Method for synchronizing control electronics to a rotating motor with sinusoidal control

Abstract

Method for synchronizing an output voltage of a half-bridge with a power switch for a negative supply voltage and a power switch for a positive supply voltage for an already moving electric motor, characterized in that the method comprises: - Controlling the half-bridge at the beginning of the synchronization process with a dead time during which neither a control signal of the power switch for the positive supply voltage nor a control signal of the power switch for the negative supply voltage is active, wherein the dead time is chosen to be large enough to generate an uncertainty range of the output voltage of the half-bridge corresponding to the dead time, within which lies an actual output voltage to be generated for the moving electric motor, wherein the uncertainty range of the output voltage of the half-bridge represents a range of voltage values ​​that the output voltage can assume depending on an output current of the half-bridge; - Reducing the dead time during the synchronization process such that a. the dead time (6) at the beginning of the synchronization process differs in percentage from the dead time (6) at the end of the synchronization process or b. the dead time (6) at an earlier point in the synchronization process than the end of the synchronization process differs proportionally from the dead time (6) at the end of the synchronization process, such that at the end of the synchronization process a small uncertainty range corresponding to the dead time remains; wherein the output voltage is provided for a sinusoidal control of the electric motor; and wherein the synchronization of the output voltage of the half-bridge includes or consists of adjusting an amplitude of the output voltage of the half-bridge.

Description

Introduction

[0001] The control of permanent magnet synchronous machines (PMSMs) is a task that always requires the generation of a rotating field that has a fixed relationship to the rotor field in terms of its phase position, amplitude, and field frequency. A number of state-of-the-art methods for generating such a rotating field exist. These solve the control task more or less effectively during steady-state operation, during load and speed changes, and during starting from standstill.

[0002] However, a major problem in the current state of the art is still synchronizing to a machine that is already rotating. In this operating case, no control takes place. The machine's connections have high resistance and the machine is already rotating, either due to an external drive or due to its inertia. Such operating cases occur, for example, in wind turbines, cooling fans or motors that drive vehicles. In the former case, the wind turbine is already set in motion, for example, by the wind. With cooling fans, this can happen, for example, through the airflow from the vehicle. In electric vehicles, this can be the operating case when the electric drive is switched on while the vehicle is already moving.

[0003] The problems described below typically occur when synchronizing to a rotating machine with sinusoidal control. This can occur, for example, with radiator fans, air conditioning fans, and various pumps, but also in other applications such as air conditioning damper controls in homes.

[0004] Generating a phase- and frequency-correct control is not a problem in itself, since both can be determined with sufficient accuracy either by evaluating sensor signals or, for example, measured voltages.

[0005] However, generating the correct amplitude for a smooth transfer of motor control by the control circuit remains a problem. Especially in high-power machines with low internal resistance, even very small deviations in the control amplitude compared to the amplitude specified by the motor lead to strong current increases during the transition from the high-impedance state of the motor to the normal controlled state. The steep current increase, in turn, leads to strong voltage changes in the supply voltage as well as to strong torque changes and possibly to noise, which is disruptive, for example, in automotive applications. The resulting parasitic strong torque changes can, in turn, lead to damage to the mechanical system connected to the motor. In existing control systems, for example,By measuring the amplitude or calculating it from the field speed using constants stored in the system's memory, an attempt is made to generate the most accurate amplitude possible at the time of takeover. However, this is not always successful, which leads to the aforementioned, sometimes unacceptable effects.

[0006] DE 10 2010 030 239 A1 discloses a method for starting a three-phase electric motor in which individual winding phases are not energized in phases. Two of the winding phases are always energized (see page 5, left column, lines 1 to 2 of DE 10 2010 030 239 A1). During motor start-up (see Fig. 5 Reference number 432 of DE 10 2010 030 239 A1), this currentless dead time of the respective winding phase is compressed inversely proportional to the rotational speed. Relative to a control cycle, the percentage of dead time relative to the total current flow time does not change.

[0007] DE 10 2008 059 052 A1 discloses a method for determining the rotor position within a measuring period (reference symbol T M DE 10 2008 059 052 A1) in which the motor is not energized and the motor voltages are measured. A specialist will typically choose this measurement period to be around the zero crossing of the winding currents.

[0008] The generic document DE 10 2008 013 521 A1 appears to describe a method and device for controlling the start-up of a sensorless, brushless DC motor. The starting current is increased to reduce the number of false starts.

[0009] The previously described problem of synchronizing to an already rotating machine has not yet been solved for sinusoidal control. This particularly applies to combinations from the previously mentioned publications. Object of the invention

[0010] The objective is to create a method for synchronization with sinusoidal control that does not exhibit any of the aforementioned problems and thus avoids them. This objective is achieved by a method, a control unit, a control system, and a machine having the features of the respective independent claim. Description of the invention

[0011] In contrast to the prior art, the invention allows for trouble-free synchronization to an already rotating motor. Furthermore, the otherwise necessary parameterization of the motor constant in the control system can be eliminated. The invention is explained below.

[0012] It is the essential inventive idea disclosed in this description to solve the problem described above by using a special method which changes the dead time during synchronization as a percentage of a sine period.

[0013] This is explained in more detail below: When controlling half-bridges, a dead time is used to prevent cross-current flow through the high-side driver transistor and the low-side driver transistor during the switching transition phases. Such cross-current flow would lead to unnecessary heating and / or even destruction of the half-bridge, which could only be avoided by a more resilient design and thus an increase in the cost of the half-bridge. This dead time, during which control is suspended to avoid cross-current flow, is minimized according to the state of the art, as it causes deviations between the desired and the actual duty cycle. The deviation of the actual duty cycle, in turn, depends on the load current direction.

[0014] The synchronization method according to the invention exploits this effect. At the beginning of the process for synchronizing the control to a machine that may already be rotating, it deliberately generates a significantly increased dead time, unlike prior art methods that typically minimize dead time. The duty cycle "error" generated as a result according to the prior art is used in the method as the "uncertainty" of the output voltage. This "uncertainty" is set in the method so that at the moment of synchronization it is at least as large as the uncertainty that the output voltage to be generated already has, e.g. due to measurement errors and parameterization errors. The aim is therefore to use an artificially greatly increased dead time to generate an output voltage with an "uncertainty range" such that the actual, exact output voltage to be generated lies within this "uncertainty range".The dead time is then slowly reduced to the minimum possible value.

[0015] This minimum possible value is detected when the value of a register containing the current dead time no longer exceeds a previously parameterized value stored elsewhere, e.g., in another register. This parameterized value depends only on the dimensioning of the half-bridges and not on the load or motor. Of course, it is also conceivable, for example, to set this target value externally or permanently using analogue technology and to compare this externally specified, previously parameterized value with the value of the register. Instead of a digital solution, a purely analog solution is also possible.

[0016] The slow reduction enables a continuous takeover with a smooth current and torque curve.

[0017] In addition, this method eliminates the need for complex parameterization of the motor, so that, for example, the approximate amplitude can be measured while the motor is rotating without any calibration procedures during production or commissioning, and the synchronization can be started with a correspondingly very long dead time.

[0018] The overall system thus shows a continuous torque and current curve when synchronizing the control to a rotating machine.

[0019] Furthermore, some machine-specific parameterizations can be eliminated and replaced by a universal parameterization of the dead time generation. In typical applications, the method according to the invention is preferably implemented in such a way that initially only the amplitude uncertainty is compensated. Typically, phase synchronization is a minor problem. This phase synchronization can be achieved, for example, by time measurements between the zero crossings of the measured voltages at the motor terminals.

[0020] Nevertheless, an increased dead time is also very well suited to compensating for phase uncertainties. This is because it can be assumed that a motor that is already rotating will certainly change its speed. This can be caused, for example, by an external braking torque or even torque fluctuations. Typically, such an output signal can only be generated after a corresponding time measurement. Therefore, a small phase difference between the output voltage and the motor voltage can be expected.

[0021] It is obvious to the person skilled in the art that, based on the method, it is possible to operate a device that executes the method described above. In this case, the reduction of the dead time (6) of an output signal of a half-bridge and the correction of the phase / amplitude of this output signal can occur simultaneously.

[0022] In this way, a control system for a permanent magnet synchronous machine can be constructed in which the reduction of the dead time of an output signal of a half-bridge and the correction of phase / amplitude of this output signal occur simultaneously.

[0023] This control can be part of an electrical machine, which is typically a permanent magnet synchronous machine.

[0024] The invention is further explained with reference to the attached exemplary schematically simplified figures.

[0025] The figures show: Fig. 1 shows a comparison between EMF of the machine and generated voltages at the beginning of synchronization according to the state of the art Fig. Figure 2 shows the generated signals with dead time according to the state of the art (Note: For better visibility and better understanding by the reader, the dead time is greatly enlarged compared to reality and is therefore not shown to scale). Fig. Figure 3 shows the uncertainty range of a generated output voltage caused by the dead time according to the state-of-the-art technology. (Note: For better visibility and better understanding by the reader, the uncertainty range is greatly enlarged compared to the signal and is therefore not shown to scale.) Fig. 4 shows a signal generated according to the invention at the beginning of the synchronization Fig. 5 shows a signal generated according to the invention at the end of the synchronization Figure 1

[0026] Fig. Figure 1 shows the comparison between the first curve (1) of the electromotive force (EMF) of the machine and the voltages generated at the beginning of synchronization according to the state-of-the-art technology. The second curve (2) represents a voltage with a slightly too large amplitude. This voltage would lead to strong acceleration with a correspondingly high current and a strong torque change at the beginning of synchronization.

[0027] The third curve 3 represents a voltage with a slightly too low amplitude. This would lead to a large, undesirable braking torque at the beginning of synchronization. As a result, a high, undesirable current also arises through the driving half-bridge (not shown). The two operating cases, represented by the second curve (2) and third curve (3), thus lead to thermal stress on the driving half-bridges in the state of the art, which is why they must be designed larger to avoid damage. In addition, increased mechanical stress can arise from the resulting torque changes, which must also be absorbed by increased and therefore more expensive dimensioning to avoid damage. Figure 2

[0028] Fig. Figure 2 illustrates the generation of exemplary control signals for an exemplary half-bridge of the power circuit according to the state of the art for controlling the machine. The half-bridge should consist of a power switch for the positive supply voltage, the high-side driver, and a power switch for the negative supply voltage, the low-side driver. In this example, the power switch for the positive supply voltage switches the positive supply voltage to the output of the half-bridge when its control signal (4) is positive. Fig. 2, the fourth curve (4) represents the control signal for the power switch to provide a positive supply voltage at the output of the half-bridge. In this example, the power switch for the negative supply voltage switches the negative supply voltage to the output of the half-bridge when its control signal (5) is positive. Fig. 2, the fifth curve (5) thus represents the control signal for the power switch to provide a negative supply voltage at the output of the half-bridge. The seventh curve (7) is an example of the resulting voltage curve of the output voltage of the half-bridge with an output current flowing out of the half-bridge. The eighth curve (8) is an example of the resulting voltage curve of the output voltage with an output current flowing into the half-bridge.

[0029] Between the control pulses of the half-bridge, there is a period of time in which neither the control signal of the power switch for the negative supply voltage (low-side driver) nor the control signal of the power switch for the positive supply voltage (high-side driver) are active. This period is the dead time (6). It is of course conceivable, but typically not sensible, for a residual cross-current other than zero to flow through the bridge during this dead time (6), or for one of the two switches to not be completely turned off. The dead time (6), as an undesirable side effect according to the state of the art, ensures that there are time intervals (9) in which the instantaneous output voltage corresponds to either the positive or the negative supply voltage, depending on the sign of the output current. If the output current is zero, the output voltage can assume any value during these time intervals. Figure 3

[0030] Fig. Figure 3 shows the curve of a generated output voltage in the presence of a dead time according to the state of the art. It contains an "uncertainty region" (10), which is undesirable according to the state of the art and surrounds the actual output voltage, which, since it is unknown, is not shown. For better representation, the uncertainty region is greatly enlarged compared to the generated signal and is not shown to scale. Within this uncertainty region, the output voltage can assume any value depending solely on the output current at the respective time. If the current direction out of the half-bridge were always positive, the actual output voltage would typically run along the upper limit of the hatched region (10). If the current direction were always negative, the actual output voltage would typically run along the lower limit of the hatched region (10).

[0031] A change in current direction leads to a change in the actual curve between the lower and upper limits. Values ​​within the hatched area are assumed when the output current is zero or during a current direction transition. Figure 4

[0032] The method according to the invention exploits this previously undesirable behavior to generate a gently increasing motor current and thus a gently increasing torque during synchronization. For this purpose, a very long dead time is selected at the beginning of synchronization. This ensures a correspondingly large uncertainty range (11). This uncertainty range (11) is generated according to the invention such that the actual EMF of the motor (1) always lies within the uncertainty range (11). If the amplitude of the EMF is completely unknown, it is even possible to start with a dead time of 100%. The synchronization process can therefore be started for the affected output signal of the respective half-bridge with a dead time of 100% or more than 99% and / or 98% and / or 96% and / or 90% and / or 80% and / or 60% and / or 40% and / or 10% and / or 5%.

[0033] According to the invention, the uncertainty range can also be used to include remaining uncertainties regarding the phase of the output voltage to be generated.

[0034] During the synchronization process, the dead time is reduced slowly and gradually until it reaches the target value.

[0035] According to the invention, the amplitude and / or phase of the output voltage can also be continuously corrected until a certain load current flows or a certain load torque is generated before the dead time is reduced. This can be done in such a way that no sign changes are generated in the load torque during the dead time reduction.

[0036] In addition, the dead time reduction can also be interrupted at any time to adjust amplitude / phase and then further reduce the dead time.

[0037] According to the invention, the reduction of dead time and the correction of phase / amplitude can also be carried out simultaneously. Figure 5

[0038] Fig. Figure 5 shows the EMF curve (1) and the generated signal at the end of the synchronization process (12). The dead time is reduced to a typically specified minimum possible value (target value). This target value is typically specified by the controller design and / or by an external control signal and / or by programming.

[0039] The remaining uncertainty range at the end of the synchronization process (12) is correspondingly small. The control generates a signal that is appropriate for the speed and load without causing significant torque or current fluctuations.

Claims

[1] Method for synchronising an output voltage of a half-bridge with a power switch for a negative supply voltage and a power switch for a positive supply voltage for an already moving electric motor, characterized by that the procedure includes: - controlling the half-bridge at the beginning of the synchronization process with a dead time during which neither a control signal of the power switch for the positive supply voltage nor a control signal of the power switch for the negative supply voltage is active, wherein the dead time is selected to be so long that the dead time generates an uncertainty range of the output voltage of the half-bridge which is correspondingly large to the dead time and in which an actual output voltage to be generated for the moving electric motor lies, wherein the uncertainty range of the output voltage of the half-bridge represents a range of voltage values ​​which the output voltage can assume depending on an output current of the half-bridge; - Reducing the dead time during the synchronization process so that a. the dead time (6) at the beginning of the synchronization process differs in percentage from the dead time (6) at the end of the synchronization process or b. the dead time (6) at an earlier point in time of the synchronization process than the end of the synchronization process differs in percentage from the dead time (6) at the end of the synchronization process, so that at the end of the synchronization process an uncertainty range corresponding to the dead time remains; wherein the output of the output voltage is output for a sinusoidal control of the electric motor; and wherein the synchronization of the output voltage of the half-bridge comprises or consists in adjusting an amplitude of the output voltage of the half-bridge. [2] Method according to claim 1, wherein the uncertainty range of the output voltage is determined such that the uncertainty range of the output voltage is at least as large as an uncertainty of the actual output voltage to be generated due to measurement errors and / or parameterization errors. [3] Method according to one of claims 1 and 2, wherein the reduction of the dead time occurs during the synchronization process until the dead time has reached or fallen below a predetermined target value. [4] Method according to claim 3, wherein the target value is predetermined by a design of a controller and / or by an external control signal and / or by programming. [5] A method according to any one of the preceding claims, wherein the reduction is carried out stepwise. [6] Method according to one of the preceding claims, wherein the control is carried out with at least two and / or three half bridges. [7] Method according to one of the preceding claims, wherein the dead time (6) of at least one output signal of at least one half-bridge is greater in percentage terms at the beginning of the synchronization process than at the end of the synchronization process. [8] Method according to one of the preceding claims, wherein the dead time at the beginning of the synchronization process is more than 99% and / or 98% and / or 96% and / or 90% and / or 80% and / or 60% and / or 40% and / or 10% and / or 5%. [9] Method according to one of the preceding claims, wherein remaining uncertainties with regard to the phase of an output voltage to be generated of an output signal of the half-bridge are enclosed by an uncertainty range (11, 12) by a dead time (6) selected to be correspondingly large in percentage terms. [10] Method according to one of the preceding claims, wherein the amplitude and / or the phase of the output voltage of the output signal of the half-bridge are first corrected until a load current whose magnitude or amplitude is greater than a predetermined load current flows or a torque occurs which has a magnitude greater than a predetermined torque, before the dead time (6) of this output signal of this half-bridge is reduced in percentage terms. [11] Method according to claim 10, wherein the dead time (6) of the output signal of the half-bridge is reduced in percentage terms such that no sign changes in the torque are generated during the percentage reduction of the dead time (6) of this output signal of the half-bridge. [12] Method according to one or more of the preceding claims, wherein the percentage reduction of the dead time (6) of the output signal of the half-bridge is interrupted at least at one point in time and the amplitude and / or phase of this output signal of this half-bridge is adjusted after this interruption and the dead time (6) of the output signal of the half-bridge is further reduced in percentage after this adjustment. [13] Method according to one or more of the preceding claims, wherein the percentage reduction of the dead time (6) of the output signal of the half-bridge and the correction of phase / amplitude of this output signal take place simultaneously. [14] Control device for a permanent magnet synchronous machine, wherein the control device is designed to carry out a method according to one or more of the preceding claims. [15] Control for at least one half-bridge, which is suitable and intended to carry out a method according to one or more of claims 1 to 13 as part of a device according to claim 14. [16] An electrical machine which is a permanent magnet synchronous machine, comprising a control device according to claim 14 and / or a control according to claim 15.

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