Method for starting up a permanent-magnet synchronous machine, and permanent-magnet synchronous machine

Abstract

In order to achieve the energy efficiency class IE4 defined in IEC standard 60034, it is necessary to operate permanent-magnet synchronous machines directly from the supply system. Since this is not readily possible, soft-starting devices come into consideration as cost-effective solutions. The problem of transmitter-free running up can be split into two component problems: determining the initial rotor angle and running up the machine. The present invention describes a (rotary) transmitter-free starting method with which the motor can be started using a soft-starting device.

Claims

1. A method for starting-up a permanent-magnet synchronous machine, said method comprising: a) setting initial values of a rotor angle .sub.End and an average rotation speed .sub.Mean of a rotor of the permanent-magnet synchronous machine to zero, wherein the rotor angle .sub.End and the average rotation speed .sub.Mean are determined solely from a measured terminal voltage of the permanent-magnet synchronous machine without use of an external shaft sensor; b) orienting the rotor to an initial position; c) rotating the rotor from the initial position with a maximum torque by firing thyristors, wherein the maximum torque is determined by a maximum permissible current for power semiconductors of the thyristors; d) measuring a voltage induced by a rotation of the rotor; e) determining an optimum firing angle of the permanent-magnet synchronous machine based on a measured rotor angle .sub.End and a measured average rotation speed .sub.Mean of the rotor, and f) repeating steps a) through e) when a difference .sub.End or .sub.Mean between successive measured rotor angles .sub.End and measured average rotation speeds .sub.Mean is greater than a predetermined threshold value.

2. The method of claim 1, wherein the permanent-magnet synchronous machine is a multi-phase machine having a dedicated thyristor for each phase, and wherein the rotor is rotated by firing two thyristors of at least three thyristors of the permanent-magnet synchronous machine at a maximum permissible current.

3. The method of claim 1, wherein the voltage is measured in a blocking time of the thyristors.

4. The method of claim 1, wherein the voltage is measured by a soft starter of the permanent-magnet synchronous motor.

5. The method of claim 1, wherein an initial value of the optimum firing angle is calculated once, and the once calculated value is used for each subsequent start-up of the permanent-magnet synchronous machine.

6. A permanent-magnet synchronous machine, comprising: a rotor; a plurality of thyristors connected to phases of the permanent-magnet synchronous machine; and a soft starter configured to a) set initial values of a rotor angle .sub.End and an average rotation speed .sub.Mean of a rotor of the permanent-magnet synchronous machine to zero, wherein the rotor angle .sub.End and the average rotation speed .sub.Mean are determined solely from a measured terminal voltage of the permanent-magnet synchronous machine without use of an external shaft sensor, b) orient the rotor to an initial position, c) rotate the rotor with a maximum torque from the initial position by firing at least some of the plurality of the thyristors, wherein the maximum torque is determined by a maximum permissible current for power semiconductors of the thyristors, d) measure a voltage induced by the rotation of the rotor, e) determine an optimum firing angle of the permanent-magnet synchronous machine based on a measured rotor angle .sub.End and a measured average rotation speed .sub.Mean of the rotor, and f) repeat steps a) through e) when a deviation .sub.End or .sub.Mean between successive measured rotor angles .sub.End and measured average rotation speeds .sub.Mean is greater than a predetermined threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is also illustrated by the following figures:

(2) FIG. 1 shows a section through an exemplary three-phase machine;

(3) FIG. 2 is a schematic representation of the assembly according to the invention;

(4) FIG. 3 shows a flowchart;

(5) FIG. 4 shows the measured profile of the electromotive force EMF on rundown;

(6) FIGS. 5 and 7 respectively show the profile of a measured EMF; and

(7) FIGS. 6 and 8 show the associated resulting angle from arctangent (ATAN) calculation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) FIG. 2 shows the basic desired assembly of the permanent-magnet synchronous machine (M) with soft starter (SS) without sensors and with sensors (G) on the left.

(9) The individual steps are explained in greater detail hereinafter.

(10) Step 1: Determining the Optimum Firing Angle:

(11) Once the process for initially aligning the machine has been completed, the current angle of the motor is known. On the basis of this known starting angle, that firing angle of the soft starter for which the torque generated in the motor is maximum for a given maximum current can be calculated according to the method described in published US Patent Application US-2020/0059183 A1. To produce a highest possible torque on the first firing of the thyristors, the maximum permissible current on the initial firing is set to the maximum permissible current for the power semiconductors.

(12) When calculating the optimum firing angle, the profile of the rotation angle and speed during the firing of the thyristors is also generally input, but these are not known when calculating the firing angle. For this reason, the optimum firing angle should first be determined for the initial firing in the context of a startup procedure for the drive.

(13) The flowchart of FIG. 3 illustrates one possible approach. The optimum firing angle is calculated, the soft starter is fired once using same and the final angle and the average rotational speed are subsequently determined. Using these values, an optimum firing angle is calculated again, the motor is aligned according to the method described in published US Patent Application US-2020/0059183 A1 and restarted. This procedure is repeated until the stop criterion (e.g. change in the values between runs) is met.

(14) In step 10, the values .sub.End and .sub.Mean are set to 0.

(15) In step 11, the permanent-magnet synchronous machine is initially aligned.

(16) In the next step, 12, the optimum firing angle is calculated, for example according to the method cited in the introduction to the description (Benecke method).

(17) Step 13 comprises the firing of the thyristors (controllers).

(18) Next, .sub.End and .sub.Mean are determined, in step 17.

(19) As long as .sub.End, .sub.Mean and firing angle are all below a determined threshold value, the optimum firing angle is calculated, 18. Otherwise, if one of the values is too high, the method must be rerun.

(20) It is conceivable for the optimum firing angle to be determined for the initial firing not through calculation, but instead only on the basis of the quantities .sub.End and .sub.Mean, which are calculated during startup. That angle for which .sub.End or .sub.Mean is maximum constitutes the optimum firing angle.

(21) Step 2: Switching to the EMF (Electromotive Force) Method:

(22) Once the permanent-magnet synchronous machine has been accelerated by the initial firing, the voltages induced by the rotation of the machine are high enough that they can be measured during the blocking phase of the thyristors. On the basis of the measured voltages, the flux angle of the machine can subsequently be determined e.g. by an observer or by a straightforward arctangent calculation. Similarly, it is conceivable for the rotation angle to be determined only on the basis of excited voltages, measured currents and machine equations, i.e. using an algorithm.

(23) Regardless of the chosen approach, in the aforementioned cases, numerous methods are already known from the field of sensorless control and these may be used.

(24) The flux angle determined using the EMF method is transferred to the Benecke method as an actual value and the next optimum firing angle on rotation of the machine is determined herefrom.

(25) Measurements:

(26) In FIGS. 4 to 8, diagrams based on measurements from a real permanent-magnet three-phase machine in the laboratory are shown. These demonstrate that it is already possible to determine the flux angle from the measured voltages by means of a straightforward arctangent calculation.

(27) FIG. 4 shows the profile of the measured electromotive force EMF on rundown of the machine, in which the voltage U is plotted against time t.

(28) FIGS. 5 and 7 show measurements relating to the measured EMF over time, and the respective angle calculated thereby from an arctangent calculation.

(29) To achieve the energy efficiency class IE4 defined in IEC standard 60034, it is necessary to operate permanent-magnet synchronous machines (PMSM) directly from the power supply system. Since this is not readily possible (see above), soft start devices come into consideration as a cost-effective solution. To achieve this, an (expensive) sensor system is required in the prior art. For an economically practical solution, sensorless ramp-up must be made possible.

(30) The required starting method differs from the sensorless methods scientifically and technologically known in that it needs to be usable for a thyristor controller and not a frequency converter. As such, these known methods are not suitable.

(31) In summary, the fundamental principle is based on the motor being accelerated at maximum using the initial firing of the thyristors and subsequently calculating the flux angle of the machine on the basis of the measured induced voltages. After the first firing procedure, the flux angle of the machine can already be determined directly from the measured terminal voltage (the phase currents are meanwhile zero). The determination operation is not based on a calculation model, but rather on the direct measurement of the induced voltages, i.e. the electromotive force, EMF. For the second firing procedure, the calculated angle can then be used. Measurements show that the angle can be determined from the measured voltages very successfully, even at low speeds.

(32) In order to actually accelerate the machine at maximum during the initial firing, the optimum firing angle can be precisely determined when starting the machine (the starting angle is known) in the context of a described startup procedure. The described starting procedure is based only on the measurement values that are already present in the series device and requires no additional sensors. Thus, it is possible to upgrade an existing product for operating an IE4 motor using only a software solution.