Method and apparatus for adjustment of the rotor angle of an elevator motor

Description of equivalent WO 2004077655 A2

METHOD AND APPARATUS FOR ADJUSTMENT OF THE ROTOR ANGLE OF AN ELEVATOR MOTOR

The present invention relates to a method as defined in the preamble of claim 1 and to an apparatus as defined in the preamble of claim 4 for adjustment of the rotor angle of an elevator motor.

The torque of a synchronous motor is proportional to the angular difference between the magnetic field of the rotor and the magnetic field of the stator, i.e. to the rotor angle. The torque is at a maximum when the rotor angle is 90° and decreases according to a sine function as the rotor angle changes. The torque curve of synchronous motors de- signed for use in elevator drives is a nearly sinusoidal function of the rotor angle. One of the tasks of the elevator control system is to keep the torque at the maximum point .

At present, the rotor position is typically determined by means of a resolver, which produces feedback data on the absolute rotor position, which is needed e.g. in vector control .

However, flat elevator motors designed for elevators without machine room and placed in the elevator shaft provide relatively little space, which is why it is often not possible to use a resolver in such a situation because it can not be mounted in the elevator shaft due to insufficient space. In addition, a resolver is relatively expensive and adjusting it is a complicated task.

To determine the rotor position data, it is also possible to use a pulse emitter or a tachometer. However, such sys- terns are relatively device-dependent and are therefore not directly applicable e.g. for use in elevators. The pulse emitter or tachometer is generally connected to the rotor via a belt transmission or a friction wheel. This involves a slip, which tends to increase. Thus, there is the risk that the torque will decrease. The motor may even fall out of synchronism, in which case the torque is lost completely.

The object of the present invention is to get rid of the drawbacks of prior art and achieve a new type of feedback arrangement that can be used to keep the rotor angle at an optimum point without a sensor giving absolute position data, but in which it is possible to use a pulse emitter or tachometer connected to the motor.

The system of the invention is based on adding to the rotor angle feedback data a disturbance signal, by means of which the absolute rotor angle is determined.

The features characteristic of the method and apparatus of the invention are disclosed in detail in the claims below.

The invention allows elevator motors, e.g. flat elevator motors mounted in the elevator shaft, to be more easily operated by a vector control system, leading to improvements in the operating properties of the elevator.

In the following, the invention will be described in detail with reference to an example and the attached drawing, wherein

Fig. 1 represents the apparatus of the invention for ad- justing the rotor angle of an elevator motor, and

Fig. 2 represents the torque curve of an elevator motor.

In the apparatus according to Fig. 1, there is connected to the elevator motor M a pulse emitter PE, which is connected to an angle/speed conversion unit PE2 , from which the angle data α is input to adders ADDl and ADD2. In addition, the apparatus comprises a phase detector PD (four-quadrant multiplier) to which are input an estimated torque ripple and a disturbance signal, a differentiator DIFF1, the torque being estimated from speed feedback S as the difference between a speed reference ω_r and the actual speed ω given by the angle/speed conversion unit PE2oi, and a vector rotator e ^α, which generates a three-phase current reference for the motor on the basis of signals obtained from the adder and the differentiator DIFFl .

The system works as follows. The system (pulse detector PD and adder ADD1) is supplied with e.g. a sinusoidal disturbance signal DISSIG u=sin(ωt), which is added to the angle value produced by the rotor angle feedback circuit (pulse emitter PE, angle/speed conversion unit PE2α) , with the re- suit that the angle and therefore the torque vary. Via an analysis it can be established that the 'disturbance torque' ΔT is completely different on different sides of the optimum angle (pi/2 in Fig. 2) . The analysis can be performed by computing the function:

T + ΔT = sin(pi/2+ Δ (δ) +u*sin (ωt) ) (1)

where T is torque, ΔT is disturbance torque and Δ(δ) is "DC" misalignment angle.

If the angle is below the optimum point (case: pi/2- Δ(δ)), then the disturbance torque DISTOR is in phase with the disturbance signal; and vice versa (see Fig. 2) . If the an- gle is correct, then the phase difference between the disturbance and the disturbance torque is 90 ^a and the frequency of torque ripple is twice as high as otherwise. For a larger misalignment angle, the disturbance torque is greater, which generates P-type control automatically.

If the disturbance and the signal originating it are compared by means of a phase detector, the output will give a DC control signal that keeps the angle at the optimum point .

In this case, the measurement signal is speed feedback be- cause no torque detector is used. The disturbance signal is so chosen that it will not produce any disturbances on the elevator car.

It is obvious to the person skilled in the art that differ- ent embodiments of the invention are not limited to the example described above, but that they may be varied within the scope of the claims presented below.