Synchronous machine and method for operating synchronous machine

Abstract

The invention relates to a synchronous machine (1) having a stator (3) and a rotor, the rotor having a rotor winding (5), first power semiconductors (6) for short-circuiting the rotor winding (5) being provided, the first power semiconductors (6) and the rotor winding forming a first grid (8). In a method for operating a synchronous machine (1), a rotor winding (5) is short-circuited in an operating state of the synchronous machine (1), a first short-circuiting device (6) is used for short-circuiting, and the short-circuiting device (6) and the rotor winding (5) form a first grid (8).

Description

Technical Field

[0001] The invention relates to a synchronous machine and a method for operating a synchronous machine. Background Art

[0002] In order to increase the torque during the asynchronous starting of an electrically excited synchronous machine, an additional resistor is arranged in the rotor circuit of the machine. The additional resistor only exerts its maximum effect on the torque at relatively high speeds, but during the entire acceleration period, the rotor winding AC current flows through it and thus suffers from high power losses. Correspondingly, the resistor must be designed with respect to its thermal capacity. Such an electrically excited synchronous machine can also be called a separately excited synchronous machine. The invention also relates to a device for connecting an additional rotor resistor in an asynchronously started electrically excited synchronous machine.

[0003] The synchronous machine is designed, for example, as a salient-pole synchronous motor having a rotor which is designed with solid poles and in particular without a starter cage, wherein the rotor has a slip-ring-free exciter which consists of a stator and a rotor arranged in the stator and a rectifier device associated with the rotor winding, and to which a resistor which is used, for example, to reduce the oscillation moment and increase the torque during the starting phase of the synchronous motor is electrically associated. In the case of a synchronous motor without slip rings or "brushless" excitation, in which the rotor of the synchronous motor is designed without a starter cage, it is common for the phase corresponding to the asynchronous starting to short-circuit the excitation winding via an external ohmic resistor which is approximately 10 times the excitation resistor. In order to achieve a brushless excitation that operates reliably even under difficult starting conditions, it is also possible to short-circuit the rectifier or to disconnect it from the magnetic field during the starting process, wherein the magnetic field is connected to the ohmic resistor (starting resistor). By additional measures, the resistor can be disconnected during synchronous operation.

[0004] An electrically excited synchronous machine has a rotor with a winding. If the rotor has a starting resistor, it is advantageous if the resistor is switched on only when a certain speed is reached, which results in no disadvantages in the effect of the resistor, but has advantages due to significantly lower input losses. This allows the resistor to be designed to be smaller or a more difficult start can be performed with the aid of multiple resistors or a single resistor. In this context, "difficult" also means starting with high inertia and counter-torque. The resistor can be designed with one or more resistor elements.

[0005] A synchronous machine is known from US Pat. No. 9,018,888 B2 in which the resistor is directly displaced.

[0006] If there is no possibility of connecting a resistor, the resistor is permanently operated in the rotor circuit during the starting phase and is only bridged during synchronous operation of the machine. Of course, the bridging is only done for one current direction, because during synchronous operation of the machine a direct current flows in the rotor, in contrast to starting, when an alternating current is driven in the rotor winding by the induced voltage. A circuit for continuous operation with an additional resistor is also possible, but has disadvantages. Summary of the invention

[0007] The object of the invention is to design an improved synchronous machine.

[0008] The solution to this problem is disclosed in claims 1 and 5. Further advantageous embodiments are disclosed in the dependent claims 2 to 4 and 7 to 8 thereof.

[0009] The synchronous machine has a stator and a rotor, wherein the rotor has a rotor winding, wherein a first power semiconductor for short-circuiting the rotor winding is provided, wherein the first power semiconductor and the rotor winding form a first grid. The grid can be referred to as a loop closed via a branch. At least one first power semiconductor and the rotor winding are connected in parallel and a starting resistor is connected in series with at least one first power semiconductor and the rotor winding. Thus, the rotor winding can be short-circuited by the first power semiconductor. A short-circuit circuit is obtained. The first power semiconductor is a first short-circuit device across the rotor winding. In particular, the grid does not have a starting resistor of the synchronous machine. The first power semiconductor is at least a part of a device for connecting or disconnecting a starting resistor, i.e., a rotor additional resistor, in an asynchronously started electrically excited asynchronous machine. The synchronous machine has an exciter for the rotor winding.

[0010] In one embodiment of the synchronous machine, a second power semiconductor is provided for short-circuiting the rotor winding, wherein the second power semiconductor is connected in parallel with the first power semiconductor. Thus, the rotor winding can be short-circuited in the other current direction.

[0011] In one embodiment of the synchronous machine, the power semiconductor is provided for short-circuiting the rotor winding for different current directions in the rotor winding. For this purpose, in particular a grid for the short-circuit loop is obtained, which grid has no starting resistor, ie, has no starting resistor.

[0012] In one embodiment of the synchronous machine, at least one of the power semiconductors is controllable. A control device is provided for this purpose. The control device for short-circuiting enables a short-circuit of the rotor winding in an influenceable manner.

[0013] In one embodiment of the synchronous machine, at least one first power semiconductor is connected in parallel with the rotor winding, wherein a starting resistor is connected in series with the first power semiconductor and the rotor winding. Thus, a further grid is present in which, in particular, anti-parallel-connected power semiconductors, a first power semiconductor anti-parallel to a second power semiconductor, are connected in series with a resistor, in particular a starting resistor.

[0014] In a method for operating a synchronous machine, wherein the synchronous machine to be operated has a stator and a rotor, wherein the rotor has a rotor winding, wherein the rotor winding is short-circuited in the operating state of the synchronous machine, wherein a first short-circuit device is used for the short-circuit, wherein the short-circuit device and the rotor winding form a first grid. The first short-circuit device has, in particular, a first power semiconductor. In particular, a second short-circuit device having a second power semiconductor is connected in antiparallel to the first short-circuit device.

[0015] In one embodiment of the method, the operating state is an acceleration and / or a start-up of the synchronous machine. This can have a positive influence on the formation of understanding.

[0016] In one embodiment of the method, the starting resistor and the second short-circuit device connected in parallel with the starting resistor are connected in series with the parallel circuit of the first short-circuit device and the rotor winding. This is a simple and compact possibility for influencing the behavior of a synchronous machine.

[0017] In one embodiment of the method, a synchronous machine of one of the described embodiments is used. In one embodiment, therefore, a synchronous machine of one of the described embodiments is used for the method according to one of the described methods.

[0018] In one embodiment of the method, a synchronous machine of one of the described embodiments is operated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The features of the various claimed or described subjects can be easily combined with each other. Below, the invention is shown and explained in more detail by way of example with reference to the accompanying drawings. A person skilled in the art can combine the features shown in the drawings into new embodiments without departing from the invention. The accompanying drawings show

[0020] Figure 1 A first circuit for a synchronous machine is shown,

[0021] Figure 2 A second circuit for a synchronous machine is shown,

[0022] Figure 3 A third circuit for a synchronous machine is shown, and

[0023] Figure 4 A fourth circuit for a synchronous machine is shown. DETAILED DESCRIPTION

[0024] according to Figure 1 The view shows a first circuit for a synchronous machine 1. The synchronous machine 1 has a stator 3 (the stator has stator windings 4, 4', 4"), a rotor (the rotor has a rotor winding 5) and an excitation circuit 2. The stator windings 4, 4', 4" are provided for connection to phases U, V and W. In the present example, one side of the stator windings 4, 4', 4" is star-connected to the interfaces U2, V2 and W2. Interfaces U1, V1 and W1 are shown for the second side of the stator windings 4, 4', 4". The excitation circuit has a resistor 11, in particular a starting resistor. The excitation circuit is operated via a control device A1 10 for excitation. The control device has interfaces J1A, J1B, J1C, A4, A5, A7, A8, J62 and J61.

[0025] The voltage between J1A and J1B can be measured by means of the interface J1A. Reaching the response voltage set via the Zener diode causes an ignition pulse for the thyristor T1 via the interface J1B.

[0026] The voltage between J1A and J1C can be measured by means of the interface J1C. Reaching the response voltage set via the Zener diode causes an ignition pulse for the thyristor T2 via the interface J1C. At a rotational speed of approximately 92-98%, the induced voltage is no longer sufficient to reach the response voltage. T1 and T2 no longer ignite. After the acceleration has ended, the excitation devices F1, F2 are switched on. Reaching the response voltage set via the Zener diode via the terminals A4 and A5 causes an ignition pulse for the thyristors T3.1 and T3.2 via the interfaces J61 and J62. In the subsequent synchronous operation of the machine, the thyristors T3.1 and T3.2 are continuously conducting due to the current flow.

[0027] The purpose of the interface A7 is to charge the capacitor for starting the thyristor T3.1. The purpose of the interface A8 is to charge the capacitor for starting the thyristor T3.2.

[0028] The resistor RZ 11 can also be referred to as an additional resistor. The rotor winding itself also has a resistance value. The additional resistor RZ 11 used in the field circuit influences the behavior of the synchronous machine, for example during starting or acceleration.

[0029] The circuit according to the invention allows the resistor RZ to be designed with a lower thermal capacity, since it only has to absorb a portion of the losses that would occur.

[0030] The resistor RZ can be short-circuited via the thyristors T3.1 and T3.2. Both the thyristors T3.1 and T3.2 are connected in parallel with the resistor RZ 11. The thyristor T3.1 is driven via the interface J61 of the control device A1 10. The thyristor T3.2 is driven via the interface J62 of the control device A1 10. For example, as described above, the driving is performed for a few seconds after the asynchronous acceleration. Then, the thyristor remains conductive due to the current flow caused by the excitation F1 F2. In the figure, HK represents the auxiliary terminal in the thyristor.

[0031] according to Figure 1 Also shown is a diode bridge having diodes V1 to V12. A first RC element is connected in parallel with the diodes. The first RC element has a capacitive element C1 and a resistive element R1, wherein the capacitive element C1 is connected in series with the resistive element R1.

[0032] The second RC element is connected in parallel with the first RC element. The second RC element has a capacitance element C2 and a resistance element R2, wherein the capacitance element C2 and the resistance element R3 are connected in series.

[0033] The third RC element is connected in parallel with the first and second RC elements. The third RC element has a capacitor element C3 and a resistor element R3, wherein the capacitor element C3 and the resistor element R3 are connected in series.

[0034] High-frequency voltage peaks can be diverted via the RC element in order to protect other components. Two series-connected thyristors T1 and T2 are connected in parallel with the RC element. Thyristor T1 is driven via the interface J1B. Thyristor T2 is driven via the interface J1C. The tap M1 is between the thyristors T1 and T2, which has the function of raising the potential between T1 and T2 to a defined level and thus ensuring that the two thyristors are turned on.

[0035] In order to improve the behavior of synchronous machines, the circuit can be supplemented. The basic structure of the circuit in the rotor circuit does not need to be significantly changed. This has the advantage that existing, proven components can continue to be used. This is particularly important for machines without additional resistors or replicas using older technology.

[0036] according to Figure 2 The view shows Figure 1It is a supplement to the additional resistor (RZ) 11 for speed-dependent switching of the thyristors 6 and 7, as well as the control logic and the control power components. The thyristors are switchable power semiconductors. The control power components have switchable power semiconductors. The supplement is based on the fact that a bidirectional switch or actually two anti-parallel connected power electronic one-way switches 6 and 7 are arranged in parallel with the rotor winding 5. They are therefore the first power semiconductor 6 and the second power semiconductor 7. A control device 9 is provided for switching the switches. The control device 9 has a control logic. The power semiconductors 6 and 7 are activated in the initial phase of startup.

[0037] In the first phase from 0% to 50-80% of the speed (synchronous speed / nominal speed (rated speed)), the rotor winding 5 is short-circuited by the circuit according to the invention to prevent current flow in RZ and thus prevent losses. In this phase, the slight reduction of the swing torque by RZ can be ignored.

[0038] In a second phase following a first phase of approximately 50%-80% to 95-98% of the rated speed, the circuit is locked to prevent a new short circuit and to achieve further acceleration with electrical flux via RZ, thus achieving significant advantages in this phase, such as reducing the sway moment and increasing the average torque.

[0039] In the third phase after the second phase, from 95% to 98% of the rated speed (nominal speed) until the asynchronous acceleration ends, the above-mentioned excitation and thus the bridging of RZ are performed corresponding to the synchronous operation.

[0040] In the time sequence of the phases, the time period involving the starting resistor 11 runs.

[0041] In a further example, thyristors are used in particular, which directly bridge the field winding after ignition. The alternating current in the field winding causes the field winding to extinguish again after a half-wave. Therefore, the components connected in anti-parallel must be activated alternately in order to guide the alternating current. The use of thyristors is advantageous because they cope well with the centrifugal loads in the rotor due to their so-called "press-fit" configuration. Auxiliary energy is required to trigger the switch or ignite the power electronics. The auxiliary energy is obtained, for example, directly from the voltage induced in the field winding. It is already possible to use proven types (T1, T2) in the field circuit as thyristors 6 and 7, wherein the field circuit has a corresponding cooling device, because the bridge thyristor guides the current exactly the same as T1 and T2. Now, bridging only occurs after a certain speed is reached. That is to say, the switching process described above must be controlled by an additional logic signal, which inhibits switching from a defined speed threshold. The signal can be controlled by an external source (telemetry, etc.) on the one hand, or directly generated from the voltage / current existing on the rotor on the other hand. For example, this can be implemented in a way that the time interval of the alternating switching of the switch is measured. Since the speed increases during the startup, the slip of the rotor decreases accordingly, so the frequency of switching becomes smaller and smaller, and the time interval increases. For example, the timer can now monitor whether a specific minimum duration between switching is exceeded. If this is the case, switching is prohibited. The advantage of this purely frequency-related variant is that (except for the permissible tolerance of the grid frequency) no calculation data with uncertainty is included. Then, the switching speed, for example, can be changed via a bridge configuration / jumper, etc. The following advantages can be generated by the switchability: namely, the energy conversion in the resistor is reduced without significantly impairing the effect on the torque. This means that since less thermal capacity must be maintained, the resistor can be made smaller for a specific effect. Direct cost advantages are obtained from this, but also indirect advantages, such as lighter rotor mass, advantages in rotor dynamics, etc.

[0042] The starting resistor is defined on the one hand by the ohmic resistance value and, in association therewith, by the influence of the starting resistor on the starting behavior, such as the swing moment, the average torque and the starting time. On the other hand, the starting resistor absorbs the losses formed in the starting resistor during the starting period, because only a small portion of the losses are directly output to the environment during the starting phase. By reducing the duration of use to stage 2, the thermal capacity of the starting resistor can be reduced to about 50% of the thermal capacity originally required. This means: with the same material, the mass of the starting resistor is reduced by about half. Due to the typical arrangement of the resistor on the rotor, weight saving means: a significant improvement in rotor dynamics. The weight of a typical starting resistor is in the range of 50 kg to 500 kg. By now being able to reduce the weight, a weight saving of 30%-60%, in particular 40%-50%, can be achieved.

[0043] according to Figure 3 The view of FIG. 8 shows a current flow 8 when the thyristors 6 and 7 are activated. The path of the current flow 8 is also shown as a grid 8. In the grid 8 there is one of the power semiconductors 6 for short-circuiting and the field winding 5 which is to be short-circuited at a certain time.

[0044] according to Figure 4 The diagram of FIG. 1 shows the current flow 12 when the thyristors 6 and 7 are not activated.

Claims

1. A synchronous machine (1), comprising a stator (3) and a rotor, wherein: The rotor has a rotor winding (5), wherein a first power semiconductor (6) is provided for short-circuiting the rotor winding (5), wherein the first power semiconductor (6) and the rotor winding form a first grid (8), wherein at least one of the first power semiconductors (6) and the rotor winding (5) is connected in parallel and in series with a starting resistor (11).

2. A synchronous machine (1) according to claim 1, wherein: A second power semiconductor (7) is provided for short-circuiting the rotor winding (5), wherein the second power semiconductor (7) is connected in parallel with the first power semiconductor (6).

3. The synchronous machine (1) according to claim 2, wherein: Power semiconductors (6, 7) are provided for short-circuiting the rotor winding (5) for different current directions in the rotor winding (5).

4. The synchronous machine (1) according to any one of claims 1 to 3, wherein: At least one of the power semiconductors (6, 7) is controllable.

5. A method for operating a synchronous machine (1), wherein: The synchronous machine to be operated comprises a stator (3) and a rotor, wherein the rotor comprises a rotor winding (5), wherein the rotor winding (5) is short-circuited in the operating state of the synchronous machine (1), wherein a first short-circuit device (6) is used for short-circuiting, wherein the short-circuit device (6) and the rotor winding (5) form a first grid (8), wherein a starting resistor (11) is connected to a second short-circuit device (7), wherein the second short-circuit device is connected in parallel with the starting resistor, and wherein the starting resistor is connected in series with the parallel connection of the first short-circuit device (6) and the rotor winding (5).

6. The method according to claim 5, wherein: The operating state relates to the acceleration and / or starting of the synchronous machine (1).

7. The method according to claim 5 or 6, wherein: Use of a synchronous machine according to any one of claims 1 to 4.

8. The method according to claim 5 or 6, wherein: The synchronous machine according to any one of claims 1 to 4 is operated.

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