point. In a subsequent step S2, therefore, it is determined whether the value f (i _d , i _q ) is less than zero.

If it has been determined in step S2 that the value f (i _d , i _q ) is less than zero (path "Y"), then in a subsequent step S2 to step S2 for the subsequent iteration step (n + 1) is set as start conditions : i _d1 = i _d , i _q1 = i _q .

If it has been determined in step S2 that the value f (i _d , i _q ) is not less than zero (path "N"), in a step S3 'following step S2' for the subsequent iteration step (n + 1) Start conditions set: i _d2 = i _d , i _q2 = i _q.

In particular, in step S3 or S3 ', the memory areas of the data memory provided in the control unit for the values i _d1 , i _q1 and i _d2 , i _{q2 are} overwritten or re-filed with the respective value i _d , i _q . In step S3, therefore, only the values for i _d1 , i _{q1 are} modified and the values i _d2 , i _q2 remain unchanged. Similarly, in step S3 ', only the values for i _d2 , i _{q2 are} modified and the values i _d1 , i _q1 remain unchanged.

In a step S4 subsequent to step S3 or S3 ', it is determined whether one or more conditions (stop condition) necessary for terminating the approximation method are satisfied, for example, whether a sufficient number of iteration steps have been carried out.

If the termination condition (s) is not met (path "N"), the process returns to step S1 to begin the new iteration step (n + 1). In this case, the values newly defined in the previous step S3 or S3 'for i _d1 , i _q1 or i _d2 , i _q2 and the respectively unchanged values for i _d2 , i _q2 and i _d1 , i, respectively, are used as start values for the new iteration step _q1 used, ie the value stored in the respective memory area used. By this procedure, the desired operating point PX is approximated gradually and starting from the operating points P1 and P2.

If the termination condition (s) is satisfied (path "Y"), step S5 is entered, and thus the approximation process is completed. As a result, the values i _d2 , i _{q2 are} output. These are thus the values of a d and q current of the synchronous machine approximated to the optimum operating point PX.

Out 6 By way of example, a method can be inferred, in which the method of the golden section is used as an approximation method. Here, too, the interval between the solutions / currents determined in each iteration step is gradually reduced, until a sufficient approximation has been found. 6 shows a flowchart of the method.

In 6 the index (n) indicates that it is the respective value of the current iteration step, for example a value currently stored in the respective memory area of a data memory of the controller, whereas the index (n + 1) indicates that it is the respective value for the immediately following iteration step. The index (0) indicates that the respective value is the initialization value (see step S0 in FIG 6 ).

In a step S0 (= initialization step), the quantities i _d1 , i _q1 , i _d2 , i _{q2 are} initialized. The first d and q currents i _d1 , i _q1 define the MTPA operating point P1 and the second d and q _currents i _d2 , i _q2 the MTPV operating point P2. The points P1 and P2 thus form the starting conditions for the approximation method. These values were determined in advance in particular. They may, for example, have been taken from a table or a characteristic curve or a characteristic field. They could also have been calculated analytically or approximately.

In step S0, the values y ₍₀₎ and z _{(0) are then} determined on the basis of i _d1 , i _q1 , i _d2 , i _q2 , based on: y ₍₀₎ = Y (i _d1 , i _d2 ) = i _d1 + a (i _{d2 -i d1} ), z ₍₀₎ = Z (i _d1 , i _d2 ) = i _d1 + b (i _d2 - i _d1 ).

und der Faktor a ist bevorzugt a = 1 – b. Vereinfacht können auch a = 0,382 und b = 0,618 sein, dabei können die Faktoren auch beliebig viele weitere Nachkommastellen aufweisen.The factors a and b represent the ratio (Golden Number) of the Golden Ratio. The factor b is therefore preferred

and the factor a is preferably a = 1-b. Simplified can also be a = 0.382 and b = 0.618, while the factors can also have any number of further decimal places.

mit

T

= vorgegebenes Drehmoment,

z_p

= Polpaarzahl der Synchronmaschine,

Ψ_PM

= Polradfluss der Synchronmaschine,

L_d

= Induktivität der Synchronmaschine in d-Richtung,

L_q

= Induktivität der Synchronmaschine in q-Richtung,

U

= an der Synchronmaschine anliegende Spannung, insbesondere Zwischenkreisspannung eines die Synchronmaschine ansteuernden Wechselrichters,

ω_e

= elektrische Winkelgeschwindigkeit der Synchronmaschine.

In addition, values f (y ₍₀₎ ) and f (z ₍₀₎ ) are determined based on:

With

T

= predetermined torque,

z _p

= Pole pair number of the synchronous machine,

Ψ _PM

= Pole wheel flux of the synchronous machine,

L _d

= Inductance of the synchronous machine in the d-direction,

L _q

= Inductance of the synchronous machine in q-direction,

U

= voltage applied to the synchronous machine, in particular DC link voltage of an inverter driving the synchronous machine,

ω _e

= electrical angular velocity of the synchronous machine.

In particular, the memory areas of a data memory with the respective value i _d1 , i _{q1 are} provided in a control unit for the values i _d1 , i _q1 , i _d2 , i _q2 , y, z, f (y), f (z) , i _d2 , i _q2 , y ₍₀₎ , z ₍₀₎ , f (y ₍₀₎ ), f (z ₍₀₎ ) initialized.

In a subsequent step S1, iteration step (s), the amounts of the values f (y _(n) ), f (z _(n) ) determined in the preceding step S0 or S2 or S2 'are compared with each other and it is determined whether the Amount of the value f (y _(n) ) is greater than the amount of the value f (z _(n) ). If this is the first iteration step, ie immediately before the initialization took place in step S0, then the amounts of the values f (y ₍₀₎ ), f (z ₍₀₎ ) are compared accordingly. If an iteration step already took place, ie immediately before step S3 or S3 'took place, then the amounts of the values f (y _(n) ), f (z _(n) ) are compared accordingly.

If it has been determined in step S1 that the amount of the value f (y _(n) ) is greater than the value of the value f (z _(n) ) (path "Y"), in a subsequent step S2 for the subsequent iteration step (n + 1) set as start conditions: i _{d2 (n + 1)} = z _n , z _{(n + 1)} = y _(n) , y _{(n + 1)} = Y (i _{d1 (n)} , i _{d2 (n)} ), f (z _{(n + 1)} ) = f (y _(n) ),

Here, y _{(n + 1) is} redetermined based on y _{(n + 1)} = Y (i _{d1 (n)} , i _{d2 (n)} ) = i _{d1 (n)} + a (i _{d2 (n) -i d1 (n)} ).

This determination is made in accordance with the determination of y ₍₀₎ in step S0, but with values for i _d1 , i _d2 which may have been adjusted by the iteration. Otherwise, the facts explained in step S0 also apply here.

From y _{(n + 1)} , f (y _{(n + 1)} ) is also newly determined, based on:

This determination is carried out in accordance with the determination of f (y ₍₀₎ ) in step S0, but with values for y possibly matched by the iteration. Otherwise, the facts explained in step S0 also apply here.

In particular, the memory areas of the data memory provided in the control unit for the values i _d2 , y, z, f (y), f (z) with the respective value z _n , y _(n) , y _{(n + 1)} , f (y _{(n + 1)} ), f (z _{(n + 1)} ) overwrite or condition. These values then count as start conditions for the subsequent iteration step (n + 1).

If it has been determined in step S1 that the amount of the value f (y _(n) ) is not greater than the value of the value f (z _(n) ) (path "N"), in a subsequent step S2 'for the subsequent iteration step (n + 1) set as start conditions: i _{d1 (n + 1)} = y _n , y _{(n + 1)} = z _(n), z _{(n + 1)} = Z (i _{d1 (n)} , i _{d2 (n)} ), f (y _{(n + 1)} ) = f (z _(n) ),

Here, z _{(n + 1) is} newly determined based on z _{(n + 1)} = Z (i _{d1 (n)} , i _{d2 (n)} ) = i _{d1 (n)} + b (i _{d2 (n) -i d1 (n)} ).

This determination is made in accordance with the determination of z ₍₀₎ in step S0, but with values for i _d1 , i _d2 which have possibly been adjusted by the iteration. Otherwise, the facts explained in step S0 also apply here.

From z _{(n + 1)} , f (z _{(n + 1)} ) is also newly determined based on:

This determination is carried out in accordance with the determination of f (z ₍₀₎ ) in step S0, but with values possibly adjusted by the iteration for z. Otherwise, the facts explained in step S0 also apply here.

In particular, in step S2 'the memory areas of the data memory provided in the control unit for the values i _d1 , y, z, f (y), f (z) are assigned the respective value y _n , z _(n) , y _{(n + 1 )} , f (y _{(n + 1)} ), f (z _{(n + 1)} ). These values then count as start conditions for the subsequent iteration step (n + 1).

In a subsequent step S3, it is determined whether one or more conditions (stop condition) necessary for terminating the approximation method are satisfied, for example, whether a sufficient number of iteration steps have been carried out.

If the termination condition (s) is satisfied (path "N"), step S1 is entered and the new iteration step (n + 1) is started. In this case, as starting values for the new iteration step, the values for y, z, f (y), f (z) and i _d1 or i _d2 which have been newly defined in the previous step S2 or S2 'and the respectively unchanged values for i _d2 or i _d1 used, ie the values stored in the respective memory areas used. By this procedure, the desired operating point PX is approximated gradually and starting from the operating points P1 and P2.

However, if the termination condition (s) is satisfied (path "Y"), step S4 is entered. Thus, the approximation process is completed. The result will be: i _d = i _{d2 (n)} , i _q = i _{q2 (n)} = g (i _{d2 (n)} ), where i _{q is} determined based on:

It should be noted that i _q can already be calculated in this way in steps S2 and S2 '. In step S4, i _d and i _{q would} then only be output. I _d and i _q are the values of d and q current of the synchronous machine approximated to the optimum operating point PX.

Advantage of the method of golden section ( 6 ) opposite the bisection ( 5 ) is the faster convergence towards the optimum operating point PX. This advantage increases with the number of iteration steps performed.

From the by means of the approximation method 5 or 6 determined values i _d , i _q and i _d1 , i _q1 for the d- and q-current of the synchronous machine are in an application in a drive system after 1 from this the PWM signals PWM1, PWM2, PWM3 for controlling the power semiconductors of the inverter 5 generated. Due to these, the respective d and q currents are applied to the synchronous machine 1 one. The synchronous machine 1 is then operated in an approximated to the optimal operating point PX operating point and outputs the predetermined torque T out.

Advantage of the proposed method is in particular a relatively low computational effort. This is particularly useful when the methods are performed numerically, such as on a control unit for controlling the synchronous machine. In addition, the methods are always convergent, so that an operating point which is approximated to the optimum operating point PX is always determined. In addition to the respectively mentioned, required sizes, no further sizes are required. These required sizes are typically known sizes of the synchronous machine, or they are at least easily determined. Therefore, tables for MTPA or stator flux values are not mandatory.

LIST OF REFERENCE NUMBERS

1

permanent-magnet synchronous machine (PMSM)

2

determination module

3

Decoupling network

4

(PWM) generator

5

inverter

6

control unit

MTPA

maximum torque per amp

MTPV

maximum torque per voltage

P1

Operating point at MTPA

P2

Operating point at MTPV

PX

operating point

PI

PI controller

PWM1

PWM signal

PWM 2

PWM signal

PWM3

PWM signal

T

predetermined torque

ω ...

electrical angular velocity

i, i ₁ , i ₂

electrical current

i _{d ...} , i * / d

electric current component in d-direction (d-current)

i _{q ...} , i * / q

Electric current component in q-direction (q-current)

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6936/991 B2 [0002]
• DE 102015209624 [0009, 0031, 0040]

Claims (8)

Method for determining a d-current and a q-current (i _d , i _q ) for controlling a permanent-magnet synchronous machine ( 1 ), so that this outputs a predetermined torque (T), characterized in that starting from a first d-current (i _d1 ) for adjusting the torque (T) at an MTPA operating point (P1) of the synchronous machine ( 1 ) and from a second d-current (i _d2 ) for adjusting the torque (T) at a MTPV operating point (P2) of the synchronous machine ( 1 ) the d and q currents (i _d , i _q ) for driving the synchronous machine ( 1 ) is determined iteratively by means of an approximation method. Method according to claim 1, wherein as starting conditions for a first iteration step the first d-current (i _d1 ) for setting the torque (T) at the MTPA operating point of the synchronous machine ( 1 ) and the second d-current (i _d2 ) are used to adjust the torque at the MTPV operating point of the synchronous machine, based on the d and q current (i _d , i _q ) for adjusting the torque (T) by means of be determined iteratively by the approximation method. Method according to claim 1 or 2, wherein the q-current (i _q ) for controlling the synchronous machine ( 1 ) based on:

is determined, with T = predetermined torque z _p = pole pair number of the synchronous machine ( 1 ), Ψ _PM = pole wheel flux of the synchronous machine ( 1 ), L _d = inductance of the synchronous machine in d-direction, L _q = inductance of the synchronous machine in q-direction. Method according to one of claims 1 to 3, wherein bisection is used as an approximation method. Method according to one of claims 1 to 3, wherein the method of the golden section is used as an approximation method. Control unit ( 6 ) for controlling an inverter ( 5 ) by means of which a permanent magnet synchronous machine ( 1 ) is supplied with electrical power, so that this one the control unit ( 6 ) outputs predetermined torque (T), whereby the control unit ( 6 ) a determination module ( 2 ), which is designed to a d and a q-current (i _d , i _q ) of the synchronous machine ( 1 ), which is required for it to output the predetermined torque (T), characterized in that the determination module ( 2 ), the d and q currents (i _d , i _q ) for driving the synchronous machine ( 1 ) by means of an approximation method iteratively, starting from a first d-current (i _d1 ) for setting the torque (T) at a MTPA operating point (P1) of the synchronous machine ( 1 ) and from a second d-current (i _d2 ) for adjusting the torque (T) at a MTPV operating point (P2) of the synchronous machine ( 1 ). Control unit ( 6 ) according to claim 6, wherein the determination module ( 2 ) uses the bisection as approximation method. Control unit ( 6 ) according to claim 6, wherein the determination module ( 2 ) uses the golden section method as approximation method.

Images