Multi-motor operation

Abstract

The invention relates to a method for the closed-loop and open-loop control of two or more EC motors operated using a common converter, wherein for the purpose of setting the operating point of the EC motors, common open-loop or closed-loop control using at least one controller is provided, wherein a combination of at least two control options is provided and in this case a controlled variable regulates the voltage setting at the output of the converter such that the two or more EC motors follow an intended sequence of operating points in a stable manner.

Claims

1. A method for a closed-loop and open-loop control of two or more EC motors operated using one converter for setting the operating point of the EC motors comprising: providing a common open-loop or closed-loop control using at least one controller; providing a combination of at least one control option and one sub-option for the at least one control option; a controlled variable regulating a voltage setting at an output of the converter; and operating the two or more EC motors having at least one of (a) a stable operating point and (b) following an intended sequence of operating points in a stable manner.

2. The method according to claim 1, according to the sub-option, selecting a suitable reference motor for controlling the operating points of the EC motors.

3. The method according to claim 2, wherein the motor used as the reference motor in the motor reference system is one of the motor with the highest speed, the motor with the lowest speed, a motor with a speed that is not the highest speed or the lowest speed, a weighted combination of multiple EC motors, or a factitious reference motor.

4. The method according to claim 1 further comprising setting the voltage setting at the output of the converter by an angle and speed difference evaluation between the reference motor and at least one other EC motor.

5. The method according to claim 1 further comprising a using change in amplitude of the output voltage at the converter, a change in phase position of the output voltage at the converter, or a change in amplitude and phase position of the output voltage at the converter as the controlled variable for regulating a preferred operating point of the EC motors.

6. The method according to claim 5, wherein another sub-option is combined with the control option and speed control, adjustment of the degree of level control, or mere current control are used as the another sub-option.

7. The method according to claim 1, further comprising ensuring the stable operating point as an efficient operating point of the EC motors via current phase control, a mathematical function, or value allocation tables, as another sub-option.

8. The method according to claim 4, wherein via a speed controller and by periodically or continuously comparing the actual and the target speeds that the EC motors follow any sequence of operating points via the control of the output voltage of the converter in a stable manner.

9. The method according to claim 4, further comprising setting the desired operating point of the EC motors by specifying a fixed degree of level control or duty cycle by the converter.

10. The method according to claim 7, wherein for ensuring the preferred operating point using current phase control, the resulting current to be controlled by current phase control contains the required d-current portion in a dq coordinate system, the current phase controller for this purpose sets the phase angle Δγ at its output, which in the steady state of the motor corresponds exactly to the phase shift φ resulting from the motor load.

11. A method for a closed-loop and open-loop control of two or more EC motors operated using one converter for setting the operating point of the EC motors comprising: providing a common open-loop or closed-loop control using at least one controller; providing a combination of at least one control option and one sub-option; a controlled variable regulating a voltage setting at an output of the converter; operating the two or more EC motors having at least one of (a) a stable operating point and (b) following an intended sequence of operating points in a stable manner; and setting the voltage setting at the output of the converter by an angle and speed difference evaluation between a reference motor and at least one other EC motor.

Description

(1) Other advantageous further developments of the disclosure are illustrated in the dependent claims or are explained in more detail below with reference to the figures and together with a preferred embodiment.

(2) FIG. 1 is a schematic view of a control diagram of a first embodiment;

(3) FIG. 2 is a graph of the speed curves of three EC motors at a converter according to the first exemplary embodiment;

(4) FIG. 3 is a graph of the torque curves of three EC motors at a converter according to the first exemplary embodiment, wherein an exemplary load step takes place in two of the three motors at the time t=1 s;

(5) FIG. 4 is a graph of the field oriented current curves of three EC motors at a converter according to the first exemplary embodiment and the exemplary load curve according to FIG. 3;

(6) FIG. 5 is a graph of the speed curves of the three EC motors at the converter according to the first exemplary embodiment and the exemplary load curve according to FIG. 3; and

(7) FIG. 6 is a schematic view of a control diagram of an alternative embodiment.

DETAILED DESCRIPTION

(8) The disclosure is described in more detail below with reference to FIGS. 1 to 6. The same reference numerals indicate the same structural and/or functional features.

(9) FIG. 1 shows a control diagram of a first embodiment using control option 3: changing the amplitude and phase position of the output voltage of the converter.

(10) As a first sub-option, the motor having the highest speed was used as a reference motor. As a second sub-option for setting the operating point, speed was controlled using the speed controller 10 shown in FIG. 1. As a third sub-option, current phase controlling was used to set the phase angle Δγ at the output, namely for controlling the field-oriented current indicator in the dq reference coordinate system using a phase controller 20.

(11) In the exemplary embodiment shown here, the fastest motor, the motor with the smallest load, is used as reference motor. It is at the same time, the reference for the reference coordinate system. Selecting the fastest or the least loaded motor as reference motor ensures the highest dynamics in the closed-loop control system.

(12) In another step, the way in which the operating point is to be set is specified. In the case shown here, a speed controller is used. By specifying a target speed ω*, the speed controller 10 (here in the form of a PI controller) calculates a target voltage u by comparison to the returned weighted speeds of all motors ω.sub.x. This just leads to a voltage in the q direction in the dq coordinate system at the reference motor by transformation with the phase angle γ.sub.ref (that is, without taking into account a phase correction). If the equivalent circuit diagram of the EC motors is taken into account, this voltage results in an emerging field-producing current portion in the d direction and to another torque-producing current portion in the q direction. The other motors are thus subjected to a moment and reach a stable operating point. This operating point is typically not the most efficient operating point due to the uninfluenced d portion. To this end, the phase position and thus the phase angle of the output voltage at the converter must be adequately adjusted.

(13) To adjust the phase position and thus to set a preferred operating point, a phase controller 20 is used in this embodiment. The phase controller 20 ensures the desired phase position of the current. The phase controller 20 determines the current field-oriented portions of the current in the d direction and the q direction relative to the dq reference coordinate system. This occurs by a suitable weighting of the measured currents i.sub.x (in the most simple case just i.sub.converter). The deviation from the target value determined by the phase controller is sent to a controller (e.g. a PI controller). The value Δγ for the phase angle calculated by the controller 21 now ensures in the steady state that the d current desired from the point of view of the reference system is set.

(14) The different load of the EC motors or deviating motor parameters of the respective EC motors can result in difference in speed or angles of rotation of the individual motors. This is when the stabilizing controller 30 shown in FIG. 1 comes into play. If the system was in the steady state before the deviation occurred, this means that u.sub.y points exactly into the direction of i.sub.q. Depending on the magnitude of the differences in speed and angle of rotation, the stabilizing controller now calculates a voltage ux, that is perpendicular to the voltage uy, determined by the speed controller and thus also perpendicular to iq. In the first moment, this voltage generates a purely field-producing current. If one of the EC motors trails the reference motor, a negative ux=ud voltage indicator is set. It generates a purely field-weakening effect in the faster running reference motor. This only has a small impact on the torque produced in the reference motor. Due to the difference in angles of rotation, both a field-weakening effect and a torque-producing effect are generated in the trailing motor. This results in an increase in torque-producing current in the trailing motor. The trailing motor is thereby accelerated. The speed difference reduces along the control section, preferably down to zero. This control method inversely has a braking effect on motors which lead with respect to the reference motor.

(15) If therefore one of the EC motors trails the reference motor, the correction angle determined ensures additional torsion of the voltage indicator set. As a result, all trailing motors undergo a negative change in the d-current portion. Thus, these motors produce a greater torque than in the preceding uncorrected operating point. These motors are thus accelerated or increase their speed, respectively.

(16) Likewise, a positive change in the d-current portion is caused in all leading EC motors. Thus, these EC motors produce a smaller torque than in the previous operating point and are braked.

(17) The illustrations in FIGS. 2, 3, and 4 show the torque curves, the speed curves, and the field-oriented current curves of three exemplary EC motors connected in parallel using one converter in regular operation according to the first exemplary embodiment.

(18) As shown in FIG. 2, the EC motors are started from standstill up to a speed of 600 rpm, that is reached at t=0.4 s after the start. The reference motor is the fastest EC motor. At the time t=1 s, the two other EC motors undergo different load steps, as shown in FIG. 3. results in a speed deviation as shown in FIG. 5. These load steps are absorbed by the stabilizing controller shown in FIG. 1. The phase controller subsequently ensures minimization of the resulting d-current. For the field-oriented current curve, see FIG. 4.

(19) FIG. 6 shows a control diagram for a second embodiment of the disclosure with another control topology. Here, control option 2: changing the phase position of the output voltage of the converter, is applied. Like in the first exemplary embodiment, sub-options used were using the motor with the highest speed as reference motor, setting an operating point by means of speed control, and setting a preferred operating point by phase control. This embodiment further includes a voltage limiter.

(20) As explained for the first exemplary embodiment, different motor loads or deviating motor parameters can result in differences in speeds and angles of rotation of the EC motors. The stabilizing controller calculates a correction angle γ.sub.stab depending on the differences in speed and angle of rotation. If one of the EC motors trails the reference motor, the correction angle determined ensures additional torsion of the voltage indicator set. As a result, all trailing motors undergo a negative change in the d-current portion. Thus, these motors produce a greater torque than in the preceding uncorrected operating point. These motors are thus accelerated or increase their speed, respectively. Likewise, a positive change in the d-current portion is caused in all leading EC motors. Thus, these EC motors produce a smaller torque than in the previous operating point and are thus braked.

(21) The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.