WO2019209110A1

WO2019209110A1 - Electrical machine drive system with flywheel-based energy storage units

Info

Publication number: WO2019209110A1
Application number: PCT/NO2019/050073
Authority: WO
Inventors: Alexey Matveev
Original assignee: Kongsberg Maritime CM AS
Priority date: 2018-04-26
Filing date: 2019-04-08
Publication date: 2019-10-31
Also published as: NO20180594A1; NO344061B1

Abstract

Electrical machine drive system comprising at least two AC/DC converters (41) and at least two flywheel-based energy storage units (30), wherein the at least two AC/DC converters (41) are arranged in parallel and connected to the AC electrical machine (20) individually via DC/AC converters (42) or via a common DC-link (45) at DC converter side, and that AC side of the AC/DC converters (41) are selectively connectable to the AC power supply source (100) or respective flywheel-based energy storage units (30) via respective switching units (50).

Description

Electrical machine drive system with flywheel-based energy storage units

The present invention is related to an electrical machine drive system according to the preamble of claim 1.

The present invention is especially related to an electrical machine drive system with the need to store energy from changing motoring-to-generation modes.

Background

Electrical machine drive systems comprising the use of energy storages have been widely used in different applications. Examples of such systems are disclosed for example in US2012326641A, DE102009014495A1, W010003469A1. Energy can be stored electrically, e.g. in batteries or supercapacitors, or mechanically - in flywheels. Example of flywheel-based energy storage system is disclosed in WO16041987A3. Lately, with an increasing focus on electrically driven applications this also results in a demand for solutions for storing energy that provides higher efficiency and requires lower installations and maintenance costs. Further, it is important not only how one stores energy, but also how this stored energy can be utilized in a more effective way. Example of an application where the above mentioned is actual is electrically driven marine winches with active heave compensation using flywheel for storing heave energy. An example of such a system is disclosed in US20100314168A (US7923946B2).

Conventional solutions for electrically driven winches with active heave compensation, as e.g. shown in Figures la-c (the system topology here is like in DE102009014495A1) will require 3 pcs of full-power rated AC/DC converters. Drawback of this solution is low efficiency of the invertor interfacing the grid in the low current mode when energy is cycling between the load and the energy storage through the corresponding converters and quite small amount of energy is supplied from the grid to compensate for the losses during active heave compensation mode. Another drawback is that failure of any of the AC-DC converters will stop the operation.

There is accordingly a need for an electrical machine drive system which provides high efficiency in all modes.

It is further a need for an electrical machine drive system which provides redundancy in all modes.

It is also a need for an electrical machine drive system with lower costs than prior art solutions. Object

The main object of the present invention is to provide an electrical machine drive system partly or entirely solving the drawbacks of prior art solutions.

An object of the present invention is to provide an electrical machine drive system that provides high efficiency in all operating modes.

There is an object of the present invention to provide an electrical machine drive system that provides redundancy in all operating modes.

An object of the present invention is to provide an electrical machine drive system enabling opportunities for adapting the number of converters in use to the required load of an AC electrical machine, changing from motoring to generating mode and back.

There is an object of the present invention to provide an electrical machine drive system reducing the costs of converters compared to prior art solutions.

Further objects of the present invention will appear from the following description, claims and attached drawings.

The invention

An electrical machine drive system according to the present invention is disclosed in claim 1. Preferable features of the electrical machine drive system according to the present invention are disclosed in the dependent claims.

The present invention is related to an electrical machine drive system comprising an AC electrical machine arranged for driving a load, wherein the AC electrical machine is arranged to operate as both generator and motor. The electrical machine drive system further comprising an AC power supply source and flywheel-based energy storage units, wherein the AC power supply source and flywheel-based energy storage units are selectively connectable to the AC electrical machine via at least one AC/DC converter. In general, there can be several electric machines and multiple loads but for simplicity, the invention is described for one electric machine driving one load.

According to a first embodiment of the electrical machine drive system it comprises at least two AC/DC converters and at least two flywheel-based energy storage units, wherein the at least two AC/DC converters are arranged in parallel and at DC side thereof connected to the AC electrical machine individually via DC/AC converters. In this embodiment the AC electrical machine is a multi winding machine, such as for example a machine comprising more than two electrically de-coupled sets of three-phase windings.

In a second embodiment of the electrical machine drive system it comprises at least two AC/DC converters and at least two flywheel-based energy storage units, wherein the at least two AC/DC converters are arranged in parallel and at DC side thereof connected to the AC electrical machine via a common DC-link. The common DC link is provided by an AC/DC converter connected to the AC electrical machine at AC side and the AC electrical machine is in this embodiment a single-winding machine, such as for example machine comprising one three-phase winding.

The first and second embodiment of the electrical machine drive system further comprises that AC side of the AC/DC converters are selectively connectable to the AC power supply source or respective flywheel-based energy storage units via respective switching units.

The flywheel-based energy storage unit is according to the present invention formed by an electrical machine and a flywheel.

According to a further embodiment of the electrical machine drive system according to the present invention it comprises at least three AC/DC converters arranged in parallel, each AC/DC converter selectively connectable to the AC power supply source or respective flywheel-based energy storage unit via respective switching units.

The electrical machine drive system is especially suitable for applications where the load is frequently changing between motoring and generating modes, for example on mechanism performing all kinds of cyclic and/or reciprocating motion. An example of such an application is where the load is a marine winch requiring active heave compensation. In active heave compensation mode the electrical machine drive system is arranged to operate with at least one energy storage unit connected to the AC electrical machine via an AC/DC converter and connected to the AC power supply source via at least one AC/DC converter. Further, in connection with long lifting or long lowering mode for winches the electrical machine drive system is arranged to operate with the AC power supply source connected to the AC electrical machine via the at least two AC/DC converters arranged in parallel.

According to one embodiment of the electrical machine drive system, the number of connected AC/DC converters in parallel connected to the AC power supply source and/or flywheel-based energy storage units, respectively, are adapted the required load of the AC/DC converters and thus required load of the AC electrical machine.

This arrangement allows, when being in active heave mode, using at least one of the AC/DC converters for compensation of losses in the systems and at least one of the other AC/DC converters for operating the electric machines driving the flywheels. Since size of each of the parallel-connected converters is just a part of the converter in conventional system it will be better suited for the power flow from the AC power supply source (e.g. grid) compensating for the losses, and, consequently will have higher efficiency. Number of parallel-connected converters can be 2, 3, 4, 5, 6 or even more. This will provide high redundancy as failure of one converter will result in a loss of just a fraction of the total load handling capacity. Further, when not being in active heave mode, some or all of the AC/DC converters can be reconnected from the energy storage units to the AC power supply source (grid). Thus, the same AC/DC converters can play two roles.

According to a further embodiment of the electrical machine drive system according to the present invention the electrical machine drive system comprises at least two AC electrical machines supplied by the above-described principles driving the same load via e.g. a pinion gear or similar.

In a further embodiment of the present invention, the electrical machine drive system comprises at least two AC electrical machines supplied by the above-described principles each driving a separate load.

According to a further embodiment of the electrical machine drive system according to the present invention the electrical machine and flywheel of the energy storage units are integrated in a drum of a winch for saving space.

The electrical machine drive system according to the present invention is also suitable for other applications with the need to store energy for motoring-to-generation modes of an electrical machine driving a load, such as characterized by cyclic or reciprocating motion. The electrical machine drive system according to the present invention provides a solution with high efficiency in all modes by that the number of AC/DC converters in use can be selectively chosen and adapted the current requirements of the AC electrical machine driving the load.

The electrical machine drive system according to the present invention further provides a solution with redundancy for all operating modes.

As the electrical machine drive system according to the present invention makes use of at least two AC/DC converters arranged in parallel, which can selectively be connected to either AC power supply source (grid) or the energy storage units. This result in lower costs compared to prior art solutions where different AC/DC converters are used for connection to the AC power supply source (grid) and connection to the energy storage units.

Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

Example The present invention will below be described in further detail with references to the attached drawings, where:

Fig. la-c are principle drawings of an electrical machine drive system according to prior art,

Fig. 2a-c are principle drawings of an electrical machine drive system according to the present invention, Fig. 3a-e are principle drawings of alternative embodiments of the electrical machine drive system according to the present invention, and

Fig. 4 is a principle drawing for arrangement of flywheel-based energy storages in a winch.

Note that electric connections are illustrated as single lines represent three phase AC connections, while the double lines between the AC/DC converters represent DC connections.

Reference is now made to Figures la-c showing principle drawings of an electrical machine drive system according to prior art solution. The example shown in Figures la-c is related to a winch system with active heave compensation comprising a winch 10 with winch wire 11 driven by an AC electrical machine 20 via a shaft 21, wherein the AC electrical machine can operate as both generator and motor. The electrical machine drive system further comprises an AC/DC converter 41 which converts AC power supplied from an AC power supply source 100, such as an AC grid, to DC power. The electrical machine drive system further comprises a DC/AC converter 42 which converts DC power to AC power for driving the AC electrical machine 20 or converts AC power regenerated by the AC electrical machine 20 to DC power, wherein the converters 41 and 42 are arranged in series between the AC electrical machine 20 and the AC power supply source 100. The electrical machine drive system further comprises a flywheel-based energy storage unit 30 comprising an AC electrical machine 31 connected to a flywheel 32 via a shaft 33, wherein the AC electrical machine 31 is connected to a DC/AC converter 43 which converts DC power to AC power for driving the AC electrical machine 31 or converts AC power regenerated by the AC electrical machine 31 back to DC power, wherein the DC/AC converter 43 is connected in series between the mentioned converters 41-42. The electrical machine 31 of the energy storage is typically a single-winding machine. The mentioned converters 41-43 are arranged to suppress power peaks of the AC power supply source 100, as well as enhancing energy utilization in the flywheel-based energy storage unit 30.

In Figure la is shown a situation where long lifting is performed, where the AC electrical machine 20 is powered from the AC grid 100 via the converters 41-42. In Figure lb is shown a situation where long lowering is performed where the AC electrical machine 20 regenerated AC power is supplied to the AC grid 100. In Figure lc is shown a situation where the flywheel-based energy storage unit 30 is used for active heave compensation of the winch 10. In this situation the AC electrical machine 20 of the winch 10 is powered by the energy storage unit 30 and the AC electrical machine 20 is supplying power to the flywheel-based energy storage unit 30, respectively, via the converters 42- 43, while the AC grid 100 supplies AC power to compensate for losses via the converter 41. In active heave compensation mode the main drawback of this solution is that there is low efficiency of the converter 41 interfacing the AC grid 100 in the low current mode when energy is supplied from the AC grid 100 to compensate for the losses. A further considerable drawback with this solution is that failure of any of the converters 41-43 will prevent the active heave compensation operation.

Reference is now made to Figures 2a-c showing principle drawings of an embodiment of an electrical machine drive system according to the present invention where the load is a winch, similar to the system described above. According to the first embodiment of the electrical machine drive system according to the present invention the AC electrical machine 20 driving the winch 10 is a multi winding machine. The electrical machine drive system according to the first embodiment of the present invention further comprises multiple flywheel-based energy storage units 30, i.e. at least two. According to the present invention the electrical drive system further comprises multiple converter units 40 comprising an AC/DC converter 41 which converts AC power supplied from an AC power supply source 100, such as an AC grid, to DC power, and a DC/AC converter 42 which converts DC power to AC power for driving the AC electrical machine 20 or converts AC power regenerated by the AC electrical machine 20 to DC power, wherein the converters 41 and 42 are arranged in series. The converter unit 40 is according to the present invention arranged selectively in series between the AC electrical machine 20 and the AC power supply source 100 and between the AC electrical machine 20 and the respective flywheel-based energy storage units 30, respectively, via a switching unit 50, arranged at AC power supply source 100 side (grid side) of the converter units 40.

Accordingly, in the electrical drive system according to the present invention the number of flywheel-based energy storage units 30 and AC/DC converters 41 in parallel corresponds.

In the prior art solutions one will have to use over-dimensioned converters, while in the present invention one utilize smaller dimensioned converters 41-42. Accordingly, in the present invention the converter units 40 are arranged in parallel between the AC multi-winding electrical machine 20 and AC grid 100, as well as to separate flywheel-based energy storage units 30. According to the electrical machine drive system according to the present invention, it comprises at least two converter units 40, switching units 50 and flywheel-based energy storage units 30, arranged in parallel. In the shown example, there are arranged three converter units 40 with associated switching units 50 and flywheel-based energy storage units 30, in parallel, but according to the present invention there can be more than three parallel branches or can be two parallel branches.

Note that the switching units are illustrated with open switches, but they can be closed in different arrangements according to respective operational modes.

In Figure 2a is shown a situation where long lifting is performed, where the AC multi-winding electrical machine 20 is powered from the AC grid 100 via the at least two converter units 40. In Figure 2b is shown a situation where long lowering is performed where the AC multi-winding electrical machine 20 regenerated AC power is supplied to the AC grid 100 via the at least two converter units 40. In Figure 2c is shown a situation where two of the converter units 40 are used for connecting the AC multi-winding electrical machine 20 to two of the flywheel-based energy storage units 30 pumping energy to the flywheel-based energy storage units 30 from the AC multi winding electrical machine 20 and from the flywheel-based energy storage units 30 to the AC multi- winding electrical machine 20, respectively, in active heave compensation of a marine winch 10. The third converter unit 40 is set to supply AC power from the AC grid 100 to compensate for losses.

The electrical machine drive system according to the present invention provides a solution that is redundant, as the converter units 40, via the switching units 50 can be individually controlled. In this way, if a converter 41-42 fails, active heave compensation can be maintained by using the other two converter units 40.

A further advantage with the electrical machine drive system according to the present invention is that the number of converter units 40, via the switching units 50 connecting them to the AC grid 100 and flywheel-based energy storage units 30, respectively can be adapted the application by controlling the switching units 50.

Further, an advantage with the electrical machine drive system according to the present invention is that one can selectively chose the number of converter units 40 to be loaded according to the required load of the AC electrical machine 20. E.g., one can use only one or two converter units 40 connected to the AC power supply grid 100 at low load. Accordingly, the electrical machine drive system according to the present invention is far more energy effective than prior art systems.

Reference is now made to Figure 3a which is a principle drawing of a second embodiment of the electrical machine drive system according to the present invention. In the second embodiment the AC electrical machine 20 driving the winch 10 is a single-winding electrical machine. This embodiment comprises, as for the first embodiment AC/DC converters 41 arranged in parallel, switching units 50 and flywheel-based energy storage units 50, but the DC/AC converters 42 have been replaced with a common AC/DC converter 44 connected to the AC electrical machine 20 at AC side, providing a common DC-link 45 which the AC/DC converters 41 are connected to at DC side. Accordingly, the second embodiment comprises as above parallel braches with AC/DC converters 41, switching units 50 and flywheel-based energy storage units 30. The second embodiment will work as the first embodiment as described above.

The switching units 50 will be arranged to a separate control unit or an associated control unit of the load the AC electrical machine 20 is arranged to drive. As the electrical machine drive system according to the present invention can use the same AC/DC converters 41 for connection to either grid or the energy storage units, the cost of the converter system will be 2/3 of their cost in prior art systems, as shown in Figures la-c.

Reference is now made to Figure 3b which shows an alternative embodiment of the electrical machine drive system according to the present invention where the AC electrical machine 20 is two- winding machine, such as a machine comprising two electrically de-coupled sets of three-phase windings, and wherein the AC electrical machine 20 is supplied by individual AC/DC converters 44 connected to a common DC-link 45.

In Figure 3c is shown a further alternative embodiment of the electrical machine drive system according to the present invention where the electrical machine drive system comprises several electrical machines 20 driving the same winch 10 via a pinion gear (not shown). In the shown embodiment there are two electrical machines 20, e.g. single-winding machine with one three- phase winding, wherein the AC electrical machines 20 are individually supplied by individual AC/DC converters 44 connected to a common DC-link 45.

Reference is now made to Figure 3d showing a further alternative embodiment of the electrical machine drive system according to the present invention where the electrical machine drive system comprises several AC electrical machines 20 driving the same winch 10 via a pinion gear (not shown). In the shown embodiment there are two AC electrical machines 20, e.g. single-winding machine with one three-phase winding, wherein the AC electrical machines 20 are individually supplied by individual AC/DC converters 44 connected to separate electrical machine drive systems as described above in Figure 3a. For this embodiment, the embodiment of Figure 2a can be used for multi-phase electrical machines 20.

Reference is now made to Figure 3e showing a further alternative embodiment of the electrical drive system according to the present invention where the electrical machine drive system comprises several electrical machines 20 driving the separate winches 10. In the shown embodiment there are two electrical machines 20, e.g. single-winding machine with one three-phase winding, wherein the AC electrical machines 20 are individually supplied by individual AC/DC converters 44 connected to separate electrical machine drive systems as described above in Figure 3a. Also for this embodiment, the embodiment of Figure 2a can be used for multi-phase electrical machines 20.

Reference is now made to Figure 4 which is a principle drawing of how the multiple flywheel-based energy storage units 30 can be implemented to save space, which will be valuable on deck of a vessel were limited space are available. According to the present invention the electrical machine 31 and flywheel 32 can be arranged inside a winch drum 12 of the winch 10.

All the above-described embodiments can be combined to form other embodiments within the scope of the attached claims. The present invention is described for winches but it should be made clear that it is applicable on all kinds of lifting mechanisms such as hoists, cranes, etc. Moreover, it is applicable on all kinds of mechanisms and systems where the load is frequently changing between motoring and generating modes, for example on mechanism performing all kinds of cyclic and/or reciprocating motion.

Claims

1. Electrical machine drive system comprising at least one AC electrical machine (20) arranged for driving at least one load (10), the AC electrical machine (20) arranged to operate as both generator and motor, the electrical machine drive system further comprising an AC power supply source (100) and flywheel-based energy storage units (30), characterized in that it comprises at least two AC/DC converters (41) and at least two flywheel-based energy storage units (30), wherein the at least two AC/DC converters (41) are arranged in parallel and connected to the at least one AC electrical machine (20) individually via DC/AC converters (42) or via a common DC-link (45) at DC converter side, and that AC side of the AC/DC converters (41) are selectively connectable to the AC power supply source (100) or respective flywheel-based energy storage units (30) via respective switching units (50).

2. Electrical machine drive system according to claim 1, characterized in that it comprises at least two AC electrical machines (20) driving the same load (10).

3. Electrical machine drive system according to claim 1, characterized in that it comprises at least two AC electric machines (20) each driving a separate load (10).

4. Electrical machine drive system according to any one of the preceding claims, characterized in that the at least one AC electrical machine (20) is a single-winding electrical machine or a multi winding electrical machine.

5. Electrical machine drive system according to claim 1, characterized in that the flywheel-based energy storage units (30) are formed by an electrical machine (31) and a flywheel (32).

6. Electrical machine drive system according to any one of the preceding claims, characterized in that it comprises at least three AC/DC converters (41) arranged in parallel, each AC/DC converter (41) at AC side being selectively connectable to the AC power supply source (100) or respective flywheel-based energy storage units (30) via respective switching units (50).

7. Electrical machine drive system according to any one of the preceding claims, characterized in that the load (10) is a marine winch and that the electrical machine drive system in active heave compensation mode is arranged to operate with at least two energy storage units (30).

8. Electrical machine drive system according to any one of the preceding claims, characterized in that the load (10) is a winch and that the electrical machine drive system in long lifting or long lowering mode is arranged to operate with the AC power supply source (100) connected to the AC electrical machine (20) via the at least two AC/DC converters (41) arranged in parallel.

9. Electrical machine drive system according to claim 7 or 8, characterized in that the number of connected AC/DC converters (41) in parallel connected to the AC power supply source (100) or flywheel-based energy storage unit (30), respectively, is adapted to the required load of the AC/DC converters (41) and thus required load of the AC electrical machine (20).

10. Electrical machine drive system according to claim 5, characterized in that the electrical machine (31) and flywheel (32) of the energy storage units (30) are integrated in a drum (12) of a winch (10).