DE10028492A1 - System for controlling mains controlled a.c. synchronous motor, operates motor in asynchronous mode at reduced speed if speed deviation persists for defined period - Google Patents

Abstract

The system has a control unit (4) for monitoring the actual revolution rate of the motor and for exerting control influence on the motor if the actual revolution rate deviates from the synchronous revolution rate over a defined time. The control unit operates the motor in asynchronous mode at reduced revolution rate if the deviation persists for a defined period.

Description

The present invention relates to a system for controlling a permanently excited, in a synchronous speed dependent on a network frequency AC synchronous motor, with one the motor with respect to its respective actual speed monitoring and at least in the case of a certain time existing deviation of the actual speed from the synchronous speed Control unit acting on the engine in terms of control technology.

From DE 299 17 700 U1 it is for an electronic starting device for Synchronous motors are known to monitor synchronous operation. In the event of a deviation of the respective engine speed from the synchronous speed, a so-called fall-out fall, a new attempt is attempted with the aim of Engine attributed back to synchronism. After a vain Start attempts can also be carried out periodically, and always with the aim of achieving synchronous operation again. In addition, the affected motor possibly also after a certain maximum number of unsuccessful start-up attempts are completely switched off. It can Operating conditions exist that make it impossible to achieve synchronism do. Therefore, the known measures would take a certain amount of time ultimately lead to the complete shutdown of the engine.

In many applications, for example in refrigeration, would be a complete one Shutdown of the engine with disadvantages due to additional requirements, for example Monitoring devices or redundancy connected.

It is also known from EP 0 666 639 A1 that one is not correctly synchronized accelerate the running machine again up to the synchronous speed. Is that enough Supply voltage for synchronous operation is not off or the load is too  high, the engine remains in this acceleration mode, but without actually to accelerate. In certain cases this can lead to a thermal Overload and lead to failure.

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

• 1. Align the rotor in a defined rotational position,
• 2. Start the rotor to initially rotate into a desired one Direction of rotation by control with voltage (or current) pulses,
• 3. Stabilization phase with one below synchronism Speed and
• 4. Synchronization phase.

The 3rd phase is optional and is inserted if the load is an initial one Stabilization at a speed lower than the synchronous speed requires. As An example of such a load is called a pump. Obviously this will be third Operating phase for the purpose of optimizing the startup of the motor certain loads introduced. In any case, the three or four phases always run successively in succession with the aim of at least reaching the engine Bring synchronism.

DE 197 01 856 A1 describes a further electronic start-up and Operation control for a single-phase synchronous motor. Here too are Different operating phases are defined, namely start-up, run-up and synchronous operation. If an overload occurs in synchronous operation, the speed may drop. In In this case, the control laws of synchronous operation should be switched off and that of Startup can be switched on. Possibly the following will also be mentioned Tax laws switched over for startup. So the engine should again accelerated and returned to synchronism.

EP 0 574 823 B1 describes a starting device for a synchronous motor, the start-up via an appropriately controlled static switch, e.g. B. Triac, he follows. The motor flow can optionally be increased in that the Supply voltage to a tap of the Motor winding is switched. After a given time, the corresponding one  Switch turned off, and the switch that connects the entire motor winding to the grid switches, is switched on. A position sensor also enables monitoring of the Rotational speed. After the specified start-up time has elapsed, the speed is checked. If the synchronous speed has not been reached, the motor is disconnected from the mains. To the To be able to start the engine again afterwards, the engine system and the electronic circuitry for a short period of time entirely from the AC voltage source are disconnected.

Finally, EP 0 682 404 B1 also describes a start-up control for a single-phase synchronous motor with permanent magnets. The motor should be accelerated by a specific control until 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 it at a lower synchronous speed. Possible synchronous speeds result from dividing the maximum synchronous speed by an integer ( 2 , 3 ,...)

The present invention has for its object a control system to create the type mentioned, with which even in problematic operating situations, especially in the event of an overload, a complete failure of the motor or a forced one Switching off is largely avoided.

According to the invention, this is achieved in that the control unit is designed in this way is that after a certain time a deviation of the actual speed from the Synchronous speed of the motor in an asynchronous emergency mode with respect to its synchronous speed reduced speed is operated.

The control unit thus monitors start-up and synchronous operation and intervenes then on when the synchronous speed is not reached or the engine later falls out of sync. The control unit can then possibly have another make certain number of attempts to start. But if it doesn't it is possible to bring the motor in synchronism or in synchronism hold, the control unit switches over to emergency operation according to the invention. In this In operation, the motor works asynchronously, similar to starting, but not with Aim to accelerate to synchronous speed. To in this invention  Emergency operation to avoid overheating, it is advantageous if the emergency operation with a winding current is reduced compared to the acceleration phase. This reduction of the winding current can be in an advantageous embodiment by reducing the Winding voltage. Alternatively or in addition, a reduction can be made of the current also by changing the winding to a larger number of turns respectively.

The emergency operation of a network-controlled synchronous motor according to the invention relates to primarily applications in the field of fans and pumps. Here it rises Torque with the third power of the speed, which is why in the rated point of the Motors, d. H. at the highest speed, the greatest torque occurs. With not achievable synchronism is therefore possible to operate at a lower speed, without thermally overloading the motor.

One is striving to achieve high engine efficiency, the Motor dimensioning so that the efficiency at Design torque becomes maximum. However, this has the consequence that security against a falling out of the engine in the event of a brief overload or brief drop in the mains voltage is relatively small.

Oversizing the motor to safely avoid such cases would have occurred a deterioration in engine efficiency. The engine efficiency is however, one of the key advantages of a permanently excited network-based Synchronous motor. Especially with synchronous motors with low power competing inexpensive shaded-pole or capacitor motors would be one such measure in addition to reducing the efficiency with a economic disadvantage associated with a greater use of materials.

Due to the emergency operation according to the invention, the disadvantages mentioned State of the art can be avoided. The engine can run with minimal reserve for maximum efficiency can be designed under nominal conditions. Is the Synchronous operation no longer due to short-term overload or insufficient mains voltage possible, then in the described emergency mode with reduced speed and Torque passed. In this temporary fault case, the  Efficiency compared to synchronous operation, but the motor is still able to deliver the required minimum (air) performance here too.

The invention therefore has significant technical and economic advantages compared to the state of the art.

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

The invention will be explained in more detail by way of example with reference to the drawing. there demonstrate:

Fig. 1 is a schematic principle diagram of a system according to the invention, in a first embodiment of a line-commutated, permanent-magnet synchronous motor

Fig. 2 is a similar schematic diagram with a synchronous motor with a winding tap for the run,

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

Fig. 4 is an exemplary flow chart to explain the functions of the system according to the invention.

In Figs. 1 and 2, the motor coil 2 and the permanent magnetic rotor 1 is represented by a permanent-magnet synchronous AC motor, respectively. In the embodiment of Fig. 1, a static switch Tr ₁ is connected in series to the motor winding 2, and this series circuit lies at an AC line voltage, that is, at a phase conductor L ₁ and a neutral conductor N. The static switch Tr ₁ of controlled a control unit 4 . In the embodiment according to FIG. 2, the motor winding 2 has a tap 6 , via which part of the motor winding 2 can be controlled by means of a first static switch Tr ₁ . The entire motor winding 2 can be controlled via a second static switch Tr ₂ . Both switches Tr ₁ and Tr ₂ are optionally controlled by the control unit 4 . The static switches can in particular be triac or thyristors.

To detect the rotor speed, 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 rotation frequency is not, as shown in a simplified manner in FIG. 1 or FIG. 2, restricted to the use of a rotor position sensor, but can also be done without sensors. In this embodiment, instead of the rotor position sensor ( 3 ), a suitable sensorless detection circuit is provided, which provides the control unit ( 4 ) with information about the rotational frequency of the rotor by directly measuring the course of the rotating permanent magnetic pole wheel ( 1 ) in the motor winding ( 2 ) induced voltage, or by providing an indirect determination via the measurement of winding currents and voltages.

Based on the flowchart shown in FIG. 4, the invention for the embodiment according to FIG. 1 without winding tapping for the start-up process will first be explained.

For the start-up of a mains-operated, permanently excited synchronous motor is in Generally a higher flow is required than for synchronous operation. The The motor must therefore be designed in such a way that the maximum permissible mechanical load and the start-up is still safe with a minimum permissible mains voltage is possible. The startup is a temporary process that generally does not take long continues. In many cases, the winding is designed so that the Startup represents an overload case. The large flow required for the run-up will be in synchronous operation in order to achieve good efficiency by Phase angle of the mains voltage reduced. The effective one is advantageous Adapted winding voltage depending on the load, so that a high in a wide range Efficiency is achieved.

If the mechanical load is too high and / or the mains voltage is too low, the motor can fall out of step. According to the invention, such a case is recognized by the control unit 4 . This can advantageously be done by comparing the 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 determined. Thereupon, renewed start-up attempts can be initiated.

Start-up attempts and monitoring

A run-up attempt with a high flow takes place until a predetermined time period t _{1 has} passed and the synchronous speed n _S could not be reached during this time. The motor is then disconnected from the mains for a defined period of time t _{2 in} order to prevent the winding from overheating. After t ₂ has elapsed, another high-speed start-up is carried out. After a specified number Z ₁ of successive run-up attempts, the synchronous speed could not be reached, which is evident from the comparison of the rotor rotational frequency, e.g. B. is detected via the rotor position sensor 3 , is determined with the known network frequency, the emergency operation according to the invention is activated. Especially in applications of the motor as a drive for fans or pumps, it is advantageous if, despite an existing fault, for. B. mechanical overload or mains undervoltage, a certain, depending on the respective fault delivery capacity is still provided, ie the motor does not fail. In emergency operation, the motor is controlled in such a way that in asynchronous, ie under-synchronous operation, the winding does not assume inadmissibly high temperatures despite a possible overload situation. This is preferably done by reducing the applied winding voltage. The winding voltage is preferably reduced via the phase angle of the mains voltage compared to the regular startup process. The control unit 4 controls the static switch Tr _{1 in} accordance with the desired phase control. The phase gating angle is advantageously determined as a function of the speed of the motor at the maximum permissible mains voltage so that the motor windings do not assume an impermissibly high temperature. Each motor speed, ie certain speed ranges, is assigned a certain phase gating angle at which the winding is not yet overheating. This assignment is stored in the control unit 4 , preferably in a microcontroller, in the form of a speed-gating angle table. During emergency operation, the current motor speed is continuously recorded by the control unit 4 via the rotor position sensor 3 and the corresponding phase angle is used to reduce the voltage connected to the winding. In this way, overheating of the motor winding during emergency operation in a wide load range can be avoided despite changing loads.

In addition, a lower _{limit speed} n _{Limit1 is} defined in order to protect the motor against severe overload during emergency operation. If the engine speed _drops below n _limit1 as a result of a large load torque, the engine is switched off and, if necessary, a new _attempt to start.

So-called quasi-synchronous speeds, for example 1/2 or 1/3 synchronous speeds, are particularly favorable for the described emergency operation (cf. FIG. 3). Here the motor works with a higher efficiency than at the other sub-synchronous speeds. In this version, in addition to reducing the effective winding voltage, for. B., as described above, phase cut, network half-waves selectively hidden by the control unit 4 in order to generate a fundamental oscillation with a lower frequency than the network voltage. This results in a lower speed of the motor than with synchronism with the mains frequency and - assuming a load torque that increases with the speed, as is always the case with fans or blowers - a lower load on the motor. For half the network frequency, e.g. B. two consecutive, also cut line half-waves can be switched to the motor winding, whereas the two subsequent line half-waves are blocked. This procedure is used advantageously for emergency operation.

Start-up attempts and monitoring

In an advantageous embodiment of the invention, the run-up attempt is supplemented by a measure described below in order to reliably cover extreme overload cases during start-up. If the rotor is heavily braked or even completely blocked, which is recognized by the control unit 4 in that, despite energization of the winding, a lower _{limit speed} n _limit2 , which in turn is less than n _limit1 , for a fixed period of time t ₃ that is shorter than t ₁ is not reached, the engine is switched off. Here, repeated start-up attempts are made at recurring intervals t ₄ . If, after a number of Z ₂ successive start-up _attempts , no speed greater than n _Limit2 can be achieved, the motor is switched off permanently. However, _{if the} limit _speed n _Limit2 can be exceeded within t ₃ , start-up _attempts and monitoring are carried out using the method already described above.

Retry attempts after permanent shutdown or in emergency operation

New start-up and start-up attempts are only started again when the operating voltage is briefly switched off, or when - as implemented in a preferred embodiment of the invention - a corresponding command for this is given via an actuating input of the control unit 4 (not shown in FIGS. 1 and 2).

Periodically initiated start-up attempts

In a particularly advantageous embodiment, the control unit 4 periodically interrupts the emergency operation or the shutdown of the engine at defined intervals t ₅ or t ₆ , which are longer than t ₂ and t ₃ , and initiates renewed start-up or start-up attempts. If it is still not possible to reach the synchronous speed, the control unit 4 continues the emergency operation or switches the engine off again, depending on the load situation at hand.

With regard to the previous explanations, reference is again made to the flow chart in FIG. 4, in which the processes and conditions described are illustrated.

The invention for the embodiment according to FIG. 2 with winding tapping 6 for the startup process will now be described.

As has already been mentioned, a higher flux is required for the startup of a mains-operated, permanently excited synchronous motor than for synchronous operation. The winding tapping 6 can be provided for this purpose. The run-up process is then carried out with a smaller number of turns via the tap 6 , which results in a larger flow. In order to achieve good motor utilization, the winding is usually designed so that operation during the start-up with the smaller number of turns represents an overload case. The entire winding is then switched on in synchronous operation. Because of the larger number of turns, there is then a smaller winding current and therefore a smaller flux than during startup, which results in a high degree of efficiency.

The measures described above for monitoring synchronous operation and for starting or starting can also be used without restriction for this motor type with tap 6 . If the motor cannot reach its synchronous speed, the emergency mode is activated, in which it operates at a lower speed, ie with a lower mechanical load, if there is a load torque that increases with the speed. In order to protect the winding against overheating in under-synchronous operation, where the motor is less efficient than in synchronous operation, the currents must be limited. This can be achieved either by reducing the winding voltage as described above or here by increasing the number of turns. According to the invention, both can also be carried out, ie a reduction in the winding voltage and an increase in the number of turns to limit the winding currents during emergency operation at sub-synchronous speeds.

With active emergency operation (sub-synchronous speed), one can preferably The entire motor winding is energized as in synchronous operation instead only one part of the winding via the tapping as during startup. By the bigger one Number of turns (= greater impedance and magnet wheel voltage) are the currents in the Winding reduced compared to the run-up process.

In many cases this measure is sufficient for engines with lower power, to bring the currents to a sufficiently small value so that the motor in Protected against overheating by the method described above can. The winding voltage is also used for motors with higher power decreased to further reduce the current.

To carry out the measures according to the invention, the control unit 4 has a corresponding control logic which, for. B. can contain a programmable module, microprocessor or microcontroller.

The invention is not based on the illustrated and described embodiment and Application examples limited, but also includes all within the meaning of the invention equivalent designs.

Claims (10)

1. System for controlling a monitoring and at least in the case of existing a certain time deviation in one of its respective actual speed _(n) with respect to a mains frequency (f _N) dependent synchronous speed (n _S) line-commutated AC synchronous motor with a motor the actual speed _(n) of the synchronous speed (n _s) of control technology on the engine acting control unit (4), characterized in that the control unit (4) is designed such that after a certain time of a deviation of the actual speed _(n) of the synchronous speed (n _S ) the motor is operated in an asynchronous emergency mode at a speed (n _U ) which is reduced with respect to its synchronous speed. 2. System according to claim 1, characterized in that before an activation of the emergency operation and / or after a certain time (t ₆ ) after an 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 ) several attempts are made in succession to bring the motor back to the synchronous speed (n _S ). 3. System according to one of claims 1 or 2, characterized in that after a certain number of unsuccessful attempts to synchronize the Emergency operation continues or the engine is switched off completely. 4. System according to one of claims 1 to 3, characterized in that the control unit ( 4 ) for speed monitoring compares the respective rotational frequency (f _D ) of the motor with the mains frequency (f _N ). 5. System according to one of claims 1 to 4, characterized in that the control unit ( 4 ) detects the rotational frequency (f _D ) of the motor by a rotor position sensor, in particular a Hall sensor ( 3 ) coupled to the permanent magnetic rotor field. 6. System according to one of claims 1 to 5, characterized in that the emergency operation with a compared to synchronous operation reduced winding current takes place, the Reduction of the winding current through a particular Phase cut caused reduction of the winding voltage and / or by a winding changeover to a larger number of turns takes place. 7. System according to any one of claims 1 to 6, characterized in that a defined, preferably quasi-synchronous speed of, for example, 1/2 or 1/3 of the synchronous speed is selected as the sub-synchronous speed (n _U ) in emergency operation. 8. System according to one of claims 1 to 7, characterized in that the control unit ( 4 ) controls the motor via at least one static switch (Tr1, Tr2), such as triac and / or thyristor. 9. System according to claim 8, characterized in that at least during emergency operation depending on the rotor position with respect to the current phase position of the mains frequency control of the static switch (Tr ₁ , Tr ₂ ) by the control unit ( 4 ) in the sense of torque formation in the desired Direction. 10. System according to one of claims 1 to 9, characterized in that the rotor ( 1 ) of the AC synchronous motor is connected to a load whose torque increases progressively with the speed, in particular with fans or pumps.