Synchronous machine and method for operating a synchronous machine

Abstract

A synchronous machine (1) has 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 mesh (8). In a method for operating a synchronous machine (1), the rotor winding (5) is short circuited when the synchronous machine (1) is in an operating state, wherein a first short circuiter (6) is used for short circuiting, wherein the short circuiter (6) and the rotor winding (5) form a first mesh (8).

Description

[0001]202204988 Foreign version 1 Description Synchronous machine and method for operating a synchronous machine The invention relates to a synchronous machine and a method for operating a synchronous machine. In order to increase the torque during the asynchronous start-up of electrically excited synchronous machines, an additional resistor is arranged in the rotor circuit of the machine. This develops its greatest effect with regard to the torque only at relatively high speeds, but is traversed by the rotor winding alternating current during the entire start-up and is therefore exposed to high power losses. The resistor must be dimensioned accordingly with regard to its thermal capacity. Such a synchronous machine, which is electrically excited, can also be referred to as a separately excited synchronous machine. The invention also relates to a device for connecting the additional rotor resistor in an electrically excited synchronous machine with asynchronous start-up.A synchronous machine, for example, is designed as a salient-pole synchronous motor, which has a rotor with solid poles, in particular without a starting cage. This rotor has a slip-ringless excitation machine consisting of a stator and a rotor arranged within the stator, and a rectifier arrangement associated with the rotor winding. A resistor is electrically associated with the rectifier arrangement, e.g., to reduce oscillation torque and increase torque during the starting phase of the synchronous motor. For slip-ringless or "brushless" excited synchronous motors, whose rotor is designed without a starting cage, it is common practice for the asynchronous starting phase to short-circuit the field winding via an external ohmic resistor of approximately 10 times the field resistance.In order to achieve reliable brushless excitation even under difficult starting conditions, it is also possible to either short-circuit the rectifier or separate it from the field during the starting process, whereby the field is connected to an ohmic resistor (starting resistor). This resistor can be switched off during synchronous operation using additional measures. The electrically excited synchronous machine has a rotor with one winding. If the rotor has a starting resistor, it is advantageous if the resistor can be switched on only once a certain speed has been reached. In this case, there is no disadvantage in terms of its effectiveness, but rather an advantage due to the significantly lower loss input. This allows the resistor to be dimensioned smaller, or more difficult starts can be carried out using existing resistors.In this context, heavy also means starting with high inertia and counter-torque. The resistor can be designed with one or a plurality of resistance elements. US 9018888 B2 describes a synchronous machine in which the resistor is switched directly. If there is no possibility of switching on the resistor, the resistor is operated continuously in the rotor circuit during start-up and is only bridged during synchronized operation of the machine. However, this bridging only occurs for one current direction, since during synchronized operation of the machine a direct current flows in the rotor, in contrast to start-up, where an alternating current is driven in the rotor winding by the induced voltage. A circuit that provides for continuous operation with additional resistor is also possible, but disadvantageous. One object of the invention is to design an improved synchronous machine.202204988 Foreign version 3 A solution to the problem arises according to claims 1 and 5. Further exemplary embodiments arise from the dependent claims 2 to 4 and 7 to 8. A synchronous machine has a stator and a rotor, wherein the rotor has a rotor winding, wherein a first power semiconductor is provided for short-circuiting the rotor winding, wherein the first power semiconductor and the rotor winding form a first loop. A loop can be referred to as a circuit closed via branches. The rotor winding can therefore be short-circuited by the first power semiconductor. This results in a short-circuit circuit. The first power semiconductor is a first short-circuiter across the rotor winding. The loop is in particular free of a starting resistor of the synchronous machine. The first power semiconductor is at least part of a device for switching a starting resistor on or off, i.e.i.e., an additional rotor resistance, in an electrically excited synchronous machine with asynchronous starting. The synchronous machine has an excitation machine for the rotor winding. 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 to the first power semiconductor. This allows the rotor winding to be short-circuited in a further current direction. In one embodiment of the synchronous machine, the power semiconductors are provided for short-circuiting the rotor winding for different current directions in the rotor winding. This results in, in particular, loops for a short-circuit circuit which do not have the starting resistance, i.e. are free of it. In one embodiment of the synchronous machine, at least one of the power semiconductors is controllable. A control is provided for this purpose.This control for the short circuit enables a controllable short circuit of the rotor winding. In one embodiment of the synchronous machine, at least one first power semiconductor and the rotor winding are connected in parallel, with a starting resistor connected in series. There is therefore a further loop in which in particular the anti-parallel connected power semiconductors, the first power semiconductor anti-parallel to the second power semiconductor, are connected in series with the resistor, in particular the starting resistor. 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, the rotor winding is short-circuited in an operating state of the synchronous machine, wherein a first short-circuiter is used for short-circuiting, wherein the short-circuiter and the rotor winding form a first loop.The first short-circuiter has, in particular, the first power semiconductor. In particular, a second short-circuiter, which has the second power semiconductor, is connected anti-parallel to the first short-circuiter. In one embodiment of the method, the operating state relates to a run-up and / or start-up of the synchronous machine. This can have a positive effect on torque generation. In one embodiment of the method, a starting resistor is connected in series with a second short-circuiter connected in parallel to it, in parallel with the first short-circuiter and the rotor winding. This is a simple and compact way of influencing the behavior of the synchronous machine. 202204988 Foreign version 5 In one embodiment of the method, a synchronous machine in one of the described embodiments is used.In one embodiment, a synchronous machine in one of the described embodiments is used for the method according to one of the described methods. In one embodiment of the method, a synchronous machine in one of the described embodiments is operated. Operation takes place according to one of the described methods. The features of the individual claimed or described subject matters can be easily combined with one another. The invention is illustrated and explained in more detail below using figures as examples. The features shown in the figures can be combined by a person skilled in the art to form new embodiments without departing from the invention. FIG. 1 shows a first circuit for a synchronous machine, FIG. 2 shows a second circuit for a synchronous machine, FIG. 3 shows a third circuit for a synchronous machine and FIG. 4 shows a fourth circuit for a synchronous machine.The illustration in Figure 1 shows a first circuit for a synchronous machine 1. The synchronous machine 1 has a stator 3 with stator windings 4, 4', 4'', a rotor with a rotor winding 5 and an excitation circuit 2. The stator windings 4, 4', 4'' are intended for connection to the phases U, V and W. In the present example, one side of the stator windings 4, 4', 4'' is connected in a star configuration with the terminals U2, V2 and W2. The terminals U1, V1 and W1 are shown for a further 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 A1 10 for the excitation. The controller has connectors J1A, J1B, J1C, A4, A5, A7, A8, J62, and J61. Connector J1A allows for measuring the voltage between J1A and J1B.Reaching the response voltage set via Zener diodes triggers a firing pulse to thyristor T1 via terminal J1B. Connection J1C allows measurement of the voltage between J1A and J1C. Reaching the response voltage set via Zener diodes triggers a firing pulse to thyristor T2 via terminal J1C. At approximately 92-98% speed, the induced voltage is no longer sufficient to reach the response voltage. T1 and T2 no longer fire. After the end of the run-up, the excitation F1, F2 is switched on. Reaching the response voltage set via Zener diodes across terminals A4 and A5 triggers a firing pulse to thyristors T3.1 and T3.2 via terminals J61 and J62. During subsequent synchronous operation of the machine, thyristors T3.1 and T3.2 remain permanently conductive due to the current flow. Terminal A7 serves as the capacitor for firing thyristors T3.1. Terminal A8 is used to charge the capacitor for firing thyristors T3.2. Resistor RZ11 can also be referred to as an additional resistor. The rotor winding itself already has a resistance value. The additional resistor RZ11 used in the excitation circuit influences the behavior of the synchronous machine, for example during startup or run-up. The circuit according to the invention allows resistor RZ to be designed with a smaller heat capacity, as it only has to absorb a portion of the losses that would otherwise occur. Resistor RZ can be short-circuited via thyristors T3.1 and T3.2. Thyristors T3.1 and T3.2 are both connected in parallel to resistor RZ11. Thyristor T3.1 is controlled via terminal J61 of control unit A110. Thyristor T3.2 is controlled via terminal J62 of control unit A110.Control occurs, for example, a few seconds after asynchronous start-up as described above. The thyristors then remain conductive due to the current flow caused by the excitation F1 F2. In the figures, HK for the thyristors means auxiliary terminal. Figure 1 also shows a diode bridge with the diodes V1 to V12. A first RC element is connected in parallel. This first RC element has a capacitor element C1 and a resistor element R1, with the capacitor element C1 being connected in series with the resistor element R1. A second RC element is connected in parallel with the first RC element. This second RC element has a capacitor element C2 and a resistor element R2, with the capacitor element C2 being connected in series with the resistor element R3. A third RC element is connected in parallel to the first and second RC elements.This third RC element has a capacitor element C3 and a resistor element R3, with the capacitor element C3 being connected in series with the resistor element R3. High-frequency voltage peaks can be diverted via the RC elements in order to protect the other components. Two thyristors T1 and T2 connected in series are connected in parallel to the RC elements. The thyristor T1 is controlled via terminal J1B. The thyristor T2 is controlled via terminal J1C. Between the thyristors T1 and T2 there is a tap M1, which has the function of raising the potential between T1 and T2 to a defined level and thus ensuring the switching of both thyristors. The circuit can be supplemented to improve the behavior of the synchronous machine. The basic structure of the circuit in the rotor circuit does not require major changes. This has the advantage that existing, proven components can continue to be used.This is particularly important so that there are machines without additional resistance or replicas that use the older technology. 202204988 Foreign version 8 The illustration in Figure 2 shows an addition to Figure 1. It is an added circuit for the speed-dependent switching on of the additional resistance (RZ) 11 with thyristors 6 and 7, which are switchable power semiconductors, as well as a control logic and a control power section. The control power section has the switchable power semiconductors. The addition is based on the fact that a bidirectional switch or, in practice, two anti-parallel connected power electronic unidirectional switches 6 and 7 are arranged parallel to the rotor winding 5. These are therefore a first power semiconductor 6 and a second power semiconductor 7. A control 9 is provided to switch these switches. The control 9 has the control logic.The power semiconductors 6 and 7 are activated in the initial start-up phase. In a first phase from 0% to 50-80% of the speed (synchronous speed / nominal speed (rated speed)), the circuit according to the invention short-circuits the rotor winding 5 in order to prevent current flow and thus losses in RZ. The marginal reduction of the oscillation torques by RZ can be dispensed with in this phase. In a second phase following the first phase, from approximately 50-80% of the rated speed to 95-98% of the rated speed, the circuit is locked to prevent further short-circuiting and to enable further start-up with current flow via RZ and thus to achieve the significant advantages in this phase, such as the reduction of the oscillation torques and the increase in the average torque.In a third phase following the second phase, from 95%-98% of the rated speed (nominal speed) until the end of the asynchronous start-up, the excitation described above takes place and thus the bridging of RZ for synchronous operation. The temporal sequence of these phases includes periods that affect the starting resistor 11. 202204988 Foreign version 9 In the following example, thyristors are used in particular, which directly bridge the excitation winding after firing. The alternating current in the excitation winding causes them to extinguish again after a half-wave. The anti-parallel connected components must therefore be activated alternately in order to carry an alternating current. The use of thyristors is advantageous because, due to their so-called "presspack" design, they can cope well with the centrifugal force loading in the rotor. Auxiliary energy is required to trigger the switch or to ignite the power electronic components.This is obtained, for example, directly from the voltage induced in the excitation winding. Already proven types (T1, T2) from the excitation circuit can be used as thyristors 6 and 7, with appropriate cooling, since the bypass thyristors carry exactly the same current as T1 and T2. The bridging should now only occur until a certain speed is reached. This means that the switching process described above must be controlled by an additional logic signal, which suppresses switching above a defined speed threshold. This signal can be controlled by an external source (telemetry or similar) or generated directly from the existing voltages / currents on the rotor. This can be done, for example, by measuring the time intervals between the alternate switching of the switches. Since the speed increases during start-up and the rotor slip decreases accordingly, the switching frequency becomes increasingly smaller.The time intervals increase. For example, a timer can now monitor whether a certain minimum time period between switching operations has been exceeded. If this is the case, switching is suppressed. This purely frequency-dependent variant has the advantage that - apart from permissible tolerances of the mains frequency - no calculation data subject to uncertainty is used. The connection speed can then be varied, for example, using bridge configurations / jumpers or similar. The switchability can have the advantage that the energy conversion in the resistor is reduced without noticeably impairing the effect in terms of torque. This means that the resistor can be made smaller for a specific effect, since less thermal capacity has to be provided. This results in direct cost advantages in particular, but also indirect advantages, such as lower mass on the rotor and advantages in terms ofthe rotor dynamics, etc. The starting resistor is defined on the one hand by an ohmic resistance value and thus its associated influence on the starting behavior, such as the oscillation torque, the mean torque and the starting time. On the other hand, the starting resistor absorbs the losses that occur during start-up, since only a small proportion of these are released directly into the environment during the start-up phase. By reducing the operating time to phase 2, the heat capacity of the starting resistor can be reduced to around 50% of the otherwise necessary heat capacity. With the same materials, this means roughly halving the mass of the starting resistor. Due to the typical arrangement of the resistor on the rotor, the weight saving means a significant improvement in rotor dynamics. A typical starting resistor weighs in the range of 50 kg to 500 kg.The now possible weight reduction allows for weight savings of 30%-60%, and in particular 40-50%. The diagram in Figure 3 shows a current flow 8 with thyristors 6 and 7 activated. The path of the current flow 8 also indicates a loop 8. Located in the loop 8 is one of the power semiconductors 6 for short-circuiting and the excitation winding 5, which is to be short-circuited at certain times. The diagram in Figure 4 shows a current flow 12 with thyristors 6 and 7 deactivated.

Claims

202204988 Foreign version 11 patent claims 1. Synchronous machine (1) with 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 loop (8), wherein the at least one first power semiconductor (6) and the rotor winding (5) are connected in parallel and a starting resistor (11) is connected in series thereto.

2. 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 to the first power semiconductor (6).

3. Synchronous machine (1) according to claim 2, wherein the power semiconductors (6, 7) are provided for short-circuiting the rotor winding (5) for different current directions in the rotor winding (5).Synchronous machine (1) according to one of claims 1 to 3, wherein at least one of the power semiconductors (6, 7) is controllable.

5. Method for operating a synchronous machine (1), wherein the synchronous machine to be operated has a stator (3) and a rotor, wherein the rotor has a rotor winding (5), wherein the rotor winding (5) is short-circuited in an operating state of the synchronous machine (1), wherein a first short-circuiter (6) is used for short-circuiting, wherein the short-circuiter (6) and the rotor winding (5) form a first loop (8), wherein a starting resistor (11) is connected in series with a second short-circuiter (7) connected in parallel to it, in order to connect the first short-circuiter (6) and the rotor winding (5) in parallel. 202204988 Foreign version 12 6. The method according to claim 5, wherein the operating state relates to a run-up and / or start-up of the synchronous machine (1).

7. The method according to one of claims 5 or 6, wherein a synchronous machine according to one of claims 1 to 4 is used.

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

Images