DE10028492B4 - System for controlling a mains AC synchronous motor - Google Patents

Abstract

System for controlling a in one of a mains frequency (f _N ) dependent synchronous speed (n _S ) mains AC synchronous motor with a permanent magnet rotor (1), with a motor with respect to its respective actual speed (n _is ) monitoring and at least in the case of over a certain time existing deviation of the actual speed _(n) of the synchronous speed (n _S) of control technology on the engine acting control unit (4), characterized in that the rotor (1) of the alternating current synchronous motor connected to a load or is to be connected, the torque of which progressively increases with the speed, wherein the control unit (4) is designed so that after a certain time of deviation of the actual speed (n _is ) from the synchronous speed (n _S ), the motor in an asynchronous emergency operation reduced with respect to its synchronous speed Speed (n _U ) is operated, wherein the emergency operation with a relation to the synchronous operation red Induced winding current, wherein the reduction of the winding current by reducing the winding voltage due to speed-dependent phase control and suppression of certain, z. B. second or third half-waves and / or ...

Description

The The present invention relates to a system for controlling a permanently excited, in a dependent of a mains frequency synchronous speed line-commutated AC synchronous motor with a permanent magnetic rotor, with a motor with respect to his respective actual speed monitoring and at least in case of over a certain time existing deviation of the actual speed of the Synchronous speed control technology acting on the motor Control unit.

Such a generic system is in principle in the publication JP 56 035 696 A with English abstract from Patent Abstracts of Japan. It is a control circuit for a synchronous motor, wherein in case of failure (out-kick) a trip winding is energized via an OR gate. An out-of-tread fall is detected via a relay. This is stored by a memory unit and a field-cutting device is triggered, closing a contact and turning on a timer, and if the motor does not start within a timer-specified time, the trip winding will be triggered by the timer's output Thus, in this publication, only an error handling with start attempt is described, but how other processes are, remains completely open.

The JP 62 077 086 A merely describes an alarm device for indicating an out-of-step falling of a synchronous motor. More is not to be found in this document. In particular, nothing is said about what happens to the engine if it can not be operated at synchronous speed.

The US 4,430,681 A describes a series motor with brushes, so a mechanical commutator, via which a correct commutation is always ensured. In an overload case, only a lowering of the voltage, whereby the speed is reduced. Due to the mechanical commutator the commutation time is still correct. An out-kicking is not possible here. In this respect, this does not raise the problem of correcting a speed deviating from the synchronous speed.

From the DE 299 17 700 U1 It is also known in an electronic starting device for synchronous motors to perform a monitoring of the synchronous operation. In the case of a deviation of the respective engine speed from the synchronous speed, a so-called. Out-of-treading falling, a restart is attempted with the aim of returning the engine back to synchronism. After a futile attempt to start further periodic start attempts can be carried out, always with the aim to achieve synchronous operation again. In addition, the affected motor may eventually be switched off completely even after a certain maximum number of failed start-up attempts. There may be operating conditions that make synchronism impossible. Therefore, the known measures would eventually inevitably lead to a complete shutdown of the engine after a certain time.

at many applications, such as in refrigeration, but would be a complete one Shutdown of the engine with disadvantages by, for example, additionally required monitoring devices or Redundancy connected.

Also from the EP 0 666 639 A1 It is known to accelerate a not correctly in synchronism running machine again up to the synchronous speed. If the supply voltage for synchronous operation is insufficient or if the load is too high, the motor will remain in this acceleration mode without, however, actually being able to accelerate. In certain cases, this can lead to thermal overload and thus failure.

• 1. Ausrichten des Rotors in eine definierte Drehstellung,
• 2. Starten des Rotors zur anfänglichen Rotation in eine gewünschte Drehrichtung durch Ansteuerung mit Spannungs-(oder Strom-)Impulsen,
• 3. Stabilisierungsphase mit einer unterhalb des Synchronismus liegenden Drehzahl und
• 4. Synchronisierungsphase.

From the EP 0 872 949 A2 it is known to divide the startup process of a synchronous motor in 4 phases:

• 1. Aligning the rotor in a defined rotational position,
• 2. starting the rotor for initial rotation in a desired direction of rotation by driving with voltage (or current) pulses,
• 3. stabilization phase with a lying below the synchronism speed and
• 4. Synchronization phase.

there the 3rd phase is optional and will be inserted if the load is an initial one Stabilization at a lower speed than the synchronous speed requires. As an example for such a load is called a pump. Obviously this will third operating phase for the purpose of optimizing the run - up of the Motors introduced at certain loads. Anyway, the run three or four phases successively successively with the aim of In any case, to bring the engine into sync.

The DE 197 018 56 A1 describes another electronic start-up and operation control for a single-phase synchronous motor. Here, too, different operating phases are defined, namely startup, startup and synchronous operation. If overload occurs in synchronous operation, the speed may drop. In this case, the tax returns of synchronous operation are switched off and those of the startup are switched on. Possibly will be switched to the tax laws for startup below. Thus, here too, the engine should be accelerated again and returned to synchronism.

In the EP 0 574 823 B1 is described a starting device for a synchronous motor, wherein the start-up via a correspondingly controlled static switch, for. B. triac occurs. The motor flux can optionally be increased by switching the supply voltage to a tap of the motor winding during the start-up phase. After a predetermined time, the corresponding switch is turned off, and the switch that turns the whole motor winding to the mains is turned on. A position sensor also allows the monitoring of the speed. After the predetermined start-up time, the speed is checked. If the synchronous speed has not been reached, the motor is disconnected from the mains. In order to start the engine again below, the engine system and the electronic circuit must be completely disconnected from the AC supply source for a short period of time.

Finally, also describes the EP 0 682 404 A2 a start-up control for a single-phase permanent magnet synchronous motor. By a certain control, the motor should be accelerated until the synchronization with the mains voltage and thus the maximum speed is reached, which is known to be a function of the mains frequency and the number of poles of the motor. It is mentioned that it is possible to reduce the speed with a certain control and to stabilize at a lower synchronous speed. Possible synchronous speeds result from dividing the maximum synchronous speed by an integer (2, 3, ...)

Of the present invention is based on the object, a control system of the type mentioned, with which even in problematic operating situations, especially in case of overload, a complete one Failure of the engine or a forced shutdown largely avoided becomes.

According to the invention this is achieved by the features of claim 1. Accordingly, the Synchronous motor designed to drive a load by means of the rotor, whose torque increases progressively with the speed. This is especially true at Fans and pumps are the case. For this purpose, the control unit is such that after a certain time a deviation of the Actual speed of the synchronous speed of the motor in an asynchronous Emergency operation with a re its synchronous speed reduced speed is operated, the Emergency operation with one opposite the synchronous operation reduced winding current takes place, the reduction the winding current by reducing the winding voltage as a result of speed-dependent Phase control and suppression of certain, z. B. second or third half-waves and / or by a winding switch to a larger number of turns takes place, wherein the control unit, the engine via at least one static Switch, such as triac and / or thyristor, controls and at least while of the emergency operation one of the rotor position with respect to the current phase position the mains frequency dependent Control of the static switch by the control unit in Meaning of torque formation in the desired direction.

The Control unit monitored thus startup and synchronous operation and then intervenes when when starting the synchronous speed is not reached or the engine later falls out of synchronism. The control unit can then possibly still a certain number start-up attempts. But if it is not possible then to bring the engine into synchronism or in synchronism to keep the control unit according to the invention switches to emergency operation around. In this mode the motor works asynchronously, much like at start-up, but not with the target, up to the synchronous speed to accelerate. To overheat in this emergency operation according to the invention To avoid, it is advantageous if the emergency operation with a across from the acceleration phase reduced winding current occurs. These Reduction of the winding current can in an advantageous embodiment by a reduction in particular caused by phase gating the winding voltage. Alternatively or in addition, a Reduction of the current also by a winding switch on a larger number of turns take place.

Of the Emergency operation according to the invention a net-guided Synchronous motor thus relates primarily to applications in the field Fans and pumps. Here the torque increases with the third power the speed, which is why at the design point of the engine, d. H. at the highest speed, the biggest torque occurs. With unavailable synchronism is thereby an enterprise at lower speed possible, without thermally overloading the engine.

It is with regard to the achievement of high engine efficiency endeavors to make the motor dimensioning so that the efficiency at the rated torque is maximum. However, this has the consequence that the security against an out-of-step falling of the engine in case of short-term overload or temporary drop in Netzspan is relatively small.

An oversizing the engine to safely avoid such cases would have worsened the Motor efficiency result. The engine efficiency is however one of the decisive advantages of a permanently excited line-commutated synchronous motor. Especially for low-power synchronous motors, which are equipped with cost-effective shading poles. or capacitor motors would have to compete, such a measure would be in addition the reduction of the efficiency with an economic disadvantage connected by a larger material usage.

By the emergency operation according to the invention, the mentioned disadvantages of the prior art can be avoided. Of the Motor can with minimal reserve for maximum efficiency below Rated conditions are designed. Is the synchronous operation by short-term overload or too small mains voltage is no longer possible, then in the described Emergency operation with reduced speed and torque passed. In this temporary In the event of a fault, the efficiency drops compared to synchronous operation, the However, engine is still able, even here, the required minimum To deliver (air) power.

The Invention therefore has significant technical and economic Advantages over that State of the art.

Further advantageous design features are in the dependent claims and included in the following description.

Based the drawing, the invention will be explained in more detail by way of example. Showing:

1 FIG. 2 shows a schematic block diagram of a system according to the invention in a first embodiment of a line-commutated, permanently excited synchronous motor, FIG.

2 a similar block diagram with a synchronous motor with a winding tap for the run-up,

3 a diagram of the winding current course in a possible quasi-synchronous operating point for emergency operation (for example, 16 2/3 Hz) and

4 an exemplary flowchart for explaining the functions of the system according to the invention.

In the 1 and 2 is of a permanent-magnet AC synchronous motor in each case the motor winding 2 and the permanent magnetic rotor 1 shown. In the execution after 1 is a static switch Tr ₁ in series with the motor winding 2 , and this series circuit is connected to a mains AC voltage, ie to a phase conductor L ₁ and a neutral conductor N. The static switch Tr ₁ is controlled by a control unit 4 driven. In the execution after 2 owns the motor winding 2 a tap 6 , about which part of the motor winding 2 by means of a first static switch Tr _{1 is} controlled. The entire motor winding 2 is controlled by a second static switch Tr ₂ . Both switches Tr ₁ and Tr ₂ are optionally from the control unit 4 driven. The static switches may in particular be triac or thyristors.

To detect the rotor speed is a rotor position sensor 3 is provided, which is preferably a Hall sensor that detects the magnetic field of the rotor.

The determination of the rotor rotational frequency is not as simplistic in 1 or 2 shown limited to the application of a rotor position sensor, but can also be done sensorless. In this embodiment, instead of the rotor position sensor ( 3 ) provided a suitable sensorless detection circuit, the control unit ( 4 ) Provides information about the rotational frequency of the rotor by measuring directly the course of the rotating permanent magnet rotor ( 1 ) in the motor winding ( 2 ) or by indirectly determining the measurement of winding currents and voltages.

Based on the in 4 illustrated flow chart is first to the invention for the execution of 1 without winding tapping for the run-up procedure are explained.

For the run-up a net-guided, permanently excited synchronous motor, a higher flux is generally required as for the synchronous operation. The winding design of the motor must therefore done so that at maximum permissible mechanical load and at minimum permissible mains voltage the run-up still possible is. The run-up is a temporary one Process that generally does not last long. In many cases the design of the winding therefore so that the run-up an overload case represents. The for the run-up required large River becomes in synchronous operation to achieve good efficiency, through Phase cut of the mains voltage reduced. Advantageously, the adapted effective winding voltage load dependent, so that in a wide range high efficiency is achieved.

If the mechanical load is too high and / or the mains voltage is too low, the motor may fall out of step. Such a case is inventively by the control unit 4 recognized. This can advantageously be done by a comparison of z. B. via the rotor position sensor 3 detected rotational frequency of the motor with the mains frequency of the AC supply voltage and a deviation is detected. Subsequently, new startup attempts can be initiated.

Start-up tests and monitoring

A run-up test with a high flux takes place until a predetermined time t _{1 has} elapsed and the synchronous speed n _S could not be reached during this time. Then, the motor for a predetermined period of time t ₂ is isolated from the mains in order to avoid overheating of the coil. After the expiration of t ₂ , a renewed start-up with high flow is performed. Could not be reached after a specified number Z ₁ of successive run-up tests, the synchronous speed, which by comparing the rotor rotational frequency, the z. B. via the rotor position sensor 3 is detected, is detected with the known network frequency, the emergency operation according to the invention is activated. In particular, in applications of the motor as a drive for blowers or pumps, it is advantageous if, despite an existing fault, z. As mechanical overload or mains undervoltage, nor a certain, depending on the respective error case flow rate is provided, ie the engine is not completely failed. In emergency operation, the motor is controlled such that in asynchronous, ie undersynchronous operation, the winding does not assume unacceptably high temperatures despite a possibly existing overload case. This is preferably done by reducing the applied winding voltage. Preferably, the winding voltage is reduced via phase control of the mains voltage compared to the regular startup process. According to the desired phase angle is from the control unit 4 the static switch Tr _{1 is} activated. The phase angle is advantageously set as a function of the speed of the motor at the maximum permissible mains voltage so that the motor windings does not assume an unacceptably high temperature. Each engine speed, ie specific speed ranges, is so assigned a certain phase angle, in which the winding just barely overheated. This assignment is in the control unit 4 , preferably stored in a microcontroller in the form of a speed gate angle table. During emergency operation, the current engine speed is determined by the control unit 4 continuously via the rotor position sensor 3 detected and applied the corresponding phase angle for reducing the voltage connected to the winding. In this way, despite changing load overheating of the motor winding can be avoided during emergency operation in a wide load range.

In addition, a lower _{limit speed} n _{Grenz1 is} defined in order to protect the motor during emergency operation, even against heavy overload. If the engine speed _drops below n _{limit 1} as a result of a large load torque, the engine is switched off and, if necessary, a new _{startup attempt} .

Particularly favorable for the emergency operation described are so-called quasi-synchronous speeds, for example 1/2 or 1/3 synchronous speed (cf. 3 ). Here, the engine works with a better efficiency than the other subsynchronous speeds. In this embodiment, in addition to reducing the effective winding voltage, z. B. as described above via phase control, mains half-waves from the control unit 4 specifically faded out to produce a fundamental frequency lower than the mains voltage. This results in a smaller speed of the motor than in synchronism with the mains frequency and - assuming a rising with the speed load torque, as is always the case with fans or blowers - a smaller load on the engine. For half mains frequency z. B. two consecutive, even truncated mains half-waves are switched to the motor winding, whereas the two subsequent network half-waves are blocked. This method is advantageously used for emergency operation.

Start-up attempts and monitoring

In an advantageous embodiment of the invention, the run-up test is supplemented by a measure described below, to cover even extreme overloads during startup safe. Is the rotor severely braked or even completely blocked, resulting from the control unit 4 is detected, that despite energization of the winding, during a fixed period t ₃ which is shorter than t ₁ , a lower _{limit speed} n _Grenz2 , which in turn is smaller than n _Grenz1 , can not be achieved, the engine is switched off. In this case, repeated start-up tests are carried out at recurring intervals t ₄ . If, after a number of Z ₂ consecutive start-up _attempts , no speed greater than _{limit 2} can be reached, the motor is switched off permanently. However, _{if the} limit _speed n _{limit 2} can be exceeded within t ₃ , run-up _tests and monitoring take place according to the method already described above.

Renewed startup attempts after permanent shutdown or emergency operation

Renewed startup and startup attempts are only restarted when the operating voltage is switched off for a short time, or when - as realized in a preferred embodiment of the invention - via a in 1 and 2 not shown control input of the control unit 4 a corresponding command is given for this.

Periodically initiated startup attempts

In a particularly advantageous embodiment, the control unit interrupts 4 periodic emergency operation or shutdown of the engine at predetermined intervals t ₅ and t ₆ , which are longer than t ₂ and t ₃ , and initiates renewed start-up or run-up attempts. If it still fails to reach the synchronous speed, the control unit continues 4 the emergency operation or switches off the engine again, depending on the present load case.

The previous explanations will be made again to the flowchart in 4 which illustrates the described procedures and conditions.

It will now be the invention for the execution 2 with winding tap 6 described for the startup process.

As already mentioned, a higher flux is required for the run-up of a mains-controlled, permanent-magnet synchronous motor than for synchronous operation. This can be the winding tap 6 be provided. The startup process is then with a smaller number of turns on the tap 6 carried out, creating a larger river. In order to achieve a good engine utilization, usually the design of the winding is done so that the operation during startup with the smaller number of turns represents an overload case. In synchronous operation then the entire winding is turned on. Due to the larger number of turns then results in a smaller winding current and thus a smaller flux than at run-up, resulting in a high efficiency results.

The above-described measures for monitoring the synchronous operation and the start-up or run-up can also be unrestricted for this type of motor with tap 6 be applied. If the engine can not reach its synchronous speed, the emergency mode is activated, in which it operates at a lower speed, ie with a lower mechanical load, when there is a load torque increasing with the speed. In order to protect the winding from overheating during under-synchronous operation, whereby the motor has a lower efficiency than in synchronous operation, the currents must be limited. This can either be achieved as described above by reducing the winding voltage or here by a larger number of turns. According to the invention, both can be done, ie a reduction of the winding voltage and an increase in the number of turns for limiting the winding currents during emergency operation at subsynchronous speeds.

at the active emergency operation (subsynchronous speed) may be preferred an energization of the entire motor winding as in synchronous operation instead of just one winding part over the tapping as in Run-up. Due to the larger number of turns (= greater impedance and Polradspannung) are the currents in the winding relative to the Startup process reduced.

For engines with smaller power this measure is sufficient in many cases around the streams on one enough to bring small value to the engine in conjunction with the above described method against overheating protected can be. For Engines with greater power will be added reduces the winding voltage to further reduce the current.

For carrying out the measures according to the invention, the control unit 4 a corresponding control logic on the z. B. may contain a programmable device, microprocessor or microcontroller.

The The invention is not limited to the illustrated and described embodiments. and application examples limited, but includes also all the same in the context of the invention embodiments.

Claims (8)

System for controlling a synchronous speed (n _S ) of a line-commutated AC synchronous motor which is dependent on a mains frequency (f _N ) and which has a permanent magnet rotor ( 1 ), with a control of the engine with respect to its respective actual speed (n _is ) and at least in the case of over a certain time existing deviation of the actual speed (n _is ) from the synchronous speed (n _S ) control technology acting on the engine control unit ( 4 ), characterized in that the rotor ( 1 ) of the AC synchronous motor is connected to a load or to be connected, whose torque progressively increases with the speed, wherein the control unit ( 4 ) is designed such that after a certain time of a deviation of the actual speed (n _is ) from the synchronous speed (n _S ) of the engine in an asynchronous emergency operation with a speed reduced with respect to its synchronous speed (n _U ) is operated, wherein the emergency operation is carried out with respect to the synchronous operation reduced winding current, the reduction of the winding current by reducing the winding voltage due to speed-dependent phase control and suppression of certain, z. B. second or third half-waves and / or takes place by a winding switch to a larger number of turns, wherein the control unit ( 4 ) controls the motor via at least one static switch (Tr1 or Tr2), such as triac and / or thyristor, and at least during the emergency operation by the control unit dependent on the rotor position with respect to the current phase position of the mains frequency control of the static switch (Tr1 or Tr2) ( 4 ) in the sense of torque formation in the desired direction. System according to claim 1, characterized in that before activation of the emergency operation and / or after a certain time (t ₆ ) after activation of the emergency operation by the control unit ( 4 ) at least one synchronization attempt, in particular periodically a certain number (Z ₁ / Z ₂ ) of several attempts is made in succession to bring the engine back to the synchronous speed (n _S ). System according to one of claims 1 or 2, characterized that after a certain number of failed synchronization attempts the emergency operation continues or the engine is completely switched off. System according to one of claims 1 to 3, characterized in that the control unit ( 4 ) for speed monitoring the respective rotational frequency (f _D ) of the motor with the mains frequency (f _N ) compares. System according to one of claims 1 to 4, characterized in that the control unit ( 4 ) the rotational frequency (f _D ) of the motor by a rotor position sensor, in particular a coupled to the permanent magnetic rotor field Hall sensor ( 3 ), detected. System according to one of claims 1 to 5, characterized that the reduction of the winding voltage by phase control is effected. System according to one of claims 1 to 6, characterized in that as sub-synchronous speed (n _U ) in emergency operation, a defined, preferably quasi-synchronous speed of, for example 1/2 or 1/3 of the synchronous speed is selected. System according to one of claims 1 to 7, characterized in that the with the rotor ( 1 ) connected or to be connected load is a fan or a pump.