WO2011159241A1

WO2011159241A1 - Electrical apparatus comprising drive system and electrical machine with reconnectable stator winding

Info

Publication number: WO2011159241A1
Application number: PCT/SE2011/050745
Authority: WO
Inventors: Mats ALAKÜLA; Saeid Haghbin
Original assignee: Aktiebolaget Chalmersinvest
Priority date: 2010-06-14
Filing date: 2011-06-15
Publication date: 2011-12-22
Also published as: SE534910C2; SE1050607A1

Abstract

Electrical apparatus, comprising a drive system (14) and an electrical machine (16) for propulsion of a vehicle (10), wherein the electrical machine comprises at least one rotor and at least one stator winding (26) and can be connected via a connection point to a three-phase network (20). The stator winding (26) can be switched between at least a first position in which it is electrically controlled by the drive system during propulsion of the vehicle, and a second position in which it is divided into at least two separate and magnetically coupled three-phase windings for converting of a voltage level that is available in the three-phase network. One divided first three-phase winding, consisting of a first set of windings, at a rotor speed corresponding to the frequency of the three-phase network has a voltage corresponding to the voltage level at the connection point. One divided second three-phase winding, consisting of a second set of windings, is electrically matched to the drive system and the windings in the first set and the windings in the second set are each connected to each other via a switching layout.

Description

Electrical Apparatus Comprising Drive System and Electrical Machine with Reconnectable Stator Winding

FIELD OF THE INVENTION

The invention concerns an electrical apparatus, comprising a drive system and an electrical machine for propulsion of a vehicle.

The share of electrically driven vehicles is expected to increase radically in the next 10 to 20 years. This also means a corresponding increase in the need to charge such vehicles. In principle, the charging is done by con- necting the vehicle to the electrical network, either directly to one of the ordinary outlets used for other equipment, or to a special charger. Charging current is transferred from the network to a battery on board the vehicle. In the latter case, standardization is needed so that vehicles from different manufacturers can all be charged from the same type of outlet.

A passenger car uses around 2 kWh of electrical energy per mile for its propulsion. An ordinary single-phase outlet is usually fuse-protected with 10 A, which gives just 2 kW at 230 V. This means that a vehicle which is charged from such an outlet receives energy for around 10 kilometres of driving each hour it is connected to the charge. Heavier vehicles use even more energy per kilometre.

To increase the power it is possible to use a 3-phase outlet. These are found in many locations, fuse-protected with 16, 32 and 63 A, and possibly even higher amperages. The connectors used are strictly standardized but already for 63 A they are so large and cumbersome that one cannot expect a normal person, perhaps wearing good clothing, to manually handle the connecting process. Hence 32 A could be considered to be an upper practical limit on the current level which a manually operated 3-phase contact device can utilize. It should be noted that 32 A is considerably more than the fuse protection of a normal house. At 400 V 3-phase 32 A, the effective power is 22 kW, i.e. a passenger car connected to such a charging outlet will receive energy for just 100 kilometres driving for each hour it is connected for charging. Charging times for electric vehicles are thus significantly longer than when conventional vehicles are fuelled with typically 1000 kilometres driving range in 5 minutes. A relatively large portion of a hypothetical electrical vehicle fleet will probably be charged at night from ordinary 10 A outlets, which still gives a relatively long driving distance during a night of 10 hours, probably more than the battery on board can accept. With a large share of electrical vehicles, however, it is likely that many of them will need to be "quick- charged" also in the daytime, e.g. with 22 kW as from a 400 V 3-phase 32 A outlet. Since the charging time for these still will be relatively long (typically 30 to 60 minutes), it probably does not make sense to have special charging outlets, since very many of them would be needed as compared to today's petrol stations. Instead, it is necessary for the vehicle to be charged from an ordinary outlet, e.g. ranging from 230 V 10 A 1 -phase to 400 V 32 A 3-phase These can be installed at very low costs at very many locations, e.g. parking structures in residential districts, shopping centres, offices, industrial sites, etc.

PRIOR ART

In order for a vehicle to make use of an ordinary electrical outlet, it is necessary that the vehicle itself carries the necessary charging equipment. With a charging capacity of up to 400 V 32 A 3-phase a rather heavy (> 100 kg) and costly (> 10,000 SEK) equipment is needed on board. Since an electric vehicle is costly already from the outset, especially on account of the costs of the batteries, it is burdened with additional costs for the charger requirement.

One example of a design consisting of a divisible motor winding is exhibited and described in JP10248172. One part of the motor winding can be connected to the network during charging. The design calls for a single- phase connection and driving with so-called "common mode" current, that is, the same current in all three phases of the motor.

In US5341075 there is disclosed a combined motor power and battery charging system. Two of the motor's three phase windings are used as in- ductors during single-phase charging of an electric vehicle battery. One requirement is that the battery voltage be higher than the highest instantaneous value of the network voltage. A significant disadvantage is that no galvanic isolation can be provided between network and battery. A similar solu- tion is described in US5099186. However, two totally separate motor windings are used. Yet another solution is disclosed in US4920475.

In accordance with the above described prior art, galvanic isolation is not possible in connection with the charging of the batteries. Another drawback is that the power made available for the charging is too low. Special charging equipment can be used but then the weight as well as the costs increase.

THE INVENTION IN SUMMARY

One way of reducing these costs is to make use of equipment already on board in a new way. An electric vehicle has at least one so-called electric drive system, comprising an electronic power transducer and a traction motor. The traction motor is an electric machine/electric motor with a plurality of windings. Thanks to an advanced dividing and switching of the windings and other components, they can be used as a charger in certain circumstances.

The electric motor is provided with at least one three-phase winding, comprising a plurality of windings, which are connected via a set of switches. By setting the switches in various positions, the windings can be connected in series and connected in parallel in different ways in each phase. In this way, the electrical properties of the electric motor can be fundamentally changed.

According to the invention, the traction motor is used as a transformer, wherein one portion of the windings is used as the primary winding, driven by the electrical network, and one portion as a secondary winding, where the power-electronic motor drive unit acts as a rectifier. One requirement is that the windings during normal motor operation can take up the voltage that is matched to the battery, and that the windings which are connected at a con- nection point to a three-phase network at frequency of 50 Hz (in some countries 60 Hz) hold the network voltage at the connection point.

During charging, the electrical network drives the traction machine (as a motor) through the winding connected to the network. At the same time, the motor drive system brakes the traction machine (as a generator). One portion of the power is provided via the rotor, but another portion is provided via the magnetic coupling between what can be called the primary and secondary winding of the divided windings.

The solution has two major advantages in regard to the prior art. First, charging is possible from a conventional three-phase mains outlet. Second, complete galvanic isolation is created between mains and battery circuit. Even single-phase charging can be implemented by special connection.

The description below uses the following: mains voltage is Un, [Volt RMS, phase-phase], mains frequency is fn and motor drive system's maxi- mum output voltage is Urn, [Volt RMS, phase-phase] (often determined by the battery voltage).

The stator winding can be connected in two different operating modes, either driving (traction) or charging. In driving, the stator winding is divided into a number {n_3ph) of groups of three-phase windings {n_3ph = 1 , 2, 3, ...), each group consisting of n_pd parallel-connected and n_sd series-connected sections in each phase winding. These three-phase windings can be connected in either a Y or a D connection to match the voltage of the motor drive system.

One of two alternatives can be used for charging: I) One or more of the groups of three-phase windings, collectively

¾>Α^, are separated for connection to the mains. The remaining three-phase groups {n_3ph-n_3phJ) are used by the motor drive system.

II) The windings in one or more of the groups of three-phase wind- ings are switched over to two electrically separate three-phase windings one of these being connected to the three-phase elec- trical network and the other being connected to the motor drive system.

The portion that is connected to the three-phase electrical network consists of n_pCg parallel-connected and n_scg series-connected winding sec- tions. The winding then can be connected in either a Y or a Delta arrangement. The number of series- and parallel-connected winding sections is chosen so that the voltage across these windings at a motor rpm corresponding to the network frequency (normally 50 Hz, in some countries 60 Hz) is very close to the nominal mains voltage. This varies in some countries. In Europe it is 400 V principal voltage.

The portion that is connected to the motor drive system consists of n_pcd parallel-connected and n_scd series-connected winding sections. The connection is chosen such that they form a three-phase system with the highest possible voltage, but lower than the highest voltage that the motor drive sys- tern can put out.

In accordance with the invention charging can occur as follows after the switching.

I) The traction motor is disengaged from the vehicle's transmission by placing the gearbox in neutral and possibly releasing the clutch.

II) The motor drive system detects voltage and phase sequence at the connection point in the network from which the charging will take place.

III) The motor drive system runs the traction motor up to the speed and the phase position corresponding to mains frequency and phase position of the mains voltage.

IV) The motor drive system adjusts the traction motor's voltage in the three-phase winding that will be connected to the electrical network so that the voltage across the three-phase winding cor- responds to the mains voltage. V) The motor drive system then connects the three-phase winding that will be connected to the mains during the charging.

VI) The motor drive system finally loads the electrical network by braking the traction motor through control of its currents, where- upon electric power flows from the electrical network via the traction motor to the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above recited and other advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

Fig. 1 shows schematically a vehicle with battery and drive system, which is connected by a switching layout to an electrical network for charging of the battery,

Fig. 2 shows schematically a drive system connected for propulsion of a vehicle by means of current from a battery,

Fig. 3 shows schematically the drive system shown in Fig. 1 , but now

connected for charging of the battery,

Fig. 4 is a block diagram schematically showing an electrical apparatus according to the invention, connected to a battery,

Fig. 5 shows the electrical apparatus of Fig. 4 connected in a first position intended for driving,

Fig. 6 shows the electrical apparatus of Fig. 4 connected in a second position intended for charging,

Fig. 7 shows schematically an embodiment of the invention with a stator winding in Y-connection for driving, Fig. 8 shows schematically an embodiment of the invention with a stator winding divided into two Y-connected three-phase windings connected to the three-phase network and the drive system, respectively, each of them comprising a plurality of series- and parallel- connected winding sections,

Fig. 9 shows schematically an embodiment of the invention with a stator winding divided into a D-connected three-phase winding for connection to the three-phase network and a Y-connected three-phase winding connected to the drive system, each three-phase winding comprising a plurality of series- and parallel-connected winding sections and

Fig. 10 shows schematically an embodiment of the invention with two separate stator windings divided into a D-connected three-phase winding for connection to the three-phase network and a Y-connected three-phase winding connected to the drive system, each three- phase winding comprising a plurality of series- and parallel- connected winding sections.

THE INVENTION

In the embodiment shown in Fig. 1 , a vehicle 10 is provided with an electrical apparatus 12 according to the invention. The electrical apparatus 12 comprises a drive system 14 and an electrical machine 16 for propulsion of the vehicle 10. A battery 18 is arranged in the vehicle for driving of the electrical apparatus. The battery 18 can be charged by connecting to a three-phase network 20. In the embodiment shown in Fig. 1 , the battery is connected to the three-phase network 20 via a so-called charging pole 22 constituting the connection point and the electrical apparatus 12. The electrical apparatus 12 also comprises a switching layout 24 and at least one stator winding 26.

When driving the vehicle 10, the electrical apparatus 12 is connected and controlled so as to correspond to the circuit diagram shown in Fig. 2. The stator winding 26 is D-connected to two pairs of series-connected and parallel-connected winding sections L1-L12, respectively, in three phases. The drive system 14 comprises a converter 28, which converts the direct current available from the battery 18 into an alternating voltage matched to the electrical machine 16. The drive system 14 is controlled by a control unit 30, which is operated by the driver of the vehicle with a control 32. The electrical machine in this setup is used as a traction motor.

When charging the battery 18 in the vehicle 10, the electrical apparatus 12 is connected and controlled according to the circuit diagram shown in Fig. 3. The stator winding 26 is divided by means of the switching layout into a Y-connected first part and a D-connected second part. Both parts of the stator winding 26 are magnetically coupled to each other in that the Y- connected first part works as a primary winding and the D-connected second part works as a secondary winding.

The primary winding with the winding sections L1-L6 is connected to the three-phase network 20 and the secondary winding with the winding sections L7-L12 is connected to the battery via a rectifier 34 of the drive system 14. During charging the three-phase network drives the electrical machine as a motor through the mains-connected primary winding, while at the same time the drive system 14 controlled by the control unit 30 brakes the traction motor as a generator. Part of the power is transferred magnetically via a rotor and another part of the power is transferred via the direct magnetic coupling between primary and secondary winding, as indicated by arrow C. The winding sections preferably are divided so that primary winding and secondary winding have the same power.

Fig. 4 shows an alternative electrical apparatus 12 according to the invention connected to an electrical network 20 and a battery 18. The drive system 4 with its control unit 30 sets the stator winding 26 in suitable manner for driving or charging via the switching arrangement 24. The switching arrangement 24 preferably comprises mechanical switches, but various types of electronic switches and semiconductor switches can also be used.

The electrical apparatus 12 shown in Fig. 4 is connected for driving in the connection diagram of Fig. 5. By suitable choice of the connection points of the switching arrangement 24, the stator winding 26 is Y-connected to four parallel-connected pairs of series-connected winding sections in each phase. The battery 18 drives via the drive system 14 and the converter 28 in a conventional manner. The three-phase network 20 in this position is not con- nected to the electrical apparatus. The stator winding can also be D- con nected.

In the example of Fig. 6 the electrical apparatus 12 instead is connected for charging. The same set of winding sections as in the embodiment of Fig. 5 is divided, after switching the switching arrangement 24, into a Y- connected primary winding and a Y-connected secondary winding. The primary winding comprises four series-connected winding sections in each phase, like the secondary winding. One or both windings can also be D- con nected.

Fig. 7 shows an example of connection of an electrical apparatus ac- cording to the invention with a three-phase network Y-connected for driving. In each phase there are n_pd parallel-connected groups of n_sd series- connected winding sections connected with the drive system 14. All winding sections are part of the stator winding 26.

In Fig. 8 the electrical apparatus according to the invention is connect- ed for charging. A Y-connected primary winding with n_pcg groups of n_scg series-connected winding sections is connected to the three-phase network 20. A Y-connected secondary winding with n_pcd groups of n_scd series-connected winding sections is connected to the drive system 14. All winding sections are part of the stator winding 26. Either or both windings can be D-connected instead.

Charging from a single-phase system is also possible according to the invention. In the event that the primary winding is Y-connected, the zero of the three-phase network can also be connected as shown at A in Fig. 8, and two of the three phases in the primary winding can be disconnected, as indi- cated at B and C, also in Fig. 8. In the event that the primary winding is instead D-connected, one of the three phases in the primary winding can be disconnected. In Fig. 9, the electrical apparatus according to the invention is connected for charging. A D-connected primary winding with n_pcg groups of n_scg series-connected winding sections is connected to the three-phase network 20. A Y-connected secondary winding with n_pcd groups of n_scd series- connected winding sections is connected to the drive system 14. All winding sections are part of the stator winding 26.

In the sample embodiment shown in Fig. 10, two three-phase systems are used. A first three-phase system is D-connected and constitutes a primary winding connected to the three-phase network 20. The primary winding comprises n_pcg groups of n_scg series-connected winding sections. A second separate three-phase system is Y-connected and constitutes a secondary winding connected to the drive system 14. The secondary winding comprises Pcd groups of n_scd series-connected winding sections.

While certain illustrative embodiments of the invention have been de- scribed above, it will be understood that various other modifications will be readily apparent to those skilled in the art without departing from the scope and spirit of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description set forth herein but rather that the claims be construed as encompassing all equivalents of the present invention which are apparent to those skilled in the art to which the invention pertains.

Claims

PATENT CLAIMS

1. An electrical apparatus (12), comprising a drive system (14) and an elec- trical machine (16) for propulsion of a vehicle (10), wherein the electrical machine comprises at least one rotor and at least one stator winding (26) and can be connected via a connection point to a three-phase network (20), c h a ra c t e ri s e d in that

the stator winding is switchable between at least a first position in which it is electrically controlled by the drive system (14) during propulsion of the vehicle, and a second position in which it is divided into at least two separate three-phase windings, coupled directly magnetically and indirectly via the rotor, for converting of a voltage level that is available in the three-phase network,

a divided first three-phase winding, consisting of a first set of windings, at a rotor speed corresponding to the frequency of the three-phase network has a voltage corresponding to the voltage level at the connection point,

a divided second three-phase winding, consisting of a second set of windings, is electrically matched to the drive system, and

the windings in the first set and the windings in the second set are each connected to the same switching layout.

2. An electrical apparatus according to claim 1 , comprising a converter (28) for converting of direct current to alternating current.

3. An electrical apparatus according to claim 1 , comprising a rectifier (34) for rectifying the alternating current available from the three-phase network into direct current.

4. An electrical apparatus according to claim , wherein the electrical machine comprises a stator winding arranged to be divided into a first three- phase winding that can be connected separately to the three-phase network and a second three-phase winding connected to the drive system.

5. An electrical apparatus according to claim 1 , wherein the electrical ma- chine comprises at least two stator windings, at least one of which stator windings being dividable into a first three-phase winding that can be connected separately to the three-phase network and at least one second three- phase winding connected together with the remaining stator windings to the drive system.

6. An electrical apparatus according to claim 4 or 5, wherein the winding that is divided for connection to the three-phase network is only connected with its zero and one of the three phase connections.

7. An electrical apparatus according to any one of the above claims, wherein the electrical machine is constituted by a permanently magnetized synchronous machine.

8. An electrical apparatus according to any one of the above claims, wherein the electrical machine is constituted by an asynchronous machine.

9. An electrical apparatus according to any one of the above claims, wherein the electrical machine is constituted by an electrically magnetized synchronous machine.

10. An electrical apparatus according to any one of the above claims, wherein the electrical machine is constituted by a synchronous reluctance machine.

11. An electrical apparatus according to any one of the above claims, wherein the electrical machine is constituted by a switched reluctance machine.

12. A method for generating of rectified charging current from an electrical drive system (14), wherein the drive system is connected to a stator winding contained in an electrical machine (16), c h a r a c t e r i s e d by

switching the stator winding from a first position in which it is connected as a motor for propulsion of a vehicle (10) to a second position, disengaging the electrical machine in the second position from the vehicle,

connecting the electrical machine in the second position at a connection point to a three-phase network,

dividing the stator winding in the second position into at least two separate and magnetically coupled three-phase windings for converting a voltage level available in the three-phase network,

speeding up the electrical machine to a speed and phase position corresponding to mains frequency and phase position in the three-phase network,

adjusting the voltage across a divided first three-phase winding, consisting of a first set of windings, by controlling the currents across a second three-phase winding, consisting of a second set of windings, to a voltage corresponding to the voltage level in the three-phase network at the connection point,

forming a primary winding of the first set of windings and connecting it to the three-phase network,

controlling the current in the second set of windings so that the electrical machine is braked, whereupon electric power is transferred from the three-phase network through the second set of windings acting as a secondary winding, and

rectifying a current leaving the secondary winding.