DE4122393A1 - Compensating pendulum movement for sync. motor - regulating motor current via reference system attached to rotor - Google Patents

Abstract

Pref., the reference system attached to the rotor is used in conjunction with the required motor r.p.m. to calculate the required values for the direct and the transverse current, the calculated values being weighted according to a given function and subjected to at least one transformation into a stator system. Pref., the values for the latter function are contained in a value table. USE - Preventing unwanted rotation variation of electronically commutated servomotor.

Description

State of the art

The invention is based on a method according to the genus Main claim. Due to the system, more and more available Shortcomings, e.g. B. regarding the arrangement of Permanent magnets or in terms of the course of the induced Electrical synchronous machines usually have voltage for the formation of field harmonics. These in turn lead, provided they cannot be compensated for with sinusoidal power supply systematic pendulum moments, which are undesirable Cause speed fluctuations. Pendulum moments are therefore possible to avoid.

There is a simple method for preventing field harmonics in dampening them. However, there is also an associated one Reduction of machine utilization. From the scripture of M. Schröder, high-speed brushless positioning drive with extreme low moment ripple, dissertation, Stuttgart 1986, is a Proposal known, the appropriate current control To exploit field harmonics for the formation of moment while Compensation of the pendulum moments. The current control is based on a calculation using the variation calculation method. The However, the process is tied to two basic requirements:

• 1. The machine must be magnetically symmetrical,
• 2. The rotor-fixed longitudinal current must be 0 in order to meet the constraint to meet minimal electricity heat loss.

Both preconditions require the use of a feedforward control, which use the magnetic asymmetry of a machine makes, excluded.

The process according to the invention has the advantage that it is independent works from the magnetic symmetry of the machine. The hardware or computer effort for the implementation of the control is extreme low. The control according to the invention delivers one of the rotor position independent torque, which is an improvement in Machine utilization allowed. Requirements for the Synchronous properties, for example for high-precision machine tools, are met. The method according to the invention offers the advantage that a feedforward control of the current can also be provided.

An embodiment of the invention is in the drawing shown and will be described in more detail below.

drawing

The figure shows a structural diagram of an inventive one Motor control circuit.

description

The heart of the closed loop is the control section with blocks 10 and 11 . The control signals generated in the control are fed to the pulse-controlled inverter PWM, which drives the synchronous motor M in accordance with the control signals. The speed or the rotor angular position are detected and returned via a position sensor L or a tachometer T. The control loop shown controls to the target speed, which in turn results from the selected target torque. For reasons of clarity, the control section is shown in several functional stages 10 to 15 .

For the practical implementation of a controller according to the invention the division, however, is of no importance.

The desired target torque m is initially specified, which is supplied to the controller 10 via an additional input 16 . From this, the controller 10 determines the amplitude of the target motor current on the basis of the difference between the target speed ω _target and the actual speed measured by the tachometer T so that the desired torque m is reached. The current is calculated in a two-phase rotor-fixed reference system. This means that the current setpoint comprises a partial setpoint for the "direct current" and a partial setpoint for the "cross current".

The determined current value is fed to stage 11 , which contains logic blocks 12 to 14 . In this, the control signals for controlling the pulse-controlled inverter PWM are generated in a three-phase, fixed-frame reference system by means of a suitable transformation from the values determined with respect to a rotor-fixed reference system.

For this purpose, the current values for the direct or cross current are first weighted in block 12 with shape functions which take into account asymmetrical components of the induced voltage. This weighting of the current signals with the shape functions forms the core of the method according to the invention. Regulation with the proposed method can only be carried out if suitable form functions are known. A method of determination will be given later. The shape functions depend on the position.

The block 12 is therefore supplied with the position angle measured by the position encoder as an additional input variable. The shape functions are expediently determined by accessing a table in which they are stored.

After the current setpoints have been established in this way in the two-phase rotor-fixed reference system, the reverse transformation is first carried out in block 13 into a two-stranded stationary reference system. The reverse transformation is in turn dependent on the position, so that the position angle signal emitted by the position encoder is also supplied in block 13 . Finally, in block 14 , a three-phase control signal suitable for the pulse-controlled inverter PWM is generated from the two-phase current by a suitable transformation. The two-stage re-transformation primarily serves to make it easier to understand. For the practical implementation, of course, a direct inverse transformation of the rotor-fixed values to three-phase stator-fixed can also take place.

Below is a way to determine the shape functions described.

The determination procedure is based on a performance invariant (LIV) transformation of the shape function of the magnet wheel voltage to a two-phase rotor-fixed reference system. The following applies:

u _p2 (t) = _M - ω (t) f _up2 (λ)

u _p3 (t) = _M - ω (t) f _up3 (λ)

In many cases:

with this follows:

the following applies to the transformation matrix [T₃₂]:

In general, the relationship between rotor-proof and stator-proof applies Reference system:

Since the transformation was performed with an invariant performance, in two-phase, rotor-fixed reference system specified the electrical torque will:

_el m = (L _d - L _q) i ^r _d · i · ^r + _q û _p (f ^r _ud (γ) · i ^r _d f ^r + _uq (γ) · ^r i _q)

The following applies to the current components in the d and q axes:

i ^r _d = ^r _d · f ^r _id (γ)

i ^r _q = ^r _qf ^r _iq (γ)

After insertion, the following applies for the electrical torque:

m _el = (L _d - L _q ) · ^r _d · f ^r _id (γ) · ^r _q · f ^r _iq (γ) + (f ^r _ud (γ) · ^r _d · f ^r _id (γ) + f ^r _uq (γ) · ^r _q · f ^r _iq (γ)) (21)

The shape functions of the currents in the d-axis (f ^r _id (γ)) and in the q-axis (f ^r _iq (γ)) are to be determined in such a way that the electrical moment is formed independently of the position angle (γ). The amplitude of the rotor-fixed magnet wheel voltage û _p can be standardized as required, so that in the following oBdA û _p = 1.

To determine the two current control functions f ^r _id (γ) and f ^r _iq (γ) sought, only the moment equation 21 has so far been available. First, the auxiliary variable a is introduced:

^r _d = ^arq _q

a = f ( ^r _q )

Used for the electrical torque:

m _el = ^r _q [(L _d - L _q ) · a · f ^r _id (γ) · ^r _q · f ^r _iq (γ) + (f ^r _ud (γ) · a · f ^r _id (γ) + f ^r _uq (γ) · f ^r _iq (γ))]

The solution is approached:

The solution remains to show that f ^r _iq (γ) ≠ 0 is always fulfilled. Then:

The moment is independent of the position angle γ if:

or with appropriate standardization:

the equation of determination follows from this:

Equation 29 represents the general solution. For a = 0, the minus sign leads to the trivial solution f ^r _iq (γ) = 0. The derivation assumed that f ^r _iq (γ) ≠ should be 0. This is true for:

With the standardization chosen here, the estimates are:

1.1 <f ^r _uq (γ) <1.4

-0.05 <f ^r _ud (γ) <0.05

allowed. For f ^r _ud (γ) = 0 the condition from Eq. 30 always met. For f ^r _ud (γ) ≠ 0, the permissible range of a can be estimated well

-2.5 <a <2.5

In principle, the value for a can be freely selected as long as it does not lead to the singularity with respect to f ^r _iq (γ) = 0. A reasonable choice of a can be found e.g. B. by constraint of the minimum power consumption of the machine. Since L _d <L _{q is} selected very often, the minimum current results in any case for ^r _d <0. The sign reversal of the moment is effected by ^r _q .

For the special case a = 0 applies

Formula symbols used

i electricity
I _N rated current
I unity matrix
J moment of inertia
γ attitude angle
l length
L inductance
m moment
p number of pole pairs
T sampling time, time constant
u tension
Γ Input matrix for system noise
ξ winding factor
Φ transfer function
Ψ River chaining
ω speed, angular frequency

indices used:

1, 2, 3 Designation of the corresponding stator string
d, q longitudinal, transverse axis
i induced inner moment
k kth harmonic (wave)
M magnet
N nominal value
P magnet wheel (voltage)
r rotor-fixed reference system
s frame-fixed reference system
u (form function of) tension
- Average
ˆ peak value
∼ zero system

Claims (7)

1. A method for compensating for pendulum torques in a synchronous motor, preferably an electronically commutated servo motor, by regulating the motor current, characterized in that the motor current is regulated on the basis of a rotor-fixed reference system. 2. The method according to claim 1, characterized in that in one rotor-fixed reference system taking into account the required Speed setpoints for direct and cross flow are calculated are then weighted with suitable form functions and finally by at least one transformation to one stand-fixed system can be transformed back. 3. The method according to claim 1, 2, characterized in that the Form function values are stored in a table. 4. The method according to any one of the preceding claims, characterized characterized in that the signal of the position angle as an input variable in the formation of the form function is included.   5. The method according to any one of the preceding claims, characterized characterized in that the weighted with the form functions Current setpoints are initially based on a two-phase, stationary system be transformed and then another transformation on a three-phase, stand-fixed system. 6. The method according to any one of the preceding claims, characterized characterized that the formation of the form functions based on the measured magnet wheel voltage. 7. The method according to any one of the preceding claims, characterized characterized in that the shape functions are calculated only once will.