TWIN-FED ASYNCHRONOUS MACHINE HAVING FLYWHEEL AS PHASE SHIFTER AND ENERGY SOURCE

Abstract

A system that is directly coupled to the transmission network or the distribution network, wherein a variable-speed, twin-fed asynchronous machine is combined with a flywheel. Besides the function as a voltage-regulating phase shifter, energy in the flywheel can at the same time be stored or removed as the speed changes. The provided properties relate to a combination of frequency support, voltage stabilisation, energy storage and short-circuit capacity. In a particular embodiment the speed of the flywheel is increased in relation to the speed of the rotor by a transmission, wherein the capability of the flywheel to store energy advantageously rises disproportionally with the speed.

Claims

1. A system for supporting a three-phase supply grid but also in the form of an energy store, comprising: an asynchronous machine whose rotor interacts with a flywheel, wherein the asynchronous machine is fed firstly from the three-phase supply grid and is fed secondly with a variable-frequency three-phase current.

2. The system as claimed in claim 1, wherein the flywheel is connected directly to the rotor of the asynchronous machine.

3. The system as claimed in claim 1, wherein the flywheel is connected to the rotor of the asynchronous machine via a transmission (xn).

4. The system as claimed in claim 3, wherein the transmission has a transmission ratio that increases the speed of the flywheel with respect to the speed of the rotor.

5. The system as claimed in claim 3, wherein the transmission is provided with a structure having an infinitely variable transmission ratio.

6. The system as claimed in claim 1, wherein the rotor is fed with variable-frequency three-phase current.

7. The system as claimed in claim 6, wherein the rotor is fed from the three-phase supply grid via a frequency converter.

8. The system as claimed in claim 1, wherein the three-phase supply grid is provided by a distribution grid.

9. The system as claimed in claim 1, wherein the three-phase supply grid is provided by a transmission grid.

10. The system as claimed in claim 1, wherein power/time control of energy charging or energy discharging is provided.

11. The system as claimed in claim 1, wherein a power absorption or a power output is controlled in accordance with a measured grid frequency.

12. The system as claimed in claim 1, wherein a power absorption or a power output is controlled in accordance with a grid frequency gradient.

13. The system as claimed in claim 1, wherein a power absorption or a power output is controlled in accordance with a speed gradient.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention is explained in more detail below in the form of an exemplary embodiment, in a scope required for understanding, with reference to a figure, in which:

[0015] FIG. 1 shows a variable-speed doubly fed asynchronous machine in combination with a flywheel.

DETAILED DESCRIPTION OF INVENTION

[0016] The system illustrated in FIG. 1 has an asynchronous machine DFIG that is connected to a three-phase grid GRID via a transformer TRAFO. The rotor of the asynchronous machine is electrically connected to the grid via a frequency converter FC and coupled mechanically to a flywheel FW. The stator of the asynchronous machine is electrically connected to the grid.

[0017] The variable-speed doubly fed asynchronous machine, in combination with a flywheel, offers a combination of the properties of frequency support, voltage stabilization, energy store and short-circuit power.

[0018] In contrast to the conventional synchronous machine, the rotor is fed with a variable-frequency three-phase current and is therefore able to control the speed of the rotor, and thus of the flywheel, when all of the requirements in terms of a synchronous phase shifter are met. In addition to the function as a voltage-regulating phase shifter, energy in the flywheel is at the same time able to be stored or drawn by changing the speed.

[0019] The amount of energy depends on the design of the flywheel (for example coupled directly or via a transmission xn that boosts the speed) and the speed range that is implemented. The transmission xn has a transmission ratio times n, wherein n is a natural number.

[0020] The power available in the short term corresponds to the power class of the phase shifter. It is possible to achieve very high power classes and power densities.

[0021] Power/time control of the charging or discharging of the mechanical energy store is possible for example using the following modes: measuring the grid frequency and automatically setting the power absorption or power output in accordance with the requirement profile of the grid operator for the services PCP (primary control power) or EFR (enhanced frequency response, Great Britain); measuring the grid frequency gradient and setting the power as a countermeasure for rapid frequency changes (active damping of the RoCoF: rate of change of frequency); controlling the speed gradient in order to control power absorption and output in a targeted manner, for example in order to store energy over day/night cycles or as a preventive measure for predictable stability bottlenecks. The voltage-regulating properties of a synchronous phase shifter are in this case also ensured.

[0022] In comparison with alternative variable-frequency solutions involving full inverter systems (such as for example turbogenerators having frequency converters at the output terminals, synchronous grid up to 380 MW), the system according to the invention advantageously has lower losses and considerably reduced expenditure.

[0023] In comparison with other technical solutions based on expensive large power electronics components, such as for example SVC Plus Supercapacitors and battery stores, the system according to the invention has considerably improved core grid stabilization properties.

[0024] The power balance of the system will be approximately zero (absorbed minus output energy), as a result of which the system form does not fit in with generator technology, but rather with energy stores on the one hand and grid support systems on the other hand.

[0025] The present invention has been explained in detail for illustrative purposes on the basis of specific exemplary embodiments. Elements of the individual exemplary embodiments may in this case also be combined with one another. The invention is therefore not intended to be restricted to individual exemplary embodiments, but rather only to be restricted by the appended claims.