Regulation system and method for operating brushless dc motors in parallel on common multi-motor frequency converter using regulation system

Abstract

The invention relates to a regulating system (1) and a method for operating brushless direct current motors in parallel on a common multi-motor frequency converter using the regulating system. The regulation system comprises a multi-motor frequency converter (PWR) for the regulated parallel operation of n brushless DC motors (M1,..., Mn), the respective rotor positions of which are each detected without sensors and controlled by a common frequency converter.

Description

Technical Field

[0001] The invention relates to a sensorless multi-motor frequency converter for the parallel operation of at least two, in particular a plurality of, electric motors, and a control method for operating two or more electric motors on a common multi-motor frequency converter. Background Art

[0002] For sensorless or rotor position sensorless operation of electrically commutated motors (permanent magnet synchronous motors / brushless DC motors) on a frequency converter, the voltages applied to the motor terminals and the currents flowing in the motor phases are usually detected and evaluated in a suitable manner in order to determine the rotor position and commutate the motor accordingly. However, in the prior art, no satisfactory solutions are known for operating two or more such motors (permanent magnet synchronous motors / brushless DC motors) on a single frequency converter. When motors are mentioned in the following description, this refers to sensorless-controlled permanent magnet synchronous motors or sensorless-regulated brushless DC motors.

[0003] KR 101 687 556 B1 discloses a publication relating to a motor drive for two motors. According to one embodiment of this publication, the motor drive includes an inverter comprising a plurality of matching switching elements, which converts direct current into alternating current by switching the switching elements to supply alternating current to a first motor and a second motor, and a control unit for controlling the inverter. The control unit sets a flux current set value based on the speed difference or phase difference between the first motor and the second motor, and controls the inverter based on a switching control signal based on the set flux current set value. This reduces speed errors when simultaneously controlling multiple motors connected in parallel.

[0004] DE 10 2018 124 209 A1 describes another concept of the applicant. To avoid repeating individual structural modules, it is noted that this information is already known to those skilled in the art from this publication. The basic idea of ​​the concept described therein is that for the parallel operation of multiple, at least two, electrically commutated motors at a common frequency converter without rotor position sensors, the phase current is detected individually for each connected motor. However, only one voltage measurement is required per frequency converter output phase, since the same terminal voltage is present at all motors due to the parallel operation of the motors. Alternatively, it is also conceivable that the terminal voltage is not measured but instead calculated based on the control level output by the controller. Summary of the Invention

[0005] The multi-motor frequency converter according to the present invention essentially differs from conventional frequency converters in that the measurement signals used to determine the rotor position of the multiple motors are detected and processed. To this end, individual current measurements are performed for each motor connected to the multi-motor frequency converter. Furthermore, DE 10 2018 124209 A1 describes a method for operating multiple brushless DC motors in parallel on a common multi-motor frequency converter, which employs the following steps: detecting the individual phase currents and terminal voltages of the brushless DC motors; determining the rotor position and speed using previously measured parameters; generating current and / or voltage variables in space vector representation or dq space vector coordinates using the previously determined rotor position and speed, and transmitting these to a control device; and generating three-phase voltage variables from the current and / or voltage variables in space vector representation using a Clarke-Park transformation, and transmitting these to a modulator. This generates switching commands for the multi-motor frequency converter to operate the multiple brushless DC motors in parallel.

[0006] It is therefore an object of the present invention to provide an alternative solution for operating a plurality of electric motors on a frequency converter, which alternative solution can be realized inexpensively and can be used as universally as possible.

[0007] The present invention solves the problem based on the features of the first aspect.

[0008] The basic idea of ​​the present invention is to perform a separate determination of the rotor position for each motor (permanent-magnet synchronous motor / brushless DC motor) when operating multiple, at least two, electrically commutated motors in parallel at a common frequency converter without rotor position sensors. This is possible because current sensing is performed individually for each motor at the frequency converter, for example using one of the many known methods for sensorless rotor position determination. This has the advantage that each motor can be described individually in its own separate coordinate system (KOS) for control purposes.

[0009] Another aspect relates to the fact that by adding the respective motor currents of the brushless DC motors, the total current in the frequency converter and thus the coordinate system of the frequency converter can be determined.

[0010] In a preferred embodiment of the adjustment method described here as an example, the coordinate system of the main motor is used as the reference coordinate system. One of the motors is used as the main motor, while the other motors do not have the function of the main motor.

[0011] However, any other coordinate system (KOS), or alternatively a suitable virtual coordinate system (KOS), may also be used as the reference system specified in the system.

[0012] According to the invention, two alternative control concepts are implemented. On the one hand, control is performed using a nonlinear state-space controller, and alternatively, control is performed using a linear state-space controller. Both variants are suitable for implementing the idea of ​​the invention.

[0013] Tuning using a nonlinear state-space regulator

[0014] The multi-motor system can be regulated by a regulator with a nonlinear state-space regulator in state space. Regulation can be based on nonlinear differential equations of the machine equations. Furthermore, according to a preferred embodiment of the present invention, a stabilizing regulator is also required to guide the motor back to a stable operating point after a load jump by applying a d current.

[0015] Tuning using a linear state-space regulator

[0016] The control of a multi-motor system does not have to be based on nonlinear motor differential equations, i.e., machine equations. Instead, the differential equations can be linearized at any selectable operating point. The advantage of linear state-space control is that linearization simplifies the design of the controller. The controller can now be calculated based on design variants of linear state-space control known to those skilled in the art.

[0017] Because there are multiple motors and, therefore, multiple coordinate systems for each motor, it is necessary to determine a suitable reference coordinate system for the inverter commutation. In the control method described here, the coordinate system of the master motor is used as the reference coordinate system. However, any other coordinate system, even a suitable virtual coordinate system (KOS), can be used as the reference system.

[0018] Another aspect of the present invention relates to a method for operating n brushless DC motors (n≥2, i.e. at least two brushless DC motors) in parallel on a common multi-motor frequency converter, in particular using a control system as described above, comprising the following steps:

[0019] a. Detect each phase current I of n brushless DC motors respectively M1 ,...,I Mn ,

[0020] b. With the help of the previously measured phase currents I of the n brushless DC motors M1 ,...,I Mn to determine the rotor position and speed of the n brushless DC motors in order to determine therefrom a separate, in particular independent, coordinate system (KOS) for each of the n brushless DC motors;

[0021] c. Based on the value of the determined rotor position determined in step b), generating a current variable and / or a voltage variable in space vector representation and transmitting it to the regulating device,

[0022] d. Generate three-phase voltage variable U from voltage variable represented by space vector through Clarke-Park transformation uvw , and pass it to the modulator;

[0023] e. Using the modulator to obtain the voltage variable U of the multi-motor inverter uvw Generates switching commands for controlling the operation of n brushless DC motors,

[0024] f. Wherein, n brushless DC motors are regulated by frequency converters relative to a selected reference motor and its reference coordinate system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Further advantageous developments of the invention are characterized in other respects and are described in more detail below together with the description of preferred embodiments of the invention in conjunction with the accompanying drawings. In the drawings:

[0026] Figure 1 shows a block diagram of a regulation system according to a first embodiment of the invention, which is configured for regulation with a nonlinear or linear state-space regulator R;

[0027] Figure 2 The block diagram of the nonlinear state-space regulator R is shown, and the resulting block diagram is as follows,

[0028] Figure 3 An exemplary trajectory preset for the rotational speed is shown,

[0029] Figure 4 shows a curve showing the transient response of the rotation speed of the two motors M1 and M2,

[0030] Figure 5 shows the torque change after a load jump,

[0031] Figure 6 shows the field-oriented current curve in regulated operation with the aid of a stabilizing regulator,

[0032] Figure 7 The angular difference between the two motors in regulated operation is shown. DETAILED DESCRIPTION

[0033] Refer to the following Figure 1 The invention is explained in more detail with reference to two exemplary embodiments, wherein identical reference numerals in the figures denote identical structural and / or functional features.

[0034] These two implementations can be Figure 1 The representation is identical, since the difference lies in the state-space regulator R, which is either designed as a nonlinear state-space regulator R (as shown) or alternatively as a linear state-space regulator R. Figure 1 A control system 1 is shown, comprising a multi-motor frequency converter PWR, which is shown for the controlled parallel operation of a plurality of brushless DC motors M1 , M2 (here n=2), the respective rotor positions of which are detected without sensors.

[0035] For this purpose, a detection device 10 is provided with rotor position determiners RLM1, RLM2 for determining the position of the phase current I M1 , I M2 and the terminal voltage U of the two brushless DC motors u,v,w To determine at least the rotor position Φ of the two brushless DC motors (M1, M2) M1 , Φ M2 and speed ω M1 and ω M2 The detection device 10 is also configured to obtain the total current I uvw , where the total current I uvw =I M1 +I M2 , and in addition to the terminal voltage U uvw In addition, it is also used to determine the rotor position and speed ω U The input variables of the variables.

[0036] The detection device 10 therefore has devices RLM1, RLM2 which are designed to determine the rotor position and the corresponding rotational speed ω of the two electrical machines M1, M2. M1 、ω M2 .

[0037] Furthermore, in both embodiments, a control and transformation device 20 is provided for generating corresponding d currents I in the dq coordinate system via a stabilization controller RS ​​using the determined rotor position and speed for regulating the two electric machines. d,Soll , and is provided as a setting preset to the linear or nonlinear state regulator R, or applied for stabilization in order to Figure 5 In addition, a transformer T is provided. The regulating and transforming device 20 preferably adopts a Clarke-Park transformer for transforming the detected rotor position and the total current I uvw The variable is transformed into a dq current variable I represented by a space vector for the regulating device 30 d,q_ist .

[0038] Therefore, as an input variable, I dq,Ist The current is supplied to the non-linear or linear state regulator R of the regulating device 30. In addition to the determined rotational speed, in each case the rotational speed ω is set Soll It is also applied or made available to the state controller R accordingly as a manipulated variable.

[0039] Figure 2 The block diagram of the nonlinear state-space controller R is shown. By means of trajectory presetting, a mathematical function of the startup behavior of the speed and current id is realized, which is used as a dynamic presetting for defining the setpoint change of the state-space controller. This dynamic presetting reduces the setpoint error between the setpoint and the actual value, thus regulating the system. The inverse system is then used to convert the manipulated variables id and ω calculated based on the system differential equations into el Converted into voltage variables Ud and Uq to be set.

[0040] Figure 3 An exemplary speed trajectory is shown. In the nonlinear state space regulator R, the corresponding trajectory presets are used as input variables. In addition to the speed and I dq In addition to the actual current variable, the speed and current preset values ​​are also input to the state-space controller R via trajectory presets. The trajectory presets the system's startup dynamics. The dynamics of the control loop can be set based on the system's characteristic values ​​or freely selectable poles. This corresponds to the standard design methods for state-space controllers found in the literature. The changes in the set variables are then passed to the inverse system, which calculates the terminal voltage U to be applied based on the variables preset by the controller. d,q .

[0041] The regulating device 30 also generates switching commands SZB for the multi-motor frequency converter PWR for operating the two motors M1 , M2 .

[0042] As mentioned above, the trajectory of the rotation frequency is as follows Figure 3 In this case, a speed of 300 rpm is reached within 1.5 seconds. Based on the given setpoint trajectory, the state controller R now regulates the speed to the desired setpoint value.

[0043] Figure 4 The speed transient behavior of the two motors M1 and M2 is shown. After about 2 seconds of simulation time, the steady-state system is excited by the load jump shown. In this case, the torque on motor 1 doubles, as shown by Figure 5 The stabilized regulator now operates by applying a current d (as Figure 6 As shown) intervene and bring the two motors M1 and M2 back to a stable operating point, as shown Figure 7 shown.

[0044] exist Figure 7As can be seen in the angular difference graph in Figure 1, after the load jump, the system stabilizes with a constant angular difference. Before the load jump, the angular difference in steady state was close to zero. After the load jump, the deviation is approximately 0.03 radians, equivalent to approximately 1.71 degrees. This deviation is within the expected range, as the motors' coordinate systems are slightly rotated relative to each other due to the now different loads.

[0045] In an alternative embodiment with a linear state-space regulator, one can in principle refer to Figure 1 、 3 -7, since the characteristics of the resulting multi-motor systems are in principle comparable. In this case, the angle of the rotor position determination RML1 is used as the reference coordinate system. On the one hand, the regulator is based on the Figure 1 The stabilization regulator provides a preset current setting. This can correspond to the concept in DE 10 2018 124 209 A1, for example.

[0046] The set rotational frequency can be preset by a trajectory or, alternatively, by a fixed setpoint. The state regulator R then sets the appropriate voltage based on the measured d current and the measured rotational frequency. Switching commands are then sent to the frequency converter via a Clarke-Park transformation and subsequent PWM modulation.

[0047] The linear regulator system reacts equally well to the applied load jump after about two seconds. The stabilizing regulator also intervenes by applying a d current and brings both machines back to a stable operating point (see Figure 7 ). However, the linearized regulator cannot reduce the d component of the motor current to zero as well. In addition, under the same system dynamics, the regulated current has a slightly higher ripple.

[0048] The embodiments of the invention are not limited to the preferred embodiments described above. On the contrary, many variations of the solutions shown are conceivable, even in the case of fundamentally different types of embodiments.

Claims

1. A control system (1) comprising a multi-motor frequency converter (PWR) for controlled parallel operation of n brushless DC motors (M1, ..., Mn), wherein the respective rotor positions of the n brushless DC motors are detected in each case without sensors, wherein: n≥2, including a. at least one detection device (20) for measuring the phase current I M1 ,..,I Mn and current detection performed separately and optionally the terminal voltage U of the n brushless DC motors (M1, ..., Mn) at the frequency converter u,v,w determining at least a rotor position and a rotational speed of the n brushless DC motors (M1, . . . , Mn), each of the n brushless DC motors (M1, . . . , Mn) being described for regulation in its own coordinate system (KOS), b. a regulating and transforming device (20), comprising a stabilizing regulator (RS) which generates a current d according to the determined rotor position and speed of the n motors, c. A regulating device (30) connected downstream of the regulating and conversion device (20), having a linear or nonlinear state regulator (R) to which the current variable output from the regulating and conversion device (20) is fed in order to generate therefrom a switching command (SZB) for the multi-motor frequency converter to operate the n motors.

2. The regulating system (1) according to claim 1, characterized in that A trajectory specification or a fixed setpoint is used for the speed specification of the state controller (R).

3. The regulating system (1) according to claim 1 or 2, characterized in that The detection device RLM1, RLM2 has at least one measuring device for detecting the corresponding phase current I of the n brushless DC motors (M1, . . . , Mn) without sensors. M1 ,..,I Mn .

4. The regulating system (1) according to any one of claims 1 to 3, characterized in that The control and conversion device (20) has a Clarke-Park transformer (TP) for converting at least the rotor position and the total current I uvw The variable is transformed into a dq current variable I represented by a space vector for the regulating device (30) d,q_ist .

5. The regulating system (1) according to any one of claims 1 to 4, characterized in that The regulating device (30) has a Clarke-Park transformer (TC) for converting the voltage variable U expressed as a space vector obtained from the state space regulator (T) by means of a Clarke-Park transformation. d,q Converted into three-phase voltage variable U uvw and converts it into a DC voltage switching signal (SZB) for the frequency converter (PWR) through a PWM modulator (PWM).

6. The regulating system (1) according to any one of claims 1 to 5, characterized in that The stabilizing regulator (R) is arranged to provide a suitable current variable I d_SOLL , to apply the current variable to the state regulator to return the motor to a stable operating point after a load jump of one of the brushless DC motors.

7. The regulating system (1) according to any one of claims 1 to 6, characterized in that The regulating device (30) has a Clarke-Park transformer (TC) for converting the state space regulator (R) from the state space regulator (R) to the state space regulator (R) by Clarke-Park transformation. dq ) The voltage variable U expressed as a space vector is obtained d,q Converted into three-phase voltage variable U uvw and converts it into a switching signal (SZB) for the frequency converter (PWR) through a PWM modulator (PWM).

8. A method for operating n brushless DC motors with n≥2 in parallel on a common multi-motor frequency converter (PWR) using a regulation system (1) according to any one of claims 1 to 7, comprising the following steps: a. Detecting the phase current I of the n brushless DC motors (M1, ..., Mn) respectively M1 ,..,I Mn , b. With the help of the previously measured phase current I of the n brushless DC motors (M1, ..., Mn) M1 ,..,I Mn to determine the rotor position and the rotational speed of the n brushless DC motors (M1, . . . , Mn) in order to determine therefrom a separate, in particular independent, coordinate system (KOS) for each of the n brushless DC motors (M1, . . . , Mn), c. generating a current variable and / or a voltage variable in space vector representation based on the value of the determined rotor position determined in step b) and transmitting it to the regulating device (30), d. Generate three-phase voltage variable U from voltage variable represented by space vector by Clarke-Park transformation uvw , and pass it to the modulator (PWM); e. By means of the modulator (PWM) from the voltage variable U of the multi-motor inverter (PWR) uvw generating a switch command (SZB) for controlling the operation of the n brushless DC motors, f. Wherein, the n brushless DC motors are adjusted relative to a selected reference motor and its reference coordinate system.

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