WO2015139063A1 - Method for operating a powertrain, and powertrain - Google Patents

Abstract

The invention relates to a method and a drive for starting-up a powertrain comprising a driveshaft 2, a drive machine 4, and a differential transmission 3 with three drives or outputs. One output is connected to the driveshaft 2, one first drive is connected to the drive machine 4, and one second drive is connected to a differential drive 5. The drive machine 4 is accelerated by the differential drive 5 and is synchronized with the grid 12 while a braking torque acts on the driveshaft 2. In an acceleration phase of the driveshaft 2, the second drive is braked.

Description

 Method of operating a drive train and drive train

The invention relates to a method for starting a drive train with a drive shaft, a prime mover and with a

Differential gearbox with three input and output drives, wherein an output to the drive shaft, a first drive to the prime mover and a second drive is connected to a differential drive.

The invention further relates to a drive train for carrying out the method with a drive shaft, a prime mover and with a differential gear with three inputs and outputs, wherein an output to the drive shaft, a drive to the drive machine and a second drive is connected to a differential drive ,

An ever more frequently demanded to the drive of

Work machines, such as conveyors, e.g. Pumps, compressors, fans, etc., is an efficient variable speed operation. In the following, electric machines are used as examples of corresponding drive machines, but the principle applies to all possible types of drive machines, such as e.g. also for

Internal combustion engines.

The most commonly used electric drives today are three-phase machines such as e.g. Asynchronous motors and synchronous motors.

Although these three-phase machines are robust and inexpensive, they can not operate at variable speed. At the same time, the current consumption of a three-phase machine at the start of zero speed typically corresponds to approximately 10 times the rated current, which causes a correspondingly high electrical load for the network during the starting process.

For this reason, electrical machines, rather than being connected directly to a grid, are often implemented in combination with a frequency converter as a variable-speed drive. So you can on the one hand to realize a zero speed start, without burdening the network, and on the other hand drive the machine at the optimum speed. However, the solution is expensive and associated with significant loss of efficiency. One in comparison More cost-effective and also better in terms of efficiency alternative is the use of differential systems, for example according to AT 507394 A. Fundamental limitation in known designs here is that depending on the gear ratio of the differential stage only a relatively small working speed range or virtually no low speeds on the drive shaft

Working machine can be achieved.

To realize this there are different possibilities. According to German Utility Model DE 20 2012 101 708 U, for example, one can set the transmission ratio of the differential gear to 1. So you can drive the complete powertrain with the differential drive or bring the prime mover to synchronous speed and synchronize them subsequently with the network.

Disadvantage of this solution is that the differential drive or its frequency converter is dimensioned much smaller than that

Drive machine and therefore only a correspondingly small

Can deliver torque.

The object of the invention is therefore to find a solution with which you drive machines with the network substantially bumpless

synchronize and additionally the work machine can start from zero speed away.

This object is achieved in a method of the type mentioned in that the drive machine is accelerated with the differential drive and synchronized with the network, while acting on the drive shaft, a braking torque, and that is braked in an acceleration phase of the drive shaft, the second drive.

This task is also solved with a drive train through a brake or backstop, which acts on the output.

The core of a differential system is a di fferenzialgetriebe, which may be a simple planetary gear stage with three inputs and outputs in a simple, with a downforce with the Drive shaft of a working machine, a first drive with the

Drive machine and a second drive is connected to a differential drive. Thus, the machine can be operated at variable speed of the prime mover variable speed by the di fferenzialantrieb compensates for the speed difference.

To a prime mover from standstill preferably on

To bring synchronous speed and in addition to be able to start a work machine of zero speed, starting the system according to the invention, e.g. take place in 2 phases as follows:

Phase 1: The prime mover is preferably first brought to (at least approximately) synchronous speed with a differential drive and then synchronized with the network. That remains that

Di fferenzialgetriebe during this starting process, apart from the mass moment of inertia caused by reaction forces from the first drive or the associated drive machine, largely free of external mechanical loads. Conversely, this means that until the prime mover has reached its rated speed, on the drive shaft of the machine a correspondingly small

driving torque acts, causing the working machine in the

Essentially stops. The differential drive achieved during this phase a the transmission ratio of the differential gear corresponding multiple of its synchronous speed.

Phase 2: After the prime mover is connected to the grid, in the second phase the actual acceleration or

Starting the work machine under load by the second drive of the differential gear stage by means of a di fferenzialantriebes

is delayed. For this second phase of the differential drive is dimensioned accordingly (especially in view of the high speeds) and can generate the required for the acceleration of the machine braking torque by means of the frequency converter at the maximum speed required.

Preferred embodiments of the invention are the subject of

Subclaims. Hereinafter, preferred embodiments of the invention will be explained with reference to the accompanying drawings. It shows: the principle of a differential system according to the invention for a drive of a pump,

 a torque characteristic of a three-phase machine,

 the torques which can be achieved in the so-called field weakening range of a variable-speed drive according to the invention,

 the comparison of the torque characteristics for a pump and a variable speed drive when starting the

 Di fferenzialantriebes and

 the sequence of a startup process according to the present invention.

1 shows the structure according to the invention of a drive or

Differential system for a drive train using the example of a pump. In this case, the working machine 1, the rotor of a pump, which via a drive shaft 2 and a differential gear 3 of a

Drive machine 4 is driven. The prime mover 4 in this embodiment is preferably a medium-voltage three-phase machine connected to a network 12, which in the example shown on the basis of a medium-voltage three-phase machine

Medium voltage network is connected. The chosen one

However, voltage level depends on the application and above all on the

Performance level of the engine 4 and can be any desired without affecting the basic function of the system according to the invention

Have voltage level. A planet carrier 7 is connected to the drive shaft 2, the drive machine 4 with a ring gear 8 and a

The core of the differential system in this embodiment is thus a simple planetary gear stage with three inputs or outputs, with a drive output to the drive shaft 2 of the work machine 1, a first drive with the prime mover 4 and a second drive is connected to the differential drive 5.

In order to be able to optimally adjust the speed range of the differential drive 5, an adaptation gear 10 between the sun gear 9 and the differential drive 5 is optionally implemented. Alternative to

shown spur gear, the adjustment gear 10, for example Also be multi-stage or running as a toothed belt or chain drive and / or combined with a planetary gear stage or be executed as a planetary gear stage. With the adjustment gear 10 can also realize an axial offset for the differential drive 5, which allows a simple design of the differential drive 5 due to the coaxial arrangement of the working machine 1 and the prime mover 4 shown by way of example. With the differential drive 5, a motor brake 13 is connected, which brakes the differential drive 5 when needed. Electric is the

Differential drive 5 by means of preferably a low-voltage frequency converter, consisting of a motor-side inverter 6a and a grid-side inverter 6b, and a transformer 11 connected to the network 12. The transformer is equal to any existing voltage differences between the network 12 and the

Mains-side inverter 6b and can be dispensed with voltage equality between the prime mover 4, the network-side inverter 6b and the network 12. The inverters 6a and 6b are connected by a DC intermediate circuit. The essential advantage of this concept is that the main load leading prime mover 4 can be connected to a network 12 directly, that is without complex power electronics. The compensation between the variable rotor speed and the fixed speed of the network-connected drive machine 4 is realized by the variable-speed differential drive 5.

The torque equation for the differential system is: Torque.t _Di ferenciadir ⁼ torque _Antrie and * y / X / where the magnitude factor y / x is a measure of the gear ratios in the differential gear 3 and in the gearing 10. The performance of the differential drive 5 is substantially proportional to the

Product of percentage deviation of the pump speed from its basic speed x drive shaft power. Accordingly, a large speed range basically requires a correspondingly large

Dimensioning of the differential drive 5. This is also the reason to see why differential systems for small speed ranges are particularly well suited, but basically everyone

Speed range is feasible. A differential drive 5 for a pump as a work machine 1, for example, has an output of about 15% of the total system power. This in turn means that with the differential system no low speeds (near zero speed) can be realized on the work machine 1, without accelerating the differential drive 5 to about 4 times its synchronous speed.

Thus, in the prior art, for example, the work machine 1 of speed zero in its working speed range (this is the

Speed range in which the work machine 1 operates substantially = working operation) are brought by the differential drive 5 braked (either electrically or by means of engine brake 13) and the prime mover 4 is connected to the network. The work machine 4 in turn draws but up to a 10-fold rated current to accelerate to their synchronous speed. By using a

So-called star / delta circuit can be the starting current

reduce, but also reduces the feasible

Starting torque.

According to the invention, an improvement of the problem of a high starting current is achieved by the differential drive 5 at the beginning of the

Start process on one over the control speed range

(Control speed range is the speed range in which the

Differenzialant ieb 5 works to realize the working speed range of the working machine 1) going beyond

Operating speed is brought. By using modern

Frequency converter technologies this can be a multiple of

Synchronous speed of the differential drive 5, if the

Differential drive 5 is designed for these speeds. Due to external loads while the work machine 1 remains in a range of very low speed or the machine 1 can also be braked in case of need or by means of backstop one

Rotary movement counter to the direction of rotation can be prevented. As a result, the prime mover 4 is subjected to a (at least

approximately) network-synchronous speed (= idle point according to FIG. 2) brought and then connected to the network. In the case of an asynchronous machine, one remains in comparison with the starting method from zero speed much lower inrush current. Above all, the duration of this inrush current peak is only a few grid periods. Measures to reduce this remaining inrush current are, for example, a small isolation transformer for biasing via a bypass, or a so-called thyristor regulator. The described

Problem of the inrush current does not occur at e.g. externally excited synchronous generators, since these have an excitation unit.

After the engine 4 is connected to the network, the differential drive 5 is decelerated or braked, whereby the speed of the working machine 1 increases in the working speed range, while the drive machine 4 with approximately fixed speed depends on the network 12.

The speed control or the deceleration of the speed of the

Differential drive 5 is preferably carried out electrically by the inverter 6a, 6b and / or by means of motor brake 13. Since the inverter operates in this case as a generator, the resulting braking energy is either fed into the network 12 or in the inverter intermediate circuit (= electrical connection of

motor-side and mains side inverter) preferably by means of so-called chopper in a resistor. This is especially necessary when e.g. in a particularly simple embodiment of the differential system of the differential drive 5 is only operated by a motor and thus the network-side inverter 6b can be designed as a preferably simple and robust diode rectifier, whereby a power feedback is not possible.

The engine brake 13 can also be used to

Differential drive 5 to protect against overspeed when, for. the prime mover 4 fails and the work machine 1 stops or rotates in the opposite direction. Due to the high speeds during the starting process, it is recommended to use a wear-free motor brake 13. In this regard, the use of so-called retarders is recommended.

First of all, the group of hydrodynamic retarders (= hydraulic brake) should be mentioned here. Hydrodynamic retarders usually work with oil or water, which when needed in a converter housing is directed. The Wandiergehäuse consists of two

rotationally symmetrical and opposing paddle wheels and previously a rotor, which is connected to the drive train of the system, and a fixed stator. The rotor accelerates the supplied oil and the centrifugal force pushes it outwards. Due to the shape of the rotor blades, the oil is conducted into the stator, which thereby induces a braking torque in the rotor and subsequently also brakes the entire drive train. In an electrodynamic retarder (= electric brake), e.g. an eddy current brake, are e.g. two steel discs (rotors), which are not magnetized, connected to the drive train. In between is the stator with

electric coils. When power is applied by activation of the retarder, magnetic fields are generated which are closed by the rotors. The opposing magnetic fields then generate the braking effect. The resulting heat is e.g. discharged through internally ventilated rotor discs again. A major advantage of a

Retarders as a service brake is its freedom from wear and good controllability. The engine brake 13 can basically be any type of brake.

Fig. 2 shows one of the technical literature (exercises on "electrical

Energietechnik II "Institute for Power Electronics and Electric Drives, University of Stuttgart, Prof. Dr.-Ing .. J. Roth-Stieflow) Representation of the torque characteristic of a three-phase machine (in this case, an asynchronous machine) The torque characteristic shows important points such as tilt point, nominal point and

Idle point. The three-phase machine delivers a so-called tilting torque at the tipping point, a so-called at the nominal point

Nominal torque and runs at idle point torque-free with the grid synchronously. The tilting torque is approximately 2-3 times the rated torque, for example, in conventional asynchronous machines. For the following versions, a tilting torque in the amount of twice the rated torque was assumed. With higher or lower overturning torques, the achievable torque can be scaled linearly. Typically, a tilting torque can be provided only for a limited time; a rated torque is a torque that can be realized in continuous operation (= working operation). Another way to set the speed range for the

Differential drive 5 to expand, offers the so-called 87Hz characteristic for the operation of the inverter 6a, 6b. The principle is the following: Motors can typically operate in star (400V) or delta (230V) circuits. If one operates a motor as usual with 400V in star connection, then one reaches with 50Hz its nominal point. This characteristic is set in the frequency converter. You can also run a motor with 400V in delta connection and parameterize the frequency converter so that it reaches the 50Hz at 230V. As a result, the frequency converter reaches its rated voltage (400V) only at 87Hz (A / 3 X 50Hz). Since the motor torque is constant up to the nominal point, a higher power is achieved with the 87 Hz characteristic. It should be noted, however, that in comparison with the star connection in the delta connection, there is a higher current by V3. That The frequency converter must be larger in size.

In addition, the motor generates higher losses due to the higher frequency, for which the motor must be thermally designed.

Ultimately, however, one reaches with the 87Hz characteristic one

according to (^ 3) larger speed range with - in contrast to the field weakening - not reduced torque. The torques with 4-fold field weakening are higher by a factor of 3. Do you want the

Inverter 6a, 6b not for a higher current to 3

dimensioning, you have to work in the back in the

Change star connection. This requires v.a. an extra effort regarding switchgear.

For power grids that are not operated at 50Hz, the specified frequency of 87Hz changes accordingly. For a 60Hz network this is about 104Hz.

In principle, it is also possible between the differential drive 5 and the second drive, a transmission with variable

Gear ratio (in stages or continuously) to integrate (in addition to or instead of a matching gear 10), so as to reduce the required speed of the differential drive 5 for the starting operation accordingly. This option can also be used to further the working speed range of

Work machine 1 to enlarge. Work machines 1 such as pumps, Fans, compressors and the like have an exponential speed / power curve, which the required

Drive torque in the partial load range is correspondingly small (see also Fig. 4). Although you can not realize much higher torques on the second drive with this method, but you can thereby reduce the maximum occurring speeds at the differential drive 5.

3 shows one of the specialist literature (three-phase motors, Part 2,

Electrical Engineering and Information Technology, Darmstadt University of Applied Sciences, Prof. Dr.-Ing. Heinz Schmidt-Walter) representation of the im

Field weakening range maximum achievable torque of

Variable speed, electric drive. The

 The inverter output voltage is increased proportionally with the speed up to the rated speed. This results in a nearly constant torque up to the field weakening limit. From the

Field weakening limit, the output voltage at the inverter can not be increased further. The voltage and the power remain constant and the tilting torque decreases with ~ 1 / n ² .

4 shows the torques (M / M__n [pu]) that can be realized depending on the rotational speed of the differential drive 5 (n_s / n_max [pu] (["per unit"])) n_s being the variable rotational speed, n_max the nominal rotational speed of the Differential drive 5 and M__n whose rated torque.

The curve M_k / M_n shows a realizable tilting torque (mechanically on the shaft of the differential drive 5). However, this tilting torque, the differential drive 5 but limited in time

provide, e.g. for the starting process of the differential system. The curve M_max / M_n, however, shows a permanently realizable

Drive torque of the differential drive 5, based on its rated torque.

As a third curve (M__Pumpe) an example of a required for the starting process and the working operation of a pump drive torque is shown. The marked "maximum working range" is the range in which the curve M_max / M_n lies above the curve M_Pumpe and thus the system can be operated permanently.When the system is operated even further in the field weakening range, then the curve M max / M n falls below the curve M_Pumpe. The curve M_k / M_n, however, is in the entire speed range shown above the curve M_Pumpe, so that the

Work machine 1 can be started from zero speed. Since a starting operation is limited in time, the differential drive 5 is thereby not thermally overloaded.

The "maximum working range" also represents a typical limit for the operation of permanent magnet synchronous machines (as

Differential drive 5) in the field weakening range. Since in such machines, the voltage increases proportionally with the speed (also beyond the rated speed) and thereby compensated in the field weakening beyond the rated voltage voltage component be compensated rauss, twice the rated speed is a

Typical design speed limit.

The characteristic curve M_Pump shown in FIG. 4 is a typical one

Characteristic for turbomachines such as pumps, compressors, fans and the like. The required torque for the starting process can be achieved by using adjustment mechanisms, such as.

Reduce bucket wheel or rotor blade adjustment if this is designed. Thus, the torque required for the starting process is correspondingly smaller.

The system according to the invention can also be used to bring the prime mover 4 into phase-shifting operation for the time being. That is, the prime mover 4, after being connected to the grid 12, can only supply reactive power to the grid 12, or can draw it from the grid 12, without operating the work machine 1. The drive machine 4 is connected to the network 12, without the further steps of the invention

Startup process to perform. In this case, the differential drive 5, after the prime mover 1 has been connected to the network 12, are switched load-free, whereby this is no longer electrically and only mechanically (due to the adjusting speeds) is charged. The further steps of the described starting process take place when the working machine 1 has to take up the working operation. 5 shows a summary of the sequence of a starting process according to the present invention.

Claims

Claims : 1. A method for starting a drive train with a drive shaft (2), a prime mover (4) and with a Differenzialget iebe (3) with three inputs and outputs, with a downforce with the  Drive shaft (2), a first drive with the drive machine (4) and a second drive with a differential drive (5)  is connected, characterized in that the drive machine (4) is accelerated with the differential drive (5) and synchronized with the network (12), while on the drive shaft (2) acts a braking torque, and that in one  Acceleration phase of the drive shaft (2), the second drive is braked. 2. The method according to claim 1, characterized in that the  Drive shaft (4) starting from a speed of zero or approximately zero starting with the differential drive (5) is accelerated. 3. The method according to claim 1 or 2, characterized in that after the drive machine (4) is synchronized with the network (12), the second drive is braked. 4. The method according to any one of claims 1 to 3, characterized  characterized in that the second drive from the differential drive (5) is braked. 5. The method according to any one of claims 1 to 4, characterized  in that at least part of the braking power is generated by a mechanical, electric or hydraulic brake (13) connected to the differential drive (5). 6. The method according to any one of claims 1 to 5, characterized  characterized in that the second drive is directly mechanically, electrically or hydraulically braked. 7. The method according to any one of claims 1 to 6, characterized  characterized in that at startup to control the Torque one with the drive shaft (2) connected Working machine (1) a Schaufelrad- or rotor blade position of the working machine (1) is changed. 8. The method according to any one of claims 1 to 7, characterized  characterized in that the differential drive with both 50Hz or 60Hz and 87Hz or 104Hz is operated. 9. Driveline for performing a method according to one of  Claims 1 to 8 with a drive shaft (2), a  Drive machine (4) and with a differential gear (3) with three input and output drives, wherein an output to the drive shaft (2), a drive to the drive machine (4) and a second drive with a differential drive (5) is connected,  characterized by a brake or backstop, which acts on the output. 10. Driveline according to claim 9, characterized in that the drive machine (4) is connected to a power grid (12) three-phase machine. 11. Driveline according to claim 9, characterized in that the drive machine is an internal combustion engine. 12. drivetrain according to one of claims 9 to 11, characterized  characterized in that the differential drive (5) a  Three-phase machine is. 13. Driveline according to one of claims 9 to 11, characterized  characterized in that the differential drive is a hydraulic pump / motor. 14. Driveline according to one of claims 9 to 13, characterized  characterized in that differential drive (5) via a  Adaptation gear stage (10) is connected to the second drive. 15. Driveline according to one of claims 9 to 14, characterized characterized in that the differential drive (5) via an optionally continuously variable adjusting gear is connected to the second drive. 16. Driveline according to one of claims 9 to 15, characterized  characterized in that the brake (13) is a retarder. 17. Driveline according to one of claims 9 to 16, characterized  characterized in that the differential drive (5) via an inverter (6a, 6b) to the network (12) is connected and that in the inverter (6a, 6b) of the differential drive (5), a chopper and a resistor are arranged. Drive train according to one of claims 9 to, characterized  characterized in that the working machine (1) is a pump, a compressor or a fan.